In-plane Simultaneous Multi-segment (IP-SMS) Imaging Using a 2D RF Pulse

PURPOSE: To develop an in-plane simultaneous multi-segment (IP-SMS) imaging technique using a 2D RF pulse and to demonstrate its ability to achieve high spatial resolution in echo planar imaging (EPI) while reducing image distortion. METHODS: The proposed IP-SMS technique takes advantage of periodic replicates of the excitation profile of a 2D RF pulse to simultaneously excite multiple segments within a slice. These segments were acquired over a reduced field-of-view (FOV) and separated using a joint GRAPPA reconstruction by leveraging virtual coils that combined the physical coil sensitivity and 2D RF pulse spatial response. Two excitations were employed with complementary spatial response profiles to adequately cover a full FOV, producing a full-FOV image that had the benefits of reduced FOV with high spatial resolution and reduced distortion. The IP-SMS technique was implemented in a diffusion-weighted single-shot EPI sequence. Experimental demonstrations were performed on a phantom and healthy human brain. RESULTS: In the phantom experiment, IP-SMS enabled a four-fold acceleration using an eight-channel coil without causing residual aliasing artifacts. In the human brain experiment, diffusion-weighted images with high in-plane resolution (1×1 mm(2)) and substantially reduced image distortion were obtained in all imaging planes in comparison with a commercial diffusion-weighted EPI sequence. The capability of IP-SMS for contiguous whole-brain coverage was also demonstrated. CONCLUSION: The proposed IP-SMS technique can realize the benefits of reduced-FOV imaging while achieving a full-FOV coverage with good image quality and time efficiency.