Frequency modulated semi-continuous wave Doppler ultrasound: A novel method for the detection of scatterer velocity and range using wearable ultrasound instrumentation

Doppler ultrasound imaging has become a key tool for clinicians and researchers to measure the velocity of blood and tissues within the human body. Presently pulsed wave and continuous wave Doppler imaging dominate the space as the two most prominent methods and are considered distinct from one another. However, these two techniques can also be considered as ends of a continuum along which Doppler imaging and phase tracking techniques exist. At the midpoint between these methods exists another underexplored Doppler imaging technique we refer to as frequency modulated semi-continuous wave (FMSCW) Doppler. We present a full technical overview of this technique, simulations exploring the impact of selected imaging parameters as well as how noise impacts imaging, and present three exemplary imaging sessions collected from human participants using FMSCW Doppler collected from a wearable ultrasound system. The results of the simulations evaluating the impact of imaging parameters demonstrate the trade-off between resolution in the range and velocity axis as well as the impact of scatterer range and speed on the measurement error. The three sets of images collected from human participants serve to demonstrate FMSCW Doppler used in a variety of wearable ultrasound applications including cardiovascular monitoring, rehabilitation assessment, and prosthetic device control. Furthermore, we discuss the relationship between FMSCW Doppler and isomorphic techniques from radar as well as potential inspiration for improvements for FMSCW Doppler inspired by the echolocation of bats.