Susceptibility-weighted imaging (SWI) is a MRI sequence which exploits the susceptibility contrast between various tissues by incorporating MRI phase data. In some clinical applications it may be useful to increase such contrast (e.g. identification of plaque associated veins) and in other cases it may be useful to suppress or decrease such contrast (e.g. visualization of microhemorrhage). Here we explore the use of gas inhalation (oxygen and carbogen) to modulate the conspicuity of brain vasculature.