Development of Measuring Apparatus of Bone Density with Ultrasonic CT

本课题旨在研制一种超声CT骨密度测量仪。由于超声波束在穿过骨骼时会发生很大的衰减和折射，因此将CT方法应用于骨密度测量有许多难题需要解决。本研究主要按照以下几个方面进行：1）研究超声波在骨等类似材料中的传播特性。2)寻找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。4)开发一种实用的仪器。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CT法获取数据的必要条件.新开发的重建算法被证实适用于声束折射的情况。该重建方法大大减小了声束折射的影响，从而使实际物体体积增大，声速降低.对于人的食指，本方法可以得到与实际值相差不大的骨骼形状和声速分布.这项研究将继续进行，以开发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.