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

描述（由申请人提供）：评估骨质流失随年龄增长的黄金标准是骨密度（BMD），因为这一测量与骨量高度相关。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，这表明骨量以外的其他因素也起着重要作用。超声也被用来通过测量纵波的速度和衰减来评估骨的特性。不幸的是，目前大多数临床超声设备的目的是确定骨量密度，就像DXA一样，没有利用超声对几何形状、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纵波模式在松质骨中传播的证据，正如Maurice A. Biot最初提出的波传播的孔隙弹性方法所预测的那样。然而，目前大多数超声方法只考虑一个波在松质骨中传播，并且通常只分析波速/衰减作为骨量密度的函数。值得注意的是，报告中高度骨质疏松的骨骼（例如90%的液体和10%的固体）的速度从未低于1450m/s，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，被测量波表征的介质部分是流体，而不是固体小梁结构。因此，超声黑箱方法区分小梁微结构变化的相关性受到了挑战。在本提案中，我们打算将Biot的孔隙弹性方法与基于断层扫描（多向）的骨声学特性评估相结合。孔隙弹性方法的主要优点是它预测了两波的存在，并表征了固体和液体骨组分对超声波速/衰减的相对贡献。研究了各向异性固体结构和流体在快慢波速度变化中的作用。从声学特性出发，推导出骨的弹性特性，并与力学测试结果进行比较。这种方法有可能更好地描述骨质流失随年龄的变化，并为定义骨矿物质密度以外的骨质流失标准提供第一步。项目说明和相关性：拟议的研究有可能产生具有高度医学意义的结果。实现所提出的目标将使进一步的研究可能导致开发新的诊断设备，能够更敏感和特异性地检测和分级骨质疏松症的风险。

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.