Optics: measuring and testing – By polarized light examination
Reexamination Certificate
2002-12-11
2004-10-12
Statira, Michael P. (Department: 2877)
Optics: measuring and testing
By polarized light examination
C600S322000
Reexamination Certificate
active
06804002
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of optical measurement techniques, and relates to a method and deuce for measuring the concentration of glucose or other substances in blood, such as cholesterol albumin, etc. The present invention is useful for both in vitro and in vivo measurements.
BACKGROUND OF THE INVENTION
Optical methods for determining the chemical composition of blood are known and are typically based on spectrophotometric measurements enabling the indication of the presence of various blood constituents based on known spectral behaviors of these constituents. These spectrophotometric measurements can be effected either In vitro or in vivo. The measurements in vitro are invasive, i.e., require a blood sample to be physically withdrawn and examined. At present, these measurement have become unpopular, due to the creasing danger of infection.
The only accepted non-invasive optical measurement technique for measuring blood parameters is pulse oximetry. However, pulse oximetry provides solely for the determination of oxygen saturation in blood. For other blood parameters, the determination is too problematic, because their absorption spectral behavior in red-NIR regions is not as reliable as for oxygenized and non-oxygenized hemoglobin. As a result, patients suffering from diabetes who need to control their disease by monitoring their blood glucose levels, especially after walking, eating or exercising, still have to draw a small blood sample from their fingertip, apply and use monitoring strips and use a small machine.
Various techniques have been developed aimed at facilitating the measurement of the concentration of glucose in a patient's blood. These techniques are disclosed, for example, in the following publications:
“
Blood Analysis: Noninvasive Methods Hover on Horizon
”, K. Robinson, Biophotonics International, May/June 1998;
“
Glucose- and Blood-Monitoring Systems Vie for Top Spot
”, Susan M. Reiss, Biophotonics International, May/June 1997;
“Optical Glucose Sensing in Biological fluids: and Overiew”, Roger J. McNichols, Gerard Cote, Journal of Biomedical Optics, January 2000, Vol. 5. No. 1, pp. 5-16; and
U.S. Pat. Nos. 5,209,231; 5,398,681; 5,448,992; 5,687,721; 5,692,504; 5,551,422; 5,676,143; 5,533,509; 5,687,721; 4,901,728.
Most of the above techniques are based on the known phenomenon consisting in that glucose, being an optically active medium, rotates polarized light, and the higher the concentration of glucose, the greater the rotation.
According to all prior art techniques, measurements are applied to a blood flow containing medium during the state of normal blood flow, and the measured signals are pulsatile-related signals.
A different technique for measuring various blood-related parameters has been developed and disclosed in WO 99/65384, assigned to the assignee of the present application. This technique utilizes the so-called occlusion-release mode, wherein over-systolic pressure is applied to a patient's blood perfused fleshy medium so as to create the state of blood flow cessation at a measurement location. Optical measurements are applied during a time period including cessation time, during which the state of blood flow cessation is maintained, and time dependencies of “non-pulsatile” light responses of the medium are determined for at least two wavelengths of incident radiation. This technique enables to significantly enhance the light response signal, as compared to that obtained with the pulse oximetry.
GENERAL DESCRIPTION OF THE INVENTION
The main idea of the present invention is based on measuring the time variations of light responses of a blood containing medium corresponding to different polarization states of detected light. Generally speaking, the present invention is based on establishing the correlation between the kinetics of changes in the properties of blood containing scattering affecting or optically active substances (mainly, glucose), and the kinetics of changes in the state of polarization of linearly polarized radiation scattered by tissue containing blood vessels and capillaries.
Thus, according to one aspect of the present invention, there is provided a method of optical measurements for determining the concentration of a substance in a patient's blood, the method comprising the steps of
performing optical measurement sessions within a certain period of time by illuminating a measurement location in a blood containing medium with incident light of at least one selected wavelength, detecting, at each measurement session, at least two light responses of the medium characterized by at least two different polarization states of detected light, respectively, and generating data representative thereof and
obtaining measured data in the form of at least two time variations of the light responses of the medium, a relation between the time variations being indicative of the concentration of the substance in blood
It should be understood that the term “measurement session” signifies at least two measurements, taken either sequentially or simultaneously, including the illumination of the measurement location with at least one wavelength of incident light and the detection of at least two light responses characterized by different polarization states of the detected light, respectively. By performing more than one measurement session, either continuously or timely separated, the time variations of light responses of different polarization states are obtained.
Preferably, the present invention utilizes the principles of the above-indicated occlusion-release technique to apply optical measurements during the state of blood flow cessation at a measurement location. Accord to the present invention, however, measurements are carried out in a manner to detect at least two light responses of the medium characterized by two different states of polarization, respectively, and to measure time variations of the light responses. To this end, pressure is applied to a location on the blood containing medium (e.g, over-systolic pressure applied to the patient's blood perfused fleshy medium, in the case of non-invasive measurements), and the measurement location to which the optical measurement sessions are applied, is located downstream of the pressed location with respect to the blood flow direction. The application of pressure causes artificial change in the velocity of blood, namely, causes the state of blood flow cessation at a location downstream of the pressurized location. The artificial change in the blood results in the aggregation of red blood cells (Rouleaux effect) with time-varying shape and size of aggregates. At the state of the blood flow cessation, when there is actually no blood flow, no shear forces prevent the erythrocytes' aggregation process. Hence, the light response (transmission or reflection) of the blood perfused fleshy medium at the state of the blood flow cessation can be considered as the time dependence of scattering in a system growing scatterers.
Glucose, being the main optically active substance in blood, influences the optical characteristics of scattered and partly absorbed radiation in a complicated manner. More specifically, glucose introduces changes in the ratio of refraction indices of erythrocytes and surrounding plasma, and introduces spectrally dependent optical rotation (rotary dispersion). These-factors lead to dynamic changes in the state of polarization, in particular the polarization or depolarization degree, under the condition of kinetic changes in the aggregates in the case of periodical application of occlusion (occlusion-release sessions).
Dynamic multiple scattering increases the optical path of radiation scattered from a blood sample and, consequently, the angle of rotation of polarization of incident light. Additionally, it is known that the state of polarization of incident light affects the light scattering properties (via the Stokes parameters). Thus, the results of the transmission or reflection measurement will be governed by the state of pola
Fikhte Boris
Fine Ilya
Vinokur Mark
Browdy and Neimark , P.L.L.C.
Orsense Ltd.
Statira Michael P.
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