Optimizing enhanced hybrid medical imaging through dual-mode contrast agents

Only recently, dual-mode agents able to combine ultrasound and magnetic resonance imaging have been proposed. In this paper, two types of innovative dual-mode contrast agents are investigated and compared in terms of imaging performance. Existing ultrasound contrast agents composed of gas-filled microbubbles covered by a polymeric shell were modified to obtain dual-mode contrast agents. Different densities of superparamagnetic iron oxide nanoparticles were anchored to the external bubble surface or physically embedded into the bubble shell. The goal of this paper is to individuate the setup parameters and imaging techniques able to optimize the microbubble detection with both imaging modalities. Moreover, the type of dual-mode agent and nanoparticle density that offer the best balance between magnetic resonance and ultrasound contrast enhancement is identified. In vitro imaging experiments were carried out by applying low magnetic field (0.25 T), low acoustic pressures (<; 300 kPa) and low concentrations of dual-mode contrast agents. Modified microbubbles with nanoparticles loaded on the external shell surface were found to provide the best contrast both in ultrasound and magnetic resonance imaging.