Abstract:
A method of conducting endoscopic surgeries places the camera outside the sterile field, freeing the physicians hands and eliminating costs and inconveniences associated with sterilizing the camera between surgeries. Images may be relayed to the camera by means of a fiber optic cable. Cost issues associated with the long fiber optic cable are avoided by breaking it into two segments, only one of which is likely to be damaged during use. An image preserving connection is formed between the cable segments by a connector that fixes the ends of the cables in close proximity to one another, but a certain fixed distance apart. An image preserving connection is made between two fiber optic cables without the aide of a lens.

Description:
FIELD OF THE INVENTION 
     This invention arose in the field of endoscopic surgical devices but also pertains to the field of fiber optics. 
     BACKGROUND 
     There is great incentive to make endoscopes smaller. Smaller endoscopes make endoscopic surgeries less invasive and healing times shorter. If the endoscopes are small enough, the entire procedure can be carried out in a doctor&#39;s office, without general anesthetic, on an outpatient basis, resulting in a substantial cost savings. Today, most endoscopes in use are rigid endoscopes, comprising chains of lenses. An introducer at least 6 millimeters in diameter must be inserted in the patient&#39;s body to conduct surgery with the smallest of these. Applicants are working to develop flexible, serviceable, and affordable fiber optic endoscopes by means of which surgeries may be conducted through an introducer 2 millimeters or less in diameter. 
     In a typical endoscopic surgery, the introducer is a cannula with a trocar through its center, which is inserted into the patient&#39;s joint. The trocar is then withdrawn and the endoscope inserted. The endoscope is connected to a camera through an adapter that clips on to the base of the endoscope. A wire from the camera carries the image to a video processor. 
     The person conducting the surgery holds the camera while manipulating the endoscope. Although orthopedic surgeons have become used to holding cameras while conducting these surgeries, relieving them of this burden could only enhance their ability to conduct them. 
     An important issue in conducting surgeries of this type is maintaining sterile conditions. For this purpose, a sterile field is created. A sterile field is an area around the point of incision that is prepared before a surgical procedure and maintained during the procedure. The preparation and maintenance of a sterile field is described in Atkinson and Fortunato, Berry &amp; Kohn&#39;s Operating Room Technique (8th ed. 1996). All items within the sterile field must be sterilized. In prior art endoscopic surgeries, the camera, wire, and adapter are within the sterile field. Federal regulations and good practice therefore require these parts to be sterilized between uses. This is inconvenient, time consuming, and reduces the availability of the apparatus for use in other surgeries. Furthermore, the sterilization procedure can damage the electronic components. 
     SUMMARY OF THE INVENTION 
     In one respect, the present invention comprises a method of conducting endoscopic surgery in which the camera is outside the sterile field. According to this method, the camera is placed outside the sterile field and the image is transmitted to the camera by a fiber optic cable. Preferably, the apparatus for conducting the surgery is organized so that the person conducting the surgery does not have to hold the camera while manipulating the endoscope. 
     The inventors observed that use of a single long fiber optic cable to carry the image outside the sterile field would makes this procedure expensive. The initial cost of such a cable would be high and even with care it is inevitable that it would be damaged during use. The cable would probably not last through ten surgeries. 
     To ameliorate this expense, the inventors developed a segmented fiber optic cable. By a segmented fiber optic cable, applicants mean an image transmitting fiber optic cable formed by the union of two or more separate fiber optic cables. Applicants observed that a short segment of the cable nearest the patient is the portion most likely to be damaged during use. In a segmented fiber optic cable, this portion (called the “disposable cable portion”, although it may be used several times) may be replaced while the longer portion of the cable (the “reusable cable portion”) continues to be reused. The reusable cable portion can also be armored. While such armoring on the disposable cable portion might interfere with the operation of the endoscope and would, in any case, excessively increase the diameter of the introducer, armoring on the reusable cable portion presents no disadvantages. An armored reusable cable portion is expected to withstand upwards of a hundred surgeries. 
