On the application of a non-CPMG single-shot fast spin-echo sequence to diffusion tensor MRI of the human brain

The strong sensitivity of Carr-Purcell-Meiboom-Gill (CPMG) fast spin-echo (FSE) sequences, such as rapid acquisition with relaxation enhancement (RARE), to the phase of the prepared transverse magnetization means that artifact-free single-shot diffusion-weighted images can currently only be obtained with a 30-50% reduction in the signal-to-noise ratio (SNR). However, this phase sensitivity and signal loss can be addressed in FSE sequences that use quadratic phase modulation of the radiofrequency (RF) refocusing pulses to generate a sustained train of stable echoes. Here the first application of such a non-CPMG single-shot FSE (ssFSE) sequence to diffusion tensor MR imaging (DT-MRI) of the human brain is described. This approach provides high SNR diffusion-weighted images that have little or no susceptibility to poor B(0) magnetic field homogeneity and the strong eddy currents typically present in DT-MRI experiments.