Imperial College London, Charing Cross Campus, London, UK.
Bone. 2010 Nov;47(5):882-7. doi: 10.1016/j.bone.2010.08.005. Epub 2010 Aug 10.
Osteoporotic patients treated with strontium ranelate show relatively large increases in bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) due to the replacement of some of the calcium atoms in bone by strontium. A study published by Pors Nielsen and colleagues reported that replacement of 1% of calcium atoms by strontium causes a 10% increase in BMD. We refer to the ratio of the percentage increase in BMD to the molar percentage of strontium in bone as the strontium ratio. Theoretically it is expected that the strontium ratio should vary between different manufacturers' DXA equipment depending on the effective photon energy of the device, an effect that arises because of the proximity of the X-ray energies produced by lower energy devices to the strontium K-edge at 16 keV. In this study we report theoretical estimates of the strontium ratio for two axial DXA systems and two peripheral DXA devices based on their broad spectrum X-ray emission. The theoretical figures were verified in an experimental study in which the strontium ratio for each device was measured using phantoms containing mixtures of hydroxyapatite and strontium hydrogen-phosphate. The theoretical values of the strontium ratio were 11.0 for the Hologic Discovery, 9.9 for the GE-Lunar Prodigy, 9.1 for the Demetech Calscan, and 8.5 for the Osteometer Dexacare G4. Experimental results were 11.2 for the Discovery, 9.9 for the Prodigy, 8.6 for the Calscan and 6.3 for the Dexacare G4. The results confirm both theoretically and experimentally that the effect of bone strontium on BMD measurements is different for different DXA systems. In the future it might be possible to exploit this effect to make a non-invasive estimate of average bone strontium content in groups of patients receiving strontium medication for osteoporosis.
锶雷酸盐治疗的骨质疏松患者的骨密度（BMD）会有较大的增加，这是通过双能 X 射线吸收法（DXA）测量得出的，这是由于锶取代了骨中的一些钙原子。Pors Nielsen 及其同事发表的一项研究报告称，1%的钙原子被锶取代会导致 BMD 增加 10%。我们将 BMD 增加的百分比与骨中锶的摩尔百分比之比称为锶比。理论上，由于能量较低的设备产生的 X 射线能量接近 16keV 的锶 K 边，不同制造商的 DXA 设备的有效光子能量不同，因此预计锶比会有所不同。在这项研究中，我们根据其广谱 X 射线发射，报告了两种轴向 DXA 系统和两种外周 DXA 设备的锶比的理论估计。通过使用含有羟基磷灰石和锶磷酸氢盐混合物的体模，在实验研究中验证了理论数值。对于每种设备，锶比的理论值分别为 11.0（Hologic Discovery）、9.9（GE-Lunar Prodigy）、9.1（Demetech Calscan）和 8.5（Osteometer Dexacare G4）。实验结果分别为 11.2（Discovery）、9.9（Prodigy）、8.6（Calscan）和 6.3（Dexacare G4）。理论和实验结果均证实，不同的 DXA 系统对骨锶对 BMD 测量的影响不同。将来，有可能利用这种效果，对接受锶药物治疗骨质疏松症的患者群体的平均骨锶含量进行非侵入性估计。
