Abstract:
A fiber bundle confocal microscope or endoscope ( 200 ), comprising a light source ( 142 ) for providing a beam of light ( 160 ), a coherent fiber bundle of optical fibers ( 152 ), a scanner ( 202 ) for receiving the beam and scanning the beam over a proximal end of the bundle ( 162 ), so that the beam is launched into a plurality of the fibers sequentially, a plurality of the fibers thereby acting sequentially as an at least one delivery fiber ( 204 ), a spatial filter ( 172 ), and a photodetector ( 174 ) operatively associated with the spatial filter to receive return light from one or more of the fibers. The return light from the delivery fiber is excluded from the photodetector by the spatial filter.

Description:
RELATED APPLICATION 
     This application claims priority to PCT Application No. PCT/AU2006/000069 filed Jan. 20, 2006, and Australian Application No. 2005900259 filed Jan. 21, 2005, the disclosures of which are hereby incorporated by reference in their entireties. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of fiber bundle confocal microscopy and endoscopy, and is of particular but by no means exclusive application in endomicroscopy. 
     BACKGROUND OF THE INVENTION 
     Image transfer (coherent) optical fiber bundles have been used to inspect the interior cavities of the body for the diagnosis and monitoring of disease. They can also be used as the image optical transfer path component in confocal systems. Unlike in the case of a vibrating single fiber, the cores in the tips of the bundle are not acting as confocal pinholes; this function is provided by a spatial filter or filters, such as in the form of a pinhole, associated with a scanning mechanism outside the subject. 
     Existing fiber bundle confocal systems generally scan a single laser point in a raster pattern on the surface of the tips of the fibers of the bundle, using X and Y mirrors to effect the scan, although the same principle also works with line-scan, Nipkow disc or other confocal systems. 
       FIG. 1  is a schematic view of a basic point-scanning laser confocal system  10  of the background art that employs a coherent fiber bundle as an image transfer element. A beam of light  12  from a laser  14  shines on a beam-splitter  16  and a portion  18  of the light  12  is reflected onto an x-y beam-scanner  20 . The scanned beam  22  passes through lens  24  to focus to a spot at the entry of core  26  of a respective optic fiber  28  on the polished proximal face  30  of the coherent fiber bundle  32 . The light passes down the fiber  28  to the distal end  34  of fiber  28 , from which it emerges as a divergent beam  36  that is completely captured by collimating lens  38 . This light proceeds as a parallel, collimated beam  40  to an objective lens  42  that brings it to a focus as a diffraction-limited Gaussian waist  44  within the specimen under examination. If a portion of the specimen within that waist region  44  fluoresces or reflects light then that light travels in the reverse direction (via the same path as the excitation light described above) until it reaches beam-splitter  16 . Some of this return light exits the beam-splitter  16  as a beam  46  and is focussed by lens  48  to a diffraction limited Gaussian waist  50  bounded by a spatial filter pinhole  52 . The light passing through pinhole  52  impinges on a photodetector (such as a PMT)  54  and generates an electrical signal. This signal is fed into a bitmap in a frame-store  56  and is displayed as a point  58  on the screen of a monitor  60 . 
     A scan generator  62  shifts the x-y beam-scanner  20  and hence beam  22  to a new path  64  so that the light travels through a different fiber  66  (at a considerable distance from the first fiber  28 ), illuminating another portion of the specimen at a different Gaussian waist  68 ; this portion is displayed on the screen of monitor  60  at  70 . The scan generator  62  also provides an output signal to frame-store  56  so that frame-store  56  can assign the correct instantaneous x and y coordinates to the signal received from photodetector  54 . Ultimately system  10  builds up a final image  72 . 
     Coherent bundles have the major advantage in endoscopy of eliminating any need for a mechanical scanning mechanism within the subject. However, as each fiber core is discrete and separate, with six neighbouring fibers, there is the risk of undersampling and a hexagonal honeycomb overlay is imposed on the ultimate images. 
     Further, the fiber bundle loses a considerable amount of light, which is further compounded by the undersampling, for the following reasons. If the fiber cores were touching and were arranged in a square array, that is, centred on a rectangular grid, then from information theory principles the figure for linear undersampling in one row should be 2.3 (the Nyquist number) and the a real undersampling 2.3 2 . In fact the cores in a fiber bundle are hexagonally close packed, so that the next row of fibers is actually 0.7071 diameters below the first row and the figure for undersampling in this direction is 2.3×0.7071=1.61. This makes the average figure for (linear) undersampling slightly less than 2 (or in terms of areal undersampling, somewhat less than 4). 
     In this example, if a purely geometric analysis is performed, approximately 9% of the light falling on a hexagonally close packed array of circular fibers will pass into the gaps between the fibers. However the fiber cores are separated by the combined cladding of each pair of adjacent fibers and, as described above, this cladding must be of finite thickness to avoid photon tunneling between the cores; such tunneling would otherwise cause optical crosstalk and image degradation. Photons which arrive at the bundle tip in the cladding region are either absorbed by the cladding within a short distance of the tip or are diverted at such a high angle that they are not guided but traverse across the cores to be absorbed at the outer sheath of the bundle. The cladding does not act as a funnel at the tip for the photons, there has to be a “dead zone” in between the cores to stop tunneling. 
     Apart from causing light loss, this dead-zone also adds to the undersampling; if the laser input beam were carefully matched to a single fiber in a polished tip of a bundle, it is possible to launch over 80% of light to reach the other end of the bundle. The loss is from tip reflections (˜8%), Raleigh scattering, and glass absorption. 
