Разрешающая способность и линейное разрешение для оценки качества и проектирования аэрокосмических систем дистанционного зондирования Земли

Small-animal PET has become a rapidly growing approach to problems in human health, from addiction to cancer to drug development. However, the best presently available PET technology (/spl sim/2 mm resolution) still has significant limitations in spatial resolution and sensitivity which are particularly problematic for applications attempting to take advantage of powerful transgenic mouse models. Most currently proposed approaches to improving resolution face a number of technical obstacles which force trade-offs in performance. A novel design which circumvents many of these compromises is a miniaturized and modernized "Anger" or "gamma" camera, with a principle similar to well-known detectors for SPECT, in which a continuous scintillator crystal is used and position is determined from light-sharing among groups of photodetectors. Critical improvements over the traditional Anger design include a more appropriate scintillator for PET (LSO), a thinner crystal for higher spatial resolution, and large-area avalanche photodiode (APD) technology as the photodetector which allows layering of the detector to improve sensitivity, among other benefits. The feasibility of the approach has been studied in terms of spatial and energy resolution, sensitivity, and cost, with promising results. A prototype is complete and preliminary measurements have been performed.

After the Sendai Framework for Disaster Risk Reduction is adopted, a global database as a tool to monitor disaster loss and damage databases is required. Several disaster loss and damage databases are in use globally. This paper aims to explore how the existing databases vary in three aspects of threshold, spatial resolution, and data quality control, as well as the limitations of the existing databases. We review previous studies comparing the existing global databases and extract the differences and limitations. The threshold of EM-DAT is clear, but its threshold results in ignoring small-scale disasters that DesInventar captures. The differences in disaster threshold create different pictures of disaster losses and/or risks. Regarding spatial resolution, only DesInventar provides disaster impact data at a municipal level, while others provide information at a country level. The limitations of the existing global database are categorized into four aspects, as follows: lack of disaggregated data, limited spatial coverage and resolution, insufficiency of completeness and reliability of data, and insufficient information on indirect loss. The implication from our findings is that, in order to complement the limitations of the existing disaster loss databases to use for decision making on disaster risk reduction, the following are required: cross-checking of data across different databases; complementary disaster loss data; and collection of an exhaustive and firsthand dataset with a transparent and internationally consistent methodology by policy makers.

Damage development in fiber-reinforced polymer-matrix (FRP) composites under service loads is complex. The main reason for this is the micro- and meso-scale morphology interacting with the different microscopic damage mechanisms. Experimental approaches for investigation of microscopic damage mechanisms in FRP are, e.g., X-ray micro-computed tomography and acoustic emission monitoring. While X-ray micro-computed tomography achieves high local spatial resolution (down to sub-micrometer range), essential for identifying the different mechanisms, time-resolution and material volume that can be investigated are limited. Acoustic emission, on the other hand, is applicable to larger specimens and yields high time resolution (below microseconds) but limited spatial resolution only (a few millimeters at best). This contribution discusses which statistical information on microscopic damage in FRP is provided by acoustic emission based on quasi-static fracture mechanics test standards. Pattern recognition applied to acoustic emission signals allows distinguishing different damage mechanisms, e.g., for understanding delamination processes and correlating these with observed fracture surface features. For micromechanical modelling, acoustic emission will answer questions such as, e.g., “What are average microscopic damage sizes during delamination propagation and how much do they vary?” or “Do these damage sizes depend on fracture toughness, specimen load rates, or resulting delamination speed?” This information is relevant for selecting proper spatial and time resolutions for micro-mechanical modelling of damage accumulation in FRP composites.

In a recent paper, Leka at al. (Solar Phys. 260, 83, 2009)constructed a synthetic vector magnetogram representing a three-dimensional magnetic structure defined only within a fraction of an arcsec in height. They rebinned the magnetogram to simulate conditions of limited spatial resolution and then compared the results of various azimuth disambiguation methods on the resampled data. Methods relying on the physical calculation of potential and/or non-potential magnetic fields failed in nearly the same, extended parts of the field of view and Leka et al. (2009) attributed these failures to the limited spatial resolution. This study shows that the failure of these methods is not due to the limited spatial resolution but due to the narrowly defined test data. Such narrow magnetic structures are not realistic in the real Sun. Physics-based disambiguation methods, adapted for solar magnetic fields extending to infinity, are not designed to handle such data; hence, they could only fail this test. I demonstrate how an appropriate limited-resolution disambiguation test can be performed by constructing a synthetic vector magnetogram very similar to that of Leka et al. (2009) but representing a structure defined in the semi-infinite space above the solar photosphere. For this magnetogram I find that even a simple potential-field disambiguation method manages to resolve the ambiguity very successfully, regardless of limited spatial resolution. Therefore, despite the conclusions of Leka et al. (2009), a proper limited-spatial-resolution test of azimuth disambiguation methods is yet to be performed in order to identify the best ideas and algorithms.

