Functional quantitative susceptibility mapping (fQSM) of rat brain during flashing light stimulation

Chia-Ming Shih; Hsin-Chih Lo; Meng-Chi Hsieh; Jyh-Horng Chen

doi:10.1016/j.neuroimage.2021.117924

Functional quantitative susceptibility mapping (fQSM) of rat brain during flashing light stimulation

Neuroimage. 2021 Jun:233:117924. doi: 10.1016/j.neuroimage.2021.117924. Epub 2021 Mar 19.

Authors

Chia-Ming Shih¹, Hsin-Chih Lo¹, Meng-Chi Hsieh¹, Jyh-Horng Chen²

Affiliations

¹ Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei 106, Taiwan; Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei 106, Taiwan; Molecular Imaging Center, National Taiwan University, Taipei 106, Taiwan.
² Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei 106, Taiwan; Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei 106, Taiwan; Molecular Imaging Center, National Taiwan University, Taipei 106, Taiwan. Electronic address: jhchen@ntu.edu.tw.

PMID: 33753240
DOI: 10.1016/j.neuroimage.2021.117924

Abstract

Functional magnetic resonance imaging (fMRI) based on the blood oxygenation level-dependent (BOLD) contrast has become an indispensable tool in neuroscience. However, the BOLD signal is nonlocal, lacking quantitative measurement of oxygenation fluctuation. This preclinical study aimed to introduced functional quantitative susceptibility mapping (fQSM) to complement BOLD-fMRI to quantitatively assess the local susceptibility and venous oxygen saturation (SvO₂). Rats were subjected to a 5 Hz flashing light and the different inhaled oxygenation levels (30% and 100%) were used to observe the venous susceptibility to quantify SvO₂. Phase information was extracted to produce QSM, and the activation responses of magnitude (conventional BOLD) and the QSM time-series were analyzed. During light stimulation, the susceptibility change of fQSM was four times larger than the BOLD signal change in both inhalation oxygenation conditions. Moreover, the responses in the fQSM map were more restricted to the visual pathway, such as the lateral geniculate nucleus and superior colliculus, compared with the relatively diffuse distributions in the BOLD map. Also, the calibrated SvO₂ was approximately 84% (88%) when the task was on, 83% (87%) when the task was off during 30% (and during 100%) oxygen inhalation. This is the first fQSM study in a small animal model and increases our understanding of fQSM in the brains of small animals. This study demonstrated the feasibility, sensitivity, and specificity of fQSM using light stimulus, as fQSM provides quantitative clues as well as localized information, complementing the defects of BOLD-fMRI. In addition to neural activity, fQSM also assesses SvO₂ as supplementary information while BOLD-fMRI dose not. Accordingly, the fQSM technique could be a useful quantitative tool for functional studies, such as longitudinal follow up of neurodegenerative diseases, functional recovery after brain surgery, and negative BOLD studies.

Keywords: Functional MRI; Functional quantitative susceptibility mapping; Quantitative susceptibility mapping; Venous oxygen saturation; Visual stimuli.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Brain / diagnostic imaging
Brain / physiology
Brain Mapping / methods*
Geniculate Bodies / diagnostic imaging*
Geniculate Bodies / physiology
Magnetic Resonance Imaging / methods*
Male
Photic Stimulation / methods*
Rats
Rats, Sprague-Dawley
Superior Colliculi / diagnostic imaging*
Superior Colliculi / physiology
Visual Pathways / diagnostic imaging*
Visual Pathways / physiology