Acceleration of Multi-b-value Multi-shot Diffusion-weighted Imaging using Interleaved Keyhole-EPI and Locally Low Rank Reconstruction.

Muti-b-value Diffusion Weighted Imaging (DWI) is commonly used in clinical and neuroscientific applications. The traditional single-shot Echo-Planer Imaging (EPI) sequence suffers from low image resolution. Although the multi-shot EPI sequence can increase spatial resolution, the multi-shot k-space sampling causes linearly increased scan time. An interleaved EPI acquisition can significantly reduce the scan time; however, the dynamic change of image phase and image contrast causes aliasing artifacts. To improve the scan efficiency and preserve the image quality, an interleaved keyhole-EPI multi-b-value multi-shot sequence is proposed, with the image reconstruction formulated as a Locally Low Rank (LLR) constrained problem. The resultant cost function is minimized by a computationally efficient ADMM algorithm. The proposed method was compared with interleaved EPI acquisition using the state-of-the-art SPatial-Angular Locally Low Rank (SPA-LLR) algorithm in two healthy subjects. The results showed that the proposed method achieved superior image quality and fewer aliasing artifacts compared with the state-of-the-art method in both the raw DWI images and Apparent Diffusion Coefficient (ADC) maps.