MRI T2-Weighted Imaging and Fat-Suppressed T2-Weighted Imaging Image Fusion Technology Improves Image Discriminability for the Evaluation of Anal Fistulas

ABSTRACT

OBJECTIVE: To explore whether MRI fusion technology (combined T2-weighted imaging [T2WI] and fat-suppressed T2WI [T2WI-(FS)]) improves signal differences between anal fistulas and surrounding structures. MATERIALS AND METHODS: A total of 32 patients with confirmed diagnoses of anal fistula were retrospectively studied. All available T2WI and T2WI-(FS) images for each patient were used to generate fusion image (T2WI-(Fusion)) based on the addition of gray values obtained from each pixel via an MR post-processing work station. The discriminability of fistula, perianal sphincter, and perianal fat in T2WI, T2WI-(FS), and T2WI-(Fusion) images was quantified with Fisher's scoring algorithm. For subjective visual image assessment by researchers, five-point scale scores were determined using a modified double-stimulus continuous quality-scale test to evaluate T2WI-(FS), T2WI, enhanced axial three-dimensional-volumetric interpolated breath-hold examination (3D-VIBE), and T2WI-(Fusion) sequence images. The differences were subsequently compared. RESULTS: Mean Fisher scores for fistulas vs. sphincters obtained from T2WI-(Fusion) (F(Fusion-fistula) = 6.56) were significantly higher than those from T2WI (F(T2WI-fistula) = 3.35) (p = 0.001). Mean Fisher scores for sphincters vs. fat from T2WI-(Fusion) (F(Fusion-sphincter) = 10.84) were significantly higher than those from T2WI-(FS) (FS(FS-sphincter) = 2.57) (p = 0.001). In human assessment, T2WI-(Fusion) showed the same fistula discriminability as T2WI-(FS), and better sphincter discriminability than T2WI. Overall, T2WI-(Fusion) showed better discriminability than T2WI, T2WI-(FS), and enhanced 3D-VIBE images. CONCLUSION: T2WI and T2WI-(FS) fusion technology improves signal differences between anal fistulas and surrounding structures, and may facilitate better evaluation of anal fistulas and sphincters.