Search

We report that diffusion tensor imaging (DTI) and tractography (DTT) of the pyramidal tracts using multi-band (MB) EPI could be a useful tool with a 1.5T MRI. We compared images using single-band EPI (SB-EPI) and MB-EPI. MB-EPI could reduce the scanning time by about 40%. We demonstrated that it is comparable between image qualities of SB-EPI and MB-EPI using tract-specific analysis and dice coefficients. Therefore, MB-EPI can promote high-speed DTI and DTT in clinical applications.

Objectives The aim of this study was to evaluate the linearity, bias, intrascanner repeatability, and interscanner reproducibility of quantitative values derived from a multidynamic multiecho (MDME) sequence for rapid simultaneous relaxometry. Materials and methods The NIST/ISMRM (National Institute of Standards and Technology/International Society for Magnetic Resonance in Medicine) phantom, containing spheres with standardized T1 and T2 relaxation times and proton density (PD), and 10 healthy volunteers, were scanned 10 times on different days and 2 times during the same session, using the MDME sequence, on three 3 T scanners from different vendors. For healthy volunteers, brain volumetry and myelin estimation were performed based on the measured T1, T2, and PD. The measured phantom values were compared with reference values; volunteer values were compared with their averages across 3 scanners. Results The linearity of both phantom and volunteer measurements in T1, T2, and PD values was very strong (R = 0.973-1.000, 0.979-1.000, and 0.982-0.999, respectively) The highest intrascanner coefficients of variation (CVs) for T1, T2, and PD were 2.07%, 7.60%, and 12.86% for phantom data, and 1.33%, 0.89%, and 0.77% for volunteer data, respectively. The highest interscanner CVs of T1, T2, and PD were 10.86%, 15.27%, and 9.95% for phantom data, and 3.15%, 5.76%, and 3.21% for volunteer data, respectively. Variation of T1 and T2 tended to be larger at higher values outside the range of those typically observed in brain tissue. The highest intrascanner and interscanner CVs for brain tissue volumetry were 2.50% and 5.74%, respectively, for cerebrospinal fluid. Conclusions Quantitative values derived from the MDME sequence are overall robust for brain relaxometry and volumetry on 3 T scanners from different vendors. Caution is warranted when applying MDME sequence on anatomies with relaxometry values outside the range of those typically observed in brain tissue.

We evaluated not only total hydrogen content in duplex stainless steel and its weld metal but also hydrogen content in austenite by using internal friction measurement. The internal friction measurement was conducted over the temperature range from liquid nitrogen temperature to room temperature at a frequency of about 1.5 Hz. We investigated relationship between peak height and volume fraction of austenite and, also cleared influence of microstructure on internal friction peak.(1) SUS304 austenitic stainless steel was cathodically charged with hydrogen. After charging, internal friction peak due to hydrogen was found at 260 K. This hydrogen induced peak height increased with increase of hydrogen content. Consequently it is apparent that this peak is attributed to hydrogen in austenite.(2) The internal friction peak was observed at 260 K in SUS329J1 duplex stainless steel subjected to hydrogen charging. However this peak was not found for SUS444 ferritic stainless steel. Therefore it is clear that this peak is associated with hydrogen in austenite in SUS329J1 duplex stainless steel.(3) The volume fraction of austenite for SUS329J1 duplex stainless steel and SMAW 329J4L and SMAW 329J3L weld metal was approximately 40%. The base metal has the microstructure with austenite elongated toward rolling direction in rod shape in ferrite matrix, and the weld metal has the microstructure with widmanstatten austenite in ferrite matrix. Hydrogen content and peak height value was plotted on same straight line, therefore their relationship is independent of microstructure morphology. The relationship between peak height and hydrogen content in austenite in SUS329J1 base metal is applicable to that of weld metal. Internal friction peak height due to hydrogen is proportional to volume fraction of austenite in case hydrogen content in austenite is same.

