Abstract:
A tissue treatment system includes a radio frequency (r.f.) generator, a treatment instrument connectible to the generator and to a source of ionisable gas and operable to produce a plasma jet at a nozzle of the instrument when supplied with the ionisable gas and energised by the generator. The generator is adapted to supply treatment energy to the instrument in the form of at least one discrete burst of pulses of r.f. energy, the burst having a preset number n of pulses, where 2≦n≦5.

Description:
[0001]    This application claims the benefit of priority from U.S. Provisional Patent Application No. 60/907,655 filed Apr. 12, 2007. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a tissue treatment system, particularly a skin treatment system which produces a gas plasma jet for application to the surface of skin. The invention also includes a method of skin treatment, particularly a cosmetic method of regenerating the reticular architecture of skin tissue using a gas plasma jet. 
       BACKGROUND OF THE INVENTION 
       [0003]    A known skin treatment system comprises a radio frequency (r.f.) generator for providing pulses of r.f. energy to a handheld instrument where it is applied to a stream of ionisable gas, such as nitrogen, as a pulsed electric field to produce a plasma jet for application to the surface of the skin. Such a system is disclosed in U.S. Pat. Nos. 6,629,974 and 6,723,091, and U.S. patent application Ser. No. 10/792,765, the entire disclosures of which are incorporated in the present application by reference. As described in these patent specifications, and in U.S. patent application Ser. No. 11/281,594 (the entire disclosure of which is also incorporated herein by reference), application of the plasma jet can be used to regenerate the reticular architecture of the skin tissue adjacent a line or wrinkle in the tissue. Typically, a single plasma pulse is applied to a given area of target tissue. The handpiece is then moved and another pulse applied to treat an adjacent area of tissue, and so on in this manner to cover a complete area of tissue to be treated, successive pulses being applied at neighbouring locations such that a uniform effect is achieved across the complete area. The r.f. generator may be operated to generate a single pulse for each actuation of a user-operated actuator or the pulses may be generated as a series of pulses continuing for as long as the actuator remains depressed, the operator moving the handpiece to select different treatment locations between the generation of consecutive plasma pulses. 
         [0004]    As described in U.S. Pat. No. 6,629,974, the known system produces plasma pulses of predetermined energy, typical pulse energy settings being 2, 2.5, 3, 3.5 and 4 joules. 
         [0005]    Treatment may be performed in a single “pass” of the instrument over the surface area to be treated, each pass comprising a plurality of plasma pulse applications at successive locations within the area. However, subsequently, a second pass may be applied, sufficient time having elapsed since the first pass to a given area of tissue such that the skin has cooled. 
         [0006]    Pulse width and energy settings employed for patient treatment have been determined by pre-clinical study and confirmed by subsequent clinical study as providing beneficial results. 
         [0007]    It is an object of the invention to improve the treatment results. 
       SUMMARY OF THE INVENTION 
       [0008]    According to a first aspect of the invention, a tissue treatment system includes a r.f. generator, a treatment instrument connectible to the generator and to a source of ionisable gas and operable to produce a plasma jet at a nozzle of the instrument when supplied with the ionisable gas and energised by the generator, wherein the generator is adapted to supply treatment energy to the instrument in the form of at least one burst of pulses of r.f. energy, the burst having a preset number n of pulses, where 2≦n≦5. Preferably, each pulse of the burst has a pulse width in the range of from 2 ms to 20 ms, the time interval between each pulse of the burst being less than 100 ms and, more preferably, between 10 ms and 40 ms. Typically, the energy of each pulse of the burst is in the range of from one joule to two joules. 
         [0009]    In the case of the pulse burst having at least three pulses, the time interval between successive pairs of pulses may be different. 
         [0010]    The preferred system has a user-operated actuator in the form of a footswitch. In one mode of the generator, depression of the footswitch causes the generator to supply a single burst of pulses. In an alternative mode, depression of the footswitch causes the generator to supply a series of bursts of pulses, each burst being as described above. In this case, the pulses are typically produced at a predetermined repetition rate until the actuator is released. Repetition rates of 0.5 Hz to 4 Hz or 5 Hz are preferred, with 2.5 Hz being a typical preferred value. The repetition rate is preferably presettable. 
         [0011]    Configuration of the generator may be such that not only is the number of pulses within each burst presettable, but also the time interval between successive pulses and the width and amplitude of the pulses of the burst. Thus, for example, the separation between pulses may be varied between 10 ms and 100 ms and the pulse width may be varied between 2 ms and 20 ms. 
