1. A method for displaying blood flow, comprising: generating a temporal sequence of 2D phase images representing blood flow through a selected anatomical plane using PCMR imaging, wherein each 2D phase image is made up of pixels with each pixel having an intensity corresponding to the phase of a spin density function at the location of the pixel; for each 2D phase image, deriving a 3D flow image by mapping location and size information of one or more pixels in the 2D phase image into coordinates of a surface element in an X-Y plane corresponding to the anatomical plane and mapping the intensity of the one or more pixels into a height or Z coordinate for the surface element so that the 3D flow image includes one or more flow surfaces plotted above or below the anatomical plane at a height corresponding to the phase in the 2D phase image; creating a temporal sequence of the derived 3D flow images that correspond to the temporal sequence of 2D phase images; and, displaying the sequence of 3D flow images serially to form a four-dimensional flow presentation.