Laser emission modulation for soft tissue treatment.

Abstract

The systems and methods can be used to treat soft tissue. The systems can include a laser configured to emit pulsed laser energy that can be modulated to maximize ablation efficiency during cutting, dissection, or ablation of soft tissue while simultaneously optimizing hemostasis and reducing concomitant side effects such as tissue charring and scar formation. According to certain aspects, the coagulation laser mode power is adjusted primarily for hemostasis without dehydration, and the ablative laser mode power is optimized to provide efficient ablation.

Description

[Technical Field]

[0001] (Related Applications) This application claims priority to U.S. Provisional Patent Application No. 63 / 440,149, entitled "LASER EMISSION MODULATION FOR TREATMENT OF SOFT TISSUE," filed January 20, 2023, the entire contents of which are incorporated herein by reference.

[0002] FIELD OF THE INVENTION The technical field relates generally to laser treatment of soft tissue, and more particularly to modulated pulsed energy in the treatment of soft tissue. [Background technology]

[0003] In addition to being used to treat hard tissue (e.g., kidney stones, bladder stones), laser energy is also widely used to treat various soft tissue conditions (e.g., BPH, bladder tumors, etc.) through tissue ablation, cutting, vaporization, and coagulation.

[0004] Until recently, relevant laser sources (e.g., Ho:YAG lasers) were extremely limited in their ability to modulate laser emission, i.e., pulse shape, energy, and pulse peak power, and these types of lasers were limited in pulse frequency (pulse repetition rate). However, the emergence of new diode-pumped laser sources (e.g., thulium (Tm) fiber lasers, Tm:YAG lasers) offers the possibility to modulate lasers over a wider range of power values. There is a need to optimize soft tissue treatment through modulation of laser emission. Summary of the Invention

[0005] Aspects and embodiments are directed to methods and systems for modulating laser emission for treating soft tissue using pulsed laser energy.

[0006] According to an exemplary embodiment, a laser system for treating soft tissue is provided, the laser system comprising: a laser configured to emit pulsed laser energy having a wavelength in the range of 1.85 to 2.2 microns (μm); and a controller configured to control the laser such that each pulse of the emitted pulsed energy includes two sub-pulses, one of the two sub-pulses, an ablative sub-pulse, configured to ablate and incise the target soft tissue, and the other of the two sub-pulses, a hemostatic sub-pulse, configured to coagulate the target soft tissue.

[0007] According to another exemplary embodiment, a method for treating soft tissue is provided, the method comprising: generating pulsed laser energy having a wavelength in a range of 1.85 to 2.2 microns (μm); emitting each pulse of the emitted pulsed energy as two sub-pulses, one of the two sub-pulses, an ablative sub-pulse, configured to ablate and incise the target soft tissue, and the other of the two sub-pulses, a hemostatic sub-pulse, configured to coagulate the target soft tissue; and directing the pulsed laser energy to the target soft tissue. In one example, the target soft tissue is hyperplastic prostate tissue.

[0008] In one example, the ablative sub-pulse is followed by a hemostatic sub-pulse. In a further example, the ablative sub-pulse and the hemostatic sub-pulse are separated by a sub-pulse interval, the sub-pulse interval being in the range of 0 to 5 milliseconds (ms).

[0009] In one example, the hemostatic sub-pulse is followed by an ablative sub-pulse. In a further example, the hemostatic sub-pulse and the ablative sub-pulse are separated by a sub-pulse interval, the sub-pulse interval being in the range of 0 to 100 ms.

[0010] In one example, the ablative sub-pulses have a peak power in the range of 400 to 20,000 watts (W). In another example, the ablative sub-pulses have a peak power in the range of 600 to 1,500 W. In one example, the energy of the ablative sub-pulses is in the range of 1 to 10 joules (J). In one example, the duration of the ablative sub-pulses is in the range of 0.05 to 10 milliseconds (ms). In a further example, the duration of the ablative sub-pulses is in the range of 1 to 10 ms.

[0011] In one example, the target soft tissue has a tissue coagulation threshold and a tissue ablation threshold, and the hemostatic sub-pulses have a peak power and energy greater than the tissue coagulation threshold and less than the tissue ablation threshold.

[0012] In one example, the target soft tissue has a tissue coagulation threshold and a tissue ablation threshold, and the hemostatic sub-pulses have peak power and energy that meet or exceed the tissue coagulation threshold and meet or less than the tissue ablation threshold multiplied by a factor of 1.5.

[0013] In one example, the hemostatic sub-pulse has a peak power in the range of 10 to 250 W. In a further example, the hemostatic sub-pulse has a peak power in the range of 50 to 150 W. In one example, the energy of the hemostatic sub-pulse is in the range of 0.5 to 10 J. In one example, the duration of the hemostatic sub-pulse is in the range of 2 to 1000 ms. In a further example, the duration of the hemostatic sub-pulse configured to cause coagulation is in the range of 10 to 100 ms.

[0014] In one example, the ablative sub-pulses are configured to generate laser-induced gas bubbles in water surrounding the target soft tissue at a pressure sufficient to induce mechanical tissue dissection in the target soft tissue.

[0015] In one example, the laser is a thulium fiber laser, a thulium solid state laser, or a holmium solid state laser.

[0016] According to another exemplary embodiment, there is provided a laser system for treating soft tissue, comprising: a laser configured to emit pulsed laser energy having a wavelength in a range of 1.85 to 2.2 microns (μm); and a controller configured to control the laser such that the pulsed laser energy is emitted as a sequence of pulse groups, each pulse group including two sub-pulses, a first sub-pulse having a peak power in a range of 10 to 250 watts (W) and a duration of 0.5 to 100 milliseconds (ms), and a second sub-pulse having a peak power in a range of 400 to 20,000 W and a duration of 0.01 to 5 ms, the pulse groups separated in time by a group interval in a range of 3 to 250 ms.

[0017] According to another exemplary embodiment, a method for treating target soft tissue by controlling laser emission to prevent carbonization of the soft tissue is provided, the method comprising: generating pulsed laser energy having a wavelength in a range of 1.85 to 2.2 microns (μm); emitting the pulsed laser energy as a sequence of pulse groups, each pulse group including two sub-pulses, a first sub-pulse having a peak power in a range of 10 to 250 watts (W) and a duration of 0.5 to 100 milliseconds (ms), and a second sub-pulse having a peak power in a range of 400 to 20,000 W and a duration of 0.01 to 5 ms, the pulse groups being separated in time by a group interval in a range of 3 to 250 ms; and directing the pulsed laser energy to the target soft tissue.

