Design of a wearable ultrasound Doppler sensor to monitor blood flow in the common carotid artery

Abstract

A novel design for a wearable and non-invasive ultrasound Doppler blood flow measuring device is presented. The device consists of an array of piezoelectric transducers that mount at the neck and generate different ultrasonic beams directed at the common carotid artery. The Doppler frequency shift generated by the moving blood is then processed to reconstruct the centerline velocity of the artery as well as to provide an estimate of the velocity profile and other physiological parameters. The presented design covers key issues relevant to making this technology wearable mainly handling the location uncertainty of the artery and interpreting the measurement without human assistance with the restriction of keeping the technical complexity of the device low for all cases. The array of transducers is designed to enable the coverage of a wide sector in the neck that encompasses the artery. Different beams can be produced by the array depending on the number of transducers that are excited. The centerline velocity of the artery is used as a criterion to decide which transducers are favorably oriented and hence should be operated. Novel algorithms to process the received signal to estimate the velocity profile and the time derivative of pressure are presented. The thesis builds upon theoretical analysis and includes computer simulation and experimental verification of the key ideas.