Recent trend of research on the adaptive response induced by low dose radiation and its significance

本総説は,低線量放射線に対する生体の適応応答(以下,適応応答)に関してその効果を含む最近の研究動向,さらに放射線防護との関係についてまとめたものである｡特にこの分野で最も検討が進んでいる｢低線量放射線照射の生物学的影響｣に関する国際研究組織(BELLE)での動向を中心に報告するものである｡即ち,ヒトと自然放射線との共存などヒトの生活環境と適応応答について,適応応答の短期的･長期的効果など適応応答の効果とその生物学的意義について言及した｡次に,適応応答の医療などへの応用の可能性について,また,適応応答と放射線防護との関係についても言及した｡ここで,低線量放射線にはヒトへの有益な効果があるとの多くの報告例がある半面,放射線防護の面では微量放射線でも危険とする考え方がその根拠にあることがわかった｡このため,今後は更なる低線量放射線の生体影響研究を進めるとともに,両者の間の隙間をなくす現実的･合理的な対応が求められている｡We reviewed the recent trend of research on the adaptive response induced by low dose radiation and its significance. The following view were obtained. Risk assessment is fundamental to the protection of public health from radiation exposure, but any estimate of risk is subject to numerous major uncertainties. In view of the uncertainties surrounding the shape of dose-response curves at low doses of ionizing radiation. the linear nonthreshold dose-response model is now widely accepted as a paradigm in radiation protection practice and risk analysis. However, interest among scientists in obtaining a more conclusive understanding of the effects of low dose radiation has been evident in recent initiatives, such as adaptive response of low dose radiation, in part to help verify or disprove the linear model. A vigorous worldwide effort is now apparently underway to understand the basic mechanisms underlying the biological effects of low dose radiation. This review presents a series of papers representing the progress going on, which will undoubtably make an important contribution to this field of research

Basic study on the effects of the archeological investigation and the construction work on the environmental radiation

In this paper, we investigated how the excavation of ruins and the construction work affected the environmental radiation in the Shikata campus of Okayama University (S-campus). The environmental radiation was steady in the S-campus until 1997, but began to change since 1998, while the ruin's survey and the construction work started frequently after 1998 in the S-campus. In general, the soil and the concrete include the natural radioisotope (uranium series and thorium series, etc). When ruins are surveyed, it is necessary to move a large amount of the soil. In addition, a large amount of the concrete is used for the construction work. To measure the environmental radiation, the monitor posts were set up on the east and west sides of the building of the Radioisotope Center (RIC). We sampled the soil in the container in each place. We used the high-purity germanium detector to analyze them. The monitor posts showed the difference in the in-air dose rate in each place in the S-campus. The in-air dose rate at the east side of the RIC was higher than that at the west side. The result of analysis showed that the soil includes the (40)K at the east side. While the specific activity of the 40K was 0.849Bq/g at the east side, the (40)K was hardly detected in the soil at the west side. The each soil included the 214-lead and 214-bismus ((214)Pb, (214)Bi), however, there was no significant difference in the specific activity of the each soil. The concrete included (40)K, whose specific activity was 0.492Bq/g. It was suggested that the change of the environmental radiation was attributed to radon and its daughter nuclides in the soil rather than the radiation from the concrete in the buildings

岡山大学における核燃料物質の安全管理のための劣化ウランと天然ウランの鑑別について

In Japan, the Law for the Regulation of Nuclear Source Materials, Nuclear Fuel Materials and Reactors (Regulation Law) controls the nuclear fuel materials such as thorium (Th), uranium (U) and plutonium (Pu). Under the Regulation Law, all related materials and reactors are needed to register to the Government. In Okayama University, many nuclear fuel materials, mainly uranium compounds, are registered and stored in 11 departments, separately. Discrimination between depleted uranium and natural uranium is important for the observance of the Regulation Law and the safety management of the nuclear fuel materials in the Okayama University. However, the discrimination of the two kind of uranium has poorly analyzed. In this study, we analyzed several uranium compounds by using γ-ray spectrometry to determine whether the depleted uranium or not

The Effects of Low-Dose-Rate γ-irradiation on Forced Swim Test-Induced Immobility and Oxidative Stress in Mice

