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795 results on '"Obata, Takayuki"'

2. Oscillating-gradient spin-echo diffusion-weighted imaging (OGSE-DWI) with a limited number of oscillations: II. Asymptotics

Author

Kershaw, Jeff and Obata, Takayuki

Subjects
Physics - Medical Physics, Electrical Engineering and Systems Science - Image and Video Processing
Abstract

Oscillating-gradient spin-echo diffusion-weighted magnetic resonance imaging (OGSE-DWI) has been promoted as a promising technique for studying the microstructure of complex hydrated matter in the frequency domain. The target of the OGSE-DWI technique is the spectral density of molecular diffusion, $u_{2}(\omega)$, which is predicted to obey a set of asymptotic universality relations that are linked to the global organisation of the sample. So, in principle the complex microstructure of a medium can be classified by measuring the spectral density in its low- and high-frequency limits. However, due to practical limitations on the spectral resolution and range of the technique, it is not possible to directly sample the spectral density with OGSE-DWI. Rather, information about the spectral density can be obtained only indirectly through the quantities $U_{kk}$ & $U_{k0}$, which are filtered representations of $u_{2}(\omega)$. The purpose of this study is to investigate how the universal behaviour of $u_{2}(\omega)$ emerges in the asymptotic behaviour of OGSE-DWI signal., Comment: 16 pages + supplementary material

Published
2023

6. Increased glutamate and glutamine levels and their relationship to astrocytes and dopaminergic transmissions in the brains of adults with autism

Author

Oya, Masaki, Matsuoka, Kiwamu, Kubota, Manabu, Fujino, Junya, Tei, Shisei, Takahata, Keisuke, Tagai, Kenji, Yamamoto, Yasuharu, Shimada, Hitoshi, Seki, Chie, Itahashi, Takashi, Aoki, Yuta Y., Ohta, Haruhisa, Hashimoto, Ryu-ichiro, Sugihara, Genichi, Obata, Takayuki, Zhang, Ming-Rong, Suhara, Tetsuya, Nakamura, Motoaki, Kato, Nobumasa, Takado, Yuhei, Takahashi, Hidehiko, and Higuchi, Makoto

Published
2023
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7. A neural network model that learns differences in diagnosis strategies among radiologists has an improved area under the curve for aneurysm status classification in magnetic resonance angiography image series

Author

Tachibana, Yasuhiko, Nishimori, Masataka, Kitamura, Naoyuki, Umehara, Kensuke, Ota, Junko, Obata, Takayuki, and Higashi, Tatsuya

Subjects
Electrical Engineering and Systems Science - Image and Video Processing, Computer Science - Computer Vision and Pattern Recognition, Computer Science - Machine Learning, Statistics - Machine Learning
Abstract

Purpose: To construct a neural network model that can learn the different diagnosing strategies of radiologists to better classify aneurysm status in magnetic resonance angiography images. Materials and methods: This retrospective study included 3423 time-of-flight brain magnetic resonance angiography image series (subjects: male 1843 [mean age, 50.2 +/- 11.7 years], female 1580 [50.8 +/- 11.3 years]) recorded from November 2017 through January 2019. The image series were read independently for aneurysm status by one of four board-certified radiologists, who were assisted by an established deep learning-based computer-assisted diagnosis (CAD) system. The constructed neural networks were trained to classify the aneurysm status of zero to five aneurysm-suspicious areas suggested by the CAD system for each image series, and any additional aneurysm areas added by the radiologists, and this classification was compared with the judgment of the annotating radiologist. Image series were randomly allocated to training and testing data in an 8:2 ratio. The accuracy of the classification was compared by receiver operating characteristic analysis between the control model that accepted only image data as input and the proposed model that additionally accepted the information of who the annotating radiologist was. The DeLong test was used to compare areas under the curves (P < 0.05 was considered significant). Results: The area under the curve was larger in the proposed model (0.845) than in the control model (0.793), and the difference was significant (P < 0.0001). Conclusion: The proposed model improved classification accuracy by learning the diagnosis strategies of individual annotating radiologists.

