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 OEMON and OEMOFF 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.
Highlights
Ultrasonography (US) is commonly used for prenatal image-based diagnosis of pregnancy [1,2,3], opinion is divided on this matter, as some reports state that the reliability of US is limited by acoustic impedance [4, 5]
Given that this study evaluates pregnant women and fetuses and verifies the effects of Organ-effective modulation (OEM) per patient, we chose to evaluate the effect of OEM using effective dose (ED)(Sv), a parameter that goes beyond the scope of the prescribed definition of ED
Given that DM increases at higher tube currents, DM is absent at 80 mA or below, and that n is higher in the 0° ± 90° range at a tube voltage of 80 kV but this difference is absent at 100 kV, these tube current characteristics and image quality characteristics must be considered when setting scanning conditions for OEMON,front
Summary
Ultrasonography (US) is commonly used for prenatal image-based diagnosis of pregnancy [1,2,3], opinion is divided on this matter, as some reports state that the reliability of US is limited by acoustic impedance [4, 5]. 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 informed consent is required when the fetal exposure dose exceeds 1 mGy and that methods of reducing exposure should be investigated when the fetus is exposed directly [6]. For these reasons, we should endeavor to reduce exposure through introduction of exposure-reducing techniques when using radiation in prenatal image-based diagnoses. The American College of Radiology and the Society for Pediatric Radiology have recommended the use of auto-exposure control techniques but have not discussed the possibility of reducing patient exposure with the recently developed OEM technique [13]
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