Magnetic liposomal phase convertible nanodroplets as bimodal contrast agent for ultrasound and magnetic resonance imaging

Multimodal imaging is a recent idea of combining two or more imaging methods synergistically to overcome the weakness of individual imaging modalities and utilizing complementary benefits. Ultrasound (US) and magnetic resonance imaging (MRI) are widely used imaging techniques in healthcare. To fully utilize the potential of fusion imaging, bimodal contrast agents are necessary to improve disease diagnosis by enhancing contrast resolution and reducing health risks associated with the dual dosage of contrast agents. In this study, magnetic liposomal phase convertible nano droplets (PCNDs) were synthesized by incorporating oleic acid stabilized superparamagnetic iron oxide nanoparticles (OA-SPIONs) into lecithin microbubbles, encapsulating the perfluoropentane (PFP) core. The magnetic PCNDs were characterized by FTIR, SEM, MFM, zeta potential, in vitro MRI, and ultrasound. Upon in vitro MRI, magnetic PCNDs showed a negative contrast effect by producing darker T2 weighted images. The PCNDs showed concentration-dependent response with a decrease in signal intensity with an increase in the concentration of OA-IONP in microbubbles. However, a decrease in acoustic enhancement was also observed with an increase in OA-IONP concentration, therefore concentration was optimized to achieve the best effect on both modalities. The magnetic liposomal PCND with 10 mg SPIONs provided the best contrast on both US and MR imaging. The hemocompatibility testing resulted in hemolysis less than 7% with plasma recalcification time and thrombin time of 240 s and 6 s corresponding to excellent hemocompatibility. The biocompatibility testing on MCF-7 lines was performed that showed PCNDs to be biocompatible. Thus the magnetic liposomal phase convertible PFP nanodroplet can serve as a potential bimodal contrast agent for both US and MRI imaging.