Developments in positron emission tomography (PET) technology have resulted in systems with finer detector elements designed to further improve spatial resolution. However, there is a limit to what extent reducing detector element size will improve spatial resolution in PET. The spatial resolution of PET imaging is limited by several other factors, such as annihilation photon non-collinearity, positron range, off-axis detector penetration, detector Compton scatter, undersampling of the signal in the linear or angular directions for the image reconstruction process, and patient motion. The overall spatial resolution of the systems is a convolution of these components. Of these other factors that contribute to resolution broadening, perhaps the most uncertain, poorly understood, and, for certain isotopes, the most dominant effect is from positron range. To study this latter effect we have developed a Monte Carlo simulation code that models positron trajectories and calculates the distribution of the end point coordinates in water for the most common PET isotopes used: F, N, C and O. In this work we present some results from these positron trajectory studies and calculate what effect positron range has on the overall PET system spatial resolution, and how this influences the choice of PET system design parameters such as detector element size and system diameter. We found that the fundamental PET system spatial resolution limit set from detector size, photon non-collinearity and positron range alone varied from nearly 1 mm FWHM (2 mm FWTM) for a 10-20 cm diameter system typical for animal studies with F to roughly 4 mm FWHM (7 mm FWTM) for an 80 cm diameter system typical for human imaging using O.

Super resolution PLIF demonstrated in turbulent jet flows seeded with I2

X rays have been used for medical imaging since RÖNTGEN's fascinating discovery 125 years ago. The first radiographs of human hands were made public less than a month after his famous paper. The conventional X-ray sources integrated into the CT-machines of today’s hospitals still rely on the same physical principles. X-ray imaging has traditionally offered high spatial resolution and low contrast for soft tissues such as the brain. Magnetic resonance imaging is therefore the method of choice for brain imaging in a clinical setting, although for cellular resolution studies it suffers from limited spatial resolution. The gold standard in post mortem brain imaging is histology, which involves fixation, embedding, physical sectioning, staining, and optical microscopy. Currently, section thickness limits isotropic voxel sizes to 20 μm. Advanced X-ray sources including synchrotron radiation facilities offer complementary modalities such as phase-contrast imaging and spatially resolved small-angle X-ray scattering. We showed that X-ray phase contrast of the human cerebellum with micrometer resolution yields complementary three-dimensional images to magnetic resonance microscopy with even better contrast and spatial resolution. Grating interferometry enabled us to visualize individual Purkinje cells in the nonstained cerebellum. Taking advantage of well-established paraffin embedding, Purkinje cells were visualized within the human cerebellum even with conventional instrumentation. Hard X-ray nano-holotomography allowed for label-free, three-dimensional neuroimaging beyond the optical limit with a spatial resolution below 100 nm. Spatially resolved smallangle X-ray scattering permitted the localization of periodic nanostructures such as myelin sheaths on square-inch brain slices and included the orientational information on the axons. These developments have contributed to the establishment of virtual histology and extended the conventional histology to the third dimension. Further advances are required to image the entire human brain with an isotropic micrometer resolution and to suitably handle the petabyte datasets.

Scalp surface Laplacian potential monitoring system based on novel hydrogel active tri-polar concentric ring electrodes

Streak camera based diagnostics are vital to the inertial confinement fusion program at Sandia National Laboratories. Performance characteristics of various readout systems coupled to an EGG-AVO streak camera were analyzed and compared to scaling estimates. The purpose of the work was to determine the limits of the streak camera performance and the optimal fielding conditions for the Amador Valley Operations (AVO) streak camera systems. The authors measured streak camera limitations in spatial resolution and sensitivity. Streak camera limits on spatial resolution are greater than 18 lp/mm at 4% contrast. However, it will be difficult to make use of any resolution greater than this because of high spatial frequency variation in the photocathode sensitivity. They have measured a signal to noise of 3,000 with 0.3 mW/cm{sup 2} of 830 nm light at a 10 ns/mm sweep speed. They have compared lens coupling systems with and without micro-channel plate intensifiers and systems using film or charge coupled device (CCD) readout. There were no conditions where film was found to be an improvement over the CCD readout. Systems utilizing a CCD readout without an intensifier have comparable resolution, for these source sizes and at a nominal cost in signal to noise of 3, over those with an intensifier. Estimates of the signal-to-noise for different light coupling methods show how performance can be improved.

Although flat panel detectors are preferred for image-guided interventional endo-vascular treatments of stroke, they still have limitations in spatial resolution and excess additive noise, which restricts their low-dose performance. The Micro-Angiographic Fluoroscope (MAF), a CCD-based region-of-interest indirect X-ray imager recently developed, can meet the needs for high-resolution, high-sensitivity, real-time image guidance. Although the prototype MAF has better resolution (MTF) and detective quantum efficiency (DQE) than a standard flat panel detector, its performance could be improved by a change in the phosphor. The spatial resolution of such X-ray-to-light converting phosphors is limited by stochastic blurring and k-fluorescent X-ray reabsorption. Thinner phosphors generally improve resolution at the cost of lowering quantum detection efficiency (QDE) and increasing Swank noise, while thicker phosphors provide better absorption at the expense of spatial resolution. Two other Hamamatsu CsI(Tl) phosphors, 300- μm-thick HR, and 500- μm-thick HR, both without front reflective surface, were compared with the current 300- μm HL phosphor with front reflective surface. The phosphors were evaluated by comparing the MTF, NNPS, and DQE of the MAF detector used with each phosphor. All detector configurations showed linearity and quantum noise limited operation for a large range of exposures appropriate for both fluoroscopy and angiography. While the 300- μm HR type prototype demonstrated better resolution than the 500- μm HR type, the latter demonstrated better overall DQE and improved resolution compared to the original 300- μm HL, suggesting it would be the better choice for the MAF design.

