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Quantitative study of changes in oxidative metabolism during visual stimulation using absolute relaxation rates
Author(s) -
Fujita Norihiko,
Matsumoto Kenji,
Tanaka Hisashi,
Watanabe Yoshiyuki,
Murase Kenya
Publication year - 2006
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.1001
Subject(s) - visual cortex , chemistry , stimulation , cerebral blood flow , functional magnetic resonance imaging , relaxation (psychology) , context (archaeology) , blood flow , nuclear magnetic resonance , neuroscience , medicine , psychology , biology , physics , paleontology
In the context of quantitative functional MRI (fMRI), deoxyhemoglobin (dHb) content is the essential physiological parameter for calibrating the blood oxygenation level‐dependent (BOLD) signal. In studies on humans, the baseline dHb content or its equivalent has been evaluated indirectly by means of carbon dioxide breathing as a physiological reference condition. In this study with normal volunteers, quantitative mapping of baseline dHb content was performed in a direct manner by measuring the reversible contribution of the effective transverse relaxation rate. The BOLD signal change in the visual cortex during 8 Hz flicker visual stimulation was calibrated based on the quantitative map of baseline dHb content. The calibrated relaxation rate change that represents the stimulation‐induced fractional change of dHb content decreased by 14% within the activated visual cortex. Simultaneous measurement of cerebral blood flow (CBF) with BOLD showed an increase of 59%. From the calibrated relaxation rate and CBF changes, the cerebral metabolic rate of oxygen (CMRO 2 ) was calculated to increase by 19–28% within the activated visual cortex. The ratio of the CBF increase to the CMRO 2 increase was 2–3:1, which agreed well with results of similar quantitative fMRI studies for humans. The method proposed here for quantitative evaluation of the BOLD signal may be applicable not only to fMRI for normal human subjects, but also to physiologically altered or diseased states, because it requires no physiological perturbation. Copyright © 2005 John Wiley & Sons, Ltd.