WO1996018347A1

WO1996018347A1 - Optical fibre laser delivery probe and use thereof

Info

Publication number: WO1996018347A1
Application number: PCT/GB1995/002920
Authority: WO
Inventors: Lee Brine; David James Pointer
Original assignee: Lee Brine; David James Pointer
Priority date: 1994-12-14
Filing date: 1995-12-14
Publication date: 1996-06-20
Also published as: GB9514872D0; AU4184596A

Abstract

An optical fibre laser delivery probe for the endoscopic delivery of laser radiation to a target has an optical fibre for receiving laser radiation from a laser source and adapted to transmit the laser radiation (14) from its distal end for delivery to the target. The fibre has a core (8) whose end surface (13) is suitably polished to reflect the laser radiation travelling along the fibre out of the end of the probe as a divergent, forward-firing beam (14) by internal reflection. The distal end of the optical fibre is enclosed by a fused silica or synthetic fused silica sheath (11) which is transparent to the laser radiation and can withstand the high temperatures encountered in use. The sheath protects the probe from destruction in use by the high temperatures frequently encountered in endoscopic applications. The probe has particular application in the treatment of benign Prostatic Hyperplasia.

Description

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The present invention relates to a probe for the delivery of laser radiation through an optical fibre to a desired target, and in particular to a probe for use in internal endoscopic treatment of the body with laser radiation. It is applicable to any treatment in which laser radiation is incident on body tissue to, for example, coagulate or vaporise the tissue. One such form of treatment is photo-dynamic therapy. Another is in urological applications, such as the treatment of benign Prostatic Hyperplasia (BPH) . BPH is a long term condition where the outflow of urine from the bladder is restricted by an enlarged prostate gland. It is very common among elderly men. This condition was previously treated by surgical resection of the prostate to remove the obstruction. However, although offering good, immediate relief of the obstructed symptoms, this technique has disadvantages such as relatively high mortality rates, high incidence of morbidity, post-operative bleeding and long recovery times. There is therefore a desire to find an alternative form of treatment.

Endoscopic optical fibre laser probes are used as an alternative method of treating BPH. The probes are inserted via an endoscope into the urethra and used to deliver laser radiation to the urethral wall and underlying prostatic tissue. The laser energy coagulates, vaporises and in some cases chars the tissue, thereby effecting removal of the obstruction.

Laser treatment of BPH is preferred in many cases to resection, in view of its minimally invasive nature. This results in less post-operative trauma and risk to the patient. However, the laser probes which are currently in use suffer from a number of disadvantages which limit their usefulness and practicability. One problem encountered with prior art laser probes is the inability of the end of the probe and in particular the optical fibre, to withstand the high temperatures which can occur in use in the region of the operating tip of the probe. The tissue temperature can exceed 1000°C, and the optical fibre probes frequently fail at these temperatures. Thus destruction of the probe in use is a relatively common occurrence. This is particularly the case if the probe touches the tissue being treated, as this creates intense local temperatures. This is, as might be expected, a relatively frequent event in the confined environment of endoscopic treatment.

In order to negate this problem, probes have been designed with some form of protective, metal-coated cap surrounding the fibre tip, which is designed to hold the fibre tip away from the tissue. However, as the caps are covered with a metallic coating an opening in the cap must be left to allow the laser radiation to exit, thus exposing the optical fibre tip. It is still therefore possible to touch the optical fibre onto the tissue being treated. Furthermore, even probes with such protective caps have been found to fail at the temperatures encountered. The problem of destruction of the probe by high temperatures is exacerbated by the preferred practice of irrigating the probe and treated tissue during treatment with, for example, water or saline solution. The irrigant acts to cool the probe and the tissue surface, and to remove any debris. However, the cool irrigant can lead to a high temperature gradient across the probe, and thus cause failure by thermal shock.

Current laser probes are also limited in the effectiveness of their treatment of BPH, because of the difficulty in achieving the desired effects in the treated tissue with the probes currently available. The practical limitations of current probes also directly increase the risk of high temperatures which lead to the destruction of the probe occurring in use.

^"It has been found that laser treatment for BPH is more effective the greater the depth of the necrotic zone in the body tissue. The depth of this zone is limited by the extent to which the laser energy can penetrate and heat the surrounding tissue.

