Abstract:
A dermatological treatment method includes directing laser energy having a wavelength of 2.79 μm onto skin. According to disclosed methods, the energy can function to ablate a first portion of epidermal tissue, coagulate an underlying second portion of epidermal tissue, and promote collagen formation in tissue of the underlying dermis. In an exemplary treatment apparatus, a laser using a YSGG gain medium is mounted in a handpiece. The handpiece may include a two-axis scanner to allow for uniform scanning of the energy over the tissue surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/681,700, filed Mar. 2, 2007, which claims the benefit of U.S. Provisional Application No. 60/778,896, filed Mar. 3, 2006, and U.S. Provisional Application No. 60/888,061, filed Feb. 2, 2007, all which are incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The subject invention relates to a dermatological treatment method and apparatus using laser energy for resurfacing and/or rejuvenating skin. 
       BACKGROUND 
       [0003]    Ablative skin resurfacing has been performed using carbon dioxide lasers emitting radiation at 10.6 microns. (See for example, U.S. Pat. No. 5,335,242). While these lasers could provide good results, recovery times were long. The long recovery times have been attributed to the significant depth of thermal damage associated with this longer wavelength radiation. 
         [0004]    In an effort to reduce recovery time, Er:YAG lasers, operating at an output wavelength of 2.94 μm, have been used to ablate tissue. The very high water absorption associated with the 2.94 μm wavelength decreased thermal damage and decreased recovery times, although a reduction in efficacy was sometimes observed. Generally, this reduction in efficacy is thought to be a consequence of a reduced thermal damage profile in skin, post-ablation. An example of the use of Er:YAG lasers for tissue treatment can be found in U.S. Pat. No. 6,395,000 which utilizes high repetition rate pulses (greater than 100 hertz). Another approach is to treat the tissue with micropulses within a relatively long pulse envelope. See U.S. Patent Applications 2001/0016732 and 2004/0133190. See also U.S. Pat. No. 6,193,711. All of these patent documents are incorporated by reference. The approach described herein is intended to both increase efficacy and reduce recovery time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1A  is a schematic block diagram illustrating a dermatological treatment apparatus of the type disclosed herein. 
           [0006]      FIG. 1B  is a perspective view of a handpiece of the apparatus of  FIG. 1A . 
           [0007]      FIG. 2  is an optical schematic illustrating optical components within the handpiece of  FIG. 1A . 
           [0008]      FIG. 3  is a schematic block diagram illustrating basic control electronics and associated components of the treatments apparatus of  FIG. 1A . 
           [0009]      FIG. 4  is a high level block diagram schematically illustrating components of the X, Y scanner assembly of the treatment apparatus of  FIG. 1A . 
           [0010]      FIG. 5  schematically illustrates X and Y scanning movement of the mirror mount supporting the mirror shown in the optical schematic of  FIG. 2 . 
           [0011]      FIG. 6A  is a rear perspective view of the X, Y scanning assembly of the treatment apparatus of  FIG. 1A . 
           [0012]      FIG. 6B  is a front perspective view of the X, Y scanning assembly of  FIG. 6A . 
           [0013]      FIG. 7A  is a cross-sectional side elevation view of the scanning assembly of  FIG. 6A . 
           [0014]      FIG. 7B  is a cross-sectional side elevation view of the scanning assembly of  FIG. 6A . 
           [0015]      FIG. 8  is an exemplary control panel for the console of the treatment apparatus of  FIG. 1A . 
           [0016]      FIG. 9  schematically illustrates the coagulative and ablative effects of the treatment apparatus of  FIG. 1A  on skin tissue. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Referring to  FIG. 1A , in an exemplary embodiment of a treatment apparatus  10  includes a handpiece  12  coupled to a treatment console  14  housing a power supply  16 . Power supply  16  may be a high voltage power supply of the type provided by Cutera, Inc. (Brisbane Calif.) in consoles for use with its Nd:YAG laser product line, and in particular any of the power supplies used with the CoolGlide family of lasers (CoolGlide CV, CoolGlide Excel, and CoolGlide Vantage), or with the CoolGlide Xeo, Xeo SA and Solera Opus consoles. 
