A microstrip transmission line volume coil for human head MR imaging at 4T

A high-frequency RF volume coil based on the use of microstrip transmission line (MTL) has been developed for in vivo 1H MR applications on the human head at 4T. This coil is characterized by major advantages: (i) completely distributed coil circuit, (ii) high-quality factor (Q), (iii) simple coil structure, and (iv) better sensitivity and less signal-intensity variation in the MR image of the human head compared with an RF shielded birdcage coil of similar coil size. The proposed MTL volume coil does not require additional RF shielding for preventing Q degradation from radiation losses due to the unique MTL structure; thus, it provides a maximal useable space inside the volume coil when compared with most volume coils available at high fields with the same overall coil size. The intrinsic B(1) distribution of the MTL volume coil effectively compensates for the dielectric resonance effect at 4T and improves the signal homogeneity in human head MR images in the transaxial planes. The results of this study demonstrate that the MTL volume coil design provides an efficient and simple solution to RF volume coil design for human MR studies at high fields.     

Treatment-related central nervous system toxicity: MR imaging evaluation with CT and clinical correlation

Thirteen patients with abnormal brain MR scans attributable to treatment-induced injury were retrospectively reviewed. All patients were treated with radiation therapy and 62% received chemotherapy. Five patients were graded as having severe white matter (WM) changes, four had moderate WM changes, and four had mild WM changes. CT was generally equivalent to MR in evaluation of severe and moderate WM abnormalities, whereas MR was superior to CT in detection of mild WM abnormalities. In general, the severity of changes depicted by MR/CT correlated with the extent of neurologic dysfunction. The most severe changes were seen in those patients treated with combination irradiation and chemotherapy.     

基于倾斜阵的距离与方位联合估计*

针对阵列倾斜引起的阵不变量方法定位精度下降的问题,该文结合倾斜阵声源定位的三维模型提出一种基于倾斜阵的距离与方位联合估计算法。该算法通过联合自校正方位距离联合估计方法对阵列倾角在声源-接收平面的投影量进行估计和补偿,改善目标距离估计误差的同时,利用匹配出的阵列倾角投影量反向估计目标方位,获得对声源二维位置的估计。通过仿真验证了该算法能够在阵列倾角较小时实现目标方位与距离的联合估计。     

A finite difference beam propagation algorithm based on generalized transmission line equations

A wide angle beam propagation algorithm is presented, which is based on generalized transmission line (GTL) equations. Besides the discretization, no further approximation is introduced. In principle, a full vectorial analysis is possible, and anisotropic material can be taken into account. The algorithm has been verified for planar 2D-waveguide devices. The wide angle characteristic has been examined by determining the propagation of tilted Gaussian beams in homogeneous media. Further studies were performed for tilted waveguides and for taper structures. Results for the latter devices were compared with other methods showing a very good agreement.     

MRI assisted treatment planning for radiation therapy of the head and neck

Improved visualization of head and neck tumors has been demonstrated with the use of magnetic resonance imaging (MRI). Using standard plastic radiation therapy immobilization casts and an MR positive surface marker system developed in this institution, we have utilized MRI as an adjunct to the simulation of complex radiation treatments for tumors of the head and neck. This technique includes an indirect display of field margins and/or isodose curves over selected MR images. The lack of induced artifact from the immobilization cast, improved delineation of tumor extension from normal anatomy and the ability to image in arbitrary planes without changing patient positioning favor the use of MR over CT for radiation therapy planning in the head and neck, while ensuring reproducibility of the treatment plan at subsequent therapy sessions.     

Varied MR appearance of autism: Fifty-three pediatric patients having the full autistic syndrome

Fifty-three autism patients ranging in age from 2 to 22 yr with a mean age of 9 yr were evaluated by MR imaging over a 3-yr study period. Sagittal, axial, and coronal spin-echo and short TI inversion recovery scans were performed on a 0.5 Tesla (Picker Inc., Cleveland, OH) system. Results were compared to 32 control patients age range 1 to 17 yr, mean 8.5 yr. MR scans were evaluated by three neuroradiologists. Measurements of midsagittal vermian height and AP diameter were performed. Subjective estimates were made of ventricular size, amygdala size, fourth ventricular size, and vermian shape. Results were correlated with clinical presentation, course, and lab analyses by a pediatric neurologist. MR findings did not present a single pattern capable of predicting the presence or severity of autism. The constellation of MR findings in this group of 53 patients was highly variable, thus we advise caution in the interpretation of MR images in autistic patients. Autism is a heterogeneous disease entity containing different clinical subgroups, which do not manifest similar radiologic pictures.     

