Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1998-05-06
2001-04-24
Ham, Seungsook (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C600S335000, C356S039000
Reexamination Certificate
active
06222189
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the use of radiation, preferably near-infrared radiation to detect and measure the concentration of constituents or other properties of interest of a material. More particularly, apparatus and methods have been developed for measurement of the concentration of constituents such as hemoglobin and its variants and derivatives, glucose, cholesterol and its combined forms, drugs of abuse, and other analytes of clinical and diagnostic significance in a non-invasive manner.
Because the apparatus developed for use of this method does not require the withdrawal of blood in order to perform these measurements, it is particularly suitable for testing in the home on a chronic basis such as for glucose levels in diabetics and for kidney function, e.g., urea or creatinine testing, in patients undergoing home dialysis. The present invention uses a variety of methods to change the pathlength through tissue and/or the blood volume within an optically sampled tissue to help distinguish the desired signal produced by one or more components of the blood volume from background noise produced by tissue or other components of the blood volume and from the background noise of the system itself.
The development of clinical testing procedures that do not require the withdrawal of blood has become an important goal due to the spread of AIDS and the associated fears among the public and health care personnel. Along with AIDS, other diseases, such as hepatitis, can be spread through the use of invasive procedures without stringent precautions to assure sterility. “Nosocomial transmission of hepatitis B virus associated with the use of a spring-loaded finger-stick device,”
New England Journal of Medicine.
326(1 1), 721-725 (1992), disclosed a hepatitis mini-epidemic in a hospital caused by the improper use of an instrument for obtaining blood samples. The article describes how the hospital personnel unintentionally transmitted the virus from patient to patient by misuse of the sampling device. Such transfers, potentially hazardous to health care personnel as well as to patients, are eliminated by the non-invasive testing method performed by the apparatus and method of the invention.
Non-invasive testing will become particularly effective in the long-term management of diabetes. Improperly controlled glucose levels in diabetics can result in damage to the circulatory system, the nervous system, the retina and other organs. This damage can be largely eliminated by more effective control of glucose levels. However, this level of control requires the measurement of glucose levels four or more times a day. With current apparatus and methods, a painful finger prick is required for each such measurement. Furthermore, that part of the apparatus that contacts the blood to produce the required chemical change used in the measurement is disposed of after each measurement. The cost of these disposables can run thousands of dollars per year. The inconvenience and discomfort of glucose measurement exacts a further psychological toll from the diabetic. Finally, because the sampling process is conducted by relatively untrained personnel, it is prone to error. These errors have been reported to be as high as three to five times the inherent error in the process. Errors in the sampling process can occur either as a result of failure to obtain a proper blood sample (e.g., the sample may be an admixture of intracellular or interstitial fluid or blood) or failure to correctly apply the sample to the disposable part of the apparatus, or both.
These deficiencies in currently available apparatus and methods have caused a number of groups to attempt to develop devices for non-invasively measuring concentrations of various blood constituents. The most commercially successful devices for the non-invasive measurement of chemical constituents of blood are those that use “pulse oximetry” to measure the relative concentrations of oxyhemoglobin and deoxyhemoglobin. Because these two constituents are both highly absorptive in the near infrared and because of their crossing broadband features, the ratio of radiation intensities at two wavelengths can provide the requisite information. Based in part on the success of hemoglobin ratio measurements, much current work on non-invasive concentration measurements for chemical constituents of blood has also used the near-infrared region of the electromagnetic spectrum. Because of the number of diabetics most of this research is directed to techniques for the non-invasive measurement of blood glucose levels. Although glucose is present in low concentration, and although glucose has low absorptivity, the wavelength band between 700 nm and 1100 nm contains the third overtones of the glucose absorption spectrum. This band theoretically allows minimization of interference due to water absorption and exhibits good penetration of human tissue. Other promising research has used longer wavelengths, from 1100 nm to about 2500 nm.
Substantially all of this work has been carried out using variants on classic spectrophotometric methods. Classical methods typically use detectors which measure the radiation transmitted through or reflected from the sample in a relatively narrow wavelength passband. The passband is kept narrow for several reasons. First, a narrow passband reduces the practical deviations that can occur relative to the theoretical relationships between constituent concentration and absorbance. Second, a narrow detector passband allows better measurement of sharply peaked spectra by providing a measurement closer to the spectral peak of the constituent of interest. According to classical methods, this improves specificity, and for full-spectrum measurements, provides a more faithful rendition of the absorbance or reflectance spectrum.
The wavelength passband within which the detector operates can either be a property of the source or can be obtained by placement of an appropriate filter between the source and the sample, between the sample and the detector, or both. The width of the passband in classic spectrophotometry is ordinarily chosen to be small relative to the width of the spectral features of the constituent of interest and of the sample. Typically, a passband half-width of less than 10% of the spectral half-width is recommended.
In some spectrophotometric devices, the source is designed to scan the spectral region of interest so that the measured wavelength varies with time in a controlled manner. In other cases, the source is transformed into a coded broadband source whose interaction with the sample is later decomposed into narrow-band responses.
In most classic spectrophotometric devices and methods, the measured data is initially in the form of an uncorrected intensity versus wavelength. The next important step, performed within the spectrophotometric apparatus, is a logarithmic conversion of the data into absorbance or reflectance units using some reference intensity versus wavelength data for normalization. Extensive data processing of the transformed data is then employed in an attempt to isolate the components of the data arising from the constituent(s) of interest from the components arising from the background (due to constituents that are not of interest and instrumental artifacts). Many techniques are available for this isolation, virtually all of which are based on statistical regression techniques. Examples of this general approach include the works of Rosenthal, U.S. Pat. No. 5,023,737, and of Clarke, U.S. Pat. No. 5,054,487.
All of these classical spectrophotometric methods essentially search for a unique response or pattern of responses due to the constituent of interest at one or more specific wavelengths (or narrow wavelength passbands) and then attempt to separate these effects from the effects due to background constituents at those same narrow wavelength passbands. However, glucose and many other constituents of interest possess only weak broadband spectral features in the wavelength ranges of interest.
Block Myron J.
Guthermann Howard E.
Misner Michael
Ham Seungsook
Hanig Richard
Lahive & Cockfield LLP
Optix LP
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