A method and apparatus is disclosed to rapidly assess the severity of a stenosis using MR technology. The invention includes identifying a suspected stenotic vessel and applying a phase contrast pulse sequence to the stenotic vessel in which the MR operator is allowed to control the amplitude and direction of the flow encoding gradient. Peak flow velocity is determined in the suspected stenotic vessel by correlating the flow encoding gradient with the onset of flow velocity aliasing. In a preferred embodiment, the invention utilizes a 2D fast gradient echo pulse sequence having flow sensitizing bipolar gradient waveforms. The resulting flow sensitizing gradients are substantially coincident in time, thereby allowing rotation of the resultant flow sensitizing gradient direction. The amplitude of the flow encoding gradient is increased until the observance of flow related aliasing. Once flow related aliasing is observed, the velocity encoding (VENC) value is recorded and used as the indicator of peak flow velocity in the suspected stenotic vessel. The process can be repeated along the suspected stenosis vessel to isolate and assess the severity of the stenosis by comparing the peak flow velocity VENC values obtained at various locations along the suspected stenosis.