Abstract:
An apparatus for transcutaneously treating tissue beneath a skin surface using radiofrequency energy. The apparatus includes an electrode assembly supported by a handpiece. The electrode assembly includes an electrode configured to transfer the radiofrequency energy through the skin surface to the tissue. A force sensor, which is located in the handpiece, is configured to detect an amount of force applied by the electrode against the skin surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of application Ser. No. 11/531,081, filed Sep. 12, 2006, which is a continuation of application Ser. No. 10/072,610, filed Feb. 6, 2002, now U.S. Pat. No. 7,141,049, which is a continuation-in-part of application Ser. No. 09/522,275, filed Mar. 9, 2000, now U.S. Pat. No. 6,413,255, which claims the benefit of U.S. Provisional Application No. 60/123,440, filed Mar. 9, 1999. The disclosure of each of these applications is hereby incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to an electrode delivery device for treating tissue for treating skin and underlying tissues. 
       BACKGROUND OF THE INVENTION 
       [0003]    The human skin is composed of two elements: the epidermis and the underlying dermis. The epidermis with the stratum comeum serves as a biological barrier to the environment. In the basilar layer of the epidermis, pigment-forming cells called melanocytes are present. They are the main determinants of skin color. 
         [0004]    The underlying dermis provides the main structural support of the skin. It is composed mainly of an extra-cellular protein called collagen. Collagen is produced by fibroblasts and synthesized as a triple helix with three polypeptide chains that are connected with heat labile and heat stable chemical bonds. When collagen-containing tissue is heated, alterations in the physical properties of this protein matrix occur at a characteristic temperature. The structural transition of collagen contraction occurs at a specific “shrinkage” temperature. The shrinkage and remodeling of the collagen matrix with heat is the basis for the technology. 
         [0005]    Collagen crosslinks are either intramolecular (covalent or hydrogen bond) or intermolecular (covalent or ionic bonds). The thermal cleavage of intramolecular hydrogen crosslinks is a scalar process that is created by the balance between cleavage events and relaxation events (reforming of hydrogen bonds). No external force is required for this process to occur. As a result, intermolecular stress is created by the thermal cleavage of intramolecular hydrogen bonds. Essentially, the contraction of the tertiary structure of the molecule creates the initial intermolecular vector of contraction. 
         [0006]    Collagen fibrils in a matrix exhibit a variety of spatial orientations. The matrix is lengthened if the sum of all vectors acts to distract the fibril. Contraction of the matrix is facilitated if the sum of all extrinsic vectors acts to shorten the fibril. Thermal disruption of intramolecular hydrogen bonds and mechanical cleavage of intermolecular crosslinks is also affected by relaxation events that restore preexisting configurations. However, a permanent change of molecular length will occur if crosslinks are reformed after lengthening or contraction of the collagen fibril. The continuous application of an external mechanical force will increase the probability of crosslinks forming after lengthening or contraction of the fibril. 
         [0007]    Hydrogen bond cleavage is a quantum mechanical event that requires a threshold of energy. The amount of (intramolecular) hydrogen bond cleavage required corresponds to the combined ionic and covalent intermolecular bond strengths within the collagen fibril. Until this threshold is reached, little or no change in the quaternary structure of the collagen fibril will occur. When the intermolecular stress is adequate, cleavage of the ionic and covalent bonds will occur. Typically, the intermolecular cleavage of ionic and covalent bonds will occur with a ratcheting effect from the realignment of polar and nonpolar regions in the lengthened or contracted fibril. 
         [0008]    Cleavage of collagen bonds also occurs at lower temperatures but at a lower rate. Low-level thermal cleavage is frequently associated with relaxation phenomena in which bonds are reformed without a net change in molecular length. An external force that mechanically cleaves the fibril will reduce the probability of relaxation phenomena and provides a means to lengthen or contract the collagen matrix at lower temperatures while reducing the potential of surface ablation. 
         [0009]    Soft tissue remodeling is a biophysical phenomenon that occurs at cellular and molecular levels. Molecular contraction or partial denaturization of collagen involves the application of an energy source, which destabilizes the longitudinal axis of the molecule by cleaving the heat labile bonds of the triple helix. As a result, stress is created to break the intermolecular bonds of the matrix. This is essentially an immediate extra-cellular process, whereas cellular contraction requires a lag period for the migration and multiplication of fibroblasts into the wound as provided by the wound healing sequence. In higher developed animal species, the wound healing response to injury involves an initial inflammatory process that subsequently leads to the deposition of scar tissue. 
