1 X-Ray Fluorescence Computed Tomography as a 2 D / 3 D analytical tool for element-specific visualization of biological microstructures

The fundamental aim of microtomography methods is to reveal the internal microscopic structure of solid materials, in which the variation of inner properties (such as density, chemical composition and chemical state) strongly influences the X-ray absorption/emission and propagation properties. Unlike other tomographic techniques based on absorption, phase-contrast or X-ray scattering, X-ray fluorescence computed tomography (XFCT) achieves multielement capability by recording characteristic X-ray emission. Most of the scientific effort for the development of XFCT has focused on improving elemental sensitivities and reducing the analysed sample sizes (i.e. volumes), achieving a spatial resolution limited by the X-ray beamsize. In a previous work [1] we described the basic technique and experimental set-up for XFCT used at HASYLAB beamline L, for low (E<25 keV) and high (E≈60 keV) energy excitation mode using energy dispersive detectors. The applied beam size varied between 10x10 μm and 200x200 μm depending on the applied beam focusing/collimating methods (monocapillary, polycapillary and cross-slits). For the best statistical results the measuring time was set to 5-10 s for the individual measuring points of an XFCT scan. The employed back-projection [2] reconstruction procedure was based on the Riemann mathematical algorithm [3]. Here, we report on a new scanning method which reduces dramatically the data collection/irradiation time for XFCT analysis, while obtaining maximum information on the sample composition variation from the X-ray spectra.