Tissue undergoes a number of processes on heating. At temperatures above 60°C coagulation of the tissue (i.e. denaturation of the protein) occurs. This leads to marked shrinkage of the collagen matrix, therefore decreasing the tissue size. During coagulation the heat generated by the laser is conducted to the underlying tissue and thus the effectively heated region of tissue is relatively deep and so accordingly is the necrotic zone. However, at a temperature of 100°C the cell water boils and ruptures the cell walls (i.e. the tissue is vaporised) . Because of the high latent heat involved, boiling and vaporisation is more or less limited to the site of absorption of the heat radiation and thus the depth of heating (i.e. the necrotic zone) is severely restricted. Once the water is dried up, the temperature in the residual tissue rapidly rises and the tissue carbonises at 300-400°C. Carbonised tissue prevents any further transmission of laser energy and thus further deep necrosis, but causes intense local temperatures (which risks destruction of the laser probe) .

Thus the preferred method of treatment is to coagulate the tissue whilst avoiding vaporisation (and particularly carbonisation) to achieve the greatest necrotic depth. However, it is in practice difficult with current laser probes to achieve extensive, deep coagulation whilst maintaining sufficiently low surface temperatures to avoid surface vaporisation and carbonisation. This difficulty is increased by the need to work in the restricted space of the prostatic capsule. Thus in practice with presently available probes, the treatment is less effective than theoretically possible, and the limitations of the - A - probes themselves result in an increased chance of probe destruction in use.

It is also desired in some instances in BPH treatment to be able following coagulation of the tissue to raise the tissue's local temperature deliberately to vaporise and char the tissue to provide immediate removal of that tissue. This is presently achieved by using one optical fibre probe to coagulate the tissue as far as possible, and then a second, different design of probe in actual contact with the tissue to vaporise and carbonise it, since the first probe is unable to withstand the temperatures generated thereby.

The Applicants have found that a fused silica or synthetic fused silica sheath when used to cover the end of the optical fibre in an endoscopic probe will withstand the highest temperatures encountered in use, even in an irrigated environment, and protect the optical fibre therefrom and is sufficiently transparent to transmit the laser radiation. Thus, according to one aspect of the present invention, there is provided an optical fibre laser delivery probe for the endoscopic delivery of laser radiation to a target comprising: an optical fibre for receiving laser radiation from a laser source and adapted to transmit the laser radiation from its distal end for delivery to the target,• wherein the distal end of the optical fibre is enclosed by a fused silica or synthetic fused silica sheath which is affixed over the distal end of the optical fibre.

The fused or synthetic fused silica sheath is able to withstand the high temperatures encountered during use of the probe without damage thereto, even in an irrigated environment. It will also shield and protect the optical fibre from the high temperatures. Thus the probe of the present invention is significantly less likely to destruct in use. Furthermore, as fused or synthetic fused silica is transparent to the laser radiation, the sheath does not have to have a gap for the laser radiation to pass through. Thus the fibre end can be completely enclosed to prevent all possibility of it coming into contact with the tissue being treated. The sheath of the present invention protects the fibre end and substantially prevents destruction of the probe in use.

The ability of the fused silica or synthetic fused silica sheath to withstand high temperatures also means that the probe of the present invention can be used in contact with the tissue being treated, without damage thereto. Thus the probe of the present invention can be used to vaporise tissue by deliberately contacting it therewith. The same probe can therefore be used to initially coagulate and then to vaporise tissue. This is a less complicated and expensive procedure than in the prior art where different probes for each different operation are required.

The optical fibre is preferably adapted to transmit the laser radiation from its distal end at an angle to the longitudinal axis of the fibre. This allows the probe to radiate a target to the side of the probe. This permits radiating the target by placing the probe adjacent the target tissue. The probe itself does not then obstruct the operator's view of the target through the endoscope. The transmission of the laser radiation out of the fibre end can be achieved by any suitable means, such as by a mirrored surface or dielectric coating on the fibre end. in a particularly preferred embodiment, the optical fibre is adapted to be forward firing, i.e. it is adapted to transmit the laser radiation at an angle of 65°-85°, most preferably 70°-80°, to the optical fibre's longitudinal axis in a direction forward of the distal end of the probe.

