WO2009081358A1

WO2009081358A1 - Fibre-optic probe

Info

Publication number: WO2009081358A1
Application number: PCT/IB2008/055442
Authority: WO
Inventors: Jagadeesh Chandra Bose Rantham Prabhakara; Sarif Kumar Naik; Satish Prasad Rath
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-12-21
Filing date: 2008-12-19
Publication date: 2009-07-02
Also published as: CN101903762A; RU2010130472A; CN101903762B

Abstract

A fibre-optic probe (100) that minimizes the overlap between excitation light and collected light in an optical spectroscopy system is hereby disclosed. The fibre-optic probe comprises an illumination fibre (102) having a length and a tip proximal to a target, wherein the illumination fibre is configured to conduct light from a light source to the target. The fibre- optic probe also includes at least one collection fibre (104,106) having a slanted end proximal to the target, wherein the collection fibre is configured to conduct light away from the target. The illumination fibre is further configured to taper along at least part of its length towards the tip and the slanted end face of the at least one collection fibre faces the pencil-shaped tapered end face of the illumination fibre.

Description

Fibre-optic Probe

FIELD OF THE INVENTION

The invention relates to a fibre-optic probe, particularly for use in spectral analysis of biological tissue.

BACKGROUND OF THE INVENTION

The United States patent US5822072 discusses a fused fibre-optic probe useful for conducting spectral measurements. The fused fibre-optic probe comprises a probe tip having a specific geometrical configuration, an exciting optical fibre and at least one collection optical fibre fused within a housing preferably made of silica. The specific geometrical configurations in which the probe tip can be shaped include a slanted probe tip with an angle greater than 0°, an inverted cone-shaped probe tip, and a lens head. The fused fibre-optic probe is used to transmit excitation optical energy to a sample medium, and also to transmit optical signal, received from the sample medium, to a signal analyzer.

SUMMARY OF THE INVENTION

Due to the geometry of the probe tip in the prior art, there is considerable overlap between the incident or exciting light and collected light. This overlap could lead to a decrease in the intensity of the output light spectrum, which in turn, could result in reduced accuracy in the determination of peak positions in the output spectrum. It is thus desirable to have a fibre-optic probe that is capable of achieving greater accuracy in the determination of peak positions in the output spectrum. Accordingly, a fibre-optic probe that minimizes the overlap between excitation light and collected light is disclosed herein. The fibre-optic probe comprises an illumination fibre having a length and a tip proximal to a target, wherein the illumination fibre is configured to conduct light from a light source to the target. The fibre-optic probe also includes at least one collection fibre having a slanted end proximal to the target, wherein the collection fibre is configured to conduct light away from the target. The illumination fibre is further configured to taper along at least part of its length towards the tip.

Due to the tapered tip, a more focused or narrower beam of light is emitted from the illumination fibre, thus reducing the overlap between the excitation and collection light. The slanted end of the collection fibre helps in increasing the area of collection. The combination of these two features, i.e., the tapered tip and the slanted end, leads to a greater increase in the intensity of the output spectrum compared to using either of these features individually, thereby increasing the accuracy of determination of spectral peak positions.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects will be described in detail hereinafter, by way of example, on the basis of the following embodiments, with reference to the accompanying drawings, wherein:

FIGURE 1 illustrates a fibre-optic probe having a tapered illumination fibre and two collection fibres having slanted ends;

FIGURE 2a illustrates a head-on view of a single collection fibre;

FIGURE 2b illustrates a transverse cross-sectional view of the fibre-optic probe shown in FIGURE 1 ;

FIGURES 3a and 3b illustrate an embodiment of the disclosed fibre-optic probe having an adjustable illumination fibre; and

FIGURE 4 illustrates an optical spectroscopy system including the fibre-optic probe shown in FIGURE 1.

Corresponding reference numerals when used in the various figures represent corresponding elements in the figures.

DETAILED DESCRIPTION OF EMBODIMENTS

In recent years, the utilization of optical spectroscopy for the screening of cancers, especially oral cancer, has been considered. Optical spectroscopy deals with the interaction of electromagnetic radiation with matter, mainly at wavelengths in the ultraviolet (10 nm to 100 nm), visible light (400 to 700 nm), near-infrared (1000 nm to 1 μm) and infrared (10 μm to 1 mm) ranges. Screening patients for oral cancer based on the results of optical spectroscopy measurements involves irradiating a target sample (e.g., biological tissue within the mouth of a subject) with electromagnetic radiation, measuring the amount of light absorbed, emitted and/or scattered from the sample, and analyzing and interpreting the spectral components of the measured light. A promising optical technique is laser induced fluorescence spectroscopy

(LIFS), also called auto-fluorescence spectroscopy (AFS). In this technique, a tissue of interest is excited by a light source, which can be a laser or a high intensity broadband light source and the fluorescence spectrum of the tissue is measured. Additional information about LIFS may be found in the article "Fluorescence Spectroscopy of Neoplastic and Non- Neoplastic Tissue" by Nirmala Ramanujam, Neoplasia, Vol. 2, Nos. 1-2, January- April 2000, pp. 89-117. Though most of the description in this document may refer to LIFS by way of illustration, it is to be noted that the disclosed fibre-optic probe may be used with other spectroscopic techniques as well.

