Diffusion-weighted radial fast spin-echo for high-resolution diffusion tensor imaging at 3T.

There is a need for an imaging sequence that can provide high-resolution diffusion tensor images at 3T near air-tissue interfaces. By employing a radial fast spin-echo (FSE) collection in conjunction with magnitude filtered back-projection reconstruction, high-resolution diffusion-weighted images can be produced without susceptibility artifacts. However, violation of the Carr-Purcell-Meiboom-Gill (CPMG) condition of diffusion prepared magnetization is a prominent problem for FSE trains that is magnified at higher fields. The unique aspect of violating the CPMG condition in trajectories that oversample the center of k-space and the implications for choosing the solution are examined. For collecting diffusion-weighted radial-FSE data at 3T we propose mixed-CPMG phase cycling of RF refocusing pulses combined with a 300% wider refocusing than excitation slice. It is shown that this approach produces accurate diffusion values in a phantom, and can be used to collect undistorted, high-resolution diffusion tensor images of the human brain.