Patent Application
20230101488
The invention relates to a surgical laser fiber.
More particularly, the present invention relates to configuration of an end-firing surgical laser fiber, and in particular to an end-firing surgical laser fiber having a distal end section to which is fixed a sleeve or tube having a highly reflective inner diameter to maintain fiber output power density by acting as a waveguide for laser radiation exiting the fiber and incident on the inner wall of the sleeve or tube, and which further serves as a standoff sleeve to provide a minimum spacing between the end face of the fiber and a target of the surgical laser.
The invention also relates to a method of preventing accumulation of dust particles and stone fragments on inside diameter of a standoff sleeve.
The surgical laser fiber and method of the invention may be used with a variety of different laser types, including Thulium Fiber Lasers (TFLs) of the type used in laser lithotripsy (urological stone fragmentation) procedures.
Laser lithotripsy is a surgical procedure developed during the 1980s to remove impacted stones from the urinary tract, i.e., kidney, ureter, bladder, or urethra, by fragmenting or breaking apart the stones so that they can be more easily excreted by the patient. Early laser lithotripsy used pulsed-dye lasers with picosecond pulse durations to create cavitation bubbles whose collapse caused laser induced shockwaves to fragment the stone. However, the induced shockwave caused a high degree of retro-repulsion, i.e., pushing of the stone way from the laser delivery fiber, and therefore the pulse dye lasers were replaced by pulsed Holmium lasers having longer pulse durations (250 micro seconds) that produced a weaker pressure wave, and therefore less retro-repulsion.
Such laser lithotripsy procedures required frequent replacement of the laser delivery fibers due to fiber degradation. In addition, operators of the Holmium laser frequently encountered sudden flashes that temporarily prevented the operator from viewing the treatment site, forcing stoppage of the laser and prolonging the lithotripsy procedure. It was found that both problems could be traced back to free electron absorption (FEA) by the fiber-as a result of contact between the tip of the fiber and the stone being targeted, and therefore the current inventors proposed to eliminate the possibility of fiber-to-stone contact by providing a standoff sleeve that extended beyond the tip of the fiber to physically maintain a minimum spacing between the fiber and the stone. As described in the inventor's PCT Appl. Ser. No. PCT/US2017/031091 (PCT Publ. No. WO/2017/192869), filed May 4, 2017, the spacer tip or standoff sleeve consisted of a non-reflective cylindrical structure placed over a stripped end of the fiber, and arranged to extend a predetermined distance beyond the end to act as a physical barrier between the fiber and a stone. Not only did the standoff sleeve prevent contact between the fiber and the stone but, by making the sleeve out of a relatively soft material such as PTFE or ETFE, the standoff sleeve could be used to protect the inner surface of an endoscope during insertion of the fiber through the scope to the treatment site.
Further enhancements to the spacer tips or standoff sleeves, and/or methods of utilizing the spacer tips or sleeves during laser lithotripsy procedures included the arrangements and methods disclosed by the inventors in U.S. patent application Ser. No. 15/992,609, filed May 30, 2018, now U.S. Pat. No. 11,109,911; Ser. No. 16/234,690, filed Dec. 28, 2018; Ser. No. 16/353,225, filed Mar. 14, 2019; Ser. No. 16/414,255, filed May 16, 2019; and Ser. No. 16/546,992, filed Aug. 21, 2019. For example, it was found that by appropriately controlling the laser, or by use of an additional continuous wave laser, liquid in the interior passage between the end of the fiber and the end of the sleeve could be vaporized, resulting in a “Moses” effect that reduces retro-repulsion of the stone, resulting in reduced power requirements, enhanced stone fragmentation efficiency, and shorter treatment times.
