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444 results on '"Chida, Koichi"'

23. Internal organ dose rate conversion coefficients of Japanese macaques to 134Cs,137Cs and 131I.

Author

Takamura, Yuta, Kajimoto, Tsuyoshi, Tanaka, Kenichi, Yamamoto, Tomoya, Suzuki, Masatoshi, Inaba, Yohei, Chida, Koichi, Fukumoto, Manabu, Rangacharyulu, Chary, and Endo, Satoru

Abstract

The purpose of this study was to estimate the internal dose of radiation in Japanese macaques (aka Nihonzaru or snow monkey) due to the Fukushima nuclear power plant accident. Images of a male Japanese macaque weighing ~10 kg were acquired using a multi-slice computed tomography (CT) scan with a 64-row segment detector. The CT images were used to create voxel phantoms of the bones, bone marrow, brain, eyes, heart, lungs, stomach, liver, spleen, pancreas, kidneys, intestines, bladder, testes, thyroid and miscellaneous tissue. The Particle and Heavy Ion Transport System (PHITS) Monte Carlo code was used to calculate the internal exposure rate conversion factors for 134Cs, 137Cs and 131I isotopes for the created voxel phantoms with a statistical precision higher than 1%. The PHITS-calculated energy deposits were compared with those for rhesus monkeys. The results showed that the fractions of energy deposits for β-radiation in different organs were almost identical between the two species. For γ-radiation, there was excellent agreement in the self-absorption rate with the approximate curve of the Japanese macaque, with an average deviation of 2%. The maximum deviation of 12% was for the kidney, which has two organs, so the error with the approximate curve is slightly larger due to the energy loss created between organs. [ABSTRACT FROM AUTHOR]

Published
2023
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29. Analysis of whole-blood antioxidant capacity after chronic and localized irradiation using the i-STrap method

Author

Sun, Lue, Inaba, Yohei, Sogo, Yu, Morikawa, Kumi, Kunugita, Naoki, Chida, Koichi, Moritake, Takashi, Naoki, Kunugita, and Takashi, Moritake

Abstract

Ionizing radiation exposure affects the redox state in vivo. Recently, whole-blood antioxidant capacity (WBAC) has been reported to decrease in a dose-dependent manner after acute total body irradiation (TBI). However, changes in WBAC after localized and chronic irradiations have not been reported. This study analyzed changes to WBAC in mice after either localized irradiation (irradiation of the left hind leg only) or chronic TBI using the i-STrap method. Leg-localized irradiation exerted limited effects on WBAC, while WBAC decreased in a dose rate-dependent manner after TBI. Further, the WBAC reached the minimum value in a shorter period at a smaller dose rate. Our results suggest that changes in WBAC do not directly reflect absorbed dose, but may reflect radiation-induced biological damage at the systemic level. This study will contribute to the understanding of radiation-induced injuries and diseases, and will facilitate the establishment of biomarkers for radiation exposure.

Published
2022

35. Radioprotection of eye lens using protective material in neuro cone-beam computed tomography: Estimation of dose reduction rate and image quality

Author

Kawauchi, Satoru, Chida, Koichi, Moritake, Takashi, Hamada, Yusuke, Tsuruta, Wataro, and Takashi, Moritake

Subjects
genetic structures, sense organs
Abstract

In cerebral angiography, for diagnosis and interventional neuroradiology, cone-beam computed tomography (CBCT) scan is frequently performed for evaluating brain parenchyma, cerebral hemorrhage, and cerebral infarction. However, the patient's eye lens is more frequently exposed to excessive doses in these scans than in the previous angiography and interventional neuroradiology (INR) procedures. Hence, radioprotection for the lenses is needed. This study selects the most suitable eye lens protection material for CBCT from among nine materials by evaluating the dose reduction rate and image quality.

Published
2021

37. Evaluation of radiation dose for inferior vena cava filter placement during pregnancy: A comparison of dosimetry and dose calculation software.

Author

Matsunaga, Yuta, Haba, Tomonobu, Kobayashi, Masanao, Suzuki, Shoichi, Asada, Yasuki, and Chida, Koichi

Subjects
VENA cava inferior, IMAGING phantoms, RADIATION doses, RADIATION dosimetry, PREGNANT women, SOFTWARE measurement
Abstract

Numerous medical conditions are associated with pregnancy in women, including pulmonary thromboembolism, which can be fatal. An effective treatment of this condition is the positioning of an inferior vena cava filter (IVC‐F) under the guidance of X‐ray imaging. However, this procedure involves the risk of high radiation exposure to pregnant women and fetuses. Moreover, there are no published reports comparing the values of fetal dose, received during IVC‐F placement in pregnant women, determined using dose calculation software and actual measurements. To address this issue, we compared the fetal radiation dose and entrance surface dose (ESD) for pregnant women for gestation periods of 6 and 9 months based on software calculations and actual measurements. The ESD and fetal doses were estimated for a pregnant woman for gestation periods of 6 and 9 months during IVC‐F placement. For actual measurements, one pregnant model phantom was constructed using an anthropomorphic phantom, and two custom‐made different‐sized abdomen phantoms were used to simulate pregnancy. The custom‐made abdomen phantoms were constructed using polyurethane. For software calculations, the software utilized a set of anatomically realistic pregnant patient phantoms. The ESD estimated using the software was consistent with the measured ESD, but the fetal dose estimations were more complicated due to fetal positioning. During fetal dose evaluation using software calculations, the user must carefully consider how much of the fetal length is in the irradiation field to prevent underestimation or overestimation. Despite the errors, the software can assist the user in identifying the magnitude of the dose approaching critical limits. [ABSTRACT FROM AUTHOR]

Published
2023
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