Patent Publication Number: US-2006009763-A1

Title: Tissue treatment system

Description:
This application claims priority of U.S. Provisional Patent Application No. 60/653,481, filed Feb. 17, 2005. This application is a Continuation-in-Part of U.S. patent application Ser. No. 10/792,765, filed Mar. 5, 2004 that is a Continuation-in-Part Application of U.S. patent application Ser. No. 09/789,500, filed Feb. 22, 2001, that in turn claims the benefit of priority of U.S. Provisional Patent Application No. 60/183,785, filed Feb. 22, 2000. The complete disclosures of U.S. Provisional Patent Application No. 60/653,481, U.S. patent application Ser. No. 10/792,765, U.S. patent application Ser. No. 09/789,500, and U.S. Provisional Patent Application No. 60/183,785, including the specifications, drawings, and claims are incorporated herein by reference in their entirety 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of Invention This invention relates to a tissue treatment system including a radio frequency (r.f.) generator and a treatment instrument connectible to the generator and to a source of ionisable gas for producing a plasma jet. The primary use of the system is skin resurfacing. The invention also relates to a method of regenerating the reticular architecture of the dermis.  
     CROSS-REFERENCE TO RELATED PATENTS AND PATENT APPLICATIONS  
      A tissue-treatment system is disclosed in related U.S. Pat. No. 6,629,974, filed Feb. 13, 2002 and U.S. Pat. No. 6,723,091, filed Feb. 22, 2001. The complete disclosures of U.S. Pat. No. 6,629,974 and U.S. Pat. No. 6,723,091, including the specifications, drawings, and claims are incorporated herein by reference in their entirety.  
     SUMMARY OF THE INVENTION  
      In the system disclosed in the above patents and applications, a handheld treatment instrument has a gas conduit terminating in a plasma exit nozzle. There is an electrode associated with the conduit, and this electrode is coupled to a separate r.f. power generator which is arranged to deliver r.f. power to the electrode for creating a plasma from gas fed through the conduit. The delivered radio frequency power is typically at UHF frequencies in the region of 2.45 GHz and the instrument includes a structure resonant in that frequency region in order to provide an electric field concentration in the conduit for striking the plasma upstream of the exit nozzle, the plasma forming a jet which emerges from the nozzle and which can be used to effect local heating of a tissue surface.  
      It has been found that the clinical effect caused through energy delivered by the pulsed plasma instrument is, for a given instrument design and generator energy setting, dependent, firstly, on the distance of the plasma exit nozzle from the tissue to be treated; as the distance increases the plasma jet beam or plume becomes more diffuse, causing the energy and the energy per unit area to decrease, so reducing the heating effect. Secondly, the clinical effect is dependent on the angle of the direction of the plasma jet (in the known system the jet is coaxial with the longitudinal axis of the instrument) with respect to the tissue to be treated. It will be appreciated that, as the angle becomes more extreme then, for an otherwise circular distribution of energy, the distribution becomes elliptical or oval with differing concentration of energy per unit area at either end of the long axis of the oval.  
      It is desirable to indicate to the user the area of the tissue that will be heated to produce desirable clinical effects so that the user may accurately target areas of tissue. More accurate overlapping of adjacent treatments can be achieved, giving an overall uniform delivery of energy to the patient&#39;s tissue to be treated.  
      According to a first aspect of this invention, a tissue treatment system includes a treatment instrument in the form of a handpiece which is arranged to direct a beam of treatment energy from a distal end of the handpiece for treating a tissue surface spaced from the distal end, the treatment energy being produced by a treatment energy emitter, wherein the handpiece incorporates at least part of an optical target marking projector for projecting a visible target marker onto a plane at a predetermined spacing from the handpiece distal end. The invention has particular application to a tissue treatment system which operates by delivering thermal energy to a tissue surface such as human skin. Such thermal energy treatment may be performed by a treatment energy emitter in the form of a gas plasma generator, the above-mentioned handpiece having a nozzle at its distal end for directing a thermal energy beam in the form of a plasma jet outwardly from the nozzle.  
      Preferably, the target marking projector has a light exit aperture at the distal end of the handpiece, the exit aperture being offset from a treatment beam axis of the handpiece.  