         [0010]    The initial inflammatory response consists of the infiltration by white blood cells or leukocytes that dispose of cellular debris. Seventy-two hours later, proliferation of fibroblasts at the injured site occurs. These cells differentiate into contractile myofibroblasts, which are the source of cellular soft tissue contraction. Following cellular contraction, collagen is laid down as a static supporting matrix in the tightened soft tissue structure. The deposition and subsequent remodeling of this nascent scar matrix provides the means to alter the consistency and geometry of soft tissue for aesthetic purposes. 
         [0011]    In light of the preceding discussion, there are a number of dermatological procedures that lend themselves to treatments which deliver thermal energy to the skin and underlying tissue to cause a contraction of collagen, and/or initiate a would healing response. Such procedures include skin remodeling/resurfacing, wrinkle removal, and treatment of the sebaceous glands, hair follicles adipose tissue and spider veins. Currently available technologies that deliver thermal energy to the skin and underlying tissue include Radio Frequency (RF), optical (laser) and other forms of electromagnetic energy. However, these technologies have a number of technical limitations and clinical issues which limit the effectiveness of the treatment and/or preclude treatment altogether. These issues include the following: i) achieving a uniform thermal effect across a large area of tissue, ii) controlling the depth of the thermal effect to target selected tissue and prevent unwanted thermal damage to both target and non-target tissue, iii) reducing adverse tissue effects such as burns, redness blistering, iv) replacing the practice of delivery energy/treatment in a patchwork fashion with a more continuous delivery of treatment (e.g. by a sliding or painting motion), v) improving access to difficult-to-reach areas of the skin surface and vi) reducing procedure time and number of patient visits required to complete treatment. As will be discussed herein the current invention provides an apparatus for solving these and other limitations. 
         [0012]    One of the key shortcomings of currently available RF technology for treating the skin is the edge effect phenomenon. In general, when RF energy is being applied or delivered to tissue through an electrode which is in contact with that tissue, the current patterns concentrate around the edges of the electrode, sharp edges in particular. This effect is generally known as the edge effect. In the case of a circular disc electrode, the effect manifests as a higher current density around the perimeter of that circular disc and a relatively low current density in the center. For a square-shaped electrode there is typically a high current density around the entire perimeter, and an even higher current density at the corners where there is a sharp edge. 
         [0013]    Edge effects cause problems in treating the skin for several reasons. First, they result in a non-uniform thermal effect over the electrode surface. In various treatments of the skin, it is important to have a uniform thermal effect over a relatively large surface area, particularly for dermatologic treatments. Large in this case being on the order of several square millimeters or even several square centimeters. In electrosurgical applications for cutting tissue, there typically is a point type applicator designed with the goal of getting a hot spot at that point for cutting or even coagulating tissue. However, this point design is undesirable for creating a reasonably gentle thermal effect over a large surface area. What is needed is an electrode design to deliver uniform thermal energy to skin and underlying tissue without hot spots. 
         [0014]    A uniform thermal effect is particularly important when cooling is combined with heating in skin/tissue treatment procedure. As is discussed below, a non-uniform thermal pattern makes cooling of the skin difficult and hence the resulting treatment process as well. When heating the skin with RF energy, the tissue at the electrode surface tends to be warmest with a decrease in temperature moving deeper into the tissue. One approach to overcome this thermal gradient and create a thermal effect at a set distance away from the electrode is to cool the layers of skin that are in contact with the electrode. However, cooling of the skin is made difficult if there is a non-uniform heating pattern. If the skin is sufficiently cooled such that there are no burns at the corners of a square or rectangular electrode, or at the perimeter of a circular disc electrode, then there will probably be overcooling in the center and there won&#39;t be any significant thermal effect (i.e. tissue heating) under the center of the electrode. Contrarily, if the cooling effect is decreased to the point where there is a good thermal effect in the center of the electrode, then there probably will not be sufficient cooling to protect tissue in contact with the edges of the electrode. As a result of these limitations, in the typical application of a standard electrode there is usually an area of non-uniform treatment and/or burns on the skin surface. So uniformity of the heating pattern is very important. It is particularly important in applications treating skin where collagen-containing layers are heated to produce a collagen contraction response for tightening of the skin. For this and related applications, if the collagen contraction and resulting skin tightening effect are non-uniform, then a medically undesirable result may occur. 
