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

Abstract

Due to the relatively complex nature of spectral measurements from x-raymachines, many researchers use mathematical models to simulate the spectrathey need. However, there is concern over their accuracy, and hence the impactthat their accuracy may have, on subsequent calculations that rely upon thespectra modelled. With this in mind spectral measurements have been performedon a mammography machine and a comparison with spectra calculated usingseveral different models is presented.Several different techniques have been investigated in the spectralmeasurements to allow for pulse pileup and other effects of high count rate.Comparison with half value layer (HVL) measurements shows that the use of agating signal in conjunction with the air-free path provides accurate resultswithout the need for a pinhole collimator.Comparison of the measured spectra with those calculated using differentmodels proposed in the literaturesuggests that accurate results can be produced by all models, but only if theuser attempts to match the calculated HVL of the modelled spectrum with thephysically measured HVL. If this is not done the modelled spectra may be inerror. The impact of such an error is demonstrated in calculations of meanglandular dose, which indicate a possible underestimate of the dose by up to20%.