Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
1999-07-19
2001-05-08
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S310000
Reexamination Certificate
active
06230035
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for determining concentrations of light absorbing materials in a living tissue by the utilization of intensities of light transmitted through or light reflected from the living tissue.
2. Related Art
A pulse oximetry is known as one of this type of instrument. The pulse oximetry noninvasively measures an oxygen saturation in arterial blood by the utilization of pulsations of light transmitted through a living tissue. To this end, the oximetry irradiates a living tissue with light of two wavelengths to produce pulsations of light L
1
and L
2
; obtains changes &Dgr;A
1
and &Dgr;A
2
of the optical densities of the living tissue by the utilization of the pulsations of light; and computes an arterial oxygen saturation SaO
2
. Before computing the SaO
2
from the &Dgr;A
1
and &Dgr;A
2
, &PHgr;
12
=&Dgr;A
1
/&Dgr;A
2
must be computed. Conversion of &PHgr;
12
into SaO
2
is carried out by use of a relationship between &PHgr;
12
and SaO
2
of a human body, which are actually measured. The principle of this method is applicable to the measurement of every kind of light absorbing material contained in arterial blood. This method, called a pulse photometry, is practically used for the measurement of a dye dilution curve.
A near-infrared spectrometry (NIRS) is also known as another example of this type of measuring technique. The NIRS noninvasively measures an average oxygen saturation in arterial blood and venous blood by use of a light transmitted through the living tissue. This measuring technique is also applied to the method of measuring light absorbing materials in any of the other tissues than the blood. Example of those light absorbing materials are cytochrome and myoglobin. The near-infrared spectrometry produces an intended value from a received light by substituting measured intensities of light of wavelengths for a theoretical formula of light scattering Various theoretical formulae have been proposed.
Errors inevitably occur in noninvasively measuring a ratio of concentrations of light absorbing materials in a living tissue or in blood. Many causes for the error are known. In the case of the pulse oximetry, there exist many light absorbing materials and the pulsation of the living tissue exists as well as SaO
2
as an object to be measured, those factors will cause errors in the SaO
2
measurement.
Where an attempt is made to remove the adverse effects by those factors and to improve a measurement accuracy, the necessity is to increase the number of wavelengths of light used and the number of the related formulae, and to arrange those formulae into simultaneous equations and to solve the resultant.
The blood as one of the key light absorbing materials as well as the tissue, exhibits a nature of light scattering. Many factors are involved in the optical measurement of scattering material. Light tends to scatter in a short wavelength region. Then, when incident and collimated light rays propagate through the tissue, scattering of light gradually grows and the propagating paths of light are different with their wavelengths This fact is essential to secure an improved accuracy of measurement, and requires complicated numerical correction.
A variety of methods have been used for the near-infrared spectrometry (NIRS), but reliable methods have never been presented so far as we know. This fact shows an intricacy of the problem by the scattering nature.
SUMMARY OF THE INVENTION
For the above background reasons, the present invention provides an inventive and creative approach to an optical measuring system which enables a measuring system of light scattering material to be described by theoretical expressions, whereby simple calculations and an improved measuring accuracy are both realized.
A first aspect of the invention provides an apparatus which irradiates a living tissue with light of different wavelengths, receives light transmitted through or light reflected from the living tissue, converts the light into a corresponding electrical signal, and computes a ratio of concentrations of light absorbing materials in the living tissue, the apparatus comprising: irradiating means being arranged such that a scattering level of the irradiating light on the tissue is sufficiently large, and concentration-ratio computing means for computing a ratio of concentrations of light absorbing materials on the assumption that non-absorptive attenuations are equal independently of the wavelengths of light
Preferably, the concentration-ratio computing means computes a ratio of concentrations of light absorbing materials by a theoretical formula where the terms of tissue exculsive of the blood about respective wavelengths are equal.
Alternatively, the. concentration-ratio computing means computes changes of optical densities of the living tissue by use of pulsations of intensities of transmitted light, and computes a ratio of concentrations of light absorbing materials by use of the computed changes of the optical densities.
Preferably, the concentration-ratio computing means comprises: optical density-change calculating means for calculating optical density changes &Dgr;A
1
to &Dgr;A
2
, . . . &Dgr;An of an n number of wavelengths from the pulsations of light transmitted through or light reflected from the living tissue, which is irradiated with the irradiating means; optical density change-ratio calculating means for calculating a ratio &PHgr;ij of two optical density changes (&Dgr;Ai, &Dgr;Aj) of each of an n−1 number of combinations each consisting of two optical density changes (&Dgr;Ai, &Dgr;Aj), which are preselected from among the n number of optical density changes &Dgr;A
1
to &Dgr;An calculated by the optical density-change calculating means; computing means for computing an arterial oxygen saturation or a ratio of concentrations of another in-blood light absorbing material by use of the n−1 number of &PHgr;ij obtained by the optical density change-ratio calculating means and an n−1 number of simultaneous equations constructed such that the terms of tissue exculsive of the blood about respective wavelengths are equal on the assumption that the optical density change is equal to a difference between an optical density change of blood and that of tissue exculsive of the blood.
In the present invention, the irradiating means includes a scattering plate and a light source for irradiating a living tissue with light through the scattering plate.
In the present invention, the irradiating means includes a reflecting plate with a reflecting surface, a scattering plate and a light source :or irradiating a living tissue with light with the aid of the reflecting plate and the scattering plate.
In the present invention, an area for receiving light transmitted through or light reflected from the living tissue is selected to be sufficiently large or small with relation to an irradiation area on the living tissue.
Specifically, a ratio of the irradiating area on the living tissue to an effective area of the light receiving area on the living tissue is 1:2 or more or 2 or more: 1.
Preferably, the light scattering plate is a white acrylic plate.
REFERENCES:
patent: 5385143 (1995-01-01), Aoyagi
patent: 5596987 (1997-01-01), Chance
patent: 53-26437 (1978-08-01), None
Shibata, Kazuo,Spectrophotometry of Translucent Biological Materials—Opal Glass Transmission Method, Methods of Biochemical Analysis, vol. VII, New York, 1959, pp. 77-109.
Aoyagi Takuo
Fuse Masayoshi
Kanemoto Michio
Xie Chen-tai
Nihon Kohden Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Winakur Eric F.
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