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Sample records for susceptibility-based contrast mechanisms

  1. A novel technique for modeling susceptibility-based contrast mechanisms for arbitrary microvascular geometries: the finite perturber method.

    PubMed

    Pathak, Arvind P; Ward, B Douglas; Schmainda, Kathleen M

    2008-04-15

    Recently, we demonstrated that vessel geometry is a significant determinant of susceptibility-induced contrast in MRI. This is especially relevant for susceptibility-contrast enhanced MRI of tumors with their characteristically abnormal vessel morphology. In order to better understand the biophysics of this contrast mechanism, it is of interest to model how various factors, including microvessel morphology contribute to the measured MR signal, and was the primary motivation for developing a novel computer modeling approach called the Finite Perturber Method (FPM). The FPM circumvents the limitations of traditional fixed-geometry approaches, and enables us to study susceptibility-induced contrast arising from arbitrary microvascular morphologies in 3D, such as those typically observed with brain tumor angiogenesis. Here we describe this new modeling methodology and some of its applications. The excellent agreement of the FPM with theory and the extant susceptibility modeling data, coupled with its computational efficiency demonstrates its potential to transform our understanding of the factors that engender susceptibility contrast in MRI. PMID:18308587

  2. "Basic MR Relaxation Mechanisms & Contrast Agent Design"

    PubMed Central

    De León-Rodríguez, Luis M.; Martins, André F.; Pinho, Marco; Rofsky, Neil; Sherry, A. Dean

    2015-01-01

    The diagnostic capabilities of magnetic resonance imaging (MRI) have undergone continuous and substantial evolution by virtue of hardware and software innovations and the development and implementation of exogenous contrast media. Thirty years since the first MRI contrast agent was approved for clinical use, a reliance on MR contrast media persists largely to improve image quality with higher contrast resolution and to provide additional functional characterization of normal and abnormal tissues. Further development of MR contrast media is an important component in the quest for continued augmentation of diagnostic capabilities. In this review we will detail the many important considerations when pursuing the design and use of MR contrast media. We will offer a perspective on the importance of chemical stability, particularly kinetic stability, and how this influences one's thinking about the safety of metal-ligand based contrast agents. We will discuss the mechanisms involved in magnetic resonance relaxation in the context of probe design strategies. A brief description of currently available contrast agents will be accompanied by an in-depth discussion that highlights promising MRI contrast agents in development for future clinical and research applications. Our intention is to give a diverse audience an improved understanding of the factors involved in developing new types of safe and highly efficient MR contrast agents and, at the same time, provide an appreciation of the insights into physiology and disease that newer types of responsive agents can provide. PMID:25975847

  3. Basic MR relaxation mechanisms and contrast agent design.

    PubMed

    De León-Rodríguez, Luis M; Martins, André F; Pinho, Marco C; Rofsky, Neil M; Sherry, A Dean

    2015-09-01

    The diagnostic capabilities of magnetic resonance imaging (MRI) have undergone continuous and substantial evolution by virtue of hardware and software innovations and the development and implementation of exogenous contrast media. Thirty years since the first MRI contrast agent was approved for clinical use, a reliance on MR contrast media persists, largely to improve image quality with higher contrast resolution and to provide additional functional characterization of normal and abnormal tissues. Further development of MR contrast media is an important component in the quest for continued augmentation of diagnostic capabilities. In this review we detail the many important considerations when pursuing the design and use of MR contrast media. We offer a perspective on the importance of chemical stability, particularly kinetic stability, and how this influences one's thinking about the safety of metal-ligand-based contrast agents. We discuss the mechanisms involved in MR relaxation in the context of probe design strategies. A brief description of currently available contrast agents is accompanied by an in-depth discussion that highlights promising MRI contrast agents in the development of future clinical and research applications. Our intention is to give a diverse audience an improved understanding of the factors involved in developing new types of safe and highly efficient MR contrast agents and, at the same time, provide an appreciation of the insights into physiology and disease that newer types of responsive agents can provide. PMID:25975847

  4. A synaptic mechanism for retinal adaptation to luminance and contrast.

    PubMed

    Jarsky, Tim; Cembrowski, Mark; Logan, Stephen M; Kath, William L; Riecke, Hermann; Demb, Jonathan B; Singer, Joshua H

    2011-07-27

    The gain of signaling in primary sensory circuits is matched to the stimulus intensity by the process of adaptation. Retinal neural circuits adapt to visual scene statistics, including the mean (background adaptation) and the temporal variance (contrast adaptation) of the light stimulus. The intrinsic properties of retinal bipolar cells and synapses contribute to background and contrast adaptation, but it is unclear whether both forms of adaptation depend on the same cellular mechanisms. Studies of bipolar cell synapses identified synaptic mechanisms of gain control, but the relevance of these mechanisms to visual processing is uncertain because of the historical focus on fast, phasic transmission rather than the tonic transmission evoked by ambient light. Here, we studied use-dependent regulation of bipolar cell synaptic transmission evoked by small, ongoing modulations of membrane potential (V(M)) in the physiological range. We made paired whole-cell recordings from rod bipolar (RB) and AII amacrine cells in a mouse retinal slice preparation. Quasi-white noise voltage commands modulated RB V(M) and evoked EPSCs in the AII. We mimicked changes in background luminance or contrast, respectively, by depolarizing the V(M) or increasing its variance. A linear systems analysis of synaptic transmission showed that increasing either the mean or the variance of the presynaptic V(M) reduced gain. Further electrophysiological and computational analyses demonstrated that adaptation to mean potential resulted from both Ca channel inactivation and vesicle depletion, whereas adaptation to variance resulted from vesicle depletion alone. Thus, background and contrast adaptation apparently depend in part on a common synaptic mechanism. PMID:21795549

  5. Examination of contrast mechanisms in optoacoustic imaging of thermal lesions

    NASA Astrophysics Data System (ADS)

    Richter, Christian; Spirou, Gloria; Oraevsky, Alexander A.; Whelan, William M.; Kolios, Michael C.

    2006-02-01

    Optoacoustic Imaging is based on the thermal expansion of tissue caused by a temperature rise due to absorption of short laser pulses. At constant laser fluence, optoacoustic image contrast is proportional to differences in optical absorption and the thermoacoustic efficiency, expressed by the Grueuneisen parameter, Γ. Γ is proportional to the thermal expansion coefficient, the sound velocity squared and the inverse heat capacity at constant pressure. In thermal therapies, these parameters may be modified in the treated area. In this work experiments were performed to examine the influence of these parameters on image contrast. A Laser Optoacoustic Imaging System (LOIS, Fairway Medical Technologies, Houston, Texas) was used to image tissue phantoms comprised of cylindrical Polyvinyl Chloride Plastisol (PVCP) optical absorbing targets imbedded in either gelatin or PVCP as the background medium. Varying concentrations of Black Plastic Color (BPC) and titanium dioxide (TiO II) were added to targets and background to yield desired tissue relevant optical absorption and effective scattering coefficients, respectively. In thermal therapy experiments, ex-vivo bovine liver was heated with laser fibres (805nm laser at 5 W for 600s) to create regions of tissue coagulation. Lesions formed in the liver tissue were visible using the LOIS system with reasonable correspondence to the actual region of tissue coagulation. In the phantom experiments, contrast could be seen with low optical absorbing targets (μ a of 0.50cm -1 down to 0.13cm-1) embedded in a gelatin background (see manuscript for formula). Therefore, the data suggest that small objects (< 5mm) with low absorption coefficients (in the range < 1cm -1) can be imaged using LOIS. PVCP-targets in gelatin were visible, even with the same optical properties as the gelatin, but different Γ. The enhanced contrast may also be caused by differences in the mechanical properties between the target and the surrounding medium

  6. Mechanically Tunable Hollow Silica Ultrathin Nanoshells for Ultrasound Contrast Agents

    PubMed Central

    Liberman, A.; Wang, J.; Lu, N.; Viveros, R.D.; Allen, C. A.; Mattrey, R.F.; Blair, S.L.; Trogler, W.C.; Kim, M. J.; Kummel, A.C.

    2015-01-01

    Perfluoropentane (PFP) gas filled biodegradable iron-doped silica nanoshells have been demonstrated as long-lived ultrasound contrast agents. Nanoshells are synthesized by a sol-gel process with tetramethyl orthosilicate (TMOS) and iron ethoxide. Substituting a fraction of the TMOS with R-substituted trialkoxysilanes produces ultrathin nanoshells with varying shell thicknesses and morphologies composed of fused nanoflakes. The ultrathin nanoshells had continuous ultrasound Doppler imaging lifetimes exceeding 3 hours, were twice as bright using contrast specific imaging, and had decreased pressure thresholds compared to control nanoshells synthesized with just TMOS. Transmission electron microscopy (TEM) showed that the R-group substituted trialkoxysilanes could reduce the mechanically critical nanoshell layer to 1.4 nm. These ultrathin nanoshells have the mechanical behavior of weakly linked nanoflakes but the chemical stability of silica. The synthesis can be adapted for general fabrication of three-dimensional nanostructures composed of nanoflakes, which have thicknesses from 1.4–3.8 nm and diameters from 2–23 nm. PMID:26955300

  7. Quantitative Susceptibility Mapping: Contrast Mechanisms and Clinical Applications

    PubMed Central

    Liu, Chunlei; Wei, Hongjiang; Gong, Nan-Jie; Cronin, Matthew; Dibb, Russel; Decker, Kyle

    2016-01-01

    Quantitative susceptibility mapping (QSM) is a recently developed MRI technique for quantifying the spatial distribution of magnetic susceptibility within biological tissues. It first uses the frequency shift in the MRI signal to map the magnetic field profile within the tissue. The resulting field map is then used to determine the spatial distribution of the underlying magnetic susceptibility by solving an inverse problem. The solution is achieved by deconvolving the field map with a dipole field, under the assumption that the magnetic field is a result of the superposition of the dipole fields generated by all voxels and that each voxel has its unique magnetic susceptibility. QSM provides improved contrast to noise ratio for certain tissues and structures compared to its magnitude counterpart. More importantly, magnetic susceptibility is a direct reflection of the molecular composition and cellular architecture of the tissue. Consequently, by quantifying magnetic susceptibility, QSM is becoming a quantitative imaging approach for characterizing normal and pathological tissue properties. This article reviews the mechanism generating susceptibility contrast within tissues and some associated applications. PMID:26844301

  8. Allergic reactions following contrast material administration: nomenclature, classification, and mechanisms.

    PubMed

    Palmiere, Cristian; Comment, Lionel; Mangin, Patrice

    2014-01-01

    In forensic pathology routine, fatal cases of contrast agent exposure can be occasionally encountered. In such situations, beyond the difficulties inherent in establishing the cause of death due to nonspecific or absent autopsy and histology findings as well as limited laboratory investigations, pathologists may face other problems in formulating exhaustive, complete reports, and conclusions that are scientifically accurate. Indeed, terminology concerning adverse drug reactions and allergy nomenclature is confusing. Some terms, still utilized in forensic and radiological reports, are outdated and should be avoided. Additionally, not all forensic pathologists master contrast material classification and pathogenesis of contrast agent reactions. We present a review of the literature covering allergic reactions to contrast material exposure in order to update used terminology, explain the pathophysiology, and list currently available laboratory investigations for diagnosis in the forensic setting. PMID:24061700

  9. Section 6—Mechanical Bioeffects in the Presence of Gas-Carrier Ultrasound Contrast Agents

    PubMed Central

    2007-01-01

    This review addresses the issue of mechanical ultrasound-induced bioeffects in the presence of gas carrier contrast agents (GCAs). Here, the term “contrast agent” refers to those agents that provide ultrasound contrast by being composed of microbubbles, encapsulated or not, containing one or more gases. Provided in this section are summaries on how contrast agents work, some of their current uses, and the potential for bio-effects associated with their presence in an ultrasonic field. PMID:10680618

  10. Do common mechanisms of adaptation mediate color discrimination and appearance? Contrast adaptation

    NASA Astrophysics Data System (ADS)

    Hillis, James M.; Brainard, David H.

    2007-08-01

    Are effects of background contrast on color appearance and sensitivity controlled by the same mechanism of adaptation? We examined the effects of background color contrast on color appearance and on color-difference sensitivity under well-matched conditions. We linked the data using Fechner's hypothesis that the rate of apparent stimulus change is proportional to sensitivity and examined a family of parametric models of adaptation. Our results show that both appearance and discrimination are consistent with the same mechanism of adaptation.

  11. The ups and downs of social comparison: mechanisms of assimilation and contrast.

    PubMed

    Mussweiler, Thomas; Rüter, Katja; Epstude, Kai

    2004-12-01

    Social comparisons influence self-evaluations in multiple ways. Sometimes self-evaluations are assimilated toward a given standard. At other times, they are contrasted away from the standard. On the basis of the selective accessibility model (T. Mussweiler, 2003a), the authors hypothesized that assimilation results if judges engage in the comparison process of similarity testing and selectively focus on similarities to the standard, whereas contrast occurs if judges engage in dissimilarity testing and selectively focus on differences. If these alternative comparison mechanisms are indeed at play, then assimilative and contrastive social comparisons should be accompanied by diverging informational foci on similarities versus differences. Results of 5 studies support this reasoning, demonstrating that assimilation results under conditions that foster similarity testing, whereas contrast occurs under conditions that foster dissimilarity testing. Furthermore, assimilative social comparisons are accompanied by a general informational focus on similarities, whereas contrastive comparisons are accompanied by a focus on differences. PMID:15598109

  12. Do common mechanisms of adaptation mediate color discrimination and appearance? Contrast adaptation

    PubMed Central

    Hillis, James M.; Brainard, David H.

    2009-01-01

    Are effects of background contrast on color appearance and sensitivity controlled by the same mechanism of adaptation? We examined the effects of background color contrast on color appearance and on color-difference sensitivity under well-matched conditions. We linked the data using Fechner’s hypothesis that the rate of apparent stimulus change is proportional to sensitivity and examined a family of parametric models of adaptation. Our results show that both appearance and discrimination are consistent with the same mechanism of adaptation. PMID:17621318

  13. Ion mobility imaging and contrast mechanism of apparent conductivity in MREIT.

    PubMed

    Oh, Tong In; Kim, Young Tae; Minhas, Atul; Seo, Jin Keun; Kwon, Oh In; Woo, Eung Je

    2011-04-01

    Magnetic resonance electrical impedance tomography (MREIT) aims to produce high-resolution cross-sectional images of conductivity distribution inside the human body. Injected current into an imaging object induces a distribution of internal magnetic flux density, which is measured by using an MRI scanner. We can reconstruct a conductivity image based on its relation with the measured magnetic flux density. In this paper, we explain the contrast mechanism in MREIT by performing and analyzing a series of numerical simulations and imaging experiments. We built a stable conductivity phantom including a hollow insulating cylinder with holes. Filling both inside and outside the hollow cylinder with the same saline, we controlled ion mobilities to create a conductivity contrast without being affected by the ion diffusion process. From numerical simulations and imaging experiments, we found that slopes of induced magnetic flux densities change with hole diameters and therefore conductivity contrasts. Associating the hole diameter with apparent conductivity of the region inside the hollow cylinder with holes, we could experimentally validate the contrast mechanism in MREIT. Interpreting reconstructed apparent conductivity images of the phantom as ion mobility images, we discuss the meaning of the apparent conductivity seen by a certain probing method. In designing MREIT imaging experiments, the ion mobility imaging method using the proposed stable conductivity phantom will enable us to estimate a distinguishable conductivity contrast for a given set of imaging parameters. PMID:21411866

  14. Reflective THz and MR imaging of burn wounds: a potential clinical validation of THz contrast mechanisms

    NASA Astrophysics Data System (ADS)

    Bajwa, Neha; Nowroozi, Bryan; Sung, Shijun; Garritano, James; Maccabi, Ashkan; Tewari, Priyamvada; Culjat, Martin; Singh, Rahul; Alger, Jeffry; Grundfest, Warren; Taylor, Zachary

    2012-10-01

    Terahertz (THz) imaging is an expanding area of research in the field of medical imaging due to its high sensitivity to changes in tissue water content. Previously reported in vivo rat studies demonstrate that spatially resolved hydration mapping with THz illumination can be used to rapidly and accurately detect fluid shifts following induction of burns and provide highly resolved spatial and temporal characterization of edematous tissue. THz imagery of partial and full thickness burn wounds acquired by our group correlate well with burn severity and suggest that hydration gradients are responsible for the observed contrast. This research aims to confirm the dominant contrast mechanism of THz burn imaging using a clinically accepted diagnostic method that relies on tissue water content for contrast generation to support the translation of this technology to clinical application. The hydration contrast sensing capabilities of magnetic resonance imaging (MRI), specifically T2 relaxation times and proton density values N(H), are well established and provide measures of mobile water content, lending MRI as a suitable method to validate hydration states of skin burns. This paper presents correlational studies performed with MR imaging of ex vivo porcine skin that confirm tissue hydration as the principal sensing mechanism in THz burn imaging. Insights from this preliminary research will be used to lay the groundwork for future, parallel MRI and THz imaging of in vivo rat models to further substantiate the clinical efficacy of reflective THz imaging in burn wound care.

  15. Optical coherence micro-elastography: mechanical-contrast imaging of tissue microstructure.

    PubMed

    Kennedy, Brendan F; McLaughlin, Robert A; Kennedy, Kelsey M; Chin, Lixin; Curatolo, Andrea; Tien, Alan; Latham, Bruce; Saunders, Christobel M; Sampson, David D

    2014-07-01

    We present optical coherence micro-elastography, an improved form of compression optical coherence elastography. We demonstrate the capacity of this technique to produce en face images, closely corresponding with histology, that reveal micro-scale mechanical contrast in human breast and lymph node tissues. We use phase-sensitive, three-dimensional optical coherence tomography (OCT) to probe the nanometer-to-micrometer-scale axial displacements in tissues induced by compressive loading. Optical coherence micro-elastography incorporates common-path interferometry, weighted averaging of the complex OCT signal and weighted least-squares regression. Using three-dimensional phase unwrapping, we have increased the maximum detectable strain eleven-fold over no unwrapping and the minimum detectable strain is 2.6 με. We demonstrate the potential of mechanical over optical contrast for visualizing micro-scale tissue structures in human breast cancer pathology and lymph node morphology. PMID:25071952

  16. In vivo confirmation of hydration based contrast mechanisms for terahertz medical imaging using MRI

    NASA Astrophysics Data System (ADS)

    Bajwa, Neha; Sung, Shijun; Garritano, James; Nowroozi, Bryan; Tewari, Priyamvada; Ennis, Daniel B.; Alger, Jeffery; Grundfest, Warren; Taylor, Zachary

    2014-09-01

    Terahertz (THz) detection has been proposed and applied to a variety of medical imaging applications in view of its unrivaled hydration profiling capabilities. Variations in tissue dielectric function have been demonstrated at THz frequencies to generate high contrast imagery of tissue, however, the source of image contrast remains to be verified using a modality with a comparable sensing scheme. To investigate the primary contrast mechanism, a pilot comparison study was performed in a burn wound rat model, widely known to create detectable gradients in tissue hydration through both injured and surrounding tissue. Parallel T2 weighted multi slice multi echo (T2w MSME) 7T Magnetic Resonance (MR) scans and THz surface reflectance maps were acquired of a full thickness skin burn in a rat model over a 5 hour time period. A comparison of uninjured and injured regions in the full thickness burn demonstrates a 3-fold increase in average T2 relaxation times and a 15% increase in average THz reflectivity, respectively. These results support the sensitivity and specificity of MRI for measuring in vivo burn tissue water content and the use of this modality to verify and understand the hydration sensing capabilities of THz imaging for acute assessments of the onset and evolution of diseases that affect the skin. A starting point for more sophisticated in vivo studies, this preliminary analysis may be used in the future to explore how and to what extent the release of unbound water affects imaging contrast in THz burn sensing.

  17. Do conscious perception and unconscious processing rely on independent mechanisms? A meta-contrast study.

    PubMed

    Peremen, Ziv; Lamy, Dominique

    2014-02-01

    There is currently no consensus regarding what measures are most valid to demonstrate perceptual processing without awareness. Likewise, whether conscious perception and unconscious processing rely on independent mechanisms or lie on a continuum remains a matter of debate. Here, we addressed these issues by comparing the time courses of subjective reports, objective discrimination performance and response priming during meta-contrast masking, under similar attentional demands. We found these to be strikingly similar, suggesting that conscious perception and unconscious processing cannot be dissociated by their time course. Our results also demonstrate that unconscious processing, indexed by response priming, occurs, and that objective discrimination performance indexes the same conscious processes as subjective visibility reports. Finally, our results underscore the role of attention by showing that how much attention the stimulus receives relative to the mask, rather than whether processing is measured by conscious discrimination or by priming, determines the time course of meta-contrast masking. PMID:24398259

  18. Renal Protective Effect of Probucol in Rats with Contrast-Induced Nephropathy and its Underlying Mechanism

    PubMed Central

    Wang, Na; Wei, Ri-bao; Li, Qing-ping; Yang, Xi; Li, Ping; Huang, Meng-jie; Wang, Rui; Cai, Guang-yan; Chen, Xiang-mei

    2015-01-01

    Background Contrast-induced nephropathy (CIN) refers to acute renal damage that occurs after the use of contrast agents. This study investigated the renal protective effect of probucol in a rat model of contrast-induced nephropathy and the mechanism of its effect. Material/Methods Twenty-eight Wistar rats were randomly divided into the control group, model group, N-acetylcysteine(NAC) group, and probucol group. We used a rat model of iopromide-induced CIN. One day prior to modeling, the rats received gavage. At 24 h after the modeling, blood biochemistry and urine protein were assessed. Malondialdehyde (MDA) and superoxide dismutase (SOD) were measured in renal tissue. Kidney sections were created for histopathological examination. Results The model group of rats showed significantly elevated levels of blood creatinine, urea nitrogen, 24-h urine protein, histopathological scores, and parameters of oxidative stress (P<0.05). Both the NAC and probucol groups demonstrated significantly lower Scr, BUN, and urine protein levels compared to the model group (P<0.05), with no significant difference between these 2 groups. The NAC group and the probucol group had significantly lower MDA and higher SOD than the model group at 24 h after modeling (P<0.05). The 8-OHdG-positive tubule of the probucol group and NAC group were significantly lower than those of the model group (p=0.046, P=0.0008), with significant difference between these 2 groups (P=0.024). Conclusions Probucol can effectively reduce kidney damage caused by contrast agent. The underlying mechanism may be that probucol accelerates the recovery of renal function and renal pathology by reducing local renal oxidative stress. PMID:26408630

  19. Mechanical stability of hollow spherical nano-aggregates as ultrasound contrast agent.

    PubMed

    Hadinoto, Kunn

    2009-06-01

    Gas-filled hollow nanoparticulate aggregates designed for use as an ultrasound contrast agent and as an ultrasound-mediated nanoparticulate drug delivery vehicle are manufactured by spray drying of nanoparticulate suspension at a fast convective drying rate. The gas outward diffusion from the hollow particles during insonication reduces the shell mechanical stability hence shortening the lifespan of the ultrasound contrast agent. The present work aims to develop a formulation method to produce micron-size hollow nanoparticulate aggregates with high shell mechanical stability by controlling the shell thickness-to-particle radius (S/R) ratio. The impacts of changing (1) the spray drying parameters, (2) nanoparticulate suspension concentration, and (3) surfactant inclusion (i.e. phospholipids) on the particle morphology and the S/R ratio are investigated. Biocompatible PMMA-MeOPEGMA nanoparticles of varying sizes (i.e. 50+/-20, 110+/-40, and 230+/-80 nm) are used as the model nanoparticles. The results indicate that the S/R ratio increases with decreasing particle size and the shell mechanical stability is linearly dependent on the S/R ratio. The effects of the spray drying parameters and nanoparticle concentration are found to be minimal in the absence of the phospholipids. The S/R ratio can be significantly increased by using larger size nanoparticles with the phospholipids inclusion. PMID:19446772

  20. Understanding Physiological and Degenerative Natural Vision Mechanisms to Define Contrast and Contour Operators

    PubMed Central

    Demongeot, Jacques; Fouquet, Yannick; Tayyab, Muhammad; Vuillerme, Nicolas

    2009-01-01

    Background Dynamical systems like neural networks based on lateral inhibition have a large field of applications in image processing, robotics and morphogenesis modeling. In this paper, we will propose some examples of dynamical flows used in image contrasting and contouring. Methodology First we present the physiological basis of the retina function by showing the role of the lateral inhibition in the optical illusions and pathologic processes generation. Then, based on these biological considerations about the real vision mechanisms, we study an enhancement method for contrasting medical images, using either a discrete neural network approach, or its continuous version, i.e. a non-isotropic diffusion reaction partial differential system. Following this, we introduce other continuous operators based on similar biomimetic approaches: a chemotactic contrasting method, a viability contouring algorithm and an attentional focus operator. Then, we introduce the new notion of mixed potential Hamiltonian flows; we compare it with the watershed method and we use it for contouring. Conclusions We conclude by showing the utility of these biomimetic methods with some examples of application in medical imaging and computed assisted surgery. PMID:19547712

  1. Characterization of Mechanical Properties of Tissue Scaffolds by Phase Contrast Imaging and Finite Element Modeling.

    PubMed

    Bawolin, Nahshon K; Dolovich, Allan T; Chen, Daniel X B; Zhang, Chris W J

    2015-08-01

    In tissue engineering, the cell and scaffold approach has shown promise as a treatment to regenerate diseased and/or damaged tissue. In this treatment, an artificial construct (scaffold) is seeded with cells, which organize and proliferate into new tissue. The scaffold itself biodegrades with time, leaving behind only newly formed tissue. The degradation qualities of the scaffold are critical during the treatment period, since the change in the mechanical properties of the scaffold with time can influence cell behavior. To observe in time the scaffold's mechanical properties, a straightforward method is to deform the scaffold and then characterize scaffold deflection accordingly. However, experimentally observing the scaffold deflection is challenging. This paper presents a novel study on characterization of mechanical properties of scaffolds by phase contrast imaging and finite element modeling, which specifically includes scaffold fabrication, scaffold imaging, image analysis, and finite elements (FEs) modeling of the scaffold mechanical properties. The innovation of the work rests on the use of in-line phase contrast X-ray imaging at 20 KeV to characterize tissue scaffold deformation caused by ultrasound radiation forces and the use of the Fourier transform to identify movement. Once deformation has been determined experimentally, it is then compared with the predictions given by the forward solution of a finite element model. A consideration of the number of separate loading conditions necessary to uniquely identify the material properties of transversely isotropic and fully orthotropic scaffolds is also presented, along with the use of an FE as a form of regularization. PMID:25902011

  2. Two Rumex species from contrasting hydrological niches regulate flooding tolerance through distinct mechanisms.

    PubMed

    van Veen, Hans; Mustroph, Angelika; Barding, Gregory A; Vergeer-van Eijk, Marleen; Welschen-Evertman, Rob A M; Pedersen, Ole; Visser, Eric J W; Larive, Cynthia K; Pierik, Ronald; Bailey-Serres, Julia; Voesenek, Laurentius A C J; Sasidharan, Rashmi

    2013-11-01

    Global climate change has increased flooding events, which affect both natural vegetation dynamics and crop productivity. The flooded environment is lethal for most plant species because it restricts gas exchange and induces an energy and carbon crisis. Flooding survival strategies have been studied in Oryza sativa, a cultivated monocot. However, our understanding of plant adaptation to natural flood-prone environments remains scant, even though wild plants represent a valuable resource of tolerance mechanisms that could be used to generate stress-tolerant crops. Here we identify mechanisms that mediate the distinct flooding survival strategies of two related wild dicot species: Rumex palustris and Rumex acetosa. Whole transcriptome sequencing and metabolite profiling reveal flooding-induced metabolic reprogramming specific to R. acetosa. By contrast, R. palustris uses the early flooding signal ethylene to increase survival by regulating shade avoidance and photomorphogenesis genes to outgrow submergence and by priming submerged plants for future low oxygen stress. These results provide molecular resolution of flooding survival strategies of two species occupying distinct hydrological niches. Learning how these contrasting flood adaptive strategies evolved in nature will be instrumental for the development of stress-tolerant crop varieties that deliver enhanced yields in a changing climate. PMID:24285788

  3. Bogi and Capiron fields, Oriente Basin, Ecuador: Similar reservoirs but contrasting drive mechanisms and recoveries

    SciTech Connect

    Sanchez, H.; Morales, M.; Young, R.; Zambrano, H.

    1996-08-01

    Bogi and Capiron fields are being developed under a unit agreement with Petroecuador. These adjoining fields straddle Block 16 in the Oriente Basin and probably share a common oil water contact. Both fields are simple four-way-dip closures which produce heavy oil from Campanian sandstones of similar quality. However, the two fields are remarkably different in terms of oil production and projected recovery as a result of differing structural closures, reservoir distributions and, hence, differing drive mechanisms. The main reservoir at Bogi field is an amalgamation of two fluvial sheet sandstones thought to be low-stand deposits associated with two falls in relative sea level. The reservoir is thick (56-78 ft) and, with an observed oil column of only 38 feet, a bottom-water drive mechanism is ubiquitous. The oil is heavy (18 API) and mobility ratios unfavorable; water production is high and oil recovery from conventional drilling is expected to be 3-5%. In contrast, only the upper fluvial sheet sandstone is present in Capiron field and a reservoir thickness of 32-48 ft combined with an oil column of 99 ft ensures an edge-water drive mechanism over most of the field with concomitant initial low water production and oil recoveries of approximately 30%. The contrast between Bogi and Capiron fields highlights the problems and challenges in the Block 16 area. Small structural closures filled with heavy oil are abundant and an accurate seismic depth map coupled with an understanding of reservoir distribution are vital to economic success.

  4. Gadolinium-based contrast agent toxicity: a review of known and proposed mechanisms.

    PubMed

    Rogosnitzky, Moshe; Branch, Stacy

    2016-06-01

    Gadolinium chelates are widely used as contrast media for magnetic resonance imaging. The approved gadolinium-based contrast agents (GBCAs) have historically been considered safe and well tolerated when used at recommended dosing levels. However, for nearly a decade, an association between GBCA administration and the development of nephrogenic systemic fibrosis (NSF) has been recognized in patients with severe renal impairment. This has led to modifications in clinical practices aimed at reducing the potential and incidence of NSF development. Newer reports have emerged regarding the accumulation of gadolinium in various tissues of patients who do not have renal impairment, including bone, brain, and kidneys. Despite the observations of gadolinium accumulation in tissues regardless of renal function, very limited clinical data regarding the potential for and mechanisms of toxicity is available. This significant gap in knowledge warrants retrospective cohort study efforts, as well as prospective studies that involve gadolinium ion (Gd(3+)) testing in patients exposed to GBCA. This review examines the potential biochemical and molecular basis of gadolinium toxicity, possible clinical significance of gadolinium tissue retention and accumulation, and methods that can limit gadolinium body burden. PMID:27053146

  5. Contrast mechanism due to interface trapped charges for a buried SiO2 microstructure in scanning electron microscopy.

    PubMed

    Zhang, Hai-Bo; Li, Wei-Qin; Wu, Dan-Wei

    2009-01-01

    We clarify the scanning electron microscopic contrast mechanism for imaging a buried SiO(2) trench microstructure with interface trapped charges by simulating both electron scattering and transport. Here, the interface trapped charges make the SiO(2) film more negatively charged and increase excess holes in the space charge distribution of the electron scattering region. The generated positive surface electric field thus redistributes some emitted secondary electrons and results in the dark contrast. This contrast mechanism is validated by comparing with experiments, and it may also provide an interesting approach for imaging and detecting deep interface trapped charges in insulating films. PMID:19029106

  6. The Mechanical Effects of Ultrasound Contrast Agents on Micro-vessels

    NASA Astrophysics Data System (ADS)

    Hosseinkhah, N.; Hynynen, K.

    2011-09-01

    Ultrasound activated contrast agents inside microvessels induce mechanical effects on the vessel wall. It is important to use the bubbles safely and avoid rupturing the vessels. The objective of this work was to develop a three dimensional model of a bubble, blood and micro-vessels in order to investigate the mechanical effects (mainly the fluid shear stress and the circumferential stress) by a non-inertial microbubble on the vessel wall. A finite element method was used to solve for this model numerically. The blood vessel was simulated as having a viscoelastic, elastic or a rigid wall. Acoustic pressure and frequency were varied and the values for fluid shear stress and circumferential stress on the vessel wall were calculated. The circumferential stress could exceed the vascular strength in rigid microvessels if the applied acoustic pressure is above 260 kPa. Also the values for fluid shear stress are large enough to induce hemolysis or damage the cell membrane close to the oscillating bubble. Next, the streamlines and stagnation points are obtained for a rigid and a flexible vessel.

  7. Visual Contrast Sensitivity Improvement by Right Frontal High-Beta Activity Is Mediated by Contrast Gain Mechanisms and Influenced by Fronto-Parietal White Matter Microstructure.

    PubMed

    Quentin, Romain; Elkin Frankston, Seth; Vernet, Marine; Toba, Monica N; Bartolomeo, Paolo; Chanes, Lorena; Valero-Cabré, Antoni

    2016-06-01

    Behavioral and electrophysiological studies in humans and non-human primates have correlated frontal high-beta activity with the orienting of endogenous attention and shown the ability of the latter function to modulate visual performance. We here combined rhythmic transcranial magnetic stimulation (TMS) and diffusion imaging to study the relation between frontal oscillatory activity and visual performance, and we associated these phenomena to a specific set of white matter pathways that in humans subtend attentional processes. High-beta rhythmic activity on the right frontal eye field (FEF) was induced with TMS and its causal effects on a contrast sensitivity function were recorded to explore its ability to improve visual detection performance across different stimulus contrast levels. Our results show that frequency-specific activity patterns engaged in the right FEF have the ability to induce a leftward shift of the psychometric function. This increase in visual performance across different levels of stimulus contrast is likely mediated by a contrast gain mechanism. Interestingly, microstructural measures of white matter connectivity suggest a strong implication of right fronto-parietal connectivity linking the FEF and the intraparietal sulcus in propagating high-beta rhythmic signals across brain networks and subtending top-down frontal influences on visual performance. PMID:25899709

  8. Satellite Solar-induced Chlorophyll Fluorescence Reveals Drought Onset Mechanisms: Insights from Two Contrasting Extreme Events

    NASA Astrophysics Data System (ADS)

    Sun, Y.; Fu, R.; Dickinson, R. E.; Joiner, J.; Frankenberg, C.; Gu, L.; Xia, Y.; Fernando, N.

    2015-12-01

    This study uses the droughts of 2011 in Texas and 2012 over the central Great Plains as case studies to explore the potential of satellite-observed solar-induced chlorophyll fluorescence (SIF) for monitoring drought dynamics. We find that the spatial patterns of negative SIF anomalies from the Global Ozone Monitoring Instrument 2 (GOME-2) closely resembled drought intensity maps from the US Drought Monitor for both events. The drought-induced suppression of SIF occurred throughout 2011 but was exacerbated in summer in the Texas drought. This event was characterized by a persistent depletion of root-zone soil moisture caused by year-long below-normal precipitation. In contrast, for the central Great Plains drought, warmer temperatures and ample precipitation boosted SIF in the spring of 2012; however, a sudden drop in precipitation coupled with unusually high temperatures rapidly depleted soil moisture through evapotranspiration, leading to a rapid onset of drought in early summer. Accordingly, SIF reversed from above to below normal. For both regions, the GOME-2 SIF anomalies were significantly correlated with those of root-zone soil moisture, indicating that the former can potentially be used as proxy of the latter for monitoring agricultural droughts with different onset mechanisms. Further analyses indicate that the contrasting dynamics of SIF during these two extreme events were caused by changes in both fraction of absorbed photosynthetically active radiation (fPAR) and fluorescence yield, suggesting that satellite SIF is sensitive to both structural and physiological/biochemical variations of vegetation. We conclude that the emerging satellite SIF has excellent potential for dynamic drought monitoring.

  9. Contrasting macrophage activation by fine and ultrafine titanium dioxide particles is associated with different uptake mechanisms

    PubMed Central

    2011-01-01

    Inhalation of (nano)particles may lead to pulmonary inflammation. However, the precise mechanisms of particle uptake and generation of inflammatory mediators by alveolar macrophages (AM) are still poorly understood. The aim of this study was to investigate the interactions between particles and AM and their associated pro-inflammatory effects in relation to particle size and physico-chemical properties. NR8383 rat lung AM were treated with ultrafine (uf), fine (f) TiO2 or fine crystalline silica (DQ12 quartz). Physico-chemical particle properties were investigated by transmission electron microscopy, elemental analysis and thermogravimetry. Aggregation and agglomeration tendency of the particles were determined in assay-specific suspensions by means of dynamic light scattering. All three particle types were rapidly taken up by AM. DQ12 and ufTiO2 , but not fTiO2 , caused increased extracellular reactive oxygen species (ROS), heme oxygenase 1 (HO-1) mRNA expression and tumor necrosis factor (TNF)-α release. Inducible nitric oxide synthase (iNOS) mRNA expression was increased most strongly by ufTiO2 , while DQ12 exclusively triggered interleukin (IL) 1β release. However, oscillations of intracellular calcium concentration and increased intracellular ROS were observed with all three samples. Uptake inhibition experiments with cytochalasin D, chlorpromazine and a Fcγ receptor II (FcγRII) antibody revealed that the endocytosis of fTiO2 by the macrophages involves actin-dependent phagocytosis and macropinocytosis as well as clathrin-coated pit formation, whereas the uptake of ufTiO2 was dominated by FcγIIR. The uptake of DQ12 was found to be significantly reduced by all three inhibitors. Our findings suggest that the contrasting AM responses to fTiO2 , ufTiO2 and DQ12 relate to differences in the involvement of specific uptake mechanisms. PMID:21995556

  10. Fluid Dynamics of Contrast Dispersion in Coronary Arteries: Mechanism and Implications for Identification of Flow-Limiting Lesions

    NASA Astrophysics Data System (ADS)

    Eslami, Parastou; Seo, Jung-Hee; Lardo, Albert C.; Mittal, Rajat

    2013-11-01

    Recent coronary computed tomography angiography studies have noted the presence of axial contrast concentration gradients in stenosed coronary arteries, but the mechanism responsible for this phenomenon is not well understood. We use computational fluid dynamics to study intracoronary contrast dispersion and the correlation of concentration gradients with intracoronary blood flow and stenotic severity. Simulations of flow and contrast dispersion in both canonical and patient derived models of the left coronary artery (LCA) are carried out with a prescribed contrast bolus profile, and stenoses of varying severities (0% to 80%) considered. Data from our CFD simulations show the presence of measurable contrast gradients, the magnitude of which is found to decrease monotonically with stenotic severity and increase monotonically with the pressure drop across the stenosis. All simulated cases indicate a strong inverse correlation between contrast gradients and coronary flow rate. The study reveals that contrast gradients are generated by intracoronary advection effects, and therefore, encode coronary flow velocity. This research is supported by a grant from Coulter Foundation.

  11. Grid-texture mechanisms in human vision: Contrast detection of regular sparse micro-patterns requires specialist templates

    PubMed Central

    Baker, Daniel H.; Meese, Tim S.

    2016-01-01

    Previous work has shown that human vision performs spatial integration of luminance contrast energy, where signals are squared and summed (with internal noise) over area at detection threshold. We tested that model here in an experiment using arrays of micro-pattern textures that varied in overall stimulus area and sparseness of their target elements, where the contrast of each element was normalised for sensitivity across the visual field. We found a power-law improvement in performance with stimulus area, and a decrease in sensitivity with sparseness. While the contrast integrator model performed well when target elements constituted 50–100% of the target area (replicating previous results), observers outperformed the model when texture elements were sparser than this. This result required the inclusion of further templates in our model, selective for grids of various regular texture densities. By assuming a MAX operation across these noisy mechanisms the model also accounted for the increase in the slope of the psychometric function that occurred as texture density decreased. Thus, for the first time, mechanisms that are selective for texture density have been revealed at contrast detection threshold. We suggest that these mechanisms have a role to play in the perception of visual textures. PMID:27460430

  12. Grid-texture mechanisms in human vision: Contrast detection of regular sparse micro-patterns requires specialist templates.

    PubMed

    Baker, Daniel H; Meese, Tim S

    2016-01-01

    Previous work has shown that human vision performs spatial integration of luminance contrast energy, where signals are squared and summed (with internal noise) over area at detection threshold. We tested that model here in an experiment using arrays of micro-pattern textures that varied in overall stimulus area and sparseness of their target elements, where the contrast of each element was normalised for sensitivity across the visual field. We found a power-law improvement in performance with stimulus area, and a decrease in sensitivity with sparseness. While the contrast integrator model performed well when target elements constituted 50-100% of the target area (replicating previous results), observers outperformed the model when texture elements were sparser than this. This result required the inclusion of further templates in our model, selective for grids of various regular texture densities. By assuming a MAX operation across these noisy mechanisms the model also accounted for the increase in the slope of the psychometric function that occurred as texture density decreased. Thus, for the first time, mechanisms that are selective for texture density have been revealed at contrast detection threshold. We suggest that these mechanisms have a role to play in the perception of visual textures. PMID:27460430

  13. Susceptibility-Based Analysis Of Dynamic Gadolinium Bolus Perfusion MRI

    PubMed Central

    Bonekamp, David; Barker, Peter B.; Leigh, Richard; van Zijl, Peter C.M.; Li, Xu

    2014-01-01

    Purpose An algorithm is developed for the reconstruction of dynamic, gadolinium (Gd) bolus MR perfusion images of the human brain, based on quantitative susceptibility mapping (QSM). Methods The method is evaluated in 5 perfusion scans obtained from 4 different patients scanned at 3T, and compared to the conventional analysis based on changes in the transverse relaxation rate ΔR2* and to theoretical predictions. QSM images were referenced to ventricular CSF for each dynamic of the perfusion sequence. Results Images of cerebral blood flow and blood volume were successfully reconstructed from the QSM-analysis, and were comparable to those reconstructed using ΔR2*. The magnitudes of the Gd-associated susceptibility effects in gray and white matter were consistent with theoretical predictions. Conclusion QSM-based analysis may have some theoretical advantages compared to ΔR2*, including a simpler relationship between signal change and Gd concentration. However, disadvantages are its much lower contrast-to-noise ratio, artifacts due to respiration and other effects, and more complicated reconstruction methods. More work is required to optimize data acquisition protocols for QSM-based perfusion imaging. PMID:24604343

  14. RENAL RETENTION OF LIPID MICROBUBBLES: A POTENTIAL MECHANISM FOR FLANK DISCOMFORT DURING ULTRASOUND CONTRAST ADMINISTRATION

    PubMed Central

    Liu, Ya Ni; Khangura, Jaspreet; Xie, Aris; Belcik, J. Todd; Qi, Yue; Davidson, Brian P.; Zhao, Yan; Kim, Sajeevani; Inaba, Yoichi; Lindner, Jonathan R.

    2013-01-01

    Background The etiology for flank pain sometimes experienced during administration of ultrasound contrast agents is unknown. We investigated whether microbubble ultrasound contrast agents are retained within the renal microcirculation which could lead to either flow disturbance or local release of vasoactive and pain mediators downstream from complement activation. Methods Retention of lipid-shelled microbubbles in the renal microcirculation of mice was assessed by confocal fluorescent microscopy and contrast-enhanced ultrasound (CEU) imaging with dose-escalating intravenous injection. Studies were performed with size-segregated microbubbles to investigate physical entrapment, after glycocalyx degradation, and in wild-type and C3-deficient mice to investigate complement-mediated retention. Urinary bradykinin was measured before and after microbubbles. Renal CEU in human subjects (n=13) was performed 7–10 min after completion of lipid microbubble administration. Results In both mice and humans, microbubble retention was detected in the renal cortex by persistent CEU signal enhancement. Microbubble retention in mice was linearly related to dose and occurred almost exclusively in cortical glomerular microvessels. Microbubble retention did not affect microsphere-derived renal blood flow. Microbubble retention was not influenced by glycocalyx degradation nor by microbubble size, thereby excluding lodging, but was reduced by 90% (p<0.01) in C3-deficient mice. Urinary bradykinin increased by 65% five minutes after microbubble injection. Conclusion Lipid-shelled microbubbles are retained in the renal cortex due to complement-mediated interactions with glomerular microvascular endothelium. Microbubble retention does not adversely affect renal perfusion but does generate complement-related intermediates that are known to mediate nociception and could be responsible for flank pain. PMID:24035699

  15. Hydrology and seasonality determine distinct DOC export mechanisms in contrasting upland catchments in Scotland

    NASA Astrophysics Data System (ADS)

    Dawson, J. J. C.; Soulsby, C.; Tetzlaff, D.; Hrachowitz, M.; Dunn, S. M.; Malcolm, I. A.

    2009-04-01

    How climate variability influences soil processes, production and export of DOC are important in understanding hydrologically mediated carbon losses from soils and its affect on stream and river water quality. This necessitates understanding both biogeochemical and hydrological factors that control the quantity and timing of carbon availability for export from soils to the drainage network. Long-term records of DOC concentrations at upland catchments with contrasting climatic characteristics in Scotland were investigated for intra-annual relationships to evaluate potential long-term seasonal as well as inter-annual patterns. Catchments in West-Central Scotland (>2000 mm/yr rainfall) with high rainfall-runoff ratios, short transit times and well-connected responsive soils show a distinct annual periodicity in DOC concentrations throughout the long-term datasets. Increased DOC concentrations occurred between June and November with correspondingly lower DOC concentrations from December to May. This appears unrelated to discharge, and is dependent mainly on higher temperatures driving biological activity, increasing decomposition of available organic matter for rapid export. Relatively drier catchments (ca. 1000 mm/yr) have lower rainfall-runoff ratios, longer transit times and annual drying-wetting regimes linked to changing connectivity of soils. These are characterised by seasonal DOC concentration-discharge relationships with an autumnal flush of DOC. Temperature influences the availability of organic matter for eventual DOC transport producing a high DOC concentration-discharge relationship in summer/autumn and low DOC concentration-discharge relationship in winter/spring. These two distinct modes of seasonal DOC transport have important implications for understanding changes in DOC concentrations and export brought about by climate changes (temperature, rainfall and deposition patterns) and modeling of aquatic carbon losses from soil-types under different

  16. Iron isotope differences between Earth, Moon, Mars and Vesta as possible records of contrasted accretion mechanisms

    NASA Astrophysics Data System (ADS)

    Poitrasson, Franck; Halliday, Alexander N.; Lee, Der-Chuen; Levasseur, Sylvain; Teutsch, Nadya

    2004-07-01

    The iron isotope compositions of Shergotty-Nakhla-Chassigny (SNC) meteorites thought to come from Mars, eucrites and diogenites assumed to sample asteroid 4 Vesta, and rocks from the Moon and Earth have been measured using high precision plasma source mass spectrometry. The means of eight samples from Mars and nine samples from Vesta are within error identical despite a range of rock types. They are lighter by ˜0.1‰ in δ57Fe/ 54Fe compared to the average of 13 terrestrial mantle-derived rocks. The latter value is identical within uncertainty with a previously published mean of 46 igneous rocks from the Earth. The average for 14 lunar basalts and highland plutonic rocks covering a broad spectrum of major element composition is heavier by ˜0.1‰ in δ57Fe/ 54Fe relative to our estimate for the Earth's mantle, and therefore ˜0.2‰ heavier than the eucrites, diogenites and SNC meteorites. However, the data scatter somewhat and the Apollo 15 green glass and Apollo 17 orange glass are identical to samples from Mars and Vesta. There is no clear relationship between petrological characteristics and Fe isotope composition despite a wide spectrum of samples. Instead, contrasted planetary isotopic signatures are clearly resolved statistically. After evaluating alternative scenario, it appears that the most plausible explanation for the heavier Fe in the Earth and Moon is that both objects grew via processes that involved partial vaporisation leading to kinetic iron isotope fractionation followed by minor loss. This is consistent with the theory in which the Moon is thought to have originated from a giant impact between the proto-Earth and another planet. Combined with numerical simulations, Fe isotope data can offer the potential to provide constraints on the processes that occurred in planetary accretion.

  17. Contrasting Potato Foliage and Tuber Defense Mechanisms against the Late Blight Pathogen Phytophthora infestans.

    PubMed

    Gao, Liangliang; Bradeen, James M

    2016-01-01

    The late blight pathogen Phytophthora infestans can attack both potato foliage and tubers. When inoculated with P. infestans, foliage of nontransformed 'Russet Burbank' (WT) develops late blight disease while that of transgenic 'Russet Burbank' line SP2211 (+RB) does not. We compared the foliar transcriptome responses of these two lines to P. infestans inoculation using an RNA-seq approach. A total of 515 million paired end RNA-seq reads were generated, representing the transcription of 29,970 genes. We also compared the differences and similarities of defense mechanisms against P. infestans in potato foliage and tubers. Differentially expressed genes, gene groups and ontology bins were identified to show similarities and differences in foliage and tuber defense mechanisms. Our results suggest that R gene dosage and shared biochemical pathways (such as ethylene and stress bins) contribute to RB-mediated incompatible potato-P. infestans interactions in both the foliage and tubers. Certain ontology bins such as cell wall and lipid metabolisms are potentially organ-specific. PMID:27441721

  18. Contrasting Potato Foliage and Tuber Defense Mechanisms against the Late Blight Pathogen Phytophthora infestans

    PubMed Central

    Bradeen, James M.

    2016-01-01

    The late blight pathogen Phytophthora infestans can attack both potato foliage and tubers. When inoculated with P. infestans, foliage of nontransformed ‘Russet Burbank’ (WT) develops late blight disease while that of transgenic ‘Russet Burbank’ line SP2211 (+RB) does not. We compared the foliar transcriptome responses of these two lines to P. infestans inoculation using an RNA-seq approach. A total of 515 million paired end RNA-seq reads were generated, representing the transcription of 29,970 genes. We also compared the differences and similarities of defense mechanisms against P. infestans in potato foliage and tubers. Differentially expressed genes, gene groups and ontology bins were identified to show similarities and differences in foliage and tuber defense mechanisms. Our results suggest that R gene dosage and shared biochemical pathways (such as ethylene and stress bins) contribute to RB-mediated incompatible potato-P. infestans interactions in both the foliage and tubers. Certain ontology bins such as cell wall and lipid metabolisms are potentially organ-specific. PMID:27441721

  19. Characterization of mechanical properties of hybrid contrast agents by combining atomic force microscopy with acoustic/optic assessments.

    PubMed

    Guo, Gepu; Tu, Juan; Guo, Xiasheng; Huang, Pintong; Wu, Junru; Zhang, Dong

    2016-02-01

    Multi-parameter fitting algorithms, which are currently used for the characterization of coated-bubbles, inevitably introduce uncertainty into the results. Therefore, a better technique that can accurately determine the microbubbles׳ mechanical properties is urgently needed. A comprehensive technology combining atomic force microscopy, optical, and acoustic measurements with simulations of coated-bubble dynamics was developed. Using this technique, the mechanical parameters (size distribution, shell thickness, elasticity, and viscosity) of hybrid (ultrasound/magnetic-resonance-imaging) contrast microbubbles and their structure-property relationship were determined. The measurements indicate that when more superparamagnetic iron oxide nanoparticles are embedded in the microbubbles׳ shells, their mean diameter and effective viscosity increase, and their elastic modulus decreases. This reduces the microbubbles׳ resonance frequency and thus enhances acoustic scattering and attenuation effects. PMID:26726783

  20. Root Antioxidant Mechanisms in Relation to Root Thermotolerance in Perennial Grass Species Contrasting in Heat Tolerance.

    PubMed

    Xu, Yi; Burgess, Patrick; Huang, Bingru

    2015-01-01

    Mechanisms of plant root tolerance to high temperatures through antioxidant defense are not well understood. The objective of this study was to investigate whether superior root thermotolerance of heat-tolerant Agrostis scabra relative to its congeneric heat-sensitive Agrostis stolonifera was associated with differential accumulation of reactive oxygen species and antioxidant scavenging systems. A. scabra 'NTAS' and A. stolonifera 'Penncross' plants were exposed to heat stress (35/30°C, day/night) in growth chambers for 24 d. Superoxide (O2(-)) content increased in both A. stolonifera and A. scabra roots under heat stress but to a far lesser extent in A. scabra than in A. stolonifera. Hydrogen peroxide (H2O2) content increased significantly in A. stolonifera roots but not in A. scabra roots responding to heat stress. The content of antioxidant compounds (ascorbate and glutathione) did not differ between A. stolonifera and A. scabra under heat stress. Enzymatic activity of superoxide dismutase was less suppressed in A. scabra than that in A. stolonifera under heat stress, while peroxidase and catalase were more induced in A. scabra than in A. stolonifera. Similarly, their encoded transcript levels were either less suppressed, or more induced in A. scabra roots than those in A. stolonifera during heat stress. Roots of A. scabra exhibited greater alternative respiration rate and lower cytochrome respiration rate under heat stress, which was associated with suppression of O2(-) and H2O2 production as shown by respiration inhibitors. Superior root thermotolerance of A. scabra was related to decreases in H2O2 and O2(-) accumulation facilitated by active enzymatic antioxidant defense systems and the maintenance of alternative respiration, alleviating cellular damages by heat-induced oxidative stress. PMID:26382960

  1. Telomerase inhibitors and 'T-oligo' as cancer therapeutics: contrasting molecular mechanisms of cytotoxicity.

    PubMed

    Rankin, Andrew M; Faller, Douglas V; Spanjaard, Remco A

    2008-04-01

    Telomeres, the specialized structures that comprise the ends of chromosomes, form a closed structure, or t-loop, that is important in preventing genomic instability. Forced modulation of this structure, via overexpression of a dominant-negative form of telomere repeat binding factor 2, a protein critical for maintaining t-loop structure, for example, can result in the activation of DNA-damage responses, and ultimately cellular senescence or apoptosis. This response is also seen in normal somatic cells, where telomeres steadily decrease in length as cellular proliferation occurs owing to inefficient replication of terminal telomeric DNA. When telomere length becomes critically short, t-loop structure is compromised, and the cell undergoes senescence. Telomerase, the enzyme responsible for telomere length maintenance, is overexpressed in a majority of cancers. Its lack of expression in most normal somatic cells makes it an attractive target in designing cancer therapeutics. Compounds currently under development that seek to inhibit hTERT, the reverse transcriptase component of telomerase, include nucleoside analogs and the small molecule BIBR1532. Compounds inhibiting the RNA component of telomerase, hTERC, include peptide nucleic acids, 2-5A antisense oligonucleotides, and N3'-P5' thio-phosphoramidates. Recently, an oligonucleotide sharing sequence homology with terminal telomeric DNA, termed 'T-oligo', has shown cytotoxic effects in multiple cancers in culture and animal models. Independent of telomerase function, T-oligo is thought to mimic the DNA-damage response a cell normally experiences when the telomere t-loop structure becomes dysfunctional. In this review, the molecular mechanisms attributed to telomerase inhibitors and T-oligo, as well as their potential as cancer therapeutics, are discussed. PMID:18454043

  2. Root Antioxidant Mechanisms in Relation to Root Thermotolerance in Perennial Grass Species Contrasting in Heat Tolerance

    PubMed Central

    Xu, Yi; Burgess, Patrick; Huang, Bingru

    2015-01-01

    Mechanisms of plant root tolerance to high temperatures through antioxidant defense are not well understood. The objective of this study was to investigate whether superior root thermotolerance of heat-tolerant Agrostis scabra relative to its congeneric heat-sensitive Agrostis stolonifera was associated with differential accumulation of reactive oxygen species and antioxidant scavenging systems. A. scabra ‘NTAS’ and A. stolonifera ‘Penncross’ plants were exposed to heat stress (35/30°C, day/night) in growth chambers for 24 d. Superoxide (O2-) content increased in both A. stolonifera and A. scabra roots under heat stress but to a far lesser extent in A. scabra than in A. stolonifera. Hydrogen peroxide (H2O2) content increased significantly in A. stolonifera roots but not in A. scabra roots responding to heat stress. The content of antioxidant compounds (ascorbate and glutathione) did not differ between A. stolonifera and A. scabra under heat stress. Enzymatic activity of superoxide dismutase was less suppressed in A. scabra than that in A. stolonifera under heat stress, while peroxidase and catalase were more induced in A. scabra than in A. stolonifera. Similarly, their encoded transcript levels were either less suppressed, or more induced in A. scabra roots than those in A. stolonifera during heat stress. Roots of A. scabra exhibited greater alternative respiration rate and lower cytochrome respiration rate under heat stress, which was associated with suppression of O2- and H2O2 production as shown by respiration inhibitors. Superior root thermotolerance of A. scabra was related to decreases in H2O2 and O2- accumulation facilitated by active enzymatic antioxidant defense systems and the maintenance of alternative respiration, alleviating cellular damages by heat-induced oxidative stress. PMID:26382960

  3. Two Rumex Species from Contrasting Hydrological Niches Regulate Flooding Tolerance through Distinct Mechanisms[C][W][OPEN

    PubMed Central

    van Veen, Hans; Mustroph, Angelika; Barding, Gregory A.; Vergeer-van Eijk, Marleen; Welschen-Evertman, Rob A.M.; Pedersen, Ole; Visser, Eric J.W.; Larive, Cynthia K.; Pierik, Ronald; Bailey-Serres, Julia; Voesenek, Laurentius A.C.J.; Sasidharan, Rashmi

    2013-01-01

    Global climate change has increased flooding events, which affect both natural vegetation dynamics and crop productivity. The flooded environment is lethal for most plant species because it restricts gas exchange and induces an energy and carbon crisis. Flooding survival strategies have been studied in Oryza sativa, a cultivated monocot. However, our understanding of plant adaptation to natural flood-prone environments remains scant, even though wild plants represent a valuable resource of tolerance mechanisms that could be used to generate stress-tolerant crops. Here we identify mechanisms that mediate the distinct flooding survival strategies of two related wild dicot species: Rumex palustris and Rumex acetosa. Whole transcriptome sequencing and metabolite profiling reveal flooding-induced metabolic reprogramming specific to R. acetosa. By contrast, R. palustris uses the early flooding signal ethylene to increase survival by regulating shade avoidance and photomorphogenesis genes to outgrow submergence and by priming submerged plants for future low oxygen stress. These results provide molecular resolution of flooding survival strategies of two species occupying distinct hydrological niches. Learning how these contrasting flood adaptive strategies evolved in nature will be instrumental for the development of stress-tolerant crop varieties that deliver enhanced yields in a changing climate. PMID:24285788

  4. Motionless electromagnetic phase stepping versus mechanical phase stepping in x-ray phase-contrast imaging with a compact source.

    PubMed

    Harmon, Katherine J; Miao, Houxun; Gomella, Andrew A; Bennett, Eric E; Foster, Barbara A; Bhandarkar, Priya; Wen, Han

    2015-04-21

    X-ray phase contrast imaging based on grating interferometers detects the refractive index distribution of an object without relying on radiation attenuation, thereby having the potential for reduced radiation absorption. These techniques belong to the broader category of optical wavefront measurement, which requires stepping the phase of the interference pattern to obtain a pixel-wise map of the phase distortion of the wavefront. While phase stepping traditionally involves mechanical scanning of a grating or mirror, we developed electromagnetic phase stepping (EPS) for imaging with compact sources to obviate the need for mechanical movement. In EPS a solenoid coil is placed outside the x-ray tube to shift its focal spot with a magnetic field, causing a relative movement between the projection of the sample and the interference pattern in the image. Here we present two embodiments of this method. We verified experimentally that electromagnetic and mechanical phase stepping give the same results and attain the same signal-to-noise ratios under the same radiation dose. We found that the relative changes of interference fringe visibility were within 3.0% when the x-ray focal spot was shifted by up to 1.0 mm in either direction. We conclude that when using x-ray tube sources, EPS is an effective means of phase stepping without the need for mechanical movement. PMID:25803511

  5. A phase-contrast microscopy-based method for modeling the mechanical behavior of mesenchymal stem cells.

    PubMed

    Saeed, Mayssam; Sharabani-Yosef, Orna; Weihs, Daphne; Gefen, Amit

    2016-10-01

    We present three-dimensional (3D) finite element (FE) models of single, mesenchymal stem cells (MSCs), generated from images obtained by optical phase-contrast microscopy and used to quantify the structural responses of the studied cells to externally applied mechanical loads. Mechanical loading has been shown to affect cell morphology and structure, phenotype, motility and other biological functions. Cells experience mechanical loads naturally, yet under prolonged or sizable loading, damage and cell death may occur, which motivates research regarding the structural behavior of loaded cells. For example, near the weight-bearing boney prominences of the buttocks of immobile persons, tissues may become highly loaded, eventually leading to massive cell death that manifests as pressure ulcers. Cell-specific computational models have previously been developed by our group, allowing simulations of cell deformations under compressive or stretching loads. These models were obtained by reconstructing specific cell structures from series of 2D fluorescence, confocal image-slices, requiring cell-specific fluorescent-staining protocols and costly (confocal) microscopy equipment. Alternative modeling approaches represent cells simply as half-spheres or half-ellipsoids (i.e. idealized geometries), which neglects the curvature details of the cell surfaces associated with changes in concentrations of strains and stresses. Thus, we introduce here for the first time an optical image-based FE modeling, where loads are simulated on reconstructed 3D geometrical cell models from a single 2D, phase-contrast image. Our novel modeling method eliminates the need for confocal imaging and fluorescent staining preparations (both expensive), and makes cell-specific FE modeling affordable and accessible to the biomechanics community. We demonstrate the utility of this cost-effective modeling method by performing simulations of compression of MSCs embedded in a gel. PMID:26856632

  6. Transcriptome Analysis of Sunflower Genotypes with Contrasting Oxidative Stress Tolerance Reveals Individual- and Combined- Biotic and Abiotic Stress Tolerance Mechanisms

    PubMed Central

    Ramu, Vemanna S.; Paramanantham, Anjugam; Ramegowda, Venkategowda; Mohan-Raju, Basavaiah; Udayakumar, Makarla

    2016-01-01

    In nature plants are often simultaneously challenged by different biotic and abiotic stresses. Although the mechanisms underlying plant responses against single stress have been studied considerably, plant tolerance mechanisms under combined stress is not understood. Also, the mechanism used to combat independently and sequentially occurring many number of biotic and abiotic stresses has also not systematically studied. From this context, in this study, we attempted to explore the shared response of sunflower plants to many independent stresses by using meta-analysis of publically available transcriptome data and transcript profiling by quantitative PCR. Further, we have also analyzed the possible role of the genes so identified in contributing to combined stress tolerance. Meta-analysis of transcriptomic data from many abiotic and biotic stresses indicated the common representation of oxidative stress responsive genes. Further, menadione-mediated oxidative stress in sunflower seedlings showed similar pattern of changes in the oxidative stress related genes. Based on this a large scale screening of 55 sunflower genotypes was performed under menadione stress and those contrasting in oxidative stress tolerance were identified. Further to confirm the role of genes identified in individual and combined stress tolerance the contrasting genotypes were individually and simultaneously challenged with few abiotic and biotic stresses. The tolerant hybrid showed reduced levels of stress damage both under combined stress and few independent stresses. Transcript profiling of the genes identified from meta-analysis in the tolerant hybrid also indicated that the selected genes were up-regulated under individual and combined stresses. Our results indicate that menadione-based screening can identify genotypes not only tolerant to multiple number of individual biotic and abiotic stresses, but also the combined stresses. PMID:27314499

  7. Drought onset mechanisms revealed by satellite solar-induced chlorophyll fluorescence: Insights from two contrasting extreme events

    NASA Astrophysics Data System (ADS)

    Sun, Ying; Fu, Rong; Dickinson, Robert; Joiner, Joanna; Frankenberg, Christian; Gu, Lianhong; Xia, Youlong; Fernando, Nelun

    2015-11-01

    This study uses the droughts of 2011 in Texas and 2012 over the central Great Plains as case studies to explore the potential of satellite-observed solar-induced chlorophyll fluorescence (SIF) for monitoring drought dynamics. We find that the spatial patterns of negative SIF anomalies from the Global Ozone Monitoring Experiment 2 (GOME-2) closely resembled drought intensity maps from the U.S. Drought Monitor for both events. The drought-induced suppression of SIF occurred throughout 2011 but was exacerbated in summer in the Texas drought. This event was characterized by a persistent depletion of root zone soil moisture caused by yearlong below-normal precipitation. In contrast, for the central Great Plains drought, warmer temperatures and relatively normal precipitation boosted SIF in the spring of 2012; however, a sudden drop in precipitation coupled with unusually high temperatures rapidly depleted soil moisture through evapotranspiration, leading to a rapid onset of drought in early summer. Accordingly, SIF reversed from above to below normal. For both regions, the GOME-2 SIF anomalies were significantly correlated with those of root zone soil moisture, indicating that the former can potentially be used as proxy of the latter for monitoring agricultural droughts with different onset mechanisms. Further analyses indicate that the contrasting dynamics of SIF during these two extreme events were caused by changes in both fraction of absorbed photosynthetically active radiation fPAR and fluorescence yield, suggesting that satellite SIF is sensitive to both structural and physiological/biochemical variations of vegetation. We conclude that the emerging satellite SIF has excellent potential for dynamic drought monitoring.

  8. A three dimensional model of an ultrasound contrast agent gas bubble and its mechanical effects on microvessels

    PubMed Central

    Hosseinkhah, N.; Hynynen, K.

    2012-01-01

    Ultrasound contrast agents inside a microvessel, when driven by ultrasound, oscillate and induce mechanical stresses on the vessel wall. These mechanical stresses can produce beneficial therapeutic effects but also induce vessel rupture if the stresses are too high. Therefore, it is important to use sufficiently low pressure amplitudes to avoid rupturing the vessels while still inducing the desired therapeutic effects. In this work, we developed a comprehensive three dimensional model of a confined microbubble inside a vessel while considering the bubble shell properties, blood viscosity, vessel wall curvature and the mechanical properties of the vessel wall. Two bubble models with the assumption of a spherical symmetric bubble and a simple asymmetrical bubble were simulated. This work was validated with previous experimental results and enabled us to evaluate the microbubbles’ behaviour and the resulting mechanical stresses induced on the vessel walls. In this study the fluid shear and circumferential stresses were evaluated as indicators of the mechanical stresses. The effects of acoustical parameters, vessel viscoelasticity and rigidity, vessel/bubble size and off-center bubbles on bubble behaviour and stresses on the vessel were investigated. The fluid shear and circumferential stresses acting on the vessel varied with time and location. As the frequency changed, the microbubble oscillated with the highest amplitude at its resonance frequency which was different from the resonance frequency of an unbound bubble. The bubble resonance frequency increased as the rigidity of a flexible vessel increased. The fluid shear and circumferential stresses peaked at frequencies above the bubble’s resonance frequency. The more rigid the vessels were, the more damped the bubble oscillations. The synergistic effect of acoustic frequency and vessel elasticity had also been investigated, since the circumferential stress showed either an increasing trend or a decreasing one

  9. Contrasting oxidative stress response mechanisms in novel strains of Bacillus isolated from the Mars-analog, Mojave Desert

    NASA Astrophysics Data System (ADS)

    Lera, M.; Marcu, O.

