Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
2001-01-11
2003-10-21
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C250S339030, C250S341600
Reexamination Certificate
active
06636753
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and apparatus for inducing a transient thermal gradient in human or animal tissue, and for obtaining thermal gradient spectra from the tissue as the thermal gradient propagates through the tissue. The resulting thermal gradient spectra can then be converted to conventional infrared spectra, which in turn can be used to determine concentrations of substances present in the tissue, such as glucose.
BACKGROUND OF THE INVENTION
Millions of diabetics are forced to draw blood daily to determine their blood sugar levels. To alleviate the constant discomfort of these individuals, substantial effort has been expanded in the search for a non-invasive methodology to accurately determine blood glucose levels. Two patent applications, each assigned to Optiscan Biomedical Corporation of Alameda, Calif., have significantly advanced the state of the art of non-invasive blood glucose analysis. The methodology taught in U.S. patent application Ser. No. 08/820,378 is performed by the apparatus taught in U.S. patent application Ser. No. 08/816,723, and each of these references is herewith incorporated by reference.
By way of introduction, the methodology taught in U. S. patent application Ser. No. 08/820,378 is introduced as follows.
Any object at a temperature above absolute zero (−273.16 degrees Celsius) emits infrared energy. The energy density of such emissions is described by Planck's law and are often referred to as a blackbody curves. Theoretically, a body with emissivity 1.0 would exhibit this emission spectra according to Planck's Equation. Many objects have emissivities close to 1.0. Human tissue for instance has an emissivity of approximately 0.9 to 0.98. It is well known that infrared emissions from the human body obey Planck's law and yield a black body type emission spectra.
Although a human body may emit energy that follows Planck's Equation, Planck's Equation does not completely describe the sum total of all energy emitted from a human body for two reasons:
1. The layers of the tissue and body fluids are selectively absorptive to some wavelengths of infrared energy. Thus, layers of tissue and blood or other fluids may selectively absorb energy emitted by the deeper layers before that energy can reach the surface of the skin.
2. There is a temperature gradient within a body, the deeper layers being warmer than the outer layers, which causes further deviation from the theoretical black body emissions.
Whenever these two conditions exist naturally, or can be forced to exist, the inventors have determined that a composition-dependent absorption spectra can be constructed from proper analysis of the total energy emitted from the body. For heterogeneous bodies, composition may be depth dependent and conversely, absorption spectra generated from deeper layers can contain sufficient composition information to allow quantification of the concentrations of individual constituents at that depth into the tissue. This is possible when a temperature gradient either occurs or is induced in the body. The slope of the temperature gradient is such that the temperature is cooler at the surface of the body closer to an infrared detector than at a more distant location from the detector, typically deep within the body.
The invention taught in U.S. patent application Ser. No. 08/820,378 uses the natural temperature within the body as the source of the infrared emissions. As will be explained in more detail below, as these deep infrared emissions pass through layers of tissue that are at a lower temperature than the deeper emitting layer, they are selectively self absorbed. This selective self-absorption produces bands of reduced energy in the resulting emission spectra when the energy finally exits the material under study. The spectra containing the bands where energy has been self absorbed is called an absorption spectra.
The invention taught in U.S. patent application Ser. No. 08/816,723 employs cooling to promote “self-absorption” by letting the temperature gradient propagate to selected layers typically between 40 and 150 microns below the surface. When the temperature gradient has sufficiently propagated, the techniques presented therein can non-invasively deliver absorption spectra of the tissue, blood, and interstitial fluid containing glucose. The inventions incorporated by reference can deliver precise information about the composition of individual layers deep within a heterogeneous body of material by measuring the absorption spectra at different times as a temperature gradient propagates from the surface to deep within the material under test.
According to Ser. No. 08/820,378, there is provided a spectrometer for the non-invasive generation and capture of thermal gradient spectra from human or animal tissue. The spectrometer includes an infrared transmissive thermal mass for inducing a transient temperature gradient in the tissue by means of conductive heat transfer with the tissue, and cooling means in operative combination with the thermal mass for cooling the thermal mass.
Also provided is an infrared sensor means for detecting infrared emissions emanating from the tissue as the transient temperature gradient progresses into the tissue, and for providing output signals proportional to the detected infrared emissions. Data capture means is provided for sampling the output signals received from the infrared sensor means as the transient temperature gradient progresses into the tissue.
The invention of Ser. No. 08/820,378 also provides a method for the non-invasive generation and capture of thermal gradient spectra from living tissue. The method comprises the steps of:
cooling an infrared transmissive mass;
placing the infrared transmissive mass into a conductive heat transfer relationship with the tissue, thereby generating a transient temperature gradient in the tissue;
detecting infrared emissions emanating from the tissue and passing through the infrared transmissive mass;
providing output signals proportional to the detected infrared emissions; and
sampling the output signals as the transient temperature gradient progresses into the tissue.
In one preferred embodiment taught in Ser. No. 08/816,723 a germanium cylinder, cooled to 0° C., is brought into intermittent contact with the patient's warm skin, and the resulting thermal gradients so formed are used to perform the methodology taught in Ser. No. 08/820,378. Skin warming, according to this invention, may be accomplished by simply allowing the patient's skin to naturally re-warm between cooling contact. Alternatively, an external heat source in the form of a second, warmer germanium cylinder may be utilized to facilitate skin warming. The intermittent heating and cooling of the patient's skin results in the creation of transient thermal gradients. In this manner, useful spectra are generated which in turn yield very good measurements of the patient's blood glucose levels.
While the methodology taught in the incorporated references presents a significant advance in non-invasive glucose metrology, there exists room for further improvements.
One such improvement lies in the manner in which the data collected by the apparatus are manipulated. In the methodology taught in Ser. No. 08/820,378 a volts-to-watts radiometric calibration step is often required. To preclude this requirement, the teachings of U.S. Pat. No. 6,161,028 were developed; this patent is herewith incorporated by reference. The methodology taught therein takes advantage of the fact that by inducing a temperature gradient, a difference parameter between the signal at a reference wavelength and the signal of an analyte absorption wavelength may be detected. The frequency or magnitude or phase difference of this parameter may be used to determine analyte concentration. A further object of the invention taught therein is to provide a method of inducing intermittent temperature modulation and using the frequency, magnitude, or phase differences caused by analyte abso
Braig James R.
Correia David J.
Cortella Julian
Godfrey Joan C.
Goldberger Daniel S.
Knobbe Martens & Olson Bear LLP.
OptiScan Biomedical Corporation
Winakur Eric F.
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