Post-processing water-fat imaging technique for fat suppression in a low-field MR imaging system,evaluation in patients with rheumatoid arthritis

Purpose: To evaluate the feasibility of the phase difference-based post-processing water-fat imaging method for fat suppression at low-field in imaging of arthritic joints.Materials and methods: Thirty joints (wrist, 10; elbow, 10; knee, 10) in 30 patients with rheumatoid arthritis were imaged using a 0.23TMRI unit. Contrast-enhanced Tl-weighted (Tlw) three-dimensional (3D) gradient-echo (GRE) images with and without fat suppression along with short inversion time inversion-recovery (STIR) images were evaluated by two radiologists. Contrast-enhanced Tlw 3D GRE images and corresponding post-processed fat-suppressed images were scored for conspicuity and delineation of enhancing synovial hypertrophy. The uniformity of fat suppression was evaluated between Tlw 3D GRE fat-suppressed images and STIR images, and general image quality was estimated for all of the three techniques by consensus. For a quantitative analysis, the enhancing synovial hypertrophy-to-fat contrast-to-noise (CNR) values for the T1W 3D GRE images with and without fat suppression were measured. For comparison, synovial bright signal-to-fat CNR values for the STIR images were measured.Results: The post-processing water-fat imaging technique for fat suppression was successfully applied in all examinations. Conspicuity and delineation of enhancing tissue were superior in fat-suppressed Tlw 3D GRE images compared to non-fat-suppressed images (P < 0.0001). As expected, the enhancing synovial hypertrophy tissue-to-fat CNRs were significantly higher in fat-suppressed Tlw 3D GRE images compared to non-fat-suppressed images (P < 0.0001). General image quality was assessed to be best in non-fat-suppressed images, and the difference was significant compared to fat-suppressed images (P < 0.05) and STIR images (P < 0.05).Conclusion: The phase difference-based post-processing water-fat imaging technique for fat suppression can be successfully used at low-field, and it provides high-quality fat suppression images in imaging of arthritic joints.     

3D imaging of lightning channel and leader progression velocity

Three‐dimensional imaging of lightning channels by means of UHF interferometers is performed. To realize this, a field campaign was conducted with two observation sites in Darwin, Australia. The distance between the two sites is about 14 km, and the triangulation scheme is applied to estimate locations of UHF radiation sources. Since the UHF radiation is more likely during the leader progression than in the return stroke phase, imaging of lightning channels is obtained mainly for downward leaders. Velocities of downward leaders are estimated and statistics are presented for first and subsequent strokes. The result is consistent with those of former investigations obtained by optical observations. The statistics for the velocity of leader propagation inside thunderclouds are presented herein. Using optical measurement, velocity estimation of leader progressions inside thunderclouds is impossible, and the presented results are concluded to be the first results of their kind. © 2001 Scripta Technica, Electr Eng Jpn, 137(3): 22–28, 2001     

基于相关型图像传感器的3D AAMs人脸特征自动定位

在基于相关型图像传感器（corre lation image sensor,CIS）三维人脸成像的基础上,利用由CIS得到的深度信息和与之对应的亮度信息,提出一种建立三维人脸模型的方法,将二维AAMs扩展为三维AAMs,融合人脸的形状,纹理和深度信息来构建三维人脸模型。同时,采用三维曲率对人脸特征进行初步定位来解决AAMs初始姿态参数选择问题。人脸面部定位实验证明此方法在不同人脸姿态,表情和光照条件下定位效果要优于传统的2DAAMs。     

基于压缩感知的稀疏阵列近景微波三维成像

近景微波成像技术在隐藏武器检测、生物医学成像、无损检测等领域具有广阔的应用前景.将压缩感知理论应用于近景微波成像系统,提出了基于稀疏阵列天线的三维成像几何及相应的回波模型,该几何通过高度向的稀疏阵列电子扫描、方位向的机械扫描及距离向发射宽带信号来实现三维分辨;文中将压缩感知理论应用于稀疏阵列三维成像,提出了基于压缩感知...     

基于三维人脸成像系统的复数域人脸识别方法

三维人脸识别是模式识别和人工智能领域的研究热点。提出了一种利用人脸图像的二维灰度信息和三维深度信息进行人脸识别的算法。首先利用相关型图像传感器构成三维实时人脸成像系统,并将获得的三维人脸物理数据用复数形式表达。再将特征脸（Eigenface）方法和Fisherface方法拓展到复数域,提出了复数域特征脸方法和复数域Fisherface方法。改进的复数域人脸识别方法在三维实时成像系统的人脸数据库中进行的人脸识别实验表明,复数域的三维人脸识别方法明显优于传统的人脸识别方法。     

