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Contrast Imaging (contrast + imaging)
Selected AbstractsMeasuring the Plastic Zone Size by Orientation Gradient Mapping (OGM) and Electron Channeling Contrast Imaging (ECCI)ADVANCED ENGINEERING MATERIALS, Issue 1-2 2007T. Welsch Abstract For the local investigation of plastic deformation mechanisms non-destructive methods are needed to image the distribution of dislocations and to measure dislocation densities. Additionally these methods should be usable in situ. Therefore the well known methods EBSD and ECCI are improved by an appropriate processing of the measured data. The resulting two new techniques OGM and ECCI-plus are validated in detail for two complex sets of experiments. Both techniques are used to image plastic deformation zones and to measure the size of plastic zones on a macro scale (hardness indents) as well as on a micro scale (crack tips) as demonstrated in this paper. Additionally OGM gives even quantitative data of the degree of deformation. The capability of both methods is discussed in detail and it is shown that they are independent from the topography which is critically surveyed. [source] Real-Time Contrast Imaging: A New Method to Monitor Capillary Recruitment in Human Forearm Skeletal MuscleMICROCIRCULATION, Issue 3 2008Alexandra H. Mulder ABSTRACT Objective: Muscle capillary perfusion can be measured by contrast-enhanced ultrasound. We examined whether a less time-consuming ultrasound technique, called "real-time imaging," could be used to measure capillary recruitment in human forearm skeletal muscle. Methods: We measured microvascular blood volume and microvascular flow velocity using bolus injections of contrast microbubbles after forearm muscle exercise and a two-hour infusion of insulin into the brachial artery (both associated with capillary recruitment) and after sodium nitroprusside infusion (no changes in flow distribution). Results: After an intravenous bolus injection of the contrast agent, the steady-state concentration of contrast agent in forearm muscle lasted long enough (approximately 190 seconds) for the duration of the measurements (which take 70,80 seconds), rendering the continuous infusion of microbubbles unnecessary. Microvascular blood-volume measurements showed a good short-time reproducibility and a good reproducibility after repositioning of the forearm. Reproducibility of microvascular flow velocity was too low. Exercise and insulin infusion both increased microvascular blood volume, consistent with capillary recruitment. Sodium nitroprusside had no effect. Conclusion: Real-time contrast imaging, after bolus injections of an ultrasound contrast agent, provides reliable information about capillary recruitment in human forearm skeletal muscle, and may offer a valuable tool in studying human (patho)physiology. [source] Three-Dimensional Geometry of Nanometer-Scale AlN Pits: A New Template for Quantum Dots?,ADVANCED MATERIALS, Issue 1 2008F. Liu The exact 3D geometry of nanometer-scale AlN pits is determined by Z -contrast imaging. The figure shows the 3D geometry of an AlN nano-pit and its corresponding GaN quantum dot. An atomic-resolution Z -contrast image is displayed in false color to clearly show the Z -contrast of the image, while the other panel displays a schematic 3D view. [source] Development of garnet porphyroblasts by multiple nucleation, coalescence and boundary misorientation-driven rotationsJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2001R. Spiess Abstract Two types of garnet porphyroblast occur in the Schneeberg Complex of the Italian Alps. Type 1 porphyroblasts form ellipsoidal pods with a centre consisting of unstrained quartz, decussate mica and small garnet grains, and a margin containing large garnet grains. Orientation contrast imaging using the scanning electron microscope shows that the larger marginal garnet grains comprise a number of orientation subdomains. Individual garnet grains without subdomains are small (< 50 µm), faceted and idioblastic, and have simple zoning profiles with Ca-rich cores and Ca-poor rims. Subdomains of larger garnet grains are similar in size to the individual, small garnet grains. Type 2 porphyroblasts comprise only ellipsoidal garnet, with small subdomains in the centre and larger subdomains at the margin. Each subdomain has its own Ca high, Ca dropping towards subdomain boundaries. Garnet grains, with or without subdomains, all have the same Ca-poor composition at rims in contact with other minerals. The compositional zonation patterns are best explained by simultaneous, multiple nucleation, followed by growth and amalgamation of individual garnet grains. The range of individual garnet and garnet subdomain sizes can be explained by a faster growth rate at the porphyroblast margin than in the centre. The difference between Type 1 and Type 2 porphyroblasts is probably related to the growth rate differential across the porphyroblast. Electron backscatter diffraction shows that small, individual garnet grains are randomly oriented. Large marginal garnet grains and subdomain-bearing garnet grains have a strong preferred orientation, clustering around a single garnet orientation. Misorientations across subdomain boundaries are small