         [0012]    In addition, the r.f. power level of the pulses may be preset to different values, typically between 800 W and 2 kW. Although it is possible to supply a stream of ionisable gas to the instrument continuously during application of a series of pulse bursts, it is preferred that the gas is supplied as gas pulses, each pulse commencing in the interval before a respective burst of r.f. pulses and finishing substantially at the same time as the r.f. pulse burst commences or during the respective r.f. pulse burst. 
         [0013]    According to another aspect of the invention, a tissue treatment system includes a r.f. generator, a treatment instrument connectable to the generator and to a source of ionisable gas and operable to produce a plasma jet at a nozzle of the instrument when supplied with the ionisable gas an energised by the generator, wherein the system is adapted to supply treatment energy to the instrument in the form of a burst of pulses of r.f. energy, the energy level of the individual pulses of the burst being below the threshold energy level required typically to induce epidermal vacuolation. In the preferred embodiment, the energy of each pulse of the burst is not less than 1 joule but not greater than 2 joules. The energy of the r.f. pulses may be presettable between these two values. 
         [0014]    According to a third aspect of the invention, there is provided a method of cosmetically regenerating the reticular architecture of the dermis by the application of thermal plasma energy, wherein the method comprises applying the thermal plasma energy to the skin surface as bursts of plasma pulses, the energy level of the pulses within the burst being below that required typically to induce epidermal vacuolation, and the application of the pulse bursts being substantially uniform over an area of the skin surface to be treated so as to produce a zone of thermal modification in the dermis in which the inflammatory response produces regeneration of the reticular architecture of the dermis. Nitrogen gas may be used as the ionisable gas. 
         [0015]    In the preferred method, the thermal plasma energy is applied using a handheld instrument, the instrument being moved between successive treatment locations during the periods between successive pulse bursts. The energy may be applied to a predetermined skin surface area in a plurality of passes, each pass comprising the application of thermal plasma energy at successive treatment locations. 
         [0016]    According to a fourth aspect of the invention, there is provided a method of removing photodamaged tissue from an area of the dermis and regenerating the reticular architecture of the dermis in the said area by the application of thermal plasma energy, wherein the method comprises applying the thermal plasma energy to the said skin surface area as a series of bursts of plasma pulses, the energy level of the pulses within each burst being below that required typically to induce epidermal vacuolation, and the application of the pulse bursts being substantially uniform over the said area to produce a zone of thermal damage that includes at least part of the photodamaged papillary dermis, the method further comprising inducing an inflammatory response below the level of thermal damage to produce regeneration of the reticular architecture of the dermis that replaces at least a portion of the photodamaged dermis. Advantageously, the replacement of photodamaged dermis reduces the depth of surface wrinkles, at least part of the solar elastotic changes associated with photodamage are replaced. Typically, the depth of thermal damage removal includes removal of the epidermis and the pigmentary changes associated with the photodamage, as well as pre-malignant cellular changes. Associated with the thermal modification and reticular regeneration, skin laxity and sagging is tightened, at least in part. 
         [0017]    According to a further aspect of the invention, a cosmetic method of regenerating the reticular architecture of the skin tissue adjacent to a line or wrinkle in the tissue using a source of thermal energy adapted to supply thermal energy as a plasma pulse burst comprises the step of operating the thermal energy source to form first and second adjacent regions of thermally-modified tissue in the region of the DE Junction associated with said line or wrinkle, said first region overlying said second region and being thermally modified to a greater extent than said second region. 
         [0018]    According to yet a further aspect of the invention, there is provided a cosmetic method of regenerating the reticular architecture of the dermis adjacent to a line or wrinkle using a source of thermal energy with a low thermal time constant and adapted to supply thermal energy as a plasma pulse burst, the method comprising the step of operating the thermal energy source and directing it at the surface of the skin adjacent to said line or wrinkle to form first and second adjacent regions of thermally-modified tissue in the region of the epidermis and dermis of the skin, said first region overlying said second region and being thermally modified to an extent that it separates from said second region some days after the delivery of the thermal energy, and the depth of said separation being dependent on the amount of energy delivered and the thermal capacity of the skin. 
