Focused ultrasound combined with magnetic resonance imaging (FUS/MRI) is a promising approach for noninvasive therapy that requires precise imaging of tissue using MRI to guide the FUS process. The MRI suffers from interference from water baths commonly used to transmit the focused ultrasound waves from a transmitter to the tissue. In this work, iron oxide nanoparticles were synthesized with a polymer coating using a rapid mixing process. These nanoparticles remain dispersed and unaggregated in aqueous suspension for periods of months or longer. The nanoparticles become magnetized in the presence of an external magnetic field and, in aqueous suspensions in a magnetic resonance imaging (MRI) device, serve to reduce or eliminate interference of the water in MRI imaging when the aqueous suspension is used as an acoustic coupling medium in a combined focused ultrasound/MRI (FUS/MRI) instrument. These aqueous suspensions also exhibit low tendency to generate bubbles in an FUS instrument. This combination of reduced imaging interference and reduced cavitation makes these aqueous suspensions of nanoparticles useful for significant improvements in using FUS/MRI technology for more precise, noninvasive therapies.
