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Ex vivo evaluation of a coherent normalization procedure to quantify in vivo finger strontium XRS measurements
Author(s) -
Heirwegh C. M.,
Chettle D. R.,
PejovićMilić A.
Publication year - 2012
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3673787
Subject(s) - strontium , normalization (sociology) , materials science , soft tissue , biomedical engineering , nuclear medicine , optics , physics , pathology , medicine , nuclear physics , sociology , anthropology
Purpose: Energy dispersive x‐ray fluorescence spectroscopy (XRS) measurements were performed on human cadaver index fingers to measure bone strontium content in the presence of intact overlying soft‐tissue. This work assesses the feasibility of applying a normalization procedure including soft‐tissue correction of x‐ray absorption as a means to quantify an ex vivo bone strontium XRS measurement. Methods: Bone strontium measurements were made using an excitation‐detection system incorporating an 125 I x‐ray excitation source and an Ortec® Ametek‐AMT Si(Li) detector in 180° backscatter geometry. Spectral processing was accomplished using an in‐house nonlinear least‐squares Marquardt fitting routine. Bone strontium was quantified using an egs 5 Monte Carlo based x‐ray soft‐tissue correction algorithm in conjunction with the normalization of strontium x‐rays to the coherent scatter peaks of 35.5 keV 125 I γ‐rays. Results: Comparison of tissue intact and bare bone finger XRS measurement quantification attempts revealed an overall discrepancy of 18.6% that is attributed primarily to the significant contribution of soft‐tissue to coherent scatter of 35.5 keV source γ‐rays and to a lesser degree, inconsistencies with the simulated tissue correction model. Work toward the beginnings of an experimentally derived tissue correction model, as a means to validate the simulated model, have been reported. Two observations hinted at a systematic inflation of the observed Kβ peak area. First, strontium concentrations estimated by Kα peak areas were less than the Kβ peak areas by 28.6% ( p < 0.0001) and 10.5% ( p < 0.001) for tissue intact and bare bone measurements, respectively. Second, the Kα:Kβ x‐ray average ratios between tissue corrected (3.61 ± 0.55) and bare bone predicted (4.4 ± 0.4) did not agree ( p < 0.0001) and pointed to shortcomings with the current processing treatment of strontium K x‐ray peak area extraction. Through finger bone XRS measurements, bone strontium concentration in the Caucasian population was estimated at 95 ± 15 μ g Sr/g dry bone. Conclusions: The discrepancies observed: between quantification attempts of tissue corrected and bare bone measurements, the inflated estimates of Kβ relative to Kα peak concentrations and between observed and expected Kα:Kβ ratios, have indicated that shortcomings with the bone strontium coherent normalization and tissue correction procedure exist. Coherent scatter contribution of soft‐tissue overlying bone, tissue correction model limitations, and spectra processing issues are all mentioned as sources of observed discrepancies.