Contrast-enhanced MR imaging of two superparamagnetic RES-contrast agents:Functional assessment of experimental radiation-induced liver injury

The purpose of this study was to compare liver contrast-enhancing character istics of two superparamagnetic reticuloendothelial system (RES)-directed a gents with different particle sizes, polycrystalline iron oxide nanocompoun ds (PION) and carboxydextran-coated maghemite (DDM128N/389, later referred to as DDM128), in an experimental model of focal radiation-induced hepatiti s, PION, for the small particle size (31 nm), and DDM128, for the large par ticle size (59 nm), RES-directed agents were compared for liver enhancement after radiation-induced lives injury. A single x-irradiation exposure vary ing from 10 to 60 Gy was delivered to one side of the liver, Ta-weighted sp in-echo magnetic resonance imaging was performed 3 days after x-irradiation at 30 minutes post-contrast. Using the RES-directed PION, the normal, non- irradiated portion of the liver decreased in signal intensity with a maximu m negative enhancement of -66%, while the irradiated portion of the liver d ecreased in signal intensity by -24% (60 Gy). The signal intensity decline of irradiated liver tissue using PION was dose dependent, but was found at all radiation dose levels (10-60 Gy), The difference in signal intensity be tween irradiated (-63%) and non-irradiated (-82%) portions was also statist ically different using DDM128 at 60 Gy, However, lower irradiation doses (1 0 and 30 Gy) failed to produce a statistically significantly different enha ncement in the irradiated and non-irradiated portion of the liver. Sensitiv ity of liver enhancement with RES-directed agents is size dependent. The sm aller particle (PION) is more sensitive for detection of radiation-induced hepatitis than the larger particle (DDM128). The relative insensitivity of DDM128 enhancement for diffuse liver injury will be clinically advantageous for detecting focal lesions in the presence of diffuse hepatic injury. J. Magn. Reson. Imaging 1999; 10:52-56. (C) 1999 Wiley-Liss, Inc.