X-UV lamellar multilayer amplitude gratings

The concept of X-UV Lamellar Multilayer Amplitude Grating (LMAG) is introduced and a method of fabrication is given. Dynamical and kinematic theories of the diffraction by a LMAG are presented. Different applications of the LMAGs are considered. The first one is the achievement of a narrow bandpass multilayer monochromator for the X-UV domain. The second one is the reduction of specular background in the reflectivity curve of a multilayer structure. The third one is the polychromator system which allows one to split spatially and to perform a spectral sampling of a polychromatic beam. Finally we studied experimentally the behavior of an LMAG in conical mounting.     

Electron beam dosimetry for a multilayer absorber

Depth dose distributions were measured in a multilayer absorber of Ti-air-cellulose triacetate (CTA)-backing material (Pb, Sn, Fe, Al and CTA) irradiated with 300 and 800-keV electrons. The results are compared with the calculated value using computational code for multilayer absorbers (EDMULT) developed by Tabata et al. (1989, 1990). The absorbed dose in CTA exceeds the calculated value near the surface, while it is smaller than the calculated dose as the penetration depth becomes closer to the range of incident electrons. The measurements and computations show better agreement for the high-energy (800-keV) electrons than for the 300-keV electrons, probably because of the greater obiqueness of incidence at lower energies, which is not taken into account by the computation code.     

Characterization of pinhole transmission gratings

Gold pinhole transmission gratings fabricated by Heidenhain GmbH primarily for the purpose of studying the radiation of intense soft x-ray sources have been tested with the synchrotron radiation of BESSY. Typical results for the spectral dependence of the grating efficiency into the various diffraction orders are presented in a wavelength region ranging from 4 to 20 nm. Also the influence of grating irregularities has been studied. With appropriate grating parameters quite good agreement between the experimental results and theoretical Calculations is Obtained.     

Two-period multilayer mirrors for the soft x-ray region

The problem of multilayer mirrors which are capable of reflecting x-ray radiation at two given wavelengths is discussed. Three kinds of two-period multilayers are considered and a comparison of their properties in the soft x-ray region is presented. The scheme of a soft x-ray scanning microscope based on a Schwarzschild objective with a two-period multilayer coating is proposed for chemical microanalysis of biological samples.     

Assessment of scatter compensation strategies for (67)Ga SPECT using numerical observers and human LROC studies.

67Ga citrate is an oncologic SPECT imaging agent often used to diagnose or stage patients with non-Hodgkin's lymphoma. As (67)Ga decay involves the emission of multiple-energy gamma-rays, significant photon downscatter will be present within each photopeak energy window. We have previously shown that the inclusion of these scattered photons significantly degrades lesion detectability. The goal of this study was to investigate the extent to which this decrease in detectability can be reversed by applying scatter compensation strategies. METHODS: We have compared 5 different scatter compensation methods to the case of no scatter compensation in iterative SPECT image reconstruction. The strategies consisted of (a). perfect scatter rejection, (b). ideal scatter compensation, (c). triple-energy window (TEW) scatter estimation, (d). effective scatter source estimation (ESSE), and (e). postreconstruction scatter subtraction. Reconstruction parameters used for each method were first optimized using a channelized Hotelling numerical observer. Strategies were then ranked in terms of lesion detectability using a human observer localization receiver operating characteristic (LROC) study. An additional comparison was made comparing the human LROC rankings with a recently developed channelized nonprewhitening (CNPW) LROC numerical observer. RESULTS: Using the area-under-the-LROC-curve (A(LROC)) as the assessment criterion, our results indicate that the TEW and ESSE scatter compensation methods are able to significantly improve lesion detectability over no compensation (A(LROC) = 0.75 and 0.73 vs. 0.67, respectively). However, these compensations failed to achieve the same detectability as perfect scatter rejection (A(LROC) = 0.84). Both ideal scatter compensation and postreconstruction scatter subtraction resulted in numerical increases in detection accuracy that were not statistically significant from no scatter compensation. Good agreement is seen between the CNPW observer and human LROC studies (Spearman rank order coefficient, r(s) = 0.74), thus indicating that the LROC observer may be a good predictor of human observer performance in (67)Ga SPECT. CONCLUSION: Scatter compensation in (67)Ga SPECT imaging using techniques such as TEW or ESSE is able to improve lesion detectability compared with no scatter compensation. A recently developed numerical observer model appears to be a good predictor of human observer performance and may be used to perform imaging optimizations, thereby reducing the need for human LROC studies.     

Asymmetric spin-echo imaging of magnetically inhomogeneous systems: Theory,experiment, and numerical studies

The ability of the asymmetric spin-echo (ASE) pulse sequence to provide different degrees of spin-echo (SE)-type and gradient-echo (GE)-type contrast when imaging media containing magnetic inhomogeneities is investigated. The dependence of the ASE signal on the size of magnetic field perturbers is examined using theory, computer simulations, and experiment. A theoretical prediction of the ASE signal is obtained using the Anderson-Weiss mean field theory, the results of which are qualitatively supported by computer simulations and experimental studies. It is shown that the ASE sequence can be used to tune the range of perturber sizes that provide the largest contributions to susceptibility contrast effects.     

Three-tesla diffusion tensor imaging of Meyer's loop by tractography, color-coded fractional anisotropy maps, and eigenvectors

The aim of this study was to evaluate Meyer's loop by 3-T MRI with fiber tractography, color-coded fractional anisotropy maps, and eigenvector maps. The anteroposterior distance from the anterior bundle of the Meyer's loop to temporal pole ranged from 26.3 to 34 mm, overlapping with the previously published anatomical dissection studies. Diffusion tensor imaging with fiber tractography, color-coded FA maps, and color maps of the principal eigenvector at 3 T appear to be promising techniques for the virtual dissection of Meyer's loop.     