    2011-12-01

    Environmental conditions that limit the presence of life include ionizing radiation, extreme temperatures, and lack of water. These environments are common in our solar system and may contribute to the lack of apparent life. However, analogous environments here on Earth are host to a multitude of thriving microbial life. In order for microbes to survive in dry deserts, they must be must be able to adapt to transient diurnal and seasonal changes in the environment (water, temperature). To uncover response strategies to environmental stress that may prevent cellular damage and ensure adaptation and survival, two distinct, novel strains of Bacillus were isolated from the Mojave Desert (a Mars analog due to its arid conditions and high incidence of ultraviolet light) and classified by their partial 16S RNA gene sequences. These species, despite being closely related, exhibited radically different phenotypes and contrasting strategies for mitigating stress. The two strains had different growth rates, metabolic capacities and sporulation onset times when challenged by crowding and heat-shock. In response to hydrogen peroxide challenge, the intracellular levels of catalase activity, a peroxide-scavenging enzyme, differed for each strain, and were surprisingly lower than that of a non-desert control species of Bacillus. DNA repair mechanisms were more active in one strain than the other, and one isolate responded with an increase in expression of longevity gene orthologs involved in stress response. After multiple rounds of culturing, the peroxide degradation capacity, as well as the growth and sporulation rates remained constant for each strain, which suggests these are permanent features of each strain rather than transient responses. Taken together, these data uncover a diverse arsenal of response mechanisms employed by closely related species to combat stress. These adaptations may provide environmental-niche specificity and the diversity of life even in a scarce

  10. Contrast studies.

    PubMed

    Anderson, Susan M

    2006-01-01

    Contrast media plays an important role in imaging soft tissues and organs. Though contrast imaging is considered safe, radiologic technologists can improve the safety of contrast examinations by reviewing institutional safety procedures, safe practices for different methods of contrast administration and possible complications. The need for efficient communication and attention to detail during contrast procedures is essential for patient safety. PMID:16998193

  11. Optimisation of image reconstruction for phase-contrast x-ray Talbot–Lau imaging with regard to mechanical robustness

    NASA Astrophysics Data System (ADS)

    Seifert, M.; Kaeppler, S.; Hauke, C.; Horn, F.; Pelzer, G.; Rieger, J.; Michel, T.; Riess, C.; Anton, G.

    2016-09-01

    X-ray grating-based phase-contrast imaging opens new opportunities, inter alia, in medical imaging and non-destructive testing. Because, information about the attenuation properties and about the refractive properties of an object are gained simultaneously. Talbot–Lau imaging requires the knowledge of a reference or free-field image. The long-term stability of a Talbot–Lau interferometer is related to the time span of the validity of a measured reference image. It would be desirable to keep the validity of the reference image for a day or longer to improve feasibility of Talbot–Lau imaging. However, for example thermal and other long-term external influences result in drifting effects of the phase images. Therefore, phases are shifting over time and the reference image is not valid for long-term measurements. Thus, artifacts occur in differential phase-contrast images. We developed an algorithm to determine the differential phase-contrast image with the help of just one calibration image, which is valid for a long time-period. With the help of this algorithm, called phase-plane-fit method, it is possible to save measurement-time, as it is not necessary to take a reference image for each measurement. Additionally, transferring the interferometer technique from laboratory setups to conventional imaging systems the necessary rigidity of the system is difficult to achieve. Therefore, short-term effects like vibrations or distortions of the system lead to imperfections within the phase-stepping procedure. Consequently, artifacts occur in all three image modalities (differential phase-contrast image, attenuation image and dark-field image) of Talbot–Lau imaging. This is a problem with regard to the intended use of phase-contrast imaging for example in clinical routine or non-destructive testing. In this publication an algorithm of Vargas et al is applied and complemented to correct inaccurate phase-step positions with the help of a principal component analysis

  12. Optimisation of image reconstruction for phase-contrast x-ray Talbot-Lau imaging with regard to mechanical robustness.

    PubMed

    Seifert, M; Kaeppler, S; Hauke, C; Horn, F; Pelzer, G; Rieger, J; Michel, T; Riess, C; Anton, G

    2016-09-01

    X-ray grating-based phase-contrast imaging opens new opportunities, inter alia, in medical imaging and non-destructive testing. Because, information about the attenuation properties and about the refractive properties of an object are gained simultaneously. Talbot-Lau imaging requires the knowledge of a reference or free-field image. The long-term stability of a Talbot-Lau interferometer is related to the time span of the validity of a measured reference image. It would be desirable to keep the validity of the reference image for a day or longer to improve feasibility of Talbot-Lau imaging. However, for example thermal and other long-term external influences result in drifting effects of the phase images. Therefore, phases are shifting over time and the reference image is not valid for long-term measurements. Thus, artifacts occur in differential phase-contrast images. We developed an algorithm to determine the differential phase-contrast image with the help of just one calibration image, which is valid for a long time-period. With the help of this algorithm, called phase-plane-fit method, it is possible to save measurement-time, as it is not necessary to take a reference image for each measurement. Additionally, transferring the interferometer technique from laboratory setups to conventional imaging systems the necessary rigidity of the system is difficult to achieve. Therefore, short-term effects like vibrations or distortions of the system lead to imperfections within the phase-stepping procedure. Consequently, artifacts occur in all three image modalities (differential phase-contrast image, attenuation image and dark-field image) of Talbot-Lau imaging. This is a problem with regard to the intended use of phase-contrast imaging for example in clinical routine or non-destructive testing. In this publication an algorithm of Vargas et al is applied and complemented to correct inaccurate phase-step positions with the help of a principal component analysis (PCA

  13. Simultaneous X-ray diffraction and phase-contrast imaging for investigating material deformation mechanisms during high-rate loading

    SciTech Connect

    Hudspeth, M.; Sun, T.; Parab, N.; Guo, Z.; Fezzaa, K.; Luo, S.; Chen, W.

    2015-01-01

    Using a high-speed camera and an intensified charge-coupled device (ICCD), a simultaneous X-ray imaging and diffraction technique has been developed for studying dynamic material behaviors during high-rate tensile loading. A Kolsky tension bar has been used to pull samples at 1000 s–1and 5000 s–1strain-rates for super-elastic equiatomic NiTi and 1100-O series aluminium, respectively. By altering the ICCD gating time, temporal resolutions of 100 ps and 3.37 µs have been achieved in capturing the diffraction patterns of interest, thus equating to single-pulse and 22-pulse X-ray exposure. Furthermore, the sample through-thickness deformation process has been simultaneously imagedviaphase-contrast imaging. It is also shown that adequate signal-to-noise ratios are achieved for the detected white-beam diffraction patterns, thereby allowing sufficient information to perform quantitative data analysis diffractionviain-house software (WBXRD_GUI). Finally, of current interest is the ability to evaluate crystald-spacing, texture evolution and material phase transitions, all of which will be established from experiments performed at the aforementioned elevated strain-rates.

  14. Simultaneous X-ray diffraction and phase-contrast imaging for investigating material deformation mechanisms during high-rate loading

    PubMed Central

    Hudspeth, M.; Sun, T.; Parab, N.; Guo, Z.; Fezzaa, K.; Luo, S.; Chen, W.

    2015-01-01

    Using a high-speed camera and an intensified charge-coupled device (ICCD), a simultaneous X-ray imaging and diffraction technique has been developed for studying dynamic material behaviors during high-rate tensile loading. A Kolsky tension bar has been used to pull samples at 1000 s−1 and 5000 s−1 strain-rates for super-elastic equiatomic NiTi and 1100-O series aluminium, respectively. By altering the ICCD gating time, temporal resolutions of 100 ps and 3.37 µs have been achieved in capturing the diffraction patterns of interest, thus equating to single-pulse and 22-pulse X-ray exposure. Furthermore, the sample through-thickness deformation process has been simultaneously imaged via phase-contrast imaging. It is also shown that adequate signal-to-noise ratios are achieved for the detected white-beam diffraction patterns, thereby allowing sufficient information to perform quantitative data analysis diffraction via in-house software (WBXRD_GUI). Of current interest is the ability to evaluate crystal d-spacing, texture evolution and material phase transitions, all of which will be established from experiments performed at the aforementioned elevated strain-rates. PMID:25537588

  15. Simultaneous X-ray diffraction and phase-contrast imaging for investigating material deformation mechanisms during high-rate loading

    DOE PAGESBeta

    Hudspeth, M.; Sun, T.; Parab, N.; Guo, Z.; Fezzaa, K.; Luo, S.; Chen, W.

    2015-01-01

    Using a high-speed camera and an intensified charge-coupled device (ICCD), a simultaneous X-ray imaging and diffraction technique has been developed for studying dynamic material behaviors during high-rate tensile loading. A Kolsky tension bar has been used to pull samples at 1000 s–1and 5000 s–1strain-rates for super-elastic equiatomic NiTi and 1100-O series aluminium, respectively. By altering the ICCD gating time, temporal resolutions of 100 ps and 3.37 µs have been achieved in capturing the diffraction patterns of interest, thus equating to single-pulse and 22-pulse X-ray exposure. Furthermore, the sample through-thickness deformation process has been simultaneously imagedviaphase-contrast imaging. It is also shownmore » that adequate signal-to-noise ratios are achieved for the detected white-beam diffraction patterns, thereby allowing sufficient information to perform quantitative data analysis diffractionviain-house software (WBXRD_GUI). Finally, of current interest is the ability to evaluate crystald-spacing, texture evolution and material phase transitions, all of which will be established from experiments performed at the aforementioned elevated strain-rates.« less

  16. Contrastive Lexicology.

    ERIC Educational Resources Information Center

    Hartmann, R. R. K.

    This paper deals with the relation between etymologically related words in different languages. A survey is made of seven stages in the development of contrastive lexicology. These are: prelinguistic word studies, semantics, lexicography, translation, foreign language learning, bilingualism, and finally contrastive analysis. Concerning contrastive…

  17. Unique pumping-out fracturing mechanism of a polymer-shelled contrast agent: an acoustic characterization and optical visualization.

    PubMed

    Kothapalli, Satya V V N; Daeichin, Verya; Mastik, Frits; Brodin, Lars Åke; Janerot-Sjoberg, Birgitta; Paradossi, Gaio; de Jong, Nico; Grishenkov, Dmitry

    2015-03-01

    This work describes the fracturing mechanism of air-filled microbubbles (MBs) encapsulated by a cross-linked poly(vinyl alcohol) (PVA) shell. The radial oscillation and fracturing events following the ultrasound exposure were visualized with an ultrahigh-speed camera, and backscattered timedomain signals were acquired with the acoustic setup specific for harmonic detection. No evidence of gas emerging from defects in the shell with the arrival of the first insonation burst was found. In optical recordings, more than one shell defect was noted, and the gas core was drained without any sign of air extrusion when several consecutive bursts of 1 MPa amplitude were applied. In acoustic tests, the backscattered peak-to-peak voltage gradually reached its maximum and exponentially decreased when the PVA-based MB suspension was exposed to approximately 20 consecutive bursts arriving at pulse repetition frequencies of 100 and 500 Hz. Taking into account that the PVA shell is porous and possibly contains large air pockets between the cross-linked PVA chains, the aforementioned acoustic behavior might be attributed to pumping gas from these pockets in combination with gas release from the core through shell defects. We refer to this fracturing mechanism as pumping-out behavior, and this behavior could have potential use for the local delivery of therapeutic gases, such as nitric oxide. PMID:25768814

  18. Contrast Materials

    MedlinePlus

    ... or other reactions to contrast materials are rare, radiology departments are well-equipped to deal with them. ... is given. However, both the American College of Radiology (ACR) and the European Society of Urogenital Radiology ...

  19. Unraveling the mechanism responsible for the contrasting tolerance of Synechocystis and Synechococcus to Cr(VI): Enzymatic and non-enzymatic antioxidants.

    PubMed

    Gupta, Alka; Ballal, Anand

    2015-07-01

    Two unicellular cyanobacteria, Synechocystis and Synechococcus, showed contrasting tolerance to Cr(VI); with Synechococcus being 12-fold more tolerant than Synechocystis to potassium dichromate. The mechanism responsible for this differential sensitivity to Cr(VI) was explored in this study. Total content of photosynthetic pigments as well as photosynthetic activity decreased at lower concentration of Cr(VI) in Synechocystis as compared to Synechococcus. Experiments with (51)Cr showed Cr to accumulate intracellularly in both the cyanobacteria. At lower concentrations, Cr(VI) caused excessive ROS generation in Synechocystis as compared to that observed in Synechococcus. Intrinsic levels of enzymatic antioxidants, i.e., superoxide dismutase, catalase and 2-Cys-peroxiredoxin were considerably higher in Synechococcus than Synechocystis. Content of total thiols (both protein as well as non-protein) and reduced glutathione (GSH) was also higher in Synechococcus as compared to Synechocystis. This correlated well with higher content of carbonylated proteins observed in Synechocystis than Synechococcus. Additionally, in contrast to Synechocystis, Synechococcus exhibited better tolerance to other oxidative stresses like high intensity light and H2O2. The data indicate that the disparity in the ability to detoxify ROS could be the primary mechanism responsible for the differential tolerance of these cyanobacteria to Cr(VI). PMID:25956322

  20. Persistence of uranium groundwater plumes: Contrasting mechanisms at two DOE sites in the groundwater-river interaction zone

    SciTech Connect

    Zachara, John M.; Long, Philip E.; Bargar, John; Davis, James A.; Fox, Patricia M.; Fredrickson, Jim K.; Freshley, Mark D.; Konopka, Allan; Liu, Chongxuan; McKinley, James P.; Rockhold, Mark L.; Williams, Kenneth H.; Yabusaki, Steven B.

    2013-04-01

    We examine subsurface uranium (U) plumes at two U.S. Department of Energy sites that are located near large river systems and that are influenced by groundwater-river hydrologic interaction. Following surface excavation of contaminated materials, both sites were projected to naturally flush remnant uranium contamination to levels below regulatory limits (e.g., 30 µg/L or 0.126 µmol/L; U.S. EPA drinking water standard), with 10 years projected for the Hanford 300 Area (Columbia River) and 12 years for the Rifle site (Colorado River). The rate of observed uranium decrease was much lower than expected at both sites. While uncertainty remains, a comparison of current understanding suggests that the two sites have common, but also different mechanisms controlling plume persistence. At the Hanford 300 A, the persistent source is adsorbed U(VI) in the vadose zone that is released to the aquifer during spring water table excursions. The release of U(VI) from the vadose zone and its transport within the oxic, coarse-textured aquifer sediments is dominated by kinetically-limited surface complexation. Modeling implies that annual plume discharge volumes to the Columbia River are small (< one pore volume). At the Rifle site, slow oxidation of naturally reduced, contaminant U(IV) in the saturated zone and a continuous influx of U(VI) from natural, up-gradient sources influences plume persistence. Rate-limited mass transfer and surface complexation also control U(VI) migration velocity in the sub-oxic Rifle groundwater. Flux of U(VI) from the vadose zone at the Rifle site may be locally important, but it is not the dominant process that sustains the plume. A wide range in microbiologic functional diversity exists at both sites. Strains of Geobacter and other metal reducing bacteria are present at low natural abundance that are capable of enzymatic U(VI) reduction in localized zones of accumulated detrital organic carbon or after organic carbon amendment. Major differences

  1. Persistence of uranium groundwater plumes: contrasting mechanisms at two DOE sites in the groundwater-river interaction zone.

    PubMed

    Zachara, John M; Long, Philip E; Bargar, John; Davis, James A; Fox, Patricia; Fredrickson, Jim K; Freshley, Mark D; Konopka, Allan E; Liu, Chongxuan; McKinley, James P; Rockhold, Mark L; Williams, Kenneth H; Yabusaki, Steve B

    2013-04-01

    We examine subsurface uranium (U) plumes at two U.S. Department of Energy sites that are located near large river systems and are influenced by groundwater-river hydrologic interaction. Following surface excavation of contaminated materials, both sites were projected to naturally flush remnant uranium contamination to levels below regulatory limits (e.g., 30 μg/L or 0.126 μmol/L; U.S. EPA drinking water standard), with 10 years projected for the Hanford 300 Area (Columbia River) and 12 years for the Rifle site (Colorado River). The rate of observed uranium decrease was much lower than expected at both sites. While uncertainty remains, a comparison of current understanding suggests that the two sites have common, but also different mechanisms controlling plume persistence. At the Hanford 300 A, the persistent source is adsorbed U(VI) in the vadose zone that is released to the aquifer during spring water table excursions. The release of U(VI) from the vadose zone and its transport within the oxic, coarse-textured aquifer sediments is dominated by kinetically-limited surface complexation. Modeling implies that annual plume discharge volumes to the Columbia River are small (

  2. Persistence of uranium groundwater plumes: Contrasting mechanisms at two DOE sites in the groundwater-river interaction zone

    NASA Astrophysics Data System (ADS)

    Zachara, John M.; Long, Philip E.; Bargar, John; Davis, James A.; Fox, Patricia; Fredrickson, Jim K.; Freshley, Mark D.; Konopka, Allan E.; Liu, Chongxuan; McKinley, James P.; Rockhold, Mark L.; Williams, Kenneth H.; Yabusaki, Steve B.

    2013-04-01

    We examine subsurface uranium (U) plumes at two U.S. Department of Energy sites that are located near large river systems and are influenced by groundwater-river hydrologic interaction. Following surface excavation of contaminated materials, both sites were projected to naturally flush remnant uranium contamination to levels below regulatory limits (e.g., 30 μg/L or 0.126 μmol/L; U.S. EPA drinking water standard), with 10 years projected for the Hanford 300 Area (Columbia River) and 12 years for the Rifle site (Colorado River). The rate of observed uranium decrease was much lower than expected at both sites. While uncertainty remains, a comparison of current understanding suggests that the two sites have common, but also different mechanisms controlling plume persistence. At the Hanford 300 A, the persistent source is adsorbed U(VI) in the vadose zone that is released to the aquifer during spring water table excursions. The release of U(VI) from the vadose zone and its transport within the oxic, coarse-textured aquifer sediments is dominated by kinetically-limited surface complexation. Modeling implies that annual plume discharge volumes to the Columbia River are small (< one pore volume). At the Rifle site, slow oxidation of naturally reduced, contaminant U(IV) in the saturated zone and a continuous influx of U(VI) from natural, up-gradient sources influence plume persistence. Rate-limited mass transfer and surface complexation also control U(VI) migration velocity in the sub-oxic Rifle groundwater. Flux of U(VI) from the vadose zone at the Rifle site may be locally important, but it is not the dominant process that sustains the plume. A wide range in microbiologic functional diversity exists at both sites. Strains of Geobacter and other metal reducing bacteria are present at low natural abundance that are capable of enzymatic U(VI) reduction in localized zones of accumulated detrital organic carbon or after organic carbon amendment. Major differences between

  3. Contrast lipocryolysis

    PubMed Central

    Pinto, Hernán; Melamed, Graciela

    2014-01-01

    Alternative crystal structures are possible for all lipids and each different crystal structure is called a polymorphic form. Inter-conversion between polymorphisms would imply the possibility of leaning crystal formation toward the most effective polymorphism for adipocyte destruction. Food industry has been tempering lipids for decades. Tempering technology applied to lipocryolysis gave birth to “contrast lipocryolysis”, which involves pre- and post-lipocryolysis fat layer heating as part of a specific tempering protocol. In this study, we evaluated the skinfold thickness of 10 subjects after a single contrast lipocryolysis session and witnessed important and fast reductions. PMID:25068088

  4. Abeta25-35 induces rapid lysis of red blood cells: contrast with Abeta1-42 and examination of underlying mechanisms.

    PubMed

    Mattson, M P; Begley, J G; Mark, R J; Furukawa, K

    1997-10-10

    Amyloid beta-peptide (A beta) is produced by many different cell types and circulates in blood and cerebrospinal fluid in a soluble form. In Alzheimer's disease (AD), A beta forms insoluble fibrillar aggregates that accumulate in association with cells of the brain parenchyma and vasculature. Both full-length A beta (A beta1-40/42) and the A beta25-35 fragment can damage and kill neurons by a mechanism that may involve oxidative stress and disruption of calcium homeostasis. Circulating blood cells are exposed to soluble A beta1-40/42 and may also be exposed to A beta aggregates associated with the luminal surfaces of cerebral microvessels. We therefore examined the effects of A beta25-35 and A beta1-42 on human red blood cells (RBCs) and report that A beta25-35, in contrast to A beta1-42, induces rapid (10-60 min) lysis of RBCs. The mechanism of RBC lysis by A beta25-35 involved ion channel formation and calcium influx, but did not involve oxidative stress because antioxidants did not prevent cell lysis. In contrast, A beta1-42 induced a delayed (4-24 h) damage to RBCs which was attenuated by antioxidants. The damaging effects of both A beta25-35 and A beta1-42 towards RBCs were completely prevented by Congo red indicating a requirement for peptide fibril formation. A beta1-42 induced membrane lipid peroxidation in RBC, and basal levels of lipid peroxidation in RBCs from AD patients were significantly greater than in age-matched controls, suggesting a possible role for A beta1-42 in previously reported alterations in RBCs from AD patients. PMID:9383018

  5. Three-dimensional shear wave imaging based on full-field laser speckle contrast imaging with one-dimensional mechanical scanning.

    PubMed

    Chao, Pei-Yu; Li, Pai-Chi

    2016-08-22

    The high imaging resolution and motion sensitivity of optical-based shear wave detection has made it an attractive technique in biomechanics studies with potential for improving the capabilities of shear wave elasticity imaging. In this study we implemented laser speckle contrast imaging for two-dimensional (X-Z) tracking of transient shear wave propagation in agarose phantoms. The mechanical disturbances induced by the propagation of the shear wave caused temporal and spatial fluctuations in the local speckle pattern, which manifested as local blurring. By mechanically moving the sample in the third dimension (Y), and performing two-dimensional shear wave imaging at every scan position, the three-dimensional shear wave velocity distribution of the phantom could be reconstructed. Based on comparisons with the reference shear wave velocity measurements obtained using a commercial ultrasound shear wave imaging system, the developed system can estimate the shear wave velocity with an error of less than 6% for homogeneous phantoms with shear moduli ranging from 1.52 kPa to 7.99 kPa. The imaging sensitivity of our system makes it capable of measuring small variations in shear modulus; the estimated standard deviation of the shear modulus was found to be less than 0.07 kPa. A submillimeter spatial resolution for three-dimensional shear wave imaging has been achieved, as demonstrated by the ability to detect a 1-mm-thick stiff plate embedded inside heterogeneous agarose phantoms. PMID:27557169

  6. Mechanism underlying unaltered cortical inhibitory synaptic transmission in contrast with enhanced excitatory transmission in CaV2.1 knockin migraine mice.

    PubMed

    Vecchia, Dania; Tottene, Angelita; van den Maagdenberg, Arn M J M; Pietrobon, Daniela

    2014-09-01

    Familial hemiplegic migraine type 1 (FHM1), a monogenic subtype of migraine with aura, is caused by gain-of-function mutations in CaV2.1 (P/Q-type) calcium channels. In FHM1 knockin mice, excitatory neurotransmission at cortical pyramidal cell synapses is enhanced, but inhibitory neurotransmission at connected pairs of fast-spiking (FS) interneurons and pyramidal cells is unaltered, despite being initiated by CaV2.1 channels. The mechanism underlying the unaltered GABA release at cortical FS interneuron synapses remains unknown. Here, we show that the FHM1 R192Q mutation does not affect inhibitory transmission at autapses of cortical FS and other types of multipolar interneurons in microculture from R192Q knockin mice, and investigate the underlying mechanism. Lowering the extracellular [Ca(2+)] did not reveal gain-of-function of evoked transmission neither in control nor after prolongation of the action potential (AP) with tetraethylammonium, indicating unaltered AP-evoked presynaptic calcium influx at inhibitory autapses in FHM1 KI mice. Neither saturation of the presynaptic calcium sensor nor short duration of the AP can explain the unaltered inhibitory transmission in the mutant mice. Recordings of the P/Q-type calcium current in multipolar interneurons in microculture revealed that the current density and the gating properties of the CaV2.1 channels expressed in these interneurons are barely affected by the FHM1 mutation, in contrast with the enhanced current density and left-shifted activation gating of mutant CaV2.1 channels in cortical pyramidal cells. Our findings suggest that expression of specific CaV2.1 channels differentially sensitive to modulation by FHM1 mutations in inhibitory and excitatory cortical neurons underlies the gain-of-function of excitatory but unaltered inhibitory synaptic transmission and the likely consequent dysregulation of the cortical excitatory-inhibitory balance in FHM1. PMID:24907493

  7. X-ray contrast media mechanisms in the release of mast cell contents: understanding these leads to a treatment for allergies.

    PubMed

    Lasser, Elliott C

    2011-01-01

    A long history of searching for the etiology of X-ray contrast material (CM) reactions has led to the understanding that the CM do not produce anti-CM antigens. Since CM reactions are anaphylactoid in nature, however, a source for mast cell activation was sought. This resulted in the finding that concentrated CM could suppress mast cell activation by attachment to the Fc portion of IgE and IgG. This is presumed to be a steric hindrance effect. In a study of the effects of CM on BP and a study of the effects of CM in sensitized rats, it was concluded that less concentrated CM activated mast cells and that this mechanism was best explained by bridging of adjacent IgE molecules via attachment to their Fc segments. The mast cell release of heparin activating the contact system, as well as the release of histamine, is believed to be responsible for CM reactions and allergic diatheses. PMID:21941574

  8. Gadofullerene MRI contrast agents.

    PubMed

    Bolskar, Robert D

    2008-04-01

    A promising new class of MRI contrast-enhancing agents with high relaxivities is based on gadolinium-containing metallofullerenes, which are also termed gadofullerenes. Detailed study of the water-proton relaxivity properties and intermolecular nanoclustering behavior of gadofullerene derivatives has revealed valuable information about their relaxivity mechanisms and given a deeper understanding of this new class of paramagnetic contrast agent. Here, the latest findings on water-solubilized gadofullerene materials and how these findings relate to their future applications in MRI are reviewed and discussed. PMID:18373426

  9. Aspiration of Barium Contrast

    PubMed Central

    Fuentes Santos, Cristina; Steen, Bárbara

    2014-01-01

    The aspiration of barium contrast is a rare complication that may occur during studies of the digestive tract. Barium is an inert material that can cause anywhere from an asymptomatic mechanical obstruction to serious symptoms of respiratory distress that can result in patient death. We present the case of a 79-year-old male patient in whom we observed the presence of contrast medium residue in the lung parenchyma as an incidental finding during hospitalization. When the patient's medical file was reviewed, images were found of a barium swallow study that the patient had undergone months earlier, and we were able to observe the exact moment of the aspiration of the contrast material. The patient had been asymptomatic since the test. PMID:25309769

  10. Tree ring isotopes of beech and spruce in response to short-term climate variability across Central European sites: Common and contrasting physiological mechanisms

    NASA Astrophysics Data System (ADS)

    Weigt, Rosemarie; Klesse, Stefan; Treydte, Kerstin; Frank, David; Saurer, Matthias; Siegwolf, Rolf T. W.

    2016-04-01

    The combined study of tree-ring width and stable C and O isotopes provides insight in the coherences between carbon allocation during stem growth and the preceding conditions of gas exchange and formation of photosynthates as all influenced by environmental variation. In this large-scale study comprising 10 sites across a range of climate gradients (temperature, precipitation) throughout Central Europe, we investigated tree-rings in European beech (Fagus sylvatica) and Norway spruce (Picea abies) trees. The sampling design included larger and smaller trees. The short-term, i.e. year-to-year, variability in the isotope time series over 100 yrs was analyzed in relation to tree-ring growth and climate variation. The generally strong correlation between the year-to-year differences in δ13C (corrected for the atmospheric shift due to 13C-depleted CO2 from fossil combustion) and δ18O across most sites emphasized the role of stomatal conductance in controlling leaf gas exchange. However, the correlation between both isotopes decreased during some periods. At several sites this reduction in correlation was particularly pronounced during recent decades. This suggests a decoupling between stomatal and photosynthetic responses to environmental conditions on the one hand, and carbon allocation to stem tissue on the other hand. Variability in the isotopic ratio largely responded to summer climate, but was weakly correlated to annual stem growth. In contrast, climate sensitivity of radial growth in both species was rather site-dependent, and was strongest at the driest (in terms of soil water capacity) site. We will also present results of isotope responses with respect to extreme climate events. Understanding the underlying physiological mechanisms controlling the short-term variation in tree-ring signals will help to assess and more precisely constrain the possible range of growth performance of these ecologically and economically important tree species under future climate

  11. Chromatic masking in the (delta L/L, delta M/M) plane of cone-contrast space reveals only two detection mechanisms.

    PubMed

    Giulianini, F; Eskew, R T

    1998-12-01

    The post-receptoral mechanisms that mediate detection of stimuli in the (delta L/L, delta M/M) plane of color space were characterized using noise masking. Chromatic masking noises of different chromaticities and spatial configurations were used, and threshold contours for the detection of Gaussian and Gabor tests were measured. The results do not show masking that is narrowly-selective for the chromaticity of the noise. On the contrary, our findings suggest that detection of these tests is mediated only by an opponent chromatic mechanism (a red-green mechanism) and a non-opponent luminance mechanism. These results are not consistent with the hypothesis of multiple chromatic mechanisms mediating detection in this color plane [1]. PMID:10211383

  12. Does the mechanism of sex determination constrain the potential for sex manipulation? A test in geckos with contrasting sex-determining systems.

    PubMed

    Kratochvíl, Lukás; Kubicka, Lukás; Landová, Eva

    2008-03-01

    The concentration of yolk steroids was suggested to influence offspring gender in oviparous animals subject to both temperature-dependent sex determination (TSD) and genotypic sex determination (GSD). However, the proposed mechanisms of steroid effects are thought to differ between TSD and GSD: a direct effect of oestrogens on gonad feminisation in TSD species vs a differential induction of male-producing or female-producing gametes in GSD species. Geckos offer an ideal opportunity for testing these suggested mechanisms. Closely related gecko species differ in their modes of sex determination. They lay clutches of two synchronously formed eggs; both eggs share equal steroid levels. If identical hormonal composition and environment during vitellogenesis, gravidity and incubation determine the sex of the progeny, siblings should share the same gender in both TSD and GSD geckos. We found strong support for this prediction in a TSD gecko species. Among clutches that were incubated at the temperature that produced both sexes, there were no clutches with siblings of the opposite sex. On the other hand, about half of the clutches yielded siblings of the opposite sex in four GSD species. These results suggest that sex-determining systems constrain the ability of the female to produce single-sex siblings and, hence, it seems that the GSD mechanism constrains the opportunities for sex ratio manipulation in geckos via yolk steroid manipulation. PMID:17994209

  13. Does the mechanism of sex determination constrain the potential for sex manipulation? A test in geckos with contrasting sex-determining systems

    NASA Astrophysics Data System (ADS)

    Kratochvíl, Lukáš; Kubička, Lukáš; Landová, Eva

    2008-03-01

    The concentration of yolk steroids was suggested to influence offspring gender in oviparous animals subject to both temperature-dependent sex determination (TSD) and genotypic sex determination (GSD). However, the proposed mechanisms of steroid effects are thought to differ between TSD and GSD: a direct effect of oestrogens on gonad feminisation in TSD species vs a differential induction of male-producing or female-producing gametes in GSD species. Geckos offer an ideal opportunity for testing these suggested mechanisms. Closely related gecko species differ in their modes of sex determination. They lay clutches of two synchronously formed eggs; both eggs share equal steroid levels. If identical hormonal composition and environment during vitellogenesis, gravidity and incubation determine the sex of the progeny, siblings should share the same gender in both TSD and GSD geckos. We found strong support for this prediction in a TSD gecko species. Among clutches that were incubated at the temperature that produced both sexes, there were no clutches with siblings of the opposite sex. On the other hand, about half of the clutches yielded siblings of the opposite sex in four GSD species. These results suggest that sex-determining systems constrain the ability of the female to produce single-sex siblings and, hence, it seems that the GSD mechanism constrains the opportunities for sex ratio manipulation in geckos via yolk steroid manipulation.

  14. Contrasting the Cartesian and polar forms of the shedding-induced force vector in response to 12 subharmonic and superharmonic mechanical excitations

    NASA Astrophysics Data System (ADS)

    Marzouk, Osama A.

    2010-06-01

    We mechanically excited the near-field shedding of the von Kármán vortex street of a stationary cylinder at Reynolds number 300 by moving it sinusoidally with 12 different frequencies. We first solved the incompressible Navier-Stokes equations using the finite difference method and obtained unexcited shedding, which occurs at the Strouhal frequency. Then, we applied six subharmonic excitations with rational frequency ratios (defined as the excitation frequency to the Strouhal frequency) in the form 1/n and six superharmonic excitations with frequency ratios n, where n is an integer taking values between 2 and 7. We compared the behavior of the shedding-induced force vector acting on the cylinder in each excitation case to their counterparts in the other excitation cases and to the case of the stationary cylinder. This force vector has two representations: lift and drag (Cartesian) or magnitude and direction (polar). Whereas the first representation is commonly used in theoretical fluid mechanics and engineering applications, we found that the second representation is favored in terms of revealing how the force vector responds to the applied excitations. For example, the mean and standard deviation of the drag do not show clear trends with the excitation frequency, whereas the force magnitude changes quadratically with it. We showed that the theoretical analysis of a simplified nonlinear wake model does in fact support this behavior. We found three modes of shedding-induced force in response to mechanical excitation, depending on the ratio of excitation frequency to Strouhal frequency. Near-field shedding is not entrained by excitation for all subharmonic excitations, but it is entrained for all superharmonic excitations. For entrained shedding, we found two behaviors of the shedding-induced force vector, which is periodic only at odd frequency ratios.

  15. Contrasting Evolutionary Dynamics of the Developmental Regulator PAX9, among Bats, with Evidence for a Novel Post-Transcriptional Regulatory Mechanism

    PubMed Central

    Phillips, Caleb D.; Butler, Boyd; Fondon, John W.; Mantilla-Meluk, Hugo; Baker, Robert J.

    2013-01-01

    Morphological evolution can be the result of natural selection favoring modification of developmental signaling pathways. However, little is known about the genetic basis of such phenotypic diversity. Understanding these mechanisms is difficult for numerous reasons, yet studies in model organisms often provide clues about the major developmental pathways involved. The paired-domain gene, PAX9, is known to be a key regulator of development, particularly of the face and teeth. In this study, using a comparative genetics approach, we investigate PAX9 molecular evolution among mammals, focusing on craniofacially diversified (Phyllostomidae) and conserved (Vespertilionidae) bat families, and extend our comparison to other orders of mammal. Open-reading frame analysis disclosed signatures of selection, in which a small percentage of residues vary, and lineages acquire different combinations of variation through recurrent substitution and lineage specific changes. A few instances of convergence for specific residues were observed between morphologically convergent bat lineages. Bioinformatic analysis for unknown PAX9 regulatory motifs indicated a novel post-transcriptional regulatory mechanism involving a Musashi protein. This regulation was assessed through fluorescent reporter assays and gene knockdowns. Results are compatible with the hypothesis that the number of Musashi binding-elements in PAX9 mRNA proportionally regulates protein translation rate. Although a connection between morphology and binding element frequency was not apparent, results indicate this regulation would vary among craniofacially divergent bat species, but be static among conserved species. Under this model, Musashi’s regulatory control of alternative human PAX9 isoforms would also vary. The presence of Musashi-binding elements within PAX9 of all mammals examined, chicken, zebrafish, and the fly homolog of PAX9, indicates this regulatory mechanism is ancient, originating basal to much of the

  16. Contrast-Enhanced Endoscopic Ultrasound

    PubMed Central

    Dietrich, Christoph F.; Sharma, M.; Hocke, M.

    2012-01-01

    The European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) introduced guidelines on the use of contrast-enhanced ultrasound (CEUS) in 2004. This EFSUMB-document focused mainly on liver applications. However, new applications extending beyond the liver were developed thereafter. Increased interest in recent years in CEUS technique and in the application of CEUS in novel fields like endoscopic ultrasound (EUS) has revolutionized indications and applications. As a result, the EFSUMB initiated a new update of the guidelines in 2011 to include this additional knowledge. Some of the contrast-enhanced EUS (CE-EUS) indications are established, whereas others are preliminary; these latter indications are categorized as emergent CEUS applications since the available evidence is insufficient for general recommendation. This article focuses on the use of CE-EUS in various clinical settings. The reader will get an overview of current indications and possible applications of CE-EUS. This involves the introduction of different contrast studies including color Doppler techniques (known as contrast-enhanced high mechanical index endosonography or CEHMI-EUS) as well as more modern high-resolution contrast-enhanced techniques (known as contrast-enhanced low mechanical index endosonography or CELMI EUS). PMID:24949350

  17. Polarization contrast vision

    NASA Astrophysics Data System (ADS)

    Pugh, Edward N.

    1990-05-01

    An attempt is made to establish the possibility that the geometry of certain classes of vertebrate photoreceptors results in a birefringence that allows the animals to utilize the state of polarization of light striking their retinas as a meaningful stimulus parameter. Simulate the photoreceptors as dielectric waveguides using a simple physical model, and augment this theoretical work with empirical measurements of the light guiding properties of photoreceptors in isolated pieces of retina from a green sunfish (Lepomis cyanellus). With a classical conditioning paradigm, this fish's sensitivity to light is modulated by the orientation of the plane of polarization of linearly polarized light. This functional dependence was predicted by a hypothetical antagonistic mechanism between twin cones of two orientations in the animal's retinal mosaic. Further study is planned for the nature of the stimulus to which the fish is sensitive by creating a camera that will generate images based purely upon the contrast between orthogonal polarizations at each point in space.

  18. Contrasting regional and national mechanisms for predicting elevated arsenic in private wells across the United States using classification and regression trees.

    PubMed

    Frederick, Logan; VanDerslice, James; Taddie, Marissa; Malecki, Kristen; Gregg, Josh; Faust, Nicholas; Johnson, William P

    2016-03-15

    Arsenic contamination in groundwater is a public health and environmental concern in the United States (U.S.) particularly where monitoring is not required under the Safe Water Drinking Act. Previous studies suggest the influence of regional mechanisms for arsenic mobilization into groundwater; however, no study has examined how influencing parameters change at a continental scale spanning multiple regions. We herein examine covariates for groundwater in the western, central and eastern U.S. regions representing mechanisms associated with arsenic concentrations exceeding the U.S. Environmental Protection Agency maximum contamination level (MCL) of 10 parts per billion (ppb). Statistically significant covariates were identified via classification and regression tree (CART) analysis, and included hydrometeorological and groundwater chemical parameters. The CART analyses were performed at two scales: national and regional; for which three physiographic regions located in the western (Payette Section and the Snake River Plain), central (Osage Plains of the Central Lowlands), and eastern (Embayed Section of the Coastal Plains) U.S. were examined. Validity of each of the three regional CART models was indicated by values >85% for the area under the receiver-operating characteristic curve. Aridity (precipitation minus potential evapotranspiration) was identified as the primary covariate associated with elevated arsenic at the national scale. At the regional scale, aridity and pH were the major covariates in the arid to semi-arid (western) region; whereas dissolved iron (taken to represent chemically reducing conditions) and pH were major covariates in the temperate (eastern) region, although additional important covariates emerged, including elevated phosphate. Analysis in the central U.S. region indicated that elevated arsenic concentrations were driven by a mixture of those observed in the western and eastern regions. PMID:26803265

  19. Binocular contrast discrimination needs monocular multiplicative noise

    PubMed Central

    Ding, Jian; Levi, Dennis M.

    2016-01-01

    The effects of signal and noise on contrast discrimination are difficult to separate because of a singularity in the signal-detection-theory model of two-alternative forced-choice contrast discrimination (Katkov, Tsodyks, & Sagi, 2006). In this article, we show that it is possible to eliminate the singularity by combining that model with a binocular combination model to fit monocular, dichoptic, and binocular contrast discrimination. We performed three experiments using identical stimuli to measure the perceived phase, perceived contrast, and contrast discrimination of a cyclopean sine wave. In the absence of a fixation point, we found a binocular advantage in contrast discrimination both at low contrasts (<4%), consistent with previous studies, and at high contrasts (≥34%), which has not been previously reported. However, control experiments showed no binocular advantage at high contrasts in the presence of a fixation point or for observers without accommodation. We evaluated two putative contrast-discrimination mechanisms: a nonlinear contrast transducer and multiplicative noise (MN). A binocular combination model (the DSKL model; Ding, Klein, & Levi, 2013b) was first fitted to both the perceived-phase and the perceived-contrast data sets, then combined with either the nonlinear contrast transducer or the MN mechanism to fit the contrast-discrimination data. We found that the best model combined the DSKL model with early MN. Model simulations showed that, after going through interocular suppression, the uncorrelated noise in the two eyes became anticorrelated, resulting in less binocular noise and therefore a binocular advantage in the discrimination task. Combining a nonlinear contrast transducer or MN with a binocular combination model (DSKL) provides a powerful method for evaluating the two putative contrast-discrimination mechanisms. PMID:26982370

  20. Binocular contrast discrimination needs monocular multiplicative noise.

    PubMed

    Ding, Jian; Levi, Dennis M

    2016-01-01

    The effects of signal and noise on contrast discrimination are difficult to separate because of a singularity in the signal-detection-theory model of two-alternative forced-choice contrast discrimination (Katkov, Tsodyks, & Sagi, 2006). In this article, we show that it is possible to eliminate the singularity by combining that model with a binocular combination model to fit monocular, dichoptic, and binocular contrast discrimination. We performed three experiments using identical stimuli to measure the perceived phase, perceived contrast, and contrast discrimination of a cyclopean sine wave. In the absence of a fixation point, we found a binocular advantage in contrast discrimination both at low contrasts (<4%), consistent with previous studies, and at high contrasts (≥34%), which has not been previously reported. However, control experiments showed no binocular advantage at high contrasts in the presence of a fixation point or for observers without accommodation. We evaluated two putative contrast-discrimination mechanisms: a nonlinear contrast transducer and multiplicative noise (MN). A binocular combination model (the DSKL model; Ding, Klein, & Levi, 2013b) was first fitted to both the perceived-phase and the perceived-contrast data sets, then combined with either the nonlinear contrast transducer or the MN mechanism to fit the contrast-discrimination data. We found that the best model combined the DSKL model with early MN. Model simulations showed that, after going through interocular suppression, the uncorrelated noise in the two eyes became anticorrelated, resulting in less binocular noise and therefore a binocular advantage in the discrimination task. Combining a nonlinear contrast transducer or MN with a binocular combination model (DSKL) provides a powerful method for evaluating the two putative contrast-discrimination mechanisms. PMID:26982370

  1. [Contrast sensitivity in glaucoma].

    PubMed

    Bartos, D

    1989-05-01

    Author reports on results of the contrast sensitivity examinations using the Cambridge low-contrast lattice test supplied by Clement Clarke International LTD, in patients with open-angle glaucoma and ocular hypertension. In glaucoma patients there was observed statistically significant decrease of the contrast sensitivity. In patients with ocular hypertension decrease of the contrast sensitivity was in patients affected by corresponding changes of the visual field and of the optical disc. The main advantages of the Cambridge low-contrast lattice test were simplicity, rapidity and precision of its performance. PMID:2743444

  2. MR contrast due to intravascular magnetic susceptibility perturbations.

    PubMed

    Boxerman, J L; Hamberg, L M; Rosen, B R; Weisskoff, R M

    1995-10-01

    A particularly powerful paradigm for functional MR imaging of microvascular hemodynamics incorporates paramagnetic materials that create significant image contrast. These include exogenous (lanthanide chelates) and endogenous (deoxygenated hemoglobin) agents for mapping cerebral blood volume and neuronal activity, respectively. Accurate interpretation of these maps requires an understanding of the biophysics of susceptibility-based image contrast. The authors developed a novel Monte Carlo model with which the authors quantified the relationship between microscopic tissue parameters, NMR imaging parameters, and susceptibility contrast in vivo. The authors found vascular permeability to water and the flow of erythrocytes to be relatively unimportant contributors to susceptibility-induced delta R2. However, pulse sequence, echo time, and concentration of contrast agent have profound effects on the vessel size dependence of delta R2. For a model vasculature containing both capillaries and venules, the authors predicted a linear volume fraction dependence for physiological volume changes based on recruitment and dilation, and a concentration dependence that is nonlinear and pulse sequence dependent. Using the model, the authors demonstrated that spin echo functional images have greater microvascular sensitivity than gradient echo images, and that the specifies of the volume fraction and concentration dependence of transverse relaxivity change should allow for robust mapping of relative blood volume. The authors also demonstrated excellent agreement between the predictions of their model and experimental data obtained from the serial injection of superparamagnetic contrast agent in a rat model. PMID:8524024

  3. Phase Contrast Imaging in Neonates

    PubMed Central

    Zhong, Kai; Ernst, Thomas; Buchthal, Steve; Speck, Oliver; Anderson, Lynn; Chang, Linda

    2011-01-01

    Magnetic resonance phase images can yield superior gray and white matter contrast compared to conventional magnitude images. However, the underlying contrast mechanisms are not yet fully understood. Previous studies have been limited to high field acquisitions in adult volunteers and patients. In this study, phase imaging in the neonatal brain is demonstrated for the first time. Compared to adults, phase differences between gray and white matter are significantly reduced but not inverted in neonates with little myelination and iron deposits in their brains. The remaining phase difference between the neonatal and adult brains may be due to different macromolecule concentration in the unmyelinated brain of the neonates and thus different frequency due to water macromolecule exchange. Additionally, the susceptibility contrast from brain myelination can be separately studied in neonates during brain development. Therefore, magnetic resonance phase imaging is suggested as a novel tool to study neonatal brain development and pathologies in neonates. PMID:21232619

  4. Contrast Intravasation During Hysterosalpingography

    PubMed Central

    Bhoil, Rohit; Sood, Dinesh; Sharma, Tanupriya; Sood, Shilpa; Sharma, Jiten; Kumar, Nitesh; Ahluwalia, Ajay; Parekh, Dipen; Mistry, Kewal A.; Sood, Saurav

    2016-01-01

    Summary Hysterosalpingography is an imaging method to evaluate the endometrial and uterine morphology and fallopian tube patency. Contrast intravasation implies backflow of injected contrast into the adjoining vessels mostly the veins and may be related to factors altering endometrial vascularity and permeability. Radiologists and gynaecologists should be well acquainted with the technique of hysterosalpingography, its interpretation, and intravasation of contrast agents for safer procedure and to minimize the associated complications. PMID:27279925

  5. Toward Critical Contrastive Rhetoric

    ERIC Educational Resources Information Center

    Kubota, Ryuko; Lehner, Al

    2004-01-01

    A traditional approach to contrastive rhetoric has emphasized cultural difference in rhetorical patterns among various languages. Despite its laudable pedagogical intentions to raise teachers' and students' cultural and rhetorical awareness in second language writing, traditional contrastive rhetoric has perpetuated static binaries between English…

  6. Contrast adaptation in the Limulus lateral eye.

    PubMed

    Valtcheva, Tchoudomira M; Passaglia, Christopher L

    2015-12-01

    Luminance and contrast adaptation are neuronal mechanisms employed by the visual system to adjust our sensitivity to light. They are mediated by an assortment of cellular and network processes distributed across the retina and visual cortex. Both have been demonstrated in the eyes of many vertebrates, but only luminance adaptation has been shown in invertebrate eyes to date. Since the computational benefits of contrast adaptation should apply to all visual systems, we investigated whether this mechanism operates in horseshoe crab eyes, one of the best-understood neural networks in the animal kingdom. The spike trains of optic nerve fibers were recorded in response to light stimuli modulated randomly in time and delivered to single ommatidia or the whole eye. We found that the retina adapts to both the mean luminance and contrast of a white-noise stimulus, that luminance- and contrast-adaptive processes are largely independent, and that they originate within an ommatidium. Network interactions are not involved. A published computer model that simulates existing knowledge of the horseshoe crab eye did not show contrast adaptation, suggesting that a heretofore unknown mechanism may underlie the phenomenon. This mechanism does not appear to reside in photoreceptors because white-noise analysis of electroretinogram recordings did not show contrast adaptation. The likely site of origin is therefore the spike discharge mechanism of optic nerve fibers. The finding of contrast adaption in a retinal network as simple as the horseshoe crab eye underscores the broader importance of this image processing strategy to vision. PMID:26445869

  7. Compressive phase contrast tomography

    NASA Astrophysics Data System (ADS)

    Maia, F.; MacDowell, A.; Marchesini, S.; Padmore, H. A.; Parkinson, D. Y.; Pien, J.; Schirotzek, A.; Yang, C.

    2010-08-01

    When x-rays penetrate soft matter, their phase changes more rapidly than their amplitude. Interference effects visible with high brightness sources creates higher contrast, edge enhanced images. When the object is piecewise smooth (made of big blocks of a few components), such higher contrast datasets have a sparse solution. We apply basis pursuit solvers to improve SNR, remove ring artifacts, reduce the number of views and radiation dose from phase contrast datasets collected at the Hard X-Ray Micro Tomography Beamline at the Advanced Light Source. We report a GPU code for the most computationally intensive task, the gridding and inverse gridding algorithm (non uniform sampled Fourier transform).

  8. Compressive Phase Contrast Tomography

    SciTech Connect

    Maia, Filipe; MacDowell, Alastair; Marchesini, Stefano; Padmore, Howard A.; Parkinson, Dula Y.; Pien, Jack; Schirotzek, Andre; Yang, Chao

    2010-09-01

    When x-rays penetrate soft matter, their phase changes more rapidly than their amplitude. Interference effects visible with high brightness sources creates higher contrast, edge enhanced images. When the object is piecewise smooth (made of big blocks of a few components), such higher contrast datasets have a sparse solution. We apply basis pursuit solvers to improve SNR, remove ring artifacts, reduce the number of views and radiation dose from phase contrast datasets collected at the Hard X-Ray Micro Tomography Beamline at the Advanced Light Source. We report a GPU code for the most computationally intensive task, the gridding and inverse gridding algorithm (non uniform sampled Fourier transform).

  9. Stimulus Contrast and Retinogeniculate Signal Processing

    PubMed Central

    Rathbun, Daniel L.; Alitto, Henry J.; Warland, David K.; Usrey, W. Martin

    2016-01-01

    Neuronal signals conveying luminance contrast play a key role in nearly all aspects of perception, including depth perception, texture discrimination, and motion perception. Although much is known about the retinal mechanisms responsible for encoding contrast information, relatively little is known about the relationship between stimulus contrast and the processing of neuronal signals between visual structures. Here, we describe simultaneous recordings from monosynaptically connected retinal ganglion cells and lateral geniculate nucleus (LGN) neurons in the cat to determine how stimulus contrast affects the communication of visual signals between the two structures. Our results indicate that: (1) LGN neurons typically reach their half-maximal response at lower contrasts than their individual retinal inputs and (2) LGN neurons exhibit greater contrast-dependent phase advance (CDPA) than their retinal inputs. Further analyses suggests that increased sensitivity relies on spatial convergence of multiple retinal inputs, while increased CDPA is achieved, in part, on temporal summation of arriving signals. PMID:26924964

  10. Stimulus Contrast and Retinogeniculate Signal Processing.

    PubMed

    Rathbun, Daniel L; Alitto, Henry J; Warland, David K; Usrey, W Martin

    2016-01-01

    Neuronal signals conveying luminance contrast play a key role in nearly all aspects of perception, including depth perception, texture discrimination, and motion perception. Although much is known about the retinal mechanisms responsible for encoding contrast information, relatively little is known about the relationship between stimulus contrast and the processing of neuronal signals between visual structures. Here, we describe simultaneous recordings from monosynaptically connected retinal ganglion cells and lateral geniculate nucleus (LGN) neurons in the cat to determine how stimulus contrast affects the communication of visual signals between the two structures. Our results indicate that: (1) LGN neurons typically reach their half-maximal response at lower contrasts than their individual retinal inputs and (2) LGN neurons exhibit greater contrast-dependent phase advance (CDPA) than their retinal inputs. Further analyses suggests that increased sensitivity relies on spatial convergence of multiple retinal inputs, while increased CDPA is achieved, in part, on temporal summation of arriving signals. PMID:26924964

  11. Psychophysical contrast calibration

    PubMed Central

    To, Long; Woods, Russell L; Goldstein, Robert B; Peli, Eli

    2013-01-01

    Electronic displays and computer systems offer numerous advantages for clinical vision testing. Laboratory and clinical measurements of various functions and in particular of (letter) contrast sensitivity require accurately calibrated display contrast. In the laboratory this is achieved using expensive light meters. We developed and evaluated a novel method that uses only psychophysical responses of a person with normal vision to calibrate the luminance contrast of displays for experimental and clinical applications. Our method combines psychophysical techniques (1) for detection (and thus elimination or reduction) of display saturating nonlinearities; (2) for luminance (gamma function) estimation and linearization without use of a photometer; and (3) to measure without a photometer the luminance ratios of the display’s three color channels that are used in a bit-stealing procedure to expand the luminance resolution of the display. Using a photometer we verified that the calibration achieved with this procedure is accurate for both LCD and CRT displays enabling testing of letter contrast sensitivity to 0.5%. Our visual calibration procedure enables clinical, internet and home implementation and calibration verification of electronic contrast testing. PMID:23643843

  12. Hadamard speckle contrast reduction

    NASA Astrophysics Data System (ADS)

    Trisnadi, Jahja I.

    2004-01-01

    The condition for a diffuser to produce the maximum speckle contrast reduction with the minimum number of distinct phase patterns is derived. A binary realization of this optimum diffuser is obtained by mapping the rows or columns of a Hadamard matrix to the phase patterns. The method is experimentally verified in the Grating Light Valve laser projection display.

  13. Phonation in Tonal Contrasts

    ERIC Educational Resources Information Center

    Kuang, Jianjing

    2013-01-01

    Phonation is used in many tonal languages, but how it should be incorporated into tonal systems is not well understood. The purpose of this dissertation thus is to examine the role of phonation in tonal contrasts, and to investigate how phonation and pitch interact in the tonal space. This dissertation presents close studies of tonal contrasts…

  14. Flashing anomalous color contrast.

    PubMed

    Pinna, Baingio; Spillmann, Lothar; Werner, John S

    2004-01-01

    A new visual phenomenon that we call flashing anomalous color contrast is described. This phenomenon arises from the interaction between a gray central disk and a chromatic annulus surrounded by black radial lines. In an array of such figures, the central gray disk no longer appears gray, but assumes a color complementary to that of the surrounding annulus. The induced color appears: (1) vivid and saturated; (2) self-luminous, not a surface property; (3) flashing with eye or stimulus movement; (4) floating out of its confines; and (5) stronger in extrafoveal than in foveal vision. The strength of the effect depends on the number, length, width, and luminance contrast of the radial lines. The results suggest that the chromatic ring bounding the inner tips of the black radial lines induces simultaneous color contrast, whereas the radial lines elicit, in conjunction with the gray disk and the ring, the flashing, vividness, and high saturation of the effect. The stimulus properties inducing the illusion suggest that flashing anomalous color contrast may be based on asynchronous interactions among multiple visual pathways. PMID:15518215

  15. Local contrast and Pavlovian induction1

    PubMed Central

    Malone, John C.

    1976-01-01

    Two experiments examined the effects of number and similarity of stimuli on local contrast. In the first experiment, local contrast effects differed in magnitude as a function of the similarity among stimuli; greater positive local contrast appeared when stimuli were less similar, though this effect sometimes reversed for very dissimilar stimuli. In the second experiment, both positive and negative local contrast appeared transiently during the course of training a discrimination including two quite dissimilar stimuli. When two new stimuli were added, both effects reappeared in several cases. The effects remained when the discrimination was rendered more difficult by substituting a new stimulus very similar to one of the original pair. These and other data suggest that local contrast depends on the same factors that produce Pavlovian induction; in the absence of an alternative account, Pavlov's interpretation may be useful in suggesting further research that will help identify the mechanisms involved in both classical and operant discrimination learning. PMID:16811958

  16. Measuring contrast sensitivity

    PubMed Central

    Pelli, Denis G.; Bex, Peter

    2013-01-01

    Contrast sensitivity defines the threshold between the visible and invisible, which has obvious significance for basic and clinical vision science. Fechner's 1860 review reported that threshold contrast is 1% for a remarkably wide range of targets and conditions. While printed charts are still in use, computer testing is becoming more popular because it offers efficient adaptive measurement of threshold for a wide range of stimuli. Both basic and clinical studies usually want to know fundamental visual capability, regardless of the observer's subjective criterion. Criterion effects are minimized by the use of an objective task: multiple-alternative forced-choice detection or identification. Having many alternatives reduces the guessing rate, which makes each trial more informative, so fewer trials are needed. Finally, populations who may experience crowding or target confusion should be tested with one target at a time. PMID:23643905

  17. Chromatography: concepts and contrasts

    SciTech Connect

    Miller, J.M.

    1988-01-01

    As the author states in the Preface, this text attempts to provide a unified approach to chromatography (hence the title) by way of contrasting similarities and differences between gas chromatography (GC), column liquid chromatography (LC), and thin-layer chromatography (TLC). This book is also said to be pitched at an elementary level, suitable for most newcomers to the field (e.g., advanced undergraduates and beginning graduate students in the academic world, as well as bench-level chemists in industry).

  18. Stereopsis from contrast envelopes.

    PubMed

    Langley, K; Fleet, D J; Hibbard, P B

    1999-07-01

    We report two experiments concerning the site of the principal nonlinearity in second-order stereopsis. The first exploits the asymmetry in perceiving transparency with second-order stimuli found by Langley et al. (1998) (Proceedings of the Royal Society of London B, 265, 1837-1845) i.e. the product of a positive-valued contrast envelope and a mean-zero carrier grating can be seen transparently only when the disparities are consistent with the envelope appearing in front of the carrier. We measured the energy at the envelope frequencies that must be added in order to negate this asymmetry. We report that this amplitude can be predicted from the envelope sidebands and not from the magnitude of compressive pre-cortical nonlinearities measured by other researchers. In the second experiment, contrast threshold elevations were measured for the discrimination of envelope disparities following adaptation to sinusoidal gratings. It is reported that perception of the envelope's depth was affected most when the adapting grating was similar (in orientation and frequency) to the carrier, rather than to the contrast envelope. These results suggest that the principal nonlinearity in second-order stereopsis is cortical, occurring after orientation- and frequency-selective linear filtering. PMID:10367053

  19. Polychromatic diffraction contrast tomography

    SciTech Connect

    King, A.; Reischig, P.; Adrien, J.; Peetermans, S.; Ludwig, W.

    2014-11-15

    This tutorial review introduces the use of polychromatic radiation for 3D grain mapping using X-ray diffraction contrast tomography. The objective is to produce a 3D map of the grain shapes and orientations within a bulk, millimeter-sized polycrystalline sample. The use of polychromatic radiation enables the standard synchrotron X-ray technique to be applied in a wider range of contexts: 1) Using laboratory X-ray sources allows a much wider application of the diffraction contrast tomography technique. 2) Neutron sources allow large samples, or samples containing high Z elements to be studied. 3) Applied to synchrotron sources, smaller samples may be treated, or faster measurements may be possible. Challenges and particularities in the data acquisition and processing, and the limitations of the different variants, are discussed. - Highlights: • We present a tutorial review of polychromatic diffraction contrast tomography techniques. • The use of polychromatic radiation allows the standard synchrotron DCT technique to be extended to a range of other sources. • The characteristics and limitations of all variants of the techniques are derived, discussed and compared. • Examples using laboratory X-ray and cold neutron radiation are presented. • Suggestions for the future development of these techniques are presented.

  20. Orientation contrast of secondary electron images from electropolished metals.

    PubMed

    Chen, D; Chang, C P; Loretto, M H

    2015-09-01

    Orientation contrast obtained by an in-lens secondary electron detector in a scanning electron microscope from electropolished/etched metals is reported. The imaging conditions for obtaining such orientation contrast are defined. The mechanism responsible for the formation of the orientation contrast is explained, and an application example of this new imaging method is given. PMID:25980953

  1. On Establishing Underlying Tonal Contrast

    ERIC Educational Resources Information Center

    Snider, Keith

    2014-01-01

    Phonological field work is largely about establishing contrast in comparable environments. The notion of phonological contrast, however, can be confusing, particularly in its application to tone analysis. Does it mean phonemic contrast in the structuralist sense, or does it mean underlying contrast in the generative sense? Many linguists, in…

  2. Contrast affects flicker and speed perception differently

    NASA Technical Reports Server (NTRS)

    Thompson, P.; Stone, L. S.

    1997-01-01

    We have previously shown that contrast affects speed perception, with lower-contrast, drifting gratings perceived as moving slower. In a recent study, we examined the implications of this result on models of speed perception that use the amplitude of the response of linear spatio-temporal filters to determine speed. In this study, we investigate whether the contrast dependence of speed can be understood within the context of models in which speed estimation is made using the temporal frequency of the response of linear spatio-temporal filters. We measured the effect of contrast on flicker perception and found that contrast manipulations produce opposite effects on perceived drift rate and perceived flicker rate, i.e., reducing contrast increases the apparent temporal frequency of counterphase modulated gratings. This finding argues that, if a temporal frequency-based algorithm underlies speed perception, either flicker and speed perception must not be based on the output of the same mechanism or contrast effects on perceived spatial frequency reconcile the disparate effects observed for perceived temporal frequency and speed.

  3. Differential interference contrast tomography.

    PubMed

    Vishnyakov, Gennady; Levin, Gennady; Minaev, Vladimir; Latushko, Mikhail; Nekrasov, Nikolay; Pickalov, Valery

    2016-07-01

    We present a new approach to optical tomography of phase objects that is referred to as differential interference contrast tomography (DICT). The main feature of DICT is that the result of tomographic reconstruction is a 3D DIC image. This image is described by partial derivative of 3D refractive index distribution in one direction. The DICT setup consists of a lateral shearing phase-shifting interference microscope with low-coherent LED illumination. To create projections of the sample at various illumination angles, an angular scanning beam was used. 3D DIC tomograms of a white blood cell are presented. The comparison between the reconstructed DIC tomogram slices and the conventional DIC images of the same sample at the same depths are also represented. PMID:27367095

  4. Optical imaging with dynamic contrast agents.

    PubMed

    Wei, Qingshan; Wei, Alexander

    2011-01-24

    Biological imaging applications often employ molecular probes or nanoparticles for enhanced contrast. However, resolution and detection are still often limited by the intrinsic heterogeneity of the sample, which can produce high levels of background that obscure the signals of interest. Herein, we describe approaches to overcome this obstacle based on the concept of dynamic contrast: a strategy for elucidating signals by the suppression or removal of background noise. Dynamic contrast mechanisms can greatly reduce the loading requirement of contrast agents, and may be especially useful for single-probe imaging. Dynamic contrast modalities are also platform-independent, and can enhance the performance of sophisticated biomedical imaging systems or simple optical microscopes alike. Dynamic contrast is performed in two stages: 1) a signal modulation scheme to introduce time-dependent changes in amplitude or phase, and 2) a demodulation step for signal recovery. Optical signals can be coupled with magnetic nanoparticles, photoswitchable probes, or plasmon-resonant nanostructures for modulation by magnetomotive, photonic, or photothermal mechanisms, respectively. With respect to image demodulation, many of the strategies developed for signal processing in electronics and communication technologies can also be applied toward the editing of digital images. The image-processing step can be as simple as differential imaging, or may involve multiple reference points for deconvolution by using cross-correlation algorithms. Periodic signals are particularly amenable to image demodulation strategies based on Fourier transform; the contrast of the demodulated signal increases with acquisition time, and modulation frequencies in the kHz range are possible. Dynamic contrast is an emerging topic with considerable room for development, both with respect to molecular or nanoscale probes for signal modulation, and also to methods for more efficient image processing and editing. PMID

  5. Contrast echocardiography 1996. A review.

    PubMed Central

    Villarraga, H R; Foley, D A; Mulvagh, S L

    1996-01-01

    Remarkable advances in the field of contrast echocardiography have been made during the last decade. Interest in ultrasound contrast agents that strengthen the backscattered ultrasound signal and improve image display has stimulated further research. Echocardiographic contrast agents providing left ventricular cavity image enhancement after intravenous injection are now available. A role for contrast echocardiography in the assessment of myocardial perfusion has been established within the invasive clinical setting. With the development of newer contrast agents and new ultrasound technology, myocardial perfusion imaging using contrast echocardiography after venous injection is no longer the unattainable "holy grail," but is fast approaching clinical applicability. Images PMID:8792539

  6. Pedagogical Implications of Contrastive Studies

    ERIC Educational Resources Information Center

    Marton, Waldemar

    1972-01-01

    Pessimism regarding pedagogical applications of contrastive studies, and reasons therefore, are described. Several misunderstandings believed to contribute to this pessimism, and several areas of controversy concerning uses of contrastive studies, are discussed. See FL 508 197 for availability. (RM)

  7. Recognition memory reveals just how CONTRASTIVE contrastive accenting really is

    PubMed Central

    Fraundorf, Scott H.; Watson, Duane G.; Benjamin, Aaron S.