         [0015]    There is a need for an improved RF handpiece for cosmetic applications. 
       SUMMARY OF THE INVENTION 
       [0016]    Accordingly, an object of the present invention is to provide an RF handpiece which provides a substantially uniform delivery of energy to a target tissue site. 
         [0017]    Another object of the present invention is to provide an RF handpiece which includes at least one RF electrode that is capacitively coupled to a skin surface when at least a portion of the RF electrode is in contact with the skin surface. 
         [0018]    Yet another object of the present invention is to provide an RF handpiece that provides a uniform thermal effect in tissue at a selected depth, while preventing or minimizing thermal damage to a skin surface and other non-target tissue. 
         [0019]    A further object of the present invention is to provide an RF handpiece configured to reduce or eliminate the edge effects and hot spots of RF electrodes applied to skin surfaces. 
         [0020]    Another object of the present invention is to provide an RF handpiece configured to provide an atomizing delivery of a cooling fluidic medium to the RF electrode. 
         [0021]    Still another object of the present invention is to provide an RF handpiece configured to evaporatively cool the back surface of the RF electrode, and conductively cool a skin surface adjacent to a front surface of the RF electrode. 
         [0022]    A further object of the present invention is to provide an RF handpiece configured to controllably deliver a cooling fluidic medium to the back surface of the RF electrode at substantially any orientation of the front surface of the RF electrode relative to a direction of gravity. 
         [0023]    Yet another object of the present invention is to provide an RF handpiece that includes an RF electrode with both conductive and dielectric portions. 
         [0024]    Another object of the present invention is to provide an RF handpiece that includes a force sensor that zeros out gravity effects created by the weight of the electrode assembly of the RF handpiece in any orientation of the front surface of the RF electrode relative to a direction of gravity. 
         [0025]    These and other objects of the present invention are achieved in a handpiece that has a handpiece assembly. The handpiece assembly includes a handpiece housing and a cooling fluidic medium valve member. An electrode assembly is coupled to the handpiece housing. The electrode assembly has a least one RF electrode that is capacitively coupled to a skin surface when at least a portion of the RF electrode is in contact with the skin surface. 
         [0026]    In another embodiment of the present invention a handpiece, a handpiece assembly includes a handpiece housing and a cooling fluidic medium valve member with an inlet and an outlet. An electrode assembly is removeably coupled to the handpiece housing. The electrode assembly has a least one RF electrode with a front surface and a back surface. The RF electrode is capacitively coupled to a skin surface when at least a portion of the RF electrode is in contact with the skin surface. 
         [0027]    In another embodiment of the present invention, a handpiece includes a handpiece assembly with a handpiece housing. An insert is at least partially positionable in the handpiece housing. An RF electrode is coupled to the insert. The RF electrode has a back surface that faces the handpiece housing and an opposing front surface. A cooling fluidic medium dispensing assembly is coupled to the handpiece housing and the insert. 
         [0028]    In another embodiment of the present invention, a handpiece includes a handpiece assembly with a handpiece housing. An insert is detachably coupled to the handpiece housing. The insert includes an RF electrode with a conductive portion and a dielectric. 
         [0029]    In another embodiment of the present invention, a handpiece includes a handpiece assembly with a handpiece housing. An insert is detachably coupled to the handpiece housing. An RF electrode is positioned in the insert. The RF electrode includes a flex circuit. 
         [0030]    In another embodiment of the present invention, a handpiece includes a handpiece assembly with a handpiece housing. An insert is detachably coupled to the handpiece housing. The insert includes a flex circuit and an RF electrode that with a conductive portion and a dielectric. 
         [0031]    In another embodiment, an electrode assembly is adapted to be coupled with a handpiece and powered to treat skin and underlying tissues. A sensor is coupled to the energy delivery device. The sensor may comprise, for example, a force sensor or a thermal sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0032]      FIG. 1  is a cross-sectional view of one embodiment of the handpiece of the present invention. 
           [0033]      FIG. 2  is an exploded view of the  FIG. 1  insert assembly. 
           [0034]      FIG. 3  is a close-up view of one embodiment of an RF electrode of the present invention. 
           [0035]      FIG. 4  is another cross-sectional view of a portion of the handpiece housing from  FIG. 1 . 
