Age Related Bone Loss Assessed by Ultrasound Tomography: Bone Quality Beyond BMD

描述(由申请人提供)：评估随年龄变化的骨丢失的黄金标准是骨密度(BMD)，因为该测量与骨量高度相关。然而，骨密度不能完全解释骨强度下降和相关的骨折风险，表明除骨量以外的其他因素起着重要作用。超声波也被用来通过测量纵波的速度和衰减来评估骨骼特性。不幸的是，目前的大多数临床超声设备都像DXA一样，旨在确定骨密度，而没有利用超声对几何形状、骨小梁方向和组织成分敏感的事实。最近的体外研究已经提供了两种不同的纵波模式在松质骨中传播的证据，正如最初由Maurice A.Biot发展的波传播的孔弹性方法所预测的那样。然而，目前的大多数超声方法只考虑一个波在松质骨中传播，并且通常只将波的速度/衰减作为骨密度的函数进行分析。值得注意的是，报道的高度骨质疏松骨中的速度(例如90%液体和10%固体)从来没有低于1450m/S的值，这是骨髓中的声速。这一观察结果表明，在高孔隙率的样品中，被测量的波所表征的介质的部分是流体的，而不是固体的小梁结构。因此，超声黑盒方法区分骨小梁微结构变化的相关性受到了挑战。在这项建议中，我们打算将Biot的孔弹性方法与基于断层摄影术的(多方向)骨声学特性评估相结合。孔弹性方法的主要优点是它预测了两个波的存在，并表征了固体和液体骨分数对超声波速度/衰减的相对贡献。研究了各向异性固体结构和流体在快波和慢波速度行为中的作用。从声学特性推导出骨的弹性特性，并将其与力学测试测量结果进行比较。这种方法有可能更好地表征骨丢失随年龄的变化，并为定义骨密度以外的骨丢失标准提供第一步。项目叙述和相关性：拟议的研究有可能产生具有高度医学意义的结果。拟议目标的实现将使进一步的研究有可能导致开发新的诊断设备，能够对骨质疏松风险进行检测和分级，具有更高的灵敏度和特异性。

DESCRIPTION (provided by applicant): The gold standard to assess bone loss with age is the Bone Mineral Density (BMD), because this measurement highly correlates to bone mass. However, the BMD cannot fully explain the decrease in bone strength and the associated risk of fracture, indicating that other factors beside bone mass play an important role. Ultrasound is also used to evaluate bone properties by measuring the velocity and the attenuation of longitudinal waves. Unfortunately, most of current clinical ultrasound devices aim to determine bone mass density, as DXA does, without taking advantage of the fact that ultrasound is sensitive to geometry, trabecular orientation and tissue composition. Recent in vitro studies have provided evidence of the propagation of two different longitudinal wave modes in cancellous bone, as predicted by the poroelastic approach of wave propagation originally developed by Maurice A. Biot. However, most current ultrasound approaches consider only one wave to propagate in cancellous bone, and the wave velocity/attenuation is usually analyzed as a function of the bone mass density only. It is important to note that reported velocities in highly osteoporotic bone (for instance 90% fluid and 10% solid) never shows values below 1450m/s, which is the speed of sound in marrow. This observation suggests that in highly porous samples, the fraction of the media being characterized by the measured wave is the fluid one, as opposed to the solid trabecular structure. The relevance of the ultrasound black box approach to distinguish the changes in the trabecular microstructure is therefore challenged. In this proposal, we intent to combine Biot's poroelastic approach with a tomography based (multidirectional) assessment of acoustic properties in bone. The major advantage of the poroelastic approach is that it predicts the existence of two waves and characterizes the relative contribution of the solid and fluid bone fractions on ultrasound wave velocity/attenuation. The role of the anisotropic solid structure and fluid in the behavior of the fast and slow wave velocities is examined. From the acoustic properties, the elastic properties of bone are derived and then compared to mechanical testing measurements. This approach has the potential to better characterize changes due to bone loss with age and to provide a first step for defining a criterion for bone loss beyond bone mineral density. Project Narrative and Relevance: The proposed study has the potential to produce a highly medically significant result. Achievement of the proposed aims would enable further research possibly leading to the development of new diagnostic devices capable of greater sensitivity and specificity for the detection and grading of osteoporosis risk.