Blood-oxygen-level-dependent imaging, or BOLD-contrast imaging, is a method used in functional magnetic resonance imaging (fMRI) to observe different areas of the brain or other organs, which are found to be active at any given time.[1]
The fMRI signal is usually referred to as the blood-oxygen-level-dependent (BOLD) signal because the imaging method relies on changes in the level of oxygen in the human brain induced by alterations in blood flow.