Toshiyuki Tsujimoto

Effects of structural anisotropy of cancellous bone on speed of ultrasonic fast waves in the bovine femur

Ultrasonic waves in cancellous bone change dramatically depending on its structural complexity. One good example is the separation of an ultrasonic longitudinal wave into fast and slow waves during propagation. In this study, we examined fast wave propagation in cancellous bone obtained from the head of the bovine femur, taking the bone structure into consideration. We investigated the wave propagation perpendicular to the bone axis and found the two-wave phenomenon. By rotating the cylindrical cancellous bone specimen, changes in the fast wave speed due to the rotation angle then were observed. In addition to the ultrasonic evaluation, the structural anisotropy of each specimen was measured by X-ray micro-computed tomography (CT). From the CT images, we obtained the mean intercept length (MIL), degree of anisotropy (DA), and angle of insonification relative to the trabecular orientation. The ultrasonic and CT results showed that the fast wave speed was dependent on the structural anisotropy, especially on the trabecular orientation and length. The fast wave speeds always were higher for propagation parallel to the trabecular orientation. In addition, there was a strong correlation between the DA and the ratio between maximum and minimum speeds (Vmax/Vmin) (R2 = 0.63).

Influence of cancellous bone microstructure on two ultrasonic wave propagations in bovine femur: An in vitro study

The influence of cancellous bone microstructure on the ultrasonic wave propagation of fast and slow waves was experimentally investigated. Four spherical cancellous bone specimens extracted from two bovine femora were prepared for the estimation of acoustical and structural anisotropies of cancellous bone. In vitro measurements were performed using a PVDF transducer (excited by a single sinusoidal wave at 1 MHz) by rotating the spherical specimens. In addition, the mean intercept length (MIL) and bone volume fraction (BV/TV) were estimated by X-ray micro-computed tomography. Separation of the fast and slow waves was clearly observed in two specimens. The fast wave speed was strongly dependent on the wave propagation direction, with the maximum speed along the main trabecular direction. The fast wave speed increased with the MIL. The slow wave speed, however, was almost constant. The fast wave speeds were statistically higher, and their amplitudes were statistically lower in the case of wave separation than in that of wave overlap.

Estimation of In vivo Cancellous Bone Elasticity

The 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, the bone density or bone mineral density of cancellous bone is generally used to estimate the onset of osteoporosis. Elasticity or elastic constant is a fundamental mechanical parameter and is directly related to the mechanical strength of bone. Accordingly, elasticity is a preferable parameter for assessing fracture risk. A novel ultrasonic bone densitometer LD-100 has been developed to determine the mass density and elasticity of cancellous bone with a spatial resolution comparable to that of peripheral quantitative computed tomography. Bone density and bone elasticity are evaluated using ultrasonic parameters based on fast and slow waves in cancellous bone by modeling the ultrasonic wave propagation path. Elasticity is deduced from the measured bone density and the propagation speed of the fast wave. Thus, the elasticity of cancellous bone is approximately expressed by a cubic equation of bone density.

Ultrasonic Transmission Characteristics of In vitro Human Cancellous Bone

An ultrasonic wave transmitted through an in vitro human cancellous bone was experimentally investigated. An osteoporotic cancellous bone specimen was obtained from an in vitro femoral head. A narrow ultrasonic beam was scanned on the specimen surface over an area of 30×30 mm2 and the transmitted ultrasonic wave was obtained at an interval of 1 mm. Local bone densities corresponding to measurement points using the ultrasonic beam were obtained using a microfocus X-ray computed tomography system. Transmitted slow wave signals were detected at all measurements points; however, the measurable area of a fast wave was greatly reduced and limited because of the osteoporotic low-density specimen. The propagation speed of a slow wave was almost independent of bone density. The propagation speed of the fast wave and the amplitudes of the fast and slow waves considerably depended on bone density. The obtained results imply that the scattered values of the propagation speed of the fast wave and the amplitudes of the fast and slow waves reflect the ultrasonic characteristics of the cancellous bone, which depend on both the bone density and the trabecular macro- and micro-structures.

Generation Mechanism of Heat Flows near the Stack as a Prime Mover in a Thermoacoustic Cooling System

Temperature variations in a thermoacoustic cooling system consisting of a loop-tube were investigated. The heat flows were discussed using observation results of the temperature variations in the tube. The regenerator, stack 1, was employed as a prime mover and stack 2 as a heat pump. At the cooling point, on the stack 2, the temperature decrease of 22°C was confirmed. Heat flows did not appear in the location far from the stack 1 except near the stack 2. On the other hand, heat flows induced by the sound energy flow and acoustic streaming, appeared near the stack 1. The sound energy flow was caused by the thermoacoustic effect. The directions of the sound energy flow and heat flow were opposite, according to the energy conservation law. In the loop-tube, the strong nonlinearity was observed in the generated sound, and the acoustic streaming was induced.

Estimation of in vivo cancellous bone elasticity

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...

Distribution and anisotropy of fast wave speed in the cancellous bone of bovine femur

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).

P5A-2 An Experimental Study on the Ultrasonic Wave Propagation and Structural Anisotropy in Bovine Cancellous Bone

It is known that the ultrasonic longitudinal wave which passed through the cancellous bone is separated into two waves, the fast and the slow waves. The fast wave, especially, reflects the bone structure because it mostly passes though the trabeculae. Then, we have focused on the fast wave speed in the cancellous bone obtained from the head of bovine femur, taking the bone structure into consideration. In the ultrasonic measurement, the changes in the fast wave speed due to the trabecular orientation have been observed with rotating the cylindrical cancellous bone specimen. In addition to the ultrasonic measurements, structural anisotropy of each specimen was measured by X-ray micro CT (Hitachi). From CT images, we obtained the mean intercept length (MIL), degree of anisotropy (DA) and an angle thetas, which is the angle of insonification relative to trabecular orientation. The ultrasonic and CT results showed that the fast wave was strongly affected by the structural anisotropy, especially on the trabecular orientation and length.

Ultrasonic characteristics of invitro human cancellous bone

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 s...