Papers - KODERA Sachiko
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Accurate localization of motor function using transcranial magnetic stimulation with segmentation-free head modeling in patients with brain tumors. International journal
Yoshiki Kubota, Ryusei Moriyama, Yosuke Nagata, Sachiko Kodera, Manabu Tamura, Yoshihiro Muragaki, Akimasa Hirata
Physics in medicine and biology 2025.10
Language：English Publishing type：Research paper (scientific journal)
OBJECTIVES: Transcranial magnetic stimulation (TMS) is widely employed for preoperative functional mapping and neurological diagnosis. However, accurately localizing motor functions is often compromised by distortions in the electric field (EF) caused by the complex interplay of anatomical and electrical properties, especially in patients with brain tumors. Conventional head models, which rely on tissue segmentation and uniform conductivity assumptions, fail to capture the heterogeneity and variability inherent to tumor tissues. This study aims to enhance EF localization accuracy by employing segmentation-free head models that directly estimate voxel-level conductivity from MRI data. APPROACH: Four patients with intraaxial brain tumors near motor eloquent areas underwent preoperative TMS mapping and intraoperative direct electrical stimulation (DES). Individualized head models were created using both segmentation-based and segmentation-free approaches. EF distributions and localization accuracy were evaluated using DES as the gold standard. MAIN RESULTS: For the first time, this study demonstrated that tumor conductivity is both case-specific and spatially dependent, revealing substantial heterogeneity across tumor regions. The segmentation-free model effectively captured this variability, achieving superior localization accuracy with a center-of-gravity (CoG) to DES distance of 3.60 ± 0.95 mm-approximately half that of conventional navigated TMS. By incorporating smooth, voxel-level conductivity variations, the model reduced reliance on extensive stimulation samples and accounted for tumor-induced distortions.
Significance: By accurately modeling the non-uniform conductivity of tumor and surrounding brain tissues, segmentation-free head models significantly enhance EF localization in TMS applications. This novel approach offers improved precision and efficiency in preoperative planning and warrants further validation in diverse patient cohorts.
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Diabetes as a risk factor for heatstroke: insights from a nationwide Japanese health insurance database Reviewed
Akimasa Hirata, Yoko Takayama, Keiko Saito, Yuya Yamada, Sachiko Kodera
Environmental Science and Pollution Research 2025.10
Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC
DOI： 10.1007/s11356-025-37007-w
Other Link： https://link.springer.com/article/10.1007/s11356-025-37007-w/fulltext.html
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Activation site estimation using induced current simulation and motor evoked potential latency in transcranial magnetic stimulation Reviewed
Takumi Tanabe, Akimasa Hirata, Keita Iijima, Sachiko Kodera, Masaki Fukunaga, Yoshikazu Ugawa, Ilkka Laakso
Clinical Neurophysiology 177 2110801 - 2110801 2025.09
Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier BV
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Conformity Assessment of Human Exposed to Radiation From Millimeter-Wave Vehicles Radars Reviewed
Ryota Morimoto, Sachiko Kodera, Yuma Kobayashi, Keishi Miwa, Akimasa Hirata
IEEE Journal of Microwaves 5 ( 4 ) 793 - 803 2025.07
Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers (IEEE)
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SHARM: Segmented Head Anatomical Reference Models Reviewed
E. A. Rashed, M. Al-Shatouri, I. Laakso, S. Kodera, A. Hirata
Biomedical Signal Processing and Control 104 107481 2025.06
Language：English Publishing type：Research paper (scientific journal)
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A novel transfer learning framework for non-uniform conductivity estimation with limited data in personalized brain stimulation Reviewed
Yoshiki Kubota, Sachiko Kodera, Akimasa Hirata
Physics in Medicine & Biology 70 105002 2025.05
Language：English Publishing type：Research paper (scientific journal)