     If the laser beam is defocused to cover several cores, the transmission typically drops to ˜20%. This implies by geometric arguments that the dead zone makes up around 75% of the polished tip area. It follows from this that the cores are effectively separated by a full core diameter of cladding and that the linear undersampling figure is approximately double that for cores in close contact. This number will vary slightly with wavelength, bundle type and beam profile. (As a separate issue the dead area also implies that 75% of the scanning acquisition time will not be used, unless the laser spot is scanned along the lines of cores only.) 
       FIG. 2  is another schematic view of the background art system  10  of  FIG. 1 , and illustrates under-sampling resulting from the discrete nature of the separate fibers of the bundle  32  when using the illustrated system. For the purposes of explanation the illumination of the specimen is shown as being carried out (successively) by two adjacent fibers  80   a  and  80   b . The respective Gaussian waists  82   a  and  82   b  of the light focussed by the objective lens  42  do not overlap. Hence respective portions of the specimen in Gaussian waists  82   a  and  82   b  will be imaged as  84   a  and  84   b  on the screen of monitor  60 , but a portion of the specimen at  86  between Gaussian waists  82   a  and  82   b  will not be imaged. This constitutes a high degree of under-sampling. 
     The most obvious feature of fiber bundle images is the reticulated or hexagonal pattern overlay. In some approaches this is removed by acquiring a (highly oversampled) image of the bundle tip and using it to subtract pixel for pixel from the raw images. The pattern can also be removed by deliberately blurring the image or by filter transform processing. These methods improve viewability but at the cost of some information. 
     To obtain full resolution with maximum light efficiency, however, it would be necessary to sample at points between the discrete core positions shown. The vibrating tip fiber system is able to sample at as many points as desired during the scan. 
     Another existing approach avoids undersampling and attains full resolution potential as follows. If the numerical aperture (NA) of the fibers in the bundle is matched to the back NA of the lens (as is done in a scanning tip system), then the optical efficiency is at a maximum but the image is undersampled. Pixel intensity values for points building up the image can only be obtained from one fiber and then from the next adjacent fiber core, but the Nyquist sampling criterion requires measurements from points in between. The finite cladding thickness needed to prevent evanescent coupling and cross-talk (i.e. light leakage) between adjacent fibers further separates the cores, and the total linear undersampling value is then close to 4. Full optical resolution can be obtained by synchronized mechanical movement (“dithering”) of the fiber bundle tips at both ends by a few core diameters in X and Y during image acquisition. This allows intensities of pixels to be obtained between the static core positions and eliminate the hexagonal honeycomb overlay pattern of the close packed fibers. From the discussion above it can be seen that it would be necessary to integrate approximately 16 scans (i.e. the square of the linear undersampling figure) to produce one image with full resolution. Mechanical scanning at the distal tip can be effected with piezo actuator elements of the type used to shift a CCD or CMOS chip in a digital camera, to increase resolution or to act as image stabilizers. At the proximal (i.e. laser source) end of the bundle an identical piezomechanical system can be used, or an equivalent result could be achieved in the computer by a shift in the frame register of the image. 
       FIG. 3  is a schematic view illustrating this background art technique for removing under-sampling by simultaneously dithering proximal and distal tips of the fiber bundle, and thereby obtaining samples at intermediate positions. The system  90  of  FIG. 3  is generally like laser confocal system  10  of  FIGS. 1 and 2 , and like reference numerals have been used to identify like features. In addition, system  90  includes mini x actuators  92   a ,  92   b  (at the proximal and distal tips of the fiber bundle  32  respectively) controlled by controller  94  and mini y actuators  96   a ,  96   b  (at the proximal and distal tips of the fiber bundle  32  respectively) controlled by controller  98 ; these mini x and y actuators  92   a ,  92   b ,  96   a ,  96   b  simultaneously dither the proximal and distal tips of fiber bundle  32 . When combined with the effects of beam-scanner  20 , imagining can thereby be performed at intermediate positions. 
     Another existing method to obtain full resolution is to deliberately mismatch the fiber NA and the lens back-NA. A fiber bundle with smaller, high NA cores or a longer focal length collimating lens is used, so that the excitation light overfills the focussing lens. With this approach, the Airy discs projected within the specimen from adjacent fibers overlap, thus allowing the specimen fluorescence to be sampled at intermediate positions and satisfy the Nyquist criterion. The confocal light returning from each of these points (which are acting as sources) in the specimen projects its own Airy disc onto several fiber cores, most of which overlap from one pixel to the next. The return confocal pinhole at the proximal end must then accept light from this cluster of cores. 
       FIGS. 4A and 5  are schematic views of a background art system  100  in which the distal lens is highly overfilled. System  100  can give full resolution by allowing sampling at the Nyquist criterion intervals. In  FIG. 4A  the optical system is generally identical with that of  FIG. 1 , and like reference numerals have been used to identify like features. However, system  100  includes a collimating lens  102  of greater focal length than that of  FIG. 1 . This means that the distal lens assembly (comprising collimating lens  102  and objective lens  42 ) is further from the distal tip of fiber bundle  32 , and the Gaussian waists  104  (which are identical in size with those in  FIG. 2 ) now overlap and give proper sampling within the specimen being observed. 
     For clarity the illumination of the specimen is shown in  FIG. 4A  as being carried out by two adjacent fiber cores  106   a ,  106   b  in the fiber bundle  32 . This does not occur simultaneously. 
       FIG. 4B  is an enlarged view of region  108  of  FIG. 4A . As is more apparent in this detail, Gaussian waist  110   a  resulting from the light transmitted along core  106   a  overlaps Gaussian waist  110   b  resulting from the light transmitted along core  106   b.    