3D diffusion tensor imaging with 2D navigated turbo spin echo

A Cartesian two-dimensional navigator with variable orientation for online motion correction is introduced. It corrects for all possible zeroth- and first-order phase errors due to rigid-body motion of a subject during the diffusion-weighting preparation. The technique is developed for the application of three-dimensional (3D) imaging sequences, which offer the opportunity of high-resolution diffusion-weighted imaging, or diffusion tensor imaging (DTI) with isotropic voxel resolution. The navigator was applied to a displaced 3D turbo spin-echo sequence with an ECG-gated diffusion preparation to avoid phase errors due to gross brain pulsation. Online and offline corrected in vivo images acquired with this sequence are compared to investigate the advantages of online correction. Also eigenvector maps of the diffusion tensor are presented with an isotropic resolution of 1 mm³, which indicate that this new navigator technique is a promising approach for high-resolution DTI.     

Contrast-enhanced pulmonary MR imaging

The present paper reports our own experience with MR perfusion imaging and gives an overview of contrast-enhanced pulmonary MR perfusion imaging, MR angiography, and ventilation MR imaging using hyperpolarized gases or oxygen as contrast agent. These methods are discussed within the context of their possible role in the diagnosis of pulmonary diseases, particularly embolism and emphysema.     

Left ventricular quantification with breath-hold MR imaging: comparison with echocardiography

To evaluate the reproducibility of measurements of left ventricular (LV) dimensions, function, and myocardial mass, segmentedk-space gradient-recalled-echo (GRE) magnetic resonance (MR) imaging was performed on two occasions on 12 healthy volunteers. To compare the MR data, all volunteers underwent a two-dimensional echocardiography with determination of LV dimensions and function. The left ventricle was imaged during breath-hold by consecutive, contiguous short-axis views at end-diastole and end-systole. An average of eight short-axis views was needed to encompass the whole left ventricle. This fast MR sequence limited the total acquisition time to 12 min. LV volumes and masses were calculated after manual delineation of epicardial and endocardial surfaces by two observers in a blinded fashion. Interstudy variability varied between 4.1% and 10.3% for LV end-diastolic volume and end-systolic volume, respectively. Differences in interobserver variability were smaller and varied between 3.6% and 7.3% for LV ejection fraction and end-diastolic volume, respectively. Intraobserver variabilities ranged between 2.0% and 7.0% for LV ejection fraction and end-systolic volume, respectively. These variability percentages agree very well with other studies in literature using other MR sequences. No significant differences in LV dimensions or function were found between MR imaging and echocardiography. In conclusion, this MR sequence allows fast and reproducible LV quantification.     

Echo-volumar imaging

Echo-volumar imaging is a hyperfast technique capable of producing volumetric magnetic resonance images in times of the order of 100 ms. By increasing the gradient strengths and introducing real-time processing and display, we have been able to produce the first 16×16×16 voxel snapshot head images on volunteers.     

MR venography of the human brain using susceptibility weighted imaging at very high field strength

Objective We investigate the implications of high magnetic field strength on MR venography based on susceptibility-weighted imaging (SWI) and estimate the optimum echo time to obtain maximum contrast between blood and brain tissue. Materials and methods We measured tissue contrast and relaxation times at 7 T of gray matter, white matter, and venous blood in vivo. Results relaxation times of gray matter, white matter, and venous blood in vivo yielded 32.9 ± 2.3, 27.7 ± 4.3, and 7.4 ± 1.4 ms, respectively. Optimum TE was found to be 15 ms which is supported by theoretical considerations. Using this optimum TE, we acquired 3D high resolution datasets with a large volume coverage in a short measurement time that show very detailed microanatomical structures of the human brain such as intracortical veins and laminar cortical substructures. Conclusions By applying optimised vessel filters (vesselness filter and vessel enhancing diffusion) whole brain MR venograms can be obtained at 7 T with a significantly reduced measurement time compared to 3 T.     

Auto-SENSE view-sharing cine cardiac imaging

Cardiac MR cine imaging during breath hold is a compromise between spatial and temporal resolution and duration of breath hold. Especially for sick patients who have problems holding their breath, a short acquisition time is mandatory for all sequences. A combination of Auto-SENSE parallel imaging and view-sharing was implemented for fast cine imaging of the human heart and applied to healthy volunteers. Compared to conventional Fourier imaging, data acquisition could be accelerated by a factor of 3.6. Neither a pre-scan nor additional lines in k-space are required to generate the sensitivity maps in Auto-SENSE.     

