Nicholson Patrick H F, Moilanen Petro, Kärkkäinen Tommi, Timonen Jussi, Cheng Sulin
Department of Health Sciences, University of Jyväskylä, Finland.
Physiol Meas. 2002 Nov;23(4):755-68. doi: 10.1088/0967-3334/23/4/313.
Existing ultrasound devices for assessing the human tibia are based on detecting the first arriving signal, corresponding to a wave propagating at, or close to, the bulk longitudinal velocity in bone. However, human long bones are effectively irregular hollow tubes and should theoretically support the propagation of more complex guided modes similar to Lamb waves in plates. Guided waves are attractive because they propagate throughout the bone thickness and can potentially yield more information on bone material properties and architecture. In this study, Lamb wave theory and numerical simulations of wave propagation were used to gain insights into the expected behaviour of guided waves in bone. Experimental measurements in acrylic plates, using a prototype low-frequency axial pulse transmission device, confirmed the presence of two distinct propagating waves: the first arriving wave propagating at, or close to, the longitudinal velocity, and a slower second wave whose behaviour was consistent with the lowest order Lamb antisymmetrical (A0) mode. In a pilot study of healthy and osteoporotic subjects, the velocity of the second wave differed significantly between the two groups, whereas the first arriving wave velocity did not, suggesting the former to be a more sensitive indicator of osteoporosis. We conclude that guided wave measurements may offer an enhanced approach to the ultrasonic characterization of long bones.
现有的用于评估人体胫骨的超声设备是基于检测首个到达信号，该信号对应于以骨中的体纵向速度或接近该速度传播的波。然而，人体长骨实际上是不规则的空心管，理论上应支持类似于板中兰姆波的更复杂导波模式的传播。导波很有吸引力，因为它们在整个骨厚度中传播，并且有可能产生更多关于骨材料特性和结构的信息。在本研究中，使用兰姆波理论和波传播的数值模拟来深入了解骨中导波的预期行为。使用原型低频轴向脉冲传输设备在丙烯酸板上进行的实验测量证实存在两种不同的传播波：首个到达波以纵向速度或接近纵向速度传播，以及一个较慢的第二波，其行为与最低阶兰姆反对称（A0）模式一致。在一项针对健康和骨质疏松受试者的初步研究中，两组之间第二波的速度存在显著差异，而首个到达波的速度则没有，这表明前者是骨质疏松更敏感的指标。我们得出结论，导波测量可能为长骨的超声表征提供一种改进的方法。
