医用MRI系统快速获取梯度回波脉冲序列开发

目的:探讨在i_Open 0.36T医用磁共振成像(MRI)系统上开发快速获取梯度回波脉冲序列(RAGE)的可行性与实现方法。方法:pascal语言编辑源程序,可调参数控制激发层数,相位编码时序,激发脉冲相位循环,数据采集次数,各段梯度脉冲开关时序等,编排k空间数据记录方式,满足快速傅立叶变换重建需要。编译源程序,调试图像。结果:在256×256采集矩阵的情况下,单层面成像时间最小值4s,所获图像分辨率、信噪比等指标能满足临床诊断需要。结论:利用该方法设计快速获取梯度回波脉冲序列是可行的。     

流动质子NMR信号强度与梯度回波中翻转角间的关系

梯度回波脉冲序列对血流分布和血管结构极其敏感。当脉冲序列中的参数发生变化时 ,血流的NMR(NuclearMagneticResonance)信号也发生改变。本文阐述了流动质子NMR信号强度与FLASH(fastlowangleshot)序列中的射频翻转角间的关系。并通过模拟实验验证了此关系的有效性。这种关系对在临床应用NMR血管成像时选取梯度回波脉冲序列有一定的指导意义。     

快速自旋回波脉冲序列的设计与实现

快速自旋回波序列可减少磁共振成像的数据扫描时间,提高成像速度,是国内外MR扫描仪必备的快速序列之一。本研究对快速自旋回波序列的设计、编程和实现方法进行了研究,对快速自旋回波序列与自旋回波序列的成像结果进行了比较和分析。该方法为国内MR扫描仪的自主研发提供了重要参考。     

核磁共振超短回波时间序列技术研究进展

核磁共振成像（MRI）技术拥有良好的软组织分辨率且无电离辐射,在临床和科研方面均得到了广泛应用。超短回波时间序列（UTE）在一定程度上弥补了MRI在短T2组织成像的弱点,使MRI的应用更加广泛。由UTE得到的派生序列有脂肪抑制UTE、单绝热反转恢复UTE、双回波差UTE等。本文介绍核磁共振超短时间回波序列（MR-UTE）技术的发展、原理及其应用,并对MR-UTE技术的发展方向进行展望。     

抑制MRI运动伪影的双脉冲预饱和技术的实现

目的 设计双预饱和脉冲序列，要求被激发块边缘锐利、无交叉激发，并且要求其宽度、位置可调。方法 在磁场强度为0．23T的全身开放式永磁磁共振成像仪上通过扫描水模进行研究，依据结果修改设计编写的脉冲序列直至达到期望的结果。结果 双预饱和RF脉冲、SincG RF函数及扰相梯度的联合使用，成功地得到了边缘锐利、饱和均匀的预饱和带，减小了弛豫时间对数据采集的约束和限制。结论 采用本文所述方法，可以有效实现预饱和扫描功能，获得边缘锐利的预饱和带。     

FIESTA和SSFSE序列在胎盘植入磁共振成像技术中的应用

目的:比较磁共振成像技术中快速平衡稳态采集（FIESTA）和单次激发快速自旋回波（SSFSE）序列在胎盘植入中的应用价值,为胎盘植入产前诊断序列选择提供参考。方法:选取佛山市第一人民医院2018年1月~2018年12月收治的35例胎盘植入作为研究对象,患者均采用FIESTA和SSFSE序列检查胎盘植入情况。比较两种序列图像质量,直接与间接征象,两种序列检查诊断价值。结果:FIESTA序列扫描对胎盘子宫轮廓和分界、图像信噪比显示情况优于SSFSE序列扫描,差异均有统计学意义（P<0.05）;FIESTA序列植入型、粘连型及穿透型等直接征象检出率高于SSFSE序列,仅植入型检出率差异具有统计学意义（P<0.05）,胎盘内部存在低状信号、胎盘内部实质不匀信号、胎盘内部变粗变多血管影等间接征象检出率低于SSFSE序列,仅胎盘内部存在低状信号检出率差异具有统计学意义（P<0.05）;以手术病理检查结果作为金标准,FIESTA序列与SSFSE序列联合检出植入型、粘连型及穿透型灵敏度、特异度、准确度均高于单一序列。结论:在胎盘植入患者检查中,FIESTA序列对胎盘子宫情况显示清晰,影像质量优异,但两者在直接与间接征象检出上各有优势,两种序列联合可以有效提高胎盘植入诊断价值。     

快速回波平面磁共振谱成像数据重建算法

传统的相位编码磁共振谱成像采集数据需要很长的时间,使得其在临床上的应用受阻。快速回波平面谱成像(Echoplanarspectroscopicimaging,EPSI)技术采用随时间变化的梯度对谱维和空间维同时进行编码,大大减少了数据采集时间。同时,改进EPSI的读出梯度形式还可以提高‘空间-谱’的分辨率。EPSI数据重建算法比较复杂在t方向先分别对奇偶回波数据进行快速傅立叶变换(FastFouriertranslation,FFT),再利用‘偏移’理论进行组合;在kx方向采用网格化算法将不等间隔采集的数据转换到等间隔的直线网格上,再利用FFT进行图像重建;ky方向是相位编码,不需要转换,直接进行FFT即可。     