     In developing a segmented fiber optic cable, the inventors were faced with the problem of connecting the segments in a way that would preserve the image quality required for surgical procedures. Fiber optic cables comprise bundles of optical fibers. Thousands of fibers are required to form a satisfactory image. Image preserving connections between such bundles of image transmitting fibers appear to have been unknown prior to applicant&#39;s invention. By an image preserving connection, applicants mean a connection across which simple images, such as those of grids, that do not push the resolution limits of the image conveying apparatus, are not degraded beyond recognition. Applicants have invented an image preserving fiber optic cable connector that preserves images to the degree required for endoscopic surgery. 
     Applicants&#39; preferred connector functions by holding the tips of the fibers a certain small distance apart. It was unexpected that two fiber optic cables could be connected in this way. If the fibers were butted against one another, the image would suffer from fixed pattern noise, giving the image a mottled appearance and making it essentially useless. If the fibers were too far apart, the image would be blurred. Applicants unexpectedly discovered that there is a fiber tip spacing that allows the image to be transferred without noticeable fixed pattern noise, substantial loss of resolution, or excessive loss of image quality. 
     Applicants endoscopic surgical apparatus is expected to change the economics that affect the way endoscopic surgeries are performed. By placing the camera outside the sterile field, the expense and damage associated with sterilizing the camera can be avoided. By using a segmented fiber optic cable, the expenses associated with the cable itself can be kept under control. If the connection between the cable segments is made, according to applicants&#39; preferred embodiment, using a connector that functions by holding the ends of the cables a small distance apart, rather than by means of a lens, problems associated with connector itself will not present problems comparable to those that were associated with a camera within the sterile field. 
     Applicants&#39; invention is also expected to have a direct effect on the mechanics of endoscopic surgeries. The person conducting the procedure will no longer have to hold the camera, allowing greater control of the endoscope. In conjunction with other advances made by applicants, the invention is expected to contribute to the adoption of small diameter fiber optic endoscopes, which will mean less invasive surgeries, surgeries that can be performed on smaller joints, and surgeries that no longer have to be performed in a hospital. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of a preferred endoscopic surgical apparatus comprising a segmented fibre optic cable. 
     FIG. 2 is a plot showing how the width and intensity of an image of a line vary with the gap between the ends of two fiber optic cables. 
     FIG. 3 is an exploded isometric view of a preferred fiber optic cable connector that connects both image transmitting fibers and illumination transmitting fibers. 
     FIG. 4 shows a preferred fiber optic cable image transmitting sub-connector with the two portions disconnected. 
     FIG. 5 shows the fiber optic cable image transmitting sub-connector of FIG. 4 with the two portions connected. 
     FIG. 6 shows another example of a fiber optic cable image transmitting sub-connector. 
     FIG. 7 demonstrates a method of setting the gap during assembly of the sub-connector of FIG.  6 . 
    
    
     DETAILED DESCRIPTION 
     In one embodiment, applicants invention is an endoscopic surgical technique that places the camera outside the sterile field. Preferably the image is transmitted to the camera using a segmented fiber optic cable. Preferably, the fiber optic cable, with sheath, is four millimeters in diameter or less, more preferably 1.4 millimeters in diameter or less. In another embodiment, the invention is a method of conducting surgeries using a segmented fiber optic cable to transmit an image from within a patient&#39;s body to where it can be viewed by a person conducting the surgery. 
     A method of conducting multiple surgeries in accordance with the present invention treats one end of the cable, the one nearest the patient, as being disposable or interchangeable. For example, the end of the cable nearest the patient may be separated from the rest of the cable and sterilized between one surgery and the next. Alternatively, the end of the cable nearest the patient may be disposed of and replaced between one surgery and the next. 
     A preferred apparatus for conducting endoscope surgeries in accordance with the invention is shown schematically in FIG.  1 . It comprises a lens  12 , a disposable fiber optic cable  16 , a connecter  20 , a reusable fiber optic cable  24 , a camera  36 , an image processor  38 , a monitor  40 , and an illumination light source  34 . The illuminating light is generally transmitted to the target area  10  through a set of fibers  32  that are bundled with, but separate from, the image transmitting fibers  26 . As described in co-pending application Ser. No. 08/890,803, which is incorporated herein by reference, it is also possible to combine the functions of channeling illuminating light and image light in one set of fibers thereby further reducing the size of the device that must be inserted in the patient. 
