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論文

Overview of computational frog models

木名瀬 栄; Mohammadi, A.*; G$'o$mez-Ros, J.-M.*

Computational Anatomical Animal Models; Methodological Developments and Research Applications, p.5_1 - 5_9, 2018/12

There are limited investigations on the computational frog models and the organ dose evaluations for frogs in environmental protection. In this article, computational frog models and their applications are reviewed to share some perspectives of frog model development in the near future. The authors hope that 3D printing frog phantoms with adequate tissue substitutes should be developed for the validation of the dosimetric quantities by the Monte Carlo simulations.

論文

Overview of computational mouse models

Mohammadi, A.*; 木名瀬 栄; Safavi-Naeini, M.*

Computational Anatomical Animal Models; Methodological Developments and Research Applications, p.3_1 - 3_27, 2018/12

The review summarizes the history of development of the computational models during the last 24 years with some provision about what to expect in the near future for their application in preclinical research, radiation dosimetry calculations and imaging physics research. Around 26 computational mouse models have been constructed for various researches in ionizing and nonionizing radiation dosimetry, preclinical imaging including multimodality imaging and instrumentation, image processing and analysis. The approach of using the computational mouse models and simulation tools are very useful comparing the experimental approach using physical phantoms or real mice due to high cost and complexity of organizing an experimental research.

論文

Evaluation of absorbed doses in voxel-based and simplified models for small animals

Mohammadi, A.; 木名瀬 栄; 斎藤 公明

Radiation Protection Dosimetry, 150(3), p.283 - 291, 2012/07

 被引用回数:9 パーセンタイル:29.05(Environmental Sciences)

Internal dosimetry in non-human biota is desirable from the viewpoint of radiation protection of the environment. The ICRP proposed the Reference Animals and Plants using simplified models, such as ellipsoids and spheres, and calculated absorbed fractions (AFs) for whole bodies. In this study, photon and electron AFs in whole bodies of voxel-based rat and frog models have been calculated and compared with reported AFs in the ICRP Reference models. It was found that the voxel-based and the reference frog (or rat) models can be consistent for the whole-body AFs within discrepancy of 25%, as source uniformly distributed in the whole body. The electron SAFs (specific absorbed fractions) in the whole body could predict organs SAFs with discrepancies up to 40% for all organs as source distributed uniformly per mass however the differences were up to 260% for the lungs as source distributed uniformly per volume. It can be stated that whole-body SAFs or $$S$$ values in simplified models without internal organs are not sufficient for accurate internal dosimetry because they do not reflect SAFs or $$S$$ values of all individual organs as source was not distributed uniformly in whole body. Thus, voxel-based models would be good candidates for dosimetry in non-human biota in case that further accuracy in environmental dosimetry would be desired.

論文

Electron absorbed fractions and S values in a voxel-based mouse phantom

Mohammadi, A.; 木名瀬 栄

Radioisotopes, 60(12), p.505 - 512, 2011/12

放射性医薬品の開発においては、放射線によりさまざまな臓器,組織に付与される線量を正確に評価することが重要である。本研究では、がん治療に有用な$$beta$$線放出核種の線量評価基礎データとして、モンテカルロ計算を用いたシミュレーション手法により、マウスボクセルファントム(マウスの数値モデル)の電子吸収割合(AF)とS値を取得した。線源は、10keVから4MeVの単色電子とし、臓器内均一分布と仮定した。その結果、線源臓器と標的臓器が同一の場合、臓器自己AFは、電子のエネルギーが増加するにつれて減少すること、すなわち、電子のエネルギーが線源臓器内においてすべて吸収されるわけではないことがわかった。また、線源臓器と標的臓器が異なる場合、臓器間AFは、電子エネルギー,線源と標的間の幾何学的条件(臓器の体積,密度,ジオメトリー)に依存することを明らかにした。加えて、$$^{131}$$I, $$^{153}$$Sm, $$^{188}$$Re, $$^{90}$$Yについて、マウス臓器S値を表にとりまとめた。

論文

Comparison of photon and electron absorbed fractions in voxel-based and simplified phantoms for small animals

Mohammadi, A.; 木名瀬 栄; 斎藤 公明

Progress in Nuclear Science and Technology (Internet), 2, p.365 - 368, 2011/10

ICRP proposed the reference animals and plants using simplified phantoms, such as ellipsoids and spheres, and assessed absorbed fractions (AFs) for the whole bodies. In this study, photon and electron AFs in whole body of voxel-based frog and mouse phantoms were evaluated and compared with AFs in simplified phantoms. The evaluations were done by Monte Carlo methods for voxel-based and simplified phantoms. There were very small differences (less than 2%) between whole-body AFs in voxel-based and simplified mouse phantoms however the differences were up to 24% for the voxel-based and the Reference Frog phantoms. Whole-body AFs in voxel-based and simplified phantoms demonstrated that not only mass but also shape of whole body effected on AFs significantly. The results of this study suggest the replacement of the Reference Animal phantoms by voxel-based animal phantoms to improve the accuracy of the whole-body AFs.