MRI矩形表面线圈的磁场强度分析和实验

人体不同部位成象的最佳表面线圈与线圈的几何形状及大小有关。表面线圈的几何形状和大小决定了线圈的磁场强度大小,而后者与线圈接收的信号强度成正比。本文对脊柱成象用的矩形表而线圈进行了理论分析和实验研究,为设计最佳的脊柱成象表面线圈提供了科学的依据。     

压缩感知磁共振成像脉冲序列的设计与实现

为了进一步减少数据扫描时间,提高磁共振成像速度,我们对压缩感知MRI脉冲序列进行了研究。采用相位编码方向变密度欠采集的方式,设计了基于自旋回波的压缩感知序列;并采用PPL语言编程,在永磁和超导MR扫描仪上实现了该序列,对压缩感知欠采集与自旋回波全采集的数据进行了图象重建和分析。结果表明:该序列达到了压缩感知的要求,采集的头部和膝盖数据的最佳欠采样加速因子分别为2和4,大大节省了数据采集时间。该序列的实现使得低场强MR扫描仪在不提高梯度性能的情况下,便可实现快速成像,为提高我国在MR扫描仪上的研发水平奠定了基础。     

On the Use of Optical Flow Methods with Spin-Tagging Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a versatile noninvasive tool for achieving full-field quantitative visualization of biomedical fluid flows. In this study, two MRI velocimetry techniques (spin tagging and phase contrast) are used to obtain velocity measurements in a Poiseuille flow for Reynolds numbers below 1000. Spin-tagging MRI velocimetry supplies the displacement of tagged grids of nuclear spins from which the velocity field can be inferred, while phase contrast MRI velocimetry directly provides velocity data for every pixel in the field of view. Although the phase contrast method is more accurate for this flow, this technique is more sensitive to errors from magnetic susceptibility gradients, higher order motions, and has limited dynamic range. Spin-tagging MRI velocimetry is a viable alternative if automatic methods for extracting velocity fields from the tags can be found. Optical flow, a technique originally developed for machine vision applications, is proposed here as a postprocessing step to obtain two-dimensional velocity fields from spin-tagging MRI images. Results with artificially generated grids demonstrate the robustness of the optical flow algorithm to noise and indicate that a 7%–10% average error can be expected from the optical flow calculations alone, independent of MRI image artifacts. Experiments on spin-tagging MRI images for a Re=230 Poiseuille flow gave an average error of 6.41%, which was consistent with the measurement error of the generated (synthetic) images with the same level of random noise superimposed. © 2001 Biomedical Engineering Society. PAC01: 8761-c, 8719Uv, 8757Ce     

XNAT-PIC: Extending XNAT to Preclinical Imaging Centers

Molecular imaging generates large volumes of heterogeneous biomedical imagery with an impelling need of guidelines for handling image data. Although several successful solutions have been implemented for human epidemiologic studies, few and limited approaches have been proposed for animal population studies. Preclinical imaging research deals with a variety of machinery yielding tons of raw data but the current practices to store and distribute image data are inadequate. Therefore, standard tools for the analysis of large image datasets need to be established. In this paper, we present an extension of XNAT for Preclinical Imaging Centers (XNAT-PIC). XNAT is a worldwide used, open-source platform for securely hosting, sharing, and processing of clinical imaging studies. Despite its success, neither tools for importing large, multimodal preclinical image datasets nor pipelines for processing whole imaging studies are yet available in XNAT. In order to overcome these limitations, we have developed several tools to expand the XNAT core functionalities for supporting preclinical imaging facilities. Our aim is to streamline the management and exchange of image data within the preclinical imaging community, thereby enhancing the reproducibility of the results of image processing and promoting open science practices.     

Two applications of wavelets and related techniques in medical imaging

We present two applications of wavelet and related techniques to problems arising in medical imaging. Both make considerable use of the edge detection and classification properties of wavelet-type representations. First we describe simple and effective techniques for image denoising and contrast enhancement based on the multiscale edge representation of images. These techniques are sufficiently flexible to successfully address the varying requirements posed by several different medical imaging modalities in common use today. Experimental results are presented to illustrate the application of these techniques to various types of medical images. Next we describe adapted waveform encoding, a technique for magnetic resonance imaging. One advantage of this technique istthat it can be used to efficiently encode edge features of the object being imaged. This has a particular diagnostic application in tracking heart wall thickness during the cardiac cycle, which we present along with some experimental results along this line. We also present an analysis of the signal-to-noise ratios of images formed with this technique, as this is a factor of paramount importance in MRI. The fact that wavelet schemes tend to concentrate energy near edge features makes the result rather different than that found in standard Fourier based approaches. We indicate an exciting potential application of our technique: reducing spectral leakage in phosphorus spectroscopy.     

