射线数字成像检测系统不均匀性分析与校正

Analysis and correction for non-uniformity of a digital radiographic apparatus

图像高低频畸变(即不均匀)会导致射线数字检测系统检测灵敏度的下降和误判,而造成畸变的原因是系统中射线源强度分布不均匀、闪烁体屏发光不均匀、镜头渐晕、科学级CCD暗电流和光响应不均匀。在此分析的基础上提出了一种校正方法,该方法利用实验得出校正矩阵,通过软件校正,先校正CCD暗电流和光响应不均匀性,再对其它三个因素合并校正。在便携式X射线源下,对三号透度计在15mm均匀钢板上的图像进行了校正实验,结果表明,灵敏度由校正前的1.67%提高到1.33%,图像不均匀性得到明显改善,空间分辨力大于3.5lp/mm。系统具有检测灵敏度高(≤1.5%)和适应射线能量范围大(50keV-15MeV)的优点。

High and low frequency aberration (i.e., non-uniformity) of an image will lead to reduction of inspection sensitivity and false conclusion for a digital radiographic apparatus. Reasons for inducing aberrations come from non-uniformity of radiographic source intensity distribution, light non-uniformity of scintillator screen, lens vignetting, dark current and light response non-uniformity of scientific grade CCD camera. Based on the analysis, a correction method is proposed, by which a correction matrix is obtained by experiments and image is corrected through software, the CCD dark current and light response non-uniformity are firstly corrected, three other factors then by coalition correction. The after and before correction images of No.3 transmissometer (GB4730) attached on 15mm uniformity steel plate gained by portable X-ray source are given. The results show that the sensitivity has been improved from 1.67% before correction to 1.33% and the image non-uniformity has been obviously improved with a spatial resolution more than 3.51 p/mm. The system has advantages of high inspecting sensitivity ( greater than or equal 1.5%) and supporting large ray energy range (50 keV-15 MeV).