HEPATIC MRI WITH SPIO - DETECTION AND CHARACTERIZATION OF FOCAL LIVER-LESIONS

A variety of parenterally administered iron oxides have been developed fur contrast-enhanced MRI of the liver. Two different classes of iron oxides are currently clinically approved or in phase 3 trials: superp aramagnetic iron oxides (SPIO) with a high R2/R1 relaxivity ratio and short blood half-life (AMI-25 and SH U 555 A), and ultrasmall paramagn etic iron oxides (USPIO) with a lower R2/R1 relaxivity ratio and longe r blood half-life (AMI-227). All iron oxides significantly increase tu mor-to-liver contrast and allow detection of more lesions than unenhan ced MRI on T2-weighted images at a field strength of 0.2-1.5 T. Malign ant lesions without phagocytic cells exhibit constant signal on T2-wei ghted accumulation phase images with all three iron oxides. All iron o xides cause a signal decrease of benign lesions with either phagocytic cells or a significant blood pool on T2-weighted accumulation phase i mages. The signal decrease of benign lesions is proportional to the Ku pffer cell activity or tumor vascularity and is useful for lesion char acterization. Another enhancement feature for the differentiation of b enign from malignant lesions is ring enhancement of malignant lesions (metastases) on T1-weighted enhanced images either during the perfusio n phase with SH U 555 A or during the accumulation phase with AMI-227, which is attributed to the blood pool effects of the compounds. Diffe rentiation of lesions and vessels is easier on enhanced images with an giographic effects than on unenhanced images. Iron oxides improve the quality of two-dimensional MR angiography techniques of the portal ven ous system by decreasing background signal (liver tissue with all iron oxides) and increasing intravascular signal (AMI-227). The use of iro n oxides for hepatic MRI provides an alternative to the existing multi step diagnosis with CT, CT portography, MRI and biopsy.