基于椭圆参数的牙科CT几何校准方法

Geometric Calibration Method of Dental-CT Based on Ellipse Parameters

基于F.Noo提出的校准方法,采用一种嵌有小钢球的塑料平板作为校准模板,由模的投影数据计算描述牙科CT系统的几何参数,评估当前系统几何结构与理想几何结构的偏差。首先采集校准模的投影图像,然后运用阈值分割的方法将小球分离出来,提取小球的运动轨迹并拟合椭圆,最后由椭圆参数计算出几何参数。经过几何校准后的重建图像更加清晰,具有较好的空间分辨率。

In order to calculate a set of parameters that describes the geometry of dental-CT system and estimate the deviation between real geometry and virtual geometry of the system, a phantom which consists of two steel balls mounted on a plastic plate is designed based on the calibration method proposed by F.Noo. At first, projection image of the phantom is gathered, then motion trace of the two balls is extracted to fit ellipse through threshold segmentation. At last, a set of geometric parameters is calculated by estimating ellipse parameters. Reconstructed image after geometric calibration has a higher spatial resolution.