IEEE Trans Ultrason Ferroelectr Freq Control. 2019 May;66(5):939-948. doi: 10.1109/TUFFC.2019.2906434. Epub 2019 Mar 21.
Three-dimensional imaging is valuable to noninvasively assess angiogenesis given the complex 3-D architecture of vascular networks. The emergence of high frame rate (HFR) ultrasound, which can produce thousands of images per second, has inspired novel signal processing techniques and their applications in structural and functional imaging of blood vessels. Although highly sensitive vascular mapping has been demonstrated using ultrafast Doppler, the detectability of microvasculature from the background noise may be hindered by the low signal-to-noise ratio (SNR) particularly in the deeper region and without the use of contrast agents. We have recently demonstrated a coherence-based technique, acoustic subaperture imaging (ASAP), for super-contrast vascular imaging and illustrated the contrast improvement using HFR contrast-enhanced ultrasound. In this work, we provide a feasibility study for microvascular imaging using ASAP without contrast agents, and extend its capability from 2-D to volumetric vascular mapping. Using an ultrasound research system and a preclinical probe, we demonstrated the improved visibility of microvascular mapping using ASAP in comparison to ultrafast power Doppler (PD) on a mouse kidney, liver, and tumor without contrast agent injection. The SNR of ASAP images improves in average by 10 dB when compared to PD. In addition, directional velocity mappings were also demonstrated by combining ASAP with the phase information extracted from lag-1 autocorrelation. The 3-D vascular and velocity mapping of the mouse kidney, liver, and tumor were demonstrated by stacking the ASAP images acquired using 2-D ultrasound imaging and a trigger-controlled linear translation stage. The 3-D results depicted clear microvasculature morphologies and functional information in terms of flow direction and velocity in two nontumor models and a tumor model. In conclusion, we have demonstrated a new 3-D in vivo ultrasound microvascular imaging technique with significantly improved SNR over existing ultrafast Doppler.
三维成像是评估血管生成的一种有价值的非侵入性方法，因为血管网络具有复杂的 3D 结构。高帧率（HFR）超声的出现，每秒可以产生数千张图像，激发了新的信号处理技术及其在血管结构和功能成像中的应用。虽然使用超快速多普勒已经证明了高度敏感的血管绘图，但由于信噪比（SNR）低，特别是在较深的区域和没有使用对比剂的情况下，从背景噪声中检测微血管的能力可能会受到阻碍。我们最近展示了一种基于相干的技术，声亚孔径成像（ASAP），用于超级对比血管成像，并说明了使用 HFR 对比增强超声的对比改善。在这项工作中，我们提供了一种使用 ASAP 进行无造影剂微血管成像的可行性研究，并将其从 2D 扩展到容积血管测绘。使用超声研究系统和临床前探头，我们在没有对比剂注射的情况下，在小鼠肾脏、肝脏和肿瘤上，与超快速功率多普勒（PD）相比，证明了 ASAP 进行微血管绘图的可视性得到了改善。与 PD 相比，ASAP 图像的 SNR 平均提高了 10dB。此外，还通过将 ASAP 与从滞后 1 自相关提取的相位信息相结合，演示了定向速度映射。通过使用 2D 超声成像和触发控制的线性平移台获取 ASAP 图像，并对其进行堆叠，展示了小鼠肾脏、肝脏和肿瘤的 3D 血管和速度映射。3D 结果清晰地描绘了两个非肿瘤模型和一个肿瘤模型中微血管的形态和功能信息，包括血流方向和速度。总之，我们展示了一种新的 3D 体内超声微血管成像技术，与现有的超快速多普勒相比，具有显著提高的 SNR。
