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 u ses measurements of the transmission of the x-ray beam through a serie s of filters. The transmissions are fitted to values calculated using tables of mammographic x-ray spectra, thus providing an estimate of tu be potential. The performance of the method was studied using a Monte Carlo simulation of experimental errors. The number of measurements an d 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 comb inations of two filter materials, a high transmission (25%) K-edge fil ter in combination with a low transmission (3%) non-K-edge filter prod uced results comparable to the best results obtained from seven transm ission measurements using a single filter material. By reducing the no n-K-edge filter transmission to 1%, an accuracy of +/-0.4% and a preci sion of +/-1.4% were achieved at both 25 kV and 30 kV.