The impact of vertical off-centering on image noise and breast dose in chest CT with organ-based tube current modulation : A phantom study

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Mäkelä , T , Kortesniemi , M & Kaasalainen , T 2022 , ' The impact of vertical off-centering on image noise and breast dose in chest CT with organ-based tube current modulation : A phantom study ' , Physica Medica , vol. 100 , pp. 153-163 . https://doi.org/10.1016/j.ejmp.2022.06.014

Title: The impact of vertical off-centering on image noise and breast dose in chest CT with organ-based tube current modulation : A phantom study
Author: Mäkelä, Teemu; Kortesniemi, Mika; Kaasalainen, Touko
Contributor organization: HUS Medical Imaging Center
Department of Diagnostics and Therapeutics
HUS Diagnostic Center
Department of Physics
Date: 2022-08
Language: eng
Number of pages: 11
Belongs to series: Physica Medica
ISSN: 1120-1797
DOI: https://doi.org/10.1016/j.ejmp.2022.06.014
URI: http://hdl.handle.net/10138/346688
Abstract: Purpose: To determine the effects of patient vertical off-centering when using organ-based tube current modulation (OBTCM) in chest computed tomography (CT) with focus on breast dose. Materials and methods: An anthropomorphic adult female phantom with two different breast attachment sizes was scanned on GE Revolution EVO and Siemens Definition Edge CT systems using clinical chest CT protocols and anterior-to-posterior scouts. Scans with and without OBTCM were performed at different table heights (GE: centered, ±6 cm, and ± 3 cm; Siemens: centered, −6 cm, and ± 3 cm). The dose effects were studied with metal-oxidesemiconductor field-effect transistor dosimeters with complementary Monte Carlo simulations to determine full dose maps. Changes in image noise were studied using standard deviations of subtraction images from repeated acquisitions without dosimeters. Results: Patient off-centering affected both the behavior of the normal tube current modulation as well as the extent of the OBTCM. Generally, both OBTCM techniques provided a substantial decrease in the breast doses (up to 30% local decrease). Lateral breast regions may, however, in some cases receive higher doses when OBTCM is enabled. This effect becomes more prominent when the patient is centered too low in the CT gantry. Changes in noise roughly followed the expected inverse of the change in dose. Conclusions: Patient off-centering was shown to affect the outcome of OBTCM in chest CT examination, and on some occasions, resulting in higher exposure. The use of modern dose optimization tools such as OBTCM emphasizes the importance of proper centering when preparing patients to CT scans.
Description: Publisher Copyright: © 2022 Associazione Italiana di Fisica Medica e Sanitaria
Subject: Chest CT
Image quality
Off-centering
Optimization
Organ-based tube current modulation
3126 Surgery, anesthesiology, intensive care, radiology
Peer reviewed: Yes
Rights: cc_by
Usage restriction: openAccess
Self-archived version: publishedVersion


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