       FIG. 5  depicts the same optical arrangement as that of  FIG. 4A  but showing the return light rays from one point in the specimen. The Airy disc of the return light now falls on a cluster fiber tips  112  of seven fibers  114  at the distal end of the bundle  32 . (For clarity, only the three fiber tips in the central plane of the cluster are shown.) The pinhole  52  is enlarged to allow the light emitted from the seven proximal cores  116  to pass to the photodetector  54 . This gives full resolution but with a worse signal/noise ratio owing to the wasting of excitation light from the overfilling and the loss of return light in the cladding. 
       FIG. 6  is a schematic view of another background art system  120 , similar to system  10  of  FIG. 1  and like reference numerals have been used to identify like features. However, distal lenses (cf. lenses  38  and  42  in  FIG. 1 ) are not used; instead, the distal face  122  (which is polished) of the fiber bundle  32  directly touches the tissue  124  to be imaged. Excitation light passes along a single fiber  28  of the bundle  32  and light from components  126  of the tissue  124  close to the distal face  122  returns back along the same fiber  28 , passes through the beam-splitter  16  and pinhole  52  to a single photodetector  54 , and is imaged at  128  on the screen of monitor  60 . Similarly (though not simultaneously), excitation light transmitted by another fiber  66  illuminates another portion  130  of the tissue  124 , and is ultimately imaged at  132  on the screen of monitor  60 . A complete, contact microscopy image is eventually generated. The signal to noise ratio of the image, however, is degraded by Raman, Raleigh and Fresnel noise, and is affected by dirt on the polished bundle face  122 . 
     However, in order to obtain full optical resolution using available bundles and the above techniques that employ distal tip lenses, over 95% of the laser excitation light is discarded. The mismatch also means that, in the return direction, the cladding absorbs about 75% of the return confocal light as the mode fields no longer match. In order to compensate for the poor light budget, the input power must be increased, but this increases the level of Raman scattering within the bundle and hence degrades the S/N ratio. 
     Hence, both the signal is reduced and the higher laser power generates correspondingly more noise within the fiber cores. Indeed, if full optical resolution with a bundle system is desired in existing systems, the laser power required to achieve the same level of fluorescent return signal will be 50 times greater. That is, the optical efficiency will be much less than 5% (i.e. 1/16th of 25%) of that of a single fiber tip scanner. 
     This degrades the S/N ratio in three ways:
         1) Statistical noise due to photon arrival variation is worse if laser power is limited by medical safety requirement;   2) Noise from Raman scattering in the fiber core is very much worse; and   3) Fluorescence saturates (and fluorescent return tails off) while Raman generation increases linearly with laser intensity. The 25% confocal return figure pushes the fluorophore more into the saturated region.       

     Of these the noise from Raman scattering is generally the most significant. Spectral filtering can be used to remove some of this noise, but Raman lines from glass are broad because of the range of bond energies in the liquid glass. Methods of removing Raman interference do exist. For example, Raman noise is generated instantaneously so can be removed from the fluorescent signal using a FLIM system, but this requires pulsed lasers and time gated detectors. 
     SUMMARY OF THE INVENTION 
     According to the present invention, therefore, there is provided a fiber bundle confocal microscope or endoscope, comprising:
         a light source for providing a beam of light;   a coherent fiber bundle of optical fibers;   a scanner for receiving the beam and scanning the beam over a proximal end of the bundle (as, for example, a line or spot), so that the beam is launched into a plurality of the fibers sequentially, a plurality of the fibers thereby acting sequentially as an at least one delivery fiber;   a spatial filter; and   a photodetector operatively associated with the spatial filter to receive return light from one or more of the fibers;   wherein return light from the delivery fiber is excluded from the photodetector by the spatial filter.       

     Thus, the fiber bundle confocal microscope or endoscope of this embodiment takes advantage of the fact that all the excitation light at any instant is delivered by one or more “delivery” fibers, whilst the confocal return light is carried by the delivery fiber or fibers and—principally—the six immediately surrounding fibers. Almost all the noise returning to the photodetector, however, is generated in the core of the delivery fiber or fibers. Occluding the return and other light emitted towards the photodetector by the delivery fiber or fibers reduces the intensity of that light by less than half, but reduces the noise—especially from Raman scattering—dramatically. 
     It is then possible, by means—for example—of an annular spatial filter provided in a detector pinhole plane—to block the region corresponding to the core of the delivery fiber, and thus eliminate almost all of the Raman noise while losing only a fraction of the confocal return signal. 
     Also, the substantial dead zone between the cores is, in this invention, advantageous in that it allows one to ensure that light is not launched into two cores simultaneously. 
     The microscope or endoscope may comprise a further photodetector for receiving return light transmitted by the delivery fiber. 
     The microscope or endoscope may comprise an endomicrosope, and in other aspects the invention provides an endoscope for internal or external use. 
     The spatial filter may comprise a mechanical filter with an occlusion to intercept return light from the delivery fiber. In one embodiment the light source is a laser source and the occlusion a spot; in another embodiment the light source is a line source and the occlusion is linear. 
     The spatial filter may comprise one or more optical elements (such as a mirror, a lens, an array of mirrors or an array of lenses) arranged to direct return light other than return light from the delivery fiber to the photodetector. 
     In some embodiments, a plurality of the fibers act simultaneously as delivery fibers, and return light from the delivery fibers is excluded from the photodetector by the spatial filter 
     The spatial filter may comprise an entry aperture of the photodetector. 
     The microscope or endoscope may include a plurality of photodetectors operatively associated with the spatial filter to receive return light from one or more of the fibers. 
     The microscope or endoscope may include one or more optical transmitters for transmitting return light to the photodetector. The spatial filter may comprise an entry of the one or more optical transmitters. 