           [0036]      FIG. 5  is a cross-sectional view of the insert from  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION  
       [0037]    Referring now to  FIG. 1 , one embodiment of the present invention is a handpiece  10  with a handpiece assembly  12 . Handpiece assembly  12  includes a handpiece housing  14  and a cooling fluidic medium valve member  16 . An electrode assembly  18  is coupled to handpiece housing  14 . Electrode assembly  18  has a least one RF electrode  20  that is capacitively coupled to a skin surface when at least a portion of RF electrode  20  is in contact with the skin surface. Without limiting the scope of the present invention, RF electrode  20  can have a thickness in the range of 0.010 to 1.0 mm. 
         [0038]    Handpiece  10  provides a more uniform thermal effect in tissue at a selected depth, while preventing or minimizing thermal damage to the skin surface and other non-target tissue. Handpiece  10  is coupled to an RF generator. RF electrode  20  can be operated either in mono-polar or bi-polar modes. Handpiece  10  is configured to reduce, or preferably eliminate edge effects and hot spots. The result is an improved aesthetic result/clinical outcome with an elimination/reduction in adverse effects and healing time. 
         [0039]    A fluid delivery member  22  is coupled to cooling fluidic medium valve member  16 . Fluid delivery member  22  and cooling fluidic medium valve member  16  collectively form a cooling fluidic medium dispensing assembly. Fluid delivery member  16  is configured to provide an atomizing delivery of a cooling fluidic medium to RF electrode  20 . The atomizing delivery is a mist or fine spray. A phase transition, from liquid to gas, of the cooling fluidic medium occurs when it hits the surface of RF electrode  20 . The transition from liquid to gas creates the cooling. If the transition before the cooling fluidic medium hits RF electrode  20  the cooling of RF electrode  20  will not be as effective. 
         [0040]    In one embodiment, the cooling fluidic medium is a cryogenic spray, commercially available from Honeywell, Morristown, N.J. A specific example of a suitable cryogenic spray is R134A 2 , available from Refron, Inc., 38-18 33 rd  St., Long Island City, N.Y. 11101. The use of a cryogenic cooling fluidic medium provides the capability to use a number of different types of algorithms for skin treatment. For example, the cryogenic cooling fluidic medium can be applied milliseconds before and after the delivery of RF energy to the desired tissue. This is achieved with the use of cooling fluidic medium valve member  16  coupled to a cryogen supply, including but not limited to a compressed gas canister. In various embodiments, cooling fluidic medium valve member  16  can be coupled to a computer control system and/or manually controlled by the physician by means of a foot switch or similar device. 
         [0041]    A key advantage of providing a spray, or atomization, of cryogenic cooling fluidic medium is the availability to implement rapid on and off control. Cryogenic cooling fluidic medium allows more precise temporal control of the cooling process. This is because cooling only occurs when the refrigerant is sprayed and is in an evaporative state, the latter being a very fast short-lived event. Thus, cooling ceases rapidly after the cryogenic cooling fluidic medium is stopped. The overall effect is to confer very precise time on-off control of cryogenic cooling fluidic medium. 
         [0042]    Referring now to  FIG. 2 , fluid delivery member  22  can be positioned in handpiece housing  14  or electrode assembly  18 . Fluid delivery member  22  is configured to controllably deliver a cooling fluidic medium to a back surface  24  of RF electrode  20  and maintain back surface  24  at a desired temperature. The cooling fluidic medium evaporatively cools RF electrode  20  and maintains a substantially uniform temperature of front surface  26  of RF electrode  20 . Front surface  26  can be sufficiently flexible and conformable to the skin, but still have sufficient strength and/or structure to provide good thermal coupling when pressed against the skin surface. 
         [0043]    RF electrode  20  then conductively cools a skin surface that is adjacent to a front surface  26  of RF electrode  20 . Suitable fluidic media include a variety of refrigerants such as R134A and freon. Fluid delivery member  22  is configured to controllably deliver the cooling fluidic medium to back surface  24  at substantially any orientation of front surface  26  relative to a direction of gravity. A geometry and positioning of fluid delivery member  22  are selected to provide a substantially uniform distribution of cooling fluidic medium on back surface  24 . The delivery of the cooling fluidic medium can be by spray of droplets or fine mist, flooding back surface  24 , and the like. Cooling occurs at the interface of the cooling fluidic medium with atmosphere, which is where evaporation occurs. If there is a thick layer of fluid on back surface  24  the heat removed from the treated skin will need to pass through the thick layer of cooling fluidic medium, increasing thermal resistance. To maximize cooling rates, it is desirable to apply a very thin layer of cooling fluidic medium. If RF electrode  20  is not horizontal, and if there is a thick layer of cooling fluidic medium, or if there are large drops of cooling fluidic medium on back surface  24 , the cooling fluidic medium can run down the surface of RF electrode  20  and pool at one edge or corner, causing uneven cooling. Therefore, it is desirable to apply a thin layer of cooling fluidic medium with a fine spray. 