      In the preferred handpiece, light for the visible target marker is projected from the distal end of the handpiece and centred on a projection axis which is inclined towards the treatment beam axis so as to intersect the latter approximately at the said predetermined spacing from the handpiece distal end.  
      The projected target marker preferably defines an area indicative of the tissue area which will be subjected to thermal treatment when the distal end of the handpiece is located at the predetermined spacing from a tissue surface. Thus, for instance, a circular treatment area may be indicated by a target marker in the form of a generally circular ring of projected light. Other markers can be used, such as a plurality of light dots arranged in a suitable pattern, a square, parts of a circle, and so on.  
      The projector typically comprises a light source and an optical fibre light guide, at least a distal portion of the light guide being housed in the handpiece and terminating in the exit aperture.  
      The light source itself may be formed in the shape of the required marker and may be an illuminated mask having a marker aperture of the required shape. Thus, for a ring marker, the mask may have an annular aperture or an aperture forming a part or parts of an annulus. Alternatively, the light source may be a light emitter which is, itself, in the form of an annulus.  
      The projector preferably includes at least one lens for concentrating light from the light source onto a proximal end of the fibre guide, light reaching the end of the fibre guide at an angle within the acceptance angle for the material of the fibre or fibres. Under such conditions, light incident at a given angle on the proximal end of the fibre is emitted from the distal end at the same angle with respect to the fibre axis. This property of optical fibres may, therefore, be used to form an image of the light source in the projection plane.  
      Although the projector may be battery-powered and may be contained entirely within the handpiece, the preferred embodiment has the light source in the same housing as the treatment energy power source (which may be a radio frequency generator housing) and light radiation is transmitted via an optical fibre contained within a cord connecting the handpiece to the power source housing. In the case of a gas plasma system this cord also contains a coaxial cable and a gas supply tube.  
      Projecting a target marker as described onto the tissue surface indicates the area on the tissue surface that will be treated. The size of the marker indicates the spacing of the handpiece from the tissue surface since, with diverging light emitted from the exit aperture, the size of the marker increases as the distance of the tissue surface from the handpiece increases. In general terms, because the size of the marker varies as the distance varies, the marker size indicates the distance.  
      The shape of the marker indicates the angle at which the instrument is held with respect to the target tissue surface. Thus, if the light source is circular, a circular marker image indicates that the treatment beam axis is approximately perpendicular to the target tissue surface. If the marker image is elliptical, then this is an indication of an inclined target beam axis.  
      According to a second aspect of the invention, a tissue treatment instrument for tissue treatment system comprises a handpiece which is arranged to direct a beam of treatment energy from a distal end thereof for treating a tissue surface spaced from the said distal end, wherein the handpiece incorporates optical means for projecting a visible target marker onto a plane spaced from the handpiece distal end.  
      Human skin has two principal layers: the epidermis, which is the outer layer and typically has a thickness of around 120μ in the region of the face, and the dermis which is typically 20-30 times thicker than the epidermis, and contains hair follicles, sebaceous glands, nerve endings and fine blood capillaries. By volume the dermis is made up predominantly of the protein collagen.  
      Ageing and exposure to ultraviolet (UV) light result in changes to the structure of the skin, these changes including a loss of elasticity, sagging, wrinkling and a pallor or yellowing of the skin consistent with reduced vascularity. The background to these effects is explained in our co-pending patent application entitled “Method of Regenerating the Reticular Architecture of the Dermis” filed on even date herewith, the disclosure of which is incorporated herein by reference.  
      According to a third aspect of the present invention, there is provided a cosmetic method of regenerating the reticular architecture of tissue using a handheld tissue treatment instrument as a source of thermal energy, wherein the method comprises locating the instrument over the tissue to be treated whilst illuminating the surface of the tissue with a visible target marker projected from the instrument, the position of the instrument with respect o the tissue surface being selected according to the appearance of the marker, and operating the thermal energy source whilst the instrument is in the said position.  
      Preferably it is the spacing of the instrument from the tissue surface which is selected according to the appearance of the marker. In addition, the angle of the instrument with respect to the tissue surface may be selected in this way.  
      The instrument nozzle may be used as a size reference feature, the method including comparing the marker size with the nozzle diameter to achieve optimum instrument spacing. The selected spacing of the nozzle from the tissue surface is preferably in the range of from 2 mm to 10 mm and, most normally, in the range of from 4 mm to 7 mm.  
