VENC
VENC stands for velocity encoding, a parameter that must be specified before performing a phase-contrast (PC) MRI or MRA study. VENC, measured in cm/sec, should be chosen to encompass the highest velocities likely to be encountered within the vessel of interest. If VENC is set to 50 cm/sec, for example, flows in the range of ±50 cm/sec can be accurately represented by a set of phase shifts spanning from −180° to +180°. If VENC is picked too low, velocity aliasing may occur with faster flows not being appropriately represented. Fig (left) PC study of pulmonary artery with VENC set too low (15 cm/sec). Note velocity aliasing (white areas) which appears to be flow in the wrong direction. (right) PC study of pulmonary artery with VENC set properly (30 cm/sec). The vessel is properly displayed as black with velocity aliasing no longer apparent.