However, while the above-described PTFE or ETFE spacer tips or standoff sleeves are well-suited for use with existing pulsed Holmium:YAG laser systems, problems arise when used in continuous wave/high frequency Thulium fiber lasers (TFLs), which have recently replaced pulsed Holmium:YAG lasers for many lithotripsy applications because of their relatively small Gaussian beam profile, which allows use of smaller fiber core diameters (improving fiber flexibility and irrigation in the single working channel of the scope), and because the lack of pulse intervals prevents fragments of stone from breaking away and escaping the path of the laser during the intervals. On the other hand, the smaller cross-section and higher power density of a TFL fiber leaves the fiber more vulnerable to degradation due to free electron absorption and increased temperatures at the treatment site. Thulium fiber lasers typically have an output frequency of 5-2500 Hz, as compared to 5-100 Hz for a pulsed Holmium laser, resulting in substantially increased heat generation at the treatment site, which can destroy spacer tips or standoff sleeves of the type described above, leaving no way to prevent fiber-to-stone contact.
One solution to reducing fiber degradation is simply to increase the size of the fiber, resulting in a more robust fiber that is able to withstand higher temperatures and to absorb reflected radiation, but this would negate the advantages of increased flexibility and enhanced irrigation resulting from the smaller fiber diameter made possible by the use of continuous wave Thulium fiber lasers. In order to maintain the advantages of a thinner fiber while at the same time reducing fiber degradation by providing a more robust fiber exit surface, it was proposed to provide an outward taper at the end of the fiber, for example as disclosed in copending U.S. patent application Ser. No. 15/417,934, filed Jan. 27, 2017 (BROW3039CIP). However, as discussed in Section 1.3 on page 2 of the article by Thomas C. Hutchens et al. entitled “Hollow Steel tips for Reducing Distal Fiber Burn-Back During Thulium Fiber Laser Lithotripsy,” Journal of Biomedical Optics, 18(7), 078001 (July 2013), the tapered fiber was still vulnerable to damage and burn-back, and furthermore more delicate and subject to fracture during handling. Consequently, the Hutchens article proposed to replace the tapered fiber tip with a hollow steel tube glued to, and arranged to surround and extend beyond, the end of a conventional non-tapered, cylindrical fiber.
Neither of these prior solutions to the problem of fiber degradation in a Thulium laser system completely addresses the problems of fiber degradation and maintaining spacing between the fiber tip and a target stone. As a result, there is still a need for fiber tip configurations or arrangements that can prevent fiber degradation in systems such as Thulium laser lithotripsy system that use higher power lasers and smaller diameter fibers.
In addition, the prior solutions to the problem of fiber degradation in any type of laser lithotripsy system that utilizes a standoff sleeve fail to address another cause of fiber degradation, namely degradation caused by a buildup of dust particles on the inside of the standoff sleeve.
While high power lasers, including continuous wave Thulium lasers, have the advantage of more completely pulverizing stone fragments, this can lead to the creation of additional suspended dust particles. If too many dust particles build up inside the sleeve, the temperature of the fiber tip can still exceed 1000° C. and create Free Electron Absorption (FEA) similar to the FEA that occurs when a fiber tip contacts a stone in the absence of a sleeve, resulting in rapid fiber degradation despite the standoff sleeve.
It is accordingly an objective of the present invention to provide an improved optical fiber arrangement for laser surgery applications.
It is a second objective of the invention to provide a surgical laser system that takes advantage of the smaller fiber diameter made possible by the use of higher power density lasers, while still providing durability advantages of a larger diameter fiber, i.e., lower vulnerability to fiber degradation due caused by energy reflected or emitted by the target.
It is a third objective of the invention to provide an optical fiber arrangement for continuous wave laser lithotripsy applications, which further includes a standoff sleeve that prevents the fiber tip from contacting a stone, and that is capable of withstanding the higher treatment site temperatures generated by the continuous wave lasers, including relatively high power lasers such as Thulium fiber lasers having wavelengths of, for example, 1900 to 2200 nm.
It is a fourth objective of the invention to provide a surgical laser system having an optical fiber configured at the treatment end to offer both enhanced resistance to damage caused by higher treatment site temperatures, and a minimum spacing between the end of the fiber and a target of the laser to prevent fiber degradation due to FEA and other problems resulting from contact between the fiber tip and the stone.