By having a forward-firing laser beam, the distance travelled by the laser radiation before it reaches the target is increased, therefore allowing greater beam divergence. Greater beam divergence provides a larger spot size on the target and thus lowers the power density of the laser energy at the target. A lower power density means that more energy can.be supplied to the target whilst maintaining the superficial tissue below the vaporisation threshold temperature. Thus with lower power densities it is more readily possible to provide sufficient energy to achieve a deep necrotic zone of coagulation without vaporisation or charring occurring accidentally during treatment.

The forward-firing transmission of the laser beam from the optical fibre end can again be achieved by an appropriately positioned mirrored or dielectric surface in the path of the laser beam. However, this is preferably achieved by partial or total internal reflection at the suitably polished distal end of the optical fibre. A polished fibre end is generally less expensive and complex to provide than a mirrored or dielectric surface. Furthermore, the use of total internal reflection, for example, to deflect the laser beam is more efficient than using mirrored coatings, etc., alone and thus there is less energy loss at the fibre tip.

In a particularly preferred embodiment of the invention the forward firing transmission of the laser beam is achieved by means of partial internal reflection at the suitably polished distal end of the optical fibre. Preferably the internal reflectivity of the distal end surface of the optical fibre is 80-90%, most preferably 82%. The use of partial internal reflection allows some energy to be delivered into areas other than the main exit area of the beam. This diffusion of the energy reduces the amount of thermal shock across the outer cap, thus helping to alleviate cracking and failure at higher power settings and/or in contact mode. The non-reflected radiation can, for example, gently heat the probe tip, which increases the durability of the probe tip in particular with respect to sudden contact with tissue and/or when the irrigant flow is stopped.

In the case of internal reflection, the sheath covering the fibre end is preferably arranged to maintain a sealed chamber enclosing the fibre end and containing air or any other suitable gas, such that partial or total internal reflection can occur at the glass-to-air or glass-to-gas interface at the distal end of the fibre. By polishing the fibre end to an appropriate angle, partial or total internal reflection can be achieved and the angle of the transmitted laser radiation can be selected. A mirror coating may also be provided on the polished end surface to increase the efficiency of the partial or total internal reflection. The sealed glass-to-air or glass-to-gas interface provided by the sheath of the present invention also ensures that partial or total internal reflection will still occur even in a completely irrigated environment. The optical fibre of the present invention is also preferably arranged to provide a widely divergent laser beam i.e. one having a cone angle of at least 20°. For the purposes of the present application, the cone angle of the laser beam is defined as the cone angle of the cone which encompasses 86% of the total energy of the laser beam. This widely divergent beam also helps to provide the largest possible spot size on the target being treated, thus again lowering the power density at the target.

A widely divergent beam can be achieved by the lensing effect of the curved surface of the optical fibre and/or sheath through which the beam exits the fibre and sheath (when the beam exits at an angle to the optical axis of the fibre) . The curvature and shape of the end portion of the fibre, the curved fibre surface, the fibre end surface, and/or sheath can be varied appropriately to select the divergence of the beam. The sheath covering the fibre is preferably spaced from the curved surface of the optical fibre at the point where the beam exits the fibre to create an glass-to-air or glass-to-gas interface, as this enhances the lensing effect of the optical fibre surface.

The optical fibre used preferably has the largest diameter suitable for endoscopic use in the application concerned. Fibres having diameters of 500-1200 μm are suitable. For BPH treatment, for example, a fibre of 1000 μm diameter is preferably used. A large fibre provides a large initial spot and thus facilitates a larger spot size and lower power density on the target. A large fibre is also inherently more rigid, enabling more control and accurate positioning of the fibre whilst in the body lumen.

The sheath of the present invention is preferably of sufficient diameter to space the tissue being treated from the optical fibre as far as is practicable. It should preferably achieve a stand-off or spacing between the target and fibre, whilst still passing through the working endoscope. A sheath outer diameter of at least 1.5 mm is preferred. In BPH applications an outer diameter of at least 2 mm, preferably 2-2.8 mm, is most suitable. This spacing of the tissue from the fibre by the sheath lengthens the distance the laser beam must travel from the fibre to its target and thus leads to an increased spot size and lower power density on the target.