         [0044]    In various embodiments, RF electrode  20 , as illustrated in  FIG. 3 , has a conductive portion  28  and a dielectric portion  30 . Conductive portion  28  can be a metal including but not limited to copper, gold, silver, aluminum and the like. Dielectric portion  30  can be made of a variety of different materials including but not limited to polyimide, and the like. Other dielectric materials include but are not limited to silicon, sapphire, diamond, zirconium-toughened alumina (ZTA), alumina and the like. Dielectric portion  30  can be positioned around at least a portion, or the entirety of a periphery of conductive portion  28 . Suitable materials for a dielectric portion  30  include, but are not limited to, Teflon® and the like, silicon nitride, polysilanes, polysilazanes, polyimides, Kapton and other polymers, antenna dielectrics and other dielectric materials well known in the art. In another embodiment, RF electrode  20  is made of a composite material, including but not limited to gold-plated copper, copper-polyimide, silicon/silicon-nitride and the like. 
         [0045]    Dielectric portion  30  creates an increased impedance to the flow of electrical current through RF electrode  20 . This increased impedance causes current to travel a path straight down through conductive portion  28  to the skin surface. Electric field edge effects, caused by a concentration of current flowing out of the edges of RF electrode  20 , are reduced. 
         [0046]    Dielectric portion  30  produces a more uniform impedance through RF electrode  20  and causes a more uniform current to flow through conductive portion  28 . The resulting effect minimizes or even eliminates, edge effects around the edges of RF electrode  20 . 
         [0047]    In one embodiment, conductive portion  28  adheres to dielectric portion  30  which can be substrate with a thickness, by way of example and without limitation, of about 0.001″. This embodiment is similar to a standard flex circuit board material commercially available in the electronics industry. In this embodiment, dielectric portion  30  is in contact with the tissue, the skin, and conductive portion  28  is separated from the skin. The thickness of the dielectric portion  30  can be decreased by growing conductive portion  28  on dielectric portion  30  using a variety of techniques, including but not limited to, sputtering, electro deposition, chemical vapor deposition, plasma deposition and other deposition techniques known in the art. Additionally, these same processes can be used to deposit dielectric portion  30  onto conductive portion  28 . In one embodiment dielectric portion  30  is an oxide layer which can be grown on conductive portion  28 . An oxide layer has a low thermal resistance and improves the cooling efficiency of the skin compared with many other dielectrics such as polymers. 
         [0048]    Fluid delivery member  22  has an inlet  32  and an outlet  34 . Outlet  34  can have a smaller cross-sectional area than a cross-sectional area of inlet  32 . In one embodiment, fluid delivery member  22  is a nozzle  36 . 
         [0049]    Cooling fluidic medium valve member  16  can be configured to provide a pulsed delivery of the cooling fluidic medium. Pulsing the delivery of cooling fluidic medium is a simple way to control the rate of cooling fluidic medium application. In one embodiment, cooling fluidic medium valve member  16  is a solenoid valve. An example of a suitable solenoid valve is a solenoid pinch valve manufactured by the N-Research Corporation, West Caldwell, N.J. If the fluid is pressurized, then opening of the valve results in fluid flow. If the fluid is maintained at a constant pressure, then the flow rate is constant and a simple open/close solenoid valve can be used, the effective flow rate being determined by the pulse duty cycle. A higher duty cycle, close to 100% increases cooling, while a lower duty cycle, closer to 0%, reduces cooling. The duty cycle can be achieved by turning on the valve for a short duration of time at a set frequency. The duration of the open time can be 1 to 50 milliseconds or longer. The frequency of pulsing can be 1 to 50 Hz or faster. 
         [0050]    Alternatively, cooling fluidic medium flow rate can be controlled by a metering valve or controllable-rate pump such as a peristaltic pump. One advantage of pulsing is that it is easy to control using simple electronics and control algorithms. 
