Non-contact measurement of propagation speed in tissue-mimicking phantom using pass-through airborne ultrasound

The elastic properties of human tissues can be quantitatively evaluated from the ultrasonic propagation speed in tissues. To effectively propagate ultrasound in human tissues, ultrasonic transducers are typically brought into contact with tissue surfaces. In this study, the non-contact evaluation of human tissues using pass-through airborne ultrasound has been proposed. When airborne ultrasound propagates and passes through tissues, the pass-through wave is extremely attenuated. To detect the attenuated pass-through wave in the received signal, the signal-to-noise ratio (SNR) of the received signal is improved by pulse compression using a higher-order M-sequence in the proposed method. In this paper, the estimation of ultrasonic propagation speeds in tissue-mimicking phantoms is described. The urethane-rubber phantom and solutions of ethanol in water are used as the phantoms. The time of flight (TOF) of the pass-through wave in the phantom is determined from the wave front. The propagation speed in the phantom is estimated using the determined TOF. Propagation speeds in the urethane-rubber phantom and ethanol solutions can be estimated within errors of 3 and 2% in experiments.