Abstract:
A micro-endoscopic system employs a pulsed xenon light source and novel image collection optics with a fine diameter optical probe for an endoscope. Very bright pulses of light emitted by a xenon flash tube increase the intensity of light incident on the light transmitting optics, allowing a reduction in size of the optical components, resulting in a corresponding reduction in the size of the optical probe. A novel segmented glass image guide directs the reflected light to a sensor array. Segmentation of the image guide avoids the birefringence problems associated with fine diameter glass optical structures. Conventional optical fiber imaging and light delivery apparatus may also be used in conjunction with the pulsed xenon light source.

Description:
REFERENCE TO COPENDING APPLICATION 
     This application is a continuation in part of application Ser. No. 09/625,425, filed Jul. 25, 2000, now U.S. Pat. No. 6,561,973. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to endoscopes which are widely used in the field of medicine and in particular to a compact endoscope having a fine diameter probe for use in hospitals and doctors&#39; offices for outpatient procedures. 
     2. Description of the Related Art 
     Currently, orthopedic surgeons perform the greatest number of arthroscopic in-hospital procedures, approximately half of which could be performed on an outpatient basis. Almost 2.5 million such procedures are undertaken annually. Of these, 510,000 are for shoulder injuries, 1.7 million are for knee injuries, and 200,000 are for such procedures as elbows, ankles and wrists. The future arthroscopic market will be additionally enhanced by anticipated developments in the fields of synthetic bone and tissue transplantation. 
     Commercially available endoscopes have the disadvantages of being bulky, expensive instruments that are typically found only in hospitals. Available endoscopes have relatively large diameter optical probes, requiring proportionately large incisions to permit their use. There is a need in the art for a compact, small diameter endoscope, which may be purchased and used by medical professionals in their offices to perform outpatient diagnostic and surgical procedures. 
     There are at least two major technical obstacles to the design of an endoscope having an outside diameter of less than 2 mm. The first obstacle is that of insufficient illumination. An endoscope must both provide light to the area within the body being viewed and collect sufficient reflected light to be detected by available sensor arrays. The narrow optical pathways available in a very small diameter endoscope have typically not been capable of transmitting or collecting sufficient light. 
     The quantity of light transmitted in any optical arrangement is principally determined by two factors: 1) the optical characteristics of the light receiving surface of the arrangement (surface area, curvature, etc.); and 2) the intensity of the light energy incident upon that surface. Reduction in either factor reduces the amount of light transmitted. 
     In conventional endoscopic systems, these transmission constraints restrict the ability to effectively reduce the diameter of the probe that delivers light into the cavity to be viewed and collects the reflected image. Light sources of conventional brightness are not compatible with optical transmission systems that employ a significant reduction in the surface area of the light transmission pathway. Accordingly, there is a need in the art for an endoscopic system that can deliver sufficiently intense light energy to an endoscope to permit reduction in the light transmission portion of an endoscope probe. 
     Collection of the reflected light, which will form an image of the viewing area, presents another set of technical difficulties. Prior art endoscopes typically focus the image on either a charge coupled device (CCD) sensor array or magnify the image into an eye piece that the surgeon or medical professional can view directly. Ideally, a single glass rod could be used to transmit image light from an object lens to the sensor array. Such a construction is employed in many larger diameter conventional endoscopes. However, as the diameter of such a glass rod is reduced, the rod becomes vulnerable to stress induced birefringence, which distorts the image being transmitted. 
     Conventional optical fibers, while they are thin enough to be flexible and avoid the problem of birefringence, have cross sectional surface areas which individually collect only limited amounts of light. No matter how many such fibers are used, the brightness of the transmitted image is not enhanced because the optical characteristics of the receiving or input face of each fiber do not change. Thus, there is also a need in the art for a fine diameter endoscope probe which uses a single optical pathway to collect and deliver image light to a suitable sensor array. 
