Enhanced 4D diffusion-weighted PROPELLER echo-planar imaging with collaborative blade reconstruction

Objective: Four-dimensional diffusion-weighted imaging (4D-DWI) offers enhanced soft-tissue contrast for image-guided radiotherapy (IGRT) compared to conventional 4D-MRI. However, its clinical application has been hindered by geometric distortion or prolonged acquisition times. This study introduces an improved respiratory-correlated 4D-DWI technique to address these critical limitations. Approach: The proposed 4D-DW-PROP-EPI-JBCR technique consists of four key steps: data acquisition, coil sensitivity and phase error maps estimation, retrospective data sorting, and a core joint-blade collaborative reconstruction (JBCR) step. We primarily evaluated its performance against the previous 4D-DW-PROPELLER-EPI via both simulations and in vivo experiments. Evaluation metrics covered k-space uniformity requirements, point spread function (PSF) quality, minimum required repeated acquisitions, image quality, geometric fidelity, and acquisition time. Image quality was assessed using peak signal-to-noise ratio (PSNR), structural similarity (SSIM), high-frequency error norm (HFEN), and signal-to-noise ratio (SNR); geometric fidelity was evaluated via Dice similarity coefficient (DSC) and Hausdorff distance (HD). Paired t-tests were used for metric comparisons, with statistical significance set at P < 0.05. Main results: Compared to 4D-DW-PROPELLER-EPI, the proposed 4D-DW-PROP-EPI-JBCR eliminates the requirement for strict k-space uniformity while achieving enhanced PSFs with fewer acquisitions. Additionally, 4D-DW-PROP-EPI-JBCR yields significant improvements in image quality relative to 4D-DW-PROPELLER-EPI across all key metrics: SSIM (0.83–0.92 vs. 0.81–0.90, P < 0.05), PSNR (20.56–25.20 vs. 20.24–24.48, P < 0.05), HFEN (0.49–0.678 vs. 0.52–0.80, P < 0.05), and SNR (31.1–32.6 dB vs. 28.6–29.5 dB, P < 0.05). It also exhibits excellent geometric fidelity, as evidenced by DSC and HD. Most notably, all these performance gains are achieved using only 70 blades per diffusion direction, compared to the conventional 90 blades required by 4D-DW-PROPELLER-EPI. Significance: By enabling distortion-free respiratory-correlated 4D-DWI and reducing acquisition time by 22% relative to 4D-DW-PROPELLER-EPI, the 4D-DW-PROP-EPI-JBCR technique markedly improves the clinical utility of 4D-DWI for abdominal IGRT.