牙槽骨密度定量测量系统的建立及测量精确性、有效性的检验

A system for quantitatively measurement of alveolar bone density and the evaluation of its precision and validity

目的：建立牙槽骨密度定量测量系统并检验其测量的精确性、有效性。方法：在X线骨密度测量法的基础上建立牙槽骨密度定量测量系统。用计算机测量定位投照的直接数字化牙片上感兴趣区（region of interest,ROI）的灰度,拍片时将一个铝制梯级同时曝光,根据已知的铝梯灰度和厚度推算ROI区灰度所对应的等效铝厚度和校正灰度来反映骨密度,从而校正由于投照条件差异造成的灰度误差。用该系统对19个含有不同质量羟基磷灰石的样本进行测试,选取2个样本反复测量来检验该系统的测量精确性,并检验该系统对改变曝光时间投照的两套羟基磷灰石样本测量数据校正的有效性。结果：该系统测量等效铝厚度、校正灰度的相对标准误差（RSD）为0.83% -2.15%;在95%的置信水平下,如果ROI区等效铝厚度的变化大于0.05mm或校正灰度的变化大于3个灰阶,就说明该区域羟基磷灰石的含量发生了变化;对不同曝光时间下拍摄的两套羟基磷灰石样本的测量数据进行Wilcoxon Signed Ranks检验,结果该系统对曝光时间差异造成的灰度差异能够有效校正。结论：本研究建立的牙槽骨密度定量测量系统有较好的精确性与有效性,可用于对牙槽骨密度横向和纵向的比较。

Objective：To establish a system for quantitatively measuring alveolar bone density and to test its precision and validity. Methods： With the aid of computer technique, the system measured the average gray level intensity of regions of interest （ROIs） on standardized exposed direct digital periapical radiograph. To correct the variation resulting from exposure condition, an aluminum stepwedge was exposed simultaneously. By referring the image of aluminum stepwedge on each radiograph the equivalent aluminum thickness（EAT） and corrected gray level intensity（CGL） of the ROIs could be calculated as indicators of alveolar bone density. Nineteen specimens containing different amounts of hydroxy-phosphorite were radiographed. The precision of the system was tested by repeatedly measuring 2 of the specimens. The set of specimens was exposed under two different exposure time in order to test the system＇ s validity to correct the gray level difference caused by different exposure time. Results： After repeated measurement of specimens, we found the Relative Standard Deviation （ RSD ） of EAT and CGL was between 0. 83% -2. 15% ; At the level of 95%, if the difference of EAT between the two ROIs was larger than 0. 05 mm or the difference of CGL was larger than 3, the content of hydroxy-phosphorite in them was different; The two sets of data during different exposure time were processed with Wilcoxon Signed Ranks Test, and the result showed effective correction of the variation caused by different exposure time. Conclusion ： The precision and validity of the quantitative alveolar bone density measuring system are acceptable. The system can be used to compare alveolar bone density longitudinally and cross-sectionally