Oversampling is the increase in data to avoid aliasing and wrap around artifacts. Aliasing is the incorrectly mapping of tissue signal from outside the FOV to a location inside the FOV. This is caused by the fact, that the acquired k-space frequency data is not sampled density enough.
Oversampling in frequency direction, done by increasing the sampling frequency, prevents this aliasing artifact. The proper frequency based on the sampling theorem (Shannon sampling theorem/Nyquist sampling theorem) must be at least twice the frequency of each frequency component in the incoming signal. All frequency components above this limit will be aliased to frequencies between zero and half of the sampling frequency and combined with the proper signal information, which creates the artifact. Oversampling creates a larger field of view, more data needs to be stored and processed, but this is for modern MRI systems not a real problem. Oversampling in phase direction (no phase wrap), to eliminate wrap around artifacts, by increasing the number of phase encoding steps, results in longer scan/processing times.

The activation of the brain is mirrored in the local changes in metabolism and hemodynamics (brit. haemodynamics). By using heavily T2 weighted scans activated brain areas show an increase in signal intensity as oxyhaemoglobin (brit. oxyhaemoglobin) is diamagnetic and deoxyhemoglobin (brit. deoxyhaemoglobin) is paramagnetic. Oxygen mapping will benefit from high field strength.

See also Blood Oxygenation Level Dependent Contrast, Haemoglobin, Perfusion Imaging, Diamagnetism, Paramagnetism.