1. A method of displaying a structure that represents three-spatial dimensions using a computer, a data base that includes an image data set in which the structure is defined, and a display monitor, comprising: analyzing the image data set with the computer to determine a set of medial axis points of the structure which extends through the three-spatial dimensions; extruding a display data set using the computer, the display set being a subset of the image data set, by defining an extrusion vector in the three spatial dimensions, defining the display data set data to include data from the image data set that lies within a set of vectors that are both (a) parallel to the extrusion vector, and (b) that also pass through one of the medial axis points; wherein both of the image data set and the display data set include data representing three-spatial dimensions; and generating a display image from the display data set.