[0018] In one example, the group interval is in the range of 3 to 8 ms.

[0019] In one example, the sub-pulses of the group of pulses are separated in time by a sub-pulse interval of a duration to prevent fluid penetration into the region of the target soft tissue exposed to the pulsed laser energy. In another example, the sub-pulse interval is in the range of 0-30 ms. In another example, the sub-pulse interval is in the range of 0-10 ms. In another example, the sub-pulse interval is in the range of 0-3 ms.

[0020] In another example, the peak power of the second sub-pulse is in the range of 600 to 1500 W.

[0021] In one example, the peak power of the first sub-pulse is in the range of 50 to 250 W. In a further example, the peak power of the first sub-pulse is in the range of 100 to 250 W.

[0022] In one example, the second sub-pulse is configured to ablate the char layer to prevent charring of the target soft tissue being treated by the pulsed laser energy. In another example, the second sub-pulse is configured to prevent charring by ablating any accumulating charred tissue layer on the target soft tissue.

[0023] In one example, the laser is a thulium fiber laser, a thulium solid state laser, or a holmium solid state laser.

[0024] According to another exemplary embodiment, there is provided a laser system for treating soft tissue, the laser system including: a laser configured to emit pulsed laser energy having a wavelength in the range of 1.85 to 2.2 microns (μm); and a controller configured to control the laser such that the pulsed laser energy is emitted as a sequence of pulses, wherein each Nth pulse in the sequence has a peak power in the range of 400 to 20,000 W and has a duration of 0.05 to 5 ms, and other pulses in the sequence have peak power in the range of 10 to 250 W and have durations of 0.5 to 100 milliseconds (ms).

[0025] According to another exemplary embodiment, there is provided a method for treating soft tissue, the method including generating pulsed laser energy having a wavelength in a range of 1.85 to 2.2 microns (μm); emitting the pulsed laser energy as a sequence of pulses, wherein each Nth pulse in the sequence has a peak power in a range of 400 to 20,000 W and has a duration of 0.05 to 5 ms, and other pulses in the sequence have peak power in a range of 10 to 250 W and have durations of 0.5 to 100 milliseconds (ms); and directing the pulsed laser energy to a target soft tissue.

[0026] In one example, N is 2-10.

[0027] In one example, the Nth pulse is configured to ablate the char layer to prevent charring of the target soft tissue being treated by the pulsed laser energy. In another example, the Nth pulse is configured to prevent charring by ablating any accumulating charred tissue layer on the target soft tissue.

[0028] In one example, the Nth pulse has a peak power in the range of 600 to 1500 W.

[0029] In one example, the energy of the Nth pulse is in the range of 0.5 to 5 joules (J).

[0030] In one example, the other pulses in the sequence have durations between 2 and 100 ms.

[0031] In one example, the peak power of the other pulses in the sequence is in the range of 50-250W.

[0032] In one example, the laser is a thulium fiber laser, a thulium solid state laser, or a holmium solid state laser.

[0033] According to another exemplary embodiment, there is provided a laser system for treating soft tissue, comprising: a laser configured to emit laser energy having a wavelength in the range of 1.85 to 2.2 microns (μm); and a controller configured to control the laser such that the power of the laser energy is emitted as continuous-wave (CW) laser power with modulation to provide overlapping pulses of laser energy.

[0034] According to another exemplary embodiment, there is provided a method for treating soft tissue, the method including generating laser energy having a wavelength in a range of 1.85 to 2.2 microns (μm); emitting the laser energy such that the power of the laser energy is emitted as continuous wave (CW) laser power with modulation providing overlapping pulses of laser energy; and directing the laser energy to a target soft tissue.

[0035] In one example, the CW laser power is in the range of 10 to 250 watts (W), the overlapped pulses each have a peak power in the range of 500 to 20,000 W, and the average power of the overlapped pulses is in the range of 1 to 30% of the CW laser power. In another example, the peak power of each overlapped pulse is in the range of 600 to 1,500 W. In another example, the energy of each overlapped pulse is in the range of 0.5 to 5 joules (J). In another example, the duration of each overlapped pulse is in the range of 0.05 to 5 milliseconds (ms). In another example, the CW laser power is in the range of 50 to 250 W.

[0036] In one example, each pulse of overlapping laser energy is configured to ablate the char layer to prevent charring of the target soft tissue being treated by the laser energy. In another example, each pulse of overlapping laser energy is configured to prevent charring by ablating any accumulating charred tissue layer on the target soft tissue.

[0037] In one example, the overlapping pulses are separated in time by a pulse interval in the range of 5 to 200 ms.

[0038] In one example, the overlapping pulses have a repetition rate in the range of 5 to 200 Hertz (Hz). In a further example, the overlapping pulses have a repetition rate in the range of 5 to 50 Hz.

[0039] In one example, the laser is a thulium fiber laser, a thulium solid state laser, or a holmium solid state laser.

[0040] Still other aspects, embodiments, and advantages of these exemplary aspects and embodiments are discussed in detail below. Furthermore, it should be understood that the foregoing information and the following detailed description are merely illustrative examples of various aspects and embodiments and are intended to provide an overview or framework for understanding the nature and characteristics of the claimed aspects and embodiments. The embodiments disclosed herein may be combined with other embodiments, and references to "one embodiment," "one example," "some embodiments," "some examples," "an alternative embodiment," "various embodiments," "one embodiment," "at least one embodiment," "this embodiment and other embodiments," "a particular embodiment," etc. are not necessarily mutually exclusive and are intended to indicate that a particular described feature, structure, or characteristic may be included in at least one embodiment. Appearances of such terms herein do not necessarily all refer to the same embodiment. [Brief explanation of the drawings]

