Aca. Aro et al., IMPROVEMENTS IN THE CALIBRATION OF CD-109-K X-RAY-FLUORESCENCE SYSTEMS FOR MEASURING BONE LEAD IN-VIVO, Physics in medicine and biology, 39(12), 1994, pp. 2263-2271
A Cd-109 K x-ray fluorescence (XRF) system using a point source in a b
ackscatter geometry is described. The suitability of plaster-of-Paris
phantoms as targets for intercalibration standards was evaluated. When
the phantom concentrations were measured by inductively-coupled-plasm
a mass spectrometry (ICPMS), the calculated phantom concentrations und
erestimated true concentrations by an average of 15%. Since calculated
values are used to calibrate the K XRF system, in vivo bone-lead conc
entrations may be similarly underestimated. The difference between cal
culated and measured concentration is attributable to impurities in th
e plaster of Paris (e.g. calcium carbonate). The ICPMS-measured concen
trations were used to calibrate the K XRF system. The same phantoms we
re also measured as 'unknowns' by a bone-lead measurement system (Abio
med, Danvers, MA, USA). The commercial system overestimated the lowest
-concentration phantoms and underestimated the phantoms with concentra
tions above 15 mu g Pb/g plaster of Paris, The commercial system and o
ur system were compared by measurement of the new phantoms in air and
in water. The K XRF system exhibited better precision in both situatio
ns. On the basis of this work, we recommend that plaster-of-Paris phan
toms used to calibrate K XRF measurement systems be analysed first by
ICP,MS or another valid analytical technique.