【Q&A in MRI】9.1.3 MR Perfusion Overview 磁共振灌注综述

一切权利归原作者所有。 仅供学习交流使用，严禁用作商业用途。 网站： https://www.mriquestions.com/ 原著：Allen D. Elster, MD 译注：蒋强盛 What are the differences between DSC, DCE and ASL perfusion methods used in MRI? 磁共振中使用的 DSC，DCE 和 ASL 三种灌注方法有什么不同？

Three methods are commonly used to measure perfusion using MRI: Dynamic Susceptibility Contrast (DSC) , Dynamic Contrast Enhanced (DCE) , and  Arterial Spin Labeling (ASL) . Both DSC and DCE require intravenous bolus administration of gadolinium, while ASL is performed without exogenous contrast. These techniques will be briefly described below, with more detailed explanations in subsequent Q&A's. 磁共振灌注通常使用三种方法： 动态磁敏感对比（DSC） ， 动态对比增强（DCE） 和 动脉自旋标记（ASL） 。DSC 与 DCE 都需要静脉团注钆剂，而 ASL 不需要注射外源性对比剂。下面简要地介绍下这三种灌注方法，更详细的解释请参考后续的 Q&A's。

Dynamic Susceptibility Contrast (DSC) Perfusion MRI 动态磁敏感对比（DSC）灌注 DSC perfusion imaging begins with a bolus of gadolinium chelate injected intravenously, followed by a series of rapidly acquired gradient or spin echo images over the organ of interest. As the gadolinium first passes through the regional circulation, it remains largely confined to the intravascular space. Due to its paramagnetic properties, gadolinium creates a local magnetic field distortion around vessels, with T2 (T2*) dephasing and loss of signal as the bolus passes.By measuring signal intensity as a function of time and fitting to a mathematical model, various perfusion parameters (e.g., blood volume, blood flow, mean transit time) can be extracted. Because DSC imaging depends only on the first pass of the contrast agent, it is sometimes known as bolus tracking MRI . Image acquisition time is therefore very short (~2 min). DSC 灌注成像先通过静脉团注钆螯合物，随后使用一系列的梯度回波序列或自旋回波序列对感兴趣的器官进行快速采集。当钆剂首次通过局部组织循环时，钆剂大多还是仅限于血管腔内。由于钆金属离子的顺磁性，在血管周围产生局部磁场的畸变，那么当钆剂团注通过时，由于 T2(T2*) 散相，就导致信号的丢失。通过测量时间信号强度曲线函数，并拟合数学模型，可以得到各种灌注参数（如，血容量、血流量和平均通过时间）。由于 DSC 成像仅依赖对比剂的首过，有时也称作 团注追踪 MRI ，因此图像采集时间非常短（约 2 分钟）。 Dynamic Contrast Enhanced (DCE) Perfusion MRI 动态对比增强（DCE）灌注 Like DSC imaging, DCE also requires exogenous administration of a gadolinium-based contrast agent. DCE, however, exploits the T1 shortening effects of gadolinium, acquiring repeated T1-weighted images over an approximately 5-10 minute interval. During this time frame, gadolinium contrast accumulates within the tissue extracellular space at a rate determined by perfusion, capillary permeability, and surface area. The image data may be analyzed visually or semiquantitatively. Full quantification may be obtained by applying a compartmental model allowing several physiological parameters to be derived, including the transfer constant (Ktrans), fractional plasma volume (vp), andfractional volume of the tissue extracellular space (ve). 与 DSC 成像一样，DCE 也需要注射外源性的钆对比剂。然而，DCE 利用的是钆剂缩短组织 T1 弛豫时间的效应，使用 T1 加权序列对组织进行重复采集大约 5-10 分钟。在这段时间内，钆对比剂以一定的速率在组织细胞外间隙不断累积，此速率由灌注、毛细血管通透性和表面积决定。采集的图像数据可以通过视觉观察分析或通过半定量分析。全定量分析可以使用房室模型来获得，并且能够导出一些生理参数，包括转移常数（Ktrans）、血浆容积分数（vp），和组织细胞外间隙容积分数（ve）。 %%%%%%%%%%%%%%% 【译者注1】

%%%%%%%%%%%%%%% Arterial Spin Labeling (ASL) 动脉自旋标记（ASL） Unlike DSC and DCE perfusion MRI, ASL does not require the administration of gadolinium contrast. Instead, the patient's own water molecules serve as an endogenous diffusible tracer. This is accomplished by "magnetically labeling" water molecules in proximal blood vessels with radiofrequency pulses. As these molecules flow into the organ of interest they reduce tissue signal intensity in proportion to perfusion.  In the typical ASL pulse sequence, images are acquired both with and without labeling pulses, then subtracted. By applying a mathematical model, various perfusion parameters (principally blood flow) can be obtained. The signal-to-noise of ASL techniques is inherently low, and somultiple signal averages must be acquired resulting in 3-5 minute minimum imaging times to obtain useful data. Because it is signal-to-noise limited, ASL performs significantly better at 3T than 1.5T. 与 DSC 和 DCE 灌注不同，ASL 不需要注射钆对比剂，而是使用患者体内的水分子作为内源性扩散示踪剂。这是通过射频脉冲“磁化标记”近心端血管中的水分子实现的。当这些被标记的水分子流入感兴趣的器官时，它会根据灌注情况按比例降低组织的信号强度。在经典的 ASL 脉冲序列中，采集有标记脉冲与无标记脉冲的两组图像，然后做减影。通过运用数学模型，就可以得到不同的灌注参数（主要是血流量）。由于 ASL 技术的固有信噪比低，因此需要多次采集取平均，这样需要最短 3-5 分钟的成像时间来获得有用的数据。因为信噪比的限制，ASL 在 3.0T 上采集的效果要比 1.5T 好的多。 More detailed descriptions of DSC, DCE, and ASL are provided in subsequent Q&A's. A summary table comparing the techniques is provided below. 关于 DSC，DCE 和 ASL 更详细的内容请参考后续的 Q&A's。如下是它们之间技术对比的一个汇总表：

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