Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
2001-06-07
2003-07-01
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S322000, C600S328000
Reexamination Certificate
active
06587703
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to apparatus and methods for determining absolute values of various properties of a physiological medium. In particular, the present invention relates to non-invasive optical systems and methods for determining absolute values of concentrations of oxygenated and deoxygenated hemoglobins (and/or their ratios). The present invention also relates to apparatus and methods for obtaining such absolute values by solving generalized photon diffusion equations and their simplified variations such as modified Beer-Lambert equations.
BACKGROUND OF THE INVENTION
Near-infrared spectroscopy has been used for non-invasive measurement of various physiological properties in animal and human subjects. The basic principle underlying the near-infrared spectroscopy is that physiological tissues include various highly-scattering chromophores to the near-infrared waves with relatively low absorption. Many substances in a physiological medium may interact or interfere with the near-infrared light waves that propagate therethrough. Human tissues and cells, e.g., include numerous chromophores such as oxygenated hemoglobins, deoxygenated hemoglobins, water, cytochromes, and lipids, where the hemoglobins are the dominant chromophores in the spectrum range of 700 nm to 900 nm. Accordingly, the near-infrared spectroscopy has been applied to measure oxygen levels in the medium such as tissue hemoglobin oxygen saturation (abbreviated as “oxygen saturation” hereinafter) and total hemoglobin concentrations. Various techniques have been developed for the near-infrared spectroscopy, e.g., time-resolved spectroscopy (TRS), phase modulation spectroscopy (PMS), and continuous wave spectroscopy (CWS).
The TRS technology is based on operational principles such as pulse-time measurements and pulse-code modulation. In particular, it measures a time delay between an entry and an exit of electromagnetic waves to and from the physiological medium. Typically, the TRS applies to the medium an impulse or pulse sequence of electromagnetic waves having a duration in the order of a few pico-seconds. Photon diffusion encodes tissue characteristics not only in the timing of the delayed pulse received by a detector, but also in the received intensity time profile. Therefore, instead of receiving a “clean” replica of the transmitted pulse, the return signals are spread out in time, and have greatly reduced amplitudes. Accordingly, the TRS measures the intensity of the return signals over a finite period of time, which is long enough to detect an entire portion of the delayed return signals. Based on such shape changes and amplitude attenuation of the input impulse or pulse, different times of arrival of photons and the mean time delay between the light (or wave) source and detector are used to obtain the tissue absorption and tissue scattering through, e.g., deconvolution of the return signals. Information on the tissues traversed (such as optical pathlengths and their changes) is then readily obtained. Details of the TRS technology are provided, for example, in D. A. Boas et al., Proc. Natl. Acad. Sci., vol. 91, p. 4887 (1994); R. P. Spencer and G. Weber, Ann. (N.Y.) Acad. Sci., vol. 158, p. 3631 (1996); and J. Sipior et al., Rev. Sci. Instrum., vol. 68, p. 2666 (1997), all of which are incorporated herein by reference for background.
The PMS technology employs phase-modulated electromagnetic waves irradiated by the wave source and transmitted through the physiological medium. Typical examples of PMS include homodyne systems, heterodyne systems, single side-band systems, and other systems based on transmitter-receiver cross-coupling and phase correction algorithms. Like TRS, PMS systems monitor the intensities of the attenuated electromagnetic waves. In addition, it is necessary for the PMS system to measure frequency-domain parameters, such as phase shift of the electromagnetic waves which is independent of the wave intensities. Based on such time-domain and frequency-domain information, PMS systems determine spectra of an absorption coefficient and/or scattering coefficient of the chromophores of the medium, and calculate absolute values of the hemoglobin concentrations. Details of the PMS technology are provided, for example, in U.S. Pat. No. 5,820,558 and a technical article by B. Chance et al. in Rev. Sci. Instrum., vol. 69, p. 3457 (1998), both of which are incorporated herein by reference in their entirety.
By contrast, CWS systems employ electromagnetic waves that are non-impulsive and not phase modulated. That is, CWS systems apply to the medium electromagnetic waves having at least substantially identical amplitude over a measurable period of time. On the detection side, CWS systems only measure intensities of the irradiated and detected electromagnetic waves and does not assess any frequency-domain parameters thereof.
In a homogeneous and semi-infinite medium model, both of the TRS and PMS have been used to obtain spectra of an absorption coefficient and (reduced) scattering coefficient of the physiological medium by solving a photon diffusion equation, and to calculate the absolute values of the concentrations of oxygenated and deoxygenated hemoglobins as well as tissue oxygen saturation. Despite their capability of providing such absolute values of the hemoglobin concentrations and the oxygen saturation, one major drawback of TRS and PMS is that the TRS equipment requires a pulse generator and detector and that the PMS needs additional hardware and signal processing capabilities to determine frequency-domain parameters. Accordingly, in practice both TRS and PMS systems are bulky and expensive. To the contrary, the CWS may be manufactured at a lower cost because all it needs to do is to perform intensity measurement. However, prior art CWS technology was limited in its utility because it can only provide the relative values or changes in the oxygenated and deoxygenated hemoglobin concentrations. Therefore, the conventional CWS cannot estimate the tissue oxygen saturation from such changes in the hemoglobin concentrations. Thus, there is a need for novel CWS systems and methods for measuring absolute value of concentrations of the hemoglobins and the oxygen saturation in the physiological medium.
SUMMARY OF THE INVENTION
The present invention generally relates to apparatus and methods for obtaining the absolute values of concentrations of chromophores of a medium and/or absolute values of their ratios. More particularly, the present invention relates to non-invasive optical systems and methods based on continuous wave spectroscopy (CWS) methods for determining absolute values of concentrations of the oxygenated and deoxygenated hemoglobins and their ratios in a physiological medium.
In general, wave propagation or photon migration in a medium is described by a generalized photon diffusion equation:
I
=
α
·
β
·
γ
·
I
o
·
e
{
-
B
·
L
·
δ
·
∑
i
(
ϵ
i
C
i
)
+
σ
}
(
1
)
where “I
0
” is a system variable representing an intensity of the electromagnetic waves or photons (e.g., in the near-infrared ranges) irradiated by a wave source and where “I” is another variable denoting an intensity of the electromagnetic waves detected by a wave detector. Parameter “&agr;” is generally associated with the wave source and medium and accounts for, e.g., characteristics of the wave source such as irradiation power and configuration thereof, mode of optical coupling between the wave source and medium, and/or optical coupling loss therebetween. Parameter “&bgr;” is generally associated with the wave detector and medium and accounts for, e.g., characteristics of the wave detector such as detection range and sensitivity, optical coupling mode between the wave detector and medium, and associated coupling loss. Parameters “&agr;” and “&bgr;” may also depend upon, to some extent, other system characteristics and/or optical properties of the medium, including tho
Cheng Xuefeng
Wang Lai
Xu Xiaorong
Zhou Shuoming
Photonify Technologies, Inc.
Ritter Lang & Kaplan LLP
Winakur Eric F.
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