Physical evaluation of a system for direct digital intra-oral radiography based on a charge-coupled device

Objectives: To determine technical properties of a direct digital intra-oral radiographic system, the Dixel® (J Morita Corporation, Kyoto, Japan). Methods: A dose response function and the dark current were calculated from two series of exposures to a homogeneous radiation field. The line spread function (LSF) and the modulation transfer function (MTF) were determined from radiographs of an edge. The noise power spectrum (NPS) was determined at three exposures from radiographs exposed to homogeneous radiation fields. Noise equivalent quanta (NEQ) were calculated from the one-dimensional NPS and the MTF. The detective quantum efficiency (DQE) was determined from the NEQ and a representative value of the photon fluence. Signal-to-noise ratios (SNR) were calculated from the NEQs and different signal contrasts. Results: The dose response function demonstrated a slight curvature. There was no effect of the dark current. NPS ranged from 10^-5-10^-7 mm² depending on exposure and frequency. At a peak of about 2 cycles/mm the DQE is on an average about 30 per cent. SNRs are favorable. Conclusion: The technical properties found in this study indicate that the Dixel® system is suitable for intra-oral dental radiography.