      In the preferred method, the thermal energy source is operated to form first and second adjacent regions of thermally-modified tissue in the region of the DE Junction, the first region overlying the second region and being thermally modified to a greater extent than the second region.  
      In particular, the thermal energy source may be operated to direct thermal energy at the surface of human skin to form first and second adjacent regions of thermally-modified tissue in the region of the epidermis and dermis of the skin, the first region overlying the second region and being thermally modified to an extent that it separated from the second region some days after the delivery of thermal energy, the depth of the separation being dependent on the amount of energy delivered and the thermal capacity of the skin.  
      In a preferred embodiment, the thermal energy source is operated for a single pass over the skin surface, the thermal energy source being arranged to have an energy setting dependent on the desired depth of effect. Alternatively, the thermal energy source is operated over at least two passes over the skin surface, the energy levels of the passes being chosen dependent on the desired depth of effect.  
      In either case, the energy setting of the thermal energy source may be such as to create vacuolation on the first pass. In the latter case, the energy setting of the thermal energy source may be such as not to create vacuolation on the first pass, thereby enabling a second pass without removing the treated skin.  
      Preferably, the energy setting of the thermal energy source is such as to preserve the integrity of the epidermis as a biological dressing.  
      In a preferred embodiment, the thermal energy source is operated so that a line of cleavage occurs within the skin 2 to 5 days following treatment, the line of cleavage occurring between said first and second regions. In one particular case, the operation of the thermal energy source may be such as to form a line of cleavage from 2 to 3 cells deep in the stratum corneum of the superficial epidermis and the upper dermis.  
      Advantageously, the operation of the thermal energy source is such that the tissue in the first region is sloughed tissue. In this case, the sloughed tissue is removed once a new epidermis has been substantially generated in the region of the line of cleavage.  
      Preferably, the tissue below the line of cleavage in said second region includes the lower epidermis, the basal membrane and the DE Junction. More preferably, at least the thermally-modified basal membrane and the DE Junction are regenerated.  
      In one particular case, the line of cleavage forms below areas of solar elastosis, such that the solar elastosis and deranged fibroblasts are sloughed.  
      Preferably, the operation of the thermal energy source is such as to denature dermal collagen in the second region.  
      In a preferred embodiment, the tissue in said second region undergoes a regenerative process following regeneration of the epidermis.  
      In this case, the reticular architecture of the dermis is regenerated in whole, or in part, by fibroblasts less exposed to the effects of UV radiation.  
      The collagen architecture and/or elastin architecture and/or the GAGS of the dermis is regenerated in whole, or in part, by fibroblasts less exposed to the effects of UV radiation.  
      Preferably, the healing process is such that risk of scarring and hypo pigmentation is substantially eliminated.  
      Advantageously, a progressive improvement in skin changes associated with ageing and photodamage occur over a period of between 6 and 12 months following treatment.  
      In a preferred embodiment, the source of thermal energy is an instrument having an electrode connected to a power output device, and wherein the power output device is operated to create an electric field in the region of the electrode; a flow of gas is directed through the electric field to generate, by virtue of the interaction of the electric field with the gas, a plasma; the plasma is directed onto the tissue for a predetermined period of time; and the power transferred into the plasma from the electric field is controlled so as to desiccate at least a portion of the dermis with vapour pockets formed in dermis cells.  
      Preferably, the power output device is operated to deliver discrete pulses of heat of millisecond duration.  
      Advantageously, the pulses have a duration in the range of from about 0.5 to about 100 milliseconds, and preferably a duration in the range of from about 4.5 to about 15.4 milliseconds.  
      Conveniently, the power output device is operated to deliver energy in the range of from about 1 Joule to about 4 Joules for an instrument having a first predetermined nozzle diameter, and to deliver energy in the range of from less than 0.5. Joules to about 2.0 Joules for an instrument having a second predetermined diameter that is less than the first predetermined diameter.  
      Preferably, the first predetermined diameter is substantially 5 mm and the second predetermined diameter is substantially 1.5 mm.  
      The thermal energy may be delivered to the tissue from a thermal energy source as a jet of fluid having stored heat energy at the tissue surface, the jet of fluid typically comprising a jet of ionised diatomic gas.  