抑郁症的功能磁共振研究进展

抑郁症的发病率逐年上升,磁共振成像能在脑结构及功能方面揭示抑郁症患者存在的脑组织异常,并对治疗效果起到评估作用。本文综述了功能磁共振成像在评价抑郁症的研究近展。     

视神经磁共振成像方法研究

目的　探讨视神经磁共振 (MRI)成像最佳方法及正常视神经MRI征象 .方法　随机选择 4 0例进行头部检查 ,无眼部疾患或视力障碍患者作为正常视神经研究对象 .使用PhilipsACS -NT15 1.5T超导型磁共振成像仪及正交头线圈 .成像序列包括自旋回波T1加权成像 (SET1WI)及超快速自旋回波加或不加脂肪频谱饱和技术成像 (TSE±SPIRT2WI) .扫描方位包括与视神经平行轴位、斜矢状位及与视神经长轴垂直冠状位和标准冠状位 .结果　视神经眶内段、管内段及视束粗细均匀 .SET1WI显示视神经较周围的蛛网膜下腔信号强度稍高 ,T2WI显示视神经呈相对低信号 ,与脑髓质信号相等 ,周围包绕高信号脑脊液 .与视神经长轴平行的轴位及斜矢状位T1WI及T2WI均可显示视神经全貌 ,与视神经长轴垂直冠状位TSE +SPIRT2WI技术显示视神经信号均匀 .结论　MRI可以较好地显示视神经解剖 ,与视神经长轴垂直冠状位TSE +SPIRT2WI可以较好地显示信号特征 .     

磁共振波谱成像技术的研究现状及发展趋势

磁共振波谱成像是21世纪生物医学研究进入分子水平的重要检测工具之一,它对各种严重疾病具有早期诊断和疗效监控能力。本文介绍了磁共振波谱成像在成像技术与数据重建、波谱量化和临床研究等方面的研究现状,并探讨了其发展趋势。     

基于SE序列的MR图像权重计算方法

目的：探究一种基于SE序列的MR图像权重计算方法,为判定sE加权像提供更加科学及准确的判定依据。方法：提出一种计算两种生物组织的质子密度特性差异、纵向弛豫时间特性差异及横向弛豫时间特性差异各自对磁共振图像对比度的贡献比例方法,首先,将磁共振图像对比度公式进行等量变换,建立SE序列权重对比度数学关系式;其次,对该关系式进行对数变换,在对数坐标下,乘性权重因子转化为加性权重因子;最后,利用比例计算公式计算生物组织的三种特性差异各自对磁共振图像的贡献比例。结果：利用医用核磁共振仪器,通过对重复时间及回波时间不同设置后,获得两幅关于白质和灰质的MR图像,然后利用本文介绍的基于SE序列的MR图像权重计算方法,获得质子密度特性差异、纵向弛豫时间特性差异及横向弛豫时间特性差异各自对MR图像对比度贡献比例,并显示于这两幅MR图像上．可定量判定SE加权像。结论：通过本文介绍的基于sE序列的MR图像权重计算方法,对精确判定磁共振SE加权像有极大的帮助。     

Cardiac Flow Analysis Applied to Phase Contrast Magnetic Resonance Imaging of the Heart

Phase contrast magnetic resonance imaging is performed to produce flow fields of blood in the heart. The aim of this study is to demonstrate the state of change in swirling blood flow within cardiac chambers and to quantify it for clinical analysis. Velocity fields based on the projection of the three dimensional blood flow onto multiple planes are scanned. The flow patterns can be illustrated using streamlines and vector plots to show the blood dynamical behavior at every cardiac phase. Large-scale vortices can be observed in the heart chambers, and we have developed a technique for characterizing their locations and strength. From our results, we are able to acquire an indication of the changes in blood swirls over one cardiac cycle by using temporal vorticity fields of the cardiac flow. This can improve our understanding of blood dynamics within the heart that may have implications in blood circulation efficiency. The results presented in this paper can establish a set of reference data to compare with unusual flow patterns due to cardiac abnormalities. The calibration of other flow-imaging modalities can also be achieved using this well-established velocity-encoding standard. Medical image processing software named Medflovan, which is developed by Kelvin K. L. Wong, is used to produce the results displayed in this paper. The research-based version of this software system is utilized to provide cardiac flow visualization and analysis effectively.     

扩散加权成像（DWI）在肝硬化后脾脏增大的研究

目的探讨扩散加权成像ADC值在正常脾脏与肝硬化后脾肿大间的差异。方法对12例正常志愿者及20例肝硬化脾肿大者行常规MRI平扫及扩散加权成像检查。结果正常脾脏平均ADC值为1.45×10-3mm2/s,肿大脾平均ADC值为1.49×10-3mm2/s。结论正常脾脏与肝硬化后脾肿大的ADC值间无统计学差异。