Iron-Based Coupling Medium: Comprehensive Report to FUS Foundation

This report gives comprehensive review of the nano-emulsion project between UVA and Virginia Tech which has been generously supported by the Focused Ultrasound Foundation. The purpose of this project is to develop an acoustic coupling bath that is effectively invisible to MRI scans and also remains acoustically compatible with clinical transcranial FUS procedures. This remains important to the clinical translation of FUS because the commonly used acoustic coupling bath of degassed water persistently degrades the quality of MR guidance imaging. Our project proposes an acoustic coupling bath doped with specially designed iron oxide nanoparticles that 1) have a high ability to decay MRI signals, (as quantified by the r2 relaxivity), 2) have diameters less than 100 nm, and 3) are coated with a hydrophilic coating. We hypothesize that these three innovations will produce a lightly doped water bath with identical mechanical, acoustic, thermal, biocompatibility, and electromagnetic properties as water, but with virtually no observable appearance or effect on guidance MR imaging. Finally, the low particle concentrations, small particle sizes, and specific coating will prevent the particles from stabilizing gas bubbles and seeding cavitation nuclei in the transducer’s pre-focal field.We are pleased to report nearly total success on this project, with an affirmation of all hypotheses stated above.