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 (V(max)/V(min)) (R(2) = 0.63).

Nambu PVA gel which is produced by repeated freezing and thawing of PVA solution has overcome almost all of the problems which present substances have: It is close to human soft tissue in MRI parameters. MRI parameters (1H density, T1, T2) are adjustable to some extent. It has appropriate physical characteristics. The important problem with PVA gel is long-term stability. It is assumed that this problem can be solved by its periodic calibration and replacement.

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/cm 3 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.

The LD-100 system is a useful bone densitometry device and the database of age-related changes in TBD, CoTh, and EMTb established in this study will provide fundamental data for future studies related to bone status.

The newly developed QUS technique reflects the three-dimensional structure and is a promising method to evaluate fracture risk.