Pathlength corrected oximeter and the like

Abstract

A pathlength corrected spectrophotometer for tissue examination includes an oscillator for generating a carrier waveform of a selected frequency, an LED light source for generating light of a selected wavelength that is intensity modulated at the selected frequency introduced to a subject, and a photodiode detector for detecting light that has migrated in the tissue of the subject. The spectrophotometer also includes a phase detector for measuring a phase shift between the introduced and detected light, a magnitude detector for determination of light attenuation in the examined tissue, and a processor adapted to calculate the photon migration pathlength and determine a physiological property of the examined tissue based on the pathlength and on the attenuation data.

1 . A spectrophotometer for tissue examination utilizing a measured average pathlength of migrating photons, comprising: 
 an oscillator adapted to generate a carrier waveform of a selected frequency comparable to an average migration time of photons scattered in tissue on paths from an optical input port to an optical detection port;    a light source, operatively connected to said oscillator, adapted to generate light of a selected wavelength that is intensity modulated at said frequency, said light being introduced to a subject at said input port;    a photodiode detector adapted to detect, at said detection port, light of said wavelength that has migrated in said tissue of the subject between said input and detection ports;    a phase detector, operatively connected to receive signals from said oscillator and said diode detector, adapted to measure a phase shift between said introduced and said detected light;    a processor adapted to determine said pathlength based on said phase shift; and    said processor further adapted to determine a physiological property of the examined tissue based on said pathlength.    
     
     
         2 . A spectrophotometer for tissue examination utilizing a measured average pathlength of migrating photons, comprising: 
 an oscillator adapted to generate a carrier waveform of a selected frequency comparable to an average migration time of photons scattered in tissue on paths from an optical input port to an optical detection port;    a light source, operatively connected to said oscillator, adapted to generate light of a selected wavelength that is intensity modulated at said frequency, said light being introduced to a subject at said input port;    a photodiode detector adapted to detect, at said detection port, light of said wavelength that has migrated in said tissue of the subject between said input and detection ports;    a phase splitter adapted to produce, based on said carrier waveform, first and second reference phase signals of predefined substantially different phase;    first and second double balanced mixers adapted to correlate said reference phase signals and signals of said detected radiation to produce therefrom a real output signal and an imaginary output signal, respectively;    a processor adapted to determine, on the basis of said real output signal and said imaginary output signal, a phase shift between said introduced light and said detected light; and    said processor further adapted to determine a physiological property of the examined tissue based on said phase shift.    
     
     
         3 . A spectrophotometer for tissue examination utilizing a measured average pathlength of migrating photons, comprising: 
 a first oscillator adapted to generate a carrier waveform of a first selected frequency comparable to an average migration time of photons scattered in tissue on paths from an optical input port to an optical detection port;    a light source, operatively connected to said oscillator, adapted to generate light of a selected wavelength that is intensity modulated at said first frequency, said light being introduced to a subject at said input port;    a photodiode detector adapted to detect, at said detection port, light of said wavelength that has migrated in said tissue of the subject between said input and detection ports, said detector producing a detection signal at said first frequency corresponding to said detected light;    a second oscillator adapted to generate a carrier waveform of a second frequency that is offset on the order of 10 4  Hz from said first frequency;    a reference mixer, connected to said first and second oscillators, adapted to generate a reference signal of a frequency approximately equal to the difference between said first and second frequencies;    a mixer connected to receive signals from said second oscillator and said detection signal and adapted to convert said detection signal to said difference frequency;    a phase detector, operatively connected to receive signals from said reference mixer and said converted detection signal, adapted to measure a phase shift between said introduced light and said detected light,    a processor adapted to determine said pathlength based on said phase shift; and    said processor further adapted to determine a physiological property of the examined tissue based on said pathlength.    
     
     
         4 . The spectrophotometer of claims  1 ,  2  or  3  further comprising: 
 a magnitude detector, connected to said photodiode detector, adapted to measure magnitude of said detected light, and  
 said processor further adapted to receive said magnitude for determination of said physiological property.  
 
     
     
         5 . The spectrophotometer of claims  1 ,  2  or  3  further comprising: 
 a low frequency oximeter circuit, switchably connected to said source and said photodiode, adapted to determine absorption of light at said wavelength; and  
 said processor further adapted to receive absorption values from said oximeter circuit for determination of said physiological property.  
 
     
     
         6 . The spectrophotometer of claims  1  or  3  further comprising two automatic gain controls adapted to level signals corresponding to said introduced light and said detected light, both said leveled signals being introduced to said phase detector.  
     
