一种以超分辨率理论为基础的磁共振眼球成像方法

磁共振成像（MRI）是一种无电离辐射的非介入性的眼内肿瘤检测方法,但分辨率和运动伪影是成像过程中不易克服的困难．以往的扫描方法或是不可避免的引入运动伪影,或是需要受试者做精确的配合,增加了成像的难度,给受试者带来不舒适的体验．本文提出了一种以超分辨率理论为基础的新的磁共振眼球成像方法,使用一种特制的眼球线圈,对眼部区域扫描一系列动态的图像,使得不同方向上的采集分辨率互补．最后经过预处理、配准、超分辨率重建等操作,得到高质量的磁共振眼球图像．实验结果表明,这种方法可以在不需要受试者做额外配合工作的情况下,得到更加清晰的磁共振眼球图像．     

磁共振成像的正交线圈数字合成方法研究

当采用正交线圈来提高接收通道的性能时,合成方法对整体效果有很大的影响. 由于在一般情况下正交线圈的2个线圈的信噪比存在不平衡,故需要采用加权合成的方法来优化合成图像的信噪比. 在现有的模拟合成方法中,加权系数是固定的,不能根据每次扫描的实际情况来确定最优的参数,因此无法得到最佳的合成效果. 该文提出一种简单的磁共振正交线圈成像的数字合成方法,它采用2个完全独立的接收通道来采集磁共振信号,根据两通道信号的特性来动态地确定I/Q线圈的加权因子,最后进行加权合成.     

利用主动式回馈场的磁共振成像研究

磁共振成像在现今临床医学诊断上占有相当重要的地位.如何增强成像对比度是磁共振成像研究领域中极为重要的课题.传统成像中利用磁共振性质的差异性来获得成像对比度,然而当这些性质的差异性小时,即使经过时间演化,还是难以得到可视的对比度.为了解决此问题,辐射阻尼是其中一个可能的方案.之前的研究显示,辐射阻尼对极小频率差亦能够在短时间的演化下得到相当强的对比度.然而辐射阻尼的产生需要高敏感度的射频线圈等限制.该研究将介绍如何利用外加的线路,模拟辐射阻尼现象,进而控制自旋动态,以达到增强成像对比度并进一步设计新的磁共振成像方式.     

基于单片FPGA的多通道磁共振成像接收模块

提出了一种基于FPGA的多通道磁共振成像接收模块,能对多个独立通道的磁共振信号进行直接采样、数字下变频,以及数据流控制,并对其进行了成像实验. 设计中采用Xilinx公司的系统级DSP开发工具--System Generator对FPGA内部所有功能进行建模、仿真并生成相应的硬件描述语言. 模块的采样速率为80MSPS,能灵活实现1 kHz~1 MHz范围的可变接收带宽,适用于1 T以下的磁共振成像系统;在单片FPGA内完成1~4个通道采样信号的数字正交解调,抽取滤波和数据流的处理,并可扩展至8通道. 实验证明模块具有体积小,集成度高,可重构性强和成本低等特点,为磁共振成像谱仪的多通道接收系统提供了一种高性能的数字化解决方案.     

增强低场下脑功能磁共振成像显著性的研究

实现了基于低场0.35 T磁共振成像系统的大脑功能磁共振成像（functional Magnetic Resonance Imaging,fMRI）的研究. 基于质子密度加权的快速自旋回波(Turbo Spin Echo,TSE)图像,重点研究增强低场fMRI显著性的方法,目的在于提高低场fMRI的可用性. 结果表明：健康受试者在执行手动任务期间,大脑运动区的信号强度变化可以由基于血管外质子信号增强 (Signal Enhancement by Extravascular water Protons,EEP)的对比机制探测. 优化TSE序列参数能提高图像SNR和扫描速度,并在统计分析中增加外在屏蔽图像,可以有效地提高低场下fMRI研究结果的显著性.     

基于反转恢复技术的水脂分离磁共振成像方法

提出了使用反转恢复技术获得独立的水和脂肪图像的磁共振成像（MRI）方法. 该方法利用水和脂肪T₁值的差异,在施加选择性180°准备脉冲后, 采用不同的反转恢复时间（T_I）2次采集MRI图像,计算出水和脂肪的信号贡献,获得水和脂肪独立的2套图像. 该方法可对水和脂肪进行良好的分离,避免常规水脂分离方法Dixon技术偶发的水-脂互换伪影的产生,同时,可避开相位校正,因此可使计算过程更为简单稳定.     