     In operation, the lens  12  gathers an image from a target area  10  illuminated by light channeled from light source  34 . The lens  12  directs the image into the polished ends of the fibers at one end  14  of disposable fiber optic cable  16 . Light is transmitted down the length of the fibers to the other end  18  of the disposable fiber optic cable  16 . The light within each fiber of the cable comprises a single point of image data. The data from a group of fibers must be in proper spacial relation for an image from one cable end to form at the other end. The disposable fiber optic cable  16  is a coherent optical fiber bundle, in that the spacial relationship between the fibers is the same at both ends of the cable. Thus an image of the target area  10  appears at the end  18  of the disposable fiber optic cable  16 . 
     In the preferred embodiment, the image from the end  18  of the disposable fiber optic cable  16  falls directly upon the end  22  of the reusable fiber optic cable  24 . Alternatively, the connector  20  could comprise a lens that directs the image from the end  18  onto the end  22 . Such a lens would need to be somewhat out of focus to avoid fixed pattern noise. The reusable fiber optic cable  24  channels the image to the lens  30  associated with camera  36 . 
     The camera  36  generates a signal coding the image. The signal coding the image is transferred from the camera  36  to the image processor  38 . The image processor  38  contains software and operates to remove artifacts from the image and enhance it. The output of the image processor  38  is displayed on the monitor  40 . The delay in processing the image is minimal, so that the image displayed is current with the image being gathered by the lens  12 . In other words, the image displayed is a real time image. 
     When, as in the preferred embodiment, the apparatus comprises a segmented fiber optic cable, a fiber optic cable connector is necessary. For surgical applications, the connector is preferably small, easy to operate, and essentially fool proof. Ideally, the connector should operate to form an image transmitting connection between the cables when the two ends of the connector are pushed together with a minimum of force. If the connector is of the type that requires the ends to be oriented correctly in terms of rotations about the cable axes, the two ends of the connector should provide both visual and tactile indications as to the correct orientation. 
     The preferred connector is one that can hold the ends of the cables a fixed distance apart. Theoretically, the connection could be made using a lens. Lenses have a number of drawbacks however, which drawbacks relate to the logistics of aligning the lens and the fibers with sufficient precision and the trade-offs that must be made between size of the lens, its precision, and its cost. 
     Applicants have experimentally determined the positioning required to form an image preserving connection between the ends of two 1.0 millimeter diameter fiber optical cables each having 30,000 close packed fibers, each fiber having a diameter of approximately 4 micrometers and a numerical aperture of approximately 0.35. The solid line  56  in FIG. 2 plots the variation of intensity  50  of an image, which is that of a line, with a gap  52  between the cable ends. By cable ends, the applicants mean the surfaces formed by the ends of the fibers of the cables when the ends of the cables have been polished. The dashed line  58  plots the variation of the image width  54  with the gap  52 . The width of the line&#39;s image is a measure of the image resolution. Resolution was deemed adequate for medical diagnostic purposes when the gap was 20 micrometers or less, although resolution was noticeably better when the gap was 10 micrometers or less. When the gap was essentially zero, the image suffered from severe fixed pattern noise. This fixed pattern noise decreased to a satisfactorily low level when the gap was increased to 4 micrometers. The optimal gap was 4 to 8 micrometers. The offset of the axes of the two cables is preferably also controlled to some degree. Preferably, the offset is not more than 10 micrometers. 
     The preferred gap between cable ends is expected to vary proportionally with fiber diameter and inversely proportionally with numerical aperture, at least for small numerical apertures. As a first approximation, the applicants suggest that, when working with fibers having substantially different diameters and/or numerical apertures from the ones used in the examples given here, the gap be selected in the range:          .35        d   NA       &lt;   g   &lt;     .70        d   NA                              
     where g is the gap, d is the mean fiber diameter for the two cables, and NA is the numerical aperture of the cable from which the image is to be transmitted. Ultimately, however, the ideal gap may need to be determined empirically. 