     SUMMARY OF THE INVENTION 
     Briefly stated, the invention in a preferred form comprises a compact, office-based fine diameter endoscope system which employs a pulsed xenon light source and novel image delivery optics to provide an endoscope probe having a diameter which is reduced in comparison to comparable conventional probes. The micro-endoscope system (ME system) includes a service module, a combined optical and electronic service cable and a micro-endoscopic device (MED). The service module houses the system power supply, the pulsed xenon light source, the image processor and the control electronics as well as the display/monitor. The combined optical and electronic cable contains a fiber optic bundle to transmit light from the service module to the MED and conductors to communicate with the electronic portion of the MED. 
     The MED comprises a sensor head that contains a sensitive charge coupled device (CCD) sensor array, a light pulse transfer interface and image focus optics. Controls allow the user to control the focus and magnification functions. A removable, one-piece optical probe and ergonomic grip slides over the sensor head to mate with the light pulse transfer interface. The optical probe includes a light pipe to deliver light from the pulse transfer interface to the viewing area and an image path for collecting and guiding reflected light back to the image focus optics. The pulse transfer interface facilitates light transfer from the fiber optic bundle to the light pipe. Light travels the length of the light pipe and is directed upon the area to be viewed. Light reflected from the viewing area is collected by an object lens and focused into the image path. The image path guides reflected light to the image focus optics in the sensor head where the image is focused on the CCD array. Image data from the CCD array is communicated to the service module electronics through the service cable. 
     To enhance the intensity of light incident on the optical components of the light path, the MED utilizes a pulsed xenon light source which emits short duration, very high-energy pulses of light. Each pulse of light may be in the energy range of 100,000 watts and have a duration of approximately 10 microseconds. The pulsed xenon light source is essentially a point source of light. The pulsed xenon light source is positioned so the emitted pulses of light pass directly into the input end of the fiber optic bundle. The highly concentrated light energy provides sufficient illumination of the viewing area while employing a smaller diameter light path. 
     The MED may incorporate a rigid optical probe. Light transmission and image collection pathways can have reduced cross-sectional area due to the intensity of light delivered by the pulsed xenon light source. The rigid probe includes a light pipe configured to surround a central image optical pathway. Image path optics having a diameter of approximately 1 mm address the issue of birefringence by using an image guide comprised of glass rod segments. Short rod segments are not prone to the stresses which induce birefringence. The sections of the image guide are assembled to form an integrated guide having the length desired for the optical probe. An alternate embodiment of the image guide may be constructed of optical grade plastic, such as polyethylene. 
     Alternatively, a more conventional optical probe will incorporate conventional fiber optic light transmission and image collection pathways. Increased light intensity provided by the pulsed xenon light source permits the use of fewer fibers for light transmission, freeing more probe fibers for image collection. The result is a flexible optical probe having approximately the same diameter as the rigid probe with performance superior to available products using conventional light sources. The problems of birefringence are avoided entirely in an optical probe using optical fibers for the delivery and collection of light. 
     An object of the present invention is to provide a new and improved fine diameter endoscope having an efficient and cost effective construction and which is adaptable for use in out-patient clinics and doctor&#39;s offices. 
     Another object of the present invention is to provide a new and improved fine diameter endoscope which employs novel image collection optics to enhance image quality. 
     A further object of the present invention is to provide a new and improved fine diameter endoscope which uses a novel pulsed xenon light source to increase the illumination of the viewing area. 
     A yet further object of the present invention is to provide a new and improved fine diameter endoscope which may be used as an inexpensive real-time diagnostic tool. 
