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High-resolution Images (high-resolution + image)

Distribution by Scientific Domains

Medical Sciences	69%
Earth and Environmental Science	11%
Physics and Astronomy	7%
Chemistry	7%

Selected Abstracts

High-resolution images from compressed low-resolution video: Motion estimation and observable pixels

INTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 2 2004
L. D. Alvarez
Abstract In this article, we address the problem of obtaining a high-resolution (HR) image from a compressed low-resolution (LR) video sequence. Motion information plays a critical role in solving this problem, and we determine which pixels in the sequence provide useful information for calculating the high-resolution image. The bit stream of hybrid motion compensated video compression methods includes low-resolution motion-compensated images; we therefore also study which pixels in these images should be used to increase the quality of the reconstructed image. Once the useful (observable) pixels in the low-resolution and motion-compensated sequences have been detected, we modify the acquisition model to only account for these observations. The proposed approach is tested on real compressed video sequences and the improved performance is reported. © 2004 Wiley Periodicals, Inc. Int J Imaging Syst Technol 14, 58,66, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20008 [source]

Local staging of rectal carcinoma and assessment of the circumferential resection margin with high-resolution MRI using an integrated parallel acquisition technique

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2005
Katja Oberholzer MD
Abstract Purpose To assess the diagnostic accuracy of integrated parallel acquisition technique (iPAT) in local staging of rectal carcinoma in comparison to conventional high-resolution MRI. Materials and Methods A total of 28 patients with a neoplasm of the rectum and 15 control patients underwent MRI of the pelvis. High-resolution images were acquired conventionally and with iPAT using a modified sensitivity encoding (mSENSE). Image quality, signal-to-noise and contrast-to-noise ratios (SNR, CNR), tumor extent, nodal status, and delineation of the circumferential resection margin (CRM) were compared. In 19 patients with a carcinoma, MR findings were correlated with the histopathological diagnosis. Tumor distance to the CRM was matched with resection specimen in 12 cases. Results The comparison of both MR techniques revealed no clinically relevant differences in tumor staging and delineation of the CRM, though SNR and CNR were significantly lower in mSENSE images. Tumor stage was concordant in 17 of 19 cases compared to histopathology. In four of nine patients with T3 and T4 carcinomas, the histopathological resection margin was ,2 mm, in five cases MRI predicted a margin of ,2 mm. Conclusion The application of iPAT in local staging of rectal carcinoma is time-saving and does not degrade diagnostic accuracy. Tumor stage, nodal status, and the CRM can be assessed equally compared to conventional acquisition techniques. J. Magn. Reson. Imaging 2005;22:101,108. © 2005 Wiley-Liss, Inc. [source]

Necropsy by magnetic resonance in a case of conjoined thoracopagus twins

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2001
A.C. Manzano MD
Abstract A case of thoracopagus conjoined stillborn twins studied with magnetic resonance imaging (MRI) is presented. Due to the parents' denial of authorization for an autopsy of the fetuses, the MRI study was performed as an alternative to necropsy. High-resolution images of the fetuses demonstrated relevant anatomic features, providing noninvasive pathological insight with preservation of the fetal specimen. J. Magn. Reson. Imaging 2001;13:976,981. © 2001 Wiley-Liss, Inc. [source]

