| CPC A61B 8/06 (2013.01) [A61B 8/0866 (2013.01); A61B 8/0883 (2013.01); A61B 8/4227 (2013.01); A61B 8/4483 (2013.01); A61B 8/461 (2013.01); A61B 8/488 (2013.01); A61B 8/5207 (2013.01)] | 17 Claims |
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1. A method for monitoring a characteristic of blood flow in a vertebrate animal subject, wherein the characteristic of blood flow relates to the velocity of the blood flow and/or wherein the characteristic of blood flow relates to the total blood flow within a region within the subject, the method comprising:
transmitting unfocussed plane-wave ultrasound pulses into the subject from a single-element ultrasound transducer that is fastened to the subject;
receiving reflections of the ultrasound pulses at the single-element ultrasound transducer;
generating a time series of pulse-Doppler response signals from the received reflections;
selecting a depth or depth range at which to monitor the characteristic of blood flow within the subject;
identifying a time-series of one or more heartbeats from the pulse-Doppler response signals from the selected depth or depth range;
evaluating a quality metric for each of the identified one or more heartbeats from the selected depth or depth range, by comparing data associated with successive heartbeats by autocorrelation, to determine a respective quality value associated with each of the identified one or more heartbeats, wherein the quality value associated with each heartbeat depends on a similarity of data derived from the pulse-Doppler response signals for the respective heartbeat, to data derived from the pulse-Doppler response signals for a preceding heartbeat and wherein a higher value of the quality metric indicates a higher confidence that a heartbeat has been identified correctly;
determining a set of valid heartbeats consisting of heartbeats for which the respective quality value exceeds a threshold level;
processing the pulse-Doppler response signals from the selected depth or depth range over a time window to determine values of the characteristic of blood flow within the subject, over time, at the selected depth or depth range for the set of valid heartbeats, comprising excluding from the time window periods of time covering pulse-Doppler response signals for which the identified heartbeats are determined as having a quality value below the threshold level, so as to evaluate the characteristic of blood flow only over those heartbeats for which the associated quality value exceeds the threshold level; and
detecting when one or more of the determined values of the characteristic of blood flow, for the set of valid heartbeats, satisfies a predetermined alert criterion, and, in response, signalling an audible or visual alert.
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