title: Calibration of the125I-induced x-ray fluorescence spectrometry-based system of in vivo bone strontium determinations using hydroxyapatite as a phantom material: a simulation study.
abstract: OBJECTIVE
  The calibration of in vivo x-ray fluorescence systems of bone strontium quantification, based on125I excitation, is dependent on a coherent normalization procedure. Application of this procedure with the use of plaster of Paris (poP) as a phantom material requires the application of a coherent conversion factor (CCF) to make the calibration functions transferable between the phantom material and human bone. In this work we evaluate, with the use of Monte Carlo simulation, the potential benefit of employing a newly developed hydroxyapatite phantom material into the calibration protocol.
  
  
  METHODS
  Simulations being performed on bare bone phantoms, as the emission spectrum in this case is equivalent to an emission spectrum of an adequately corrected measurement for soft tissue attenuation of emitted strontium signal. We report that the application of hydroxyapatite phantoms does in fact remove the need for a coherent correction factor (CCF).
  
  
  RESULTS
  The newly developed phantoms can thus be used for the calibration of in vivo bone strontium systems removing one step of the calibration protocol. Calibration is, however, limited to cases in which the concentration is relative to the amount of calcium in the specimen, which is, the most useful quantity in a clinical sense. Determining concentrations on a per-mass-of-material basis, that is, a concentration not normalized to the calcium content of the phantom/bone, results in large biases in estimated bone strontium content.
  
  
  CONCLUSIONS
  The use of an HAp phantom material was found to remove the need for a CCF. It was also found that in the case of an incomplete conversion ratio when preparing the phantom material that there would be little effect on the differential coherent cross-section and thereby the coherent normalization-based calibration protocol.
authors.affiliation: Department of Physics, Faculty of Science, Ryerson University, 350 Victoria Street, Toronto, Ontario M5B 2K3, Canada.
authors.forename: Eric
authors.initials: E
authors.lastname: Da Silva
authors.forename: Ana
authors.initials: A
authors.lastname: Pejović-Milić
mesh_terms: D002138:Calibration; D000071538:Cortical Bone / Q000378:metabolism*; D017886:Durapatite / Q000378:metabolism*; D006801:Humans; D007457:Iodine Radioisotopes / Q000737:chemistry*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D013052:Spectrometry, X-Ray Emission / Q000295:instrumentation*; D013324:Strontium / Q000378:metabolism*
chemical_list: D007457:Iodine Radioisotopes; D017886:Durapatite; C000614960:Iodine-125; D013324:Strontium