Development of Measuring Apparatus of Bone Density with Ultrasonic CT

本课题的目的是研制一种用超声CT法测量骨密度分布的仪器。由于超声波束在穿过骨骼时存在衰减和较大折射，因此应用CT方法进行骨密度测量有许多难题需要解决。本研究是按照以下计划进行的：1)估计超声波通过类似骨头的材料时的特性。2)找出最有效的波信号处理方法。3)建立一种适用于折射波束投影的有效重建方法。研制：研制一种实用的仪器主要研究结果如下：1。通过对已知声传播特性的材料进行测量和数值模拟，确定了获得CT法d.2数据的必要条件。新提出的声束重构算法适用于声束折射的情况。这种重建方法在很大程度上减小了光束折射的影响，这种影响使实际物体变大，从而使声速降低。以人食指为例，目前的CT方法可以获得骨的形状和骨的声速分布与实际值相差不大。将继续进行这项研究，以研制一种实用的紧凑型测量仪器。

The purpose of the present project is to develop an apparatus for measuring the bone density distribution with ultrasonic CT method. Because the ultrasound wave beam is attenuated and also refracted largely when it passes through the bone, there are many difficult problems to be solved to apply the CT method for bone density measurement. The present study has done according to the following schedule : 1) To estimate the characteristics of the ultrasound wave passed through a similar material like bone. 2) To find out the most effective method of wave signal processing. 3) To establish an effective reconstruction method applicable for the projection of refracted wave beam. 4) To develop an apparatus of practical use. The main results are as follows :1. Through the measurements and numerical simulations for a material with known sound propagation characteristics, the necessary conditions are determined to obtain the data for CT metho d.2. A reconstruction algorithm newly developed is confirmed to be applicable for the case where the sound beam is refracted. The reconstruction method reduces largely the effect of the beam refraction that causes the enlargement of the actual body and reduction of sound velocity as a result.3. In the case of human forefinger, the present CT method can obtain the bone shape and the sound velocity distribution of the bone not different much from the actual value.4. The study will be continued to develop a compact measuring apparatus for practical use.