Practical aspects of Compton scatter densitometry

A technique for determining the physical density distribution within an object using Compton scattered radiation is described. The technique is based on measuring the variation with the depth of 90° scattered radiation flux from an external monoenergetic photon source using a high-resolution solid-state detector. The measured scattered signal from an isolated volume element of the interrogated object is proportional to its electron density. For a definite region within the scanned object, the variation of the scattered yield with depth, along the direction of the incident beam, will give a counting curve with slope proportional to the density of the examined region. The spatial resolution of the system, determined by the collimator width, is 2 mm. The mathematical aspects of the technique are presented and the experimental data obtained in line scans of representative tissue equivalent materials are also shown to demonstrate the validity of the method.