It is a fifth objective of the invention to provide a method of preventing damage caused by dust particle buildup on the inside diameter of a standoff sleeve, by adding lower power single or multiple pulses to the laser output in order to flush suspended dust particles from the interior of the standoff sleeve.
These and other objectives of the invention are achieved, in accordance with the principles of an exemplary embodiment of the invention, by replacing the relatively soft PTFE or ETFE standoff sleeves utilized with conventional Holmium fiber lasers, and the hollow steel tube proposed in the Hutchens article cited above, with a standoff sleeve having a reflective inner diameter to maintain power density, and yet that is capable of withstanding the higher treatment temperatures of, for example, a high pulse frequency Thulium fiber laser.
The objectives of the invention are also achieved by providing a method of preventing buildup of dust particles within a standoff sleeve, whether conventional or modified to include a reflective inner diameter, by modifying the laser output to include low power long-duration single or multiple pulses that serve to flush suspended dust particles from the inside of the standoff sleeve. The particle-flushing pulses could be applied periodically, as a pre-pulse or in response to detection of excess radiation or FEA, for example by using the stone-sensing method described in copending U.S. patent application Ser. No. 15/992,609, filed May 30, 2018 (now U.S. Pat. No. 11,109,911), and Ser. No. 17/400,380, filed Aug. 12, 2021, both of which are incorporated herein by reference.
In exemplary embodiments of the invention, the internally-reflective standoff sleeve may be made of metal, a glass material such as silica glass, or sapphire. In addition or alternatively, the inner diameter of the sleeve may be provided with coatings to enhance reflectivity. Preferably, the standoff sleeve is fixed to the outer diameter of an end section of the fiber by welding, and the end section of the fiber to which the standoff sleeve is welded be tapered or non-tapered. If a taper is provided, the region around the circumference of the outwardly-expanded planar end face of the fiber is welded to the standoff sleeve, and the space between the tapered section and the sleeve may be filled with a filler material or reinforcing structure, such as an insert sleeve, so that the advantages of a tapered tip can be obtained without the disadvantages of fragility and susceptibility to fracture of the tapered joint. Welding of the standoff sleeve to the fiber provides the further advantage of providing a heat conductive connection that enable the sleeve to serve as a heat sink, although it is also within the scope of the invention to utilize other adhesive or mechanical methods (such as crimping) to fix the reflective standoff sleeve to the fiber, depending on the material of the reflective standoff sleeve. In addition, the filler material or reinforcing structure may be index matched to the material of the sleeve and have an index of refraction that matches, or is higher than, that of the cladding to absorb, transmit, or scatter energy that might otherwise back-propagate through the fiber towards the scope.
Although the reflective standoff sleeve is not limited to use with tapered fibers, tapering of the fiber provides the advantage of lowering the numerical aperture of the fiber to concentrate laser power, while index matching of the sleeve and fiber cladding prevents free electron absorption (FEA) radiation from traveling back down the fiber and causing fiber breakage within the scope through which the fiber has been inserted. In addition, the reflective standoff sleeve acts a heat sink to further help prevent damage due to free electron absorption, and as a waveguide for laser radiation incident on the inner wall of the sleeve. Although made of a relatively hard material, damage to the scope during insertion of the fiber may be prevented by rounding the distal end of the sleeve. Unlike a bare fiber which can erode exposing sharp tip edges, the sleeve does not erode and a smooth edge is maintained to prevent scope damage.
In a second exemplary embodiment of the invention, the end of the fiber is formed as or includes a convex lens structure to further focus the laser output of the fiber. It will be appreciated that the convex lens structure may include a variety of shapes, including planar, tapered, and/or curved shapes, and combinations thereof.
In addition to cylindrical standoff sleeve shapes, it will be appreciated that the shape of the reflective standoff sleeve may also be varied to increase or decrease power density output, by expanding or reducing the diameter of the distal or output end of the reflective standoff sleeve.
