Sagittal FOCUS-MUSE Diffusion-weighted Imaging MRI Improves the Accuracy of Rectal Cancer Location: A Prospective Observational Study.

Rationale And Objectives: Precise preoperative location on MRI is critical for rectal cancer management. This study aimed to evaluate whether integrating sagittal FOCUS-MUSE diffusion-weighted imaging (SDWI) sequence into MRI would improve the accuracy of the distance from tumor's inferior boundary to the anal verge (DTAV) measurements.

Methods: Consecutive 96 biopsy-confirmed rectal cancer patients underwent preoperative rigid rectoscopy (RRS), PET/CT, and rectal MRI (with/without SDWI) within one month. DTAV measurements from two MRI protocols (protocol 1: conventional sequences; protocol 2: including SDWI sequence) were compared against RRS (primary reference) and PET/CT (secondary reference), respectively. Interobserver agreement and Pearson's correlation coefficient (r) between modalities were analyzed. The Bland-Altman method was used for the graphical representation of agreement. Diagnostic performance of two MRI protocols for low rectal cancer under different reference standards was evaluated using ROC curves and Delong's test.

Results: The reviewers showed excellent interobserver agreement (ICC > 0.8) for PET/CT and protocol 2, rather than protocol 1. In addition, protocol 2 demonstrated stronger correlations with reference standards: RRS vs. protocol 1: r = 0.849 (P < 0.001), RRS vs. protocol 2: r = 0.969 (P < 0.001), PET/CT vs. protocol 1: r = 0.856 (P < 0.001), PET/CT vs. protocol 2: r = 0.974 (P < 0.001). Regardless of the reference standard (RRS or PET/CT), protocol 2 exhibited superior diagnostic performance in identifying low rectal cancer, with higher sensitivity, specificity, PPV, NPV, and AUC compared to protocol 1. ROC analysis further confirmed protocol 2's enhanced accuracy.

Conclusion: Incorporating SDWI sequence into standard MRI protocols would make the results of DTAV measurements more accurate for rectal cancer, precisely determining the location of the tumor and helping surgeons to make appropriate preoperative plans and clinical decisions.