Hakulinen M A, Saarakkala S, Töyräs J, Kröger H, Jurvelin J S
Department of Applied Physics, University of Kuopio, Kuopio, Finland.
Phys Med Biol. 2003 Jun 21;48(12):1741-52. doi: 10.1088/0031-9155/48/12/305.
In dual energy x-ray absorptiometry (DXA) the photon attenuation is assumed to be similar in soft tissue overlying, adjacent to and inside the measured bone. In the calcaneal dual energy x-ray laser (DXL) technique, this assumption is not needed as attenuation by soft tissues at the local bone site is determined by combining DXA and heel thickness measurements. In the present study, 38 subjects were measured with DXL Calscan, Lunar PIXI and Lunar DPX-IQ DXA instruments and Hologic Sahara ultrasound instrument, and the performance and agreement of the instruments were analysed. Furthermore, numerical simulations on the effect of non-uniform fat-to-lean tissue ratio within soft tissue in heel were conducted. In vivo short-term precision (CV%, sCV%) of DXL Calscan (1.24%, 1.48%) was similar to that of Lunar PIXI (1.28%, 1.60%). Calcaneal areal bone mineral densities (BMD, g cm(-2)) measured using DXL Calscan and Lunar PIXI predicted equally well variations in BMD of femoral neck (r2 = 0.63 and 0.52, respectively) or lumbar spine (r2 = 0.61 and 0.64, respectively), determined with Lunar DPX-IQ. BMD values measured with DXL Calscan were, on average, 19% lower (p < 0.01) than those determined with Lunar PIXI. Interestingly, the difference in BMD values between instruments increased as a function of body mass index (BMI) (r2 = 0.17, p < 0.02) or heel thickness (r2 = 0.37, p < 0.01). Numerical simulations suggested that the spatial variation of soft tissue composition in heel can induce incontrollable inaccuracy in BMD when measured with the DXA technique. Theoretically, in contrast to DXA instruments, elimination of the effect of non-uniform soft tissue is possible with DXL Calscan.
在双能X线吸收法（DXA）中，假定覆盖、相邻于以及位于被测骨骼内部的软组织中的光子衰减情况相似。在跟骨双能X线激光（DXL）技术中，无需此假定，因为通过结合DXA和足跟厚度测量可确定局部骨部位软组织的衰减情况。在本研究中，使用DXL Calscan、Lunar PIXI和Lunar DPX - IQ DXA仪器以及Hologic Sahara超声仪器对38名受试者进行了测量，并分析了这些仪器的性能和一致性。此外，还对足跟软组织内脂肪与瘦组织比例不均匀的影响进行了数值模拟。DXL Calscan的体内短期精密度（CV%，sCV%）为（1.24%，1.48%），与Lunar PIXI的（1.28%，1.60%）相似。使用DXL Calscan和Lunar PIXI测量的跟骨面积骨密度（BMD，g/cm²）对用Lunar DPX - IQ测定的股骨颈（r²分别为0.63和0.52）或腰椎（r²分别为0.61和0.64）的BMD变化预测效果相当。用DXL Calscan测量的BMD值平均比用Lunar PIXI测定的值低19%（p < 0.01）。有趣的是，仪器之间BMD值的差异随体重指数（BMI）（r² = 0.17，p < 0.02）或足跟厚度（r² = 0.37，p < 0.01）的变化而增大。数值模拟表明，当用DXA技术测量时，足跟软组织成分的空间变化会在BMD测量中引起无法控制的误差。理论上，与DXA仪器不同，DXL Calscan可以消除软组织不均匀的影响。