Published
2020

8. The utility of a convolutional neural network for generating a myelin volume index map from rapid simultaneous relaxometry imaging

Author

Tachibana, Yasuhiko, Hagiwara, Akifumi, Hori, Masaaki, Kershaw, Jeff, Nakazawa, Misaki, Omatsu, Tokuhiko, Kishimoto, Riwa, Yokoyama, Kazumasa, Hattori, Nobutaka, Aoki, Shigeki, Higashi, Tatsuya, and Obata, Takayuki

Subjects
Electrical Engineering and Systems Science - Image and Video Processing, Computer Science - Artificial Intelligence
Abstract

Background and Purpose: A current algorithm to obtain a synthetic myelin volume fraction map (SyMVF) from rapid simultaneous relaxometry imaging (RSRI) has a potential problem, that it does not incorporate information from surrounding pixels. The purpose of this study was to develop a method that utilizes a convolutional neural network (CNN) to overcome this problem. Methods: RSRI and magnetization transfer images from 20 healthy volunteers were included. A CNN was trained to reconstruct RSRI-related metric maps into a myelin volume-related index (generated myelin volume index: GenMVI) map using the myelin volume index map calculated from magnetization transfer images (MTMVI) as reference. The SyMVF and GenMVI maps were statistically compared by testing how well they correlated with the MTMVI map. The correlations were evaluated based on: (i) averaged values obtained from 164 atlas-based ROIs, and (ii) pixel-based comparison for ROIs defined in four different tissue types (cortical and subcortical gray matter, white matter, and whole brain). Results: For atlas-based ROIs, the overall correlation with the MTMVI map was higher for the GenMVI map than for the SyMVF map. In the pixel-based comparison, correlation with the MTMVI map was stronger for the GenMVI map than for the SyMVF map, and the difference in the distribution for the volunteers was significant (Wilcoxon sign-rank test, P<.001) in all tissue types. Conclusion: The proposed method is useful, as it can incorporate more specific information about local tissue properties than the existing method.

Published
2019

9. Two pathways differentially linking tau depositions, oxidative stress, and neuronal loss to apathetic phenotypes in progressive supranuclear palsy

Author

Matsuoka, Kiwamu, Takado, Yuhei, Tagai, Kenji, Kubota, Manabu, Sano, Yasunori, Takahata, Keisuke, Ono, Maiko, Seki, Chie, Matsumoto, Hideki, Endo, Hironobu, Shinotoh, Hitoshi, Sahara, Yasuka, Obata, Takayuki, Near, Jamie, Kawamura, Kazunori, Zhang, Ming-Rong, Suhara, Tetsuya, Shimada, Hitoshi, and Higuchi, Makoto

Published
2023
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10. In Vivo Assessment of Astrocyte Reactivity in Patients with Progressive Supranuclear Palsy

Author

Hirata, Kosei, primary, Matsuoka, Kiwamu, additional, Tagai, Kenji, additional, Endo, Hironobu, additional, Tatebe, Harutsugu, additional, Ono, Maiko, additional, Kokubo, Naomi, additional, Kataoka, Yuko, additional, Oyama, Asaka, additional, Shinotoh, Hitoshi, additional, Takahata, Keisuke, additional, Obata, Takayuki, additional, Dehghani, Masoumeh, additional, Near, Jamie, additional, Kawamura, Kazunori, additional, Zhang, Ming‐Rong, additional, Shimada, Hitoshi, additional, Shimizu, Hiroshi, additional, Kakita, Akiyoshi, additional, Yokota, Takanori, additional, Tokuda, Takahiko, additional, Higuchi, Makoto, additional, and Takado, Yuhei, additional

Published
2024
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23. In vivoassessment of astrocyte reactivity in patients with progressive supranuclear palsy

Author

Hirata, Kosei, primary, Matsuoka, Kiwamu, additional, Tagai, Kenji, additional, Endo, Hironobu, additional, Tatebe, Harutsugu, additional, Ono, Maiko, additional, Kokubo, Naomi, additional, Kataoka, Yuko, additional, Oyama, Asaka, additional, Shinotoh, Hitoshi, additional, Takahata, Keisuke, additional, Obata, Takayuki, additional, Dehghani, Masoumeh, additional, Near, Jamie, additional, Kawamura, Kazunari, additional, Zhang, Ming-Rong, additional, Shimada, Hitoshi, additional, Shimizu, Hiroshi, additional, Kakita, Akiyoshi, additional, Yokota, Takanori, additional, Tokuda, Takahiko, additional, Higuchi, Makoto, additional, and Takado, Yuhei, additional

Published
2023
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32. Altered Brain Energy Metabolism Related to Astrocytes in Alzheimer's Disease.

