X-ray fluorescence computed tomography (XFCT) is an emerging imaging modality that maps the three-dimensional (3D) distribution of elements, generally metals, in ex vivo specimens and potentially in living animals and humans. Many endogenous metals and metal ions, such as Fe, Cu, and Zn, play critical roles in signal transduction and reaction catalysis, while others (Hg, Cd, Pb) are quite toxic even in trace quantities.In the postgenomic era, the new disciplines of metallogenomics, metalloproteomics, and metallomics are emerging for the systematic study of endogenous metals. These disciplines would benefit greatly from the spatially resolved maps of trace-element distribution provided by XFCT. In addition, exogenous metals are often critical components of new in vivo molecular imaging agents: Gd and Mn are used in magnetic resonance imaging agents, and Cd and Au are used in nanoparticle-based optical imaging agents. When applied to tissue samples excised from animal models, for instance, XFCT techniques could provide calibration and subcellular localization information critical for the continued advancement of these technologies.

G. Fu, L.-J. Meng, P. Eng, M. Newville, P. Vargas, P. LaRiviere, “Experimental demonstration of novel imaging geometries for x-ray fluorescence computed tomography”, Medical Physics,  40, issue 6, (2013), https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3663849/

Standard line-by-line scanning method. A pencil beam illuminates a line through the object, stimulating emission of characteristic x-rays that are detected by an uncollimated, nonposition sensitive detector. The object must be translated and rotated in order to build up a sinogram.