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 non-resonant 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 results can be used to guide experimental planning for studies of the role of low-concentration elements in biological tissues.