A Tale of Two Methods: Combining Near-Infrared Spectroscopy with MRI for Studies of Brain Oxygenation and Metabolism

Combining magnetic resonance imaging (MRI) with near-infrared spectroscopy (NIRS) leads to excellent synergies which can improve the interpretation of either method and can provide novel data with respect to measuring brain oxygenation and metabolism. MRI has good spatial resolution, can detect a range of physiological parameters and is sensitive to changes in deoxyhemoglobin content. NIRS has lower spatial resolution, but can detect, and with specific technologies, quantify, deoxyhemoglobin, oxyhemoglobin, total hemoglobin and cytochrome oxidase. This paper reviews the application of both methods, as a multimodal technology, for assessing changes in brain oxygenation that may occur with changes in functional activation state or metabolic rate. Examples of hypoxia and ischemia are shown. Data support the concept of reduced metabolic rate resulting from hypoxia/ischemia and that metabolic rate in brain is not close to oxygen limitation during normoxia. We show that multimodal MRI and NIRS can provide novel information for studies of brain metabolism.