         [0051]    Electrode assembly  18  is sufficiently sealed so that the cooling fluidic medium does not leak from back surface  24  onto a skin surface in contact with a front surface of RF electrode  20 . This helps provide an even energy delivery through the skin surface. In one embodiment, electrode assembly  18 , and more specifically RF electrode  20 , has a geometry that creates a reservoir at back surface  24  to hold and gather cooling fluidic medium that has collected at back surface  24 . Back surface  24  can be formed with “hospital corners” to create this reservoir. Optionally, electrode assembly  18  includes a vent  38  that permits vaporized cooling fluidic medium to escape from electrode assembly  18 . This reduces the chance of cooling fluidic medium collecting at back surface  24 . This can occur when cooling fluidic medium is delivered to back surface  24  in vapor form and then, following cooling of back surface  24 , the vapor condenses to a liquid. 
         [0052]    Vent  38  prevents pressure from building up in electrode assembly  18 . Vent  38  can be a pressure relief valve that is vented to the atmosphere or a vent line. When the cooling fluidic medium comes into contact with RF electrode  20  and evaporates, the resulting gas pressurizes the inside of electrode assembly  18 . This can cause RF electrode  20  to partially inflate and bow out from front surface  26 . The inflated RF electrode  20  can enhance the thermal contact with the skin and also result in some degree of conformance of RF electrode  20  to the skin surface. An electronic controller can be provided. The electronic controller sends a signal to open vent  38  when a programmed pressure has been reached. 
         [0053]    Various leads  40  are coupled to RF electrode  20 . One or more thermal sensors  42  are coupled to RF electrode. Suitable thermal sensors  42  include but are not limited to thermocouples, thermistors, infrared photo-emitters and a thermally sensitive diode. In one embodiment, a thermal sensor  42  is positioned at each corner of RF electrode  20 . A sufficient number of thermal sensors  42  are provided in order to acquire sufficient thermal data of the skin surface. Thermal sensors  42  are electrically isolated from RF electrode  20 . 
         [0054]    Thermal sensors  42  measure temperature and can provide feedback for monitoring temperature of RF electrode  20  and/or the tissue during treatment. Thermal sensors  42  can be thermistors, thermocouples, thermally sensitive diodes, capacitors, inductors or other devices for measuring temperature. Preferably, thermal sensors  42  provide electronic feedback to a microprocessor of the RF generator coupled to RF electrode  20  in order to facilitate control of the treatment. 
         [0055]    The measurements from thermal sensors  42  can be used to help control the rate of application of cooling fluidic medium. For example, the cooling control algorithm can be used to apply cooling fluidic medium to RF electrode  20  at a high flow rate until the temperature fell below a target temperature, and then slow down or stop. A PID, or proportional-integral-differential, algorithm can be used to precisely control RF electrode  20  temperature to a predetermined value. 
         [0056]    Thermal sensors  42  can be positioned placed on back surface  24  of RF electrode  20  away from the tissue. This configuration is preferable ideal for controlling the temperature of the RF electrode  20 . Alternatively, thermal sensors  42  can be positioned on front surface  26  of RF electrode  10  in direct contact with the tissue. This embodiment can be more suitable for monitoring tissue temperature. Algorithms are utilized with thermal sensors  42  to calculate a temperature profile of the treated tissue. Thermal sensors  42  can be used to develop a temperature profile of the skin which is then used for process control purposes to assure that the proper amounts of heating and cooling are delivered to achieve a desired elevated deep tissue temperature while maintaining skin tissue layers below a threshold temperature and avoid thermal injury. The physician can use the measured temperature profile to assure that he stays within the boundary of an ideal/average profile for a given type of treatment. Thermal sensors  42  can be used for additional purposes. When the temperature of thermal sensors  42  is monitored it is possible to detect when RF electrode  20  is in contact with the skin surface. This can be achieved by detecting a direct change in temperature when skin contact is made or examining the rate of change of temperature which is affected by contact with the skin. Similarly, if there is more than one thermal sensor  42 , the thermal sensors  42  can be used to detect whether a portion of RF electrode  20  is lifted or out of contact with skin. This can be important because the current density (amperes per unit area) delivered to the skin can vary if the contact area changes. In particular, if part of the surface of RF electrode  20  is not in contact with the skin, the resulting current density is higher than expected. 
         [0057]    Referring now to  FIG. 4 , a force sensor  44  is also coupled to electrode assembly  18 . Force sensor  44  detects an amount of force applied by electrode assembly  18 , via the physician, against an applied skin surface. Force sensor  44  zeros out gravity effects of the weight of electrode assembly  18  in any orientation of front surface  26  of RF electrode  20  relative to a direction of gravity. Additionally, force sensor  44  provides an indication when RF electrode  20  is in contact with a skin surface. Force sensor  44  also provides a signal indicating that a force applied by RF electrode  20  to a contacted skin surface is, (i) below a minimum threshold or (ii) above a maximum threshold. 