     The microscope or endoscope may include a beam splitter that also acts as the spatial filter. 
     The scanner may comprise a pair of scannable mirrors. The microscope or endoscope may further comprise a second scanner for scanning an image formed by the microscope or endoscope and operable to scan synchronously with the scanner. The scanner may comprise a stationary mirror and a scannable mirror, and the second scanner comprises a stationary mirror and a scannable mirror. 
     The microscope or endoscope may further comprise a double sided mirror with a first side comprising the scannable mirror of the scanner and a second side comprising the scannable mirror of the second scanner. 
     In one particular embodiment, the invention provides a fiber bundle confocal microscope or endoscope, comprising:
         a laser source for providing a beam of coherent light;   a coherent fiber bundle of optical fibers;   a scanner for receiving the beam and scanning the beam over a proximal end of the bundle, so that the beam is launched into a plurality of the fibers sequentially, each of the fibers thereby acting sequentially as a delivery fiber;   a spatial filter defining an aperture;   a photodetector operatively associated with the spatial filter; and   an occlusion operatively associated with the spatial filter to intercept at least a portion of light emitted by the delivery fiber at the proximal end of the bundle.       

     In one embodiment, the spatial filter includes the occlusion, wherein the occlusion is located at the centre of the aperture defined by the spatial filter. In a particular embodiment, the spatial filter defines an annular aperture, wherein the occlusion comprises the centre of the annulus. 
     The central portion of the annulus can be supported by a “spider”, or it could be supported by a glass sheet. An occlusion in the form of a variable central occluding stop could also be advantageous and this feature is achievable by the use of a Travis stop which can be expanded or contracted to adjust the amount of central blocking. 
     The invention also provides a method of providing confocal microscopy or endoscopy, comprising excluding from a photodetector return light from one or more delivery fibers in a fiber bundle confocal microscope or endoscope. 
     The photodetector may comprise a plurality of separate photodetectors. 
     The method may include excluding from the photodetector return light from one or more delivery fibers by means of a spatial filter operatively associated with the photodetector. 
     In one embodiment, the method comprises occluding the return light from the delivery fiber in a fiber bundle confocal microscope or endoscope. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       In order that the invention may be more clearly ascertained, embodiments will now be described, by way of example, with reference to the accompanying drawing, in which: 
         FIG. 1  is a schematic view of a basic point-scanning laser confocal system of the background art; 
         FIG. 2  is another schematic view of the background art system of  FIG. 1  illustrating under-sampling; 
         FIG. 3  is a schematic view illustrating a background art method for removing under-sampling by simultaneously dithering proximal and distal tips of a fiber bundle; 
         FIG. 4A  is a schematic view of a prior art system in which the distal lens is highly overfilled; 
         FIG. 4B  is an enlarged view of the Gaussian waists region of the prior art system of  FIG. 4A ; 
         FIG. 5  is another schematic view of the prior art system of  FIG. 4A . 
         FIG. 6  is a schematic view of a contact microscopy system of a background art system, in which the bundle tip is made to directly touch a tissue to be imaged; 
         FIG. 7  is a schematic view of a fiber bundle confocal endomicroscope according to an embodiment of the present invention; 
         FIG. 8  is a schematic view of the annular aperture of the fiber bundle confocal endomicroscope of  FIG. 7 ; 
         FIG. 9  is a schematic view of an annular aperture according to another embodiment of the present invention; 
         FIG. 10  is a schematic view of an aperture according to another embodiment of the present invention; 
         FIG. 11  is a schematic view of a fiber bundle confocal endomicroscope according to another embodiment of the present invention; 
         FIG. 12  is a schematic view of a fiber bundle confocal microscope for contact bundle microscopy according to a further embodiment of the present invention; 
         FIG. 13  is a schematic view of a fiber bundle confocal microscope for contact bundle microscopy according to a still another embodiment of the present invention; 
         FIG. 14  is a schematic view of a fiber bundle confocal microscope for contact bundle microscopy according to another embodiment of the present invention; 
         FIG. 15  is a schematic view of a fiber bundle confocal microscope for contact bundle microscopy according to yet another embodiment of the present invention; 
         FIG. 16  is a schematic view of a fiber bundle confocal microscope for contact bundle microscopy according to another embodiment of the present invention that is a variation of the microscope of  FIG. 15 ; 
         FIG. 17  is a schematic view of a fiber bundle confocal microscope for contact bundle microscopy according to another embodiment of the present invention that is another variation of the microscope of  FIG. 15 ; 
         FIG. 18  is a schematic view of a fiber bundle confocal microscope for contact bundle microscopy according to yet another embodiment of the present invention; 
         FIG. 19  is a schematic view of a fiber bundle confocal microscope for contact bundle microscopy according to another embodiment of the present invention; 
         FIG. 20  is a schematic view of a fiber bundle confocal microscope for contact bundle microscopy according to still another embodiment of the present invention; and 
         FIG. 21  is a schematic view of a fiber bundle confocal microscope for contact bundle microscopy according to a further embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A fiber bundle confocal endomicroscope according to an embodiment of the invention is shown generally at  140  in  FIG. 8 . The endomicroscope  140  comprises a TEM00 laser source  142 , a beam splitter  144 , x and y scanning mirrors  146 ,  148 , a field lens  150 , a fiber optic bundle  152 , a collimating lens  154  and a focussing lens  156  (located for focussing light onto or into a sample  158 ). 
     In use, the laser source  142  emits a beam of light  160  which passes through beam splitter  144  onto the x and y scanning mirrors  146 ,  148  and to the field lens  150 . The field lens  150  focuses the beam onto the proximal polished face  162  of fiber optic bundle  152 . 
