Scanning thermoacoustic tomography in biological tissue

Microwave-induced thermoacoustic tomography was explored to image biologica l tissue. Short microwave pulses irradiated tissue to generate acoustic wav es by thermoelastic expansion. The microwave-induced thermoacoustic waves w ere detected with a focused ultrasonic transducer. Each time-domain signal from the ultrasonic transducer represented a one-dimensional image along th e acoustic axis of the ultrasonic transducer similar to an ultrasonic A-sca n. Scanning the system perpendicularly to the acoustic axis of the ultrason ic transducer would generate multi-dimensional images. Two-dimensional tomo graphic images of biological tissue were obtained with 3-GHz microwaves. Th e axial and lateral resolutions were characterized. The time-domain piezo-e lectric signal from the ultrasonic transducer in response to the thermoacou stic signal was simulated theoretically, and the theoretical result agreed with the experimental result very well. (C) 2000 American Association of Ph ysicists in Medicine. [S0094-2405(00)03105-9].