Non-contact and passive measurement of arterial pulse through thermal IR imaging, and analysis of thermal IR imagery

• US 20080045847A1
• Filed: 07/02/2007
• Published: 02/21/2008
• Est. Priority Date: 06/30/2006
• Status: Active Grant

• Current Assignee: University of Louisville
• Original Assignee: University of Louisville
• Inventors: Chekmenev, Sergey, Farag, Aly
• Granted Patent: US 8,360,986 B2
• Time in Patent Office: Days
• US Class Current: 600/500
• CPC Class Codes: A61B 5/0082 adapted for particular medical purposes
• CPC Class Codes: A61B 5/02055 Simultaneously evaluating both cardiovascular condition and temperature
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/726 using Wavelet transforms

Abstract

A non-contact, passive method for measurement of arterial pulse from areas such as the major superficial arteries of the body through analysis of thermal IR images acquired by passive thermal IR imaging sensors, and through the modeling of the pulsatile nature of the blood flow and arterial pulse propagation in the circulatory system. The method is automatic and does not need operator input. The output waveform readily contains the information on heart rate, cardiac interbeat intervals, heart-rate variability and other features inherent in arterial pulse. The potential applications of this method, device and system are in the fields of non-contact and passive measuring cardiovascular and autonomic regulatory functions, mental and emotional loads, assessment of health in general, prediction of ill physiological and mental conditions, smart rooms, human-computer interaction, polygraph testing, intent identification, and any other fields where non-contact, passive monitoring of heart-rate and its variability is needed.

Claims

1. A method for measuring of arterial pulse comprising steps of:

obtaining a sequence of thermal infrared images from a subject, wherein each said thermal infrared image is obtained without skin contact with said subject;

performing a first analysis of said sequence of obtained thermal infrared images to detect at least one region of interest for further analysis;

performing a second analysis of said sequence of obtained thermal infrared images to track said at least one region of interest, wherein said second analysis includes detecting a corresponding spatial location of each of said at least one region of interest;

performing a third analysis of said at least one region of interest to select at least one configuration of a region of measurement of arterial pulse within said corresponding region of interest; and

determining at least one arterial pulse waveform from said selected configuration of region of measurement.

2. The method according to claim 1, wherein said first analysis includes automatic selection of a pixel area using multiscale image decomposition and multiresolution analysis.

3. The method according to claim 2, wherein:

said multiscale decomposition analysis includes at least one of the following;

Laplacian pyramid structures, Gaussian pyramid structures, Gradient Pyramid structures, ratio-of-low pass pyramid structures and wavelet decomposition schemes; and

said multiresolution analysis includes application of convolution filters to determine said at least one region of interest.

4. The method according to claim 1, wherein said second analysis automatically tracks said at least one region of interest on every thermal infrared image using at least one of the following:

Laplacian pyramid structures, Gaussian pyramid structures, gradient pyramid structures, ratio-of-low pass pyramid structures and wavelet decomposition schemes; and

said multiresolution analysis includes application of convolution filters to “

determine salient, robust and permanent features for tracking of said region of interest.

5. The method according to claim 1, wherein said second analysis automatically tracks said at least one region of interest on every thermal infrared image using at least one of the following:

Laplacian pyramid structures, Gaussian pyramid structures, gradient pyramid structures, ratio-of-low pass pyramid structures and wavelet decomposition schemes; and

said multiresolution analysis includes application of convolution filters for identification and configurations of said region of measurement.

6. The method according to claim 1, wherein said second analysis automatically tracks said at least one region of interest on every thermal infrared image using at least one of the following:

Laplacian pyramid structures, Gaussian pyramid structures, gradient pyramid structures, ratio-of-low pass pyramid structures and wavelet decomposition schemes; and

said multiresolution analysis includes application of convolution filters for identification of arterial pulse structures in measurement of arterial pulse waveforms.

7. The method according to claim 1, wherein said second analysis automatically tracks said at least one region of interest on every thermal infrared image using at least one of the following:

Laplacian pyramid structures, Gaussian pyramid structures, gradient pyramid structures, ratio-of-low pass pyramid structures and wavelet decomposition schemes; and

said multiresolution analysis includes application of convolution filters for determining periodicity measures for the arterial pulse waveforms measured from a plurality of said configurations.

8. The method according to claim 1, wherein said second analysis automatically tracks said at least one region of interest on every thermal infrared image using at least one of the following:

Laplacian pyramid structures, Gaussian pyramid structures, gradient pyramid structures, ratio-of-low pass pyramid structures and wavelet decomposition schemes; and

said multiresolution analysis includes application of convolution filters for filtering the arterial pulse waveforms to minimize noise and data irrelevant to arterial pulse structures.