[0041] [Figure 1] 1 is a chart illustrating an example of a pulse sequence optimized for soft tissue cutting, in accordance with one or more embodiments of the present invention. [Figure 2] 10 is a chart illustrating another example of a pulse sequence optimized for soft tissue cutting in accordance with one or more embodiments of the present invention. [Figure 3A]10 is a chart illustrating yet another example of a pulse sequence optimized for soft tissue cutting in accordance with one or more aspects of the present invention. [Figure 3B] 10 is a chart illustrating yet another example of a pulse sequence optimized for soft tissue cutting in accordance with one or more aspects of the present invention. [Figure 4] 10 is a chart illustrating yet another example of a pulse sequence optimized for soft tissue cutting in accordance with one or more aspects of the present invention. [Figure 5] 10 is a chart illustrating yet another example of a pulse sequence optimized for soft tissue cutting in accordance with one or more aspects of the present invention. [Figure 6] 1 is a block diagram of a laser system for treating soft tissue in accordance with one or more embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0042] Various aspects of at least one embodiment are discussed below with reference to the accompanying drawings, which are not intended to be drawn to scale. The drawings are included to provide illustration and a further understanding of the various aspects and embodiments, and are incorporated into and constitute a part of this specification, but are not intended as a definition of the limitations of any particular embodiment. The drawings, together with the remainder of the specification, serve to explain the principles and operation of the aspects and embodiments described and claimed herein. In the drawings, each identical or nearly identical component illustrated in the various drawings is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure.

[0043] According to one or more embodiments, specific systems and methods for modulating laser emission are discussed below for the specific purpose of treating soft tissue. As used herein, the term "soft tissue" refers to tissues that connect, support, or surround other structures and organs of the body (human or animal), as well as soft tissue mucosa, tumors, which may be located in anatomical locations in the body (e.g., bladder, prostate, kidney). One or more aspects of the present disclosure can be used with diode-pumped Tm- and holmium (Ho)-doped crystal or fiber lasers having output wavelengths in the 1.85-2.2 μm range. According to certain embodiments, the methods and systems disclosed herein can be implemented or otherwise provided by thulium fiber lasers, thulium solid-state lasers, or holmium solid-state lasers.

[0044] As mentioned above, laser energy can be used for the treatment of various urological conditions, ranging from lithotripsy to soft tissue surgery (e.g., benign prostate hyperplasia (BPH) removal as ablative enucleation or vaporization). The delivery of laser energy can be optimized through modulation of laser output, as shown in International Application No. PCT / US2019 / 042491, published as WO 2020 / 033121, owned by the applicant and incorporated herein by reference in its entirety.

[0045] According to one or more embodiments, systems and methods for optimizing laser output are disclosed herein for the purposes of: Maximizing ablation efficiency during soft tissue cutting / incision / resection, Optimizing hemostasis, Improving certain specific surgical procedures, such as enucleation of the prostate using laser pulses for separation of hyperplastic tissue from the prostate capsule; and · Reducing collateral side effects such as tissue charring, scarring, and loss of viable material for biopsy.

[0046] Furthermore, according to certain embodiments, another object is to provide a laser system comprising a laser source and a control unit providing means for modulating the output of the laser source according to the pulse modulation mode described herein.

[0047] Yet another object, according to some embodiments, is to provide specific optimal pulse shapes for diode-pumped laser systems, such as Thulium Fiber Laser (TFL) and Tm:YAG-based (thulium solid-state laser) laser systems, as well as Holmium solid-state lasers, that may be used in one or more embodiments of the present disclosure.

[0048] Although the primary disclosure of the present invention is directed to the application of laser energy in urology, it is understood that application of these teachings to other medical fields is also within the scope of this disclosure.

[0049] Maximize soft tissue cutting / dissection / excision / nucleation efficiency, optimize hemostasis, and reduce charring. Successful cutting / dissection / resection / nucleation of soft tissue using directed energy (e.g., laser energy) requires the fulfillment of three conditions: [1] efficient ablation that provides a sufficiently deep cut per unit of energy consumed; [2] minimal (ideally, no) charred tissue (charring) on ​​the surface of the laser cut; and [3] creation of an optimally deep and uniform coagulation margin to ensure good hemostasis (i.e., prevention and reduction of bleeding, cessation of blood flow).

[0050] Conventional approaches to soft tissue treatment show that pulsed, low peak power (or continuous wave (CW)) treatment results in sufficient cutting depth and good hemostasis, but creates unacceptable levels of charring. Conventional approaches to soft tissue treatment using pulsed, high peak power minimize charring, but reduce ablation efficiency and often result in non-uniform hemostasis that is insufficient to alleviate bleeding. Therefore, according to at least one embodiment, the goal of pulse shape optimization is to combine the benefits of the two modes. In certain embodiments, the coagulation laser mode power is adjusted primarily for hemostasis without dehydration, and the ablative laser mode power is optimized to provide efficient ablation.

[0051] The target soft tissue treated by certain methods and systems disclosed herein is associated with benign prostatic hyperplasia (BPH). According to certain embodiments, the target soft tissue treated by the methods and systems disclosed herein is hyperplastic prostate tissue. The BPH enucleation process involves removing a prostate adenoma within the prostate capsule. Conventional Ho:YAG lasers configured to perform HoLEP (Ho Laser Enucleation Procedure) generate high peak power (up to 20 kilowatts (kW)) in short pulses due to a thermomechanical mechanism of separation. This process involves the separation of adenoma tissue from the prostate capsule. This separation can be described as a precise tissue cut or incision at the connection plane between the capsule and the adenoma. This mechanism combines the creation of mechanical forces in the tissue through laser-induced vapor bubbles, which create high mechanical pressure in the tissue, and simultaneous laser ablation and coagulation via laser pulses propagating through these bubbles, which have a primarily thermal effect. Disadvantages of this treatment using Ho:YAG include significant incidence of uncontrolled hemostasis and bleeding. In contrast, thulium fiber lasers configured to perform TFLEP (Thulium Fiber Laser Enucleation Procedure) provide excellent hemostasis but do not provide good separation of the adenoma tissue within the prostate capsule. Furthermore, tissue carbonization impairs the visibility of the separation surface.

[0052] One or more embodiments disclosed herein overcome the problems presented by diode-pumped TFL or Tm:YAG lasers through the combination of two sub-pulses: an ablative sub-pulse with a high peak power followed by a coagulation (hemostatic) sub-pulse with a lower peak power. According to at least one embodiment, one of the two sub-pulses (referred to as the ablative or ablative sub-pulse) is configured to ablate and incise the target soft tissue, and the other of the two sub-pulses (referred to as the hemostatic sub-pulse) is configured to coagulate the target soft tissue.

