Effects of the Use of Automatic Tube Current Modulation on Patient Dose and Image Quality in Computed Tomography

Ayşegül Yurt,İsmail Özsoykal,Funda Obuz

doi:10.4274/mirt.galenos.2019.83723

Ayşegül Yurt, İsmail Özsoykal + Show 1 more

Open Access

https://doi.org/10.4274/mirt.galenos.2019.83723

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Abstract

Objectives:The frequency of abdominal computed tomography examinations is increasing, leading to a significant level of patient dose. This study aims to quantify and evaluate the effects of automatic tube current modulation (ATCM) technique on patient dose and image quality in contrast-enhanced biphasic abdominal examinations.Methods:Two different scan protocols, based on constant tube current and ATCM technique, were used on 64 patients who visited our radiology department periodically. For three patient groups with different patient size, results from two protocols were compared with respect to patient dose and image quality. Dosimetric evaluations were based on the Computed Tomography Dose Index, dose length product, and effective dose. For the comparison of image qualities between two protocols, Noise Index (NI) and Contrast to Noise Ratio (CNR) values were determined for each image. Additionally, the quality of each image was evaluated subjectively by an experienced radiologist, and the results were compared between the two protocols.Results:Dose reductions of 31% and 21% were achieved by the ATCM protocol in the arterial and portal phases, respectively. On the other hand, NI exhibited an increase between 9% and 46% for liver, fat and aorta. CNR values were observed to decrease between 5% and 19%. All images were evaluated by a radiologist, and no obstacle limiting a reliable diagnostic evaluation was found in any image obtained by either technique.Conclusion:These results showed that the ATCM technique reduces patient dose significantly while maintaining a certain level of image quality.

Highlights

In the early 1990s, helical computed tomography (CT) devices were introduced for medical imaging
The most common strategy among these is the use of Automatic Exposure Control (AEC), where the tube current is adjusted by the scanner according to the patient size
This study aims to focus on the use of Z-DOM in contrast-enhanced biphasic abdominal examinations and to make evaluations on image quality and patient dose

Summary

Introduction

In the early 1990s, helical computed tomography (CT) devices were introduced for medical imaging. Images from 64 to 320 slices can be acquired in a single rotation of the X-ray tube within one-third of a second These advances led to a further increase in the use of CT for cardiovascular examinations, perfusion imaging, brain, heart, breast, colon, and whole body studies [1]. In MSCT, over-beaming and end effect terms refer to the necessity of beam and scan widths extending beyond detector area and imaged region, respectively These conditions that arise due to image reconstruction purposes lead to increase in radiation dose to the patient, when compared to single slice CT scanners. Smaller gantry designs for MSCT devices led to a shorter patient-tube distance which obviously affects patient dose [3] These conditions have forced CT manufacturers to develop dose optimization strategies either based on image processing or the prevention of unnecessary radiation. Since the beginning of the 2000s, AEC systems have been developed by the manufacturers based on different operating mechanisms; offering similar opportunities on patient dose control, image quality, and tube life [4,5]

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