The sheath of the present invention preferably has a relatively rounded, blunt end so as to prevent damage to any tissue it may contact. The sheath is preferably arranged such that the laser beam exiting the fibre passes through a sheath wall of uniform thickness. This can be achieved by spacing the sheath a suitable distance e.g. 2-3 mm, from the fibre end, such that the curved end surface of the sheath has ended by the fibre exit point.

The sheath also acts as a heat sink in use, and thus is preferably sufficiently large to do this effectively. In the case of BPH, it is preferably at least 12 mm in length in order to act as a suitable heat sink.

The above features of the present invention which result in a larger spot size can in combination be used to provide a probe which is able to cause coagulation with a significantly reduced risk of vaporisation and carbonisation occurring. This arrangement is believed to be applicable to probes which do not necessarily also have the fused silica or synthetic fused silica sheath of the present invention.

Thus according to a second aspect of the present invention, there is provided an optical fibre laser delivery probe for the endoscopic delivery of laser radiation to a target, comprising: an optical fibre for receiving laser radiation from a laser source and adapted to transmit the laser radiation from its distal end for delivery to the target; wherein the optical fibre is adapted to transmit the laser radiation at an angle of 65°-85° to the longitudinal axis of the optical fibre in a direction forward of the fibre distal end and is adapted to provide a laser beam having a cone angle as defined herein of greater than 20°, the probe further comprising a sheath transparent to the laser radiation enclosing the distal end of the optical fibre and having an outer diameter of at least 1.5 mm.

The probe according to the second aspect of the present invention can include any or all of the preferred features of the invention. The sheath for the second aspect does not have to be of fused silica or synthetic fused silica, although it is preferably made from either of those materials. It could comprise for example borosilicate glass (e.g. Pyrex (RT ) ) , or any other suitably transparent substance which can withstand temperatures up to 1000°C.

The probe of the present invention including a synthetic fused silica or a fused silica sheath is suitable for use in contact with the tissue being treated, i.e. it can cause high local temperatures in order to vaporise the tissue without damage to the probe itself. Thus the probe can be used in contact mode using high power settings to achieve charring and vaporisation, thus allowing debulking of obstructive tissue. It is therefore possible to use the probe of the present invention initially to coagulate tissue and then to place it in contact with the tissue to vaporise it.

According to a third aspect of the present invention therefore, there is provided a method of treating body tissue using the optical fibre delivery probe of the present invention, including a fused silica or synthetic fused silica sheath, comprising: delivering laser radiation to the tissue target using the probe without deliberately contacting the tissue to coagulate the tissue; and then moving said probe into contact with the tissue and increasing the laser power to the probe to vaporise the tissue. A preferred embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of the laser delivery probe of the present invention,- Figure 2 is a cross section of the laser delivery probe of the present invention; and

Figure 3 is a cross section along ZZ of the probe shown in Figure 2.

In Figure 1, the laser treatment assembly 1 includes a length of flexible of optical fibre 2 which can be connected via a connector 3 at one end to a laser source 4. The connector 3 can be any standard connector, such as an S A 905 connector. The laser 4 used with the probe can suitably for BPH applications be one generating energy within the infrared wavelength range of 750 to 1500 nanometers which has a low absorption coefficient in water. An Nd-Yag laser with an output of 1064 nanometers is preferred. For other applications, lasers having wavelengths within the transmission range of silica optical fibres, i.e. approximately 300-2400 nm, can be used.

A handle 5 is fitted on to the fibre 2 at an appropriate point thereon. A suitable handle is a movable lockable standard commercially available Torey Borst handle. The distal end of the fibre 2 comprises the probe 6 which is to be inserted into the body lumen during treatment. Figure 2 shows a cross section of the probe 6. The optical fibre 2 includes a round core 8 and a surrounding polymer cladding 9. The fibre is preferably 1000 μm in diameter for BPH treatment. The fibre core 8 and the cladding 9 have centres of curvature at the longitudinal axis,10 of the fibre. The cladding 9 is stripped back from the distal end of the fibre for a distance not less than 4 mm.

