Cancer is a major public health problem in the United States and other developed countries. According to the American Cancer Society (ACS), one in four deaths in the United States is due to cancer, of which skin cancer is the most common form. One in five Americans will contract skin cancer in the course of a lifetime and, on average, one person dies every hour from skin cancer, primarily melanoma, the most deadly form of skin cancer.
Although melanoma can quickly spread to other body parts, it is curable if detected early and properly treated. For most present-day medical practitioners, the final cancer or pre-cancer diagnosis is based on excisional (surgical) biopsy. To date, excisional biopsy has been the only certain method to determine if a growth is cancerous. While excisional biopsy is the standard method for cancer detection, many biopsies are done on a hit-or-miss basis because only small pieces of tissue are excised at random and dissected to check for cancerous cells. Moreover, excisional biopsy imposes problems, like the risk of cancer cell spreading, infection, and hemorrhage.
Due to the invasiveness of excisional biopsy, there is a present desire for a non-invasive, early-stage method for detecting cancer or pre-cancer. Photonics solutions have carried justified hopes in providing such a non-invasive method. One such photonics solution is optical coherence tomography (OCT). OCT can be used to capture high-resolution, cross-sectional images of tissues, such as the skin, to facilitate diagnosis of cancer and pre-cancer. Another photonics solution is fluorescence spectroscopy. Fluorescence spectroscopy can be used to capture cross-sectional images of fluorescent light emitted from features within tissue that may be indicative of cancer or pre-cancer.
Recently it has been proposed to use OCT in conjunction with fluorescence spectroscopy to diagnose cancer or pre-cancer. The desirable optical sectioning of OCT combined with the information provided by fluorescence spectroscopy enables imaging of microscopic structures in tissues at depths well beyond the reach of conventional confocal microscopes and simultaneously provides valuable chemical composition information about the tissue.
Current systems for simultaneously performing OCT and fluorescense spectroscopy require separate light detectors for the OCT and the spectroscopy information obtained from the tissue under evaluation. Given the expense and complexity of such systems, it would be desirable to have a system and method for simultaneously performing OCT and fluorescence spectroscopy that uses a single light detector that collects both the OCT/OCM and the spectroscopy information.
Disclosed are systems and method for performing simultaneous optical coherence tomography and spectroscopy. In one embodiment, a system includes a light source that emits light to be delivered to a material under evaluation, and a receiver that collects both light that is backscattered by features of the material and fluorescent light that is emitted by features of the material.
In one embodiment, a method includes simultaneously collecting near-infrared light backscattered by a material under evaluation and fluorescent light emitted by the material under evaluation using a single light detector.
The components in the figures are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. In the figures, like reference numerals designate corresponding parts throughout the several views.
As described above, there is a current desire for photonics solutions that may be used to aid in the detection and diagnosis of cancer or pre-cancer. More particularly, desired are systems that can simultaneously perform optical coherence tomography (OCT) and fluorescence spectroscopy to aid in the detection and diagnosis of cancer or pre-cancer. Unfortunately, current systems require separate light detectors for the OCT and the spectroscopy information obtained from the tissue under evaluation.
As described in the following, disclosed are systems and methods for performing simultaneous tomography and spectroscopy in which a single receiver or detector is used to collect the information used in both the tomography and spectroscopy. In some embodiments, Fourier-domain OCT is simultaneously performed along with two-photon fluorescence spectroscopy. In such a case, high-resolution morphological (i.e., structural) information and biochemical information about the tissue under evaluation can be obtained. Moreover, OCT images and fluorescence spectroscopy images of discrete portions of the tissue can be generated that can be compared or superimposed on top of each other for visual inspection and computer analysis.
In the following, described are various embodiments of systems and methods for performing simultaneous tomography and spectroscopy. Although particular embodiments are described, the disclosed systems and methods are not limited in their application to those particular embodiments. Instead, the described embodiments are mere example implementations of the disclosed systems and methods. Furthermore, although the systems and methods are described as being particularly suitable for use in the detection and diagnosis of cancer and pre-cancer of animal tissue, it is to be understood that the methods and systems are not limited to that application and can be used to image and evaluate tissue, or non-biological materials, for other purposes.
Positioned between the light source 102 and the material 104 under evaluation is a beam splitter 106 and an objective 108. The beam splitter 106 is configured to both reflect and transmit light in the visible and NIR spectra and, for example, comprises a 50/50 beam splitter. Therefore, the light emitted by the light source 102 can pass through the beam splitter 106 and be focused by the objective 108 on a desired location of the material 104, for example at a point below the surface 110 of the material. By way of example, the objective 108 has a numerical aperture of 0.3, which yields a transverse resolution of approximately 1.6 microns (μm) and a depth of focus of approximately 20 μm.
In addition, the system 100 comprises mirrors 112 and 114, which form part of a reference path for the light emitted by the source 102. As shown in
Further comprised by the system 100 is a receiver 116 that collects light information that is backscattered (OCT) and emitted (fluorescence spectroscopy) by the material 104 under evaluation. As indicated in
In communication with the receiver 116 is a computer 122 that can be used to manipulate intensity data from the light detector 120. Such manipulation can comprise the generation of images and/or qualitative analysis of the data.
As described above, the system 100 can be used to perform Fourier-domain OCT. To that end, NIR light is emitted by the light source 102 along path a. A portion of that light is transmitted by the beam splitter 106 toward the objective 108 along path b. The objective 108 focuses the light at a desired location within the material 104 under evaluation. Some of that light is then backscattered by features contained within the material 104 and travels back through the objective 108 toward the beam splitter 106 along path c. A portion of that light is then reflected by the beam splitter 106 along path d to the receiver 116.
