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金标准是骨矿物质密度（BMD），因为该测量值与骨量高度相关。然而，骨密度不能完全解释骨强度的下降和相关的骨折风险，表明除骨量外的其他因素也起着重要作用。超声波还可用于通过测量纵波的速度和衰减来评估骨特性。不幸的是，目前大多数临床超声设备的目标是确定骨质量密度，如DXA，而没有利用超声对几何形状、骨小梁取向和组织组成敏感的事实。最近的体外研究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.毕奥。然而，大多数当前的超声方法仅考虑一个波在松质骨中传播，并且波的速度/衰减通常仅被分析为骨质量密度的函数。 值得注意的是，在高度骨质疏松的骨（例如90%的液体和10%的固体）中，报告的速度从未显示低于1450 m/s的值，这是骨髓中的声速。这一观察结果表明，在高度多孔的样品中，由测量的波表征的介质的部分是流体的，而不是固体小梁结构。因此，超声黑箱方法区分骨小梁微观结构变化的相关性受到挑战。在这个提议中，我们打算将联合收割机毕奥的多孔弹性方法与骨中声学特性的基于断层扫描的（多方向）评估相结合。多孔弹性方法的主要优点是它预测了两种波的存在，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，骨的弹性特性推导出，然后进行比较，机械测试测量。这种方法有可能更好地表征由于骨丢失随年龄的变化，并提供了第一步，定义骨密度以外的骨丢失的标准。项目叙述和相关性：拟定研究有可能产生高度医学显著性结果。实现拟议的目标将使进一步的研究可能导致新的诊断设备的开发能够更高的灵敏度和特异性的检测和骨质疏松症的风险分级。

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.