Investigation on accuracy and sensitibity of three-dimensional computed tomography, and its application for simulation surgery.

本研究的目的如下：3D-CT图像与颅骨复制品准确性的探讨CT影像及颅骨复制品骨缺损原因的探讨。寻找减少假阴性数据的方法。无帧三维数据配准系统精度评价。累积全头螺旋容积CT资料。使用这个体积数据；制备0.2 mm切片数据，制作颅骨复制品，CT阈值为200 HU。颅骨在额鼻缝合线处切开，并从上方拍摄眶底照片。利用CT阈值分别为200hu和100HU的0.2 mm切片数据重建眶底骨面三维图像。然后以2.0 mm的间隔准备切片数据，并在工作站以0.2 mm的间隔插值图像。利用插值后的切片数据，分别以200 HU和100HU的CT阈值重建眶底骨面三维图像。用个人计算机计算骨量丢失面积占眶底总面积的比例，并与三维骨面图像进行比较。通过这些研究，我们可以得出如下结论。阈值和插值过程中产生的误差是造成颅骨复制品眶底假骨缺损的主要原因。在通过制作CAD数据积累数据的过程中产生了假阴性骨缺损。采用阈值CT值为100hu的数据可以减小误差。颅骨模型精度较高，误差最大为1.96 mm，最小为0.25 mm，平均为0.73 mm。平均配准误差小于1个像素（=0.39 mm）。

The purpose of this research were as follows.1.Investigation of accuracy of 3D-CT image and skull replicas.2.Investigation of the cause of bone deficits on CT image and skull replicas.3.Search the way to reduce the false negative data.4.Evaluation of the accuracy of the frameless three-dimensional data registration system.Helical volume CT data of the whole head were accumulated. Using this volume data ; 0.2 mm slice data were prepared and a skull replica fabricated with a threshold CT value of 200 HU.The skull was cut at the level of the frontonaseal suture and a photograph of the orbital floors was taken from above.3D osseous surface images of the orbital floors then were reconstructed with the 0.2 mm slice data with threshold CT values of 200 HU and 100HU.Slice data then were prepared with an interval of 2.0 mm and images interpolated at 0.2 mm on the workstation. From these interpolated slice data, 3D osseous surface images of the orbital floors were reconstructed with threshold CT values of 200 HU and 100HU.The ratios of the area of bone loss to the whole orbital floors in the photograph and 3D osseous surface images were evaluated with a personal computer and then compared with each other.We could conclude by the studies as follows.1.The errors produced during the precess of thresholding and interpolation had play the main role in causing false bone deficits in the orbital floors of skull replicas.2.False negative bone deficits were created on the way from accumlating data through making CAD data. The error could be reduced by taking data with a threshold CT value of 100HU.3.Skull model have relatively high accuracy which errors are 1.96 mm maximum, 0.25 mm minimum, 0.73 mm average.4.The average registration error was liss than one pixel (=0.39 mm)