Dose Correction in Medical X-ray Imaging in Low Dose Regime

The purposes of this work were to examine the output behavior of X-ray tubes and to seek dose corrections in medical X-ray imaging in low dose regime. Entrance surface doses (ESD) and CT dose index (CTDIv) were measured under various exposures (mAs) and peak voltage (kVp) by employing a Direct Radiography (DR) system from GE Health care and previously reported an Afga Computed Radiography (CR) system and three Computed Tomography (CT) systems (one from Toshiba, one from GE and one from Philips). Dose output models of X-ray tubes were employed to determine the X-ray tubes' output powers under various doses ESD or CTDIv. The X-ray tubes' output powers were found to be varied rapidly in the low dose regime. Both increased and decreased powers were demonstrated from various imaging systems below some dose thresholds. The dose thresholds are about 50 μGy for the digital radiography imaging systems and 2 mGy for the CT systems. A dose correction factor was proposed as a result. Application of this dose correction factor to an earlier abdomen phantom study using the Toshiba CT scanner showed improved logistic curve estimation for the relationship between image quality and radiation dose. As output powers of X-ray tubes vary rapidly in low dose regime, the reported low doses based on theoretical models or extrapolated from high dose measurements should be corrected using the proposed dose correction factor.