Determination of elemental concentrations in a thin lamb bone slice from x-ray fluorescence measurements at the Canadian Light Source (CLS) synchrotron

In vitro x-ray fluorescence (XRF) studies using synchrotron radiation (SR) can probe microscopic 2D elemental distributions in tissues by employing raster scanning techniques. In most SR studies, however, elemental concentrations are not estimated, 2D XRF maps being typically linked to normal or abnormal histology and physiology. Elemental concentrations are important in comparative studies and in accurate determination of elemental mass ratios. In this study, a model linked elemental concentration to the measured ratio between the sum of Kα and Kβ peak areas and the sum of coherent and incoherent (Compton) x-ray scatter peak areas. Its numerical implementation used the XCOM photon cross section database, tabulated coherent and incoherent scattering form factors, and a 12-element human cortical bone composition from literature to compute the linear attenuation coefficient (µ) of the sample at any photon energy. Experimentally, a 0.38-mm thick semicircular slice was cut from a larger lamb bone sample. Two equal rectangular areas (0.4 mm x 0.6 mm) of the inner and the outer regions of the bone slice were examined by a 10- m step 2D XRF raster scan using a 6 m FWHM x-ray beam from the VESPERS beamline at the Canadian Light Source synchrotron. 2D maps of P, Ca, Fe, Ni, Cu, Zn, and Sr distributions in the bone slice were obtained for each region at four photon energies: 12, 15, 18.6, and 20 keV. Averaged across each region and the four energies, elemental mass concentrations were (value in round parantheses is the uncertainty in the last significant figure): 0.14(1), 0.260(4), 4(1)x10^-5, 2.3(3)x10^-5, 9(2)x10^-6, 1.1(2)x10^-4, and 3.6(6)x10^-4, respectively, for the inner region, and 0.14(1), 0.262(6), 4(1)x10^-5, 2.4(3)x10^-5, 1.0(2)x10^-5, 1.4(2)x10^-4, and 5.0(3)x10^-4, respectively, for the outer region.