Physical properties of a photostimulable phosphor system for intra-oral radiography

Objectives: To determine physical properties of the Digora(R): digital intr a-oral radiographic system (Soredex Orion Corporation, Helsinki, Finland) f or different calibration settings and beam energies. Methods: The line spread function (LSF) and the modulation transfer functio n (MTF) were determined from radiographs of a slit. Noise power spectra. (N PS) were determined from radiographs exposed to homogeneous radiation field s at 10, 50 and 100% of the calibration exposure for three tube potentials. All calculations were performed using relative values of exposure comprise d of gray level, the signal at the photomultiplier tube and the amplified s ignal in order to confirm agreement between these different approaches, Noi se equivalent quanta (NEQ) were calculated from the one-dimensional NPSs an d the MTF. Detective quantum efficiencies (DQE) were determined from the NE Qs and representative values of the photon fluence. Signal-to-noise ratios (SNR) were calculated for different signal contrasts applying the NEQs. Results: The MTF of the system exhibited typical characteristics and falls to a value close to zero at the Nyquist frequency of about 7 cycles/mm. Noi se as expressed by the NPS was found to be relatively low, i.e. about 10(-9 ) to 10(-)6 mm(2) depending on exposure and frequency. There was no signifi cant difference between data obtained at different beam energies. The NEQ a nd hence the DQE were relatively high. DQE decreased with increased exposur e. For exposures in the clinical range of the DQE reached a peak value of a bout 25%. SNRs are favorable. Conclusion: The physical properties of the Digora(R) intra-oral system indi cate that it is suitable for digital intra-oral radiography.