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Statistical analysis and machine learning of TMS-induced MEPs for predicting poststroke motor impairment and performance Reviewed International coauthorship
Chun-Ren Phang, Shintaro Uehara, Sachiko Kodera, Akiko Yuasa, Shin Kitamura, Yohei Otaka, Akimasa Hirata
Informatics in Medicine Unlocked 55 101643 2025.04
Language：English Publishing type：Research paper (scientific journal)
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Recent advances and future perspective in computational bioelectromagnetics for exposure assessments. Reviewed International coauthorship International journal
Yinliang Diao, Wout Joseph, Dragan Poljak, Luca Giaccone, Sachiko Kodera, Ilkka Laakso, Kenichi Yamazaki, Kun Li, Kensuke Sasaki, Emmeric Tanghe, Mario Cvetković, Walid El Hajj, Takashi Hikage, Fatih Kaburcuk, Gernot Schmid, Anna Šušnjara Nejašmić, Thomas Tarnaud, Vitas Anderson, Kenneth R Foster, Theodoros Samaras, Richard A Tell, Soichi Watanabe, Chung-Kwang Chou, Akimasa Hirata
Bioelectromagnetics 46 ( 3 ) e70002 2025.04
Language：English Publishing type：Research paper (scientific journal)
In the last few decades, extensive efforts have been dedicated to developing computational methods for modeling the interaction of the human body with electromagnetic fields (EMFs). These studies are crucial for the establishment of exposure limits in international standards and guidelines for human protection from EMF, as well as for advancing personalized dosimetry assessment for medical applications using EMF. To summarize the state-of-the-art knowledge in this field, the IEEE International Committee on Electromagnetic Safety (ICES) held an International Workshop on Computational Bioelectromagnetics in February 2024. This review summarizes the technical presentations and discussions from the workshop and was contributed by multiple authors, encompassing topics such as the tissue dielectric property measurement, low-frequency and radio-frequency bioelectromagnetic modeling methods, stochastic modeling in electromagnetic-thermal dosimetry, intercomparison studies, and computational uncertainties. The insights gained from this workshop will guide future research and aid in the development of more accurate and reliable exposure assessment methods.
DOI： 10.1002/bem.70002
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Single exposure to near-threshold 5G millimeter wave modifies restraint stress responses in rats Reviewed
A. Matsumoto, I. Endo, E. Ijima, A. Hirata, S. Kodera, M. Ichiba, M. Tokiya, T. Hikage, and H. Masuda
Environmental Health and Preventive Medicine 2025.04
Language：English Publishing type：Research paper (scientific journal)
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Predicting heat-related morbidity in Japan through Integrated meteorological and behavioral factors Reviewed
T. Matsuura, S. Kodera, and A. Hirata
Environmental Challenges 18 101106 2025.04
Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal)
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Power absorption and temperature rise in deep learning based head models for local radiofrequency exposures Reviewed International coauthorship International journal
Sachiko Kodera, Reina Yoshida, Essam A Rashed, Yinliang Diao, Hiroyuki Takizawa, Akimasa Hirata
Physics in medicine & biology 2025.02
Authorship：Lead author, Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：IOP publishing
Abstract
Objective: Computational uncertainty and variability of power absorption and temperature rise in humans for radiofrequency (RF) exposure is a critical factor in ensuring human protection. This aspect has been emphasized as a priority. However, accurately modeling head tissue composition and assigning tissue dielectric and thermal properties remains a challenging task. This study investigated the impact of segmentation-based versus segmentation-free models for assessing localized RF exposure. 
Approach: Two computational head models were compared: one employing traditional tissue segmentation and the other leveraging deep learning to estimate tissue dielectric and thermal properties directly from magnetic resonance images. The finite-difference time-domain method and the bioheat transfer equation was solved to assess temperature rise for local exposure. Inter-subject variability and dosimetric uncertainties were analyzed across multiple frequencies.
