Evaluation of an ultrasmall superparamagnetic iron oxide in MRI in a bone tumor model in rabbits

Ultrasmall superparamagnetic iron oxides (USPIOs) are a class of MRI contrast agents having moderately selective affinity for the reticuloendothelial cells of lymph nodes and bone marrow. This study evaluated a USPIO preparation, Combidex (Code 7227), in MRI of a rabbit bone tumor model. VX2 carcinoma implanted into the tibial marrow of nine subject rabbits was studied. After tumor growth, the subjects underwent MRI of their lesions both before and after intravenous administration of Code 7227. Code 7227 was judged subjectively to conspicuously reduce the signal intensity of normal marrow on some pulse sequences. A hypointense zone outlined the tumor margins on postcontrast imaging, which allowed improved visualization of the soft tissue component of the larger lesions. Accumulation of the contrast agent in a zone of inflammation outside the tumor margin was demonstrated on histologic sections of the lesions. Code 7227 deserves additional study as a potential contrast agent for MRI of bone tumors.