Ferumoxtran-10-enhanced MR lymphangiography: Does contrast-enhanced imaging alone suffice for accurate lymph node characterization?

OBJECTIVE. Ferumoxtran-10 is a lymphotropic MR contrast agent that is currently under investigation. It has been shown to be effective in staging lymph nodes of patients with various primary malignancies. The current technique with ferumoxtran-10 involves imaging before and 24 hr after contrast administration. The purpose of this study was to evaluate the accuracy of ferumoxtran-10-enhanced images alone in characterizing lymph nodes for oncologic staging 24 hr after contrast enhancement. MATERIALS AND METHODS. Seventy-seven patients (58 men. 19 women) with proven primary cancer(bladder [n = 20], breast [n = 10], endometrial [n = 1], renal [n = 3], penile [n = 4], prostate [n = 31], rectal [n = 1], testicular [n = 5], and ureteral [n = 2]) who were scheduled for surgical lymph node dissection were enrolled in the study. In these patients, 169 lymph nodes (mean size, 11.2 mm) were evaluated on T2*-weighted gradient-refocused echo MRI at 1.5 T both before and 24-36 hr after the IV administration of ferumoxtran-10 (2.6 mg Fe/kg). Two blinded reviewers with differing levels of interpreting experience separately performed qualitative image evaluation. A 6-point scale was used to characterize lymph nodes on contrast-enhanced images alone and on combined unenhanced and contrast-enhanced images. Receiver operating characteristic (ROC) analysis was, performed separately for both reviewers. RESULTS. Of the 169 lymph nodes evaluated, 55 were benign and 114 malignant by histopathologic analysis. The results of the ROC analysis comparing contrast-enhanced images ([A(z)= areaunder ROC curve] reviewer 1, A(z)= 0.92; reviewer 2, A(z)= 0.94) alone with combined unenhanced and contrast-enhanced images (reviewer 1, A(z)= 0.94; reviewer 2, A(z)= 0.93) showed a statistically significant difference (p = 0.01) for reviewer I but no difference for reviewer 2 (p = 0.88). Reviewer 2 was more experienced in interpreting ferumoxtran-10-enhanced images than reviewer 1. CONCLUSION. On ferumoxtran-10-enhanced MR lymphangiography, contrast-enhanced images alone may suffice for lymph node characterization, However, a certain level of interpretation experience may be required before contrast-enhanced images can be used alone.