A numerical comparison of 2D resistivity imaging with 10 electrode arrays

GEOPHYSICAL PROSPECTING, Issue 5 2004
Torleif Dahlin
ABSTRACT Numerical simulations are used to compare the resolution and efficiency of 2D resistivity imaging surveys for 10 electrode arrays. The arrays analysed include pole-pole (PP), pole-dipole (PD), half-Wenner (HW), Wenner-, (WN), Schlumberger (SC), dipole-dipole (DD), Wenner-, (WB), ,-array (GM), multiple or moving gradient array (GD) and midpoint-potential-referred measurement (MPR) arrays. Five synthetic geological models, simulating a buried channel, a narrow conductive dike, a narrow resistive dike, dipping blocks and covered waste ponds, were used to examine the surveying efficiency (anomaly effects, signal-to-noise ratios) and the imaging capabilities of these arrays. The responses to variations in the data density and noise sensitivities of these electrode configurations were also investigated using robust (L1 -norm) inversion and smoothness-constrained least-squares (L2 -norm) inversion for the five synthetic models. The results show the following. (i) GM and WN are less contaminated by noise than the other electrode arrays. (ii) The relative anomaly effects for the different arrays vary with the geological models. However, the relatively high anomaly effects of PP, GM and WB surveys do not always give a high-resolution image. PD, DD and GD can yield better resolution images than GM, PP, WN and WB, although they are more susceptible to noise contamination. SC is also a strong candidate but is expected to give more edge effects. (iii) The imaging quality of these arrays is relatively robust with respect to reductions in the data density of a multi-electrode layout within the tested ranges. (iv) The robust inversion generally gives better imaging results than the L2 -norm inversion, especially with noisy data, except for the dipping block structure presented here. (v) GD and MPR are well suited to multichannel surveying and GD may produce images that are comparable to those obtained with DD and PD. Accordingly, the GD, PD, DD and SC arrays are strongly recommended for 2D resistivity imaging, where the final choice will be determined by the expected geology, the purpose of the survey and logistical considerations. [source]

MAP fusion method for superresolution of images with locally varying pixel quality

INTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 4 2008
Kio Kim
Abstract Superresolution is a procedure that produces a high-resolution image from a set of low-resolution images. Many of superresolution techniques are designed for optical cameras, which produce pixel values of well-defined uncertainty, while there are still various imaging modalities for which the uncertainty of the images is difficult to control. To construct a superresolution image from low-resolution images with varying uncertainty, one needs to keep track of the uncertainty values in addition to the pixel values. In this paper, we develop a probabilistic approach to superresolution to address the problem of varying uncertainty. As direct computation of the analytic solution for the superresolution problem is difficult, we suggest a novel algorithm for computing the approximate solution. As this algorithm is a noniterative method based on Kalman filter-like recursion relations, there is a potential for real-time implementation of the algorithm. To show the efficiency of our method, we apply this algorithm to a video sequence acquired by a forward looking sonar system. © 2008 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 18, 242,250, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). [source]

High-resolution images from compressed low-resolution video: Motion estimation and observable pixels

High-resolution imaging using integrated optical systems

INTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 2 2004
S. Prasad
Abstract Certain optical aberrations, such as defocus, can significantly degrade the signal collected by an imaging system, producing images with low resolution. In images with depth-dependent detail, such degradations are difficult to remove due to their inherent spatially varying nature. In 1995, Dowski and Cathey introduced the concept of wavefront coding to extend the depth of field. They showed that wavefront coding and decoding enables quality control of such images using integrated optical-digital imaging systems. With wavefront coding, a high-resolution image can be efficiently obtained without the need to resort to expensive algorithms for spatially varying restoration. In this article, we discuss a novel and effective multiple-design-parameter approach for optimizing the processes of encoding and decoding the wavefront phase in integrated optical-digital imaging systems. Our approach involves the use of information metrics, such as the Strehl ratio and Fisher information, for determining the optimal pupil-phase distribution for which the resulting image is insensitive to certain aberrations, such as focus errors. The effectiveness of this approach is illustrated with a number of numerical simulation experiments, and applications to the development of iris recognition systems with high-resolution capabilities are briefly discussed. © 2004 Wiley Periodicals, Inc. Int J Imaging Syst Technol 14, 67,74, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20009 [source]

