Gadolinium-free extracellular MR contrast agent for tumor imaging.

PurposeTo 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 MethodsA 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). T-1 relaxation time measurements and DCE-MRI were performed. ResultsEnhancement and clearance patterns were visually similar between MnTCP and Gd-DTPA. However, relative R-1 increases in all 11 tumors were larger for MnTCP over 60 minutes postcontrast, the difference being significant as late as 20 minutes (R-1post/R-1pre=1.420.15 for MnTCP vs. 1.20 +/- 0.08 for Gd-DTPA, P<0.05). R-1-related effects for MnTCP were largely reduced after 60 minutes (R-1post/R-1pre=1.13 +/- 0.07) and completely gone within 24 hours (R-1post/R-1pre=0.97 +/- 0.06). DCE-MRI revealed a consistently larger (1.5 to over 2-fold) peak enhancement and higher values of the steepest slope, time-to-peak, and AUC(60) in all tumors with MnTCP (P<0.01). ConclusionMnTCP is an alternative to extracellular Gd agents for tumor imaging, offering sensitive detection and rapid renal clearance. J. Magn. Reson. Imaging 2015;41:397-403.(c) 2013 Wiley Periodicals, Inc.