     Field lens  150  is chosen so as to project a Gaussian waist spot into the core of a single fiber of the bundle  152  at any one time. As will be appreciated by those skilled in the art, the identity of the single fiber changes as the beam is scanned over the proximal face  162  of the bundle  152 . This fiber is thus referred to as the delivery fiber, but the identity of the delivery fiber changes as scanning moves the beam to the next fiber (whether adjacent or otherwise) sequentially. 
     The beam then travels along the core of the delivery fiber until it reaches the distal end of the delivery fiber at the distal end  164  of the bundle  152 . The light emerges from the distal end of the delivery fiber and falls on collimating lens  154 . A fibers of the fiber bundle  152  have small, high NA cores, so that the excitation light overfills the collimating lens. The solid angle of the emitted cone of light  166  thus considerably exceeds the solid angle of acceptance of the collimating lens  154 . 
     Owing to this over filling, the spots from adjacent fiber cores when focussed in the sample  158  overlap considerably. This allows a sampling frequency which satisfies the Nyquist criterion and provides full resolution of structures in the tissue which can be chosen or adjusted to admit only the “confocal” rays. 
     Endomicroscope  140  also includes, for collecting return light, a condensing lens  170 , a spatial filter with a central occlusion, in the form of annular aperture or spatial filter  172 , and a photodetector in the form of photomultiplier  174 . Although light is delivered to the sample along a single delivery fiber, it returns along multiple fibers centred on the delivery fiber. Typically the bulk of the return signal is transmitted by seven fibers: the delivery fiber and the six fibers immediately adjacent to the delivery fiber, hence arranged in a honeycomb pattern. The return light is imaged on the aperture defined by the annular aperture  172 , so the light emitted by the delivery fiber—being central in that image—is occluded by the central portion of the annulus. Most of the noise, particularly from Raman scattering, originates in the delivery fiber, so noise is thereby blocked by the central portion of the annular aperture  172 . Although some signal is also thus lost, a great improvement in signal to noise ratio is produced. 
       FIG. 8  is a schematic view of the annular aperture  172 . The annular aperture  172  includes outer ring  176  and central, occluding portion  178 . The central portion  178  is supported on ring  176  by three legs  180 . 
     The occluding portion need not be in the precise plane of the aperture. Indeed, in some applications it may be more convenient if it is displaced slightly either optically before or after the aperture or other spatial filter. This is possible because of the finite distance between the core of the delivery and the cores of the adjacent fibers so, even when the return light is somewhat out of focus (such as just before the aperture) there will be little if any overlap between the light returned by the delivery fiber and that returned by the adjacent fibers. 
       FIG. 9  is a schematic view of an alternative annular aperture  182 . The annular aperture  182  is mounted on glass  184 , so that the central, occluding portion  186  can be attached to the glass  184 . This obviates the need for supporting legs (like legs  180  of  FIG. 8 ). 
       FIG. 10  is a schematic view of a still further alternative aperture  190 . This aperture  190  is similar to aperture  182  of  FIG. 9  and includes supporting glass  192  and central, occluding portion  194 . However, it omits an outer ring (cf. ring  176  of  FIG. 8 ). Hence, this aperture will either have much reduced depth resolution, as any spatial filtering will be provided by whatever supporting structure is employed to support aperture  190 , or would be used in conjunction with a conventional spatial filter, possibly optically immediately before that conventional spatial filter. 
     In an alternative embodiment, an occlusion can be provided in the form of a variable central occluding stop, such as a Travis stop, which can be expanded or contracted to adjust the amount of central blocking. 
       FIG. 11  is a schematic view of a fiber bundle confocal endomicroscope  200  according to another embodiment of the present invention. Endomicroscope  200  is similar to endomicroscope  140  of  FIG. 7 , and like reference numerals have been used to identify like features. However, rather than x and y scanning mirrors  146 ,  148 , endomicroscope  200  includes a x-y beam-scanner  202  for performing x-y scanning. In practice beam-scanner  202  can be in the form of any suitable scanning mechanism that can provide x and y scanning, including (for example) a pair of mirrors comparable to x and y scanning mirrors  146 ,  148  of  FIG. 7 . 
     Occlusion or stop  178  is located at a position where it intercepts light returning from the central (light delivery) fiber  204  at any time, but aperture  172  passes return light transmitted by the six fibers adjacent to the delivery fiber (e.g. fibers  206   a  and  206   b ). This allows the majority of the signal light to return but eliminates almost all the Raman, Raleigh and Fresnel noise. 
     The return light passed by aperture  172  is detected by photomultiplier  174 , which generates an electrical signal. This signal is fed into a bitmap in a frame-store  208  and is displayed as a point on the screen of a monitor  210 . Scan generator  212  shifts the x-y beam-scanner  202  and hence the beam to a new path so that the light travels through a different fiber, illuminating another portion of the specimen at a different Gaussian waist. This portion is also displayed on the screen of monitor  210 . The scan generator  212  provides an output signal to frame-store  208  so that frame-store  208  can assign the correct instantaneous x and y coordinates to the signal received from photomultiplier  174 . Ultimately endomicroscope  200  builds up a final image on the screen. 
       FIG. 12  is a schematic view of a fiber bundle confocal microscope  220  (which, like all the other described embodiments of the invention, may be used as an endomicroscope) for contact bundle microscopy according to a further embodiment of the present invention. Microscope  220  is similar to endomicroscope  200  of  FIG. 11 , and like reference numerals have been used to identify like features; being for contact microscopy, however, microscope  220  omits any distal lenses (cf. lenses  154  and  156  in  FIG. 11 ). Further, instead of employing a single photomultiplier (cf. photomultiplier  174  of  FIG. 11 ) to detect return light, microscope  220  includes six photodetectors  222  arranged hexagonally and located optically after aperture  172 . (In the figure, a representative pair of these photodetectors  222 —being those in the plane of the figure—are shown.) 
