鈴木 昇一

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.

Our aim in this study was to investigate the incident air kerma (IAK) and average glandular dose (AGD) for polymethylmethacrylate (PMMA) phantoms and patient breasts for each thickness by use of digital mammography units, and to determine the correlation between phantom and patient measurements. An additional aim was to calculate the numerical value of the diagnostic reference level (DRL) for digital mammography in Japan based on the AGD from patient measurements. Patient-based IAK and AGD values were calculated for 300 patients who underwent mammographic examinations at three institutions. On examination of a 40-mm PMMA phantom, the IAK and the AGD were 7.89 and 1.84 mGy, respectively. The mean patient breast thickness was 37.6 mm, and the mean IAK and the AGD calculated from actual patient data for breast thicknesses between 40 mm and 50 mm were 8.91 and 2.08 mGy, respectively. Approximately 20% of the 300 patients had IAK &gt 10 mGy. The distributions of patient-based IAK and AGD values were higher than the IAK and AGD values for the PMMA phantom. The patient dose with use of the PMMA phantom can be underestimated. The DRL was calculated from patient-based AGDs of the regular breast thickness as 2.0 mGy in Japan. © Japanese Society of Radiological Technology and Japan Society of Medical Physics 2013.

Background: Although different gait analysis methods such as Walking Track Analysis exist, they cannot be used to demonstrate the physical condition of mice with specific gait disorder characteristic. Therefore, we developed a new method for the gait analysis of such mice to accurately assess hind limb angle based on the pelvic axis. New method: We established and verified a gait analysis method capable of pelvic axis-based limb angle measurement by video-recording the gait of a control mice group (C57BL/6J(B6)) and three ataxic mice (ataxic B6-wob/t, Parkinson's disease model (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treated (MPTP)), and cerebellum hypoplasia (cytosine-beta-D-arabinofuranoside treated)) from the ventral side. Results: The assessed hind limb angles of B6-wob/t and MPTP-treated mice were significantly wider than B6 mice (p<0.01). Moreover, we could draw separating lines with slopes of minus one that could separate the data of each group in-the scatter plot of the normalized hind limb step width and angle. Comparison with existing methods: We found no significance when we applied the already existing nose-tail method for the analysis of the hind limb angles of B6 and B6-woblt mice. In the nose-tail method, since the whole body axis of the trunk varies while the trunk of the mouse is laterally bent changing the hind limb angle, B6 and B6-wob/t mice could not be differentiated. However, the two mice groups could be differentiated by the pelvic axis-based gait analysis method. Conclusion: The pelvic axis-based gait analysis method is promising and valid for mice with gait disorder. (C) 2013 Elsevier B.V. All rights reserved.

The purpose of this paper is to reappraise the accuracy of a conversion coefficient (k) reported by International Commission on Radiological Protection Publication 102 Table A.2. The effective doses of the routine head computed tomography (CT), the routine chest CT, the perfusion CT, and the coronary CT were evaluated using the conversion coefficient (adult head: 0.021 mSv·mGy^－1·cm^－1, adult chest: 0.014 mSv·mGy^－1·cm^－1). The dose length product (DLP) used the value displayed on the console on each scanning condition. The effective doses were evaluated using a human body type phantom (Alderson Rando phantom) and thermoluminescent dosimeter (TLD) elements for comparison with the converted value. This paper reported that the effective doses evaluated from conversion coefficient became different by 0.3 mSv (17%) compared with measurements, the effective dose computed with the conversion coefficient of the adult chest may be underestimated by 45%, and the bolus-tracking which scans the narrow beams should not use a conversion coefficient.

We have investigated radiation doses to patients in selected types of examinations in Japan since 1974 and have analyzed the trend of patient radiation doses during a period of 37 years. This study covered regular plain X-ray scanning (including mammography) and computed tomography (CT) scanning. Dose evaluation was performed in terms of entrance skin dose (ESD) for regular plain X-ray scanning, average glandular dose (AGD) for mammography, and volume CT dose index (CTDIvol) for CT scanning. Evaluation was performed in 26 orientations at 21 sites for regular plain X-rays, and for cranial, thoracic, and abdominal scans of children and adults for CT scanning. With the exception of chest X-rays, the dose during regular plain X-ray scanning had decreased by approximately 50% compared with scans performed in 1974, The dose during mammography had decreased to less than 10% of its former level. In scans performed in 2011, doses at all sites were within International Atomic Energy Authority (IAEA) guidance levels. The increasing use of multiple detectors in CT scanning devices was evident in CT scanning. A comparison of doses from cranial non-helical scans performed in 2007 and 2011 found that the latter were higher. An examination of changes in doses between 1997 and 2011 revealed that doses had tended to increase in cranial scans of adults, but had hardly changed at all in abdominal scans. Doses during CT scanning of children were around half those for adults in cranial, thoracic, and abdominal scans. We have ascertained changes in the doses to which patients have been exposed during X-ray scanning in Japan.

