Moilanen P, Nicholson P H F, Kilappa V, Cheng S, Timonen J
Department of Physics, University of Jyväskylä, Jyväskylä, Finland.
Ultrasound Med Biol. 2006 May;32(5):709-19. doi: 10.1016/j.ultrasmedbio.2006.02.1402.
Guided waves, consistent with the A0 Lamb mode, have previously been observed in bone phantoms and human long bones. Reported velocity measurements relied on line fitting of the observed wave fronts. Such an approach has limited ability to assess dispersion and is affected by interference by other wave modes. For a more robust identification of modes and determination of phase velocities, signal processing techniques using the fast Fourier transform (FFT) were investigated. The limitations of FFT because of spatial resolution were addressed to improve the precision of the measured modes. An inversion scheme was developed for determining the plate thickness from the measured velocity. Experiments were performed on free and immersed plates, mimicking bone without and with an overlying tissue. With group velocity filtering, modes could be identified reliably with precise phase velocities and thicknesses. These methods were essential for the immersed plates and they should lead to more reliable in vivo measurements.
与A0兰姆波模式一致的导波此前已在骨模型和人类长骨中被观测到。报告的速度测量依赖于对观测到的波前进行线性拟合。这种方法评估频散的能力有限，并且会受到其他波模式干扰的影响。为了更可靠地识别模式并确定相速度，研究了使用快速傅里叶变换（FFT）的信号处理技术。针对由于空间分辨率导致的FFT局限性进行了处理，以提高所测模式的精度。开发了一种反演方案，用于根据测量速度确定板的厚度。对自由板和浸没板进行了实验，分别模拟没有覆盖组织和有覆盖组织的骨骼。通过群速度滤波，可以可靠地识别模式，并获得精确的相速度和厚度。这些方法对于浸没板至关重要，并且应该会使体内测量更加可靠。
