Attenuation, scattering, and absorption of ultrasound in the skull bone
Attenuation, scattering, and absorption of ultrasound in the skull bone
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DOI：
10.1118/1.3668316
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发表时间：
2012-01-01
期刊：
影响因子：
3.8
通讯作者：
Tanter, Mickael
中科院分区：
文献类型：
--
作者：
Pinton, Gianmarco;Aubry, Jean-Francois;Tanter, Mickael
目的：超声在骨中衰减的测量值代表了不同损耗机制的组合。当波从液体传播到骨骼时，界面上就会发生反射。在骨骼中，纵向和剪切模式之间发生模式转换，机械波因其复杂的内部微结构而被散射。最后，部分波能被骨骼吸收并转化为热量。由于波传播的复杂性，以及进行能够分离各种损失机制的测量的困难，目前还没有关于骨吸收的估计。因此，本文的目的是量化骨中波的衰减、散射和热吸收。方法：建立波在骨中传播的衰减模型，并利用该模型开发三维时域有限差分数值算法。声场的水听器和光学外差干涉仪测量以及骨骼样品的X射线显微层析成像被用来驱动模拟和测量衰减。声学测量与红外摄像机同时进行，红外摄像机可以测量辐射过程中的温度升高。然后通过三维热模拟将温度与吸收之间的联系用于量化皮质骨中纵波和横波的吸收系数。结果：我们证明只有一小部分衰减是由于在骨中的吸收，而大部分衰减是由于反射、散射和模式转换。在9例人体标本中，皮质骨吸收时间常数为1.04亩S+/-28%。这相当于纵向吸收为2.7分贝/厘米，剪切吸收为5.4分贝/厘米。实验测得的厚度约为8 mm的样品的衰减为13.3+/-0.97dB/cm。结论：首次测量的超声在骨中的吸收可以根据声场的知识来估计骨中的热沉降量。(C)2012年美国医学物理学家协会。[DOI：10.1118/1.3668316]
Purpose: Measured values of ultrasound attenuation in bone represent a combination of different loss mechanisms. As a wave is transmitted from a fluid into bone, reflections occur at the interface. In the bone, mode conversion occurs between longitudinal and shear modes and the mechanical wave is scattered by its complex internal microstructure. Finally, part of the wave energy is absorbed by the bone and converted into heat. Due to the complexity of the wave propagation and the difficulty in performing measurements that are capable of separating the various loss mechanisms, there are currently no estimates of the absorption in bone. The aim of this paper is, thus, to quantify the attenuation, scattering, and thermal absorption in bone.Methods: An attenuating model of wave propagation in bone is established and used to develop a three-dimensional finite difference time domain numerical algorithm. Hydrophone and optical heterodyne interferometer measurements of the acoustic field as well as a x-ray microtomography of the bone sample are used to drive the simulations and to measure the attenuation. The acoustic measurements are performed concurrently with an infrared camera that can measure the temperature elevation during insonication. A link between the temperature and the absorption via a three-dimensional thermal simulation is then used to quantify the absorption coefficients for longitudinal and shear waves in cortical bone.Results: We demonstrate that only a small part of the attenuation is due to absorption in bone and that the majority of the attenuation is due to reflection, scattering, and mode conversion. In the nine samples of a human used for the study, the absorption time constant for cortical bone was determined to be 1.04 mu s +/- 28%. This corresponds to a longitudinal absorption of 2.7 dB/cm and a shear absorption of 5.4 dB/cm. The experimentally measured attenuation across the approximately 8 mm thick samples was 13.3 +/- 0.97 dB/cm.Conclusions: This first measurement of ultrasound absorption in bone can be used to estimate the amount of heat deposition based on knowledge of the acoustic field. (C) 2012 American Association of Physicists in Medicine. [DOI: 10.1118/1.3668316]