Microwave-excited hybrid thermoacoustic and ultrasound imaging with microwave pulse-width modulation

We present a method that allows for hybrid microwave-excited thermoacoustic and ultrasound (HMTAU) imaging without an additional ultrasound transmitting circuitry. The same microwave pulse is used to simultaneously generate thermoacoustic (TA) signals from the sample by the thermoacoustic effect, and ultrasound (US) signals from the piezoelectric transducer by the inverse piezoelectric effect. The same transducer collects the US signals reflected from the sample as a result of the US pulse (pulse-echo) and the TA signals as a result of the sample absorbing microwaves. Experiments are conducted to show how the microwave pulse-width significantly impacts the excitation efficiency of ultrasonic waves, which can reduce the requirement for microwave power. We found that the mechanical response of the US transducer to this transient expansion shows a maximum if the pulse-width of the microwave is close to half of the center period of the US transducer. We also use phantom experiments to demonstrate the complementary contrast mechanisms of the two modalities. The results obtained indicate that our method offers the potential of a low-cost dual-modality technique for noninvasive biomedical imaging.