Abstract:
A laser instrument that can perform effective vaporization of biological tissue and stabilization of the application cap during tissue removal is provided. The laser instrument includes an optical waveguide with a light guide portion that emits light and an application cap coupled to the optical waveguide that transmits light. The laser instrument can be inserted into an endoscope and extended or retracted to position the application cap for vaporization and removal of biological tissue.

Description:
TECHNICAL FIELD 
     The invention pertains to a laser instrument for use in non-invasive or minimally invasive operations for the vaporization of biological tissue. 
     BACKGROUND OF THE INVENTION 
     Laser instruments are used in combination with an endoscope for non-invasive or minimally invasive operations for the vaporization by contact of biological tissue, primarily in narrow-lumen hollow organs, for example, for transurethral tissue resection of the prostate in cases of benign prostatic hyperplasia. With one such laser instrument, known from EP 0 514 258 A1, the application cap fastened on the distal end of the laser light guide is bent, along with the light guide end, so that the laser irradiation emerges from the application tip in the form of a ray which is slanted at an angle to the axis of the instrument. In this regard, a danger exists that the application cap will drift in an uncontrolled fashion in the direction of the application tip during the treatment, i.e., laterally to the direction of movement, so that a target-precise, patient-friendly removal of tissue is made extremely difficult or even impossible within a closely surrounded treatment area. 
     Further, known from EP 0 433 464 B1 is a laser surgery applicator with a bent application tip which is topically coated with radiation-absorbing and light-scattering particles in order to obtain different treatment effects in individual surface sections of the applicator. Specifically, a more coagulating radiation treatment effect and a more cutting radiation treatment effect are obtained. The upward-bent application tip is illuminated on the surface areas on the outside of the bend primarily by diffuse light, so that a weak vaporization effect results there, and this applicator can thus be used for effective tissue ablation only to a very limited extent. 
     The objective of the invention is to provide a laser instrument similar to the types cited above that can perform effective biological tissue vaporization in both the prograde and the lateral directions relative to the instrument axis, and at the same time, can perform stabilization of the application cap during the tissue removal. 
     SUMMARY OF THE INVENTION 
     According to the invention, the above objective is achieved with a laser instrument that includes a special geometric configuration of the application cap. With this special geometric configuration of the application cap, the exit surface of the laser light bundle becomes significant. Namely, the laser light bundle becomes widened outward over the entire surface region o of the outer part of the bend at least as far as the outermost distal tip, but not over the radially outermost surface point of the bent part. As a result, with only a slight enlargement of the external dimensions of the application cap, an extremely effective vaporization of tissue is achieved. More specifically effective vaporization of tissue is achieved not just laterally, but also in the direction of the instrument axis, so that in addition to a long removal of tissue, a rechannelization of stenosed hollow organs is easily possible as well. Furthermore, the part of the bent applicator surface on the inner part of the bend is masked from the ray path of the laser light bundle. As a result of the distribution of vaporization and non-irradiated applicator sub-surfaces that is achieved, in combination with the sliding effect on the bent part, an automatic stabilization of the applicator cap is assured, and the danger of an uncontrolled vaporization of tissue or a adhering of tissue to the applicator tip is largely eliminated. 
     An especially advantageous aspect of the invention provides that at least the region of the bent part from which the ray emerges is roughened. As a result, when the laser instrument according to the invention is moved, small parts of the tissue to be vaporized are mechanically abraded and remain adhered to the roughened surface of the bent part. Under the effects of the laser irradiation, these tissue parts begin to carbonize, and the absorbed laser irradiation generates directly on the surface of the bent part a temperature which allows the tissue material coming into contact with the bent part to be vaporized rapidly. 
     Another advantageous aspect of the invention; is that the axial cap part is configured on the proximal end as the fiber core of the light guide with a receiving sleeve at a radial distance. This provides the advantage that the light guide is accommodated in a protected position within the applicator cap, while at the same time, a sure guiding of the laser light through the light guide to the distal end of the light guide is retained. In addition to that advantage, the light guide is preferably bonded to the proximal end of the receiving sleeve, and the receiving is designed as a thermal insulation zone according to the length of the sleeve. As a result, a high-strength mechanical coupling between the light guide and application cap is achieved. Furthermore individual heat-sensitive parts, such as the bonding location on the proximal end of the applicator, are effectively protected against overheating. 
     According to another aspect of the invention, the laser instrument is preferably used in conjunction with an endoscope, and the application cap is the guided in a sliding fashion within the working channel of the endoscope, so that pressure can be exerted on the tissue from the proximal end of the light guide and target-precise handling is made possible. In regard to this aspect of the invention, the length of the receiving sleeve is expediently dimensioned, not just from the standpoint of the thermal insulation zone, but also in such a way that the application cap is guided by means of the receiving sleeve over its entire motion path within the endoscope. 