     These and other objects, features, and advantages of the invention will become readily apparent to those skilled in the art from the specification and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic block diagram of a micro-endoscopic system (ME system) in accordance with the present invention; 
     FIG. 2 is a schematic block diagram of the light path for the ME system of FIG. 1; 
     FIG. 3 is a schematic block diagram of the image path for the ME system of FIG. 1; 
     FIG. 4 is an enlarged fragmentary side view of an image guide structure which may be employed in the optical probe of the MED in accordance with the present invention; 
     FIG. 5 is an enlarged fragmentary perspective side view of an optical probe of an MED in accordance with the present invention; 
     FIG. 6 is a side view of an MED in accordance with the present invention; 
     FIG. 7 is a side view, partly broken away, partly in section, and partly in schematic of the MED of FIG. 6; 
     FIG. 8 is a sectional view of the MED of FIG. 6 with the optical probe removed; 
     FIG. 9 is a sectional view of the optical probe of the MED of FIG. 6; 
     FIG. 9A is a sectional view of an alternative optical probe for use in conjunction with the MED of FIG. 6; 
     FIG. 9B is a cut away view, partly in section, of an alternative fiber optic light pipe for use in conjunction with the image guide of FIG. 4; 
     FIG. 10 is a fragmentary perspective side view of an alternative embodiment of the light pipe component of an optical probe for an MED in accordance with the present invention; 
     FIG. 11 is a side view, partially in phantom, of the optical probe of the MED of FIG. 6; 
     FIG. 12 is a side view, partially in phantom, of an alternative embodiment of an optical probe for use in conjunction with the MED of FIG. 6; 
     FIG. 13 is a side view, partially in phantom of an alternative embodiment of an optical probe for use in conjunction with the MED of FIG. 6; 
     FIG. 14 is a schematic view showing the relationship of the pulsed xenon light source to the light transmitting fiber optic bundle; 
     FIG. 15 is a graphical illustration of the light output distribution of a xenon flashtube appropriate for use in conjunction with a Micro-Endoscopic System in accordance with the present invention; and 
     FIG. 16, is a graphical illustration of the energy with respect to time of a pulse of light emitted by a xenon flashtube appropriate for use in conjunction with a Micro-Endoscopic System in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A micro-endoscopic system (ME system) incorporating a micro-endoscopic device (MED)  40  in accordance with the present invention is generally designated by the numeral  10 . With reference to FIG. 1, one embodiment of the ME system is comprised of a service module  20 , service cable  30  and a MED  40 . The service module  20  contains a video monitor  22 , a pulsed xenon light source  28 , system power supplies  26  and system processing and control electronics  24 . 
     A service cable  30  connects the service module  20  with the MED  40 . The service cable includes a fiber optic bundle  32  to transmit light from the light source  28  to the MED  40 . The service cable  30  also incorporates electrical conductors  34  to allow the service module  20  to communicate with the electronic portions of the MED  40 . Because of the compact size of the ME system  10 , the service cable may be as short as 2 meters. A short service cable  20  increases the amount of light reaching the viewing area by limiting the distance dependent losses associated with transmittal of light through long fiber optic cables. The service cable  20  may be permanently affixed to the service module  20  and MED  40  or may be equipped with couplings at one or both ends to allow removal from the service module  20  and/or the MED  40 . A permanent installation has the advantage of eliminating the light losses associated with fiber optic couplings. 
     The functional components of the MED  40  are illustrated in FIG.  1 . The MED  40  comprises an optical probe  50 , a sensor head  49  which contains a zoom/image focus optics package  42 , a CCD sensor array (which may also be referred to as a camera)  44  and a light pulse transfer interface  46 . With reference to FIG. 6, an MED housing  48  is a rigid structure which may be integrally connected to the optical probe  50 . In a preferred embodiment, an integrated optical probe  50  and housing  48  slidably mount over the sensor head  49  and lock in place. The housing  48  has a compact hand-held configuration that is exteriorly contoured to fit the hand of a user to facilitate dexterous and versatile usage. 
     The removable integrated optical probe  50  and MED housing  48  permit replacement of the entire exterior of the MED  40 . Once used, the integrated optical probe  50  and MED housing  48  may be replaced with a sterile unit. Probes having alternative magnifications and fields of view are also possible. A removable optical probe/housing allows the MED to be efficiently prepared for the next patient by simply replacing a used probe with a new probe/housing. An interchangeable probe/housing also allow the physician to easily alter the field of view. 