Author

Hirata, Kosei, Matsuoka, Kiwamu, Tagai, Kenji, Endo, Hironobu, Tatebe, Harutsugu, Ono, Maiko, Kokubo, Naomi, Oyama, Asaka, Shinotoh, Hitoshi, Takahata, Keisuke, Obata, Takayuki, Dehghani, Masoumeh, Near, Jamie, Kawamura, Kazunori, Zhang, Ming‐Rong, Shimada, Hitoshi, Yokota, Takanori, Tokuda, Takahiko, Higuchi, Makoto, and Takado, Yuhei

Subjects
BRAIN metabolism, ALZHEIMER'S disease, GLIAL fibrillary acidic protein, ENERGY metabolism, NUCLEAR magnetic resonance spectroscopy
Abstract

Objective: Increasing evidence suggests that reactive astrocytes are associated with Alzheimer's disease (AD). However, its underlying pathogenesis remains unknown. Given the role of astrocytes in energy metabolism, reactive astrocytes may contribute to altered brain energy metabolism. Astrocytes are primarily considered glycolytic cells, suggesting a preference for lactate production. This study aimed to examine alterations in astrocytic activities and their association with brain lactate levels in AD. Methods: The study included 30 AD and 30 cognitively unimpaired participants. For AD participants, amyloid and tau depositions were confirmed by positron emission tomography using [11C]PiB and [18F]florzolotau, respectively. Myo‐inositol, an astroglial marker, and lactate in the posterior cingulate cortex were quantified by magnetic resonance spectroscopy. These magnetic resonance spectroscopy metabolites were compared with plasma biomarkers, including glial fibrillary acidic protein as another astrocytic marker, and amyloid and tau positron emission tomography. Results: Myo‐inositol and lactate levels were higher in AD patients than in cognitively unimpaired participants (p < 0.05). Myo‐inositol levels correlated with lactate levels (r = 0.272, p = 0.047). Myo‐inositol and lactate levels were positively associated with the Clinical Dementia Rating sum‐of‐boxes scores (p < 0.05). Significant correlations were noted between myo‐inositol levels and plasma glial fibrillary acidic protein, tau phosphorylated at threonine 181 levels, and amyloid and tau positron emission tomography accumulation in the posterior cingulate cortex (p < 0.05). Interpretation: We found high myo‐inositol levels accompanied by increased lactate levels in the posterior cingulate cortex in AD patients, indicating a link between reactive astrocytes and altered brain energy metabolism. Myo‐inositol and plasma glial fibrillary acidic protein may reflect similar astrocytic changes as biomarkers of AD. ANN NEUROL 2024;95:104–115 [ABSTRACT FROM AUTHOR]

Published
2024
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33. Neon ion (20Ne10+) charged particle beams manipulate rapid tumor reoxygenation in syngeneic mouse models.

Author

Imaizumi, Akiko, Hirayama, Ryoichi, Ikoma, Yoko, Nitta, Nobuhiro, Obata, Takayuki, and Hasegawa, Sumitaka

Abstract

Charged particle beams induce various biological effects by creating high‐density ionization through the deposition of energy along the beam's trajectory. Charged particle beams composed of neon ions (20Ne10+) hold great potential for biomedical applications, but their physiological effects on living organs remain uncertain. In this study, we demonstrate that neon‐ion beams expedite the process of reoxygenation in tumor models. We simulated mouse SCCVII syngeneic tumors and exposed them to either X‐ray or neon‐ion beams. Through an in vivo radiobiological assay, we observed a reduction in the hypoxic fraction in tumors irradiated with 8.2 Gy of neon‐ion beams 30 h after irradiation compared to 6 h post‐irradiation. Conversely, no significant changes in hypoxia were observed in tumors irradiated with 8.2 Gy of X‐rays. To directly quantify hypoxia in the irradiated living tumors, we utilized dynamic contrast‐enhanced magnetic resonance imaging (MRI) and diffusion‐weighted imaging. These combined MRI techniques revealed that the non‐hypoxic fraction in neon‐irradiated tumors was significantly higher than that in X‐irradiated tumors (69.53% vs. 47.67%). Simultaneously, the hypoxic fraction in neon‐ion‐irradiated tumors (2.77%) was lower than that in X‐irradiated tumors (4.27%) and non‐irradiated tumors (32.44%). These results support the notion that accelerated reoxygenation occurs more effectively with neon‐ion beam irradiation compared to X‐rays. These findings shed light on the physiological effects of neon‐ion beams on tumors and their microenvironment, emphasizing the therapeutic advantage of using neon‐ion charged particle beams to manipulate tumor reoxygenation. [ABSTRACT FROM AUTHOR]

