Time‐dependent diffusion MRI using multiple stimulated echoes

Abstract

PurposeTo develop a time‐efficient pulse sequence that acquires multiple diffusion‐weighted images with distinct diffusion times in a single shot by using multiple stimulated echoes (mSTE) with variable flip angles (VFA).MethodsThe proposed diffusion‐weighted mSTE with VFA (DW‐mSTE‐VFA) sequence begins with two 90° RF pulses that straddle a diffusion gradient lobe (GD) to excite and restore one half of the magnetization into the longitudinal axis. The restored longitudinal magnetization was successively re‐excited by a series of RF pulses with VFA, each followed by another GD, to generate a set of stimulated echoes. Each of the multiple stimulated echoes was acquired with an EPI echo train. As such, the train of multiple stimulated echoes produced a set of diffusion‐weighted images with varying diffusion times in a single shot. This technique was experimentally demonstrated on a diffusion phantom, a fruit, and healthy human brain and prostate at 3 T.ResultsIn the phantom experiment, the mean ADC measured at different diffusion times using DW‐mSTE‐VFA were highly consistent (r = 0.999) with those from a commercial spin‐echo diffusion‐weighted EPI sequence. In the fruit and brain experiments, DW‐mSTE‐VFA exhibited similar diffusion‐time dependence to a standard diffusion‐weighted stimulated echo sequence. The ADC showed significant time dependence in the human brain (p = 0.003 in both white matter and gray matter) and prostate tissues (p = 0.003 in both peripheral zone and central gland).ConclusionDW‐mSTE‐VFA offers a time‐efficient tool for investigating the diffusion‐time dependency in diffusion MRI studies.