Coherent nano-area electron diffraction

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 5-6 2004
J.M. Zuo
We describe the new coherent nano-area electron diffraction (NED) and its application for structure determination of individual nanostructures. The study is motivated by the challenge and the general lack of analytical techniques for characterizing nanometer-sized, heterogeneous phases. We show that by focusing electrons on the focal plane of the pre-objective lens using a 3rd condenser lens and a small condense aperture, it is possible to achieve a nanometer-sized highly parallel illumination or probe. The high angular resolution of diffraction pattern from the parallel illumination allows over-sampling and consequently the solution of phase problem based on the recently developed ab initio phase retrieval technique. From this, a high-contrast and high-resolution image can be reconstructed at resolution beyond the performance limit of the image-forming objective lens. The significance of NED for nanostructure characterization will be exemplified by single-wall carbon nanotubes and small metallic clusters. Imaging from diffraction patterns, or diffractive imaging, will be demonstrated using double-wall carbon nanotubes. Microsc. Res. Tech. 64:347,355, 2004. © 2004 Wiley-Liss, Inc. [source]

Achieving super-resolution X-ray imaging with mobile C-arm devices

THE INTERNATIONAL JOURNAL OF MEDICAL ROBOTICS AND COMPUTER ASSISTED SURGERY, Issue 3 2009
C. Bodensteiner
Abstract Background The term super-resolution refers to the process of combining a set of low-resolution images into a high-resolution image using image processing methods. This work is concerned with the reconstruction of high-resolution X-ray images. Specifically, we address the problem of acquiring X-ray images from multiple, very close view points. Methods We propose to use a novel experimental robotic C-arm device to create high-resolution X-ray images. For this purpose, we suggest different strategies for acquiring multiple low-resolution images, and we provide the steps to achieve acquisition-error compensation. Compared to visible light images, X-ray images have the particularity that parallax effects render super-resolution very difficult. Using the acquired multi-frame data, we evaluate recent well-known super-resolution reconstruction algorithms. The same algorithms are evaluated based on synthetic 3D phantom data and real X-ray images. Results In experiments with both synthetic and real projection data, we successfully reconstruct up to four times higher-resolution images. These images reveal structures and details which are not perceivable in the low-resolution images. Conclusions The advantage of super-resolution techniques for X-ray is the potential reduction of radiation dose for patients and medical personnel. Potential medical applications include the diagnosis of early-stage osteoporosis and the detection of very small calcifications. Copyright © 2009 John Wiley & Sons, Ltd. [source]

MR imaging in assessing cardiovascular interventions and myocardial injury

CONTRAST MEDIA & MOLECULAR IMAGING, Issue 1 2007
Alexis Jacquier
Abstract Performing an MR-guided endovascular intervention requires (1) real-time tracking and guidance of catheters/guide wires to the target, (2) high-resolution images of the target and its surroundings in order to define the extent of the target, (3) performing a therapeutic procedure (delivery of stent or injection of gene or cells) and (4) evaluating the outcome of the therapeutic procedure. The combination of X-ray and MR imaging (XMR) in a single suite was designed for new interventional procedures. MR contrast media can be used to delineate myocardial infarcts and microvascular obstruction, thereby defining the target for local delivery of therapeutic agents under MR-guidance. Iron particles, or gadolinium- or dysprosium-chelates are mixed with the soluble injectates or stem cells in order to track intramyocardial delivery and distribution. Preliminary results show that genes encoded for vascular endothelial and fibroblast growth factor and cells are effective in promoting angiogenesis, arteriogenesis, perfusion and LV function. Angiogenic growth factors, genes and cells administered under MR-guided minimally invasive catheter-based procedures will open up new avenues in treating end-stage ischemic heart disease. The optimum dose of the therapeutic agents, delivery devices and real-time imaging techniques to guide the delivery are currently the subject of ongoing research. The aim of this review is to (1) provide an updated review of experiences using MR imaging to guide transcatheter therapy, (2) address the potential of cardiovascular magnetic resonance (MR) imaging and MR contrast media in assessing myocardial injury at a molecular level and labeling cells and (3) illustrate the applicability of the non-invasive MR imaging in the field of angiogenic therapies through recent clinical and experimental publications. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Advances and challenges in super-resolution

INTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 2 2004
Sina Farsiu
Abstract Super-Resolution reconstruction produces one or a set of high-resolution images from a sequence of low-resolution frames. This article reviews a variety of Super-Resolution methods proposed in the last 20 years, and provides some insight into, and a summary of, our recent contributions to the general Super-Resolution problem. In the process, a detailed study of several very important aspects of Super-Resolution, often ignored in the literature, is presented. Specifically, we discuss robustness, treatment of color, and dynamic operation modes. Novel methods for addressing these issues are accompanied by experimental results on simulated and real data. Finally, some future challenges in Super-Resolution are outlined and discussed. © 2004 Wiley Periodicals, Inc. Int J Imaging Syst Technol 14, 47,57, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20007 [source]

Quantified characterization of human cutaneous normal scar using multiphoton microscopy

JOURNAL OF BIOPHOTONICS, Issue 1-2 2010
Xiaoqin Zhu
Abstract The morphological alterations of human cutaneous normal scar were quantitatively analyzed using multiphoton microscopy (MPM) based on two-photon excited fluorescence and second harmonic generation. High-contrast, high-resolution images of normal scar and uninjured skin were obtained for comparison. In addition, some quantitative parameters have been extracted to quantitatively discriminate between normal scar and uninjured skin. The MPM combined with quantitative method enable a better understanding of microstructual alterations of the epidermis, elastic fiber, and collagen in normal scar. It may lead the way to making know the mechanism of normal scar formation and identifying feasible therapeutic options. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Mechanical implications of estrogen supplementation in early postmenopausal women

JOURNAL OF BONE AND MINERAL RESEARCH, Issue 6 2010
Felix W Wehrli
Abstract Whereas the structural implications of drug intervention are well established, there are few data on the possible mechanical consequences of treatment. In this work we examined the changes in elastic and shear moduli (EM and SM) in a region of trabecular bone in the distal radius and distal tibia of early postmenopausal women on the basis of MRI-based micro-finite-element (µFE) analysis. Whole-section axial stiffness (AS) encompassing both trabecular and cortical compartments was evaluated as well. The study was conducted on previously acquired high-resolution images at the two anatomic sites. Images were processed to yield a 3D voxel array of bone-volume fraction (BVF), which was converted to a µFE model of hexahedral elements in which tissue modulus was set proportional to voxel BVF. The study comprised 65 early postmenopausal women (age range 45 to 55 years), of whom 32 had chosen estrogen supplementation (estradiol group); the remainder had not (control group). Subjects had been scanned at baseline and 12 and 24 months thereafter. At the distal tibia, EM and SM were reduced by 2.9% to 5.5% in the control group (p,<,.05 to <.005), but there was no change in the estradiol subjects. AS decreased 3.9% (4.0%) in controls (p,<,.005) and increased by 5.8% (6.2%) in estradiol group subjects (p,<,.05) at 12 (24) months. At the distal radius, EM and SM changes from baseline were not significant, but at both time points AS was increased in estradiol group subjects and decreased in controls (p,<,.005 to <.05), albeit by a smaller margin than at the tibia. EM and SM were strongly correlated with BV/TV (r2,=,0.44 to 0.92) as well as with topologic parameters expressing the ratio of plates to rods (r2,=,0.45 to 0.82), jointly explaining up to 96% of the variation in the mechanical parameters. Finally, baseline AS was strongly correlated between the two anatomic sites (r2,=,0.58), suggesting that intersubject variations in the bone's mechanical competence follows similar mechanisms. In conclusion, the results demonstrate that micro-MRI-based µFE models are suited for the study of the mechanical implications of antiresorptive treatment. The data further highlight the anabolic effect of short-term estrogen supplementation. © 2010 American Society for Bone and Mineral Research [source]

Two- and three-dimensional multinuclear stray-field imaging of rotating samples with magic-angle spinning (STRAFI-MAS): From bio to inorganic materials