     In terms of a high-quality optical coupling of the light guide and the application cap, the distal end of the light guide is expediently fused with the axial cap part. Furthermore, in order to minimize reflections on the light guide-applicator interface, the application cap and the fiber core of the light guide are expediently made of materials with the identical index of refraction and specifically for reasons of a high thermal loading capacity, preferably from quartz glass. For production reasons, the bent part is not continuously curved, but instead expediently runs at an angle to the axial cap part, and preferably, at a bending angle of between 5° and 30°. 
     Because of its accurately controllable, patient-friendly vaporization effect, the laser instrument according to the invention can be used in many ways, but is used in an especially preferred way for transurethral prostate treatment, particularly in the case of benign prostatic hyperplasia. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be explained in more detail through the use of exemplary embodiments in combination with the drawings. Shown in schematic form are the following: 
     FIG. 1 is a partially sectioned side view of a laser instrument according to the invention in the region of the distal end of the applicators. 
     FIG. 2 is a complete section view of the applicator and the light guide in conjunction with the distal end of the working channel of an endoscope. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The laser instrument shown in the Figures contains as its main parts an application cap  2  and an optical waveguide  4 , which per FIG. 2 can be accommodated in the working channel  6  of an endoscope (not shown). The proximal connection of the optical waveguide  4  to a laser light source, like the remaining parts of the endoscope, including the rinsing agent channels and the visual control function, is of conventional design and therefore not shown in the Figures in detail. 
     The application cap  2  consists of a cylindrical cap part  8  which is coaxial with the optical waveguide  4 , and a bent part  10  which is at an angle to the waveguide  4 . The bent part  10  is also cylindrical, but it is rounded at the distal end and is made of the same material as the fiber core  12  of the optical waveguide  4 , namely, quartz glass with the same or nearly the same index of refraction. At the proximal end, the axial cap part  8  forms a receiving sleeve  14  for the optical waveguide  4 , whereby the lumen  16  of the receiving sleeve  14  has essentially the same diameter as the sheathing  18  of the optical waveguide  4 . By means of a bonding  20  between the sheathing  18  and the receiving sleeve  14 , the optical waveguide  4  is joined to the application cap  2  in a mechanically fixed and sealed manners. However, the sheathing  18  immediately beyond the bonding location  20  is removed exposing an annular gap between a portion of the wave guide  4  and the receiving sleeve  14 , so that only the “light guide” portion of the optical waveguide  4  (for example, the fiber core  12  and possibly the fiber cladding, not shown), runs to the distal end of the receiving sleeve  14 . The light guide end  22  is fused to provide a high-quality, low-reflection laser light coupling with the cap part  8 . 
     As shown in FIG. 1, the axial cap part  8  extends beyond the surface of the distal light guide end  22 . The length _“a”_ of the extended cap section  24  is dimensioned, in dependency on the angle of divergence _“α”_ of the ray bundle (i.e., the ray path of the laser light bundle) inside the cap part  8 , in such a way that the outer bend marginal ray _“Ra”_ of the ray bundle emerges at a maximum exterior angle in the transition region between the axial cap part  8  and the bent part  10 . By contrast, the inner bend marginal ray _“Ri”_ of the ray bundle inside the cap  2  remains within cap part  8  and bent part  10  which form a minimum exterior angle on this side, and emerges only at the rounded end of the bent part  10  between the outermost distal tip S and the radially outermost surface point P of the bent part  10 . In this regard, the bending angle _“P”_ of the bent part  10  is equal to or greater than the angle of divergence α. However, the bending angle β is also small enough, taking into account the length of the bent part  10 , that the entire bend surface area (shaded in FIG. 1) of bent part  10 , including the distal application tip S but not the radially inner surface point P, are illuminated from the therapy light (i.e., the laser light), and the remaining surface areas of the cap part  8  and the bent part  10  are masked from the ray path of the laser light bundle. 
     The application cap  2  is guided within the working channel  6  of the endoscope by the axial part  8 , whereby the entire length of the receiving sleeve  14  and the cap section  24  corresponds to the maximum motion path of the application cap  2 . As a result, pressure can be exerted on the tissue from the proximal end of the optical waveguide  4  via the application cap  2  without the optical waveguide  4  being pressed, unsupported, out of the distal end of the working channel  6 . In addition to the guiding function, the receiving sleeve  14  also takes on the task of thermal insulation, through which temperature sensitive parts, i.e., the bonding  20  in the case of the embodiment shown, are protected from the excessive effects of heat coming from bending part  10 , which heats up considerably during the vaporization of tissue. 
     A typical embodiment of the invention has the following dimensional features. The application cap  2  possesses a total length of 25 mm, the receiving sleeve  14  has a length of 18 mm, the cap section  24  is 2 to 4 mm in length, and the bent part  10  is between 3 and 5 mm long. The outside diameter of the cap  2  is about 1.6 mm and the distance of the radially outermost surface point P from the centerline of the cap part  8  is 1.5 mm. The angle of divergence α of the therapy light within the cap material typically has a value between 3° and 10°, and the bent part  10  is bent at an angle β of 10° to 20° relative to the cap part  8 .