Quantification of bone strontium levels in humans byin vivox-ray fluorescence

Abstract

The need for in vivo bone strontium assessment arises because strontium may exert a number of effects on bone, which may be either beneficial or toxic. Measurements discussed here are noninvasive, no sample is taken, nor is there discomfort to patients. The developed source excited x-ray fluorescence system employs a 109Cd source to excite the strontium K x rays, with the source and detector in approximately 90 degree geometry relative to the sample position. The factors affecting the accuracy and minimal detectable limit for bone strontium in vivo measurements are discussed. A system calibration revealed a minimum detectible limit of approximately 0.25 mg Sr/g Ca, which is sufficient for the monitoring of strontium levels in healthy subjects and patients with elevated bone strontium concentrations. Preliminary in vivo measurements in ten healthy subjects at two bone sites (phalanx and tibia) indicated that this system can be applied for cumulative bone strontium estimation while delivering a low effective dose of 80 nSv during the measurement time. Future work will involve attempts to enhance system precision with alternative fluorescing sources and further optimization of the detection system.

In vivo applications of X-ray fluorescence in human subjects

“…In the initial pilot study [11] it was possible to detect strontium in only about half the subjects. In the second pilot study, with the improved system [45] it was possible to detect strontium in all 22 volunteers.…”

“…As mentioned earlier, Pejović-Milić et al [11] developed an X-ray fluorescence system using a range of emissions from 125 I (in fact, brachytherapy seeds in which the 125 I is adsorbed onto Ag beads, further complicating and enhancing the emission spectrum) for a pilot study of strontium in human bone. Snyder and Secord measured bone strontium in rabbits [43] and, in a totally separate development, Wielopolski and his colleagues demonstrated that they were able to measure bone strontium in human subjects [44].…”

“…Given the low energy of the Fe K X-rays, sampling tissues at greater depth is effectively precluded. In 2004, Graham and O'Meara reported an X-ray fluorescence technique for measurement of silver [10], and in the same year Pejović-Milić et al reported the use of the emissions from a 125 I source to excite strontium K X-rays for measuring the element in bone [11]. Strontium, as well as the original iodine and later iron are in the minority, as they are elements which are essential or beneficial, as opposed to the majority of elements measured by X-ray fluorescence for which it is their toxicity which provides the primary reason for their measurement.…”

XRF measurements of Zn, Sr and Pb in archaeological bone

“…[11,12] The presence of Sr in bone, predominantly received from dietary intake, is important in bone strength. [13] Treatment of osteoporosal conditions is offered through daily doses of the drug strontium ranelate, an example being the reduction in pelvic and vertebral fracture incidence in post-menopausal women. [14] Finally, it should be emphasised that the XRF technique has been demonstrated to be effective both at photon energies offering a high probability of K-shell electron excitation or at energies preferentially exciting L-shell electrons.…”

Imágenes de Fluorescencia de Rayos X en Huesos Humanos y su Potencial Aplicación in vivo

“…Por otra parte, el estroncio (Sr) estable posee efectos anti-osteoporóticos, ya que inhibe la resorción ósea y contribuye a aumentar la masa ósea, en contraste con el estroncio radiactivo, el cuál induce efectos tóxi-cos en las células óseas Pors Nielsen, 2004;Marie, 1996;Marie et al 2001). Debido a que puede ejercer efectos tanto benéficos como tóxicos en los huesos, es necesario evaluar su concentración in vivo (Pejovic-Milic, 2004). Mediante un dispositivo portátil la técnica de fluores-* Departamento de Física, FICA, Universidad de La Frontera, Temuco, Chile, ** Instituto Nacional del Cáncer, Santiago, Chile.…”