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2010
Alan Wong PhD
Abstract Purpose: To revisit and illustrate the potential of a simple and effective multidimensional stray-field imaging technique with magic-angle spinning, known as STRAFI-MAS. Materials and Methods: STRAFI-MAS images are acquired with a standard NMR magnet and a traditional magic-angle sample spinning (MAS) probe. The stray-field gradients are achieved by placing the MAS probe, along the z -direction, at a distance from the center of the magnet. No pulsed-field gradients are applied. The multidimensional spatial encoding is carried out by synchronizing the radiofrequency pulses with the sample MAS rotation. Results: Two-dimensional (2D) and 3D multinuclear images of various phantoms, including a tibia bone and silicon carbide, are recorded. Images of inorganic solids containing quadrupolar nuclei, 23Na and 27Al, are also explored for the first time by STRAFI-MAS. Conclusion: We have demonstrated that STRAFI-MAS is a simple and user-friendly technique for multidimensional imaging without the need of imaging equipment. With the current advancements in NMR and MRI methodologies, STRAFI-MAS is expected to be further developed and improved. We anticipate that STRAFI-MAS can spark a wide spectrum of interest, from material to bio science, where can benefit from high-resolution images. J. Magn. Reson. Imaging 2010;32:418,423. © 2010 Wiley-Liss, Inc. [source]

3D coronary motion tracking in swine models with MR tracking catheters

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2009
Ehud J. Schmidt PhD
Abstract Purpose To develop MR-tracked catheters to delineate the three-dimensional motion of coronary arteries at high spatial and temporal resolution. Materials and Methods Catheters with three tracking microcoils were placed into nine swine. During breath-holds, electrocardiographic (ECG)-synchronized 3D motion was measured at varying vessel depths. 3D motion was measured in American Heart Association left anterior descending (LAD) segments 6,7, left circumflex (LCX) segments 11,15, and right coronary artery (RCA) segments 2,3, at 60,115 beats/min heart rates. Similar-length cardiac cycles were averaged. Intercoil cross-correlation identified early systolic phase (ES) and determined segment motion delay. Results Translational and rotational motion, as a function of cardiac phase, is shown, with directionality and amplitude varying along the vessel length. Rotation (peak-to-peak solid-angle RCA ,0.10, LAD ,0.06, LCX ,0.18 radian) occurs primarily during fast translational motion and increases distally. LCX displacement increases with heart rate by 18%. Phantom simulations of motion effects on high-resolution images, using RCA results, show artifacts due to translation and rotation. Conclusion Magnetic resonance imaging (MRI) tracking catheters quantify motion at 20 fps and 1 mm3 resolution at multiple vessel depths, exceeding that available with other techniques. Imaging artifacts due to rotation are demonstrated. Motion-tracking catheters may provide physiological information during interventions and improve imaging spatial resolution. J. Magn. Reson. Imaging 2009;29:86,98. © 2008 Wiley-Liss, Inc. [source]

Apparent wall thickening of cystic renal lesions on MRI

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2008
Vikas Gulani MD
Abstract Purpose To show that cystic renal lesions that would otherwise meet criteria for simple cysts can demonstrate perceptible walls or increased wall thickness on MRI, sometimes causing these lesions to be "upgraded." It was hypothesized that thickening of cyst walls on MRI can be artifactual, due to data truncation, applied filtering, and low signal-to-noise ratio (SNR). Materials and Methods k-Space data for a 4-cm cyst were created in a 40-cm field of view (FOV) (512 × 512 matrix). Additional data sets were created using the central 512 × 256 and 512 × 128 points. Noise was simulated so that the cyst SNR was approximately 7, 14, and 20, respectively. Actual wall thickness was set at 0.25 mm, and cyst:wall signal at 1:4. An inverse two-dimensional (2D) fast Fourier transform (FFT) yielded simulated images. A Fermi filter was applied to reduce ringing. Images/projections were examined for wall thickening. Seven patients with initially thick-walled cysts on fat-saturated spoiled gradient-echo (FS-SPGR) images were scanned with increasing resolution (256 × 128 and 256 × 256; four patients were also scanned with 512 × 512). Average wall thickness at each resolution was compared using a two-tailed paired Student's t -test. Results Simulations showed apparent wall thickening at low resolution, improving with higher resolutions. Low SNR and application of the Fermi filter made it difficult to identify ringing as the cause of this thickening. The simulation results were confirmed on seven patients, whose cyst walls proved to be artifactually thickened (P < 0.01). Conclusion Thickening of cyst walls on MRI can be artifactual. Upon encountering thick-walled cystic renal lesions, high-resolution images can be acquired to exclude apparent thickening. J. Magn. Reson. Imaging 2008;28103,110. © 2008 Wiley-Liss, Inc. [source]

