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Quantitative study of changes in oxidative metabolism during visual stimulation using absolute relaxation rates
Norihiko Fujita1, Kenji Matsumoto, Hisashi Tanaka
1Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. nofujita@radiol.med.osaka-u.ac.jp
NMR in Biomedicine
|November 18, 2005
Summary
This study directly maps deoxyhemoglobin (dHb) content for precise blood oxygen-level dependent (BOLD) signal calibration in functional MRI (fMRI). This novel method enhances accuracy for human brain studies without physiological intervention.
Area of Science:
- Neuroimaging
- Physiology
- Biophysics
Background:
- Quantitative functional MRI (fMRI) relies on calibrating the blood oxygen-level dependent (BOLD) signal using deoxyhemoglobin (dHb) content.
- Previous methods for assessing dHb content in humans were indirect, often involving physiological perturbations like carbon dioxide breathing.
Purpose of the Study:
- To develop and validate a direct quantitative mapping method for baseline dHb content in the human brain.
- To calibrate the BOLD signal using this direct dHb measurement during visual stimulation.
Main Methods:
- Quantitative mapping of baseline dHb content was achieved by measuring the reversible contribution to the effective transverse relaxation rate.
- The BOLD signal change in the visual cortex during 8 Hz flicker stimulation was calibrated using the quantitative dHb map.
- Simultaneous measurements of cerebral blood flow (CBF) were performed.
Main Results:
- The calibrated relaxation rate change, representing stimulation-induced fractional dHb change, decreased by 14% in the activated visual cortex.
- Simultaneously, cerebral blood flow (CBF) increased by 59%.
- Calculated cerebral metabolic rate of oxygen (CMRO2) increased by 19-28%, with a CBF/CMRO2 increase ratio of 2-3:1.
Conclusions:
- The proposed direct quantitative evaluation of the BOLD signal offers improved accuracy for fMRI studies.
- This method eliminates the need for physiological perturbations, making it suitable for both healthy and diseased states.
- The findings align with previous quantitative fMRI studies, validating the approach.
