Diagnostic image quality and dose reduction using niobium filtration for cephalometric radiography

The usefulness of added filtration is contingent upon the maintenance of high image quality while effectively reducing the radiation dose. High-quality cephalometric radiographs, defined objectively by a panel of orthodontists, were obtained of a tissue-equivalent phantom both without and with 30 microns and 50 microns supplemental niobium filtration. Skin entrance doses in the temporomandibular joint region were compared at diagnostically acceptable exposures where there was no significant difference in radiographic image quality. Dose reductions ranged from 17% to 31% with 30 microns niobium filtration, and 17% to 39% with 50 microns. However, as kVp and HVL were increased to maintain the same level of perceived image quality, image contrast decreased. Contrast loss with 30 microns and 50 microns niobium filtration averaged 8% and 22% respectively compared with standard aluminium filtration. It would appear that additional niobium filtration can be used to reduce radiation dose without significant loss of image quality.