TEMPORAL OXIMETER

• US 20120093389A1
• Filed: 06/11/2010
• Published: 04/19/2012
• Est. Priority Date: 06/12/2009
• Status: Active Grant

• Current Assignee: Oxymap Ehf
• Original Assignee: Oxymap Ehf
• Inventors: Halldorsson, Gisli Hreinn, Karlsson, Robert Arnar, Hardarson, Sveinn Hakon, Stefannsson, Einar
• Granted Patent: US 9,579,052 B2
• Time in Patent Office: Days
• US Class Current: 382/134
• CPC Class Codes: A61B 5/14535 for measuring haematocrit
• CPC Class Codes: A61B 5/14555 specially adapted for the eye fundus
• CPC Class Codes: A61B 5/726 using Wavelet transforms

Abstract

The present invention discloses a method and an apparatus for detecting change in retinal oxygen saturation over time. The method comprises the steps of capturing a first group of images of two or more wavelengths, calculating oxygen saturation of a vessel in the first group of images, storing the first group of images on a data storage device, capturing a second group of images of two or more wavelengths, calculating the oxygen saturation of a vessels in the second group of images, storing the second group of images on a data storage device, spatially registering the pair of the group of images, captured at different time and calculate the change in oxygen saturation.

Claims

1-25. -25. (canceled)

26. A method for detecting change in optical density over time, said method comprising the steps of:

capturing a first group of images of two or more narrow band wavelengths, wherein at least one of said narrow band wavelengths is at one or more isobestic wavelengths, by means of camera;

measuring optical density of one or more areas of interest in the first group of images;

storing said first group of images on a data storage device;

capturing a second group of images of two or more narrow band wavelengths, wherein said at least one of said narrow band wavelengths is at one or more isobestic wavelengths, by means of camera;

measuring the optical density of one or more areas of interest in the second group of images;

storing said second group of images on a data storage device; and

said pair of said group of images, captured at different time is spatially registered, by mapping features in the first group of images to the corresponding features of the second group of images,

wherein image comparability of said first and second groups of images is captured at said one or more narrow band wavelengths, is quantized based on said optical density, to determine if comparison between oxygen saturation measurements at different point in time is valid, and said change in optical density is measured by calculating the difference of said optical density between said pair of image groups.

27. A method according to claim 26, wherein said quantized image comparability comprises the steps of:

measuring the optical density of said images at one or more isobestic wavelength;

scaling said optical density according to vessel width; and

measuring the difference of said scaled optical density between said pair of image groups by calculating the difference of said optical densities.

28. A method according to claim 26, wherein said quantized image comparability comprises the steps of:

Measuring the optical density of said images at one or more isobestic wavelength;

measuring relative change in hematocrit;

scaling said optical density according to vessel width and relative change in hematocrit; and

measuring the change of said scaled optical density between said pair of image groups by calculating the difference of said optical densities.

29. A method according to claim 26, wherein said isobestic wavelength is a narrow band wavelength centered around said isobestic wavelength.

30. A method according to claim 26, wherein said quantized image comparability comprises the steps of:

measuring the background reflectance of said images by filtering and averaging the background; and

measuring the changes of said background reflectance between said pair of image groups by calculating the ratio of said background reflection.

31. A method according to claim 30, wherein said changes in background reflectance comprises the step of:

measuring the background reflection on either side of said vessel calculating the ratio of said background reflection on either side of the vessel.

32. A method according to claim 30, wherein said changes in background reflectance comprises the step of:

measuring change in texture on either side of said vessel by calculating texture variability of the area on either side of said vessel.

33. A method according to claim 26, wherein said quantized image comparability comprises the steps of:

detect the illumination distribution of the optical system, by capturing an image of a homogenous region; and

calculating the difference in illumination distribution of the area where the vessel is located within the said images based on the illumination distribution.

34. A method according to claim 26, wherein said quantized image comparability comprises the step of:

measuring the vessel shift distance between successive groups of images, by applying distance metric.

35. A method according to claim 26, wherein said quantized image comparability comprises the step of:

using one or more image quality parameters to reject images.

36. A method according to claim 35, wherein said quantized image quality parameter comprises the steps of:

measuring the information degradation of said images, by degrading each image with wavelet transformation function;

quantizing wavelets coefficients;

transforming the image back;

measuring the similarity between original and degraded image.

37. A method according to claim 35, wherein said quantized image quality parameter comprises the step of:

measuring the focus of said images by applying contrast measurements.

38. A method according to claim 35, wherein said quantized image quality parameter comprises the step of:

detecting if lens reflection is present in said images, by applying morphological filter to detect bright area in the image.

39. A method according to claim 26, wherein said change in optical density is used to calculate change in parameters derived from the optical density.

40. A method according to claim 39, wherein said change in parameters derived from optical density is the difference between the parameters derived from the optical density level calculated from the said pair of groups of images captured at different time.

41. A method according to claim 39, wherein standard deviation of population similar to the one being measured is used to determine if the said change in the parameters derived from the optical density is statistically significant change.

42. A method according to claim 39, wherein said parameter is oxygen saturation.

43. A computer program or suite of computer programs embodied on a non-transitory computer readable medium, and so arranged such that when executed on a processor said program or suite of programs cause(s) said processor to perform the method of claim 26.

44. A non-transitory computer readable data storage medium storing the computer program or at least one of the suites of computer programs of claim 43.

45. A computer program product according to claim 43, wherein a database resides on the same computer as said computing program product.

46. A computer program product according to claim 43, wherein a database, and said computing program product reside on different computers.

47. An apparatus for measuring change in optical density over time, said apparatus comprising:

a camera, wherein said camera captures a group of images of two or more narrow band wavelengths, wherein at least one of said narrow band wavelengths is at one or more isobestic wavelengths;

a data storage device;

a computer wherein said computer receives said group of images from said camera and stores said group of images on said data storage device;

said computer is furthermore adapted to calculate the optical density in said group of images;

said computer is furthermore adapted to evaluate comparability between successive group of images; and

said computer is adapted to spatially register a pair of said group of images captured at different time by mapping features in the first group of images to the corresponding features in the second group of images,

wherein said computer is adapted to quantize image comparability of said first and second group of images based on said optical density, captured at said one or more narrow band wavelengths, and determine if comparison between oxygen saturation measurements at different point in time are valid, and calculate change in said optical density by calculating the difference of said optical density between said pair of image groups.

48. An apparatus according to claim 47, wherein said optical density is used to measure oxygen saturation.

49. An apparatus according to claim 47, wherein said change in said optical density is used to measure change in oxygen saturation.