     
         7 . The spectrophotometer of claims  1  or  3  further comprising: 
 a magnitude detector, connected to said photodiode detector, adapted to measure magnitude of said detected light, and  
 two automatic gain controls adapted to level signals corresponding to said introduced light and said detected light, both said leveled signals being introduced to said phase detector.  
 
     
     
         8 . The spectrophotometer of claims  1 ,  2  or  3  wherein said light source is a light emitting diode and said selected wavelength is in the visible or infra-red range.  
     
     
         9 . The spectrophotometer of claims  1 ,  2  or  3  wherein said photodiode detector is a PIN diode.  
     
     
         10 . The spectrophotometer of claims  1 ,  2  or  3  wherein said photodiode detector is an avalanche diode.  
     
     
         11 . The spectrophotometer of claims  1 ,  2  or  3  wherein said photodiode detector further comprises a substantially single wavelength filter.  
     
     
         12 . The spectrophotometer of claims  1 ,  2  or  3  further comprising: 
 a second light source, operatively connected to said oscillator, adapted to generate light of a second selected wavelength that is intensity modulated at said first frequency, said radiation being introduced to a subject at a second input port;  
 said photodiode detector further adapted to detect alternately, at said detection port, light of said first and second wavelengths that have migrated in said tissue of the subject between the first and said second input ports and said detection port, respectively;  
 said phase detector further adapted to receive alternately signals corresponding to said detected first and second wavelengths; and  
 said processor further adapted to receive alternately phase shifts from said phase detector, said phase shifts being subsequently used for determination of said physiological property.  
 
     
     
         13 . The spectrophotometer of  claim 12  further comprising: 
 a magnitude detector, connected to said photodiode detector, adapted to measure magnitude of said detected light at each of said wavelengths, and  
 said processor further adapted to receive said magnitudes for determination of said physiological property.  
 
     
     
         14 . The spectrophotometer of claims  1  or  3  further comprising: 
 a second light source, operatively connected to said oscillator, adapted to generate light of a second selected wavelength that is intensity modulated at said first frequency, said radiation being introduced to a subject at a second input port;  
 a second photodiode detector adapted to detect, at a second detection port, light of said second wavelength that has migrated in said tissue of the subject between said second input port and said second detection port, respectively;  
 a second phase detector, operatively connected to receive a reference signal and a detection signal from said third diode detector, adapted to measure a phase shift between said introduced and said detected light at said second wavelength; and  
 said processor further adapted to receive a second phase shift at said second wavelength, said first and second phase shifts being subsequently used for determination of said physiological property.  
 
     
     
         15 . The spectrophotometer of  claim 14  further comprising: 
 a first and a second magnitude detector connected to said first and second photodiode detectors, respectively, said magnitude detectors being adapted to measure magnitude of said detected light at each of said wavelengths, and  
 said processor further adapted to receive said magnitudes for determination of said physiological property.  
 
     
     
         16 . The spectrophotometer of claims  14  further comprising: 
 a third light source, operatively connected to said oscillator, adapted to generate light of a third selected wavelength that is intensity modulated at said first frequency, said radiation being introduced to a subject at a third input port;  
 a third photodiode detector adapted to detect, at a third detection port, light of said third wavelength that has migrated in said tissue of the subject between said third input port and said third detection port, respectively;  
 a third phase detector, operatively connected to receive a reference signal and a detection signal from said third diode detector, adapted to measure a phase shift between said introduced and said detected light at said third wavelength; and  
 said processor further adapted to receive phase shifts from said phase detector, said first second and third phase shifts being subsequently used for determination of said physiological property.  
 
     
     
         17 . The spectrophotometer of  claim 14  further comprising: 
 a first, a second and a third magnitude detector connected to said first, second and third photodiode detectors, respectively, said magnitude detectors being adapted to measure magnitude of said detected light at each of said wavelengths; and  
 said processor further adapted to receive said magnitudes for determination of said physiological property.  
 
     
     
         18 . The spectrophotometer of  claim 16  wherein each said light source is a light emitting diode and said selected wavelength is in the visible or infra-red range.  
     
     
         19 . The spectrophotometer of  claim 16  wherein each said photodiode detector is a PIN diode.  
     
     
         20 . The spectrophotometer of  claim 16  wherein each said photodiode detector is an avalanche diode.  
     
     
         21 . The spectrophotometer of  claim 16  wherein each said photodiode detector further comprises a substantially single wavelength filter.