3D multi-slab is SNR-efficient for isotropic high-resolution diffusion imaging. It can be combined with simultaneous multi-slice, namely SMSlab, for optimal SNR efficiency. In multi-slab, either 2D or 3D navigators can be acquired for inter-shot phase correction, while in SMSlab, only 2D navigators can be acquired. One study has proposed to synthesize a 3D navigator from a 2D navigator in SMSlab, yet lacking a comparison. This study compares the performance of 2D, 3D acquired and synthesized navigators. The synthesized 3D navigator shows similar performance with the acquired 3D navigator in multi-slab and outperforms the 2D navigator in both multi-slab and SMSlab.