An ultrasonic diagnostic imaging system scans a plurality of planar slices in a volumetric region containing tissue which has been perfused by a contrast agent. The plurality of slices scanned are parallel to each other. Following detection of the image data of the slices the slice data is combined by projecting the data in the elevation dimension to produce an elevationally combined slice image. Combining may be by means of an averaging or maximum intensity detection or weighting process or by raycasting in the elevation dimension in a volumetric rendering process. The elevationally combined slice image is processed to produce a qualitative or quantitative measure of perfusion, such as an image with degrees of perfusion indicated by a range of brightness levels, an image of color perfusion parameters, or a perfusion curve or curve parameter indicating rate of perfusion.