[0053] One non-limiting example of such a sub-pulse combination is shown in Figure 1. In this embodiment, an ablative sub-pulse is followed by a hemostatic sub-pulse (or the ablative sub-pulse is directed to the target soft tissue before the hemostatic sub-pulse). In at least one embodiment, the ablative sub-pulse and the hemostatic sub-pulse are separated by a sub-pulse interval, which is in the range of 0 to 5 milliseconds (ms). In the non-limiting example shown in Figure 1, the ablative sub-pulse and the hemostatic sub-pulse have a sub-pulse interval of 0, meaning that they are linked.

[0054] In alternative embodiments, the hemostatic sub-pulse can precede the ablative sub-pulse (i.e., the hemostatic sub-pulse is followed by the ablative sub-pulse), a non-limiting example of which is shown in Figure 2. In at least one embodiment, the hemostatic sub-pulse and the ablative sub-pulse are separated by a sub-pulse interval, which is in the range of 0 to 100 ms. In the non-limiting example shown in Figure 2, the hemostatic sub-pulse and the ablative sub-pulse have a sub-pulse interval of 0, meaning they are linked.

[0055] In both scenarios provided above, the following laser operating parameters may be applied, which were arrived at by applicant after conducting pre-clinical and clinical studies: The peak power of the ablative sub-pulses may be in the range of 400 to 20,000 W, preferably in the range of 600 to 1,500 W; The energy of the ablative sub-pulse can be in the range of 1-10 J; The pulse duration of the ablative sub-pulses may be in the range of 0.05 to 10 ms, preferably in the range of 1 to 10 ms; The peak power of the hemostatic subpulse may be in the range of 10 to 250 W, preferably in the range of 50 to 150 W; The energy of the hemostatic subpulse can be in the range of 0.5-10 J. The pulse duration of the hemostatic sub-pulse may be in the range of 2-1000 ms, preferably in the range of 10-100 ms.

[0056] According to at least one embodiment and various aspects of the present disclosure, the target soft tissue (being treated with pulsed laser energy) has a tissue coagulation threshold and a tissue ablation threshold, and the hemostatic sub-pulses have a peak power and energy greater than the tissue coagulation threshold and less than the tissue ablation threshold. In another embodiment, the hemostatic sub-pulses have a peak power and energy that meet or exceed the tissue coagulation threshold but meet or less than the tissue ablation threshold multiplied by a factor of 1.5. For example, for a given set of surgical conditions (e.g., fiber diameter, cutting speed, gap between tissue and fiber), if the tissue coagulation threshold is 50 W and the tissue ablation threshold is 100 W, the peak power of the hemostatic sub-pulses can be in the range of 50-150 W.

[0057] Experiments conducted by applicants have shown that the thermomechanical effects generated by pulses such as those described above can be similar to or even better than those of conventional TFL or Ho:YAG lasers due to the superior thermal ablation effect of Tm:YAG laser-induced vaporized bubbles. The mechanical action of these laser-induced bubbles can be optimized by utilizing the effect of laser-induced bubble oscillations occurring between the fiber tip and the tissue, a phenomenon discovered by applicants. These oscillations generate tissue separation using multiple oscillations of positive and negative pressure, as opposed to a single positive and negative pressure cycle (as in Ho:YAG procedures). This phenomenon can be observed for both types of sub-pulses, but the positive and negative mechanical pressure amplitudes are much higher for the ablative sub-pulses, which can be used to better separate the adenoma tissue from the capsule. According to at least one embodiment, the ablative sub-pulses are configured to generate laser-induced bubbles in water surrounding the target soft tissue with sufficient pressure to induce mechanical tissue dissection in the target soft tissue. In another embodiment, the ablative sub-pulses are further configured to apply a positive pressure and at least two negative pressures to the target soft tissue.

[0058] According to other embodiments, the concept of a "cleaning pulse" can be implemented with the goal of reducing or otherwise preventing carbon buildup (charred tissue layer, or "charring") during tissue vaporization, cutting, dissection, ablation, and enucleation. The rationale is that high peak power cleaning pulses periodically ablate any accumulating carbon. In at least one embodiment, this can be achieved through the addition of a high peak power post-cleaning sub-pulse to each "normal" pulse. For example, in one embodiment, the second sub-pulse (described in more detail below and also referred to herein as a cleaning pulse) is configured to ablate the char layer to prevent charring of the target soft tissue being treated by the pulsed laser energy, and in further embodiments, the second sub-pulse is configured to prevent charring by ablating any accumulating charred tissue layer on the target soft tissue. A charred tissue layer or charring layer forms on the surface of a laser crater or cut during a tissue ablation procedure. After tissue ablation and water evaporation (e.g., tissue temperatures of 100–300°C), the dry tissue continues to heat. When temperatures reach approximately 150°C, a thermochemical reaction (pyrolysis) occurs, causing tissue proteins to release carbon atoms. This process is completed at temperatures ranging from 250–300°C and involves the formation of a charred layer of tissue with a typical thickness of 50–500 microns (µm) on the laser cut surface. The charred layer impacts the surgeon's ability to recognize the tissue type and condition of the treatment area, slowing the healing process. The thickness of such a layer increases with lower power and with increasing pulse width or dwell time on the tissue. However, lower power and longer pulse width result in higher ablation efficiency and better coagulation margins. Treatment with shorter pulses and higher peak power results in lower hemostatic effects, but also results in better ablation of a thin layer of charred dry tissue due to a better match of the layer's thermal relaxation time and the higher absorption coefficient of dry, charred tissue relative to non-carbonized dry tissue.

[0059] According to certain embodiments, the controller is configured to control the laser so that pulsed laser energy is emitted as a sequence of pulse groups, each pulse group including two sub-pulses. Two non-limiting examples of such a configuration are shown in FIGS. 3A and 3B. According to certain embodiments, the peak power of the post-cleaning sub-pulse (second sub-pulse) can be in the range of 400-20,000 W, preferably in the range of 600-1,500 W, and have a duration of 0.01-5 ms. In certain embodiments, the peak power of the normal portion of the pulse (first sub-pulse) is in the range of 10-250 W, preferably in the range of 50-250 W, or in the range of 100-250 W, and the normal portion of the pulse has a duration of 0.5-100 ms. In some embodiments, the pulse groups are separated in time by a group interval (shown in FIGS. 3A and 3B) in the range of 3-250 ms, which corresponds to a repetition rate of the pulse groups in the range of 3-300 Hz. In other embodiments, the group interval is in the range of 3-8 ms, corresponding to a repetition rate of 10-50 Hz.

