Minimally invasive image-based determination of carbon dioxide (CO
View Patent ↗What is disclosed is a system and method for image-based determination of carbon dioxide (CO 2 ) concentration in exhaled breath. In one embodiment, an image of the exhaled airstream of a subject of interest is received. The image is captured using a mid-wave infrared camera system having an optical filter tuned to the infrared absorption band of CO 2 . The image is preprocessed to isolate a region of pixels containing the exhaled airstream and intensity values of pixels in the identified region are normalized by a value of a known radiance such as that of the subject's nose or face. The image is analyzed to determine CO 2 concentration levels of the exhaled airstream using a calibration curve which relates pixel intensity to CO 2 concentrations. The calibration curve is derived using a physics-based parameterized model. The CO 2 concentration levels are determined and communicated to a computer workstation. Various embodiments are disclosed.
1. A method for image-based determination of carbon dioxide (CO 2 ) concentration in exhaled breath in a non-contact, minimally invasive, respiration measurement environment, the method comprising:
receiving at least one IR image of the exhaled airstream of a subject of interest, said image having been captured using a mid-wave infrared camera system having at least one optical filter tuned to an infrared absorption band of CO 2 , each of said received images comprising, in part, an array of pixels having respective measured intensity values obtained at an absorption band of CO 2 ;
processing, via a processor, said IR image to isolate pixels in regions associated with background objects in said image, an area of said subject's nose and face, and said exhaled airstream; and to obtain a digital intensity value for each region comprising values of I O , I BB and I CO 2 , respectively, where I O is the intensity value in said area of said subject's nose and face, I BB is the intensity value in said background, and I CO 2 is the intensity value of said exhaled airstream;
determining respective radiances R BB and R O from each of said digital intensity values I BB and I O , where R BB is a background radiance and, R O is a radiance of said nose and face;
determining a radiance of said subject's exhaled airstream, R CO 2 , based upon said radiances R BB and R O and said digital intensities I O , I BB and I CO 2 ; and
determining CO 2 concentration level of said subject's exhaled airstream based on said determined radiance R CO 2 .
2. The method of claim 1 , wherein said camera system is designed to collect the light emitted by the roto-vibrational radiation from CO 2 molecules, said system including an infrared camera with a sensitivity band that includes 4.0-4.5 um and a spectral band-pass filter which allows CO 2 emission light to enter a lens of said camera.
3. The method of claim 1 , wherein said optical filter comprises a narrow band-pass filter which increases a contrast of CO 2 relative to background radiation.
4. The method of claim 1 , further comprising, in the instance wherein a video stream of time sequential images has been received, determining a respiration rate for said subject of interest based upon a mathematical analysis of time-dynamics of an inhalation-exhalation pattern of said subject.
5. The method of claim 4 , further comprising using said CO 2 concentration levels and said respiration rate to determine whether said subject of interest is in a state of any of: hyperventilation and hypoventilation.
6. The method of claim 1 , further comprising communicating said CO 2 concentration levels to any of: a memory, a storage device, a graphical display, a telephonic messaging system, and a computer workstation.
7. The method of claim 1 , wherein said radiance R CO 2 comprises:
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8. A system for image-based determination of carbon dioxide (CO 2 ) concentration in exhaled breath, the system comprising:
a processor in communication with a camera system, said processor configured to execute machine readable instructions for performing the method of:
receiving at least one IR image of the exhaled airstream of a subject of interest, said image having been captured using a mid-wave infrared camera system having at least one optical filter tuned to an infrared absorption band of CO 2 , each of said received images comprising, in part, an array of pixels having respective measured intensity values obtained at an absorption band of CO 2 ;
processing said IR image to isolate pixels in regions associated with background objects in said image, an area of said subject's nose and face, and said exhaled airstream; and to obtain a digital intensity value for each region comprising values of I O , I BB and I CO 2 , respectively, where I O is the intensity value in said area of said subject's nose and face, I BB is the intensity value in said background, and I CO 2 is the intensity value of said exhaled airstream;
determining respective radiances R BB and R O from each of said digital intensity values I BB and I O , where R BB is a background radiance and, R O is a radiance of said nose and face;
determining a radiance of said subject's exhaled airstream, R CO 2 , based upon said radiances R BB and R O and said digital intensities I O , I BB and I CO 2 ; and
determining CO 2 concentration level of said subject's exhaled airstream based on said determined radiance R CO 2 .
