Figure 5.

Detectability index computed as a function of w and A for a low-frequency detection task at (a) 15 mGy, (b) 1.5 mGy, and (c) 0.15 mGy, and for (e) a midfrequency task and (f) a high-frequency task at 15 mGy. The integral of the quantum noise NEQ [Eq. 5] at 15 mGy is plotted in (d). Superimposed on (a) are plots of the absolute values of dual-energy contrast between a breast tumor and fibroglandular tissue, |C^DE|, and the dual-energy anatomical “clutter” magnitude, |κ^DE|. A clear optimum in d^′ is observed in (a) at w = ∼0.6 where κ^DE is reduced to 0 (i.e., cancellation of background clutter). As dose is lowered or the spatial frequency content of the tasks increases, canceling anatomical noise becomes less important, and the DE contrast eventually becomes the dominant factor in driving d^′.