    2010-01-01

    The effects of pitch accenting on memory were investigated in three experiments. Participants listened to short recorded discourses that contained contrast sets with two items (e.g. British scientists and French scientists); a continuation specified one item from the set. Pitch accenting on the critical word in the continuation was manipulated between non-contrastive (H* in the ToBI system) and contrastive (L+H*). On subsequent recognition memory tests, the L+H* accent increased hits to correct statements and correct rejections of the contrast item (Experiments 1–3), but did not impair memory for other parts of the discourse (Experiment 2). L+H* also did not facilitate correct rejections of lures not in the contrast set (Experiment 3), indicating that contrastive accents do not simply strengthen the representation of the target item. These results suggest comprehenders use pitch accenting to encode and update information about multiple elements in a contrast set. PMID:20835405

  8. Phase Contrast Imaging

    SciTech Connect

    Menk, Ralf Hendrik

    2008-11-13

    All standard (medical) x-ray imaging technologies, rely primarily on the amplitude properties of the incident radiation, and do not depend on its phase. This is unchanged since the discovery by Roentgen that the intensity of an x-ray beam, as measured by the exposure on a film, was related to the relative transmission properties of an object. However, recently various imaging techniques have emerged which depend on the phase of the x-rays as well as the amplitude. Phase becomes important when the beam is coherent and the imaging system is sensitive to interference phenomena. Significant new advances have been made in coherent optic theory and techniques, which now promise phase information in medical imaging. The development of perfect crystal optics and the increasing availability of synchrotron radiation facilities have contributed to a significant increase in the application of phase based imaging in materials and life sciences. Unique source characteristics such as high intensity, monochromaticity, coherence and high collimating provide an ideal source for advanced imaging. Phase contrast imaging has been applied in both projection and computed tomography modes, and recent applications have been made in the field of medical imaging. Due to the underlying principle of X-ray detection conventional image receptors register only intensities of wave fields and not their phases. During the last decade basically five different methods were developed that translate the phase information into intensity variations. These methods are based on measuring the phase shift {phi} directly (using interference phenomena), the gradient {nabla}{sub {phi}}, or the Laplacian {nabla}{sup 2}{phi}. All three methods can be applied to polychromatic X-ray sources keeping in mind that the native source is synchrotron radiation, featuring monochromatic and reasonable coherent X-ray beams. Due to the vast difference in the coefficients that are driven absorption and phase effects (factor 1

  9. High contrast electrochromic iris.

    PubMed

    Deutschmann, T; Kortz, C; Walder, L; Oesterschulze, E

    2015-11-30

    We present a non-mechanical microiris based on two complementary electrochromic (EC) materials, namely viologens and phenozines, with an almost neutral spectral behavior. Measurements concerning the spectral light transmission, modulation transfer function, and response time validate that the optical performance of the EC-iris is comparable to that of a classical blade iris. The time constant is limited due to diffusive mass transport of the molecules, but can be reduced by a short voltage pulse. The current controlled transmission of the EC-material renders the individual control of each iris segment without crosstalk possible, allowing its usage as tunable spatial filter. PMID:26698777

  10. Perceived contrast in complex images

    PubMed Central

    Haun, Andrew M.; Peli, Eli

    2013-01-01

    To understand how different spatial frequencies contribute to the overall perceived contrast of complex, broadband photographic images, we adapted the classification image paradigm. Using natural images as stimuli, we randomly varied relative contrast amplitude at different spatial frequencies and had human subjects determine which images had higher contrast. Then, we determined how the random variations corresponded with the human judgments. We found that the overall contrast of an image is disproportionately determined by how much contrast is between 1 and 6 c/°, around the peak of the contrast sensitivity function (CSF). We then employed the basic components of contrast psychophysics modeling to show that the CSF alone is not enough to account for our results and that an increase in gain control strength toward low spatial frequencies is necessary. One important consequence of this is that contrast constancy, the apparent independence of suprathreshold perceived contrast and spatial frequency, will not hold during viewing of natural images. We also found that images with darker low-luminance regions tended to be judged as having higher overall contrast, which we interpret as the consequence of darker local backgrounds resulting in higher band-limited contrast response in the visual system. PMID:24190908

  11. Transparency perception: the key to understanding simultaneous color contrast.

    PubMed

    Ekroll, Vebjørn; Faul, Franz

    2013-03-01

    The well-known simultaneous color contrast effect is traditionally explained in terms of visual color constancy mechanisms correcting for the confounding influence of ambient illumination on the retinal color signal. Recent research, however, suggests that the traditional gross quantitative laws of simultaneous color contrast, which are readily compatible with this functional explanation, should be revised and replaced by others, which are not readily understandable in terms of this perspective. Here, we show that the revised laws of simultaneous color contrast are well accounted for by an alternative theory explaining the simultaneous contrast effect in terms of mechanisms subserving the perception of transparent media. PMID:23456110

  12. Grouping Factors and the Reverse Contrast Illusion.

    PubMed

    Economou, Elias; Zdravković, Sunčica; Gilchrist, Alan

    2015-12-01

    In simultaneous lightness contrast, two identical gray target squares lying on backgrounds of different intensities appear different in lightness. Traditionally, this illusion was explained by lateral inhibitory mechanisms operating retinotopically. More recently, spatial filtering models have been preferred. We report tests of an anchoring theory account in which the illusion is attributed to grouping rules used by the visual system to compute lightness. We parametrically varied the belongingness of two gray target bars to their respective backgrounds so that they either appeared to group with a set of bars flanking them, or they appeared to group with their respective backgrounds. In all variations, the retinal adjacency of the gray squares and their backgrounds was essentially unchanged. We report data from seven experiments showing that manipulation of the grouping rules governs the size and direction of the simultaneous lightness contrast illusion. These results support the idea that simultaneous lightness contrast is the product of anchoring within perceptual groups. PMID:26562863

  13. Pattern specificity of contrast adaptation

    PubMed Central

    Anstis, Stuart

    2014-01-01

    Contrast adaptation is specific to precisely localised edges, so that adapting to a flickering photograph makes one less sensitive to that same photograph, but not to similar photographs. When two low-contrast photos, A and B, are transparently superimposed, then adapting to a flickering high-contrast B leaves no net afterimage, but it makes B disappear from the A+B picture, which now simply looks like A. PMID:25165518

  14. Nuclear magnetic resonance contrast agents

    DOEpatents

    Smith, Paul H.; Brainard, James R.; Jarvinen, Gordon D.; Ryan, Robert R.

    1997-01-01

    A family of contrast agents for use in magnetic resonance imaging and a method of enhancing the contrast of magnetic resonance images of an object by incorporating a contrast agent of this invention into the object prior to forming the images or during formation of the images. A contrast agent of this invention is a paramagnetic lanthanide hexaazamacrocyclic molecule, where a basic example has the formula LnC.sub.16 H.sub.14 N.sub.6. Important applications of the invention are in medical diagnosis, treatment, and research, where images of portions of a human body are formed by means of magnetic resonance techniques.

  15. Nuclear magnetic resonance contrast agents

    DOEpatents

    Smith, P.H.; Brainard, J.R.; Jarvinen, G.D.; Ryan, R.R.

    1997-12-30

    A family of contrast agents for use in magnetic resonance imaging and a method of enhancing the contrast of magnetic resonance images of an object by incorporating a contrast agent of this invention into the object prior to forming the images or during formation of the images. A contrast agent of this invention is a paramagnetic lanthanide hexaazamacrocyclic molecule, where a basic example has the formula LnC{sub 16}H{sub 14}N{sub 6}. Important applications of the invention are in medical diagnosis, treatment, and research, where images of portions of a human body are formed by means of magnetic resonance techniques. 10 figs.

  16. Adaptive changes in visual cortex following prolonged contrast reduction

    PubMed Central

    Kwon, MiYoung; Legge, Gordon E.; Fang, Fang; Cheong, Allen M. Y.; He, Sheng

    2009-01-01

    How does prolonged reduction in retinal-image contrast affect visual-contrast coding? Recent evidence indicates that some forms of long-term visual deprivation result in compensatory perceptual and neural changes in the adult visual pathway. It has not been established whether changes due to contrast adaptation are best characterized as “contrast gain” or “response gain.” We present a theoretical rationale for predicting that adaptation to long-term contrast reduction should result in response gain. To test this hypothesis, normally sighted subjects adapted for four hours by viewing their environment through contrast-reducing goggles. During the adaptation period, the subjects went about their usual daily activities. Subjects' contrast-discrimination thresholds and fMRI BOLD responses in cortical areas V1 and V2 were obtained before and after adaptation. Following adaptation, we observed a significant decrease in contrast-discrimination thresholds, and significant increase in BOLD responses in V1 and V2. The observed interocular transfer of the adaptation effect suggests that the adaptation has a cortical origin. These results reveal a new kind of adaptability of the adult visual cortex, an adjustment in the gain of the contrast-response in the presence of a reduced range of stimulus contrasts, which is consistent with a response-gain mechanism. The adaptation appears to be compensatory, such that the precision of contrast coding is improved for low retinal-image contrasts. PMID:19271930

  17. Multi-contrast photoacoustic microscopy

    NASA Astrophysics Data System (ADS)

    Hu, S.; Sohn, R.; Lu, Z.-H.; Soetikno, B.; Zhong, Q.; Yao, J.; Maslov, K.; Arbeit, J. M.; Wang, L. V.

    2012-02-01

    We developed multi-contrast photoacoustic microscopy (PAM) for in vivo anatomical, functional, metabolic, and molecular imaging. This technical innovation enables comprehensive understanding of the tumor microenvironment. With multi-contrast PAM, we longitudinally determined tumor vascular anatomy, blood flow, oxygen saturation of hemoglobin, and oxygen extraction fraction.

  18. Faithful Contrastive Features in Learning

    ERIC Educational Resources Information Center

    Tesar, Bruce

    2006-01-01

    This article pursues the idea of inferring aspects of phonological underlying forms directly from surface contrasts by looking at optimality theoretic linguistic systems (Prince & Smolensky, 1993/2004). The main result proves that linguistic systems satisfying certain conditions have the faithful contrastive feature property: Whenever 2 distinct…

  19. Image Contrast in Holographic Reconstructions

    ERIC Educational Resources Information Center

    Russell, B. R.

    1969-01-01

    The fundamental concepts of holography are explained using elementary wave ideas. Discusses wavefront reconstruction and contrast in hemigraphic images. The consequence of recording only the intensity at a given surface and using an oblique reference wave is shown to be an incomplete reconstruction resulting in image of low contrast. (LC)

  20. Measurement of visual contrast sensitivity

    NASA Astrophysics Data System (ADS)

    Vongierke, H. E.; Marko, A. R.

    1985-04-01

    This invention involves measurement of the visual contrast sensitivity (modulation transfer) function of a human subject by means of linear or circular spatial frequency pattern on a cathode ray tube whose contrast is automatically decreasing or increasing depending on the subject pressing or releasing a hand-switch button. The threshold of detection of the pattern modulation is found by the subject by adjusting the contrast to values which vary about the subject's threshold thereby determining the threshold and also providing by the magnitude of the contrast fluctuations between reversals some estimate of the variability of the subject's absolute threshold. The invention also involves the slow automatic sweeping of the spatial frequency of the pattern over the spatial frequencies after preset time intervals or after threshold has been defined at each frequency by a selected number of subject-determined threshold crossings; i.e., contrast reversals.

  1. Contrasting the solar winds at the solar cycle 23-24 minimum with those at the previous one: can this help tell what mechanisms are heating and accelerating the solar wind?

    NASA Astrophysics Data System (ADS)

    Li, B.

    2012-12-01

    The Solar Cycle (SC) 23-24 minimum is substantially different from the previous solar minima. From the space weather perspective, in the ecliptic plane this minimum recorded the slowest, least dense solar wind, and the weakest magnetic field, leading to the weakest geomagnetic activity. Off ecliptic measurements by Ulysses recorded similar trends even though the fast wind therein does not show as significant a drop in speeds. While the changes in the solar wind parameters are generally believed to be associated with the substantial differences in both the coronal and interplanetary magnetic fields, the precise mechanisms have yet to be named. Here in this contribution we compute a grid of multifluid, turbulence-based solar wind models where electrons and protons are distinguished, the proton temperature anisotropy is considered, and relatively complete energy equations are used for both species. The models employ the two primary competing ideas for solar wind heating and acceleration, one is based on the cyclotron resonance between ions and high frequency waves generated by a parallel cascade, while the other, developed only most recently, is based on the interaction of solar wind species with reflection-driven turbulence where the cascade proceeds primarily in the perpendicular direction. In each group of models, we construct solutions using magnetic field parameters appropriate for either the 23-24 or the 22-23 minimum. The differences in the obtained solar wind parameters from one minimum to the other are then compared with the in situ measurements, thereby helping us identify which mechanism performs better in reproducing the observations. We conclude that not only the absolute values of solar wind parameters at a specific solar minimum, but their relative changes from one minimum to another, can help tell which solar wind heating mechanism is more likely at work.

  2. Contrasting Rhetorics/Contrasting Cultures: Why Contrastive Rhetoric Needs a Better Conceptualization of Culture

    ERIC Educational Resources Information Center

    Atkinson, Dwight

    2004-01-01

    This paper deals with an underdeveloped notion in the EAP sub-discipline of contrastive rhetoric: culture. It argues that a better conceptualization of contrastive rhetoric needs to include a better conceptualization of culture. After engaging with the complex question "What is culture?" the paper moves on to consider four sets of current issues…

  3. Ultrasound Despeckling for Contrast Enhancement

    PubMed Central

    Tay, Peter C.; Garson, Christopher D.; Acton, Scott T.; Hossack, John A.

    2010-01-01

    Images produced by ultrasound systems are adversely hampered by a stochastic process known as speckle. A despeckling method based upon removing outlier is proposed. The method is developed to contrast enhance B-mode ultrasound images. The contrast enhancement is with respect to decreasing pixel variations in homogeneous regions while maintaining or improving differences in mean values of distinct regions. A comparison of the proposed despeckling filter is compared with the other well known despeckling filters. The evaluations of despeckling performance are based upon improvements to contrast enhancement, structural similarity, and segmentation results on a Field II simulated image and actual B-mode cardiac ultrasound images captured in vivo. PMID:20227984

  4. Ultrasound despeckling for contrast enhancement.

    PubMed

    Tay, Peter C; Garson, Christopher D; Acton, Scott T; Hossack, John A

    2010-07-01

    Images produced by ultrasound systems are adversely hampered by a stochastic process known as speckle. A despeckling method based upon removing outlier is proposed. The method is developed to contrast enhance B-mode ultrasound images. The contrast enhancement is with respect to decreasing pixel variations in homogeneous regions while maintaining or improving differences in mean values of distinct regions. A comparison of the proposed despeckling filter is compared with the other well known despeckling filters. The evaluations of despeckling performance are based upon improvements to contrast enhancement, structural similarity, and segmentation results on a Field II simulated image and actual B-mode cardiac ultrasound images captured in vivo. PMID:20227984

  5. Small intestine contrast injection (image)

    MedlinePlus

    ... and throat, through the stomach into the small intestine. When in place, contrast dye is introduced and ... means of demonstrating whether or not the small intestine is normal when abnormality is suspected.

  6. [Allergy to radiographic contrast media].

    PubMed

    Vionnet, Julien; Petitpierre, Stéphanie; Fumeaux, Alexandre; Meuli, Reto; Spertini, Francois; Comte, Denis

    2013-04-17

    Allergy to radiographic contrast media Hypersensitivity reactions to radio-contrast media are common in the daily practice. These products are responsible for immediate (< or = 1 hour after administration) and non immediate (> 1 hour after administration) hypersensitivity reactions. A diagnostic work-up by an allergologist with skin tests and in some cases provocation tests is of value in reducing the risk of recurrent hypersensitivity reactions to iodinated contrast media. A careful selection of the patients is required because the incidence of breakthrough reactions is still concerning, even with proper premedication. Practical recommendations are presented in this article. For gadolinium-based contrast agents, data in the literature is not sufficient for suggesting guidelines. PMID:23667970

  7. Environmentally responsive MRI contrast agents

    PubMed Central

    Davies, Gemma-Louise; Kramberger, Iris; Davis, Jason J.

    2015-01-01

    Biomedical imaging techniques can provide a vast amount of anatomical information, enabling diagnosis and the monitoring of disease and treatment profile. MRI uniquely offers convenient, non-invasive, high resolution tomographic imaging. A considerable amount of effort has been invested, across several decades, in the design of non toxic paramagnetic contrast agents capable of enhancing positive MRI signal contrast. Recently, focus has shifted towards the development of agents capable of specifically reporting on their local biochemical environment, where a switch in image contrast is triggered by a specific stimulus/biochemical variable. Such an ability would not only strengthen diagnosis but also provide unique disease-specific biochemical insight. This feature article focuses on recent progress in the development of MRI contrast switching with molecular, macromolecular and nanoparticle-based agents. PMID:24040650

  8. Contrast-controlled retinal response

    NASA Astrophysics Data System (ADS)

    Sharma, Nachieketa K.

    2015-06-01

    A beam of light stimulates the retina weakly when its entry to the pupil is gradually shifted from the centre toward the edge. For single pupil entrance point the light, irrespective of its coherence would still show the Stiles-Crawford effect with diminished visibility toward the edge of the pupil. Only when coherent light is incident from opposing points in the pupil can the effect be cancelled. This paper has attempted a theoretical computation of how the contrast in an interference pattern formed on the retina controls the retina's response in three ways; first, by completely disregarding the Stiles Crawford diminution of effective brightness for unit contrast; next, taking the traditional SCE route for zero contrast, and finally enhancing the diminution in the effective brightness by giving an opposing boost to the visibility in commensurate with a contrast intermediate between the two extremes of unity and zero.

  9. Phase Contrast X-ray Imaging Signatures for Security Applications

    SciTech Connect

    Miller, Erin A.; White, Timothy A.; McDonald, Benjamin S.; Seifert, Allen

    2013-02-01

    Abstract: Differential phase contrast imaging with a grating interferometer is a promising new radiographic technique providing three distinct contrast mechanisms - absorption, phase, and scatter (or dark field) - using a conventional x-ray tube source. We investigate the signatures available in these three contrast mechanisms with attention towards potential security applications. We find that the scatter mode in particular is sensitive to textured materials, enabling lowered detection limits than absorption for materials such as powders. We investigate the length scales to which our imaging system is sensitive.

  10. Quantum Mechanics From the Cradle?

    ERIC Educational Resources Information Center

    Martin, John L.

    1974-01-01

    States that the major problem in learning quantum mechanics is often the student's ignorance of classical mechanics and that one conceptual hurdle in quantum mechanics is its statistical nature, in contrast to the determinism of classical mechanics. (MLH)

  11. A theory of behavioral contrast.

    PubMed

    Killeen, Peter R

    2014-11-01

    The reinforcers that maintain target instrumental responses also reinforce other responses that compete with them for expression. This competition, and its imbalance at points of transition between different schedules of reinforcement, causes behavioral contrast. The imbalance is caused by differences in the rates at which different responses come under the control of component stimuli. A model for this theory of behavioral contrast is constructed by expanding the coupling coefficient of MPR (Killeen, 1994). The coupling coefficient gives the degree of association of a reinforcer with the target response (as opposed to other competing responses). Competing responses, often identified as interim or adjunctive or superstitious behavior, are intrinsic to reinforcement schedules, especially interval schedules. In addition to that base-rate of competition, additional competing responses may spill over from the prior component, causing initial contrast; and they may be modulated by conditioned reinforcement or punishment from stimuli associated with subsequent component change, causing terminal contrast. A formalization of these hypotheses employed (a) a hysteresis model of off-target responses giving rise to initial contrast, and (b) a competing traces model of the suppression or enhancement of ongoing competitive responses by signals of following-schedule transition. The theory was applied to transient contrast, the following schedule effect, and the component duration effect. PMID:25244535

  12. Advances in Magnetic Resonance Imaging Contrast Agents for Biomarker Detection

    PubMed Central

    Sinharay, Sanhita; Pagel, Mark D.

    2016-01-01

    Recent advances in magnetic resonance imaging (MRI) contrast agents have provided new capabilities for biomarker detection through molecular imaging. MRI contrast agents based on the T2 exchange mechanism have more recently expanded the armamentarium of agents for molecular imaging. Compared with T1 and T2* agents, T2 exchange agents have a slower chemical exchange rate, which improves the ability to design these MRI contrast agents with greater specificity for detecting the intended biomarker. MRI contrast agents that are detected through chemical exchange saturation transfer (CEST) have even slower chemical exchange rates. Another emerging class of MRI contrast agents uses hyperpolarized 13C to detect the agent with outstanding sensitivity. These hyperpolarized 13C agents can be used to track metabolism and monitor characteristics of the tissue microenvironment. Together, these various MRI contrast agents provide excellent opportunities to develop molecular imaging for biomarker detection. PMID:27049630

  13. Advances in Magnetic Resonance Imaging Contrast Agents for Biomarker Detection.

    PubMed

    Sinharay, Sanhita; Pagel, Mark D

    2016-06-12

    Recent advances in magnetic resonance imaging (MRI) contrast agents have provided new capabilities for biomarker detection through molecular imaging. MRI contrast agents based on the T2 exchange mechanism have more recently expanded the armamentarium of agents for molecular imaging. Compared with T1 and T2* agents, T2 exchange agents have a slower chemical exchange rate, which improves the ability to design these MRI contrast agents with greater specificity for detecting the intended biomarker. MRI contrast agents that are detected through chemical exchange saturation transfer (CEST) have even slower chemical exchange rates. Another emerging class of MRI contrast agents uses hyperpolarized (13)C to detect the agent with outstanding sensitivity. These hyperpolarized (13)C agents can be used to track metabolism and monitor characteristics of the tissue microenvironment. Together, these various MRI contrast agents provide excellent opportunities to develop molecular imaging for biomarker detection. PMID:27049630

  14. Advances in Magnetic Resonance Imaging Contrast Agents for Biomarker Detection

    NASA Astrophysics Data System (ADS)

    Sinharay, Sanhita; Pagel, Mark D.

    2016-06-01

    Recent advances in magnetic resonance imaging (MRI) contrast agents have provided new capabilities for biomarker detection through molecular imaging. MRI contrast agents based on the T2 exchange mechanism have more recently expanded the armamentarium of agents for molecular imaging. Compared with T1 and T2* agents, T2 exchange agents have a slower chemical exchange rate, which improves the ability to design these MRI contrast agents with greater specificity for detecting the intended biomarker. MRI contrast agents that are detected through chemical exchange saturation transfer (CEST) have even slower chemical exchange rates. Another emerging class of MRI contrast agents uses hyperpolarized 13C to detect the agent with outstanding sensitivity. These hyperpolarized 13C agents can be used to track metabolism and monitor characteristics of the tissue microenvironment. Together, these various MRI contrast agents provide excellent opportunities to develop molecular imaging for biomarker detection.

  15. Spontaneous recovery of effects of contrast adaptation without awareness

    PubMed Central

    Mei, Gaoxing; Dong, Xue; Dong, Bo; Bao, Min

    2015-01-01

    Prolonged exposure to a high contrast stimulus reduces the neural sensitivity to subsequent similar patterns. Recent work has disclosed that contrast adaptation is controlled by multiple mechanisms operating over differing timescales. Adaptation to high contrast for a relatively longer period can be rapidly eliminated by adaptation to a lower contrast (or meanfield in the present study). Such rapid deadaptation presumably causes a short-term mechanism to signal for a sensitivity increase, canceling ongoing signals from long-term mechanisms. Once deadaptation ends, the short-term mechanism rapidly returns to baseline, and the slowly decaying effects in the long-term mechanisms reemerge, allowing the perceptual aftereffects to recover during continued testing. Although this spontaneous recovery effect is considered strong evidence supporting the multiple mechanisms theory, it remains controversial whether the effect is mainly driven by visual memory established during the initial longer-term adaptation period. To resolve this debate, we used a modified Continuous Flash Suppression (CFS) and visual crowding paradigms to render the adapting stimuli invisible, but still observed the spontaneous recovery phenomenon. These results exclude the possibility that spontaneous recovery found in the previous work was merely the consequence of explicit visual memory. Our findings also demonstrate that contrast adaptation, even at the unconscious processing levels, is controlled by multiple mechanisms. PMID:26483723

  16. Internal polarization limits coronagraph contrast

    NASA Astrophysics Data System (ADS)

    Breckinridge, James Bernard; Lam, Wai Sze T.; Chipman, Russell A.

    2015-08-01

    The performance of exoplanet imaging coronagraphs is limited by internal polarization. The point spread function (PSF) of these systems is determined by the details of the opto-mechanical layout selected to package the system and by the highly reflective metal thin films needed to maintain high optical system transmittance. To obtain the high contrast levels needed for terrestrial exoplanet science requires a comprehensive understanding of the vector electromagnetic wave from the source through the system. The literature contains many studies of polarization transmissivity of telescopes and instruments for the purpose of photo-polarimetry. Here we report for the first time the effects of polarization on high-performance image quality.We modeled a typical 2.4-meter Cassegrain telescope system with one 90-degree fold mirror and analyzed the system for polarization aberrations.We find: 1. The image plane irradiance distribution is the linear superposition of four PSF images: One for each of the two orthogonal polarizations and one for each of two cross-product polarization terms. 2. The PSF image is brighter by 9% for one polarization component compared to its orthogonal state. 3. The image of the PSF for orthogonal components are shifted across the focal plane with respect to each other, causing the PSF image for astronomical sources (polarized or unpolarized) to become slightly elongated (elliptical) with a centroid separation of about 0.6 masec. 4. The orthogonally polarized components of unpolarized sources contain different wavefront aberrations, which are separated by approximately 32 milliwaves. This implies that a wavefront correction system cannot optimally correct the aberrations for all polarizations simultaneously. 5. The polarization aberrations couple small parts (~1E-5) of each polarization component of the light into the orthogonal polarization to create highly distorted secondary, or “ghost” PSF image.. The radius of the spatial extent of the 90

  17. Multiscale image contrast amplification (MUSICA)

    NASA Astrophysics Data System (ADS)

    Vuylsteke, Pieter; Schoeters, Emile P.

    1994-05-01

    This article presents a novel approach to the problem of detail contrast enhancement, based on multiresolution representation of the original image. The image is decomposed into a weighted sum of smooth, localized, 2D basis functions at multiple scales. Each transform coefficient represents the amount of local detail at some specific scale and at a specific position in the image. Detail contrast is enhanced by non-linear amplification of the transform coefficients. An inverse transform is then applied to the modified coefficients. This yields a uniformly contrast- enhanced image without artefacts. The MUSICA-algorithm is being applied routinely to computed radiography images of chest, skull, spine, shoulder, pelvis, extremities, and abdomen examinations, with excellent acceptance. It is useful for a wide range of applications in the medical, graphical, and industrial area.

  18. Contrast-enhanced refraction imaging

    NASA Astrophysics Data System (ADS)

    Hall, Christopher J.; Rogers, Keith D.; Lewis, Rob A.; Menk, Ralf Hendrik; Arfelli, Fulvia; Siu, Karen K.; Benci, A.; Kitchen, M.; Pillon, Alessandra; Rigon, Luigi; Round, Andrew J.; Hufton, Alan P.; Evans, Andrew; Pinder, Sarah E.; Evans, S.

    2004-01-01

    An attempt has been made, for the first time, to extend the capabilities of diffraction enhanced imaging (DEI) using low concentrations of a contrast agent. A phantom has been constructed to accommodate a systematic series of diluted bromine deoxyuridase (BrDU) samples in liquid form. This was imaged using a conventional DEI arrangement and at a range of energies traversing the Br K-edge. The images were analyzed to provide a quantitative measure of contrast as a function of X-ray energy and (BrDU) concentration. The results indicate that the particular experimental arrangement was not optimized to exploit the potential of this contrast enhancement and several suggestions are discussed to improve this further.

  19. Polycatechol Nanoparticle MRI Contrast Agents.

    PubMed

    Li, Yiwen; Huang, Yuran; Wang, Zhao; Carniato, Fabio; Xie, Yijun; Patterson, Joseph P; Thompson, Matthew P; Andolina, Christopher M; Ditri, Treffly B; Millstone, Jill E; Figueroa, Joshua S; Rinehart, Jeffrey D; Scadeng, Miriam; Botta, Mauro; Gianneschi, Nathan C

    2016-02-01

    Amphiphilic triblock copolymers containing Fe(III) -catecholate complexes formulated as spherical- or cylindrical-shaped micellar nanoparticles (SMN and CMN, respectively) are described as new T1-weighted agents with high relaxivity, low cytotoxicity, and long-term stability in biological fluids. Relaxivities of both SMN and CMN exceed those of established gadolinium chelates across a wide range of magnetic field strengths. Interestingly, shape-dependent behavior is observed in terms of the particles' interactions with HeLa cells, with CMN exhibiting enhanced uptake and contrast via magnetic resonance imaging (MRI) compared with SMN. These results suggest that control over soft nanoparticle shape will provide an avenue for optimization of particle-based contrast agents as biodiagnostics. The polycatechol nanoparticles are proposed as suitable for preclinical investigations into their viability as gadolinium-free, safe, and effective imaging agents for MRI contrast enhancement. PMID:26681255

  20. Contrasting coloration in terrestrial mammals

    PubMed Central

    Caro, Tim

    2008-01-01

    Here I survey, collate and synthesize contrasting coloration in 5000 species of terrestrial mammals focusing on black and white pelage. After briefly reviewing alternative functional hypotheses for coloration in mammals, I examine nine colour patterns and combinations on different areas of the body and for each mammalian taxon to try to identify the most likely evolutionary drivers of contrasting coloration. Aposematism and perhaps conspecific signalling are the most consistent explanations for black and white pelage in mammals; background matching may explain white pelage. Evidence for contrasting coloration is being involved in crypsis through pattern blending, disruptive coloration or serving other functions, such as signalling dominance, lures, reducing eye glare or in temperature regulation has barely moved beyond anecdotal stages of investigation. Sexual dichromatism is limited in this taxon and its basis is unclear. Astonishingly, the functional significance of pelage coloration in most large charismatic black and white mammals that were new to science 150 years ago still remains a mystery. PMID:18990666

  1. Segment aberration effects on contrast.

    PubMed

    Crossfield, Ian J; Troy, Mitchell

    2007-07-20

    High-contrast imaging, particularly the direct detection of extrasolar planets, is a major science driver for the next generation of telescopes. This science requires the suppression of scattered starlight at extremely high levels and that telescopes be correctly designed today to meet these stringent requirements in the future. The challenge increases in systems with complicated aperture geometries such as obscured, segmented telescopes. Such systems can also require intensive modeling and simulation efforts in order to understand the trade-offs between different optical parameters. The feasibility and development of a contrast prediction tool for use in the design and systems engineering of these telescopes is described. The performance of a particular starlight suppression system on a large segmented telescope is described analytically. These analytical results and the results of a contrast predictor are then compared with the results of a full wave-optics simulation. PMID:17609697

  2. Contrast stress echocardiography in hypertensive heart disease

    PubMed Central

    2011-01-01

    Hypertension is associated with atherosclerosis and cardiac and vascular structural and functional changes. Myocardial ischemia may arise in hypertension independent of coronary artery disease through an interaction between several pathophysiological mechanisms, including left ventricular hypertrophy, increased arterial stiffness and reduced coronary flow reserve associated with microvascular disease and endothelial dysfunction. The present case report demonstrates how contrast stress echocardiography can be used to diagnose myocardial ischemia in a hypertensive patient with angina pectoris but without significant obstructive coronary artery disease. The myocardial ischemia was due to severe resistant hypertension complicated with concentric left ventricular hypertrophy and increased arterial stiffness. PMID:22093163

  3. Contrast-guided image interpolation.

    PubMed

    Wei, Zhe; Ma, Kai-Kuang

    2013-11-01

    In this paper a contrast-guided image interpolation method is proposed that incorporates contrast information into the image interpolation process. Given the image under interpolation, four binary contrast-guided decision maps (CDMs) are generated and used to guide the interpolation filtering through two sequential stages: 1) the 45(°) and 135(°) CDMs for interpolating the diagonal pixels and 2) the 0(°) and 90(°) CDMs for interpolating the row and column pixels. After applying edge detection to the input image, the generation of a CDM lies in evaluating those nearby non-edge pixels of each detected edge for re-classifying them possibly as edge pixels. This decision is realized by solving two generalized diffusion equations over the computed directional variation (DV) fields using a derived numerical approach to diffuse or spread the contrast boundaries or edges, respectively. The amount of diffusion or spreading is proportional to the amount of local contrast measured at each detected edge. The diffused DV fields are then thresholded for yielding the binary CDMs, respectively. Therefore, the decision bands with variable widths will be created on each CDM. The two CDMs generated in each stage will be exploited as the guidance maps to conduct the interpolation process: for each declared edge pixel on the CDM, a 1-D directional filtering will be applied to estimate its associated to-be-interpolated pixel along the direction as indicated by the respective CDM; otherwise, a 2-D directionless or isotropic filtering will be used instead to estimate the associated missing pixels for each declared non-edge pixel. Extensive simulation results have clearly shown that the proposed contrast-guided image interpolation is superior to other state-of-the-art edge-guided image interpolation methods. In addition, the computational complexity is relatively low when compared with existing methods; hence, it is fairly attractive for real-time image applications. PMID:23846469

  4. Contrast Analysis for Scale Differences.

    ERIC Educational Resources Information Center

    Olejnik, Stephen F.; And Others

    Research on tests for scale equality have focused exclusively on an overall test statistic and have not examined procedures for identifying specific differences in multiple group designs. The present study compares four contrast analysis procedures for scale differences in the single factor four-group design: (1) Tukey HSD; (2) Kramer-Tukey; (3)…

  5. Cluster Analysis by Linear Contrasts.

    ERIC Educational Resources Information Center

    Shafto, Michael

    The purpose of this paper is to suggest a technique of cluster analysis which is similar in aim to the Interactive Intercolumnar Correlation Analysis (IICA), though different in detail. Two methods are proposed for extracting a single bipolar factor (a "contrast compenent") directly from the initial similarities matrix. The advantages of this…

  6. Optomechanics with high-contrast gratings

    NASA Astrophysics Data System (ADS)

    Kemiktarak, Utku; Stambaugh, Corey; Xu, Haitan; Taylor, Jacob; Lawall, John

    2014-02-01

    High-contrast gratings fabricated in free-standing membranes of silicon nitride are a remarkable new platform for optomechanics, as they combine high reflectivity, low mass, and a high mechanical quality factor in a single device. In an effort to further improve on our earlier designs, we are now fabricating high-contrast gratings from stoichiometric silicon nitride. The new gratings have a diameter of 80 μm, a thickness of 250 μm, and are patterned in square membranes from 100 μm to 500 μm on a side. We find reflectivities R < 0.994 for these devices, and fundamental mechanical resonance frequencies above 1.5 MHz. In addition, we have incorporated HCGs fabricated from low-stress silicon nitride into a "membrane-in-the-middle" setup, and observe that the cavity transmission spectrum is distorted from a constant free spectral range of 3 GHz to one characterized by anticrossings separated by 72 ± 2 MHz.

  7. High-contrast imaging testbed

    SciTech Connect

    Baker, K; Silva, D; Poyneer, L; Macintosh, B; Bauman, B; Palmer, D; Remington, T; Delgadillo-Lariz, M

    2008-01-23

    Several high-contrast imaging systems are currently under construction to enable the detection of extra-solar planets. In order for these systems to achieve their objectives, however, there is considerable developmental work and testing which must take place. Given the need to perform these tests, a spatially-filtered Shack-Hartmann adaptive optics system has been assembled to evaluate new algorithms and hardware configurations which will be implemented in these future high-contrast imaging systems. In this article, construction and phase measurements of a membrane 'woofer' mirror are presented. In addition, results from closed-loop operation of the assembled testbed with static phase plates are presented. The testbed is currently being upgraded to enable operation at speeds approaching 500 hz and to enable studies of the interactions between the woofer and tweeter deformable mirrors.

  8. Advancing High Contrast Adaptive Optics

    NASA Astrophysics Data System (ADS)

    Ammons, M.; Poyneer, L.; GPI Team

    2014-09-01

    A long-standing challenge has been to directly image faint extrasolar planets adjacent to their host suns, which may be ~1-10 million times brighter than the planet. Several extreme AO systems designed for high-contrast observations have been tested at this point, including SPHERE, Magellan AO, PALM-3000, Project 1640, NICI, and the Gemini Planet Imager (GPI, Macintosh et al. 2014). The GPI is the world's most advanced high-contrast adaptive optics system on an 8-meter telescope for detecting and characterizing planets outside of our solar system. GPI will detect a previously unstudied population of young analogs to the giant planets of our solar system and help determine how planetary systems form. GPI employs a 44x44 woofer-tweeter adaptive optics system with a Shack-Hartmann wavefront sensor operating at 1 kHz. The controller uses Fourier-based reconstruction and modal gains optimized from system telemetry (Poyneer et al. 2005, 2007). GPI has an apodized Lyot coronal graph to suppress diffraction and a near-infrared integral field spectrograph for obtaining planetary spectra. This paper discusses current performance limitations and presents the necessary instrumental modifications and sensitivity calculations for scenarios related to high-contrast observations of non-sidereal targets.

  9. Electrofluidic systems for contrast management

    NASA Astrophysics Data System (ADS)

    Rebello, Keith J.; Maranchi, Jeffrey P.; Tiffany, Jason E.; Brown, Christopher Y.; Maisano, Adam J.; Hagedon, Matthew A.; Heikenfeld, Jason C.

    2012-06-01

    Operating in dynamic lighting conditions and in greatly varying backgrounds is challenging. Current paints and state-ofthe- art passive adaptive coatings (e.g. photochromics) are not suitable for multi- environment situations. A semi-active, low power, skin is needed that can adapt its reflective properties based on the background environment to minimize contrast through the development and incorporation of suitable pigment materials. Electrofluidic skins are a reflective display technology for electronic ink and paper applications. The technology is similar to that in E Ink but makes use of MEMS based microfluidic structures, instead of simple black and white ink microcapsules dispersed in clear oil. Electrofluidic skin's low power operation and fast switching speeds (~20 ms) are an improvement over current state-ofthe- art contrast management technologies. We report on a microfluidic display which utilizes diffuse pigment dispersion inks to change the contrast of the underlying substrate from 5.8% to 100%. Voltage is applied and an electromechanical pressure is used to pull a pigment dispersion based ink from a hydrophobic coated reservoir into a hydrophobic coated surface channel. When no voltage is applied, the Young-Laplace pressure pushes the pigment dispersion ink back down into the reservoir. This allows the pixel to switch from the on and off state by balancing the two pressures. Taking a systems engineering approach from the beginning of development has enabled the technology to be integrated into larger systems.

  10. Hemodynamic and tubular changes induced by contrast media.

    PubMed

    Caiazza, Antonella; Russo, Luigi; Sabbatini, Massimo; Russo, Domenico

    2014-01-01

    The incidence of acute kidney injury induced by contrast media (CI-AKI) is the third cause of AKI in hospitalized patients. Contrast media cause relevant alterations both in renal hemodynamics and in renal tubular cell function that lead to CI-AKI. The vasoconstriction of intrarenal vasculature is the main hemodynamic change induced by contrast media; the vasoconstriction is accompanied by a cascade of events leading to ischemia and reduction of glomerular filtration rate. Cytotoxicity of contrast media causes apoptosis of tubular cells with consequent formation of casts and worsening of ischemia. There is an interplay between the negative effects of contrast media on renal hemodynamics and on tubular cell function that leads to activation of renin-angiotensin system and increased production of reactive oxygen species (ROS) within the kidney. Production of ROS intensifies cellular hypoxia through endothelial dysfunction and alteration of mechanisms regulating tubular cells transport. The physiochemical characteristics of contrast media play a critical role in the incidence of CI-AKI. Guidelines suggest the use of either isoosmolar or low-osmolar contrast media rather than high-osmolar contrast media particularly in patients at increased risk of CI-AKI. Older age, presence of atherosclerosis, congestive heart failure, chronic renal disease, nephrotoxic drugs, and diuretics may multiply the risk of CI-AKI. PMID:24678510

  11. Hemodynamic and Tubular Changes Induced by Contrast Media

    PubMed Central

    Caiazza, Antonella; Russo, Luigi; Russo, Domenico

    2014-01-01

    The incidence of acute kidney injury induced by contrast media (CI-AKI) is the third cause of AKI in hospitalized patients. Contrast media cause relevant alterations both in renal hemodynamics and in renal tubular cell function that lead to CI-AKI. The vasoconstriction of intrarenal vasculature is the main hemodynamic change induced by contrast media; the vasoconstriction is accompanied by a cascade of events leading to ischemia and reduction of glomerular filtration rate. Cytotoxicity of contrast media causes apoptosis of tubular cells with consequent formation of casts and worsening of ischemia. There is an interplay between the negative effects of contrast media on renal hemodynamics and on tubular cell function that leads to activation of renin-angiotensin system and increased production of reactive oxygen species (ROS) within the kidney. Production of ROS intensifies cellular hypoxia through endothelial dysfunction and alteration of mechanisms regulating tubular cells transport. The physiochemical characteristics of contrast media play a critical role in the incidence of CI-AKI. Guidelines suggest the use of either isoosmolar or low-osmolar contrast media rather than high-osmolar contrast media particularly in patients at increased risk of CI-AKI. Older age, presence of atherosclerosis, congestive heart failure, chronic renal disease, nephrotoxic drugs, and diuretics may multiply the risk of CI-AKI. PMID:24678510

  12. Effective contrast of colored stimuli in the mesopic range: a metric for perceived contrast based on achromatic luminance contrast.

    PubMed

    Walkey, Helen C; Barbur, John L; Harlow, J Alister; Hurden, Antony; Moorhead, Ian R; Taylor, Julie A F

    2005-01-01

    Little is known about how color signals and cone- and rod-based luminance signals contribute to perceived contrast in the mesopic range. In this study the perceived contrast of colored, mesopic stimuli was matched with that of spatially equivalent achromatic stimuli. The objective was to develop a metric for perceived contrast in the mesopic range in terms of an equivalent achromatic luminance contrast, referred to here as effective contrast. Stimulus photopic luminance contrast, scotopic luminance contrast, and chromatic difference from the background all contributed to effective contrast over the mid-mesopic range, but their contributions were not independent and varied markedly with background luminance. Surprisingly, color made a significant contribution to effective contrast from 10 to approximately 0.003 cd m(-2). A model describing this relationship is introduced (R2 = 0.89) and compared with predictions of mesopic luminance contrast obtained from a number of models proposed as systems of mesopic photometry. PMID:15669611

  13. Effective contrast of colored stimuli in the mesopic range: a metric for perceived contrast based on achromatic luminance contrast

    NASA Astrophysics Data System (ADS)

    Walkey, Helen C.; Barbur, John L.; Harlow, J. Alister; Hurden, Antony; Moorhead, Ian R.; Taylor, Julie A. F.

    2005-01-01

    Little is known about how color signals and cone- and rod-based luminance signals contribute to perceived contrast in the mesopic range. In this study the perceived contrast of colored, mesopic stimuli was matched with that of spatially equivalent achromatic stimuli. The objective was to develop a metric for perceived contrast in the mesopic range in terms of an equivalent achromatic luminance contrast, referred to here as effective contrast. Stimulus photopic luminance contrast, scotopic luminance contrast, and chromatic difference from the background all contributed to effective contrast over the mid-mesopic range, but their contributions were not independent and varied markedly with background luminance. Surprisingly, color made a significant contribution to effective contrast from 10 to approximately 0.003 cd m-2. A model describing this relationship is introduced (R2=0.89) and compared with predictions of mesopic luminance contrast obtained from a number of models proposed as systems of mesopic photometry.

  14. Improving photoacoustic imaging contrast of brachytherapy seeds

    NASA Astrophysics Data System (ADS)

    Pan, Leo; Baghani, Ali; Rohling, Robert; Abolmaesumi, Purang; Salcudean, Septimiu; Tang, Shuo

    2013-03-01

    Prostate brachytherapy is a form of radiotherapy for treating prostate cancer where the radiation sources are seeds inserted into the prostate. Accurate localization of seeds during prostate brachytherapy is essential to the success of intraoperative treatment planning. The current standard modality used in intraoperative seeds localization is transrectal ultrasound. Transrectal ultrasound, however, suffers in image quality due to several factors such speckle, shadowing, and off-axis seed orientation. Photoacoustic imaging, based on the photoacoustic phenomenon, is an emerging imaging modality. The contrast generating mechanism in photoacoustic imaging is optical absorption that is fundamentally different from conventional B-mode ultrasound which depicts changes in acoustic impedance. A photoacoustic imaging system is developed using a commercial ultrasound system. To improve imaging contrast and depth penetration, absorption enhancing coating is applied to the seeds. In comparison to bare seeds, approximately 18.5 dB increase in signal-to-noise ratio as well as a doubling of imaging depth are achieved. Our results demonstrate that the coating of the seeds can further improve the discernibility of the seeds.

  15. Thermal detection contrast of human targets

    SciTech Connect

    Arlowe, H.D.

    1992-01-01

    There is an emerging interest in using thermal IR to automatically detect human intruders over wide areas. Such a capability could provide early warning beyond the perimeter at fixed sites, and could be used for portable security around mobile military assets. Sandia National Laboratories has been working on automatic detection systems based on the thermal contrast and motion of human intruders for several years, and has found that detection is sometimes difficult, depending on solar and other environmental conditions. Solar heating can dominate human thermal radiation by 100 fold, and dynamic background temperature changes can limit detector sensitivity. This paper explains those conditions and energy transfer mechanisms that lead to difficult thermal detection. We will not cover those adverse conditions that are more widely understood and previously reported on, such as fog, smoke, rain and falling snow. This work was sponsored by the Defense Nuclear Agency. 6 Refs.

  16. Contrasting persistence strategies in Salmonella and Mycobacterium

    PubMed Central

    McKinney, John D.

    2009-01-01

    Summary Long-term survival of persistent bacterial pathogens in mammalian hosts critically depends on their ability to avoid elimination by innate and adaptive immune responses. The persistent human pathogens that cause typhoid fever and tuberculosis exemplify alternative strategies for survival in the host: immune evasion and immune adaptation, respectively. Salmonella enterica serotype Typhi evades host innate immune responses and inflammation by expressing factors that interfere with its detection as a Gram-negative bacterium, enabling persistent colonization of an immunologically privileged niche, the gallbladder. In contrast, Mycobacterium tuberculosis has adapted to survive within phagocytic cells, which typically eliminate invading microbes, by deploying stress resistance mechanisms that counteract the harsh environment of the phagolysosome. PMID:20056478

  17. Stabilizing method for reflection interference contrast microscopy

    PubMed Central

    Kim, Kipom; Saleh, Omar A.

    2009-01-01

    Reflection interference contrast microscopy (RICM) is a technique for measuring the shape and position of microscopic objects in solution; it has many biological and biophysical applications. Use of RICM for long-time acquisitions requires minimizing defocusing effects that are due to thermal and mechanical drift. We present a simple stabilizing method that accomplishes this using an image-analysis-based linear focus function to establish feedback control of the focal position. While implementing this routine, we used RICM for independent measurement of the apparent fluctuation in the vertical position of an immobilized bead: the measured height had a standard deviation of 0.12 nm during a 45 min acquisition while under feedback control, demonstrating the high stability achievable with our approach. PMID:18425180

  18. Biofluid Mechanics

    NASA Astrophysics Data System (ADS)

    Oertel, Herbert

    In contrast to the topics discussed in previous chapters, biofluid mechanics is concerned with flows that are influenced by flexible biological surfaces. We distinguish between flows past living bodies in air or in water, such as bird flight or the swimming of fish, and internal flows, such as the closed blood circulation of living beings. In the previous millions of years, evolution has developed crawling, running, swimming, gliding, and flying as methods of motion of living beings, depending on their size and weight.

  19. Perceived contrast following adaptation to gratings of different orientations.

    PubMed

    Ross, J; Speed, H D

    1996-06-01

    Using a contrast matching procedure, we measured the perceived contrast of vertical test gratings after adapting to other gratings of either vertical or horizontal orientation. The results show that both parallel and orthogonal adapting gratings reduce perceived contrast and do so proportionally more at low test contrasts than at high. The results are consistent with a single mechanism model proposed by Ross and Speed [(1991). Proceedings of the Royal Society (Series B), 246, 61-69] that assumes that adaptation to gratings repositions contrast-response transducer functions. They are not consistent with the notion of two different forms of adaptation, subtractive for parallel and multiplicative for orthogonal adaptors as proposed by Snowden and Hammett [(1992). Nature, 355, 248-250]. Nowhere is the reduction in perceived contrast by an orthogonal grating greater than that by a parallel grating of the same contrast. A direct comparison using two orthogonal adaptors confirms the greater potency of parallel adaptors, but also reveals interactions between the adaptors. PMID:8759449

  20. [Uroangiographic contrast media, today. Elements of interest for the urologist].

    PubMed

    Alberti, C

    1997-03-01

    Uroangiographic contrast media, as well as magnetic resonance or ultrasound contrast agents, are substances which are able to artificially enhance the contrast between different tissues, or between normal tissue and pathological areas. The design of ionic and nonionic, monomeric or dimeric, iodobenzene derivatives is outlined with attention given to historical developments and breakthroughs. Relationships between physicochemical properties (osmolality, viscosity, molecular structure, etc.) and pharmacological profile are described. Nonionic compounds display favourable physicochemical characteristics: high water solubility, low osmolality and viscosity and good systemic tolerability. Recent surveys on adverse reactions to uroangiographic iodinated contrast media have shown that the risk of severe reactions is about six times lower with nonionic than ionic X-ray contrast agents. The pathogenetic mechanisms of adverse reactions, generally classified as either anaphylactoid or osmotoxic and chemotoxic, are still not well understood. It has been proposed that leukotrienes, prostaglandins, kinins, etc., may be involved. Nitric oxide appears to play a crucial role in the final common pathway by which anaphylaxis-like reactions occur in response to contrast agent administration. The margin of safety (median lethal dose/diagnostic dose) for nonionic compounds is two- to three-fold greater than for ionic compounds. As a look at the future, an approach to molecules potentially useful as "blood pool X-ray contrast agents" is based on iodinated dendrimeric macromolecules, in which the core is triazacyclononane and branches are represented by trioodobenzene derivatives. PMID:9198904

  1. Engineering of Nanoscale Contrast Agents for Optical Coherence Tomography

    PubMed Central

    Gordon, Andrew Y; Jayagopal, Ashwath

    2014-01-01

    Optical coherence tomography has emerged as valuable imaging modalityin ophthalmology and other fields by enabling high-resolution three-dimensional imaging of tissue. In this paper, we review recent progress in the field of contrast-enhanced optical coherence tomography (OCT). We discuss exogenous and endogenous sources of OCT contrast, focusing on their use with standard OCT systems as well as emerging OCT-based imaging modalities. We include advances in the processing of OCT data that generate improved tissue contrast, including spectroscopic OCT (SOCT), as well as work utilizing secondary light sources and/or detection mechanisms to create and detect enhanced contrast, including photothermal OCT (PTOCT) and photoacoustic OCT (PAOCT). Finally, we conclude with a discussion of the translational potential of these developments as well as barriers to their clinical use. PMID:25009761

  2. Extracellular gadolinium-based contrast media: an overview.

    PubMed

    Bellin, Marie-France; Van Der Molen, Aart J

    2008-05-01

    Increasing use is made of extracellular MRI contrast agents that alter the image contrast following intravenous administration; they predominantly shorten the T1 relaxation time of tissues. The degree and location of these changes provide substantial diagnostic information. However gadolinium-based contrast agents (Gd-CA) are not inert drugs. They may cause acute non-renal adverse reactions (e.g. anaphylactoid reactions), acute renal adverse reactions (e.g. contrast induced nephropathy), delayed adverse reactions (nephrogenic systemic fibrosis) and problems at the site of injection (e.g. local necrosis). This review describes the current status of Gd-CA, their mechanism of action, chemical structure, pharmacokinetics, dosage, elimination, nephrotoxicity and adverse events. PMID:18358659

  3. Helical x-ray differential phase contrast computed tomography

    NASA Astrophysics Data System (ADS)

    Qi, Zhihua; Thériault-Lauzier, Pascal; Bevins, Nicholas; Zambelli, Joseph; Li, Ke; Chen, Guang-Hong

    2011-03-01

    Helical computed tomography revolutionized the field of x-ray computed tomography two decades ago. The simultaneous translation of an image object with a standard computed tomography acquisition allows for fast volumetric scan for long image objects. X-ray phase sensitive imaging methods have been studied over the past few decades to provide new contrast mechanisms for imaging an object. A Talbot-Lau grating interferometer based differential phase contrast imaging method has recently demonstrated its potential for implementation in clinical and industrial applications. In this work, the principles of helical computed tomography are extended to differential phase contrast imaging to produce volumetric reconstructions based on fan-beam data. The method demonstrates the potential for helical differential phase contrast CT to scan long objects with relatively small detector coverage in the axial direction.

  4. Multi-contrast Photoacoustic Microscopy

    NASA Astrophysics Data System (ADS)

    Yao, Junjie

    Photoacoustic microscopy is a hybrid imaging modality with high spatial resolution, moderate imaging depth, excellent imaging contrast and functional imaging capability. Taking full advantage of this powerful weapon, we have investigated different anatomical, functional, flow dynamic and metabolic parameter measurements using photoacoustic microscopy. Specifically, Evans-blue dye was used to enhance photoacoustic microscopy of capillaries; label-free transverse and axial blood flow was measured based on bandwidth broadening and time shift of the photoacoustic signals; metabolic rate of oxygen was quantified in vivo from all the five parameters measured by photoacoustic microcopy; whole cross-sectional imaging of small intestine was achieved on a double-illumination photoacoustic microscopy with extended depth of focus and imaging depth; hemodynamic imaging was performed on a MEMS-mirror enhanced photoacoustic microscopy with a cross-sectional imaging rate of 400 Hz. As a maturing imaging technique, PAM is expected to find new applications in both fundamental life science and clinical practice.

  5. Sensitivity to Auditory Velocity Contrast.

    PubMed

    Locke, Shannon M; Leung, Johahn; Carlile, Simon

    2016-01-01

    A natural auditory scene often contains sound moving at varying velocities. Using a velocity contrast paradigm, we compared sensitivity to velocity changes between continuous and discontinuous trajectories. Subjects compared the velocities of two stimulus intervals that moved along a single trajectory, with and without a 1 second inter stimulus interval (ISI). We found thresholds were threefold larger for velocity increases in the instantaneous velocity change condition, as compared to instantaneous velocity decreases or thresholds for the delayed velocity transition condition. This result cannot be explained by the current static "snapshot" model of auditory motion perception and suggest a continuous process where the percept of velocity is influenced by previous history of stimulation. PMID:27291488

  6. Sensitivity to Auditory Velocity Contrast

    PubMed Central

    Locke, Shannon M.; Leung, Johahn; Carlile, Simon

    2016-01-01

    A natural auditory scene often contains sound moving at varying velocities. Using a velocity contrast paradigm, we compared sensitivity to velocity changes between continuous and discontinuous trajectories. Subjects compared the velocities of two stimulus intervals that moved along a single trajectory, with and without a 1 second inter stimulus interval (ISI). We found thresholds were threefold larger for velocity increases in the instantaneous velocity change condition, as compared to instantaneous velocity decreases or thresholds for the delayed velocity transition condition. This result cannot be explained by the current static “snapshot” model of auditory motion perception and suggest a continuous process where the percept of velocity is influenced by previous history of stimulation. PMID:27291488

  7. Contrasting Causatives: A Minimalist Approach

    ERIC Educational Resources Information Center

    Tubino Blanco, Mercedes

    2010-01-01

    This dissertation explores the mechanisms behind the linguistic expression of causation in English, Hiaki (Uto-Aztecan) and Spanish. Pylkkanen's (2002, 2008) analysis of causatives as dependent on the parameterization of the functional head v[subscript CAUSE] is chosen as a point of departure. The studies conducted in this dissertation confirm…

  8. Quantitative mammography contrast threshold test tool.

    PubMed

    Wagner, A J; Frey, G D

    1995-02-01

    Mammographic contrast is commonly evaluated by visualizing small objects of varying size or mass divided by projected area. These qualitative contrast determinations are commonly performed by imaging a phantom like the American College of Radiology accreditation phantom at clinical mammographic settings. However, this contrast assessment does not take into account the kVp of the machine. This work describes a quantitative mammography contrast threshold test tool which examines light object contrast on a uniform background for a contrast range of 0.32% to 1.38% at 25 kVp. For this mammography contrast threshold test tool, contrast is defined by delta I/I = loge (psi O/ psi b), where psi O is the target energy flux, and psi b is the background energy flux. Contrast threshold is defined as the lowest contrast value for which the objects are visible. Unlike traditional assessments of mammographic contrast, this measurement of contrast threshold is kVp corrected. The mammography contrast threshold test tool is constructed out of common plastics and provides a quantitative means of assessing contrast threshold for individual mammographic units and total mammographic systems. PMID:7565343

  9. Immobilized Contrast Enhanced (ICE) MRI: Gadolinium-based long-term MR Contrast Enhancement of the Vein Graft Vessel Wall*

    PubMed Central

    Mitsouras, Dimitris; Vemula, Praveen Kumar; Yu, Peng; Tao, Ming; Nguyen, Binh T.; Campagna, Christina M.; Karp, Jeffrey M.; Mulkern, Robert V.; Ozaki, C. Keith; Rybicki, Frank J.

    2010-01-01

    An implantable MR contrast agent that can be covalently immobilized on tissue during surgery has been developed. The rationale is that a durable increase in tissue contrast using an implantable contrast agent can enhance post-surgical tissue differentiation using MRI. For small vessel (e.g., vein graft) MRI, the direct benefit of such permanent “labeling” of the vessel wall by modification of its relaxation properties is to achieve more efficient imaging. This efficiency can be realized as either increased contrast leading to more accurate delineation of vessel wall and lesion tissue boundaries, or, faster imaging without penalizing contrast-to-noise ratio, or a combination thereof. We demonstrate, for the first time, stable long-term MRI enhancement using such an exogenous contrast mechanism based on immobilizing a modified Gd-DTPA complex on a human vein using a covalent amide bond. Signal enhancement due to the covalently immobilized contrast agent is demonstrated for excised human vein specimens imaged at 3T, and its long-term stability is demonstrated during a 4-month incubation period. PMID:20859994

  10. Contrast dependency and prior expectations in human speed perception

    PubMed Central

    Sotiropoulos, Grigorios; Seitz, Aaron R.; Seriès, Peggy

    2016-01-01

    The perceived speed of moving objects has long been known to depend on image contrast. Lowering the contrast of first-order motion stimuli typically decreases perceived speed – the well-known “Thompson effect”. It has been suggested that contrast-dependent biases are the result of optimal inference by the visual system, whereby unreliable sensory information is combined with prior beliefs. The Thompson effect is thought to result from the prior belief that objects move slowly (in Bayesian terminology, a “slow speed prior”). However, there is some evidence that the Thompson effect is attenuated or even reversed at higher speeds. Does the effect of contrast on perceived speed depend on absolute speed and what does this imply for Bayesian models with a slow speed prior? We asked subjects to compare the speeds of simultaneously presented drifting gratings of different contrasts. At low contrasts (3–15%), we found that the Thompson effect was attenuated at high speeds: at 8 and 12 deg/s, perceived speed increased less with contrast than at 1 and 4 deg/s; however, at higher contrasts (15–95%), the situation was reversed. A semi-parametric Bayesian model was used to extract the subjects’ speed priors and was subsequently improved by combining it with a model of speed tuning. These novel findings regarding the dual, contrast-dependent effect of high speeds help reconcile existing conflicting literature and suggest that physiologically plausible mechanisms of representation of speed in the visual cortex may need to be incorporated into Bayesian models to account for certain subtleties of human speed perception. PMID:24503425

  11. Neural correlates of stimulus spatial frequency-dependent contrast detection

    PubMed Central

    Meng, Jianjun; Liu, Ruilong; Wang, Ke; Hua, Tianmiao; Lu, Zhong-Lin; Xi, Minmin

    2016-01-01

    Psychophysical studies on human and non-human vertebrate species have shown that visual contrast sensitivity function (CSF) peaks at a certain stimulus spatial frequency and declines in both lower and higher spatial frequencies. The underlying neural substrate and mechanisms remain in debate. Here, we investigated the role of primary visual cortex (V1: area 17) in spatial frequency-dependent contrast detection in cats. Perceptual CSFs of three cats were measured using a two-alternative forced choice task. The responses of V1 neurons to their optimal visual stimuli in a range of luminance contrast levels (from 0 to 1.0) were recorded subsequently using in vivo extracellular single-unit recording techniques. The contrast sensitivity of each neuron was determined. The neuronal CSF for each cat was constructed from the mean contrast sensitivity of neurons with different preferred stimulus spatial frequencies. Results (1) The perceptual and neuronal CSFs of each of the three cats exhibited a similar shape with peak amplitude near 0.4 c/deg. (2) The neuronal CSF of each cat was highly correlated with its perceptual CSF. (3) V1 neurons with different preferred stimulus spatial frequencies had different contrast gains. Conclusion (1) Contrast detection of visual stimuli with different spatial frequencies may likely involve population coding of V1 neurons with different preferred stimulus spatial frequencies. (2) Difference in contrast-gain may underlie the observed contrast sensitivity variation of V1 neurons with different preferred stimulus spatial frequencies, possibly from either evolution or postnatal visual experiences. PMID:23314692

  12. Brute force absorption contrast microtomography

    NASA Astrophysics Data System (ADS)

    Davis, Graham R.; Mills, David

    2014-09-01

    In laboratory X-ray microtomography (XMT) systems, the signal-to-noise ratio (SNR) is typically determined by the X-ray exposure due to the low flux associated with microfocus X-ray tubes. As the exposure time is increased, the SNR improves up to a point where other sources of variability dominate, such as differences in the sensitivities of adjacent X-ray detector elements. Linear time-delay integration (TDI) readout averages out detector sensitivities on the critical horizontal direction and equiangular TDI also averages out the X-ray field. This allows the SNR to be increased further with increasing exposure. This has been used in dentistry to great effect, allowing subtle variations in dentine mineralisation to be visualised in 3 dimensions. It has also been used to detect ink in ancient parchments that are too damaged to physically unroll. If sufficient contrast between the ink and parchment exists, it is possible to virtually unroll the tomographic image of the scroll in order that the text can be read. Following on from this work, a feasibility test was carried out to determine if it might be possible to recover images from decaying film reels. A successful attempt was made to re-create a short film sequence from a rolled length of 16mm film using XMT. However, the "brute force" method of scaling this up to allow an entire film reel to be imaged presents a significant challenge.

  13. Low resistivity, low contrast pays

    SciTech Connect

    Sneider, R.M.; Kulha, J.T. |

    1996-08-01

    Major hydrocarbon accumulations have been produced over the past 40 years in low resistivity, low contrast (LRLC) sands in the Gulf of Mexico Basin (GOM). LRLC reservoirs were commonly considered wet, tight, misidentified as a shale or overlooked, but are being re-evaluated now in other world basins, including Latin America. Seismic response, drill cuttings, cores, log response, petrophysical models, and production testing provide an integrated LRLC evaluation. Causes of LRLC pay in the GOM include: laminated clean sands with shales; silts or shaly sands; clay-coated sands; glauconitic sands; sands with interstitial dispersed clay; sands with disseminated pyrite or other conductive minerals; clay-lined burrows; clay clasts; altered volcanic/feldspathic framework grains; and very fine-grained sand with very saline water. LRLC depositional systems include: deepwater fans, with levee-channel complexes; delta front and toe deposits; shingle turbidites; and alluvial and deltaic channel fills. Geological and petrophysical models developed in the GOM for evaluation of LRLC pay are applicable in Latin America. An Archie clean sand or Waxman-Smits shaly sand model are commonly used to evaluate LRLC anomalies. Often, shaly sand models are not necessarily suited for LRLC evaluation. The Archie lithology exponent (m) and saturation exponent (n) for many LRLC reservoirs range from 1.4 to 1.85, and 1.2 to 1.8, respectively. In thinly laminated LRLC reservoirs, net sand distribution is identified with high resolution logging tools, rock examination and interval testing.

  14. Surface metrology by phase contrast

    NASA Astrophysics Data System (ADS)

    Baker, Lionel R.

    1990-08-01

    Increasing use of electrooptical imaging and detection systems in thermography high density information storage laser instrumentation and X-ray optics has led to a pressing need for machinecompatible sensors for the measurement of surface texture. This paper reviews recent advances in the use of deterministic and parametric noncontact methods for texture measurement and justifies the need for objective simple and yet precise means for displaying the microfinish of a machined surface. The design of a simple two channel phase contrast microscope is described which can be calibrated by test pieces and used as a means for optimising the process parameters involved in the generation of high quality surfaces. Typical results obtained with this technique including dynamic range and ultimate sensitivity are discussed. 1 . NEED FOR SURFACE METROLOGY Surface quality has a direct influence on product acceptability in many different industries including those concerned with optoelectronics and engineering. The influence may be cosmetic as with paint finish on a motor car body or functional for example when excessive wear rates may occur in a bearing surface with inadequate oil retention. Since perfection can never be achieved and overspecification can be costly it is clearly necessary to be able to define thresholds of acceptance in relation to different situations. Such thresholds do of course require agreed methods of measurement with traceability to national standards. The current trends in surface metrology are towards higher

  15. Laser Image Contrast Enhancement System

    NASA Technical Reports Server (NTRS)

    Kurtz, Robert L. (Inventor); Holmes, Richard R. (Inventor); Witherow, William K. (Inventor)

    2002-01-01

    An optical image enhancement system provides improved image contrast in imaging of a target in high temperature surroundings such as a furnace. The optical system includes a source of vertically polarized light such as laser and a beam splitter for receiving the light and directing the light toward the target. A retardation plate is affixed to a target-facing surface of the beam splitter and a vertical polarizer is disposed along a common optical path with the beam splitter between the retardation plate and the target. A horizontal polarizer disposed in the common optical path, receives light passing through a surface of the beam splitter opposed to the target-facing surface. An image detector is disposed at one end of the optical path. A band pass filter having a band pass filter characteristic matching the frequency of the vertically polarized light source is disposed in the path between the horizontal polarizer and the image detector. The use of circular polarization, together with cross polarizers, enables the reflected light to be passed to the detector while blocking thermal radiation.

  16. Laser speckle contrast imaging in biomedical optics

    PubMed Central

    Boas, David A.; Dunn, Andrew K.

    2010-01-01

    First introduced in the 1980s, laser speckle contrast imaging is a powerful tool for full-field imaging of blood flow. Recently laser speckle contrast imaging has gained increased attention, in part due to its rapid adoption for blood flow studies in the brain. We review the underlying physics of speckle contrast imaging and discuss recent developments to improve the quantitative accuracy of blood flow measures. We also review applications of laser speckle contrast imaging in neuroscience, dermatology and ophthalmology. PMID:20210435

  17. Acute Kidney Injury by Radiographic Contrast Media: Pathogenesis and Prevention

    PubMed Central

    Faga, Teresa; Pisani, Antonio; Michael, Ashour

    2014-01-01

    It is well known that iodinated radiographic contrast media may cause kidney dysfunction, particularly in patients with preexisting renal impairment associated with diabetes. This dysfunction, when severe, will cause acute renal failure (ARF). We may define contrast-induced Acute Kidney Injury (AKI) as ARF occurring within 24–72 hrs after the intravascular injection of iodinated radiographic contrast media that cannot be attributed to other causes. The mechanisms underlying contrast media nephrotoxicity have not been fully elucidated and may be due to several factors, including renal ischaemia, particularly in the renal medulla, the formation of reactive oxygen species (ROS), reduction of nitric oxide (NO) production, and tubular epithelial and vascular endothelial injury. However, contrast-induced AKI can be prevented, but in order to do so, we need to know the risk factors. We have reviewed the risk factors for contrast-induced AKI and measures for its prevention, providing a long list of references enabling readers to deeply evaluate them both. PMID:25197639

  18. Contrast polarity and edge integration in achromatic color perception.

    PubMed

    Rudd, Michael E; Zemach, Iris K

    2007-08-01

    Previous work has shown that the achromatic color of a target patch embedded in simple two-dimensional display depends not only on the luminance contrast between the target and its immediate surround but also on the contrasts of other nearby edges. Quantitative models have been proposed in which the target color is modeled as a spatially weighted sum of edge contrasts in which the target edge receives the largest weight. Rudd and Arrington [Vision Res.41, 3649 (2001)] elaborated on this idea to include an additional mechanism whereby effects of individual color-inducing edges are "partially blocked" by edges lying along the path between the inducing edge and the target. We tested the blockage model in appearance matching experiments performed with disk-and-single-ring stimuli having all four possible combinations of inner and outer ring edge contrast polarities. Evidence was obtained for both "blockage" (attenuation) and "antiblockage" (amplification) of achromatic color induction signals, depending on the contrast polarities of the inner and outer ring edges. A neural model is proposed to account for our data on the basis of the contrast gain control occurring between cortical edge detector neurons. PMID:17621319

  19. Acute kidney injury by radiographic contrast media: pathogenesis and prevention.

    PubMed

    Andreucci, Michele; Faga, Teresa; Pisani, Antonio; Sabbatini, Massimo; Michael, Ashour

    2014-01-01

    It is well known that iodinated radiographic contrast media may cause kidney dysfunction, particularly in patients with preexisting renal impairment associated with diabetes. This dysfunction, when severe, will cause acute renal failure (ARF). We may define contrast-induced Acute Kidney Injury (AKI) as ARF occurring within 24-72 hrs after the intravascular injection of iodinated radiographic contrast media that cannot be attributed to other causes. The mechanisms underlying contrast media nephrotoxicity have not been fully elucidated and may be due to several factors, including renal ischaemia, particularly in the renal medulla, the formation of reactive oxygen species (ROS), reduction of nitric oxide (NO) production, and tubular epithelial and vascular endothelial injury. However, contrast-induced AKI can be prevented, but in order to do so, we need to know the risk factors. We have reviewed the risk factors for contrast-induced AKI and measures for its prevention, providing a long list of references enabling readers to deeply evaluate them both. PMID:25197639

  20. System and method for floating-substrate passive voltage contrast

    DOEpatents

    Jenkins, Mark W.; Cole, Jr., Edward I.; Tangyunyong, Paiboon; Soden, Jerry M.; Walraven, Jeremy A.; Pimentel, Alejandro A.

