US 5,582,169 AGranted

Method and apparatus for measuring concentration of absorptive constituent in scattering medium

AssigneeHamamatsu Photonics K.K.

InventorsMotoki Oda, Yutaka Yamashita, Kazuyoshi Ohta, Mamoru Tamura, Goro Nishimura

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Abstract

Optical pulses emitted from an optical pulse source is incident on a living tissue and is input to an optical sampling unit. An optical sampling unit detects intensities, f, of optical pulses detected at the respective timings of trigger signals input from a delay unit. A first accumulator calculates products, t.multidot.f, of the intensities f and the delay times t from the delay unit. A second accumulator accumulates the light intensities f. An average optical pathlength calculating unit calculates an average optical pathlength using the accumulation results as the products t.multidot.f and the intensities f. An SO.sub.2 value calculating unit calculates a ratio of V.sub.HbO2 to V.sub.Hb from the average optical pathlength to calculate an SO.sub.2 value.

Claims7

Dependent claims

A method of measuring a concentration of an absorptive constituent in a scattering medium, comprising the steps of:

(a) causing light having a wavelength to be incident on a scattering medium at a first position, said scattering medium containing two types of absorptive constituents, A and B;
(b) detecting light scattered by said scattering medium at a second position;
(c) calculating at least one of an average optical pathlength and a mean flight time of the light in the scattering medium;
(d) changing the wavelength of the light and repeating step (a), step (b) and step (c) n+1 times;
(e) obtaining a difference between values calculated in step (c), wherein said difference is at least one of an average optical pathlength difference and a mean flight time difference of light of different wavelengths in the scattering medium;
(f) obtaining a concentration ratio of respective absorptive constituents in said scattering medium in accordance with a relationship representing that one of the average optical pathlength difference and the mean flight time difference is inversely proportional to a difference in absorbance of the absorptive constituents for light of different wavelengths;
wherein the light incident on said scattering medium has three different wavelengths .lambda.1, .lambda.2, and .lambda.3;
and
wherein a ratio V.sub.A :
V.sub.B of a concentration V.sub.A to a concentration V.sub.B of said absorptive constituents A and B in said scattering medium is determined according to the following equation:
V.sub.A :
V.sub.B ={(.epsilon..sub.B.lambda.3 -.epsilon..sub.B.lambda.1)A.DELTA.<t>.sub..lambda.2,.lambda.1 -(.epsilon..sub.B.lambda.2 -.epsilon..sub.B.lambda.1).DELTA.<t>.sub..lambda.3,.lambda.1 }:
{-(.epsilon..sub.A.lambda.3 -.epsilon..sub.A.lambda.1).DELTA.<t>.sub..lambda.2,.lambda.1 +(.epsilon..sub.A.lambda.2 -.epsilon..sub.A.lambda.1).DELTA.<t>.sub..lambda.3,.lambda.1 }
where A<t>.sub..lambda.2,.lambda.1 is the mean flight time difference between the light incident on said scattering medium having wavelengths .lambda.2 and .lambda.1;
.DELTA.<t>.sub..lambda.3,.lambda.1 is a mean flight time difference between the incident light having wavelengths .lambda.3 and .lambda.1;
.epsilon..sub.A.lambda.1 and .epsilon..sub.B.lambda.1 are extinction coefficients of said absorptive constituents A and B with respect to the incident light having the wavelength .lambda.1;
.epsilon..sub.A.lambda.2 and .epsilon..sub.B.lambda.2 are extinction coefficients of said absorptive constituents A and B with respect to the incident light having the wavelength .lambda.2;
and
.epsilon..sub.A.lambda.3 and .epsilon..sub.B.lambda.3 are extinction coefficients of said absorptive constituents A and B with respect to the incident light having the wavelength .lambda.3.

16 more elements

An apparatus for measuring a concentration of an absorptive constituent in a scattering medium, comprising:

a light source for generating light pulses;
wavelength control means for controlling a wavelength of each said light pulse;
light guide means for causing the light from said light source to be incident on a scattering medium at a first position, said scattering medium containing two types of absorptive constituents, A and B;
photodetecting means for receiving, at a second position, light pulses scattered within said scattering medium, and time-resolved measuring each received light pulse;
one of optical pathlength calculating means and flight time calculating means for calculating one of n+1 average optical pathlengths and n+1 mean flight times of respective n+1 light pulses having n+1 wavelengths in accordance with time-resolved measurement results of said photodetecting means;
concentration calculating means for obtaining one of an average optical pathlength difference and a mean flight time difference between light pulses having two wavelengths from one of the average optical pathlengths and the mean flight times calculated by one of said optical pathlength calculating means and said flight time calculating means, and for obtaining a ratio of the absorptive constituent concentrations in said scattering medium in accordance with a relationship representing that one of the average optical pathlength difference and the mean flight time difference is inversely proportional to a difference in absorbance of the absorptive constituent for light of two wavelengths;
wherein said light source emits light pulses having three different wavelengths .lambda.1, .lambda.2, and .lambda.3;
and
wherein said concentration calculating means calculates a ratio V.sub.A :
V.sub.B of a concentration V.sub.A to a concentration V.sub.B of said absorptive constituents A and B in said scattering medium according to the following formula:
V.sub.A :
V.sub.B ={(.epsilon..sub.B.lambda.3 -.epsilon..sub.B.lambda.1).DELTA.<t>.sub..lambda.2,.lambda.1 -(.epsilon..sub.B.lambda.2 -.epsilon..sub.B.lambda.1).DELTA.<t>.sub..lambda.3,.lambda.1 }:
{-(.epsilon..sub.A.lambda.3 -.epsilon..sub.A.lambda.1).DELTA.<>.sub..lambda.2,.lambda.1 +(.epsilon..sub.A.lambda.2 -.epsilon..sub.A.lambda.1).DELTA.<t>.sub..lambda.3,.lambda.1 }
where A<t>.sub..lambda.2,.lambda.1 is a mean flight time difference between incident light pulses having wavelengths .lambda.2 and .lambda.1;
A<t>.sub..lambda.3,.lambda.1 is a mean flight time difference between incident light pulses having wavelengths .lambda.3 and .lambda.1;
.epsilon..sub.B.lambda.1 are extinction coefficients of said absorptive constituents A and B with respect to the incident light pulses having the wavelength .lambda.1;
.epsilon..sub.A.lambda.2 and .epsilon..sub.B.lambda.2 are extinction coefficients of said absorptive constituents A and B with respect to the incident light pulses having the wavelength .lambda.2;
and
.epsilon..sub.A.lambda.3 and .epsilon..sub.B.lambda.3 are extinction coefficients of said absorptive constituents A and B with respect to the incident light pulses having the wavelength .lambda.3.

16 more elements

Dependencies are inferred from the claim text.