A comparison of mammography spectral measurements with spectra produced using several different mathematical models

Due to the relatively complex nature of spectral measurements from x-ray ma chines, many researchers use mathematical models to simulate the spectra th ey need. However, there is concern over their accuracy, and hence the impac t that their accuracy may have, on subsequent calculations that rely upon t he spectra modelled, With this in mind spectral measurements have been perf ormed on a mammography machine and a comparison with spectra calculated usi ng several different models is presented, Several different techniques have been investigated in the spectral measure ments to allow for pulse pileup and other effects of high count rate. Compa rison with half value layer (HVL) measurements shows that the use of a gati ng signal in conjunction with the air-free path provides accurate results w ithout the need for a pinhole collimator. Comparison of the measured spectra with those calculated using different mo dels proposed in the literature suggests that accurate results can be produ ced by all models, but only if the user attempts to match the calculated HV L of the modelled spectrum with the physically measured HVL. If this is not done the modelled spectra may be in error The impact of such an error is d emonstrated in calculations of mean glandular dose, which indicate a possib le underestimate of the dose by up to 20%.