Coherent frequency-domain microwave-induced thermoacoustic imaging

Microwave-induced thermoacoustic (TA) imaging combines the soft-tissue contrast of microwave signals with the resolution of ultrasound (US) imaging without posing any ionizing radiation. Prior work uses short but powerful pulses from a large vacuum source to excite tissue and requires an output power in excess of several kW to achieve sufficient SNR. This poses safety concerns as well as to render the imager large and bulky. In this paper, we propose and demonstrate stepped-frequency continuous-wave (SFCW) and frequency-modulated continuous-wave (FMCW) approaches for microwave-induced thermoacoustic imaging at 2GHz. In the experiment, the FMCW approach achieves a 26dB SNR improvement compared to pulse approach with the same peak output power, averaging window, and receiver gain. To the best of our knowledge this is the first demonstration of full coherency across microwave and acoustic domains with the thermo-elastic response and successful demonstration of frequency-domain microwave TA imaging.