Consequences of the Patient's Mis-centering on the Radiation Dose and Image Quality in CT Imaging – Phantom and Clinical Study

The position of the patient highly influences the functioning of the ATCM in CT imaging. The effect of different mis-centerings on the CTDIvol dose was determined during PMMA and water phantom simulations, which were also used for noise assessment. The results show that a 50 mm mis-centering (with the phantom placed above the isocenter) can cause an increase of the CTDIvol by 47 % associated with the lower standard deviation of the HU signal, whilst a -50 mm mis-centering (with the phantom placed below the isocenter) leads to a decrease of the CTDIvol by 35% and is associated with a noisier image. A mean value of the mis-centering determined for 473 patients was -43 mm. A total of 470 of 473 patients were mis-centered below the X-ray tube, which shows an inclination of radiographers to place patients below the isocenter. This inclination was more significant for smaller patients.