Multi-frequency characterization of the speed of sound and attenuation coefficient for longitudinal transmission of freshly excised human skulls.
Multi-frequency characterization of the speed of sound and attenuation coefficient for longitudinal transmission of freshly excised human skulls.
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DOI：
10.1088/0031-9155/56/1/014
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发表时间：
2011-01-07
影响因子：
3.5
通讯作者：
Hynynen K
中科院分区：
文献类型：
--
作者：
Pichardo S;Sin VW;Hynynen K
对于脑内超声的医学应用，有必要了解颅骨的表观密度与其相应的声速和衰减系数之间的关系。虽然之前已经有研究探索这种现象，但仍然需要扩展测量以覆盖更多的临床相关频率范围。本文给出了对人颅骨标本的纵向声速和衰减系数的测量结果。该研究针对0.27、0.836、1.402、1.965和2.525 MHz的频率进行。通过多伦多大学解剖学部的协议从新鲜尸体中获得标本。该方案由Sunnybrook Health Sciences Centre的研究伦理委员会批准。将标本固定在聚碳酸酯支架上，支架上标记有立体定位。对安装在其支架上的颅骨进行计算机断层扫描（CT），并重建三维颅骨表面。该表面用于引导定位系统，以确保声信号的正常声入射。该信号由直径为5 cm且焦距为10 cm的聚焦装置产生。使用针状水听器进行了飞行时间延迟的测量。有效透射能量的测量使用辐射力方法进行，分辨率为10 μg。声速和衰减系数的初步功能，这两者都与表观密度，建立了一个多层传播模型，考虑到声速，密度和厚度的层。从一个大的随机函数集合中执行优化过程，并为最接近再现实验观察结果的那些函数选择最佳函数。最终的函数是在执行第二遍优化过程后获得的，但这次使用的是韦斯特丙酮方程的有限差分时间差解，这比多层模型更精确，但计算耗时更长。对于七个样本中的六个，在颅骨上的五个位置上进行测量，对于其他样本进行三次测量。总共在33个地点进行了测量。结果表明存在分散效应，并且这些效应根据颅骨中的骨类型（皮质骨和小梁骨）而不同。此外，声速和衰减都显示出对随频率变化的颅骨密度的依赖性。利用最优函数和CT扫描的密度信息，计算出平均值（±s.d.）在270、836、1402、1965和2526 kHz的频率下，皮质骨的声速分别为2384（±130）、2471（± 90）、2504（±120）、2327（±90）和2053（±40）m s-1。对于松质骨，在相同的频率值顺序下，声速分别为2140（±130）、2300（±100）、2219（±200）、2133（±130）和1937（±40）m s-1。在频率为270、836和1402时，皮质骨的衰减系数平均值分别为33（±9）、240（±9）和307（±30）Np m−1。对于松质骨，在相同的频率值顺序下，衰减系数的平均值分别为34（±13）、216（±16）和375（±30）Npm −1。对于1.965和2.525 MHz的频率，使用所用设置未检测到可测量的辐射力。
For medical applications of ultrasound inside the brain, it is necessary to understand the relationship between the apparent density of skull bone and its corresponding speed of sound and attenuation coefficient. Although there have been previous studies exploring this phenomenon, there is still a need to extend the measurements to cover more of the clinically relevant frequency range. The results of measurements of the longitudinal speed of sound and attenuation coefficient are presented for specimens of human calvaria. The study was performed for the frequencies of 0.27, 0.836, 1.402, 1.965 and 2.525 MHz. Specimens were obtained from fresh cadavers through a protocol with the Division of Anatomy of the University of Toronto. The protocol was approved by the Research Ethics Board of Sunnybrook Health Sciences Centre. The specimens were mounted in polycarbonate supports that were marked for stereoscopic positioning. Computer tomography (CT) scans of the skulls mounted on their supports were performed, and a three-dimensional skull surface was reconstructed. This surface was used to guide a positioning system to ensure the normal sound incidence of an acoustic signal. This signal was produced by a focused device with a diameter of 5 cm and a focal length of 10 cm. Measurements of delay in time of flight were carried out using a needle hydrophone. Measurements of effective transmitted energy were carried out using a radiation force method with a 10 μg resolution scale. Preliminary functions of speed of sound and attenuation coefficient, both of which are related to apparent density, were established using a multi-layer propagation model that takes into account speed of sound, density and thickness of the layer. An optimization process was executed from a large set of random functions and the best functions were chosen for those ones that closest reproduced the experimental observations. The final functions were obtained after a second pass of the optimization process was executed, but this time using a finite-difference time-difference solution of the Westervelt equation, which is more precise than the multi-layer model but much more time consuming for computation. For six of seven specimens, measurements were carried out on five locations on the calvaria, and for the other specimen three measurements were made. In total, measurements were carried out on 33 locations. Results indicated the presence of dispersion effects and that these effects are different according to the type of bone in the skull (cortical and trabecular). Additionally, both the speed of sound and attenuation showed dependence on the skull density that varied with the frequency. Using the optimal functions and the information of density from the CT scans, the average values (±s.d.) of the speed of sound for cortical bone were estimated to be 2384(±130), 2471(±90), 2504(±120), 2327(±90) and 2053(±40) m s−1 for the frequencies of 270, 836, 1402, 1965 and 2526 kHz, respectively. For trabecular bone, and in the same order of frequency values, the speeds of sound were 2140(±130), 2300(±100), 2219(±200), 2133(±130) and 1937(±40) m s−1, respectively. The average values of the attenuation coefficient for cortical bone were 33(±9), 240(±9) and 307(±30) Np m−1 for the frequencies of 270, 836, and 1402, respectively. For trabecular bone, and in the same order of frequency values, the average values of the attenuation coefficient were 34(±13), 216(±16) and 375(±30) Np m−1, respectively. For frequencies of 1.965 and 2.525 MHz, no measurable radiation force was detected with the setup used.
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影响因子：
3.8
作者：
HYNYNEN, K
通讯作者：
HYNYNEN, K
影响因子：
2.4
作者：
FRY, FJ;BARGER, JE
通讯作者：
BARGER, JE
影响因子：
3.5
作者：
Clement, GT;White, J;Hynynen, K
通讯作者：
Hynynen, K
影响因子：
2.4
作者：
Anderson, Christian C.;Marutyan, Karen R.;Miller, James G.
通讯作者：
Miller, James G.
DOI：
10.1118/1.594318
发表时间：
1977-01-01
期刊：
Medical Physics (Woodbury)
影响因子：
--
作者：
CARSON P L;OUGHTON T V;AHUJA A S
通讯作者：
AHUJA A S