A comparison between different imaging strategies for diffusion measurements with the centric phase-encoded turboFLASH sequence.

The study compared the results of three centrally reordered phase-encoded turboFLASH sequences for diffusion-weighted imaging (DWI). The sequences were conventional turboFLASH, turboFLASH with subtraction of T1-related effects, and turboFLASH with correction for T1-related effects during the imaging period only. The relative merits were studied with respect to image quality and accuracy by computer simulation and by experimental validation on phantoms and on in vivo rat brain. A T1-related underestimation of the diffusion coefficient ranging from -30% (T1 approximately 200 ms) to -5% (T1 approximately 1 s) was found to exist for the conventional sequence. Image artifacts, caused by longitudinal relaxation during the imaging period, are reflected in calculated diffusion maps. When the correction sequence is used, the artifacts and the systematic errors are reduced but longitudinal relaxation during the delay between preparation and imaging periods remains large enough to induce significant errors (-15% for T1 approximately 200 ms to -3% for T1 approximately 1 s). The subtraction sequence eliminates the influence of T1 effects on the calibrations, but leads to identical artifacts for all diffusion-weighted images.