  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.