and misorientation axes are randomly oriented with respect to crystallographic orientations. The only explanation that fits the observational data is that individual garnet grains rotated towards coincident orientations once they came into contact with each other. This process was driven by the reduction of subdomain boundary energy associated with misorientation loss. Rotation of garnet grains was accommodated by diffusion in the subdomain boundary and diffusional creep and rigid body rotation of other minerals (quartz and mica) around the garnet. An analytical model, in which the kinetics of garnet rotation are controlled by the rheology of surrounding quartz, suggests that, at the conditions of metamorphism, the rotation required to give a strong preferred orientation can occur on a similar time-scale to that of porphyroblast growth. [source] Bilious vomiting in the newborn: 6 years data from a Level III CentreJOURNAL OF PAEDIATRICS AND CHILD HEALTH, Issue 5 2010Atul Malhotra Background: Bilious vomiting in the newborn is an urgent condition that frequently requires neonatal and paediatric surgical involvement. Investigations involve abdominal X-ray and contrast imaging in most cases. We aimed to describe the prevalence of surgical intervention in this cohort and assess the reliability of contrast imaging in accurate prediction of underlying condition. Methods: A retrospective audit of data from December 2001 to October 2007 was undertaken. Data on newborns admitted to a level III unit with bilious vomiting was extracted. Infants with bilious aspirates but no vomiting were excluded. Results: Sixty-one infants were admitted to the unit during the period with bilious vomiting. Most of them were out born (83.6%). Mean (and standard deviation) gestation was 38.3 weeks (±3.2); weight was 3173.5 grams (±717.6); day of admission was 3.68 days (1,28); and length of stay in the unit was 9.96 days (1,48). There were 52 (85.2%) abnormal X-rays and 21 (34.4%) abnormal contrast studies. Sixteen (26.6%) babies had laparotomies of which 6 were malrotations with volvulus, 2 small bowel obstructions, 2 meconium ileus, 2 Hirschsprung's disease, 2 other findings, while 2 were normal. Positive predictive value (number of accurate predictions of surgical findings) for barium contrast studies was 85.7% in this series. Conclusion: Bile stained vomiting is a surgical emergency and prompt investigation is the key in the management. Contrast studies still form the backbone of such investigations. [source] Positive contrast imaging of iron oxide nanoparticles with susceptibility-weighted imagingMAGNETIC RESONANCE IN MEDICINE, Issue 4 2010Frank Eibofner Abstract Superparamagnetic iron oxide particles can be utilized to label cells for immune cell and stem cell therapy. The labeled cells cause significant field distortions induced in their vicinity, which can be detected with magnetic resonance imaging (MRI). In conventional imaging, the signal voids arising from the field distortions lead to negative contrast, which is not desirable, as detection of the cells can be masked by native low signal tissue. In this work, a new method for visualizing magnetically labeled cells with positive contrast is proposed and described. The technique presented is based on the susceptibility-weighted imaging (SWI) post-processing algorithm. Phase images from gradient-echo sequences are evaluated pixel by pixel, and a mask is created with values ranging from 0 to 1, depending on the phase value of the pixel. The magnitude image is then multiplied by the mask. With an appropriate mask function, positive contrast in the vicinity of the labeled cells is created. The feasibility of this technique is proved using an agar phantom containing superparamagnetic iron oxide particles,labeled cells and an ex vivo bovine liver. The results show high potential for detecting even small labeled cell concentrations in structurally inhomogeneous tissue types. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source] Time-resolved flow measurement in the isolated rat heart: Characterization of left coronary artery stenosisMAGNETIC RESONANCE IN MEDICINE, Issue 3 2003Sascha Köhler Abstract The investigation of flow behavior in coronary arteries is of great importance for an understanding of heart failure and heart regulation mechanisms. The purpose of the present study was to demonstrate that flow velocity can be quantified in the coronary arteries of the isolated rat heart with high-resolution phase contrast MRI. A phase contrast cine-FLASH imaging sequence was used for flow quantification with an in-plane resolution of 70 ,m and a slice thickness of 500 ,m. With time-resolved measurements, coronary flow over the heart cycle was analyzed. Furthermore, the flow behavior in coronary stenosis was investigated and the degree of stenosis was quantified with MR phase contrast imaging. To achieve the required spatial resolution and a satisfactory signal-to-noise ratio, the experiments were performed at 11.75 T. Magn Reson Med 50:449,452, 2003. © 2003 Wiley-Liss, Inc. [source] Real-Time Contrast Imaging: A New Method to Monitor Capillary Recruitment in Human Forearm Skeletal MuscleMICROCIRCULATION, Issue 3 2008Alexandra H. Mulder ABSTRACT Objective: Muscle capillary