Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-01-18
2001-12-18
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06332091
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method and apparatus for detecting pulmonary edema.
BACKGROUND ART
Pulmonary edema is an abnormal accumulation of fluid in the extravascular tissue and spaces of the lung which results in poor respiration.
Pulmonary edema represents a common problem seen in many clinical settings, and there are a number of causes of pulmonary edema such as an increase in hydrostatic pressure, increase in capillary permeability and a decrease in lymphatic clearance (Ref.
1
).
The increase in hydrostatic pressure is caused by an increase in the venous pressure which usually occurs due to heart failure. The change in the permeability of the capillaries is also an important cause of pulmonary edema. If the exchange between plasma and tissue is altered in such a manner as to allow the exchange of fluid between the interstitial space and plasma more readily, then this results in an increase in fluid. The third possible cause of pulmonary edema is the decrease in lymphatic clearance. In the case where this is altered there will be an accumulation of fluid in the interstitial space. The two distinct consequences of the fluid increase are, 1) the alveoli volume will decrease in size due to the volume increase of the interstitial space and 2) a reduction in the alveoli space due to fluid accumulation.
Pulmonary edema is readily detectable by conventional chest radiographs, the present standard being X-ray. Attempts have been made to use X-rays as both a qualitative and quantitative assessment of edema (Ref.
2
). The method can be performed in one of two ways, a visual inspection or a Computed Tomography (CT) of the radiograph. There are a number of small features which can be seen on plain chest radiographs. The most common is a scattered increase in lung radiographic density sometimes referred to as “clouding” (Ref.
3
). This change is often difficult to recognize. CT scans involve a densitometric analysis of the radiograph (Refs.
4
and
6
). However, this approach to quantitative pulmonary edema is limited. The problem with the diagnosis of pulmonary edema is the interpretation of the radiographs. The methods involve observing the physiological changes experienced pre- and post-pulmonary edema. The changes involved are increases in vessel diameters, bronchial wall thickening, and opacities associated with fluid accumulation. In the extreme case of pulmonary edema, a dense spot on the radiograph as well as physiological enlargement of the chest cavity make the identification simple. In the early stages of edema, radiographs can be misleading and interpreted in a number of manners making detection virtually impossible. Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) are also used but experience the same problem of identification (Ref.
5
).
While chest radiographs are an invaluable asset to the qualitative identification of edema, they are of limited value in diagnosis of pulmonary edema in early stages of its development. Pulmonary edema is life-threatening and difficult to treat; existing radiographic methods for its diagnosis only provide effective diagnosis at an advanced stage of development.
DISCLOSURE OF THE INVENTION
It would be highly advantageous to have other methods for detecting pulmonary edema, especially methods capable of providing a diagnosis of pulmonary edema at an early stage of its development.
In accordance with one aspect of the invention, there is provided a method of detecting pulmonary edema in a lung comprising:
a) exposing a lung under investigation to infrared radiation,
b) measuring reflected infrared radiation scattered by the lung as a spectral response to the presence of water in the lung,
c) comparing the reflected radiation with calibrated values of reflected radiation for lung water levels indicative of pulmonary edema, and
d) evaluating occurrence of pulmonary edema in the lung from the comparison developed in step c).
In accordance with another aspect of the invention there is provided an apparatus for detecting pulmonary edema in a lung comprising:
i) a plurality of optical fibers effective to transmit infrared radiation from a source to a lung under investigation and to transmit reflected scattered radiation from said lung,
ii) a source of infrared radiation operatively associated with said fibers for transmission of infrared radiation,
iii) detector means for receiving reflected scattered radiation from said fibers, and issuing signals responsive thereto,
iv) evaluating means for receiving said signals and comparing the received signals with calibrated values.
In accordance with another aspect of the invention there is provided use of infrared radiation to detect pulmonary edema in a lung.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
The invention provides an alternative non-invasive method in the detection of pulmonary edema employing infrared spectroscopy especially near-infrared spectroscopy. The Near-Infrared (NIR) region is composed of wavelengths from 700-2500 nm. The spectral region between 600-1300 nm provides a therapeutic window having special significance in biomedical applications. The main absorptions in this region are due to components which contain C—H, O—H, and N—H vibrations. When tissue becomes irradiated with light in this region, some of the light is absorbed by the tissue while a large portion of the light is diffusely scattered. Most of the interactions of light with tissue are scattering events and such events are highly forward scattering, i.e. light propagates in a forward direction. The combined attributes of the low absorption and the highly forward scattering nature of tissue allows for a substantial penetration and a high remittance of the scattered light whereby the near infrared is suitable for studying biological and physiological characteristics such as changed levels of water as exhibited in pulmonary edema.
In preferred embodiments the infrared radiation has a wavelength between 600 and 1300 nm.
In the method, the lung is typically exposed in step a) to the radiation at a plurality of sites of the lung, and step b) comprises measuring the reflected radiation scattered by this plurality of sites.
REFERENCES:
patent: 4874949 (1989-10-01), Harris et al.
patent: 5601080 (1997-02-01), Oppenheimer
patent: 5645061 (1997-07-01), Kessler et al.
patent: 5916152 (1999-06-01), Oppenheimer et al.
patent: 44 10 888 (1995-05-01), None
patent: 0 575 712 (1993-12-01), None
patent: WO 96/04535 (1996-02-01), None
Burns David Hugh
Leonardi Lorenzo
Oppenheimer Luis
Lateef Marvin M.
Mantis Mercader Eleni
McGill University
Swabey Ogilvy Renault
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