[Evaluation of AEC Consistency in Digital X-ray Imaging Systems]

The Japan Network for Research and Information on Medical Exposures (J-RIME) established the diagnostic reference level (DRL) and is advancing optimization of radiation protection. We believe that the difference in the imaging dose between facilities may be due to the fact that automatic exposure control (AEC) adjustment is not unified among manufacturers. The consistency of AEC is specified in JIS 4751-2-54, but it is not applicable to digital X-ray imaging systems because it is for optical density of analog X-ray imaging systems. This article evaluates the consistency of AEC in digital X-ray imaging systems. The AEC consistency was compared with the AEC-estimated dose from the air kerma (K_AEC) using the phosphor-based imaging plate placed at the back of the AEC detector. We measured the AEC tube voltage and subject thickness characteristics (tracking) of four types of digital X-ray imaging systems at three facilities. In the test of tube voltage characteristics, the average K_AEC values at all tube voltages were 2.37±0.04  µGy for A system, 7.30±1.44  µGy for B system, 3.53±0.13  µGy for C system, and 5.70±0.18  µGy for D system. The relative errors were +2.6 to -1.8% for A system, +25.3 to -22.6% for B system, +5.2 to -1.4% for C system, and +2.5 to -4.4% for D system. In the subject thickness characteristics test, the average K_AEC values for all Al thicknesses were 2.34±0.02  µGy for A system, 5.95±0.23  µGy for B system, 4.25±1.12  µGy for C system, and 5.03±1.27  µGy for D system. The relative errors were +1.0 to -0.9% for A system, +4.1 to -5.0% for B system, +40.5 to -28.1% for C system, and +19.7 to -42.9% for D system.