     As illustrated in FIG. 2, the ME system provides a light source  28  and light path  60  which enhance the illumination of the viewing area. The pulsed xenon light source  28  incorporates a flash tube  28   a  which emits a pulse of light of great intensity and broad spectrum but extremely short duration. The duration of the light source pulses is preferably less than 15 micro-seconds. For example, the flash tube may emit a light pulse having the equivalent of 100,000 watts of light power, but last only 10 micro-seconds. A continuous source of light having this intensity would generate significant and unwanted quantities of heat. the short duration of the light pulses from the flash tube  28   a  avoids any significant heat buildup. Light generated by the flash tube  28   a  is focused on the light receiving face of the fiber optic bundle  32  by light focus optics  28   b . Light focus optics  28   b  further enhance the intensity of light incident on the receiving face by gathering, directing and focusing the light. 
     FIGS. 15 and 16 illustrate the characteristics of a representative light pulse emitted by the pulsed xenon light source. FIG. 15 illustrates the time/power relationship of a typical light pulse emitted by a pulsed xenon light source. FIG. 16 illustrates the distribution of light emitted from the xenon light source across the spectrum classified as light, i.e. wavelengths from 100 nm (ultraviolet)-1100 nm (infra-red). From the curve labeled “Pulsed Xenon”, it can be seen that the light emitted is substantially evenly distributed across the entire spectrum, with the exception of a major peak between 200 and 300 nm in the ultra-violet and a minor peak between 450 and 500 nm in the visible. The limited “Photopic Response” of the human eye is illustrated in comparison to the spectral response of silicon. 
     The human eye is sensitive to a relatively narrow spectrum of light having a wavelength between approximately 400 and 700 nm. The spectral response of an electronic camera is much broader, approximately 300-1100 nm. The electronic camera is particularly sensitive in the infra-red wavelengths from 700-1100 nm. Approximately 26% of the light emitted by the pulsed xenon light source is in the visible spectrum from 400-700 nm with approximately 21% in the range between 400 and 600 nm where the electronic camera has low sensitivity. The extra light energy provided by the minor peak (between 450 and 500 nm) is well matched to the weakness of the electronic camera. 
     The human eye has difficulty in responding to the short pulses and pulse to pulse repetition. Therefore, no provisions for direct human viewing through the optical system have been provided. An electronic camera is a preferred receiver because the electronic camera is sensitive to non-visible light emitted by the pulsed xenon light source. Image processing electronics can then produce and freeze an image on the monitor that can be used by the surgeon. 
     According to a preferred embodiment of the invention, the camera is active only during a light pulse. The image is projected on the monitor until the next light pulse produces another image. The display is updated between 15 and 25 times per second, providing the equivalent of current integrated images. The camera is synchronized to the pulsed xenon light source. This design results in an improved signal to noise ratio and improved image contrast. 
     FIG. 14 illustrates one embodiment of a light source  28  incorporating a point source xenon flash tube S, focus reflector M, ultra violet filter  27  and infra red filter  29 . The maximum fiber bundle acceptance angle θ of the fiber optic bundle  32  is calculated using the formula θ=sin −1  NA where NA is the numerical aperture of each fiber. Point source xenon flash tube S is positioned distance d and reflecting mirror M is positioned distance d M  from the light-receiving end of the fiber optic bundle  32 . Distances d and d M  are calculated with reference to the maximum fiber bundle acceptance angle θ so that most of the light emitted by point source xenon flash tube S directly incident upon or reflected by mirror M to be incident upon the light receiving end of the fiber optic bundle  32  at an angle of θ or less. This arrangement maximizes the light incident upon the light-receiving end, and ultimately transmitted by the fiber optic bundle  32 . 
     For most purposes ultra violet filter  27  and infra red filter  29  are used to exclude undesirable portions of the broad spectrum emitted by the flash tube S, i.e., far ultra violet not useful for the electronic camera and far infra-red representing unwanted heat. However, the filters are preferably removable so that the UV and IR energy may be utilized for such procedures as cauterization or polyp removal. This would enable the physician to seal bleeding areas in the body cavity without any additional incisions or procedures. 
