DEVELOPMENT OF GLOBAL STANDARD PHANTOM TO OPTIMIZE DIGITAL

本研究的目的是开发一个标准的假体用于牙科放射照相，并比较胶片图像和数字图像的图像质量。首先，开发了一个12个台阶的铝块，上面有7个孔，上面覆盖着丙烯酸块。在三种不同的管电压下，用两种类型的胶片对这个幻影进行了无线电成像。修正后的感知曲线是通过计算每次曝光时最大的可感知孔来生成的。根据该曲线确定了最佳曝光量，并与标准铝阶梯楔法和x光机预设时间测定的曝光量进行了比较。该幻像的x射线衰减范围似乎接近临床情况。此外，图像质量的差异可以通过在幻影中看到的孔的数量来评估。接下来，通过使用该模型，比较了2种胶片系统和几种数字口内系统的视觉图像质量。建立了改进的感知曲线，并进行了比较。除Digora系统外，所有数码系统的最佳曝光都低于e速胶片。然而，在所有没有增强的数字图像中，最大可感知孔的数量明显低于该曝光下的胶片系统。对比度增强后，除Sens-A-Ray系统外，所有数字系统的可视性都优于胶片系统。使用CDR， Digora和Dixel系统，曝光可以减少相当大的数量，与胶卷相比，保留了更多的信息。这些结果强烈表明，数字系统，如果使用得当，可以超过胶片系统在检测小质量变化。

The purpose of this investigation was to develop a standard phantom for dental radiography and to compare image quality of film and digitally acquired images.First, an aluminum block of 12 steps with 7 holes covered by acrylic blocks was developed. This phantom was radio graphed with two types of films at 3 different tube voltages. The modified perceptibility curve was generated by counting maximum perceptible holes at each exposure. Optimum exposure level was determined from this curve and compared with that determined by means of the standard aluminum stepwedge and the preset time o the x-ray machine. The x-ray attenuation range for this phantom seemed to approximate clinical conditions. In addition, differences in image quality could be evaluated by means of the number of the holes seen in the phantom.Next, 2 film systems and several digital intraoral systems were compared with regard to visual image quality through use of this phantom. Modified perceptibility curves were created and compared each other. All digital systems except the Digora system showed lower optimum optimum exposures than E-speed film. In all digital images without enhancement, however, the maximum number of perceptible holes was significantly lower than that for the film systems at that exposure. With contrast enhancement, all digital systems except the Sens-A-Ray system showed visibility superior to that of the film systems. With CDR, Digora, and Dixel systems, exposures could be reduced by a considerable amount, with greater retention of information than was associated with film.These results strongly suggest that digital systems, if properly used, can exceed film systems in the detection of small mass changes.