     Each of the photodetectors  222  corresponds to and feeds into a separate position in the image in the bitmap frame-store  208 . The elimination of light from the central area minimises Raman, Raleigh and Fresnel noise and allows imaging deeper into the tissue  224 . Furthermore, the relative spatial relationships between each of the proximal and distal ends of each of the fibers of fiber bundle  152  are preserved, so there is a one-to-one relationship between the six photodetectors  222  (e.g. photodetectors  226   a ,  226   b ) and the six fibers (e.g. fibers  206   a ,  206   b ) surrounding the delivery fiber  204 . 
     Each of the photodetectors  222  corresponds to and feeds into a separate position in the image in the bitmap frame-store  208 , ultimately for display on the screen of monitor  210 . 
       FIG. 13  is a schematic view of a fiber bundle confocal microscope  230  for contact bundle microscopy according to a still another embodiment of the present invention. Microscope  230  is similar to microscope  220  of  FIG. 12 , and like reference numerals have been used to identify like features. However, microscope  230  does not include an annular spatial filter (cf. aperture  172  of  FIG. 12 ). Instead, microscope  230  tips has a spatial filter defined by the entry tips  232  of six large gradient index multimode optic fibers  234  arranged hexagonally. These optic fibers  234  are located to collect the return light and transmit it to photodetectors  236 . In this figure, for clarity only two of the optic fibers  234  are shown (at  238   a ,  238   b ), being those in the plane of the figure, and only their corresponding two photodetectors  240   a  and  240   b  are shown. 
     Each of the photodetectors  236  corresponds to and feeds into a separate position in the image in the bitmap frame-store  208 . As with microscope  220  of  FIG. 12 , there is a one-to-one relationship between the six photodetectors  236  (e.g. photodetectors  240   a ,  240   b ) and the six fibers  234  (e.g. fibers  238   a ,  238   b ) surrounding the delivery fiber  204 . Each of the six photodetectors  236  corresponds to and feeds into a separate position in the image in the bitmap frame-store  208 , ultimately for display on the screen of monitor  210 . 
     Microscope  230  also has a central fiber  242  to collect return light from the delivery fiber  204 ; this return light may be used to give a near field image in a separate channel and display screen. Hence, central fiber  242  transmits this light to a separate photodetector  244  coupled to a separate frame-store  246  for display on the screen of a separate monitor  248  (though in some embodiments the output of frame-store  246  may be displayed on the screen of monitor  210 ). 
       FIG. 14  is a schematic view of a fiber bundle confocal microscope  250  for contact bundle microscopy according to another embodiment of the present invention. Microscope  250  comprises a TEM00 laser source  252 , a beam splitter  254 , x and y scanning mirrors  256 ,  258 , a field lens  260  and a fiber bundle  262 . 
     In use, the laser source  252  emits a beam of light  264  which passes through beam splitter  254  onto the x and y scanning mirrors  256 ,  258  and to the field lens  260 . The field lens  260  focuses the beam onto the proximal polished face  266  of the fiber optic bundle  262 . Field lens  260  is chosen so as to project a Gaussian waist spot into the core of a single delivery fiber (e.g. fiber  268 ) of the bundle  262  at any one time. 
     On reaching the distal end of the core of the delivery fiber, the light energy leaves the bundle  262  and enters the specimen  270  to be examined (which is in contact with the polished bundle tip  272 ). Portions  274   a ,  274   b  of the specimen  270  nearby reflect (i.e. backscatter) the light or cause fluorescence, and some of this re-emitted light returns to the fiber bundle tip  272  and is conveyed back along the delivery fiber (e.g.  268 ) and other fibers adjacent to the delivery fiber, but only return light that enters the six fibers (e.g.  276   a ,  276   b ) immediately adjacent to the delivery fiber is employed in forming an image. The return light in these six adjacent fibers retraces the original optical path, is converged by lens  260  and de-scanned by scanning mirrors  258 ,  256 . A portion of this light  278  passes back through the beam-splitter  254  (following the path not traversed by the excitation laser beam  264 ). This light is then reflected by a mirror  280 , passes through a condensing lens  282  that brings the light to a focus as an image of the core of the delivery fiber and of the cores of the six surrounding fibers at an annular spatial filter  284  (similar to aperture  172  of  FIG. 8 ). Filter  284  is arranged to have a central blocking area or occlusion  286  that occludes and absorbs the light that forms the image of the central delivery fiber (e.g.  268 ) but to pass the light from the cores of the six surrounding fibers (e.g.  276   a ,  276   b ). The width of the annular opening in filter  284  is such that filter  284  blocks the light from the central delivery fiber and only allows light from the immediately surrounding fibers to pass. 
     The return light that passes through the filter  284  is reflected from six small mirrors  288  (or which two are shown in the figure for illustrative purposes) arranged in a hexagonal array behind filter  284 ; the light is reflected laterally onto six corresponding photodetectors (of which two are shown at  290   a  and  290   b ). The signal from each of these photodetectors is fed to a computer  292  and stored in an x,y bitmap for simultaneous or subsequent display on the screen of a monitor  294 . 