    2009-04-28

    A passive voltage contrast (PVC) system and method are disclosed for analyzing ICs to locate defects and failure mechanisms. During analysis a device side of a semiconductor die containing the IC is maintained in an electrically-floating condition without any ground electrical connection while a charged particle beam is scanned over the device side. Secondary particle emission from the device side of the IC is detected to form an image of device features, including electrical vias connected to transistor gates or to other structures in the IC. A difference in image contrast allows the defects or failure mechanisms be pinpointed. Varying the scan rate can, in some instances, produce an image reversal to facilitate precisely locating the defects or failure mechanisms in the IC. The system and method are useful for failure analysis of ICs formed on substrates (e.g. bulk semiconductor substrates and SOI substrates) and other types of structures.

  1. A Contrast Analysis Approach to Change

    ERIC Educational Resources Information Center

    Furr, R. Michael

    2008-01-01

    This paper presents the foundations of contrast analysis as a method for examining change. Contrast analysis is a relatively high-powered, simple, and informative procedure for evaluating hypotheses about specific patterns of change. This paper reviews the general purpose and nature of contrast analysis, it discusses some of the advantages of…

  2. Using Contrastive Rhetoric in the ESL Classroom

    ERIC Educational Resources Information Center

    Quinn, Janet M.

    2012-01-01

    Contrastive rhetoric studies the writing of second language learners to understand how it is affected by their first language and culture. The field of contrastive rhetoric is as multidimensional as second language writing is complex. It draws on the work of contrastive analysis, anthropology, linguistics, pedagogy, culture studies, translation…

  3. Bilingual Evidence against the Principle of Contrast.

    ERIC Educational Resources Information Center

    Quay, Suzanne

    Prior research on early lexical acquisition in bilingual infants has been used by Clark (1987) to support the Principle of Contrast, which states that every two forms contrast in meaning. In this study of an English-Spanish bilingual child, it is argued that the Principle of Contrast is not applicable to bilingual acquisition in general. Daily…

  4. Electronic magnification and perceived contrast of video

    PubMed Central

    Haun, Andrew; Woods, Russell L; Peli, Eli

    2012-01-01

    Electronic magnification of an image results in a decrease in its perceived contrast. The decrease in perceived contrast could be due to a perceived blur or to limited sampling of the range of contrasts in the original image. We measured the effect on perceived contrast of magnification in two contexts: either a small video was enlarged to fill a larger area, or a portion of a larger video was enlarged to fill the same area as the original. Subjects attenuated the source video contrast to match the perceived contrast of the magnified videos, with the effect increasing with magnification and decreasing with viewing distance. These effects are consistent with expectations based on both the contrast statistics of natural images and the contrast sensitivity of the human visual system. We demonstrate that local regions within videos usually have lower physical contrast than the whole, and that this difference accounts for a minor part of the perceived differences. Instead, visibility of ‘missing content’ (blur) in a video is misinterpreted as a decrease in contrast. We detail how the effects of magnification on perceived contrast can be measured while avoiding confounding factors. PMID:23483111

  5. Dispersive Transport of Angiographic Contrast During Antegrade Arterial Injection

    PubMed Central

    Hao, Qing; Lieber, Baruch B.

    2012-01-01

    Purpose Angiography is commonly used during endovascular procedures to navigate catheters into a target artery and for evaluation of the arterial luminal geometry. X-ray attenuating contrast material is injected into the arteries and transported into pathologies such as aneurysms or arteriovenous malformations. Images of the transported contrast are used to guide therapeutic decisions. Experience and intuition of the interventionalist are often serving as guide for the injection force, and hence, the speed and volume of the bolus. Forceful injections of small boluses can evoke local turbulence and dispersive mixing in the zone immediately distal to the catheter tip. Turbulence by its nature acts as a strong agitating mechanism such that the bolus of contrast quickly mixes with the flowing blood to occupy the entire lumen so the artery can be visualized. The aims of the present study are (a) to determine the distance from catheter tip beyond which contrast can consider to be fully mixed with the blood during antegrade injection and (b) to determine the thickness of the boundary layer in which contrast concentration is poor, which can contribute to underestimation of vascular diameter using this method. Methods We performed in silico experiments to describe blood and angiographic contrast transport in a straight artery model. The conditions investigated are derived from clinical contrast injection rates typically found in cerebral angiography. Results A recirculation flow exists in the mixing zone distal to the catheter tip issuing the contrast and convective mixing rather than diffusion is dominating the rapid mixing process. In the vicinity of the arterial wall in the mass transfer boundary layer, however, transport is dominated by molecular diffusion. For lower molecule diffusion coefficient, the mass transfer boundary layer contains a lower concentration of contrast than for a higher molecular diffusion coefficient. Conclusions These findings imply that contrast

  6. Model of visual contrast gain control and pattern masking

    NASA Technical Reports Server (NTRS)

    Watson, A. B.; Solomon, J. A.

    1997-01-01

    We have implemented a model of contrast gain and control in human vision that incorporates a number of key features, including a contrast sensitivity function, multiple oriented bandpass channels, accelerating nonlinearities, and a devisive inhibitory gain control pool. The parameters of this model have been optimized through a fit to the recent data that describe masking of a Gabor function by cosine and Gabor masks [J. M. Foley, "Human luminance pattern mechanisms: masking experiments require a new model," J. Opt. Soc. Am. A 11, 1710 (1994)]. The model achieves a good fit to the data. We also demonstrate how the concept of recruitment may accommodate a variant of this model in which excitatory and inhibitory paths have a common accelerating nonlinearity, but which include multiple channels tuned to different levels of contrast.

  7. Nucleotide-Specific Contrast for DNA Sequencing by Electron Spectroscopy

    PubMed Central

    Schmid, Andreas K.; Davis, Ronald W.

    2016-01-01

    DNA sequencing by imaging in an electron microscope is an approach that holds promise to deliver long reads with low error rates and without the need for amplification. Earlier work using transmission electron microscopes, which use high electron energies on the order of 100 keV, has shown that low contrast and radiation damage necessitates the use of heavy atom labeling of individual nucleotides, which increases the read error rates. Other prior work using scattering electrons with much lower energy has shown to suppress beam damage on DNA. Here we explore possibilities to increase contrast by employing two methods, X-ray photoelectron and Auger electron spectroscopy. Using bulk DNA samples with monomers of each base, both methods are shown to provide contrast mechanisms that can distinguish individual nucleotides without labels. Both spectroscopic techniques can be readily implemented in a low energy electron microscope, which may enable label-free DNA sequencing by direct imaging. PMID:27149617

  8. Monitoring stem cells in phase contrast imaging

    NASA Astrophysics Data System (ADS)

    Lam, K. P.; Dempsey, K. P.; Collins, D. J.; Richardson, J. B.

    2016-04-01

    Understanding the mechanisms behind the proliferation of Mesenchymal Stem cells (MSCs) can offer a greater insight into the behaviour of these cells throughout their life cycles. Traditional methods of determining the rate of MSC differentiation rely on population based studies over an extended time period. However, such methods can be inadequate as they are unable to track cells as they interact; for example, in autologous cell therapies for osteoarthritis, the development of biological assays that could predict in vivo functional activity and biological action are particularly challenging. Here further research is required to determine non-histochemical biomarkers which provide correlations between cell survival and predictive functional outcome. This paper proposes using a (previously developed) advanced texture-based analysis algorithm to facilitate in vitro cells tracking using time-lapsed microscopy. The technique was adopted to monitor stem cells in the context of unlabelled, phase contrast imaging, with the goal of examining the cell to cell interactions in both monoculture and co-culture systems. The results obtained are analysed using established exploratory procedures developed for time series data and compared with the typical fluorescent-based approach of cell labelling. A review of the progress and the lessons learned are also presented.

  9. Tumor-specific fluorescent contrast agents

    NASA Astrophysics Data System (ADS)

    Achilefu, Samuel I.; Dorshow, Richard B.; Bugaj, Joseph E.; Rajagopalan, Raghavan

    2000-04-01

    Several dyes are currently used for various biomedical applications due to their biocompatibility and high molar absorptivity. Localization of dyes in tumors may be mediated by several factors such as leaky vasculature and high metabolic activity in proliferating cells. However, these mechanisms of action make it difficult to differentiate inflammation from benign or malignant tumors. In order to enhance their tumor specificity, dyes have been conjugated to biomolecules that target unique factors in various diseased state. However, such large biomolecules can elicit adverse immunogenic reactions in humans, and are often preferentially taken up by the liver. Furthermore, for solid tumors which may rely on diffusion of the biomarkers from the vascular, penetration of large dye conjugates is not favorable. To overcome these problems, we designed and synthesized novel dye-peptide conjugates that are receptor specific. The efficacy of these new fluorescent contrast agents was tested in vivo in well-characterized rat tumor lines. The resulting optical images demonstrate that successful specific tumor targeting was achieved.

  10. Flash Infrared Thermography Contrast Data Analysis Technique

    NASA Technical Reports Server (NTRS)

    Koshti, Ajay

    2014-01-01

    This paper provides information on an IR Contrast technique that involves extracting normalized contrast versus time evolutions from the flash thermography inspection infrared video data. The analysis calculates thermal measurement features from the contrast evolution. In addition, simulation of the contrast evolution is achieved through calibration on measured contrast evolutions from many flat-bottom holes in the subject material. The measurement features and the contrast simulation are used to evaluate flash thermography data in order to characterize delamination-like anomalies. The thermal measurement features relate to the anomaly characteristics. The contrast evolution simulation is matched to the measured contrast evolution over an anomaly to provide an assessment of the anomaly depth and width which correspond to the depth and diameter of the equivalent flat-bottom hole (EFBH) similar to that used as input to the simulation. A similar analysis, in terms of diameter and depth of an equivalent uniform gap (EUG) providing a best match with the measured contrast evolution, is also provided. An edge detection technique called the half-max is used to measure width and length of the anomaly. Results of the half-max width and the EFBH/EUG diameter are compared to evaluate the anomaly. The information provided here is geared towards explaining the IR Contrast technique. Results from a limited amount of validation data on reinforced carbon-carbon (RCC) hardware are included in this paper.

  11. Papers and Studies in Contrastive Linguistics. Vol. 6. The Polish-English Contrastive Project.

    ERIC Educational Resources Information Center

    Fisiak, Jacek

    This volume of contrastive studies of English and Polish includes the following papers: (1) "Contrastive Analysis in a New Dimension," by Tomasz P. Krzeszowski; (2) "On the Feasibility of Pedagogical Contrastive Sociolinguistics," by Karol Janicki; (3) "The Lexicon and Contrastive Language Studies," by Miroslaw Nowakowski; (4) "Variation and…

  12. Role of Contrast in MR Imaging.

    PubMed

    Chandra, Tushar; Mohan, Suyash

    2016-08-01

    Magnetic resonance (MR) contrast agents have been widely used over the last 3 decades in routine clinical practice. Paul Lauterbur recognized the presence of these contrast agents, which act as paramagnetic catalysts that accelerate the T1 relaxation process. The first MR contrast agent to be approved for clinical use was in 1988, and since then, it is estimated that 200 million doses have been administered worldwide. These contrast agents have diverse clinical as well as research applications, involving almost all the body organs. This review will cover some existing as well as many new applications that have emerged over the last few decades. MR imaging now has the potential of being used to monitor enzymatic activity, gene expression, metal ion homeostasis, and cell death in vivo. In future, newer contrast agents will develop and become commercially available, expanding the current clinical applications of MR contrast media. PMID:27367311

  13. Development of infant contrast sensitivity to chromatic stimuli.

    PubMed

    Morrone, M C; Burr, D C; Fiorentini, A

    1993-12-01

    We have monitored the development of contrast sensitivity to equiluminant red-green chromatic patterns by monitoring visual evoked potentials (VEPs) in 13 infants. The results confirm our previous report [Morrone, Burr and Fiorentini, Proceedings of the Royal Society B, 242 (1990a)] that, before 7-8 weeks of age, there was no response to purely chromatic stimuli, while at the same age luminance stimuli of 20% contrast produced reliable responses. At all ages (even before the onset of a chromatic response) the colour mixture to yield equiluminance was similar to that of adults, suggesting that the relative proportion and efficacy of medium- and long-wave cones is similar for infants as for adults. For both luminance and chromatic stimuli, amplitude increased roughly linearly with log-contrast, so sensitivity thresholds could be predicted by linear extrapolation to the abscissa. Detailed contrast sensitivity curves were measured for four infants at various ages. The results show that luminance and chromatic contrast sensitivity develop independently at different rates, probably reflecting differential development of postreceptoral neural mechanisms. PMID:8249333

  14. Gd-HOPO Based High Relaxivity MRI Contrast Agents

    SciTech Connect

    Datta, Ankona; Raymond, Kenneth

    2008-11-06

    Tris-bidentate HOPO-based ligands developed in our laboratory were designed to complement the coordination preferences of Gd{sup 3+}, especially its oxophilicity. The HOPO ligands provide a hexadentate coordination environment for Gd{sup 3+} in which all he donor atoms are oxygen. Because Gd{sup 3+} favors eight or nine coordination, this design provides two to three open sites for inner-sphere water molecules. These water molecules rapidly exchange with bulk solution, hence affecting the relaxation rates of bulk water olecules. The parameters affecting the efficiency of these contrast agents have been tuned to improve contrast while still maintaining a high thermodynamic stability for Gd{sup 3+} binding. The Gd- HOPO-based contrast agents surpass current commercially available agents ecause of a higher number of inner-sphere water molecules, rapid exchange of inner-sphere water molecules via an associative mechanism, and a long electronic relaxation time. The contrast enhancement provided by these agents is at least twice that of commercial contrast gents, which are based on polyaminocarboxylate ligands.

  15. Effect of contrast on human speed perception

    NASA Technical Reports Server (NTRS)

    Stone, Leland S.; Thompson, Peter

    1992-01-01

    This study is part of an ongoing collaborative research effort between the Life Science and Human Factors Divisions at NASA ARC to measure the accuracy of human motion perception in order to predict potential errors in human perception/performance and to facilitate the design of display systems that minimize the effects of such deficits. The study describes how contrast manipulations can produce significant errors in human speed perception. Specifically, when two simultaneously presented parallel gratings are moving at the same speed within stationary windows, the lower-contrast grating appears to move more slowly. This contrast-induced misperception of relative speed is evident across a wide range of contrasts (2.5-50 percent) and does not appear to saturate (e.g., a 50 percent contrast grating appears slower than a 70 percent contrast grating moving at the same speed). The misperception is large: a 70 percent contrast grating must, on average, be slowed by 35 percent to match a 10 percent contrast grating moving at 2 deg/sec (N = 6). Furthermore, it is largely independent of the absolute contrast level and is a quasilinear function of log contrast ratio. A preliminary parametric study shows that, although spatial frequency has little effect, the relative orientation of the two gratings is important. Finally, the effect depends on the temporal presentation of the stimuli: the effects of contrast on perceived speed appears lessened when the stimuli to be matched are presented sequentially. These data constrain both physiological models of visual cortex and models of human performance. We conclude that viewing conditions that effect contrast, such as fog, may cause significant errors in speed judgments.

  16. Anaphylactoid reactions with gastrointestinal contrast media.

    PubMed

    Skucas, J

    1997-04-01

    Significant anaphylactoid reactions to gastrointestinal contrast media are rare. Whether a patient who is atopic or has asthma is predisposed to these reactions is speculative. The rare patient who previously had a severe allergic reaction to such a product probably should not undergo a subsequent examination with a similar agent. The American College of Radiology classification of contrast media side effects can also be applied to the gastrointestinal contrast media. PMID:9124150

  17. Multi-step contrast sensitivity gauge

    SciTech Connect

    Quintana, Enrico C; Thompson, Kyle R; Moore, David G; Heister, Jack D; Poland, Richard W; Ellegood, John P; Hodges, George K; Prindville, James E

    2014-10-14

    An X-ray contrast sensitivity gauge is described herein. The contrast sensitivity gauge comprises a plurality of steps of varying thicknesses. Each step in the gauge includes a plurality of recesses of differing depths, wherein the depths are a function of the thickness of their respective step. An X-ray image of the gauge is analyzed to determine a contrast-to-noise ratio of a detector employed to generate the image.

  18. Clouds of high contrast on Uranus.

    PubMed

    Karkoschka, E

    1998-04-24

    Near-infrared images of Uranus taken with the Hubble Space Telescope in July and October 1997 revealed discrete clouds with contrasts exceeding 10 times the highest contrast observed before with other techniques. At visible wavelengths, these 10 clouds had lower contrasts than clouds seen by Voyager 2 in 1986. Uranus' rotational rates for southern latitudes were identical in 1986 and 1997. Clouds in northern latitudes rotate slightly more slowly than clouds in opposite southern latitudes. PMID:9554844

  19. Motion contrast using optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Fingler, Jeffrey Paul

    Diagnosis of ophthalmic diseases like age-related macular degeneration is very important for treatment of the disease as well as the development of future treatments. Optical coherence tomography (OCT) is an optical interference technique which can measure the three-dimensional structural information of the reflecting layers within a sample. In retinal imaging, OCT is used as the primary diagnostic tool for structural abnormalities such as retinal holes and detachments. The contrast within the images of this technique is based upon reflectivity changes from different regions of the retina. This thesis demonstrates the developments of methods used to produce additional contrast to the structural OCT images based on the tiny fluctuations of motion experienced by the mobile scatterers within a sample. Motion contrast was observed for motions smaller than 50 nm in images of a variety of samples. Initial contrast method demonstrations used Brownian motion differences to separate regions of a mobile Intralipid solution from a static agarose gel, chosen in concentration to minimize reflectivity contrast. Zebrafish embryos in the range of 3-4 days post fertilization were imaged using several motion contrast methods to determine the capabilities of identifying regions of vascular flow. Vasculature identification was demonstrated in zebrafish for blood vessels of all orientations as small as 10 microns in diameter. Mouse retinal imaging utilized the same motion contrast methods to determine the contrast capabilities for motions associated with vasculature within the retina. Improved contrast imaging techniques demonstrated comparable images to fluorescein angiography, the gold standard of retinal vascular imaging. Future studies can improve the demonstrated contrast analysis techniques and apply them towards human retinal motion contrast imaging for ophthalmic diagnostic purposes.

  20. Image contrast reversals in contact resonance atomic force microscopy

    SciTech Connect

    Ma, Chengfu; Chen, Yuhang Wang, Tian

    2015-02-15

    Multiple image contrast inversions are observed along with the increase of modulation frequency for contact resonance atomic force microscopy (CR-AFM) imaging of a highly oriented pyrolytic graphite (HOPG) specimen. Analysis of the contact vibrational spectra indicates that the inversions can be attributed to structure-induced variations of tip-sample contact mechanics. Contact stiffness and damping at HOPG step edges exhibit significant increases relative to those in the flat regions. For quantitative evaluation of mechanical properties in CR-AFM, coupling effects of the surface geometry must be considered.

  1. Contrastive Linguistics in Textbook and Classroom.

    ERIC Educational Resources Information Center

    Rivers, Wilga M.

    The need for a contrastive approach in foreign language teaching has long been recognized, but in the construction of textbook materials and in classroom practice it has rarely been realized. For pedagogical purposes a useful distinction can be drawn between difference and contrast. Differences can be taught as new items of knowledge, whereas…

  2. Comparison and Contrast in Perceptual Categorization

    ERIC Educational Resources Information Center

    Hampton, James A.; Estes, Zachary; Simmons, Claire L.

    2005-01-01

    People categorized pairs of perceptual stimuli that varied in both category membership and pairwise similarity. Experiments 1 and 2 showed categorization of 1 color of a pair to be reliably contrasted from that of the other. This similarity-based contrast effect occurred only when the context stimulus was relevant for the categorization of the…

  3. Antibody-mediated red blood cell agglutination resulting in spontaneous echocardiographic contrast.

    PubMed

    Miller, M R; Thompson, W R; Casella, J F; Spevak, P J

    1999-01-01

    Spontaneous echocardiographic contrast is well reported in states of low flow and low shear stress, and the primary blood component involved has been reported as red blood cells via rouleaux formation. This report describes the occurrence of spontaneous echocardiographic contrast from a unique mechanism of IgM-mediated red blood cell agglutination and describes the clinical sequelae. PMID:10368455

  4. Contrast-Enhanced Digital Mammography and Angiogenesis

    SciTech Connect

    Rosado-Mendez, I.; Palma, B. A.; Villasenor, Y.; Benitez-Bribiesca, L.; Brandan, M. E.

    2007-11-26

    Angiogenesis could be a means for pouring contrast media around tumors. In this work, optimization of radiological parameters for contrast-enhanced subtraction techniques in mammography has been performed. A modification of Lemacks' analytical formalism was implemented to model the X-ray absorption in the breast with contrast medium and detection by a digital image receptor. Preliminary results of signal-to-noise ratio analysis show the advantage of subtracting two images taken at different energies, one prior and one posterior to the injection of contrast medium. Preliminary experimental results using a custom-made phantom have shown good agreement with calculations. A proposal is presented for the clinical application of the optimized technique, which aims at finding correlations between angiogenesis indicators and dynamic variables of contrast medium uptake.

  5. Imaging Contrast Effects in Alginate Microbeads

    NASA Astrophysics Data System (ADS)

    Shapley, Nina; Hester-Reilly, Holly

    2007-03-01

    We have investigated the use of alginate gel microbeads as contrast agents for the study of suspension flows in complex geometries using nuclear magnetic resonance (NMR) imaging. These deformable particles can provide imaging contrast to rigid polymer particles in a bimodal suspension (two particle sizes). Microbeads were formed of crosslinked alginate gel, with or without trapped oil droplets. Crosslinking of the aqueous sodium alginate solution or the continuous phase of an oil-in-water emulsion occurred rapidly at gentle processing conditions. The alginate microbeads exhibit both spin-spin relaxation time (T2) contrast and diffusion contrast relative to both the suspending fluid and rigid polystyrene particles. Large alginate emulsion microbeads flowing in the abrupt, axisymmetric expansion geometry can be clearly distinguished from the suspending fluid and from rigid polymer particles in both spin-echo and diffusion weighted imaging. The alginate microbeads, particularly those containing trapped emulsion droplets, offer potential as a positive contrast agent in multiple NMR imaging applications.

  6. Rhizosphere priming effects in two contrasting soils

    NASA Astrophysics Data System (ADS)

    Lloyd, Davidson; Kirk, Guy; Ritz, Karl

    2015-04-01

    Inputs of fresh plant-derived carbon may stimulate the turnover of existing soil organic matter by so-called priming effects. Priming may occur directly, as a result of nutrient 'mining' by existing microbial communities, or indirectly via population adjustments. However the mechanisms are poorly understood. We planted C4 Kikuyu grass (Pennisetum clandestinum) in pots with two contrasting C3 soils (clayey, fertile TB and sandy, acid SH), and followed the soil CO2 efflux and its δ13C. The extent of C deposition in the rhizosphere was altered by intermittently clipping the grass in half the pots; there were also unplanted controls. At intervals, pots were destructively sampled for root and shoot biomass. Total soil CO2 efflux was measured using a gas-tight PVC chamber fitted over bare soil, and connected to an infra-red gas analyser; the δ13C of efflux was measured in air sub-samples withdrawn by syringe. The extent of priming was inferred from the δ13C of efflux and the δ13C of the plant and soil end-members. In unclipped treatments, in both soils, increased total soil respiration and rhizosphere priming effects (RPE) were apparent compared to the unplanted controls. The TB soil had greater RPE overall. The total respiration in clipped TB soil was significantly greater than in the unplanted controls, but in the clipped SH soil it was not significantly different from the controls. Clipping affected plant C partitioning with greater allocation to shoot regrowth from about 4 weeks after planting. Total plant biomass decreased in the order TB unclipped > SH unclipped >TB clipped > SH clipped. The results are consistent with priming driven by microbial activation stimulated by rhizodeposits and by nitrogen demand from the growing plants under N limited conditions. Our data suggest that photosynthesis drives RPE and soil differences may alter the rate and intensity of RPE but not the direction.

  7. Carbon dynamics of contrasting agricultural practices

    NASA Astrophysics Data System (ADS)

    Ghee, Claire; Hallett, Paul; Neilson, Roy; Robinson, David; Paterson, Eric

    2013-04-01

    Application of organic amendments can improve soil quality and provide crop nutrients. To optimise these agricultural benefits from organic applications, the capacity of microbe-driven nutrient and carbon cycling must be understood and exploited. Consideration is therefore required of the complex interactions between the rhizosphere, microbial biomass and organic amendment. We hypothesise that the labile C present in root exudates of plants increases the mineralisation of organic matter in soil, constituting a mechanism to promote nutrient acquisition. This mechanism is known as the 'priming effect', but is poorly understood in the context of agricultural carbon and nutrient management. Field data from the Centre of Sustainable Cropping (CSC) research platform (Dundee, Scotland, UK) are utilised to build an understanding of soil C and N fluxes between contrasting agricultural practices. The field site uses a split-plot design to compare (i) compost amended soils with reduced tillage and chemical inputs and (ii) conventionally managed soils, reflective of current UK commercial arable practice. Significant differences (p= <0.001) were identified between compost amended and conventionally managed soils at field-scale with respect to soil microbial biomass (SMB), total organic carbon (TOC) and mineral nitrogen. Investigation into the priming effect within compost amended soils was subsequently undertaken under laboratory conditions. Stable isotope analysis and measurements of soil biotic parameters were used to quantify priming resulting from Spring Barley (Hordeum vulgare cv. Optic) cultivation for (i) unamended and (ii) municipal compost incorporated soils. Compost treatments comprised amendments of 25, 50 and 150 t/Ha and planted soils were compared with unplanted controls. Soil mesocosms were maintained under controlled environmental conditions within labelling chambers supplied continuously with 13C-depleted CO2. Throughout a 41-day incubation period, soil CO2

  8. Exogenous attention enhances 2nd-order contrast sensitivity.

    PubMed

    Barbot, Antoine; Landy, Michael S; Carrasco, Marisa

    2011-05-11

    Natural scenes contain a rich variety of contours that the visual system extracts to segregate the retinal image into perceptually coherent regions. Covert spatial attention helps extract contours by enhancing contrast sensitivity for 1st-order, luminance-defined patterns at attended locations, while reducing sensitivity at unattended locations, relative to neutral attention allocation. However, humans are also sensitive to 2nd-order patterns such as spatial variations of texture, which are predominant in natural scenes and cannot be detected by linear mechanisms. We assess whether and how exogenous attention--the involuntary and transient capture of spatial attention--affects the contrast sensitivity of channels sensitive to 2nd-order, texture-defined patterns. Using 2nd-order, texture-defined stimuli, we demonstrate that exogenous attention increases 2nd-order contrast sensitivity at the attended location, while decreasing it at unattended locations, relative to a neutral condition. By manipulating both 1st- and 2nd-order spatial frequency, we find that the effects of attention depend both on 2nd-order spatial frequency of the stimulus and the observer's 2nd-order spatial resolution at the target location. At parafoveal locations, attention enhances 2nd-order contrast sensitivity to high, but not to low 2nd-order spatial frequencies; at peripheral locations attention also enhances sensitivity to low 2nd-order spatial frequencies. Control experiments rule out the possibility that these effects might be due to an increase in contrast sensitivity at the 1st-order stage of visual processing. Thus, exogenous attention affects 2nd-order contrast sensitivity at both attended and unattended locations. PMID:21356228

  9. Exogenous attention enhances 2nd-order contrast sensitivity

    PubMed Central

    Barbot, Antoine; Landy, Michael S.; Carrasco, Marisa

    2011-01-01

    Natural scenes contain a rich variety of contours that the visual system extracts to segregrate the retinal image into perceptually coherent regions. Covert spatial attention helps extract contours by enhancing contrast sensitivity for 1st-order, luminance-defined patterns at attended locations, while reducing sensitivity at unattended locations, relative to neutral attention allocation. However, humans are also sensitive to 2nd-order patterns such as spatial variations of texture, which are predominant in natural scenes and cannot be detected by linear mechanisms. We assess whether and how exogenous attention—the involuntary and transient capture of spatial attention—affects the contrast sensitivity of channels sensitive to 2nd-order, texture-defined patterns. Using 2nd-order, texture-defined stimuli, we demonstrate that exogenous attention increases 2nd-order contrast sensitivity at the attended location, while decreasing it at unattended locations, relative to a neutral condition. By manipulating both 1st- and 2nd-order spatial frequency, we find that the effects of attention depend both on 2nd-order spatial frequency of the stimulus and the observer’s 2nd-order spatial resolution at the target location. At parafoveal locations, attention enhances 2nd-order contrast sensitivity to high, but not to low 2nd-order spatial frequencies; at peripheral locations attention also enhances sensitivity to low 2nd-order spatial frequencies. Control experiments rule out the possibility that these effects might be due to an increase in contrast sensitivity at the 1st-order stage of visual processing. Thus, exogenous attention affects 2nd-order contrast sensitivity at both attended and unattended locations. PMID:21356228

  10. Myopes experience greater contrast adaptation during reading.

    PubMed

    McGonigle, Colm; van der Linde, Ian; Pardhan, Shahina; Engel, Stephen A; Mallen, Edward A H; Allen, Peter M

    2016-04-01

    In this study, we investigated whether reading influences contrast adaptation differently in young adult emmetropic and myopic participants at the spatial frequencies created by text rows and character strokes. Pre-adaptation contrast sensitivity was measured for test gratings with spatial frequencies of 1cdeg(-1) and 4cdeg(-1), presented horizontally and vertically. Participants then adapted to reading text corresponding to the horizontal "row frequency" of text (1cdeg(-1)), and vertical "stroke frequency" of the characters (4cdeg(-1)) for 180s. Following this, post-adaptation contrast sensitivity was measured. Twenty young adults (10 myopes, 10 emmetropes) optimally corrected for the viewing distance participated. There was a significant reduction in logCS post-text adaptation (relative to pre-adaptation logCS) at the row frequency (1cdeg(-1) horizontal) but not at the stroke frequency (4cdeg(-1) vertical). logCS changes due to adaptation at 1cdeg(-1) horizontal were significant in both emmetropes and myopes. Comparing the two refractive groups, myopic participants showed significantly greater adaptation compared to emmetropic participants. Reading text on a screen induces contrast adaptation in young adult observers. Myopic participants were found to exhibit greater contrast adaptation than emmetropes at the spatial frequency corresponding to the text row frequency. No contrast adaptation was observed at the text stroke frequency in either participant group. The greater contrast adaptation experienced by myopes after reading warrants further investigation to better understand the relationship between near work and myopia development. PMID:26804636

  11. Perception of familiar contrasts in unfamiliar positions

    NASA Astrophysics Data System (ADS)

    Broersma, Mirjam

    2005-06-01

    This paper investigates the perception of non-native phoneme contrasts which exist in the native language, but not in the position tested. Like English, Dutch contrasts voiced and voiceless obstruents. Unlike English, Dutch allows only voiceless obstruents in word-final position. Dutch and English listeners' accuracy on English final voicing contrasts and their use of preceding vowel duration as a voicing cue were tested. The phonetic structure of Dutch should provide the necessary experience for a native-like use of this cue. Experiment 1 showed that Dutch listeners categorized English final /zee/-/ess/, /vee/-/eff/, /bee/-/pee/, and /dee/-/tee/ contrasts in nonwords as accurately as initial contrasts, and as accurately as English listeners did, even when release bursts were removed. In experiment 2, English listeners used vowel duration as a cue for one final contrast, although it was uninformative and sometimes mismatched other voicing characteristics, whereas Dutch listeners did not. Although it should be relatively easy for them, Dutch listeners did not use vowel duration. Nevertheless, they attained native-like accuracy, and sometimes even outperformed the native listeners who were liable to be misled by uninformative vowel duration information. Thus, native-like use of cues for non-native but familiar contrasts in unfamiliar positions may hardly ever be attained. .

  12. Contrast enhanced ultrasound of breast cancer

    PubMed Central

    Cassano, E; Rizzo, S; Bozzini, A; Menna, S; Bellomi, M

    2006-01-01

    The importance of ultrasound examination in the diagnosis of breast cancer has been widely demonstrated. During the last few years, the introduction of ultrasound contrast media has been considered a promising tool for studying the vascular pattern of focal lesions within the breast. Our purpose was to assess whether contrast-enhanced (CE) ultrasound examination, performed using specific contrast imaging modes, can be helpful for detection and characterization of breast lesions, and for prediction of the response of breast cancer to therapy. PMID:16478698

  13. Partially coherent contrast-transfer-function approximation.

    PubMed

    Nesterets, Yakov I; Gureyev, Timur E

    2016-04-01

    The contrast-transfer-function (CTF) approximation, widely used in various phase-contrast imaging techniques, is revisited. CTF validity conditions are extended to a wide class of strongly absorbing and refracting objects, as well as to nonuniform partially coherent incident illumination. Partially coherent free-space propagators, describing amplitude and phase in-line contrast, are introduced and their properties are investigated. The present results are relevant to the design of imaging experiments with partially coherent sources, as well as to the analysis and interpretation of the corresponding images. PMID:27140752

  14. [Iodinated contrast agents used in Radiology].

    PubMed

    Ramírez Ribelles, C; Sánchez Fuster, M A; Pamies Guilabert, J

    2014-06-01

    Iodinated contrast media are widely used in Radiology practices with a very low rate of adverse effects, being contrast-induced nephropathy the most serious one. In the majority of cases it is temporary and reversible, even though it can increase the inhospital morbidity and mortality in patients with risk factors. We will describe the various measures of prevention, being hydration and use of non-ionic contrast low osmolality those which have demonstrated greater effectiveness. Precautions to be taken in some risk situations, as patients treated with metformin or with impaired renal function, are also discussed. PMID:25267147

  15. Contrast enhanced spectroscopic optical coherence tomography

    NASA Technical Reports Server (NTRS)

    Boppart, Stephen A. (Inventor); Xu, Chenyang (Inventor)

    2010-01-01

    A method of forming an image of a sample includes performing SOCT on a sample. The sample may include a contrast agent, which may include an absorbing agent and/or a scattering agent. A method of forming an image of tissue may include selecting a contrast agent, delivering the contrast agent to the tissue, acquiring SOCT data from the tissue, and converting the SOCT data into an image. The contributions to the SOCT data of an absorbing agent and a scattering agent in a sample may be quantified separately.

  16. Frequently asked questions: iodinated contrast agents.

    PubMed

    Bettmann, Michael A

    2004-10-01

    Although iodinated contrast agents are safe and widely used, adverse events occur and questions remain about their use, safety, and interactions. Some questions are easily answered and others still require extensive investigation. For one frequent question--is informed consent necessary before all contrast media injections--the simple answer is no. Another question concerns use of contrast media in patients with prior reactions or allergies. Contrast agents can be safely used in such patients, but special care must be taken to be aware of what the previous reaction was and to be ready to treat any reaction. The protective role of pre-treatment with steroids is well established for minor reactions, but they may not prevent major reactions. It is important to realize that even life-threatening, anaphylactoid reactions are not the result of a true allergy to contrast media. Many questions arise about contrast agent-induced nephropathy. Baseline serum creatinine values should be obtained in patients who are at risk, not all patients. The incidence and natural history of contrast agent-induced nephropathy remain unclear. It occurs only in patients with compromised renal function before contrast agent injection, but even patients with normal serum creatinine levels can have renal dysfunction. Calculated creatinine clearance is a better way to determine risk and to follow this complication. The outcome in almost all patients is benign, with progression to end-stage renal disease being rare. The major risk factors, in addition to renal dysfunction, are long-standing diabetes mellitus, dehydration, and use of other nephrotoxic medications. Recent work in preventing and ameliorating contrast agent-induced nephropathy with N-acetyl cysteine, substitution of an isosmolal nonionic contrast agent, and various hydration regimens has been promising. Another common concern is use of iodinated contrast agents in pregnant or breast-feeding women. In both cases, there is no evidence

  17. Phase-contrast and holographic computed laminography

    SciTech Connect

    Helfen, L.; Baumbach, T.; Cloetens, P.; Baruchel, J.

    2009-03-09

    In-line phase contrast is combined with laminography to image in three dimensions regions of interest in laterally extended flat specimens of weak absorption contrast. The principle of the method and a theoretical description of the imaging process are outlined. The present instrumental implementation enables reconstructing nondestructively the internal structure at different lateral specimen positions with micron resolution. The feasibility and application potential are demonstrated for both phase-contrast and holographic (i.e., using phase retrieval) laminography by the three-dimensional imaging of fuel-cell diffusion layers.

  18. Contrast enhanced ultrasound of breast cancer.

    PubMed

    Cassano, E; Rizzo, S; Bozzini, A; Menna, S; Bellomi, M

    2006-01-01

    The importance of ultrasound examination in the diagnosis of breast cancer has been widely demonstrated. During the last few years, the introduction of ultrasound contrast media has been considered a promising tool for studying the vascular pattern of focal lesions within the breast. Our purpose was to assess whether contrast-enhanced (CE) ultrasound examination, performed using specific contrast imaging modes, can be helpful for detection and characterization of breast lesions, and for prediction of the response of breast cancer to therapy. PMID:16478698

  19. Phase-contrast and holographic computed laminography

    NASA Astrophysics Data System (ADS)

    Helfen, L.; Baumbach, T.; Cloetens, P.; Baruchel, J.

    2009-03-01

    In-line phase contrast is combined with laminography to image in three dimensions regions of interest in laterally extended flat specimens of weak absorption contrast. The principle of the method and a theoretical description of the imaging process are outlined. The present instrumental implementation enables reconstructing nondestructively the internal structure at different lateral specimen positions with micron resolution. The feasibility and application potential are demonstrated for both phase-contrast and holographic (i.e., using phase retrieval) laminography by the three-dimensional imaging of fuel-cell diffusion layers.

  20. In vivo imaging with near-infrared fluorescence lifetime contrast

    NASA Astrophysics Data System (ADS)

    Akers, Walter J.; Berezin, Mikhail Y.; Lee, Hyeran; Achilefu, Samuel

    2009-02-01

    Fluorescence imaging is a mainstay of biomedical research, allowing detection of molecular events in both fixed and living cells, tissues and whole animals. Such high resolution fluorescence imaging is hampered by unwanted signal from intrinsic background fluorescence and scattered light. The signal to background ratio can be improved by using extrinsic contrast agents and greatly enhanced by multispectral imaging methods. Unfortunately, these methods are insufficient for deep tissue imaging where high contrast and speedy acquisition are necessary. Fluorescence lifetime (FLT) is an inherent characteristic of each fluorescent species that can be independent of intensity and spectral properties. Accordingly, FLT-based detection provides an additional contrast mechanism to optical measurements. This contrast is particularly important in the near-infrared (NIR) due to relative transparency of tissue as well as the broad absorption and emission spectra of dyes that are active in this region. Here we report comparative analysis of signal distribution of several NIR fluorescent polymethine dyes in living mice and their correlations with lifetimes obtained in vitro using solution models. The FLT data obtained from dyes dissolved in serum albumin solution correlated well with FLTs measured in vivo. Thus the albumin solution model could be used as a good predictive model for in vivo FLT behavior of newly developed fluorescent reporters. Subsequent experiments in vivo, including monitoring slow release kinetics and detecting proteinuria, demonstrate the complementary nature of FLT for fluorescence intensity imaging.

  1. Phase contrast image segmentation using a Laue analyser crystal

    NASA Astrophysics Data System (ADS)

    Kitchen, Marcus J.; Paganin, David M.; Uesugi, Kentaro; Allison, Beth J.; Lewis, Robert A.; Hooper, Stuart B.; Pavlov, Konstantin M.

    2011-02-01

    Dual-energy x-ray imaging is a powerful tool enabling two-component samples to be separated into their constituent objects from two-dimensional images. Phase contrast x-ray imaging can render the boundaries between media of differing refractive indices visible, despite them having similar attenuation properties; this is important for imaging biological soft tissues. We have used a Laue analyser crystal and a monochromatic x-ray source to combine the benefits of both techniques. The Laue analyser creates two distinct phase contrast images that can be simultaneously acquired on a high-resolution detector. These images can be combined to separate the effects of x-ray phase, absorption and scattering and, using the known complex refractive indices of the sample, to quantitatively segment its component materials. We have successfully validated this phase contrast image segmentation (PCIS) using a two-component phantom, containing an iodinated contrast agent, and have also separated the lungs and ribcage in images of a mouse thorax. Simultaneous image acquisition has enabled us to perform functional segmentation of the mouse thorax throughout the respiratory cycle during mechanical ventilation.

  2. Compare, Contrast, Comprehend: Using Compare-Contrast Text Structures with ELLs in K-3 Classrooms

    ERIC Educational Resources Information Center

    Dreher, Mariam Jean; Gray, Jennifer Letcher

    2009-01-01

    In this article, we describe how to help primary-grade English language learners use compare-contrast text structures. Specifically, we explain (a) how to teach students to identify the compare-contrast text structure, and to use this structure to support their comprehension, (b) how to use compare-contrast texts to activate and extend students'…

  3. Papers and Studies in Contrastive Linguistics, Volume Twenty Three. The Polish-English Contrastive Project.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    1988-01-01

    Ten articles are presented in this volume on contrastive linguistics. The articles and authors are as follows: "Contrastive Grammar: Theory and Practice" (F. Aarts and H. Wekker); "On the Semantic and Morphological Status of Reversative Verbs in English and German" (W.-P. Funk); "The Problem of Directionality in Contrastive Studies Based on…

  4. Papers and Studies in Contrastive Linguistics, Volume Twelve. The Polish-English Contrastive Project.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    This volume contains six articles. In "Integrational Linguistics as a Basis for Contrastive Studies," Hans-Heinrich Lieb discusses the problems associated with complex contrastive analysis. Hanne Martinet's "A Functional and Contrastive Analysis of Attributive Adjectives Endings in '-ant' and in '-ende' in French and Danish, Respectively," shows…

  5. Papers and Studies in Contrastive Linguistics, Volume 5. The Polish-English Contrastive Project.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    This collection includes twenty-one papers, a book review, and a bibliography of English-Polish contrastive studies in Poland, and is the fifth volume resulting from the Polish-English Contrastive Project. The overall purpose of the project is to prepare a Polish-English contrastive grammar and to develop pedagogical materials. Topics covered in…

  6. NMDA receptor contributions to visual contrast coding

    PubMed Central

    Manookin, Michael B.; Weick, Michael; Stafford, Benjamin K.; Demb, Jonathan B.

    2010-01-01

    Summary In the retina, it is not well understood how visual processing depends on AMPA- and NMDA-type glutamate receptors. Here, we investigated how these receptors contribute to contrast coding in identified guinea pig ganglion cell types, in vitro. NMDA-mediated responses were negligible in ON α cells but substantial in OFF α and δ cells. OFF δ cell NMDA receptors were composed of GluN2B subunits. Using a novel deconvolution method, we determined the individual contributions of AMPA, NMDA and inhibitory currents to light responses of each cell type. OFF α and δ cells used NMDA receptors for encoding either the full contrast range (α), including near-threshold responses, or only a high range (δ). However, contrast sensitivity depended substantially on NMDA receptors only in OFF α cells. NMDA receptors contribute to visual contrast coding in a cell-type specific manner. Certain cell types generate excitatory responses using primarily AMPA receptors or disinhibition. PMID:20670835

  7. Ultrasound microbubble contrast and current clinical applications.

    PubMed

    Dindyal, Shiva; Kyriakides, Constantinos

    2011-01-01

    Ultrasound imaging is widely used worldwide principally because it is cheap, easily available and contains no exposure to ionizing radiation. The advent of microbubble ultrasound contrast has further increased the diagnostic sensitivity and specificity of this technique thus widening its clinical applications. The third generation of ultrasound contrast agents consist of sulphur hexafluoride microbubbles encased in a phospholipid shell. This review will elaborate on the pharmacology, safety profile and method of action of these agents. We also aim to discuss the ever expanding uses for contrast enhanced ultrasound in a number of clinical specialities which include the liver, kidney, prostate, sentinel node detection, vascular tree and endovascular stent surveillance. We will also discuss some of the recent patents regarding the future uses of ultrasound microbubble contrast and recent technological advances in clinical applications. PMID:21222650

  8. Mental contrasting and transfer of energization.

    PubMed

    Sevincer, A Timur; Busatta, P Daniel; Oettingen, Gabriele

    2014-02-01

    Mental contrasting a desired future with present reality is a self-regulation strategy that fosters energization in line with a person's expectations of successfully attaining the desired future. We investigated whether physiological energization (measured by systolic blood pressure) elicited by mental contrasting a desired future of solving a given task transfers to effort in an unrelated task. As predicted, mental contrasting a desired future of excelling in an intelligence test (Study 1) and of writing an excellent essay (Study 2) triggered changes in energization that translated into physical effort in squeezing a handgrip (Study 1) and translated into mental effort in writing a get-well letter (Study 2). Results suggest that mental contrasting of solving one task triggers energization that may fuel effort for performing an unrelated task. Implications for intervention research are discussed. PMID:24145296

  9. Planning and Measuring Luminance Contrast in Staircases.

    PubMed

    Houck, Leif D; Gundersen, Kristoffer; Strengen, Ola

    2016-01-01

    Norwegian legislation has requirements concerning luminance contrast for different elements in staircases. This paper investigates how architects work to meet the requirements, how to measure the actual built luminance contrasts and finally 21 staircases are measured using two different methods. The results show that some architects do not reflect on luminance contrasts at all, some use their "experience" and some try to measure the reflectance value of different materials during planning. The investigations also reveal that there is not any official predefined way to control luminance contrast, and this investigation shows that different approaches will give different results. To perform the measuring of the built staircases, it has been necessary to develop a defined measuring method. The results of the measuring generally shows that only a few of the staircases studied fully meet the legislation requirements. PMID:27534331

  10. Phase contrast imaging of cochlear soft tissue.

    SciTech Connect

    Smith, S.; Hwang, M.; Rau, C.; Fishman, A.; Lee, W.; Richter, C.

    2011-01-01

    A noninvasive technique to image soft tissue could expedite diagnosis and disease management in the auditory system. We propose inline phase contrast imaging with hard X-rays as a novel method that overcomes the limitations of conventional absorption radiography for imaging soft tissue. In this study, phase contrast imaging of mouse cochleae was performed at the Argonne National Laboratory Advanced Photon Source. The phase contrast tomographic reconstructions show soft tissue structures of the cochlea, including the inner pillar cells, the inner spiral sulcus, the tectorial membrane, the basilar membrane, and the Reissner's membrane. The results suggest that phase contrast X-ray imaging and tomographic techniques hold promise to noninvasively image cochlear structures at an unprecedented cellular level.

  11. NASA High Contrast Imaging for Exoplanets

    NASA Technical Reports Server (NTRS)

    Lyon, Richard G.

    2008-01-01

    Described is NASA's ongoing program for the detection and characterization of exosolar planets via high-contrast imaging. Some of the more promising proposed techniques under assessment may enable detection of life outside our solar system. In visible light terrestrial planets are approximately 10(exp -10) dimmer than the parent star. Issues such as diffraction, scatter, wavefront, amplitude and polarization all contribute to a reduction in contrast. An overview of the techniques will be discussed.

  12. [Contrast transfer function of the visual system].

    PubMed

    Pak, M A; Cleveland, S J

    1991-09-01

    Visually evoked potentials were used to determine the spatial contrast response function of the visual system and the visual acuity of the pigeon. The spatial contrast response describes the relationship between the contrast in a pattern of vertical stripes, whose luminance is a function of position, and the amplitude of the visually evoked response at various spatial frequencies for a given temporal frequency (pattern reversal frequency); it indicates how particular spatial frequencies are attenuated in the visual system. The visually evoked responses were recorded using monopolar stainless steel electrodes inserted into the stratum griseum superficiale of the optic tectum; the depth of penetration was determined on the basis of a stereotactic atlas. The stimulus patterns were generated on a video monitor placed 75 cm in front of the animal's eye perpendicular to the optic axis. The spatial contrast response function measured at 10% contrast and 0.5 Hz reversal frequency shows a peak at a spatial frequency of 0.5 c/deg, corresponding to 1 degree of visual angle, and decreases progressively at higher spatial frequencies. The high-frequency limit (cut-off frequency) for resolution of sinusoidal gratings, estimated from the contrast response function, is 15.5 c/deg, corresponding to a visual acuity of 1.9 min of arc. PMID:1657228

  13. Contrast sensitivity and discrimination of complex scenes

    NASA Astrophysics Data System (ADS)

    Triantaphillidou, S.; Jarvis, J.; Gupta, G.

    2013-01-01

    The aim of our research is to specify experimentally and further model spatial frequency response functions, which quantify human sensitivity to spatial information in real complex images. Three visual response functions are measured: the isolated Contrast Sensitivity Function (iCSF), which describes the ability of the visual system to detect any spatial signal in a given spatial frequency octave in isolation, the contextual Contrast Sensitivity Function (cCSF), which describes the ability of the visual system to detect a spatial signal in a given octave in an image and the contextual Visual Perception Function (VPF), which describes visual sensitivity to changes in suprathreshold contrast in an image. In this paper we present relevant background, along with our first attempts to derive experimentally and further model the VPF and CSFs. We examine the contrast detection and discrimination frameworks developed by Barten, which we find provide a sound starting position for our own modeling purposes. Progress is presented in the following areas: verification of the chosen model for detection and discrimination; choice of contrast metrics for defining contrast sensitivity; apparatus, laboratory set-up and imaging system characterization; stimuli acquisition and stimuli variations; spatial decomposition; methodology for subjective tests. Initial iCSFs are presented and compared with `classical' findings that have used simple visual stimuli, as well as with more recent relevant work in the literature.

  14. Contrast-Medium-Enhanced Digital Mammography: Contrast vs. Iodine Concentration Phantom Calibration

    SciTech Connect

    Rosado-Mendez, I.; Brandan, M. E.; Villasenor, Y.; Benitez-Bribiesca, L.

    2008-08-11

    This work deals with the application of the contrast-medium-enhanced digital subtraction mammography technique in order to calibrate the contrast level in subtracted phantom images as function of iodine concentration to perform dynamic studies of the contrast-medium uptake in the breast. Previously optimized dual-energy temporal subtraction modalities were used (a) to determine radiological parameters for a dynamic clinical study composed of 1 mask+3 post-contrast images limiting the total mean glandular dose to 2.5 mGy, and (b) to perform a contrast vs iodine concentration calibration using a custom-made phantom. Calculated exposure values were applied using a commercial full-field digital mammography unit. Contrast in subtracted phantom images (one mask and one post-CM) is linear as function of iodine concentration, although the sensitivity (contrast per iodine concentration) decreases beyond 8 mg/mL. This calibration seems to apply only to thin and normal thickness breasts.

  15. Microbubbles as contrast agent for in-line x-ray phase-contrast imaging

    SciTech Connect

    Xi Yan; Zhao Jun; Tang Rongbiao; Wang Yujie

    2011-07-04

    In the present study, we investigated the potential of gas-filled microbubbles as contrast agents for in-line x-ray phase-contrast imaging (PCI) in biomedical applications. When imaging parameters are optimized, the microbubbles function as microlenses that focus the incoming x-rays to form bright spots, which can significantly enhance the image contrast. Since microbubbles have been shown to be safe contrast agents in clinical ultrasonography, this contrast-enhancement procedure for PCI may have promising utility in biomedical applications, especially when the dose of radiation is a serious concern. In this study, we performed both numerical simulations and ex vivo experiments to investigate the formation of the contrast and the effectiveness of microbubbles as contrast agents in PCI.

  16. Variable multimodal light microscopy with interference contrast and phase contrast; dark or bright field.

    PubMed

    Piper, T; Piper, J

    2014-07-01

    Using the optical methods described, specimens can be observed with modified multimodal light microscopes based on interference contrast combined with phase contrast, dark- or bright-field illumination. Thus, the particular visual information associated with interference and phase contrast, dark- and bright-field illumination is joined in real-time composite images appearing in enhanced clarity and purified from typical artefacts, which are apparent in standard phase contrast and dark-field illumination. In particular, haloing and shade-off are absent or significantly reduced as well as marginal blooming and scattering. The background brightness and thus the range of contrast can be continuously modulated and variable transitions can be achieved between interference contrast and complementary illumination techniques. The methods reported should be of general interest for all disciplines using phase and interference contrast microscopy, especially in biology and medicine, and also in material sciences when implemented in vertical illuminators. PMID:24832212

  17. Unlocking new contrast in a scanning helium microscope.

    PubMed

    Barr, M; Fahy, A; Martens, J; Jardine, A P; Ward, D J; Ellis, J; Allison, W; Dastoor, P C

    2016-01-01

    Delicate structures (such as biological samples, organic films for polymer electronics and adsorbate layers) suffer degradation under the energetic probes of traditional microscopies. Furthermore, the charged nature of these probes presents difficulties when imaging with electric or magnetic fields, or for insulating materials where the addition of a conductive coating is not desirable. Scanning helium microscopy is able to image such structures completely non-destructively by taking advantage of a neutral helium beam as a chemically, electrically and magnetically inert probe of the sample surface. Here we present scanning helium micrographs demonstrating image contrast arising from a range of mechanisms including, for the first time, chemical contrast observed from a series of metal-semiconductor interfaces. The ability of scanning helium microscopy to distinguish between materials without the risk of damage makes it ideal for investigating a wide range of systems. PMID:26727303

  18. Unlocking new contrast in a scanning helium microscope

    NASA Astrophysics Data System (ADS)

    Barr, M.; Fahy, A.; Martens, J.; Jardine, A. P.; Ward, D. J.; Ellis, J.; Allison, W.; Dastoor, P. C.

    2016-01-01

    Delicate structures (such as biological samples, organic films for polymer electronics and adsorbate layers) suffer degradation under the energetic probes of traditional microscopies. Furthermore, the charged nature of these probes presents difficulties when imaging with electric or magnetic fields, or for insulating materials where the addition of a conductive coating is not desirable. Scanning helium microscopy is able to image such structures completely non-destructively by taking advantage of a neutral helium beam as a chemically, electrically and magnetically inert probe of the sample surface. Here we present scanning helium micrographs demonstrating image contrast arising from a range of mechanisms including, for the first time, chemical contrast observed from a series of metal-semiconductor interfaces. The ability of scanning helium microscopy to distinguish between materials without the risk of damage makes it ideal for investigating a wide range of systems.

  19. Sonophoresis Using Ultrasound Contrast Agents: Dependence on Concentration

    PubMed Central

    Park, Donghee; Song, Gillsoo; Jo, Yongjun; Won, Jongho; Son, Taeyoon; Cha, Ohrum; Kim, Jinho; Jung, Byungjo; Park, Hyunjin; Kim, Chul-Woo; Seo, Jongbum

    2016-01-01

    Sonophoresis can increase skin permeability to various drugs in transdermal drug delivery. Cavitation is recognized as the predominant mechanism of sonophoresis. Recently, a new logical approach to enhance the efficiency of transdermal drug delivery was tried. It is to utilize the engineered microbubble and its resonant frequency for increase of cavitation activity. Actively-induced cavitation with low-intensity ultrasound (less than ~1 MPa) causes disordering of the lipid bilayers and the formation of aqueous channels by stable cavitation which indicates a continuous oscillation of bubbles. Furthermore, the mutual interactions of microbubble determined by concentration of added bubble are also thought to be an important factor for activity of stable cavitation, even in different characteristics of drug. In the present study, we addressed the dependence of ultrasound contrast agent concentration using two types of drug on the efficiency of transdermal drug delivery. Two types of experiment were designed to quantitatively evaluate the efficiency of transdermal drug delivery according to ultrasound contrast agent concentration. First, an experiment of optical clearing using a tissue optical clearing agent was designed to assess the efficiency of sonophoresis with ultrasound contrast agents. Second, a Franz diffusion cell with ferulic acid was used to quantitatively determine the amount of drug delivered to the skin sample by sonophoresis with ultrasound contrast agents. The maximum enhancement ratio of sonophoresis with a concentration of 1:1,000 was approximately 3.1 times greater than that in the ultrasound group without ultrasound contrast agent and approximately 7.5 times greater than that in the control group. These results support our hypothesis that sonophoresis becomes more effective in transdermal drug delivery due to the presence of engineered bubbles, and that the efficiency of transdermal drug delivery using sonophoresis with microbubbles depends on the

  20. Sonophoresis Using Ultrasound Contrast Agents: Dependence on Concentration.

    PubMed

    Park, Donghee; Song, Gillsoo; Jo, Yongjun; Won, Jongho; Son, Taeyoon; Cha, Ohrum; Kim, Jinho; Jung, Byungjo; Park, Hyunjin; Kim, Chul-Woo; Seo, Jongbum

    2016-01-01

    Sonophoresis can increase skin permeability to various drugs in transdermal drug delivery. Cavitation is recognized as the predominant mechanism of sonophoresis. Recently, a new logical approach to enhance the efficiency of transdermal drug delivery was tried. It is to utilize the engineered microbubble and its resonant frequency for increase of cavitation activity. Actively-induced cavitation with low-intensity ultrasound (less than ~1 MPa) causes disordering of the lipid bilayers and the formation of aqueous channels by stable cavitation which indicates a continuous oscillation of bubbles. Furthermore, the mutual interactions of microbubble determined by concentration of added bubble are also thought to be an important factor for activity of stable cavitation, even in different characteristics of drug. In the present study, we addressed the dependence of ultrasound contrast agent concentration using two types of drug on the efficiency of transdermal drug delivery. Two types of experiment were designed to quantitatively evaluate the efficiency of transdermal drug delivery according to ultrasound contrast agent concentration. First, an experiment of optical clearing using a tissue optical clearing agent was designed to assess the efficiency of sonophoresis with ultrasound contrast agents. Second, a Franz diffusion cell with ferulic acid was used to quantitatively determine the amount of drug delivered to the skin sample by sonophoresis with ultrasound contrast agents. The maximum enhancement ratio of sonophoresis with a concentration of 1:1,000 was approximately 3.1 times greater than that in the ultrasound group without ultrasound contrast agent and approximately 7.5 times greater than that in the control group. These results support our hypothesis that sonophoresis becomes more effective in transdermal drug delivery due to the presence of engineered bubbles, and that the efficiency of transdermal drug delivery using sonophoresis with microbubbles depends on the

  1. Cardiac arrhythmias produced by ultrasound and contrast agents

    NASA Astrophysics Data System (ADS)

    Rota, Claudio

    Ultrasound is used widely in medicine for both diagnostic and therapeutic applications. Ultrasound contrast agents are suspensions of gas-filled microbubbles used to enhance diagnostic imaging. Microbubble contrast agents can increase the likelihood of bioeffects of ultrasound associated with acoustic cavitation. Under certain exposure conditions, the interaction of ultrasound with cardiac tissues can produce cardiac arrhythmias. The general objective of this thesis was to develop a greater understanding of ultrasound-induced premature cardiac beats. The hypothesis guiding this work was that acoustic cavitation is the physical mechanism for the production of arrhythmias with ultrasound. This hypothesis was tested through a series of experiments with mice in vivo and theoretical investigations. Results of this research supported the acoustic cavitation hypothesis. The acoustic pressure threshold for premature beats was significantly lower with microbubble contrast agents present in the blood than without. With microbubbles, the threshold for premature beats was below the current output limits of diagnostic devices. The threshold was not significantly dependent upon contrast agent type and was not influenced by contrast agent dose over three orders of magnitude. Furthermore, the dependence of the threshold on acoustic frequency was consistent with the frequency dependence of acoustic cavitation. Experimentally determined thresholds for premature beats in vivo were in excellent agreement with theoretically estimated thresholds for inertial cavitation. A passive cavitation detector (PCD) was used to measure the acoustic emissions produced by cavitating microbubbles in vivo. A direct correlation between the amplitude of the PCD and the percentage of ultrasound pulses producing a premature beat was consistent with cavitation as a mechanism for this bioeffect. Although this thesis focused on the mechanistic understanding of ultrasound-induced arrhythmias, more persistent

  2. Spatiotemporal laser speckle contrast analysis for blood flow imaging with maximized speckle contrast

    NASA Astrophysics Data System (ADS)

    Qiu, Jianjun; Li, Pengcheng; Luo, Weihua; Wang, Jia; Zhang, Hongyan; Luo, Qingming

    2010-01-01

    Laser speckle contrast imaging is a technique used for imaging blood flow without scanning. Though several studies have attempted to combine spatial and temporal statistics of laser speckle images for reducing image noise as well as preserving acceptable spatiotemporal resolution, the statistical accuracy of these spatiotemporal methods has not been thoroughly compared. Through numerical simulation and animal experiments, this study investigates the changes in the mean speckle contrast values and the relative noise of the speckle contrast images computed by these methods with various numbers of frames and spatial windows. The simulation results show that the maximum relative error of the mean speckle contrast computed by the spatiotemporal laser speckle contrast analysis (STLASCA) method, in which the speckle contrast images are computed by analyzing the 3-D spatiotemporal speckle image cube, is approximately 5%, while it is higher than 13% for other methods. Changes in the mean speckle contrast values and the relative noise computed by these methods for animal experiment data are consistent with the simulation results. Our results demonstrate that STLASCA achieves more accurate speckle contrast, and suggest that STLASCA most effectively utilizes the number of pixels, thus achieving maximized speckle contrast, and thereby maximizing the variation of the laser speckle contrast image.

  3. Complex dark-field contrast in grating-based x-ray phase contrast imaging

    NASA Astrophysics Data System (ADS)

    Yang, Yi; Tang, Xiangyang

    2015-03-01

    Without assuming that the sub-pixel microstructures of an object to be imaged distribute in space randomly, we investigate the influence of the object's microstructures on grating-based x-ray phase contrast imaging. Our theoretical analysis and 3D computer simulation study based on the paraxial Fresnel-Kirchhoff theory show that the existing dark-field contrast can be generalized into a complex dark-field contrast in a way such that its imaginary part quantifies the effect of the object's sub-pixel microstructures on the phase of intensity oscillations. A method based on the phase-attenuation duality that holds for soft tissues to be imaged at high x-ray energies is proposed to retrieve the imaginary part of the complex dark-field contrast for imaging. In comparison to the existing dark-field contrast, the imaginary part of complex dark-field contrast exhibits significantly stronger selectivity on the shape of the object's sub-pixel microstructures. Thus the x-ray imaging corresponding to the imaginary part of complex dark-field contrast can provide additional and complementary information to that corresponding to the attenuation contrast, phase contrast and the existing dark-field contrast.

  4. Contrast enhanced ultrasound of sentinel lymph nodes

    PubMed Central

    Cui, XinWu; Ignee, Andre; Nielsen, Michael Bachmann; Schreiber-Dietrich, Dagmar; De Molo, Chiara; Pirri, Clara; Jedrzejczyk, Maciej

    2013-01-01

    Sentinel lymph nodes are the first lymph nodes in the region that receive lymphatic drainage from a primary tumor. The detection or exclusion of sentinel lymph node micrometastases is critical in the staging of cancer, especially breast cancer and melanoma because it directly affects patient's prognosis and surgical management. Currently, intraoperative sentinel lymph node biopsies using blue dye and radioisotopes are the method of choice for the detection of sentinel lymph node with high identification rate. In contrast, conventional ultrasound is not capable of detecting sentinel lymph nodes in most cases. Contrast enhanced ultrasound with contrast specific imaging modes has been used for the evaluation and diagnostic work-up of peripherally located suspected lymphadenopathy. The method allows for real-time analysis of all vascular phases and the visualization of intranodal focal “avascular” areas that represent necrosis or deposits of neoplastic cells. In recent years, a number of animal and human studies showed that contrast enhanced ultrasound can be also used for the detection of sentinel lymph node, and may become a potential application in clinical routine. Several contrast agents have been used in those studies, including albumin solution, hydroxyethylated starch, SonoVue®, Sonazoid® and Definity®. This review summarizes the current knowledge about the use of ultrasound techniques in detection and evaluation of sentinel lymph node. PMID:26675994

  5. Contrast media use in the operating room.

    PubMed

    Bickham, Peggy; Golembiewski, Julie

    2010-04-01

    Iodinated contrast media is frequently used in the OR, but often is not well understood by health care providers who are administering it. Although used for diagnosis rather than treatment, contrast media is classified as a drug by the FDA, and has indications, contraindications, adverse effects, drug interactions, disease interactions, and laboratory interference issues related to its use. Iodinated contrast media is classified according to osmolarity and ionicity, and these characteristics contribute to potential for adverse effects and choice of agent. Financial and safety concerns are factors to be considered when selecting an appropriate agent. Adverse effects can range from mild and self-limited to severe and life threatening; potentially the most serious of these are anaphylactoid reactions and contrast-induced acute renal failure. Knowledge of risk factors and preventive strategies is vital, as are issues related to substitution of gadolinium-based contrast, an off-label use. It is important for the perianesthesia nurse to become familiar with these commonly used imaging medications. PMID:20359644

  6. [Spatial contrast sensitivity in multiple sclerosis].

    PubMed

    Vighetto, A; Grochowicki, M; Cousin, J

    1990-01-01

    Spatial contrast sensitivity was measured in 110 patients with multiple sclerosis (definite = 72, probable = 22, possible = 16) as part of a routine evaluation in a neuro-ophthalmological clinic. Results were compared with those of 37 normal controls matched for age. The test was abnormal in 71 p. 100 of patients. Contrast sensitivity was attenuated for 97 p. 100 of the eyes with optic neuritis and visual acuity drop, for 60 p. 100 of the eyes with recovered optic neuritis and for 36 p. 100 of the non affected eyes in the cases of unilateral optic neuritis. Among the 57 patients with normal visual acuity and no history of optic neuritis, 62 p. 100 had abnormal findings. Globally, contrast sensitivity was reduced on the whole spatial frequency range in cases of current optic neuritis, and mostly on the high or high and medium frequencies in the other cases. Our study confirms that spatial contrast sensitivity is the most sensitive of psychophysical methods to detect subclinical visual impairement in multiple sclerosis. Comparison with VEP's was performed in 66 patients. Both tests were roughly equally sensitive, but findings were concordant in only 63 p. 100 of the cases. The use of both VEP's and spatial contrast sensitivity increases the detection of latent optic neuritis. PMID:2359900

  7. New and contrastive focus in Taiwan Mandarin

    NASA Astrophysics Data System (ADS)

    Li, Jia-Rong

    2005-09-01

    This study investigated the influence of information structure on surface acoustical parameters in Taiwan Mandarin. There were two experiments, i.e., GN and GC experiment. In GN experiment, the noun phrases placed in initial (NP1) or medial (NP2) position in a Mandarin sentence were elicited through a game. Subjects answered experimenter's questions, e.g., ``What is on pink truck's right side?'' according to colored pictures in a 4 by 4 matrix. New or given information was placed on either NP1 or NP2. In GC experiment, subjects corrected or confirmed expeirmenter's description, such as Pink truck is yellow IDs right side, by placing either contrastive information on the color term and given information on noun (cg), given information on the color term and contrastive information on noun (gc), given information on both color term and noun (gg), or contrastive information on both color term and noun (cc). Results showed that the F0 range expansion and duration lengthening were observed on syllables carrying new and contrastive information. Moreover, duration lengthening is more pronunced than F0 range expansion. Furthermore, syllables with contrastive information were lengthened more than syllables with new information.

