Multimodal contrast agent for combined computed tomography and magnetic resonance imaging applications

The objective of this study was to examine the feasibility of a multimodal system to effectively induce and maintain contrast enhancement in both computed tomography (CT) and magnetic resonance (MR) for radiation therapy applications.

The physicochemical characteristics of a liposome-encapsulated iohexol and gadoteridol formulation were assessed in terms of agent loading efficiencies, size and morphology, in vitro stability, and release kinetics. The imaging properties of the liposome formulation were assessed based on T1 and T2 relaxivity measurements and in vitro CT and MR imaging in a phantom. A preliminary imaging-based evaluation of the in vivo stability of this multimodal contrast agent was also performed in a lupine model.

The average agent loading levels achieved were 26.5+/-3.8 mg/mL for iodine and 6.6+/- 1.5 mg/mL for gadolinium. These concentrations correspond to approximately 10% of that found in the commercially available preparations of each of these agents. However, this liposome-based formulation is expected to have a smaller volume of distribution and prolonged circulation lifetime in vivo. This multimodal system was found to have high agent retention in vitro, which translated into maintained contrast enhancement (up to 3 days) and stability in vivo.

This study demonstrated the feasibility of engineering a multimodal contrast agent with prolonged contrast enhancement in vivo for use in CT and MR. This contrast agent may serve as a valuable tool for cardiovascular imaging as well as image registration and guidance applications in radiation therapy.