Optimum x-ray spectra for mammography.
A number of authors have calculated x-ray energies for mammography using, as a criterion, the maximum signal-to-noise ratio (SNR) obtainable per unit dose to the breast or conversely the minimum exposure for constant SNR. The predicted optimum energy increases with increasing breast thickness. Tungsten anode x-ray spectra have been measured with and without various added filter materials to determine how close the resultant spectra can be brought to the predicted optimum energies without reducing the x-ray output to unacceptable levels. The proportion of the total number of x-rays in a measured spectrum lying within a narrow energy band centred on the predicted optimum has been used as an optimum energy index. The effect of various filter materials on the measured x-ray spectra has been investigated both experimentally and theoretically. The resulting spectra have been compared with molybdenum anode, molybdenum filtered x-ray spectra normally used for mammography. It is shown that filters with K-absorption edges close to the predicted optimum energies are the most effective at producing the desired spectral shape. The choices of filter thickness and Vp are also explored in relationship to their effect on the resultant x-ray spectral shape and intensity.
D000535:Aluminum; D001940:Breast / Q000528:radiation effects*; D001943:Breast Neoplasms / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D008327:Mammography / Q000379:methods*; D008982:Molybdenum; D010165:Palladium; D012238:Rhodium; D014414:Tungsten
D010165:Palladium; D008982:Molybdenum; D000535:Aluminum; D012238:Rhodium; D014414:Tungsten