Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
1997-02-13
2001-06-12
Shay, David M. (Department: 3739)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S407000, C600S473000, C600S476000, C600S477000
Reexamination Certificate
active
06246892
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to quantitative analyses of absorptive constituents in biological tissues by employing a phase modulation spectroscopy.
Continuous wave (CW) tissue oximeters have been widely used to determine in vivo concentration of an optically absorbing pigment (e.g., hemoglobin, oxyhemoglobin) in biological tissue. The CW oximeters measure attenuation of continuous light in the tissue and evaluate the concentration based on the Beer Lambert equation or a modified Beer Lambert absorbance equation. The Beer Lambert equation (1) describes the relationship between the concentration of an absorbent constituent (C), the extinction coefficient (&egr;), the photon migration pathlength <L>, and the attenuated light intensity (I/I
0
).
log
[
I
/
I
0
]
⟨
L
⟩
=
∑
ε
i
C
i
(
1
)
The CW spectrophotometric techniques can not determine &egr;, C, and <L> at the same time. If one could assume that the photon pathlength were constant and uniform throughout all subjects, direct quantitation of the constituent concentration (C) using CW oximeters would be possible.
In tissue, the optical migration pathlength varies with the size, structure, and physiology of the internal tissue examined by the CW oximeters. For example, in the brain, the gray and white matter and the structures thereof are different in various individuals. In addition, the photon migration pathlength itself is a function of the relative concentration of absorbing constituents. As a result, the pathlength through an organ with a high blood, hemoglobin concentration, for example, will be different from the same with a low blood hemoglobin concentration. Furthermore, the pathlength is frequently dependent upon the wavelength of the light since the absorption coefficient of many tissue constituents is wavelength dependent. Thus, where possible, it is advantageous to measure the pathlength directly when quantifying the hemoglobin concentration in tissue.
SUMMARY OF THE INVENTION
In general, in one aspect, a spectroscopic system for quantifying in vivo concentration of an absorptive pigment in biological tissue includes an oscillator constructed to generate a first carrier waveform of a first frequency on the order of 10
8
Hz (i.e., in the range of 10 MHz to 1 GHz), a light source constructed to generate light of at least two selected wavelengths modulated by the carrier waveform, and a detector constructed to detect radiation that has migrated over photon migration paths in the tissue from an input port to a detection port spaced several centimeters apart. At least one of the wavelengths is sensitive to concentration of an absorptive pigment present in the tissue, while the tissue exhibits similar scattering properties at the two wavelengths. A phase detector is constructed to compare, at each wavelength, the detected radiation with the introduced radiation and determine therefrom the phase shift of the detected radiation at each wavelength. A processor is constructed to quantify the concentration of the absorptive pigment based on the phase shifts measured at the two wavelengths and based on a scattering property of the tissue.
In general, in another aspect, a spectroscopic system for quantifying in vivo concentration of an absorptive pigment in biological tissue includes an oscillator constructed to generate a first carrier waveform of a first frequency on the order of 10
8
Hz (i.e., in the range of 10 MHz to 1 GHz), a light source constructed to generate light of at least two selected wavelengths modulated by the carrier waveform, and a detector constructed to detect radiation that has migrated over photon migration paths in the tissue from an input port to a detection port spaced several centimeters apart. At least one of the wavelengths is sensitive to concentration of an absorptive pigment present in the tissue, while the tissue exhibits similar scattering properties at the two wavelengths. The spectroscopic system also includes a phase splitter, two double balanced mixers, and a processor. The phase splitter is constructed to receive the carrier waveform and produce first and second reference phase signals of predefined substantially different phases. The first and second double balanced mixers are constructed to receive from the phase splitter the first and second reference phase signals, respectively, and also receive from the detector the detector signal to produce therefrom a real output signal and an imaginary output signal, respectively. The processor is constructed to receive a scattering property of the examined tissue and the real output signal and the imaginary output signal and quantify therefrom the concentration of the absorptive pigment in the examined tissue.
Different embodiments of this type of the spectrophotometer may include one or more of the following features. The processor may calculate, at each wavelength, a phase shift of the detected radiation as the inverse tangent of the ratio of the imaginary output signal and the real output signal. The processor may calculate, at each wavelength, a detected amplitude as the square root of the sum of the squares of the real output signal and the imaginary output signal.
In different embodiments, the spectrophotometer may be a dual wavelength, single frequency system or a dual wavelength, dual frequency system. Each system can measure data for a single source-detector separation (i.e., separation of the input port and the detection port) or for several source-detector separations.
Different embodiments of the spectrophotometer may include one or more of the following features.
The spectrophotometer may include a second oscillator constructed to generate a second carrier waveform of a second selected frequency on the order of 10
8
Hz, while the tissue exhibits similar scattering properties at the selected frequencies. The source of the spectrophotometer is operatively coupled to the second oscillator and is constructed to generate electromagnetic radiation of the two wavelengths modulated by the second carrier waveform. The detector is further constructed to detect the radiation modulated by the second carrier waveform. The phase detector is further constructed to compare, at each the wavelength, the detected radiation of the second carrier waveform with the introduced radiation and determine therefrom the phase shift of the detected radiation of the second frequency.
The processor may calculate a ratio of absorption coefficients at the two wavelengths, and calculate a value of oxygen saturation based on the ratio.
The processor may calculates the ratio of absorption coefficients by taking a ratio of the phase shift and a square root of the frequency for each the wavelength and each the frequency.
The processor may calculate the ratio of absorption coefficients by taking a ratio of the phase shifts detected at the two wavelengths. The phase shift of each the wavelength may be corrected for &thgr;
0
.
The spectrophotometer may include a mechanism for positioning the input and detection ports at several selected relative distances.
The spectrophotometer may include a look up table comprising values of the scattering property for different tissue types. These values may be the effective scattering coefficients, (1−g)&mgr;
s
.
The spectrophotometer may further include a magnitude detector constructed to measure an amplitude of the detected radiation. The processor may calculate the scattering property based on the measured amplitude. The processor may calculate the concentration by employing Eq. 5.
The absorptive pigment may be an endogenous pigment, such as oxy-hemoglobin or deoxy-hemoglobin. The absorptive pigment may be an exogenous contrast agent.
REFERENCES:
patent: 3360987 (1968-01-01), Flower et al.
patent: 3365717 (1968-01-01), Holscher
patent: 3522992 (1970-08-01), Jaffe
patent: 3638640 (1972-02-01), Shaw
patent: 4138727 (1979-02-01), Mantz
patent: 4223680 (1980-09-01), Jobsis
patent: 4281645 (1981-08-01), Jobsis
patent: 4321930 (1982-03-01
Fish & Richardson P.C.
Non-Invasive Technology
Shay David M.
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