Greene T, Nishino T, Willis C
UT M D Anderson Cancer Center, Houston, TX.
Med Phys. 2012 Jun;39(6Part5):3648. doi: 10.1118/1.4734819.
To determine whether a proposed suite of generic tests for digital radiography (DR) detectors could be reduced to practice.
MATLAB software was developed to analyze images according to descriptions in a document drafted by the TG150 Detector Subgroup. Forprocessing images were acquired directly from the acquisition stations of three DR and one Computed Radiography system. Images included flat-field exposures at the manufacturer's calibration condition, twice the exposure, ½ the exposure, and a low exposure, plus three images of a lead bar pattern in different orientations, also at the calibration condition. The flat field images were analyzed to determine Detector Response; Gain Correction; Signal, Noise, and Signal-to-noise (SNR) Uniformity; SNR Magnitude; and Anomalous Detector Element (del) Identification. The program also allowed visual inspection for evaluation of collimation and non-uniformity. Bar pattern images were analyzed to evaluate spatial resolution by a variance method.
Acquisition revealed a number of pitfalls. Some manufacturers have multiple calibration points. For-processing images are not directly available from all systems, and PACS may modify them from their original state. The orientation of the flat field with respect to the anodecathode axis may not be defined by the manufacturer. Care must be taken to ensure collimation outside the edges of detectors, or the software must exclude collimator shadows. The matrix size of images differs among manufacturers, so the size of the region of interest (ROI) for analysis varies from the default size of 100×100 dels, as does the number of ROIs. The approach for dealing with edges and ROIs may affect the numerical results. The detector response function may also affect the interpretation of results.
The software successfully implements most of the detector tests recommended by TG150. Comparison of these results with those of the parallel effort will validate the draft test definition.
确定一套针对数字射线摄影（DR）探测器的通用测试方案是否能够付诸实践。
开发了MATLAB软件，根据TG150探测器子组起草的文档中的描述来分析图像。处理的图像直接从三个DR系统和一个计算机射线摄影系统的采集站获取。图像包括在制造商校准条件下的平板场曝光、两倍曝光、一半曝光和低曝光，以及在校准条件下不同方向的铅条图案的三张图像。对平板场图像进行分析，以确定探测器响应、增益校正、信号、噪声和信噪比（SNR）均匀性、SNR幅度以及异常探测器元件（del）识别。该程序还允许进行目视检查，以评估准直和不均匀性。对条形图案图像采用方差法进行分析，以评估空间分辨率。
采集过程中发现了一些问题。一些制造商有多个校准点。并非所有系统都能直接获取处理后的图像，并且图像存档与通信系统（PACS）可能会改变其原始状态。制造商可能未定义平板场相对于阳极 - 阴极轴的方向。必须注意确保探测器边缘外的准直，或者软件必须排除准直器阴影。不同制造商的图像矩阵大小不同，因此分析的感兴趣区域（ROI）大小与默认的100×100 dels大小不同，ROI数量也不同。处理边缘和ROI的方法可能会影响数值结果。探测器响应函数也可能影响结果的解释。
该软件成功实现了TG150推荐的大部分探测器测试。将这些结果与并行工作的结果进行比较将验证测试定义草案。
