title: Factors affecting in vivo measurement precision and accuracy of 109Cd K x-ray fluorescence measurements.
abstract: 109Cd K x-ray fluorescence (XRF) measurement systems from two research centres were used to measure tibia lead content in a population (n = 530) of young adults. The group mean bone lead contents (+/-SEM) determined by McMaster University (n = 214) and the University of Maryland (n = 316) were 2.80 +/- 0.51 and 2.33 +/- 0.50 microg Pb/(g bone mineral) respectively. The mean difference of 0.47 +/- 0.71 microg Pb/(g bone mineral) was not significant. There was no evidence of a systematic difference between measurements from the two systems. Measurement uncertainties for the young adults were poorer overall than uncertainties for a population of occupationally exposed men. This was because obese subjects and women were included in the study. Regressions of precision against body mass index (BMI, defined as weight/height2) determined that uncertainties increased with BMI and were poorer for women than men. Measurement uncertainties (1sigma) were >8 microg Pb/(g bone mineral) for women with a BMI > 0.004 kg cm(-2). Poor-precision data affected population estimates of bone lead content; an inverse correlation was found between precision and bone lead content. A small number (0.4%) of individual measurements with poor uncertainties were inaccurate to within the precision. It is suggested that obese subjects, whose BMI > 0.004 kg cm(-2), should be excluded from 109Cd K XRF studies, as the measurement provides limited information and may be inaccurate.
authors.affiliation: Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada. fmcneill@mcmaster.ca
authors.forename: F E
authors.initials: FE
authors.lastname: McNeill
authors.forename: L
authors.initials: L
authors.lastname: Stokes
authors.forename: D R
authors.initials: DR
authors.lastname: Chettle
authors.forename: W E
authors.initials: WE
authors.lastname: Kaye
mesh_terms: D000328:Adult; D015992:Body Mass Index; D001835:Body Weight; D015519:Bone Density; D001842:Bone and Bones / Q000737:chemistry* / Q000000981:diagnostic imaging; D002106:Cadmium Radioisotopes; D002138:Calibration; D005260:Female; D006801:Humans; D007854:Lead / Q000032:analysis*; D007855:Lead Poisoning / Q000150:complications / Q000000981:diagnostic imaging*; D008297:Male; D009765:Obesity / Q000150:complications; D019047:Phantoms, Imaging; D011197:Potassium Radioisotopes; D011877:Radionuclide Imaging; D012044:Regression Analysis; D015203:Reproducibility of Results; D012737:Sex Factors; D013052:Spectrometry, X-Ray Emission / Q000295:instrumentation / Q000379:methods*; D013977:Tibia / Q000737:chemistry / Q000000981:diagnostic imaging; D014018:Tissue Distribution
chemical_list: D002106:Cadmium Radioisotopes; D011197:Potassium Radioisotopes; D007854:Lead