光电经纬仪异面交会测量及组网布站优化设计

提出了一种基于空间两异面光轴公垂线估计目标真实位置及组网布站站址几何的优化设计方法.通过光电经纬仪观测目标方位角、俯仰角和基线长度,计算两光轴在待估目标上的两交点,得到目标位置的公垂线.依据两台光电经纬仪的测角准确度作为权系数,估计目标真实位置.通过误差仿真及定位准确度分析,研究了组网测量中交会角、方位角、高低角和基线长度对定位准确度的影响.     

Diagnosis of peripheral pulmonary emboli by MR imaging: an experimental study in dogs

The peripheral pulmonary arteries of 5 dogs were embolized with boiled autologous clots via the external right jugular vein. Angiography determined the location and approximate size of the emboli in the peripheral pulmonary arteries. With spin echo techniques, transverse axial magnetic resonance (MR) images (0.3 T, 12.77 MHz) were obtained in each animal from apex to thorax base, on a permanent magnet scanner. The sensitivity of MR imaging was assessed to detect these clots and to determine their size and location. In 2 dogs, scans were also obtained before embolization in order to exclude possible artifactual areas of increased signal. Fourteen out of 19 emboli were identified on the MR scans as areas of increased signal. Their diameter measured a minimum of 2.7 mm matching the filling defects seen on the angiograms. There were three false positive emboli on MR probably related to slow blood flow in the inferior vena cava. There were 9 false negative emboli on MR. The increased MR signal seen in dogs with pulmonary emboli results from the embolus itself and from slow blood flow distal to the obstructive embolus.     

Liquid crystal alignment in cylindrical microcapillaries

A variety of alignment configurations of liquid crystals (LCs) inside the glassy cylindrical capillaries is realized by using alignment materials providing different anchoring. The radial configuration with central disclination line is obtained for homeotropic boundary conditions. In turn, the axial, transversal and tilted alignment structures are realized by using materials for planar anchoring. The uniformity and controlling of the latter structures were provided by photoalignment method. This approach can be further used to control LC alignment in the photonic crystal fibers recognized as advanced elements for different optical devices.     

Magnetization reversal of single domain permalloy nanowires

Magnetization reversal process and magnetoresistance (MR) hysteresis of single domain permalloy nanowires are numerically investigated by using OOMMF. It is shown that the abrupt jumps in the magnetoresistance are due to the domain formation and domain wall propagation so that a magnetic domain suddenly switches from one state into another. A nonmonotonic angular dependence of the jump (switching) field is found. Coherent rotation mode is responsible for the smooth variation of MR curves. The nucleation pattern of newly born domains depends on the tilted angle of external field.     

Quantification of complex flow using MR phase imaging--a study of parameters influencing the phase/velocity relation.

In this study, we describe how motion-induced phase angle is affected by different flow models and imaging parameters when using the MR flow phase mapping technique. In a phantom with straight as well as constricted tubes, simulating healthy and stenotic vessels, nonpulsatile flow in the velocity range 0-1 m/sec was maintained. The phase/velocity relation was studied for various degrees of complex flow caused by the constriction, and regions with a breakdown in linearity were determined. Further studies in these regions were made regarding the influence of pulse sequence parameters on the phase/velocity relation. The results showed that in poststenotic areas characterized by so-called separated flow, the phase/velocity relation became nonlinear due to dephasing effects. In regions with fully developed turbulent flow in straight tubes, however, no breakdown in linearity was observed. Parameters seen to have a substantial influence on the phase/velocity relation were first- and second-order velocity encoding and voxel size. Finally, a pilot in vivo demonstration of complex flow was done using a sequence designed to be robust with respect to linearity of the phase/velocity relation. The results indicate that the MR phase mapping technique can be used to measure flow quantitatively in regions with complex flow. This opens possibilities for future clinical use of the technique in the study of areas of complex flow such as valvular heart disease.     