[0060] Water can penetrate into the laser crater between pulses, and additional laser energy is required to vaporize this water. This particular phenomenon is the reason for a significant decrease in tissue ablation efficiency and a reduced depth of ablation. To prevent this from happening, according to at least one embodiment, the subpulses of a pulse group are separated in time by a subpulse interval of a certain duration to prevent fluid penetration into the area of ​​the target soft tissue exposed to the pulsed laser energy. In other words, the subpulse interval should be shorter than the time it takes for water (fluid) to fill the laser crater (formed on the soft tissue by the laser energy) between subpulses. The duration of the subpulse interval varies depending on the ablation depth. According to some embodiments, the subpulse interval is in the range of 0 to 30 ms; in further embodiments, the subpulse interval is in the range of 0 to 10 ms; and in further embodiments, the subpulse interval is in the range of 0 to 3 ms. The non-limiting example shown in FIG. 3B shows a subpulse interval with a value of zero, meaning that the first and second subpulses are coupled together.

[0061] According to at least one embodiment, the goal of reducing charring via cleaning pulse techniques is achieved by employing an amplitude-modulated (AM) sequence, where each Nth pulse (N=2-10, i.e., N is a positive integer between 2 and 10) in the sequence is a high peak power pulse (a "cleaning pulse") and the remaining pulses in the sequence are low peak power pulses (ablative pulses). For example, in one embodiment, the controller is configured to control the laser such that pulsed laser energy is emitted as a sequence of pulses, where each Nth pulse in the sequence is configured as a cleaning pulse. The Nth pulse is configured to ablate the char layer to prevent charring of the target soft tissue being treated by the pulsed laser energy; in a further embodiment, the Nth pulse is configured to prevent charring by ablating any accumulating charred tissue on the target soft tissue in a manner similar to that described above.

[0062] One non-limiting example of such a sequence is shown in FIG. 4, where N=4 and every fourth pulse is a cleaning pulse. In a manner similar to that described above, the peak power of the cleaning pulse (i.e., each Nth pulse in the sequence) can be in the range of 400-20,000 W, preferably in the range of 600-1,500 W, and the cleaning pulse has a duration in the range of 0.01-5 ms. In certain embodiments, the Nth pulse has an energy in the range of 0.5-5 J. In certain embodiments, the peak power of the normal pulse (the other pulses in the sequence) is in the range of 10-250 W, preferably in the range of 50-250 W, and the normal pulse has a duration in the range of 0.5-100 ms, in some embodiments, 2-100 ms, and in other embodiments, 10-100 ms. According to some embodiments, the pulse repetition rate can be in the range of 2-1,000 Hz. In some embodiments, the sequence of pulses may include groups of pulses separated by group intervals, for example, in Figure 4, there are four sub-pulses in each pulse group.

[0063] In yet another embodiment, a continuous wave (CW) mode is used and is overlaid with a sequence of cleaning pulses. According to at least one embodiment, the controller is configured to control the laser such that the power of the laser energy is emitted as continuous wave laser power with modulation to provide overlapping pulses of laser energy.

[0064] A non-limiting example of the aforementioned pulse sequence is shown in FIG. 5. In this configuration, the CW background power ("baseline" laser emission) can be in the range of 10-250 W, preferably 50-250 W, and is modulated to provide overlapping pulses of laser energy that function as cleaning pulses. In some embodiments, the overlapping pulses each have a peak power in the range of 500-20,000 W, in some embodiments, a peak power in the range of 500-1500 W, and in other embodiments, a peak power in the range of 600-1500 W. According to at least one embodiment, the average power of the overlapping pulses is in the range of 1-30% of the CW laser power. For example, if the CW laser power is 100 W, the average power of the overlapping pulses can be in the range of 1-30 W. In certain embodiments, the cleaning pulses (i.e., overlapping pulses) have a duration in the range of 0.05-5 ms. According to at least one embodiment, the energy of the overlapping pulses is in the range of 0.5-5 J. In some embodiments, the repetition rate of the cleaning pulses (overlapping pulses) is in the range of 5-200 Hz, preferably in the range of 5-50 Hz. In some embodiments, the overlapping pulses are separated in time by a pulse interval in the range of 0.3-10 ms, and in other embodiments, the pulse interval is in the range of 5-200 ms. The CW pulsed operation mode described herein has been found by the applicant to be the most efficient mode for deep tissue ablation, cutting, and dissection. In one embodiment, each pulse of overlapping laser energy is configured to ablate a char layer to prevent charring of the treatment target soft tissue being treated by the laser energy, and in a further embodiment, each pulse of overlapping laser energy is configured to prevent charring by ablating any charred tissue that accumulates on the target soft tissue, similar to that described above.

[0065] [Laser System] 6 is a block diagram illustrating one non-limiting example of a laser system configured to generate the laser pulse modes described above. It should be understood that other configurations may be used to implement the aforementioned pulse modes.

[0066] Laser system 100 includes a power supply 103, a laser driver 125, which may include an optional energy storage device 120, a pump 115, a laser module 130, and a controller 150, also referred to herein as a control module. Laser energy from laser module 130 is directed to target soft tissue 160. Laser system 100 may also include a beam delivery system 145 or module and an optical coupler 140.

[0067] The pump 115 is configured with one or more diode lasers that energize the laser module 130. The power supply 103 provides power to the system and to an optional energy storage device 125 (e.g., an electrical capacitor and / or inductor), which may be configured to store a sufficient amount of energy necessary to form a laser pulse. The laser driver 125 of the pump 115 forms electrical pulses of specified characteristics in response to control signals from a controller (control module) 150. The electrical pulses are received by one or more diodes of the pump 115, which form the optical pulses necessary to pump the laser medium in the laser module 130. The output of the laser module 130 is coupled to a beam delivery system 145; in some cases, this coupling occurs via an optical coupler 140.

[0068] One or more components of laser system 100 are controlled by controller 150, which is programmed with control signals used to control laser driver 125, power supply 103, and / or laser module 130. For example, control signals from controller 150 can be used to directly modulate the pump current of laser driver 125 used to pump diode 115 to output a desired pulse energy, power, and temporal configuration, as will be understood by those skilled in the art. In some embodiments, a single charge-discharge cycle of energy storage device 120 can be used to modulate the diode current.

