Quantitative mapping of cerebral deoxyhemoglobin content using MR imaging.

Area of Science:

• Neuroimaging
• Biophysics
• Medical Physics

Background:

• Cerebral deoxyhemoglobin content is crucial for BOLD-based functional MRI (fMRI).
• Accurate quantification of deoxyhemoglobin is essential for calibrating fMRI signals and mapping neuronal activity.
• Existing methods may face limitations in precise deoxyhemoglobin measurement.

Purpose of the Study:

• To develop and validate a novel magnetic resonance imaging (MRI) method for quantifying cerebral deoxyhemoglobin content.
• To establish a quantitative relationship between R'2 and deoxyhemoglobin concentration.
• To enable precise calibration of BOLD signal changes in fMRI.

Main Methods:

• Utilized magnetic resonance imaging (MRI) to measure the reversible transverse relaxation rate (R'2).
• Performed numerical simulations to assess the relationship between R'2 and deoxyhemoglobin content.
• Employed a modified method to correct for multiexponential signal decay in brain parenchyma.
• Validated R'2 measurements against PET-derived physiological parameters in normal volunteers.

Main Results:

• Demonstrated a near-linear relationship between R'2 and deoxyhemoglobin content in physiological ranges for most vessel sizes.
• Identified diffusion effects in capillary-sized vessels as a factor compromising this relationship.
• Showed that a modified R'2 quantification method corrects for multiexponential signal decay.
• Achieved high agreement between MRI-derived R'2 values and PET-estimated physiological parameters.

Conclusions:

• The proposed MRI method provides a quantitative map of baseline cerebral deoxyhemoglobin content.
• This method is vital for accurate calibration of BOLD signal changes in fMRI.
• Enables more quantitative mapping of neuronal activity using functional MRI.