The purpose of this research was to set-up a protocol for using the CeIT elliptical test phantom to test the performance of Automatic Exposure Control (AEC) systems on the CT scanners in use at Aberdeen Royal Infirmary (ARI). These are the GE Lightspeed, GE Optima 6600 and Siemens Somaton Definition in Radiology and the Philips Brilliance in Radiotherapy treatment planning. The variation of image noise and the tube current-time product (mAs) were studied from images obtained from each scanner. Noise was measured using the standard deviation of five selected regions of interest in the images of the phantom obtained from the CT scanners. Normalised percentage noise (noise %) was then calculated to compare how the scanners dealt with image noise with relation to the mAs. The results showed an increase in mAs values (increase in dose) with the phantom and regulation of the noise leading to acquisition of quality images from all three scanners. Offcentering, using the AP scout increased the dose to the phantom when the patient table was above the isocenter and reduced the dose to the phantom when the table was below the isocenter. This shows the importance of patient centering for effective AEC system ’ s dose regulation. Different SPRs also affected the operations of the AEC systems differently, with PA giving more dose followed by LAT and AP in the GE and Philips scanners which were studied on this aspect. The Philips D-DOM modulation kept almost constant dose across the scanning process regardless of the phantom size, hence D-DOM should be used with care. CeLT phantom was useful in studying dose regulation by different AEC systems, hence it is useful in quality control (QC) tests of AEC systems on CT scanners as a testing protocol was formulated from this study.

The increased worldwide demand for computed tomography (CT) scans to provide quality images and faster scans for patient care and management has led to the introduction of multidetector technology of CT scanners that provide faster scan times, longer scan ranges and higher resolution for better image quality. The demand for CT scans has therefore resulted in the use of more ionising radiation for diagnostic and radiotherapy treatment planning purposes. Radiation dose should be as low as reasonably achievable (ALARA) and the benefits of the radiation procedure should outweigh the risks. The International Commission on Radiation Protection (ICRP) requires diagnostic reference levels (DRLs) to be established to identify abnormally high dose levels by setting an upper threshold, which standard dose levels are not expected to exceed when good practice is applied. The radiation dose received from a CT scan varies from person to person as it depends on the individual’s size, the type of CT procedure used, as well as the type of the CT scanner used. Various dose reduction techniques have been studied to cater for adverse radiation effects, while maintaining the diagnostic utility of the acquired images. Automatic exposure control, minimising scanning times and optimization of system parameters are some of the techniques used in dose reduction to patients.

With Regards,
Sara Giselle
Associate Managing Editor
Journal of Medical Physics and Applied Scinces