以实物拍摄为依据, 用一种最简便的修正方法解决计算机X射线层析术成像时由于硬化效应引起的切片图灰度失真问题。用高性能数字X射线机FAXITRON MX-20(射线管焦点20 μm, 探测板灰度等级16位)对不同厚度的物体进行透射成像, 测得对应的透射光强度, 并利用新创的指数拟合法得到理想的拟合曲线, 由此推导硬化效应的指数校正公式;最后利用实验室的微型计算机层析设备进行扇形束扫描, 并逆投影重建生成计算层析断层图像, 验证了该校正方法的实用性。该指数拟合法的误差不到常用的二阶多项式拟合法的1/3, 对物体计算层析重构, 硬化校正以前有明显的“杯状”伪迹, 切片灰度不均匀, 用指数法修正以后该伪迹消失, 切片灰度均匀。

Based on practical experiments, a new method to eliminate beam hardening effect causing cup-like artifacts in CT reconstruction, is demonstrated. The digital X-ray set FAXITRON MX-20 with a high resolution, of which the focal length of the X-ray tube is 20 μm, and the gray scale of the detecting board is 16 bit, is adopted to detect samples with different thickness. Intensities of the X-ray transmitting samples of different thickness are recorded. The exponential fitting method is used to fit the related curves, and by the fitting curves the exponential correction formula is derived. By taking photons of a cylindrical sample by the micro-CT system, we reconstruct a slice of the sample with the fan-beam filtered back-projection algorithm and validate the method. The error of the exponential fitting is less than 1/3 of the results by the conventional two-order polynomial fitting. In the CT reconstruction, the clear cup-like artifact and gray scale ununiformity of the slice before hardening correction are eliminated by the exponential fitting.