IEEE Trans Med Imaging. 2015 Feb;34(2):433-40. doi: 10.1109/TMI.2014.2359650. Epub 2014 Sep 23.
The structure of microvasculature cannot be resolved using standard clinical ultrasound (US) imaging frequencies due to the fundamental diffraction limit of US waves. In this work, we use a standard clinical US system to perform in vivo sub-diffraction imaging on a CD1, female mouse aged eight weeks by localizing isolated US signals from microbubbles flowing within the ear microvasculature, and compare our results to optical microscopy. Furthermore, we develop a new technique to map blood velocity at super-resolution by tracking individual bubbles through the vasculature. Resolution is improved from a measured lateral and axial resolution of 112 μm and 94 μ m respectively in original US data, to super-resolved images of microvasculature where vessel features as fine as 19 μm are clearly visualized. Velocity maps clearly distinguish opposing flow direction and separated speed distributions in adjacent vessels, thereby enabling further differentiation between vessels otherwise not spatially separated in the image. This technique overcomes the diffraction limit to provide a noninvasive means of imaging the microvasculature at super-resolution, to depths of many centimeters. In the future, this method could noninvasively image pathological or therapeutic changes in the microvasculature at centimeter depths in vivo.
由于超声（US）波的基本衍射限制，标准临床 US 成像频率无法解析微血管结构。在这项工作中，我们使用标准的临床 US 系统，通过定位耳微血管中流动的微泡的孤立 US 信号，在体内对 CD1 雌性小鼠（年龄 8 周）进行亚衍射成像，并将我们的结果与光学显微镜进行比较。此外，我们开发了一种新技术，通过在血管中跟踪单个微泡来以超分辨率绘制血流速度图。分辨率从原始 US 数据中分别测量的横向和轴向分辨率 112μm 和 94μm 提高到超分辨微血管图像，其中可以清楚地看到 19μm 精细的血管特征。速度图可以清楚地区分相反的流动方向和相邻血管中的分离速度分布，从而能够进一步区分图像中空间上未分离的血管。该技术克服了衍射极限，提供了一种非侵入性的超分辨率微血管成像方法，深度可达数厘米。将来，这种方法可以非侵入性地在体内厘米深度处对微血管的病理或治疗变化进行成像。