X-ray spectromicroscopy in soil and environmental sciences

JOURNAL OF SYNCHROTRON RADIATION, Issue 2 2010
J. Thieme
X-ray microscopy is capable of imaging particles in the nanometer size range directly with sub-micrometer spatial resolution and can be combined with high spectral resolution for spectromicroscopy studies. Two types of microscopes are common in X-ray microscopy: the transmission X-ray microscope and the scanning transmission X-ray microscope; their set-ups are explained in this paper. While the former takes high-resolution images from an object with exposure times of seconds or faster, the latter is very well suited as an analytical instrument for spectromicroscopy. The morphology of clusters or particles from soil and sediment samples has been visualized using a transmission X-ray microscope. Images are shown from a cryo-tomography experiment based on X-ray microscopy images to obtain information about the three-dimensional structure of clusters of humic substances. The analysis of a stack of images taken with a scanning transmission X-ray microscope to combine morphology and chemistry within a soil sample is shown. X-ray fluorescence is a method ideally applicable to the study of elemental distributions and binding states of elements even on a trace level using X-ray energies above 1,keV. [source]

Direct Scanning Electron Microscopy Imaging of Ferroelectric Domains After Ion Milling

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010
Daniel Grüner
A method for directly observing the ferroelectric domain structure by scanning electron microscopy after argon ion milling has been established. Its advantages are exemplified by exposing the domain structure in three widely used ferroelectric ceramics, BaTiO3, (Na,K)NbO3, and Pb(Ti,Zr)O3. Stable high-resolution images revealing domains with widths <30 nm have been obtained. The domain contrast is caused by electron channeling and is strongly dependent on the sample tilt angle. Owing to a strain- and defect-free surface generated by gentle ion milling, pronounced orientation contrast is observed. [source]

Rangeland development of the Mu Us Sandy Land in semiarid China: an analysis using Landsat and NOAA remote sensing data

LAND DEGRADATION AND DEVELOPMENT, Issue 2 2003
M. C. Runnström
Abstract Degradation of the dry semiarid ecosystems in the Mu Us Sandy Land of north central China was explored using high-resolution satellite images from 1978, 1987 and 1996. This study monitored both changes in grassland biomass production and reclamation activities to detect the nature and scale of land degradation since major economic reforms were introduced in 1978. The position of the high-resolution images within the vegetation cycles was inspected from National Oceanographic and Atmospheric Administration (NOAA) NDVI images at 10-day repetition and seasonal precipitation patterns. A model was developed to categorize changes in the vegetation signal activity from 30,×,30,m pixels into vegetation cover development and land-use changes between 1987 and 1996. A general increase of biomass production was evident despite the rapid increase in numbers of grazing animals. This increase in biomass was confirmed by the NOAA time series, which also revealed annual variability related to the amount and pattern of the seasonal rains. Rangeland conversion to farmland was detected, and this process has increased the area of cultivation almost fivefold. The classified area of cultivation corresponds with reported statistical records, also showing that irrigation features in virtually 100 per cent of the sown area. Signs of declining biological production, indicating land degradation processes, are few. Biomass production has increased, with a gain in the economic output from both crop and animal production. The early start of active measures to halt desertification has increased vegetation cover and lowered wind erosion potential and grasslands seems to be managing the high levels of grazing pressure. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Wall ultrastructure of an Ediacaran acritarch from the Officer Basin, Australia

