WRAP AROUND OR ALIASING ARTEFACT Wrap or aliasing produces an image where anatomy that exists outside the FOV is folded on to the top of the anatomy inside the FOV.
CAUSE Aliasing is cause when anatomy that exists outside the FOV is mismapped inside the FOV. Anatomy outside the FOV still produces a signal if it is in close proximity to the receiver coil.
CAUSE Data from this signals must be encoded, i.e. allocated a pixel position. If the data are under sampled, the signal is mismapped into pixels within the FOV rather than outside. This can occur in both frequency encoding and phase encoding axis
This is termed as no phase wrap or anti-fold over.
It increases the number of phase encoding performed (achieved by enlarging the FOV)
Increasing the FOV will avoid duplication of phase values so that each and every point will have a different phase than another.
PHASE WRAP REDUCTION THE ABOVE METHOD DECREASES THE SPATIAL RESOLUTION(phase encoding is increased to compensate this) INCREASING THE PHASE ENCODING INCREASES SCAN TIME (system automatically reduce the NEX in order to compensate for this) REDUCING NEX WILL INCREASE MOTION ARTEFACT