Dave J, Gingold E, Yorkston J, Bercha I, Goldman L, Walz-Flannigan A, Willis C
Thomas Jefferson UniversityHospital, Philadelphia, PA.
Carestream Health, Inc, Penfield, NY.
Med Phys. 2012 Jun;39(6Part5):3648. doi: 10.1118/1.4734818.
To implement in software the procedures described in AAPM Task Group 150's draft recommendations for image receptor performance testing, and to evaluate the effectiveness and practicality of these procedures.
Images of flat fields were acquired using digital x-ray image receptors at 6 cooperating institutions. Four flat field images obtained with each detector spanned a range of input detector air kerma. Software based on AAPM TG150's draft report processed the test images and generated results. Image receptor response and several measures of non-uniformity were evaluated. Images were divided into 10 mm square regions, after eliminating 10 mm borders. For each region, signal (mean), noise (standard deviation) and SNR were calculated. Characteristic signal, noise and SNR were calculated based on average values from all regions. Local non-uniformity for signal (SLN), noise (NLN) and SNR (SNRLN) were expressed as the maximum ratio of the absolute difference between each region's value and its 4 nearest neighbors, to the respective characteristic value. Global non-uniformity (SGN, NGN, SNRGN) were expressed similarly but differences between maximum and minimum values obtained from the regions were used (without comparison to local neighbors).
TG150 tests discriminated between good and poorly performing detectors. Improper detector calibration was detectable, with noise non-uniformity proving to be a more sensitive measure than signal or SNR non-uniformity. Detector rotation relative to calibration conditions produced a greater change in signal non-uniformity than the other measures. Image receptor structured noise was characterized by an increase in noise non-uniformity with incident air kerma.
AAPM TG150's proposed approach to image receptor testing was implemented and evaluated. The approach appears to be an effective and practical one for routine quality assurance testing of digital radiographic image receptors.
在软件中实现美国医学物理学家协会（AAPM）任务组150关于图像受体性能测试的建议草案中所述的程序，并评估这些程序的有效性和实用性。
在6个合作机构使用数字X射线图像受体采集平野图像。每个探测器获得的4幅平野图像涵盖了一系列输入探测器空气比释动能。基于AAPM TG150建议草案的软件处理测试图像并生成结果。评估了图像受体响应和几种不均匀性测量指标。在去除10mm边界后，将图像划分为10mm见方的区域。对于每个区域，计算信号（均值）、噪声（标准差）和信噪比。基于所有区域的平均值计算特征信号、噪声和信噪比。信号（SLN）、噪声（NLN）和信噪比（SNRLN）的局部不均匀性表示为每个区域的值与其4个最近邻域值之间绝对差值的最大比值与相应特征值的比值。全局不均匀性（SGN、NGN、SNRGN）的表示方式类似，但使用的是从各区域获得的最大值与最小值之间的差值（不与局部邻域进行比较）。
TG150测试能够区分性能良好和较差的探测器。可检测到探测器校准不当，事实证明噪声不均匀性比信号或信噪比不均匀性更敏感。相对于校准条件的探测器旋转在信号不均匀性方面产生的变化比其他测量指标更大。图像受体的结构噪声表现为噪声不均匀性随入射空气比释动能增加。
实施并评估了AAPM TG150提出的图像受体测试方法。该方法对于数字射线摄影图像受体的常规质量保证测试似乎是一种有效且实用的方法。
