Niimi Takanaga, Imai Kuniharu, Maeda Hisatoshi, Ikeda Mitsuru
Department of Radiological Technology, Nagoya University School of Health Sciences, 1-1-20 Daiko-minami, Higashi-ku, Nagoya 461-8673, Japan.
Eur J Radiol. 2007 Feb;61(2):362-6. doi: 10.1016/j.ejrad.2006.09.009. Epub 2006 Oct 25.
We applied information theory to quantify information losses in assessing contrast-detail (C-D) analysis. Images of a C-D phantom were acquired with a flat panel detector (FPD) and a computed radiography (CR) by changing surface entrance doses. Six phantom radiographs (FPD: five images; CR: one image) were prepared for visual evaluations. Thirteen radiographers and two radiologists participated in the observation test. Detectability was defined as the shortest length of the cylinders of which border the observers could recognize from the background, and was recorded using row number. Information content was defined as the entropy summation operatorp(i)log(1/p(i)) with detection probabilities p(i), which were calculated from distribution of detection rate of the ith column. Information loss, in unit of bits, was calculated as the difference between information obtained and information content when all the columns were detected. The information losses decreased with the increase in cylinder diameters and with the increase in surface entrance dose. Because the information loss varies depending on distribution of detection rate, this method of using the information theory was expected to be more sensitive in evaluating the C-D image quality than using the averaged values of detectability.
我们应用信息论来量化在评估对比度-细节（C-D）分析中的信息损失。通过改变表面入射剂量，使用平板探测器（FPD）和计算机X线摄影（CR）获取C-D体模的图像。准备了六张体模射线照片（FPD：五张图像；CR：一张图像）用于视觉评估。13名放射技师和两名放射科医生参与了观察测试。可检测性定义为观察者能够从背景中识别出的圆柱体边界的最短长度，并使用行数进行记录。信息内容定义为熵求和算子p(i)log(1/p(i))，其中检测概率p(i)是根据第i列的检测率分布计算得出的。信息损失以比特为单位，计算为当所有列都被检测到时获得的信息与信息内容之间的差值。信息损失随着圆柱体直径的增加和表面入射剂量的增加而降低。由于信息损失根据检测率的分布而变化，因此预期这种使用信息论的方法在评估C-D图像质量方面比使用可检测性的平均值更敏感。
