Scanning microwave-induced thermoacoustic tomography: Signal, resolution, and contrast

Scanning thermoacoustic tomography was explored in the microwave region of the electromagnetic spectrum. Short microwave pulses were used to induce ac oustic waves by thermoelastic expansion in biological tissues. Cross sectio ns of tissue samples were imaged by a linear scan of the samples while a fo cused ultrasonic transducer detected the time-resolved thermoacoustic signa ls. Based on the microwave-absorption properties of normal and cancerous br east tissues, the piezoelectric signals in response to the thermoacoustic c ontrast were investigated over a wide range of electromagnetic frequencies and depths of tumor locations. The axial resolution is related to the tempo ral profile of the microwave pulses and to the impulse response of the ultr asonic transducer. The lateral resolution is related to the numerical apert ure of the ultrasonic transducer as well as to the frequency spectra of the piezoelectric signals in the time window corresponding to the axial resolu tion. Gain compensation, counteracting the microwave attenuation, was appli ed to enhance the image contrast. (C) 2001 American Association of Physicis ts in Medicine.