Published
2024
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34. Magnetic Resonance Water Tracer Imaging Using 17O-Labeled Water

Author

Kameda, Hiroyuki, primary, Kinota, Naoya, additional, Kato, Daisuke, additional, Fujii, Takaaki, additional, Harada, Taisuke, additional, Komaki, Yuji, additional, Sugimori, Hiroyuki, additional, Onodera, Tomohiro, additional, Tomiyasu, Moyoko, additional, Obata, Takayuki, additional, and Kudo, Kohsuke, additional

Published
2023
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35. Altered brain energy metabolism related to astrocytes in Alzheimer's disease

Author

Hirata, Kosei, primary, Matsuoka, Kiwamu, additional, Tagai, Kenji, additional, Endo, Hironobu, additional, Tatebe, Harutsugu, additional, Ono, Maiko, additional, Kokubo, Naomi, additional, Oyama, Asaka, additional, Shinotoh, Hitoshi, additional, Keisuke, Takahata, additional, Obata, Takayuki, additional, Dehghani, Masoumeh, additional, Near, Jamie, additional, Kawamura, Kazunori, additional, Zhang, Ming‐Rong, additional, Shimada, Hitoshi, additional, Yokota, Takanori, additional, Tokuda, Takahiko, additional, Higuchi, Makoto, additional, and Takado, Yuhei, additional

Published
2023
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38. Magnetic Resonance Water Tracer Imaging Using 17O-Labeled Water

Author

Kameda, Hiroyuki, Kinota, Naoya, Kato, Daisuke, Fujii, Takaaki, Harada, Taisuke, Komaki, Yuji, Sugimori, Hiroyuki, Onodera, Tomohiro, Tomiyasu, Moyoko, Obata, Takayuki, and Kudo, Kohsuke

Abstract

Magnetic resonance imaging (MRI) is a crucial imaging technique for visualizing water in living organisms. Besides proton MRI, which is widely available and enables direct visualization of intrinsic water distribution and dynamics in various environments, MR-WTI (MR water tracer imaging) using 17O-labeled water has been developed, benefiting from the many advancements in MRI software and hardware that have substantially improved the signal-to-noise ratio and made possible faster imaging. This cutting-edge technique allows the generation of novel and valuable images for clinical use. This review elucidates the studies related to MRI water tracer techniques centered around 17O-labeled water, explaining the fundamental principles of imaging and providing clinical application examples. Anticipating continued progress in studies involving isotope-labeled water, this review is expected to contribute to elucidating the pathophysiology of various diseases related to water dynamics abnormalities and establishing novel imaging diagnostic methods for associated diseases.

Published
2024
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46. Distribution of intraperitoneally administered D2O in AQP4-knockout mouse brain after MCA occlusion

Author

Takuya Urushihata, Hiroyuki Takuwa, Manami Takahashi, Je◻ Kershaw, Sayaka Shibata, Nobuhiro Nitta, Yasuhiko Tachibana, Masato Yasui, Makoto Higuchi, and Obata Takayuki

