Quantifying the total blood supply to the brain and relating that to brain tissue mass gives a measure of global cerebral blood flow (CBFglo). The cerebral blood flow can be measured using phase contrast MRI in the supplying arteries. For accuracy, separate 2D flow measurements for each vessel has been recommended. An alternative is to use one 4D flow measurement that covers all vessels of interest and allows flexible definition of measurement planes. The aim of this work is to compare the flow results obtained from a single 2D flow measurement to those from a 4D flow scan.