Lymph node metastasis: ultrasmall superparamagnetic iron oxide-enhanced MR imaging versus PET/CT in a rabbit model.
OBJECTIVE
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.


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).


CONCLUSIONS
USPIO-enhanced MR imaging results in higher diagnostic accuracy for depicting lymph node metastasis than does PET/CT.
Choi
Seung Hong
SH
Department of Radiology and Clinical Research Institute, Seoul National University Hospital, Korea.
Moon
Woo Kyung
WK
Hong
Ju Hee
JH
Son
Kyu Ri
KR
Cho
Nariya
N
Kwon
Bae Ju
BJ
Lee
Jong Jin
JJ
Chung
June-Key
JK
Min
Hye Sook
HS
Park
Seong Ho
SH
D000818:Animals; D002277:Carcinoma / Q000175:diagnosis* / Q000556:secondary*; D003287:Contrast Media; D003911:Dextrans; D004195:Disease Models, Animal; D052203:Ferrosoferric Oxide; D007089:Image Enhancement / Q000379:methods*; D007501:Iron; D008198:Lymph Nodes / Q000000981:diagnostic imaging / Q000473:pathology*; D008207:Lymphatic Metastasis / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D058185:Magnetite Nanoparticles; D010087:Oxides; D049268:Positron-Emission Tomography; D011817:Rabbits; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed
D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; D010087:Oxides; C097921:ferumoxtran-10; D007501:Iron; D052203:Ferrosoferric Oxide