         [0019]    The invention also includes a method of regenerating the reticular architecture of skin tissue using a plasma jet formed by applying a radio frequency field to a stream of ionisable gas, wherein the method comprises applying the radio frequency field as at least one discrete burst of radio frequency pulses, the burst having a preset number n of pulses, where n is in the range of from 2 to 5. 
         [0020]    The applicants have found that applying a plasma jet to the skin surface as a burst of two, three or more individual plasma pulses at a single location, each pulse having an energy amount somewhat lower than the pulse energies typically employed in the known system, the pulses in the burst being separated by a relatively short time such that the skin does not have time to cool significantly between each individual plasma pulse, produces superior neocollagenesis when compared with the same total energy delivery in a single pulse. This improvement is thought to be the result of lower skin surface temperatures at the skin surface but higher temperatures at the dermal-epidermal junction. Theoretical modelling has shown that varying the pulse width, all other factors being equal, alters the temperature profile at a given skin depth over time. Thus, for instance, comparing short and long pulse delivery, application of a given energy amount in a relatively short time results in higher skin surface temperatures, but lower temperatures at significant depths (e.g. at the dermal-epidermal junction), whereas application of the same amount of energy in a relatively long time results in lower skin surface temperature, but higher temperatures at the same depth. 
         [0021]    The invention will be described below by way of example with reference to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    In the drawings: 
           [0023]      FIG. 1  is a diagrammatic view of a tissue treatment system in accordance with the invention; 
           [0024]      FIG. 2  is a longitudinal cross section of a tissue treatment instrument forming part of the system of  FIG. 1 ; 
           [0025]      FIG. 3  is a block diagram of a radio frequency generator for use in the system of  FIG. 1 ; 
           [0026]      FIGS. 4A ,  4 B and  4 C are oscilloscope plots indicating the operation of a solenoid valve controlling gas flow and the supply of radio frequency energy to the tissue treatment instrument; 
           [0027]      FIG. 5  is a histological slide showing reticular regeneration of the reticular architecture of skin tissue obtained following treatment using a known system; 
           [0028]      FIG. 6  is a histological slide showing tissue regeneration after treatment using a system in accordance with the invention; and 
           [0029]      FIG. 7  constitutes two histological slides from a strip biopsy taken five days after treatment using a system in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0030]    Referring to  FIG. 1 , a tissue treatment system in accordance with the invention has a treatment power source in the form of an r.f. generator  10  mounted in a floor-standing generator housing  12  and having a user interface  14  for setting the generator to different energy level settings. A handheld tissue treatment instrument  16  is connected to the generator by means of a cord  18 . The instrument  16  comprises a handpiece having a re-usable handpiece body  16 A and a disposable nose assembly  16 B. 
         [0031]    The generator housing  12  has an instrument holder  20  for storing the instrument when not in use. 
         [0032]    Within the cord  18  there is a coaxial cable for conveying r.f. energy from the generator  10  to the instrument  16 , and a gas supply pipe for supplying nitrogen gas from a gas reservoir or source (not shown) inside the generator housing  12 . The cord also contains an optical fibre line for transmitting visible light to the instrument from a light source in the generator housing. At its distal end, the cord  18  passes into the casing  22  of the handpiece body  16 A 
         [0033]    In the re-usable handpiece body  16 A, the coaxial cable  18 A is connected to inner and outer electrodes  26  and  27 , as shown in  FIG. 2 . The inner electrode  26  extends longitudinally within the outer electrode  27 . Between them is a heat-resistant tube  29  (preferably made of quartz) housed in the disposable instrument nose assembly  16 B. When the nose assembly  16 B is secured to the handpiece body  16 A, the interior of the tube  29  is in communication with the gas supply pipe interior, the nose assembly  16 B being received within the body  16 A such that the inner electrode  26  extends axially into the tube  29  and the outer electrode  27  extends around the outside of the tube  29 . 
         [0034]    A resonator in the form of a helically wound tungsten coil  31  is located within the quartz tube  29 , the coil being positioned such that, when the disposable nose assembly  16 B is secured in position on the handpiece body  16 A, the proximal end of the coil is adjacent the distal end of the inner electrode  26 . The coil is wound such that it is adjacent and in intimate contact with the inner surface of the quartz tube  29 . 