多通道磁共振成像仪控制台数据传输模块设计

当前临床高场磁共振成像（MRI）系统要求成像仪控制台支持16个甚至32个接收通道,可以频繁和高速地进行数据传输并支持快速成像．基于此要求,本文研发了一个基于PowerPC处理器的数据传输模块,将其集成于自行研发的MRI成像仪控制台中,用于成像过程中控制台与计算机之间数据的高速传输．该模块以飞思卡尔公司的高性能PowerPC处理器—MPC8270为核心,运行嵌入式Linux操作系统．处理器与用户计算机之间通过百兆以太网连接,使用局部总线连接控制台的序列运行模块和数据采集模块（数量可扩展）．处理器响应数据采集模块发来的中断请求以快速读取和上传数据．本设计通过驱动程序的设计以保障响应的速度与可靠性．成像实验表明此设计方案能够满足多个接收通道数据快速获取与传输的需求．     

磁共振成像发展与超高场磁共振成像技术

20世纪70年代磁共振成像技术的发明为生物医学成像开辟了一个极富生命力的领域。随着技术的进步和生命科学研究的深入,磁共振成像技术正向超高场发展。文章将在介绍磁共振成像技术发展的历史后,结合作者的认识,简要介绍超高磁共振成像技术的发展现状和关键技术方面的进展。     

超高场磁共振人体成像应用研究和医学前景

20世纪90年代初,随着第一代超高场磁共振成像仪的投入使用,因其诸多的优点,如更高的检测信噪比、更好的对比度、更强的BOLD效应和更宽的波谱,超高场磁共振成像成为国际医学磁共振领域最热门的研究方向之一.该文以最新一代的7.0 T MRI成像仪为例,简述超高场磁共振人体成像仪的系统结构、研究进展,并展望其在神经科学、认知科学和医学的应用前景.     

磁共振结构成像在自闭症研究中的应用

自闭症,又称作孤独症,是一种常发生在儿童中的广泛性发育障碍,表现为交流障碍、语言障碍以及重复刻板的行为和狭窄的兴趣爱好. 磁共振成像作为一种无损伤的和多参数的影像方法,其各种检测手段均被应用于自闭症实验研究,其中结构磁共振成像(sMRI)和功能磁共振成像(fMRI)研究居多. 研究表明自闭症患者脑部结构发生了显著性改变. 该文综述了当前世界上利用磁共振结构成像研究自闭症的主要成果,包括结构磁共振成像研究脑体积变化,扩散张量成像研究自闭症的脑白质损伤. 该文也说明磁共振成像是一种十分有用的研究工具,有望在将来更多被用于探索自闭症的未知领域.     

大白鼠脑中风模型的核磁共振成像(英文)

核磁共振成像现今已经成为临床神经影像的常规工具.在诊断、评估和监测中风从急性到慢性的各个阶段的脑组织的变化过程中,核磁共振成像扮演了一个重要的角色.该综述提供了多种核磁共振成像方法的描述,以及选择性地展示了作者在美国亨利福特医院神经科核磁共振成像实验室所获得的大白鼠栓塞中风模型的核磁共振成像研究成果.     

超极化Xenon 对慢阻肺的可视化加权成像

超极化气体3He 或者¹²⁹Xe 扩散加权成像已经被证明了能够有效检测慢性阻塞性肺部疾病(COPD)中肺部微结构的改变．相比于³He,¹²⁹Xe 更便宜而且更容易获得,但是¹²⁹Xe 成像中较低的信噪比致使¹²⁹Xe 的肺部表面扩散系数(ADC)的测量面临着许多困难．在该研究中,为了得到更高的图像信噪比,作者对气球模型,健康大鼠和COPD大鼠进行了单个b 值(14 cm2/s)的扩散加权超极化¹²⁹Xe 磁共振成像(MRI)．所有的COPD模型大鼠是通过烟熏和注射内毒素(LPS)进行诱导得到的．在7 T 磁共振成像仪上面获得了大鼠肺实质的超极化¹²⁹Xe ADC 值分布图．COPD 大鼠肺实质的¹²⁹Xe ADC 值是0.044 22±0.002 9 和0.042 34±0.002 3 cm2/s (Δ = 0.8/1.2 ms),远大于健康大鼠肺实质的¹²⁹Xe ADC 值0.037 7±0.002 3 和0.036 7±0.001 3 cm2/s．而且COPD 大鼠肺实质相关的¹²⁹Xe ADC 直方图也表现出了一定的展宽．这些结果说明了COPD 大鼠肺泡空腔的增大能够通过129Xe 在肺里面的ADC 增长和相关直方图的拓宽反应出来,从而证明了单个b 值的扩散加权MRI 方法可以有效地对COPD 大鼠进行检测．     

Assessment of peripheral tissue perfusion disorder in streptozotocin-induced diabetic rats using dynamic contrast-enhanced MRI

Purpose

To assess peripheral tissue perfusion disorder in streptozotocin (STZ)-induced diabetic rats by using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

Materials and Methods

A rat diabetes model was produced by intravenous injection of STZ. Diabetic rats were sustainably treated with either saline or insulin using an Alzet osmotic pump. Hind paw tissue perfusion was measured by signal intensity (SI) enhancement after gadolinium diethylenetriaminepentaacetic acid injection in DCE-MRI study and quantified using the initial area under the SI-time curve (IAUC). Peripheral tissue uptake of [¹⁴C]iodoantipyrine (IAP) was also determined as a marker of tissue blood flow for comparison with the IAUC value indicating tissue perfusion.

