Validity of coherent normalization for an in vivo X-ray fluorescence (XRF) system optimised for human finger strontium measurement: A simulation study

In vivo X-ray fluorescence (XRF) measurements are sensitive to changes in source-subject distance resulting from the thickness of soft tissue or patient motion. This impacts precision and can introduce inaccuracies. Previously, a technique called coherent normalization was developed for in vivo bone lead XRF. An EGS5 Monte Carlo simulation, developed and validated against experiment, showed that coherent normalisation is valid for a 109 Cd-based in vivo strontium XRF system. The signals from a phantom approximating a human finger were estimated, and the phantom moved to various positions back and off-centre from the detector face. Phantom soft tissue thickness was also varied. Results showed that while normalization cannot correct for soft tissue overlay, it can correct for changes in position. Soft tissue thickness correction can be performed, however, using a Compton scattering correction and thus both soft tissue and positioning effects can be corrected using information available in the measurement spectrum.