[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.