Recently, attempts to develop new types of swallowing function analysis with 320-detector-row multislice CT (320-MDCT) have been reported. The present report addresses (1) patient exposure, (2) operator exposure, and (3) spatial dose distribution. For dose measurement, a human-body phantom in which 303 thermoluminescent dosimeter elements were inserted and a survey meter was used. The patient position was confirmed with a singlevolume scan at a tube voltage of 120 kV, a tube current of 10 mA, a rotation speed of 0.35 s/rot., a slice thickness of 0.5 mm, coverage of 160 mm, a scan field of view of 240 mm, a small focal spot size, and a gantry tilt angle of 22° (volume CT dose index displayed on the console 0.8 mGy, dose-length product 12.1 mGy cm). The effective dose for the patient in swallowing CT (SCT) was 3.9 mSv. The conversion factor for obtaining the effective dose was 0.0066 mSv/mGy cm. The effective dose for the operator was 0.002 mSv. In the operator exposure measurement, the ambient dose equivalent H*(10), that would be produced by an expanded and aligned radiation field at a depth 10 mm in the International Commission on Radiation Units and Measurements sphere, was 0.012 mSv. In this report, the safety of SCT, which has become possible with the introduction of 320-MDCT, was evaluated by measurement of the exposure to the patient and operator. © Japanese Society of Radiological Technology and Japan Society of Medical Physics 2012.

Breast X-ray computed tomography(breast CT)has been developed in some research groups to overcome the limitations of mammography. However, the spatial resolution of the existing system is not sufficient to identify microcalcifications within the breast. The purpose of this study was to develop a prototype of high-resolution breast CT system, and to evaluate the developed system. Our prototype system consists of a micro-focus X-ray tube and a flat panel detector; a spatial resolution of 20µm is attained. In the experiments, we evaluated physical properties and image quality. As a result, a resolution of proposed system was better than conventional CT system used in clinical practice. As for evaluation of image quality using a breast phantom, mass lesion and microcalcifications within the phantom were clearly confirmed in 3-dimensions.

We carried out a questionnaire survey to research on radiographic conditions in 3000 institutes. We discussed on radiographic conditions to estimate patient exposures. The collection rate was 24.7%. Most of the institutes shifted to the use of high-voltage generator, digital devices, and filmless equipment. We did not see a shift in this survey of radiographic conditions compared with the 2007 survey.

The characteristics of flat-panel detectors (FPD) are degraded by exposure to radiation. Degradation in a FPD progresses locally and has a nonlinear relationship to the radiation dose. In order to manage FPD systems properly, one must perform quality control (QC) such as evaluation of image degradation. However, no evaluation method for degradation has been established. In this paper, we first review the structure and degradation mechanism of FPDs, and then we propose a daily QC system for FPDs. To evaluate the degradation of FPDs, we investigated the number of defective pixels and lines, as well as the offset level of the pixel output. Furthermore, we developed daily QC software for FPD that can evaluate the image quality and is operationally simple. In the experiments, an indirect-conversion type FPD was evaluated by our proposed system. The offset level of FPD increased exponentially with X-ray exposure no trends were seen for the number of defective pixels and defective lines. The required time for the evaluation of an FPD was about 1 min, and no special skills were needed for the analysis. These results indicate that our system may be useful for daily QC of FPDs. © 2011 Japanese Society of Radiological Technology and Japan Society of Medical Physics.

The recent increase in the incidence of SAR and fever contracted during medical examinations has raised concerns about transmission from the WB coil used during magnetic resonance imaging(MRI)using SENSE. We measured changes in temperature at the body surface during MRI medical examinations using T₂ Fast Spin Echo(T₂FSE)and Hahn T₂ Fast Spin Echo(Hahn-T₂FSE). We initially calibrated the thermometer in an incubator and confirmed that it operated normally in a high magnetic field and that it was not damaged or influenced by heat generated by RF pulses. All experiments were performed using an Excel ART Pianissimo 1.0T(Toshiba Medical Systems)and Thermo clone SL type(KN Laboratories). The temperature at the body surface changed according to the measurement point. The temperature increase was lower when measured with Hahn-T₂FSE than with T₂FSE. One limitation of this study was that temperature was measured only during 1.0 T MRI.

