Detection of experimental hepatic tumors using long circulating - Superparamagnetic particles

RATIONALE AND OBJECTIVES. TO evaluate the potential of an iron oxide-based MR contrast agent for the detection and delineation of experimental liver t umors during the early vascular phase of the compound. METHODS. Superparamagnetic blood pool agent (SBPA) was administered intrave nously to rabbits bearing VX2 tumors. Images were acquired before the injec tion, immediately after, and 1 or 3 weeks later. The variations of signal i ntensity were measured in the tumors and in several tissues for various T1- weighted spin-echo, T2-weighted fast spin-echo, and T2-weighted gradient-re called-echo sequences. RESULTS. Fourteen and 12 of the 16 tumors were detected immediately after S BPA injection using, respectively, the T2-weighted fast spin-echo and T2-we ighted gradient-recalled-echo sequences, A significant decrease in signal i ntensity was observed in well-perfused organs, and blood signal was abolish ed even at the lowest injected dose and using a T1-weighted sequence. In th e late phase, the loss in signal intensity of the liver was even more prono unced. CONCLUSION. The dominant T2 effect of SBPA induces an increase in the tumor -to-liver and tumor-to-blood contrast during the vascular phase, improving the detection of the tumors and allowing the distinction between small lesi ons and vessels through plane. This effect on the Liver signal persists for several days because of the incorporation of SBPA in the reticuloendotheli al system.