锥形束计算机断层扫描中牙齿的分割精度

Validity of tooth volume determinations using cone beam computed tomography

目的:研究锥形束计算机断层扫描(cone beam computerized tomography,CBCT)影像中分割提取正常牙齿体积的精度。方法:选择10例正畸减数病例拔除的双尖牙24颗,采用排水法物理测量其体积(volume of water,Vw),其中7例(16颗牙齿)在减数前采用i-CAT进行三维扫描,3例(8颗牙齿)使用CB MercuRay。使用Amira4.0软件在CBCT影像中分割提取减数双尖牙并测量其体积(volume in amira,Va)。所有的测量均由两名操作者测量两次。采用配对t检验对Vw与Va进行统计学分析,用Pearson相关分析及组内相关系数确定组内及组间的相关性。结果:样本总体平均Vw为(0.553±0.082)cm3,平均Va为(0.548±0.079)cm3[操作者1为(0.529±0.078)cm3,操作者2为(0.567±0.085)cm3],Va与Vw之间差异有统计意义(P<0.05),Va的测量在两个操作者之间差异也有统计学意义(P<0.05),组内与组间相关系数高。Amira软件中表面光滑处理的过程可以损失3%～12%的体积。结论:利用CBCT分割提取双尖牙根是可行的,但分割提取的体积与正常相比有小范围的差异(本研究为-4%～7%),表面处理功能中虽然能美化视觉效果,但有体积的丢失。

Objective：To determine the accuracy of volumetric analysis of teeth in vivo using cone beam computed tomography（CBCT）.Methods： The physical volume（Vw） of 24 bicuspids extracted for orthodontic purposes（16 were imaged with the i-CAT and 8 with the CB MercuRay before extraction） was determined using water displacement technique.Corresponding pre-treatment CBCT image data were uploaded into Amira 4.0 for segmentation and radiographic volume（Va）.All measurements were performed twice by two observers.The statistical difference between Vw and Va was assessed using a paired t-test.The intra-and inter-observer reliability was determined by calculating Pearson correlation coefficients and intraclass correlation coefficients（ICC）.Results： The overall mean Vw of teeth specimens was 0.553±0.082 cm3,while the mean Va was 0.548±0.079 cm3,0.529±0.078 cm3 for observer 1,and 0.567±0.085 cm3 for observer 2.There were statistically significant differences between Va and Vw（P〈0.05）.Between two observers,Va had statistically significant difference（P〈0.05）.The inter-and intra-observers correlation coefficient for Vw was high.Lastly,surface smoothing reduced the volume by 3%-12%.Conclusion： In vivo determination of tooth volumes from CBCT data is feasible.The measurements slightly deviate from the physical volumes within-4% to 7%.Smoothing operations reduce volume measurements.