Real-time imaging and triggering of 3D contrast-enhanced MR angiograms using MR fluoroscopy

Although a variety of timing techniques and data acquisition strategies have been, used for three-dimensional contrast-enhanced MR angiography, many are still limited by inadequate overall reliability, limited spatial resolution, or complexity. A technique is presented in this work in which contrast arrival is detected in the targeted vasculature in real time using MR fluoroscopy. Upon detection the operator triggers a 3D MR angiographic acquisition which uses an elliptical centric view order. It is shown that the view order intrinsically provides a high degree of venous suppression which in turn allows acquisition times of 30 s or longer. permitting high spatial resolution. The reliability of fluoroscopic triggering in bolus detection is shown to be over 90%. The technique provides high quality contrast-enhanced MR angiograms for many vascular regions.     

2D sense for faster 3D MRI

Sensitivity encoding in two spatial dimensions (2D SENSE) with a receiver coil array is discussed as a means of improving the encoding efficiency of three-dimensional (3D) Fourier MRI. it is shown that in Fourier imaging with two phase encoding directions, 2D SENSE has key advantages over one-dimensional parallel imaging approaches. By exploiting two dimensions for hybrid encoding, the conditioning of the reconstruction problem can be considerably improved, resulting in superior signal-to-noise behavior. As a consequence, 2D SENSE permits greater scan time reduction, which particularly benefits the inherently time-consuming 3D techniques. Along with the principles of 2D SENSE imaging, the properties of the technique are discussed and investigated by means of simulations. Special attention is given to the role of the coil configuration, yielding practical setups with four and six coils. The in vivo feasibility of the two-dimensional approach is demonstrated for 3D head imaging, permitting four-fold scan time reduction. Presented in parts at the 16th meeting of the ESMRMB, Sevilla, September, 1999.     

High-resolution MR imaging in mice

6. Conclusions Due to its high temporal and spatial resolution, the described MR technique is able to face the requirements of the small sized, fast beating mouse heart, resulting in time-resolved visualization of the cardiac morphology and function in great detail. This allows for accurate and reproducible quantification of LV performance including wall motion and contraction-relaxation dynamics. Hence, MRI offers the non-invasive investigation of physiological and pathophysiological changes of cardiac function over time, both under acute and chronic myocardial stress. Applied in models of cardiac failure, the MR method should aid understanding the mechanisms of LV remodeling after myocardial infarction and LV hypertrophy due to pressure overload in gene-targeted mouse models.     

地形要素的三维显示漫游

本文提供了基于OpenGL技术进行三维显示漫游软件编制的整体思路和技术细节     

三维恒定磁场的唯一性

本文首先说明用场量Ｂ，Ｈ或用向量磁住Ａ表述时，三维恒定磁场解答的唯一性；然后着重研究Ａ的向量泊蚣方程混合边值问题和Ａ的旋度旋度方程混合边值问题的唯一性，并进一步讨论了两者的等价性。     

不同姿态人脸深度图识别的研究

因易受到姿态等因素的影响,传统二维人脸识别的结果往往难以令人满意.针对不同姿态下的三维人脸深度图提出一种新的图像处理方法:首先利用面部特征点定位和偏转角度的计算将人脸深度图旋转到“正中面”位置;然后根据人脸对称性和ICP相关理论,对旋转后的深度图进行插值.通过该方法处理后的三维人脸深度图与原始数据相比,在人脸识别实验中...     

基于Java3D的网络物理实验室的研究与实践

选用Java平台实现大学物理课程的网络实验室,使用Java3D实现了物理实验室的三维虚拟与仿真,阐述了建模、编译、发布资源的完整过程,学生通过网络访问并进行实验仿真,可在普通浏览器内打开虚拟实验,不需要安装任何插件.三维立体效果和交互设计既提高了学生的实验兴趣,也丰富了学习体验.     

Maxwell 3D在开关磁阻平面电机结构设计中的应用

利用Maxwell 3D电磁场有限元分析软件对开关磁阻平面电机结构进行优化设计.对两种电机结构(动子宽齿结构、动子等齿结构)进行3D静磁场建模与仿真,获得磁场分布特性和电磁推力特性.仿真结果表明,等齿结构与宽齿结构相比,饱和程度低.而且等齿结构电磁推力的最大值较大,可控范围宽,即等齿结构要优于宽齿结构.仿真结果为电机结构设计和研制提供了一定的理论依据.     

微波三维成像离散点目标回波数据模拟

成像雷达一般可分为合成孔径雷达(SAR)和逆合成孔径雷达(ISAR).研究目标的RCS特性当前普遍应用ISAR成像技术,而这些目标的成像能力都依赖于目标的回波信号.在ISAR三维成像理论的基础上,模拟离散点目标的回波信号,为三维成像软件提供三维空间的模拟数据,用来验证成像软件的正确性.基于已有的一维和二维成像软件对模拟数据进行了分析.从三维数据中提取出一维和二维数据,成像结果证明了模拟数据在一维和二维的有效性,从而保证了模拟数据三维成像可靠性.