Diffusion imaging with the MP-RAGE sequence.

Diffusion-weighted magnetic resonance (MR) images obtained with conventional spin-echo techniques are known to be sensitive to subject motion because of long image acquisition times. To reduce the acquisition time, use of a magnetization-prepared rapid gradient-echo (MP-RAGE) sequence modified for diffusion sensitivity was studied. In this sequence, a preparation phase with a 90 degrees-180 degrees-90 degrees pulse train is used to sensitize the magnetization to diffusion. Centric-ordered phase encoding, short TRs (5.2-6.5 msec), and small flip angles (5 degrees-8 degrees) are necessary to minimize saturation effects from tissues with short relaxation times. Phantom studies with various concentrations of copper sulfate (T1 ranging from 2,459 to 90 msec) were performed to validate that the diffusion-weighted signal obtained with the MP-RAGE sequence was independent of relaxation time. Diffusion-weighted images of water, isopropyl alcohol, and acetone were acquired to confirm the accuracy of measured diffusion coefficients. Brain images of healthy normal volunteers were obtained to demonstrate motion insensitivity and general image quality of the technique. The results indicate that accurate diffusion-weighted images can be obtained with a diffusion-weighted MP-RAGE sequence, with imaging times of about 1 second.