         [0058]    An activation button  46  is used in conjunction with the force sensor. Just prior to activating RF electrode  20 , the physician holds handpiece  10  in position just off the surface of the skin. The orientation of handpiece  10  can be any angle relative to the angle of gravity. To arm handpiece  10 , the physician can press activation button  46  which tares force sensor  44 , by setting it to read zero. This cancels the force due to gravity in that particular treatment orientation. This method allows consistent force application of RF electrode  20  to the skin surface regardless of the angle of handpiece  10  relative to the direction of gravity. 
         [0059]    RF electrode  20  can be a flex circuit, which can include trace components. Additionally, thermal sensor  42  and force sensor  44  can be part of the flex circuit. Further, the flex circuit can include a dielectric that forms a part of RF electrode  20 . 
         [0060]    Electrode assembly  18  can be moveable positioned within handpiece housing  12 . In one embodiment, electrode assembly  18  is slideably moveable along a longitudinal axis of handpiece housing  12 . Electrode assembly  18  can be rotatably mounted in handpiece housing  12 . Additionally, RF electrode  20  can be rotatably positioned in electrode assembly  18 . Electrode assembly  18  can be removably coupled to handpiece housing  12  as a disposable or non-disposable insert  52 , see  FIG. 5 . For purposes of this disclosure, electrode assembly  18  is the same as insert  52 . Once movably mounted to handpiece housing  12 , insert  52  can be coupled to handpiece housing  12  via force sensor  44 . Force sensor  44  can be of the type that is capable of measuring both compressive and tensile forces. In other embodiments, force sensor  44  only measures compressive forces, or only measures tensile forces. 
         [0061]    Insert  52  can be spring-loaded with a spring  48 . In one embodiment, spring  48  biases RF electrode  20  in a direction toward handpiece housing  12 . This pre-loads force sensor  44  and keeps insert  52  pressed against force sensor  44 . The pre-load force is tared when activation button  46  is pressed just prior to application of RF electrode  20  to the skin surface. 
         [0062]    A shroud  50  is optionally coupled to handpiece  10 . Shroud  50  serves to keep the user from touching insert  52  during use which can cause erroneous force readings. 
         [0063]    A non-volatile memory  54  can be included with insert  52 . Additionally, non-volatile memory can be included with handpiece housing  12 . Non-volatile memory  54  can be an EPROM and the like. Additionally, a second non-volatile memory  56  can be included in handpiece housing  12  for purposes of storing handpiece  10  information such as but not limited to, handpiece model number or version, handpiece software version, number of RF applications that handpiece  10  has delivered, expiration date and manufacture date. Handpiece housing  12  can also contain a microprocessor  58  for purposes of acquiring and analyzing data from various sensors on handpiece housing  12  or insert  52  including but not limited to thermal sensors  42 , force sensors  44 , fluid pressure gauges, switches, buttons and the like. Microprocessor  58  can also control components on handpiece  10  including but not limited to lights, LEDs, valves, pumps or other electronic components. Microprocessor  58  can also communicate data to a microprocessor of the RF generator. 
         [0064]    Non-volatile memory  54  can store a variety of data that can facilitate control and operation of handpiece  10  and its associated system including but not limited to, (i) controlling the amount of current delivered by RF electrode  20 , (ii) controlling the duty cycle of the fluid delivery member  22 , (iii) controlling the energy delivery duration time of the RF electrode  20 , (iv) controlling the temperature of RF electrode  20  relative to a target temperature, (v) providing a maximum number of firings of RF electrode  20 , (vi) providing a maximum allowed voltage that is deliverable by RF electrode  20 , (vii) providing a history of RF electrode  20  use, (viii) providing a controllable duty cycle to fluid delivery member  22  for the delivery of the cooling fluidic medium to back surface  24  of RF electrode  20 , (ix) providing a controllable delivery rate of cooling fluidic medium delivered from fluid delivery member  22  to back surface  24 , and the like. 
         [0065]    Handpiece  10  can be used to deliver thermal energy to modify tissue including, but not limited to, collagen containing tissue, in the epidermal, dermal and subcutaneous tissue layers, including adipose tissue. The modification of the tissue includes modifying a physical feature of the tissue, a structure of the tissue or a physical property of the tissue. The modification can be achieved by delivering sufficient energy to cause collagen shrinkage, and/or a wound healing response including the deposition of new or nascent collagen. 