A new electrostatic torsion mirror with a silicon/silicon structure has been developed for optical heads. It positions the beam spot accurately on an optical disk having a high track density. This torsion mirror is composed of a hexagonal mirror plate, twin supporting beams, and a pair of driving electrodes. The natural frequency of mirror rotation is defined by the moment of inertia of the mirror plate and the stiffness of the beams. The squeeze effect between the mirror plate and the electrodes generates the damping force. These mechanical parameters are designed to satisfy the specifications for a high-frequency positioning of the beam spot. Experimental frequency responses showed that a test model had a second modal mechanical frequency of over 50 kHz, and the characteristics were in good agreement with the designed values. This torsion mirror will make possible more accurate spot positioning than can be achieved using conventional electromagnetic actuators.

Hydrogen content in SUS329J1 duplex stainless steel SUS329J4L (DP3) weld metal and SUS329J3L (DP8) weld metal has been evaluated by using internal friction measurement at a frequency of about 1.5Hz and for the temperature range from liquid nitrogen temperature to 310K. The internal friction peak by hydrogen was recognized at 260K in steels fully or partially composed of austenite such as SUS304, duplex stainless steel and the weld metal, but no peak occurred in ferritic stainless steel such as SUS444. This fact means that the peak is originated from hydrogen in austenite. The linear relationship between the peak height and hydrogen content in austenite, which is independent of the microstructure, is applicable to evaluate hydrogen occlusion behavior in base metal as well as weld metal.

Serial magnetic resonance imaging (MRI) images acquired from multisite and multivendor MRI scanners are widely used in measuring longitudinal structural changes in the brain. Precise and accurate measurements are important in understanding the natural progression of neurodegenerative disorders such as Alzheimer's disease. However, geometric distortions in MRI images decrease the accuracy and precision of volumetric or morphometric measurements. To solve this problem, the authors suggest a commercially available phantom-based distortion correction method that accommodates the variation in geometric distortion within MRI images obtained with multivendor MRI scanners.The authors' method is based on image warping using a polynomial function. The method detects fiducial points within a phantom image using phantom analysis software developed by the Mayo Clinic and calculates warping functions for distortion correction. To quantify the effectiveness of the authors' method, the authors corrected phantom images obtained from multivendor MRI scanners and calculated the root-mean-square (RMS) of fiducial errors and the circularity ratio as evaluation values. The authors also compared the performance of the authors' method with that of a distortion correction method based on a spherical harmonics description of the generic gradient design parameters. Moreover, the authors evaluated whether this correction improves the test-retest reproducibility of voxel-based morphometry in human studies.A Wilcoxon signed-rank test with uncorrected and corrected images was performed. The root-mean-square errors and circularity ratios for all slices significantly improved (p0.0001) after the authors' distortion correction. Additionally, the authors' method was significantly better than a distortion correction method based on a description of spherical harmonics in improving the distortion of root-mean-square errors (p0.001 and 0.0337, respectively). Moreover, the authors' method reduced the RMS error arising from gradient nonlinearity more than gradwarp methods. In human studies, the coefficient of variation of voxel-based morphometry analysis of the whole brain improved significantly from 3.46% to 2.70% after distortion correction of the whole gray matter using the authors' method (Wilcoxon signed-rank test, p0.05).The authors proposed a phantom-based distortion correction method to improve reproducibility in longitudinal structural brain analysis using multivendor MRI. The authors evaluated the authors' method for phantom images in terms of two geometrical values and for human images in terms of test-retest reproducibility. The results showed that distortion was corrected significantly using the authors' method. In human studies, the reproducibility of voxel-based morphometry analysis for the whole gray matter significantly improved after distortion correction using the authors' method.

