Iron oxide nanoparticles as a contrast agent for thermoacoustic tomography

Abstract

An exogenous contrast agent has been developed to enhance the contrast achievable in Thermoacoustic Tomography (TAT). TAT utilizes the penetration depth of microwave energy while producing high resolution images through acoustic waves. A sample irradiated by a microwave source expands due to thermoelastic expansion. The acoustic wave created by this expansion is recorded by an ultrasonic transducer. The water content in biological samples poses an obstacle, as it is the primary absorber of microwave radiation. The addition of an exogenous contrast agent improves image quality by more effectively converting microwave energy to heat. The use of iron oxide nanoparticles in MRI applications has been explored but super paramagnetic iron oxide nanoparticles (SPION) have benefits in microwave applications, as well. Through ferromagnetic resonance, SPION samples more effectively convert microwave energy into heat. This transduction to heat creates significantly larger thermoacoustic waves than water, alone. Characterization of the SPION samples is executed through TAT, TEM, XPS, EDS, and a vector network analyzer with a dielectric probe kit. Onedimensional and phantom model imaging with an iron oxide nanoparticle contrast agent provide a two-fold improvement in contrast at current system configurations. Further enhancement is possible through adjustments to the nanoparticles and TAT system.