BOLD functional MRI may overlook activation areas in the damaged brain

Area of Science:

• Neuroimaging
• Clinical Neuroscience
• Biomedical Engineering

Background:

• Blood-oxygenation-level-dependent contrast functional MRI (BOLD-fMRI) is increasingly used for non-invasive cortical mapping in brain disorders.
• The reliability of BOLD-fMRI in detecting neuronal activation in damaged brains remains uncertain compared to healthy adults.

Purpose of the Study:

• To compare BOLD-fMRI activation mapping with near-infrared spectroscopy (NIRS) measurements of cerebral blood oxygenation (CBO) changes during neuronal activation.
• To investigate differences in CBO responses between normal adults and patients with damaged brains (cerebral ischemia, brain tumors).

Main Methods:

• BOLD-fMRI and NIRS were used to assess brain activation during hand grasping tasks.
• Participants included normal adults (6) and patients with damaged motor cortex (6 cerebral ischemia, 10 brain tumors).

Main Results:

• BOLD-fMRI showed robust activation in normal adults but limited areas in patients with brain damage.
• NIRS detected increased oxyhemoglobin and total hemoglobin (indicating rCBF increase) in all participants.
• Deoxyhemoglobin decreased in normal adults but increased in patients with limited BOLD-fMRI activation.

Conclusions:

• Evoked-CBO changes in damaged brains differ significantly from those in normal brains.
• BOLD-fMRI may underestimate or overlook functional activation areas in patients with brain lesions.
• NIRS provides complementary information on cerebral hemodynamics in damaged brain tissue.