Method of and apparatus for measurement of blood flow using coherent light
First Claim
1. An apparatus for measuring blood flow in a vascular bed, the apparatus comprising:
- means for illuminating a region of tissue having a vascular bed with coherent light;
means responsive to light backscattered from the region of tissue for producing a broadened spectrum signal output;
circuit means coupled to said means for producing a broadened spectrum signal output and responsive to its broadened spectrum signal output for producing a signal representative of the blood flow in the vascular bed;
means for collecting backscattered light from the region of tissue;
wherein said means responsive to backscattered light comprise photo-detector means responsive to the collected light for developing a broadened spectrum of low frequency signals, said photo-detector means producing a means current and having a substantially constant shot noise output S;
wherein said circuit means comprise means coupled to said photo-detector means and responsive to its output for developing an output signal I representative of the mean current thereof, weighted detector means coupled to said photo-detector and responsive to the broadened spectrum of low frequency signals for developing an output signal R; and
calculating circuit means coupled to said weighted detector means and to said means for developing an output signal I and responsive to outputs thereof for producing an output signal F representative of the blood flow in the vascular bed.
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Accused Products
Abstract
An apparatus for measuring the flow parameter of blood flowing in an organ includes a laser and associated optics which effect the illumination of tissues. The laser light, scattered by the tissues, emerges with a spectrum broadened by Doppler effect due to motion of red blood cells in the micro-circulation vessels. The light from the tissues is fed to a photomultiplier tube or photodiode via a pinhole mask and interference filter. The photomultiplier tube or photodiode, as a result of beating of various components of the light it receives, produces as its output signals a homodyne or heterodyne spectrum or both. These output signals are fed, via a low pass filter, to a differentiator, which differentiates the output signals from the multiplier tube or photodiode, which are passed by the filter, with respect to time. The output of the differentiator is fed to a root-mean-square (RMS) detector. The low pass filter passes, for example, signals having a frequency up to about 20 KHz. The output (R) from the detector, which represents the blood flow (average percolation) in the tissues plus shot noise, a constant (S), is fed to a digital voltmeter. The voltmeter produces a visible read-out indicative of the output from the detector. The output from the detector is also fed to a calculating circuit which also receives a signal corresponding to the mean current (I) produced by the photomultiplier or photodiode, the calculating circuit effecting a solution to the equation ##EQU1## Fnorm is a normalized output signal representation of blood flow parameter.
166 Citations
39 Claims
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1. An apparatus for measuring blood flow in a vascular bed, the apparatus comprising:
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means for illuminating a region of tissue having a vascular bed with coherent light; means responsive to light backscattered from the region of tissue for producing a broadened spectrum signal output; circuit means coupled to said means for producing a broadened spectrum signal output and responsive to its broadened spectrum signal output for producing a signal representative of the blood flow in the vascular bed; means for collecting backscattered light from the region of tissue; wherein said means responsive to backscattered light comprise photo-detector means responsive to the collected light for developing a broadened spectrum of low frequency signals, said photo-detector means producing a means current and having a substantially constant shot noise output S; wherein said circuit means comprise means coupled to said photo-detector means and responsive to its output for developing an output signal I representative of the mean current thereof, weighted detector means coupled to said photo-detector and responsive to the broadened spectrum of low frequency signals for developing an output signal R; and
calculating circuit means coupled to said weighted detector means and to said means for developing an output signal I and responsive to outputs thereof for producing an output signal F representative of the blood flow in the vascular bed. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An apparatus for measuring blood flow in a vascular bed, the apparatus comprising:
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means for illuminating a region of tissue having a vascular bed with coherent light; means responsive to light backscattered from the region of tissue for producing a broadened spectrum signal output; circuit means coupled to said means for producing a broadened spectrum signal output and responsive to its broadened spectrum signal output for producing a signal representative of the blood flow in the vascular bed; and means for collecting backscattered light from the region of tissue; wherein said means responsive to backscattered light comprise photo-detector means responsive to the collected light for developing a broadened spectrum of low frequency signals, said photo-detector means producing a mean current and having a substantially constant shot noise output S; wherein said circuit means comprise means coupled to said photo-detector means and responsive to its output for developing an output signal I representative of the mean current thereof, weighted detector means coupled to said photodetector and responsive to the broadened spectrum of low frequency signals for developing an output signal R;
including calculating circuit means coupled to said weighted detector means and to said means for developing an output signal I and responsive to outputs thereof for producing an output signal F representative of the blood flow in the vascular bed, anda differentiator means and a low pass filter connected between said photo-detector means and said weighted detector means. - View Dependent Claims (13, 14)
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15. A method of measuring the blood flow in a vascular bed, the method comprising:
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illuminating a region of tissue having a vasuclar bed with coherent light; collecting at least some of the scattered light from the region; detecting the collected light to determine its broadened spectrum; and determining the blood flow in the vascular bed from said broadened spectrum; wherein said detecting step comprises non-linearly detecting the backscattered light in a photo-detector to produce a broadened spectrum of low frequency signals and a mean current signal I; and
wherein the determining step comprises producing a weighted output signal R from the broadened spectrum of low frequency signals, determining the shot noise constant S of the photo-detector, and producing a signal representation F, from the shot noise constant, the weighted output signal R and the mean current signal I. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22)
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23. A method of measuring the blood flow in a vascular bed, the method comprising:
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illuminating a region of tissue having a vascular bed with coherent light; collecting at least some of the scattered light from the region; detecting the collected light to determine its broadened spectrum; determining the blood flow in the vascular bed from said broadened spectrum; wherein said detecting step comprises non-linearly detecting the backscattered light in a photo-detector to produce a broadened spectrum of low frequency signals and a mean current signal I; and
wherein the determining step comprises producing a weighted output signal R from the broadened spectrum of low frequency signals, determining the shot noise constant S of the photo-detector, and producing a signal representation F, from the shot noise constant, the weighted output signal R and the mean current signal I;filtering the broadened spectrum of low frequency signals to pass only signals below a given frequency prior to detecting the broadened spectrum of low frequency signals; and differentiating the filtered low frequency signals with respect to time prior to detecting the broadened spectrum of low frequency signals.
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24. An apparatus for measuring the flow of flowing material, the apparatus comprising:
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means for illuminating at least a portion of the flowing material with coherent light; means for collecting backscattered light from the material; photo-detector means responsive to the collected light for developing a broadened spectrum of low frequency signals, said photo-detector means producing a mean current and having a substantially constant shot noise output S; means coupled to said photo-detector means and responsive to its output for developing an output signal I representative of the mean current thereof; weighted detector means coupled to said photo-detector and responsive to the broadened spectrum of low frequency signals for developing an output signal R; and calculating circuit means coupled to said weighted detector means and to said means for developing an output signal I and responsive to outputs thereof for producing an output signal F representative of the flow. - View Dependent Claims (25, 26, 27, 28, 29, 30)
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31. An apparatus for measuring the flow of flowing material, the apparatus comprising:
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means for illuminating at least a portion of the flowing material with coherent light; means for collecting backscattered light from the material; photo-detector means responsive to the collected light for developing a broadened spectrum of low frequency signals, said photo-detector means producing a mean current and having a substantially constant shot noise output S; means coupled to said photo-detector means and responsive to its output for developing an output signal I representative of the mean current thereof; weighted detector means coupled to said photodetector and responsive to the broadened spectrum of low frequency signals for developing an output signal R; calculating circuit means coupled to said weighted detector means and to said means for developing an output signal I and responsive to outputs thereof for producing an output signal F representative of the flow; and a differentiator means and a low pass filter connected between said photo-detector means and said weighted detector means. - View Dependent Claims (32, 33)
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34. A method of measuring the flow parameter of flowing material, the method comprising:
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illuminating at least a portion of the flowing material with coherent light; collecting at least some of the light scattered from the material; non-linearly detecting the collected light in a photo-detector to produce a broadened spectrum of low frequency signals and a mean current signal I; detecting the broadened spectrum of low frequency signals to produce a weighted output signal R; determining the shot noise constant S of the photodetector; and producing a signal representation F, from the shot noise constant, the weighted output signal R and the mean current signal I. - View Dependent Claims (35, 36, 37, 38)
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39. A method of measuring the flow parameter of flowing material, the method comprising:
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illuminating at least a portion of the flowing material with coherent light; collecting at least some of the light scattered from the material; non-linearly detecting the collected light in a photo-detector to produce a broadened spectrum of low frequency signals and a mean current signal I; detecting the broadened spectrum of low frequency signals to produce a weighted output signal R; determining the shot noise constant S of the photo-detector; producing a signal representation F, from the shot noise constant, the weighted output signal R and the mean current signal I; wherein the step of detecting the broadened spectrum of low frequency signals comprises detecting the broadened spectrum of low frequency signals to produce a root-mean-square output signal R; filtering the broadened spectrum of low frequency signals to pass only signals below a given frequency prior to detecting the broadened spectrum of low frequency singals, and differentiating the filtered low frequency signals with respect to time prior to detecting the broadened spectrum of low frequency signals.
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Specification