Analysis of Signal Fading of Photostimulable Phosphor Plate System and Its Effect on the Accuracy in Detecting Proximal Caries

Abstract

: To clarify 1) how the signal fading effect occurs and 2) the diagnostic quality of the signal fading image in caries diagnosis. The Digora Optime (Soredex, Helsinki, Finland) system was used. Aluminum step wedges of 1 to 10 mm thickness and 1-mm-thick lead were used. Exposed photo-stimulated phosphor imaging plates (PSP-IPs) were scanned at six different intervals: immediately, 3, 6, 24, 72, and 144 h. Two kinds of scanning modes were used: with and without auto enhancement correction (AEC). The gray value difference between the immediate and delayed scanning images in the same objective area was calculated as the signal fading effect value (FEV). Thirty extracted upper premolar teeth (carious: 42 surfaces) were used. Immediate, 3, 24, and 72 h delayed scan images were created. Four observers assessed them. The Friedman test was used for statistical analysis and statistical signi fi cance was p <0. 05. Analysis of the without AEC image revealed that the signal fading had the same gray value change. This change was not related to the initial gray value. In the processing of AEC, the middle part of the gray value tended to be more enhanced. Signi fi cant differences in gray value changes were observed after 3 h, but no statistically signi fi cant difference was seen in the caries diagnosis. The area under the receiver operating characteristic (ROC) curve (Az) from immediate, 3, 24, and 72 h delayed images was 0. 61±0. 17, 0. 56±0. 04, 0. 67±0. 04, and 0. 58±0. 06.