referring to fig1 a first embodiment of the present invention provides an endoscope 14 , a light source 11 , an optical filter wheel 20 for filtering of light of predetermined wavelengths located at the light source 11 , a charge coupled device ( ccd ) 19 located at the distal end 16 of the endoscope 14 , and a lens 17 for directing the light towards a scene 30 . preferably the light source is a white light source . the optical filter wheel 20 comprises three filters 21 , 22 , and 23 corresponding to three light components 1 , 2 , and 3 ( fig5 ). each light component corresponds to a particular wavelength or band of wavelengths of light . the light source 11 is strobed at a given frequency , causing light to be transmitted through optical fibers 12 which extend to the distal end 16 of the endoscope 14 . the light is emitted from the fibers 12 and focused with the lens 17 towards the scene 30 which is comprised of blood perfused tissue . the filters 21 , 22 , and 23 cycle through an alternating pattern at a frequency of 180 hz , filtering light of the light source , and causing emission of a repeating series of corresponding light components 1 , 2 , and 3 at the distal end 16 of the endoscope 14 . each light component 1 , 2 , and 3 corresponds to a band of wavelengths described below and is filtered at one of three distinct intervals , each light component or band of wavelengths thus being cycled at 60 hz . the ccd 19 comprises an array of sensors which detects and images the intensity of the light backscattered to the distal end of the endoscope at each of the three intervals , i . e ., for each of the three components 1 , 2 , and 3 , emitted . the ccd 19 provides an array of electrical signals corresponding to the light reflected back from the tissue . the electrical signals are communicated to a video processor 24 . the video processor 24 processes and enhances the signal and determines oxygen saturation levels , on a pixel by pixel basis . the video processor provides the resulting information to a display monitor 25 to be displayed . an example of a scope which may be used is , an olympus model evis200 endoscope . referring now to fig2 there is illustrated another embodiment of a video oximeter of the present invention . a light source 41 sends light through light fibers 42 to the distal end 46 of an endoscope 44 . the light fibers 42 at the distal end 46 of the endoscope 44 direct the light at a scene 90 comprised of blood perfused tissue . a camera 48 is coupled to the proximal end 45 of the scope 44 . a filter 51 is inserted at the distal end of the camera . an array of light sensors 49 is located at the distal end of the camera 48 proximal to the filter 51 . the filter 51 is comprised of an array of pixel filters 52 , each associated with a corresponding light sensor 49 . light is backscattered through the relay lens 50 at the distal end 46 . the backscattered light is transmitted to the camera 48 through a series of rod relay lenses 47 extending from the distal end 46 to the proximal end 45 of the scope 44 . the relay lenses 47 focus the backscattered light from the tissue to an image at the proximal end 45 . the light is passed through the filter 51 and sensed by the light sensors 49 . each pixel filter 52 filters one of three light components 1 , 2 , or 3 . each light component corresponds to a predetermined light wavelength or bandwidth of wavelengths . the filtered light from each pixel filter 52 is then detected by a corresponding one of the light sensors 49 . each of the light sensors 49 convert the light energy into an electrical signal corresponding to the intensity of light received by the sensor . each subset 56 of filters 52 and corresponding light sensors 49 corresponds to 1 pixel of information . thus , for each light sensor 49 there is an electrical signal relative to the amount of light of a particular bandwidth reflected from an area of the tissue 90 . the light components 1 , 2 , and 3 ( fig3 ) are arranged in an alternating fashion on the array 51 so that a subset area 56 of filters 52 contains representative information for each of the three light components 1 , 2 , and 3 . the subsets 56 may be overlapping or may represent numerous configurations of filters on the array . a variety of patterns of filter subsets are established for color ccd cameras . any one of these patterns may be use for image processing depending on what information is of interest . the array of information is communicated to a video processor 54 which processes the input signal using known signal processing techniques and displays a resulting image on a display monitor 55 . the resulting signal of either the first or second embodiment described above is sent to a video processor 24 or 54 , respectively , which forms an image based on the output signal from the ccd 19 or the array of sensors 51 , respectively . the image may be displayed on a display monitor using image enhancement to illustrate tissue oxygen saturation levels . in a preferred embodiment , a glare elimination filter ( not shown ) is added to the endoscope to improve the accuracy of the oximetry data by helping insure that only light backscattering from the volume of the tissue is analyzed and confounding reflections from the surface of the tissue are eliminated . a glare elimination device is intended to virtually eliminate the specular light reflected back to the endoscope . in a preferred embodiment backscattering oximetry is used . backscattering oximetry is described in donahoe , t . m ., and longini , r . l . &# 34 ; a new non - invasive backscattering oximeter &# 34 ; ieee seventh annual conference of the engineering in medicine and biology society , p . 