System and method for monitoring blood perfusion
An apparatus (and method) is for monitoring blood perfusion. A plurality of photoplethysmography, PPG, signals are acquired indicative of light detected in a region of interest of tissue at a plurality of respective locations within the region. The PPG signals are processed to determine an amplitude and preferably also a phase of each of the plurality of PPG signals, and a blood perfusion level is determined at the region of interest based on the amplitudes and preferably also the phases of the PPG signals.
1 . An apparatus for monitoring blood perfusion, the apparatus comprising a processor configured to:
acquire, from at least one sensor, a plurality of photoplethysmography, PPG, signals indicative of light detected in a region of interest of tissue at a plurality of respective locations within the region;
process the acquired plurality of PPG signals to determine an amplitude and a phase of each of the plurality of PPG signals, wherein the phase indicates a relative pulse arrival time to the respective locations; and
determine a blood perfusion level at the region of interest based on a ratio of a first value indicating the amplitudes of the PPG signals within the region of interest and a second value indicating a measure of distribution of phases of the PPG signals across the region of interest.
2 . The apparatus of claim 1 , wherein the processor is configured to:
determine the first value from an average of the determined amplitude value for the locations within the region of interest; and
determine the second value from a distribution of the phase values for the locations within the region of interest.
3 . The apparatus of claim 2 , wherein the first value is a median or mean of the amplitudes for the locations.
4 . The apparatus of claim 2 , wherein the second value is an interquartile range or standard deviation of the phase for the locations.
5 . The apparatus of claim 1 , wherein the processor is configured to determine the blood perfusion at the region of interest as a value relative to the blood perfusion for the region of interest at a previous time.
6 . The apparatus of claim 1 , wherein the processor is further configured to:
acquire from at least one further sensor a plurality of photoplethysmography, PPG, signals, indicative of light detected in a reference region and to determine a blood perfusion level for the reference region; and
determine the blood perfusion at the region of interest as a value relative to the blood perfusion for the reference region.
7 . The apparatus of claim 1 , wherein the at least one sensor is a non-contact PPG sensor.
8 . A method for monitoring blood perfusion, comprising:
acquiring, from at least one sensor, a plurality of photoplethysmography, PPG, signals indicative of light detected in a region of interest of tissue at a plurality of respective locations within the region;
processing the acquired plurality of PPG signals to determine an amplitude and a phase of each of the plurality of PPG signals, wherein the phase indicates a relative pulse arrival time to the respective locations; and
determining a blood perfusion level at the region of interest based on a ratio of a first value indicating the amplitudes of the PPG signals within the region of interest and a second value indicating a measure of distribution of phases of the PPG signals across the region of interest.
9 . The method of claim 8 , comprising:
determining the first value relating to an average of the determined amplitude value for the locations within the region of interest; and
determining the second value relating to a distribution of the phase values for the locations within the region of interest.
10 . The method of claim 9 , wherein the first value is a median or men of the amplitudes for the locations and the second value is an interquartile range or standard deviation of the phase for the locations.
11 . The method of claim 9 , comprising:
determining the blood perfusion at the region of interest as a value relative to the blood perfusion for the region of interest at a previous time; or
determining the blood perfusion at the region of interest as a value relative to the blood perfusion for a reference region.
12 . A computer program comprising computer program code means which is adapted, when said program is run on a computer of an apparatus for monitoring blood perfusion which includes a PPG sensor, to implement the method of claim 9 .