Welander U, Nelvig P, Tronje G, McDavid W D, Dove S B, Mörner A C, Cederlund T
Department of Oral Radiology, Karolinska Institutet, Huddinge, Sweden.
Oral Surg Oral Med Oral Pathol. 1993 Apr;75(4):506-16. doi: 10.1016/0030-4220(93)90180-c.
The Sens-A-Ray system for direct digital intraoral radiography may be used with any computer compatible with an IBM PC/AT. The system relies on a charge-coupled device designed for direct conversion of x-ray energy to an electronic signal. It is the first such device for direct acquisition of radiographs. Technical properties of charge-coupled device detectors when exposed to radiation energies in the range of x-rays used in dental radiography have been studied. Even in the absence of light or x-radiation there is a spontaneous generation of charge within a charge-coupled device detector that gives rise to a background signal, a dark current. It was found that the dark current is a linear function of exposure time. The dose response of the charge-coupled device detector was determined at nominal kilovoltages that range from 50 to 90 kVp. The dose response was shown to be a linear function of exposure. The functions for all kVp settings were practically identical. The charge-coupled device detector is more sensitive to x-radiation than conventional dental films and, consequently, its exposure range is more narrow. The signal-to-noise ratio was calculated from the digital radiographs used for the dose response test. The ratio is above 10 for exposures higher than about 2 microC/kg. The line spread function was determined from test radiographs of a 10 microns wide slit in a test object of 1.5 mm thick tantalum. After curve fitting, the line spread function could be expressed as the sum of a Gaussian and an exponential function. Presampling modulation transfer functions valid at the detector plane and at an object plane were calculated from fitted data on the line spread function. It is concluded that the Sens-A-Ray system has such technical properties that it may replace conventional film-based systems.
用于直接数字口腔内放射摄影的Sens-A-Ray系统可与任何与IBM PC/AT兼容的计算机配合使用。该系统依赖于一种电荷耦合器件，该器件设计用于将X射线能量直接转换为电子信号。它是首个用于直接获取射线照片的此类器件。已经研究了电荷耦合器件探测器在暴露于牙科放射摄影中使用的X射线能量范围内时的技术特性。即使在没有光或X射线辐射的情况下，电荷耦合器件探测器内也会自发产生电荷，从而产生背景信号，即暗电流。研究发现暗电流是曝光时间的线性函数。在50至90 kVp的标称千伏电压下测定了电荷耦合器件探测器的剂量响应。结果表明剂量响应是曝光量的线性函数。所有千伏电压设置下的函数实际上是相同的。电荷耦合器件探测器对X射线辐射比传统牙科胶片更敏感，因此其曝光范围更窄。根据用于剂量响应测试的数字射线照片计算信噪比。对于高于约2微库仑/千克的曝光量，该比值高于10。线扩展函数是根据在1.5毫米厚的钽测试对象中10微米宽狭缝的测试射线照片确定的。经过曲线拟合后，线扩展函数可以表示为高斯函数和指数函数的和。根据线扩展函数的拟合数据计算了在探测器平面和物体平面有效的预采样调制传递函数。得出的结论是，Sens-A-Ray系统具有这样的技术特性，它可以取代传统的基于胶片的系统。
