On the optimization of imaging protocol for the mapping of cerebrovascular reactivity.
On the optimization of imaging protocol for the mapping of cerebrovascular reactivity.
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DOI：
10.1002/jmri.25028
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发表时间：
2016-03
期刊：
影响因子：
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通讯作者：
Lu H
中科院分区：
文献类型：
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作者：
Ravi H;Thomas BP;Peng SL;Liu H;Lu H
设计一种用于脑血管反应性(CVR)测量的改进的血氧水平依赖(BOLD)成像方案，该方案可以消除已知的负值伪影。首先对负CVR信号的生物物理机制进行了理论和仿真研究，并提出了改进的BOLD序列参数。这是通过缩短BOLD序列的回声时间(TE)使脑脊液(CSF)和血液之间的信号强度相等来实现的。然后，我们招募了10名健康志愿者参与了一项实验研究，在3T时，我们比较了两个版本的优化方案(OPT1和OPT2)与标准方案的CVR结果。对每个受试者进行两次会议，以测试所有三种方案的重复性。实验结果表明，优化后的算法消除了负CVR体素。对不同方案的定量CVR结果进行了比较，结果表明，优化方案的CVR值(OPT1：0.16±0.01%BOLD/mm HgCO2；OPT2：0.15±0.01%BOLD/mm HgCO2)比(p<；0.001)标准方案(0.21±0.01%BOLD/mm HgCO2)小，但CNR与标准方案相当(P=0.10)。三种方案的重复性变异系数分别为5.6±1.4%、6.3±1.6%和6.9±0.9%，但差异无统计学意义(p=0.65)。根据这项研究的理论和实验结果，我们建议使用比fMRI中使用的TE更短的TE，以最大限度地减少CVR结果中的负面伪影。
To devise an improved Blood-Oxygen-Level-Dependent (BOLD) imaging protocol for cerebrovascular reactivity (CVR) measurement that can remove a known artifact of negative values. Theoretical and simulation studies were first performed to understand the biophysical mechanism of the negative CVR signals, through which improved BOLD sequence parameters were proposed. This was achieved by equating signal intensities between cerebrospinal fluid (CSF) and blood, via shortening the echo time (TE) of the BOLD sequence. Then, ten healthy volunteers were recruited to participate in an experimental study, in which we compared the CVR results of two versions of the optimized (“Opt1” and “Opt2”) protocols to that of the standard protocol at 3T. Two sessions were performed for each subject to test the reproducibility of all three protocols. Experimental results demonstrated that the optimized protocols resulted in elimination of negative-CVR voxels. Quantitative CVR results were compared across protocols, which show that the optimized protocols yielded smaller CVR values (Opt1: 0.16±0.01 %BOLD/mmHg CO2; Opt2: 0.15±0.01 %BOLD/mmHg CO2) than (p<0.001) the standard protocol (0.21±0.01 %BOLD/mmHg CO2), but the CNR was comparable (p=0.1) to the standard protocol. The coefficient-of-variation between repetitions was found to be 5.6±1.4%, 6.3±1.6% and 6.9±0.9% for the three protocols, but there were no significant differences (p=0.65). Based on the theoretical and experimental results obtained from this study, we suggest that the use of a TE shorter than those used in fMRI is necessary in order to minimize negative artifact in CVR results.