A fibre-optic probe is useful in irradiating and collecting data from hard-to- reach parts of a human anatomy. However, the design of the probe is critical, as it can affect the light delivery to and light propagation into the tissue, the collection efficiency (i.e., the total number of photons collected vs. the total number of photons launched) and the origin of the collected light. The configuration of the illumination (i.e., excitation) and collection fibres in the fibre-optic device plays an important role in deciding the quality of the recorded spectra. The design parameters include choice of single fibre vs. multiple fibres, the size of the illumination and collection fibres, the aperture of the light/excitation source, and the source-to-detector separation. Further information on the design considerations for fibre-optic probes may be found in the articles "Fiber optic probes for biomedical optical spectroscopy" by Urs Utzinger and Rebecca R. Richards-Kortum, Journal of Biomedical Optics 8(1), 121- 147 (January 2003), and "Depth-sensitive reflectance measurements using obliquely oriented fiber probes" by Adrien Ming Jer Wang, Janelle Elise Bender, Joshua Pfefer, Urs Utzinger and Rebekah Anna Drezek, Journal of Biomedical Optics 10(4), 044017 (July/August 2005).

FIGURE 1 shows an embodiment of the disclosed fibre-optic probe 100. An illumination fibre (IF) 102 transmits incident light 108 from a light source (402 shown in FIGURE 4) to a tissue of interest (TIS) 114. Light that is returned 110, 112 after interaction with the tissue of interest 114 is collected by collection fibres (CF) 104, 106, to be transmitted to a processing unit (404 shown in FIGURE 4).

The illumination fibre 102 is tapered at the tip in order to produce a narrower beam of incident light. This reduces the interference of the incident light 108 with the light collected 110, 112 by the collection fibres 104, 106. The collection fibres 104, 106 have slanted ends to maximize the collection area, i.e., the area of the tissue 114 from which reflected light is collected. Instead of reflected light, the collection fibres could also collect scattered light or emitted light, for instance, due to fluorescence from the tissue.

Though the ends of the collection fibres 104, 106 are shown to be slanted in a direction so as to make an acute angle with the longitudinal axis of the illumination fibre 102, an end slanting in the other direction, i.e., so as to make an obtuse angle with the longitudinal axis of the illumination fibre 102 is also considered. Furthermore, various angles for the slanted end are also considered, for example, 30°, 45°, etc. Though only two collection fibres 104, 106 are shown in the figure, a single collection fibre could be used as well. Alternatively, more than two collection fibres could also be used.

FIGURE 2a shows a single collection fibre 204 with a slanted end 202, when the fibre is oriented with the collection surface parallel to the plane of the page. FIGURE 2b shows an end-view or a projection of a bundle of optical fibres in a fibre-optic probe 200 (i.e., when viewed from the tip end of the probe) consisting of a single illumination fibre 208 and six collection fibres 206a, 206b, 206c, 206d, 206e and 206f, each having the slanted end shown in FIGURE 2a.

Due to the slanted ends of the collection fibres 206a-206f, their projections on the plane of the page appear elliptical in cross-section. The two circles 208a, 208b show the projections of the two end-cross sections of the illumination fibre208. In other words, with reference also to FIGURE 1, the illumination fibre 102 has a broad portion and a tapered portion culminating in a narrow tip. The circle 208a illustrates the projection of the broader portion, while the smaller circle 208b is indicative of the tip. It is to be noted that though the illumination fibre 102 shown in FIGURE 1 is pencil-shaped, other tapered shapes are also possible. For example, it might be possible to have an illumination fibre that is tapered all the way from one end, say the end connected to a light source, to the tip. Alternatively, other shapes such as multiple tapered portions interspersed with straight portions are also considered.

