Hayakawa Y, Kitagawa H, Wakoh M, Kuroyanagi K, Welander U
Department of Oral and Maxillofacial Radiology, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan.
Bull Tokyo Dent Coll. 2000 Feb;41(1):9-14. doi: 10.2209/tdcpublication.41.9.
The perceptibility curve test is a method for evaluating the psychophysical properties of radiographic systems. The concept of the perceptibility curve is based on the minimum perceptible exposure differences that are recorded by a particular imaging system. The perceptibility curve test was applied to a Charge-Coupled Device (CCD)-based digital intraoral radiography system in this study. A test object was made of a square aluminum block, 28 mm in both height and length and 10 mm in thickness. The test object had ten contrast details in the form of round holes with diameters of 1.5 mm. The depths of the holes ranged from 0.05 mm to 0.5 mm in steps of 0.05 +/- 0.01 mm. An X-ray unit was used that operated in the range of 60 to 90 kVp. Test radiographs were shown to observers in random order. Six observers were asked to rate them regarding the number of spots representing holes that they could perceive. The smallest perceptible difference in gray level on the computer monitor, a 15-inch cathode-ray tube (CRT), was then found. The minimum difference in gray level between a perceptible detail and the background was determined. Dose response functions were employed to determine exposures corresponding to these gray levels. For each case, delta logE as a function of the number of object details was calculated. Finally the reciprocal of all values of (delta logE)min were calculated. The number of details which the observers perceived decreased linearly with decreasing delta logE values. The maximum number of details that observers perceived was eight or nine. The perceptibility curves showed that their peaks shifted slightly with a change of the kVp but that their shapes were similar at different kVp settings.
可感知性曲线测试是一种评估射线照相系统心理物理学特性的方法。可感知性曲线的概念基于特定成像系统记录的最小可感知曝光差异。在本研究中，可感知性曲线测试应用于基于电荷耦合器件（CCD）的数字化口腔内射线照相系统。测试对象由一个方形铝块制成，高度和长度均为28毫米，厚度为10毫米。测试对象有十个呈圆孔形式的对比度细节，直径为1.5毫米。孔的深度范围从0.05毫米到0.5毫米，步长为0.05 +/- 0.01毫米。使用了一台在60至90 kVp范围内运行的X射线设备。测试射线照片以随机顺序展示给观察者。要求六名观察者对他们能感知到的代表孔的斑点数量进行评分。然后找到了15英寸阴极射线管（CRT）计算机显示器上灰度级的最小可感知差异。确定了可感知细节与背景之间灰度级的最小差异。使用剂量响应函数来确定与这些灰度级对应的曝光量。对于每种情况，计算作为物体细节数量函数的δlogE。最后计算所有（δlogE）min值的倒数。观察者感知到的细节数量随着δlogE值的减小而线性减少。观察者感知到的细节的最大数量为八个或九个。可感知性曲线表明，随着kVp的变化，它们的峰值略有移动，但在不同的kVp设置下它们的形状相似。