      The invention also includes a cosmetic method of regenerating the reticular architecture of the dermis using a tissue treatment system including a treatment instrument in the form of a handpiece having a gas plasma generator, wherein the method comprises locating the instrument over the tissue to be treated and projecting a visible marker from the instrument onto the tissue surface beneath the instrument and positioning the instrument to cause the marker to adopt a required configuration associated with predetermined position of the instrument with respect to the tissue surface, and operating the gas plasma generator whilst the instrument is in the predetermined position to direct a gas plasma jet onto the tissue surface.  
      According to another aspect of the invention, a cosmetic method of regenerating the reticular architecture of tissue using a handheld tissue treatment instrument as a source of thermal energy comprises locating the instrument over the tissue to be treated, illuminating the surface of the tissue with a visible target marker projected from the instrument, and using the marker as a positioning aid. Typically, this method includes operating the thermal energy source with the instrument located at a plurality of different positions to produce a graduated clinical effect at the periphery of a treated tissue area. The instrument positions may be selected by locating the instrument so as to produce different respective marker configurations on the tissue surface.  
      The gradation of effect may be produced by positioning the instrument at different spacings or at different angles with respect to the tissue surface. Thus, the gradation of effect may be produced by increasing the spacing on each successive pass of the instrument from treated to untreated areas of tissue, using the projected marker as a spacing guide or by angling the instrument at a greater angle in respect of the perpendicular at the boundaries of a treated area, the angle being selected by observing the shape of the marker. In the case of a marker which is generally circular when the instrument is perpendicular to the tissue surface, the instrument may be increasingly inclined by selecting orientations which produce a marker shape which is increasingly elliptical. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be described below by way of example with reference to the drawings in which:  
       FIG. 1  is a diagrammatic view of a tissue treatment system in accordance with the invention;  
       FIG. 2  is a longitudinal cross-section of a tissue treatment instrument forming part of the system of  FIG. 1 ;  
       FIG. 3  is a block diagram of a radio frequency generator for use in the system of  FIG. 1 ;  
       FIG. 4  is a diagram showing an optical target marking projector of the system of  FIG. 1 ;  
       FIG. 5  is an exploded perspective view of the tissue treatment instrument shown in  FIG. 2 ;  
       FIG. 6  is a cross-section of a light source forming part of the target marking projector of  FIG. 4 ;  
       FIG. 7  is an axial view of a light source mask;  
       FIG. 8  is a diagram showing the principle of the transmission of a target marker image in an optical fibre;  
       FIG. 9  is a detail from  FIG. 4  showing the distal end of the treatment instrument and the projection of the marker image onto a tissue surface;  
       FIG. 10  is a composite diagram showing the regeneration of the reticular architecture of the dermis when using the system of FIGS.  1  to  9  for different pulse widths and energy settings; and  
      FIGS.  11  to  13  show the process of reticular regeneration at the day of treatment, at four days after treatment, and at ten days after treatment respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      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.  
      The generator housing  12  has an instrument holder  20  for storing the instrument when not in use.  
      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  
      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 .  
      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 .  
      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 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.  
      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, as will be described in more detail below.  
      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 .  
      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 an inverter  202  supplied from a 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 supply represented by the inverter  202  and the filament 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 power output mode, amongst other functions.  
      The magnetron  200  operates in the high UHF band, typically at 2.475 GHz, producing an output on an output line which feeds a feed transition stage  213  for converting the magnetron output to a coaxial 50 ohms feeder, low frequency AC isolation also being provided by this stage. Thereafter, a circulator  214  provides a constant 50 ohms load impedance for the output of the feed transition stage  213 . Apart from a first port coupled to the transition stage  213 , the circulator  214  has a second port  214 A coupled to a UHF isolation stage  215  and hence to the output terminal  216  of the generator for delivering RF power to the handheld instrument  16  ( FIG. 1 ). Reflected power is fed from the circulator  214  to a resistive power dump  215 . Forward and reflected power sensing connections  216  and  218  provide sensing signals for the controller  210 .  
      The controller  210  also applies via line  219  a control signal for opening and closing a gas supply valve  220  so that nitrogen gas is supplied from the source  221  to a gas supply outlet  222  from where it is fed through the gas supply pipe in the cord  18  to the instrument  16  ( FIG. 1 ), when required. A light source  224 , forming part of the above-mentioned optical target marker projector, is connected to the controller  210  by a control line  225  and produces a target marker light beam at an optical marker light output  226 .  