Abstract

As the movement of water in the brain is known to be involved in neural activity and various brain pathologies, the ability to assess water dynamics in the brain will be important for the understanding of brain function and the diagnosis and treatment of brain diseases. Aquaporin-4 (AQP4) is a membrane channel protein that is highly expressed in brain astrocytes and is important for the movement of water molecules in the brain. In this study, we investigated the contribution of AQP4 to brain water dynamics by administering deuterium-labeled water (D2O) intraperitoneally to wild-type and AQP4 knockout (AQP4-ko) mice that had undergone surgical occlusion of the middle cerebral artery. Water dynamics in the infarct region and on either side of the anterior cerebral artery (ACA) was monitored with proton-density-weighted imaging (PDWI) performed on a 7T animal MRI. D2O caused a negative signal change quickly after administration. The AQP4-ko mice showed a delay of the time-to-minimum in both contralateral and ipsilateral ACA region compared to wild-type mice. Also, only the AQP4-ko mice showed a delay of the time-to-minimum in the ipsilateral ACA region compared to the contralateral side. In only the wild-type mice, the signal minimum in the ipsilateral ACA region was higher than that in the contralateral ACA region. In the infarct region, the signal attenuation was slower for the AQP4-ko mice in comparison to the wild-type mice. These results suggest that AQP4 loss affects water dynamics in the ACA region not only in the infarct region. Dynamic PDWI after D2O administration may be a useful tool for showing the effects of AQP4 in vivo.HighlightsThe measurement of brain water dynamics with D2O.In vivo investigation of AQP4 loss and focal brain ischemia.AQP4 loss affects water dynamics in the ACA region not only in the infarct region.

Published
2022

47. Measurement of Striatal Dopamine Release Induced by Neuropsychological Stimulation in Positron Emission Tomography With Dual Injections of [11C]Raclopride

Author

Ikoma, Yoko, Kimura, Yasuyuki, Yamada, Makiko, Obata, Takayuki, Suhara, Tetsuya, and Ito, Hiroshi

Subjects
Psychiatry and Mental health
Abstract

ObjectivesPositron emission tomography (PET) with [11C]raclopride has been applied to measure changes in the concentration of endogenous dopamine induced by pharmacological challenge or neuropsychological stimulation by evaluating the binding potential (BP) between the baseline and activated state. Recently, to reliably estimate BP in the activated state, a new approach with dual-bolus injections in a single PET scan was developed. In this study, we investigated the feasibility of applying this dual-bolus injection approach to measure changes in endogenous dopamine levels induced by cognitive tasks in humans.MethodsFirst, the reproducibility of BP estimation using the dual-bolus injection approach was evaluated using PET scans without stimulation in nine healthy volunteers. A 90-min scan was performed with bolus injections of [11C]raclopride administered at the beginning of the scan and 45 min after the first injection. BPs in the striatum for the first injection (BP1) and second injection (BP2) were estimated using an extended simplified reference tissue model, and the mean absolute difference (MAD) between the two BPs was calculated. The MAD was also compared with the conventional bolus-plus-continuous infusion approach. Next, PET studies with a cognitive reinforcement learning task were performed on 10 healthy volunteers using the dual-bolus injection approach. The BP1 at baseline and BP2 at the activated state were estimated, and the reduction in BP was evaluated.ResultsIn the PET scans without stimulation, the dual-bolus injection approach showed a smaller MAD (1 and BP2 than the bolus-plus-continuous infusion approach, demonstrating good reproducibility of this approach. In the PET scans with the cognitive task performance, the reduction in BP was not observed in the striatum by either approach, showing that the changes in dopamine level induced by the cognitive tasks performed in this study were not sufficient to be detected by PET.ConclusionOur results indicate that the cognitive task-induced changes in dopamine-related systems may be complex and difficult to measure accurately using PET scans. However, the proposed dual-bolus injection approach provided reliable BP estimates with high reproducibility, suggesting that it has the potential to improve the accuracy of PET scans for measuring changes in dopamine concentrations.

Published
2022

49. Intraocular Water Movement Visualization Using1 H‐MRIWith Eye Drops of O‐17‐Labeled Saline: First‐in‐Human Study

Author

Tomiyasu, Moyoko, primary, Sahara, Yasuka, additional, Mitsui, Etsuko, additional, Tsuchiya, Hiroki, additional, Maeda, Takamasa, additional, Tomoyori, Nobuhiro, additional, Kawashima, Makoto, additional, Nogawa, Toshifumi, additional, Kishimoto, Riwa, additional, Takado, Yuhei, additional, Higashi, Tatsuya, additional, Mizota, Atsushi, additional, Kudo, Kohsuke, additional, and Obata, Takayuki, additional

Published
2022
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