  8. Contrast agent choice for intravenous coronary angiography

    SciTech Connect

    Zeman, H.D.; Siddons, D.P.

    1989-01-01

    The screening of the general population for coronary artery disease would be practical if a method existed for visualizing the extent of occlusion after an intravenous injection of contrast agent. Measurements performed with monochromatic synchrotron radiation x-rays and an iodine containing contrast agent at the Stanford Synchrotron Radiation Laboratory have shown that such an intravenous angiography procedure would be possible with an adequately intense monochromatic x-ray source. Because of the size and cost of synchrotron radiation facilities it would be desirable to make the most efficient use of the intensity available, while reducing as much as possible the radiation dose experienced by the patient. By choosing contrast agents containing elements with a higher atomic number than iodine, it is possible to both improve the image quality and reduce the patient radiation dose, while using the same synchrotron source. By using Si monochromator crystals with a small mosaic spread, it is possible to increase the x-ray flux available for imaging by over an order of magnitude, without any changes in the storage ring or wiggler magnet. The most critical imaging task for intravenous coronary angiography utilizing synchrotron radiation x-rays is visualizing a coronary artery through the left ventricle or aorta which also contains a contrast agent. Calculations have been made of the signal to noise ratio expected for this imaging task for various contrast agents with atomic numbers between that of iodine and bismuth.

  9. Multifunctional nanoparticles as coupled contrast agents

    PubMed Central

    Jin, Yongdong; Jia, Congxian; Huang, Sheng-Wen; O’Donnell, Matthew; Gao, Xiaohu

    2011-01-01

    Engineering compact imaging probes with highly integrated modalities is a key focus in bionanotechnology and will have profound impact on molecular diagnostics, imaging, and therapeutics. However, combining multiple components on a nanometer scale to create new imaging modalities unavailable from individual components has proven challenging. Here, we demonstrate iron oxide and gold coupled core-shell nanoparticles with well defined structural characteristics (e.g., size, shell thickness, and core-shell separation) and physical properties (e.g., electronic, magnetic, optical, thermal, and acoustic). The resulting multifunctional nanoprobes not only offer contrast for electron microscopy, magnetic resonance imaging, and scattering-based imaging, but more importantly, enable a new imaging mode, magnetomotive photoacoustic (mmPA) imaging, with remarkable contrast enhancement compared to PA images using conventional nanoparticle contrast agents. PMID:20975706

  10. Reconstruction methods for phase-contrast tomography

    SciTech Connect

    Raven, C.

    1997-02-01

    Phase contrast imaging with coherent x-rays can be distinguished in outline imaging and holography, depending on the wavelength {lambda}, the object size d and the object-to-detector distance r. When r << d{sup 2}{lambda}, phase contrast occurs only in regions where the refractive index fastly changes, i.e. at interfaces and edges in the sample. With increasing object-to-detector distance we come in the area of holographic imaging. The image contrast outside the shadow region of the object is due to interference of the direct, undiffracted beam and a beam diffracted by the object, or, in terms of holography, the interference of a reference wave with the object wave. Both, outline imaging and holography, offer the possibility to obtain three dimensional information of the sample in conjunction with a tomographic technique. But the data treatment and the kind of information one can obtain from the reconstruction is different.

  11. Toward Clinically Compatible Phase-Contrast Mammography

    PubMed Central

    Scherer, Kai; Willer, Konstantin; Gromann, Lukas; Birnbacher, Lorenz; Braig, Eva; Grandl, Susanne; Sztrókay-Gaul, Anikó; Herzen, Julia; Mayr, Doris; Hellerhoff, Karin; Pfeiffer, Franz

    2015-01-01

    Phase-contrast mammography using laboratory X-ray sources is a promising approach to overcome the relatively low sensitivity and specificity of clinical, absorption-based screening. Current research is mostly centered on identifying potential diagnostic benefits arising from phase-contrast and dark-field mammography and benchmarking the latter with conventional state-of-the-art imaging methods. So far, little effort has been made to adjust this novel imaging technique to clinical needs. In this article, we address the key points for a successful implementation to a clinical routine in the near future and present the very first dose-compatible and rapid scan-time phase-contrast mammograms of both a freshly dissected, cancer-bearing mastectomy specimen and a mammographic accreditation phantom. PMID:26110618

  12. Enhancing the contrast of subcutaneous veins

    NASA Astrophysics Data System (ADS)

    Zeman, Herbert D.; Lovhoiden, Gunnar

    1999-07-01

    A technique for enhancing the contrast of subcutaneous veins has been demonstrated. This technique uses a near infrared light source and one or more infrared sensitive CCD TV cameras to produce a contrast enhanced image of the subcutaneous veins. This video image of the veins is projected back onto the patient's skin using an LCD vein projector. The use of an infrared transmitting filter in front of the video cameras prevents any positive feedback from the visible light from the video projector from causing instabilities in the projected image. The demonstration contrast enhancing illuminator has been tested on adults, both Caucasian and African-American, and it enhances veins quite well in most cases. Preliminary studies on a 9 month old girl indicate promise for pediatric use.

  13. Optical Image Contrast Reversal Using Bacteriorhodopsin Films

    NASA Astrophysics Data System (ADS)

    Wang, Ying-Li; Yao, Bao-Li; Menke, Neimule; Zheng, Yuan; Lei, Ming; Chen, Guo-Fu

    2005-05-01

    The implementation of image contrast reversal by using a photochromic material of Bacteriorhodopsin (BR) films is demonstrated with two methods based on the optical properties of BR. One is based on the absorption difference between the B and M states. Images recorded by green light can be contrast reversed readout by violet light. The other is based on the photoinduced anisotropy of BR when it is excited by linear polarization light. By placing the BR film between two crossed polarizers (i.e. a polarizer and an analyser), the difference of polarization states of the recorded area and the unrecorded area can be detected, and thus different contrast images can be obtained by rotating the polarization axis of the analyser.

  14. Phase contrast portal imaging using synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Umetani, K.; Kondoh, T.

    2014-07-01

    Microbeam radiation therapy is an experimental form of radiation treatment with great potential to improve the treatment of many types of cancer. We applied a synchrotron radiation phase contrast technique to portal imaging to improve targeting accuracy for microbeam radiation therapy in experiments using small animals. An X-ray imaging detector was installed 6.0 m downstream from an object to produce a high-contrast edge enhancement effect in propagation-based phase contrast imaging. Images of a mouse head sample were obtained using therapeutic white synchrotron radiation with a mean beam energy of 130 keV. Compared to conventional portal images, remarkably clear images of bones surrounding the cerebrum were acquired in an air environment for positioning brain lesions with respect to the skull structure without confusion with overlapping surface structures.

  15. Phase contrast portal imaging using synchrotron radiation

    SciTech Connect

    Umetani, K.; Kondoh, T.

    2014-07-15

    Microbeam radiation therapy is an experimental form of radiation treatment with great potential to improve the treatment of many types of cancer. We applied a synchrotron radiation phase contrast technique to portal imaging to improve targeting accuracy for microbeam radiation therapy in experiments using small animals. An X-ray imaging detector was installed 6.0 m downstream from an object to produce a high-contrast edge enhancement effect in propagation-based phase contrast imaging. Images of a mouse head sample were obtained using therapeutic white synchrotron radiation with a mean beam energy of 130 keV. Compared to conventional portal images, remarkably clear images of bones surrounding the cerebrum were acquired in an air environment for positioning brain lesions with respect to the skull structure without confusion with overlapping surface structures.

  16. Contrast induced nephropathy in vascular surgery.

    PubMed

    Wong, G T C; Lee, E Y P; Irwin, M G

    2016-09-01

    Contrast induced nephropathy (CIN) is traditionally associated with outpatient imaging studies. More recently, patients afflicted with vascular pathologies are increasingly undergoing endovascular treatments that require the use of iodinated contrast media (CM) agents, thus placing them as risk of developing CIN. As perioperative physicians, anaesthetists should be aware of the risk factors and measures that might minimize acute kidney injury caused by CM. This review evaluates recent data regarding preventive measures against CIN and where possible, places the evidence in the context of the patient receiving endovascular surgical treatment. Measures including the use of peri-procedural hydration, N-acetylcysteine, statins, remote ischaemic preconditioning, renal vasodilators and renal replacement therapy and the use of alternatives to iodinated contrast agents are discussed. It should be noted that most of the available data regarding CIN are from non-surgical patients. PMID:27566809

  17. Contrast dispersion imaging for cancer localization.

    PubMed

    Mischi, Massimo; Wijkstra, Hessel

    2014-01-01

    Cancer growth is associated with angiogenic processes in many types of cancer. Several imaging strategies have therefore been developed that target angiogenesis as a marker for cancer localization. To this end, intravascular and extravascular tissue perfusion is typically assessed by dynamic contrast enhanced (DCE) ultrasound (US) and MRI. All the proposed strategies, however, overlook important changes in the microvascular architecture that result from angiogenic processes. To overcome these limitations, we have recently introduced a new imaging strategy that analyzes the intravascular dispersion kinetics of contrast agents spreading through the microvasculature. Contrast dispersion is mainly determined by microvascular multi-path trajectories, reflecting the underlying microvascular architecture. This paper reviews the results obtained for prostate cancer localization by US and MRI dispersion imaging, also presenting the latest new developments and future perspectives. PMID:25570935

  18. Applications of energy loss contrast STIM

    SciTech Connect

    Bench, G.; Saint, A.; Legge, G.J.F.; Cholewa, M.

    1992-05-26

    Scanning Transmission Ion Microscopy (STIM) with energy loss contrast is a quantitative imaging technique. A focussed MeV ion microbeam is scanned over the sample and measured energy losses of residual ions at each beam location are used to provide the contrast in the image. The technique is highly efficient as almost every ion carries useful information from which quantitative data can be obtained. The high efficiency of data collection at present necessitates the use of small beam currents. Therefore small apertures can be used and fine spatial resolution can be achieved. High efficiency also makes it possible to collect large data sets for high definition imaging with a small radiation dose. Owing to the simple relationship between energy loss and areal density, STIM with energy loss contrast can provide a quantitative image that can be used to obtain areal density information on the sample. These areal density maps can be used not only to provide a high resolution image of the sample but also to normalise Particle Induced Xray Emission (PIXE) data. The small radiation dose required to form these areal density maps also allows one to use STIM with energy loss contrast to quantitatively monitor ion beam induced specimen changes caused by higher doses and dose rates used in other microanalytical techniques. STIM with energy loss contrast also provides the possibility of stereo imaging and ion microtomography. STIM has also been used in conjunction with channeling to explore transmission channeling in thin crystals. This paper will discuss these applications of STIM with energy loss contrast and look at further developments from them.

  19. Contrast of Subpicosecond Microelectron Bunch Trains

    SciTech Connect

    Muggli, Patric; Kallos, Efthymios; Yakimenko, Vitaly; Kusche, Karl; Babzien, Marcus; Park, Jangho

    2009-01-22

    We recently demonstrated that electron bunch trains with a controllable number of bunches and adjustable subpicosecond spacing can be produced using a mask technique. In this paper we calculate the bunch train contrast as a function of the beam betatron size at the mask {sigma}{sub {beta}} and of the diameter d of the mask wires separated by a period D. As expected, when {sigma}{sub {beta}}/(d/2) the contrast is high and decreases with increasing {sigma}{sub {beta}}/(d/2)

  20. Stereomotion speed perception is contrast dependent

    NASA Technical Reports Server (NTRS)

    Brooks, K.

    2001-01-01

    The effect of contrast on the perception of stimulus speed for stereomotion and monocular lateral motion was investigated for successive matches in random-dot stimuli. The familiar 'Thompson effect'--that a reduction in contrast leads to a reduction in perceived speed--was found in similar proportions for both binocular images moving in depth, and for monocular images translating laterally. This result is consistent with the idea that the monocular motion system has a significant input to the stereomotion system, and dominates the speed percept for approaching motion.

  1. [Lethal reaction after contrast medium administration].

    PubMed

    Risgaard, Ole; Søe, Charlotte Krabbe; Zejden, Anna

    2008-04-21

    A 49-year-old healthy woman was admitted after a horse-riding accident. On arrival to the emergency department she complained of lower abdominal pain. A CT-scan of the abdomen with non ionic contrast media (iomeprol, 150 ml 4 ml/s) was conducted. The patient died nine hours later due to an anaphylactoid reaction to radio contrast media. The autopsy showed pulmonary oedema and pleural effusion, but did not show any sign of trauma. Early interventions with appropriate therapy had no effect on the fatal outcome. PMID:18462629

  2. X-ray phase-contrast methods

    SciTech Connect

    Lider, V. V. Kovalchuk, M. V.

    2013-11-15

    This review is devoted to a comparative description of the methods for forming X-ray phase-contrast images of weakly absorbing (phase) objects. These include the crystal interferometer method, the Talbot interferometer method, diffraction-enhanced X-ray imaging, and the in-line method. The potential of their practical application in various fields of science and technology is discussed. The publications on the development and optimization of X-ray phase-contrast methods and the experimental study of phase objects are analyzed.

  3. Contrast agent choice for intravenous coronary angiography

    NASA Astrophysics Data System (ADS)

    Zeman, H. D.; Siddons, D. P.

    1990-05-01

    The screening of the general population for coronary artery disease would be practical if a method existed for visualizing the extent of occlusion after an intravenous injection of contrast agent. Measurements performed with monochromatic synchrotron radiation X-rays and an iodine-containing contrast agent at the Stanford Synchrotron Radiation Laboratory have shown that such an intravenous angiography procedure would be possible with an adequately intense monochromatic X-ray source. Because of the size and cost of synchrotron radiation facilities it would be desirable to make the most efficient use of the intensity available, while reducing as much as possible the radiation dose experienced by the patient. By choosing contrast agents containing elements with a higher atomic number than iodine, it is possible to both improve the image quality and reduce the patient radiation dose, while using the same synchrotron radiation source. By using Si monochromator crystals with a small mosaic spread, it is possible to increase the X-ray flux available for imaging by over an order of magnitude, without any changes in the storage ring or wiggler magnet. The most critical imaging task for intravenous coronary angiography utilizing synchrotron radiation X-rays is visualizing a coronary artery through the left ventricle or aorta which also contain contrast agent. Calculations have been made of the signal to noise ratio expected for this imaging task for various contrast agents with atomic numbers between that of iodine and bismuth. The X-ray energy spectrum of the X-17 superconduction wiggler beam line at the National Synchrotron Light Source at Brookhaven National Laboratory has been used for these calculations. Both perfect Si crystals and Si crystals with a small mosaic spread are considered as monochromators. Contrast agents containing Gd or Yb seem to have about the optimal calculated signal to noise ratio. Gd-DTPA is already approved for use as a contrast agent for

  4. The Potential of High-Contrast Coronagraphy

    NASA Technical Reports Server (NTRS)

    Serabyn, E.

    2008-01-01

    The direct detection of faint companions near much brighter stars requires the development of very high-contrast, small field-of-view detection techniques, and the past decade has seen remarkable conceptual and instrumental progress in this area. New coronagraphic techniques are being developed and deployed, as are extreme adaptive optics (ExAO) systems that will enable the advantageous exploitation of these new techniques. This paper provides a short overview of promising high contrast coronagraphic techniques, as well as recent examples of ExAO coronagraphy and transit measurements obtained with the ExAO-level "well-corrected subaperture" at Palomar.

  5. Phase contrast laminography based on Talbot interferometry.

    PubMed

    Altapova, Venera; Helfen, Lukas; Myagotin, Anton; Hänschke, Daniel; Moosmann, Julian; Gunneweg, Jan; Baumbach, Tilo

    2012-03-12

    Synchrotron laminography is combined with Talbot grating interferometry to address weakly absorbing specimens. Integrating both methods into one set-up provides a powerful x-ray diagnostical technique for multiple contrast screening of macroscopically large flat specimen and a subsequent non-destructive three-dimensional (3-D) inspection of regions of interest. The technique simultaneously yields the reconstruction of the 3-D absorption, phase, and the so-called dark-field contrast maps. We report on the theoretical and instrumental implementation of of this novel technique. Its broad application potential is exemplarily demonstrated for the field of cultural heritage, namely study of the historical Dead Sea parchment. PMID:22418532

  6. Orion: a high contrast user facility

    NASA Astrophysics Data System (ADS)

    Hillier, D. I.; Danson, C. N.; Duffield, S. J.; Egan, D. A.; Elsmere, S. P.; Girling, M. T.; Harvey, E. J.; Hopps, N. W.; Norman, M. J.; Parker, S. J. F.; Treadwell, P. T.; Winter, D. N.; Bett, T. H.

    2016-03-01

    The Orion facility consists of two synchronized laser systems: two CPA (Chirped Pulse Amplification) beamlines each deliver 500J to target in a 0.5ps pulse (1PW) at 1054nm; and ten long pulse beamlines each deliver 500J in 0.1-5ns temporally shaped pulse at 351nm. One of the CPA beamlines has the option to be frequency doubled at sub-aperture to produce 100J laser pulses with a nanosecond contrast of ∼ 1014. Further work is under way to enhance the contrast of both CPA beamlines in the first harmonic.

  7. Hypersensitivity to contrast media and dyes.

    PubMed

    Brockow, Knut; Sánchez-Borges, Mario

    2014-08-01

    This article updates current knowledge on hypersensitivity reactions to diagnostic contrast media and dyes. After application of a single iodinated radiocontrast medium (RCM), gadolinium-based contrast medium, fluorescein, or a blue dye, a hypersensitivity reaction is not a common finding; however, because of the high and still increasing frequency of those procedures, patients who have experienced severe reactions are nevertheless frequently encountered in allergy departments. Evidence on allergologic testing and management is best for iodinated RCM, limited for blue dyes, and insufficient for fluorescein. Skin tests can be helpful in the diagnosis of patients with hypersensitivity reactions to these compounds. PMID:25017677

  8. Exogenous contrast agents for thermoacoustic imaging: An investigation into the underlying sources of contrast

    SciTech Connect

    Ogunlade, Olumide Beard, Paul

    2015-01-15

    Purpose: Thermoacoustic imaging at microwave excitation frequencies is limited by the low differential contrast exhibited by high water content tissues. To overcome this, exogenous thermoacoustic contrast agents based on gadolinium compounds, iron oxide, and single wall carbon nanotubes have previously been suggested and investigated. However, these previous studies did not fully characterize the electric, magnetic, and thermodynamic properties of these agents thus precluding identification of the underlying sources of contrast. To address this, measurements of the complex permittivity, complex permeability, DC conductivity, and Grüneisen parameter have been made. These measurements allowed the origins of the contrast provided by each substance to be identified. Methods: The electric and magnetic properties of the contrast agents were characterized at 3 GHz using two rectangular waveguide cavities. The DC conductivity was measured separately using a conductivity meter. Thermoacoustic signals were then acquired and compared to those generated in water. Finally, 3D electromagnetic simulations were used to decouple the different contributions to the absorbed power density. Results: It was found that the gadolinium compounds provided appreciable electric contrast but not originating from the gadolinium itself. The contrast was either due to dissociation of the gadolinium salt which increased ionic conductivity or its nondissociated polar fraction which increased dielectric polarization loss or a combination of both. In addition, very high concentrations were required to achieve appreciable contrast, to the extent that the Grüneisen parameter increased significantly and became a source of contrast. Iron oxide particles were found to produce low but measurable dielectric contrast due to dielectric polarization loss, but this is attributed to the coating of the particles not the iron oxide. Single wall carbon nanotubes did not provide measurable contrast of any type

  9. Contrast, contours and the confusion effect in dazzle camouflage

    PubMed Central

    Scott-Samuel, Nicholas E.; Cuthill, Innes C.

    2016-01-01

    ‘Motion dazzle camouflage’ is the name for the putative effects of highly conspicuous, often repetitive or complex, patterns on parameters important in prey capture, such as the perception of speed, direction and identity. Research into motion dazzle camouflage is increasing our understanding of the interactions between visual tracking, the confusion effect and defensive coloration. However, there is a paucity of research into the effects of contrast on motion dazzle camouflage: is maximal contrast a prerequisite for effectiveness? If not, this has important implications for our recognition of the phenotype and understanding of the function and mechanisms of potential motion dazzle camouflage patterns. Here we tested human participants' ability to track one moving target among many identical distractors with surface patterns designed to test the influence of these factors. In line with previous evidence, we found that targets with stripes parallel to the object direction of motion were hardest to track. However, reduction in contrast did not significantly influence this result. This finding may bring into question the utility of current definitions of motion dazzle camouflage, and means that some animal patterns, such as aposematic or mimetic stripes, may have previously unrecognized multiple functions. PMID:27493775

  10. Contrast, contours and the confusion effect in dazzle camouflage.

    PubMed

    Hogan, Benedict G; Scott-Samuel, Nicholas E; Cuthill, Innes C

    2016-07-01

    'Motion dazzle camouflage' is the name for the putative effects of highly conspicuous, often repetitive or complex, patterns on parameters important in prey capture, such as the perception of speed, direction and identity. Research into motion dazzle camouflage is increasing our understanding of the interactions between visual tracking, the confusion effect and defensive coloration. However, there is a paucity of research into the effects of contrast on motion dazzle camouflage: is maximal contrast a prerequisite for effectiveness? If not, this has important implications for our recognition of the phenotype and understanding of the function and mechanisms of potential motion dazzle camouflage patterns. Here we tested human participants' ability to track one moving target among many identical distractors with surface patterns designed to test the influence of these factors. In line with previous evidence, we found that targets with stripes parallel to the object direction of motion were hardest to track. However, reduction in contrast did not significantly influence this result. This finding may bring into question the utility of current definitions of motion dazzle camouflage, and means that some animal patterns, such as aposematic or mimetic stripes, may have previously unrecognized multiple functions. PMID:27493775

  11. Processing Implied Meaning through Contrastive Prosody

    ERIC Educational Resources Information Center

    Dennison, Heeyeon Yoon

    2010-01-01

    Understanding implicature--something meant, implied, or suggested distinct from what is said--is paramount for successful human communication. Yet, it is unclear how our cognitive abilities fill in gaps of unspecified information. This study presents three distinct sets of experiments investigating how people understand implied contrasts conveyed…

  12. The Contrast Theory of Negative Input.

    ERIC Educational Resources Information Center

    Saxton, Matthew

    1997-01-01

    Presents an alternative definition of negative evidence, based on the idea that the unique discourse structure created in the juxtaposition of child error and adult correct form can reveal the child in contrast or conflict between the two forms. Findings reveal that children reproduced the correct irregular model more often and persisted with…

  13. Nature versus Nurture: The Simple Contrast

    ERIC Educational Resources Information Center

    Davidoff, Jules; Goldstein, Julie; Roberson, Debi

    2009-01-01

    We respond to the commentary of Franklin, Wright, and Davies ("Journal of Experimental Child Psychology, 102", 239-245 [2009]) by returning to the simple contrast between nature and nurture. We find no evidence from the toddler data that makes us revise our ideas that color categories are learned and never innate. (Contains 1 figure.)

  14. Processing of Contrastiveness by Heritage Russian Bilinguals

    ERIC Educational Resources Information Center

    Sekerina, Irina A.; Trueswell, John C.

    2011-01-01

    Two eye-tracking experiments in the Visual World paradigm compared how monolingual Russian (Experiment 1) and heritage Russian-English bilingual (Experiment 2) listeners process contrastiveness online in Russian. Materials were color adjective-noun phrases embedded into the split-constituent construction Krasnuju polozite zvezdovku..."Red put…

  15. Multi-contrast magnetic resonance image reconstruction

    NASA Astrophysics Data System (ADS)

    Liu, Meng; Chen, Yunmei; Zhang, Hao; Huang, Feng

    2015-03-01

    In clinical exams, multi-contrast images from conventional MRI are scanned with the same field of view (FOV) for complementary diagnostic information, such as proton density- (PD-), T1- and T2-weighted images. Their sharable information can be utilized for more robust and accurate image reconstruction. In this work, we propose a novel model and an efficient algorithm for joint image reconstruction and coil sensitivity estimation in multi-contrast partially parallel imaging (PPI) in MRI. Our algorithm restores the multi-contrast images by minimizing an energy function consisting of an L2-norm fidelity term to reduce construction errors caused by motion, a regularization term of underlying images to preserve common anatomical features by using vectorial total variation (VTV) regularizer, and updating sensitivity maps by Tikhonov smoothness based on their physical property. We present the numerical results including T1- and T2-weighted MR images recovered from partially scanned k-space data and provide the comparisons between our results and those obtained from the related existing works. Our numerical results indicate that the proposed method using vectorial TV and penalties on sensitivities can be made promising and widely used for multi-contrast multi-channel MR image reconstruction.

  16. Contrast-enhanced and targeted ultrasound

    PubMed Central

    Postema, Michiel; Gilja, Odd Helge

    2011-01-01

    Ultrasonic imaging is becoming the most popular medical imaging modality, owing to the low price per examination and its safety. However, blood is a poor scatterer of ultrasound waves at clinical diagnostic transmit frequencies. For perfusion imaging, markers have been designed to enhance the contrast in B-mode imaging. These so-called ultrasound contrast agents consist of microscopically small gas bubbles encapsulated in biodegradable shells. In this review, the physical principles of ultrasound contrast agent microbubble behavior and their adjustment for drug delivery including sonoporation are described. Furthermore, an outline of clinical imaging applications of contrast-enhanced ultrasound is given. It is a challenging task to quantify and predict which bubble phenomenon occurs under which acoustic condition, and how these phenomena may be utilized in ultrasonic imaging. Aided by high-speed photography, our improved understanding of encapsulated microbubble behavior will lead to more sophisticated detection and delivery techniques. More sophisticated methods use quantitative approaches to measure the amount and the time course of bolus or reperfusion curves, and have shown great promise in revealing effective tumor responses to anti-angiogenic drugs in humans before tumor shrinkage occurs. These are beginning to be accepted into clinical practice. In the long term, targeted microbubbles for molecular imaging and eventually for directed anti-tumor therapy are expected to be tested. PMID:21218081

  17. Phased Contrast X-Ray Imaging

    ScienceCinema

    Erin Miller

    2012-12-31

    The Pacific Northwest National Laboratory is developing a range of technologies to broaden the field of explosives detection. Phased contrast X-ray imaging, which uses silicon gratings to detect distortions in the X-ray wave front, may be applicable to mail or luggage scanning for explosives; it can also be used in detecting other contraband, small-parts inspection, or materials characterization.

  18. DOBIS and NOTIS: A Contrast in Design.

    ERIC Educational Resources Information Center

    Juergens, Bonnie; Blake, Ruth

    1987-01-01

    Compares and contrasts two systems designed for library automation applications--NOTIS, which was developed in the United States, and DOBIS, which was developed in Europe. The differences in the systems are discussed in terms of the availability or absence of machine readable bibliographic sharing capacities in the countries of origin. (CLB)

  19. Enhancement of fluoroscopic images with varying contrast.

    PubMed

    Ozanian, T O; Phillips, R

    2001-04-01

    A heuristic algorithm for enhancement of fluoroscopic images of varying contrast is proposed. The new technique aims at identifying a suitable type of enhancement for different locations in an image. The estimation relies on simple preliminary classification of image parts into one of the following types: uniform, sharp (with sufficient contrast), detail-containing (structure present) and unknown (for the cases where it is difficult to make a decision). Different smoothing techniques are applied locally in the different types of image parts. For those parts that are classified as detail-containing, probable object boundaries are identified and local sharpening is carried out to increase the contrast at these places. The adopted approach attempts to improve the quality of an image by reducing available noise and simultaneously increasing the contrast at probable object boundaries without increasing the overall dynamic range. In addition, it allows noise to be cleaned, that at some locations is stronger than the fine structure at other locations, whilst preserving the details. PMID:11223147

  20. Contrast-enhanced and targeted ultrasound.

    PubMed

    Postema, Michiel; Gilja, Odd Helge

    2011-01-01

    Ultrasonic imaging is becoming the most popular medical imaging modality, owing to the low price per examination and its safety. However, blood is a poor scatterer of ultrasound waves at clinical diagnostic transmit frequencies. For perfusion imaging, markers have been designed to enhance the contrast in B-mode imaging. These so-called ultrasound contrast agents consist of microscopically small gas bubbles encapsulated in biodegradable shells. In this review, the physical principles of ultrasound contrast agent microbubble behavior and their adjustment for drug delivery including sonoporation are described. Furthermore, an outline of clinical imaging applications of contrast-enhanced ultrasound is given. It is a challenging task to quantify and predict which bubble phenomenon occurs under which acoustic condition, and how these phenomena may be utilized in ultrasonic imaging. Aided by high-speed photography, our improved understanding of encapsulated microbubble behavior will lead to more sophisticated detection and delivery techniques. More sophisticated methods use quantitative approaches to measure the amount and the time course of bolus or reperfusion curves, and have shown great promise in revealing effective tumor responses to anti-angiogenic drugs in humans before tumor shrinkage occurs. These are beginning to be accepted into clinical practice. In the long term, targeted microbubbles for molecular imaging and eventually for directed anti-tumor therapy are expected to be tested. PMID:21218081

  1. Contrast enhancement of mail piece images

    NASA Astrophysics Data System (ADS)

    Shin, Yong-Chul; Sridhar, Ramalingam; Demjanenko, Victor; Palumbo, Paul W.; Hull, Jonathan J.

    1992-08-01

    A New approach to contrast enhancement of mail piece images is presented. The contrast enhancement is used as a preprocessing step in the real-time address block location (RT-ABL) system. The RT-ABL system processes a stream of mail piece images and locates destination address blocks. Most of the mail pieces (classified into letters) show high contrast between background and foreground. As an extreme case, however, the seasonal greeting cards usually use colored envelopes which results in reduced contrast osured by an error rate by using a linear distributed associative memory (DAM). The DAM is trained to recognize the spectra of three classes of images: with high, medium, and low OCR error rates. The DAM is not forced to make a classification every time. It is allowed to reject as unknown a spectrum presented that does not closely resemble any that has been stored in the DAM. The DAM was fairly accurate with noisy images but conservative (i.e., rejected several text images as unknowns) when there was little ground and foreground degradations without affecting the nondegraded images. This approach provides local enhancement which adapts to local features. In order to simplify the computation of A and (sigma) , dynamic programming technique is used. Implementation details, performance, and the results on test images are presented in this paper.

  2. [Contrast and exposure in xeroradiography (author's transl)].

    PubMed

    Wegener, O H; Schoenfelder, T

    1977-07-01

    Systematic sensitometric measurements of xero-radiographs were carried out and compared with ordinary X-ray films. The effect of kilovoltage and exposure on image contrast and resolution was investigated; optimal exposure and kilovoltage were sought and sources of loss of information are pointed out. PMID:142734

  3. Contrastive and contextual vowel nasalization in Ottawa

    NASA Astrophysics Data System (ADS)

    Klopfenstein, Marie

    2005-09-01

    Ottawa is a Central Algonquian language that possesses the recent innovation of contrastive vowel nasalization. Most phonetic studies done to date on contrastive vowel nasalization have investigated Indo-European languages; therefore, a study of Ottawa could prove to be a valuable addition to the literature. To this end, a percentage of nasalization (nasal airflow/oral + nasal airflow) was measured during target vowels produced by native Ottawa speakers using a Nasometer 6200-3. Nasalized vowels in the target word set were either contrastively or contextually nasalized: candidates for contextual nasalization were either regressive or perserverative in word-initial and word-final syllables. Subjects were asked to read words containing target vowels in a carrier sentence. Mean, minimum, and maximum nasalance were obtained for each target vowel across its full duration. Target vowels were compared across context (regressive or perseverative and word-initial or word-final). In addition, contexts were compared to determine whether a significant difference existed between contrastive and contextual nasalization. Results for Ottawa will be compared with results for vowels in similar contexts in other languages including Hindi, Breton, Bengali, and French.

  4. Lexical representation of novel L2 contrasts

    NASA Astrophysics Data System (ADS)

    Hayes-Harb, Rachel; Masuda, Kyoko

    2005-04-01

    There is much interest among psychologists and linguists in the influence of the native language sound system on the acquisition of second languages (Best, 1995; Flege, 1995). Most studies of second language (L2) speech focus on how learners perceive and produce L2 sounds, but we know of only two that have considered how novel sound contrasts are encoded in learners' lexical representations of L2 words (Pallier et al., 2001; Ota et al., 2002). In this study we investigated how native speakers of English encode Japanese consonant quantity contrasts in their developing Japanese lexicons at different stages of acquisition (Japanese contrasts singleton versus geminate consonants but English does not). Monolingual English speakers, native English speakers learning Japanese for one year, and native speakers of Japanese were taught a set of Japanese nonwords containing singleton and geminate consonants. Subjects then performed memory tasks eliciting perception and production data to determine whether they encoded the Japanese consonant quantity contrast lexically. Overall accuracy in these tasks was a function of Japanese language experience, and acoustic analysis of the production data revealed non-native-like patterns of differentiation of singleton and geminate consonants among the L2 learners of Japanese. Implications for theories of L2 speech are discussed.

  5. Literature Review of Japanese Contrastive Rhetoric

    ERIC Educational Resources Information Center

    Cumming, Brett

    2012-01-01

    This literature review serves to inform the reader on current literature on Contrastive Rhetoric (CR), with specific reference to teaching writing to Japanese students of English. It will examine the historical developments of CR and its present significance before then looking at possible reasons for unique characteristics of Japanese L2 writers…

  6. Angiography contrast injector safety. Visualizing the marketplace.

    PubMed

    2010-06-01

    The most common risk associated with angiography contrast injectors is air embolism. Injector manufacturers have attempted to address this concern by adding air detection systems and other safety features. Find out which injectors do the best job of protecting patients. PMID:21309283

  7. Adaptive contrast imaging: transmit frequency optimization

    NASA Astrophysics Data System (ADS)

    Ménigot, Sébastien; Novell, Anthony; Voicu, Iulian; Bouakaz, Ayache; Girault, Jean-Marc

    2010-01-01

    Introduction: Since the introduction of ultrasound (US) contrast imaging, the imaging systems use a fixed emitting frequency. However it is known that the insonified medium is time-varying and therefore an adapted time-varying excitation is expected. We suggest an adaptive imaging technique which selects the optimal transmit frequency that maximizes the acoustic contrast. Two algorithms have been proposed to find an US excitation for which the frequency was optimal with microbubbles. Methods and Materials: Simulations were carried out for encapsulated microbubbles of 2 microns by considering the modified Rayleigh-Plesset equation for 2 MHz transmit frequency and for various pressure levels (20 kPa up to 420kPa). In vitro experiments were carried out using a transducer operating at 2 MHz and using a programmable waveform generator. Contrast agent was then injected into a small container filled with water. Results and discussions: We show through simulations and in vitro experiments that our adaptive imaging technique gives: 1) in case of simulations, a gain of acoustic contrast which can reach 9 dB compared to the traditional technique without optimization and 2) for in vitro experiments, a gain which can reach 18 dB. There is a non negligible discrepancy between simulations and experiments. These differences are certainly due to the fact that our simulations do not take into account the diffraction and nonlinear propagation effects. Further optimizations are underway.

  8. Embedded high-contrast distributed grating structures

    DOEpatents

    Zubrzycki, Walter J.; Vawter, Gregory A.; Allerman, Andrew A.

    2002-01-01

    A new class of fabrication methods for embedded distributed grating structures is claimed, together with optical devices which include such structures. These new methods are the only known approach to making defect-free high-dielectric contrast grating structures, which are smaller and more efficient than are conventional grating structures.

  9. Three-dimensional image contrast using biospeckle

    NASA Astrophysics Data System (ADS)

    Godinho, Robson Pierangeli; Braga, Roberto A., Jr.

    2010-09-01

    The biospeckle laser (BSL) has been applied in many areas of knowledge and a variety of approaches has been presented to address the best results in biological and non-biological samples, in fast or slow activities, or else in defined flow of materials or in random activities. The methodologies accounted in the literature consider the apparatus used in the image assembling and the way the collected data is processed. The image processing steps presents in turn a variety of procedures with first or second order statistics analysis, and as well with different sizes of data collected. One way to access the biospeckle in defined flow, such as in capillary blood flow in alive animals, was the adoption of the image contrast technique which uses only one image from the illuminated sample. That approach presents some problems related to the resolution of the image, which is reduced during the image contrast processing. In order to help the visualization of the low resolution image formed by the contrast technique, this work presents the three-dimensional procedure as a reliable alternative to enhance the final image. The work based on a parallel processing, with the generation of a virtual map of amplitudes, and maintaining the quasi-online characteristic of the contrast technique. Therefore, it was possible to generate in the same display the observed material, the image contrast result and in addiction the three-dimensional image with adjustable options of rotation. The platform also offers to the user the possibility to access the 3D image offline.

  10. Contrast-enhanced ultrasound: The evolving applications

    PubMed Central

    Xu, Hui-Xiong

    2009-01-01

    Contrast-enhanced ultrasound (CEUS) is a major breakthrough for ultrasound imaging in recent years. By using a microbubble contrast agent and contrast-specific imaging software, CEUS is able to depict the micro- and macro-circulation of the targeted organ, which in turn leads to improved performance in diagnosis. Due to the special dual blood supply system in the liver, CEUS is particularly suitable for liver imaging. It is evident that CEUS facilitates improvement for characterization of focal liver lesions (FLLs), detection of liver malignancy, guidance for interventional procedures, and evaluation of treatment response after local therapies. CEUS has been demonstrated to be equal to contrast-enhanced computed tomography or magnetic resonance imaging for the characterization of FLLs. In addition, the applicability of CEUS has expanded to non-liver structures such as gallbladder, bile duct, pancreas, kidney, spleen, breast, thyroid, and prostate. The usefulness of CEUS in these applications is confirmed by extensive literature production. Novel applications include detecting bleeding sites and hematomas in patients with abdominal trauma, guiding percutaneous injection therapy and therefore achieving the goal of using interventional ultrasonography in managing splenic trauma, assessing the activity of Crohn’s disease, and detecting suspected endoleaks after endovascular abdominal aneurysm repair. Contrast-enhanced intraoperative ultrasound (US) and intracavitary use of CEUS have been developed and clinically studied. The potential use of CEUS involves sentinel lymph node detection, drug or gene delivery, and molecular imaging. In conclusion, the advent of CEUS has greatly enhanced the usefulness of US and even changed the status of US in clinical practice. The application of CEUS in the clinic is continuously evolving and it is expected that its use will be expanded further in the future. PMID:21160717

  11. Peripheral contrast sensitivity and attention in myopia.

    PubMed

    Kerber, Kristen L; Thorn, Frank; Bex, Peter J; Vera-Diaz, Fuensanta A

    2016-08-01

    Disruption of normal visual experience or changes in the normal interaction between central and peripheral retinal input may lead to the development of myopia. In order to examine the relationship between peripheral contrast sensitivity and myopia, we manipulated attentional load for foveal vision in emmetropes and myopes while observers detected targets with peripheral vision. Peripheral contrast detection thresholds were measured binocularly using vertical Gabor stimuli presented at three eccentricities (±8°, 17°, 30°) in a spatial 2 alternative forced choice task. Contrast thresholds were measured in young adult (mean age 24.5±2.6years) emmetropes (n=17; group SE: +0.19±0.32D) and myopes (n=25; group SE: -3.74±1.99D). Attention at central fixation was manipulated with: (1) a low attention task, requiring simple fixation; or (2) a high attention task, which required subjects to perform a mathematical task. We found that at 30° all subjects exhibited lower contrast sensitivity (higher thresholds). In addition, myopes (Wilcoxon, p<0.01), but not emmetropes (Wilcoxon, p=0.1), had a significant decrease in sensitivity at 30° during the high attention task. However, the attention dependent threshold increase for myopes was not significantly greater than for emmetropes (Wilcoxon, p=0.27). Attentional load did not increase thresholds at 8° or 17° for either refractive group. These data indicate that myopes experience a greater decrease in contrast sensitivity in the far periphery than emmetropes when attention is deployed in central vision. PMID:27264028

  12. INTRAARTERIAL INJECTION OF IODINATED CONTRAST MEDIUM FOR CONTRAST ENHANCED COMPUTED TOMOGRAPHY OF THE EQUINE HEAD.

    PubMed

    Carmalt, James L; Montgomery, James

    2015-01-01

    Minimizing the volume of contrast administered for contrast-enhanced computed tomography (CT) of the equine head is desirable for reducing costs and risks of adverse reactions, however evidence-based studies on the effects of varying volumes on image quality are currently lacking. The objective of the current study was to determine whether low-volume intraarterial administration of contrast medium would result in an equivalent image quality and tissue attenuation vs. high-volume intravenous bolus administration. A prospective cross-over experimental design was used in a sample of six horses. After anesthetic induction, the right carotid artery was exposed surgically and catheterized. Four CT scans of the cranium were performed for each horse: baseline, immediately following intraarterial contrast injection, five-min postinjection (return to baseline) and a final scan after intravenous contrast administration. Soft tissue attenuation in predetermined regions of interest (ROI); and length, width, and height measurements of the pituitary gland were recorded at each time point. Horses were euthanized and measurements of the pituitary gland were repeated postmortem. No adverse reactions to contrast administration were observed. Intraarterial and intravenous administration of contrast medium resulted in significantly greater soft tissue enhancement of some brain ROI's and the pituitary gland vs. baseline values. Pituitary gland measurements made on postcontrast CT images did not differ from those obtained during postmortem examination. Findings indicated that low-dose intraarterial administration of contrast material in the equine head resulted in comparable soft tissue enhancement vs. high volume intravenous administration. PMID:25782997

  13. Papers and Studies in Contrastive Linguistics, Volume Twenty-Six. The Polish-English Contrastive Project.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    1990-01-01

    Fourteen articles are presented in this volume on contrastive linguistics. The articles and authors are as follows: "A Brief Falsificationist Look at Contrastive Sociolinguistics" (K. Janicki); "The Locus of French Gender Control" (W. A. Bennett); "On the English Perfect Tense and Current Relevance Implicatures" (J. R. Canavan); "Teaching French…

  14. The Romanian-English Contrastive Analysis Project; Contrastive Studies in Phonetics and Phonology, Vol. 4.

    ERIC Educational Resources Information Center

    Center for Applied Linguistics, Arlington, VA.

    The fourth volume in this series contains nine contrastive studies in phonetics and phonology. They are: "Remarks on the Physical Manifestation of Internal Open Juncture in the English of Romanians," by Andrei Avram; "The Back Vowels of Romanian and English--A Contrastive Study," by Laurentia Dascalu; "Remarks on the English Diphthongs and…

  15. The Romanian-English Contrastive Analysis Project; Further Developments in Contrastive Studies, Vol. 5.

    ERIC Educational Resources Information Center

    Chitoran, Dumitru, Ed.

    The fifth volume in this series contains ten articles dealing with various aspects of Romanian-English contrastive analysis. They are: "Theoretical Interpretation and Methodological Consequences of 'REGULARIZATION'," by Tatiana Slama-Cazacu; "On Error Analysis," by Charles M. Carlton; "The Contrastive Hypothesis in Second Language Acquisition," by…

  16. Acquiring color names via linguistic contrast: the influence of contrasting terms.

    PubMed

    Au, T K; Laframboise, D E

    1990-12-01

    Linguistic contrast of the form "It's not X; it's Y" is often used by adults to correct children's naming errors. The present studies examined whether such linguistic contrast could help preschoolers learn a novel color name. In Experiment 1, a novel color term was contrasted only once with 1 or 2 familiar color names. Contrasting a new color term with children's own label for the stimulus color helped 5-year-olds learn the new term, but contrasting the new term with randomly chosen familiar color terms did not. For 4-year-olds, neither kind of contrast helped much. Experiments 2 and 3 showed that when the contrastive information was presented more than once, even 3- and 4-year-olds performed much like the 5-year-olds in Experiment 1. Together, these findings suggest that contrasting a new term with a child's own term facilitates the acquisition of the new term, perhaps because it gives the child specific information about how two terms are related in meaning. PMID:2083500

  17. Papers and Studies in Contrastive Linguistics, Volume 4. The Polish-English Contrastive Project.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    This collection of twenty-six papers is the fourth resulting from the Polish-English Contrastive Project. The overall purpose of the project is to prepare a Polish-English contrastive grammar and to develop pedagogical materials. The basic model used for research is the transformational generative one. Among the papers on phonology, topics such as…

  18. Papers and Studies in Contrastive Linguistics, Volume Twenty-Two. The Polish-English Contrastive Project.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    1988-01-01

    Fifteen articles are presented in this collection on contrastive linguistics: "On Syntactic Levels--One Tertium Comparison is in Contrastive Linguistics" (L. F. Jakobsen and J. Olsen); "Equivalence in Bilingual Lexicography: From Correspondence Relation to Communicative Strategy" (R. R. K. Hartmann); "How Useful Are Word Lists in Contrastive…

  19. Papers and Studies in Contrastive Linguistics, Volume Eleven. The Polish-English Contrastive Project.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    This volume contains ten articles and a book review. Josef Vachek talks about "Vilem Mathesius as Forerunner of Contrastive Linguistic Studies." In "Contrastive Generative Grammar and the Psycholinguistic Fallacy," Andrew Chesterman discusses methods for accounting for simplification in foreign language learning. Michael Post compares "English…

  20. Papers and Studies in Contrastive Linguistics, Vol. 1. The Polish--English Contrastive Project.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    This collection of papers is the first in a series resulting from the Polish-English Contrastive Project. The overall purposes of the project are to prepare a Polish-English contrastive grammar and to develop pedagogical materials. The basic model used for the research is the transformational generative one. The papers included in this volume are…

  1. Papers and Studies in Contrastive Linguistics, Vol. 3. The Polish-English Contrastive Project.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    This collection of 19 papers is the third resulting from the Polish-English Contrastive Project. The overall purposes of the project are to prepare a Polish-English contrastive grammar and to develop pedagogical material. The basic model used for the research is the transformational generative one. This volume is divided into 3 sections: (1)…

  2. Structured Mechanical Collage.

    PubMed

    Huang, Zhe; Wang, Jiang; Fu, Hongbo; Lau, Rynson W H

    2014-07-01

    We present a method to build 3D structured mechanical collages consisting of numerous elements from the database given artist-designed proxy models. The construction is guided by some graphic design principles, namely unity, variety and contrast. Our results are visually more pleasing than previous works as confirmed by a user study. PMID:26357362

  3. The Clinical Epidemiology of Contrast-Induced Nephropathy

    SciTech Connect

    Parfrey, Patrick

    2005-12-15

    Recent improvements in contrast agents and radiologic imaging tools have resulted in an increasing number of patients undergoing contrast media (CM)-enhanced examinations. Although the majority of patients undergoing these diagnostic and therapeutic procedures experience only mild adverse events, some patient subpopulations are at risk for developing contrast-induced nephropathy (CIN), an adverse event that is associated with high morbidity and mortality. Contrast-induced nephropathy is usually defined as an increase of {>=}25% in the serum creatinine level relative to baseline. Pathophysiologic mechanisms underlying this disorder are not fully understood, but it is currently believed that disturbances in renal hemodynamics and a direct effect of CM on renal tubules are involved. In the general population, the incidence of CIN is estimated to be 1% to 6%. However, the risk may be as high as 50% in some patient subgroups. Patients with diabetes and pre-existing renal impairment are at high risk, and CIN incidence increases in patients with multiple comorbidities. The volume and osmolality of CM used also play a role in the development of CIN. Patients who develop CIN are more likely to die in-hospital and, for those who are discharged, 1-year mortality rates are high. Whether this is due to CM, comorbidity, or concurrent comorbid events is unclear. Randomized controlled trials that measure non-renal clinical outcomes are necessary to determine whether interventions that prevent CIN can also prevent non-renal adverse events. A review of the incidence, pathogenesis, and clinical consequences of CIN is provided.

  4. Contrast Adaptation Implies Two Spatiotemporal Channels but Three Adapting Processes

    ERIC Educational Resources Information Center

    Langley, Keith; Bex, Peter J.

    2007-01-01

    The contrast gain control model of adaptation predicts that the effects of contrast adaptation correlate with contrast sensitivity. This article reports that the effects of high contrast spatiotemporal adaptors are maximum when adapting around 19 Hz, which is a factor of two or more greater than the peak in contrast sensitivity. To explain the…

  5. Contrast-to-noise ratio optimization for a prototype phase-contrast computed tomography scanner

    SciTech Connect

    Müller, Mark Yaroshenko, Andre; Velroyen, Astrid; Tapfer, Arne; Bech, Martin; Pauwels, Bart; Bruyndonckx, Peter; Sasov, Alexander; Pfeiffer, Franz

    2015-12-15

    In the field of biomedical X-ray imaging, novel techniques, such as phase-contrast and dark-field imaging, have the potential to enhance the contrast and provide complementary structural information about a specimen. In this paper, a first prototype of a preclinical X-ray phase-contrast CT scanner based on a Talbot-Lau interferometer is characterized. We present a study of the contrast-to-noise ratios for attenuation and phase-contrast images acquired with the prototype scanner. The shown results are based on a series of projection images and tomographic data sets of a plastic phantom in phase and attenuation-contrast recorded with varying acquisition settings. Subsequently, the signal and noise distribution of different regions in the phantom were determined. We present a novel method for estimation of contrast-to-noise ratios for projection images based on the cylindrical geometry of the phantom. Analytical functions, representing the expected signal in phase and attenuation-contrast for a circular object, are fitted to individual line profiles of the projection data. The free parameter of the fit function is used to estimate the contrast and the goodness of the fit is determined to assess the noise in the respective signal. The results depict the dependence of the contrast-to-noise ratios on the applied source voltages, the number of steps of the phase stepping routine, and the exposure times for an individual step. Moreover, the influence of the number of projection angles on the image quality of CT slices is investigated. Finally, the implications for future imaging purposes with the scanner are discussed.

  6. Contrast-to-noise ratio optimization for a prototype phase-contrast computed tomography scanner.

    PubMed

    Müller, Mark; Yaroshenko, Andre; Velroyen, Astrid; Bech, Martin; Tapfer, Arne; Pauwels, Bart; Bruyndonckx, Peter; Sasov, Alexander; Pfeiffer, Franz

    2015-12-01

    In the field of biomedical X-ray imaging, novel techniques, such as phase-contrast and dark-field imaging, have the potential to enhance the contrast and provide complementary structural information about a specimen. In this paper, a first prototype of a preclinical X-ray phase-contrast CT scanner based on a Talbot-Lau interferometer is characterized. We present a study of the contrast-to-noise ratios for attenuation and phase-contrast images acquired with the prototype scanner. The shown results are based on a series of projection images and tomographic data sets of a plastic phantom in phase and attenuation-contrast recorded with varying acquisition settings. Subsequently, the signal and noise distribution of different regions in the phantom were determined. We present a novel method for estimation of contrast-to-noise ratios for projection images based on the cylindrical geometry of the phantom. Analytical functions, representing the expected signal in phase and attenuation-contrast for a circular object, are fitted to individual line profiles of the projection data. The free parameter of the fit function is used to estimate the contrast and the goodness of the fit is determined to assess the noise in the respective signal. The results depict the dependence of the contrast-to-noise ratios on the applied source voltages, the number of steps of the phase stepping routine, and the exposure times for an individual step. Moreover, the influence of the number of projection angles on the image quality of CT slices is investigated. Finally, the implications for future imaging purposes with the scanner are discussed. PMID:26724040

  7. Contrast-to-noise ratio optimization for a prototype phase-contrast computed tomography scanner

    NASA Astrophysics Data System (ADS)

    Müller, Mark; Yaroshenko, Andre; Velroyen, Astrid; Bech, Martin; Tapfer, Arne; Pauwels, Bart; Bruyndonckx, Peter; Sasov, Alexander; Pfeiffer, Franz

    2015-12-01

    In the field of biomedical X-ray imaging, novel techniques, such as phase-contrast and dark-field imaging, have the potential to enhance the contrast and provide complementary structural information about a specimen. In this paper, a first prototype of a preclinical X-ray phase-contrast CT scanner based on a Talbot-Lau interferometer is characterized. We present a study of the contrast-to-noise ratios for attenuation and phase-contrast images acquired with the prototype scanner. The shown results are based on a series of projection images and tomographic data sets of a plastic phantom in phase and attenuation-contrast recorded with varying acquisition settings. Subsequently, the signal and noise distribution of different regions in the phantom were determined. We present a novel method for estimation of contrast-to-noise ratios for projection images based on the cylindrical geometry of the phantom. Analytical functions, representing the expected signal in phase and attenuation-contrast for a circular object, are fitted to individual line profiles of the projection data. The free parameter of the fit function is used to estimate the contrast and the goodness of the fit is determined to assess the noise in the respective signal. The results depict the dependence of the contrast-to-noise ratios on the applied source voltages, the number of steps of the phase stepping routine, and the exposure times for an individual step. Moreover, the influence of the number of projection angles on the image quality of CT slices is investigated. Finally, the implications for future imaging purposes with the scanner are discussed.

  8. Bioinspired steel surfaces with extreme wettability contrast

    NASA Astrophysics Data System (ADS)

    Her, Eun Kyu; Ko, Tae-Jun; Lee, Kwang-Ryeol; Oh, Kyu Hwan; Moon, Myoung-Woon

    2012-04-01

    The exterior structures of natural organisms have continuously evolved by controlling wettability, such as the Namib Desert beetle, whose back has hydrophilic/hydrophobic contrast for water harvesting by mist condensation in dry desert environments, and some plant leaves that have hierarchical micro/nanostructures to collect or repel liquid water. In this work, we have provided a method for wettability contrast on alloy steels by both nano-flake or needle patterns and tuning of the surface energy. Steels were provided with hierarchical micro/nanostructures of Fe oxides by fluorination and by a subsequent catalytic reaction of fluorine ions on the steel surfaces in water. A hydrophobic material was deposited on the structured surfaces, rendering superhydrophobicity. Plasma oxidization induces the formation of superhydrophilic surfaces on selective regions surrounded by superhydrophobic surfaces. We show that wettability contrast surfaces align liquid water within patterned hydrophilic regions during the condensation process. Furthermore, this method could have a greater potential to align other liquids or living cells.The exterior structures of natural organisms have continuously evolved by controlling wettability, such as the Namib Desert beetle, whose back has hydrophilic/hydrophobic contrast for water harvesting by mist condensation in dry desert environments, and some plant leaves that have hierarchical micro/nanostructures to collect or repel liquid water. In this work, we have provided a method for wettability contrast on alloy steels by both nano-flake or needle patterns and tuning of the surface energy. Steels were provided with hierarchical micro/nanostructures of Fe oxides by fluorination and by a subsequent catalytic reaction of fluorine ions on the steel surfaces in water. A hydrophobic material was deposited on the structured surfaces, rendering superhydrophobicity. Plasma oxidization induces the formation of superhydrophilic surfaces on selective

  9. Nanoparticle contrast agents for optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Gabriele, Michelle Lynn

    Optical coherence tomography (OCT) provides real-time, objective, in-vivo, optical cross-sectional representations of the retina and optic nerve. Recent innovations in image acquisition, including the incorporation of Fourier/spectral-domain detection, have improved imaging speed, sensitivity and resolution. Still, there remain specific structures within ocular OCT images, such as retinal ganglion cells (RGCs), which are of clinical interest but consistently have low contrast. This makes it difficult to differentiate between surrounding layers and structures. The objectives of this project were: (1) To establish a reliable method for OCT imaging of the healthy and diseased mouse eye in order to provide a platform for testing the utility of OCT contrast agents for ocular imaging, (2) To develop antibody-conjugated gold nanoparticles suitable for targeting specific structures and enhancing OCT image contrast in the mouse eye, and (3) To examine the localized contrast-enhancing ability and biocompatibility of gold nanoparticle contrast agents in-vivo. Our organizing hypotheses were that nanoparticles could improve contrast by modulating the intensity of backscattered light detected by OCT and that they could be directed to ocular structures of interest using antibodies specific to cellular markers. A reproducible method for imaging the mouse retina and quantifying retinal thickness was developed and this technique was then applied to a mouse model for retinal ganglion cell loss, optic nerve crush. Gold nanorods were designed specifically to augment the backscattering OCT signal at the same wavelengths of light used in current ophthalmic OCT imaging schemes (resonant wavelength lambda = 840 nm). Anti-CD90.1 (Thy1.1) antibodies were conjugated to the gold nanorods and a protocol for characterization of the success of antibody conjugation was developed. Upon injection, the gold nanorods were found to remain in the vitreous post-injection, with many consumed by an early

  10. DNA-Coated Microbubbles with Biochemically-Tunable Ultrasound Contrast Activity

    PubMed Central

    Nakatsuka, Matthew A.; Hsu, Mark J.

    2013-01-01

    Changing the mechanical properties of the microbubble shell in response to a biochemical stimulus leads to vast changes in both ultrasound-induced bubble dynamics and contrast-enhanced ultrasound imaging. Here, DNA-coated microbubbles are shown to be a simple and highly versatile platform that can silence and re-activate contrast activity in response to the introduction and removal of biochemical stimuli. PMID:21956383

  11. Automatic contrast phase estimation in CT volumes.

    PubMed

    Sofka, Michal; Wu, Dijia; Sühling, Michael; Liu, David; Tietjen, Christian; Soza, Grzegorz; Zhou, S Kevin

    2011-01-01

    We propose an automatic algorithm for phase labeling that relies on the intensity changes in anatomical regions due to the contrast agent propagation. The regions (specified by aorta, vena cava, liver, and kidneys) are first detected by a robust learning-based discriminative algorithm. The intensities inside each region are then used in multi-class LogitBoost classifiers to independently estimate the contrast phase. Each classifier forms a node in a decision tree which is used to obtain the final phase label. Combining independent classification from multiple regions in a tree has the advantage when one of the region detectors fail or when the phase training example database is imbalanced. We show on a dataset of 1016 volumes that the system correctly classifies native phase in 96.2% of the cases, hepatic dominant phase (92.2%), hepatic venous phase (96.7%), and equilibrium phase (86.4%) in 7 seconds on average. PMID:22003696

  12. Contrast Medium-Induced Acute Kidney Injury

    PubMed Central

    Sadat, Umar; Usman, Ammara; Boyle, Jonathan R.; Hayes, Paul D.; Solomon, Richard J.

    2015-01-01

    Contrast medium-induced acute kidney injury (CI-AKI) is a predominant cause of hospital-acquired renal insufficiency. With an increasing number of contrast medium-enhanced radiological procedures being performed in a rapidly increasing ageing population in the Western world, it is imperative that more attention is given to understand the aetiology of CI-AKI to devise novel diagnostic methods and to formulate effective prophylactic and therapeutic regimens to reduce its incidence and its associated morbidity and mortality. This article presents high-yield information on the above-mentioned aspects of CI-AKI, primarily based on results of randomised controlled trials, meta-analyses, systematic reviews and international consensus guidelines. PMID:26195974

  13. Safety of magnetic resonance contrast media.

    PubMed

    Runge, V M

    2001-08-01

    Intravenous contrast media, specifically the gadolinium chelates, are well accepted for use in the clinical practice of magnetic resonance imaging. The gadolinium chelates are considered to be very safe and lack (in intravenous use) the nephrotoxicity found with iodinated contrast media. Minor adverse reactions, including nausea and hives, occur in a low percentage of cases. The four agents currently available in the United States cannot be differentiated on the basis of these adverse reactions. Severe anaphylactoid reactions are also known to occur with all agents, although these are uncommon. This review discusses the safety issues involved with intravenous administration of the gadolinium chelates and off-label use. The latter is common in clinical practice and permits broader application of these agents. PMID:11687717

  14. Phase contrast in high resolution electron microscopy

    DOEpatents

    Rose, H.H.

    1975-09-23

    This patent relates to a device for developing a phase contrast signal for a scanning transmission electron microscope. The lens system of the microscope is operated in a condition of defocus so that predictable alternate concentric regions of high and low electron density exist in the cone of illumination. Two phase detectors are placed beneath the object inside the cone of illumination, with the first detector having the form of a zone plate, each of its rings covering alternate regions of either higher or lower electron density. The second detector is so configured that it covers the regions of electron density not covered by the first detector. Each detector measures the number of electrons incident thereon and the signal developed by the first detector is subtracted from the signal developed by the record detector to provide a phase contrast signal. (auth)

  15. Uniform apparent contrast noise: A picture of the noise of the visual contrast detection system

    NASA Technical Reports Server (NTRS)

    Ahumada, A. J., Jr.; Watson, A. B.

    1984-01-01

    A picture which is a sample of random contrast noise is generated. The noise amplitude spectrum in each region of the picture is inversely proportional to spatial frequency contrast sensitivity for that region, assuming the observer fixates the center of the picture and is the appropriate distance from it. In this case, the picture appears to have approximately the same contrast everywhere. To the extent that contrast detection thresholds are determined by visual system noise, this picture can be regarded as a picture of the noise of that system. There is evidence that, at different eccentricities, contrast sensitivity functions differ only by a magnification factor. The picture was generated by filtering a sample of white noise with a filter whose frequency response is inversely proportional to foveal contrast sensitivity. It was then stretched by a space-varying magnification function. The picture summmarizes a noise linear model of detection and discrimination of contrast signals by referring the model noise to the input picture domain.

  16. Determination of contrast media administration to achieve a targeted contrast enhancement in CT

    NASA Astrophysics Data System (ADS)

    Sahbaee, Pooyan; Li, Yuan; Segars, Paul; Marin, Daniele; Nelson, Rendon; Samei, Ehsan

    2015-03-01

    Contrast enhancement is a key component of CT imaging and offer opportunities for optimization. The design and optimization of new techniques however requires orchestration with the scan parameters and further a methodology to relate contrast enhancement and injection function. In this study, we used such a methodology to develop a method, analytical inverse method, to predict the required injection function to achieve a desired contrast enhancement in a given organ by incorporation of a physiologically based compartmental model. The method was evaluated across 32 different target contrast enhancement functions for aorta, kidney, stomach, small intestine, and liver. The results exhibited that the analytical inverse method offers accurate performance with error in the range of 10% deviation between the predicted and desired organ enhancement curves. However, this method is incapable of predicting the injection function based on the liver enhancement. The findings of this study can be useful in optimizing contrast medium injection function as well as the scan timing to provide more consistency in the way that the contrast enhanced CT examinations are performed. To our knowledge, this work is one of the first attempts to predict the contrast material injection function for a desired organ enhancement curve.

  17. Contrast transfer function in grating-based x-ray phase-contrast imaging

    NASA Astrophysics Data System (ADS)

    Huang, Jianheng; Du, Yang; Lin, Danying; Liu, Xin; Niu, Hanben

    2014-05-01

    x-Ray grating interferometry is a method for x-ray wave front sensing and phase-contrast imaging that has been developed over past few years. Contrast and resolution are the criteria used to specify the quality of an image. In characterizing the performance of this interferometer, the contrast transfer function is considered in this paper. The oscillatory nature of the contrast transfer function (CTF) is derived and quantified for this interferometer. The illumination source and digital detector are both considered as significant factors controlling image quality, and it can be noted that contrast and resolution in turn depends primarily on the projected intensity profile of the array source and the pixel size of the detector. Furthermore, a test pattern phantom with a well-controlled range of spatial frequencies was designed and imaging of this phantom was simulated by a computer. Contrast transfer function behavior observed in the simulated image is consistent with our theoretical CTF. This might be beneficial for the evaluation and optimization of a grating-based x-ray phase contrast imaging system.

  18. Imaging features of rhinosporidiosis on contrast CT

    PubMed Central

    Prabhu, Shailesh M; Irodi, Aparna; Khiangte, Hannah L; Rupa, V; Naina, P

    2013-01-01

    Context: Rhinosporidiosis is a chronic granulomatous disease endemic in certain regions of India. Computed tomography (CT) imaging appearances of rhinosporidiosis have not been previously described in the literature. Aims: To study imaging features in rhinosporidiosis with contrast-enhanced CT and elucidate its role in the evaluation of this disease. Materials and Methods: Sixteen patients with pathologically proven rhinosporidiosis were included in the study. Contrast-enhanced CT images were analyzed retrospectively and imaging findings were correlated with surgical and histopathologic findings. Results: A total of 29 lesions were found and evaluated. On contrast-enhanced CT, rhinosporidiosis was seen as moderately enhancing lobulated or irregular soft tissue mass lesions in the nasal cavity (n = 13), lesions arising in nasal cavity and extending through choana into nasopharynx (n = 5), pedunculated polypoidal lesions arising from the nasopharyngeal wall (n = 5), oropharyngeal wall (n = 2), larynx (n = 1), bronchus (n = 1), skin and subcutaneous tissue (n = 2). The inferior nasal cavity comprising nasal floor, inferior turbinate, and inferior meatus was the most common site of involvement (n = 13). Surrounding bone involvement was seen in the form of rarefaction (n = 6), partial (n = 3) or complete erosion (n = 3) of inferior turbinate, thinning of medial maxillary wall (n = 2), and septal erosion (n = 2). Nasolacrimal duct involvement was seen in four cases. Conclusions: Contrast-enhanced CT has an important role in delineating the site and extent of the disease, as well as the involvement of surrounding bone, nasolacrimal duct and tracheobronchial tree. This provides a useful roadmap prior to surgery. PMID:24347850

  19. Spatiotemporal contrast sensitivity of early vision.

    PubMed

    Van Hateren, J H

    1993-01-01

    Based on the spatial and temporal statistics of natural images, a theory is developed that specifies spatiotemporal filters that maximize the flow of information through noisy channels of limited dynamic range. Sensitivities resulting from these spatiotemporal filters are very similar to the human spatiotemporal contrast sensitivity, including the dependence on ambient light intensity. The theory predicts several psychophysical laws: Ferry-Porter's law, the de Vries-Rose law, Weber's law, Bloch's law, Ricco's law, and Piper's law. PMID:8447098

  20. Refracting Roentgen's rays: Propagation-based x-ray phase contrast for biomedical imaging

    SciTech Connect

    Gureyev, T. E.; Mayo, S. C.; Nesterets, Ya.; Pogany, A.; Stevenson, A. W.; Wilkins, S. W.; Myers, D. E.; Paganin, D. M.

    2009-05-15

    Absorption-contrast x-ray imaging serves to visualize the variation in x-ray attenuation within the volume of a given sample, whereas phase contrast allows one to visualize variations in x-ray refractive index. The former imaging mechanism has been well known and widely utilized since the time of Roentgen's Nobel prize winning work, whereas the latter mechanism--sought for, but not found, by Roentgen himself--has laid the foundation for a revolution in x-ray imaging which is the central topic of this review. We consider the physical imaging mechanisms underlying both absorption contrast and phase contrast, together with the associated inverse problem of how one may obtain quantitative two- or three-dimensional information regarding a sample, given one or more phase-contrast images of the same. Practical questions are considered, regarding optimized phase-contrast imaging geometries as a function of detector resolution, source size, x-ray spectrum, and dose. Experimental examples pertaining to biomedical applications are given, and prospects for the future outlined.