[0069] Aspects disclosed herein in accordance with the present invention are not limited in their application to the details of construction and arrangements of components set forth in the following description or illustrated in the accompanying drawings. These aspects may incorporate other embodiments and may be practiced or carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, operations, components, elements, and features discussed in connection with any one or more embodiments are not intended to be excluded from a similar role in any other embodiment.

[0070] Additionally, the phraseology and terminology used herein are for purposes of description and should not be considered limiting. Any reference herein to system and method examples, embodiments, components, elements, or acts in the singular may also encompass embodiments that include the plural, and any reference herein to any embodiment, component, element, or act in the plural may also encompass embodiments that include only the singular. References in the singular or plural are not intended to limit the systems or methods of the present disclosure, their components, acts, or elements. The use herein of "including," "comprising," "having," "containing," "involving," and variations thereof, is meant to encompass the items listed thereafter and equivalents thereof, as well as additional items. References to "or" may be construed as inclusive, such that any term described with "or" may refer to one, more than one, and all of the listed terms. Furthermore, if there is a discrepancy in term usage between this document and a document incorporated herein by reference, the term usage in the incorporated reference should be considered secondary to the usage in this document. In the event of a contradictory discrepancy, the term usage in this document shall control. Furthermore, titles or subtitles may be used herein for the convenience of the reader and shall not affect the scope of the present invention.

[0071] Having thus described several aspects of at least one example, it should be understood that various alterations, modifications, and improvements will readily occur to those skilled in the art. For example, the examples disclosed herein may be used in other contexts. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the examples discussed herein. Accordingly, the foregoing description and drawings are by way of example only.

Claims

1. 1. A laser system for treating soft tissue, comprising: a laser configured to emit pulsed laser energy having a wavelength in the range of 1.85 to 2.2 microns (μm); a controller configured to control the laser such that each pulse of emitted pulsed laser energy has two sub-pulses; Equipped with A laser system, wherein one of the two sub-pulses, an ablative sub-pulse, is configured to ablate and incise target soft tissue, and the other of the two sub-pulses, a hemostatic sub-pulse, is configured to coagulate the target soft tissue.

2. The laser system of claim 1 , wherein the ablative sub-pulse is followed by the hemostatic sub-pulse.

3. 3. The laser system of claim 2, wherein the ablative sub-pulse and the hemostatic sub-pulse are separated by a sub-pulse interval, the sub-pulse interval being in the range of 0 to 5 milliseconds (ms).

4. The laser system of claim 1 , wherein the hemostatic sub-pulse is followed by the ablative sub-pulse.

5. 5. The laser system of claim 4, wherein the hemostatic sub-pulse and the ablative sub-pulse are separated by a sub-pulse interval, the sub-pulse interval being in the range of 0 to 100 ms.

6. 10. The laser system of claim 1, wherein the ablative sub-pulses have a peak power in the range of 400 to 20,000 watts (W).

7. 7. The laser system of claim 6, wherein the ablative sub-pulses have a peak power in the range of 600 to 1500 W.

8. 10. The laser system of claim 1, wherein the energy of the ablative sub-pulses is in the range of 1 to 10 Joules (J).

9. 10. The laser system of claim 1, wherein the duration of the ablative sub-pulses is in the range of 0.05 to 10 milliseconds (ms).

10. 10. The laser system of claim 9, wherein the duration of the ablative sub-pulses is in the range of 1 to 10 ms.

11. 10. The laser system of claim 1, wherein the target soft tissue has a tissue coagulation threshold and a tissue ablation threshold, and the hemostatic sub-pulses have a peak power and energy greater than the tissue coagulation threshold and less than the tissue ablation threshold.

12. 10. The laser system of claim 1, wherein the target soft tissue has a tissue coagulation threshold and a tissue ablation threshold, and the hemostatic sub-pulses have peak power and energy that meet or exceed the tissue coagulation threshold and meet or less than the tissue ablation threshold multiplied by a factor of 1.

5.

13. 10. The laser system of claim 1, wherein the hemostatic sub-pulses have a peak power in the range of 10 to 250 W.

14. 14. The laser system of claim 13, wherein the hemostatic sub-pulses have a peak power in the range of 50 to 150 W.

15. 10. The laser system of claim 1, wherein the energy of the hemostatic sub-pulse is in the range of 0.5 to 10 J.

16. 10. The laser system of claim 1, wherein the duration of the hemostatic sub-pulse is in the range of 2 to 1000 ms.

17. 17. The laser system of claim 16, wherein the duration of the hemostatic sub-pulse configured to coagulate is in the range of 10-100 ms.

18. 10. The laser system of claim 1, wherein the ablative sub-pulses are configured to generate laser-induced gas bubbles in water surrounding the target soft tissue at a pressure sufficient to induce mechanical tissue dissection in the target soft tissue.

19. 10. The laser system of claim 1, wherein the laser is a thulium fiber laser, a thulium solid state laser, or a holmium solid state laser.

20. 1. A method for treating soft tissue, comprising: generating pulsed laser energy having a wavelength in the range of 1.85 to 2.2 microns (μm); emitting each pulse of emitted pulsed laser energy as two sub-pulses; one of the two sub-pulses, an ablative sub-pulse, configured to ablate and incise target soft tissue, and the other of the two sub-pulses, a hemostatic sub-pulse, configured to coagulate the target soft tissue; directing the pulsed laser energy to the target soft tissue.

21. The method of claim 20 , wherein the ablative sub-pulse is directed to the target soft tissue before the hemostatic sub-pulse.

22. 22. The method of claim 21, wherein the ablative sub-pulse and the hemostatic sub-pulse are separated by a sub-pulse interval, the sub-pulse interval being in the range of 0 to 5 milliseconds (ms).

23. The method of claim 20 , wherein the hemostatic sub-pulse is directed to the target soft tissue before the ablative sub-pulse.

24. 24. The method of claim 23, wherein the hemostatic sub-pulse and the ablative sub-pulse are separated by a sub-pulse interval, the sub-pulse interval being in the range of 0 to 100 ms.

25. 21. The method of claim 20, wherein the ablative sub-pulses have a peak power in the range of 400 to 20,000 watts (W).

26. 26. The method of claim 25, wherein the ablative sub-pulses have a peak power in the range of 600 to 1500 W.