A cylindrical protective sheath 11 of fused silica or synthetic fused silica is placed over the exposed end of the fibre and forms an airtight attachment to the cladding 9 (which also spaces the sheath from the curved walls of the fibre core 8) . The sheath 11 encloses a trapped volume of air 12. This trapped volume of air ensures a glass to air interface at the end 13 of fibre core 8, and around the curved surface of the exposed core of the fibre 8 (due to the walls of the sheath 11 being spaced apart from the core 8 by the cladding 9) . The sheath 11 is held in position by a high temperature heat shrink outer cover 16. The sheath 11 will often be in contact with the tissue during use, which creates very high local temperature. It should therefore be at least 12 mm in length, most preferably be 14 to 16 mm in length, in order to provide sufficient heat sink capability. The heat shrink outer cover 16 is approximately 50 mm in length and terminates at the same location as the cladding 9 at its distal end. A coloured indicator line 17 may be positioned between the sheath 16 and the cladding 9 in line focus with the exiting laser beam 14 on the opposite side of the probe to the exit side of the laser beam. This line 17 acts as an alignment mark for the surgeon to show the direction of .the laser beam in use.

The sheath 11 is positioned at least 2 mm from the tip of the polished fibre core 8, such that the laser beam does not exit the sheath through any part of its curved end. This ensures that the laser beam exits via a uniform thickness wall of the sheath. This reduces thermal shock across the sheath wall, and the risk of distortion being introduced into the laser beam by any variations in the sheath wall.

The probe should be a relatively large diameter to achieve a relatively large stand-off (i.e. spacing) between the tissue and fibre, but small enough to pass through the working endoscope. The sheath 11, therefore has an outer diameter of 2.4 mm, although this can vary from 2.0 to 2.8 mm in BPH applications in order to provide a stand-off or spacing between the tissue and optical fibre.

The end surface 13 of the fibre reflects the laser beam travelling along the optical fibre out of the end of the probe as a divergent beam 14 by internal reflection. The internal reflection results from the refractive index difference between the glass core 8 and the air 12 trapped by the sheath 11. The surface 13 is formed at an angle θ_: to the fibre axis 10 which exceeds the critical angle for total internal reflection for the majority, but not all, of the optical rays travelling down the fibre. The surface 13 directs the laser beam 14 out of the fibre with an axis 15 that is not orthogonal to, but is directed beyond the distal end of the probe at an angle to the fibre axis 10, i.e. the probe is forward-firing.

The optimum angle θ_: for a suitable forward firing angle which will also achieve sufficient radiation transmission from the optical fibre depends upon the refractive index of the core 8, the wavelength of the radiation, and the numerical aperture of the optical fibre. In general the angle θ₂ will be between 35°-45° and this will provide an exiting laser beam 14 with an axis 15 at an angle θ₂ of 65-85° to the fibre axis. For radiation within the infrared range, a refractive index of 1.47 for a typical fibre core and a numerical aperture of 0.4, an angle Q₁ which reflects a substantial amount of the laser radiation in the fibre will be about 40°. This angle would result in the exiting beam 14 having a centre line 15 making an angle θ₂ of about 75° with the optical fibre axis.

The preferred exit angles for the exiting laser beam 14 are for it to be forward-firing with the central beam axis 15 at an angle θ₂ of 65° to 85°, preferably

75°, to the core axis 10. For example, for a numerical aperture of 0.37 for the 1000 μm core 8, the angle θ-_ should be 40° (a 50° angle of polish) to achieve a central beam axis angle θ₂ of 75°. As well as being forward-firing, the probe of the present invention is adapted to deliver a widely divergent beam 14, i.e. one in which 86% of the laser beam energy is encompassed by a cone having a cone angle of at least 20°. The cone angle can suitably be from 30°-50°. This is illustrated in Figure 3. The divergent beam profile is controlled primarily by the interface between the air 12 and the curved surface of the optical fibre core 8 through which the laser radiation exits after reflection from the surface 13. This is because the outer surface of the sheath 11 will in use typically be in contact with water or some other irrigant fluid and this will therefore have little effect on the beam profile. The curved surface of the fibre core 8 acts as a cylindrical lens due to the glass-to-air interface and thus creates a widely divergent exit beam.

