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20-05-2012 | Radiology | Article

X-ray fluorescence system tracks bone strontium


Free abstract

MedWire News: A noninvasive in vivo X-ray fluorescence (IVXRF) system demonstrates that bone strontium levels continually increase during long-term strontium citrate supplementation, Canadian researchers report.

Ana Pejovic-Milic (Ryerson University, Toronto) and colleagues explain that strontium supplementation is gaining popularity as a treatment for osteoporosis.

In the present study, they used an IVXRF system to measure bone strontium levels in a woman, aged 68 years at baseline, who was taking self-prescribed over-the-counter strontium citrate (680 mg/day) supplements for osteoporosis.

The IVXRF system uses radioactive iodine (I-125) in the form of brachytherapy seeds as the photon excitation source, and is able to detect strontium K-alpha X-rays at 14.16 keV, which relate to bone strontium levels, the researchers explain.

Measurements were taken at the finger and ankle bone sites, representing primarily cortical and trabecular bone, respectively, before supplementation (baseline), 24 hours after the first dose, and at regular intervals thereafter. To date, she has been measured for more than 2.5 years and on 32 occasions.

After correction for signal attenuation by soft tissue, the baseline K-alpha strontium signal at 14.16 keV was 0.38 for the finger and 0.39 for the ankle, values that are similar to those measured among 22 healthy Caucasian volunteers in a previous trial, the researchers note.

At 24 hours, the values had increased to 0.62 and 0.45 for the finger and ankle, respectively, and by day 5, the increase was statistically significant with values reaching 0.68 and 0.93, respectively.

Following the initial steep increase in strontium levels, the rate of strontium uptake appeared to slow, but further increases occurred between days 106 and 141.

Recent measurements (days 400‑800) suggest that strontium levels in the finger may have reached a plateau, whereas those in the ankle continue to rise. After 800 days, levels at the finger and ankle were seven and 15 times higher than the initial baseline reading, respectively.

"Whether bone strontium levels will continue to increase in this individual, and if they do increase whether this should be of concern, as high strontium levels have been shown to cause skeletal abnormalities in animals, and rickets and osteomalacia in adults remains to be addressed," Pejovic-Milic and co-authors remark.

Although the IVXRF system has a 40% degree of uncertainty, it ability to monitor and measure bone strontium levels over time "provides a useful diagnostic tool to help gain insight into strontium bone kinetics," the team concludes in Bone.

By Laura Cowen

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