Department of Physics, University of Kuopio, Kuopio, Finland.
Ultrasound Med Biol. 2010 Feb;36(2):288-94. doi: 10.1016/j.ultrasmedbio.2009.10.008.
Quantitative ultrasound (QUS) measurements are used in the diagnostics of osteoporosis. However, the variation in the thickness and composition of the overlying soft tissue causes significant errors to the bone QUS parameters and diminishes the reliability of the technique in vivo. Recently, the dual frequency ultrasound (DFUS) technique was introduced to minimize the errors related to soft tissue effects. In this study, the significance of soft tissue induced errors and their elimination with the DFUS technique were simulated using the finite difference time domain technique. Furthermore, we investigated the potential of the DFUS corrected integrated reflection coefficient (IRC) of bone to detect changes in the cortical bone density. The effects of alterations in the thickness of fat and lean tissue layers and the inclination between the soft-tissues and between the soft tissue-bone layers were simulated. When the angle of the soft tissue interface was zero, i.e., perpendicular to the incident ultrasound beam, the DFUS-calculated soft tissue composition correlated highly linearly with the true soft tissue composition. The inclination between the soft tissue-bone layers was found to be critical. Even a 2-degree inclination between the soft tissue and the bone surface induced an almost 18% relative error in the corrected IRC. Increasing the inclination between the soft tissue layers increased the error in the DFUS-calculated lean and fat tissue thickness. This error was especially significant at inclination angles greater than 20 degrees. The significant soft tissue induced errors in IRC values (>300 %) could be effectively minimized (<10%) by means of the DFUS correction. Importantly, after the DFUS correction, physiologically relevant variation in the cortical bone density could be detected (p<0.05).
定量超声（QUS）测量用于骨质疏松症的诊断。然而，覆盖的软组织的厚度和组成的变化会导致骨 QUS 参数产生显著误差，并降低该技术在体内的可靠性。最近，引入了双频超声（DFUS）技术来最小化与软组织效应相关的误差。在这项研究中，使用时域有限差分技术模拟了软组织引起的误差的意义及其通过 DFUS 技术消除。此外，我们研究了 DFUS 校正的集成反射系数（IRC）检测皮质骨密度变化的潜力。模拟了脂肪和瘦组织层厚度的变化以及软组织与软组织-骨层之间的倾斜的影响。当软组织界面的角度为零时，即垂直于入射超声束，DFUS 计算的软组织组成与真实软组织组成高度线性相关。发现软组织-骨层之间的倾斜至关重要。即使软组织与骨表面之间的倾斜度为 2 度，校正后的 IRC 也会产生近 18%的相对误差。增加软组织层之间的倾斜会增加 DFUS 计算的瘦组织和脂肪组织厚度的误差。当倾斜角度大于 20 度时，该误差尤其显著。IRC 值中的显著软组织引起的误差（>300%）可以通过 DFUS 校正有效地最小化（<10%）。重要的是，校正后可以检测到皮质骨密度的生理相关变化（p<0.05）。
