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Lymph Node Metastasis: Ultrasmall Superparamagnetic Iron Oxide–enhanced MR Imaging versus PET/CT in a Rabbit Model¹

¹ From the Department of Radiology and Clinical Research Institute, Seoul National University Hospital, and Institute of Radiation Medicine, Seoul National University College of Medicine, 28 Yongon-dong, Chongno-gu, Seoul 110-744, Korea (S.H.C., W.K.M., K.R.S., N.C., B.J.K.); Department of Radiology, College of Medicine, Chung Buk National University, Cheongju, Korea (J.H.H.); Departments of Nuclear Medicine (J.J.L., J.K.C.) and Pathology (H.S.M.), Seoul National University Hospital, Seoul, Korea; and Department of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea (S.H.P.). Received January 16, 2006; revision requested March 22; revision received April 4; accepted May 9; final version accepted July 7. Supported by a grant from the National R & D Program for Cancer Control, Ministry of Health and Welfare, Republic of Korea (0420080-1). Address correspondence to W.K.M. (e-mail: moonwk{at}radcom.snu.ac.kr).

Purpose: To prospectively compare the diagnostic accuracy of ultrasmall superparamagnetic iron oxide (USPIO)-enhanced magnetic resonance (MR) imaging and integrated positron emission tomography–computed tomography (PET/CT) for the depiction of lymph node metastasis in an animal model, with histologic findings as the reference standard.

Materials and Methods: This experiment was approved by the local animal care committee. VX2 carcinoma was implanted into the thighs of 11 rabbits 4 weeks before the imaging study. T2- and T2*-weighted MR examinations were performed 24 hours after USPIO administration, followed by integrated PET/CT. USPIO-enhanced MR imaging and PET/CT analysis for the evaluation of the presence of metastasis in iliac lymph nodes were performed independently by two radiologists and two nuclear medicine physicians, respectively, without histopathologic knowledge. Results were evaluated by using receiver operating characteristic (ROC) analysis, and sensitivities and specificities were compared by using a Z test.

Results: Metastases were histopathologically confirmed in 22 of 62 iliac lymph nodes. USPIO-enhanced MR imaging showed a significantly greater area under the ROC curve than did PET/CT (0.984 vs 0.852; P = .023). The respective sensitivity and specificity for the detection of lymph node metastasis were 91% (20 of 22) and 95% (38 of 40) for USPIO-enhanced MR imaging and 64% (14 of 22) and 98% (39 of 40) for PET/CT. In terms of sensitivity, a significant difference was found between USPIO-enhanced MR imaging and PET/CT, particularly for nodal metastasis of less than 5 mm (86% [six of seven] vs 0% [zero of seven]; P = .031), whereas the specificity of the two imaging modalities was similar (P = .226).

Conclusion: USPIO-enhanced MR imaging results in higher diagnostic accuracy for depicting lymph node metastasis than does PET/CT.

© RSNA, 2006