A comparison of computed and measured heel effect for various target angles.

Two models for thick target emission spectra, one using constant depth of Bremsstrahlung and one using continuous slowing-down of electrons and multiple thin targets, were used to predict filtered emission spectra at various angles with respect to the central axis. Integration of these spectra and comparison against measured heel effect gave excellent agreement for tungsten targets with take-off angles of 7 degrees and 10 degrees at 60 and 100 kVp when the angular anisotropy of Bremsstrahlung was taken into account. Results for a 17.5 degrees target at 60 kVp were poor, possibly indicating a need for a better model of Bremsstrahlung angular dependence.