Improvement of non-contact measurement of propagation characteristics in tissues using pass-through airborne ultrasound

Measurement and evaluation of ultrasonic propagation characteristics in cancellous bone is one of the diagnosis methods of osteoporosis. Non-contact measurement of propagation characteristics in a heel using airborne ultrasound which passed through the heel has been proposed. The pass-through ultrasound is extremely attenuated due to large reflections at boundaries between air and heel surfaces. In the proposed method, therefore, the signal-to-noise ratio of the pass-through ultrasound is greatly improved by pulse compression using an higher-order M-sequence. Furthermore, the pass-through ultrasound also inflects at the boundaries. Therefore, the direction of the ultrasonic beam varies depending on the shape of the heel. In this paper, a method for reception of the pass-through ultrasound by considering inflections at the boundaries is described.