南 一幸

Abstract During fetal computed tomography (CT) imaging, because of differences in the pregnancy period and scanning conditions, different doses of radiation are absorbed by the fetus. We propose a correction coefficient for determining the fetal size-specific dose estimate (SSDE) from the CT dose index (CTDI) displayed on the console at tube voltages of 80–135 kVp. The CTDIs corresponding to pregnant women and fetuses were evaluated using a Monte Carlo (MC) simulation, and the ratio of these CTDIs was defined as the Fetus-factor. When the effective diameter of a fetus was approximately 10 cm, the Fetus-factor was 1.0. The estimated pregnant SSDE was multiplied by the Fetus-factor to estimate the fetal SSDE, which was compared with the fetal dose obtained by the MC simulation of the image of the fetal CT examination. The fetal dose could be estimated with an error of 31.5% in fetal examinations conducted using helical CT.

<title>Abstract</title> 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 OEM_ON and OEM_OFF 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 (OEM_ON,front) to reduce the exposure dose to the fetus.

<title>Abstract</title> The aim of this study was to investigate differences in volume computed tomography dose index (CTDIvol) and dose-length product (DLP) values according to facility size in Japan. A questionnaire survey was sent to 3000 facilities throughout Japan. Data from each facility were collected including bed number, computed tomography (CT) scan parameters employed and the CTDIvol and/or DLP values displayed on the CT scanner during each examination. The CTDIvol and DLP for 11 adult and 6 paediatric CT examinations were surveyed. Comparison of CTDIvol and DLP values of each examination according to facility size revealed key differences in CT dose between small and large facilities. This study highlights the importance of lowering the dose of coronary artery examination with contrast agent in smaller facilities and of lowering the dose of adult and paediatric head CT without contrast agent in larger facilities. The results of this study are valid in Japan.

In order to estimate the effective dose (E) of a person who may come into close contact to the 123I-IMP patients, exposure rates around 30 adult patients (male: 15, female: 15) were measured with three ionization survey meters (Aloka, ICS-301) at distances of 0.05, 0.5, 1.0 and 1.5m from the patients. Measurements were carried out in 1, 3, 6 and 24h after the administrations of ¹²³I-IMP. Survey meters were set up to the first cervical vertebrae (Level I), xiphoid process (Level II) and anterior superior iliac spine (Level III) of the patients who were standing erect. The maximum dose equivalent (H₁cm) rate of107.9μSv/h per 222MBq was recorded in the level II at 0.05m from the patients. Effective half life of ¹²³I-IMP was 11.0h.<BR>The E around the ¹²³I-IMP patient increases in time approaching to a saturated value, which is defined as total E. The tota1 E was calculated from initial H₁cm rates and the effective half life; estimated values/222MBq are 949μSv at 0.05m, 195μSv at 0.5m, 76μSv at 1.0m and41μSv at 1.5m.

¹²³I-BMIPPと²⁰¹TlCl心筋SPECTを一度の検査で, かっクロストークの影響なしに実施する方法として二核種連続投与連続撮像法を考案し, その有用性について検討した。¹²³I-BMIPP検査時にあらかじめ²⁰¹Tlウインドウ (71±7keV) での画像を撮像し, 終了後ただちに投与撮像して得られた²⁰¹TlCl画像から71±7keVウインドウに混入する¹²³Iの光子散乱成分を差し引くことで補正された²⁰¹TlCl画像を得ることができる。クロストークの補正精度を検証するため¹²³Iと²⁰¹Tlの面線源を使用し, ¹²³I画像が²⁰¹Tl画像に及ぼす影響を検討した。また, 心臓ファントムおよび臨床例についても検討した。結果, 面線源では¹²³lと²⁰¹Tlの混在比率の変化や散乱体の有無に対し2-3%の誤差で²⁰¹TlCl画像は復元された。心臓ファントムおよび臨床例でも純粋な²⁰¹TlCl画像に匹敵する画像が得られ, カウントプロファイルカーブ, polar mapおよび画像のコントラストにおいても純粋な²⁰¹TlCl画像とほぼ一致した。面線源の実験において, 連続する2回の撮像間で3ピクセル (約1.5cm) までの位置ずれは, 補正後の²⁰¹TlCl画像の信頼性を損なう恐れはなかった。

In order to estimate the effective dose (E) of a person who may come into close contact to the ^99mTc-GSA patients. Radiation dose rates around 21 adult patients (male: 14, female: 7) were measured with three ionization surveymeters (Aloka, ICS-301) at distances of 0.05, 0.5, 1.0 and 1.5 m from the patients. Measurements were carried out at 0.75, 3.0, 6.0 and 24.0h after the administrations of ^99mTc-GSA.Surveymeters were set up to the first cervical vertebrae (Level I), xiphoid process (Level II) and anterior superior iliac spine (Level III) of the patients with their standing erect, The maximum dose equivalent (H_lcm) rate of 64.98μSvh^-1 per 185 MBq was recorded in the LevelII. Effective half life of ^99mTc-GSA was 5.8h. Total E around the patients were calculated by the initial H_lcm rates and the effective half life. Total E were 285, 62, 23 and 13μSv per 185 MBq at distances of 0.05, 0.5, 1.0 and 1.5m, respectively. E for the first 24h was corresponding to 94.3% of the total E.