Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-12-22
2002-06-25
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S478000, C600S407000, C600S473000
Reexamination Certificate
active
06411838
ABSTRACT:
FIELD OF THE INVENTION:
This invention relates to the delivery of excitation light to a target tissue and the collection of response light therefrom for spectral analysis.
BACKGROUND OF THE INVENTION
Optical methods are being used with increasing frequency to determine the composition and state of samples. In particular, the use of optical techniques is growing in the medical arts for the diagnosis of tissue health in-vivo. In some instances, a beam of light is used to illuminate the tissue in a specific region, causing excitation of said tissue. Light emitted by the tissue is then collected by the receiving device and analyzed to determine the physical health of the tissue.
Two methods are known in the art that deliver and receive illumination from a designed region of tissue. In the first method, termed bistatic, the illuminating beam is focused on the sample from one direction, and light that is backscattered or emitted from the sample is received by an optical system located in a position different from the position of the delivery system. In the second method, termed monostatic, the illuminating beam path and the receiver beam path lie along the same line of sight. Such an optical scheme is also called confocal if the location of the sample is at the focal point of both the illumination optical system and the receiver optical system of the device.
According to the bistatic method for examining a sample, the field of illumination from the source and the field of view of the receiver are aligned so as to overlap at the sample, while illumination and viewing take place at different locations. Certain limitations are understood to accompany bistatic methods. For example, when this method is employed with an illuminating device that does not directly contact the sample, it is sensitive to misalignments of the device to the sample, so that any error in the distance of the non-contact device from the tissue may result in significant decrease in the amount of light collected by the receiver.
Bistatic optical probes may have illumination and receiving sections sufficiently separated from each other that the optical paths from the sample to each section are oriented along different directions. The effect of this optical design is that the illumination path and the receiving path form two sides of a triangle, intersecting in a single localized region. The surface of the sample may then be positioned in this overlap region. For some applications, this triangulation can be exploited. The receiver section may be configured to collect a signal only when the proper distance from the probe to the sample is achieved. In this embodiment, when the receiver section of the probe is detecting a signal, the distance from the probe to the sample can be known. This embodiment may lend itself to greater ease of analysis and probe calibration.
For many applications, however, the bistatic configuration is not useful. For example, contours to the sample may cause shadowing of the response from the surface of the sample to the receiver, or may cause the overlap of the receiver line of sight and the illumination line of sight to fall off of the surface. The monostatic optical design may overcome these problems. It is furthermore understood that misalignment problems can be overcome by use of a monostatic optical configuration. Additionally, if the monostatic optical configuration is also confocal, the optical receiver will collect only the light from the illuminated region on the sample.
In one embodiment of a monostatic device, the illuminating beam of light may be transmitted through a beamsplitter before it interacts with the sample. The light emitted by the sample returns to the beamsplitter, where it is reflected toward a receiver system in the device. If the illuminating excitation beam and the returned emission from the sample occupy different regions of the electromagnetic spectrum, the beamsplitter can be a dichroic mirror, with high transmission at the excitation wavelengths and high reflectivity at the sample emission wavelengths. This offers the possibility for high efficiency of optical throughput in the device. If, however, the spectral regions for the excitation and emission beams have significant overlap, the dichroic mirror cannot be used, and significant losses of optical signal can occur. In the case where the excitation and emission spectral regions are identical, the optimum beamsplitter will transmit only 50% of the excitation signal, and will reflect only 50% of the returned signal emitted by the sample. The overall efficiency of such a device is only 25%.
Another limitation of the use of a beamsplitter in the path of the excitation and emission beams is the possibility that light can be directly scattered from the illumination side to the receiver side of the probe without interaction with the sample. This can create large optical signals containing no information about the sample.
It is understood in the art that probes are available for multispectral imaging of a sample. A probe may comprise a housing and beam splitting apparatus within the housing, designed for imaging. Such a probe may not address the problem of scattering from the beam splitting surface and the level of interference this scatter will cause.
It is well known in the art that optical interrogation of samples may permanently alter the nature of the sample as a result of the measurement. Laser-induced fluorescence studies of samples, for example, temporarily alter the physical nature of the molecules in the sample. This alteration produces molecules in excited energy states that liberate optical radiation as they relax to the more favorable ground energy state. Chemical and biological changes in specific samples can also be created to liberate an optical response from the sample. An example of a permanent change in the sample is seen in laser breakdown spectroscopy, where a portion of the surface of the sample is ablated by the intense laser beam. The ablated material is in the form of an excited plasma that liberates light distinctive of the composition of the sample.
While some changes in the physical, chemical, or biological condition of the sample can be important for creating a response to the illumination, certain other changes in the sample that may be caused by an optical system or a probe may interfere with the desired measurement. For example, it is known from spectroscopic studies of in-vivo tissue that hemoglobin content can have diagnostic significance. Optical probes that contact the tissue can alter the flow of blood to the tissue, thereby altering the hemoglobin spectral feature. Such changes in sample characteristics adversely affect the ability of the optical device to measure the sample characteristics correctly. Contact of the probe with the target tissue may cause other relevant changes in the signals emitted from the tissue following illumination.
Probes in the art are known that identify tissue which is suspected of being physiologically changed as a result of pre-cancerous or cancerous activity by contacting the tissue, using separate optical fibers for transmitting the excitation light and receiving the emitted light, or using other conduits to direct heat, electrical, sound, or magnetic energy towards a target tissue. These devices rely upon contact with the tissues to derive their data, and do not embody a non-contact system for identifying tissue abnormalities.
Non-contact optical probes may be configured so they do not alter a sample in the same way as contact probes. Non-contact methods are particularly attractive in medical in-vivo diagnostic instrumentation because they do not perturb the tissue being investigated and because they do not carry the risk of contamination of the measurement site. However, non-contact probes can suffer from other limitations, most notably problems with alignment and focus. For proper operation, the two main components to the probe, namely the illumination section and the receiving section, must be aligned to the same location on the sample, and both m
Modell Mark
Nordstrom Robert
Zelenchuk Alexander
Lateef Marvin M.
Medispectra, Inc.
Qaderi Runa Shah
Testa Hurwitz & Thibeault LLP
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