27. The method of claim 20, wherein the energy of the ablative sub-pulses is in the range of 1 to 10 Joules (J).

28. 21. The method of claim 20, wherein the duration of the ablative sub-pulses is in the range of 0.05 to 10 milliseconds (ms).

29. 29. The method of claim 28, wherein the duration of the ablative sub-pulse is in the range of 1 to 10 ms.

30. 21. The method of claim 20, wherein the target soft tissue has a tissue coagulation threshold and a tissue ablation threshold, and the hemostatic sub-pulses have a peak power and energy greater than the tissue coagulation threshold and less than the tissue ablation threshold.

31. 21. The method of claim 20, wherein the target soft tissue has a tissue coagulation threshold and a tissue ablation threshold, and the hemostatic sub-pulses have peak power and energy that meet or exceed the tissue coagulation threshold and meet or less than the tissue ablation threshold multiplied by a factor of 1.

5.

32. The method of claim 20, wherein the hemostatic sub-pulses have a peak power in the range of 10 to 250 W.

33. 33. The method of claim 32, wherein the hemostatic sub-pulses have a peak power in the range of 50 to 150 W.

34. The method of claim 20, wherein the energy of the hemostatic sub-pulse is in the range of 0.5 to 10 J.

35. 21. The method of claim 20, wherein the duration of the hemostatic sub-pulse is in the range of 2 to 1000 ms.

36. 36. The method of claim 35, wherein the duration of the hemostatic sub-pulse is in the range of 10 to 100 ms.

37. 21. The method of claim 20, wherein the ablative sub-pulses are configured to generate laser-induced gas bubbles in water surrounding the target soft tissue at a pressure sufficient to induce mechanical tissue dissection in the target soft tissue.

38. 21. The method of claim 20, further comprising providing a thulium fiber laser, a thulium solid state laser, or a holmium solid state laser to generate the pulsed laser energy.

39. 21. The method of claim 20, wherein the target soft tissue is hyperplastic prostate tissue.

40. 1. A laser system for treating soft tissue, comprising: a laser configured to emit pulsed laser energy having a wavelength in the range of 1.85 to 2.2 microns (μm); a controller configured to control the laser such that the pulsed laser energy is emitted as a sequence of pulse groups, each pulse group including two sub-pulses; the first sub-pulse has a peak power in the range of 10 to 250 watts (W) and a duration of 0.5 to 100 milliseconds (ms); the second sub-pulse has a peak power in the range of 400 to 20,000 W and a duration of 0.01 to 5 ms; The groups of pulses are separated in time by a group interval in the range of 3 to 250 ms.

41. 41. The laser system of claim 40, wherein the group spacing is in the range of 3 to 8 ms.

42. 41. The laser system of claim 40, wherein the sub-pulses of the group of pulses are separated in time by a sub-pulse interval of a duration to prevent fluid penetration into regions of target soft tissue exposed to the pulsed laser energy.

43. 43. The laser system of claim 42, wherein the sub-pulse interval is in the range of 0 to 30 ms.

44. 44. The laser system of claim 43, wherein the sub-pulse interval is in the range of 0 to 10 ms.

45. 45. The laser system of claim 44, wherein the sub-pulse spacing is in the range of 0 to 3 ms.

46. 41. The laser system of claim 40, wherein the peak power of the second sub-pulse is in the range of 600 to 1500 W.

47. 41. The laser system of claim 40, wherein the peak power of the first sub-pulse is in the range of 50 to 250 W.

48. 48. The laser system of claim 47, wherein the peak power of the first sub-pulse is in the range of 100 to 250 W.

49. 41. The laser system of claim 40, wherein the second sub-pulse is configured to ablate a char layer to prevent charring of targeted soft tissue being treated by the pulsed laser energy.

50. 41. The laser system of claim 40, wherein the second sub-pulse is configured to prevent charring by ablating any accumulating charred tissue layer on the target soft tissue.

51. 41. The laser system of claim 40, wherein the laser is a thulium fiber laser, a thulium solid state laser, or a holmium solid state laser.

52. 1. A method for treating targeted soft tissue by controlling laser radiation to prevent carbonization of the soft tissue, comprising: generating pulsed laser energy having a wavelength in the range of 1.85 to 2.2 microns (μm); emitting the pulsed laser energy as a sequence of pulse groups, each pulse group including two sub-pulses; the first sub-pulse has a peak power in the range of 10 to 250 watts (W) and a duration of 0.5 to 100 milliseconds (ms); the second sub-pulse has a peak power in the range of 400 to 20,000 W and a duration of 0.01 to 5 ms; the pulse groups are separated in time by a group interval in the range of 3 to 250 ms; directing the pulsed laser energy to the target soft tissue.

53. 53. The method of claim 52, wherein the group interval is in the range of 3 to 8 ms.

54. 53. The method of claim 52, wherein the sub-pulses of the group of pulses are separated in time by a sub-pulse interval of a duration so as to prevent fluid penetration into the region of the target soft tissue exposed to the pulsed laser energy.

55. 55. The method of claim 54, wherein the sub-pulse interval is in the range of 0 to 30 ms.

56. 56. The method of claim 55, wherein the sub-pulse interval is in the range of 0 to 10 ms.

57. 57. The method of claim 56, wherein the sub-pulse interval is in the range of 0 to 3 ms.

58. 53. The method of claim 52, wherein the peak power of the second sub-pulse is in the range of 600 to 1500 W.

59. 53. The method of claim 52, wherein the peak power of the first sub-pulse is in the range of 50 to 250 W.

60. 60. The method of claim 59, wherein the peak power of the first sub-pulse is in the range of 100 to 250 W.

61. 53. The method of claim 52, wherein the second sub-pulse is configured to ablate a char layer to prevent charring of a target soft tissue being treated by the pulsed laser energy.

62. 53. The method of claim 52, wherein the second sub-pulse is configured to prevent charring by ablating any accumulated charred tissue layer on the target soft tissue.

63. 53. The method of claim 52, further comprising providing a thulium fiber laser, a thulium solid state laser, or a holmium solid state laser to generate the pulsed laser energy.

64. 1. A laser system for treating soft tissue, comprising: a laser configured to emit pulsed laser energy having a wavelength in the range of 1.85 to 2.2 microns (μm); a controller configured to control the laser such that the pulsed laser energy is emitted as a sequence of pulses; Equipped with each Nth pulse in the sequence has a peak power in the range of 400 to 20,000 W and a duration of 0.05 to 5 ms; The other pulses in the sequence have a peak power in the range of 10 to 250 W and a duration of 0.5 to 100 milliseconds (ms).