     The internal components of one embodiment of the MED are illustrated in FIGS. 6-9. Within the MED  40 , the light path comprises the terminus of the fiber optic bundle  32 , a pulse transfer interface  46  and a light pipe  52 . Light pulses are delivered to the MED via the fiber optic bundle  32  in the service cable  30 . Upon entering the sensor head  49 , the fiber optic bundle  32  divides into a fiber optic annulus  33 . The fiber optic annulus  33  forms the light delivery side of the pulse transfer interface  46 . The ring-shape of the fiber optic annulus  33  is optically matched by the circular entrance to the light pipe  52 . 
     The light pipe  52  comprises a core of light transmitting material  52   a  having a high index of refraction surrounded by material having a low index of refraction  52   b , thereby creating a light tunnel in a manner similar to the methods used in fiber optics. The light pipe  52  is tubular in shape and surrounds the object lens  72  and the image guide  74 . Specifically, the light emitting end of the light pipe  52  is preferably a ring approximately 2 mm in diameter with a wall thickness of 0.1 mm to 0.3 mm (best seen in FIG.  5 ). The light receiving entrance to the light pipe  52  is a cone  54 , expanding from the thin wall tube of the probe portion of the light pipe  52  to a circle which abuts the fiber optic annulus  33  at the pulse transfer interface  46 . 
     FIG. 2 is a schematic representation of the light path  60  from the light source  28  to the area to be viewed. Short duration pulses of broad spectrum light are generated by the xenon flash tube  28   a . The light focus optics  28   b  filter and focus the light onto a light receiving, or input end of the fiber optic bundle  32 . The fiber optic bundle traverses the length of the service cable, enters the MED and divides to form the fiber optic annulus  33 , or light delivery portion of the pulse transfer interface  46 . The cone  54  of the light pipe  52  forms the receiving side of the pulse transfer interface  46 . When the integrated optical probe  50  and MED housing  48  are installed over the sensor head  49 , the cone  54  and the fiber optic annulus  33  are directly coupled. Light received by the light pipe  52  travels the length of the probe and exits the light pipe  52  to illuminate the viewing area. 
     Alternative light pipes are illustrated in FIGS. 9B and 10. FIG. 9B illustrates a light pipe that uses conventional optical fibers  53  to transmit light from the fiber optic annulus to the area to be viewed. The fiber optic light pipe  52 ′ converges from a cone  55  matching the diameter of the fiber optic annulus to a tubular arrangement surrounding the image guide  74 . The fiber optic light pipe of FIG. 9A may be incorporated into the disposable optical probe. Fiber optic light transmission from the light source may in fact be preferred due to the well-established nature of the technology. FIG. 10 illustrates a fiber optic light pipe  52  that is essentially a continuation of the fiber optic bundle  32  included in the service cable. This embodiment avoids light losses at the pulse transfer interface and further simplifies the light path. 
     The ME system also comprises an image path  70  for collecting, guiding, focusing, and displaying the reflected light from which an image of the area being viewed will be constructed. A schematic representation of the ME system image path  70  is found in FIG.  3 . Reflected image light is gathered by an objective lens  72  that focuses reflected light into the first segment  74   a  of the image guide  74 . Relay optics  75  allow the image light to pass from one guide segment  74   a  to the next  74   b  without excessive loss or distortion. The image guide segments  74   a ,  74   b , etc. guide the image light to image focus optics  42  where the image light is focused on the CCD sensor array  44 . Conductors  34  in the service cable transmit the signals produced by the CCD sensor array  44  to the service module where processing electronics display the image on a monitor  22  for viewing by the physician. 
     The image guide  74  is approximately 1 mm in diameter and approximately 200 mm in length. Any rigid glass optical pathway must address the issue of birefringence or stress induced changes in the apparent index of refraction caused by stresses induced into the rod. Such changes in the apparent index of refraction will seriously disrupt delivery of image light to the camera. 