Design of a normal incidence multilayer imaging x-ray microscope

Normal incidence multilayer Cassegrain x-ray telescopes were flown on the Stanford/MSFC Rocket X-Ray Spectroheliograph. These instruments produced high spatial resolution images of the Sun and conclusively demonstrated that doubly reflecting multilayer x-ray optical systems are feasible. The images indicated that aplanatic imaging soft x-ray /EUV microscopes should be achievable using multilayer optics technology. We have designed a doubly reflecting normal incidence multilayer imaging x-ray microscope based on the Schwarzschild configuration. The Schwarzschild microscope utilizes two spherical mirrors with concentric radii of curvature which are chosen such that the third-order spherical aberration and coma are minimized. We discuss the design of the microscope and the results of the optical system ray trace analysis which indicates that diffraction-limited performance with 600 ? spatial resolution should be obtainable over a 1 mm field of view at a wavelength of 100 ?. Fabrication of several imaging soft x-ray microscopes based upon these designs, for use in conjunction with x-ray telescopes and laser fusion research, is now in progress. High resolution aplanatic imaging x-ray microscopes using normal incidence multilayer x-ray mirrors should have many important applications in advanced x-ray astronomical instrumentation, x-ray lithography, biological, biomedical, metallurgical, and laser fusion research.     

A numerical model for risk of ball-impact injury to baseball pitchers

INTRODUCTION: Metal baseball bats produce higher ball exit velocity (BEV) than wood bats, increasing the risk of impact injuries to infield players. In this paper, maximum BEV from a wood and a metal bat were determined using the finite element method. METHODS: Three-dimensional (3-D) bat kinematics at the instant of impact were determined from high-speed videography (N = 17 high-performance batters). A linear viscoelastic constitutive model was developed for stiffer and softer types of baseballs. The risk of impact injury was determined using available movement time data for adult pitchers; the data indicate that 0.400 s is required to evade a batted ball. RESULTS: The highest BEV (61.5 m.s(-1)) was obtained from the metal bat and the stiffer ball model, equating to 0.282 s of available movement time. For five impacts along the long axis of each bat, the "best case scenario" resulted from the wood bat and the softer ball (46.0 m.s(-1), 0.377 s). CONCLUSIONS: The performance difference between the bats was attributed to the preimpact linear velocity of the bat impact point and to differences in orientation on the horizontal plane. Reducing the swing moment of the baseball bat, and the shear and relaxation modulii of the baseball, increased the available movement time.     

Development of a human body model for numerical calculation of electrical fields.

Knowledge of the distribution of electrical fields in the human body is of importance for scientists, engineers and physicians. This paper shows one way to achieve this knowledge by numerical calculation based on macroscopic models of the human body. An anatomical model is created by preprocessing, segmentation and classification of the digital images within the Visible Man data set. Conductivity models are derived, which describe the distribution of electrical conductivity in the human body. A conductivity model is applied to solve an exemplary forward problem in electrophysiology, which consist of the calculation of the electrical field distribution arising from cardiac sources. The cardiac sources are obtained by a model of the excitation process within the heart. The calculation of electrical fields is carried out numerically by employing the finite difference method.     

Application of panoramic radiography with a multilayer imaging program for detecting proximal caries: a preliminary clinical study

Objective:The aim of this study is to introduce a novel program of panoramic radiography that shows 41 multilayer images from the buccal to lingual aspects in a region of interest, and to evaluate the effectiveness of this program for detecting proximal caries.Methods:In total, 480 premolars and molars on 30 panoramic radiographs taken with the multilayer imaging program were included in this study. The presence or absence of caries in 960 proximal surfaces was assessed by three experienced oral and maxillofacial radiologists as a consensus-based gold-standard. Two general dentists evaluated and scored proximal caries on 980 surfaces on panoramic radiographs with and without the multilayer imaging program. The two general dentists’ scores were compared with the gold-standard, and were analyzed for sensitivity, specificity, positive predictive value, negative predictive value, and area under the receiver operating characteristic (ROC) curve with and without using the program. The area under the ROC curve was analyzed using STATA/SE 13.1.Results:When the multilayer imaging program was used for panoramic radiography, the inter- and intraobserver agreement of the two general dentists improved. All values, including the area under the ROC curve, were higher when the multilayer imaging program was used than when it was not used. The area under the ROC curve showed a statistically significant improvement only in Observer 1, whose diagnostic ability was poorer than that of Observer 2.Conclusions:oThis multilayer imaging program might help the inexperienced dentist to improve the diagnostic accuracy of proximal caries. If further studies would be performed in various clinical application, it could be useful when intraoral radiography taking is difficult for reasons such as mouth-opening limitations and the gag reflex of the patients.     

Systems for remote interpretation of emergency studies

Telenuclear medicine facilitates a timely expert interpretation of emergency nuclear medicine studies. Current, high-speed Internet connection allows nuclear medicine physicians to be on-call from their homes. Software to support telenuclear medicine is becoming more widely available, although the design of some departments makes implementation difficult. Quality control of the remote monitor requires special attention to ensure correct interpretation. Fortunately, monitor quality control can be performed quickly using relatively simple procedures. Thus, expert interpretation of emergency nuclear medicine studies is practical.