The effect of filter material on the properties of variable-thickness equalization filters for chest radiography was investigated. Filters made of nickel, tantalum, and lead which provided very similar improvements in mediastinal penetration were compared with regard to their scatter fractions, image contrasts and patient exposures. Their performances in these terms were found to be very similar, even though they produce considerably different x-ray spectra. The K edge filters (tantalum and lead) yielded slightly higher image contrast and patient exposure than did the non-K edge filter (nickel). The effect of filter material on contrast and exposure was less than the effect of usual patient-to-patient variation on these quantities, however.
|