Abstract
The aim of this study was to optimize CT scan protocol to minimize patient exposure to ionizing radiation while maintaining CT image quality for detecting pulmonary diseases. The absorbed dose and CT scan quality were determined using dose phantoms at various tube current settings (7.5–115 mAs). The relationship between the absorbed radiation dose and CT scan quality were examined. For both 8-mm and 3-mm scanned slice thickness, the homogeneity of CT scans was within the required range (< 4 HU) at tested tube settings (> 7.5 mAs). However, the noise level of CT scans remained within the acceptance range (< 0.35%) only when the tube current was ≥ 25 mAs. The reduction of tube current from 115 mAs to 40, 25 or 7.5 mAs could decrease the CT Dose Index (CTDI) to 60, 70 or 85%, respectively. The evaluation of CT image quality suggested that there was an inflection point at 25 mAs. When the spiral chest CT scan was employed at a low tube current setting (i.e. 40 or 25 mAs), it maintained satisfactory image quality and reduced the absorbed dose of the patient, therefore protecting patients from ionizing radiation exposure.