The difference in signal on T2*-weighted images as a function of the amount of deoxygenated hemoglobin.
oxygenated hemoglobin (Hb)
Hemoglobin with attached oxygen; it is diamagnetic.
deoxygenated hemoglobin (dHb)
Hemoglobin without attached oxygen; it is paramagnetic.
Having the property of being attracted to a magnetic field, though with less concentration of magnetic flux than ferromagnetic
The intensity of magnetization of a substance when placed within a magnetic field.
hemodynamic response (HDR)
The change in MR signal on T2* images following local neuronal activity. The hemodynamic response results from a decrease in the amount of deoxigenated hemoglobin present within a voxel.
The short-term decrease in MR signal immediately following the onset of neuronal activity, before the main positive component of the hemodynamic response. The intial dip may result from initial oxygen extraction before the later overcompensatory response.
The maximal amplitude of the hemodynamic response, occuring typically about 4 to 6 s following a short-duration event.
The decrease in MR signal amplitude below baseline due to the combination of reduced blood flow and increased blood volume.
A model of the interaction between changes in blood volume and changes in blood flow associated with neuronal activity.
The change in MR signal over a series of fMRI images.
A time segmanet extracted from a larger series of images, usually corresponding to the period in time surrounding an event of interest.