Isao Mano

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).

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.

Trabecular and cortical bone separately assessed at radius with a new ultrasound device, in a young adult population with various physical activities

The aim was to evaluate a new ultrasound device in a young adult population and to assess its reproducibility via comparison to DXA measurements and geometrical measurements from high-resolution radiographs. Ninety-three subjects aged between 20 and 51 years were recruited and divided into four groups according to their gender and physical activity status: 22 male athletes, 19 male controls, 21 female athletes, and 31 female controls. Ultrasonic measurements were assessed by the prototype LD-100 (Oyo Electric Co., Kyoto, Japan) on the dominant distal radius. Attenuation in the radius (dB), cortical bone thickness (mm), radius thickness (mm), mass density of cancellous bone (mg/cm(3)), and elasticity (GPa) of cancellous bone were obtained. BMD was measured by DXA at the dominant distal radius. Radius images were obtained with a direct high-resolution digital X-ray device (BMA, D(3)A Medical Systems), and radius and cortical thicknesses were estimated using a specific software (ImageJ, Bethesda, USA), in an area site-matched with LD-100. There was a significant positive correlation between site-matched BMD measurement and LD-100 parameters (p<0.004), X-ray radius thickness, and LD-100 parameters except elasticity (p<0.05, r>0.32), X-ray cortical thickness and LD-100 attenuation and cortical thickness (p<0.01). A significantly higher attenuation, cortical and radius thicknesses were found in athletes compared to controls (p<0.05). The radius thickness measured on radiographs was significantly higher in athletes versus controls in both sexes, and cortical thickness was significantly higher in male athletes versus controls. These data suggest a positive influence of physical activity on bone cortical measurements. This study also confirmed the particular interest of bone assessment by ultrasound.

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.

Trial of Human Bone Cross-Sectional Imaging In vivo, Using Ultrasonic Echo Waves

We have tried in vivo imaging of the distal forearm bone using ultrasonic echo waves. The obtained ultrasonic echo images were compared with X-ray computed tomography (CT) images. In the case of vertical incidence of an ultrasonic wave to the cortical bone surface, not only the outer and inner boundaries of the near side of the cortical bone but also the inner and outer boundaries of the far side of the cortical bone were identified. The thicknesses of the cortical bone and cancellous bone calculated using the echo waves approximately agreed with those determined from X-ray CT images.

Two-wave propagation imaging to evaluate the structure of cancellous bone

The two-wave phenomenon reflects not only bone mass but also the complex bone structure of cancellous bone. We propose a new simple imaging technique based on the two-wave phenomenon for investigating the anisotropic structure of cancellous bone. A cylindrical specimen of cancellous bone was obtained from a bovine femur. The structure (alignment of trabeculae) of the specimen was obtained from 3-D X-ray micro computed tomography imaging. Using a conventional ultrasonic pulse technique, we rotated the receiver around the specimen to investigate the ultrasonic fields after propagation within the specimen. The ultrasonic propagation image clearly showed the effect of the bone structure. We found that the fast wave showed apparent refraction, whereas the slow wave did not. Fast-wave propagation imaging is thus a simple and convenient technique for easy interpretation of the anisotropic structure. This imaging technique has the potential to become a powerful tool to investigate the structure of trabeculae during in vivo measurements.

Influence of the circumferential wave on the fast and slow wave propagation in small distal radius bone

An ultrasonic system is good for the evaluation of children because its noninvasiveness. The ultrasonic bone measurement system LD-100 has been developed on the basis of the principle of the fast and slow wave phenomenon in the wrist bone. In the measurement of small bones such as those of children, there are some problems due to the influences of circumferential waves on the fast and slow waves. When the diameters of the focused transducers were small, the appearance of the circumferential wave around the cortical bone became late, and it could avoid one of the influences of the circumferential waves.

Two-wave propagation in in vitro swine distal ulna

Ultrasonic transmitted waves were obtained in an in vitro swine distal ulna specimen, which mimics a human distal radius, that consists of interconnected cortical bone and cancellous bone. The transmitted waveforms appeared similar to the fast waves, slow waves, and overlapping fast and slow waves measured in the specimen after removing the surface cortical bone (only cancellous bone). In addition, the circumferential waves in the cortical bone and water did not affect the fast and slow waves. This suggests that the fast-and-slow-wave phenomenon can be observed in an in vivo human distal radius.

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...