In use, the probe 6 is inserted with an endoscope into the body lumen, such as the prostatic urethra, to position the end of the probe 6 suitably adjacent to the tissue to be treated. Laser power can then be directed using the probe onto the tissue. The probe of the present invention allows a relatively large amount of laser energy to be delivered with a large spot size, thus providing a lower power density. In this manner, the probe of the present invention can achieve coagulation of a large area of tissue, without vaporisation or carbonisation occurring. Laser energy is typically delivered at power of 40W-60 for between 30-90 seconds. Laser radiation application is repeated until the desired area of tissue has been fully coagulated. During use the outer surface of the probe is typically irrigated by a cooling fluid such as water or saline solution. The probe of the present invention can also be used to vaporise and carbonise tissue, by increasing the laser power and moving the probe into direct contact with the tissue, thus creating intense local heating. This can be performed after coagulation, to immediately remove some of the obstructing tissue.

Claims

1. An optical fibre laser delivery probe for the endoscopic delivery of laser radiation to a target, comprising: an optical fibre for receiving laser radiation from a laser source and adapted to transmit the laser radiation from its distal end for delivery to the target; wherein the distal end of the optical fibre is enclosed by a fused silica or synthetic fused silica sheath which is affixed over the distal end of the optical fibre.

2. The probe of claim 1, wherein the optical fibre is adapted to transmit the laser radiation from its distal end at an angle to the longitudinal axis of the fibre.

3. The probe of claim 2, wherein the optical fibre is adapted to transmit the laser radiation at an angle of 65°-85° to the optical fibre's longitudinal axis in a direction forward of the distal end of the probe.

4. The probe of any preceding claim, wherein the sheath is of a diameter which spaces the tissue being treated from the optical fibre as far as is practicable, whilst still passing through the endoscope in use.

5. The probe of claim 5, wherein the sheath has an outer diameter of at least 1.5 mm.

6. The probe of any preceding claim, wherein the optical fibre is arranged to provide a laser beam having a cone angle of at least 20°.

7. An optical fibre laser delivery probe for the endoscopic delivery of laser radiation to a target, comprising: an optical fibre for receiving laser radiation from a laser source and adapted to transmit the laser radiation from its distal end for delivery to the target; wherein the optical fibre is adapted to transmit the laser radiation at an angle of 65°-85° to the longitudinal axis of the optical fibre in a direction forward of the fibre distal end and is adapted to provide a laser beam having a cone angle of at least 20°, the probe further comprising a sheath transparent to the laser radiation enclosing the distal end of the optical fibre and having an outer diameter of at least 1.5 mm.

8. The probe of claim 6 or 7, wherein the curvature and shape of the end portion of the fibre, the curved fibre surface, the fibre end surface, and/or sheath are adapted to control the divergence of the transmitted beam laser.

9. The probe of claim 8, wherein the sheath covering the fibre end is spaced from the curved surface of the optical fibre at the point where the beam exits the fibre to create a glass-to-air or glass-to-gas interface at said curved surface at the point where the beam exits the fibre.

10. The probe of any one of claims 2 to 9, wherein the probe is adapted to transmit laser radiation from its distal end by means of total internal reflection at the distal end of the optical fibre.

11. The probe of any one of claims 2 to 9, wherein the probe is adapted to transmit laser radiation from its distal end by means of partial internal reflection at the distal end of the optical fibre.

12. The probe of claim 11, wherein the internal reflectivity of the distal end surface of the optical fibre is 80-90%.

13. The probe of claim 10, 11 or 12, wherein the sheath covering the fibre end is arranged to maintain a sealed chamber enclosing the fibre end and containing air or any other suitable gas, such that partial or total internal reflection occurs at the glass-to-air or glass- to-gas interface at the distal end surface of the fibre.

14. The probe of claim 10, 11, 12 or 13, wherein a mirror coating is provided on the distal end surface of the fibre to increase the efficiency of the partial or total internal reflection.

15. The probe of any preceding claim, wherein the optical fibre has a diameter of around 1000 μm.

16. The probe of any preceding claim, wherein the sheath is arranged such that the laser beam exiting the fibre passes through a sheath wall of uniform thickness.

17. The probe of claim 16, wherein the sheath is arranged such that the curved end surface of the sheath has ended by the exit point of the laser radiation from the fibre.

18. The probe of any preceding claim, wherein the sheath is at least 12 mm in length.

19. A method of treating body tissue using the optical fibre delivery probe of any preceding claim, which includes a fused silica or synthetic fused silica sheath, comprising: delivering laser radiation to the tissue target using the probe without deliberately contacting the tissue to coagulate the tissue,- and then moving said probe into contact with the tissue and increasing the laser power to the probe to vaporise the tissue.