A calibration comparison of mammographic kVp meters

Modern screen-film mammography employs a molybdenum target and molybdenum filtration to obtain both high image contrast and low patient dose. Typical x-ray emission spectra are therefore dominated by molybdenum's characteristic radiation. The form of such spectra makes the accurate measurement of mammographic kVp difficult. Non-invasive digital kVp meters provide the simplest method of measuring mammographic kVp routinely, with a typical uncertainty of greater than +/- 1 kVp. With the expansion of breast screening, more stringent demands have been placed on these meters and recent calls for accuracies of better than +/- 1 kVp have been made. The responses of six popular mammographic kVp meters were compared in the range 22 to 32 kVp. Agreement between four of these meters above 24 kVp was within 1.8 kVp. The responses of the two remaining meters differed from the other meters by up to 5 kVp over the range. The results have highlighted the need for regular calibration checks on mammographic kVp meters and the provision of a national standard to which these calibrations can be traceable. Such a standard is currently not available in Australia.