Gargir Oren, Azhari Haim, Zibulevsky Michael
Department of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa, Israel.
Department of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa, Israel.
Ultrasound Med Biol. 2018 Jan;44(1):187-198. doi: 10.1016/j.ultrasmedbio.2017.09.004. Epub 2017 Oct 20.
Speed of sound (SoS) is an acoustic property that is highly sensitive to changes in tissues. SoS can be mapped non-invasively using ultrasonic through transmission wave tomography. This however, practically limits its clinical use to the breast. A pulse-echo-based method that has broader clinical use and that can reliably measure treatment-induced changes in SoS even under poor signal-to-noise ratio (SNR) is highly desirable. The aim of this study was to evaluate the implementation of coded excitations (CoEs) to improve pulse-echo monitoring of heat-induced changes in the SoS. In this study, a binary phase modulated Barker sequence and a linear frequency-modulated chirp were compared with a common Gaussian pulse transmission. The comparison was conducted using computer simulations, as well as transmissions in both agar-gelatin phantoms and ex vivo bovine liver. SoS changes were experimentally induced by heating the specimens with a therapeutic ultrasound system. The performance of each transmission signal was evaluated by correlating the relative echo shifts to the normalized SoS measured by through transmission. The computer simulations indicated that CoEs are beneficial at very low SNR. The Barker code performed better than both the chirp and Gaussian pulses, particularly at SNRs <10 dB (R = 0.81 ± 0.06, 0.68 ± 0.07 and 0.55 ± 0.08, respectively, at 0 dB). At high SNRs, the CoEs performed statistically on par with the Gaussian pulse. The experimental findings indicated that both Barker and chirp codes performed better than the Gaussian pulse on ex vivo liver (R = 0.80 ± 0.15, 0.79 ± 0.15 and 0.54 ± 0.17, respectively) and comparably on agar-gelatin phantoms. In conclusion, CoEs can be beneficial for assessing temperature-induced changes in the SoS using the pulse-echo method under poor SNR.
声速（SoS）是一种对组织变化高度敏感的声学特性。可以通过超声透射波断层扫描对SoS进行非侵入性映射。然而，这实际上将其临床应用限制在了乳腺。非常需要一种基于脉冲回波的方法，该方法具有更广泛的临床应用，并且即使在信噪比（SNR）较差的情况下也能可靠地测量治疗引起的SoS变化。本研究的目的是评估编码激励（CoE）的实施情况，以改善对热诱导的SoS变化的脉冲回波监测。在本研究中，将二进制相位调制的巴克码序列和线性调频啁啾信号与普通高斯脉冲传输进行了比较。使用计算机模拟以及在琼脂-明胶体模和离体牛肝中的传输进行了比较。通过用治疗性超声系统加热标本，实验性地诱导了SoS变化。通过将相对回波偏移与通过透射测量的归一化SoS相关联，评估了每个传输信号的性能。计算机模拟表明，在非常低的SNR下，CoE是有益的。巴克码的表现优于啁啾信号和高斯脉冲，特别是在SNR<10 dB时（在0 dB时，R分别为0.81±0.06、0.68±0.07和0.55±0.08）。在高SNR下，CoE在统计学上与高斯脉冲相当。实验结果表明，巴克码和啁啾信号在离体肝脏上的表现均优于高斯脉冲（R分别为0.80±0.15、0.79±0.15和0.54±0.17），在琼脂-明胶体模上表现相当。总之，在低SNR情况下，CoE对于使用脉冲回波方法评估温度诱导的SoS变化可能是有益的。
