Fundamental Parameter Method Application to Determinations of Absolute Elemental Concentrations in a Thin Lamb Bone Slice From Microscopic X-ray Fluorescence Measurements at the Canadian Light Source Synchrotron

In vitro x-ray fluorescence (XRF) studies using synchrotron radiation (SR) typically probe microscopic 2D elemental distributions in human tissues by employing XRF raster scanning techniques with intense small x-ray beams. In most SR studies, however, elemental concentrations are not estimated and 2D maps are linked to normal or abnormal histology and physiology. Spatial inhomogeneity of trace and bulk elements in tissues implies an inhomogeneous linear attenuation coefficient (µ). If tissue slice thickness is much smaller than µ^-1 or the mean-free-path (mfp) of characteristic x-rays, 2D XRF maps are accurate representations of elemental distributions. The mfp of Ca K-shell XRF photons in the human cortical bone is about 35 µm. Making ultrathin bone slices is labor intensive, time consuming, and prone to elemental contaminations. Therefore, developing a data analysis method which accounts for x-ray attenuation in SR XRF microscopy studies of dense tissues is a more practical alternative. In our study, a thin (0.2 mm) semicircular slice was cut from a larger lamb leg bone. Inner and outer equal rectangular areas (0.4 mm x 0.6 mm) were examined employing a raster scan by a 6 μm lateral size x-ray beam from the VESPERS beamline at the Canadian Light Source synchrotron. Four 2D maps of P, Ca, Fe, Ni, Cu, Zn, and Sr distributions in the bone slice were obtained for each of the two areas by raster scans using four different incident photon energies: 12, 15, 18.6, and 20.0 keV. Fundamental Parameter (FP) method in which measured XRF peak areas, µ of human cortical bone, and experimental setup geometry parameters served as input data was employed to compute 2D maps of elemental concentrations. Concentrations of bulk and trace elemental agreed with expected and literature values. Approximations and implications to future SR XRF studies were discussed.