Optimization of spectral shape in digital mammography: Dependence on anode material, breast thickness, and lesion type

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Abstract
It has been proposed that breast cancer detection can be improved through the use of digital mammography. It is hypothesized that the choice of proper shape of the x-ray spectrum incident upon the breast can yield an improved image signal-to-noise ratio (SNR) for a given dose. To test this hypothesis, an energy transport model incorporating measured breast tissue attenuation coefficients and published exposure-to-dose conversion values was developed to describe the image acquisition process. The choice of applied kilovoltage and filter for Mo and W target x-ray sources has been optimized with respect to SNR and absorbed dose for detectors based on a Gd2O2S scintillating screen under the conditions of perfect coupling of light between the screen and a solid state photodetector. For the W spectra, the optimum filter-kVp combinations could provide 41%, 13%, and 42% improvements in SNR for 2-cm, 6-cm and 8-cm breasts, respectively, over the conventional Mo filtration, for a practical imaging time of 1.0 s. W and Mo spectra produce similar SNR values for a given filter thickness except for the 4-cm breast. Given the limitations of current technology, however, the W spectra produce the optimum SNRs in a shorter imaging time for breast thicknesses greater than and less than 4 cm. The maximum SNR for imaging both infiltrating ductal carcinoma and calcifications is provided by the same filter-kVp combination, allowing optimization based on breast thickness and composition only. The model can now be used to compare and improve upon novel detector designs.

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