Configuration of AEC kVp dependence for digital radiography systems

摘要

As digital radiography (DR) systems are being increasingly adopted for clinical applications, automatic exposure control (AEC) has remained a critically important component. Unlike traditional screen/film systems, however, there does not currently exist a widely accepted AEC calibration criterion for DR systems. This is due mainly to the signal response characteristics and wide dynamic range of DR detectors, which are inherently different from those of a screen/film system. Consequently, the AEC cutoff dose and its dependence on the kVp selection (i.e., kVp compensation) should be calibrated differently for DR systems. In this paper, we have investigated three possible schemes to set up the AEC compensation based on a constant response of the detector in terms of the signal, receptor dose, and signal-to-noise ratio (SNR). The results for each setup scheme was evaluated on four different DR detectors (Gd_2O_2S, CsI(Tl), a-Se, or BaFBrI as X-ray absorption material) based on the measured signal and noise response of the detector under the ISO beam conditions (ISO 6236-1). The results showed that all three setup schemes produced similar results for clinical beams above 70 kVp. Significant differences were observed only at lower kVp ( ≤ 60) beams. In addition, schemes of constant signal and constant SNR produced similar results with the only exception being the a-Se detector at low kVp ( ≤ 60) beam. These results indicate that the choice of the kVp schemes would be important only for low kVp exams.