Tilted-CAIPI for highly accelerated distortion-free EPI with point spread function (PSF) encoding

Abstract

Purpose: To develop a method for fast distortion- and blurring-free imaging.

Theory: EPI with point-spread-function (PSF) mapping can achieve distortion- and blurring-free imaging at a cost of long acquisition time. In this study, an acquisition/reconstruction technique, termed "tilted-CAIPI," is proposed to achieve >20× acceleration for PSF-EPI. The proposed method systematically optimized the k-space sampling trajectory with B₀ -inhomogeneity-informed reconstruction, to exploit the inherent signal correlation in PSF-EPI and take full advantage of coil sensitivity. Susceptibility-induced phase accumulation is regarded as an additional encoding that is estimated by calibration data and integrated into reconstruction. Self-navigated phase correction was developed to correct shot-to-shot phase variation in diffusion imaging.

Methods: Tilted-CAIPI was implemented at 3T, with incorporation of partial Fourier and simultaneous multislice to achieve further accelerations. T₂ -weighted, T₂^* -weighted, and diffusion-weighted imaging experiments were conducted to evaluate the proposed method.

Results: The ability of tilted-CAIPI to provide highly accelerated imaging without distortion and blurring was demonstrated through in vivo brain experiments, where only 8 shots per simultaneous slice group were required to provide high-quality, high-SNR imaging at 0.8-1 mm resolution.

Conclusion: Tilted-CAIPI achieved fast distortion- and blurring-free imaging with high SNR. Whole-brain T₂ -weighted, T₂^* -weighted, and diffusion imaging can be obtained in just 15-60 s.

Keywords: diffusion imaging; distortion correction; echo-planar imaging; parallel imaging; point spread function mapping.