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新发传染病电子杂志

新发传染病电子杂志 ›› 2025, Vol. 10 ›› Issue (2): 54-62.doi: 10.19871/j.cnki.xfcrbzz.2025.02.010

• 新技术推介 • 上一篇    下一篇

以多相T2弛豫时间模型解释表观弥散系数对T2弛豫时间的高度依赖性

王毅翔   

  1. 香港中文大学医学院影像与介入放射学系, 香港特别行政区 沙田
  • 收稿日期:2025-01-29 发布日期:2025-06-16
  • 通讯作者: 王毅翔,Email：yixiang_wang@cuhk.edu.hk
  • 基金资助:
    香港基础研究基金项目（14112521）

High dependence of ADC on T2 relaxation time explained by the multiple T2 elements model

Wang Yixiang   

  1. Department of Imaging and Interventional Radiology, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong Special Administrative Region SAR, China.
  • Received:2025-01-29 Published:2025-06-16

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摘要： 在体内弥散加权成像时,表观弥散系数（apparent diffusion coefficient,ADC）可以反映组织弥散程度。ADC在感染性病变影像学等临床影像学中广泛使用。一般假设肿瘤的弥散会受限,而水分多的组织弥散更加自由。然而,实际临床工作得到的ADC值常常与预期的组织弥散情况相背离。比如脓肿内脓肿液测得的ADC一般非常低;而一些硬质组织如软骨、椎间盘的ADC非常高。虽然脓肿液可能有一定黏度,但黏液瘤却表现为高ADC。文献认为肝细胞癌ADC相对于肝脏弥散受限。然而,由于肝细胞癌大多血供增加、动脉血液供应比例增高并伴有水肿,因此,肝细胞癌不太可能具有真正的弥散受限。相反,按照慢速弥散系数（slow diffusion coefficient,SDC）计算方法,结果显示肝细胞癌的弥散快于周围肝脏组织。最近提出的体内ADC测量值与T2弛豫时间密切相关。T2弛豫时间可分为短T2段（<60ms）、中等T2段（60~80ms）和长T2段（>80ms,3.0T磁场值）。对于短T2段,T2弛豫时间与ADC之间为负相关;对于长T2段,T2弛豫时间与ADC之间为正相关。本文通过体素内不相干运动模型的概念来解释ADC的T2弛豫时间依赖性。我们建议在解释临床高b值弥散加权成像图像和ADC图像时不再常规使用“弥散受限”一词。

关键词: 表观弥散系数, 慢速弥散系数, 体素内不相干运动模型, 弥散受限

Abstract: For in vivo diffusion weighted imaging , apparent diffusion coefficient (ADC) has been considered to reflect tissue diffusion. The ADC is widely used in clinical practice, including in the imaging of infectious lesions. It is generally assumed that the diffusion of tumors is restricted, while the diffusion of tissues with more water will be freer. However, the ADC values obtained in actual clinical work often deviate from the expected tissue diffusion. For example, although the abscess contains liquid components, the ADC measured for the abscess fluid is generally very low; while the ADC of some hard tissues such as cartilage and intervertebral discs is very high. Although the abscess fluid may have certain viscosity, myxomas often have high ADC. HCC ADC has been noted to have restricted diffusion relative to the liver. However, as HCCs are mostly associated with increased blood supply and increased proportion of arterial blood supply and higher water content, it is unlikely that HCC has a true lower diffusion. In fact, with the slow diffusion coefficient (SDC) method recently proposed by us, we measured faster diffusion for HCC than for the adjacent liver parenchyma. We proposed that in vivo ADC measure is strongly associated with T2 relaxation time (T2). T2 can be divided into short T2 band (<60ms), intermediate T2 band (60-80ms), and long T2 band (>80 ms, all 3T values). For the short T2 time band, there is a negative correlation between T2 and ADC. For the long T2 time band, there is a positive correlation between T2 and ADC. A tissue likely measures a low ADC if its T2 is close to 70 ms. In this article, we attempt to explain the T2 dependency of ADC with the concept of the intravoxel incoherent motion model. We suggest that we do not routinely use the term of "diffusion restriction" when interpreting clinical high b-value DW images and ADC maps.

Key words: Apparent diffusion coefficient, Slow diffusion coefficient, Intravoxel incoherent motion model, Diffusion restriction

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