Phase contrast magnetic resonance imaging (PC-MRI) is a specific type of magnetic resonance imaging used primarily to determine flow velocities. PC-MRI can be considered a method of Magnetic Resonance Velocimetry. Since modern PC-MRI is typically time-resolved, it can also be referred to as 4D imaging (three spatial dimensions plus time).
Modern PC-MRI is typical time-resolved, it can also be referred to as 3D imaging( three spatial dimensions).
It should be 4D( three spatial dimensions plus time) since it is time resolved. The system might have not caught it because I did give the definition for 3D.