In vivo quantification of strontium in bone among adults using portable x-ray fluorescence.

BACKGROUND AND OBJECTIVE Bone strontium (Sr) is a reliable biomarker for studying related bone health outcomes and the effectiveness of Sr supplements in osteoporosis disease treatment. In this study, we evaluated the sensitivity of portable x-ray fluorescence (XRF) technology for in vivo bone Sr quantification among adults. MATERIALS AND METHODS Sr-doped bone-equivalent phantoms were used for system calibration. Using the portable XRF, we measured bone Sr levels in vivo in mid-tibia bone in 76 adults, 38-95 years of age, living in Indiana, US; we also analyzed bone data of 29 adults, 53-82 years of age, living in Shanghai, China. The same portable XRF device and system settings were used in measuring their mid-tibia bone. We compared bone Sr concentrations by sex, age, and recruitment site. We also used multiple linear regression model to estimate the association of age with bone Sr concentration, adjusting for sex and recruitment site. RESULTS The uncertainty of in vivo individual measurement increased with higher soft tissue thickness overlying bone, and it ranged from 1.0 ug/g dry bone (ppm) to 2.4 ppm with thickness ranging from 2 to 7 mm, with a measurement time of 5 min. Geometric mean (95% confidence interval (CI)) of the bone Sr concentration was 79.1 (70.1, 89.3) ppm. After adjustment for recruitment site and sex, an increase in five years of age was associated with a 8.9% (95% CI: 2.5%, 15.6%) increase in geometric mean bone Sr concentration. DISCUSSION AND CONCLUSION Sr concentrations were consistently well above detection limits of the portable XRF, and exhibited an expected increase with age. These data suggest that the portable XRF can be a valuable technology to quantify Sr concentration in bone, and in the study of Sr-related health outcomes among adults, such as bone mineral density (BMD) and bone fracture risk.