Microwave-Induced Thermoacoustic Imaging of Subcutaneous Vasculature With Near-Field RF Excitation

Imaging of subcutaneous vasculature is of great interest for biometric security and point-of-care medicine. We investigate the feasibility of microwave-induced thermoacoustic (TA) tomography as a safe, compact, low-power, and cost-effective imaging technique for subcutaneous vasculature by means of application-specific design of near-field, radio frequency (RF) applicators. Using commercial transducers, we demonstrate proof-of-concept TA imaging of synthetic phantoms, plant vasculature, and earthworm blood vessels with only 50 W of peak power, or 42 mW average power, at 300 μm resolution. The proposed RF applicator design enabled uniform, orientation-independent illumination of vasculature phantoms with only 10% variation. Finally, we show that the benefits of microwave contrast make possible the distinction of actual blood vessels, in an earthworm, from surrounding tissue within a modest receiver dynamic range of 40 dB.