      The controller  210  is programmed to pulse the magnetron  200  so that, when the user presses a footswitch (not shown in the drawings), r.f. energy is delivered as a pulsed waveform to the UHF output  216 , typically at a pulse repetition rate of between about 1 Hz and about 4 Hz. A single pulse mode is also provided. The controller  210  also operates the valve  220  so that nitrogen gas is supplied to the handheld instrument simultaneously with the supply of r.f. energy. The light source  224  can be actuated independently of r.f. energy and nitrogen gas supply. Further details of the modes of delivery of r.f. energy are set out in the above-mentioned U.S. Pat. No. 6,723,091.  
      The optical fibre light guide  34  and the light source  224  form part of an optical target marker projector which is shown as a whole in  FIG. 4 . The light source  224  is in the generator housing  12  (see  FIG. 1 ) and, coupled to its optical output  226 , is an optical fibre line  34  which passes through the cord  18  connecting the handpiece  16  to the generator housing  12  and, thence, into the casing  22  of the handpiece. Within the handpiece, the fibre guide  34  extends generally parallel to and offset from the treatment beam axis  32  until it reaches a distal end portion of the handpiece. There, the distal end portion  34 A of the fibre guide is bent towards the treatment beam axis  32 , as shown. The distal end of the fibre guide  34  forms an exit aperture for the guided marker beam which, when the light source  224  is activated, is projected as a diverging beam onto the tissue surface  250  to be treated.  
      The distal end portion  34 A of the optical fibre guide is supported within the disposable nose section  16 B by an elongate rigid fibre guide support  40 , as shown in the exploded view of the handpiece appearing in  FIG. 5 . When the disposable nose section  16 B is fitted to the handpiece body  16 A, the fibre guide support  40  extends through a passage  42  in the nose section  16 A and is exposed at an aperture  44  of the nose section  16 B so that the distal end of the fibre guide  34 , which is at the distal end  40 D of the support, lies adjacent the plasma nozzle  29 A. The passage  42  in the disposable nose section  16 A locates the fibre guide support  40  and, therefore, the distal end portion  34 A of the fibre guide, aligning the guide so that it is correctly positioned with respect to the plasma nozzle  29 A and the treatment beam axis  32 .  
      Referring to  FIG. 6 , the light source  224  comprises an illuminated mask  224 M mounted transversely in an elongate light source housing  230 . The mask  224 M is illuminated by a light emitting diode (LED)  232  mounted at one end of the housing  230 , visible light from the LED  232  passing through a first collimator lens  234 , then through the mask  224 M, following which it is concentrated by a second lens  236  onto the proximal end  34 B of the fibre guide  34  for transmission to the handpiece  16  shown in  FIG. 4 . The fibre guide  34  is removable from the light source housing  230  by releasing an optical fibre connector  238 .  
      The LED  232  is chosen to produce a blue light since this colour has the advantage of being easily seen on a range of skin colours from light to dark. Other colours may, of course, be used.  
      A laser diode light source may also be used.  
      Referring to  FIG. 7 , the light source mask  224 M, when viewed in the axial direction of the light source housing  230 , is seen to have an annular aperture  224 A. It is this aperture  224 A which, when illuminated by the LED  232 , is imaged on the tissue surface to be treated, albeit with some distortion in the optical fibre guide  34 . It is a property of a straight optical fibre with end faces perpendicular to its axis that when light is incident on one of the ends at a given angle to the axis, the light emitted from the other end is emitted at the same angle, providing the angle of incidence is no greater than the so-called “acceptance angle” associated with the material of the fibre. The acceptance angle is sin −1  (NA) where NA is the numerical aperture of the fibre. This property of optical fibres, insofar as it relates to the present invention is illustrated in  FIG. 8 . The light from the light source, shown as the illuminated aperture  224 A in  FIG. 8 , is focused onto the proximal end  34 B of the fibre guide  34 , the angle of the edge of the annulus with respect to the fibre axis being less than the acceptance angle for the material of the fibre. At the distal end  34 D, light transmitted from the proximal end  34 B emerges, as shown, at the same angle with respect to the fibre axis as the incident light at the proximal end, the emerging light then diverging so that an image  260  of the annulus is formed in a plane spaced from the guide distal end  34 D. As stated above, light from the light source aperture  224 A is concentrated on the guide proximal end  34 B by the second lens  236  in the light source housing as described above with reference to  FIG. 6 . In practice, the focal length of this lens is arranged to be greater than the spacing between the lens and the fibre proximal end  34 B so that the image of the aperture  224 A is spaced beyond the distal end of the fibre guide, as shown in  FIG. 8 .  