     The microscope  250  also includes a scan generator  296  for controlling the x and y scanning mirrors  256 ,  258  and hence the beam so that the excitation light travels through successive, different delivery fibers, illuminating another portion of the specimen  270 . The scan generator  296  also provides an output signal to computer  292  so that the computer  292  can assign the correct instantaneous x and y coordinates to the signal received from the six photodetectors (e.g.  286   a  and  286   b ). 
     Optionally, the six mirrors  288  can be located close to the filter  284  and be separated from each other sufficiently to allow light that would otherwise be blocked by the occlusion  286  to pass through a central region defined by the hexagonally arranged mirrors  288 . 
       FIG. 15  is a schematic view of a fiber bundle confocal microscope  300  for contact bundle microscopy according to another embodiment of the present invention. Microscope  300  is similar in many respects to microscope  250  of  FIG. 14 , and like reference numerals have been used to identify like features. However, unlike in microscope  250  of  FIG. 14 , return light (after being brought to a de-scanned focus by condensing lens  282 ) enters six large multi-mode fibers  302  arranged in a hexagonal cluster behind the filter  284  to receive light passed by the filter  284 ; each of these six fibers  302  (of which only two are shown for illustrative purposes, at  304   a  and  304   b ) conveys the received light to a corresponding individual photodetector  306  (of which only two are shown). The signal from each of these photodetectors  306  is conveyed to a computer  292  and stored in an x,y bitmap which allows it to be displayed on the screen of a monitor  294 . 
     A variation of microscope  300  is shown schematically at  310  in  FIG. 16  (in which features optically downstream of scanning mirrors  256 ,  258  have been omitted, being identical with those of microscope  300 ). Microscope  310  omits filter  284 ; instead, each of the six large core fibers  302  is positioned to correspond with a respective one of the six fibers (e.g.  276   a ,  276   b ) adjacent the delivery fiber, and to receive little or no return light from the delivery fiber. Return light from the delivery fiber simply passes between the six large core fibers  302 . 
     Another variation of microscope  300  is shown schematically at  320  in  FIG. 17  (in which, again, features optically downstream of scanning mirrors  256 ,  258  have been omitted, being identical with those of microscope  300 ). Microscope  320  is identical with microscope  310  of  FIG. 16 , but additionally includes a central fiber  322  (comparable to fiber  242  of microscope  230  of  FIG. 13 ) to collect return light from the delivery fiber. This central fiber  322  is located with its entry tip within the hexagon defined by the entry tips of the six large core fibers  302 , to receive return light from the delivery fiber; this return light may be used to give a near field image in a separate channel and display screen. Hence, central fiber  322  transmits this light to a separate photodetector  324 , whose output is stored in a separate x,y bitmap in computer  292  for display on the screen of monitor  294 . 
       FIG. 18  is a schematic view of a fiber bundle confocal microscope  330  for contact bundle microscopy according to another embodiment of the present invention. Microscope  330  is similar in many respects to microscope  250  of  FIG. 14 , and like reference numerals have been used to identify like features. However, that portion of the return used to form an image, after passing through annular aperture  284 , is re-scanned and falls on a CCD or CMOS array to produce a signal that is displayed on a monitor screen. 
     In detail, the microscope  330  includes (optically after annular aperture  284 ) a plane mirror  332 , a converging lens  334 , x and y scanning mirrors  336  and  338 , a further lens  340  and a CCD camera chip  342 . Thus, the light that is passed by the annular aperture  284  (from the six fibers adjacent the delivery fiber) is reflected off mirror  332 , through converging lens  334  and onto x and y scanning mirrors  336 ,  338 . These mirrors  336 ,  338  are scanned in exact synchrony with x and y scanning mirrors  256 ,  258  (using the same power supply  344 ). 
     This rescanned beam  346  is passed through further lens  340  that maps the return light to reconstitute the relative positions of the reflective/fluorescent objects (i.e. portions of the specimen  270 ) from the bundle tip  272  on the surface of CCD camera chip  342 . The output of the CCD CMOS chip  342  is displayed on the screen of monitor  294 . 
       FIG. 19  is a schematic view of a fiber bundle confocal microscope  350  for contact bundle microscopy according to another embodiment of the present invention. Microscope  350  is similar in many respects to microscope  330  of  FIG. 18 , and like reference numerals have been used to identify like features. However, rather than using a beam-splitter (with simple, planar partial mirror) like that used in microscope  330 , microscope  350  includes a beam-splitter  352  that also acts as the spatial filter. The beam-splitter/spatial filter  352  has an annular aperture  354  but otherwise consists of a thin sheet of a reflective substance (e.g. Al, Ag) that is completely opaque except for the annular aperture  354 . The annular aperture  284  of microscope  330  may be retained to reduce stray light, but in microscope  350  it is not essential. This configuration is expected to have an optical efficiency 400% that of the embodiments described above (owing to the use of complete rather than partial beam-splitter silvering), and beam-splitter  352  of this embodiment can be used in any of the above-described embodiments in which the return light transmitted by the delivery fiber is discarded. 
     In detail, a light beam  256  from laser  252  passes through a lens  356  and is focussed onto a central mirrored section  358  (surrounded by an annular aperture  354 ) of beam-splitter/spatial filter  352 . The reflected beam  360  from this central mirrored spot  358  diverges to a convex lens  362  which forms a collimated light beam  364  directed onto x and y scanning mirrors  256 ,  258 . The scanned beam  366  is focussed by lens  260  onto the proximal end of fiber bundle  262  and passes down the core of one of the fibers (termed, instantaneously, the delivery fiber). On reaching the distal end of the delivery fiber, the light energy leaves the bundle  262  and enters the tissue to be examined  270  that is in contact with the bundle tip. Portions of the specimen nearby reflect the light or cause fluorescence and some of this re-emitted light returns to the polished fiber tip and is conveyed back along the delivery fiber as well as along the fibers adjacent to the delivery fiber; the light is conveyed back along the bundle  262 , emerges from its proximal end  266 , is converged by lens  260  and de-scanned by the scanning mirrors  256 ,  258 . 
