使用领结式过滤器和水校准方法改善锥形束CT图像质量研究

Bowtle filter and water calibration in the improvement of cone beam CT image quality

目的评价领结式过滤器和水校准方法对锥形束CT图像质量的改善程度。方法首先用铝校准方法校准加速器锥形束CT成像系统的探测板，分别采集使用F0过滤器和F1过滤器时CATPHAN503模体的CT图像；然后用水校准方法重新校准探测板，重新采集使用两种过滤器时的CT图像。观察使用领结式过滤器和水标准方法前后图像质量指标的变化。观察的指标包括低对比度分辨率、空间均匀度、环状伪影、空间分辨率和几何准确度。结果与F0过滤器结合铝校准方法相比领结式过滤器结合水校准方法图像低对比度分辨率改善13．71％，空间均匀度改善54．42％。虽然水校准可以有效消除环状伪影，但都不能改善空间分辨率和几何准确度。结论领结式过滤器结合水标准方法可有效改善CBCT图像质量，有助于提高锥形束CT图像与定位CT图像的配准精确度。

Objective To evaluate the improvement of cone beam CT （CBCT） image quality by using bowtie filter （ F1 ） and water calibration. Methods First the multi-level gain calibration of the detector panel with the method of Cal2 calibration was performed, and the CT images of CATPHAN503 with Fo and bowtie filter were collected, respectively. Then the detector panel using water calibration kit was calibrated, and images were acquired again. Finally, the change of image quality after using F1 and （or） water calibration method was observed. The observed indexes included low contrast visibility, spatial uniformity, ring artifact, spatial resolution and geometric accuracy. Results Comparing with the traditional combination of Fo filter and Cal2 calibration, the combination of bowtie filter F1 and water calibration improves low contrast visibility by 13.71%, and spatial uniformity by 54. 42%. Water calibration removes ring artifacts effectively. However, none of them improves spatial resolution and geometric accuracy. Conclusions The combination of F1 and water calibration improves CBCT image quality effectively. This improvement is aid to the registration of CBCT images and localization images.