9. The method according to claim 1, wherein said second analysis automatically tracks said at least one region of interest on every thermal infrared image using at least one of the following:

Laplacian pyramid structures, Gaussian pyramid structures, gradient pyramid structures, ratio-of-low pass pyramid structures and wavelet decomposition schemes; and

said multiresolution analysis includes application of convolution filters for accurate localization of arterial pulse peaks within the arterial pulse waveform.

10. The method according to claim 1, wherein said second analysis automatically tracks said at least one region of interest on every thermal infrared image to establish a spatial location of said at least one region of interest on every frame.

11. The method according to claim 1, wherein said second analysis comprises:

making use of a global and local tracker to perform a robust tracking of said at least one region of interest.

12. The method according to claim 1, wherein said third analysis automatically identifies said at least one configuration of a region of measurement of the arterial pulse using quasi-periodic nature of the arterial pulse.

13. The method according to claim 1, wherein said at least one region of interest is a region in a vicinity of major superficial arteries of said subject

14. The method according to claim 13, wherein said region of interest corresponds to one of the following:

a superficial temporal artery, a frontal branch of a superficial temporal artery, a carotid artery, a radial artery of an arm and a brachial artery of an arm.

15. The method according to claim 1, wherein said third analysis comprises:

performing at least one multiscale decomposition with at least one appropriate decomposition function at each frame of said thermal infrared images;

constructing various configurations of said region of measurement in terms of at least one of scale, orientation, size and location, within limits of said at least one tracked region of interest;

computing the arterial pulse waveform from every said region of measurement configuration;

applying continuous wavelet analysis to every said arterial pulse waveform to detect arterial pulse structures;

running a periodicity detection algorithm on every set of said detected arterial pulse structures;

computing a periodicity measure for every said set of detected arterial pulse structures; and

selecting and outputting at least one optimal region of measurement configurations based on said computed periodicity measure.

16. The method according to claim 1, wherein said third analysis comprises:

performing analysis of said sequence of obtained thermal infrared images to identify heat patterns which are triggered by effects of arterial pulse propagation;

computing raw arterial pulse waveforms from a plurality of configurations of said region of measurement based on at least one of;

scale, orientation, topology, size, location;

estimate a confidence score for every computed raw arterial pulse waveform, where said confidence score represents a certain degree of relevance to pulsatile nature of arterial pulse phenomena;

identifying at least one appropriate configuration of region of measurement based on comparing said estimated confidence scores for every configuration of region of measurement;

outputting one or more of said appropriate configurations of region of measurement for determining the arterial pulse.

17. The method according to claim 1, wherein said step of obtaining a sequence of infrared thermal images is performed by measuring and imaging the thermal infrared energy naturally radiated from said subject, without projecting any kind of energy to said subject.

18. The method according to claim 1, wherein said step of determining an arterial pulse waveform determines the arterial pulse waveform based on measurement of thermal variations caused by arterial blood pressure wave propagation.

19. A system for obtaining an arterial pulse waveform comprising:

a non-contact and passive thermal radiation imaging sensor configured and arranged to obtain a sequence of thermal infrared images of a subject containing one or more regions of interest;

means for thermal infrared data translation, storing, processing and retrieving of the obtained sequence of thermal infrared images;

means for detecting at least one region of interest in the obtained sequence of thermal infrared images means for tracking aid at least one region of interest in the obtained sequence of thermal IR images

means for identification of one or more of faithful configurations of region of measurement using pulsatile nature of arterial pulse phenomena; and

means for determining the arterial pulse by analyzing the faithful configuration of region of measurement.

20. The system according to claim 19, wherein said thermal infrared images comprise electromagnetic wavelengths between approximately 3-5 μ

m and 8-14 μ

m.

21. A system for obtaining a pulse waveform comprising:

a thermal sensor configured and arranged to obtain an image of an observation area of skin;

means for automatically detecting a region of measurement, which is defined as a smaller area within said observation area, using the quasi-periodic nature of thermal patterns obtained from said thermal sensor; and

means for determining a pulse waveform by analyzing said region of measurement.

22. The system according to claim 21, wherein:

said thermal patterns comprise wavelengths between approximately 8 μ

m and approximately 14 μ

m; and

said thermal patterns are arterial thermal patterns.

23. A method for measuring heart function, comprising the steps of:

obtaining a sequence of infrared thermal images of an observation area of skin;

decomposing said sequence of infrared thermal images into a set of representations of a plurality of different scales;

selecting an appropriate scale representation on the basis of amount of heat information relevant to a pulse waveform; and

determining a pulse waveform using said selected scale representation.

24. The method according to claim 23, wherein:

said plurality of different scales includes at least a first scale and a second scale, where said second scale is more fine than said first scale;

said second scale is selected during said selecting step; and

using said first scale for tracking, from frame to frame, a region of interest within the observation area.