Radiation Dose and Image Quality in Computed Tomography Examinations: A Comparison between Automatic Exposure Control (AEC) and Fixed Tube Current (FTC) Techniques.

Abstract

The aim of this study was to evaluate and compare the radiation doses imparted to patients undergoing computed tomography (CT) examinations and image quality with the use of automatic exposure control (AEC) and fixed tube current (FTC) techniques using a head and body phantom in a Siemens emotion 16-slice multidetector computed tomography (MDCT) scanner. The head and body phantoms were scanned with AEC activated and with FTC for routine head, chest, abdomen and pelvis CT examinations. All parameters were kept constant for each technique except with varying tube current time product (mAs) for the FTC technique. Dose measurements were performed using RTI barracuda system with electrometer, and CT dose Profiler probe. Organ and effective doses were calculated using CT-Expo software. Subsequently image quality between the AEC and FTC technique were assessed using the Catphan 700 image quality phantom. The volume computed tomographic dose index (CTDIvol) values estimated with the AEC technique were; 32.8 mGy, 6.7 mGy, 14.3 mGy, and 11.7 mGy for head, chest, abdomen and pelvis respectively. The estimated volume CTDI values with the FTC technique had a range of 32.9-53.0 mGy for head, 9.5-26.2 mGy for chest, 9.5-24.2 mGy for abdomen and 9.5-26.0 mGy for pelvis respectively. The DLP values for the AEC technique were; 593 mGy.cm, 108 mGy.cm, 240 mGy.cm, and 190 mGy.cm for head, chest, abdomen and pelvis examinations respectively. With the FTC technique, the DLP values had a range of 571-946 mGy.cm for head, 284- 780 mGy.cm for chest, 165-543 mGy.cm for abdomen, and 250-690 mGy.cm for pelvis respectively. Compared with the FTC technique, the use of AEC resulted in a mean dose reduction of up to 19.4% for CTDIvol and 18.2% for DLP for the head phantom and a mean dose reduction range of 12% - 59.4% for CTDIvol and 7.1% - 78.3% for DLP for the body phantom. The overall image quality test between AE and FTC techniques for spatial resolution and low contrast detectability show no statistical significant differences (𝑃 > 0.05). There was statistical significant difference in the contrast to noise ratio scores between the AEC and FTC techniques(𝑃 = 0.008) with about 35% noise in the AEC images than the FTC images acquired. From the study results, the use of AEC showed a considerable dose reduction compared with the FTC technique with adequate image quality performance. Thus the use of AEC technique is promising and will benefit patients with less radiation being delivered to them in CT examinations.