Pelvic MRI and CT Images are Interchangeable for Measuring Peripouch Fat

Abstract

Introduction: CT and MRI images are reported to be interchangeable for quantifying abdominal subcutaneous fat and visceral fat distribution, but it is unknown for measuring peripouch fat. Our previous study showed that increased fat plane on MRI was associated with poor pouch outcomes. Our aim was to assess the agreement in measurement of peripouch fat between pelvic MRI-DIXON and CT imaging. Methods: Pouch patients with inflammatory bowel diseases, who underwent pelvic MRI-DIXON and CT scan within one year, were included. Peripouch fat areas were measured at the middle height level of pouch (AreaM) and the highest level of pouch (AreaH). Measurements of perianal fat thickness, AreaM and AreaH were gained from CT and MRI images. Intraobserver and interobserver agreements were assessed with scatter plots and Bland-Altman graphs. Results: A total of 27 patients with both pelvic MRI-DIXON and CT images were included. Scatter plots showed that measurements of perianal fat thickness, AreaM and AreaH based on MRI image were highly accurate and reproducible (correlation efficiency(r): intraobserver: 0.984-0.991; interobserver: 0.969-0.971; all P < 0.001). Bland-Altman graphs analysis showed that more than 92.593% (25/27) of dots fell within the limits of agreement. We also identified strong agreements between CT and MRI image in measuring perianal fat thickness(r=0.823, P < 0.001), AreaM (r=0.773, P < 0.001) and AreaH (r=0.862, P < 0.001). Interchangeable calculating formula to normalize measurements between CT and MRI images were created: Thickness_CT = 0.610×Thickness_MRI + 0.853; AreaM_CT = 0.865×AreaM_MRI + 1.392; AreaH_CT = 0.508×AreaH_MRI + 15.001. Conclusion: Pelvic MRI image is a feasible and reproducible method for quantifying peripouch fat. Pelvic MRI and CT images are interchangeable in retrospective measurements of peripouch fat, which will foster future investigation of the role of mesentery fat in colorectal diseases.