  1. Optimization of subcutaneous vein contrast enhancement

    NASA Astrophysics Data System (ADS)

    Zeman, Herbert D.; Lovhoiden, Gunnar; Deshmukh, Harshal

    2000-05-01

    A technique for enhancing the contrast of subcutaneous veins has been demonstrated. This techniques uses a near IR light source and one or more IR sensitive CCD TV cameras to produce a contrast enhanced image of the subcutaneous veins. This video image of the veins is projected back onto the patient's skin using a n LCD video projector. The use of an IR transmitting filter in front of the video cameras prevents any positive feedback from the visible light from the video projector from causing instabilities in the projected image. The demonstration contrast enhancing illuminator has been tested on adults and children, both Caucasian and African-American, and it enhances veins quite well in all cases. The most difficult cases are those where significant deposits of subcutaneous fat are present which make the veins invisible under normal room illumination. Recent attempts to see through fat using different IR wavelength bands and both linearly and circularly polarized light were unsuccessful. The key to seeing through fat turns out to be a very diffuse source of RI light. Results on adult and pediatric subjects are shown with this new IR light source.

  2. First Bloch eigenvalue in high contrast media

    NASA Astrophysics Data System (ADS)

    Briane, Marc; Vanninathan, Muthusamy

    2014-01-01

    This paper deals with the asymptotic behavior of the first Bloch eigenvalue in a heterogeneous medium with a high contrast ɛY-periodic conductivity. When the conductivity is bounded in L1 and the constant of the Poincaré-Wirtinger weighted by the conductivity is very small with respect to ɛ-2, the first Bloch eigenvalue converges as ɛ → 0 to a limit which preserves the second-order expansion with respect to the Bloch parameter. In dimension two the expansion of the limit can be improved until the fourth-order under the same hypotheses. On the contrary, in dimension three a fibers reinforced medium combined with a L1-unbounded conductivity leads us to a discontinuity of the limit first Bloch eigenvalue as the Bloch parameter tends to zero but remains not orthogonal to the direction of the fibers. Therefore, the high contrast conductivity of the microstructure induces an anomalous effect, since for a given low-contrast conductivity the first Bloch eigenvalue is known to be analytic with respect to the Bloch parameter around zero.

  3. HCIT Broadband Contrast Performance Sensitivity Studies

    NASA Technical Reports Server (NTRS)

    Sidick, Erkin; Shaklan, Stuart; Balasubramanian, Kunjithapatham

    2012-01-01

    One of the important milestones of the TPF Coronagraph project is to demonstrate the ability to predict the performance sensitivities of the system at levels consistent with exo-planet detection requirement. We want to gain some general understanding about the potentials and the limitations of the current single-Deformable-Mirror (DM) High-contrast imaging testbed (HCIT) system through modeling and simulations. Specifically, we want to understand the effects of some common errors on the EFC-based control of e-field over a half dark-hole region and broadband contrast. Investigated errors include: (1) Absorbing particles on a flat-mirror (2) Defects on the Occulter surface (3) Dead actuators on the DM. We also investigated the effects of control bandwidth on the broadband contrast. We used a MACOS-based simulation algorithm which (1) combines a ray trace, diffraction model, & a broadband wavefront control algorithm (2) is capable of performing full three-dimensional near-field diffraction analysis

  4. Contrast Enhancement by Nonlinear Diffusion Filtering.

    PubMed

    Liang, Zhetong; Liu, Weijian; Yao, Ruohe

    2016-02-01

    To enhance the visual quality of an image that is degraded by uneven light, an effective method is to estimate the illumination component and compress it. Some previous methods have either defects of halo artifacts or contrast loss in the enhanced image due to incorrect estimation. In this paper, we discuss this problem and propose a novel method to estimate the illumination. The illumination is obtained by iteratively solving a nonlinear diffusion equation. During the diffusion process, surround suppression is embedded in the conductance function to specially enhance the diffusive strength in textural areas of the image. The proposed estimation method has the following two merits: 1) the boundary areas are preserved in the illumination, and thus halo artifacts are prevented and 2) the textural details are preserved in the reflectance to not suffer from illumination compression, which contributes to the contrast enhancement in the result. Experimental results show that the proposed algorithm achieves excellent performance in artifact removal and local contrast enhancement. PMID:26685234

  5. Image contrast enhancement using Chebyshev wavelet moments

    NASA Astrophysics Data System (ADS)

    Uchaev, Dm. V.; Uchaev, D. V.; Malinnikov, V. A.

    2015-12-01

    A new algorithm for image contrast enhancement in the Chebyshev moment transform (CMT) domain is introduced. This algorithm is based on a contrast measure that is defined as the ratio of high-frequency to zero-frequency content in the bands of CMT matrix. Our algorithm enables to enhance a large number of high-spatial-frequency coefficients, that are responsible for image details, without severely degrading low-frequency contributions. To enhance high-frequency Chebyshev coefficients we use a multifractal spectrum of scaling exponents (SEs) for Chebyshev wavelet moment (CWM) magnitudes, where CWMs are multiscale realization of Chebyshev moments (CMs). This multifractal spectrum is very well suited to extract meaningful structures on images of natural scenes, because these images have a multifractal character. Experiments with test images show some advantages of the proposed algorithm as compared to other widely used image enhancement algorithms. The main advantage of our algorithm is the following: the algorithm very well highlights image details during image contrast enhancement.

  6. High contrast computed tomography with synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Itai, Yuji; Takeda, Tohoru; Akatsuka, Takao; Maeda, Tomokazu; Hyodo, Kazuyuki; Uchida, Akira; Yuasa, Tetsuya; Kazama, Masahiro; Wu, Jin; Ando, Masami

    1995-02-01

    This article describes a new monochromatic x-ray CT system using synchrotron radiation with applications in biomedical diagnosis which is currently under development. The system is designed to provide clear images and to detect contrast materials at low concentration for the quantitative functional evaluation of organs in correspondence with their anatomical structures. In this system, with x-ray energy changing from 30 to 52 keV, images can be obtained to detect various contrast materials (iodine, barium, and gadolinium), and K-edge energy subtraction is applied. Herein, the features of the new system designed to enhance the advantages of SR are reported. With the introduction of a double-crystal monochromator, the high-order x-ray contamination is eliminated. The newly designed CCD detector with a wide dynamic range of 60 000:1 has a spatial resolution of 200 μm. The resulting image quality, which is expected to show improved contrast and spatial resolution, is currently under investigation.

  7. Contrast enhanced ultrasound of renal masses

    PubMed Central

    Ignee, Andre; Straub, Bernd; Schuessler, Gudrun; Dietrich, Christoph Frank

    2010-01-01

    Contrast enhanced ultrasound (CEUS) has gained clinical importance over the last years for the characterization of hepatic masses. Its role in extrahepatic indications has been investigated repeatedly but has been less comprehensively studied. Currently more than 50% of renal masses are incidentally diagnosed, mostly by B-mode ultrasound. The method of choice for characterization of renal lesions is contrast enhanced computed tomography (CECT). In the case of cystic lesions CECT refers to the Bosniak classification for cystic lesions to assess the risk of malignant behavior. The majority of masses are renal cell carcinoma, but the exact proportion is controversial. Disadvantages of CECT are a significant risk for patients with impaired renal function, allergic reactions and hyperthyroidism due to iodinated contrast agents. Several studies concerning CEUS for the characterization of both solid and cystic renal lesions have been published, but prospective multicenter studies are missing, the presented data being mainly descriptive. The aim of the this manuscript is to review the current literature for CEUS in renal masses, to summarize the available data and focus on possible concepts for studies in the future. PMID:21160736

  8. Bioinspired steel surfaces with extreme wettability contrast.

    PubMed

    Her, Eun Kyu; Ko, Tae-Jun; Lee, Kwang-Ryeol; Oh, Kyu Hwan; Moon, Myoung-Woon

    2012-04-28

    The exterior structures of natural organisms have continuously evolved by controlling wettability, such as the Namib Desert beetle, whose back has hydrophilic/hydrophobic contrast for water harvesting by mist condensation in dry desert environments, and some plant leaves that have hierarchical micro/nanostructures to collect or repel liquid water. In this work, we have provided a method for wettability contrast on alloy steels by both nano-flake or needle patterns and tuning of the surface energy. Steels were provided with hierarchical micro/nanostructures of Fe oxides by fluorination and by a subsequent catalytic reaction of fluorine ions on the steel surfaces in water. A hydrophobic material was deposited on the structured surfaces, rendering superhydrophobicity. Plasma oxidization induces the formation of superhydrophilic surfaces on selective regions surrounded by superhydrophobic surfaces. We show that wettability contrast surfaces align liquid water within patterned hydrophilic regions during the condensation process. Furthermore, this method could have a greater potential to align other liquids or living cells. PMID:22456538

  9. Noise analysis in laser speckle contrast imaging

    NASA Astrophysics Data System (ADS)

    Yuan, Shuai; Chen, Yu; Dunn, Andrew K.; Boas, David A.

    2010-02-01

    Laser speckle contrast imaging (LSCI) is becoming an established method for full-field imaging of blood flow dynamics in animal models. A reliable quantitative model with comprehensive noise analysis is necessary to fully utilize this technique in biomedical applications and clinical trials. In this study, we investigated several major noise sources in LSCI: periodic physiology noise, shot noise and statistical noise. (1) We observed periodic physiology noise in our experiments and found that its sources consist principally of motions induced by heart beats and/or ventilation. (2) We found that shot noise caused an offset of speckle contrast (SC) values, and this offset is directly related to the incident light intensity. (3) A mathematical model of statistical noise was also developed. The model indicated that statistical noise in speckle contrast imaging is related to the SC values and the total number of pixels used in the SC calculation. Our experimental results are consistent with theoretical predications, as well as with other published works.

  10. Acoustics of contrastive prosody in children

    NASA Astrophysics Data System (ADS)

    Patel, Rupal; Piel, Jordan; Grigos, Maria

    2005-04-01

    Empirical data on the acoustics of prosodic control in children is limited, particularly for linguistically contrastive tasks. Twelve children aged 4, 7, and 11 years were asked to produce two utterances ``Show Bob a bot'' (voiced consonants) and ``Show Pop a pot'' (voiceless consonants) 10 times each with emphasis placed on the second word (Bob/Pop) and 10 times with emphasis placed on the last word (bot/pot). A total of 40 utterances were analyzed per child. The following acoustic measures were obtained for each word within each utterance: average fundamental frequency (f0), peak f0, average intensity, peak intensity, and duration. Preliminary results suggest that 4 year olds are unable to modulate prosodic cues to signal the linguistic contrast. The 7 year olds, however, not only signaled the appropriate stress location, but did so with the most contrastive differences in f0, intensity, and duration, of all age groups. Prosodic differences between stressed and unstressed words were more pronounced for the utterance with voiced consonants. These findings suggest that the acoustics of linguistic prosody begin to differentiate between age 4 and 7 and may be highly influenced by changes in physiological control and flexibility that may also affect segmental features.

  11. MRI Contrasts in High Rank Rotating Frames

    PubMed Central

    Liimatainen, Timo; Hakkarainen, Hanne; Mangia, Silvia; Huttunen, Janne M.J.; Storino, Christine; Idiyatullin, Djaudat; Sorce, Dennis; Garwood, Michael; Michaeli, Shalom

    2014-01-01

    Purpose MRI relaxation measurements are performed in the presence of a fictitious magnetic field in the recently described technique known as RAFF (Relaxation Along a Fictitious Field). This method operates in the 2nd rotating frame (rank n = 2) by utilizing a non-adiabatic sweep of the radiofrequency effective field to generate the fictitious magnetic field. In the present study, the RAFF method is extended for generating MRI contrasts in rotating frames of ranks 1 ≤ n ≤ 5. The developed method is entitled RAFF in rotating frame of rank n (RAFFn). Methods RAFFn pulses were designed to generate fictitious fields that allow locking of magnetization in rotating frames of rank n. Contrast generated with RAFFn was studied using Bloch-McConnell formalism together with experiments on human and rat brains. Results Tolerance to B0 and B1 inhomogeneities and reduced specific absorption rate with increasing n in RAFFn were demonstrated. Simulations of exchange-induced relaxations revealed enhanced sensitivity of RAFFn to slow exchange. Consistent with such feature, an increased grey/white matter contrast was observed in human and rat brain as n increased. Conclusion RAFFn is a robust and safe rotating frame relaxation method to access slow molecular motions in vivo. PMID:24523028

  12. Allergic reactions to iodinated contrast media: premedication considerations for patients at risk.

    PubMed

    Schopp, Jennifer G; Iyer, Ramesh S; Wang, Carolyn L; Petscavage, Jonelle M; Paladin, Angelisa M; Bush, William H; Dighe, Manjiri K

    2013-08-01

    The objectives of this article are to review allergy-type reactions to iodinated contrast media and the protocols utilized to prevent or reduce the occurrence of these adverse reactions in high-risk patients. We will begin by discussing the types or classifications of the adverse reactions to iodinated contrast media. We will then discuss reaction mechanisms, identify the patients at highest risk for adverse reactions, and clarify common misperceptions about the risk. Finally, we will discuss the actions of the medications used to help reduce or prevent allergy-type reactions to iodinated contrast media, the protocols used to help reduce or prevent contrast reactions in high-risk patients, and the potential side effects of these medications. We will also discuss the high-risk patient who has received premedication due to a prior index reaction and discuss the risk of having a subsequent reaction, termed "breakthrough reaction." Identifying patient at high risk for an "allergy-type" reaction to contrast media is an essential task of the radiologist. Prevention of or reduction of the risk of an adverse reaction is critical to patient safety. If an examination can be performed without contrast in a patient at high risk for an allergy-type reaction, it may be appropriate to avoid contrast. However, there are situations where contrast media is necessary, and the radiologist plays a vital role in preventing or mitigating an allergy-type reaction. PMID:23430296

  13. Contrast medium usage reduction in abdominal computed tomography by using high-iodinated concentration contrast medium

    NASA Astrophysics Data System (ADS)

    Suwannasri, A.; Kaewlai, R.; Asavaphatiboon, S.

    2016-03-01

    This study was to determine if administration of a low volume high-concentration iodinated contrast medium can preserve image quality in comparison with regular-concentration intravenous contrast medium in patient undergoing contrast-enhancement abdominal computed tomography (CT). Eighty-four patients were randomly divided into 3 groups of similar iodine delivery rate; A: 1.2 cc/kg of iomeprol-400, B: 1.0 cc/kg of iomeprol-400 and C: 1.5 cc/kg of ioversol-350. Contrast enhancement of the liver parenchyma, pancreas and aorta was quantitatively measured in Hounsfield units and qualitative assessed by a radiologist. T-test was used to evaluate contrast enhancement, and Chi-square test was used to evaluate qualitative image assessment, at significance level of 0.05 with 95% confidence intervals. There were no statistically significant differences in contrast enhancement of liver parenchyma and pancreas between group A and group C in both quantitative and qualitative analyses. Group C showed superior vascular enhancement to group A and B on quantitative analysis.

  14. Gadolinium nanoparticles and contrast agent as radiation sensitizers.

    PubMed

    Taupin, Florence; Flaender, Mélanie; Delorme, Rachel; Brochard, Thierry; Mayol, Jean-François; Arnaud, Josiane; Perriat, Pascal; Sancey, Lucie; Lux, François; Barth, Rolf F; Carrière, Marie; Ravanat, Jean-Luc; Elleaume, Hélène

    2015-06-01

    The goal of the present study was to evaluate and compare the radiosensitizing properties of gadolinium nanoparticles (NPs) with the gadolinium contrast agent (GdCA) Magnevist(®) in order to better understand the mechanisms by which they act as radiation sensitizers. This was determined following either low energy synchrotron irradiation or high energy gamma irradiation of F98 rat glioma cells exposed to ultrasmall gadolinium NPs (GdNPs, hydrodynamic diameter of 3 nm) or GdCA. Clonogenic assays were used to quantify cell survival after irradiation in the presence of Gd using monochromatic x-rays with energies in the 25 keV-80 keV range from a synchrotron and 1.25 MeV gamma photons from a cobalt-60 source. Radiosensitization was demonstrated with both agents in combination with X-irradiation. At the same concentration (2.1 mg mL(-1)), GdNPS had a greater effect than GdCA. The maximum sensitization-enhancement ratio at 4 Gy (SER4Gy) was observed at an energy of 65 keV for both the nanoparticles and the contrast agent (2.44   ±   0.33 and 1.50   ±   0.20, for GdNPs and GdCA, respectively). At a higher energy (1.25 MeV), radiosensitization only was observed with GdNPs (1.66   ±   0.17 and 1.01   ±   0.11, for GdNPs and GdCA, respectively). The radiation dose enhancements were highly 'energy dependent' for both agents. Secondary-electron-emission generated after photoelectric events appeared to be the primary mechanism by which Gd contrast agents functioned as radiosensitizers. On the other hand, other biological mechanisms, such as alterations in the cell cycle may explain the enhanced radiosensitizing properties of GdNPs. PMID:25988839

  15. Gadolinium nanoparticles and contrast agent as radiation sensitizers

    NASA Astrophysics Data System (ADS)

    Taupin, Florence; Flaender, Mélanie; Delorme, Rachel; Brochard, Thierry; Mayol, Jean-François; Arnaud, Josiane; Perriat, Pascal; Sancey, Lucie; Lux, François; Barth, Rolf F.; Carrière, Marie; Ravanat, Jean-Luc; Elleaume, Hélène

    2015-06-01

    The goal of the present study was to evaluate and compare the radiosensitizing properties of gadolinium nanoparticles (NPs) with the gadolinium contrast agent (GdCA) Magnevist® in order to better understand the mechanisms by which they act as radiation sensitizers. This was determined following either low energy synchrotron irradiation or high energy gamma irradiation of F98 rat glioma cells exposed to ultrasmall gadolinium NPs (GdNPs, hydrodynamic diameter of 3 nm) or GdCA. Clonogenic assays were used to quantify cell survival after irradiation in the presence of Gd using monochromatic x-rays with energies in the 25 keV-80 keV range from a synchrotron and 1.25 MeV gamma photons from a cobalt-60 source. Radiosensitization was demonstrated with both agents in combination with X-irradiation. At the same concentration (2.1 mg mL-1), GdNPS had a greater effect than GdCA. The maximum sensitization-enhancement ratio at 4 Gy (SER4Gy) was observed at an energy of 65 keV for both the nanoparticles and the contrast agent (2.44   ±   0.33 and 1.50   ±   0.20, for GdNPs and GdCA, respectively). At a higher energy (1.25 MeV), radiosensitization only was observed with GdNPs (1.66   ±   0.17 and 1.01   ±   0.11, for GdNPs and GdCA, respectively). The radiation dose enhancements were highly ‘energy dependent’ for both agents. Secondary-electron-emission generated after photoelectric events appeared to be the primary mechanism by which Gd contrast agents functioned as radiosensitizers. On the other hand, other biological mechanisms, such as alterations in the cell cycle may explain the enhanced radiosensitizing properties of GdNPs.

  16. Quick contrast sensitivity measurements in the periphery.

    PubMed

    Rosén, Robert; Lundström, Linda; Venkataraman, Abinaya Priya; Winter, Simon; Unsbo, Peter

    2014-01-01

    Measuring the contrast sensitivity function (CSF) in the periphery of the eye is complicated. The lengthy measurement time precludes all but the most determined subjects. The aim of this study was to implement and evaluate a faster routine based on the quick CSF method (qCSF) but adapted to work in the periphery. Additionally, normative data is presented on neurally limited peripheral CSFs. A peripheral qCSF measurement using 100 trials can be performed in 3 min. The precision and accuracy were tested for three subjects under different conditions (number of trials, peripheral angles, and optical corrections). The precision for estimates of contrast sensitivity at individual spatial frequencies was 0.07 log units when three qCSF measurements of 100 trials each were averaged. Accuracy was estimated by comparing the qCSF results with a more traditional measure of CSF. Average accuracy was 0.08 log units with no systematic error. In the second part of the study, we collected three CSFs of 100 trials for six persons in the 20° nasal, temporal, inferior, and superior visual fields. The measurements were performed in an adaptive optics system running in a continuous closed loop. The Tukey HSD test showed significant differences (p < 0.05) between all fields except between the nasal and the temporal fields. Contrast sensitivity was higher in the horizontal fields, and the inferior field was better than the superior. This modified qCSF method decreases the measurement time significantly and allows otherwise unfeasible studies of the peripheral CSF. PMID:24993017

  17. PROPOSED CARCINOGENIC MECHANISMS FOR ARSENIC

    EPA Science Inventory

    PROPOSED CARCINOGENIC MECHANISMS FOR ARSENIC.

    Arsenic is a human carcinogen in skin, lung, liver, urinary bladder and kidney. In contrast,
    there is no accepted experimental animal model of inorganic arsenic carcinogenesis.
    Proposed mechanisms/modes of action for a...

  18. Vessel contrast enhancement in hyperspectral images

    NASA Astrophysics Data System (ADS)

    Bjorgan, Asgeir; Denstedt, Martin; Milanič, Matija; Paluchowski, Lukasz A.; Randeberg, Lise L.

    2015-03-01

    Imaging of vessel structures can be useful for investigation of endothelial function, angiogenesis and hyper-vascularization. This can be challenging for hyperspectral tissue imaging due to photon scattering and absorption in other parts of the tissue. Real-time processing techniques for enhancement of vessel contrast in hyperspectral tissue images were investigated. Wavelet processing and an inverse diffusion model were employed, and compared to band ratio metrics and statistical methods. A multiscale vesselness filter was applied for further enhancement. The results show that vessel structures in hyperspectral images can be enhanced and characterized using a combination of statistical, numerical and more physics informed models.

  19. Myocardial perfusion imaging using contrast echocardiography.

    PubMed

    Pathan, Faraz; Marwick, Thomas H

    2015-01-01

    Microbubbles are an excellent intravascular tracer, and both the rate of myocardial opacification (analogous to coronary microvascular perfusion) and contrast intensity (analogous to myocardial blood volume) provide unique insights into myocardial perfusion. A strong evidence base has been accumulated to show comparability with nuclear perfusion imaging and incremental diagnostic and prognostic value relative to wall motion analysis. This technique also provides the possibility to measure myocardial perfusion at the bedside. Despite all of these advantages, the technique is complicated, technically challenging, and has failed to scale legislative and financial hurdles. The development of targeted imaging and therapeutic interventions will hopefully rekindle interest in this interesting modality. PMID:25817740

  20. Differential phase contrast: An integral perspective

    NASA Astrophysics Data System (ADS)

    Lubk, A.; Zweck, J.

    2015-02-01

    Differential phase contrast (DPC) in a scanning transmission electron microscope is a widely employed technique for probing electromagnetic fields on the nanoscale. We show that the DPC signal corresponds to the averaged lateral probability current of the scattered electron probe. Based on this result we discuss the interpretation of DPC in terms of the projected electric and magnetic fields and the influence of experimental parameters thereon. We further show that DPC can be interpreted as a quantum weak measurement and that the reciprocal broad beam illumination technique is given by an astigmatic transport of intensity reconstruction.

  1. Photoacoustic phasoscopy super-contrast imaging

    SciTech Connect

    Gao, Fei; Feng, Xiaohua; Zheng, Yuanjin

    2014-05-26

    Phasoscopy is a recently proposed concept correlating electromagnetic (EM) absorption and scattering properties based on energy conservation. Phase information can be extracted from EM absorption induced acoustic wave and scattered EM wave for biological tissue characterization. In this paper, an imaging modality, termed photoacoustic phasoscopy imaging (PAPS), is proposed and verified experimentally based on phasoscopy concept with laser illumination. Both endogenous photoacoustic wave and scattered photons are collected simultaneously to extract the phase information. The PAPS images are then reconstructed on vessel-mimicking phantom and ex vivo porcine tissues to show significantly improved contrast than conventional photoacoustic imaging.

  2. Contrast media in cardiovascular magnetic resonance.

    PubMed

    Lombardi, Massimo; Aquaro, Giovanni; Favilli, Brunella

    2005-01-01

    Among the available imaging techniques, Magnetic Resonance Imaging (MRI) is gaining an increasing role in the cardiologic setting because its specific properties such as the use of non ionising energies, the natural strong contrast between different tissues, the absence of spatial limitations, the good spatial and temporal resolution, the reduced operator dependency. To further improve the images quality and the histopathologic characterisation of tissues the use of contrast media (molecules containing gadolinium, manganese, iron, dysprosium ions) has been proposed both in the experimental and in the clinical settings. Among these ions gadolinium, which having 7 odd electrons in the external orbit has a strong magnetic momentum, is the most used. Gadolinium by itself is extremely toxic but once it is linked with a chelanting agent such as DTPA (Dietilen-Triamin-Penta-Acetic acid) the resulting complex shows a very low toxicity. The number of Gadolinium based compound is growing together with the use of contrast agents in MRI. These contrast agents are routinely used to perform Magnetic Resonance Angiography (MRA) and to a better definition of several cardiac diseases such as the presence of a intra- or paracardiac mass, the evaluation of myocardial perfusion and the evaluation of viability. Both the latter applications have relevant clinical implications. In fact the assessment of myocardial perfusion is one of the most used approach for detecting inducible myocardial ischemia due to major coronary artery disease or to assess the presence of a microvascular disease. The presence and the extent of viable myocardium is deeply modifying the clinical decision making as this viable tissue can recruit a normal function spontaneously or after revascularisation. Furthermore, the extent of viable myocardium has a strong correlation with negative prognosis. Clinical events are also time related to the detection of viable tissue. These evidences imply that the diagnostic

  3. The Uppsala Contrast Sensitivity Test (UCST): A fast strategy for clinical assessment of contrast sensitivity

    NASA Astrophysics Data System (ADS)

    Malmqvist, Lars D.; Söderberg, Per G.

    2014-02-01

    Routine clinical measurement of spectral contrast sensitivity is hampered by the time consumption of current methods. We are developing a system that allows instantaneous measurement of spectral contrast sensitivity. The UCST system consists of custom software running on an iPad connected to a calibrated TFT-monitor. Twenty healthy subjects were consecutively randomized to have their spectral contrast sensitivity measured with the UCST strategy or with a Vistech VCTS 6500 chart. The examination time and the spectral contrast sensitivity, respectively, were recorded for each eye in each subject. The Vistech strategy resulted in a more extended mean examination time (CI-Vistech:+/- (0.95) = 87 +/-27 s, d.f. = 9) than the UCST strategy (CI-UCST:μ (0.95) = 13 +/-4 s, d.f. = 9), and the estimated mean difference between the two strategies indicated a difference in examination time (CI-difference:μ (0.95) = [47;106] s, d.f. = 18). The overall contrast sensitivity for each group was estimated as the contrast sensitivities for the spatial frequencies sampled, integrated over the spatial frequency band sampled. The Vistech strategy resulted in a higher estimated mean overall contrast sensitivity (CI-Vistech:μ (0.95) = 116+/-24 log rel.·log [c.·deg-1], d.f. = 9) than the UCST strategy (CIUCST: μ (0.95) = 74+/-14 log rel.·log [c.·deg-1], d.f. = 9), and the estimated mean difference between the two strategies indicated a difference in overall contrast sensitivity (CI-difference:μ (0.95) = [15;68] log rel.·log [c.·deg-1]), d.f. = 18). It is concluded that the UCST strategy measures spectral contrast sensitivity on the order of 7 times faster than the Vistech strategy. The slightly lower overall contrast sensitivity recorded for the UCST strategy appeared to be due to a limitation in dynamic range that can be overcome with improved design.

  4. Cumulative phase delay imaging - A new contrast enhanced ultrasound modality

    SciTech Connect

    Demi, Libertario Sloun, Ruud J. G. van; Mischi, Massimo; Wijkstra, Hessel

    2015-10-28

    Recently, a new acoustic marker for ultrasound contrast agents (UCAs) has been introduced. A cumulative phase delay (CPD) between the second harmonic and fundamental pressure wave field components is in fact observable for ultrasound propagating through UCAs. This phenomenon is absent in the case of tissue nonlinearity and is dependent on insonating pressure and frequency, UCA concentration, and propagation path length through UCAs. In this paper, ultrasound images based on this marker are presented. The ULA-OP research platform, in combination with a LA332 linear array probe (Esaote, Firenze Italy), were used to image a gelatin phantom containing a PVC plate (used as a reflector) and a cylindrical cavity measuring 7 mm in diameter (placed in between the observation point and the PVC plate). The cavity contained a 240 µL/L SonoVueO{sup ®} UCA concentration. Two insonating frequencies (3 MHz and 2.5 MHz) were used to scan the gelatine phantom. A mechanical index MI = 0.07, measured in water at the cavity location with a HGL-0400 hydrophone (Onda, Sunnyvale, CA), was utilized. Processing the ultrasound signals backscattered from the plate, ultrasound images were generated in a tomographic fashion using the filtered back-projection method. As already observed in previous studies, significantly higher CPD values are measured when imaging at a frequency of 2.5 MHz, as compared to imaging at 3 MHz. In conclusion, these results confirm the applicability of the discussed CPD as a marker for contrast imaging. Comparison with standard contrast-enhanced ultrasound imaging modalities will be the focus of future work.

  5. Cumulative phase delay imaging - A new contrast enhanced ultrasound modality

    NASA Astrophysics Data System (ADS)

    Demi, Libertario; van Sloun, Ruud J. G.; Wijkstra, Hessel; Mischi, Massimo

    2015-10-01

    Recently, a new acoustic marker for ultrasound contrast agents (UCAs) has been introduced. A cumulative phase delay (CPD) between the second harmonic and fundamental pressure wave field components is in fact observable for ultrasound propagating through UCAs. This phenomenon is absent in the case of tissue nonlinearity and is dependent on insonating pressure and frequency, UCA concentration, and propagation path length through UCAs. In this paper, ultrasound images based on this marker are presented. The ULA-OP research platform, in combination with a LA332 linear array probe (Esaote, Firenze Italy), were used to image a gelatin phantom containing a PVC plate (used as a reflector) and a cylindrical cavity measuring 7 mm in diameter (placed in between the observation point and the PVC plate). The cavity contained a 240 µL/L SonoVueO® UCA concentration. Two insonating frequencies (3 MHz and 2.5 MHz) were used to scan the gelatine phantom. A mechanical index MI = 0.07, measured in water at the cavity location with a HGL-0400 hydrophone (Onda, Sunnyvale, CA), was utilized. Processing the ultrasound signals backscattered from the plate, ultrasound images were generated in a tomographic fashion using the filtered back-projection method. As already observed in previous studies, significantly higher CPD values are measured when imaging at a frequency of 2.5 MHz, as compared to imaging at 3 MHz. In conclusion, these results confirm the applicability of the discussed CPD as a marker for contrast imaging. Comparison with standard contrast-enhanced ultrasound imaging modalities will be the focus of future work.

  6. Proton shock acceleration using a high contrast high intensity laser

    NASA Astrophysics Data System (ADS)

    Gauthier, Maxence; Roedel, Christian; Kim, Jongjin; Aurand, Bastian; Curry, Chandra; Goede, Sebastian; Propp, Adrienne; Goyon, Clement; Pak, Art; Kerr, Shaun; Ramakrishna, Bhuvanesh; Ruby, John; William, Jackson; Glenzer, Siegfried

    2015-11-01

    Laser-driven proton acceleration is a field of intense research due to the interesting characteristics of this novel particle source including high brightness, high maximum energy, high laminarity, and short duration. Although the ion beam characteristics are promising for many future applications, such as in the medical field or hybrid accelerators, the ion beam generated using TNSA, the acceleration mechanism commonly achieved, still need to be significantly improved. Several new alternative mechanisms have been proposed such as collisionless shock acceleration (CSA) in order to produce a mono-energetic ion beam favorable for those applications. We report the first results of an experiment performed with the TITAN laser system (JLF, LLNL) dedicated to the study of CSA using a high intensity (5x1019W/cm2) high contrast ps laser pulse focused on 55 μm thick CH and CD targets. We show that the proton spectrum generated during the interaction exhibits high-energy mono-energetic features along the laser axis, characteristic of a shock mechanism.

  7. Simultaneous amplitude-contrast and phase-contrast surface plasmon resonance imaging by use of digital holography

    PubMed Central

    Li, Shiping; Zhong, Jingang

    2012-01-01

    The surface plasmon resonance imaging technique provides a tool that allows high-throughput analysis and real-time kinetic measurement. A simultaneous amplitude-contrast and phase-contrast surface plasmon resonance imaging method is presented. The amplitude-contrast and phase-contrast images are simultaneously obtained by use of digital holography. The detection sensitivity of amplitude-contrast imaging and phase-contrast imaging can compensate for each other. Thus, the detectable sample components may cover a wider range of refractive index values for the simultaneous amplitude-contrast and phase-contrast imaging method than for the phase-contrast imaging method or amplitude-contrast imaging method. A detailed description of the theory and an experiment of monitoring the evaporation process of a drop of NaCl injection in real time are presented. In addition, the amplitude-contrast image has less coherent noise by digital holography. PMID:23243569

  8. Photoacoustic cell for ultrasound contrast agent characterization.

    PubMed

    Alippi, A; Bettucci, A; Biagioni, A; D'Orazio, A; Germano, M; Passeri, D

    2010-10-01

    Photoacoustics has emerged as a tool for the study of liquid gel suspension behavior and has been recently employed in a number of new biomedical applications. In this paper, a photoacoustic sensor is presented which was designed and realized for analyzing photothermal signals from solutions filled with microbubbles, commonly used as ultrasound contrast agents in echographic imaging techniques. It is a closed cell device, where photothermal volume variation of an aqueous solution produces the periodic deflection of a thin membrane closing the cell at the end of a short pipe. The cell then acts as a Helmholtz resonator, where the displacement of the membrane is measured through a laser probe interferometer, whereas photoacoustic signal is generated by a laser chopped light beam impinging onto the solution through a glass window. Particularly, the microbubble shell has been modeled through an effective surface tension parameter, which has been then evaluated from experimental data through the shift of the resonance frequencies of the photoacoustic sensor. This shift of the resonance frequencies of the photoacoustic sensor caused by microbubble solutions is high enough for making such a cell a reliable tool for testing ultrasound contrast agent, particularly for bubble shell characterization. PMID:21034110

  9. Seeing the unseen with localized optical contrast

    NASA Astrophysics Data System (ADS)

    Suran, Swathi; Bharadwaj, Krishna; Raghavan, Srinivasan; Varma, Manoj M.

    2016-03-01

    Optical wide-field imaging of sub-diffraction limit nanostructures is of interest in a wide array of applications. In applications where the nanostructures to be visualized are well isolated, a high enough optical contrast is sufficient to detect these. Here we demonstrate a technique to visualize nanoscale features, such as grain boundaries in Chemical Vapor Deposited (CVD) single layer graphene, which are just a few atom length defects, using regular bright field optical microscopy. This remarkably low lateral length scale was imaged using of a special thin film structure consisting of a water-soluble thin film layer deposited on a metal substrate, which produces a strong color change as a function of the film thickness. Small local water transport differences in the graphene layer result in thickness variation of the underlying thin film due to its solubility in water and produces color contrast readily observable under a normal brightfield optical microscope with the naked eye. We demonstrate the use of this technique for direct optical visualization of grain boundaries in graphene as wide as 2-5 nm and sub-100 nm photoresist lines. By using super-resolution image processing algorithms, we may be able to detect structure even smaller in size than currently achieved. We believe that this technique can be extended to single molecule detection.

  10. MRI contrast enhancement using Magnetic Carbon Nanoparticles

    NASA Astrophysics Data System (ADS)

    Chaudhary, Rakesh P.; Kangasniemi, Kim; Takahashi, Masaya; Mohanty, Samarendra K.; Koymen, Ali R.; Department of Physics, University of Texas at Arlington Team; University of Texas Southwestern Medical Center Team

    2014-03-01

    In recent years, nanotechnology has become one of the most exciting forefront fields in cancer diagnosis and therapeutics such as drug delivery, thermal therapy and detection of cancer. Here, we report development of core (Fe)-shell (carbon) nanoparticles with enhanced magnetic properties for contrast enhancement in MRI imaging. These new classes of magnetic carbon nanoparticles (MCNPs) are synthesized using a bottom-up approach in various organic solvents, using the electric plasma discharge generated in the cavitation field of an ultrasonic horn. Gradient echo MRI images of well-dispersed MCNP-solutions (in tube) were acquired. For T2 measurements, a multi echo spin echo sequence was performed. From the slope of the 1/T2 versus concentration plot, the R2 value for different CMCNP-samples was measured. Since MCNPs were found to be extremely non-reactive, and highly absorbing in NIR regime, development of carbon-based MRI contrast enhancement will allow its simultaneous use in biomedical applications. We aim to localize the MCNPs in targeted tissue regions by external DC magnetic field, followed by MRI imaging and subsequent photothermal therapy.

  11. High contrast laser marking of alumina

    NASA Astrophysics Data System (ADS)

    Penide, J.; Quintero, F.; Riveiro, A.; Fernández, A.; del Val, J.; Comesaña, R.; Lusquiños, F.; Pou, J.

    2015-05-01

    Alumina serves as raw material for a broad range of advanced ceramic products. These elements should usually be identified by some characters or symbols printed directly on them. In this sense, laser marking is an efficient, reliable and widely implemented process in industry. However, laser marking of alumina still leads to poor results since the process is not able to produce a dark mark, yielding bad contrast. In this paper, we present an experimental study on the process of marking alumina by three different lasers working in two wavelengths: 1064 nm (Near-infrared) and 532 nm (visible, green radiation). A colorimetric analysis has been carried out in order to compare the resulting marks and its contrast. The most suitable laser operating conditions were also defined and are reported here. Moreover, the physical process of marking by NIR lasers is discussed in detail. Field Emission Scanning Electron Microscopy, High Resolution Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy were also employed to analyze the results. Finally, we propose an explanation for the differences of the coloration induced under different atmospheres and laser parameters. We concluded that the atmosphere is the key parameter, being the inert one the best choice to produce the darkest marks.

  12. Quantitative phase-contrast confocal microscope

    PubMed Central

    Liu, Changgeng; Marchesini, Stefano; Kim, Myung K.

    2014-01-01

    We present a quantitative phase-contrast confocal microscope (QPCCM) by combining a line-scanning confocal system with digital holography (DH). This combination can merge the merits of these two different imaging modalities. High-contrast intensity images with low coherent noise, and the optical sectioning capability are made available due to the confocality. Phase profiles of the samples become accessible thanks to DH. QPCCM is able to quantitatively measure the phase variations of optical sections of the opaque samples and has the potential to take high-quality intensity and phase images of non-opaque samples such as many biological samples. Because each line scan is recorded by a hologram that may contain the optical aberrations of the system, it opens avenues for a variety of numerical aberration compensation methods and development of full digital adaptive optics confocal system to emulate current hardware-based adaptive optics system for biomedical imaging, especially ophthalmic imaging. Preliminary experiments with a microscope objective of NA 0.65 and 40 × on opaque samples are presented to demonstrate this idea. The measured lateral and axial resolutions of the intensity images from the current system are ~0.64μm and ~2.70μm respectively. The noise level of the phase profile by QPCCM is ~2.4nm which is better than the result by DH. PMID:25089404

  13. Intraoperative imaging using intravascular contrast agent

    NASA Astrophysics Data System (ADS)

    Watson, Jeffrey R.; Martirosyan, Nikolay; Garland, Summer; Lemole, G. Michael; Romanowski, Marek

    2016-03-01

    Near-infrared (NIR) contrast agents are becoming more frequently studied in medical imaging due to their advantageous characteristics, most notably the ability to capture near-infrared signal across the tissue and the safety of the technique. This produces a need for imaging technology that can be specific for both the NIR dye and medical application. Indocyanine green (ICG) is currently the primary NIR dye used in neurosurgery. Here we report on using the augmented microscope we described previously for image guidance in a rat glioma resection. Luc-C6 cells were implanted in a rat in the left-frontal lobe and grown for 22 days. Surgical resection was performed by a neurosurgeon using augmented microscopy guidance with ICG contrast. Videos and images were acquired to evaluate image quality and resection margins. ICG accumulated in the tumor tissue due to enhanced permeation and retention from the compromised bloodbrain- barrier. The augmented microscope was capable of guiding the rat glioma resection and intraoperatively highlighted tumor tissue regions via ICG fluorescence under normal illumination of the surgical field.

  14. HCIT Broadband Contrast Performance Sensitivity Studies

    NASA Technical Reports Server (NTRS)

    Sidick, Erkin; Shaklan, Stuart; Balasubramanian, Kunjithapatham

    2012-01-01

    The High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory employs a broadband wavefront correction algorithm called Electric Field Conjugation (EFC) to obtain the required 10-10 contrast. This algorithm works with one deformable mirror (DM) to estimate the electric-field to be controlled, and with one or multiple DM's to create a "darkhole" in a predefined region of the image plane where terrestrial planets would be found. We have investigated the effects of absorbing dust particles on a flat optic, absorbing spots on the occulting mask, dead actuators on the DM, and the effects of control bandwidth on the efficiency of the EFC algorithm in a Lyot coronagraph configuration. The structural design of the optical system as well as the parameters of various optical elements used in the analysis is drawn from those of the HCIT system that have been implemented with one DM. The simulation takes into account the surface errors of various optical elements. Results of some of these studies have been verified by actual measurements.

  15. Quantitative contrast-enhanced optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Winetraub, Yonatan; SoRelle, Elliott D.; Liba, Orly; de la Zerda, Adam

    2016-01-01

    We have developed a model to accurately quantify the signals produced by exogenous scattering agents used for contrast-enhanced Optical Coherence Tomography (OCT). This model predicts distinct concentration-dependent signal trends that arise from the underlying physics of OCT detection. Accordingly, we show that real scattering particles can be described as simplified ideal scatterers with modified scattering intensity and concentration. The relation between OCT signal and particle concentration is approximately linear at concentrations lower than 0.8 particle per imaging voxel. However, at higher concentrations, interference effects cause signal to increase with a square root dependence on the number of particles within a voxel. Finally, high particle concentrations cause enough light attenuation to saturate the detected signal. Predictions were validated by comparison with measured OCT signals from gold nanorods (GNRs) prepared in water at concentrations ranging over five orders of magnitude (50 fM to 5 nM). In addition, we validated that our model accurately predicts the signal responses of GNRs in highly heterogeneous scattering environments including whole blood and living animals. By enabling particle quantification, this work provides a valuable tool for current and future contrast-enhanced in vivo OCT studies. More generally, the model described herein may inform the interpretation of detected signals in modalities that rely on coherence-based detection or are susceptible to interference effects.

  16. Global Contrast Based Salient Region Detection.

    PubMed

    Cheng, Ming-Ming; Mitra, Niloy J; Huang, Xiaolei; Torr, Philip H S; Hu, Shi-Min

    2015-03-01

    Automatic estimation of salient object regions across images, without any prior assumption or knowledge of the contents of the corresponding scenes, enhances many computer vision and computer graphics applications. We introduce a regional contrast based salient object detection algorithm, which simultaneously evaluates global contrast differences and spatial weighted coherence scores. The proposed algorithm is simple, efficient, naturally multi-scale, and produces full-resolution, high-quality saliency maps. These saliency maps are further used to initialize a novel iterative version of GrabCut, namely SaliencyCut, for high quality unsupervised salient object segmentation. We extensively evaluated our algorithm using traditional salient object detection datasets, as well as a more challenging Internet image dataset. Our experimental results demonstrate that our algorithm consistently outperforms 15 existing salient object detection and segmentation methods, yielding higher precision and better recall rates. We also show that our algorithm can be used to efficiently extract salient object masks from Internet images, enabling effective sketch-based image retrieval (SBIR) via simple shape comparisons. Despite such noisy internet images, where the saliency regions are ambiguous, our saliency guided image retrieval achieves a superior retrieval rate compared with state-of-the-art SBIR methods, and additionally provides important target object region information. PMID:26353262

  17. Photoacoustic cell for ultrasound contrast agent characterization

    NASA Astrophysics Data System (ADS)

    Alippi, A.; Bettucci, A.; Biagioni, A.; D'Orazio, A.; Germano, M.; Passeri, D.

    2010-10-01

    Photoacoustics has emerged as a tool for the study of liquid gel suspension behavior and has been recently employed in a number of new biomedical applications. In this paper, a photoacoustic sensor is presented which was designed and realized for analyzing photothermal signals from solutions filled with microbubbles, commonly used as ultrasound contrast agents in echographic imaging techniques. It is a closed cell device, where photothermal volume variation of an aqueous solution produces the periodic deflection of a thin membrane closing the cell at the end of a short pipe. The cell then acts as a Helmholtz resonator, where the displacement of the membrane is measured through a laser probe interferometer, whereas photoacoustic signal is generated by a laser chopped light beam impinging onto the solution through a glass window. Particularly, the microbubble shell has been modeled through an effective surface tension parameter, which has been then evaluated from experimental data through the shift of the resonance frequencies of the photoacoustic sensor. This shift of the resonance frequencies of the photoacoustic sensor caused by microbubble solutions is high enough for making such a cell a reliable tool for testing ultrasound contrast agent, particularly for bubble shell characterization.

  18. Contrast Driven Elastica for Image Segmentation.

    PubMed

    El-Zehiry, Noha Youssry; Grady, Leo

    2016-06-01

    Minimization of boundary curvature is a classic regularization technique for image segmentation in the presence of noisy image data. Techniques for minimizing curvature have historically been derived from gradient descent methods which could be trapped by a local minimum and, therefore, required a good initialization. Recently, combinatorial optimization techniques have overcome this barrier by providing solutions that can achieve a global optimum. However, curvature regularization methods can fail when the true object has high curvature. In these circumstances, existing methods depend on a data term to overcome the high curvature of the object. Unfortunately, the data term may be ambiguous in some images, which causes these methods also to fail. To overcome these problems, we propose a contrast driven elastica model (including curvature), which can accommodate high curvature objects and an ambiguous data model. We demonstrate that we can accurately segment extremely challenging synthetic and real images with ambiguous data discrimination, poor boundary contrast, and sharp corners. We provide a quantitative evaluation of our segmentation approach when applied to a standard image segmentation data set. PMID:27019488

  19. Contrast optimization in broadband polarimetric imaging

    NASA Astrophysics Data System (ADS)

    Thomas, Lijo; Hu, Haofeng; Boffety, Matthieu; Goudail, François

    2016-05-01

    For the sake of polarimetric accuracy, polarization imaging systems based on liquid crystal modulators often work at one given wavelength due to the strong chromatic properties of the liquid crystal retarders. This often requires the use of narrowband filters which reduces the amount of light in the system and thus the signal-to-noise ratio. For applications where the main parameter of interest is the target/background discriminability rather than polarimetric accuracy, spectral filtering may not be the best option. In this work, we investigate the impact of broadening the spectrum of the light entering the system on the discriminability performance of passive and active polarimetric systems. Through simulations, we show that broadening the bandwidth of the illumination can increase the contrast between two regions, as the increase of light flux compensates for the loss of polarimetric precision. Moreover, we show that taking into account the chromatic characteristics of the components of the imaging system can further enhance the contrast. We validate these findings through experiments in passive and active configurations, and demonstrate that the illumination bandwidth can be seen as an additional parameter to optimize polarimetric imaging set-ups.

  20. Papers and Studies in Contrastive Linguistics. Volume Twenty.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    Papers on contrastive linguistics in this volume include: "Contrastive Discourse Analysis in Language Usage" (Juliane House); "Typology and Contrastive Analysis" (Vlasta Strakova); "On the Tenability of the Notion 'Pragmatic Equivalence' in Contrastive Analysis" (Karol Janicki); "On the Relevance of Phonetic, Phonological, and Morphological Levels…

  1. The Grammatical Theory of Contrastive Analysis: A New Approach.

    ERIC Educational Resources Information Center

    Anwar, Mohamed Sami

    This work asserts that contrastive analysis should be regarded as a technique of research and not limited to error prediction and material preparation. Introductory observations are made on the state of the field, the domain of contrastive analysis, contrastive analysis and transfer, and contrastive analysis and foreign language instruction. In…

  2. Papers and Studies in Contrastive Linguistics. Volume Eighteen.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.; Drozdzial, Krystyna, Ed.

    A collection of 14 papers in contrastive linguistics includes: "Some Comments on Language Data in Contrastive Analysis" (Ruta Nagucka); "Contrastive Sociolinguistics Reconsidered" (Karol Janicki); "Variations in Polish Nasal /e/: A Contribution to the Development of Contrastive Sociolinguistic Methodology" (Jane Johnson); "Languages in Contact and…

  3. Motion corrected photoacoustic difference imaging of fluorescent contrast agents

    NASA Astrophysics Data System (ADS)

    Märk, Julia; Wagener, Asja; Pönick, Sarah; Grötzinger, Carsten; Zhang, Edward; Laufer, Jan

    2016-03-01

    In fluorophores, such as exogenous dyes and genetically expressed proteins, the excited state lifetime can be modulated using pump-probe excitation at wavelengths corresponding to the absorption and fluorescence spectra. Simultaneous pump-probe pulses induce stimulated emission (SE) which, in turn, modulates the thermalized energy, and hence the photoacoustic (PA) signal amplitude. For time-delayed pulses, by contrast, SE is suppressed. Since this is not observed in endogenous chromophores, the location of the fluorophore can be determined by subtracting images acquired using simultaneous and time-delayed pump-probe excitation. This simple experimental approach exploits a fluorophorespecific contrast mechanism, and has the potential to enable deep-tissue molecular imaging at fluences below the MPE. In this study, some of the challenges to its in vivo implementation are addressed. First, the PA signal amplitude generated in fluorophores in vivo is often much smaller than that in blood. Second, tissue motion can give rise to artifacts that correspond to endogenous chromophores in the difference image. This would not allow the unambiguous detection of fluorophores. A method to suppress motion artifacts based on fast switching between simultaneous and time-delayed pump-probe excitation was developed. This enables the acquisition of PA signals using the two excitation modes with minimal time delay (20 ms), thus minimizing the effects of tissue motion. The feasibility of this method is demonstrated by visualizing a fluorophore (Atto680) in tissue phantoms, which were moved during the image acquisition to mimic tissue motion.

  4. Magnetomotive molecular probes for targeted contrast enhancement and therapy

    NASA Astrophysics Data System (ADS)

    Boppart, Stephen A.

    2011-03-01

    The diagnostic, interrogational, and therapeutic potential of molecular probes is rapidly being investigated and exploited across virtually every biomedical imaging modality. While many types of probes enhance contrast or delivery therapy by static localization to targeted sites, significant potential exists for utilizing dynamic molecular probes. Recent examples include molecular beacons, photoactivatable probes, or controlled switchable drug-releasing particles, to name a few. In this review, we describe a novel class of dynamic molecular probes that rely on the application and control of localized external magnetic fields. These magnetomotive molecular probes can provide optical image contrast through a modulated scattering signal, can interrogate the biomechanical properties of their viscoelastic microenvironment by tracking their underdamped oscillatory step-response to applied fields, and can potentially delivery therapy through nanometer-to-micrometer mechanical displacement or local hyperthermia. This class of magnetomotive agents includes not only magnetic iron-oxide nanoparticles, but also new magnetomotive microspheres or nanostructures with embedded iron-oxide agents. In vitro three-dimensional cell assays and in vivo targeting studies in animal tumor models have demonstrated the potential for multimodal detection and imaging, using magnetic resonance imaging for whole-body localization, and magnetomotive optical coherence tomography for high-resolution localization and imaging.

  5. Spike-Triggered Covariance Analysis Reveals Phenomenological Diversity of Contrast Adaptation in the Retina

    PubMed Central

    Liu, Jian K.; Gollisch, Tim

    2015-01-01

    When visual contrast changes, retinal ganglion cells adapt by adjusting their sensitivity as well as their temporal filtering characteristics. The latter has classically been described by contrast-induced gain changes that depend on temporal frequency. Here, we explored a new perspective on contrast-induced changes in temporal filtering by using spike-triggered covariance analysis to extract multiple parallel temporal filters for individual ganglion cells. Based on multielectrode-array recordings from ganglion cells in the isolated salamander retina, we found that contrast adaptation of temporal filtering can largely be captured by contrast-invariant sets of filters with contrast-dependent weights. Moreover, differences among the ganglion cells in the filter sets and their contrast-dependent contributions allowed us to phenomenologically distinguish three types of filter changes. The first type is characterized by newly emerging features at higher contrast, which can be reproduced by computational models that contain response-triggered gain-control mechanisms. The second type follows from stronger adaptation in the Off pathway as compared to the On pathway in On-Off-type ganglion cells. Finally, we found that, in a subset of neurons, contrast-induced filter changes are governed by particularly strong spike-timing dynamics, in particular by pronounced stimulus-dependent latency shifts that can be observed in these cells. Together, our results show that the contrast dependence of temporal filtering in retinal ganglion cells has a multifaceted phenomenology and that a multi-filter analysis can provide a useful basis for capturing the underlying signal-processing dynamics. PMID:26230927

  6. Spike-Triggered Covariance Analysis Reveals Phenomenological Diversity of Contrast Adaptation in the Retina.

    PubMed

    Liu, Jian K; Gollisch, Tim

    2015-07-01

    When visual contrast changes, retinal ganglion cells adapt by adjusting their sensitivity as well as their temporal filtering characteristics. The latter has classically been described by contrast-induced gain changes that depend on temporal frequency. Here, we explored a new perspective on contrast-induced changes in temporal filtering by using spike-triggered covariance analysis to extract multiple parallel temporal filters for individual ganglion cells. Based on multielectrode-array recordings from ganglion cells in the isolated salamander retina, we found that contrast adaptation of temporal filtering can largely be captured by contrast-invariant sets of filters with contrast-dependent weights. Moreover, differences among the ganglion cells in the filter sets and their contrast-dependent contributions allowed us to phenomenologically distinguish three types of filter changes. The first type is characterized by newly emerging features at higher contrast, which can be reproduced by computational models that contain response-triggered gain-control mechanisms. The second type follows from stronger adaptation in the Off pathway as compared to the On pathway in On-Off-type ganglion cells. Finally, we found that, in a subset of neurons, contrast-induced filter changes are governed by particularly strong spike-timing dynamics, in particular by pronounced stimulus-dependent latency shifts that can be observed in these cells. Together, our results show that the contrast dependence of temporal filtering in retinal ganglion cells has a multifaceted phenomenology and that a multi-filter analysis can provide a useful basis for capturing the underlying signal-processing dynamics. PMID:26230927

  7. Syringomyelia caused by intrathecal remnants of oil-based contrast medium.

    PubMed

    Kubota, Mayumi; Shin, Masahiro; Taniguchi, Makoto; Terao, Toru; Nakauchi, Jun; Takahashi, Hiroshi

    2008-02-01

    Oily contrast medium had been in use since the early 19th century as a radiographic agent for detecting spinal lesions and spinal cord tumors until the late 20th century. At that point computed tomography scanning and magnetic resonance imaging, or other hydrophilic contrast medium substituted for it. Adverse effects of oil-based dye, both acute and chronic, had been reported since the middle of the 20th century. In this paper the authors report the case of syringomyelia that seemed to be caused mainly by remaining oily contrast medium for 44 years. Syringomyelia secondary to adhesive arachnoiditis caused by oily contrast medium after a long period of time is well known. In the present case, however, surgery revealed only mild arachnoiditis at the level of syringomyelia as well as both solid and liquid remnants of contrast medium. Generally, cerebrospinal fluid (CSF) blockage due to an arachnoid adhesion is considered to cause syringomyelia following adhesive arachnoiditis. The authors speculated that in the present case syringomyelia was induced by a mechanism different from that in the previously reported cases; the oily contrast medium itself seems to have induced the functional block of CSF and impaired the buffer system of the intrathecal pressure. No reports on thoracic adhesive arachnoiditis and syringomyelia caused by oil-based dye referred to this mechanism in reviewing the literature. PMID:18248289

  8. Computational Study of Computed Tomography Contrast Gradients in Models of Stenosed Coronary Arteries.

    PubMed

    Eslami, Parastou; Seo, Jung-Hee; Rahsepar, Amir Ali; George, Richard; Lardo, Albert C; Mittal, Rajat

    2015-09-01

    Recent computed tomography coronary angiography (CCTA) studies have noted higher transluminal contrast agent gradients in arteries with stenotic lesions, but the physical mechanism responsible for these gradients is not clear. We use computational fluid dynamics (CFD) modeling coupled with contrast agent dispersion to investigate the mechanism for these gradients. Simulations of blood flow and contrast agent dispersion in models of coronary artery are carried out for both steady and pulsatile flows, and axisymmetric stenoses of severities varying from 0% (unobstructed) to 80% are considered. Simulations show the presence of measurable gradients with magnitudes that increase monotonically with stenotic severity when other parameters are held fixed. The computational results enable us to examine and validate the hypothesis that transluminal contrast gradients (TCG) are generated due to the advection of the contrast bolus with time-varying contrast concentration that appears at the coronary ostium. Since the advection of the bolus is determined by the flow velocity in the artery, the magnitude of the gradient, therefore, encodes the coronary flow velocity. The correlation between the flow rate estimated from TCG and the actual flow rate in the computational model of a physiologically realistic coronary artery is 96% with a R2 value of 0.98. The mathematical formulae connecting TCG to flow velocity derived here represent a novel and potentially powerful approach for noninvasive estimation of coronary flow velocity from CT angiography. PMID:26102356

  9. The effects of adaptation and masking on incremental thresholds for contrast.

    PubMed

    Ross, J; Speed, H D; Morgan, M J

    1993-10-01

    Using a temporal two-alternative forced-choice procedure, we measured thresholds for detecting increments in contrast of a 2 c/deg vertical grating at a wide range of pedestal contrasts, (1) before and after adapting to a grating of the same orientation and spatial frequency, and (2) in the presence of superimposed masks that varied in either orientation or spatial frequency. The adapting grating and all masks were of fixed 40% contrast. The results show that prior adaptation and concurrent masking have qualitatively similar effects on incremental thresholds; both raise threshold at low pedestal contrasts and leave them unaltered at higher contrasts. But masks have greater effects than adaptors, the effect of an orthogonal mask, or one two octaves higher in spatial frequency, being about the same as a parallel adaptor of the same spatial frequency as the pedestal grating. The results are explained by a model of Ross and Speed [(1991) Proceedings of the Royal Society of London B, 246, 61-69] that assumes that masks and adaptors both reposition the transducer function of contrast sensitive mechanisms and that masks, but not adaptors, also stimulate the detecting mechanism. PMID:8266646

  10. Contrast-enhanced ultrasonography: advance and current status in abdominal imaging

    PubMed Central

    2015-01-01

    In the field of contrast-enhanced ultrasonography (US), contrast agents are classified as either first- or second-generation agents depending on the gas within the microbubbles. In the case of first-generation contrast agents, a high-mechanical-index technique is used and only intermittent scanning is possible due to the early destruction of the microbubbles during the scanning. The use of second-generation contrast agents in a low-mechanical-index technique enables continuous scanning. Besides the detection and characterization of focal liver lesions, contrastenhanced US is helpful in the monitoring of radiofrequency ablation therapy and in the targeting step of an US-guided biopsy. Recently, there has been a demand for new criteria to evaluate the treatment response obtained using anti-angiogenic agents because morphologic criteria alone may not reflect the treatment response of the tumor and contrast-enhanced US can provide quantitative markers of tissue perfusion. In spite of the concerns related to its cost-effectiveness, contrast-enhanced US has the potential to be more widely used as a complimentary tool or to substitute the current imaging modalities in some occasions. PMID:25342120

  11. Tumor Characterization with Dynamic Contrast Enhanced Magnetic Resonance Imaging and Biodegradable Macromolecular Contrast Agents in Mice

    PubMed Central

    Wu, Xueming; Feng, Yi; Jeong, Eun-Kee; Emerson, Lyska; Lu, Zheng-Rong

    2009-01-01

    Purpose To investigate the efficacy of polydisulfide-based biodegradable macromolecular contrast agents of different degradability and molecular weight for tumor characterization based on angiogenesis using dynamic contrast enhanced MRI (DCE-MRI). Methods Biodegradable macromolecular MRI contrast agents, GDCC and GDCP, with molecular weight of 20 and 70 KDa were evaluated for tumor characterization. The DCE-MRI studies were performed in nude mice bearing MDA PCa 2b and PC-3 human prostate tumor xenografts. Tumor angiogenic kinetic parameters, endothelium transfer coefficient (Ktrans) and fractional tumor plasma volume (fPV), were calculated from the DCE-MRI data using a two-compartment model. Results There was no significant difference in the fPV values between two tumor models estimated with the same agent except for GDCC-70. The Ktrans values in both tumor models decreased with increasing molecular weight of the agents. GDCC-70 showed a higher Ktrans values than GDCP-70 due to high degradability of the former in both tumor models (p < 0.05). The Ktrans values of MDA PCa 2b tumors were significantly higher than those of PC-3 tumors estimated by Gd(DTPA-BMA), GDCC-20, GDCC-70, GDCP-70, and albumin-(Gd-DTPA) (p < 0.05). Conclusions The polydisulfide based biodegradable macromolecular MRI contrast agents are promising in tumor characterization with dynamic contrast enhanced MRI. PMID:19597972

  12. Single-shot x-ray phase contrast imaging with an algorithmic approach using spectral detection

    NASA Astrophysics Data System (ADS)

    Das, Mini; Park, Chan-Soo; Fredette, Nathaniel R.

    2016-04-01

    X-ray phase contrast imaging has been investigated during the last two decades for potential benefits in soft tissue imaging. Long imaging time, high radiation dose and general measurement complexity involving motion of x-ray optical components have prevented the clinical translation of these methods. In all existing popular phase contrast imaging methods, multiple measurements per projection angle involving motion of optical components are required to achieve quantitatively accurate estimation of absorption, phase and differential phase. Recently we proposed an algorithmic approach to use spectral detection data in a phase contrast imaging setup to obtain absorption, phase and differential phase in a single-step. Our generic approach has been shown via simulations in all three types of phase contrast imaging: propagation, coded aperture and grating interferometry. While other groups have used spectral detector in phase contrast imaging setups, our proposed method is unique in outlining an approach to use this spectral data to simplify phase contrast imaging. In this abstract we show the first experimental proof of our single-shot phase retrieval using a Medipix3 photon counting detector in an edge illumination aperture (also referred to as coded aperture) phase contrast set up as well as for a free space propagation setup. Our preliminary results validate our new transport equation for edge illumination PCI and our spectral phase retrieval algorithm for both PCI methods being investigated. Comparison with simulations also point to excellent performance of Medipix3 built-in charge sharing correction mechanism.

  13. Encapsulated microbubbles and echogenic liposomes for contrast ultrasound imaging and targeted drug delivery

    NASA Astrophysics Data System (ADS)

    Paul, Shirshendu; Nahire, Rahul; Mallik, Sanku; Sarkar, Kausik

    2014-03-01

    Micron- to nanometer-sized ultrasound agents, like encapsulated microbubbles and echogenic liposomes, are being developed for diagnostic imaging and ultrasound mediated drug/gene delivery. This review provides an overview of the current state of the art of the mathematical models of the acoustic behavior of ultrasound contrast microbubbles. We also present a review of the in vitro experimental characterization of the acoustic properties of microbubble based contrast agents undertaken in our laboratory. The hierarchical two-pronged approach of modeling contrast agents we developed is demonstrated for a lipid coated (Sonazoid and a polymer shelled (poly D-L-lactic acid) contrast microbubbles. The acoustic and drug release properties of the newly developed echogenic liposomes are discussed for their use as simultaneous imaging and drug/gene delivery agents. Although echogenicity is conclusively demonstrated in experiments, its physical mechanisms remain uncertain. Addressing questions raised here will accelerate further development and eventual clinical approval of these novel technologies.

  14. Encapsulated microbubbles and echogenic liposomes for contrast ultrasound imaging and targeted drug delivery

    PubMed Central

    Paul, Shirshendu; Nahire, Rahul; Mallik, Sanku; Sarkar, Kausik

    2014-01-01

    Micron- to nanometer-sized ultrasound agents, like encapsulated microbubbles and echogenic liposomes, are being developed for diagnostic imaging and ultrasound mediated drug/gene delivery. This review provides an overview of the current state of the art of the mathematical models of the acoustic behavior of ultrasound contrast microbubbles. We also present a review of the in vitro experimental characterization of the acoustic properties of microbubble based contrast agents undertaken in our laboratory. The hierarchical two-pronged approach of modeling contrast agents we developed is demonstrated for a lipid coated (Sonazoid™) and a polymer shelled (poly D-L-lactic acid) contrast microbubbles. The acoustic and drug release properties of the newly developed echogenic liposomes are discussed for their use as simultaneous imaging and drug/gene delivery agents. Although echogenicity is conclusively demonstrated in experiments, its physical mechanisms remain uncertain. Addressing questions raised here will accelerate further development and eventual clinical approval of these novel technologies. PMID:26097272

  15. Robust Automatic Focus Algorithm for Low Contrast Images Using a New Contrast Measure

    PubMed Central

    Xu, Xin; Wang, Yinglin; Tang, Jinshan; Zhang, Xiaolong; Liu, Xiaoming

    2011-01-01

    Low contrast images, suffering from a lack of sharpness, are easily influenced by noise. As a result, many local false peaks may be generated in contrast measurements, making it difficult for the camera’s passive auto-focus system to perform its function of locating the focused peak. In this paper, a new passive auto-focus algorithm is proposed to address this problem. First, a noise reduction preprocessing is introduced to make our algorithm robust to both additive noise and multiplicative noise. Then, a new contrast measure is presented to bring in local false peaks, ensuring the presence of a well defined focused peak. In order to gauge the performance of our algorithm, a modified peak search algorithm is used in the experiments. The experimental results from an actual digital camera validate the effectiveness of our proposed algorithm. PMID:22164075

  16. Quantitative analysis of contrast to noise ratio using a phase contrast x-ray imaging prototype

    NASA Astrophysics Data System (ADS)

    Ghani, Muhammad U.; Wu, Di; Li, Yuhua; Kang, Minhua; Chen, Wei R.; Wu, Xizeng; Liu, Hong

    2013-02-01

    The purpose of this study was to determine the Contrast to Noise Ratio (CNR) of the x-ray images taken with the phase contrast imaging mode and compare them with the CNR of the images taken under the conventional mode. For each mode, three images were taken under three exposure conditions of 100 kVp (2.8mAs), 120 kVp (1.9mAs) and 140kVp (1.42mAs). A 1.61cm thick contrast detail phantom was used as an imaging object. For phase contrast, the source to image detector distance (SID) was 182.88 cm and the source to object (SOD) distance was 73.15 cm. The SOD was the same as SID in the conventional imaging mode. A computed radiography (CR) plate was used as a detector and the output CR images were converted to linear form in relation with the incident x-ray exposure. To calculate CNR, an image processing software was used to determine the mean pixel value and the standard deviation of the pixels in the region of interest (ROI) and in the nearby background around ROI. At any given exposure condition investigated in this study, the CNR values for the phase contrast images were better as compared to the corresponding conventional mode images. The superior image quality in terms of CNR is contributed by the phase-shifts resulted contrast, as well as the reduced scatters due to the air gap between the object and the detector.

  17. Weighted contrast metric for imaging system performance

    NASA Astrophysics Data System (ADS)

    Teaney, Brian P.

