**4.2 Need for higher resolution imaging to better define subcellular compartments**

A need exists for higher-resolution X-ray fluorescence imaging, to better identify the specific cellular compartments where metals are distributed. Many examples highlighted here look at changes in metal distributions that are either 'in' vs. 'out' of the cell, 'near' or 'away' from the nucleus. At the advent of the age of nano-scale imaging of biological samples, imaging cells at the scale of 10's of nanometers, where we can begin to see within the mitochondrion, for example, will reveal many new and exciting things about the cell biology of metals.
