Aluminum equivalence of materials used in diagnostic radiology and its dependence on beam quality.

A semi-empirical theory has been derived that relates the aluminum equivalence of various materials used in diagnostic radiology to their attenuation coefficients. The dependence of the aluminum hardness (AHE) and attenuation (AAE) equivalent on the beam quality is described in terms of effective energy. This 'aluminum equivalence approach' (ALEAP) gives estimates of the aluminum equivalent, regardless of spectral shape, that are usually within +/- 5% except when absorption edges are involved. A reasonable definition for the AHE of K-edge filters is offered. Suggestions are made for methods of testing for compliance with standards and regulations.