Principles, Techniques, and Applications of T2*-based MR Imaging and Its Special Applications
Principles, Techniques, and Applications of T2*-based MR Imaging and Its Special Applications
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DOI：
10.1148/rg.295095034
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发表时间：
2009-09-01
期刊：
影响因子：
5.5
通讯作者：
Haacke, E. Mark
中科院分区：
文献类型：
--
作者：
Chavhan, Govind B.;Babyn, Paul S.;Haacke, E. Mark
T2*弛豫指的是由自旋-自旋弛豫和磁场不均匀共同引起的横向磁化强度的衰减。T2*弛豫只有在梯度回波(GRE)成像中才能看到，因为在自旋回波成像中180脉冲消除了由磁场不均匀引起的横向弛豫。T2*弛豫是GRE序列图像对比度的主要决定因素之一，是许多磁共振(MR)应用的基础，例如磁化率加权(SW)成像、灌注MR成像和功能MR成像。通过使用低翻转角度、长回波时间和长重复时间，可以使GRE序列主要是T2*加权的。基于T2*对比度的GRE序列用于显示各种组织和病变中的出血、钙化和铁沉积。短波成像除了基于T2*的对比度外，还使用相位信息来利用血液以及不同组织中的铁和钙化的磁化率差异。磁共振灌注成像利用了高浓度的吉多喷酸地葡胺通过微血管系统时所产生的信号强度降低。在特定任务期间，血氧饱和度的变化会改变局部的T2*，从而导致在功能磁共振成像中看到的血氧水平依赖效应。介绍了T2*弛豫、T2*加权序列的基本原理及其临床应用，然后介绍了四种基于T2*的应用的原理、技术和临床应用，包括短波成像、灌注磁共振成像、功能磁共振成像和铁超载成像。(C)RSNA，2009年。Radiographics.rsna.org
T2* relaxation refers to decay of transverse magnetization caused by a combination of spin-spin relaxation and magnetic field inhomogeneity. T2* relaxation is seen only with gradient-echo (GRE) imaging because transverse relaxation caused by magnetic field inhomogeneities is eliminated by the 180 pulse at spin-echo imaging. T2* relaxation is one of the main determinants of image contrast with GRE sequences and forms the basis for many magnetic resonance (MR) applications, such as susceptibility-weighted (SW) imaging, perfusion MR imaging, and functional MR imaging. GRE sequences can be made predominantly T2* weighted by using a low flip angle, long echo time, and long repetition time. GRE sequences with T2*-based contrast are used to depict hemorrhage, calcification, and iron deposition in various tissues and lesions. SW imaging uses phase information in addition to T2*-based contrast to exploit the magnetic susceptibility differences of the blood and of iron and calcification in various tissues. Perfusion MR imaging exploits the signal intensity decrease that occurs with the passage of a high concentration of gadopentetate dimeglumine through the microvasculature. Change in oxygen saturation during specific tasks changes the local T2*, which leads to the blood oxygen level-dependent effect seen at functional MR imaging. The basics of T2* relaxation, T2*-weighted sequences, and their clinical applications are presented, followed by the principles, techniques, and clinical uses of four T2*-based applications, including SW imaging, perfusion MR imaging, functional MR imaging, and iron overload imaging. (C) RSNA, 2009. radiographics.rsna.org