As shown in
In the exemplary embodiment of
For a Thulium Laser Fiber, exemplary dimensions are as follows: the core diameter D1 of the fiber 10 is 150 μm, and the diameter of the flat distal end surface 60 of the tapered section 50 may be 180 μm. For a fiber having a numerical aperture (NA) of 0.22, the numerical aperture of the taper is 0.121 (0.22 multiplied by the ratio of start and end diameters (D1/D2)). The divergence output half angle θ from the taper end, indicated by reference numeral 80 (θ=arcsin(NA)) is 7°.
It will be appreciated by those skilled in the art that the taper, if provided, can be achieved by known optical fiber formation methods, including appropriate control of core extrusion and cladding coating processes, and that the dimensions of the taper may be varied without departing from the scope of the invention.
The standoff sleeve 20 that surrounds the tapered end 60 of the fiber 10 in the exemplary embodiment of
To prevent the end surface 60 from contacting a stone during a lithotripsy procedure, the fiber end surface 60 is set back from the distal end 100 of the standoff sleeve 20 by a set-back distance L. The standoff sleeve 20 has a thickness T and may, for example, be in the form of a silica capillary tube (SCT) 10 that is index matched to, or that has a refraction index that is higher than, the index of the fiber cladding. Such an all silica glass sleeve can handle higher temperatures than an ETFE or PTFE sleeve, while also acting as a heat sink to help prevent damage due to free electron absorption (FEA), and as a waveguide for laser radiation exiting the fiber. The distal end 100 of the standoff sleeve 20 may further be rounded to provide protection for a scope (not shown) through which the fiber 10 is inserted to the treatment site.
The space between the tapered section 50 of fiber 10 and the standoff sleeve 20 is preferably filled with an index-matching reinforcing filler material 70. Reinforcing filler material 70 preferably has an index of refraction that matches the index of refraction of the sleeve 20 and that is equal to or higher than that of the cladding 30, to facilitate dissipation of radiation reflected or emitted back into the fiber from the treatment site, so that the radiation does not travel back through the fiber and cause damage to the fiber. Although illustrated as being between the tapered section 50 and the standoff sleeve 20, the reinforcing filler material 70 may also be present between the non-tapered portion of the fiber 10 and the standoff sleeve 20.
In addition to cylindrical standoff sleeve shapes, it will be appreciated that the shape of the reflective standoff sleeve may also be varied to increase or decrease power density output, by expanding or reducing the diameter of the distal or output end of the reflective standoff sleeve as shown respectively in
Finally,
As with the reflective standoff sleeves of
A problem common to the standoff sleeves shown in
As shown in
As an alternative to insertion of low frequency, lower power pulses at regular intervals, clearing of suspended dust particles can also be achieved by use of a single continuous background pulse or waveform, or by adding a pre-pulse for each or initiated therapeutic pulse. The dust particle clearing pulses can be created by modulation or appropriate control of the main therapeutic laser, or by a secondary laser.
Although preferred embodiments of the invention have been described in connection with the appended drawings, it will be appreciated that the description of the preferred embodiments is not intended to be limiting, and that modifications of the preferred embodiments may be made without departing from the scope of the invention, which should be limited solely by the appended claims.
For example, while the tapered fiber and metal, glass, or sapphire standoff sleeve illustrated herein are particularly adapted for use with Thulium Laser Fiber (TFL) lithotripsy systems, both the taper and the standoff sleeve may be used with lasers other than continuous wave Thulium lasers, including pulsed laser systems, and end-firing lasers for procedures other than laser lithotripsy. In addition, the materials of the standoff sleeve and any filler may be varied, as may the manner in which the standoff sleeve is fixed to the tapered section of the fiber. Still further, the dust particle buildup prevention method shown in
The application claims the benefit of U.S. Provisional Appl. Ser. No. 63/324,676, filed Mar. 29, 2022, and 63/247,427, filed Sep. 23, 2021, each of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63324676 | Mar 2022 | US | |
| 63247427 | Sep 2021 | US |