Optical fiber sensor technology has progressed at a rapid pace over the last decade. Many different sensing techniques have been developed to monitor specific parameters. In particular, distributed Brillouin scattering-based sensor systems provide an excellent opportunity for structural health monitoring of civil structures by allowing measurements to be taken along the entire length of the fiber, rather than at discrete points, by using fiber itself as the sensing medium. One class of Brillouin-based sensors is based on the Brillouin loss technique, whereby two counter-propagating laser beams, a pulse and a CW, exchange energy through an induced acoustic field. This type of sensing has tremendous potential for structural health monitoring since the spatial resolution can be adjusted for different applications simply by altering the pulse duration, even after the fiber is installed. Although the spatial resolution can be improved using short pulse, the loss spectrum broadens as the pulse width decreases below the phonon lifetime t. Hence, it was generally believe that sub-meter resolutions were unachievable due to rapid linewidth increases when pulse width W < t = 10 ns provided a 1 m spatial resolution limitation. In this paper, we will report the development of distributed optical fiber sensor with centimeter spatial resolution. The sensing principle will be presented. We will also report the test results of pipeline buckling and corrosion fatigue monitoring and small damages/cracks of 1.5 cm in an optical ground wire (OPGW) cable with centimeter spatial resolution.

OA24 Magnetic resonance imaging of the trabecular bone microarchitecture at 3 Tesla - comparison with 1.5 Tesla

Pictorial review: Electron beam computed tomography and multislice spiral computed tomography for cardiac imaging

Diffusion Magnetic Resonance Imaging (dMRI) is a widely-utilized method for assessment of microstructural properties in the central nervous system i.e., the brain and spinal cord (SC). In the SC, almost all previous human studies utilized Diffusion Tensor Imaging (DTI), which cannot accurately model areas where white matter (WM) pathways cross or diverge. While High Angular Diffusion Resolution Imaging (HARDI) can overcome some of these limitations, longer acquisition times critically limit its applicability to clinical human studies. In addition, previous human HARDI studies have used limited spatial resolution, with typically a few slices and voxel size ~1 × 1 × 5 mm3 being acquired in tens of minutes. Thus, we have optimized a novel fast HARDI protocol that allows collecting dMRI data at high angular and spatial resolutions in clinically-feasible time. Our data was acquired, using a 3T Siemens Prisma scanner, in less than 9 min. It has a total of 75 diffusion-weighted volumes and high spatial resolution of 0.67 × 0.67 × 3 mm3 (after interpolation in Fourier space) covering the cervical segments C4–C6. Our preliminary results demonstrate applicability of our technique in healthy individuals with good correspondence between low fractional anisotropy (FA) gray matter areas from the dMRI scans, and the same regions delineated on T2-weighted MR images with spatial resolution of 0.35 × 0.35 × 2.5 mm3. Our data also allows the detection of crossing fibers that were previously shown in vivo only in animal studies.

Objective. Drug resistant focal epilepsy can be treated by resecting the epileptic focus requiring a precise focus localisation using stereoelectroencephalography (SEEG) probes. As commercial SEEG probes offer only a limited spatial resolution, probes of higher channel count and design freedom enabling the incorporation of macro and microelectrodes would help increasing spatial resolution and thus open new perspectives for investigating mechanisms underlying focal epilepsy and its treatment. This work describes a new fabrication process for SEEG probes with materials and dimensions similar to clinical probes enabling recording single neuron activity at high spatial resolution. Approach. Polyimide is used as a biocompatible flexible substrate into which platinum electrodes and leads are integrated with a minimal feature size of 5 μm. The polyimide foils are rolled into the cylindrical probe shape at a diameter of 0.8 mm. The resulting probe features match those of clinically approved devices. Tests in saline solution confirmed the probe stability and functionality. Probes were implanted into the brain of one monkey (Macaca mulatta), trained to perform different motor tasks. Suitable configurations including up to 128 electrode sites allow the recording of task-related neuronal signals. Main results. Probes with 32 and 64 electrode sites were implanted in the posterior parietal cortex. Local field potentials and multi-unit activity were recorded as early as one hour after implantation. Stable single-unit activity was achieved for up to 26 days after implantation of a 64-channel probe. All recorded signals showed modulation during task execution. Significance. With the novel probes it is possible to record stable biologically relevant data over a time span exceeding the usual time needed for epileptic focus localisation in human patients. This is the first time that single units are recorded along cylindrical polyimide probes chronically implanted 22 mm deep into the brain of a monkey, which suggests the potential usefulness of this probe for human applications.