1. A method for magnetic arterial spin labeling in magnetic resonance imaging (MRI), comprising: applying at an MRI system an RF pulse train to selectively tag spins according to velocities of the spins without selection based on locations of the spins; applying at the MRI system a second velocity selective pulse train after the tagging RF pulse train to destroy a signal from spins that are still moving faster than a cut off velocity; and obtaining at the MRI system MRI images of tagged spins at an area of interest to obtain information on perfusion at the area of interest.