A method for measuring shapes in thick multi-planar reformatted (MPR) digital images, including identifying a shape in a digital MPR image, scan-converting points corresponding to the identified shape on a starting plane of an MPR slab in an image volume from which the MPR was obtained to generate a plurality of starting points for the identified shape, calculating an end point in the MPR slab corresponding to each starting point, propagating a ray from each starting point to each corresponding end point, accumulating samples along each ray, and computing a desired measurement value from the accumulated samples after reaching the end point for all rays.
