Evaluation of Early Imaging Response After Chemoembolization of Hepatocellular Carcinoma by Phosphorus-31 Magnetic Resonance Spectroscopy—Initial Experience

Abstract

Purpose To evaluate the value of phosphorus-31 ( 31P) magnetic resonance (MR) spectroscopy in early monitoring and predicting the response of hepatocellular carcinoma (HCC) after chemoembolization. Materials and Methods The authors evaluated 17 HCC target tumors with 31P MR spectroscopy before and after chemoembolization. Alterations of phosphorus metabolism were analyzed by the MR spectroscopy analysis package (SAGE 7.0; GE Medical Systems, Milwaukee, Wisconsin). Ratios of the peak areas of phosphomonoesters (PME), phosphodiesters (PDE), and inorganic phosphate (Pi) to the peak area of nucleoside triphosphates (NTP) or the total phosphorus content (TPC) were measured. The changes in these ratios after chemoembolization were calculated from baseline (before chemoembolization). The therapy effect was assessed by computed tomography (CT) or MR imaging 4 weeks after chemoembolization. The ability of phosphorus metabolism in monitoring therapy effect was evaluated by using receiver operating characteristic analysis. Results Decreases in the PDE/NTP ratio (Wilcoxon signed rank test, P = .024) and the PDE/TPC ratio (Wilcoxon signed rank test, P = .011) that occurred after treatment were the most remarkable changes secondary to chemoembolization. Of the 17 lesions evaluated quantitatively, at the follow-up examination done 4 weeks after chemoembolization, 12 lesions were responsive to chemoembolization, whereas 5 were not. In the responsive group, the PDE/TPC ratio (median 24.15% vs 13.15%; P = .008) was significantly decreased after chemoembolization, whereas the NTP/TPC ratio (median 37.35% vs 49.9%; P = .024) was significantly increased. In the nonresponsive group, phosphorus metabolism had no significant changes after treatment. Results from the receiver operating curve analysis showed that the threshold percentage change of the PDE/NTP (%PDE/NTP) value was −1.25% with 91.7% sensitivity and 100% specificity for identifying tumor response to chemoembolization, and the threshold percentage change of the NTP/TPC (%NTP/NTP) value was 15.3% with 75% sensitivity and 100% specificity. Conclusions Phosphorus-31 MR spectroscopy is a promising technique for the noninvasive assessment of HCC response to chemoembolization. Future studies are necessary to confirm these preliminary results.