Quantitative mapping of cerebral deoxyhemoglobin content using MR imaging

In this study, we present a magnetic resonance imaging (MRI) method for quantifying cerebral deoxyhemoglobin content that is based on a measurement of the reversible contribution (R'(2)) of the transverse relaxation rate under the assumption of a quantitative relationship between R'(2) and deoxyhemoglobin content. A numerical simulation was performed assuming a specific pulse sequence conventionally employed for R'(2) measurement. The results showed a near linear relationship between R'(2) and deoxyhemoglobin content in the physiological range of oxygen extraction for almost all sized vessels, although a large diffusion effect for capillary sized vessels compromised the relationship. Concerning the methodology for R'(2) measurement, a theoretical analysis showed that multiexponential transverse signal decay of brain parenchyma may result in a considerable underestimation or overestimation of R'(2), if a conventional method is employed for R'(2) quantification. A modified method for correcting the effect of multiexponential signal decay was employed for R'(2) measurement of the brain in normal volunteers. The results showed a high level of agreement between the R'(2) values measured in our study and those estimated from physiological parameters obtained using other modalities such as PET. In the context of BOLD contrast-based functional MRI, the method proposed provides a quantitative mapping of baseline cerebral deoxyhemoglobin content, which is the essential physiological parameter for calibrating the stimulation-induced BOLD signal change and mapping neuronal activity in a quantitative manner by functional MRI. (C) 2003 Elsevier Inc. All rights reserved.