SYSTEM AND METHOD FOR DETERMINING VIDEO-BASED PULSE TRANSIT TIME WITH TIME-SERIES SIGNALS

• US 20140012142A1
• Filed: 09/13/2013
• Published: 01/09/2014
• Est. Priority Date: 02/21/2012
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: MESTHA, Lalit Keshav, KYAL, Survi
• Granted Patent: US 9,351,649 B2
• Time in Patent Office: Days
• US Class Current: 600/480
• CPC Class Codes: A61B 5/0075 by spectroscopy, i.e. measuring spectra, e.g. Raman spectroscopy, infrared absorption spectroscopy A61B5/0071 takes precedence
• CPC Class Codes: A61B 5/02125 of pulse wave propagation time
• CPC Class Codes: A61B 5/02427 Details of sensor
• CPC Class Codes: G06T 2207/30076 Plethysmography
• CPC Class Codes: G06T 2207/30104 Vascular flow; Blood flow; Perfusion
• CPC Class Codes: G06T 7/0012 Biomedical image inspection

Abstract

What is disclosed is a system and method for determining a subject of interest'"'"'s arterial pulse transit time from time-varying source signals generated from video images. In one embodiment, a video imaging system is used to capture a time-varying source signal of a proximal and distal region of a subject of interest. The image frames are processed to isolate localized areas of a proximal and distal region of exposed skin of the subject. A time-series signal for each of the proximal and distal regions is extracted from the source video images. A phase angle is computed with respect to frequency for each of the time-series signals to produce respective phase v/s frequency curves for each region. Slopes within a selected cardiac frequency range are extracted from each of the phase curves and a difference is computed between the two slopes to obtain an arterial pulse transit time for the subject.

Claims

1. A method for determining an arterial pulse transit time between a proximal and distal region of a subject of interest from source video images acquired using a video imaging system, the method comprising:

receiving a time-varying source images acquired over at least one channel of a video imaging system, said source images comprising video images captured of a proximal and distal region of an area of exposed skin of a subject of interest;

extracting, from said source images, a time-series signal for each of said proximal and distal regions;

computing a phase angle with respect to frequency for each of said time-series signals to obtain respective phase v/s frequency curves;

extracting, from each of said phase v/s frequency curves, corresponding slopes within a selected cardiac frequency range; and

computing a difference between said extracted slopes, said difference comprising an arterial pulse transit time for said subject between said proximal and distal regions.

2. The method of claim 1, wherein said time-varying source signal comprises any combination of:

NIR images, RGB images, RGB with NIR images, multispectral images, thermal images, and hyperspectral images.

3. The method of claim 1, further comprising converting said time-series signals to a frequency domain via a Fourier transformation.

4. The method of claim 1, wherein said proximal and distal regions comprise, respectively, a first and second localized area of said subject.

5. The method of claim 1, wherein said selected cardiac frequency range is between 0.75 to 4.0 Hz.

6. The method of claim 1, further comprising determining, from said arterial pulse transit time, any of:

a blood pressure in said subject'"'"'s vascular network, a blood vessel dilation over time, a blood vessel blockage, a blood flow velocity, and the existence of a peripheral neuropathy.

7. The method of claim 1, further comprising:

processing said video images to determine a region of skin; and

isolating said proximal and distal regions from said skin regions.

8. The method of claim 1, wherein said video images are acquired by a single NIR channel, further comprising:

partitioning frames from said channel for each region into a non-skin region and a skin region; and

performing source separation to obtain both a heart rate signal and said phase v/s frequency curve.

9. The method of claim 1, wherein, in advance of extracting said time-series signals, further comprising compensating for any of:

a motion induced blur, an imaging blur, harmonics which are not related to components of said subject'"'"'s cardiac pulse, and slow illuminant variation.

10. The method of claim 1, wherein said video imaging system used to acquire said time-varying source images of said proximal and distal regions comprises two video cameras, a first video camera acquiring a first video of said proximal region and a second video camera acquiring a second video of said distal region.

11. The method of claim 10, wherein, in advance of extracting said time-series signals, further comprising synchronizing said first and second videos with respect to time.

12. The method of claim 1, wherein the video imaging system is used in a non-contact, remote sensing environment.

13. A video based system for determining an arterial pulse transit time between a proximal and distal region of a subject of interest from source video images acquired using a video camera, the system comprising:

a video imaging system for capturing a time-varying source images over at least one channel, said source images comprising video images captured of a proximal and distal region of an exposed area of skin of a subject of interest; and

a processor in communication with said video camera and a memory, said processor executing machine readable instructions for performing;

receiving a time-varying source images acquired over at least one channel of a video imaging system, said source images comprising video images captured of a proximal and distal region of an area of exposed skin of a subject of interest;

extracting, from said source images, a time-series signal for each of said proximal and distal regions;

computing a phase angle with respect to frequency for each of said time-series signals to obtain respective phase v/s frequency curves;

extracting, from each of said phase v/s frequency curves, corresponding slopes within a selected cardiac frequency range; and

computing a difference between said extracted slopes, said difference comprising an arterial pulse transit time for said subject between said proximal and distal regions.

14. The system of claim 13, wherein said time-varying source signal comprises any combination of:

NIR images, RGB images, RGB with NIR images, multispectral images, thermal images, and hyperspectral images.

15. The system of claim 13, further comprising converting said time-series signals to a frequency domain via a Fourier transformation.

16. The system of claim 13, wherein said proximal and distal regions comprise, respectively, a first and second localized area of said subject.

17. The system of claim 13, wherein said cardiac frequency range is between 0.75 to 4.0 Hz.

18. The system of claim 13, further comprising determining, from said arterial pulse transit time, any of:

a blood pressure in said subject'"'"'s vascular network, a blood vessel dilation over time, a blood vessel blockage, a blood flow velocity, and the existence of a peripheral neuropathy.

19. The system of claim 13, further comprising:

processing said video images to determine a region of skin; and

isolating said proximal and distal regions from said skin regions.

20. The system of claim 13, wherein said video images are acquired by a single NIR channel, further comprising:

partitioning frames from said channel for each region into a non-skin region and a skin region; and

performing source separation to obtain both a heart rate signal and said phase v/s frequency curve.

21. The system of claim 13, wherein, in advance of extracting said time-series signals, further comprising compensating for any of:

a motion induced blur, an imaging blur, harmonics which are not related to components of said subject'"'"'s cardiac pulse, and slow illuminant variation.

22. The system of claim 13, wherein said video imaging system used to acquire said time-varying source images of said proximal and distal regions comprises two video cameras, a first video camera acquiring a first video of said proximal region and a second video camera acquiring a second video of said distal region.

23. The system of claim 22, wherein, in advance of extracting said time-series signals, further comprising synchronizing said first and second videos with respect to time.

24. The system of claim 13, wherein the video imaging system is used in a non-contact, remote sensing environment.