Robot-Assisted Deep Venous Thrombosis Ultrasound Examination Using Virtual Fixture

Abstract

Deep Venous Thrombosis (DVT) is a common vascular disease with blood clots inside deep veins, which may block blood flow or even cause a life-threatening pulmonary embolism. A typical exam for DVT using ultrasound (US) imaging is by pressing the target vein until its lumen is fully compressed. However, the compression exam is highly operator-dependent. To alleviate intra- and inter-variations, we present a robotic US system with a novel hybrid force motion control scheme ensuring position and force tracking accuracy, and soft landing of the probe onto the target surface. In addition, a path-based virtual fixture is proposed to realize easy human-robot interaction for repeat compression operation at the lesion location. To ensure the biometric measurements obtained in different examinations are comparable, the 6D scanning path is determined in a coarse-to-fine manner using both an external RGBD camera and US images. The RGBD camera is first used to extract a rough scanning path on the object. Then, the segmented vascular lumen from US images are used to optimize the scanning path to ensure the visibility of the target object. To generate a continuous scan path for developing virtual fixtures, an arc-length based path fitting model considering both position and orientation is proposed. Finally, the whole system is evaluated on a human-like arm phantom with an uneven surface. The code (https://github.com/dianyeHuang/RobDVTUS) and intuitive demonstration video (https://www.youtube.com/watch?v=3xFyqU1rV8c) can be publicly accessed. Note to Practitioners - Robotic ultrasound (US) systems have attracted attention for various applications in the past decades. However, the existing studies are not mature and intelligent enough for some challenging applications, such as DVT exam, which requires rich contact interaction between patients and clinicians. To tackle with this challenge, this study presents a novel human-centric robotic DVT exam program using the technique of virtual fixture. The coarse-to-fine path planning module ensures the repeatability of US acquisitions carried out at different times. During DVT exam, the proposed continuous 6D path virtual fixture can guide clinicians to freely move the probe along the scan path while limiting the probe motion in other directions. In order to perform the compress-release exam, a decoupled position/force controller is developed to precisely generate the contact force conveyed by clinicians and to restrict the probe motion along the probe centerline. We believe such a robot-assisted system is a promising solution to take both advantages of robots about the accuracy and repeatability and human operators about the advanced physiological knowledge.