Comparison of diffusion-weighted MRI and 2-[fluorine-18]-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) for detecting primary colorectal cancer and regional lymph node metastases

Purpose To examine the usefulness of diffusion‐weighted MRI (DW‐MRI) for the detection of both primary colorectal cancer and regional lymph node metastases, and compare its performance with 2‐[fluorine‐18]‐fluoro‐2‐deoxy‐D‐glucose positron emission tomography (FDG‐PET) in the same patients. Materials and Methods We studied 25 patients with known colorectal cancer. All underwent both DW‐MRI and FDG‐PET studies. The images were retrospectively assessed by visual inspection and the imaging findings were compared with histopathological findings on surgical specimens. Results Of the 27 primary colorectal lesions surgically excised in 25 patients, 23 (85.2%) were true‐positive on both DW‐MRI and FDG‐PET. Two cancers were false‐negative on DW‐MRI but true‐positive on FDG‐PET, and two were false‐negative on both DW‐MRI and FDG‐PET. With respect to the detectability of metastatic lymph nodes, DW‐MRI and FDG‐PET manifested a sensitivity of 80% (8/10) and 30.0% (3/10), a specificity of 76.9% (10/13) and 100% (13/13), and an accuracy of 78.3% (18/23) and 69.6% (16/23), respectively. Conclusion DW‐MRI is inferior to FDG‐PET for the detection of primary lesions, but superior for the detection of lymph node metastases. J. Magn. Reson. Imaging 2009;29:336–340. © 2009 Wiley‐Liss, Inc.