Department of Medical Physics, University of Wisconsin-Madison, 1111 Highland Avenue, Madison, Wisconsin 53705.
Med Phys. 2013 Nov;40(11):111905. doi: 10.1118/1.4822576.
With the recently expanding interest and developments in x-ray differential phase contrast CT (DPC-CT), the evaluation of its task-specific detection performance and comparison with the corresponding absorption CT under a given radiation dose constraint become increasingly important. Mathematical model observers are often used to quantify the performance of imaging systems, but their correlations with actual human observers need to be confirmed for each new imaging method. This work is an investigation of the effects of stochastic DPC-CT noise on the correlation of detection performance between model and human observers with signal-known-exactly (SKE) detection tasks.
The detectabilities of different objects (five disks with different diameters and two breast lesion masses) embedded in an experimental DPC-CT noise background were assessed using both model and human observers. The detectability of the disk and lesion signals was then measured using five types of model observers including the prewhitening ideal observer, the nonprewhitening (NPW) observer, the nonprewhitening observer with eye filter and internal noise (NPWEi), the prewhitening observer with eye filter and internal noise (PWEi), and the channelized Hotelling observer (CHO). The same objects were also evaluated by four human observers using the two-alternative forced choice method. The results from the model observer experiment were quantitatively compared to the human observer results to assess the correlation between the two techniques.
The contrast-to-detail (CD) curve generated by the human observers for the disk-detection experiments shows that the required contrast to detect a disk is inversely proportional to the square root of the disk size. Based on the CD curves, the ideal and NPW observers tend to systematically overestimate the performance of the human observers. The NPWEi and PWEi observers did not predict human performance well either, as the slopes of their CD curves tended to be steeper. The CHO generated the best quantitative agreement with human observers with its CD curve overlapping with that of human observer. Statistical equivalence between CHO and humans can be claimed within 11% of the human observer results, including both the disk and lesion detection experiments.
The model observer method can be used to accurately represent human observer performance with the stochastic DPC-CT noise for SKE tasks with sizes ranging from 8 to 128 pixels. The incorporation of the anatomical noise remains to be studied.
随着 X 射线差分相位对比 CT（DPC-CT）的兴趣和发展不断扩大，在给定的辐射剂量约束下，评估其特定任务的检测性能并与相应的吸收 CT 进行比较变得越来越重要。数学模型观察者通常用于量化成像系统的性能，但需要为每种新的成像方法确认它们与实际人类观察者的相关性。这项工作旨在研究随机 DPC-CT 噪声对具有信号已知（SKE）检测任务的模型和人类观察者检测性能相关性的影响。
使用模型和人类观察者评估了嵌入在实验性 DPC-CT 噪声背景中的不同物体（五个具有不同直径的圆盘和两个乳腺病变肿块）的可检测性。然后，使用五种类型的模型观察者（包括预白化理想观察者、非预白化（NPW）观察者、具有眼滤波器和内部噪声的非预白化观察者（NPWEi）、具有眼滤波器和内部噪声的预白化观察者（PWEi）和通道化 Hotelling 观察者（CHO））测量圆盘和病变信号的可检测性。同样的物体也由四名人类观察者使用二择一强迫选择法进行评估。通过定量比较模型观察者实验的结果与人类观察者的结果，评估两种技术之间的相关性。
人类观察者对圆盘检测实验生成的对比细节（CD）曲线表明，检测圆盘所需的对比度与圆盘尺寸的平方根成反比。基于 CD 曲线，理想和 NPW 观察者倾向于系统地高估人类观察者的性能。NPWEi 和 PWEi 观察者也未能很好地预测人类的表现，因为它们的 CD 曲线的斜率往往更陡。CHO 与人类观察者产生了最佳的定量一致性，其 CD 曲线与人类观察者的重叠。在人类观察者结果的 11%以内，可以声称 CHO 与人类在统计学上是等效的，包括圆盘和病变检测实验。
在 SKE 任务中，模型观察者方法可以用于在大小为 8 到 128 像素的范围内准确地表示具有随机 DPC-CT 噪声的人类观察者的性能。还需要研究包含解剖噪声的情况。