         [0066]    Handpiece  10  can be utilized for performing a number of treatments of the skin and underlying tissue including but not limited to, (i) dermal remodeling and tightening, (ii) wrinkle reduction, (iii) elastosis reduction, (iv) sebaceous gland removal/deactivation, (v) hair follicle removal, (vi) adipose tissue remodeling/removal, (vii) spider vein removal, and the like. 
         [0067]    In various embodiments, handpiece  10  can be utilized in a variety of treatment processes, including but not limited to, (i) pre-cooling, before the delivery of energy to the tissue has begun, (ii) an on phase or energy delivery phase in conjunction with cooling and (iii) post cooling after the delivery of energy to tissue has stopped. 
         [0068]    Handpiece  10  can be used to pre-cool the surface layers of the target tissue so that when RF electrode  20  is in contact with the tissue, or prior to turning on the RF energy source, the superficial layers of the target tissue are already cooled. When RF energy source is turned on or delivery of RF to the tissue otherwise begins, resulting in heating of the tissues, the tissue that has been cooled is protected from thermal effects including thermal damage. The tissue that has not been cooled will warm up to therapeutic temperatures resulting in the desired therapeutic effect. 
         [0069]    Pre-cooling gives time for the thermal effects of cooling to propagate down into the tissue. More specifically, pre-cooling allows the achievement of a desired tissue depth thermal profile, with a minimum desired temperature being achieved at a selectable depth. The amount or duration of pre-cooling can be used to select the depth of the protected zone of untreated tissue. Longer durations of pre-cooling produce a deeper protected zone and hence a deeper level in tissue for the start of the treatment zone. The opposite is true for shorter periods of pre-cooling. The temperature of front surface  26  of RF electrode  20  also affects the temperature profile. The colder the temperature of front surface  26 , the faster and deeper the cooling, and vice verse. 
         [0070]    Post-cooling can be important because it prevents and/or reduces heat delivered to the deeper layers from conducting upward and heating the more superficial layers possibly to therapeutic or damaging temperature range even though external energy delivery to the tissue has ceased. In order to prevent this and related thermal phenomena, it can be desirable to maintain cooling of the treatment surface for a period of time after application of the RF energy has ceased. In various embodiments, varying amounts of post cooling can be combined with real-time cooling and/or pre-cooling. 
         [0071]    In various embodiments, handpiece  10  can be used in a varied number of pulse on-off type cooling sequences and algorithms may be employed. In one embodiment, the treatment algorithm provides for pre-cooling of the tissue by starting a spray of cryogenic cooling fluidic medium, followed by a short pulse of RF energy into the tissue. In this embodiment, the spray of cryogenic cooling fluidic medium continues while the RF energy is delivered, and is stopping shortly thereafter, e.g. on the order of milliseconds. This or another treatment sequence can be repeated again. Thus in various embodiments, the treatment sequence can include a pulsed sequence of cooling on, heat, cooling off, cooling on, heat, cool off, and with cooling and heating durations on orders of tens of milliseconds. In these embodiments, every time the surface of the tissue of the skin is cooled, heat is removed from the skin surface. Cryogenic cooling fluidic medium spray duration, and intervals between sprays, can be in the tens of milliseconds ranges, which allows surface cooling while still delivering the desired thermal effect into the deeper target tissue. 
         [0072]    In various embodiments, the target tissue zone for therapy, also called therapeutic zone or thermal effect zone, can be at a tissue depth from approximately 100 μm beneath the surface of the skin down to as deep as 10 millimeters, depending upon the type of treatment. For treatments involving collagen contraction, it can be desirable to cool both the epidermis and the superficial layers of the dermis of the skin that lies beneath the epidermis, to a cooled depth range between 100 μm and two millimeters. Different treatment algorithms can incorporate different amounts of pre-cooling, heating and post cooling phases in order to produce a desired tissue effect at a desired depth. 
         [0073]    Various duty cycles, on and off times, of cooling and heating are utilized depending on the type of treatment. The cooling and heating duty cycles can be controlled and dynamically varied by an electronic control system known in the art. Specifically the control system can be used to control cooling fluidic medium valve member  16  and the RF power source. 
         [0074]    The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. It is intended that the scope of the invention be defined by the following claims and their equivalents.