3D Diffusion MRI Using Simultaneous Multi-slab with Blipped-CAIPI (Blipped-SMSlab) in a 4D K-space Framework

Purpose: To develop an efficient simultaneous multi-slab imaging method with blipped-controlled aliasing in parallel imaging (blipped-SMSlab) in a 4D k-space framework, and demonstrate its efficacy in high-resolution diffusion MRI (dMRI). Theory and Methods: First, the SMSlab 4D k-space signal expression is formulated, and the phase interferences from intra-slab and inter-slab encodings on the same physical z axis are analyzed. Then, the blipped-SMSlab dMRI sequence is designed, with blipped-CAIPI gradients for inter-slab encoding, and a 2D multi-band accelerated navigator for inter-kz-shot phase correction. Third, strategies are developed to remove the phase interferences, by RF phase modulation and/or phase correction during reconstruction, thus decoupling intra-slab and inter-slab encodings that are otherwise entangled. In vivo experiments are performed to validate the blipped-SMSlab method, and preliminarily evaluate its performance in high-resolution dMRI compared with traditional 2D imaging. Results: In the 4D k-space framework, inter-slab and intra-slab phase interferences of blipped-SMSlab are successfully removed using the proposed strategies. Compared with non-CAIPI sampling, the blipped-SMSlab acquisition reduces the g-factor and g-factor-related SNR penalty by about 12%. In addition, in vivo experiments show the SNR advantage of blipped-SMSlab dMRI over traditional 2D dMRI for 1.3 and 1.0 mm isotropic resolution imaging with matched acquisition time. Conclusion: Removing inter-slab and intra-slab phase interferences enables SMSlab dMRI with blipped-CAIPI in a 4D k-space framework. The proposed blipped-SMSlab dMRI is demonstrated to be more SNR-efficient than 2D dMRI and thus capable of high-quality, high-resolution fiber orientation detection.