Detection of small primary and secondary malignant hepatic tumors with superparamagnetic iron oxide-enhanced magnetic resonance imaging

Background: Superparamagnetic iron oxide (SPIO) is a new paramagnetic contrast agent used to distinguish benign and malignant hepatic tumors on magnetic resonance imaging (MRI). Objective: This prospective study was designed to compare detectability of malignant hepatic tumors using gadolinium (Gd) versus SPIO-enhanced (MRI). Methods: We selected fifteen patients suspected of malignant hepatic tumors of less than 5 cm in size. They included hepatocellular carcinoma (HCC) and hepatic metastasis. A dynamic Gd-enhanced study was performed first and followed by SPIO-enhanced study with time interval of 4 hours to one week. We performed fast spin echo T2 weighted image (FSE T2WI) with fat suppression, fast multiplana gradient echo T2* weighted image (FMPGR T2*WI), and single-shot FSE T2WI with fat suppression on SPIO study. All lesions were confirmed by histopathology, high Alpha fetoprotein level or follow up imaging. Both studies were analyzed by two independent radiologists. Results: The study included 11 cases (6 HCCs and 5 metastases). Four cases of benign lesions and unconfirmed diagnosis were excluded (2 cases of regenerating nodules and 2 cases of unconfirmed diagnosis). Range of sizes was 0.5-7.5 cm (mean = 2.0 cm). In quantitative analysis, SPIO could detect higher numbers of lesions compared with Gd, especially for small lesions (≤ 2 cm) and for HCCs. There was no difference between SPIO and Gd for detection of large malignant lesions (\>2 cm). Gd-enhanced MRI was better than SPIO for detection of the numbers of hepatic metastases. SPIO showed better imaging quality compared to Gd and the best MR sequence was FMPGR T2*WI. Conclusion: SPIO-enhanced MRI was superior to Gd-enhanced MRI for detection of small HCC, whereas Gd-enhanced MRI was better for detection of small hepatic metastases.