Effect of different exposure times on caries detection and pixel value in a wireless digital system.

Abstract

: The aim of this study was to assess, using the CDR Wireless®, the effect of different exposure times on caries detection and pixel intensity values. Forty teeth were x-rayed using a Schick CDR Wireless sensor at eight different exposure times - 0.06, 0.10, 0.13, 0.16, 0.20, 0.25, 0.30, and 0.32 s. Four observers evaluated the images for presence of carious lesions scoring proximal surfaces of each tooth on a 5-point scale. Scores were compared to histological sections of the teeth. Accuracy was evaluated by means of ROC curve analysis. Radiographs of an aluminum step wedge were obtained using the same eight exposure times. Pixel intensity measurements were obtained, and mean pixel values were statistically analyzed using linear regression. The Az for each exposure time varied from 0.53 to 0.62. Two-way analysis of variance and Tukey test demonstrated that the exposure time of 0.25 s presented the best result and was significantly higher than 0.30 s and 0.35 s. In regard to mean pixel values, two different behaviors were observed, and the exposure time of 0.20 s presented mean pixel values in both phases. The performance of the exposure times from 0.06 s to 0.25 s was satisfactory for proximal caries detection, and 0.25 s is the best as indicated for this finality. Considering that a reduction of exposure time represents a reduction of patient exposure dose, and this reduction cannot neglect image quality, the behavior of any digital system must be carefully evaluated.