A nonlinear lag correction algorithm for a-Si flat-panel x-ray detectors.
A nonlinear lag correction algorithm for a-Si flat-panel x-ray detectors.
复制标题
非晶硅平板 X 射线探测器的非线性滞后校正算法。
DOI：
10.1118/1.4752087
复制
发表时间：
2012
期刊：
影响因子：
3.8
通讯作者：
Fahrig,Rebecca
中科院分区：
文献类型：
--
作者：
Starman,Jared;Star-Lack,Josh;Virshup,Gary;Shapiro,Edward;Fahrig,Rebecca
在锥束CT重建中，a-Si平板（FP）探测器中的探测器滞后或残留信号会导致严重的阴影伪影。到目前为止，大多数校正模型都假设线性时不变（LTI）模型，并通过使用脉冲响应函数（IRF）的反卷积来校正滞后。然而，滞后校正对曝光强度和用于确定IRF的技术都敏感。即使找到产生最小误差的LTI校正，残留伪影仍然存在。一种新的非LTI方法的开发，考虑到IRF测量技术和曝光dependency.MethodsFirst，多指数（N= 4）LTI模型进行滞后校正。接下来，基于LTI多指数方法开发了非LTI滞后校正，称为非线性一致性存储电荷（NLCSC）方法。它与其他非线性滞后校正算法的不同之处在于，它保持了对FP中存储的电荷量的一致估计，并且不需要对FP特定的半导体参数的深入了解。对于NLCSC方法，IRF的所有系数是曝光强度的函数。还比较了仅使用IRF的强度加权的另一种非线性滞后校正方法。将校正算法应用于大型骨盆体模和丙烯酸头部体模的阶跃响应投影数据和CT采集。作者收集了Varian 4030 CB a-Si FP探测器的上升沿和下降沿阶跃响应数据，该探测器在9次入射曝光（探测器饱和曝光的2.0%-92%）下以15 fps的动态增益模式运行。对于投影数据，在校正之前和之后测量第1和第50帧滞后。对于CT重建，定义了五对ROI，并针对不同的曝光和阶跃响应边缘techniques.ResultsThe LTI校正将剩余第1帧和第50帧滞后降低到1.4%和0.48%，而NLCSC滞后校正将第1帧和第50帧剩余滞后降低到小于0.29%和0.0052%。对于CT重建，NLCSC滞后校正给出的骨盆体模平均误差为11 HU，头部体模平均误差为3 HU，而LTI校正为14-19 HU和2-11 HU，强度加权非LTI算法为15 HU和9 HU。对于NLCSC校正，最大ROI误差始终最小。NLCSC校正也上级强度加权algorithm.ConclusionsThe NLCSC滞后算法校正的曝光依赖性的滞后，提供了上级的图像改善骨盆体模重建，并给出了类似的结果，最好的情况下LTI的结果为头部体模。在所有情况下，NLCSC校正可以更好地消除LTI校正中遗留的模糊环形伪影。
PurposeDetector lag, or residual signal, in a‐Si flat‐panel (FP) detectors can cause significant shading artifacts in cone‐beam computed tomography reconstructions. To date, most correction models have assumed a linear, time‐invariant (LTI) model and correct lag by deconvolution with an impulse response function (IRF). However, the lag correction is sensitive to both the exposure intensity and the technique used for determining the IRF. Even when the LTI correction that produces the minimum error is found, residual artifact remains. A new non‐LTI method was developed to take into account the IRF measurement technique and exposure dependencies.MethodsFirst, a multiexponential (N= 4) LTI model was implemented for lag correction. Next, a non‐LTI lag correction, known as the nonlinear consistent stored charge (NLCSC) method, was developed based on the LTI multiexponential method. It differs from other nonlinear lag correction algorithms in that it maintains a consistent estimate of the amount of charge stored in the FP and it does not require intimate knowledge of the semiconductor parameters specific to the FP. For the NLCSC method, all coefficients of the IRF are functions of exposure intensity. Another nonlinear lag correction method that only used an intensity weighting of the IRF was also compared. The correction algorithms were applied to step‐response projection data and CT acquisitions of a large pelvic phantom and an acrylic head phantom. The authors collected rising and falling edge step‐response data on a Varian 4030CB a‐Si FP detector operating in dynamic gain mode at 15 fps at nine incident exposures (2.0%–92% of the detector saturation exposure). For projection data, 1st and 50th frame lag were measured before and after correction. For the CT reconstructions, five pairs of ROIs were defined and the maximum and mean signal differences within a pair were calculated for the different exposures and step‐response edge techniques.ResultsThe LTI corrections left residual 1st and 50th frame lag up to 1.4% and 0.48%, while the NLCSC lag correction reduced 1st and 50th frame residual lags to less than 0.29% and 0.0052%. For CT reconstructions, the NLCSC lag correction gave an average error of 11 HU for the pelvic phantom and 3 HU for the head phantom, compared to 14–19 HU and 2–11 HU for the LTI corrections and 15 HU and 9 HU for the intensity weighted non‐LTI algorithm. The maximum ROI error was always smallest for the NLCSC correction. The NLCSC correction was also superior to the intensity weighting algorithm.ConclusionsThe NLCSC lag algorithm corrected for the exposure dependence of lag, provided superior image improvement for the pelvic phantom reconstruction, and gave similar results to the best case LTI results for the head phantom. The blurred ring artifact that is left over in the LTI corrections was better removed by the NLCSC correction in all cases.