Gadolinium-free extracellular MR contrast agent for tumor imaging

Purpose To evaluate a new formulation of manganese porphyrin as a potential gadolinium (Gd)‐free extracellular magnetic resonance imaging (MRI) contrast agent for dynamic contrast‐enhanced (DCE) MRI of tumors. Materials and Methods A previously reported new contrast agent, MnTCP, was evaluated in six female tumor‐bearing nude rats. MRI was performed on a 3 T clinical scanner 3 to 4 weeks after inoculation of breast tumor cells in the mammary fat pads. Gd‐DTPA was injected intravenously, followed by injection of MnTCP at least 2 hours later (both at 0.05 mmol/kg). T1 relaxation time measurements and DCE‐MRI were performed. Results Enhancement and clearance patterns were visually similar between MnTCP and Gd‐DTPA. However, relative R1 increases in all 11 tumors were larger for MnTCP over 60 minutes postcontrast, the difference being significant as late as 20 minutes (R1post/R1pre = 1.42 ± 0.15 for MnTCP vs. 1.20 ± 0.08 for Gd‐DTPA, P