     A preferred connector in accordance with the present invention is shown disassembled in FIG.  3 . The connector  60  comprises two housing ends  62  and  64 . The end  62  shown on the left hand side of FIG. 3 comprises connector housing portions  66  and  68 , which contain sub-connector ends  74  and  76 . The other end  64  comprises connector housing portions  70  and  72 , which contain sub-connector ends  78  and  80 . Sub-connector ends  74  and  80  form and an image transmitting sub-connector. Sub-connector ends  76  and  78  form an illumination transmitting sub-connector. Connector end  62  slides within connector end  64 . Shaped corners  61  and  63  key the two connector ends so they cannot be joined unless they are properly oriented. The ends are reversibly held together by protrusions (not shown) that snap into notches  82 . 
     A detailed example of a preferred image transmitting sub-connector is shown in FIGS. 4 and 5. The female portion  74  comprises a fiber bundle  94  surrounded by a stainless steel ferrule  96 . The fiber bundle  94  is bound to the ferrule  96  by epoxy  98 . The male portion comprises a cable fiber bundle  102  surrounded by ferrule  104  and bound to it by epoxy  106 . The ends  108  and  112  of the ferrules  96  and  104  are flush with the polished ends  110  and  114  of the fiber bundles  94  and  102 . 
     The female end fiber ferrule  96  is positioned concentrically within an alignment tube  100 . A tack  116  prevents the alignment tube  100  from sliding relative to the ferrule  96 . The alignment tube  100  helps guide and axially align the fiber bundle ends  100  and  114  together when the male and female portions of the connector are being joined. 
     The alignment tube  100  is itself positioned within an elastic member  90 , which fits tightly within the connector housing  62  in the region  86 . The elastic member  90  functions to allow the fiber bundle  94  to move freely in the direction of its axis relative to the connector housing  62 . The elastic member  90  also exerts a biasing force tending to press the fiber bundle ends  110  and  114  together when the two ends  62  and  64  of the connector  60  are joined. Displacement of the end  114  of the male fiber bundle  102  is resisted by the male end ferrule  104 , which rests against the housing end  64  at the point  84 . 
     The male end ferrule  104  is positioned concentrically within elastic member  92 . Elastic member  92  fits tightly within connector housing  64  in the region  88 . The elastic member  92  allows the fiber bundle  102  to move in directions perpendicular to its axis. 
     A spacer  106  is formed by electroplating on the end  112  of the male end ferrule  104 . The spacer  106  fixes the gap between the fiber bundle ends  110  and  114  when the ends of the connector are joined. One of the advantages of forming a spacer by electroplating is that an electroplating-formed spacer compensates for the rounding that tends to occur around the perimeters  113  and  115  of the ferrule ends. FIGS. 4,  5 ,  6 , and  7  are not drawn to scale in that the gap is much narrower, and the spacer much thinner, than shown in these illustrations. 
     In the preferred embodiment, the illumination transmitting sub-connector is the same as the image transmitting sub-connector, except that the illumination transmitting sub-connector does not have a spacer. 
     Another example of a sub-connector in accordance with the invention is shown in FIG.  6 . In this example, there is an extension sleeve  120  between the female end ferrule  96  and the alignment tube  122 . When the male and female ends of this sub-connector are joined, the extension sleeve  120  meets the male end ferrule  124  and maintains the gap between the fiber bundle ends  110  and  114 . In this embodiment, the male end ferrule  124  has a larger diameter than the female end ferrule  96 . In assembling the connector with the extension sleeve, the gap can be set, as illustrated in FIG. 7, by pressing the female end ferrule  96  and the extension sleeve  120  against a shaped rubber surface  130  and sliding the extension sleeve to conform to the surface. When the extension sleeve is correctly positioned, a tack weld  126  can be used to fix it in place. 
     When a segmented fiber optic cable is used, the portion of the cable which does not have to fit in the cannula can be armored. A preferred method of armoring is by enclosing the cable in a relatively thick metal sheath. 
     A surgical apparatus constructed and operated in conformity with one or more of the preferred embodiments described above will provide convenient and cost effective means with which surgical procedures can be conducted in accordance with the applicants invention. These procedures solve important sterilization problems and contribute to the practicability of minimally invasive surgeries using fiber optics.