The forced swim test (FST) induces immobility in mice. Low-dose (high-dose-rate) X-irradiation inhibits FSTinduced immobility in mice due to its antioxidative function. We evaluated the effects of low-dose γ-irradiation at a low-dose-rate on the FST-induced depletion of antioxidants in mouse organs. Mice received whole-body low-dose-rate (0.6 or 3.0 mGy/h) of low-dose γ-irradiation for 1 week, followed by daily FSTs (5 days). The immobility rate on day 2 compared to day 1 was significantly lower in the 3.0 mGy/h irradiated mice than in sham irradiated mice. The FST significantly decreased the catalase (CAT) activity and total glutathione (t-GSH) content in the brain and kidney, respectively. The superoxide dismutase (SOD) activity and t-GSH content in the liver of the 3.0 mGy/h irradiated mice were significantly lower than those of the non-FST-treated mice. The CAT activity in the lungs of mice exposed to 3.0 mGy/h γ-irradiation was higher than that of non-FST treated mice and mice treated with FST. However, no significant differences were observed in the levels of these antioxidant markers between the sham and irradiated groups except for the CAT activity in lungs. These findings suggest that the effects of low-dose-rate and low-dose γ-irradiation on FST are highly organ-dependent

A Study of Reconstruction of Magnetic Resonance Image

磁気共鳴は医学におけるイメージングにおいて重要なモダリティーであり,高度な数学的手法が画像の再構成に取り入れられている｡画像再構成の数学的手法および画像再構成にいたるまでの数学的な過程を理解するこは,MRIを学ぶものにとって非常に重要であるが,成書において明確な説明はなされていない｡ここでは,MR画像の再構成法を,複素関数と複素フ-リェ係数を用いて導いたので報告する｡Magnetic resonance is an important modality for medical imaging, and advanced mathematical techniques are introduced into the reconstruction of images. Clearly understandable explanations of the reconstruction of the MR image and of the mathematical derivation process have not been presented in the texts. Reconstruction of MR image is presented using the complex function and its relevant Fourier coefficients

Effects of some physical conditions on leaching rate of radon from radioactive minerals originating from some hot springs

In order to determine the best physical conditions for leaching more radon from minerals into water, we measured the leaching rate of radon from radioactive minerals under the conditions of some different grain sizes and water temperatures. Water temperature affected the leaching rate of radon although the grain size did not significantly affect it. Furthermore, we proposed ultrasonic irradiation to the mixture of a mineral and water as the method of leaching more radon. Ultrasonic irradiation was efficient to leach more radon from the mineral soaked in water because of ultrasonic cavitation.</p

Basic Study on Positive Effects of Radon Inhalation on Pet's Health

著者らは今までに，共同開発したラドン吸入装置を用いマウスにラドン吸入をさせた場合，諸臓器中の抗酸化機能が亢進する可能性などを明らかにしてきた。本研究では，ラドン吸入の獣医療への応用の可能性について新たに検討するため，健常なイヌ5頭(オス：2(1，9才)，メス：3(1～5才))及び慢性腎不全症のネコ8頭(オス：3(2～6才)，メス：5(5～7才))を対象に基礎的な検討をした。すなわち，約5500Bq/m3のラドンを1回30分で隔日に30日間(計15回)それぞれ吸入させた。その結果，イヌにおいて，中性脂肪が減少する可能性が示された。また，その効果は吸入開始20～30日後に現れることも示唆できた。他方，ネコにおいて，飲水量が改善し血清中クレアチニンが基準値内に減少する症例がみられるなど，慢性腎不全症に対し一定の効果が期待できる可能性が示唆された。Radon inhalation using our radon exposure device activated anti-oxidative function in some organs of mouse. To assess the possibility of its application to veterinary care, healthy dogs and cats with chronic renal failure were inhaled radon at a concentration of 5500Bq/m3 for 30 minutes every 2 days for 30 days. In result, radon inhalation within a relatively long time period significantly decreased the triglyceride level of dogs. On the other hand, some cats increased the volume of drinking water by radon inhalation and the creatinine level in blood of these cats was decreased to normal level. These findings suggest that radon inhalation may have curative properties against chronic renal failure