論文

Computer simulations for internal dosimetry using voxel models

木名瀬 栄; Mohammadi, A.; 高橋 聖; 斎藤 公明; Zankl, M.*; Kramer, R.*

Radiation Protection Dosimetry, 146(1-3), p.191 - 194, 2011/07

 被引用回数:3 パーセンタイル:66.23(Environmental Sciences)

At the Japan Atomic Energy Agency (JAEA), several studies have been conducted on the use of voxel models for internal dosimetry. Absorbed fractions (AFs) and S values have been evaluated for preclinical assessments of radiopharmaceuticals using human voxel models and a mouse voxel model. Computational calibration of in vivo measurement system has been also made using Japanese and Caucasian voxel models. In addition, for radiation protection of the environment, AFs have been evaluated using a frog voxel model. Each study has been made by using Monte Carlo simulations. Consequently, it was concluded that these data by Monte Carlo simulations and voxel models could adequately reproduce those by measurements. Voxel models were found to be significant tools for internal dosimetry since the models are anatomically realistic.

論文

Application of Monte Carlo simulation and voxel models to internal dosimetry

木名瀬 栄; Mohammadi, A.; 高橋 聖

Applications of Monte Carlo Methods in Biology, Medicine and Other Fields of Science (Internet), p.41 - 53, 2011/02

At the Japan Atomic Energy Agency (JAEA), several studies have been conducted on the use of voxel models for internal dosimetry. Specific absorbed fractions (SAFs) and S values have been evaluated for preclinical assessments of radiopharmaceuticals using human voxel models and a mouse voxel model. Computational calibration of in vivo measurement system has been also made using Japanese and Caucasian voxel models, the knee and torso voxel models. In addition, for radiation protection of the environment, absorbed fractions (AFs) have been evaluated using a frog voxel model. Each study has been made by using Monte Carlo simulations. These data by Monte Carlo simulations and voxel models could adequately reproduce those by measurements. Voxel models are significant tools for internal dosimetry since the models are anatomically realistic.

論文

Monte Carlo simulations of photon specific absorbed fractions in a mouse voxel phantom

Mohammadi, A.; 木名瀬 栄

Progress in Nuclear Science and Technology (Internet), 1, p.126 - 129, 2011/02

For preclinical assessments of several radiopharmaceuticals, specific absorbed fractions (SAFs) were evaluated using the voxel-based mouse phantom. The sources were assumed to be monoenergetic in the photon energy range from 10 keV to 4 MeV. The radiation transport was simulated using the Monte Carlo method. Consequently, it was confirmed that the photon SAFs for organ self-absorption are dependent on the masses of the source/target organs. It would appear that the photon SAFs for organ self-absorption are expressed by a continuous function of photon energy emitted by the source. The photon SAFs for organ cross-fire might be subject to the geometry effect such as size and shape of source/target and distance between the source and target.

論文

Influence of voxel size on specific absorbed fractions and $$S$$-values in a mouse voxel phantom

Mohammadi, A.; 木名瀬 栄

Radiation Protection Dosimetry, 143(2-4), p.258 - 263, 2011/02

 被引用回数:9 パーセンタイル:30.67(Environmental Sciences)

In the study, two mouse voxel phantoms were constructed, both with cubic voxels, one with 0.1 mm sides and the other with 0.4 mm sides. The voxel phantoms with different voxel sizes were used to evaluate voxel size effect on specific absorbed fractions (SAFs). The sources were considered to be mono-energetic in the energy range of 10 keV to 4 MeV. The radiation transport was simulated using the Monte Carlo method. Consequently, it was found that the difference between two voxel phantom masses for the eyes is highest (about 8.7%) and for the kidneys is lowest (about 0.01%). A comparison of their organ masses might show that changing the voxel size from 0.1 mm cube to 0.4 mm cube does not have an appreciable effect on the masses of organs. This comparison of SAFs for self and cross-irradiation in organs of the phantoms with 0.1 mm and 0.4 mm voxel size would show how the values of SAFs depend on voxel size.

