9.1.2 PerfusionParameters 灌注参数

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网站： https://www.mriquestions.com/ 原著：Allen D. Elster, MD 译注：蒋强盛 How are parameters like BF, BV, and MTT defined and used in perfusion imaging? 灌注成像中的 BF, BV, 和 MTT 参数是如何定义的？

The simplest model of regional circulation contains a single arterial input, a tissue capillary bed, and a single venous output. This model has a long history, originally used by Fick in the 19th Century to study cardiac output. Later modifications for indicator dilution blood flow measurements were made by Kety and Schmidt in the 1940s and extended by Meier and Zierler in the 1950's.

最简单的局部循环模型包括一个动脉输入，一个组织毛细血管床和一个静脉输出。这一模型有一很长的历史，在 19 世纪，起初被 Fick 用来研究心输出量。后来，二十世纪四十年代，被 Kety 和 Schmidt 进行优化，使用指示剂稀释法来进行血流量的测量。在二十世纪五十年代，又被 Meier 和 Zierler 进行了扩展。

Simple model of regional circulation with a single arterial input and single venous output. Blood flow (BF) and Blood Volume (BV) are assumed to be constant.

Blood flow (BF) through the system and blood volume (BV) within the tissue are both assumed to be constant. The units for and are usually normalized by dividing their absolute values by the mass of tissue perfused, resulting in units of the form mL/min/100g and mL/100g respectively. No pooling or loss of blood is allowed, so that whatever flows in eventually flows out.

流过系统的血流量（BF）和组织内的血容量（BV）都假设是不变的。BF 与 BV 的单位通常用它们的绝对值除以被灌注的组织的质量进行归一化，那么 BF 和 BV 的单位就分别是 mL/min/100g 和 mL/100g。假设血液没有积蓄与流失，那么不管系统流入多少的血液最终都将流出。

Note that some paths through the tissue are relatively straight while others are highly branched. This means that each red blood cell or contrast agent molecule takes a different amount of time to traverse the capillary bed (although all will eventually appear in the venous efflux). The mean transit time (MTT), measured in sec (or min), reflects the average time an injected tracer particle following the flow of blood would reside within the system.

注意到，一些组织的血流路径是相对比较直的，而有些组织的血流路径就有很多分支。这就意味着每一个红细胞或对比剂分子通过毛细血管床所花费的时间将不同（尽管它们都将会流入流出静脉中）。平均通过时间（MTT），单位为秒（或分钟），反映了注射的示踪剂随血流在系统内流淌的平均时间。

Blood flow (BF), blood volume (BV), and mean transit time (MTT) are related by the central volume theorem, so that if two are known, the third can be computed. The connecting relationship is given by the equation

血流量（BF），血容量（BV），和平均通过时间（MTT），通过中心容积定理联系起来，因此当知道其中两个量，则可以计算第三个量。三者之间关系由下面方程给出：

BF = BV / MTT which can be easily remembered by considering units of measurement, i.e., that blood flow represents a volume of blood per unit time.

 这一方程可以通过单位来轻松地记忆，即，血流量代表每单位时间内的血容量。

In perfusion imaging studies, BF, BV, and MTT are commonly calculated and displayed as color-coded parameter maps. These provide complementary perfusion-related information that may be useful for clinical decision making.

在灌注成像研究中，通常计算血流量、血容量和平均通过时间，并通过参数的彩图来进行显示。这些定量图所代表的灌注相关的信息给临床决策提供了非常有用的补充。

For example, areas of cerebral infarction typically display decreased BV and BF, with increased MTT. Conversely, areas of ischemia without infarction (the 'penumbra') typically have reduced BF and increased MTT, but normal BV. 例如，大脑梗塞通常表现为血容量与血流量的下降，以及平均通过时间的延长。相反，没有梗塞的局部缺血区域（“半暗带”）通常表现为血流量的下降，平均通过时间延长，但血容量正常。 

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ahajournals.org 

In oncology BV is provides an index of capillary density and is often elevated in more malignant tumors.  Conversely low BV in a treated but enlarging tumor may suggest radionecrosis rather than tumor progression. 

在肿瘤疾病中，血容量是毛细血管密度的一个指标，在恶性肿瘤中血容量通常是增加的。相反，经过治疗肿瘤表现为增大、但灌注低血容量的，可能提示放射性坏死，而不是肿瘤进展。

Details of how these quantitative perfusion parameters are extracted from image data will be provided in the next several Q&A's.

关于这些灌注定量参数是如何从采集的图像中获取的，将在后续的 Q&A 中详细讨论。