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Published on: August 17, 2022
Validation and optimization of hypercapnic-calibrated fMRI from oxygen-sensitive two-photon microscopy
Louis Gagnon1, Sava Sakadžić2, Frédéric Lesage3
1Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA Department of Medicine, Laval University, Quebec City, Quebec, Canada Deparment of Electrical Engineering, École Polytechnique Montreal, Montreal, Quebec, Canada lgagnon@nmr.mgh.harvard.edu.
Hypercapnic-calibrated fMRI can quantify brain activity. Macroscopic BOLD models, when recalibrated with new parameters, accurately estimate cerebral metabolic rate of oxygen (rCMRO2), improving fMRI analysis.
Area of Science:
- Neuroimaging
- Physiology
- Biophysics
Background:
- Functional magnetic resonance imaging (fMRI) with hypercapnia calibration estimates relative cerebral metabolic rate of oxygen (rCMRO2).
- This technique relies on macroscopic models of the Blood-Oxygen-Level-Dependent (BOLD) effect.
- The accuracy of these calibrated fMRI models is not well-established, hindering widespread use.
Purpose of the Study:
- To evaluate the accuracy of macroscopic BOLD models for calibrated fMRI.
- To test the original Davis model and a simplified heuristic model using a microscopic vascular network model as a ground truth simulator.
- To determine if model parameter recalibration can improve the accuracy of rCMRO2 estimation.
Main Methods:
- Developed a microscopic vascular anatomical network model in mice to simulate BOLD signals.
- Tested the accuracy of the original Davis BOLD model and a simplified heuristic model.
- Investigated the impact of redefining model parameters, specifically α (relationship between cerebral blood volume and flow changes).
Main Results:
- Macroscopic BOLD models showed inaccuracies with original parameters.
- Recalibrating model parameters significantly improved accuracy.
- The parameter α was found to be smaller than typically assumed and dependent on magnetic field strength.
Conclusions:
- Simple BOLD models can be used to quantitatively analyze BOLD signals after parameter recalibration.
- The findings support the use of calibrated fMRI for more accurate rCMRO2 estimation.
- Further research is needed to clarify the physiological meaning of the redefined model parameters.