LETHAIA, Issue 2 2007
SEBASTIAN WILLMAN
Well-preserved organic-walled microfossils referred to as acritarchs occur abundantly in Ediacaran deposits in the Officer Basin in Australia. The assemblages are taxonomically diverse, change over short stratigraphical intervals and are largely facies independent across marine basins. Affinities of this informal group of fossils to modern biota are poorly recognized or unknown, with the exception of only a few taxa. Morphological studies by use of transmitted light microscopy, geochemical analyses and other lines of evidence, suggest that some Precambrian acritarchs are related to algae (including prasinophytes, chlorophytes, and perhaps also dinoflagellates). Limitations in magnification and resolution using transmitted light microscopy may be relevant when assessing relationships to modern taxa. Scanning electron microscopy reveals details of morphology, microstructure and wall surface microelements, whereas transmission electron microscopy provides high-resolution images of the cell wall ultrastructure. In the light of previous ultrastructural studies it can be concluded that the division of acritarchs into leiospheres (unornamented) and acanthomorphs (ornamented) is entirely artificial and has no phylogenetic meaning. Examination of Gyalosphaeridium pulchrum using transmission electron microscopy reveals a vesicle wall with four distinct layers. This multilayered wall ultrastructure is broadly shared by a range of morphologically diverse acritarchs as well as some extant microalgae. The chemically resistant biopolymers forming the comparatively thick cell, together with the overall morphology support the interpretation of the microfossil as being in the resting stage in the life cycle. The set of features, morphological and ultrastructural, suggests closer relationship to green algae than dinoflagellates. [source]

Natural linewidth chemical shift imaging (NL-CSI)

MAGNETIC RESONANCE IN MEDICINE, Issue 1 2006
Adil Bashir
Abstract The discrete Fourier transform (FT) is a conventional method for spatial reconstruction of chemical shifting imaging (CSI) data. Due to point spread function (PSF) effects, FT reconstruction leads to intervoxel signal leakage (Gibbs ringing). Spectral localization by imaging (SLIM) reconstruction was previously proposed to overcome this intervoxel signal contamination. However, the existence of magnetic field inhomogeneities creates an additional source of intervoxel signal leakage. It is demonstrated herein that even small field inhomogeneities substantially amplify intervoxel signal leakage in both FT and SLIM reconstruction approaches. A new CSI data acquisition strategy and reconstruction algorithm (natural linewidth (NL) CSI) is presented that eliminates effects of magnetic field inhomogeneity-induced intervoxel signal leakage and intravoxel phase dispersion on acquired data. The approach is based on acquired CSI data, high-resolution images, and magnetic field maps. The data are reconstructed based on the imaged object structure (as in the SLIM approach) and a reconstruction matrix that takes into account the inhomogeneous field distribution inside anatomically homogeneous compartments. Phantom and in vivo results show that the new method allows field inhomogeneity effects from the acquired MR signal to be removed so that the signal decay is determined only by the "natural" R2 relaxation rate constant (hence the term "natural linewidth" CSI). Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source]

Nuclear microscopy: A tool for imaging elemental distribution and percutaneous absorption in vivo

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 4 2007
Ana Veríssimo
Abstract Nuclear microscopy is a technique based on a focused beam of accelerated particles that has the ability of imaging the morphology of the tissue in vivo and of producing the correspondent elemental maps, whether in major, minor, or trace concentrations. These characteristics constitute a strong advantage in studying the morphology of human skin, its elemental distributions and the permeation mechanisms of chemical compounds. In this study, nuclear microscopy techniques such as scanning transmission ion microscopy and particle induced X-ray emission were applied simultaneously, to cryopreserved human skin samples with the purpose of obtaining high-resolution images of cells and tissue morphology. In addition, quantitative elemental profiling and mapping of phosphorus, calcium, chlorine, and potassium in skin cross-sections were obtained. This procedure accurately distinguishes the epidermal strata and dermis by overlapping in real time the elemental information with density images obtained from the transmitted beam. A validation procedure for elemental distributions in human skin based on differential density of epidermal strata and dermis was established. As demonstrated, this procedure can be used in future studies as a tool for the in vivo examination of trans-epidermal and -dermal delivery of products. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source]

