Investigating Improvement in Gadolinium Detection for a XRF Bone Measurement System by Averaging Spectrum

An X-ray fluorescence (XRF) measurement system involving a high purity germanium detector (HPGe) was used to quantify gadolinium and lanthanum in bone. The 24-hour ex vivo minimum detection limit (MDL) was estimated to be 1.0 µg Gd g−1 bone mineral determined from single measurements of low concentration gadolinium hydroxyapatite (HAp) calibration standards. It was thought that the average of 60 measurements at 24-minutes (equivalent to 24-hours) may improve the detection limit and signal to noise ratio (SNR). 

Curve fitting procedures applied to the 24-minute spectrum reduced the uncertainty in measurement. Detection limits from a simple averaging method were compared to the application of the inverse variance weighted mean (IVWM). The IVWM is an aggregating method that could be considered a system optimization with 60 replicates. In either case, with the assumption that gadolinium was uniformly distributed in the phantom material, the MDL was estimated to be 0.8 µg Gd g−1 bone mineral from the aggregate methods.