Optics: measuring and testing – For light transmission or absorption – Of fluent material
Reexamination Certificate
2002-07-19
2004-10-05
Rosenberger, Richard A. (Department: 2877)
Optics: measuring and testing
For light transmission or absorption
Of fluent material
Reexamination Certificate
active
06801316
ABSTRACT:
BACKGROUND OF THE INVENTION
Testing of a human sample, such as a blood sample, to determine a concentration of a particular analyte in the sample is widespread. Most of these tests are invasive in that they require the removal of, or intrusion into some tissue. For example, a conventional blood test involves the perforation of the skin with a hypodermic needle to withdraw blood. The blood sample is then examined in the laboratory to determine the concentration of some analyte, such as glucose, in the blood.
Such invasive procedures have several drawbacks associated with inconvenience, cost, and pain. Patients often detest or outright avoid the procedures. For example, many diabetics must test their blood glucose levels four or more times a day. The modern battery powered instruments for home use require a finger prick to obtain the sample. The extracted blood sample is then placed on a chemically treated carrier that is inserted into the instrument to obtain a glucose reading. This finger prick is painful and can be a problem when required often. In addition, although the price has dropped considerably on these instruments, the cost for the disposables and the mess and health risks associated with having open bleeding is undesirable. As a result, patients are reluctant to undergo such tests.
The spread of acquired immunodeficiency disease syndrome (AIDS), and the associated fear among public and healthcare personnel of AIDS has made many people afraid of invasive procedures. Not only can diseases such as AIDS be spread with invasive procedures if proper precautions are not followed, hepatitis and other similar blood diseases are more common problems in this type of testing. Nurses, for example, have been known to unintentionally transmit hepatitis from one patient to another with a sampling device itself. This type of disease transfer is eliminated with non-invasive testing.
Development of non-invasive testing methods has become an important topic in the last several years. Accordingly, a number of groups have recently tried to make non-invasive instruments for testing a variety of analytes. A recent trend in non-invasive testing has been to explore the use of the near infrared spectral region (700-2500 nm), more particularly the range from 700-1700 nm. For example, testing involving classical spectrophotometric techniques, such as disclosed in U.S. Pat. No. 5,054,487, by Clarke, and U.S. Pat. No. 5,028,787, by Rosenthal et al., have been employed. These spectrophotometric methods utilize a set of narrow wavelength sources, or scanning spectrophotometers, which scan wavelength by wavelength across a broad spectrum. The data obtained from these methods are spectra, which then require substantial data processing to eliminate background.
One problem with using these types of methods is that spectrophotometers were conceived primarily for accurate determination, in terms of wavelength, of the spectral structure, rather than for discriminating the presence of weak broadband features in strong broadband backgrounds. Since in non-invasive testing for glucose and other materials the primary information sought is the concentration, those using spectrophotometric methods here had to resort to using a number of unsatisfactory analysis techniques to suppress unwanted interference and to calculate the amplitude of the signal.
To overcome such shortcomings of conventional spectrophotometric techniques, other non-invasive methods that are analogous to colorimetry were provided in U.S. Pat. No. 5,321,265, by Block, and U.S. Pat. No. 5,424,545, by Block and Sodickson, incorporated herein by reference. These last methods, dubbed Kromoscopy™, obtain the raw data in the infrared in a manner more similar to the way the eye discriminates color in the visible, than classic spectrophotometric measurements. Colorimetry uses three dimensions to describe the color. There presently are several such three dimensional spaces in use. One of these three dimensional spaces is the CIE 1931 (x,y)-chromaticity diagram, which is based on the light sensitivities of the cones in the eye. It is the trivariant nature of color vision that permits color to be specified in a three dimensional space. Another three-dimensional space involves hue, chroma and value. An analog of colorimetry, particularly one in the infrared region that involves measuring absorbance/transmission of infrared light through a human sample containing blood, shows similar usefulness in determining analyte concentration, as described in the last two patents.
Kromoscopy yields an n-dimensional vector, or Kolor vector, of an analyte that is indicative of the concentration of the analyte. The Kolor vector is the analog of the three component CIE vector mentioned above, except that n is determined by the number of detection channels used and can therefore be made larger than three.
These non-invasive testing procedures patterned after colorimetry, while useful, have some drawbacks when in vivo measurements are attempted. Light travelling through skin and tissue is scattered. In addition, the presence of particles in blood that can also scatter the infrared light complicates measurements of analyte concentrations. Since many scatterers exist in blood, this effect can be quite troublesome. Thus, there exists a need for spectral systems and methods that can measure analyte concentration in a medium that gives rise to significant scattering of light. Such systems and methods would be particularly useful because the type of medium likely to be encountered in a clinical setting gives rise to significant scattering of light.
SUMMARY OF THE INVENTION
Systems and methods are described herein that can measure the concentration of an analyte in a scattering medium, which measurement is often performed in vivo. The systems and methods are analogous to human color vision, and to colorimetry. The response of the eye is in terms of red, green and blue sensors, the output of which are processed by the eyes and the brain to provide the perception of color. The infrared detection units of the present invention and their response to either transmitted, transflected, or reflected radiation from the sample are analogous to the color sensors of the eye and the color response of the eye, respectively. At least three detection units can be used in the present invention, each having a spectral detection range centered about a different portion of the selected spectrum but with response bands sufficiently wide that there is some overlap with at least one, and preferably more than one, other of the detection units. Moreover, the measurements by the detection units of the transmitted, transflected, or reflected light can be congruent, which means that the volume sampled by each detection unit is substantially the same. Similar to how a CIE vector in colorimetry is indicative of a particular color, the direction and magnitude of a Kolor vector obtained using the principles of the present invention are indicative of the identity and the concentration of an analyte.
The methods of the present invention allow the measurement of an analyte concentration even if the analyte is measured in a scattering medium. The Kolor vector of an analyte in a scattering medium with a particular concentration is not coincident with the Kolor vector of the analyte in a non-scattering medium with the same concentration. The invention recognizes that the angle between the Kolor vector of an analyte in a scattering medium and the Kolor vector of the analyte in a non-scattering medium is significant, measurable, and indicative of the amount of scattering that occurs in the scattering medium. The Kolor vector pertaining to the scattering medium can be made co-directional with the Kolor vector pertaining to the non-scattering medium by a rotation that can be specified by a correction vector &Dgr;. A useful property of &Dgr; is that it is independent of the particular analyte being measured. Thus, having obtained &Dgr;, the Kolor vector of a trace analyte, such as glucose, obtained in a measurement performe
Loren, Esq. Ralph A.
Optix LP
Palmer & Dodge LLP
Rosenberger Richard A.
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