Investigation of Radiation Dose Redution Potential of Multislice CT Scanners

Allen Nathan Mhagama (
Physics Department, University of Dar es Salaam
October, 2013


The rapid acquisition of multislice computed tomography (MSCT) scanners for diagnostic imaging in Tanzania had created the need to establish the magnitude of radiation dose and assess the effectiveness of the automatic exposure control (AEC) systems incorporated in these scanners. The computed tomography dose indices (CTDI) were determined using kerma-length products obtained by scanning the Unifors ion chamber positioned free in air or in standard CT phantoms of diameters 16 and 32 cm for head and body, respectively. The organ and effective doses were estimated using the CT-Expo software by entering patients data (age and sex), scan parameters, scanner types and models, obtained from the examination forms of 125 patients that underwent various routine examinations. To assess the effectiveness of the AEC systems, the standard CT phantoms of diameters 16 and 32 cm and water phantoms of diameters 20 and 22 cm were scanned with and without the AEC systems. The results showed that the weighted CTDI values obtained in this study were within the limits of the European Commissions acceptable diagnostic reference levels. The AEC systems were observed to reduce radiation dose with no significant increase in subjective image noise. These systems were found to be more effective in reduction of radiation dose for smaller patients than the large ones. The MSCT scanners were observed to deliver comparable or less organ and effective doses than those obtained from single slice computed tomography (SSCT) scanners examinations. This study recommends that the technologists and radiologists should practice the ALARA principle when selecting the exposure parameters especially for pediatric examinations. In addition, the technologists and radiologists should attend the in-service training programmes to learn the operation and effective use of the AEC systems for reducing dose. The CT scanner manufacturers should produce the standardized and more user-friendly AEC systems in future designs.