Evaluation of exposure dose in fetal computed tomography using organ-effective modulation
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SCIENTIFIC PAPER
Evaluation of exposure dose in fetal computed tomography using organ‑effective modulation Masanao Kobayashi1 · Tomonobu Haba1 · Sayaka Suzuki2 · Yusei Nishihara2 · Yasuki Asada1 · Kazuyuki Minami1 Received: 3 April 2020 / Accepted: 19 August 2020 © The Author(s) 2020
Abstract Organ-effective modulation (OEM) is a computed tomography scanning technique that reduces the exposure dose to organs at risk. Ultrasonography is commonly used for prenatal imaging, but its reliability is reported to be limited. Radiography and computed tomography (CT) are reliable but pose risk of radiation exposure to the pregnant woman and her fetus. Although there are many reports on the exposure dose associated with fetal CT scans, no reports exist on OEM use in fetal CT scans. We measured the basic characteristics of organ-effective modulation (X-ray output modulation angle, maximum X-ray output modulation rate, total X-ray output modulation rate, and noise modulation) and used them in a Monte Carlo simulation to evaluate the effect of this technique on fetal CT scans in terms of image quality and exposure dose to the pregnant woman and fetus. Using ImPACT MC software, Monte Carlo simulations of O EMON and O EMOFF were run on 8 cases involving fetal CT scans. We confirmed that the organ-effective modulation X-ray output modulation angle was 160°; the X-ray output modulation rate increased with increasing tube current; and no modulation occurred at tube currents of 80 mA or below. Our findings suggest that OEM has only a minimal effect in reducing organ exposure in pregnant women; therefore, it should be used on the anterior side (OEMON,front) to reduce the exposure dose to the fetus. Keywords Organ-effective modulation · Fetal CT scan · Organ exposure · Monte Carlo simulation
Introduction
* Masanao Kobayashi masa1121@fujita‑hu.ac.jp Tomonobu Haba habatomo@fujita‑hu.ac.jp Sayaka Suzuki sayaka.suzuki.cm@fujita‑hu.ac.jp Yusei Nishihara yusei.nishihara@fujita‑hu.ac.jp Yasuki Asada asada@fujita‑hu.ac.jp Kazuyuki Minami kminami@fujita‑hu.ac.jp 1
Graduate School of Medical Sciences, Fujita Health University, 1‑98 Dengakugakubo, Kutsukake‑cho, Toyoake, Aichi, Japan
Department of Radiology, Fujita Health University Hospital, 1‑98 Dengakugakubo, Kutsukake‑cho, Toyoake, Aichi, Japan
2
Ultrasonography (US) is commonly used for prenatal image-based diagnosis of pregnancy [1–3], although opinion is divided on this matter, as some reports state that the reliability of US is limited by acoustic impedance [4, 5]. Radiography and computed tomography (CT) both demonstrate good diagnostic performance for the bone, but they are transmission-based techniques requiring radiation exposure to both the fetus and the pregnant woman. The exposure dose received by the fetus in these radiation-based diagnostic techniques is under 100 mGy, and it almost never increases the risk of prenatal death, deformity, or mental retardation by an amount detectable above spontaneous incidence [6]. ICRP Publication 84 mentions that detailed in
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