Figure 3.

Detection of iron, zinc and copper in arterial walls using XRF. XRF was performed using the atherosclerotic aorta of a murine model (ApoE^−/− LDLR^−/− double knockout mice). Incident photon energy of 13.7 keV was chosen to excite the elements. Single 6-μm thick sections were cut from formalin fixed and paraffin embedded tissue blocks and mounted on silicon nitride membranes (Silson, Northampton, England) with a nominal field-of-view of 4 mm². An x-ray beam, focused to a spot size of 0.5 μm, was used to raster-scan the 6-μm thick section. Spectral analysis of the excited x-ray fluorescence spectrum at each raster pixel then provided spatial images for each element. Under this condition, copper, iron and zinc were readily detected. Note that the XRF image itself just describes the distribution but not concentration of metal. In a separate format of XRF, element concentrations were determined using calibrated thin-film standards of the elements-of-interest. Among them, iron is the one that is detected at the highest level, followed by zinc and then copper.