Oxygenated hemoglobin, a protein present in red blood cells or erythrocytes. The oxygen-carrying pigment of arterial red blood cells serves to convey oxygen to tissues. It is composed from hemoglobin when exposed to the alveolar gas in the lungs. Functional magnetic resonance imaging (fMRI) and other brain imaging techniques function on the basis that oxyhemoglobin has a different magnetic resonance signal than deoxyhemoglobin. Brain areas that become active take up more oxygen, which temporally decreases the levels of oxyhemoglobin while decreasing those of deoxyhemoglobin, with the effect that microvasculature in the brain increases the flow of oxygen-rich blood into the active area. This local response results in an increase in the oxyhemoglobin-deoxyhemoglobin ratio that forms the basis of the signal in fMRI (i.e., the BOLD signal).
See Blood Oxygenation Level Dependent Contrast (BOLD signal), Deoxyhemoglobin (dHB), Functional magnetic resonance imaging (fMRI), Hemoglobin, Optical imaging, Proteins