Computer-assisted Applications in Medicine group, ETH Zurich, Zurich, Switzerland.
Int J Comput Assist Radiol Surg. 2021 Jul;16(7):1201-1211. doi: 10.1007/s11548-021-02426-w. Epub 2021 Jun 23.
Due to its safe, low-cost, portable, and real-time nature, ultrasound is a prominent imaging method in computer-assisted interventions. However, typical B-mode ultrasound images have limited contrast and tissue differentiation capability for several clinical applications.
Recent introduction of imaging speed-of-sound (SoS) in soft tissues using conventional ultrasound systems and transducers has great potential in clinical translation providing additional imaging contrast, e.g., in intervention planning, navigation, and guidance applications. However, current pulse-echo SoS imaging methods relying on plane wave (PW) sequences are highly prone to aberration effects, therefore suboptimal in image quality. In this paper we propose using diverging waves (DW) for SoS imaging and study this comparatively to PW.
We demonstrate wavefront aberration and its effects on the key step of displacement tracking in the SoS reconstruction pipeline, comparatively between PW and DW on a synthetic example. We then present the parameterization sensitivity of both approaches on a set of simulated phantoms. Analyzing SoS imaging performance comparatively indicates that using DW instead of PW, the reconstruction accuracy improves by over 20% in root-mean-square-error (RMSE) and by 42% in contrast-to-noise ratio (CNR). We then demonstrate SoS reconstructions with actual US acquisitions of a breast phantom. With our proposed DW, CNR for a high contrast tumor-representative inclusion is improved by 42%, while for a low contrast cyst-representative inclusion a 2.8-fold improvement is achieved.
SoS imaging, so far only studied using a plane wave transmission scheme, can be made more reliable and accurate using DW. The high imaging contrast of DW-based SoS imaging will thus facilitate the clinical translation of the method and utilization in computer-assisted interventions such as ultrasound-guided biopsies, where B-Mode contrast is often to low to detect potential lesions.
由于其安全、低成本、便携和实时的特性，超声在计算机辅助干预中是一种重要的成像方法。然而，典型的 B 模式超声图像对于一些临床应用的对比度和组织分辨能力有限。
最近在传统超声系统和换能器中引入了软组织的成像声速（SoS），这在临床转化中具有很大的潜力，可以提供额外的成像对比度，例如在干预规划、导航和引导应用中。然而，目前依赖于平面波（PW）序列的脉冲回波 SoS 成像方法容易受到像差的影响，因此图像质量不是最佳的。在本文中，我们提出使用发散波（DW）进行 SoS 成像，并将其与 PW 进行比较研究。
我们在一个合成示例中演示了波前像差及其对 SoS 重建管道中位移跟踪关键步骤的影响，比较了 PW 和 DW 之间的差异。然后，我们在一组模拟体模上展示了这两种方法的参数敏感性。比较分析 SoS 成像性能表明，与 PW 相比，使用 DW 可以将重建精度的均方根误差（RMSE）提高 20%以上，对比度噪声比（CNR）提高 42%。然后，我们展示了使用实际 US 采集的乳腺体模进行的 SoS 重建。使用我们提出的 DW，高对比度肿瘤代表性包含物的 CNR 提高了 42%，而低对比度囊肿代表性包含物的 CNR 提高了 2.8 倍。
SoS 成像迄今为止仅使用平面波传输方案进行研究，使用 DW 可以使其更可靠和准确。DW 基于 SoS 成像的高成像对比度将有助于该方法的临床转化，并在计算机辅助干预中得到应用，如超声引导活检，在这些应用中，B 模式对比度往往太低，无法检测到潜在的病变。
