Original Research Evaluation of Lymph Node Metastases: Comparison of Gadofluorine M-Enhanced MRI and Diffusion- Weighted MRI in a Rabbit VX2 Rectal Cancer Model Seung Ho Kim, MD, 1 Jeong Min Lee, MD, 2 * Sung Kyoung Moon, MD, 3 Yong Eun Chung, MD, 4 Jin Ho Paik, MD, 5 Seung Hong Choi, MD, 2 Min Uk Kim, MD, 2 Joon Koo Han, MD, 2 and Byung Ihn Choi, MD 2 Purpose: To compare the diagnostic performance of a dif- fusion-weighted imaging (DWI) dataset and a gadofluorine M-enhanced imaging dataset for identifying lymph node (LN) metastases in a rabbit rectal cancer model. Materials and Methods: VX2 carcinomas were injected into the rectum of 26 rabbits. Four weeks later, T2- weighted imaging (T2WI), pre-T1WI, DWI, and post-T1WI were performed. Two radiologists independently reviewed the DWI set (T2WI, pre-T1WI, DWI) and the gadofluorine M set (T2WI, pre- and post-T1WI) and recorded their con- fidence scores for LN metastasis on a per-LN basis. Re- ceiver operating characteristic (ROC) analysis was per- formed to compare the area under the ROC curve (A z ) of the two imaging sets. Histopathologic results were used as the reference standard. Results: The A z and sensitivity of the gadofluorine M set were comparable to those of the DWI set (A z , for reader 1, 0.849, 0.829, P ¼ 0.571; for reader 2, 0.923, 0.876, P ¼ 0.212; sensitivity, for reader 1, 97%, 97%; for reader 2, 97%, 92%, P ¼ 0.304). The specificity of the former was greater than that of the latter (for reader 1, 65%, 53%, P ¼ 0.0003; for reader 2, 81%, 68%, P ¼ 0.01). Conclusion: Gadofluorine M-enhanced images provided greater specificity than DWI for identifying LN metastases, whereas the A z and sensitivity of the former were compa- rable to those of the latter. Key Words: experimental study; diffusion weighted mag- netic resonance imaging; gadofluorine M; apparent diffu- sion coefficient; lymph node J. Magn. Reson. Imaging 2012;35:1179–1186. V C 2012 Wiley Periodicals, Inc. COLORECTAL CANCER is the third most common cancer and the third leading cause of cancer-related death in the United States, with a 5-year survival rate reported to be 66% (1). In its treatment, neoadjuvant chemoradiation therapy (CRT) has been considered the standard of care for locally advanced rectal cancer (T3 stage, which is defined as tumor invades through the rectal wall into perirectal soft tissues or lymph node [LN] metastasis), since several investiga- tors demonstrated that neoadjuvant CRT was able to significantly decrease the local recurrence rate (2,3). As LN metastasis has been singled out to be an important prognostic factor related to disease-free survival and to the local recurrence rate (4), accurate preoperative diagnosis of LN metastasis in patients with rectal cancer is crucial not only for obtaining the optimal prognosis but also for appropriate selection of patients who will derive the most benefit from neoad- juvant CRT. However, although magnetic resonance imaging (MRI) is an excellent diagnostic tool for tu- mor-staging due to its excellent soft-tissue contrast and ability to depict all mesorectal structures (5–7), its accuracy for LN-staging has been reported to be in the range of 43%–85% (6–8). This wide range of accu- racy and relatively poor sensitivity of 66% suggest that the MR criterion for the detection of LN metasta- ses, ie, LN size, is not a reliable discriminator for met- astatic LNs (8–11). Although several attempts have been made to increase the poor sensitivity of MR for LN metastases by adding morphologic criteria such as border and internal signal intensity (11), these mor- phologic criteria seem to have intrinsic limitations in small LNs less than 5 mm in diameter (9–11). More recently, other approaches, including diffu- sion-weighted MRI (DWI) (12–15) and lymphotropic contrast agents such as gadofluorine M (16–18), have 1 Department of Radiology, Haeundae Paik Hospital, Inje University College of Medicine, Busan, Korea. 2 Department of Radiology, Seoul National University College of Medicine, Seoul, Korea. 3 Department of Radiology, Kyung Hee University Medical Center, School of Medicine, Kyung Hee University, Seoul, Republic of Korea. 4 Department of Radiology, Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea. 5 Department of Pathology, Seoul National University Bundang Hospital, Gyeonggi-do, Korea. Contract grant sponsor: Korean Health Technology R&D Project, Ministry for Health, Welfare & Family Affairs, Republic of Korea; Contract grant number: A100048. *Address reprint requests to: J.M.L., Department of Radiology, Seoul National University College of Medicine, Yongon-dong 28, Chong- no-gu, 110-744, Seoul, Korea. E-mail: jmsh@snu.ac.kr Received May 12, 2011; Accepted October 26, 2011. DOI 10.1002/jmri.23513 View this article online at wileyonlinelibrary.com. JOURNAL OF MAGNETIC RESONANCE IMAGING 35:1179–1186 (2012) CME V C 2012 Wiley Periodicals, Inc. 1179