Development of four-dimensional fMRI method for direct detection of activated neurons

2022 Fiscal Year Final Research Report

• Project/Area Number: 18K07701
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 52040:Radiological sciences-related
• Research Institution: Hokkaido University
• Principal Investigator: Yamamoto Toru 北海道大学, 保健科学研究院, 名誉教授 (80261361)
• Co-Investigator(Kenkyū-buntansha): 黄田 育宏 国立研究開発法人情報通信研究機構, 脳情報通信融合研究センター脳機能解析研究室, 主任研究員 (60374716) ; 唐 明輝 北海道大学, 医学研究院, 特任助教 (80794156)
• Project Period (FY): 2018-04-01 – 2023-03-31
• Keywords: MRI / oxygen / paramagnetism / relaxation

Outline of Final Research Achievements

Focusing on the phenomenon that the NMR relaxation due to paramagnetic substance is enhanced in viscous solution, we analyzed temporal fluctuation of diffusion-weighted MR signal which enhances intra cellular signal. Amplitude of the low frequency signal fluctuation lower than 0.1 Hz, which reflects default mode network, indicated existence of the specific TE that counterbalances signal increase due to longitudinal relaxation time shortening and signal decrease due to transverse relaxation time shortening. This low frequency signal fluctuation has been understood as appearance of intracellular oxygen concentration fluctuation. Diffusion-weighted fMRI signal also showed the existence of the specific TE in that intracellular oxygen concentration changes do not appear but hemodynamic changes appear. Using scan parameters to enhance intracellular oxygen concentration changes, fMRI signal showed rapid increases after the onset of the stimuli.

Free Research Field

医学物理

Academic Significance and Societal Importance of the Research Achievements

fMRIは，通常，神経賦活に遅れて発生する血流変化を利用するもので，神経細胞からの信号を直接捉えるものではない．fMRIを用いた論文の70％が擬陽性であるとの指摘もあり(Eklund,PNAS,2016)，神経細胞の賦活を直接捉える新しいfMRIの開発が待望されている．本研究は賦活直後から発生する神経細胞内酸素濃度の速い変化を反映する信号がMR信号に現れ得ることを示し，撮像パラメータとの関係を理論的，実験的に明らかにした．本研究の成果は新しいfMRI開発上の大きな基盤となり，血流変化とは異なるこの速い信号変化を効率的に捉えることで神経電位変化追随するfMRIの完成が近づくものと考えている．