锥束CT平板探测器成像的余晖建模与校正方法

Image lag modeling and correction method for flat panel detector in cone-beam CT

锥束CT具有高效率和高精度的显著特点,在医学成像与工业无损检测等领域已得到广泛应用,但余晖的存在降低了CT图像的质量.本文借鉴余晖多指数衰减模型的思想,结合平板探测器输出信号的实际衰减规律,提出了一种新的基于多指数拟合的余晖衰减建模及校正方法.首先进行了基于平板探测器的锥束CT成像实验,结果表明平板探测器各像素的余晖衰减规律具有良好的一致性,且余晖衰减规律与初始灰度的大小无关;其后根据建立的余晖衰减模型实现了余晖的快速校正,并分析比较了余晖校正前后投影图像和切片图像质量,表明余晖校正后的零件轮廓清晰度得到了显著提升.该方法无需获取探测器闪烁体成分及其衰减时间常数,便于实际锥束CT成像系统的余晖检测与校正.

Cone-beam computed tomography （CT） has the notable features, viz high efficiency and high precision, and is widely used in the areas such as medical imaging and industrial non-destructive testing, but the presence of image lag reduces the quality of CT images. By referencing the multi-exponential decay model for the image lag and combining with the actual decay rule of the fiat panel detector output signal, a new decay modeling and correction method for the image lag based on multi-exponential fitting is proposed. Firstly, an imaging experiment using cone-beam CT based on fiat panel detector is carded out; the results show that the image lag decay of the pixels in the fiat panel detector has a good consistency, and is irrelevant to the initial gray value. Then, the rapid image lag correction is achieved according to the image lag decay model, and the comparison of image quality of the projected images and slice images before and after image lag correction indicates that the edge sharpness of the part has been significantly improved after the lag correction. This method does not need to obtain the scintillation compositions and the decay time constants of the detector, and is easily applied to the practical cone-beam CT imaging systems for image lag detection and correction.