Results

STZ caused hyperglycemia at 1 and 2 weeks after injection. Treatment with insulin significantly alleviated hyperglycemia. At 2 weeks after STZ injection, peripheral tissue perfusion was clearly reduced in the diabetic rats and its reduction was significantly improved in the insulin-treated diabetic rats. Tissue perfusion evaluated by DCE-MRI was similar to the tissue blood flow measured by [¹⁴C]IAP uptake.

Conclusion

Our findings demonstrated that DCE-MRI can assess peripheral tissue perfusion disorder in diabetes. DCE-MRI could be suitable for noninvasive evaluation of peripheral tissue perfusion in both preclinical and clinical studies. It may also be useful for developing novel drugs to protect against diabetic vascular complications.     

Optimization of spoiler gradients in flash MRI

The FLASH technique for fast magnetic resonance (MR) imaging often employs strong magnetic field gradients, called spoiler gradients, to dephase the transverse magnetization after it has been measured. Otherwise, image artifacts can develop. The effectiveness of spoiler gradients at suppressing these artifacts was evaluated experimentally on two-dimensional MR images of a uniform phantom and patients. It was informative to compare the magnetization immediately before the RF excitation in each phase encoding step. Only spoiler gradients in the slice selection direction were effective. Spoiler gradients that decreased steadily from a large amplitude in the first phase encoding step to zero in the last minimized the transverse magnetization and suppressed the image artifact, without changing the image contrast.     

高温超导MRI磁体试验样机的设计

对MRI用高温超导磁体试验样机的设计进行了介绍,包括项目的市场需求、磁体的基本参数和系统热负荷的预设计结果等。     

Fast multi-contrast MRI reconstruction

Multi-contrast magnetic resonance imaging (MRI) is a useful technique to aid clinical diagnosis. This paper proposes an efficient algorithm to jointly reconstruct multiple T1/T2-weighted images of the same anatomical cross section from partially sampled k-space data. The joint reconstruction problem is formulated as minimizing a linear combination of three terms, corresponding to a least squares data fitting, joint total variation (TV) and group wavelet-sparsity regularization. It is rooted in two observations: 1) the variance of image gradients should be similar for the same spatial position across multiple contrasts; 2) the wavelet coefficients of all images from the same anatomical cross section should have similar sparse modes. To efficiently solve this problem, we decompose it into joint TV regularization and group sparsity subproblems, respectively. Finally, the reconstructed image is obtained from the weighted average of solutions from the two subproblems, in an iterative framework. Experiments demonstrate the efficiency and effectiveness of the proposed method compared to existing multi-contrast MRI methods.     

Parallel MRI at microtesla fields

Parallel imaging techniques have been widely used in high-field magnetic resonance imaging (MRI). Multiple receiver coils have been shown to improve image quality and allow accelerated image acquisition. Magnetic resonance imaging at ultra-low fields (ULF MRI) is a new imaging approach that uses SQUID (superconducting quantum interference device) sensors to measure the spatially encoded precession of pre-polarized nuclear spin populations at microtesla-range measurement fields. In this work, parallel imaging at microtesla fields is systematically studied for the first time. A seven-channel SQUID system, designed for both ULF MRI and magnetoencephalography (MEG), is used to acquire 3D images of a human hand, as well as 2D images of a large water phantom. The imaging is performed at 46 mu T measurement field with pre-polarization at 40 mT. It is shown how the use of seven channels increases imaging field of view and improves signal-to-noise ratio for the hand images. A simple procedure for approximate correction of concomitant gradient artifacts is described. Noise propagation is analyzed experimentally, and the main source of correlated noise is identified. Accelerated imaging based on one-dimensional undersampling and 1D SENSE (sensitivity encoding) image reconstruction is studied in the case of the 2D phantom. Actual threefold imaging acceleration in comparison to single-average fully encoded Fourier imaging is demonstrated. These results show that parallel imaging methods are efficient in ULF MRI, and that imaging performance of SQUID-based instruments improves substantially as the number of channels is increased.     

核磁共振螺旋快速成像的新进展

核磁共振快速成像能在几十毫秒内获取数据，对运动器官作适时显示，并在功能成像的研究等方面具有常规成像不能替代的优点，是核磁共振成像的发展方向．螺旋快速成像对硬件的要求较低，近年来方法上的改善，已使其趋于实用．文章简要介绍了螺旋快速成像原理及网格重建算法．     

MRI appearance of disseminated osseous tuberculosis

Disseminated osseous tuberculosis is a rare disease. This is a report of two cases of disseminated osseous tuberculosis imaged with MRI at 1.5-T, CT, plain radiography and bone scintigraphy. CT and plain radiography demonstrated either highly destructive or cystic lesions with sclerotic margins. Bone scintigraphy and plain radiography were quite insensitive in detecting areas of involvement compared to MRI. On MRI the abnormal areas had short T-1 relaxation values, which is an atypical appearance for bony infections, and prolonged T-2 relaxation values. The reason for the T-1 relaxation behavior is uncertain. MRI also provided delineation of epidural extent.