扩散时间及扩散梯度磁场对水分子表观扩散系数的影响

脉冲梯度自旋回波方法在磁共振扩散成像实验中得到广泛应用,扩散时间和扩散梯度磁场强度是脉冲梯度自旋回波方法中两个重要的参数.扩散时间对结果的影响在前人所作研究报告中存在争议, 扩散梯度磁场强度对结果的影响没有被重视.本研究用新的试验方法研究这两个参数对表观扩散系数的影响.结果显示,延长扩散时间或增加扩散梯度磁场强度均会使表观扩散系数值下降,原有理论不能解释此结果.通过理论分析,我们发现脉冲梯度自旋回波方法本身的一个缺陷, 并找到已发表文献中出现争议的原因.

Effects of Diffusion Time and Diffusion Gradient Magnetic Field on the Apparent Diffusion Coefficient of Water Molecules

Diffusion time and diffusion gradient magnetic strength are two important parameters of the pulsed gradient spin echo (PGSE) that is the most commonly used method in diffusion-weighted magnetic resonance imaging. However, the effects of the diffusion time on the apparent diffusion coefficient (ADC) in previous studies are controversial, and the effects of the diffusion gradient magnetic strength have received little attention. In this study, a new experimental protocol was designed to evaluate the effects of the two parameters on ADC. It was found that ADC decreased significantly with the increase of diffusion time or increase of diffusion gradient magnetic strength, which cannot be explained by the previous theories. Through theoretical analysis, we found the flaw of PGSE method, which is on explanation for the controversial results of diffusion time in former literatures.