Method and apparatus for vital signs measurement
Inventors
GUAZZI, Alessandro • MONTOYA, Mauricio Villarroel • Tarassenko, Lionel
Assignees
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Publication Number
US-10939852-B2
Publication Date
2021-03-09
Expiration Date
Abstract
A method of monitoring changes in oxygen saturation of a subject by analysing a three colour channel video image of the exposed skin of the subject. Within each colour channel a normalised signal obtained by dividing the intensity signal by its mean value, and the normalised signals are averaged across plural regions of interest within the exposed skin area image of the subject. Regions of interest are selected on the basis of the signal-to-noise ratios for the heart rate and breathing rate components. A single representative waveform for each colour channel is obtained by signal averaging and the ratio of the amplitudes of the representative waveforms from two different colour channels, e.g. blue and red, is taken. The changes in the ratio of amplitudes is output as a measure of changes in blood oxygen saturation.
Core Innovation
The invention determines changes in blood oxygen saturation of a subject by obtaining a video image of an area of exposed skin, where the video image comprises signals representing intensity in at least two different colour channels. A plurality of regions of interest is defined within the exposed skin area, and signals from the regions of interest are processed to represent changes in blood oxygen saturation over time.
For each region of interest, the invention determines a signal to noise ratio of a heart rate or breathing rate frequency component of one or both colour channel signals, and uses this determination to decide whether to reject or not reject the region of interest. The colour channel signals from non-rejected regions of interest are then normalised in each colour channel by dividing each signal by its baseline component.
After normalisation, the invention determines a ratio of the amplitudes of the normalised signals from two colour channel signals and outputs changes over time in the ratio as representing changes in blood oxygen saturation. The disclosed approach uses the time-varying amplitude ratio between the selected colour channels as the representation of oxygen saturation change.
Claims Coverage
The partial content provides two independent claims (a method and a system). Across these independent claims, the inventive coverage centers on video-based exposed-skin analysis with multiple colour channels, region-of-interest selection using signal to noise ratio for heart rate and/or breathing rate frequency components, rejection of low-quality regions of interest, baseline-component normalisation of colour-channel signals, and outputting changes over time in an inter-channel amplitude ratio as representing blood oxygen saturation change.
Video image of exposed skin with intensity signals in at least two colour channels
Obtaining a video image of an area of exposed skin of the subject, the video image comprising signals representing intensity in at least two different colour channels.
Regions of interest in exposed skin
Defining in the image a plurality of regions of interest in said area of exposed skin of the subject.
Signal to noise ratio of heart rate or breathing rate frequency component per region of interest
Determining a signal to noise ratio of a heart rate or breathing rate frequency component of one of the colour channel signals or both for each region of interest.
Rejecting or not rejecting regions of interest based on signal to noise ratio
Determining whether to reject or not reject regions of interest based on the determined signal to noise ratio of a heart rate or breathing rate frequency component or both.
Normalising colour-channel signals by dividing by baseline component
Normalising the signal in each of the colour channels by dividing each of the signals by its baseline component.
Ratio of amplitudes of normalised signals from two colour channels
Determining the ratio of the amplitudes of the normalised signals from two of the colour channel signals and outputting changes over time in the ratio as representing changes in blood oxygen saturation of the subject.
System comprising video camera, signal processor, and display for outputting changes over time in the ratio
A system for determining changes in blood oxygen saturation comprising a video camera, a signal processor adapted to receive signals and process them by normalising by baseline component, defining regions of interest, determining signal to noise ratio, rejecting regions of interest, determining the ratio of amplitudes of normalised signals for non-rejected regions of interest, and outputting changes over time in the ratio, and a display adapted to display the changes over time in the ratio.
The independent claims cover both a method and a system that compute changes in blood oxygen saturation by forming an inter-colour-channel amplitude ratio from normalised colour-channel signals. The claims require region-of-interest definition, determination of signal to noise ratio for heart rate or breathing rate frequency components per region, rejection decisions based on that signal to noise ratio, and outputting changes over time in the ratio as representing oxygen saturation changes.
Stated Advantages
Not explicitly described in patent.
Documented Applications
Not explicitly described in patent.
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