Comparison of standard and task-specific enhancement of Digora® storage phosphor images for approximal caries diagnosis

Objectives: To compare approximal caries detection on Digora storage phosphor images pre-enhanced with the automatic "caries-specific Oslo enhancement procedure" ("Oslo-enhanced" method) and storage phosphor images individually enhanced by observers particularly experienced in digital imaging using standard brightness and contrast functions of the Digora system ("Digora-enhanced" method). Methods: Seven staff members from four oral radiology departments rated 240 approximal surfaces for caries with regard to lesion depth in the inner and outer half of the enamel and dentine, using a 5-point confidence scale. The observations were validated histologically. A receiver operating characteristic (ROC) analysis and an analysis of variance with three dependent variables (observer confidence, observer signed error and observer absolute error) were performed. Results: The most evident difference between the methods as elucidated by the ROC analysis was the highly significant smaller interobserver and intraobserver variance with the Oslo-enhanced method for all but one observer. The methods were not different with regard to average diagnostic accuracy (A, values) as tested with paired t-tests, and there was no correlation between A, across methods. The method and lesion main effects, as well as the lesion by method interaction effect, were multivariately significant (P < 0.001) in favour of the Oslo-enhanced method. On a univariate level, the method main effect was not significant for the absolute observer error (P = 0.330). All other univariate effects were significant (P < 0.001). Conclusions: The accuracy of approximal caries detection with Digora storage phosphor images pre-enhanced and images individually enhanced was similar, but interobserver and intraobserver variability improved with the Oslo-enhanced method. Since image manipulation is not performed with the Oslo-enhanced method, the increased speed of the diagnostic procedure combined with the improved observer variability would probably be even more pronounced for the general dental practitioner.