Some characteristics of solid-state and photo-stimulable phosphor detectors for intra-oral radiography.

The general aim of the study was to evaluate and compare different solid-state and photo-stimulable phosphor systems for digital intra-oral radiography and to compare different generations of some of the systems. The evaluations concerned physical and psychophysical performance, subjective image quality and the influence of image processing. Physical performance was tested by means of large area transfer characteristics, noise, contrast, and modulation transfer function. For the physical performance it was found that grey level values in images from solid-state systems decreased faster with increasing exposure than in images from photo-stimulable phosphor systems. Noise increased with increased exposure for both solid-state and photo-stimulable phosphor systems. Solid-state systems reached their highest contrast index at lower doses than the photo-stimulable phosphor systems. Solid-state systems had better resolving power due to higher contrast and smaller pixel sizes than the PSP systems. The resolving power of the photo-stimulable phosphor systems improved when the images were enhanced. Psychophysical tests were performed by determining the sensitivity of the systems for detecting small mass differences in test objects. It was found that when contrast enhancement were applied lower exposures could be used to detect low contrast objects in images from both solid-state and photo-stimulable phosphor systems. Blooming effects deteriorated images from solid-state systems at lower doses than burn-out effects deteriorated conventional radiographs or images from a photo-stimulable phosphor system. Some improvement in physical and psychophysical performance could be seen in the new generation of solid-state systems. Subjective image quality was tested by visual grading analysis in which observers graded the visibility of structures important for the diagnosis of common dental diseases. All systems produced diagnostically acceptable image quality but the photo-stimulable phosphor systems over a much wider exposure range than the solid-state systems. Histogram equalization did not improve image quality. A common diagnostic task; measurement of marginal bone level around implants, was used to study the influence of image processing. Radiographic measurements of bone height around implants in images from a photo-stimulable phosphor system was as accurate and precise as film images. Image processing was found to be task dependent. For a specific task, related to marginal bone height measurements around implants, a strong edge enhancement algorithm was found to be best.