Effects of the apparent transverse relaxation time on cerebral blood flow measurements obtained by arterial spin labeling
Effects of the apparent transverse relaxation time on cerebral blood flow measurements obtained by arterial spin labeling
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DOI：
10.1002/mrm.20364
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发表时间：
2005-02-01
影响因子：
3.3
通讯作者：
Wang, J
中科院分区：
文献类型：
--
作者：
Lawrence, KSS;Wang, J
以前的建模研究预测，动脉自旋标记(ASL)实验中很大一部分信号来自毛细血管中标记的水。如果血液和组织中的松弛时间相似，ASL数据仍然可以用传统的一室Kty模型进行分析。这类研究主要集中在T-1差异，而忽略了横向弛豫时间(T-2和T-2*)的任何差异。这对于低视野的研究是合理的；然而，由于脱氧血液的更强的敏感性效应，它可能在高视野下无效。在这项研究中，建立了一个包括毛细血管血液和组织之间的T-2*差的示踪动力学模型。该模型预测，高场下血液T-2*的减少将减弱毛细血管对ASL信号的贡献。当用一室Kty模型分析ASL数据时，这反过来又导致对CBF的低估。我们通过比较在1.5T和4T以及在多个梯度回波(19、32、45和58ms)下收集的ASL数据证实了这一预测。静息状态脑血流量在4T时随回波时间(TE)而减少，而在1.5T时未见下降。这些结果表明，在较高的磁场下，应该使用短TES的梯度回波技术或自旋回波技术来收集AST数据。此外，CBF测量对静脉T-2的敏感性可能会影响对同时进行的ASUBOLD研究的解释。(C)2005年Wiley-Liss，Inc.
Previous modeling studies have predicted that a significant fraction of the signal in arterial spin labeling (ASL) experiments originates from labeled water in the capillaries. Provided that the relaxation times in blood and tissue are similar, ASL data can still be analyzed with the conventional one-compartment Kety model. Such studies have primarily focused on T-1 differences and have neglected any differences in transverse relaxation times (T-2 and T-2*). This is reasonable for studies at lower fields; however, it may not be valid at higher fields due to the stronger susceptibility effects of deoxygenated blood. In this study a tracer kinetic model was developed that includes T-2* differences between capillary blood and tissue. The model predicts that a reduction in blood T-2* at higher fields will attenuate the capillary contribution to the ASL signal. This in turn causes an underestimation of CBF when ASL data are analyzed with the one-compartment Kety model. We confirmed this prediction by comparing ASL data collected at 1.5 and 4 T, and at multiple gradient echoes (19, 32, 45, and 58 ms). A decrease in resting-state CBF with echo time (TE) was observed at 4 T, but not at 1.5T. These results suggest that at higher fields AST data should be collected using gradient-echo techniques with short TEs, or with spin-echo techniques. Furthermore, the sensitivity of the CBF measurements to venous T-2* may affect the interpretation of concurrent ASUBOLD studies. (C) 2005 Wiley-Liss, Inc.