         [0035]    In use of the instrument, nitrogen gas is fed by a supply pipe to the interior of the tube  29  where it reaches a location adjacent the distal end of the inner electrode  26 . When an r.f. voltage is supplied via the coaxial cable to the electrodes  26  and  27 , an intense r.f. electric field is created inside the tube  29  in the region of the distal end of the inner electrode. The field strength is aided by the helical coil  31  which is resonant at the operating frequency of the generator and, in this way, conversion of the nitrogen gas into a plasma is promoted, the plasma exiting as a jet at a nozzle  29 A of the quartz tube  29 . The nozzle  29 A has a diameter of 5 mm. The plasma jet, centred on a treatment beam axis  32  (this axis being the axis of the tube  29 ), is directed onto tissue to be treated, the nozzle  29 A typically being held a few millimetres from the surface of the tissue. 
         [0036]    The handpiece  16  also contains an optical fibre light guide  34  which extends through the core  18  into the handpiece where its distal end portion  34 A is bent inwardly towards the treatment axis defined by the quartz tube  29  to terminate at a distal end which defines an exit aperture adjacent the nozzle  29 A. The inclination of the fibre guide at this point defines a projection axis for projecting a target marker onto the tissue surface. 
         [0037]    Following repeated use of the instrument, the quartz tube  29  and its resonant coil  31  require replacement. The disposable nose assembly  16 B containing these elements is easily attached and detached from the reusable part  16 A of the instrument, the interface between the two components  16 A,  16 B of the instrument providing accurate location of the quartz tube  29  and the coil  31  with respect to the electrodes  26 ,  27 . 
         [0038]    Referring to  FIG. 3 , r.f: energy is generated in a magnetron  200 . Power for the magnetron  200  is supplied in two ways, firstly as a high DC voltage for the cathode, generated by a high voltage power supply  202  supplied from an AC power supply unit  204  and, secondly, as a filament supply for the cathode heater from a heater power supply unit  206 . Both the high voltage power supply  202  and the filament power supply  206  are coupled to a CPU controller  210  for controlling the power output of the magnetron. A user interface  212  is coupled to the controller  210  for the purpose of setting the output power mode amongst other functions. 
         [0039]    The AC power supply unit  204  is connected to external mains AC power and also generates a supply voltage for the CPU controller  210 . 
         [0040]    The magnetron  200  and its associated UHF coaxial feed transition generates r.f. energy in the high UHF band, typically at 2.475 GHz, this energy being supplied via a 50 ohm line  214  to a UHF circulator  216  and thence to a UHF isolator  218  constituting a patient isolation barrier. The output  220  from the isolator  218  is connected to the handpiece via a r.f. coaxial cable (neither of which is shown in  FIG. 3 ). 
         [0041]    Generation of a high voltage supply output for the magnetron by the high voltage power supply  202  is dependent on two control signals being simultaneously present from the CPU controller  210 : 
         [0042]    (i) A magnetron current demand signal on line  220  determines the instantaneous r.f. output power level from the magnetron  200  by controlling the high voltage power supply output current fed to the magnetron from the high voltage power supply  202 . This output current is proportional to the voltage of the signal on the first control line  222 . Since the UHF output power level from the magnetron  200  is proportional to the supply current from the high voltage power supply  202 , the magnetron current demand signal on the first control line  222  determines the r.f. output power level from the magnetron. 
         [0043]    (ii) An output enable signal on a second control line  224  from the CPU controller  210  turns the high voltage power supply output on and off. The CPU controller  210  governs the output enable control signal to determine the duration of the output current available from the high voltage power supply and, thus, the time during which power is generated by the magnetron  200  and is available on the 50 ohm line  214 . 
         [0044]    The UHF circulator  216  provides a constant 50 ohm load impedance for the output of the magnetron and its associated UHF coaxial feed transition. Apart from a first port coupled to the magnetron and feed transition stage  200 , the circulator  216  has a second port  216 A coupled to the UHF isolation stage  218  and a third port  216 B which feeds reflected power to a resistive power dump  226 . A reflected power sensing connection  228  provides a sensing signal for the controller  210 . 
         [0045]    Since UHF losses in the UHF circulator  216 , the isolator  218 , their interconnections (not illustrated) and the coaxial cable feeder to the handpiece (not illustrated) are known or may be otherwise compensated for, the UHF power level at the input to the handpiece can be controlled. 
         [0046]    Nitrogen gas for the handpiece is fed through the cord  18  (see  FIG. 1 ) from a pressurised gas supply  230  that is connected to a gas supply outlet  232  coupled to the cord  18 . Situated in the gas supply path between the gas supply  230  and the gas supply outlet  232  is a solenoid valve  234  operated by the CPU controller  210  via a control line  236 . 
