Determination of volume from computerized tomograms: finding the volume of fluid-filled brain cavities.

The concept of characteristic computed density is introduced and used as the basis of a method for computing the volume of reconstructed objects. The interpretation of a computed tomographic (CT) scan as a picture is considered to be misleading for this purpose, and is replaced by the notion of a CT scan as a reconstructed slice, or slice array. A pattern recognition system for estimating the volume of fluid-filled brain cavities is described. Operational definitions for certain structures in the brain are given. Finding the volume of brain cavities is seen to hinge on an adequate estimation of the characteristic density of brain tissue bordering the cavities. Computer methods are discussed for producing a normalized (relative distance) map of a brain slice and for searching in three dimensions through a stack of slice arrays. An evaluation of the system, on mock brain tissue and ventricles in a human skull, yielded encouraging results.