Pure Hydroxyapatite Phantoms for the Calibration of in Vivo X-ray Fluorescence Systems of Bone Lead and Strontium Quantification

Abstract

Plaster of Paris [poP, CaSO4·(1)/(2) H2O] is the standard phantom material used for the calibration of in vivo X-ray fluorescence (IVXRF)-based systems of bone metal quantification (i.e bone strontium and lead). Calibration of IVXRF systems of bone metal quantification employs the use of a coherent normalization procedure which requires the application of a coherent correction factor (CCF) to the data, calculated as the ratio of the relativistic form factors of the phantom material and bone mineral. Various issues have been raised as to the suitability of poP for the calibration of IVXRF systems of bone metal quantification which include its chemical purity and its chemical difference from bone mineral (a calcium phosphate). This work describes the preparation of a chemically pure hydroxyapatite phantom material, of known composition and stoichiometry, proposed for the purpose of calibrating IVXRF systems of bone strontium and lead quantification as a replacement for poP. The issue with contamination by the analyte was resolved by preparing pure Ca(OH)2 by hydroxide precipitation, which was found to bring strontium and lead levels to <0.7 and <0.3 μg/g Ca, respectively. HAp phantoms were prepared from known quantities of chemically pure Ca(OH)2, CaHPO4·2H2O prepared from pure Ca(OH)2, the analyte, and a HPO4(2-) containing setting solution. The final crystal structure of the material was found to be similar to that of the bone mineral component of NIST SRM 1486 (bone meal), as determined by powder X-ray diffraction spectrometry.

Technical Note: Bone mineral density measurements of strontium‐rich trabecular bone‐mimicking phantoms using quantitative ultrasound

“…To prepare bare bone trabecular-mimicking phantoms with varying BMD values, HA samples were made in-house using the method developed by Da Silva et al 42,43 The HA phantoms were prepared with a constant (Ca+Sr)/P mole ratio of 1.67. Strontium-substituted phantoms were prepared by mixing dry reagents CaHPO 4 · 2H 2 O (USP grade, Amresco, Solon, OH, USA) with Ca(OH) 2 (USP grade, Amresco, Solon, OH, USA) and Sr(OH) 2 ·8H 2 O (99% metals basis, Alfa Aesar, Ward Hill, MA, USA).…”

“…A setting solution was added to the powdered mixture in a ratio of powder-to-liquid of 2:1 and allowed to set as outlined by Da Silva et al 42 The setting solution was to 1M of Na 2 HPO 4 (ACS grade, Amresco, Solon, OH, USA) in 18.2 MΩ · cm water drawn from a MilliQ® system (used throughout this work).…”

Assessment of the effect of strontium, lead, and aluminum in bone on dual‐energy x‐ray absorptiometry and quantitative ultrasound measurements: A phantom study

“…The hydroxyapatite bone phantoms were prepared using the method developed by Da Silva and colleagues . The strontium‐substituted hydroxyapatite bone phantoms were produced by mixing CaHPO 4 ·2H 2 O, Ca(OH) 2 , and Sr(OH) 2 ·8H 2 O, while maintaining a constant (Ca+Sr)/P molar ratio of 1.67 and thus producing a mineral phase with the formula of Ca 5−x Sr x (PO 4 ) 3 OH .…”

“…Our research group has previously developed a bone‐mimicking phantom by synthesizing pure hydroxyapatite without contamination of strontium and lead and hydroxyapatite with controlled substitution of strontium . More recently, Rizvi and colleagues further developed a bone‐mimicking phantom for QUS measurements, by suspending the finely powdered hydroxyapatite homogeneously in gelatinous medium.…”

The quantification of total lead in lipstick specimens by total reflection X-ray fluorescence spectrometry

“…The quartz reflectors were subjected to a cleaning and quality assurance procedure described in another work. [25] Total reflection X-ray fluorescence spectrometry Measurements were made on an S2 PicoFox TM TXRF spectrometer (Bruker-AXS, Madison, WI, USA). The spectrometer was equipped with a monochromated molybdenum target X-ray tube (K˛D 17.5 keV) operating at 50 kV and 600 A with a nominal spot size of .50 50/ m 2 on the surface of the reflector.…”