Estimation of tube potential in mammography from transmission measurements

A computer program has been used to study the performance of a method for estimating the potential of mammographic x-ray tubes. The method uses measurements of the transmission of the x-ray beam through a series of filters. The transmissions are fitted to values calculated using tables of mammographic x-ray spectra, thus providing an estimate of tube potential. The performance of the method was studied using a Monte Carlo simulation of experimental errors. The number of measurements and the selection of filter material were both varied, and the precision and accuracy were used as performance indicators. It was found that, for a single filter material, the precision was improved by increasing the number of transmission data, but the accuracy was unaffected. The poorest accuracy and precision were obtained when K-edge filters, or filters with very high or very low atomic number were used. Using combinations of two filter materials, a high transmission (25%) K-edge filter in combination with a low transmission (3%) non-K-edge filter produced results comparable to the best results obtained from seven transmission measurements using a single filter material. By reducing the non-K-edge filter transmission to 1%, an accuracy of +/- 0.4% and a precision of +/- 1.4% were achieved at both 25 kV and 30 kV.