Assessment of Bone Quality by Quantitative Ultrasound Measurement

LD-100 can provide with bone parameters displaying similar reliability to peripheral quantitative computed tomography (pQCT). In addition, the cancellous bone elasticity related to bone quality can be obtained. I. INTRODUCTION Bone strength depends not only on bone mineral density (BMD) but also on a range of other parameters which contribute to bone quality. X-ray bone densitometer is the reference method for determining BMD. Quantitative ultrasound (QUS) is expected as a method that will give insights about the bone quality, but its parameters are not direct mechanical properties. In this paper, we propose a new evaluation method for bone quality. II. PRINCIPLES AND EQUIPMENT When a short pulse in the MHz range is applied to cancellous bone, it gives birth to two waves: a fast wave, and a slow wave. The fast wave changes according to the porous network structure of trabeculae, the bone density and its elastic coefficients. The slow wave in cancellous bone is thought to vary according to the elastic behavior of bone marrow filling the pore space (1). The authors have developed bone strength measurement equipment, LD-100 (Fig.1), based on the principle of the ultrasonic two wave phenomenon. The measurement site is selected at the distal radius, at the same spot as the peripheral quantitative computed tomography (pQCT). Making use of the two wave properties (amplitude and velocity) and echo wave, LD-100 retrieves real unit of BMD (mg/cm3) and elasticity (GPa) of the cancellous bone and also the thickness (mm) of cortical bone. Elasticity is evaluated by the velocity of fast wave and the BMD on the basis of clear causality concerning the two waves (2). III. RESULTS OF CLINICAL STUDIES (3)-(5) Authors have compared the values obtained by both LD-100 and pQCT. Fig. 2 shows the cancellous bone's BMD. Fig. 3 shows the cortical bone thickness. Highly significant correlations were found in both. In another study, the elasticity and BMD measured with LD-100 could be used to accurately discriminate whether the subjects had a vertebral fracture or not. The areas under the ROC curves were 0.842 and 0.852.