Figure 1.

Periodic table of the elements showing elements of biological interest that can be probed using X-ray fluorescence imaging. Elements are divided into three categories, those that are physiologically important, those that are pharmacologically active, and those that are toxic or of environmental concern. Those elements that can be detected using hard X-ray XFI are shown in bold color, while those that cannot are indicated by a lighter shade of the same color. Some elements will fall into more than one category; for example, selenium is both essential and toxic in excess with a relatively narrow margin separating adequate supply and the onset of toxic symptoms. Similarly, bromine is used pharmacologically but is also a physiologically important element.