Effect of tube current on diagnostic image quality in paediatric cerebral multidetector CT images

The aim of this study was to investigate the effect of tube current on diagnostic image quality in paediatric cerebral multidetector CT (MDCT) images in order to identify the minimum radiation dose required to reproduce acceptable levels of different diagnostic image qualities. Original digital scanning data (raw data) were selected retrospectively from routine MDCT brain examinations of 25 paediatric patients. All examinations had been performed using axial scanning on an eight-slice MDCT (LightSpeed Ultra, GE Healthcare). Their ages ranged from newborn to 15 years. Quantum noise was added artificially to the raw data representing dose reductions equivalent to steps of 20 mA. Patient identification information was removed. Three experienced radiologists blindly and randomly assessed the resulting images from two different levels of the brain with regard to reproduction of structures and overall image quality. Final data were evaluated using the non-parametric statistical approach of inter-scale concordance. The minimum value of tube current-time product (mAs) required to reproduce an image of sufficient diagnostic quality was established in relation to the age of the patient. The corresponding CT dose index values by volume (CTDI(vol) (mGy)) were also established. In conclusion, acceptable reproduction of low-contrast structures was possible at CTDI(vol) values down to 20 mGy (patients 1-5 years old). For acceptable reproduction of high-contrast structures, CTDI(vol) values down to 10 mGy were considered possible (patients 1-5 years old). The original image quality for patients under 6 months of age (15 mGy) was found to be inadequate for acceptable reproduction of low-contrast structures.