Early detection of radiation-induced liver injury in rat by superparamagnetic iron oxide-enhanced MR imaging.

The detectability of early liver injury induced by irradiation was studied using magnetic resonance (MR) imaging enhanced with superparamagnetic iron oxide (SPIO), a tissue-specific contrast agent against the reticuloendothelial system (RES). In rat, 3 days after focal irradiation (0-10 Gy), MR imaging was performed and specimens were obtained to observe the phagocytic function of RES. The irradiated portion of the liver was visualized with a clear demarcation from the nonirradiated part by SPIO-enhanced MR images as a decrease in negative enhancement reflecting the function of RES (P < 0.05), whereas this was impossible with nonenhanced MR images. Significant regression was observed as a dose-related change of the signal intensity in the irradiated portion on SPIO-enhanced MR images (R = 0.867, P < 0.0001). SPIO-enhanced MR imaging was reliable for detecting the range and extent of liver injury a few days after low-dose irradiation, and it may be a useful procedure for verifying the target area in clinical cases of radiation therapy.