論文

Electron absorbed fractions and S values in a mouse voxel phantom

Mohammadi, A.; 木名瀬 栄

KEK Proceedings 2010-9, p.65 - 74, 2010/11

For preclinical assessments of several radiopharmaceuticals, electron absorbed fractions (AFs) and S values were evaluated in a mouse voxel phantom. The sources were considered to be mono-energetic in the electron energy range 10 keV to 4 MeV. The radiation transport was simulated using the Monte Carlo method. Consequently, it was confirmed that the electron AFs were dependent on the masses of the source/target organs. The electron AFs for organ self-absorption (source = target) decreased with increasing electron energy which proved that it is certainly not always appropriate in small organs to assume a 100% localized electron energy absorption. The electron AFs for organ cross-fire depended on electron energy emitted by the source and the geometries of source and target. In addition, S values in the major organs of the mouse phantom were tabulated for $$^{131}$$I, $$^{153}$$Sm, $$^{188}$$Re, $$^{90}$$Y and $$^{111}$$In using the results of the photon and electron AFs. Comparison of S values in abdominal organs for only $$beta$$-spectrum of the nuclides demonstrated that $$beta$$-only S values increased with increasing mean energy of $$beta$$-spectrum of the nuclide. The results of this study will be useful in determining the dose to the organs for mice similar in size to Digimouse.

論文

Effect of density on absorbed doses in a mouse voxel phantom

Mohammadi, A.; 木名瀬 栄

Proceedings of 3rd Asian and Oceanic Congress on Radiation Protection (AOCRP-3) (CD-ROM), 3 Pages, 2010/05

The accurate dosimetry for murines such as mice is necessary since they are widely used in preclinical evaluations of new radiopharmaceuticals. Dose of organs in these animals can be evaluated in a voxel mouse phantom, which has a realistic anatomy, by Monte Carlo methods. Dose of each organ depends on density of that organ and the other organs around. In this study, we evaluated the effect of bones and lungs density on photon and electron absorbed fractions (AFs) and S values for $$^{131}$$I and $$^{90}$$Y nuclides in major organs and whole body of the Digimouse phantom. Source was considered to be distributed uniformly in the whole body of the mouse phantom. AFs and S values were evaluated by Monte Carlo methods in homogeneous and heterogeneous Digimouse phantoms. The density of skeleton and lungs in homogeneous phantom were changed to make the heterogeneous phantom. From the results it was found that the density changes affected on AFs and S values of all organs specially the heart however the effect in whole body was really much smaller than each individual organ. It shows that whole body dose is not sufficiently good as a quantity for accurate dosimetry.

論文

Simulations of photon specific absorbed fractions in a mouse voxel phantom

Mohammadi, A.; 木名瀬 栄

KEK Proceedings 2009-6, p.70 - 77, 2009/11

For preclinical assessments of several radiopharmaceuticals, photon specific absorbed fractions (SAFs) were evaluated in a mouse sophisticated model and a new set of photon SAFs were tabulated for photon energies from 10 keV to 4 MeV. In the present study, Digimouse voxel phantom was used as a sophisticated model and converted to an input file for EGS4 code, in conjunction with an EGS4 user code, UCSAF. Consequently, it was confirmed that the photon SAFs for self-irradiation depended on the photon energy and the mass of the target/source organ. The photon SAFs for cross-irradiation also was an energy dependent function but did not change by the mass of target and it might be affected by source size, target size, their shape and distance between the source and target. Organ dose evaluation should be performed in the phantom with the Monte Carlo method since the minor changes in the geometry had a large effect on photon-only S values and organ dose.

口頭

モンテカルロシミュレーションを用いた体外計測法に関するEURADOS国際相互比較研究

高橋 聖; Mohammadi, A.; 木名瀬 栄

no journal, , 

欧州線量評価委員会(EURADOS)は、さまざまなモンテカルロコードを対象として、2002年から3度の体外計測法に関する国際相互比較研究を行ってきた。評価対象は、点線源,脚部や胴体部のボクセルファントムに対するGe半導体検出器の応答解析である。2002年に実施されたQUADOSプロジェクトでは、点線源から放出される単色光子(15keV$$sim$$1000keV)に対するGe半導体検出器の応答関数解析やGe半導体検出器のモデリングに関する不確かさ解析、2005年に実施されたCONRADプロジェクトでは、膝骨中に均一に分布した$$^{241}$$Am含有ボクセルファントムに対するGe半導体検出器の応答関数解析、2009年から実施されている現在進行中のプロジェクトでは、肺中に均一に分布したウラン含有ボクセルファントムに対するGe半導体検出器の応答関数解析について検討してきた。報告者は、これまでのEURADOSの体外計測法に関する国際相互比較研究において、アジアで唯一すべてに参加し、モンテカルロモデリングの不確かさなど、さまざまな知見を得た。本報告では、EURADOS国際相互比較研究で得た知見、特に体外計測法におけるモンテカルロシミュレーションとボクセルファントムの利用法などについて述べる。

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