X-ray fluorescence microscopy exposure estimates using a single excitation energy

Scanning fluorescence X-ray microscopy is widely used for quantitative mapping of elemental concentrations, including in studies of essential but low-concentration metals in cells, tissues, and organs. Practical studies often use a single incident photon energy to excite fluorescence from many elements. We present calculations of the number of incident photons per pixel required to detect a specified areal concentration of an element in the case of far-from-threshold excitation, along with the calculated radiation dose consequently imparted in a simple model tissue. We also show how certain approximations can lead to less accurate estimates. These calculations are not specific to one particular experiment, though we also provide a comparison with one experimental result. These results can be used to guide experimental planning for studies of the role of low-concentration elements in biological tissues.