         [0047]    When a plasma jet is to be generated, the CPU controller  210  operates to open the solenoid valve  234 , allowing gas to pass under pressure to the handpiece, the gas supply control signal being applied to the solenoid valve  234  via the gas supply control line  236 . At the same time, the magnetron current demand signal is generated as a voltage level on the first control line  222 . 
         [0048]    At a predetermined time following opening of the solenoid valve  234 , such that gas is flowing in the handpiece ( FIG. 1 ), the CPU controller  210  activates the output enable signal on the second control line  224  so that UHF power is generated at a power level according to the magnitude of the control voltage on the first control line  222 . UHF power is generated at a known power level for as long as the output enable signal is present on the second control line  224 . 
         [0049]    Reference will now also be made to  FIG. 4A  which shows the gas supply solenoid valve control signal as an upper trace (CH 1 ) and the UHF power output fed from the UHF output terminal  220  as a lower trace (CH 2 ) obtained from an r.f. power detector that monitors the power applied to the handpiece and is displayed as a voltage amplitude. When the gas solenoid valve is closed, no gas flows to the handpiece and the voltage indicated by the upper trace is high. When the valve is open to allow gas to flow, the voltage is low. When r.f. power is supplied from the output terminal  220  ( FIG. 3 ) the lower trace is high, the level being proportional to the output power; when no r.f. power is supplied, the second trace is low. 
         [0050]      FIG. 4A  illustrates generation of a two-pulse burst of r.f. energy. In this example, the pulse width of each pulse is about 8.2 ms, corresponding to a pulse energy valve of 2 J, and the time interval or separation between the end of the first pulse and the start of the second is 23 ms. As will be seen from the juxtaposition of the upper and lower traces, the gas supply valve is open before the pulse burst is initiated and closes at about the time of pulse burst initiation. This means that during the pulse burst, gas is flowing through the handpiece and can be ionised by the electric field produced in the handpiece by the r.f. pulse burst. 
         [0051]    Referring to  FIG. 3  in conjunction with  FIG. 4A , during generation of a two-pulse pulse burst, as illustrated in  FIG. 4A , two pulses of width T 1  are generated, each delivering the same amount of energy and separated by a time T 2 . The CPU controller  210  operates in order that the following actions occur:— 
         [0052]    (a) Gas is released by activating the solenoid valve  234  via gas supply control line  236  and then stopped. 
         [0053]    (b) The UHF power level is set by a voltage signal on the first control line  222  between the controller  210  and the high voltage power supply  202 . 
         [0054]    (c) An individual pulse of known power level P 1  and pulse width T 1  is generated by enabling of the high voltage power supply output via second control line  224  for a period T 1  (ignoring propagation and other activation delays that are known and repeatable). 
         [0055]    (d) Disabling of the high voltage power supply  202  by removal of the enabling signal on second control line  224  causes cessation of the UHF power output after time T 1 , and continues for the period T 2 . 
         [0056]    (e) Re-enabling of the high voltage power supply  202  via the second control line  224  for a further period T 1  causes resumption of UHF power delivery for the same duration T 1  as the first pulse of the burst. 
         [0057]    Generation of a three-pulse burst, as shown in  FIG. 4B  requires repetition of steps (d) and (e). Generation of a four-pulse burst or a five-pulse burst requires repetition of steps (d) and (e) twice or three times respectively. 
         [0058]    Settings on the user interface  212  ( FIG. 3 ) determine the pulse burst parameters in terms of the number of pulses in a pulse burst, the energy of individual pulses (being proportional to the r.f. power P 1  and pulse duration T 1 ) and the time interval between consecutive pulses. Appropriate timing of gas release is automatically determined by the CPU controller  210  to ensure optimum and consistent plasma generation. 
         [0059]    The three-pulse burst illustrated in  FIG. 4B  comprises three pulses each having a pulse width of about 8 ms and each separated from the neighbouring pulse or pulses by a period of 23 ms. As in the case of the two-pulse burst described above with reference to  FIG. 4A , the pulse energy of each pulse is 2 J. The plots shown in  FIGS. 4A to 4C  represent preferred settings in that pulse bursts having two or three pulses are preferred, the energy delivered in each individual pulse being two joules, yielding a total energy per burst of 4 joules or 6 joules. The total time for the application of each burst is nominally 40 ms for a two-pulse burst and 70 ms for a three-pulse burst. Each burst is preferably applied at a repetition rate of up to 4 Hz. 
