Measuring System for Bone Mineral Content by Panoramic Radiography

骨矿物质含量（BMC）的研究有助于骨质疏松症的筛查和种植体治疗的准确预后。BMC的测量采用专用设备，如定量计算机断层扫描。本研究对BMC测量系统进行了改进，采用全景x射线系统，一次获得牙弓及相关结构的全面覆盖。我们对该系统的测量性能进行了调查。我们采用骨幻影作为参考和测试阶梯楔，X500CR（森田公司）用于全景x射线系统，Denoptix数字成像系统（Dentsply公司）用于图像输入设备。暴露条件为60kV， 10ma。将参考台阶楔固定在图像层的左侧，将测试台阶楔的位置改变为1)在图像层内或层外，2)在前磨牙区或磨牙区。验证了该系统在各种条件下的测量精度和重现性。磨牙区测量值高于前磨牙区。测量值的变化取决于测量位置。调整后的RMET值精度为1.25%（相对误差）。在放大之间的差异，在近端和远端区域进行检测。与下颌骨位置相对应的转换减小了变形。本研究的BMC值是以往方法的1.7倍，但BMC的分布与以往方法相似。结果表明，该测量系统能够测量无牙下颌骨的BMC，并可用于种植体治疗和骨质疏松症筛查的准确预后。

The investigation of bone mineral content(BMC) is useful for osteoporosis screening and for accurate prognosis for implant treatment. BMC was measured by special devices, as quantitative computed tomography. In this study, BMC measuring system was improved by using panoramic X-ray system to obtain overall coverage of the dental arches and associated structures at a time. We surveyed the measuring performance of this system.We applied bone phantom to reference and test stepwedges, X500CR(Morita Co.Ltd.) to panoramic X-ray system and Denoptix digital imaging system ( Dentsply Co. Ltd.) to image input device. The exposure condition was 60kV, 10mAs. The reference stepwedge was fixed at left side on image layer, the position of test stepwedge was changed as followings 1)inside or outside of the layer, 2) in premolar or molar region. We verified the measuring accuracy and reproducibility of this system at each condition.Measured value in molar region was higher than that in premolar region. The variation of measured value depended on the measuring position. The accuracy of adjusted RMET value was 1.25%(relative error). The difference in the magnification between in the mesial and the distal region was detected. The conversion corresponding with the position in mandible decreased the distortion. The BMC value from this study showed 1.7 times as large as from previous method, however, the distribution of BMC from this study was similar to one from previous method.The results demonstrated that the measuring system was able to measure BMC in edentulous mandible and that this system may be useful for an accurate prognosis for implant treatment and for osteoporosis screening.