9. The system of claim 8 , wherein said camera system is designed to collect the light emitted by the roto-vibrational radiation from CO 2 molecules, said system including an infrared camera with a sensitivity band that includes 4.0-4.5 um and a spectral band-pass filter which allows CO 2 emission light to enter a lens of said camera.
10. The system of claim 8 , wherein said optical filter comprises a narrow band-pass filter which increases a contrast of CO 2 relative to background radiation.
11. The system of claim 8 , further comprising, in the instance wherein a video stream of time sequential images has been received, determining a respiration rate for said subject of interest based upon a mathematical analysis of time-dynamics of an inhalation-exhalation pattern of said subject.
12. The system of claim 11 , further comprising using said CO 2 concentration levels and said respiration rate to determine whether said subject of interest is in a state of any of: hyperventilation and hypoventilation.
13. The system of claim 8 , further comprising communicating said CO 2 concentration levels to any of: a memory, a storage device, a graphical display, a telephonic messaging system, and a computer workstation.
14. The system of claim 8 , wherein said radiance R CO 2 comprises:
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15. A non-transitory computer useable medium having a computer readable program for image-based determination of carbon dioxide (CO 2 ) concentration in exhaled breath in a non-contact, minimally invasive, respiration measurement environment embodied thereon that, when executed on a computer, causes the computer to perform a method comprising:
receiving at least one IR image of the exhaled airstream of a subject of interest, said image having been captured using a mid-wave infrared camera system having at least one optical filter tuned to an infrared absorption band of CO 2 , each of said received images comprising, in part, an array of pixels having respective measured intensity values obtained at an absorption band of CO 2 ;
processing said IR image to isolate pixels in regions associated with background objects in said image, an area of said subject's nose and face, and said exhaled airstream; and to obtain a digital intensity value for each region comprising values of I O , I BB and I CO 2 , respectively, where I O is the intensity value in said area of said subject's nose and face, I BB is the intensity value in said background, and I CO 2 is the intensity value of said exhaled airstream;
determining respective radiances R BB and R O from each of said digital intensity values I BB and I O , where R BB is a background radiance and, R O is a radiance of said nose and face;
determining a radiance of said subject's exhaled airstream, R CO 2 , based upon said radiances R BB and R O and said digital intensities I O , I BB and I CO 2 ; and
determining CO 2 concentration level of said subject's exhaled airstream based on said determined radiance R CO 2 .
16. The non-transitory computer useable medium of claim 15 , wherein said camera system is designed to collect the light emitted by the roto-vibrational radiation from CO 2 molecules, said system including an infrared camera with a sensitivity band that includes 4.0-4.5 μm and a spectral band-pass filter which allows only CO 2 emission light to enter a lens of said camera.
17. The non-transitory computer useable medium of claim 15 , wherein said optical filter comprises a narrow band-pass filter which increases a contrast of CO 2 relative to a background radiation.
18. The non-transitory computer useable medium of claim 15 , further comprising, in the instance wherein a video stream of time sequential images has been received, determining a respiration rate for said subject of interest based upon a mathematical analysis of time-dynamics of an inhalation-exhalation pattern of said subject.
19. The non-transitory computer useable medium of claim 18 , further comprising using said CO 2 concentration levels and said respiration rate to determine whether said subject of interest is in a state of any of: hyperventilation and hypoventilation.
20. The non-transitory computer useable medium of claim 15 , further comprising communicating said CO 2 concentration levels to any of: a memory, a storage device, a graphical display, a telephonic messaging system, and a computer workstation.
21. The non-transitory computer useable medium of claim 15 , wherein said radiance R CO 2 comprises:
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