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A distinctive irregularity in the frequency response of a piezoelectric polymer film hydrophone, which is not predicted by the use of conventional theory, has been observed. It was confirmed in a previous study [Y. Nakamura and T. Otani, Jpn. J. Appl. Phys. Suppl. 31‐1 31, 266–268 (1992)] that the irregularity can be attributed to the radial resonance of a surface wave induced by the incident pressure on the hydrophone’s backing material. To estimate theoretically the frequency response of the hydrophone, the transient acoustic field on the receiving surface of the hydrophone was studied by time‐domain analysis. The field is theoretically described in the time domain as the superposition of an incident wave, a reflected plane wave, a diffracted edge wave, and a leaky elastic wave that originates from a surface wave propagating along the radius on the hydrophone’s backing material. The validity of the theoretical analysis of the acoustic field on receiving surface is verified by experimental observations. ...

Longitudinal wave in cancellous bone separates into fast and slow waves depending on the alignment of trabeculae. Here, the fast wave mainly propagates in trabeculae, whereas slow wave propagates in the soft tissue (bone marrow). Because these two waves usually overlap, the evaluation of each wave has still remained difficult. In this study, then, we have tried to evaluate the wave properties (attenuation and velocity), making use of the plane wave in an acoustic tube. 3-D image of the bone specimen was obtained by X-ray micro CT. In an acoustic tube, a cancellous bone specimen was set between home-made PVDF transducers. A function generator delivered a single sinusoidal signal in the range of 0.5 to 1.5 MHz to the transmitter. By filing a part of bone specimen away, we have tried to obtain the attenuation and velocity of the specimen. The two wave phenomenon clearly occurred in our specimen. In some trabecular bones of big animals, the wave separated perfectly. We have then tried to obtain ultrasonic pro...

The ultrasonic longitudinal wave in the cancellous bone is separated into two waves, fast and slow waves [1]. In this study, the relationship between the fast wave speed and the cancellous bone structure is experimentally investigated. A conventional ultrasonic pulse measurement was performed using a PVDF focus transmitter (Custom made, Toray) and a self‐made PVDF receiver. Cylindrical specimens of cancellous bone were taken from the head of bovine femur in the distal part, along the three orthogonal directions. The distribution of fast wave speed was obtained by changing the measurement position along the cylindrical axis. The anisotropy of speed was also investigated by rotating the specimens. The structural parameters of each specimen were also measured by X‐ray micro CT (MCT‐12505MF, Hitachi), which gave us the trabecular length and alignment from MIL (mean intercept length) parameters through TRI/3D‐Bon software (Ratoc). We found that the fast wave showed large distribution and strong anisotropy depending on the measurement positions and wave propagation directions in the specimens. The fast wave showed the maximum speed in case of wave propagation along the load direction. Reference [1] A. Hosokawa and T. Otani, J. Acoust. Soc. Am., 101, 558 (1997).

Effect of decreasing bone density (a symptom of osteoporosis) is greater for cancellous bone than for dense cortical bone, because cancellous bone is metabolically more active. Therefore, bone density or bone mineral density at cancellous bone is generally used to estimate the onset of osteoporosis. Elasticity or elastic constant is one of fundamental mechanical parameters and directly related to the mechanical strength of bone. Accordingly, elasticity is a preferable parameter to assess the fracture risk. A novel ultrasonic bone densitometer LD‐100 has been developed to obtain mass density and elasticity of cancellous bone with a spatial resolution comparable to that of the peripheral quantitative computed tomography system. Bone mass density and bone elasticity are evaluated using ultrasonic parameters based on fast and slow waves in cancellous bone using a modeling of ultrasonic wave propagation path. Elasticity is deduced from measured bone mass density and propagation speed of fast wave. Thus, elasti...

Cancellous bone is comprised of a connected network of trabeculae and is considered as an inhomogeneous and anisotropic acoustic medium. The fast and slow longitudinal waves are clearly observed when the ultrasonic wave propagates parallel to the direction of the trabeculae. The propagation speed of the fast wave increases with bone density and that of the slow wave is almost constant. The fast wave amplitude increases proportionally and the slow wave amplitude decreases inversely with bone density. Human in vitro femoral head was sectioned to 10‐mm‐thick slices perpendicularly to the femoral cervical axis. These cancellous bone samples were subjected to the ultrasonic measurement system LD‐100 using a narrow focused beam. The propagation speed and the amplitude of the transmitted wave both for the fast and slow waves were measured at 1‐mm intervals. The local bone density corresponding to the measured points was obtained using a microfocus x‐ray CT system. Experimental results show that the propagation speeds and amplitudes for the fast and slow waves are characterized not only by the local bone density, but also by the local trabecular structure.

Cancellous bone (spongy bone) is comprised of a porous network of numerous trabecular elements with soft tissue in the pore space. The effect of decreasing bone density, namely a symptom of osteoporosis, is greater for cancellous bone than for dense cortical bone (compact bone). Two longitudinal waves, the fast and slow waves, are clearly observed in cancellous bone, which correspond to ‘‘waves of the first and second kinds’’ as predicted by Biot’s theory. According to experimental and theoretical studies, the propagation speed of the fast wave increases with bone density and that of the slow wave is almost constant. Experimental results show that the fast wave amplitude increases proportionally and the slow wave amplitude decreases inversely with bone density. However, the attenuation constant of the fast wave is almost independent of bone density and the attenuation constant of the slow wave increases with bone density. The in vivo ultrasonic wave propagation path is composed of soft tissue, cortical bo...

Ultrasonic wave propagation in water‐saturated bovine cancellous (spongy) bone has been experimentally studied in vitro by a pulse transmission technique. Fast and slow longitudinal waves have been clearly observed in the earlier investigation when the acoustic wave propagates to the direction of the trabeculae orientation [A. Hosokawa and T. Otani, J. Acoust. Soc. Am. 101, 558–562 (1997)]. In the present study, propagation speeds of the fast and the slow waves were measured as a function of the propagation angle to the trabeculae orientation. Experimental results show that the propagation speed of the fast wave and the amplitude of the slow wave depend greatly on the angle to the trabeculae orientation, and the speed of the slow wave and the amplitude of the fast wave are little affected by the angle of the trabeculae orientation. The propagation speeds of both waves were also experimentally examined as a function of the porosity. Measured results are discussed in relation to the structural anisotropy an...