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.

With the objective of reducing patient exposure to radiation, we conducted a questionnaire survey regarding radiographic conditions in 2014. Here we report estimates of dose exposure in general radiography and mammography through an investigation and comparison of present patient exposure conditions. Questionnaires were sent to 3000 facilities nationwide in Japan. Surveys asked questions on a total of 16 items related to general radiography, including the chest, abdomen, and breast. Output data from x-ray tubes measured in the Chubu area of Japan were used as the mean in these estimates. The index of patient exposure was adopted as the entrance skin dose (ESD) for general radiography and as the mean glandular dose (MGD) for mammography. The response rate for this survey was 21.9%. Our results showed that doses received through the use of flat-panel detector (FPD) devices were lower than those received through computed radiography devices, except for the ankle joint (e.g. in chest examination, the dose from FPD and CR was 0.24 mGy, 0.31 mGy on the average, respectively). These results suggest that more widespread use of FPD devices could lead to decreases in the ESD and MGD, thereby reducing patient exposure.

Objective: The aims of this study were to estimate the effective radiation doses from CT examinations of both adults and children in Japan and to study the impact of various scan parameters on the effective doses. Methods: A questionnaire, which contained detailed questions on the CT scan parameters employed, was distributed to 3000 facilities throughout Japan. For each scanner protocol, the effective doses for head (non-helical and helical), chest and upper abdomen acquisitions were estimated using ImPACT CT Patient Dosimetry Calculator software v. 1.0.4 (St George's Hospital, London, UK). Results: The mean effective doses for chest and abdominal examinations using 80-110 kV were significantly lower than those using 120 kV. However, there was no statistically significant difference in the mean effective doses for head scans between facilities employing 80-110 kV and 120 kV. In chest and abdominal examinations, the mean effective doses using CT scanners from Western manufacturers [Siemens (Forchheim, Germany), Philips (Eindhoven, Netherlands) and GE Medical Systems (Milwaukee, WI)] were significantly lower than those of examinations using Japanese scanners [Hitachi (Kashiwa, Japan) and Toshiba (Otawara, Tochigi, Japan)], except for in paediatric chest examinations. Conclusion: The mean effective doses for adult head, chest and abdominal CT examinations were 2.9, 7.7 and 10.0 mSv, respectively, whereas the corresponding mean effective doses for paediatric examinations were 2.6, 7.1 and 7.7 mSv, respectively. Advances in knowledge: Facilities using CT scanners by Western manufacturers commonly adopt low-tube voltage techniques, and low-tube-voltage CT may be useful for reducing the radiation doses to the patients, particularly for the body region.

Objective: The aims of this study are to propose a new set of Japanese diagnostic reference levels (DRLs) for 2014 and to study the impact of tube voltage and the type of reconstruction algorithm on patient doses. The volume CT dose index (CTDIvol) for adult and paediatric patients is assessed and compared with the results of a 2011 national survey and data from other countries. Methods: Scanning procedures for the head (non-helical and helical), chest and upper abdomen were examined for adults and 5-year-old children. A questionnaire concerning the following items was sent to 3000 facilities: tube voltage, use of reconstruction algorithms and displayed CTDIvol. Results: The mean CTDIvol values for paediatric examinations using voltages ranging from 80 to 100 kV were significantly lower than those for paediatric examinations using 120 kV. For adult examinations, the use of iterative reconstruction algorithms significantly reduced the mean CTDIvol values compared with the use of filtered back projection. Paediatric chest and abdominal scans showed slightly higher mean CTDIvol values in 2014 than in 2011. The proposed DRLs for adult head and abdominal scans were higher than those reported in other countries. Conclusion: The results imply that further optimization of CT examination protocols is required for adult head and abdominal scans as well as paediatric chest and abdominal scans. Advances in knowledge: Low-tube-voltage CT may be useful for reducing radiation doses in paediatric patients. The mean CTDIvol values for paediatric scans showed little difference that could be attributed to the choice of reconstruction algorithm.

Diagnostic reference levels (DRLs) for mammography have yet to be created in Japan. A national questionnaire investigation into radiographic conditions in Japan was carried out for the purpose of creating DRLs. Items investigated included the following: tube voltage; tube current; current-time product; source-image distance; craniocaudal view; automatic exposure control (AEC) settings; name of mammography unit; image receptor system (computed radiography (CR), flat panel detector (FPD), or film/screen (F/S)); and supported or unsupported monitor diagnosis (including monitor resolution). Estimation of the mean glandular dose (MGD) for mammography was performed and compared with previous investigations. The MGD was 1.58(0.48) mGy, which did not significantly differ from a 2007 investigation. In relation to image receptors, although no difference in average MGD values was observed between CR and FPD systems, F/S systems had a significantly decreased value compared to both CR and FPDs. Concerning digital systems (FPDs), the MGD value of the direct conversion system was significantly higher than the indirect conversion system. No significant difference in MGD value was evident concerning type of monitor diagnosis for either the CR or the FPD digital systems; however, hard copies were used more often in CR. No significant difference in the MGD value was found in relation to monitor resolution. This report suggests ways to lower the doses patients undergoing mammography receive in Japan, and serves as reference data for 4.2 cm compressed breast tissue of 50% composition DRLs. Furthermore, our findings suggest that further optimisation of FPD settings can promote a reduction in the MGD value.

The conversion coefficients, H&apos;(d, alpha)/Phi, for monoenergetic positrons and positron-emitting radionuclides were calculated by using the user code UCICRPM of the Monte Carlo code EGS5 to estimate the radiation dose for medical staff involved in positron emission tomography examinations. From these coefficients, the dose equivalent rates per unit activity at 0.07 and 10 mm depths in a soft tissue for a straight-line source of 2-deoxy-2-[(18)F]fluoro-D-glucose ((18)F-FDG) were calculated by using the developed user code UCF18DOSE. The dose equivalent rates per unit activity at 0.07 and 10 mm depths were measured by using a personal dosemeter (DOSE(3)) under the same conditions as those considered in the calculation. The calculated dose equivalent rates per unit activity at 0.07 and 10 mm depths were 0.116 and 0.0352 pSv min(-1) Bq(-1), respectively, at 20 cm from the (18)F-FDG injection tube.

A 78-year-old woman with vulvar Paget's disease was examined with lymphoscintigraphy. Neither regional nor distant metastases nor inguinal or femoral lymph node metastases were evident clinically. Sentinel lymph nodes were identified before and during operation in both groin areas. The patient underwent selective sentinel lymph node sampling with a hand-held gamma probe and local vulvectomy. Histopathologic examination of the specimen revealed intraepithelial Paget's disease, and there was no evidence of cancer (stage T2N0M0). Postoperative lymphedema did not occur. The sentinel lymph node procedure for vulvar Paget's disease may be a promising technique for minimally invasive surgery.

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.

1.ポータブルグリッドは、r6N34と比べて、コントラスト改善度が約30%低く、露出倍数が約10%高くなった。2.グリッド傾斜による濃度低下はr6N34では6°、ポータブルグリッドでは10°で生じた。3.ポータブルグリッドは、物理的性能は劣るが角度ずれ等に対して許容度が大きいので、ポータブル撮影用グリッドとして有用である。