The distribution of various chemical elements in human tissue (bone and brain) has been studied by synchrotron radiation induced micro X-ray fluorescence analysis (SR-XRF) in scanning and in tomographic mode. Experiments have been performed at three different synchrotron radiation facilities, HASYLAB, Hamburg, ANKA, Karlsruhe, ESRF, Grenoble where dedicated micro-focus beamlines, offering sufficient photon flux and adequate X-ray optics for the different analytical tasks, were used.
In case of bone the matching of elemental maps from spatially resolved -XRF measurements with backscattered electron images, providing information on the bone structure, allows to assign fluorescence intensities to the features of the calcified tissue and therefore the identification of zones of increased accumulation for the different elements. Especially for lead (Pb) -a toxic metal -, which resorbs into circulation when an increased amount of Ca is needed or in times of metabolic changes of the tissue due to bone diseases, the knowledge of the Pb storage sites in bones are of great medical importance.
Starting from conventional -XRF measurements on 4mm thick samples the spatial resolution and therefore the accuracy of the method has been steadily enhanced by reduction of the sample thickness to 200m and finally employing -XRF in the confocal mode. From comparison of the determined elemental maps with backscattered electron images from the analyzed bone areas (prepared by a group from the Ludwig Boltzmann-Institut of Osteology, Vienna, Austria), it could be shown that the accumulation of Pb in bone is mostly restricted to the so called tidemark which divides noncalcified from calcified tissue and is considered as a metabolically active zone. Furthermore a strong correlation between Zn and Pb was found on this calcification front.
Results from confocal -XRF on bones with duplicated tidemarks exhibit the eventuality of a time delay in the metabolism of Pb compared to Zn.
When applying combined X-ray absorption and fluorescence tomography, similar results were obtained showing also the restriction of highest Zn and Pb intensities to small zones of the analyzed bone. Elemental mapping has been performed on various slices from different areas of human brain at ESRF, ID-22. Whereas the assignment of the maps to different structures of the brain is much more difficult than it is for bone tissue, an inhomogeneous distribution of Pb was found in all analyzed samples from frontal cortex, hippocampus and thalamus.