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.