    2012-06-01

    There have been significant improvements in the image quality metrics used in the NVESD model suite in recent years. The introduction of the Targeting Task Performance (TTP) metric to replace the Johnson criteria yielded significantly more accurate predictions for under-sampled imaging systems in particular. However, there are certain cases which cause the TTP metric to predict optimistic performance. In this paper a new metric for predicting performance of imaging systems is described. This new weighted contrast metric is characterized as a hybrid of the TTP metric and Johnson criteria. Results from a number of historical perception studies are presented to compare the performance of the TTP metric and Johnson criteria to the newly proposed metric.

  18. Contrast-enhanced ultrasound in oncology

    PubMed Central

    Rasmussen, F.

    2011-01-01

    Abstract In patients with known malignant disease, 51% of liver lesions less than 1.5 cm turn out to be benign. Whether the probability of malignancy is high or low, further investigations are often necessary to definitely exclude malignancy. Contrast-enhanced ultrasonography has a prominent role in lesion characterization with a diagnostic accuracy comparable with computed tomography and magnetic resonance imaging. Anti-angiogenic treatment is common in most oncological institutions and the response evaluation is a new challenge with a research focus on the change in tumour vasculature and perfusion. In planning biopsies, CEUS can identify necrotic and viable areas of tumours and improve the diagnostic accuracy. PMID:22186152

  19. Nonlinear phase contrast using a bacteriorhodopsin film

    NASA Astrophysics Data System (ADS)

    Iturbe Castillo, Marcelo D.; Sanchez-de-la-Llave, J. D.; Ramos Garcia, Ruben; Tepichin-Rodriguez, Eduardo; Olivos-Perez, L. I.

    2002-11-01

    In this paper we demonstrate a novel phase contrast system that employs a BR film. Since the filter is optically induced by the Fourier transform of the phase object, no alignment is necessary at the filter plane making it extremely robust. Due to the optical properties of BR films the phase filter can be induced with low light intensity levels. The material response allows operation at video frame rates, processing of high spatial resolution objects, and the use of relatively inexpensive laser sources. Such characteristics and the fact that BR films can be produced at a low cost makes the system simple to implement, relatively inexpensive and extremely robust. The effects of varying the illuminating area beyond the phase object area and filter saturation are also analyzed.

  20. Comparing and Contrasting Consensus versus Empirical Domains

    PubMed Central

    Jason, Leonard A.; Kot, Bobby; Sunnquist, Madison; Brown, Abigail; Reed, Jordan; Furst, Jacob; Newton, Julia L.; Strand, Elin Bolle; Vernon, Suzanne D.

    2015-01-01

    Background Since the publication of the CFS case definition [1], there have been a number of other criteria proposed including the Canadian Consensus Criteria [2] and the Myalgic Encephalomyelitis: International Consensus Criteria. [3] Purpose The current study compared these domains that were developed through consensus methods to one obtained through more empirical approaches using factor analysis. Methods Using data mining, we compared and contrasted fundamental features of consensus-based criteria versus empirical latent factors. In general, these approaches found the domain of Fatigue/Post-exertional malaise as best differentiating patients from controls. Results Findings indicated that the Fukuda et al. criteria had the worst sensitivity and specificity. Conclusions These outcomes might help both theorists and researchers better determine which fundamental domains to be used for the case definition. PMID:26977374

  1. Nanoparticles for enhanced contrast optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Maule, César D.; Quaresma, Pedro; Carvalho, Patrícia A.; Jorge, Pedro; Pereira, Eulália; Rosa, Carla C.

    2008-09-01

    Recently the area of bioimaging has benefited from new types of image enhancing agents such as quantum dots, carbon nanotubes and other nanoparticles. Cellular or even molecular level resolution has been achieved with different techniques during these last years (i.a. Fluorescence microscopy, PET/CT scan, AFM). Optical Coherence Tomography (OCT) as an imaging technique should also profit from newly developed probes. In this work we explored the tunable properties of different types of nanoparticles as contrast enhancers in OCT applications. We mainly studied the development and characteristics of metallic nanoparticles with tunable properties: gold nanoshells made of a silica core coated with a gold shell. Nanoshell and nanoparticles processing techniques are discussed, as well as their optimization for designing particles with specific absorption and scattering characteristics, and its use in OCT imaging.

  2. Myocardial hypoperfusion on conventional contrast computed tomography.

    PubMed

    Ching, Shing; Chung, Tak Shun

    2015-10-01

    Non–electrocardiogram (ECG)–gated contrast computed tomography (CT) is commonly performed to exclude aortic dissection in chest pain patients. Besides evaluating the aorta for dissection flap, attention should be paid to the myocardium for areas of hypoenhancement that may suggest ischemia. Current models of multidetector CT enable assessment of myocardial perfusion with minimal motion artifact even without ECG gating. Transmural hypoenhancement with preserved wall thickness in a coronary distribution is highly specific for acute myocardial infarction. We report 2 cases of acute chest pain with initial nondiagnostic studies that underwent CT aortogram to exclude dissection. Instead, the CT showed myocardial hypoenhancement in left anterior descending artery territory. Myocardial hypoenhancement occurred before ST-segment elevation on ECG, suggesting that recognition of this important finding may lead to earlier revascularization decisions. PMID:26321167

  3. Gene transfection by echo contrast agent microbubbles

    NASA Astrophysics Data System (ADS)

    Tachibana, Katsuro

    2002-11-01

    In vitro and in vivo experiments have demonstrated that various echo contrast agent microbubbles can be intentionally ruptured by diagnostic and therapeutic ultrasound. Violent microstreaming are produced during microbubble collapse. Researchers have hypothesized that these microjets or microstreaming could be applied to promote diffusion of drugs into various tissues and lesions. The most exciting application of this method is probably delivery of genes into cells. As various genes are currently under investigation for the purpose of treating diseases, ultrasound and microbubbles may be used as a modality to promote better outcome for gene therapy. Recent studies have shown that different gases contained within the bubbles greatly influence the degree of gene transfection. Also, the outer layer of the microbubbles can be custom-made for binding to target tissue. Recent advance on this topic will be discussed.

  4. Contrasts and synergies in different biofuel reports.

    PubMed

    Michalopoulos, A; Landeweerd, L; Van der Werf-Kulichova, Z; Puylaert, P G B; Osseweijer, P

    2011-04-01

    The societal debate on biofuels is characterised by increased complexity. This can hinder the effective governance of the field. This paper attempts a quantitative bird's eye meta-analysis of this complexity by mapping different stakeholder perspectives and expected outcomes as seen in the secondary literature on biofuels, along the lines of the People-Planet-Profit framework. Our analysis illustrates the tension between stated and actual drivers of large scale biofuel development, especially for first generation biofuels. Although environmental (Planet) aspects have dominated the biofuel debate, their overall assessment is mostly negative with regard to first generation biofuels. By contrast, economic (Profit) aspects are the only ones that are assessed positively with regard to first generation biofuels. Furthermore, positive and negative assessments of biofuel development are strongly influenced by the differences in focus between different stakeholder clusters. Stakeholders who appear generally supportive to biofuel development (industry) focus relatively more on aspects that are generally assessed as positive (Profit). By contrast, non-supportive stakeholders (NGO's) tend to focus mainly on aspects that are generally assessed as negative (Planet). Moreover, our analysis of reference lists revealed few citations of primary scientific data, and also that intergovernmental organizations produce the most influential publications in the debate. The surprising lack of listed references to scientific (primary) data reveals a need to assess in which arena the transition of scientific data towards secondary publications takes place, and how one can measure its quality. This work should be understood as a first effort to take some control over a complex and contradictory number of publications, and to allow the effective governance of the field through the identification of areas of overlapping consensus and persisting controversy, without reverting to claims on

  5. Contrasts and synergies in different biofuel reports

    PubMed Central

    Michalopoulos, A.; Landeweerd, L.; Van der Werf-Kulichova, Z.; Puylaert, P. G. B.; Osseweijer, P.

    2011-01-01

    The societal debate on biofuels is characterised by increased complexity. This can hinder the effective governance of the field. This paper attempts a quantitative bird's eye meta-analysis of this complexity by mapping different stakeholder perspectives and expected outcomes as seen in the secondary literature on biofuels, along the lines of the People-Planet-Profit framework. Our analysis illustrates the tension between stated and actual drivers of large scale biofuel development, especially for first generation biofuels. Although environmental (Planet) aspects have dominated the biofuel debate, their overall assessment is mostly negative with regard to first generation biofuels. By contrast, economic (Profit) aspects are the only ones that are assessed positively with regard to first generation biofuels. Furthermore, positive and negative assessments of biofuel development are strongly influenced by the differences in focus between different stakeholder clusters. Stakeholders who appear generally supportive to biofuel development (industry) focus relatively more on aspects that are generally assessed as positive (Profit). By contrast, non-supportive stakeholders (NGO's) tend to focus mainly on aspects that are generally assessed as negative (Planet). Moreover, our analysis of reference lists revealed few citations of primary scientific data, and also that intergovernmental organizations produce the most influential publications in the debate. The surprising lack of listed references to scientific (primary) data reveals a need to assess in which arena the transition of scientific data towards secondary publications takes place, and how one can measure its quality. This work should be understood as a first effort to take some control over a complex and contradictory number of publications, and to allow the effective governance of the field through the identification of areas of overlapping consensus and persisting controversy, without reverting to claims on

  6. Projection phase contrast microscopy with a hard x-ray nanofocused beam: Defocus and contrast transfer

    SciTech Connect

    Salditt, T.; Giewekemeyer, K.; Fuhse, C.; Krueger, S. P.; Tucoulou, R.; Cloetens, P.

    2009-05-01

    We report a projection phase contrast microscopy experiment using hard x-ray pink beam undulator radiation focused by an adaptive mirror system to 100-200 nm spot size. This source is used to illuminate a lithographic test pattern with a well-controlled range of spatial frequencies. The oscillatory nature of the contrast transfer function with source-to-sample distance in this holographic imaging scheme is quantified and the validity of the weak phase object approximation is confirmed for the experimental conditions.

  7. Delayed rectifier K channels contribute to contrast adaptation in mammalian retinal ganglion cells

    PubMed Central

    Weick, Michael; Demb, Jonathan B.

    2011-01-01

    SUMMARY Retinal ganglion cells adapt by reducing their sensitivity during periods of high contrast. Contrast adaptation in the firing response depends on both presynaptic and intrinsic mechanisms. Here, we investigated intrinsic mechanisms for contrast adaptation in OFF Alpha ganglion cells in the in vitro guinea pig retina. Using either visual stimulation or current injection, we show that brief depolarization evoked spiking and suppressed firing during subsequent depolarization. The suppression could be explained by Na channel inactivation, as shown in salamander cells. However, brief hyperpolarization in the physiological range (5–10 mV) also suppressed firing during subsequent depolarization. This suppression was sensitive selectively to blockers of delayed-rectifier K channels (KDR). Somatic membrane patches showed TEA-sensitive KDR currents with activation near −25 mV and removal of inactivation at voltages negative to Vrest. Brief periods of hyperpolarization apparently remove KDR inactivation and thereby increase the channel pool available to suppress excitability during subsequent depolarization. PMID:21745646

  8. Contrast-dependent orientation discrimination in the mouse

    PubMed Central

    Long, Minghai; Jiang, Weiqian; Liu, Dechen; Yao, Haishan

    2015-01-01

    As an important animal model to study the relationship between behaviour and neural activity, the mouse is able to perform a variety of visual tasks, such as orientation discrimination and contrast detection. However, it is not clear how stimulus contrast influences the performance of orientation discrimination in mice. In this study, we used two task designs, two-alternative forced choice (2AFC) and go/no-go, to examine the performance of mice to discriminate two orthogonal orientations at different contrasts. We found that the performance tended to increase with contrast, and the performance at high contrast was better when the stimulus set contained a single contrast than multiple contrasts. Physiological experiments in V1 showed that neural discriminability of two orthogonal orientations increased with contrast. Furthermore, orientation discriminability of V1 neurons at high contrast was higher in the single than in the multiple contrast condition, largely due to smaller response variance in the single contrast condition. Thus, the performance of mice to discriminate orientations at high contrast is adapted to the contrast range in the stimuli, partly attributed to the contrast-range dependent capacity of V1 neurons to discriminate orientations. PMID:26510881

  9. Contrast and covert contrast: The phonetic development of voiceless sibilant fricatives in English and Japanese toddlers

    PubMed Central

    Li, Fangfang; Edwards, Jan; Beckman, Mary E.

    2009-01-01

    This paper examines the acoustic characteristics of voiceless sibilant fricatives in English-and Japanese-speaking adults and the acquisition of contrasts involving these sounds in 2- and 3-year-old children. Both English and Japanese have a two-way contrast between an alveolar fricative (/s/), and a postalveolar fricative (/∫/ in English and /ɕ/ in Japanese). Acoustic analysis of the adult productions revealed cross-linguistic differences in what acoustic parameters were used to differentiate the two fricatives in the two languages and in how well the two fricatives were differentiated by the acoustic parameters that were investigated. For the children’s data, the transcription results showed that English-speaking children generally produced the alveolar fricative more accurately than the postalveolar one, whereas the opposite was true for Japanese-speaking children. In addition, acoustic analysis revealed the presence of covert contrast in the productions of some English-speaking and some Japanese-speaking children. The different development patterns are discussed in terms of the differences in the fine phonetic detail of the contrast in the two languages. PMID:19672472

  10. Variational contrast enhancement guided by global and local contrast measurements for single-image defogging

    NASA Astrophysics Data System (ADS)

    Zhou, Li; Bi, Du-Yan; He, Lin-Yuan

    2015-01-01

    The visibility of images captured in foggy conditions is impaired severely by a decrease in the contrasts of objects and veiling with a characteristic gray hue, which may limit the performance of visual applications out of doors. Contrast enhancement together with color restoration is a challenging mission for conventional fog-removal methods, as the degrading effect of fog is largely dependent on scene depth information. Nowadays, people change their minds by establishing a variational framework for contrast enhancement based on a physically based analytical model, unexpectedly resulting in color distortion, dark-patch distortion, or fuzzy features of local regions. Unlike previous work, our method treats an atmospheric veil as a scattering disturbance and formulates a foggy image as an energy functional minimization to estimate direct attenuation, originating from the work of image denoising. In addition to a global contrast measurement based on a total variation norm, an additional local measurement is designed in that optimal problem for the purpose of digging out more local details as well as suppressing dark-patch distortion. Moreover, we estimate the airlight precisely by maximization with a geometric constraint and a natural image prior in order to protect the faithfulness of the scene color. With the estimated direct attenuation and airlight, the fog-free image can be restored. Finally, our method is tested on several benchmark and realistic images evaluated by two assessment approaches. The experimental results imply that our proposed method works well compared with the state-of-the-art defogging methods.

  11. Papers and Studies in Contrastive Linguistics, Volume Twenty-Five. The Polish-English Contrastive Project.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    Papers in this volume on contrastive linguistics include the following: "Auxiliaries in English and Danish" (Niels Davidsen-Nielsen); "On Tongue Twisters" (Wlodzimierz Sobkowiak); "On Derivational and Phrasal Adverbials of Manner" (James L. Wyatt); "Scrambling and the Polish Word Order. An Alternative Hypothesis" (Przemyslaw Tajsner); "Verbs of…

  12. Cultural Contrasts: Hispanic-North American. Contrastes De Costumbres: El Hispano y el Norteamericano.

    ERIC Educational Resources Information Center

    Andrade, Marcel C.

    The purpose of this booklet (written in English and Spanish) is to present, to North Americans, basic cultural differences between North American and Hispanic peoples. Following an introduction to general concepts about Hispanic peoples, the cultural contrasts are presented, with cartoons which graphically illustrate the ideas put forth. The…

  13. High Contrast Vacuum Nuller Testbed (VNT) Contrast, Performance and Null Control

    NASA Technical Reports Server (NTRS)

    Lyon, Richard G.; Clampin, Mark; Petrone, Peter; Mallik, Udayan; Madison, Timothy; Bolcar, Matthew R.

    2012-01-01

    Herein we report on our Visible Nulling Coronagraph high-contrast result of 109 contrast averaged over a focal planeregion extending from 14 D with the Vacuum Nuller Testbed (VNT) in a vibration isolated vacuum chamber. TheVNC is a hybrid interferometriccoronagraphic approach for exoplanet science. It operates with high Lyot stopefficiency for filled, segmented and sparse or diluted-aperture telescopes, thereby spanning the range of potential futureNASA flight telescopes. NASAGoddard Space Flight Center (GSFC) has a well-established effort to develop the VNCand its technologies, and has developed an incremental sequence of VNC testbeds to advance this approach and itsenabling technologies. These testbeds have enabled advancement of high-contrast, visible light, nulling interferometry tounprecedented levels. The VNC is based on a modified Mach-Zehnder nulling interferometer, with a W configurationto accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters.We give an overview of the VNT and discuss the high-contrast laboratory results, the optical configuration, criticaltechnologies and null sensing and control.

  14. Gain, noise, and contrast sensitivity of linear visual neurons

    NASA Technical Reports Server (NTRS)

    Watson, Andrew B.

    1990-01-01

    Contrast sensitivity is a measure of the ability of an observer to detect contrast signals of particular spatial and temporal frequencies. A formal definition of contrast sensitivity that can be applied to individual linear visual neurons is derived. A neuron is modeled by a contrast transfer function and its modulus, contrast gain, and by a noise power spectrum. The distributions of neural responses to signal and blank presentations are derived, and from these, a definition of contrast sensitivity is obtained. This formal definition may be used to relate the sensitivities of various populations of neurons, and to relate the sensitivities of neurons to that of the behaving animal.

  15. Renal stones on portal venous phase contrast-enhanced CT: does intravenous contrast interfere with detection?

    PubMed Central

    Dym, R. Joshua; Duncan, Dameon R.; Spektor, Michael; Cohen, Hillel W.; Scheinfeld, Meir H.

    2015-01-01

    Purpose To determine the sensitivity of portal venous phase contrast-enhanced CT for the detection of renal stones. Methods This retrospective study included 97 CT examinations of the abdomen without and with intravenous contrast, including 85 (87.6%) examinations with at least one renal stone on the “gold standard” noncontrast images, as scored by a single radiologist. Three other radiologists each independently reviewed only the contrast-enhanced images from all 97 examinations and recorded all renal stones. Reviewer sensitivity for stones was categorized by stone diameter. Reviewer sensitivity and specificity for stone disease were also calculated on a per-kidney basis. Results The 97 cases included a total of 238 stones ≥1 mm, with a mean (±SD) of 1.2 ± 1.9 stones per kidney and a stone diameter of 3.5 ± 3.0 mm. Pooling data for the three reviewers, sensitivity for all stones was 81%; sensitivity for stones ≥2, ≥3, ≥4, and ≥5 mm was 88%, 95%, 99%, and 98%, respectively. Sensitivity for stone disease on a per-kidney basis was 94% when considering all stones; when considering only stones ≥2, ≥3, and ≥4 mm, sensitivity was 96%, 99%, and 100%, respectively. Specificity for stone disease on a per-kidney basis was 98% overall, 99% when considering only stones ≥2 mm, and 100% when considering only stones ≥3 mm. Conclusion: Contrast-enhanced CT is highly sensitive for the detection of renal stones ≥3 mm in diameter and less sensitive for smaller stones. In cases where the clinical diagnosis is uncertain and performance of a CT examination is being contemplated, intravenous contrast utilization would allow assessment for stone disease while also optimizing evaluation for other conditions. PMID:24504541

  16. Contrasts in Flushing Patterns Among Solutes

    NASA Astrophysics Data System (ADS)

    Shanley, J. B.; Sebestyen, S. D.; Boyer, E. W.; Ross, D. S.

    2005-12-01

    High-frequency sampling since 1991 at the 41-ha forested W-9 catchment at Sleepers River, Vermont provides a wealth of data to evaluate catchment flushing responses. Snowmelt and rain-on-snow account for about half the annual flow at Sleepers River during a 6-week period in early spring. Summer and fall storms produce frequent high-flows of short duration. Flushing of weathering products (Ca, Mg, Na, K, SO4 ANC, Si) is generally supply-limited, and is masked by rapid dilution with meteoric and soil water during events. In contrast, flushing dominates the stream dynamics of atmospheric and pedogenic solutes (NO3, DOC, Hg), causing concentration increases with increasing flow. During snowmelt, NO3 peaks well before the peak in discharge, whereas DOC tracks discharge closely and peaks concurrently. These patterns suggest that NO3 is supply-limited and DOC is transport-limited; W-9 is not N saturated and the available NO3 supply is readily leached from the soil, whereas stream DOC progressively increases as rising water tables and expanding saturated areas connect with new source areas. In summer storms, DOC and NO3 both peak simultaneously with discharge. Unlike DOC, however, NO3 concentrations are attenuated with subsequent storms that follow within a few days, consistent with a depletion of the NO3 pool available for flushing as observed during snowmelt. Sleepers River contrasts with the Snake River in Colorado, where NO3 and DOC reverse roles; DOC peaks early in snowmelt and may be supply-limited due to the paucity of organic matter. An ample supply of NO3 is available due to N saturation and N fixation, but NO3 may be transport-limited due to primary N sources in talus deposits far from the stream. Hg is an atmospheric solute that accumulates in soils because of its affinity for organic matter, and is flushed by high flows, mostly in association with suspended sediment. The concept of flushing provides a useful context for understanding the variable responses of

  17. Contrasting effects of nanoparticle-protein attraction on amyloid aggregation

    PubMed Central

    Radic, Slaven; Davis, Thomas P; Ke, Pu Chun; Ding, Feng

    2015-01-01

    Nanoparticles (NPs) have been experimentally found to either promote or inhibit amyloid aggregation of proteins, but the molecular mechanisms for such complex behaviors remain unknown. Using coarse-grained molecular dynamics simulations, we investigated the effects of varying the strength of nonspecific NP-protein attraction on amyloid aggregation of a model protein, the amyloid-beta peptide implicated in Alzheimer's disease. Specifically, with increasing NP-peptide attraction, amyloid aggregation on the NP surface was initially promoted due to increased local protein concentration on the surface and destabilization of the folded state. However, further increase of NP-peptide attraction decreased the stability of amyloid fibrils and reduced their lateral diffusion on the NP surface necessary for peptide conformational changes and self-association, thus prohibiting amyloid aggregation. Moreover, we found that the relative concentration between protein and NPs also played an important role in amyloid aggregation. With a high NP/protein ratio, NPs that intrinsically promote protein aggregation may display an inhibitive effect by depleting the proteins in solution while having a low concentration of the proteins on each NP's surface. Our coarse-grained molecular dynamics simulation study offers a molecular mechanism for delineating the contrasting and seemingly conflicting effects of NP-protein attraction on amyloid aggregation and highlights the potential of tailoring anti-aggregation nanomedicine against amyloid diseases. PMID:26989481

  18. Contrast media hypersensitivity--scope of the problem.

    PubMed

    Brockow, Knut

    2005-04-15

    Hypersensitivity reactions to contrast media (CM) are frequent causes of anaphylactically induced fatalities. Adverse events after CM exposure are classified into immediate and non-immediate reactions, with differing pathomechanisms. In the majority of patients with immediate reactions, IgE-mediated allergy can not be demonstrated and the underlying mechanism remains unknown. However, recent data has provided evidence for skin test positivity and/or specific IgE in some patients with severe reactions. Cell-mediated hypersensitivity is the responsible mechanism for the majority of non-immediate skin eruptions. Skin tests have been employed to confirm this hypersensitivity. Previous reactors have an increased risk to develop new reactions upon repeated exposure, however, other risk factors are poorly defined. The use of skin tests for the selection of a "safe" CM is controversially discussed; information on sensitivity and specificity is lacking. New in-vitro assays have to be developed and/or validated. Premedication of previous reactors is common practice among radiologists, however, its precise role in the prevention of severe CM reactions to lower-osmolality CM has not been demonstrated. Thus, the main future tasks are to develop and validate allergic tests procedures, which may identify patients at risk and/or may confirm CM tolerance, and to reassess the value of different premedications in the prevention of hypersensitivity reactions. PMID:15767034

  19. Ultrasound Induced Fluorescence of Nanoscale Liposome Contrast Agents

    PubMed Central

    Zhang, Qimei; Morgan, Stephen P.; O’Shea, Paul; Mather, Melissa L.

    2016-01-01

    A new imaging contrast agent is reported that provides an increased fluorescent signal upon application of ultrasound (US). Liposomes containing lipids labelled with pyrene were optically excited and the excimer fluorescence emission intensity was detected in the absence and presence of an ultrasound field using an acousto-fluorescence setup. The acousto-fluorescence dynamics of liposomes containing lipids with pyrene labelled on the fatty acid tail group (PyPC) and the head group (PyPE) were compared. An increase in excimer emission intensity following exposure to US was observed for both cases studied. The increased intensity and time constants were found to be different for the PyPC and PyPE systems, and dependent on the applied US pressure and exposure time. The greatest change in fluorescence intensity (130%) and smallest rise time constant (0.33 s) are achieved through the use of PyPC labelled liposomes. The mechanism underlying the observed increase of the excimer emission intensity in PyPC labelled liposomes is proposed to arise from the “wagging” of acyl chains which involves fast response and requires lower US pressure. This is accompanied by increased lipid lateral diffusivity at higher ultrasound pressures, a mechanism that is also active in the PyPE labelled liposomes. PMID:27467748

  20. Contrast Affects fMRI Activity in Middle Temporal Cortex Related to Center–Surround Interaction in Motion Perception

    PubMed Central

    Turkozer, Halide B.; Pamir, Zahide; Boyaci, Huseyin

    2016-01-01

    As the size of a high contrast drifting Gabor patch increases, perceiving its direction of motion becomes harder. However, the same behavioral effect is not observed for a low contrast Gabor patch. Neuronal mechanisms underlying this size–contrast interaction are not well understood. Here using psychophysical methods and functional magnetic resonance imaging (fMRI), we investigated the neural correlates of this behavioral effect. In the behavioral experiments, motion direction discrimination thresholds were assessed for drifting Gabor patches with different sizes and contrasts. Thresholds increased significantly as the size of the stimulus increased for high contrast (65%) but did not change for low contrast (2%) stimuli. In the fMRI experiment, cortical activity was recorded while observers viewed drifting Gabor patches with different contrasts and sizes. We found that the activity in middle temporal (MT) area increased with size at low contrast, but did not change at high contrast. Taken together, our results show that MT activity reflects the size–contrast interaction in motion perception. PMID:27065922

  1. Phase Contrast Wavefront Sensing for Adaptive Optics

    NASA Technical Reports Server (NTRS)

    Bloemhof, E. E.; Wallace, J. K.; Bloemhof, E. E.

    2004-01-01

    Most ground-based adaptive optics systems use one of a small number of wavefront sensor technologies, notably (for relatively high-order systems) the Shack-Hartmann sensor, which provides local measurements of the phase slope (first-derivative) at a number of regularly-spaced points across the telescope pupil. The curvature sensor, with response proportional to the second derivative of the phase, is also sometimes used, but has undesirable noise propagation properties during wavefront reconstruction as the number of actuators becomes large. It is interesting to consider the use for astronomical adaptive optics of the "phase contrast" technique, originally developed for microscopy by Zemike to allow convenient viewing of phase objects. In this technique, the wavefront sensor provides a direct measurement of the local value of phase in each sub-aperture of the pupil. This approach has some obvious disadvantages compared to Shack-Hartmann wavefront sensing, but has some less obvious but substantial advantages as well. Here we evaluate the relative merits in a practical ground-based adaptive optics system.

  2. Parametric mapping of contrasted ovarian transvaginal sonography.

    PubMed

    Korhonen, Katrina; Moore, Ryan; Lyshchik, Andrej; Fleischer, Arthur C

    2015-06-01

    The purpose of this study was to assess the accuracy of parametric analysis of transvaginal contrast-enhanced ultrasound (TV-CEUS) for distinguishing benign versus malignant ovarian masses. A total of 48 ovarian masses (37 benign and 11 borderline/malignant) were examined with TV-CEUS (Definity; Lantheus, North Billerica, MA; Philips iU22; Philips Medical Systems, Bothell, WA). Parametric images were created offline with a quantification software (Bracco Suisse SA, Geneva, Switzerland) with map color scales adjusted such that abnormal hemodynamics were represented by the color red and the presence of any red color could be used to differentiate benign and malignant tumors. Using these map color scales, low values of the perfusion parameter were coded in blue, and intermediate values of the perfusion parameter were coded in yellow. Additionally, for each individual color (red, blue, or yellow), a darker shade of that color indicated a higher intensity value. Our study found that the parametric mapping method was considerably more sensitive than standard region of interest (ROI) analysis for the detection of malignant tumors but was also less specific than standard ROI analysis. Parametric mapping allows for stricter cutoff criteria, as hemodynamics are visualized on a finer scale than ROI analyses, and as such, parametric maps are a useful addition to TV-CEUS analysis by allowing ROIs to be limited to areas of the highest malignant potential. PMID:26002525

  3. Contrast vs noise effects on image quality

    NASA Astrophysics Data System (ADS)

    Hadar, Ofer; Corse, N.; Rotman, Stanley R.; Kopeika, Norman S.

    1996-11-01

    Low noise images are contract-limited, and image restoration techniques can improve resolution significantly. However, as noise level increases, resolution improvements via image processing become more limited because image restoration increases noise. This research attempts to construct a reliable quantitative means of characterizing the perceptual difference between target and background. A method is suggested for evaluating the extent to which it is possible to discriminate an object which has merged with its surroundings, in noise-limited and contrast limited images, i.e., how hard it would be for an observer to recognize the object against various backgrounds as a function of noise level. The suggested model will be a first order model to begin with, using a regular bar-chart with additive uncorrelated Gaussian noise degraded by standard atmospheric blurring filters. The second phase will comprise a model dealing with higher-order images. This computational model relates the detectability or distinctness of the object to measurable parameters. It also must characterize human perceptual response, i.e. the model must develop metrics which are highly correlated to the ease or difficulty which the human observer experiences in discerning the target from its background. This requirement can be fulfilled only by conducting psychophysical experiments quantitatively comparing the perceptual evaluations of the observers with the results of the mathematical model.

  4. Optical classification of contrasted coastal waters

    NASA Astrophysics Data System (ADS)

    Vantrepotte, V.; Loisel, H.; Dessailly, D.; Mériaux, X.

    2012-04-01

    The high optical complexity of the coastal ocean prevents the development of general open ocean-like inversion algorithms needed to derive in-water bio-optical and biogeochemical parameters from satellite information. To overcome this issue, regional algorithms are generally used in order to focus on the range of optical variability specific to a defined coastal region. This regional approach presents however various limitations including its high dependency on the data set used for its development as well as its limited applicability for large scale applications. Another and more universal approach consists in classifying coastal waters according to their optical properties (independently of their location) and then in applying a class-specific algorithm (empirical or semi-analytical). The framework associated with the development of such classification-based approach is detailed from an in situ data set collected in contrasted coastal waters of the eastern English Channel, north Sea and French Guyana. The advantages of defining an optical typology of the coastal domain for monitoring coastal water masses optical quality and improving the performance of the inversion procedure is emphasized. Further, the representativeness of optical classes defined in the latter training areas for global scale applications is also illustrated.

  5. Human contrast threshold and astronomical visibility

    NASA Astrophysics Data System (ADS)

    Crumey, Andrew

    2014-08-01

    The standard visibility model in light-pollution studies is the formula of Hecht, as used e.g. by Schaefer. However, it is applicable only to point sources and is shown to be of limited accuracy. A new visibility model is presented for uniform achromatic targets of any size against background luminances ranging from zero to full daylight, produced by a systematic procedure applicable to any appropriate data set (e.g. Blackwell's), and based on a simple but previously unrecognized empirical relation between contrast threshold and adaptation luminance. The scotopic luminance correction for variable spectral radiance (colour index) is calculated. For point sources, the model is more accurate than Hecht's formula and is verified using telescopic data collected at Mount Wilson in 1947, enabling the sky brightness at that time to be determined. The result is darker than the calculation by Garstang, implying that light pollution grew more rapidly in subsequent decades than has been supposed. The model is applied to the nebular observations of William Herschel, enabling his visual performance to be quantified. Proposals are made regarding sky quality indicators for public use.

  6. Characteristics of atmospheric ions in contrasting environments

    SciTech Connect

    Wilkening, M.

    1984-01-01

    The general nature of atmospheric small ions with mobilities in the approximate range of 1-2 x 10/sup -4/ m/sup 2//Vs has been known for many decades. In this study changes in ion-pair production rates, ion density, mobility, and polar conductivity have been observed in contrasting environments with the results that new light is shed on the properties of these ions which play such an important role in atmospheric electricity. /sup 222/Rn, /sup 220/Rn and their daughter products are the chief ionizing agents in the lower layers of the atmosphere exceeding that due to cosmic rays and radioactive substances in the ground. A single alpha particle from the decay of /sup 222/Rn will produce about 150,000 ion pairs. It is important, therefore, to give careful consideration to the role of these natural radioactive nuclides when investigating the characteristics of atmospheric ions. Over a period of years studies of the behavior of positive and negative small ions have been made in outdoor environments at a mountain location, in the Rio Grande Valley at Socorro, New Mexico and in the Carlsbad Caverns. These sites provided wide variation in ion-pair production rates, water vapor mixing ratios, and condensation nuclei concentrations against which the atmospheric electrical characteristics could be measured and analyzed. The role of the radon-daughter ions in storm and fair weather conditions at the Langmuir Laboratory has been treated previously. 16 references, 2 tables.

  7. Printed Multicolor High-Contrast Electrochromic Devices.

    PubMed

    Chen, Bo-Han; Kao, Sheng-Yuan; Hu, Chih-Wei; Higuchi, Masayoshi; Ho, Kuo-Chuan; Liao, Ying-Chih

    2015-11-18

    In this study, electrochemical responses of inkjet-printed multicolored electrochromic devices (ECD) were studied to evaluate the feasibility of presenting multiple colors in one ECD. Metallo-supramolecular polymers (MEPE) solutions with two primary colors were inkjet-printed on flexible electrodes. By digitally controlling print dosages of each species, the colors of the printed EC thin film patterns can be adjusted directly without premixing or synthesizing new materials. The printed EC thin films were then laminated with a solid transparent thin film electrolyte and a transparent conductive thin film to form an ECD. After applying a dc voltage, the printed ECDs exhibited great contrast with a transmittance change (ΔT) of 40.1% and a high coloration efficiency of 445 cm(2) C(-1) within a short darkening time of 2 s. The flexible ECDs also showed the same darkening time of 2 s and still had a high ΔT of 30.1% under bending condition. This study demonstrated the feasibility to fabricate display devices with different color setups by an all-solution process and can be further extended to other types of displays. PMID:26496422

  8. Intravascular iodinated contrast media and the anaesthetist.

    PubMed

    Dickinson, M C; Kam, P C A

    2008-06-01

    The use of intravascular iodinated contrast media (ICM) in radiological investigations is common. Increasingly, anaesthetists and intensivists are involved in the care of patients undergoing these investigations. Whilst the use of ICM is generally safe there are important adverse effects that need to be recognised and measures instigated to prevent or treat these effects. In patients at risk of developing adverse reactions it is important to consider alternative modes of imaging so that ICM can be avoided. Strategies for the prevention of ICM nephropathy should be considered in all patients receiving ICM. Currently intravascular volume expansion with 0.9% saline has the strongest evidence base. The use of isotonic sodium bicarbonate combined with N-acetylcysteine appears promising in providing further benefits. Although the use of N-acetylcysteine alone has not been shown to significantly reduce the incidence of ICM nephropathy it is cheap, has few adverse effects and it would seem reasonable to continue its use in conjunction with intravascular volume expansion. The routine use of corticosteroid and antihistamine premedication is not always effective in preventing general adverse reactions. PMID:18477275

  9. High contrast imaging polarimetry of circumstellar environments

    NASA Astrophysics Data System (ADS)

    Canovas Cabrera, H.

    2011-09-01

    The work presented in this thesis is based on the analysis of the results produced by ExPo, the Extreme Polarimeter. ExPo is an imaging polarimeter that has been designed and built by the group of prof. Christoph Keller, at Utrecht University. The purpose of this instrument is to use polarimetry to detect and characterize the circumstellar environments around different types of stars. In this work I focus on the polarized features that are produced by scattering by dust grains. Depending on the properties of the particles producing the scattering (size, shape...) and the scattering angle (forward, backward scattering), the light becomes polarized in higher or lower degree. The main problem when studying circumstellar environments is the high contrast ratios that are faced. For example, a young star is typically four orders of magnitude (10000 times) brighter than its protoplanetary disk. On the other hand, the light emitted by the star is largely unpolarized, while the light that is scattered (by the protoplanetary disk in this example) is polarized. Therefore, polarimetry offers a very elegant way to remove most of the starlight, allowing the detection of only the polarized photons. Furthermore, and as explained before, by studying the polarization of the light that we measure we can learn more about the properties of the circumstellar environments (dust composition, geometry, etc.). ExPo has produced a wealth of data, combining observations of very different targets such as protoplanetary disks, post-AGB stars, comets and planets of our Solar System (Venus and Saturn).

  10. MMP-14 Triggered Fluorescence Contrast Agent.

    PubMed

    Nguyen, Mai-Dung; Kang, Kyung A

    2016-01-01

    Matrix metalloproteinase-14 (MMP-14) is involved in cancer invasion, metastasis, and angiogenesis. Therefore, it is considered to be a biomarker for aggressive cancer types, including some of the triple-negative breast cancer. Accurate (i.e., specific) and sensitive detection of MMP-14 can, thus, be important for the early diagnosis of and accurate prognosis for aggressive cancer, including the breast cancer caused by cell line MDA-MB 231. Fluorophore-mediated molecular sensing has been used for detecting biomarkers, for a long time. One way to increase the specificity of the sensing is designing the fluorophore to emit its fluorescence only when it encounters the biomarker of interest. When a fluorophore is placed on the surface of, or very close to a gold nanoparticle (GNP), its fluorescence is quenched. Applying this relationship between the GNP and fluorophore, we have developed a GNP-based, near-infrared fluorescent contrast agent that is highly specific for MMP-14. This agent normally emits only 14-17 % fluorescence of the free fluorophore. When the agent encounters MMP-14, its fluorescence gets fully restored, allowing MMP-14 specific optical signal emission. PMID:27526171

  11. Simultaneous brightness contrast of foraging Papilio butterflies

    PubMed Central

    Kinoshita, Michiyo; Takahashi, Yuki; Arikawa, Kentaro

    2012-01-01

    This study focuses on the sense of brightness in the foraging Japanese yellow swallowtail butterfly, Papilio xuthus. We presented two red discs of different intensity on a grey background to butterflies, and trained them to select one of the discs. They were successfully trained to select either a high intensity or a low intensity disc. The trained butterflies were tested on their ability to perceive brightness in two different protocols: (i) two orange discs of different intensity presented on the same intensity grey background and (ii) two orange discs of the same intensity separately presented on a grey background that was either higher or lower in intensity than the training background. The butterflies trained to high intensity red selected the orange disc of high intensity in protocol 1, and the disc on the background of low intensity grey in protocol 2. We obtained similar results in another set of experiments with purple discs instead of orange discs. The choices of the butterflies trained to low intensity red were opposite to those just described. Taken together, we conclude that Papilio has the ability to learn brightness and darkness of targets independent of colour, and that they have the so-called simultaneous brightness contrast. PMID:22179808

  12. Active coloration with flexible high contrast metastructures

    NASA Astrophysics Data System (ADS)

    Zhu, Li; Kapraun, Jonas; Ferrara, James; Chang-Hasnain, Connie J.

    2015-02-01

    The ability to actively control the perceived color of objects is highly desirable for a variety of applications, such as camouflage, sensing, and displays. Such a phenomenon can be readily found in nature - the chameleon is an excellent example. However, the capability to change color at-will has yet to be reproduced by humans. Ultra-thin dielectric high contrast metastructures (HCMs) have been shown to exhibit unique versatility to manipulate light. In this work, we report a completely new flexible HCM structure whose color can be varied by stretching the membrane. This is accomplished with a novel HCM design that annihilates the 0th order diffraction in a grating while enhancing the -1st order. The color perception of the HCM, determined by the -1st diffraction order, is thus easily changed with the variation of its period. The ultra-thin HCM is patterned on a silicon-on-insulator wafer and transferred onto a flexible membrane. We measure more than 15 times stronger intensity in the -1st order diffraction than the 0th order, in excellent agreement with theoretical results. We experimentally demonstrate brilliant colors and change the color of a 1 cm×1 cm sample from green to orange (39 nm wavelength change) with a stretch of 4.9% (25 nm period change). The same effect can be used for steering a laser beam. We demonstrate more than 40 resolvable beam spots.

  13. Diffraction contrast imaging using virtual apertures.

    PubMed

    Gammer, Christoph; Burak Ozdol, V; Liebscher, Christian H; Minor, Andrew M

    2015-08-01

    Two methods on how to obtain the full diffraction information from a sample region and the associated reconstruction of images or diffraction patterns using virtual apertures are demonstrated. In a STEM-based approach, diffraction patterns are recorded for each beam position using a small probe convergence angle. Similarly, a tilt series of TEM dark-field images is acquired. The resulting datasets allow the reconstruction of either electron diffraction patterns, or bright-, dark- or annular dark-field images using virtual apertures. The experimental procedures of both methods are presented in the paper and are applied to a precipitation strengthened and creep deformed ferritic alloy with a complex microstructure. The reconstructed virtual images are compared with conventional TEM images. The major advantage is that arbitrarily shaped virtual apertures generated with image processing software can be designed without facing any physical limitations. In addition, any virtual detector that is specifically designed according to the underlying crystal structure can be created to optimize image contrast. PMID:25840371

  14. Global fishery prospects under contrasting management regimes.

    PubMed

    Costello, Christopher; Ovando, Daniel; Clavelle, Tyler; Strauss, C Kent; Hilborn, Ray; Melnychuk, Michael C; Branch, Trevor A; Gaines, Steven D; Szuwalski, Cody S; Cabral, Reniel B; Rader, Douglas N; Leland, Amanda

    2016-05-01

    Data from 4,713 fisheries worldwide, representing 78% of global reported fish catch, are analyzed to estimate the status, trends, and benefits of alternative approaches to recovering depleted fisheries. For each fishery, we estimate current biological status and forecast the impacts of contrasting management regimes on catch, profit, and biomass of fish in the sea. We estimate unique recovery targets and trajectories for each fishery, calculate the year-by-year effects of alternative recovery approaches, and model how alternative institutional reforms affect recovery outcomes. Current status is highly heterogeneous-the median fishery is in poor health (overfished, with further overfishing occurring), although 32% of fisheries are in good biological, although not necessarily economic, condition. Our business-as-usual scenario projects further divergence and continued collapse for many of the world's fisheries. Applying sound management reforms to global fisheries in our dataset could generate annual increases exceeding 16 million metric tons (MMT) in catch, $53 billion in profit, and 619 MMT in biomass relative to business as usual. We also find that, with appropriate reforms, recovery can happen quickly, with the median fishery taking under 10 y to reach recovery targets. Our results show that commonsense reforms to fishery management would dramatically improve overall fish abundance while increasing food security and profits. PMID:27035953

  15. Ionic contrast terahertz near field imaging

    NASA Astrophysics Data System (ADS)

    Gallot, Guilhem

    2013-09-01

    We demonstrated the direct and noninvasive imaging of functional neurons by Ionic Contrast Terahertz (ICT) near-field microscopy. This technique provides quantitative measurements of ionic concentrations in both the intracellular and extracellular compartments and opens the way to direct noninvasive imaging of neurons during electrical, toxin, or thermal stresses. Furthermore, neuronal activity results from both a precise control of transient variations in ionic conductance and a much less studied water exchange between the extracellular matrix and the intraaxonal compartment. The developed ICT technique associated with a full three-dimensional simulation of the axon-aperture near-field system allows a precise measurement of the axon geometry and therefore the direct visualization of neuron swelling induced by temperature change or neurotoxin poisoning. We also developed Terahertz Attenuated Total Reflection (ATR) devices perfectly suited for studying cell layers. Inserted in a terahertz time-domain system, and using a high resistivity low loss silicon prism to couple the terahertz wave into the sample, the detection scheme is based on the relative differential spectral phase of two orthogonal polarizations. Biological sample imaging as well as subwavelength (λ/16) longitudinal resolution are demonstrated.

  16. Global fishery prospects under contrasting management regimes

    PubMed Central

    Costello, Christopher; Ovando, Daniel; Clavelle, Tyler; Strauss, C. Kent; Hilborn, Ray; Melnychuk, Michael C.; Branch, Trevor A.; Gaines, Steven D.; Szuwalski, Cody S.; Cabral, Reniel B.; Rader, Douglas N.; Leland, Amanda

    2016-01-01

    Data from 4,713 fisheries worldwide, representing 78% of global reported fish catch, are analyzed to estimate the status, trends, and benefits of alternative approaches to recovering depleted fisheries. For each fishery, we estimate current biological status and forecast the impacts of contrasting management regimes on catch, profit, and biomass of fish in the sea. We estimate unique recovery targets and trajectories for each fishery, calculate the year-by-year effects of alternative recovery approaches, and model how alternative institutional reforms affect recovery outcomes. Current status is highly heterogeneous—the median fishery is in poor health (overfished, with further overfishing occurring), although 32% of fisheries are in good biological, although not necessarily economic, condition. Our business-as-usual scenario projects further divergence and continued collapse for many of the world’s fisheries. Applying sound management reforms to global fisheries in our dataset could generate annual increases exceeding 16 million metric tons (MMT) in catch, $53 billion in profit, and 619 MMT in biomass relative to business as usual. We also find that, with appropriate reforms, recovery can happen quickly, with the median fishery taking under 10 y to reach recovery targets. Our results show that commonsense reforms to fishery management would dramatically improve overall fish abundance while increasing food security and profits. PMID:27035953

  17. Puzzling Mechanisms

    ERIC Educational Resources Information Center

    van Deventer, M. Oskar

    2009-01-01

    The basis of a good mechanical puzzle is often a puzzling mechanism. This article will introduce some new puzzling mechanisms, like two knots that engage like gears, a chain whose links can be interchanged, and flat gears that do not come apart. It illustrates how puzzling mechanisms can be transformed into real mechanical puzzles, e.g., by…

  18. A review of contrast pattern based data mining

    NASA Astrophysics Data System (ADS)

    Zhu, Shiwei; Ju, Meilong; Yu, Junfeng; Cai, Binlei; Wang, Aiping

    2015-07-01

    Contrast pattern based data mining is concerned with the mining of patterns and models that contrast two or more datasets. Contrast patterns can describe similarities or differences between the datasets. They represent strong contrast knowledge and have been shown to be very successful for constructing accurate and robust clusters and classifiers. The increasing use of contrast pattern data mining has initiated a great deal of research and development attempts in the field of data mining. A comprehensive revision on the existing contrast pattern based data mining research is given in this paper. They are generally categorized into background and representation, definitions and mining algorithms, contrast pattern based classification, clustering, and other applications, the research trends in future. The primary of this paper is to server as a glossary for interested researchers to have an overall picture on the current contrast based data mining development and identify their potential research direction to future investigation.

  19. Luminance and chromatic contributions to a hyperacuity task: isolation by contrast polarity and target separation

    PubMed Central

    Sun, Hao; Cooper, Bonnie; Lee, Barry B.

    2012-01-01

    Vernier thresholds are known to be elevated when a target pair has opposite contrast polarity. Polarity reversal is used to assess the role of luminance and chromatic pathways in hyperacuity performance. Psychophysical hyperacuity thresholds were measured for pairs of gratings of various combinations of luminance (Lum) and chromatic (Chr) contrast polarities, at different ratios of luminance to chromatic contrast. With two red-green gratings of matched luminance and chromatic polarity (+Lum+Chr), there was an elevation of threshold at isoluminance. When both luminance and chromatic polarity were mismatched (−Lum−Chr), thresholds were substantially elevated under all conditions. With the same luminance contrast polarity and opposite chromatic polarity (+Lum−Chr) thresholds were only elevated close to isoluminance; in the reverse condition (−Lum+Chr), thresholds were elevated as in the −Lum−Chr condition except close to equiluminance. Similar data were obtained for gratings isolating the short-wavelength cone mechanism. Further psychophysical measurements assessed the role of target separation with matched or mismatched contrast polarity; similar results were found for luminance and chromatic gratings. Comparison physiological data were collected from parafoveal ganglion cells of the macaque retina. Positional precision of ganglion cell signals was assessed under conditions related to the psychophysical measurements. On the basis of these combined observations, it is argued that both magnocellular, parvocellular, and koniocellular pathways have access to cortical positional mechanisms associated with vernier acuity. PMID:22306680

  20. pH-induced contrast in viscoelasticity imaging of biopolymers

    NASA Astrophysics Data System (ADS)

    Yapp, R. D.; Insana, M. F.

    2009-03-01

    Understanding contrast mechanisms and identifying discriminating features is at the heart of diagnostic imaging development. This paper focuses on how pH influences the viscoelastic properties of biopolymers to better understand the effects of extracellular pH on breast tumour elasticity imaging. Extracellular pH is known to decrease as much as 1 pH unit in breast tumours, thus creating a dangerous environment that increases cellular mutatation rates and therapeutic resistance. We used a gelatin hydrogel phantom to isolate the effects of pH on a polymer network with similarities to the extracellular matrix in breast stroma. Using compressive unconfined creep and stress relaxation measurements, we systematically measured the viscoelastic features sensitive to pH by way of time-domain models and complex modulus analysis. These results are used to determine the sensitivity of quasi-static ultrasonic elasticity imaging to pH. We found a strong elastic response of the polymer network to pH, such that the matrix stiffness decreases as pH was reduced; however, the viscous response of the medium to pH was negligible. While physiological features of breast stroma such as proteoglycans and vascular networks are not included in our hydrogel model, observations in this study provide insight into viscoelastic features specific to pH changes in the collagenous stromal network. These observations suggest that the large contrast common in breast tumours with desmoplasia may be reduced under acidic conditions, and that viscoelastic features are unlikely to improve discriminability.

  1. Successive, simultaneous, and anticipatory contrast in the consumption of saccharin solutions.

    PubMed

    Flaherty, C F; Rowan, G A

    1986-10-01

    Contrast effects were obtained in rats in the consumption of saccharin solutions in three different paradigms. Degree of negative contrast varied as a function of concentration disparity, but not equally in the three procedures. Successive negative contrast occurred following shifts from 0.15% to either 0.075% or 0.05% saccharin but did not occur following shifts to 0.10% or 0.125% saccharin. Some degree of simultaneous contrast was obtained with all four concentration disparities. Anticipatory contrast, where the intake of the first substance is suppressed by a more preferred second substance, occurred only in the case of the 0.05%-0.15% difference in concentrations. It was suggested that the several contrast paradigms engage somewhat different psychological processes differentially involving emotional, sensory, and associative mechanisms, but all lead to behavior based on relative value. A modification of Toates's (1981) incentive model of ingestive behavior was suggested to incorporate relativity effects based on both associative and nonassociative factors in the consumption of both nutritive and nonnutritive substances. PMID:3772302

  2. Contrast to Noise Ratio and Contrast Detail Analysis in Mammography:A Monte Carlo Study

    NASA Astrophysics Data System (ADS)

    Metaxas, V.; Delis, H.; Kalogeropoulou, C.; Zampakis, P.; Panayiotakis, G.

    2015-09-01

    The mammographic spectrum is one of the major factors affecting image quality in mammography. In this study, a Monte Carlo (MC) simulation model was used to evaluate image quality characteristics of various mammographic spectra. The anode/filter combinations evaluated, were those traditionally used in mammography, for tube voltages between 26 and 30 kVp. The imaging performance was investigated in terms of Contrast to Noise Ratio (CNR) and Contrast Detail (CD) analysis, by involving human observers, utilizing a mathematical CD phantom. Soft spectra provided the best characteristics in terms of both CNR and CD scores, while tube voltage had a limited effect. W-anode spectra filtered with k-edge filters demonstrated an improved performance, that sometimes was better compared to softer x-ray spectra, produced by Mo or Rh anode. Regarding the filter material, k-edge filters showed superior performance compared to Al filters.

  3. Acoustic radiation pressure: A 'phase contrast' agent for x-ray phase contrast imaging

    SciTech Connect

    Bailat, Claude J.; Hamilton, Theron J.; Rose-Petruck, Christoph; Diebold, Gerald J.

    2004-11-08

    We show that the radiation pressure exerted by a beam of ultrasound can be used for contrast enhancement in high-resolution x-ray imaging of tissue and soft materials. Interfacial features of objects are highlighted as a result of both the displacement introduced by the ultrasound and the inherent sensitivity of x-ray phase contrast imaging to density variations. The potential of the method is demonstrated by imaging microscopic tumor phantoms embedded into tissue with a thickness typically presented in mammography. The detection limit of micrometer size masses exceeds the resolution of currently available mammography imaging systems. The directionality of the acoustic radiation force and its localization in space permits the imaging of ultrasound-selected tissue volumes. The results presented here suggest that the method may permit the detection of tumors in soft tissue in their early stage of development.

  4. Papers and Studies in Contrastive Linguistics, Volume Nine.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    1979-01-01

    This issue of the journal includes these papers on contrastive linguistics: "Tag Questions, Transformational Grammar and Pragmatics" (Wolfram Bublitz); "Toward Contrasting Styles" (Karol Janicki); "Some More Remarks on the Pedagogical Uses of Contrastive Studies" (Waldemar Marton); "Stress in Polish--With Some Comparisons to English Stress" (James…

  5. Papers and Studies in Contrastive Linguistics, Volume Ten.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    1979-01-01

    This issue of the journal includes these papers on contrastive linguistics: "A Question of Imperatives" (Tom Wachtel); "Contrastive Sociolinguistics--Some Methodological Considerations" (Karol Janicki); "How to Describe Phonological Variation" (Thomas Herok, Livia Tonelli); "Towards a Contrastive Pragmalinguistics" (Philip Riley); "The Perception…

  6. Infrared Contrast Analysis Technique for Flash Thermography Nondestructive Evaluation

    NASA Technical Reports Server (NTRS)

    Koshti, Ajay

    2014-01-01

    The paper deals with the infrared flash thermography inspection to detect and analyze delamination-like anomalies in nonmetallic materials. It provides information on an IR Contrast technique that involves extracting normalized contrast verses time evolutions from the flash thermography infrared video data. The paper provides the analytical model used in the simulation of infrared image contrast. The contrast evolution simulation is achieved through calibration on measured contrast evolutions from many flat bottom holes in the subject material. The paper also provides formulas to calculate values of the thermal measurement features from the measured contrast evolution curve. Many thermal measurement features of the contrast evolution that relate to the anomaly characteristics are calculated. The measurement features and the contrast simulation are used to evaluate flash thermography inspection data in order to characterize the delamination-like anomalies. In addition, the contrast evolution prediction is matched to the measured anomaly contrast evolution to provide an assessment of the anomaly depth and width in terms of depth and diameter of the corresponding equivalent flat-bottom hole (EFBH) or equivalent uniform gap (EUG). The paper provides anomaly edge detection technique called the half-max technique which is also used to estimate width of an indication. The EFBH/EUG and half-max width estimations are used to assess anomaly size. The paper also provides some information on the "IR Contrast" software application, half-max technique and IR Contrast feature imaging application, which are based on models provided in this paper.

  7. The Study of Tone in Languages with a Quantity Contrast

    ERIC Educational Resources Information Center

    Remijsen, Bert

    2014-01-01

    This paper deals with the study of tone in languages that additionally have a phonological contrastive of quantity, such as vowel length or stress. In such complex word-prosodic systems, tone and the quantity contrast(s) can be fully independent of one another, or they may interact. Both of these configurations are illustrated in this paper, and…

  8. Papers and Studies in Contrastive Linguistics, Volume Fourteen.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    1982-01-01

    This issue of the journal includes these papers on contrastive linguistics: "Violations of Frege's Principle and Their Significance for Contrastive Semantics" (Dafydd Gibbon); "Writing the Contrastive Grammar of English and Dutch. The Treatment of Modal Notions" (Flor Aarts and Herman Wekker); "The Theory and Methodology of Speech Science and…

  9. The differing roles of comparison and contrast in children's categorization.

    PubMed

    Namy, Laura L; Clepper, Lauren E

    2010-11-01

    Comparison of perceptually similar exemplars from an object category encourages children to overlook compelling perceptual similarities and use relational and functional properties more relevant for taxonomic categorization. This article investigates whether showing children a contrasting object that is perceptually similar but out of kind serves the same function as comparison in heightening children's attention to taxonomically relevant features. In this study, 4-year-olds completed a forced-choice categorization task in which they viewed exemplars from a target category and then selected among (a) a perceptually similar out-of-kind object, (b) a category member that differed perceptually from the exemplars, and (c) a thematically related object. Children were assigned to one of four conditions: No-Compare/No-Contrast, Compare/No-Contrast, No-Compare/Contrast, or Compare/Contrast. As in previous work, comparison increased the frequency of category responses, but there was no effect of contrast on categorization. However, only those in the Compare/Contrast condition displayed consistently taxonomic patterns of responding. Follow-up studies revealed that the effect of comparison plus contrast was evident only when comparison preceded, rather than followed, contrast information and that the value added by providing contrastive information is not attributable to the perceptual similarity between the category exemplars and the contrast object. Comparison and contrast make differing contributions to children's categorization. PMID:20609449

  10. Phonetics and Phonology of Thematic Contrast in German

    ERIC Educational Resources Information Center

    Braun, Bettina

    2006-01-01

    It is acknowledged that contrast plays an important role in understanding discourse and information structure. While it is commonly assumed that contrast can be marked by intonation only, our understanding of the intonational realization of contrast is limited. For German there is mainly introspective evidence that the rising theme accent (or…

  11. Comparison versus Contrast: Task Specifics Affect Category Acquisition

    ERIC Educational Resources Information Center

    Ankowski, Amber A.; Vlach, Haley A.; Sandhofer, Catherine M.

    2013-01-01

    A large literature has documented that comparison and contrast lead to better performance in a variety of tasks. However, studies of comparison and contrast present contradictory conclusions as to when and how these processes benefit learners. Across four studies, we examined how the specifics of the comparison and contrast task affect performance…

  12. Papers and Studies in Contrastive Linguistics, Volume Nineteen.

    ERIC Educational Resources Information Center

    Fisiak, Jacek, Ed.

    1985-01-01

    This issue of the journal includes these papers on contrastive linguistics: "Contrastive Patholinguistics: The Acquisition of English Grammatical Morphemes by German Dyslexics in a Foreign-Language Teaching Context" (Udo O. H. Jung); "Contrastive Pragmatics" (Marie-Louise Liebe-Harkort); "On Questions in English and Swedish" (Kay Wikberg); "On…

  13. Triple-energy contrast enhanced digital mammography

    NASA Astrophysics Data System (ADS)

    Puong, Sylvie; Milioni de Carvalho, Pablo; Muller, Serge

    2010-04-01

    With the injection of iodine, Contrast Enhanced Digital Mammography (CEDM) provides functional information about breast tumour angiogenesis that can potentially help in cancer diagnosis. In order to generate iodine images in which the gray level is proportional to the iodine thickness, temporal and dual-energy approaches have already been considered. The dual-energy method offers the advantage of less patient motion artifacts and better comfort during the exam. However, this approach requires knowledge of the breast thickness at each pixel. Generally, as compression is applied, the breast thickness at each pixel is taken as the compression thickness. Nevertheless, in the breast border region, this assumption is not correct anymore and this causes inaccuracies in the iodine image. Triple-Energy CEDM could overcome these limitations by providing supplemental information in the form of a third image acquired with a different spectrum than the other two. This precludes the need of a priori knowledge of the breast thickness. Moreover, with Triple-Energy CEDM, breast thickness and glandularity maps could potentially be derived. In this study, we first focused on the method to recombine the three images in order to generate the iodine image, analyzing the performance of either quadratic, cubic or conic recombination functions. Then, we studied the optimal acquisition spectra in order to maximize the iodine SDNR in the recombined image for a given target total glandular dose. The concept of Triple-Energy CEDM was validated on simulated textured images and poly-energetic images acquired with a conventional X-ray mammography tube.

  14. Contrasting Controversies: Fracking and Climate Change

    NASA Astrophysics Data System (ADS)

    Duggan-Haas, D.; Zabel, I. H. H.; Ross, R. M.

    2014-12-01

    Slickwater high-volume hydraulic fracturing (commonly known as "fracking") is highly controversial. So is global warming, and the two issues are closely related, but the natures of these two controversies have substantial and important differences. Building upon years of experience in teaching and developing resources and strategies for teaching about evolution and climate change, staff at the Paleontological Research Institution have engaged in public outreach and educator professional development to help nurture understanding of fracking and the broader energy system. How are these controversies similar to and different from one another, and how should understanding these similarities and differences inform educational programming (and about how you talk about these issues with your Uncle Fred at the family holiday dinner?). It is nearly universally agreed amongst scientists who study climate that changes now underway are real and human caused, and are posing or likely to pose very serious problems for humanity. Scientists who study slickwater high-volume hydraulic fracturing agree that it causes environmental damage, but there is no consensus as to whether fracking causes more or less harm (e.g., among different kinds of environment harm, across different temporal and spatial scales, and among different social contexts) than other ways of producing energy on a large scale. In other words, the basic tenets of climate change are not a matter of scientific controversy, though the implications for policy making obviously remain politically controversial, while fracking is an issue of both scientific and political controversy. Without advocating for or against fracking, we help audiences disentangle scientific and political issues, better understand the energy resources used in their own communities, and consider issues of scale, systems, and complexity. We will compare and contrast the overlapping controversies surrounding climate change and fracking and highlight

  15. Changes in the Bolometric Contrast of Sunspots

    NASA Astrophysics Data System (ADS)

    Chapman, G. A.; Cookson, A. M.; Dobias, J. J.

    1993-12-01

    We report on photometric observations of sunspots carried out with the Cartesian Full Disk Telescope (CFDT) at the San Fernando Observatory (SFO). The pixel size is 5.1 arc-sec and the wavelength for the data discussed here is 6723 Angstroms. Fluctuations in total solar irradiance due to sunspots are often modeled using a constant value of alpha, which we are calling the bolometric contrast of a sunspot. We have defined alpha_ {eff} as DEF/(2 times PSI), where DEF is the sunspot's photometric deficit relative to the quiet photosphere, and PSI is the digitally determined Photometric Sunspot Index (Willson et al., 1981). For 40 sunspot groups, we find that alpha_ {eff} = (0.276 +/- 0.051) + (3.22 +/- 0.34) 10(-5) A_s, where A_s is the corrected area of the sunspot in micro-hemispheres. The coefficient of determination is r(2) = 0.1936, which is significant at the p = 0.005 level. We also find that alpha_ {eff} is highly correlated with the ratio of umbral to total spot area (A_u/A_s). For 86 sunspot-days we find alpha_ {eff} = (0.219 +/- 0.018) + (0.643 +/- 0.028) (A_u/A_s) with the linear coefficient of determination r(2) = 0.859. This suggests that an improved PSI can be constructed from knowledge of a sunspot's umbral to total area ratio. The use of such an improved PSI or, better still, actual photometry should reduce the statistical noise in comparisons with spacecraft measurements of the total solar irradiance. This work has been partially supported by grants from NSF and NASA.

  16. Passive millimeter wave differential interference contrast polarimetry

    DOEpatents

    Bernacki, Bruce E; Kelly, James F; Sheen, David M; Tedeschi, Jonathan R; Hall, Thomas E; Hatchell, Brian K; Valdez, Patrick; McMakin, Douglas L

    2014-04-29

    Differential polarization imaging systems include an axicon configured to provide a displacement of ray bundles associated with different image patches. The displaced ray bundles are directed to antenna horns and orthomode transducers so as to provide outputs correspond to orthogonal linear states of polarization (SOPs). The outputs are directed to a differential radiometer so that Stokes parameter differences between image patches can be obtained. The ray bundle displacements can be selected to correspond to a mechanical spacing of antenna horns. In some examples, ray bundle displacement corresponds to a displacement less than the diffraction limit.

  17. Assessment of the regional landslide susceptibility based on GIS

    NASA Astrophysics Data System (ADS)

    Sun, Ze; Xie, Shijie; Zhang, Kexin; Zheng, Xinshen; Zhu, Yunhai

    2007-06-01

    Landslide is one of the major geological disasters in Minhe area bounded on Gansu and Qinghai. Based on field detailed investigation on landslide susceptibility of Minhe area, the said paper selected four principal controlling factors to establish digital assessment standard of regional landslide susceptibility via construction of mathematical model as well as making scoring diagram of regional landslide susceptibility. Meanwhile, the method and flow of geological mapping multisource-data integration was initially set up. Two premises for conducting multisource-data integration during regional geological survey on digital basis were determined, namely, geological problem and mathematical model applicable for various geoscience research data. Two mathematical methods cited during the whole flow were Analytic Hierarchy Process (AHP) and decision tree. Digital quantification of different data types such as qualitative data and qualitative data was realized with AHP, so that those data can be imported into mathematical formula and participated in calculation as variables. Decision tree achieved artificial intelligent classification of space data such as remote sensing. Finally, landslide susceptibility assessment diagram of Minhe area was obtained, which was basically in accordance with the actual landslide distribution principle of the region via comparison with actual conditions.

  18. Contrast enhancement of propagation based X-ray phase contrast imaging

    NASA Astrophysics Data System (ADS)

    Pan, Adam; Xu, Ling; Petruccelli, Jon C.; Gupta, Rajiv; Barbastathis, George

    2014-09-01

    We demonstrate a quantitative X-ray phase contrast imaging (XPCI) technique derived from propagation dependent phase change. We assume that the absorption and phase components are correlated and solve the Transport of Intensity Equation (TIE). The experimental setup is simple compared to other XPCI techniques; the only requirements are a micro-focus X-ray source with sufficient temporal coherence and an X-ray detector of sufficient spatial resolution. This method was demonstrated in three scenarios, the first of which entails identification of an index-matched sphere. A rubber and nylon sphere were immersed in water and imaged. While the rubber sphere could be plainly seen on a radiograph, the nylon sphere was only visible in the phase reconstruction. Next, the technique was applied to differentiating liquid samples. In this scenario, three liquid samples (acetone, water, and hydrogen peroxide) were analyzed using both conventional computed tomography (CT) and phase contrast CT. While conventional CT was capable of differentiating between acetone and the other two liquids, it failed to distinguish between water and hydrogen peroxide; only phase CT was capable of differentiating all three samples. Finally, the technique was applied to CT imaging of a human artery specimen with extensive atherosclerotic plaque. This scenario demonstrated the increased sensitivity to soft tissue compared to conventional CT; it also uncovered some drawbacks of the method, which will be the target of future work. In all cases, the signal-to-noise ratio of phase contrast was greatly enhanced relative to conventional attenuation-based imaging.

  19. Practical method and device for enhancing pulse contrast ratio for lasers and electron accelerators

    DOEpatents

    Zhang, Shukui; Wilson, Guy

    2014-09-23

    An apparatus and method for enhancing pulse contrast ratios for drive lasers and electron accelerators. The invention comprises a mechanical dual-shutter system wherein the shutters are placed sequentially in series in a laser beam path. Each shutter of the dual shutter system has an individually operated trigger for opening and closing the shutter. As the triggers are operated individually, the delay between opening and closing first shutter and opening and closing the second shutter is variable providing for variable differential time windows and enhancement of pulse contrast ratio.

