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

<i>Objective.</i>Four-dimensional diffusion-weighted imaging (4D-DWI) offers enhanced soft-tissue contrast for image-guided radiotherapy (IGRT) compared to conventional 4D-magnetic resonance imaging. 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.<i>Approach.</i>The proposed 4D-DW-PROP-EPI-JBCR technique consists of four stages: data acquisition, coil sensitivity and phase error maps estimation, retrospective data sorting, and a joint-blade collaborative reconstruction (JBCR) step. We evaluated its performance against the previous 4D-DW-PROPELLER-EPI using both simulations and<i>in vivo</i>experiments. Evaluation metrics included<i>k</i>-space uniformity requirements, point spread function (PSF) quality, minimum required sampling factor (SF), 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<i>t</i>-tests were used for metric comparisons, with statistical significance set at<i>P</i>< 0.05.<i>Main results.</i>Compared to 4D-DW-PROPELLER-EPI, the proposed 4D-DW-PROP-EPI-JBCR eliminated the requirement for strict<i>k</i>-space uniformity while achieving enhanced PSFs with fewer acquisitions. Additionally, 4D-DW-PROP-EPI-JBCR yielded significant improvements in image quality compared to 4D-DW-PROPELLER-EPI across all key metrics: SSIM (0.83-0.92 vs 0.81-0.90,<i>P</i>< 0.05), PSNR (20.56-25.20 vs 20.24-24.48,<i>P</i>< 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,<i>P</i>< 0.05). It also exhibited excellent geometric fidelity, as evidenced by DSC (0.90 ± 0.03) and HD (2.37 ± 1.12). Notably, these performance gains were achieved with an SF of 1.9 per diffusion direction, compared to the SF of 2.4 for 4D-DW-PROPELLER-EPI.<i>Significance.</i>By enabling distortion-free respiratory-correlated 4D-DWI and reducing SF by more than 20% compared to 4D-DW-PROPELLER-EPI, the 4D-DW-PROP-EPI-JBCR technique markedly improves the clinical utility of 4D-DWI for abdominal IGRT.