         [0060]    The two joule per pulse setting is chosen as this approximately corresponds to the maximum energy that does not produce cellular vacuolation that would otherwise provide an insulative effect for a subsequent pulse. 
         [0061]    In order that energy delivery by each individual pulse of the burst is known and repeatable, it may be necessary to alter the timing of the gas supply to the handpiece via the solenoid valve  234  ( FIG. 3 ). According to one variation, for instance, the supply of gas may continue throughout the pulse burst, as shown in  FIG. 4C . In this case, the solenoid valve is caused to open about 70 ms before commencement of the pulse burst and remains open until the end of the third pulse, the total time during which the solenoid valve  234  is open being about 150 ms in this case. 
         [0062]    Generation of the control signals for the magnetron high voltage power supply  202  and the solenoid valve  234  by the CPU controller  210  is under firmware control. Accordingly, firmware settings in conjunction with settings of the user interface determine the r.f. pulse width for each individual pulse within the pulse burst and the timing of the gas solenoid valve activation is such that accurate and predictable energy delivery is achieved in each individual pulse, with a view to optimising the efficiency of plasma generation and minimising gas use. The firmware settings also determine the r.f. power amplitude during each individual pulse. As will be seen from the r.f. power traces of  FIGS. 4A to 4C , the r.f. power level during each individual pulse is largely constant except that each pulse has an initial power boost for a brief period following pulse commencement to assist in triggering plasma generation. 
         [0063]    In preferential treatments, the instrument  16  is passed over the area of tissue to be treated in one or two passes, the instrument being moved between application of each pulse burst to the skin surface. For a single pass treatment, pulses are preferably applied as sequential lines with the juxtaposition of lines being such as to deliver uniform coverage over the required area. For a two-pass treatment, the sequential lines formed during the first pass are in a first direction and the sequential lines of pulses formed during the second pass are in a second direction with the first and second directions at approximately 90° with respect to each other. 
         [0064]    Treatment results obtained with pulse bursts are generally superior to those obtained with single pulses of the prior technique at the maximum pulse width available from the prior system (about 30 ms at 4 joules). Pulse bursts with the same total energy produced improved results. 
         [0065]    A two-pass, two-pulse burst, with 2 joules per pulse, 4 joules total, produces improved neocollagenesis compared with the same energy delivered as a single pulse for each of two passes. Zones of thermal damage and modification also seem to be more uniform than those resulting from a single pulse. A two-pass, three-pulse burst produces similar superior results when compared with a single pulse of the same total energy. 
         [0066]      FIG. 5  shows the histology from treatment using the prior system described hereinabove. In this example, a series of single pulses of plasma energy were applied, each having a pulse energy of 3.5 J. The histology shows the skin tissue at 10 days following treatment. The sample is stained with picrosirius red (PSR) so that collagen fibres demonstrate birefringence under polarised light. Some solitary fibres of new collagen are seen lying within the zone of thermal modification which appears dark blue due to the denaturation of the collagen fibres in this zone following treatment. 
         [0067]      FIG. 6  is a histology of skin tissue at eight days from a double-pass treatment wherein the pulses are applied as discrete pulse bursts in accordance with the invention, using the same method of application, each pulse burst being made up of two pulses of energy and each of such pulses being at an energy level selected to be below the level which induces epidermal vacuolation. The polarisation applied to this slide is somewhat different from that in  FIG. 1  such that extensive new collagen fibres laid down in a matrix format are observed forming the new Rete ridges of the dermo-epidermal junction. This represents a far greater level of dermal regeneration of new collagen than has been observed in single pulse treatments. 
         [0068]      FIG. 7  is the histology from a strip biopsy taken five days following treatment in accordance with the invention, showing the characteristics of the full width of the treated epidermis as a series of sequential electromicrographs stained using H&amp;E (Haemotoxylin &amp; Eosin) and PSR. The notable feature of this histology compared to that obtained with single pulse applications is the greater uniformity of the effect throughout the zone of treatment. 
         [0069]    It will be apparent modifications could be made to the system and method described above. For example, the nozzle diameter could lie within the range of from 2 mm to 8 mm. However, the use of the nozzle diameter other than 5 mm would require a scaling of the generator energy setting according to the square of the nozzle diameter.