65. 65. The laser system of claim 64, wherein N is between 2 and 10.

66. 65. The laser system of claim 64, wherein the Nth pulse is configured to ablate a char layer to prevent charring of a target soft tissue being treated by the pulsed laser energy.

67. 65. The laser system of claim 64, wherein the Nth pulse is configured to prevent charring by ablating any accumulating charred tissue layer on the target soft tissue.

68. 65. The laser system of claim 64, wherein the Nth pulse has a peak power in the range of 600 to 1500 W.

69. 65. The laser system of claim 64, wherein the energy of the Nth pulse is in the range of 0.5 to 5 joules (J).

70. 65. The laser system of claim 64, wherein the other pulses in the sequence have a duration of 2 to 100 ms.

71. 65. The laser system of claim 64, wherein the peak power of the other pulses in the sequence is in the range of 50 to 250 W.

72. 65. The laser system of claim 64, wherein the laser is a thulium fiber laser, a thulium solid state laser, or a holmium solid state laser.

73. 1. A method for treating soft tissue, comprising: generating pulsed laser energy having a wavelength in the range of 1.85 to 2.2 microns (μm); emitting the pulsed laser energy as a sequence of pulses; each Nth pulse in the sequence has a peak power in the range of 400 to 20,000 W and a duration of 0.05 to 5 ms; other pulses in the sequence have peak powers in the range of 10 to 250 W and durations of 0.5 to 100 milliseconds (ms); directing the pulsed laser energy to a target soft tissue.

74. 74. The method of claim 73, wherein N is 2 to 10.

75. 74. The method of claim 73, wherein the Nth pulse is configured to ablate a char layer to prevent charring of the target soft tissue.

76. 74. The method of claim 73, wherein the Nth pulse is configured to prevent charring by ablating any accumulating charred tissue layer on the target soft tissue.

77. 74. The method of claim 73, further comprising providing a thulium fiber laser, a thulium solid state laser, or a holmium solid state laser to generate the pulsed laser energy.

78. 74. The method of claim 73, wherein the Nth pulse has a peak power in the range of 600 to 1500 W.

79. 74. The method of claim 73, wherein the energy of the Nth pulse is in the range of 0.5 to 5 joules (J).

80. 74. The method of claim 73, wherein the other pulses in the sequence have a duration of 2 to 100 ms.

81. 74. The method of claim 73, wherein the peak power of the other pulses in the sequence is in the range of 50 to 250 W.

82. 1. A laser system for treating soft tissue, comprising: a laser configured to emit laser energy having a wavelength in the range of 1.85 to 2.2 microns (μm); a controller configured to control the laser such that the power of the laser energy is emitted as continuous wave (CW) laser power with modulation to provide overlapping pulses of laser energy; A laser system comprising:

83. 83. The laser system of claim 82, wherein a CW laser power is in the range of 10 to 250 watts (W), the overlapped pulses each have a peak power in the range of 500 to 20,000 W, and an average power of the overlapped pulses is in the range of 1 to 30% of the CW laser power.

84. 84. The laser system of claim 83, wherein the peak power of each overlapping pulse is in the range of 600 to 1500 W.

85. 84. The laser system of claim 83, wherein the energy of each overlapping pulse is in the range of 0.5 to 5 joules (J).

86. 84. The laser system of claim 83, wherein the duration of each overlapping pulse is in the range of 0.05 to 5 milliseconds (ms).

87. 84. The laser system of claim 83, wherein the CW laser power is in the range of 50 to 250 W.

88. 83. The laser system of claim 82, wherein each pulse of overlapping laser energy is configured to ablate the char layer to prevent charring of the target soft tissue being treated by the laser energy.

89. 83. The laser system of claim 82, wherein each pulse of overlapping laser energy is configured to prevent charring by ablating any accumulating charred tissue layer on the target soft tissue.

90. 83. The laser system of claim 82, wherein the overlapping pulses are separated in time by a pulse interval in the range of 5 to 200 ms.

91. 83. The laser system of claim 82, wherein the overlapping pulses have a repetition rate in the range of 5 to 200 Hertz (Hz).

92. 92. The laser system of claim 91, wherein the overlapping pulses have a repetition rate in the range of 5 to 50 Hz.

93. 83. The laser system of claim 82, wherein the laser is a thulium fiber laser, a thulium solid state laser, or a holmium solid state laser.

94. 1. A method for treating soft tissue, comprising: generating laser energy having a wavelength in the range of 1.85 to 2.2 microns (μm); emitting the laser energy such that the power of the laser energy is emitted as continuous wave (CW) laser power with modulation to provide overlapping pulses of laser energy; directing the laser energy to a target soft tissue; A method comprising:

95. 95. The method of claim 94, wherein a CW laser power is in the range of 10 to 250 watts (W), the overlapped pulses each have a peak power in the range of 500 to 20,000 W, and an average power of the overlapped pulses is in the range of 1 to 30% of the CW laser power.

96. 96. The method of claim 95, wherein the peak power of each overlapping pulse is in the range of 600 to 1500 W.

97. 96. The method of claim 95, wherein the energy of each overlapping pulse is in the range of 0.5 to 5 joules (J).

98. 96. The method of claim 95, wherein the duration of each overlapping pulse is in the range of 0.05 to 5 milliseconds (ms).

99. 96. The method of claim 95, wherein the CW laser power is in the range of 50 to 250 W.

100. 95. The method of claim 94, wherein each pulse of overlapping laser energy is configured to ablate a char layer to prevent charring of the target soft tissue.

101. 95. The method of claim 94, wherein each pulse of overlapping laser energy is configured to prevent charring by ablating any accumulating charred tissue layer on the target soft tissue.

102. 95. The method of claim 94, wherein the overlapping pulses are separated in time by a pulse interval in the range of 5 to 200 ms.

103. 95. The method of claim 94, wherein the overlapping pulses have a repetition rate in the range of 5 to 200 Hertz (Hz).

104. 104. The method of claim 103, wherein the overlapping pulses have a repetition rate in the range of 5 to 50 Hz.

105. 95. The method of claim 94, further comprising providing a thulium fiber laser, a thulium solid state laser, or a holmium solid state laser to generate the laser energy.

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