      Multiple internal reflections, the length of the fibre, and bending of the fibre, amongst other effects, tend to spread the incident rays to some degree. The mask  224 M is located in a collimated beam of light produced between the two lenses  234 ,  236  of the light source. Accordingly, with an annular aperture  224 A, a cylindrical annulus of light is incident upon the second lens  236 . The image of the annulus is transmitted through the fibre guide with a fidelity dependent on the quality of the fibre, its length, and its degree of bending. A low cost polymer fibre may be used. The best results, however, are obtained with a silica fibre, which has lower losses and distortion. Polymer fibres typically have a numerical aperture in the range of from 0.3 to 0.75, while silica fibres have a numerical aperture generally within the range 0.12 to 0.48.  
      The projection of the annular image  260  onto a target tissue surface will now be described with reference to  FIG. 9 . In its support  40 , the distal portion  34 A of the fibre guide is bent towards the treatment beam axis  32  so that, at the exit aperture formed by the distal end  34 D of the fibre guide, light transmitted through the fibre guide  34  emerges centred in an inclined projection axis  262  which intersects the treatment beam axis  32  at a predetermined spacing from the plasma exit nozzle  29 A. The properties of the second lens  236  in the light source housing  230  and of the fibre guide  34  are such that the focused image  260  of the light source annulus  224 A appears approximately in a perpendicular plane passing through the intersection of the two axes  32 ,  262 . The degrees of divergence of the projected marker beam  264  is such that at the projection plane the size of the image marker  260  is approximately the same as the external diameter of the plasma exit nozzle  29 A. The predetermined spacing which is determined by the configuration of the projector, corresponds to the preferred spacing of a tissue surface  250  from the end of the plasma exit nozzle  29 A for optimum clinical effect. Accordingly, in use, the correct spacing of the handpiece  16  from the tissue surface  250  can be judged by the user by locating the handpiece so as to produce an image of a required size with reference to the diameter of the exit nozzle  29 A. In other words, the size of the marker image  260  indicates the handpiece stand-off distance from the tissue surface as a result of the conical nature projected beam, the axis of the cone being approximately coincident with the exit aperture of the fibre guide. In this embodiment, the handpiece is correctly spaced from the tissue surface when the diameter of the marker is approximately the same as the external diameter of the nozzle. The area occupied by the marker  260  also indicates, at least approximately, the area of clinical effect, dependent on the size of the nozzle  29 A.  
      Large deviations of the treatment beam axis  32  from the preferred perpendicular orientation with respect to the tissue surface  250  are indicated by a pronounced elliptical image (as opposed to a circular or near-circular image).  
      By actuating the light source before treatment begins, the user can position the handpiece  16  at the required spacing from the tissue surface and can identify the area of clinical effect before the gas plasma is actuated.  
      Variations to the system include the following.  
      With appropriate modification to the mask  224 M of the light source  224 , a solid circle of light may be projected on the tissue surface rather than an annulus.  
      In the preferred embodiment, the exit aperture formed by the distal end  34 D of the fibre guide  34  is radially offset with respect to the treatment beam axis, the distal end portion  34 A of the fibre guide being bent to project the annulus of light such that the centre of the projected annulus is centrally positioned with respect to the centre of the zone of treatment produced by a gas plasma jet from the nozzle  29 A. Alternatively, the distal face of the fibre may be processed such that it is not perpendicular to the fibre axis. In this case, the light is projected at an angle with respect to the fibre axis at its exit aperture and may, thereby, be used to modify the shape of the image and its spacing from the nozzle  29 A.  