Magnetic resonance imaging of the uterus in vivo and in vitro at an ultra low magnetic field (0.02 T): Assessment of its normal structure and of leiomyomas

The purpose of this investigation was to analyze the normal anatomy and leiomyomas of the uterus with an ultra low field (0.02 T) magnetic resonance imaging (MRI) device. MR imaging was performed on 18 uteri, 11 of which were imaged both preoperatively (in vivo) and as an operative specimen (in vitro), 6 only as an operative specimen, and 1 only preoperatively. All uteri were examined histologically after imaging. The junctional zone was much better delineated in vivo than in vitro, indicating that its appearance on MR is partly due to blood flow. No structures contributing to its visibility in vitro could be demonstrated histologically. Twenty leiomyomas (size range 7–79 mm) in 12 uteri were found with MRI. They were slightly better discerned in vivo than in vitro. The leiomyomas, having no degenerative changes, had a signal intensity which was the same or lower than that of the myometrium. On images obtained in vitro the signal intensity of these leiomyomas relative to that of myometrium correlated directly with their muscular content (R = 0.74, p = .002). The authors conclude that the junctional zone is a sum of physiological and structural factors, the latter being responsible for its in vitro delineation. MR imaging of the uterus in vitro did not give more information than MR imaging in vivo. All leiomyomas larger than 10 mm could be detected, indicating that MR imaging at 0.02 T is an accurate method for the imaging of the uterine leiomyomas.     

The nature of the plateau on the time-of-flight curves in molecularly doped polymers

The transient current curves for a polar molecularly doped polymer were compared for the nearsurface and bulk generation of charge carriers. The horizontal plateau on the first curve was expected to transform into a tilted straight line under the quasiequilibrium transport conditions, but it did not. Instead, for bulk generation, the curve was a hyperbola, on which the slope decreased almost sevenfold during the existence of the plateau. This behavior points to nonequilibrium charge carrier transport. The appearance of a plateau in our case is explained by the effect of the defective surface layer, as indicated in our previous communications.     

Looking back at perpendicular magnetic recording R&D in NEC

This paper reports perpendicular magnetic recording (PMR) circumstances and the results based on the reference published by NEC. The PMR flexible disks using Co-Cr-Ta films were investigated. Pass wear durability of Co-Cr-Ta film strongly depends on the base film surface roughness and Young's modulus values of Co-Cr-Ta films. Pass wear durability, more than 10 million passes, was confirmed under a high temperature (60 °C) and a high humidity (80% RH) condition, as well as a low temperature (5 °C) condition. The read/write characteristics for double-layered PMR media were examined by using a combination of a single-pole-type (SPT) write head and a magnetoresistive (MR) read head, and a conventional merged ring type inductive (ID) write head/MR read head. By differential equalization of the reproduced voltage, the bit error rate less than 10⁻⁶ at 3 Gb/in.² was obtained for the SPT/MR head combination. The antenna effect for PMR realization was analyzed using the merged ring type ID/MR head. In order to increase the magnetic circuit resistance from the ID head pole to the soft underlayer, we developed the sendust (FeAlSi) soft underlayer with low magnetic permeability. We confirmed that the recorded signal has better stability under the ID/MR head-loaded condition than the SPT head-loaded condition. These results show that there are the head and media solutions to realize PMR. We had confidence that we could use the basic structure of the commercial ID/MR head for the PMR head.     

Existence of contralateral abnormalities revealed by texture analysis in unilateral intractable hippocampal epilepsy

We selected 23 patients with unilateral temporal lobe epilepsy characterized by ipsilateral hippocampal sclerosis and an apparently normal contralateral hippocampus on MR imaging. Images were acquired on a 0.28 T MR scanner using a conventional Carr-Purcell Meiboom Gill sequence in all patients and in 9 healthy subjects. Texture analysis was applied to axial MR images of the first and tenth echoes. Texture analysis detects macroscopic lesions and microscopic abnormalities that can not be observed visually. The presence of texture differences in the between normal (controls) and sclerotic hippocampi was ascertained by statistical discriminant analysis. The apparently normal contralateral hippocampi can be classified into three categories in terms of texture: 4 apparently healthy, 8 similar to sclerosis, and 11 different from either healthy or sclerosis. These findings are related to a certain degree of hippocampal alteration, which further investigation might help better characterize.     

基于消失点检测算法的束靶红外图像畸变校正

传统的霍夫变换、Cannylines直线检测算法、霍夫概率变换方法在图像上的直线检测效果不佳,存在检测线段不连续不正确的问题,因而,利用Sobel滤波对红外图像横轴和纵轴两个方向分别进行锐化,通过线段检测(LSD)算法实现线段特征检测,进而经线段聚类拟合获得图像中完整的直线,通过对直线交点计算获得消失点,最后依据透视关系计算得到校正图像。实验结果表明,该方法可以实现对中性束红外图像的自动有效校正。     

Validation of an adapted MRI pulse sequence for quantification of fatty infiltration in muscle

Purpose

The long-term goal of our research is to develop a patient-specific biomechanical model of the supraspinatus muscle and tendon for analyzing the effects of fatty infiltration and pennation angle changes. One input of the model will be the amount and distribution of fat within the muscle. Therefore, the objective of this project was to adapt and validate a novel magnetic resonance imaging pulse sequence for quantifying the extent of fatty infiltration for the supraspinatus muscle.