Main Results: The comparison between the two methods for head modeling demonstrated strong consistency, with differences in peak temperature rise of 7.6±6.4%. The segmentation-free model showed reduced inter-subject variability, particularly at higher frequencies where superficial heating dominates. The maximum relative standard deviation in the inter-subject variability of heating factor was 15.0% at 3 GHz and decreased with increasing frequencies.
Significance: This study highlights the advantages of segmentation-free deep-learning models for RF dosimetry, particularly in reducing inter-subject variability and improving computational efficiency. While the differences between the two models are relatively small compared to overall dosimetric uncertainty, segmentation-free models offer a promising approach for refining individual-specific exposure assessments. These findings contribute to improving the accuracy and consistency of human protection guidelines against RF electromagnetic field exposure.Other Link： https://iopscience.iop.org/article/10.1088/1361-6560/adb935/pdf
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高速高精度脳機能イメージングのための脳波電流源推定精度の数値的評価 Reviewed
新津 正宗，小寺 紗千子，田中 裕士，阪本 卓也，平田 晃正
電子情報通信学会論文誌C 2025.02
Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal)
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個々人の血流ばらつきを考慮した複合物理解析による知覚温度上昇推定 Invited Reviewed
新井 紀香，湯浅 明子，上原 信太郎，牛澤 一樹，大高 洋平，Chun Ren Phang，後藤 俊幸，平田 晃正，小寺 紗千子
電子情報通信学会論文誌C 2025.01
Authorship：Last author, Corresponding author Language：Japanese Publishing type：Research paper (scientific journal)
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Estimating the perception threshold of electrostimulation and heating for radiofrequency contact current Reviewed
S. Kodera, S. Kimura, S. Uehara, A. Yuasa, K. Ushizawa, Y. Otaka, A. Hirata
IEEE Transactions on Electromagnetic Compatibility Early access 2024.11
Authorship：Lead author, Corresponding author Language：English Publishing type：Research paper (scientific journal)
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Assessment of whole-body-average SAR for exposure to electromagnetic fields up to 30 GHz using body model with scaled dielectric parameters Reviewed International coauthorship
Y. Diao, S. Kodera, K. Li, and A. Hirata
IEEE Transactions on Electromagnetic Compatibility 2024.11
Language：English Publishing type：Research paper (scientific journal)
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Differential impact of SARS-CoV-2 infection during different outbreak periods on incident diabetes in Japan: a matched cohort study utilizing health insurance claims Reviewed
Akiko Matsumoto, Sachiko Kodera, Tatsuya Matsuura, Yoko Takayama, Yuya Yamada, Akimasa Hirata
Environmental Health and Preventive Medicine 2024.10
Language：English Publishing type：Research paper (scientific journal)
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Electric field envelope focality in superficial brain areas with linear alignment montage in temporal interference stimulation Reviewed International coauthorship
A. Hirata, Y. Akazawa, S. Kodera, N. Otsuru, I. Laakso
Computers in Biology and Medicine 178 108697 2024.08
Language：English
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A novel multivariate time series forecasting dendritic neuron model for COVID-19 pandemic transmission tendency Reviewed International coauthorship
C. Tang, Y. Todo, S. Kodera, R. Sun, A. Shimada, and A. Hirata
Neural Networks 179 106527 2024.07
Language：English Publishing type：Research paper (scientific journal)
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Perceptional Threshold of Electrostimulation and Heating for Intermediate Contact Current Reviewed
A. Hirata, S. Kimura, S. Kodera, S. Uehara, A. Yuasa, K. Ushizawa,Y. Otaka
BioEM 2024 2024.06
Language：English Publishing type：Research paper (international conference proceedings)
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Core temperature rise for whole-body exposure in GHz band at different ambient temperature Reviewed
R. Okuda, S. Kodera, A. Hirata
EMC JAPAN/APEMC OKINAWA 2024.05
Language：English Publishing type：Research paper (international conference proceedings)
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