In an exemplary embodiment shown in FIGURES 3a and 3b, a fibre-optic probe 300 is provided with an adjustable illumination fibre 302. A typical fibre-optic probe has overlapping illumination and collection areas to minimize the effect of tissue turbidity and the sampling area is usually in the range of 1 mm in diameter, such that fluorescence can be measured with sufficient signal-to-noise ratio. The probe-to-target distance is known to significantly affect the intensity and the region (depth) of origin of fluorescence emission. Hence, a fixed illumination area might not cover the entire tissue of interest in many cases. Under such circumstances, an adjustable excitation probe could help in covering desired areas of the tissue more accurately. The proposed embodiment of FIGURES 3a and 3b overcomes the abovementioned problems, in that it changes the illuminated region by varying the distance between the excitation fibre 302 and the target tissue 312 while retaining the increased collection efficiency of the disclosed fibre-optic probe designs. Particularly, the illumination fibre 302 may be moved up or down within the fibre-optic probe 300 along a longitudinal axis of the fibre-optic probe, in order to move the tip of the fibre farther away or close to the target tissue 312. The longitudinal axis of the fibre-optic probe is also the longitudinal axis of the illumination fibre 302, and hence the movement of the illumination fibre 302 may be described as being along its own longitudinal axis as well. The line arrows show the direction of the light that is incident on the tissue 312 as well as light that is collected by the collection fibres 306. The block arrows illustrate the movement of the excitation or illumination fibre 302. Specifically, FIGURE 3a shows the illumination fibre 302 moved away from the tissue 312, in order to increase coverage by the excitation light, while FIGURE 3b shows the illumination fibre 302 moved closer to the target tissue 312 for a more focused excitation. When the distance between the illumination fibre 302 and the tissue 312 is changed, the intensity of the illumination light source (402 in FIGURE 4) may need to be adjusted. Details of the adjustments required are available in the prior art documents cited previously. The movement of the illumination fibre 302 may be effected through manual means, for example a handle or a screw mechanism attached to the illumination fibre 302. Alternatively, the movement may be effected automatically using stepper motors, and such.

A typical fluorescence spectroscopy system is shown in FIGURE 4. It consists of a light source (LS) 402, an illumination and collection system 100, and a detection and processing unit (DPU) 404 that can measure the emitted light as a function of wavelength.

The light source 402 may be a monochromatic source, e.g., a laser, or a source of high-intensity, broadband radiation. The illumination and collection system 100 is the fibre-optic probe as embodied in the various embodiments in this disclosure. As mentioned previously, it serves to transmit the incident light from the light source 402 to the tissue TIS, as well as to conduct reflected, scattered or emitted light from the tissue TIS to the detection and processing unit 404. The detection and processing unit 404 receives the light from the fibre-optic probe and performs a spectral analysis to detect the various frequency components in the received light. An example of such processing might be a simple Fourier transform operation that detects the spectral peaks in the received light. Other techniques, such as power spectral analysis, etc., are also considered.

Though the embodiments have often been described using light as the incident and collected electromagnetic radiation, it is to be noted that other forms of appropriate electromagnetic radiation may also be used. The order in the described embodiments of the disclosed methods is not mandatory. A person skilled in the art may change the order of steps or perform steps concurrently using threading models, multi-processor systems or multiple processes without departing from the disclosed concepts. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The disclosed method can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the system claims enumerating several means, several of these means can be embodied by one and the same item of computer readable software or hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A fibre-optic probe (100) for conducting spectral measurements, comprising: an illumination fibre (102) having a length and a tip proximal to a target (114), configured to conduct light from a light source (402) to the target (114); and at least one collection fibre (104, 106) having a slanted end proximal to the target (114), configured to conduct light away from the target (114); wherein the illumination fibre (102) is configured to taper along at least part of its length towards the tip.

2. The fibre-optic probe as claimed in claim 1, wherein the illumination fibre is pencil- shaped.

3. The fibre-optic probe as claimed in claim 1, wherein the slanted end makes an angle of 45° to a longitudinal axis of the illumination fibre (102).

4. The fibre-optic probe as claimed in claim 1, wherein the illumination fibre

(302) is moveable along a longitudinal axis of the fibre-optic probe, thereby being capable of adjusting the separation between the target (312) and the tip of the illumination fibre (302).

5. An optical spectroscopy system comprising: an excitation light source (402); an illumination and collection system (100); and a detection and processing unit (404) configured to measure the emitted light as a function of wavelength; wherein the illumination and collection system (100) includes a fibre-optic probe comprising: an illumination fibre (102) having a length and a tip proximal to a target (114), configured to conduct light from a light source (402) to the target (114); and at least one collection fibre (104, 106) having a slanted end proximal to the target (114), configured to conduct light away from the target (114); wherein the illumination fibre (102) is configured to taper along at least part of its length towards the tip.