Inadequate object positioning and improvement of automatic exposure control system calculations based on an empirical al
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SCIENTIFIC PAPER
Inadequate object positioning and improvement of automatic exposure control system calculations based on an empirical algorithm Yasushi Furukawa1,2 · Kosuke Matsubara3 · Tosiaki Miyati3 Received: 27 June 2020 / Accepted: 17 November 2020 © Australasian College of Physical Scientists and Engineers in Medicine 2020
Abstract When using automatic exposure control (AEC) systems in computed tomography (CT), miscalculation of tube current occurs when a patient is not aligned with the rotational center of the X-ray tube. A positioning compensation mechanism provides a corrective function when the patient is off-center; however, not all CT systems are equipped with this mechanism. AEC systems can broadly be divided into noise- and empirical-based. The authors studied empirical-based AEC systems to derive a compensation process to achieve an equivalent effect to that offered by the mechanism and to verify the accuracy of this process. A relational equation was derived to keep the tube current constant with variations in table height and quality reference milliampere-seconds (QRmAs), and this was adopted as the proposed compensation method. The radiation dose and image quality were evaluated for phantom imaging with and without the proposed compensation method using AEC and varying table heights. The output radiation dose and image quality were also evaluated for anthropomorphic chest phantom imaging to verify the compensatory effect of the proposed method. With the proposed compensation method, changes in the table height resulted in only small changes in the output radiation dose and noise level. Conversely, when the proposed compensation method was not used, changes in the table height resulted in widely varying output radiation dose and noise level. Imaging the anthropomorphic chest phantom with the proposed compensation method also yielded a stable output radiation dose. Keywords Computed tomography · Automatic exposure control · Miscentering · Table height · Localizer radiographs
Introduction Computed tomography (CT) involves medical exposure to radiation. Recommended countermeasures to this exposure include the proactive use of automatic exposure control (AEC) systems to control the radiation dose and image quality [1, * Yasushi Furukawa [email protected] 1
Department of Radiological Technology, Nagoya University Hospital, 65 Tsurumai‑cho, Showa‑ku, Nagoya 466‑8560, Japan
2
Department of Quantum Medical Technology, Graduate Course of Medical Science and Technology, Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, 5‑11‑80 Kodatsuno, Kanazawa 920‑0942, Japan
3
Department of Quantum Medical Technology, Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, 5‑11‑80 Kodatsuno, Kanazawa 920‑0942, Japan
2]. AEC systems can regulate the tube current and analyze subject size and shape in each slice acquired with the localizer radiographs. AEC systems may operate differently depending on the manuf
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