Parallel imaging strategies for high-speed magnetic resonance diffusion imaging

By using multiple receiver coils in conjunction with parallel MR signal reception, the speed of image acquisition can be dramatically increased. In this work the feasibility of such parallel imaging (PI) methods for fast brain imaging was studied along with their potential application for diffusion- weighted imaging (DWI). All measurements were performed by using a four-element prototype-surface coil. Parallel image reconstruction in the image domain was performed off-line on a dedicated MR image processing workstation. For appropriate image quality, coil sensitivity maps must be of sufficient quality or must be properly filtered. Thus, a novel filtering method was employed. By means of diffusion-weighted single- shot PI, the advantage of motion insensitivity of single shot echo-planar imaging (EPI) and the increased k-space velocity of multi-shot EPI can be combined; hence, they need not be phase navigated. Therefore, the images are free from ghostings, and artifacts arising from resonance offsets (e.g., B0, susceptibility artifacts, and chemical shift) are less prominent than in conventional single-shot EPI. Furthermore, image blurring was markedly reduced. Preliminary results in neuroimaging promise that PI can become a helpful tool for rapid imaging in the CNS, although further improvement of coil sensitivity is required for sufficient SNR in parallel DWI.