Velocity encoding
Velocity encoding or Venc is referred to as an operator-controlled parameter for the determination of the maximum velocity within a velocity encoded phase contrast imaging study.
Usage
Velocity-encoding (Venc) gradients are used to generate a phase shift in magnetic resonance phase contrast imaging proportional to the velocity of moving protons. This phenomenon can be used to depict and measure the velocity of spins and thus flow .
Venc has to be defined by the user before image acquisition and adapted to the anticipated peak velocities in order to obtain accurate flow measurements . In case Venc is chosen too low aliasing occurs, if it is chosen too high, flow measurements suffer from low accuracy and/or a jet might not be seen. A velocity scout may help in an improved predefinition .
Typical Venc values for different flow measurement are listed below:
- aqueduct: 8-12 cm/s
In case aliasing or mosaic patterns occur Venc should be adjusted until the latter disappears. This can be accomplished for 25-50 cm/s in regard to the aorta or main pulmonary artery.
See also