      In another embodiment, at least one additional fibre guide may be employed between the light source  224  and the distal end of the handpiece. For example, part of the marker image may be transmitted by one fibre guide and another part of the image by another fibre guide. In particular, half of the image may be projected by a fibre guide offset on one side of the plasma exit nozzle and the other half of the image may be projected by a fibre guide terminating on the diametrically opposite side of the nozzle, the respective projection axes intersecting at the required tissue treatment spacing from the nozzle. In this way, the image appears disjointed or mis-shapen at spacings of the instrument greater or less than the optimum spacing.  
      In yet a further alternative of the embodiment, the quartz tube  29  itself may be used as a light guide for projecting the marker.  
      It is possible to mount the projector completely within the handset, powering the light source from a battery.  
      Systems within the broader scope of the invention may include systems in which heating energy is delivered to the tissue from a source having a low thermal time constant. Typically, treatment energy can be delivered in pulses of very short duration (typically 0.5 to 100 ms) and without reliance on an intermediary conversion from one kind of energy to another such as a chromophore in laser energy and tissue resistivity in radio frequency energy.  
      In use, the instrument  16  is passed over the surface of tissue to be cosmetically treated, with the nozzle  29   a  typically being held a few millimetres from the surface of the tissue. The pulse duration and energy levels are chosen so as to form first and second adjacent regions of thermally-modified tissue in the region of the DE Junction. The first, upper region is termed a zone of thermal damage, having a thermal modification which is greater than that of the second, lower region. The thermally damaged zone is thermally modified to an extent that it separates from the second region some days after the delivery of the thermal energy. Following separation of the first damaged region, the epidermis and the upper region of the dermis regenerate naturally.  
      A benefit of using a diatomic plasma is that it is able to deliver a relatively large amount of energy which causes heating in a short period of time. This enables delivery in discreet pulses of millisecond duration, and is in contrast to heat conduction from a merely hot gas. In the preferred embodiment, energy from 1 Joule to 4 Joules is delivered in a period of 4.5 to 15.4 milliseconds respectively for a nozzle with an exit diameter of 5 millimetres, and delivers from less than 0.5 Joules up to 2 Joules in the same period for a nozzle with an exit diameter of less than 1.5 millimetres. Experiments have shown that useful clinical effects are achieved with yet longer pulses extending to 50 milliseconds, and further analysis shows extension up to 100 milliseconds or more will provide useful effects. In addition, the pulse width may be shortened to deliver the same, or otherwise similar, useful heating energy. Plasma pulses as short as 0.5 milliseconds have been produced with the system described above.  
      Another benefit is that oxygen is purged from the skin surface by the plasma and flow of inert gas that follows immediately following a plasma pulse. As a result, the oxidative carbonisation that often occurs at the skin surface on application of thermal energy is avoided, leaving a desiccated intact epithelium with minor structural alteration.  
      This minor structural alteration is nonetheless important in providing yet another benefit of the invention, as it changes the thermal characteristics of the epidermis at higher energy settings. Following a single pass of plasma over the skin surface at an energy setting greater than 2 Joules, the epidermal cells at the basal membrane are heated to a degree that produces vacuolation of the cellular contents. This produces a natural insulator limiting the absorption and depth of penetration of energy from subsequent passes. This is a beneficial safety feature that avoids the risk of excessive damage by inadvertent application of multiple passes to the same site on the skin surface.  
      Alternatively, when using energy pulses at or below 2 Joules, then the vacuolation is not observed, and the treated skin is still capable of absorbing the thermal energy of a second pass, by changing the energy in the second pass using either a narrow nozzle to focus the plasma or a higher energy setting will have an additive effect. The benefit of using a narrow nozzle embodiment is that the focused energy can be directed onto specific areas of the skin surface such as deeper wrinkles.  
      For example, if the skin is subjected to two passes of 4 Joules, then the depth of thermal effect is only 10-20% greater than with a single pass of 4 Joules. Alternatively, if the skin is first treated with 2 Joules, then with a second pass of 4 Joules then the effect will be consistent with a single pass with 6 Joules. Part of this benefit also relates to the water content of the skin, particularly the upper layers of the epidermis following pre-treatment with a topical anaesthetic.  