perfusion can be measured by contrast-enhanced ultrasound. We examined whether a less time-consuming ultrasound technique, called "real-time imaging," could be used to measure capillary recruitment in human forearm skeletal muscle. Methods: We measured microvascular blood volume and microvascular flow velocity using bolus injections of contrast microbubbles after forearm muscle exercise and a two-hour infusion of insulin into the brachial artery (both associated with capillary recruitment) and after sodium nitroprusside infusion (no changes in flow distribution). Results: After an intravenous bolus injection of the contrast agent, the steady-state concentration of contrast agent in forearm muscle lasted long enough (approximately 190 seconds) for the duration of the measurements (which take 70,80 seconds), rendering the continuous infusion of microbubbles unnecessary. Microvascular blood-volume measurements showed a good short-time reproducibility and a good reproducibility after repositioning of the forearm. Reproducibility of microvascular flow velocity was too low. Exercise and insulin infusion both increased microvascular blood volume, consistent with capillary recruitment. Sodium nitroprusside had no effect. Conclusion: Real-time contrast imaging, after bolus injections of an ultrasound contrast agent, provides reliable information about capillary recruitment in human forearm skeletal muscle, and may offer a valuable tool in studying human (patho)physiology. [source] Imaging of cochlear tissue with a grating interferometer and hard X-raysMICROSCOPY RESEARCH AND TECHNIQUE, Issue 12 2009Claus-Peter Richter Abstract This article addresses an important current development in medical and biological imaging: the possibility of imaging soft tissue at resolutions in the micron range using hard X-rays. Challenging environments, including the cochlea, require the imaging of soft tissue structure surrounded by bone. We demonstrate that cochlear soft tissue structures can be imaged with hard X-ray phase contrast. Furthermore, we show that only a thin slice of the tissue is required to introduce a large phase shift. It is likely that the phase contrast image of the soft tissue structures is sufficient to image the structures even if surrounded by bone. For the present set of experiments, structures with low-absorption contrast have been visualized using in-line phase contrast imaging and a grating interferometer. The experiments have been performed at the Advanced Photon Source at Argonne National Laboratories, a third generation source of synchrotron radiation. The source provides highly coherent X-ray radiation with high-photon flux (>1012 photons/s) at high-photon energies (5,70 keV). Radiographic and light microscopy images of the gerbil cochlear slice samples were compared. It has been determined that a 20-,m thick tissue slice induces a phase shift between 1/3, and 2/3,. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc. [source] TEM investigations of (In,Ga)N/GaN quantum structuresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2008P. Manolaki Abstract The paper reports on the influence of the growth temperature on the structural and chemical properties of (In,Ga)N quantum wells (QWs) on GaN. Two different samples A and B were fabricated. The QWs of the sample A were grown at a constant temperature of 600 °C. For the QWs of the sample B the temperature was 530 °C, while for the GaN barrier it was raised to 600 °C. The chemical and structural properties were studied by electron diffraction contrast imaging using the 0001 and 0002 reflection, respectively. Sample A exhibits homogeneous (In,Ga)N QWs. For sample B some undulated strain contrast of the QWs is visible hinting to the formation of quantum dots (QDs). The self-organisation of (In,Ga)N QDs in sample B is also evidenced by composition sensitive STEM-HAADF imaging, where the individual (In,Ga)N layers exhibit inhomogeneous intensity as well as varied thickness. Moreover, energy dispersive X-ray spectroscopy yielded enrichment of indium at QD sites. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Scanning Force Microscopy Based Rapid Force Curve Acquisition on Supported Lipid Bilayers: Experiments and Simulations Using Pulsed Force ModeCHEMPHYSCHEM, Issue 7 2004Stephanie Krüger Dr. Abstract In situ pulsed force mode scanning force microscopy (PFM,SFM) images of phase separated solid-supported lipid bilayers are discussed with the help of computer simulations. Simultaneous imaging of material properties and topography in a liquid environment by means of PFM,SFM is severely hampered by hydrodynamic damping of the cantilever. Stiffness and adhesion images of solid-supported membranes consisting of cholesterol, sphingomyelin, and 1,2-dioleyl-phosphatidylcholine obtained in aqueous solution exhibit contrast inversion of adhesion and stiffness images depending on parameters such as driving frequency, amplitude, and trigger setting. Simulations using a simple harmonic oscillator model explain experimental findings and give a deeper insight into the way PFM,SFM experiments have to be performed in order to obtain interpretable results and hence pave the way for reliable material contrast imaging at high speed. [source] | |||||||||||||