Pushing the Doppler envelope: From complex flow visualization to biomarker quantification

Although Doppler ultrasound has been widely used clinically, the current technology is known to lack visual intuitiveness and is often erroneous. New ultrasound flow mapping solutions are needed to more effectively diagnose a variety of medical problems that the aging population is prone to, such as atherosclerosis. In the decade of 2010s, there is a major innovation drive in high-frame-rate (or ultrafast) ultrasound imaging that is characterized by frame rates of over 1000 fps. New techniques such as vector flow imaging have become mature over this period. Building upon this success, we have now entered the era of “High-Frame-Rate Ultrasound 2.0” that makes use of time-resolved mapping to derive quantitative biomarkers that are directly linked to diseases. One example is the development of wall shear mapping techniques for next-generation cardiovascular diagnostics. Here, wall shear stress is measured as the flow velocity gradient tangential to the arterial wall by performing (1) plane-wave data acquisition, (2) dynamic wall tracking, (3) vector flow estimation with near-wall velocity regularization, and (4) spatial velocity gradient estimation. These solutions have been implemented in real-time using open-platform ultrasound scanners and high-speed GPU computing platforms. With these imaging innovations, it becomes possible to track complex cardiovascular flow phenomena and, in turn, derive hemodynamic biomarkers that are important to atherosclerosis monitoring, such as wall shear stress.