Comparison of lymph node metastases assessment with the use of USPIO-enhanced MR imaging at 1.5 T versus 3.0 T in a rabbit model.
OBJECTIVE
To prospectively compare the diagnostic performances of 1.5 T and 3.0 T ultrasmall superparamagnetic iron oxide (USPIO)-enhanced magnetic resonance imaging (MRI) for the detection of lymph node (LN) metastases in a rabbit model.


METHODS
Experiments were approved by the animal care committee. VX2 carcinomas were implanted into the thighs of 18 rabbits 3 or 4 weeks before MRI examinations. T2-weighted 1.5 T and 3.0 T MRI was performed 24 hours after USPIO (2.6 mg/kg iron) administration. Two radiologists calculated signal intensity (SI) ratios (ie, the ratios of postcontrast to precontrast signal intensity) of each LN and also evaluated for the presence of a metastasis in the iliac and retroperitoneal LNs at 1.5 T and 3.0 T MRI. Student's t-test, receiver operating characteristic (ROC) curve analysis, and a Z test were used for the statistical analysis.


RESULTS
Metastases were confirmed in 45 of 80 LNs by histopathology. For benign LNs the mean SI ratio at 1.5 T was higher (0.538) than at 3.0 T (0.463) (P = 0.004). In qualitative analysis, 1.5 T and 3.0 T USPIO-enhanced MRI showed similar Az values (0.951 vs. 0.939; P = 0.296). The specificity of 3.0 T USPIO-enhanced MRI was higher (91.4% [32 of 35]) than that of 1.5 T imaging (82.9% [29 of 35]) (P = 0.013); however, the sensitivities (88.9% [40 of 45]) were the same in the both modalities.


CONCLUSIONS
3.0 T USPIO-enhanced MRI shows a higher specificity as compared to 1.5 T imaging without a significant difference of sensitivity in a rabbit VX2 model.
Choi
Seung Hong
SH
Department of Radiology and Clinical Research Institute, Seoul National University Hospital, and Institute of Radiation Medicine, Seoul National University College of Medicine, Seoul, Korea.
Kim
Keon Ha
KH
Moon
Woo Kyung
WK
Kim
Hyo-Cheol
HC
Cha
Joo Hee
JH
Paik
Jin Ho
JH
Chang
Kee-Hyun
KH
D000818:Animals; D002277:Carcinoma / Q000175:diagnosis* / Q000556:secondary*; D045744:Cell Line, Tumor; D003287:Contrast Media; D003911:Dextrans; D004195:Disease Models, Animal; D052203:Ferrosoferric Oxide; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008198:Lymph Nodes / Q000473:pathology*; D008207:Lymphatic Metastasis; D008279:Magnetic Resonance Imaging / Q000379:methods*; D058185:Magnetite Nanoparticles; D011817:Rabbits; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; C097921:ferumoxtran-10; D052203:Ferrosoferric Oxide