Maxillofacial Radiology Department, Dentistry Faculty, Selcuk University, Kampüs, Konya 42079, Turkey.
Clin Oral Investig. 2012 Jun;16(3):719-26. doi: 10.1007/s00784-011-0587-y. Epub 2011 Jul 6.
Size reduction through compression is an important issue that needs to be investigated for possible effects on image quality. The aim of the present study was to evaluate the subjective image quality of digital panoramic radiographs which were lossless and lossy compressed for the visualization of various anatomical structures. Fifty-five digital panoramic radiographs in Tagged Image File Format (Tiff) were used in the study. Two types of lossy (Joint Photographic Experts Group (Jpeg)) and one type of lossless (Lempel-Ziv-Welch) compression were applied to the original radiographs. These radiographs were evaluated by two observers separately for the visibility of some anatomical structures with visual grading. Mean quality number for each radiograph was obtained. The differences between the mean quality numbers in each compression and original image mode were evaluated with Friedman test. Pair-wise comparisons revealed that there were statistically significant differences between all groups (p = 0.000) for all comparisons except for Jpeg_1 and Jpeg_2 groups. Kappa statistics was used to evaluate inter- and intra-observer agreements. Intra-observer agreements were ranging from 0.229 to 1.000 and inter-observer agreements were ranging from 0.154 to 1.000. The observers had better inter- and intra-observer agreements in highly compressed Jpeg_1 images. The anatomical structures evaluated in this study had better visibility in Tiff images than Jpeg images except for mandibular canal and mental foramen. While Jpeg compressed images offer high inter- and intra-observer agreements, the visibility of anatomical structures are better in Tiff images except for mandibular canal and mental foramen.
通过压缩来减小尺寸是一个需要研究的重要问题，因为这可能会影响图像质量。本研究的目的是评估数字全景放射影像的主观图像质量，这些影像经过无损和有损压缩，以可视化各种解剖结构。研究中使用了 55 张 Tagged Image File Format（Tiff）格式的数字全景放射影像。对原始放射影像应用了两种有损压缩（联合图像专家组（Jpeg））和一种无损压缩（Lempel-Ziv-Welch）。两位观察者分别对这些放射影像进行了评估，评估了一些解剖结构的可见性，并进行了视觉分级。获得了每张放射影像的平均质量数。使用 Friedman 检验评估了每种压缩和原始影像模式之间的平均质量数差异。两两比较显示，除了 Jpeg_1 和 Jpeg_2 组之外，所有组之间的差异均具有统计学意义（p = 0.000）。Kappa 统计用于评估观察者内和观察者间的一致性。观察者内的一致性范围为 0.229 到 1.000，观察者间的一致性范围为 0.154 到 1.000。观察者在高度压缩的 Jpeg_1 图像中具有更好的观察者内和观察者间一致性。在这项研究中评估的解剖结构在 Tiff 图像中的可见性优于 Jpeg 图像，除了下颌管和颏孔。虽然 Jpeg 压缩图像提供了较高的观察者内和观察者间一致性，但除了下颌管和颏孔之外，Tiff 图像中解剖结构的可见性更好。
