Quantitative Study in Absorption of Mandible Caused by Aging and Disease

下颌骨的吸收是由衰老、疾病和假体等因素引起的。很难估计这些吸收，如果可能的话，这对假肢的治疗、设计和预后是有用的信息。因此，利用放射学、组织学和生物化学等手段对下颌骨的吸收进行了大量的研究。但是，目前还没有对下颌骨的吸收进行定量研究，也没有定量测定骨矿物质含量的方法。在这方面，我们开发了一个系统，可以产生骨矿物质含量的定量图像。该系统由一个射线照相系统和一个图像处理器组成。用用锡滤光片重铬化的x射线束在一次曝光中用双x射线能量拍摄了两张x射线图。图像处理包括对x射线场中薄膜特性和非均匀性的校正，以及对重铬化光束高能分量对管侧图像的影响进行双能减法校正。为了确定x射线的曝光条件和图像分析的一些参数，用不同组分的环氧树脂和骨矿物当量材料的混合物制成楔形幻影进行了实验。结果表明：最佳管电位范围为60kV ~ 70kv， 10x10像素的图像样品适合进行图像处理，对骨矿物质含量的测定精度最高。

Absorption of mandible is caused by aging, desease, and prosthetic Factors. It is difficult to estimate these absorption, and if possible, that is useful information for the prosthetic treatment, design and prognosis of prosthetics. Therefore, there were many studies in absorption of mandible with the tool of radiology, histology and biochemistry. But, there was no quantitative study in absorption of mandible and no method which can make quantitative measurements of bone mineral content. In this respect, we developed a sistem which can produce a quantitative image of bone mineral content. The system consists of a radiographing system and an image processor. Two radiograms were taken with dual X-ray energy in a single exposure using an X-ray beam dichromized by a tin filter. The image processing included the corrections of the film characteristics and heterogeneity in the X-ray field, and the dual energy subtraction in which the effect of the high energy component of the dichromized beam on the tube side image as corrected. In order to determine conditions of exposure of X-ray and some parameters of image analysis, experiments using wedge phantoms made of mixtures of epoxy resin and bone mineral-equvalent materials in various fractions were performed. The results as follows : the best tube potetials were from 60kV to 70kV.10x10 pixels image sample was suitable for image processing and it could make the best accuracy for the measurement of bone mineral content.