     Light returning from the central delivery fiber ( 268  in the illustrated example) is deflected by the central spot  358  of the beam-splitter/spatial filter  352 , while light from the cores of the six adjacent fibers passes through the annular aperture  354 . Light from other cores still more remote from the delivery fiber is also rejected by the outer part of the beam-splitter/spatial filter  352 . 
     The light passed by the beam-splitter/spatial filter  352  is deflected by stationary mirror  280 , and refocused by lens  282  to pass through second (optional) annular spatial filter  284 . 
     The light passed by this second annular aperture  284  is then reflected off mirror  332  and through converging lens  334  onto x and y scanning mirrors  336 ,  338  that are scanned in exact synchrony with scanning mirrors  256 ,  258  using the same power supply  344 . This rescanned beam  346  is passed through lens  340  that focuses the light onto the surface of a CCD/CMOS camera chip  342 . The output of the CCD/CMOS chip  342  is displayed on the screen of monitor  294 . 
       FIG. 20  is a schematic view of a fiber bundle confocal microscope  370  for contact bundle microscopy according to another embodiment of the present invention. Microscope  370  is similar to microscope  350  of  FIG. 19 , and like reference numerals have been used to identify like features. However, microscope  370  has a linear source of light and a beam-splitter with an elongate (rather than spot-like) central occlusion, for producing line scans in the specimen. Since a line is scanned only one mirror motor is required for each pair of scanning mirrors. That is, only one of each pair of scanning mirrors need be scanned. 
     In greater detail, microscope  370  includes a divergent linear light source  372  (such as a linear tungsten filament within an incandescent globe) that produces divergent light  374 . Divergent light  374  is focussed to a line by a pair of cylindrical or spherical lenses  376  to impinge on a beam-splitter/spatial filter  378 . Beam-splitter/spatial filter  378  comprises a mirror  380  with two narrow linear apertures  382  and  384  on each side of a thin central occluding strip  386 . Apart from the two narrow linear apertures  382  and  384 , the mirror  380  consists of a thin sheet of a reflective substance (e.g. Al, Ag) that is completely opaque except for apertures  382  and  384 . 
     The line of light is thus reflected by the central occluding strip  386 , intercepted by convex lens  362  that projects it via a stationary mirror  390  onto a scanning mirror  258 . The beam then passes through lens  260  projecting it as a focussed line on the polished proximal surface  266  of the fiber bundle  262 . The light is intercepted by those fibers in the bundle  262  that have their tips disposed along that line, and conveyed along those fibers to emerge from the tips at the distal end of the bundle  262 . Reflected or fluorescent light from nearby portions of the specimen  270  is intercepted by nearby fibers within the fiber bundle, and returned to the proximal end  266  to emerge close to the excitation line of light on the end of the fiber bundle  262 . This light is de-scanned and focussed as two lines on either side of the central occluding strip  386 , and hence passes through the two narrow apertures  382 ,  384  in the mirror  380  of the beam-splitter/spatial filter  378 . Other light from the proximal end  266  face tip is blocked by the outer sections of mirror  380 . The light  392  passed by the beam-splitter/spatial filter  378  is reflected by stationary mirror  280  and focussed by lens  282  to an image of the proximal fiber tip cores at the plane of a secondary spatial filter  394 . This secondary (optional) spatial filter  394  is essential identical with mirror  380 , with a pair of elongate apertures  396 ,  398  and a central occluding strip  400 . Light passed by secondary spatial filter  394  is reflected by stationary mirror  332 , converged by lens  334 , and projected by a stationary mirror  402  and scanning mirror  338  through a focussing lens  340  as an image on the surface of a CCD or CMOS chip  342 . The output of CCD chip  342  is displayed on the screen of monitor  294 . 
       FIG. 21  is a schematic view of a fiber bundle confocal microscope  410  for contact bundle microscopy according to another embodiment of the present invention. Microscope  410  is similar to microscope  370  of  FIG. 20 , and like reference numerals have been used to identify like features. However, instead of two scanning mirrors (cf. scanning mirrors  258 ,  338  of microscope  370 ), microscope  410  has a double-sided scanning mirror, allowing an inexpensive system to be produced. 
     Thus, unlike microscope  370  of  FIG. 20 , microscope  410  includes a double-sided scanning mirror  412  that performs the functions of both scanning mirror  258  and scanning mirror  338 . Double-sided scanning mirror  412  comprises two mirrors  414 ,  416  fixed to the back of each other and thereby moving synchronously with each other. A thin flexible opaque membrane  418  and surrounding frame  420  protect the CCD chip  342  from stray light. 
     In addition, an additional stationary mirror  422  is provided optically after mirror  402  to direct light onto the back of double-sided scanning mirror  412  (i.e. mirror  416 ). The use of double-sided scanning mirror  412  ensures synchrony of scanning. 
     The light reflected from mirror  416  is directed through focussing lens  340  (as in microscope  370 ) as an image on the surface of CCD chip  342 . The output of CCD chip  342  is displayed on the screen of monitor  294 . 
     Modifications within the scope of the invention may be readily effected by those skilled in the art. It is to be understood, therefore, that this invention is not limited to the particular embodiments described by way of example hereinabove. 
     In the claims that follow and in the preceding description of the invention, except where the context requires otherwise owing to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 
     Further, any reference herein to prior art is not intended to imply that such prior art forms or formed a part of the common general knowledge.