Takahiko Otani

Propagation of two longitudinal waves in human cancellous bone: An in vitro study

The ultrasonic wave propagation of fast and slow waves was investigated in vitro in 35 cubic cancellous bone specimens extracted from human femoral heads. Measurements were performed in three orthogonal directions using home-made PVDF transducers excited by a single sinusoidal wave at 1 MHz. The apparent density of the specimens was measured. Two separated fast and slow waves were clearly observed in 16 specimens, mainly in the main load direction. The waveforms and the sound speeds of fast and slow waves were similar to the reported data in bovine bone. The group of specimens in which the two waves were observed did not exhibit statistically higher apparent density than the rest of the specimens, but did exhibit statistically higher acoustic anisotropy ratio. The speeds in the main load direction were higher than those in the other direction. The fast and slow wave speeds were in good agreement with Biots model, showing an increase with bone volume fraction (BV/TV). The ratio of peak amplitudes of the fast and slow waves nonlinearly increased as a function of BV/TV. These results open interesting perspective for acoustic assessment of cancellous bone micro-architecture and especially anisotropy that might lead to an improved assessment of bone strength.

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).

Quantitative estimation of bone density and bone quality using acoustic parameters of cancellous bone for fast and slow waves

In previous studies, two longitudinal waves, the fast and slow waves, were observed in cancellous bone. The propagation speed of the fast wave increases with bone density and that of the slow wave remains almost constant. The attenuation constant of the fast wave is much higher than that of the slow wave and is independent of bone density, but the attenuation constant of the slow wave increases with bone density. In the present study, experimental results on ultrasonic waves transmitted through cancellous bone show that the fast wave amplitude increases proportionally and the slow wave amplitude decreases inversely with bone density. The dependence of the fast wave amplitude on bone density cannot be explained by the attenuation constant. The ultrasonic wave propagation path through cancellous bone is modeled to specify the causality between ultrasonic wave parameters and bone density. Then bone density and bone elasticity are quantitatively formulated.

Applicability of Finite-Difference Time-Domain Method to Simulation of Wave Propagation in Cancellous Bone

In cancellous bone, longitudinal waves often separate into fast and slow waves depending on the alignment of bone trabeculae. This interesting phenomenon becomes an effective tool for the diagnosis of osteoporosis because wave propagation behavior depends on the bone structure. We have, therefore, simulated wave propagation in such a complex medium by the finite-difference time-domain (FDTD) method, using a three-dimensional X-ray computer tomography (CT) model of an actual cancellous bone. In this simulation, experimentally observed acoustic constants of the cortical bone were adopted. As a result, the generation of fast and slow waves was confirmed. The speed of fast waves and the amplitude of slow waves showed good correlations with the bone volume fraction. The simulated results were also compared with the experimental results obtained from the identical cancellous bone.

Development of Novel Ultrasonic Bone Densitometry Using Acoustic Parameters of Cancellous Bone for Fast and Slow Waves

A novel ultrasonic bone densitometer, prototype LD-100, has been developed to overcome problems inherent in an ultrasonic method and to obtain bone mass density in the unit of mg/cm3 and bone elasticity in the unit of GPa with a spatial resolution comparable to that of the peripheral quantitative computed tomography (pQCT) 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. A good reproducibility of measured values and two-dimensional (2D) imaging of bone density and bone quality are realized by two scannings with an automatic measurement algorithm.

Influences of Trabecular Structure on Ultrasonic Wave Propagation in Bovine Cancellous Bone

Ultrasonic wave propagation in water-saturated bovine cancellous (spongy) bone has been experimentally studied in vitro by a pulse transmission technique. The propagation of fast and slow longitudinal waves in bovine cancellous bone [rf:1] is examined in relation to porosity using Biots and Wyllies equations to estimate the measured speeds versus porosity. In the high porosity range, the trabecular structure influences the propagation of the fast and slow waves in cancellous bone.

Distribution of Longitudinal Wave Velocities in Bovine Cortical Bone in vitro

The distribution of longitudinal wave velocities and longitudinal moduli in a bovine femoral cortical bone was experimentally investigated. In all parts of the long cylindrical bone, the velocities and longitudinal moduli in the axial direction were the highest. In the anterior (A) part, the velocities in the axial direction were high and almost constant, whereas the velocities in the proximal postero medial (PM) and distal postero lateral (PL) parts markedly decreased. Classifying the cortical bone into three structures (plexiform, Haversian, and porotic), we clarify the velocity distributions in the bone with discussion from an anatomical point of view.

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.

Measurement of human trabecular bone by novel ultrasonic bone densitometry based on fast and slow waves

SummaryTwo longitudinal transmitted waves, fast and slow waves, were observed by employing a new quantitative ultrasound (QUS) method. The trabecular bone measurements generated by this method reflect three-dimensional structural information, and the new QUS parameters were able to identify vertebral fractures.IntroductionThe aims were to identify new quantitative ultrasound (QUS) parameters that based on new QUS method reflecting not only bone volume but also the microstructures of trabecular bone ex vivo and to observe how much they predict fracture risk in vivo.MethodsEx vivo measurement: Three human femoral heads were used for the experiment. Attenuation of the slow wave, attenuation of the fast wave, speed of the slow wave, speed of the fast wave (SOFW), bone mass density of trabecular bone, and elastic modulus of the trabecular bone (EMTb) of each specimen were obtained using a new QUS method and compared with three-dimensional structural parameters measured by micro-computed tomography. In vivo measurement: Eighty-nine volunteers were enrolled, and the bone status in the distal radius was measured using a new QUS method. These parameters were compared with data evaluated by peripheral quantitative computed tomography and dual X-ray absorptiometry.ResultsEx vivo measurement: SOFW and EMTb showed correlations with the parameter of trabecular anisotropy. In vivo measurement: The new QUS parameters were able to identify vertebral fractures.ConclusionThe newly developed QUS technique reflects the three-dimensional structure and is a promising method to evaluate fracture risk.

Characterization of (112̄0) Textured ZnO Films Fabricated by RF Magnetron Sputtering

Using a conventional RF magnetron sputtering system, we have obtained two types of ZnO films on various kinds of substrate. One is a film with the c-axes of crystallites unidirectionally aligned in the substrate plane {(110) textured film}. The other is a film with c-axes parallel and perpendicular to the plane (mixed texture film). The former is expected to realize a shear wave transducer on the surfaces of various materials. The alignment of c-axes of crystallites in the plane was then carefully investigated by the X-ray pole figure analysis. The elastic anisotropy in the film has been successfully measured by the Brillouin scattering method. The (110) textured film did not excite the elastic waves; however, comparatively strong shear waves were actually excited by the mixed texture film.