Evaluation of PSPL plate erasing time of a digital dental radiology system

Denoptix (CEDH Gendex Dental System, Milan, Italy) dental imaging system uses photo-stimulable phosphor luminescence (PSPL) plates to store energy during X-ray exposure, being later processed by a laser reader and digitizer. Afterwards the plate is erased and re-used. The cleaning process described by the manufacturer consists of exposing the PSPL plates to negatoscope light for 5 minutes. Proper light intensity and exact erasing time must be considered in order to guarantee good quality procedures in its re-utilization. X-ray exposed plates were submitted to four negatoscopes with different measured light intensities for several periods of light exposure, until the Denoptix system was unable to process the latent image in the plates, and we considered then that the plates were cleaned. We have found the relationships between erasing time, exposed dose and negatoscope light intensity. We have also measured the relative plate image fading with negatoscope light exposure time. We have concluded that a Poisson process governs plate erasing. Considering clinical situations, we have shown that it was possible to largely reduce erasing time and increase plate re-utilization. The exponential decay of image data also suggested a still smaller erasing time, representative of a partial cleaning status assuming that residual noise presence in the erased plate is clinically acceptable.