      Through experimentation with the invention, it has become clear that the depth of effect changes by up to 50% depending on the hydration of the upper layers of the epidermis following application of a topical anaesthetic. Topical anaesthetics include a hydrating component, as they rely on hydration of the superficial epidermis for the penetration of the anaesthetic agent through the skin. This changes the absorption of pure thermal energy, whereby a larger proportion of the energy is dissipated in the superficial epidermis, reducing the depth of penetration into the dermis. If no anaesthesia or tumescent subcuticular anaesthesia is employed, then the depth of dermal penetration for a given energy setting can be doubled. A pre-treatment with 2 Joules produces sufficient desiccation of the superficial epidermis, following use of topical anaesthesia, that an equivalent depth of effect can be produced with the second pass to that achieved with no anaesthesia or tumescent subcuticular anaesthesia.  
      The reason for using a diatomic plasma which delivers a relatively large amount of energy in a short period of time is that the irreversible clinical effects (the thermal modification and thermal damage of the tissue) occur over tissue depths that result in the desired clinical effects, whilst avoiding any undesired clinical effects. If the heating energy is delivered over too long a time, the effects of convection from the skins surface and conduction into the underlying tissue will be such that no significant temperature rise results. On the other hand, if the time is too short, then irreversible effects (such as water vaporising) at or near the skins surface will carry away otherwise useful heating energy.  
       FIG. 10  shows the regeneration of the reticular architecture of the dermis for different pulse widths and energy ratings, and illustrates the use of a thermal source with a low thermal time constant. Thus, for an energy setting of 1 Joule, a pulse width of about 4.5 or 5 milliseconds is appropriate, for an energy setting of 2.5 Joules, a pulse width of 10 milliseconds is appropriate, and for an energy setting of 4 Joules, a pulse width of about 15 milliseconds is appropriate.  FIG. 10  also shows the two regions of thermal modification T 1  and T 2 , T 1  being the upper region of thermal damage, and T 2  being the lower region of thermal modification.  FIG. 10  also shows the line of cleavage C which develops between these two regions between two and five days after treatment. As is apparent, the depth of effect increases as the energy level and pulse width used for the treatment increases. The dermatologist carrying out the procedure will, therefore, choose the appropriate energy level and pulse width depending on the depth of effect required.  
      As mentioned above, the use of a topical anaesthetic modifies the effect of the treatment. Thus, as shown in  FIG. 10  the line of cleavage C is for treatment without a topical anaesthetic, the equivalent line of cleavage (C 1 ) being higher, owing to a reduction in the depth of thermal damage and modification which results from pre-treatment with a topical anaesthetic. FIGS.  11  to  13  show a typical treatment, and the progress of regeneration of the reticular architecture after the treatment. Thus,  FIG. 11  shows the effect of treatment at 3.5 Joules and a pulse width of 13.6 milliseconds immediately following treatment. The Figure shows the dermis (including the reticular dermis and the papillary dermis), the DE Junction, the epidermis and the stratum corneum. Vacuolation of basal epidermal cells at the DE Junction is clearly visible, as indicated by the reference V.  FIG. 12  shows the position at day four following treatment at 3.5 Joules, and shows a developing line of cleavage C between the regions T 1  and T 2  of thermal damage and thermal modification. The region T 1  of thermal damage is the old epidermis and the upper dermis, which is in the process of being shed along the developing line of cleavage C. Underneath the line of cleavage C a new stratum corneum and a regenerated epidermis are being developed naturally.  FIG. 12  also shows the zone where thermal modification will later become apparent.  
       FIG. 13  shows the position at day ten following treatment at 3.5 Joules. Here, the epidermis has been fully regenerated with residual activity in the basal layer, and the zone of thermal modification is now apparent, as intense fibroblast activity regenerates the reticular architecture of the dermis.  
      Referring again to  FIG. 10 , it will be observed that, in this case, the instrument is positioned perpendicularly with respect to the tissue surface. A reduction in the clinical effect for a given energy output can be achieved by inclining the handpiece  16  with respect to the tissue surface or by increasing the spacing between the handpiece  16  and the tissue surface. Such techniques are particularly useful for blending the effect between a fully treated area of the skin and an untreated area. This can be seen as a “feathering” technique. The target marker may be used here, also, as an instrument positioning aid. As the instrument is moved outwardly towards the edge of the area to be treated, its position may be progressively changed, e.g., with increasing inclination with respect to the tissue surface, as happens when the instrument is moved so as to project a marker of increasingly elliptical shape. Alternatively or in addition, the instrument may be moved so that the marker increases in size with outward movement towards the boundary of the area of treatment.