Optimum display of the digital intraoral imaging system by quantitative evaluation on image quality

数字系统在医学成像中得到了广泛的应用，这一趋势也出现在普通牙科医生身上。然而，关于数字图像的最佳显示并没有达成共识，数字图像中的信息没有充分用于诊断和治疗计划。在本研究中，使用专门开发的图像质量幻影对数字系统中的低对比度可检测性与胶片中的低对比度可检测性进行了定量评价。然后使用相同的系统和相同的观察者评估拔牙近端龋的诊断准确性。回归分析显示，低对比检出率与诊断准确率高度相关。数字系统和胶片的诊断准确率没有统计学上的显著差异。然而，曝光对诊断准确性或低对比度检测的影响在数字系统中比在胶片系统中更大。在有自动曝光补偿的数字系统中，这种影响比没有自动曝光补偿的数字系统要小。进一步调查表明，数字系统的图像对比度与胶片完全不同。数字系统在低曝光情况下的图像对比度远不如胶片。我们开发了图像显示算法来提高低曝光下的对比度。结果表明，处理后的图像整体对比度优于原始图像，与胶片的对比度相近。该图像显示算法可普遍适用于所有数字口内成像系统。

Digital system is widely used in medical imaging and this trend is found in general dental practitioners, too. However, no consensus was obtained about the optimum display of the digital image and information in the digital images are not fully used for diagnosis and treatment planning.In this study, low contrast detectability in the digital systems was compared with that in the film using specially developed image quality phantom for quantitative evaluation. Then diagnostic accuracy for proximal caries of the extracted teeth was evaluated using the same systems and the same observers.Regression analysis showed high correlation between low contrast detectability and diagnostic accuracy. There was no statistically significant difference between diagnostic accuracy of the digital systems and that of the film. Effect of exposure on diagnostic accuracy or low contrast detectability, however, was larger in the digital systems than in the film. This effect was smaller in the digital system with automatic exposure compensation than in that without it.Further investigation clarified that image contrast of the digital system was completely different from that of the film. Image contrast of the digital system in low exposure was far inferior to that of the film. We developed the image display algorithm to improve contrast in low exposure. The result showed that overall image contrast of the processed image was better than that of the original and it was similar to that of the film.This image display algorithm may have general applicability to all digital intraoral imaging systems.