Ring enhancement in ultrasmall superparamagnetic iron oxide MR imaging: a potential new sign for characterization of liver lesions.

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Abstract
We performed this study to evaluate the incidence and significance of ring enhancement after i.v. administration of an ultrasmall superparamagnetic iron oxide (USPIO) particle (Code 7227), a reticuloendothelial contrast agent with potential use as a blood-pool agent, for characterizing focal hepatic lesions. Conventional T1-weighed imaging, fat-suppressed T1-weighted imaging, conventional T2-weighted imaging, and fast T2-weighted imaging of the liver were obtained in 27 patients with 43 liver lesions before and after i.v. administration of a USPIO preparation. All lesions were larger than 1 cm; 29 were malignant and 14 were benign. Diagnosis was confirmed in all cases, either pathologically (19 patients) or by follow-up examination (eight patients). Two readers independently evaluated each pulse sequence for the presence of ring enhancement of hepatic lesions. Ring enhancement was noted only on T1-weighted images, with no ring enhancement evident on T2-weighted images. Twenty of 43 (47%) lesions showed ring enhancement, including 18 of 29 (62%) malignant lesions and two of 14 (14%) benign lesions (p < .011); Wilcoxon signed rank test). Fat-suppressed T1-weighted imaging showed ring enhancement better than or equal to conventional T1-weighted imaging in all cases, with ring enhancement of 15 of 18 (83%) malignant lesions and two of two benign lesions better demonstrated on fat-suppressed T1-weighted imaging sequences (p < or = .025). Ring enhancement after i.v. administration of Code 7227 is a frequent finding seen more often with malignant than benign lesions, potentially identifying a new MR imaging feature for the characterization of liver lesions. The identification of ring enhancement on T1-weighted images attests to the significant blood-pool effects of USPIO particles.

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