     In one embodiment, the image guide  74  comprises a segmented glass rod approximately 1 mm in diameter and approximately 200 mm in length. Ohara type-S-TIH 23 or S-TIH 53 or Corning Type 878-385 are preferred. These materials have indices of refraction greater than 1.75 and very high light transmission levels. The glass is drawn using standard electric furnaces and allowed to slowly cool to room temperature. Once cooled, the rod is cut into lengths based upon product specifications. The 1 mm diameter optical pathway for the rigid optical probe will be cut into approximately 60-75 mm lengths. Larger diameter rods for larger diameter probes can be cut into longer lengths. 
     Breaking the image guide  74  into segments, as illustrated in FIG. 4, avoids the stresses that induce birefringence in a longer glass rod of this diameter. An interferometer can be used to select segments having appropriately low internal stresses. The segments  74   a - 74   d  are joined by relay optics  75  which facilitate the transfer of image light from one guide segment to another. 
     The image guide  74  utilizes reverse fiber optic technology. The outside surface of the guide  74  is coated with light absorbent material  76  to absorb stray light in the image guide. It is desirable to provide the coating to absorb any light that strays from the focused path within the guide to avoid the deleterious effects stray light can have on image quality. Each image path segment may also comprise an aperture stop  80  at the light entry end and at the light transmission end. In combination, the aperture stops  80  and light absorbent coatings  76  ensure that only properly focused image light will be delivered to the image focus optics  42  and in turn the CCD sensor array  44 . 
     The image guide  74  may also be comprised of high quality plastic, such as the optical grade resins used in opthalmic lenses, having an index of refraction in excess of 1.6. The segmenting of a glass rod and the relay optics necessary to transmit an image from one segment to another may be avoided. The somewhat reduced light transmission capability of a plastic material can be compensated for by the increased intensity of light from the pulsed xenon light source. 
     FIG. 9A illustrates an alternative embodiment of the image guide in conjunction with an alternative flexible optical probe  50 ″. In the flexible optical probe  50 ″, both the light pipe  52 ′ and the image guide  74 ′ comprise optical fibers  53 . This design permits the probe to flex for viewing areas of a body cavity not accessible to a rigid probe. A fiber optic probe also benefits from the high levels of light and sensitive electronic camera in accordance with the present invention. The flexible optical probe may be configured as a reusable assembly, to be sterilized and re-used. 
     The light pipe  52  may also be rigidly constructed by molding optical quality glass or plastic materials into a unitary piece. FIG. 10 illustrates an alternative configuration for the light pipe  52  incorporating optical fibers formed into a tube surrounding the image guide. In this configuration, the fibers making up the fiber optic bundle  32  are separated and arranged around the image guide  74  in a tubular configuration. The complexity and inefficiencies associated with a pulse transfer interface are thus avoided entirely. 
     FIGS. 11-13 illustrate alternative configurations of the optical probe. FIG. 11 illustrates a probe having an objective lens  72  oriented perpendicular to the length of the probe  50 . A probe having this configuration will provide an image of the viewing area directly in front of the objective lens  72 . FIGS. 12 and 13 illustrate probes  50  equipped with prisms in their objective lens assemblies  72   a ,  72   b . The angled end face of each probe houses a prism that captures and bends light into the image guide  74 . Probes so equipped will give a view of the viewing area angularly offset from the MED. Rotating the MED will allow the physician a panoramic field of view surrounding the location of the MED. 
     FIG. 7 illustrates a zoom/focus optics arrangement which may be incorporated into the MED. Zoom capability allows the physician to get a closer view of the viewing area without having to adjust the physical position of the optical probe  50 . This feature is desirable in close quarters or where movement of the probe could possibly damage sensitive tissues. The spacing of lenses  45  in the zoom/focus optics are adjustable by a zoom focus control  47  that permits user selection among multiple zoom positions. The zoom/focus control  47  is provided on the MED housing  48  (see FIG.  6 ). 
     While preferred embodiments of the foregoing invention have been set forth for purposes of illustration, the foregoing description should not be deemed a limitation of the invention herein. Accordingly, various modifications, adaptations and alternatives may occur to one skilled in the art without departing from the spirit and the scope of the present invention.