1. A scanning aid for obtaining quantified three dimensional ultrasonic diagnostic imaging data with a manually swept ultrasonic probe, comprising: a reference surface for referencing said probe with a body being examined by said probe; a holding device coupled to said reference surface for removably holding said probe in a predetermined position relative to said reference surface; a rotatable shaft coupled to said holding device for supporting movement of said probe as it is manually moved; and a position sensing device coupled to said rotatable shaft for sensing the position of said probe relative to said body as said probe is manually moved by a user to scan a volumetric region of said body.