144 - 147 ( 1985 ). backscattering oximetry involves the measurement of light that is scattered back from the surface of the tissue . backscattering oximetry is based on the application of photon diffusion theory . the spectral light which is reflected from the surface does not contain information relating to the absorption of light by tissue or blood . if the spectral light is filtered , the remaining light is the light diffused from the tissue . the diffused light is the backscattered light from which oximetry determinations can be made . both the light source and light sensors are positioned on the same tissue surface . both light absorption and light scattering are analyzed . fig5 illustrates three bands of wavelengths selected for use in the present invention . fig6 illustrates the hemoglobin extinction curves for oxygenated and reduced hemoglobin at the bands of wavelengths illustrated in fig5 . many variations of wavelengths may be selected to determine blood or tissue oxygen levels as is well known in the art . currently available finger tip oximeters , for example , use the 920 nm and 660 nm wavelengths . preferably the following criteria are met in selection of which wavelengths or bands of wavelengths are used : 1 ) an isobestic point should be used , i . e ., a point or a band of wavelength where the extinction values or averaged values for oxyhemoglobin and reduced hemoglobin are equal ; and 2 ) one or more wavelengths or bands of wavelengths for which the oxygenated and reduced hemoglobin show significantly different optic absorption should be used . the wavelengths selected in the illustrated embodiment comprise light components of three bands of wavelengths , 1 , 2 , and 3 . component 1 is comprised of light wavelengths 450 nm - 520 nm . component 2 is comprised of 520 nm - 590 nm . component 3 is comprised of wavelengths 590 nm - 800 nm . the average extinction value for oxygenated hemoglobin and reduced hemoglobin for component 2 is equal , thus representing an isobestic point . the average extinction value for reduced hemoglobin for component 1 is less than that of oxygenated hemoglobin . and , the average extinction value for reduced hemoglobin for component 3 is greater than that of oxygenated hemoglobin . thus components 1 and 3 satisfy the second criterion above where one or more wavelengths for which the oxygenated and reduced hemoglobin show significantly different optical absorption . the isobestic point helps to normalize the data for different tissue types . generally , any differences at the isobestic point can be attributed to factors other than differences in reduced and oxygenated hemoglobin levels since the extinction coefficients for each are the same at the isobestic point . there are many video processing systems available and known in the art which would perform the data processing . this processing can be performed on a computer system including a personal computer . because of movement at the scene during a heartbeat cycle , a correction for such motion is incorporated into the video processing system . images from at least two points in time , preferably at the peak and valley of the heartbeat cycle , are compared to find common physical characteristic points . the images may then be overlaid and oximetry calculations made on a pixel by pixel basis . frames of maximum and minimum value for each light component over one heartbeat cycle are identified . this will identify the peak and valley of the pulse . the frame at the maximum value is designated frame a and at the minimum value is designated frame b . using software known in the art , correction is made for motion occurring during time between frames a and b . a pixel by pixel oximetry determination is made for the overlaid images of frames a and b . algorithms which may be used to make the tissue oximetry determination are known in the art . a number is assigned to each to pixel location based on the resulting oximetry values . each number corresponds to a color where the color indicates oxygen saturation level . for example , blue would indicate no oxygen saturation and red would indicate a maximum oxygen saturation level . other colors could indicate levels in between . the resulting array of values is then presented as a false color video image . the image may also , for example , be overlaid on a black and white image of the scene . the oximetry image of the invention may be displayed in real time at a frequency of an integer fraction of the frequency of the interval on series of intervals required to obtain oxygen saturation values for the tissue image area . this invention is described in connection with a specific embodiment of a video oximeter used to measure arterial oxygen saturation levels . naturally the invention may be used to measure other tissue oxygen saturation values , for example , to determine rate of oxygen metabolism in organs or other tissue . accordingly , it will be understood by those skilled in the art that various changes and modifications may be made in the invention without departing from its scope , which is defined by the following claims and their equivalents .
a video oximetry device and method is provided in which an endoscopic device is used to obtain and determine oxygen saturation levels at a tissue site . a video image illustrating blood oxygen saturation and / or tissue perfusion is derived and displayed .