We numerically study the static structure and the mechanical response of two-dimensional granular piles. The piles consist of polydisperse disks with and without friction. Special attention is paid for the rigid grain limit by examining the systems with various disk elasticities. It is shown that the static pile structure of frictionless disks becomes isostatic in the rigid limit, while the isostaticity of frictional pile depends on the pile forming procedure, but in the case of the infinite friction is effective, the structure becomes very close to isostatic in the rigid limit. The mechanical response of the piles are studied by infinitesimally displacing one of the disks at the bottom. It is shown that the total amount of the displacement in the pile caused by the perturbation diverges in the case of frictionless pile as it becomes isostatic, while the response remains finite for the frictional pile. In the frictionless isostatic pile, the displacement response in each sample behaves rather complicated way, but its average shows wave like propagation., Comment: 23 pages, 10 figures

We study the static structure of piles made of polydisperse disks in the rigid limit with and without friction using molecular dynamic simulations for various elasticities of the disks and pile preparation procedures. The coordination numbers are calculated to examine the isostaticity of the pile structure. For the frictionless pile, it is demonstrated that the coordination number converges to 4 in the rigid limit, which implies that the structure of rigid disk pile is isostatic. On the other hand, for the frictional case with the infinite friction constant, the coordination number depends on the preparation procedure of the pile, but we find that the structure becomes very close to isostatic with the coordination number close to 3 in the rigid limit when the pile is formed through the process that tends to make a pile of random configuration., Comment: 3 pages, 3 figures, Submitted to J. Phys. Soc. Jpn

Purpose: Serial magnetic resonance imaging (MRI) images acquired from multisite and multivendor MRI scanners are widely used in measuring longitudinal structural changes in the brain. Precise and accurate measurements are important in understanding the natural progression of neurodegenerative disorders such as Alzheimer's disease. However, geometric distortions in MRI images decrease the accuracy and precision of volumetric or morphometric measurements. To solve this problem, the authors suggest a commercially available phantom-based distortion correction method that accommodates the variation in geometric distortion within MRI images obtained with multivendor MRI scanners. Methods: The authors' method is based on image warping using a polynomial function. The method detects fiducial points within a phantom image using phantom analysis software developed by the Mayo Clinic and calculates warping functions for distortion correction. To quantify the effectiveness of the authors' method, the authors corrected phantom images obtained from multivendor MRI scanners and calculated the root-mean-square (RMS) of fiducial errors and the circularity ratio as evaluation values. The authors also compared the performance of the authors' method with that of a distortion correction method based on a spherical harmonics description of the generic gradient design parameters. Moreover, the authors evaluated whether this correction improves the test–retest reproducibility of voxel-based morphometry in human studies. Results: A Wilcoxon signed-rank test with uncorrected and corrected images was performed. The root-mean-square errors and circularity ratios for all slices significantly improved (p < 0.0001) after the authors' distortion correction. Additionally, the authors' method was significantly better than a distortion correction method based on a description of spherical harmonics in improving the distortion of root-mean-square errors (p < 0.001 and 0.0337, respectively). Moreover, the authors' method reduced the RMS error arising from gradient nonlinearity more than gradwarp methods. In human studies, the coefficient of variation of voxel-based morphometry analysis of the whole brain improved significantly from 3.46% to 2.70% after distortion correction of the whole gray matter using the authors' method (Wilcoxon signed-rank test, p < 0.05). Conclusions: The authors proposed a phantom-based distortion correction method to improve reproducibility in longitudinal structural brain analysis using multivendor MRI. The authors evaluated the authors' method for phantom images in terms of two geometrical values and for human images in terms of test–retest reproducibility. The results showed that distortion was corrected significantly using the authors' method. In human studies, the reproducibility of voxel-based morphometry analysis for the whole gray matter significantly improved after distortion correction using the authors' method.

A new electrostatic torsion mirror with a silicon/silicon structure has been developed for optical disk drives. It positions the beam spot accurately on an optical disk 1),2). This mirror is mounted on a 3.8 x 4.5 mm chip and weighs approximately 25 mg. Thus, downsizing of optical heads can be realized by using this torsion mirror. This torsion mirror is composed of an elliptic mirror plate, twin supporting beams, and a pair of driving electrodes. The forms of these elements define the mechanical parameters of this torsion mirror: natural frequency and damping ratio. These mechanical parameters are designed to satisfy the specifications for a high-frequency positioning of the optical beam spot. Experimental frequency responses showed that a test model had a second modal mechanical frequency of over 50 kHz, and the characteristics were in good agreement with the designed values. This torsion mirror will make possible more accurate spot positioning than can be achieved using conventional electromagnetic actuators.