The highly spotted photosphere of the young rapid rotator Speedy Mic

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2005
J. R. Barnes
ABSTRACT We present high-resolution images of the young rapidly rotating K3 dwarf Speedy Mic (BO Mic, HD 197890). The photospheric spot maps reveal a heavily and uniformly spotted surface from equatorial to high-latitude regions. Contrary to many images of similar objects, Speedy Mic does not possess a uniform filling at high latitudes, but exhibits structure in the polar regions showing greatest concentration in a particular longitude range. The asymmetric rotation profile of Speedy Mic indicates the presence of a companion or nearby star which shows radial velocity shifts over a time-scale of several years. Using a simple dynamical argument, we show that Speedy Mic is unlikely to be a binary system, and conclude that the feature must be the result of a chance alignment with a background binary. Complete phase coverage on two consecutive nights in addition to 60 per cent phase coverage after a three-night gap has enabled us to track the evolution of spots with time. By incorporating a solar-like differential rotation model into the image reconstruction process, we find that the equator laps the polar regions once every 191 ± 17 d. This finding is in close agreement with measurements for other late-type rapid rotators. [source]

Structure of Ti2P solved by three-dimensional electron diffraction data collected with the precession technique and high-resolution electron microscopy

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2003
Xiaodong Zou
The crystal structure of Ti2P has been analysed using electron diffraction and high-resolution electron-microscopy techniques. A new unit cell was found, the compound is hexagonal with a = 19.969,(1) and c = 3.4589,(1),Å. The structure was first solved in space group in projection using direct methods on electron diffraction data from the [001] zone axis. A three-dimensional solution was obtained using again direct methods but on a three-dimensional set of electron diffraction data recorded with the precession technique. Ti2P is a distorted Fe2P structure and, based on high-resolution images, it is possible to explain that the tripling of the unit cell is due to the ordering of P vacancies that reduces the symmetry to . [source]

A new batch of high-resolution images from the HiRISE camera on Mars Reconnaissance Orbiter

ASTRONOMY & GEOPHYSICS, Issue 5 2009
Article first published online: 18 SEP 200
No abstract is available for this article. [source]

Drusen in adaptive optics and SD-OCT

ACTA OPHTHALMOLOGICA, Issue 2009
N MASSAMBA
Purpose The study objective was to explore the microscopic structure of soft macular drusen and surrounding retinal areas using an adaptive optics (AO) camera and to compare the findings to those from standard clinical examinations. Methods 18 patients of age between 65 and 85 and presenting soft macular drusen were recruited after aninitial scanning laser ophthalmoscope (SLO) examination. We used an AO flood-illumination system to acquire high-resolution images of selected drusen areas. Every acquisition provided a series of 20 consecutive reflectance images, out of which 10 were numerically averaged to produce an enhanced final image. The resulting AO images were analyzed in comparison with conventional infrared and autofluorescence fundus images and spectral optical coherence tomography scans. Results The soft drusen were visible in AO images as generally round areas delimited by a peripheral low-reflectance line. Hyper reflective spots of size comprised between 2 and 15 ,m were observed in many drusen inner areas. These bright spots were sometimes isolated, sometimes grouped into tight aggregates of 2 to 40 components. Cone photoreceptors were visible in areas between drusen in most AO images. Conclusion The microscopic structures observed in the AO images of soft drusen presents analogies with their described anatomopathologic characteristics, which could not be identified using other in vivo imaging techniques. AO technology could help to refine the clinical classification of macular drusen and obtain deeper insight in their link with the development of different types of advanced AMD. Author Disclosure Information: N. Massamba, None; B. Lamory, Imagine Eyes, G. Soubrane, None. [source]