Simultaneous to the above, a portion of the light emitted by the light source 102 is reflected by the beam splitter 106 along path e. That light is reflected by the mirror 112 and travels along path f toward the mirror 114. The mirror 114 reflects the light back toward the mirror 112 along path g. The mirror 112 then reflects that light toward the beam splitter 106 along path h. A portion of that light travels through the beam splitter 106 toward the receiver 116 along path i.
With the above-described light propagation, the receiver 116 receives both a sample signal from the signal path defined by paths b and c, and a reference signal from the reference path defined by paths e, f, g, and h. Because the reference path is configured so as to have an optical length that is substantially equal to that of the sample path, interference will occur at the receiver 116 such that a spectrally measured interferogram is generated that contains information about the structural features of material 104.
In addition to performing Fourier-domain OCT, the system 100 simultaneously performs two-photon fluorescence spectroscopy. In that regard, light emitted by the light source 102 travels along paths a and b in the manner described above. With appropriate tuning of the light source 102 and focusing of the objective, the light is highly concentrated on features of the material 104 under evaluation so as to cause two-photon excitation that results in emission of visible, fluorescent light from those features. When that occurs, the fluorescent light has a wavelength that is approximately half the wavelength of the NIR light emitted by the light source 102. Therefore, if the light source 102 emits light having a central wavelength of approximately 800 nm, fluorescent light having a wavelength of approximately 400 nm is emitted by the material features. Although such fluorescence may occur naturally, a suitable fluorescent dye can be applied to the material 104 to enable or increase fluorescence.
The emitted fluorescent light travels along path c to the beam splitter 106, which reflects the light toward the receiver 116 along path d. Therefore, the receiver 116 receives both the NIR light that is backscattered by the material and the fluorescent light that is emitted by the material.
Significantly, the use of Fourier-domain OCT, as opposed to other OCT methodologies such as time-domain OCT, enables the use of a single receiver 116, and therefore a single light detector 120, in capturing OCT and spectroscopy data. Specifically, because Fourier-domain OCT is performed by collecting spectra, a single receiver 116 and a single light detector 120 can be used to collect the spectra associated with both the OCT and the spectroscopy. Because the OCT signals are NIR spectra and the fluorescence spectroscopy signals are visible spectra, no spectral overlap occurs as between the OCT and the spectroscopy signals.
As stated above, the manipulation performed by the computer 122 can comprise the generation of OCT and fluorescence spectroscopy images that can be, for example, displayed for a medical practitioner. Given that those images are simultaneously-captured images of the discrete portions of the material, they can be displayed in association with each other for easy comparison, or can be superimposed on top of each other. In addition, the computer 122 can analyze the image data according to one or more algorithms to aid in the detection or diagnosis of a phenomenon, such as disease. For example, the computer 122 can identify the boundaries of layers of skin and calculate layer thicknesses from the structural data that results from the OCT. In addition, the computer 122 can identify features within the spectroscopy data that are considered abnormal as determined by the observed wavelengths and/or intensity of the fluorescent light. Such analyses may be facilitated by a calibration process in which the characteristics of “normal” tissue are recorded for purposes of comparison (e.g., as a control).
The use of two-photon fluorescence spectroscopy is desirable for several reasons. First, two-photon fluorescence spectroscopy enables greater imaging depth. Second, two-photon fluorescence spectroscopy enables the use of a single, NIR light source. Generally speaking, a fluorescent light source could be used to illuminate features of the material under evaluation. However, two-photon excited fluorescence, which occurs when two IR photons simultaneously collide with a feature, excites the feature to a state virtually identical to that caused by a single visible photon of about half the wavelength such that the feature emits a visible photon. Therefore, instead of illuminating the material with an NIR source for OCT and a separate fluorescent source for fluorescence spectroscopy, an NIR source alone can be used in the system. In addition to reducing the complexity of the system, avoiding the use of a separate fluorescent source also reduces noise that would occur in the form of light signals received from the source in the fluorescent signal. Third, and perhaps most significant, the use of two-photon fluorescence spectroscopy enables the collection of fluorescent light from discrete points of the material under evaluation rather than a general, undefined region because two-photon absorption only occurs at points of high light intensity (i.e., the focus point). Therefore, the fluorescent light is spatially resolved and coincident with the backscattered NIR light so that the OCT and spectroscopy images are automatically registered with each other, thereby enabling direct comparison or superimposition.
Referring to
In accordance with the above disclosure, a method for simultaneously performing OCT and fluorescence spectroscopy can be described as that illustrated in flow diagram of
The method further comprises spreading the backscattered NIR light, the NIR light from the reference path, and the fluorescent light resulting from the two-photon excitation, as indicated in block 904. Next, the spread light is collected with a single light detector, as indicated in block 906. With reference to block 908, an interference signal resulting from the interference between the backscattered NIR light and the NIR light from the reference path is manipulated. By way of example, frequency-domain analysis, for instance Fourier-transform analysis, can be performed to generate an OCT image. In addition, as indicated in block 910, the fluorescent light data is manipulated, for example to generate a fluorescence spectroscopy image.
As stated above, while particular embodiments have been described in this disclosure, alternative embodiments are possible. For example, although various embodiments have been described that comprise discrete components, it is to be understood that further alternative embodiments may comprise hybrid embodiments that include one or more components of the alternative embodiments. For instance, one such hybrid embodiment may comprise one or more of the grating and lens of
This application claims priority to copending U.S. provisional application Ser. No. 60/773,486, entitled, “Optical Apparatuses and Methods,” filed Feb. 15, 2006, which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
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60773486 | Feb 2006 | US |