Research on Image Perception of Abnormal Findings

我们研究了放射噪声和解剖噪声如何影响细微异常发现的可检出性。采用四选项强制选择方法研究了高斯白噪声背景下噪声水平对模拟肺结节检测性能的影响。结果与信号检测理论的结果基本一致。结节的可检出性与局部周围解剖结构灰度值的基本统计指标关系不大，而与信噪比有关。接下来，我们从局部角度探讨了解剖噪声对胸片上细微肺结节可检出性的影响，其中结节周围肋骨结构的存在是重点。我们的研究采用Samei等人提出的方法。从正常胸片图像中，考虑肋骨结构提取方形区域；这些方形像的中心在一根肋骨的上边缘、一根肋骨的内部、一根肋骨的下边缘和两根相邻肋骨之间的中心；将模拟的结节以数字方式叠加在提取的正方形图像的中心。利用一组经过处理的图像，我们进行了图像阅读研究。结果表明，结节周围是否存在肋骨结构对检测性能有显著影响，相邻两根肋骨中间的结节可检出性明显最好。此外，除相邻两根肋骨中间的结节外，其他结节的检出率依次为肋骨上缘、内缘和下缘，呈降低的趋势；然而，这些差异很少。一定大小的射线照相噪声也会影响结节的检测。

We have studied how radiographic noise and anatomic noise will affect the detectability of subtle abnormal findings.The influence of noise level on the detection performance of simulated lung nodules in the Gaussian white noise background has been investigated by using a four-alternative forced choice method. Results were mostly in agreement with the ones derived from the signal detection theory. The nodule detectability had little relation to the fundamental statistical measures of gray scale values of the local surrounding anatomic strucures, and was related to the signal-to-noise ratio.Next, we have accessed the influence of anatomic noise on the detectablity of subtle lung nodules depicted on chest radiographs, from a local aspect in which the existence of rib structure surrounding nodules is the focus. The method proposed by Samei et al. was applied to our study. From the normal chest radiography images, square regions were extracted by considering rib structure ; the centers of these square images were on the upper margin of a rib, the inside of a rib, the lower margin of a rib, and the center between two adjoining ribs ; and the simulated nodules were digitally superimposed on the centers of these extracted square images. By using a set of these processed images, we have performed the image reading study. Results indicated a significant effect of the existence of rib structure surrounding the nodule on the detection performance, and the detectability of the nodules on the center between two adjoining ribs was significantly the best. Further, the detectability of the nodules other than on the center between two adjoining ribs showed a tendency to decrease in the order of the upper margin, the inside, and the lower margin of a rib ; however, these differences were few. Radiographic noise of a certain size can also influence the nodule detection.