General approach to optimizing digital mammography with respect to radiation risk

Abstract

We investigated how current biological uncertainties relating to the radiation risks for breast cancer impact on the optimization of x-ray tube potential (kV) in digital mammography. Digital images were taken of an accreditation phantom using voltages between 24 and 34 kV, and output between 5 and 500 mAs. The average glandular dose (D) at each x-ray tube voltage was determined at each technique setting. Image contrast of a 4 mm thick acrylic disk and the corresponding noise were used to determine the lesion contrast to noise ratio (CNR), which was taken as a relative measure of image quality when the selected x-ray technique factors (i.e., kV/mAs) are varied. The optimal kV for the detection of this simulated mass lesion was determined by maximizing a figure of merit (FOM), the ratio of CNR²/D. The kV that maximized the traditional FOM occurred at 27.3 kVp. The implication for optimization strategies was also analyzed for a radiation risk that is proportional to Dⁿ; a value of n = 0 would correspond to no additional radiation risk, and n = 2 would correspond to a quadratic dose response curve. The x-ray voltage that yielded the highest generalized FOM value was 34 kV for n < 0.25, and 24 kV for n > 1.5. These results show that uncertainties in the form of the dose response curve for radiation induced breast cancer markedly influence the FOM parameter used for optimizing digital radiography imaging systems such as mammography.