  20. Newborns' preference for face-relevant stimuli: Effects of contrast polarity

    PubMed Central

    Farroni, Teresa; Johnson, Mark H.; Menon, Enrica; Zulian, Luisa; Faraguna, Dino; Csibra, Gergely

    2005-01-01

    There is currently no agreement as to how specific or general are the mechanisms underlying newborns' face preferences. We address this issue by manipulating the contrast polarity of schematic and naturalistic face-related images and assessing the preferences of newborns. We find that for both schematic and naturalistic face images, the contrast polarity is important. Newborns did not show a preference for an upright face-related image unless it was composed of darker areas around the eyes and mouth. This result is consistent with either sensitivity to the shadowed areas of a face with overhead (natural) illumination and/or to the detection of eye contact. PMID:16284255

  1. Dual Contrast Agent for Computed Tomography and Magnetic Resonance Hard Tissue Imaging

    PubMed Central

    Ventura, Manuela; Sun, Yi; Rusu, Viorel; Laverman, Peter; Borm, Paul; Heerschap, Arend; Oosterwijk, Egbert; Boerman, Otto C.; Walboomers, X. Frank

    2013-01-01

    Calcium phosphate cements (CPCs) are commonly used bone substitute materials, which closely resemble the composition of the mineral phase of bone. However, this high similarity to natural bone also results in difficult discrimination from the bone tissue by common imaging modalities, that is, plain X-ray radiography and three-dimensional computed tomography (CT). In addition, new imaging techniques introduced for bone tissue visualization, like magnetic resonance imaging (MRI), face a similar problem. Even at high MRI resolution, the lack of contrast between CPCs and surrounding bone is evident. Therefore, this study aimed to evaluate the feasibility of a dual contrast agent, traceable with both CT and MRI as enhancers of CPC/bone tissue contrast. Our formulation is based on the use of silica beads as vectors, which encapsulate and carry contrast-enhancing nanoparticles, in our case, colloidal Gold and Superparamagnetic Iron oxide particles (SPIO). The bead suspension was incorporated within a calcium phosphate powder. The resultant cements were then tested both in vitro and in vivo in a femoral condyle defect model in rats. Results showed that the mechanical properties of the cement were not significantly affected by the inclusion of the beads. Both in vitro and in vivo data proved the homogeneous incorporation of the contrast within the cement and its visual localization, characterized by a short-term CT contrast enhancement and a long-term MR effect recognizable by the characteristic blooming shape. Finally, no signs of adverse tissue reactions were noticed in vivo. In conclusion, this study proved the feasibility of a multimodal contrast agent as an inert and biocompatible enhancer of CaP cement versus bone tissue contrast. PMID:23259682

  2. Survey of contrast media used in coronary angiograph

    SciTech Connect

    Weikl, A.; Hubmann, M.

    1982-01-01

    In recent years, various contrast media have been developed for use in coronary angiography. These contrast media may be divided into ionic contrast media of high osmolality, those of low osmolality, and nonionic contrast materials. We conducted our own clinical studies with 40 patients. In random succession a standard contrast medium (ionic, of high osmolality) and a new-generation contrast medium (either nonionic or ionic with low osmolality) were injected into the right and left coronary arteries. After each injection we measured the systolic and diastolic blood pressure using a liquid-filled coronary catheter. In addition, the change in the length of the cardiac cycle was registered in terms of the R-R interval (in ms) and at the same time, leads I, II, and III of the ECG were recorded. We studied the influence of the various contrast media on the activity of ATPase in in vitro experiments, using Lasser and Lang's. When ionic contrast media of low osmolality and nonionic contrast media were utilized the heart rate showed no change. Disturbances of rhythm such as ventricular tachycardia or fibrillation were not observed. All of the contrast media used produced the same ECG changes. These changes can be ascribed to the inhibition of ATPase. The arterial blood pressure was lowered significantly only by ionic contrast media of high osmolality only.

  3. Covert contrast in velar fronting: An acoustic and ultrasound study.

    PubMed

    McAllister Byun, Tara; Buchwald, Adam; Mizoguchi, Ai

    2016-01-01

    There is growing evidence that speech sound acquisition is a gradual process, with instrumental measures frequently revealing covert contrast in errors perceived to involve phonemic substitution. Ultrasound imaging has the potential to expand our understanding of covert contrast by showing whether a child uses different tongue shapes while producing sounds that are perceived as neutralised. This study used an ultrasound measure (Dorsum Excursion Index) and acoustic measures (VOT and spectral moments of the burst) to investigate overt and covert contrast between velar and alveolar stops in child speech. Participants were two children who produced a perceptually overt velar-alveolar contrast and two children who neutralised the contrast via velar fronting. Both acoustic and ultrasound measures revealed significant differences between perceptually distinct velar and alveolar targets. One child with velar fronting demonstrated covert contrast in one acoustic and one ultrasound measure; the other showed no evidence of contrast. Clinical implications are discussed in this article. PMID:26325303

  4. Covert contrast in velar fronting: An acoustic and ultrasound study

    PubMed Central

    Byun, Tara McAllister; Buchwald, Adam; Mizoguchi, Ai

    2016-01-01

    There is growing evidence that speech sound acquisition is a gradual process, with instrumental measures frequently revealing covert contrast in errors perceived to involve phonemic substitution. Ultrasound imaging has the potential to expand our understanding of covert contrast by showing whether a child uses different tongue shapes while producing sounds that are perceived as neutralized. This study used an ultrasound measure (Dorsum Excursion Index) and acoustic measures (VOT and spectral moments of the burst) to investigate overt and covert contrast between velar and alveolar stops in child speech. Participants were two children who produced a perceptually overt velar-alveolar contrast and two children who neutralized the contrast via velar fronting. Both acoustic and ultrasound measures revealed significant differences between perceptually distinct velar and alveolar targets. One child with velar fronting demonstrated covert contrast in one acoustic and one ultrasound measure; the other showed no evidence of contrast. Clinical implications are discussed. PMID:26325303

  5. Apparatus for separating particles utilizing engineered acoustic contrast capture particles

    SciTech Connect

    Kaduchak, Gregory; Ward, Michael D

    2014-10-21

    An apparatus for separating particles from a medium includes a capillary defining a flow path therein that is in fluid communication with a medium source. The medium source includes engineered acoustic contrast capture particle having a predetermined acoustic contrast. The apparatus includes a vibration generator that is operable to produce at least one acoustic field within the flow path. The acoustic field produces a force potential minima for positive acoustic contrast particles and a force potential minima for negative acoustic contrast particles in the flow path and drives the engineered acoustic contrast capture particles to either the force potential minima for positive acoustic contrast particles or the force potential minima for negative acoustic contrast particles.

  6. Apparatus for separating particles utilizing engineered acoustic contrast capture particles

    DOEpatents

    Kaduchak, Gregory; Ward, Michael D.

    2011-12-27

    An apparatus for separating particles from a medium includes a capillary defining a flow path therein that is in fluid communication with a medium source. The medium source includes engineered acoustic contrast capture particle having a predetermined acoustic contrast. The apparatus includes a vibration generator that is operable to produce at least one acoustic field within the flow path. The acoustic field produces a force potential minima for positive acoustic contrast particles and a force potential minima for negative acoustic contrast particles in the flow path and drives the engineered acoustic contrast capture particles to either the force potential minima for positive acoustic contrast particles or the force potential minima for negative acoustic contrast particles.

  7. Apparatus for separating particles utilizing engineered acoustic contrast capture particles

    DOEpatents

    Kaduchak, Gregory; Ward, Michael D

    2016-05-17

    An apparatus for separating particles from a medium includes a capillary defining a flow path therein that is in fluid communication with a medium source. The medium source includes engineered acoustic contrast capture particle having a predetermined acoustic contrast. The apparatus includes a vibration generator that is operable to produce at least one acoustic field within the flow path. The acoustic field produces a force potential minima for positive acoustic contrast particles and a force potential minima for negative acoustic contrast particles in the flow path and drives the engineered acoustic contrast capture particles to either the force potential minima for positive acoustic contrast particles or the force potential minima for negative acoustic contrast particles.

  8. Mechanics of the Nucleus

    PubMed Central

    Lammerding, Jan

    2015-01-01

    The nucleus is the distinguishing feature of eukaryotic cells. Until recently, it was often considered simply as a unique compartment containing the genetic information of the cell and associated machinery, without much attention to its structure and mechanical properties. This article provides compelling examples that illustrate how specific nuclear structures are associated with important cellular functions, and how defects in nuclear mechanics can cause a multitude of human diseases. During differentiation, embryonic stem cells modify their nuclear envelope composition and chromatin structure, resulting in stiffer nuclei that reflect decreased transcriptional plasticity. In contrast, neutrophils have evolved characteristic lobulated nuclei that increase their physical plasticity, enabling passage through narrow tissue spaces in their response to inflammation. Research on diverse cell types further demonstrates how induced nuclear deformations during cellular compression or stretch can modulate cellular function. Pathological examples of disturbed nuclear mechanics include the many diseases caused by mutations in the nuclear envelope proteins lamin A/C and associated proteins, as well as cancer cells that are often characterized by abnormal nuclear morphology. In this article, we will focus on determining the functional relationship between nuclear mechanics and cellular (dys-)function, describing the molecular changes associated with physiological and pathological examples, the resulting defects in nuclear mechanics, and the effects on cellular function. New insights into the close relationship between nuclear mechanics and cellular organization and function will yield a better understanding of normal biology and will offer new clues into therapeutic approaches to the various diseases associated with defective nuclear mechanics. PMID:23737203

  9. Limitations of contrast enhancement for infrared target identification

    NASA Astrophysics Data System (ADS)

    Du Bosq, Todd W.; Fanning, Jonathan D.

    2009-05-01

    Contrast enhancement and dynamic range compression are currently being used to improve the performance of infrared imagers by increasing the contrast between the target and the scene content. Automatic contrast enhancement techniques do not always achieve this improvement. In some cases, the contrast can increase to a level of target saturation. This paper assesses the range-performance effects of contrast enhancement for target identification as a function of image saturation. Human perception experiments were performed to determine field performance using contrast enhancement on the U.S. Army RDECOM CERDEC NVESD standard military eight target set using an un-cooled LWIR camera. The experiments compare the identification performance of observers viewing contrast enhancement processed images at various levels of saturation. Contrast enhancement is modeled in the U.S. Army thermal target acquisition model (NVThermIP) by changing the scene contrast temperature. The model predicts improved performance based on any improved target contrast, regardless of specific feature saturation or enhancement. The measured results follow the predicted performance based on the target task difficulty metric used in NVThermIP for the non-saturated cases. The saturated images reduce the information contained in the target and performance suffers. The model treats the contrast of the target as uniform over spatial frequency. As the contrast is enhanced, the model assumes that the contrast is enhanced uniformly over the spatial frequencies. After saturation, the spatial cues that differentiate one tank from another are located in a limited band of spatial frequencies. A frequency dependent treatment of target contrast is needed to predict performance of over-processed images.

  10. Imaging microscopy by phase-contrast engine: retardation-modulated differential interference contrast microscope

    NASA Astrophysics Data System (ADS)

    Ishiwata, Hiroshi; Itoh, Masahide

    2014-11-01

    In the field of biology and medicine, observation object of the microscope has been changing from the thin specimen to the thick living tissue. Furthermore, observation of the internal structure of a living tissue is also desired by low invasion. However, the real structure of a phase object with three-dimensional distribution such as a living tissue is difficult to observe, because of the influence of the phase distribution before and behind of observation position. We enabled observation of the internal structure of living tissue without stain, by adding a new function to reduce the influence of phase distribution to our Retardation-Modulated differential interference contrast (RM-DIC) microscope system.

  11. Suppression of tissue harmonics for pulse-inversion contrast imaging using time reversal

    NASA Astrophysics Data System (ADS)

    Couture, Olivier; Aubry, Jean-François; Montaldo, Gabriel; Tanter, Mickael; Fink, Mathias

    2008-10-01

    Pulse-inversion (PI) sequences are sensitive to the nonlinear echoes from microbubbles allowing an improvement in the blood-to-tissue contrast. However, at larger mechanical indices, this contrast is reduced by harmonics produced during nonlinear propagation. A method for tissue harmonics cancellation exploiting time reversal is experimentally implemented using a 128-channel 12-bit emitter receiver. The probe calibration is performed by acquiring the nonlinear echo of a wire in water. These distorted pulses are time-reversed, optimized and used for the PI imaging of a tissue phantom. Compared to normal (straight) pulses, the time-reversed distorted pulses reduced the tissue signal in PI by 11 dB. The second harmonic signals from microbubbles flowing in a wall-less vessel were unaffected by the correction. This technique can thus increase the blood-to-tissue contrast ratio while keeping the pressure and the number of pulses constant.

  12. Suppression of tissue harmonics for pulse-inversion contrast imaging using time reversal.

    PubMed

    Couture, Olivier; Aubry, Jean-François; Montaldo, Gabriel; Tanter, Mickael; Fink, Mathias

    2008-10-01

    Pulse-inversion (PI) sequences are sensitive to the nonlinear echoes from microbubbles allowing an improvement in the blood-to-tissue contrast. However, at larger mechanical indices, this contrast is reduced by harmonics produced during nonlinear propagation. A method for tissue harmonics cancellation exploiting time reversal is experimentally implemented using a 128-channel 12-bit emitter receiver. The probe calibration is performed by acquiring the nonlinear echo of a wire in water. These distorted pulses are time-reversed, optimized and used for the PI imaging of a tissue phantom. Compared to normal (straight) pulses, the time-reversed distorted pulses reduced the tissue signal in PI by 11 dB. The second harmonic signals from microbubbles flowing in a wall-less vessel were unaffected by the correction. This technique can thus increase the blood-to-tissue contrast ratio while keeping the pressure and the number of pulses constant. PMID:18765888

  13. Spatio-temporal Contrast Sensitivity in the Cardinal Directions of the Colour Space. A Review

    PubMed Central

    Díez-Ajenjo, Maria Amparo; Capilla, Pascual

    2010-01-01

    We review the psychophysics of the spatio-temporal contrast sensitivity in the cardinal directions of the colour space and their correlation with those neural characteristics of the visual system that limit the ability to perform contrast detection or pattern-resolution tasks. We focus our attention particularly on the influence of luminance level, spatial extent and spatial location of the stimuli - factors that determine the characteristics of the physiological mechanisms underlying detection. Optical factors do obviously play a role, but we will refer to them only briefly. Contrast sensitivity measurements are often used in clinical practice as a method to detect, at their early stages, a variety of pathologies affecting the visual system, but their usefulness is very limited due to several reasons. We suggest some considerations about stimuli characteristics that should be taken into account in order to improve the performance of this kind of measurement.

  14. [3D real time contrast enhanced ultrasonography,a new technique].

    PubMed

    Dietrich, C F

    2002-02-01

    While 3D sonography has become established in gynecology, abdominal applications have been mainly restricted to case reports. However, recent advances in computer technology have supported the development of new systems with motion detection methods and image registration algorithms - making it possible to acquire 3D data without position sensors, before and after administration of contrast enhancing agents. Hepatic (and also splenic) applications involve the topographic localization of masses in relation to the vessels, e.g. hepatic veins and portal vein branches prior to surgical procedures (segment localization). 3D imaging in the characterization of liver tumors after administration of contrast enhancing agents could become of special importance. We report on the first use of 3D imaging of the liver and spleen under real time conditions in 10 patients, using contrast enhanced phase inversion imaging with low mechanical index, which may improve the detection rate and characterization of liver and splenic tumors. PMID:11898076

  15. Contrasting Lifestyles Within the Host Cell.

    PubMed

    Di Russo Case, Elizabeth; Samuel, James E

    2016-02-01

    Intracellular bacterial pathogens have evolved to exploit the protected niche provided within the boundaries of a eukaryotic host cell. Upon entering a host cell, some bacteria can evade the adaptive immune response of its host and replicate in a relatively nutrient-rich environment devoid of competition from other host flora. Growth within a host cell is not without their hazards, however. Many pathogens enter their hosts through receptor-mediated endocytosis or phagocytosis, two intracellular trafficking pathways that terminate in a highly degradative organelle, the phagolysosome. This usually deadly compartment is maintained at a low pH and contains degradative enzymes and reactive oxygen species, resulting in an environment to which few bacterial species are adapted. Some intracellular pathogens, such as Shigella, Listeria, Francisella, and Rickettsia, escape the phagosome to replicate within the cytosol of the host cell. Bacteria that remain within a vacuole either alter the trafficking of their initial phagosomal compartment or adapt to survive within the harsh environment it will soon become. In this chapter, we focus on the mechanisms by which different vacuolar pathogens either evade lysosomal fusion, as in the case of Mycobacterium and Chlamydia, or allow interaction with lysosomes to varying degrees, such as Brucella and Coxiella, and their specific adaptations to inhabit a replicative niche. PMID:26999394

  16. Contrasting Lifestyles Within the Host Cell

    PubMed Central

    Case, Elizabeth Di Russo; Samuel, James E.

    2015-01-01

    CHAPTER SUMMARY Intracellular bacterial pathogens have evolved to exploit the protected niche provided within the boundaries of a eukaryotic host cell. Upon entering a host cell, some bacteria can evade the adaptive immune response of its host, and replicate in a relatively nutrient-rich environment devoid of competition from other host flora. Growth within a host cell is not without its hazards, however. Many pathogens enter their hosts through receptor-mediated endocytosis or phagocytosis, two intracellular trafficking pathways that terminate in a highly degradative organelle, the phagolysosome. This usually deadly compartment is maintained at a low pH, and contains degradative enzymes, and reactive oxygen species resulting in an environment to which few bacterial species are adapted. Some intracellular pathogens, like Shigella, Listeria, Francisella, and Rickettsia escape the phagosome to replicate within the cytosol of the host cell. Bacteria that remain within a vacuole either alter the trafficking of their initial phagosomal compartment or adapt to survive within the harsh environment it will soon become. In this chapter, we focus on the mechanisms by which different vacuolar pathogens either evade lysosomal fusion, as in the case of Mycobacterium and Chlamydia, or allow interaction with lysosomes to varying degrees, such as Brucella and Coxiella, and their specific adaptations to inhabit a replicative niche. PMID:26999394

  17. Importance of Contrast-Enhanced Fluid-Attenuated Inversion Recovery Magnetic Resonance Imaging in Various Intracranial Pathologic Conditions

    PubMed Central

    Lee, Eun Kyoung; Kim, Sungwon; Lee, Yong Seok

    2016-01-01

    Intracranial lesions may show contrast enhancement through various mechanisms that are closely associated with the disease process. The preferred magnetic resonance sequence in contrast imaging is T1-weighted imaging (T1WI) at most institutions. However, lesion enhancement is occasionally inconspicuous on T1WI. Although fluid-attenuated inversion recovery (FLAIR) sequences are commonly considered as T2-weighted imaging with dark cerebrospinal fluid, they also show mild T1-weighted contrast, which is responsible for the contrast enhancement. For several years, FLAIR imaging has been successfully incorporated as a routine sequence at our institution for contrast-enhanced (CE) brain imaging in detecting various intracranial diseases. In this pictorial essay, we describe and illustrate the diagnostic importance of CE-FLAIR imaging in various intracranial pathologic conditions. PMID:26798225

  18. Image contrast enhancement of Ni/YSZ anode during the slice-and-view process in FIB-SEM.

    PubMed

    Liu, Shu-Sheng; Takayama, Akiko; Matsumura, Syo; Koyama, Michihisa

    2016-03-01

    Focused ion beam-scanning electron microscopy (FIB-SEM) is a widely used and easily operational equipment for three-dimensional reconstruction with flexible analysis volume. It has been using successfully and increasingly in the field of solid oxide fuel cell. However, the phase contrast of the SEM images is indistinct in many cases, which will bring difficulties to the image processing. Herein, the phase contrast of a conventional Ni/yttria stabilized zirconia anode is tuned in an FIB-SEM with In-Lens secondary electron (SE) and backscattered electron detectors. Two accessories, tungsten probe and carbon nozzle, are inserted during the observation. The former has no influence on the contrast. When the carbon nozzle is inserted, best and distinct contrast can be obtained by In-Lens SE detector. This method is novel for contrast enhancement. Phase segmentation of the image can be automatically performed. The related mechanism for different images is discussed. PMID:26599978

  19. Prostate cancer characterization by optical contrast enhanced photoacoustics

    NASA Astrophysics Data System (ADS)

    Xu, Guan; Qin, Ming; Mukundan, Ananya; Siddiqui, Javed; Takada, Marilia; Vilar-Saavedra, Paulo; Tomlins, Scott A.; Kopelman, Raoul; Wang, Xueding

    2016-03-01

    During the past decades, prostate cancer (PCa), with an annual incident rate much higher than any other cancer, is the most commonly diagnosed cancer in American men. PCa has a relatively low progression rate yet the survival percentage decreases dramatically once the cancer has metastasized. Identifying aggressive from indolent PCa to prevent metastasis and death is critical to improving outcomes for patients with PCa. Standard procedure for assessing the aggressiveness of PCa involves the removal of tumor tissues by transrectal (TR) ultrasound (US) guided needle biopsy. The microscopic architecture of the biopsied tissue is visualized by histological or immunohistochemical staining procedures. The heterogeneity of the microscopic architecture is characterized by a Gleason score, a quantitative description of the aggressiveness of PCa. Due to the inability to identify the cancer cells, most noninvasive imaging modalities can only provide diagnosis of PCa at limited accuracy. This study investigates the feasibility of identifying PCa tumors and characterizing the aggressiveness of PCa by photoacoustic imaging assisted by cancer targeting polyacrylamide (PAA) nanoparticles (NPs). PAA is a biocompatible material used in clinics for the past 20 years. PAA NPs can protect capsulated optical contrast agents from interference by enzymes and enable prolonged systematic circulation in the living biological environment. The cancer targeting mechanism is achieved by conjugating the NPs to F3 peptides, which trace nucleolin overexpressed on the surface of cancer cells. Preliminary studies have shown that the NPs are capable of staining the PCa cells in vivo.

  20. Anaphylactoid and anaphylactic reactions to iodinated contrast material.

    PubMed

    Laroche, D; Namour, F; Lefrançois, C; Aimone-Gastin, I; Romano, A; Sainte-Laudy, J; Laxenaire, M C; Guéant, J L

    1999-01-01

    Some adverse reactions to iodinated contrast material (ICM) are considered allergy-like, with cutaneous, cardiovascular, respiratory, and digestive symptoms. Allergy-like reactions are usually unpredictable. Reactions are more frequent with ionic than with nonionic material, but the frequency of deaths is almost identical. In a recent study, 20 severe unexpected reactions to ICM, including 10 life-threatening reactions and one death, were investigated by measuring mediators in blood, within the first minutes or hours of reaction. The responsible ICMs were mostly ionic materials. Histamine and tryptase release correlated with the severity of the reaction. Specific IgE against the responsible ICM was significantly higher in reactors than in controls. A few patients had positive skin tests to the administered ICM, suggesting type-I allergic reaction. Only 2.4% and 3.1% of the cases yielded a positive IgE-RIA, in a second retrospective study which included 165 patients recruited during a 4-year period. In conclusion, IgE-mediated anaphylaxis is rare, but it may be one of the possible mechanisms of severe adverse reactions to ICM. PMID:10735643

  1. [Immediate allergy to iodinated contrast agents and prevention of reactions].

    PubMed

    Dewachter, P; Mouton-Faivre, C; Laroche, D; Clément, O

    2009-10-01

    The incidence and morbimortality of immediate hypersensitivity reactions following iodinated contrast media (ICM) injection remain unknown. The diagnosis of an immediate hypersensitivity reaction relies on a triad associating the precise description of the initial clinical manifestations and their delay of onset, the results of the biological assessment performed after the reaction including histamine and tryptase serum level measurements, and the results of skin testing with the culprit agent. Analysis of these data allows identification of the pathophysiologic mechanism of the reaction and the allergen involved in case of allergic hypersensitivity. Skin tests should be performed according to strict criteria. Cross-reactivity with ICM has to be investigated in order to propose a nonreactive ICM for future procedures. Allergic hypersensitivity to a given ICM imposes its definitive avoidance but not the avoidance of all iodinated drugs. The allergenic sequence has not yet been identified but is not the iodine atom itself. Asthma and treatment with beta-blockers are not risk factors of immediate allergic reactions to ICM per se, but may increase their severity. The various published protocols of premedication do not prevent the occurrence of an allergic/anaphylactic reaction to an ICM. The avoidance of the culprit ICM is the only way to prevent further reactions. PMID:19375199

  2. Detecting Plasmon Resonance Energy Transfer with Differential Interference Contrast Microscopy

    SciTech Connect

    Augspurger, Ashley E.; Stender, Anthony S.; Han, Rui; Fang, Ning

    2013-12-30

    Gold nanoparticles are ideal probes for studying intracellular environments and energy transfer mechanisms due to their plasmonic properties. Plasmon resonance energy transfer (PRET) relies on a plasmonic nanoparticle to donate energy to a nearby resonant acceptor molecule, a process which can be observed due to the plasmonic quenching of the donor nanoparticle. In this study, a gold nanosphere was used as the plasmonic donor, while the metalloprotein cytochrome c was used as the acceptor molecule. Differential interference contrast (DIC) microscopy allows for simultaneous monitoring of complex environments and noble metal nanoparticles in real time. Using DIC and specially designed microfluidic channels, we were able to monitor PRET at the single gold particle level and observe the reversibility of PRET upon the introduction of phosphate-buffered saline to the channel. In an additional experiment, single gold particles were internalized by HeLa cells and were subsequently observed undergoing PRET as the cell hosts underwent morphological changes brought about by ethanol-induced apoptosis.

  3. The Westermarck Hypothesis and the Israeli Kibbutzim: Reconciling Contrasting Evidence.

    PubMed

    Shor, Eran

    2015-11-01

    The case of the communal education system in the Israeli kibbutzim is often considered to provide conclusive support for Westermarck's (1891) assertion regarding the existence of evolutionary inbreeding avoidance mechanisms in humans. However, recent studies that have gone back to the kibbutzim seem to provide contrasting evidence and reopen the discussion regarding the case of the kibbutzim and inbreeding avoidance more generally (Lieberman & Lobel, 2012; Shor & Simchai, 2009). In this article, I reassess the case of the kibbutzim, reevaluating the findings and conclusions of these recent research endeavors. I argue that the differences between recent research reports largely result from conceptual and methodological differences and that, in fact, these studies provide insights that are more similar than first meets the eye. I also suggest that we must reexamine the common assumption that the kibbutzim serve as an ideal natural experiment for examining the sources of incest avoidance and the incest taboo. Finally, I discuss the implications of these studies to the longstanding debate over the Westermarck hypothesis and call for a synthetic theoretical framework that produces more precise predictions and more rigorous empirical research designs. PMID:26014825

  4. Modeling the effects of contrast enhancement on target acquisition performance

    NASA Astrophysics Data System (ADS)

    Du Bosq, Todd W.; Fanning, Jonathan D.

    2008-04-01

    Contrast enhancement and dynamic range compression are currently being used to improve the performance of infrared imagers by increasing the contrast between the target and the scene content, by better utilizing the available gray levels either globally or locally. This paper assesses the range-performance effects of various contrast enhancement algorithms for target identification with well contrasted vehicles. Human perception experiments were performed to determine field performance using contrast enhancement on the U.S. Army RDECOM CERDEC NVESD standard military eight target set using an un-cooled LWIR camera. The experiments compare the identification performance of observers viewing linearly scaled images and various contrast enhancement processed images. Contrast enhancement is modeled in the US Army thermal target acquisition model (NVThermIP) by changing the scene contrast temperature. The model predicts improved performance based on any improved target contrast, regardless of feature saturation or enhancement. To account for the equivalent blur associated with each contrast enhancement algorithm, an additional effective MTF was calculated and added to the model. The measured results are compared with the predicted performance based on the target task difficulty metric used in NVThermIP.

  5. Characterization of novel molecular photoacoustic contrast agents for in vivo photoacoustic tomography

    NASA Astrophysics Data System (ADS)

    Laoui, Samir

    Photoacoustic tomography is a hybrid imaging modality that takes advantage of the high contrast of pure optical imaging and the high intrinsic resolution of ultrasound without the necessity of ionizing radiation. Photoacoustic imaging (PM) is neither purely optical nor purely acoustical in nature, but a combination of the two. It is fundamentally based on light excitation and ultrasonic detection. Photoacoustic imaging has been successful without the introduction of exogenous contrast agents; however, to image deeper regions of biological tissue, a contrast agent is necessary. Several types of photoacoustic contrast agents have been made available for diagnostic purposes; however, the majority of literature has focused on gold nanoparticle systems for which the surface-plasmon resonance effect is important. The only option currently available for molecular PM contrast agents is to choose an existing near infrared absorbing fluorescent probes with the hope that they may generate a substantial photoacoustic (PA) response. However, these dyes have been designed with an optimized fluorescence emission response and are not anticipated to generate an adequate photoacoustic response. This dissertation addresses this lack of precedence in the literature for understanding the mechanism of a photoacoustic signal generation from strongly absorbing dye molecules including BODIPY, cyanine and curcumin systems. This work represents preliminary efforts in bringing novel molecular photoacoustic contrast agents (MPACs) into the photoacoustic imaging arena. To this end, photoacoustic and optical Z-scan experiments, and quenching studies were employed to demonstrate correlation of photoacoustic emission enhancement with excited state absorption mechanisms. To investigate further the photoacoustic emission in a practical imaging setting, MPACs were imaged using a recently developed photoacoustic imaging tomography system which was constructed exclusively for the purpose of this study.

  6. High Contrast Vacuum Nuller Testbed (VNT) Contrast, Performance and Null Control

    NASA Technical Reports Server (NTRS)

    Lyon, Richard G.; Clampin, Mark; Petrone, Peter; Mallik, Udayan; Madison, Timothy; Bolcar, Matthew R.

    2012-01-01

    Herein we report on our contrast assessment and the development, sensing and control of the Vacuum Nuller Testbed to realize a Visible Nulling Coronagraphy (VNC) for exoplanet detection and characterization. Tbe VNC is one of the few approaches that works with filled, segmented and sparse or diluted-aperture telescope systems. It thus spans a range of potential future NASA telescopes and could be flown as a separate instrument on such a future mission. NASA/Goddard Space Flight Center has an established effort to develop VNC technologies, and an incremental sequence of testbeds to advance this approach and its critical technologies. We discuss the development of the vacuum Visible Nulling Coronagraph testbed (VNT). The VNT is an ultra-stable vibration isolated testbed that operates under closed-loop control within a vacuum chamber. It will be used to achieve an incremental sequence of three visible-light nulling milestones with sequentially higher contrasts of 10(exp 8), 10(exp 9) and ideally 10(exp 10) at an inner working angle of 2*lambda/D. The VNT is based on a modified Mach-Zehnder nulling interferometer, with a "W" configuration to accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters. We discuss the laboratory results, optical configuration, critical technologies and the null sensing and control approach.

  7. Evaluation of microbubble contrast agents for dynamic imaging with x-ray phase contrast

    PubMed Central

    Millard, T. P.; Endrizzi, M.; Everdell, N.; Rigon, L.; Arfelli, F.; Menk, R. H.; Stride, E.; Olivo, A.

    2015-01-01

    X-rays are commonly used as a means to image the inside of objects opaque to visible light, as their short wavelength allows penetration through matter and the formation of high spatial resolution images. This physical effect has found particular importance in medicine where x-ray based imaging is routinely used as a diagnostic tool. Increasingly, however, imaging modalities that provide functional as well as morphological information are required. In this study the potential to use x-ray phase based imaging as a functional modality through the use of microbubbles that can be targeted to specific biological processes is explored. We show that the concentration of a microbubble suspension can be monitored quantitatively whilst in flow using x-ray phase contrast imaging. This could provide the basis for a dynamic imaging technique that combines the tissue penetration, spatial resolution, and high contrast of x-ray phase based imaging with the functional information offered by targeted imaging modalities. PMID:26219661

  8. Potential of high-Z contrast agents in clinical contrast-enhanced computed tomography

    SciTech Connect

    Nowak, Tristan; Hupfer, Martin; Brauweiler, Robert; Eisa, Fabian; Kalender, Willi A.

    2011-12-15

    Purpose: Currently, only iodine- and barium-based contrast media (CM) are used in clinical contrast-enhanced computed tomography (CE-CT). High-Z metals would produce a higher contrast at equal mass density for the x-ray spectra used in clinical CT. Using such materials might allow for significant dose reductions in CE-CT. The purpose of this study was to quantify the potential for dose reduction when using CM based on heavy metals. Methods: The contrast-to-noise ratio weighted by dose (CNRD) was determined as a function of scan protocol by means of measurements and simulations on a clinical CT scanner. For simulations, water cylinders with diameters 160, 320, 480, and 640 mm were used to cover a broad range of patient sizes. Measurements were conducted with 160 and 320 mm water-equivalent plastic cylinders. A central bore of 13 mm diameter was present in all phantoms. The tube voltage was varied from 80 to 140 kV for measurements and from 60 to 180 kV for simulations. Additional tin filtration of thicknesses 0.4, 0.8, and 1.2 mm was applied in the simulation to evaluate a range of spectral hardness. The bore was filled with a mixture of water and 10 mg/ml of pure iodine, holmium, gadolinium, ytterbium, osmium, tungsten, gold, and bismuth for the simulations and with aqueous solutions of ytterbium, tungsten, gold, and bismuth salts as well as Iopromid containing 10 mg/ml of the pure materials for the measurements. CNRDs were compared to iodine at phantom size-dependent reference voltages for all high-Z materials and the resulting dose reduction was calculated for equal contrast-to-noise ratio. Results: Dose reduction potentials strongly depended on phantom size, spectral hardness, and tube voltage. Depending on the added filtration, a dose reduction of 19%-60% could be reached at 80 kV with gadolinium for the 160 mm phantom, 52%-69% at 100 kV with holmium for the 320 mm phantom, 62%-78% with 120 kV for hafnium and the 480 mm phantom and 74%-86% with 140 kV for gold

  9. Inorganic nanoparticle-based contrast agents for molecular imaging

    PubMed Central

    Cho, Eun Chul; Glaus, Charles; Chen, Jingyi; Welch, Michael J.; Xia, Younan

    2010-01-01

    Inorganic nanoparticles including semiconductor quantum dots, iron oxide nanoparticles, and gold nanoparticles have been developed as contrast agents for diagnostics by molecular imaging. Compared to traditional contrast agents, nanoparticles offer several advantages: their optical and magnetic properties can be tailored by engineering the composition, structure, size, and shape; their surfaces can be modified with ligands to target specific biomarkers of disease; the contrast enhancement provided can be equivalent to millions of molecular counterparts; and they can be integrated with a combination of different functions for multi-modal imaging. Here, we review recent advances in the development of contrast agents based on inorganic nanoparticles for molecular imaging, with a touch on contrast enhancement, surface modification, tissue targeting, clearance, and toxicity. As research efforts intensify, contrast agents based on inorganic nanoparticles that are highly sensitive, target-specific, and safe to use are expected to enter clinical applications in the near future. PMID:21074494

  10. Phase-contrast x-ray tomography using synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Bonse, Ulrich; Beckmann, Felix; Bartscher, Markus; Biermann, Theodor; Busch, Frank; Guennewig, Olaf

    1997-10-01

    The principle and experimental l realization of x-ray phase- contrast in compute assisted microtomography ((mu) CT) at the micrometer resolution level is described. The camera used is a modification of a setup previously developed by us for attenuation-contrast (mu) CT using synchrotron x-rays. Phase detection is accomplished by employing the x-ray interferometer. By using x-ray phase contrast it is possible to image structural details in low-z biological tissues much better than with absorption contrast. The advantage of phase over attenuation contrast is not limited to light element or to low x-ray energies. Examples of applying phase contrast (mu) CT to the structural investigation of rat trigeminal nerve are given.

  11. Thermal Excitation of Gadolinium-Based Contrast Agents Using Spin Resonance

    PubMed Central

    Fridjhon, Peter; Rubin, David M.

    2016-01-01

    Theoretical and experimental investigations into the thermal excitation of liquid paramagnetic contrast agents using the spin resonance relaxation mechanism are presented. The electronic spin-lattice relaxation time τ1e of gadolinium-based contrast agents, which is estimated at 0.1 ns, is ten orders of magnitude faster than the relaxation time of protons in water. The shorter relaxation time is found to significantly increase the rate of thermal energy deposition. To the authors’ knowledge this is the first study of gadolinium based contrast agents in a liquid state used as thermal agents. Analysis shows that when τ1e and other experimental parameters are optimally selected, a maximum theoretical heating rate of 29.4 °C.s−1 could be achieved which would suffice for clinical thermal ablation of neoplasms. The experimental results show a statistically significant thermal response for two out of the four contrast agents tested. The results are compared to the simulated estimates via analysis of a detailed model of the system. While these experimentally determined temperature rises are small and thus of no clinical utility, their presence supports the theoretical analysis and strongly suggests that the chemical structure of the selected compounds plays an important role in this mechanism of heat deposition. There exists an opportunity for the development of alternative gadolinium-based compounds with an order of magnitude longer τ1e in a diluted form to be used as an efficient hyperthermia agent for clinical use. PMID:27341338

  12. Thermal Excitation of Gadolinium-Based Contrast Agents Using Spin Resonance.

    PubMed

    Dinger, Steven C; Fridjhon, Peter; Rubin, David M

    2016-01-01

    Theoretical and experimental investigations into the thermal excitation of liquid paramagnetic contrast agents using the spin resonance relaxation mechanism are presented. The electronic spin-lattice relaxation time τ1e of gadolinium-based contrast agents, which is estimated at 0.1 ns, is ten orders of magnitude faster than the relaxation time of protons in water. The shorter relaxation time is found to significantly increase the rate of thermal energy deposition. To the authors' knowledge this is the first study of gadolinium based contrast agents in a liquid state used as thermal agents. Analysis shows that when τ1e and other experimental parameters are optimally selected, a maximum theoretical heating rate of 29.4 °C.s-1 could be achieved which would suffice for clinical thermal ablation of neoplasms. The experimental results show a statistically significant thermal response for two out of the four contrast agents tested. The results are compared to the simulated estimates via analysis of a detailed model of the system. While these experimentally determined temperature rises are small and thus of no clinical utility, their presence supports the theoretical analysis and strongly suggests that the chemical structure of the selected compounds plays an important role in this mechanism of heat deposition. There exists an opportunity for the development of alternative gadolinium-based compounds with an order of magnitude longer τ1e in a diluted form to be used as an efficient hyperthermia agent for clinical use. PMID:27341338

  13. Nuclear Mechanics in Cancer

    PubMed Central

    Denais, Celine; Lammerding, Jan

    2015-01-01

    Despite decades of research, cancer metastasis remains an incompletely understood process that is as complex as it is devastating. In recent years, there has been an increasing push to investigate the biomechanical aspects of tumorigenesis, complementing the research on genetic and biochemical changes. In contrast to the high genetic variability encountered in cancer cells, almost all metastatic cells are subject to the same physical constraints as they leave the primary tumor, invade surrounding tissues, transit through the circulatory system, and finally infiltrate new tissues. Advances in live cell imaging and other biophysical techniques, including measurements of subcellular mechanics, have yielded stunning new insights into the physics of cancer cells. While much of this research has been focused on the mechanics of the cytoskeleton and the cellular microenvironment, it is now emerging that the mechanical properties of the cell nucleus and its connection to the cytoskeleton may play a major role in cancer metastasis, as deformation of the large and stiff nucleus presents a substantial obstacle during the passage through the dense interstitial space and narrow capillaries. Here, we present an overview of the molecular components that govern the mechanical properties of the nucleus and we discuss how changes in nuclear structure and composition observed in many cancers can modulate nuclear mechanics and promote metastatic processes. Improved insights into this interplay between nuclear mechanics and metastatic progression may have powerful implications in cancer diagnostics and therapy and may reveal novel therapeutic targets for pharmacological inhibition of cancer cell invasion. PMID:24563360

  14. Visualisation of the temporary cavity by computed tomography using contrast material.

    PubMed

    Schyma, Christian; Hagemeier, Lars; Greschus, Susanne; Schild, Hans; Madea, Burkhard

    2012-01-01

    The temporary cavity of a missile produces radial tears in ordnance gelatine, which correlate to the energy transfer. Computed tomography is a useful and non-destructive method to examine gelatine blocks. However, the tears give only few radiocontrast by air filling, which decreases with the time past shooting. Therefore, systematically, a radiocontrast material was searched to enhance the contrast. Different contrast materials were amalgamated to acryl paint, and about 7 g was sealed in a foil bag, which was integrated in the front of a standard 10% gelatine cylinder. Shots with Action-5 expanding bullets were performed from a 5-m distance. Gelatine was scanned by multi-slice computed tomography. The multiplanar reconstructed images were compared to mechanically cut slices of 1 cm thickness. It was shown experimentally that iodine containing water-soluble contrast material did not give sufficient contrast and caused diffusion artefacts. Best results were obtained by barium sulphate emulsion. The amount of acryl paint was sufficient to colour the tears for optical scanning. The radiocontrast of barium leads to satisfying imaging of tears and allowed the creation of a three-dimensional reconstruction of the temporary cavity. Comparison of optical and radiological results showed an excellent correlation, but absolute measures in computed tomographic (CT) images remained lower compared with optically gathered values in the gelatine slices. Combination of paint and contrast material for CT examination will facilitate the evaluation of complex ballistic models and increase accuracy. PMID:21437598

  15. A normalized contrast-encoding model exhibits bright/dark asymmetries similar to early visual neurons.

    PubMed

    Cooper, Emily A

    2016-04-01

    Biological sensory systems share a number of organizing principles. One such principle is the formation of parallel streams. In the visual system, information about bright and dark features is largely conveyed via two separate streams: theONandOFFpathways. While brightness and darkness can be considered symmetric and opposite forms of visual contrast, the response properties of cells in theONandOFFpathways are decidedly asymmetric. Here, we ask whether a simple contrast-encoding model predicts asymmetries for brights and darks that are similar to the asymmetries found in theONandOFFpathways. Importantly, this model does not include any explicit differences in how the visual system represents brights and darks, but it does include a common normalization mechanism. The phenomena captured by the model include (1) nonlinear contrast response functions, (2) greater nonlinearities in the responses to darks, and (3) larger responses to dark contrasts. We report a direct, quantitative comparison between these model predictions and previously published electrophysiological measurements from the retina and thalamus (guinea pig and cat, respectively). This work suggests that the simple computation of visual contrast may account for a range of early visual processing nonlinearities. Assessing explicit models of sensory representations is essential for understanding which features of neuronal activity these models can and cannot predict, and for investigating how early computations may reverberate through the sensory pathways. PMID:27044852

  16. Noninvasive Assessment of Early Dental Lesion Using a Dual-Contrast Photoacoustic Tomography

    NASA Astrophysics Data System (ADS)

    Cheng, Renxiang; Shao, Jiaojiao; Gao, Xiaoxiang; Tao, Chao; Ge, Jiuyu; Liu, Xiaojun

    2016-02-01

    Dental hard tissue lesions, including caries, cracked-tooth, etc., are the most prevalent diseases of people worldwide. Dental lesions and correlative diseases greatly decrease the life quality of patients throughout their lifetime. It is still hard to noninvasively detect these dental lesions in their early stages. Photoacoustic imaging is an emerging hybrid technology combining the high spatial resolution of ultrasound in deep tissue with the rich optical contrasts. In this study, a dual-contrast photoacoustic tomography is applied to detect the early dental lesions. One contrast, named B-mode, is related to the optical absorption. It is good at providing the sharp image about the morphological and macro-structural features of the teeth. Another contrast, named S-mode, is associated with the micro-structural and mechanical properties of the hard tissue. It is sensitive to the change of tissue properties induced by the early dental lesions. Experiments show that the comprehensive analysis of dual-contrast information can provide reliable information of the early dental lesions. Moreover, the imaging parameter of S-mode is device-independent and it could measure tissue properties quantitatively. We expect that the proposed scheme could be beneficial for improving safety, accuracy and sensitivity of the clinical diagnosis of the dental lesion.

  17. Differential phase contrast with a segmented detector in a scanning X-ray microprobe

    PubMed Central

    Hornberger, B.; de Jonge, M. D.; Feser, M.; Holl, P.; Holzner, C.; Jacobsen, C.; Legnini, D.; Paterson, D.; Rehak, P.; Strüder, L.; Vogt, S.

    2008-01-01

    Scanning X-ray microprobes are unique tools for the nanoscale investigation of specimens from the life, environmental, materials and other fields of sciences. Typically they utilize absorption and fluorescence as contrast mechanisms. Phase contrast is a complementary technique that can provide strong contrast with reduced radiation dose for weakly absorbing structures in the multi-keV range. In this paper the development of a segmented charge-integrating silicon detector which provides simultaneous absorption and differential phase contrast is reported. The detector can be used together with a fluorescence detector for the simultaneous acquisition of transmission and fluorescence data. It can be used over a wide range of photon energies, photon rates and exposure times at third-generation synchrotron radiation sources, and is currently operating at two beamlines at the Advanced Photon Source. Images obtained at around 2 keV and 10 keV demonstrate the superiority of phase contrast over absorption for specimens composed of light elements. PMID:18552427

  18. Noninvasive Assessment of Early Dental Lesion Using a Dual-Contrast Photoacoustic Tomography

    PubMed Central

    Cheng, Renxiang; Shao, Jiaojiao; Gao, Xiaoxiang; Tao, Chao; Ge, Jiuyu; Liu, Xiaojun

    2016-01-01

    Dental hard tissue lesions, including caries, cracked-tooth, etc., are the most prevalent diseases of people worldwide. Dental lesions and correlative diseases greatly decrease the life quality of patients throughout their lifetime. It is still hard to noninvasively detect these dental lesions in their early stages. Photoacoustic imaging is an emerging hybrid technology combining the high spatial resolution of ultrasound in deep tissue with the rich optical contrasts. In this study, a dual-contrast photoacoustic tomography is applied to detect the early dental lesions. One contrast, named B-mode, is related to the optical absorption. It is good at providing the sharp image about the morphological and macro-structural features of the teeth. Another contrast, named S-mode, is associated with the micro-structural and mechanical properties of the hard tissue. It is sensitive to the change of tissue properties induced by the early dental lesions. Experiments show that the comprehensive analysis of dual-contrast information can provide reliable information of the early dental lesions. Moreover, the imaging parameter of S-mode is device-independent and it could measure tissue properties quantitatively. We expect that the proposed scheme could be beneficial for improving safety, accuracy and sensitivity of the clinical diagnosis of the dental lesion. PMID:26902394

  19. Larger receptive fields revealed using Battenberg stimuli to assess contrast summation with moving patterns.

    PubMed

    McDougall, Thomas J; Dickinson, J Edwin; Badcock, David R

    2016-09-01

    This study reevaluated the summation extent for moving stimuli using the Battenberg summation paradigm (Meese, 2010), which aims to circumvent internal noise changes with increasing stimulus size by holding display size constant. In the checkerboard stimulus, the size of the checks (luminance-modulated drifting gratings) was varied to measure dependence on signal area. Experiment 1 was a contrast detection task that used either signal checks alternating with uniform, mean luminance, checks (single-motion) or alternate checks containing gratings moving in opposite directions (opposing-motion). The latter was designed to test whether summation extent changes when segregating regions based on motion direction. Results showed summation over a square summation area with a side length of 3.33°, much larger than previous estimates of less than 1° for similar stimuli (Anderson & Burr, 1991). This was found for both motion combinations, providing no evidence that summation extent differs when segregating patterns based on direction, at contrast detection threshold. These results are in close agreement with those obtained for static patterns (Meese, 2010) and support the same underlying summation model. Experiment 2 was a contrast increment detection task conducted to determine whether differences in summation extent arise under suprathreshold contrast conditions. There was no dependence on check size for either condition across the range of sizes tested. This supports the suggestion that segmentation mechanisms dominate perception under high-contrast conditions, a potential adaptive strategy employed by the visual system. PMID:27604069

  20. Polarization-shaped laser pulses for improved fluorescence anisotropy contrast

    NASA Astrophysics Data System (ADS)

    Achazi, Georg; Hermes, Nils; Patas, Alexander; Tolksdorf, Daniel; Lindinger, Albrecht

    2013-08-01

    We present a method to change the fluorescence contrast between two dyes with high fluorescence anisotropy in the same solution under different polarization directions by using polarization-shaped pulses. First a theoretical relationship between contrast, anisotropy and polarization is derived for this case. Then the wavelength dependent polarization anisotropy and the change of contrast by phase-shaping for a solution of Rhodamine B and Stilbene 3 in glycerol is shown. Finally, the application of the polarization-shaped pulses is demonstrated.

  1. Localized surface plasmon assisted contrast microscopy for ultrathin transparent specimens

    SciTech Connect

    Wei, Feifei; Lu, Dylan; Aguinaldo, Ryan; Ma, Yicong; Sinha, Sunil K.; Liu, Zhaowei

    2014-10-20

    We demonstrate a high contrast imaging technique, termed localized surface plasmon assisted contrast microscopy, by combining localized surface plasmon resonances (LSPR) and dark-field microscopy technique. Due to the sensitive response of LSPR to the refractive index of the surrounding media, this technique is capable of converting a small refractive index difference to a change in scattering intensity, resulting in a high-contrast, diffraction limited image of a thin unstained specimen with small, gradual refractive-index variation.

  2. Infrared contrast of crude-oil-covered water surfaces.

    PubMed

    Shih, Wei-Chuan; Andrews, A Ballard

    2008-12-15

    Infrared oil spill detection utilizes either temperature or emissivity contrast of native and oil-covered water surfaces. In particular, the thickness dependent radiance contrast due to thin film interference has been studied. Together with detection boundaries derived from the radiative transfer equation, we can explain historically observed daytime contrast reversal and our observations during nighttime, better contrast from thin oil slicks than from thick films, which to our knowledge has not been mentioned in the literature. These findings have important implications to long-wavelength infrared (LWIR) instrument design and data interpretation for crude oil spill detection. PMID:19079527

  3. Nanoparticle Contrast Agents for Computed Tomography: A Focus on Micelles

    PubMed Central

    Cormode, David P.; Naha, Pratap C.; Fayad, Zahi A.

    2014-01-01

    Computed tomography (CT) is an X-ray based whole body imaging technique that is widely used in medicine. Clinically approved contrast agents for CT are iodinated small molecules or barium suspensions. Over the past seven years there has been a great increase in the development of nanoparticles as CT contrast agents. Nanoparticles have several advantages over small molecule CT contrast agents, such as long blood-pool residence times, and the potential for cell tracking and targeted imaging applications. Furthermore, there is a need for novel CT contrast agents, due to the growing population of renally impaired patients and patients hypersensitive to iodinated contrast. Micelles and lipoproteins, a micelle-related class of nanoparticle, have notably been adapted as CT contrast agents. In this review we discuss the principles of CT image formation and the generation of CT contrast. We discuss the progress in developing non-targeted, targeted and cell tracking nanoparticle CT contrast agents. We feature agents based on micelles and used in conjunction with spectral CT. The large contrast agent doses needed will necessitate careful toxicology studies prior to clinical translation. However, the field has seen tremendous advances in the past decade and we expect many more advances to come in the next decade. PMID:24470293

  4. The effect of contrast on monocular versus binocular reading performance.

    PubMed

    Johansson, Jan; Pansell, Tony; Ygge, Jan; Seimyr, Gustaf Öqvist

    2014-01-01

    The binocular advantage in reading performance is typically small. On the other hand research shows binocular reading to be remarkably robust to degraded stimulus properties. We hypothesized that this robustness may stem from an increasing binocular contribution. The main objective was to compare monocular and binocular performance at different stimulus contrasts and assess the level of binocular superiority. A secondary objective was to assess any asymmetry in performance related to ocular dominance. In a balanced repeated measures experiment 18 subjects read texts at three levels of contrast monocularly and binocularly while their eye movements were recorded. The binocular advantage increased with reduced contrast producing a 7% slower monocular reading at 40% contrast, 9% slower at 20% contrast, and 21% slower at 10% contrast. A statistically significant interaction effect was found in fixation duration displaying a more adverse effect in the monocular condition at lowest contrast. No significant effects of ocular dominance were observed. The outcome suggests that binocularity contributes increasingly to reading performance as stimulus contrast decreases. The strongest difference between monocular and binocular performance was due to fixation duration. The findings may pose a clinical point that it may be necessary to consider tests at different contrast levels when estimating reading performance. PMID:24829225

  5. Enhancement of chromatic contrast increases predation risk for striped butterflies

    PubMed Central

    Stobbe, Nina; Schaefer, H. Martin

    2008-01-01

    Many prey species have evolved defensive colour patterns to avoid attacks. One type of camouflage, disruptive coloration, relies on contrasting patterns that hinder predators' ability to recognize an object. While high contrasts are used to facilitate detection in many visual communication systems, they are thought to provide misleading information about prey appearance in disruptive patterns. A fundamental tenet in disruptive coloration theory is the principle of ‘maximum disruptive contrast’, i.e. disruptive patterns are more effective when higher contrasts are involved. We tested this principle in highly contrasting stripes that have often been described as disruptive patterns. Varying the strength of chromatic contrast between stripes and adjacent pattern elements in artificial butterflies, we found a strong negative correlation between survival probability and chromatic contrast strength. We conclude that too high a contrast leads to increased conspicuousness rather than to effective camouflage. However, artificial butterflies that sported contrasts similar to those of the model species Limenitis camilla survived equally well as background-matching butterflies without these stripes. Contrasting stripes do thus not necessarily increase predation rates. This result may provide new insights into the design and characteristics of a range of colour patterns such as sexual, mimetic and aposematic signals. PMID:18381256

  6. Adaptive optimisation of a generalised phase contrast beam shaping system

    NASA Astrophysics Data System (ADS)

    Kenny, F.; Choi, F. S.; Glückstad, J.; Booth, M. J.

    2015-05-01

    The generalised phase contrast (GPC) method provides versatile and efficient light shaping for a range of applications. We have implemented a generalised phase contrast system that used two passes on a single spatial light modulator (SLM). Both the pupil phase distribution and the phase contrast filter were generated by the SLM. This provided extra flexibility and control over the parameters of the system including the phase step magnitude, shape, radius and position of the filter. A feedback method for the on-line optimisation of these properties was also developed. Using feedback from images of the generated light field, it was possible to dynamically adjust the phase filter parameters to provide optimum contrast.

  7. Simultaneous de-noising in phase contrast tomography

    NASA Astrophysics Data System (ADS)

    Koehler, Thomas; Roessl, Ewald

    2012-07-01

    In this work, we investigate methods for de-noising of tomographic differential phase contrast and absorption contrast images. We exploit the fact that in grating-based differential phase contrast imaging (DPCI), first, several images are acquired simultaneously in exactly the same geometry, and second, these different images can show very different contrast-to-noise-ratios. These features of grating-based DPCI are used to generalize the conventional bilateral filter. Experiments using simulations show a superior de-noising performance of the generalized algorithm compared with the conventional one.

  8. Mechanical Selection.

    ERIC Educational Resources Information Center

    Brownson, Charles W.

    1988-01-01

    Defines mechanical and expert selection of library materials and investigates the usefulness of mechanical selection in three test cases involving popular novels, German literature, and contemporary poetry. The cost of mechanical selection is examined and more quantification in selection practice is recommended. Data are presented in eight tables,…

  9. [Pathophysiologic and immunologic mechanisms of contrast medium-induced anaphylactoid immediate hypersensitivity--an overview].

    PubMed

    Amon, U

    1997-05-01

    Since non-ionic radiocontrast media (RCM) have been introduced, the incidence of unwanted reactions has been significantly reduced in comparison to ionic compounds. However, acute anaphylactoid reactions with heterogenous symptoms within minutes after intravasal application are still a life-threatening risk of investigations with RCM. The present article summarizes the current view of the underlying pathomechanisms of such reactions. PMID:9296610

  10. Contrasting classical probability concepts with quantum mechanical behavior in the undergraduate laboratory

    NASA Astrophysics Data System (ADS)

    Guzmán, D. A.; Uribe, L. J.; Valencia, A.; Rodríguez, F. J.; Quiroga, L.

    2015-09-01

    In this paper, we report an experimental activity suitable for undergraduate students that makes them question their ideas about locality and realism. The experiment here reported complements previous educational approaches to Bell inequalities, since the usually called S function, that quantifies correlations, is mapped by measuring it for different detection angles. The students themselves worked in a pre-aligned setup that allowed them to test and violate the Clauser-Horne-Shimony-Holt-Bell inequality for two distant photons entangled in polarization.

  11. Microscopy imaging system and method employing stimulated raman spectroscopy as a contrast mechanism

    DOEpatents

    Xie, Xiaoliang Sunney; Freudiger, Christian; Min, Wei

    2011-09-27

    A microscopy imaging system includes a first light source for providing a first train of pulses at a first center optical frequency .omega..sub.1, a second light source for providing a second train of pulses at a second center optical frequency .omega..sub.2, a modulator system, an optical detector, and a processor. The modulator system is for modulating a beam property of the second train of pulses at a modulation frequency f of at least 100 kHz. The optical detector is for detecting an integrated intensity of substantially all optical frequency components of the first train of pulses from the common focal volume by blocking the second train of pulses being modulated. The processor is for detecting, a modulation at the modulation frequency f, of the integrated intensity of the optical frequency components of the first train of pulses to provide a pixel of an image for the microscopy imaging system.

  12. Interactive processing of contrastive expressions by Russian children

    PubMed Central

    Sekerina, Irina A.; Trueswell, John C.

    2013-01-01

    Children's ability to interpret color adjective noun phrases (e.g., red butterfly) as contrastive was examined in an eyetracking study with 6-year-old Russian children. Pitch accent placement (on the adjective red, or on the noun butterfly) was compared within a visual context containing two red referents (a butterfly and a fox) when only one of them had a contrast member (a purple butterfly) or when both had a contrast member (a purple butterfly and a grey fox). Contrastiveness was enhanced by the Russian-specific ‘split constituent’ construction (e.g., Red put butterfly . . .) in which a contrastive interpretation of the color term requires pitch accent on the adjective, with the nonsplit sentences serving as control. Regardless of the experimental manipulations, children had to wait until hearing the noun (butterfly) to identify the referent, even in splits. This occurred even under conditions for which the prosody and the visual context allow adult listeners to infer the relevant contrast set and anticipate the referent prior to hearing the noun (accent on the adjective in 1-Contrast scenes). Pitch accent on the adjective did facilitate children's referential processing, but only for the nonsplit constituents. Moreover, visual contexts that encouraged the correct contrast set (1-Contrast) only facilitated referential processing after hearing the noun, even in splits. Further analyses showed that children can anticipate the reference like adults but only when the contrast set is made salient by the preceding supportive discourse, that is, when the inference about the intended contrast set is provided by the preceding utterance. PMID:24465066

  13. Postseismic GRACE and GPS observations indicate a rheology contrast above and below the Sumatra slab

    NASA Astrophysics Data System (ADS)

    Broerse, Taco; Riva, Riccardo; Simons, Wim; Govers, Rob; Vermeersen, Bert

    2015-07-01

    More than 7 years of observations of postseismic relaxation after the 2004 Sumatra-Andaman earthquake provide an improving view on the deformation in the wide vicinity of the 2004 rupture. We include both Gravity Recovery and Climate Experiment (GRACE) gravity field data that show a large postseismic signal over the rupture area and GPS observations in the back arc region. With increasing time GPS and GRACE show contrasting relaxation styles that were not easily discernible on shorter time series. We investigate whether mantle creep can simultaneously explain the far-field surface displacements and the long-wavelength gravity changes. We interpret contrasts in the temporal behavior of the GPS-GRACE observations in terms of lateral variations in rheological properties of the asthenosphere below and above the slab. Based on 1-D viscoelastic models, our results support an (almost) order of magnitude contrast between oceanic lithosphere viscosity and continental viscosity, which likely means that the low viscosities frequently found from postseismic deformation after subduction earthquakes are valid only for the mantle wedge. Next to mantle creep, we also consider afterslip as an alternative mechanism for postseismic deformation. We investigate how the combination of GRACE and GPS data can better discriminate between different mechanisms of postseismic relaxation: distributed deformation (mantle creep) versus localized deformation (afterslip). We conclude that the GRACE-observed gravity changes rule out afterslip as the dominant mechanism explaining long-wavelength deformation even over the first year after the event.

  14. N-acetylcysteine for Prevention of Contrast-Induced Nephropathy: A Narrative Review.

    PubMed

    Jo, Sang-Ho

    2011-12-01

    Contrast-induced nephropathy (CIN) affects in-hospital, short- and long-term morbidity and mortality. It also leads to prolonged hospital stay and increased medical cost. Given the potential clinical severity of CIN, there has been considerable interest in the development of preventative strategies to reduce the risk of contrast-induced renal deterioration in at-risk populations. A number of pharmacologic and mechanical preventive measures have been attempted, but no method other than adequate periprocedural hydration has been conclusively successful. Since its introduction in 2000, N-acetylcysteine (NAC) has been widely investigated, albeit with conflicting findings for its nephroprotection capability in patients receiving contrast media procedures. However, there is still virtually no definitive evidence of effectiveness of NAC. Although the exact mechanism responsible for the protective action of NAC from renal function deterioration remains unclear, the antioxidant and vasodilatory properties of NAC have been suggested as the main mechanisms. This review summarizes the current status of NAC as a potential agent to prevent renal functional deterioration and its limitations. PMID:22259598

  15. Small-animal microangiography using phase-contrast X-ray imaging and gas as contrast agent

    NASA Astrophysics Data System (ADS)

    Lundström, Ulf; Larsson, Daniel H.; Westermark, Ulrica K.; Burvall, Anna; Hertz, Hans M.

    2014-03-01

    We use propagation-based phase-contrast X-ray imaging with gas as contrast agent to visualize the microvasculature in small animals like mice and rats. The radiation dose required for absorption X-ray imaging is proportional to the minus fourth power of the structure size to be detected. This makes small vessels impossible to image at reasonable radiation doses using the absorption of conventional iodinated contrast agents. Propagation-based phase contrast gives enhanced contrast for high spatial frequencies by moving the detector away from the sample to let phase variations in the transmitted X-rays develop into intensity variations at the detector. Blood vessels are normally difficult to observe in phase contrast even with iodinated contrast agents as the density difference between blood and most tissues is relatively small. By injecting gas into the blood stream this density difference can be greatly enhanced giving strong phase contrast. One possible gas to use is carbon dioxide, which is a clinically accepted X-ray contrast agent. The gas is injected into the blood stream of patients to temporarily displace the blood in a region and thereby reduce the X-ray absorption in the blood vessels. We have shown that this method can be used to image blood vessels down to 8 μm in diameter in mouse ears. The low dose requirements of this method indicate a potential for live small-animal imaging and longitudinal studies of angiogenesis.

  16. Contrast Induced Nephropathy with Intravenous Iodinated Contrast Media in Routine Diagnostic Imaging: An Initial Experience in a Tertiary Care Hospital

    PubMed Central

    Bhatt, Shuchi; Rajpal, Nipun; Rathi, Vineeta; Avasthi, Rajneesh

    2016-01-01

    Background. Contrast induced nephropathy (CIN) is common cause of hospital acquired renal failure, defined as iatrogenic deterioration of renal function following intravascular contrast administration in the absence of another nephrotoxic event. Objectives. Objectives were to calculate incidence of CIN with routine IV contrast usage and to identify its risk factors. Materials and Methods. Study was conducted on 250 patients (having eGFR ≥ 45 mL/min/1.73 m2) receiving intravenous contrast. Various clinical risk factors and details of contrast media were recorded. Patients showing 25% increase in postprocedural serum creatinine value or an absolute increase of 0.5 mg/dL (44.2 mmol/L) were diagnosed as having CIN. Results and Conclusions. Postprocedural serum creatinine showed significant increase from baseline levels. 25 patients (10%) developed CIN. CIN was transient in 21 (84%) patients developing CIN. One patient (4%) developed renal failure and another died due to unknown cause. Dehydration, preexisting renal disease, cardiac failure, previous contrast administration, and volume of contrast had significant correlation with development of CIN (p < 0.05); whereas demographic variables, baseline serum creatinine/eGFR, previous renal surgery, diabetes mellitus, hypertension, nephrotoxic drug intake, abnormal routine hematology, and contrast characteristics had no correlation with CIN. CIN is a matter of concern even in routine imaging requiring intravenous contrast media, in our set-up. PMID:27069686

  17. Verbal Behavior and Behavioral Contrast in Human Subjects

    ERIC Educational Resources Information Center

    Tarbox, Jonathan; Hayes, Linda Parrott

    2005-01-01

    Behavioral contrast can be defined as an inverse relationship between the conditions of reinforcement in one setting and the rate of responding in another setting. Behavioral contrast is a phenomenon that is reliably demonstrated in pigeons and rats and in the context of multiple experimental preparations with these animals. However, little…

  18. Complications of radiologic contrast in patients with myasthenia gravis.

    PubMed

    Mehrizi, Mehyar; Pascuzzi, Robert M

    2014-09-01

    Use of older contrast agents during radiologic imaging in patients with myasthenia gravis (MG) has been associated with increased myasthenic symptoms and adverse drug reactions (ADRs). The effects of newer contrast agents have not been determined. A retrospective review of imaging safety in MG was conducted. Three hundred fifty-four imaging studies were analyzed. Procedures included 189 computed tomography (CT) images with and 106 without intravenous (IV) contrast and 42 magnetic resonance images (MRIs) with and 17 without contrast. In 108 patients for whom there was formal documentation of presence or absence of an immediate adverse response, only 1 who received CT IV contrast had an ADR (rate 0.93%). No ADRs or weakness were reported in patients who received MRI IV contrast. Our data suggest there is no significant immediate increased risk of myasthenic weakness with the use of modern radiologic contrast agents. The rate of ADRs in MG patients who receive CT IV contrast is now very low (0.93%). PMID:24677227

  19. Spatial Contrast Sensitivity in Adolescents with Autism Spectrum Disorders

    ERIC Educational Resources Information Center

    Koh, Hwan Cui; Milne, Elizabeth; Dobkins, Karen

    2010-01-01

    Adolescents with autism spectrum disorders (ASD) and typically developing (TD) controls underwent a rigorous psychophysical assessment that measured contrast sensitivity to seven spatial frequencies (0.5-20 cycles/degree). A contrast sensitivity function (CSF) was then fitted for each participant, from which four measures were obtained: visual…

  20. Predicting contrast in sentences with and without focus marking.

    PubMed

    Carlson, Katy

    2014-10-01

    How do we know when a contrast is coming? This study explores the prediction of parallel contrastive phrases, especially NPs, in sentences with and without overt focus marking. A written sentence-completion questionnaire with clauses followed by the conjunction "but" compared unmarked initial clauses to ones with the focus marker "only" on the subject or object. Both conditions with "only" elicited more contrasts overall than the condition without focus marking, and many of the contrasts were with the focus-marked NP. While the baseline (no-only) condition had full clauses for half of the completions, subject focus increased clausal completions and object focus increased negative ellipsis completions ("not"+NP structures), both changes in syntax which make a contrast with the marked NP easy. The production of negative ellipsis sentences primarily in the object-focus condition suggests that the object bias of these sentences in comprehension could relate to their being used more frequently with this meaning. Finally, the overall pattern of results shows that overt marking of contrastive focus increases continuations with contrasts, and the conjunction "but" does not reliably predict explicitly-stated contrasts within a sentence without overt focus marking. PMID:25177047