Measurement of sampling time in MRI and reconstruction of MR image

MRIにおいてk-spaceを構築するためにはエコー信号をサンプリング時間に従って採取する必要がある.このサンプリング時間を測定するために,FOV(field of view)の左半分にファントムを置くことにより階段関数となるスピン分布を生成した｡得られたエコー信号を,階段関数をフ-リェ変換したときに得られるフ-リェ係数と比較することによりサンプリング時間を求めた｡得られたサンプリング時間を用いて,MRI MULTI-TEST PHANTOMをMRI装置でスキャンすることにより得られたエコー信号をサンプリングしk-spaceを構築した。このk-spaceをフ-リェ逆変換することによりMRI MULTI-TEST PHANTOMの画像を再構成することができた。Regarding the construction of k-space in MRI, it is necessary to extract the required data from the echo signals with the rate of sampling time. In order to measure the sampling time, a rectangular phantom was placed on the left side of the FOV in the body coil of an MRI equipment, and got analog signals in the sequence of spin echo. The sampling time was determined by comparing the measured signals with the Fourier coefficients obtained by transforming the step function which was similar to the profile of the FOV. The MRI MULTI-TEST PHANTOM was scanned, and the k-space was constructed with the extracted data from the echo signals with the rate of the determined sampling time. The MRI images of the MULTI-TEST PHANTOM were reconstructed by inverse-transforming the obtained k-space

Basic Study on Activation of Antioxidation Function in Some Organs of Mice by Radon Inhalation Using New Radon Exposure Device

ラドン療法の適応症には活性酸素に由来する生活習慣病が多く，その機構の更なる解明が期待されている。また，汎用性があり医学的効果が再現できるラドン吸入装置の構築は意義が大きい。このため，著者らは共同で開発したラドン吸入試作装置を用い，マウス諸臓器中の抗酸化機能の変化特性を検討した。ラドン吸入試作装置は，特殊加工したラドン線源を収納したユニットの数量，それへの送風量及び湿度などを調節することによりラドン濃度を自在に調整可能にするものである。この装置によりマウスに400Bq/m3あるいは4000Bq/m3のラドンを吸入させた。その結果，脳・肺・肝臓・腎臓において，抗酸化系酵素であるSODとカタラーゼの両活性が増加し，過酸化脂質量が減少した。この抗酸化機能の亢進により，本実験条件でのラドン吸入は活性酸素障害の抑制，すなわち，生活習慣病の予防や症状緩和に効果のある可能性が改めて示唆できた。There are a lot of life style diseases that are related to reactive oxygen species in indications of the radon therapy, and, the further clarification of mechanism is expected. Therefore, in this study, we investigated the activation of antioxidation function in some organs of mice by radon inhalation using the new radon exposure device. It was enable that this device was the adjustments of radon concentration by changing the air flow rate to the specially processed radon source and so on. The mice were made to inhale the radon of 400Bq/m3 or 4000Bq/m3 with this device. Results show that in brain, lungs, liver, and kidney, both the activities of superoxide dismutase(SOD) and catalase increased, and lipid peroxide levels decreased. This suggests that radon inhalation enhanced the antioxidation function. These findings are important in understanding the mechanism of diseases in which radon therapy is used as treatment, and most of which are called activated oxygen-related diseases

X-Irradiation at 0.5 Gy after the forced swim test reduces forced swimming-induced immobility in mice

The forced swim test (FST) is a screening model for antidepressant activity; it causes immobility and induces oxidative stress. We previously reported that radon inhalation has antidepressant-like effects in mice potentially through the activation of antioxidative functions upon radon inhalation. This study aimed to investigate the effect of prior and post low-dose X-irradiation (0.1, 0.5, 1.0 and 2.0 Gy) on FST-induced immobility and oxidative stress in the mouse brain, and the differences, if any, between the two. Mice received X-irradiation before or after the FST repeatedly for 5 days. In the post-FST-irradiated group, an additional FST was conducted 4h after the last irradiation. Consequently, animals receiving prior X-irradiation (0.1 Gy) had better mobility outcomes than sham-irradiated mice; however, their levels of lipid peroxide (LPO), an oxidative stress marker, remained unchanged. However, animals that received post-FST X-irradiation (0.5 Gy) had better mobility outcomes and their LPO levels were significantly lower than those of the sham-irradiated mice. The present results indicate that 0.5 Gy X-irradiation after FST inhibits FST-induced immobility and oxidative stress in mice