DIFFUSION IMAGING WITH THE MP-RAGE SEQUENCE

Diffusion-weighted magnetic resonance (MR) images obtained with conven tional spin-echo techniques are known to be sensitive to subject motio n because of long image acquisition times, To reduce the acquisition t ime, use of a magnetization-prepared rapid gradient-echo (MP-RAGE) seq uence modified for diffusion sensitivity was studied. In this sequence , a preparation phase with a 90 degrees-180 degrees-90 degrees pulse t rain is used to sensitize the magnetization to diffusion. Centric-orde red 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 conc entrations of copper sulfate (T1 ranging from 2,459 to 90 msec) were p erformed to validate that the diffusion-weighted signal obtained with the MP-RAGE sequence was independent of relaxation time. Diffusion-wei ghted 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 inse nsitivity and general image quality of the technique. The results indi cate that accurate diffusion-weighted images can be obtained with a di ffusion-weighted MP-RAGE sequence, with imaging times of about 1 secon d.