Methods

Samples of incremental combinations of muscle and fat from a cow were prepared and scanned with our quantitative MR technique. The MR results were compared to actual fat measurements taken using a Soxtec extraction analyzer.

Results

The MR fat quantification results closely match those values determined by Soxtec analysis (R²=.98, root mean square deviation=4.9).

Conclusions

Our MR fat quantification protocol can be used to accurately quantify fatty infiltration in skeletal muscle. This ability to evaluate skeletal muscle tissue noninvasively will improve the efficacy of evaluation of fatty degeneration in assessing tissue quality preoperatively. This can be important in surgical planning of any musculoskeletal repairs, particularly rotator cuff tears.     

Lesions involving the fourth ventricle evaluated by CT and MR: A comparative study

A retrospective review of 21 patients with lesions involving the fourth ventricle was performed to determine the relative capability of computed tomography (CT) and MR for detection, characterization, localization, and diagnosis. Lesions involving the fourth ventricle included ependymoma (three), subependymoma (one), glioma (five), cysticercosis cyst (three), medulloblastoma (three), bleeding into the fourth ventricle (two), epidermoid cyst (two), “trapped” fourth ventricle (one), and lymphomatoid granuloma (one). Posterior fossa lesions that displaced but did not invade the fourth ventricle were excluded. Lesion detectability on CT was judged excellent in ten, good in 8, and fair or poor in 3. Detectability of lesions by MR was judged excellent in 16 and good in 5. There was complete agreement on lesion extension between CT and MR in 6 lesions, mild disagreement in 4, and moderate to significant disagreement in 11. Preoperatively, MR alone correctly diagnosed seven lesions, and CT alone correctly diagnosed three lesions. A review of the combined scans (after the correct diagnosis was given) showed both CT and MR were equal in the diagnosis of 14 lesions, MR better than CT in six, and CT better in one. There was complete agreement on both CT and MR with the surgical/pathologic findings in three lesions. Both studies proved disappointing in their ability to make the correct histologic diagnosis, probably because CT and MR characteristics may not always offer a definitive diagnosis and because of the wide spectrum of pathologic processes that may involve the fourth ventricle.     

Optical and electronic properties of anisotropic parabolic quantum disks in the presence of tilted magnetic fields

In the present work, the electronic and optical properties of anisotropic parabolic quantum disks are studied in the presence of an applied magnetic field. For this goal, we first obtain the electron energy levels of an anisotropic parabolic quantum disk under axial, tilted, and in-plane magnetic fields. According to the results obtained for the energy levels reveal that there is no degeneracy at zero magnetic field due to symmetry breaking. With increasing the anisotropy, the energy level spacing increases. At a constant anisotropy, the energy levels splitting decreases with increasing tilt angle of magnetic field. The total refractive index changes decrease when the tilt angle of magnetic field and the anisotropy increase. Also, the total absorption coefficients increase as the tilt angle of magnetic field and anisotropy increase.     

Optimizing T2-weighted magnetic resonance sequences for surface coil microimaging of the eye with regard to lid, eyeball and head moving artifacts

PURPOSE: To acquire high-resolution magnetic resonance (MR) images, we developed a new blinking artifact reduced pulse (BARP) sequence with a surface coil specialized for microscopic imaging (47 mm in diameter). MATERIALS AND METHODS: To reduce eye movement, we ascertained that the subjects' eyes were kept open and fixated to the target in the 1.5-T MR gantry. To reduce motion artifacts from blinking, we inserted rest periods for blinking (1.5 s within every 5 s) during MR scanning (T2-weighted fast spin echo; repetition time, 5 s; echo time, 100 ms; echo train, 11; matrix, 256 x 128; field of view, 5 cm; 1-mm thickness x 30 slices). Three scans (100 s x 3) were performed for each normal subject, and they were added together after automatic adjustment for location to reduce quality loss caused by head motion. RESULTS: T2-weighted MR images were acquired with a high resolution and a high signal-to-noise ratio. Motion artifacts were reduced with BARP, as compared with those with random blinking. Intraocular structures such as the iris and ciliary muscles were clearly visualized. Because the whole eye can be covered with a 1-mm thickness by this method, three-dimensional maps can easily be generated from the obtained images. CONCLUSION: The application of BARP with a surface coil of the human eye might become a useful and widely adopted procedure for MR microimaging.