A system for tracking a cross-section geometry of a blood vessel, comprising: at least one sensor having a plurality of ultrasonic transducers configured to non-invasively sense a blood vessel and provide signals representative of the blood vessel; and a controller in communication with the at least one sensor and a non-transitory memory storing instructions, which instructions when executed cause the controller to: control the plurality of ultrasonic transducers to periodically sense the blood vessel and produce signals representative of a plurality of features of the blood vessel; and track the plurality of features of the blood vessel, using the signals representative of the plurality of features to determine a cross-section geometry of the blood vessel as a function of time; wherein the signals produced by the plurality of ultrasonic transducers signals represent an ultrasonic image of the blood vessel; and wherein the instructions when executed cause the controller to assign a first plurality of windows to a first feature of the plurality of features within a first frame, and a second plurality of windows to the first feature within a second frame, wherein the second frame is subsequent to the first frame, and to perform a two dimensional cross-correlation between the signals representative of the first feature within the first frame and the signals representative of the first feature within the second frame using at least one convex constraint. at least one sensor having a plurality of ultrasonic transducers configured to non-invasively sense a blood vessel and provide signals representative of the blood vessel; and a controller in communication with the at least one sensor and a non-transitory memory storing instructions, which instructions when executed cause the controller to: control the plurality of ultrasonic transducers to periodically sense the blood vessel and produce signals representative of a plurality of features of the blood vessel; and track the plurality of features of the blood vessel, using the signals representative of the plurality of features to determine a cross-section geometry of the blood vessel as a function of time; control the plurality of ultrasonic transducers to periodically sense the blood vessel and produce signals representative of a plurality of features of the blood vessel; and track the plurality of features of the blood vessel, using the signals representative of the plurality of features to determine a cross-section geometry of the blood vessel as a function of time; wherein the signals produced by the plurality of ultrasonic transducers signals represent an ultrasonic image of the blood vessel; and wherein the instructions when executed cause the controller to assign a first plurality of windows to a first feature of the plurality of features within a first frame, and a second plurality of windows to the first feature within a second frame, wherein the second frame is subsequent to the first frame, and to perform a two dimensional cross-correlation between the signals representative of the first feature within the first frame and the signals representative of the first feature within the second frame using at least one convex constraint. <EOS>