Mammography is an indispensable test for detecting early-stage breast cancer. In recommendations issued by the International Commission on Radiological Protection (ICRP) in 2007, the tissue-weighting factor was increased to 0.12 from the figure of 0.05 recommended in 1990. Research is therefore required to elucidate and optimize the dose received by patients during mammography. Most mammography devices incorporate automatic exposure control systems (AECs) to optimize dose and image quality. The aim of this study was to evaluate AECs at the same thickness and composition by using 80 mammography imaging devices (21 models made by seven manufacturers) currently in use, and to assess the dose received by patients during mammography in different institutions. AEC evaluation was performed by using a quality control 156 phantom and dose evaluation by using a polymethylmethacrylate phantom, and the average glandular dose was calculated from the irradiation conditions obtained. The results showed a 3.5-fold difference in average glandular dose, from 0.83 mGy to 2.90 mGy, when the 156 phantom was used. This rose to 4.38-fold for a 60-mm PMMA phantom. It was also shown that differences in dose arise from variations in pressure and detector position.

The effective energy has been generally used as a method of handily expressing an X-ray quality by one numerical value. The effective energy is a concept derived from "Half Value Layer (HVL)" that is the expressing parameter of beam quality based on the attenuation of the primary X-ray by a material. When beam quality is expressed by using HVL and / or the effective energy, it is necessary to describe the tube potential, the rectification method, and the homogeneity coefficient, etc. in parallel. However, recently feelings are that the effective energy should be handled like an absolute numerical value to physical characteristics of X-rays. In this paper, it was theoretically clarified that the effective energy had a different value depending on the absorber material used for the HVL measurement. In addition, the errors when physical characteristics of the X-rays were evaluated using the effective energy was also examined. Physical characteristics, such as interactions to the material of mono-energetic X-ray, are not equal to that of X-rays with a wide energy spectrum. It is not an easy comparison to express the quality of the diagnostic X-rays, and to calculate physical characteristics of the X-rays by using the effective energy. It is necessary to design a new method of expressing the quality of X-rays that takes the place of the "effective energy."

The International Electrotechnical Commission (IEC) recommended that a display be provided on the operating console of medical computed tomography (CT) scanners when the geometric efficiency (GE) in the z-axis is 70 % or less. Taking into account the increase in the number of detector rows and the changes in the scanning method, the present study was conducted to review the GE and to evaluate the exposure dose in the z-axis direction. The GE for a single-rotation scan was calculated in accordance with IEC-606024 Ed. 2. The findings of the present study suggest that 320-row area detector computed tomography volume scan (single axial scan with no table movement in which it just happened to use a very large beam width) extends 18.8 mm beyond the nominal beam collimation, even when the GE is >70 %. However, compared with the helical scan, which is the present mainstream of CT examinations, the dose beyond the scan length is narrower in volume scan for a limited scan length of 160 mm or less.

In one of the accidents that might happen in the nuclear power station, there is a contamination accident caused by radioactive corrosion products during a periodic inspection. It is necessary to presume the skin absorbed dose from the adhesion area and the contamination density to forecast the level of the skin hazard by the adhesion of the radioactive substance. However, the data to forecast the local skin dose when the radioactive substance adhered handily is not maintained. In this paper, the absorbed dose in the skin surface neighborhood contaminated by radioactive corrosion products was calculated, and the relation between the adhesion area and the contamination density and the local absorption dose was derived. And, the approximate equation that forecast the integrated dose was derived from these data. As for the absorbed dose rate in depth 70 μm from the skin surface that became the index of the skin hazard, the contribution rate by ⁵⁹Fe was the highest within 30 days, and the contribution of ⁶⁰Co rose most after the 30th after the radioactive substance had adhered when the contamination density the adhesion area was the same. The relation between the initial contamination density and days that required it was graphed to reaching to the threshold by the integrated dose when the threshold dose in which the necrosis of the skin was caused was assumed to be 20 Gy. The absorbed dose commitment can be presumed from measurements of the contamination density by using this graph or the approximate equation.

Radionuclide contamination is one of the accidents that might occur while carrying out a periodical inspection of nuclear power stations during normal reactor operation. When such an accident occurs, rescue and medical personnel, involved in transporting and treating affected workers run the risk of exposure to secondary radiation. In this study, the ambient dose equivalent rate at a certain distance from the surface of the human body contaminated with typical radioactive corrosion products was calculated. Further, the relationships among the adhesion area, contamination density, and secondary exposure dose were clarified. The secondary exposure dose and permissible working hours in a radiation emergency medicine were estimated by presenting these relationships in the form of a chart and by specifying the contamination levels.