Abstract
Malfunctions of oxygen metabolism are suspected to play a key role in a number of neurological and psychiatric disorders, but this hypothesis cannot be properly investigated without an in-vivo non-invasive measurement of brain oxygen consumption. We present a new way to measure the Cerebral Metabolic Rate of Oxygen (CMRO2) by combining two existing magnetic resonance imaging techniques, namely arterial spin-labelling and oxygen extraction fraction mapping. This method was validated by imaging rats under different anaesthetic regimes and was strongly correlated to glucose consumption measured by autoradiography.
Highlights
The brain requires around 20% of a human’s energy production, and requires a similar proportion of the body’s oxygen supply[1,2]
Recent years have seen the emergence of methods including whole-brain measurements of CMRO2 using a combination of T2-mapping and phase-contrast velocity measurements[10,11], voxel-wise mapping using quantitative Bloody Oxygenation Level Dependent with calibration from gas administration[12,13] and high-resolution mapping methods based on Quantitative Susceptibility Mapping (QSM)[14,15]
We demonstrated our method by imaging rats with two anaesthetics known to affect brain metabolism differently, and validated these Magnetic Resonance Imaging (MRI) measurements by comparing them to gold-standard autoradiography measurements of glucose metabolism under the same anaesthetics
Summary
The brain requires around 20% of a human’s energy production, and requires a similar proportion of the body’s oxygen supply[1,2]. There is great interest in being able to quantitatively map the Cerebral Metabolic Rate of Oxygen (CMRO ) consumption , both as a marker of pathology and for the study of healthy ageing[3,4,5,6]. Recent years have seen the emergence of methods including whole-brain measurements of CMRO2 using a combination of T2-mapping and phase-contrast velocity measurements[10,11], voxel-wise mapping using quantitative Bloody Oxygenation Level Dependent (qBOLD) with calibration from gas administration[12,13] and high-resolution mapping methods based on Quantitative Susceptibility Mapping (QSM)[14,15]. For this study we created a straightforward and robust method to measure CMRO2 by combining measurements of Cerebral Blood Flow (CBF) and Oxygen Extraction Fraction (OEF). OEF maps were constructed by measuring the reversible rate of transverse relaxation R2′, which is related to the concentration of deoxyhaemoglobin (dHb)[17,18,19]
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