SNR comparisons of absorption and fluorescence modes of edge-subtraction imaging

In this work, we calculate and compare the sensitivity achievable by synchrotron-based absorption subtraction imaging and fluorescence subtraction imaging. In biomedical synchrotron imaging, it is often desirable to be able to quantify the concentration of specific elements, including endogenous trace metals, such as zinc or copper, and exogenous metals used as contrast agents, such as iodine or gold. There are two principal ways of achieving elementally specific imaging using x-rays: through absorption-based methods or through fluorescence-based methods. When assuming the spatial resolution of the two approaches can be matched we find that, all else being held equal, the absorption edge imaging has advantages for elements that are present in high concentrations and the fluorescence imaging for elements that are present in low concentrations. These results confirm the findings of Zhang et al. but provide quantitative tools for predicting the regime where each method holds an advantage for a given elemental concentration and background.