DIFFUSION-WEIGHTED MR MICROSCOPY WITH FAST SPIN-ECHO

A diffusion-weighted fast spin-echo (FSE) imaging sequence for high-fi eld MR microscopy was developed and experimentally validated in a phan tom and in a live rat. Pulsed diffusion gradients were executed before and after the initial 180-degrees pulse in the FSE pulse train. This produced diffusion-related reductions in image signal intensity corres ponding to gradient (''b'') factors between 1.80 and 1352 s/mm2. The d egree of diffusion weighting was demonstrated to be independent of ech o train length for experiments using trains up to 16 echoes long. Quan titative measurements on a phantom and on a live rat produced diffusio n coefficients consistent with literature values. Importantly, the eig ht- to 16-fold increase in imaging efficiency with FSE was not accompa nied by a significant loss of spatial resolution or contrast. This per mits acquisition of in vivo three-dimensional data in time periods tha t are appropriate for evolving biological processes. The combination o f accurate diffusion weighting and high spatial resolution provided by FSE makes the technique particularly useful for MR microscopy.