         [0018]    Laser source  18  is provided with an Er:YSGG or a Cr,Er:YSGG gain medium. This gain medium has a primary output at 2.79 μm which has a depth of coagulation in skin that falls between the depths associated with CO 2  lasers (wavelength=10.6 μm) and Er:YAG lasers (wavelength=2.94 μm). The characteristic depth of coagulation in skin after laser ablation is 40 μm for 2.94 μm light, 75 μm for 2.79 μm light and 125 μm for 10.60 μm light (Kaufmann et al J Dermatol Surg Oncol 1994; 20:112-118). As discussed in greater detail below, use of a primary wavelength of 2.79 μm ablates to remove a precise amount of tissue, while also coagulating to create a natural dressing and to promote new collagen formation. 
         [0019]    A laser based on an Er:YSGG or Cr,Er:YSGG gain medium offers two other advantages. First, it is more efficient than Er:YAG. Second, the upper level lifetime is ten times longer, allowing low threshold operation allowing longer pulse durations relative to Er:YAG lasers at similar energy levels. Longer pulse durations may be exploited to produce different post-ablation thermal damage profiles in treated skin. In exemplary modes of operation, pulse durations on the order of 0.2 to 25 ms and preferably 0.5 to 10 ms are contemplated, with spot sizes on the order of between 1 and 10 mm, repetition rates ranging from single shots to 20 Hz, and preferred fluences within the range of 0.25 and 20 J/cm 2 . 
         [0020]    As shown in  FIG. 1A , in the exemplary embodiment, laser source  18  is integrated into the handpiece  12 . Integrating the laser components (e.g. monolithic laser rod resonator, excitation flash lamp, cooling features) and associated power detectors, optical components etc. into the handpiece avoids the problems of delivering the light from the console to the tissue. Thus, light can be delivered directly to the target tissue directly from the handpiece without having to pass through an articulated arm or fiber optic element. As discussed in greater detail below, the handpiece preferably includes a two-axis scanner  20  operable to uniformly scan the beam of light across the tissue surface to produce a two-dimensional treatment pattern on the skin. 
         [0021]    The handpiece  12  is illustrated in  FIG. 1B . Handpiece includes an umbilical cable  13  that houses electrical cables to provide power from the power supply to drive the flash lamp and scanner motors, to provide a signal path for detector signals, encoders, serial communication, a memory device that identifies the handpiece, and a supply and return water line (to remove heat generated by the flash lamp). The proximal end of the umbilical cable is semi-permanently attached to the laser system console and the distal end is permanently attached to the body of the delivery hand piece. An activation switch (not shown) such as a foot pedal is provided for use in initiating and terminating treatment. 
         [0022]      FIG. 2  schematically illustrates the optical components within the handpiece. As shown, the handpiece includes a laser resonator cavity  22  containing the excitation flash lamp, laser crystal and associated mirrors. A portion of the beam  100  exiting the laser cavity  100  is diverted to a pair of photodetectors  24   a,    24   b  by a pair of independent beam splitters  26   a,    26   b  for use in monitoring output power. An aiming diode  28  generates an aiming beam of light  102 . Beam combining mirror  30  combines the beam  100  from the laser  18  with the aiming beam  102  so that the aiming beam is parallel and coincident with the treatment beam. During use, the aiming beam shows the user where the energy from the laser is impinging on the skin. 
         [0023]    A safety shutter  32  is positioned between the laser cavity  22  and the combining mirror  30 . The shutter has open and closed positions. When the shutter is in the open position the beam  100  passes to the next optical component, which in  FIG. 2  is the combining mirror  30 . In the closed position, the beam  100  is deflected into a beam dump (not shown). 
         [0024]    When not directed to the beam dump, the beam  100  impinges onto X-Y scanning mirror  34  which is driven by stepper motors to provide X-Y movement of the beam  100  on skin S. A protective window  36  on the handpiece (see also  FIG. 1B ) protects the internal optical components. A distance guide  38 , which may be stainless steel, sets the distance between the handpiece  12  and the target treatment site. During use, the distance guide is placed in direct contact with the patient&#39;s skin. 
         [0025]    Control electronics are schematically illustrated in  FIG. 3 . Independent signals from photodetectors  24   a,    24   b  are received by microcontroller  40 , which uses the input to monitor and regulate laser power. The photodetectors utilize detector circuits that are independent from each other and that use no shared components. This ensures that no single component failure lead to generation of inaccurate readings by both detectors. This avoids delivery of improper levels laser treatment energy to the patient. 
         [0026]    Microcontroller  40  additionally provides drive signals to the stepper motors of the X, Y scanner  20 . Encoders associated with X and Y direction stepper motors provide feedback for use by the microcontroller in identifying the rotational positions of the stepper motor shafts. 
         [0027]    As discussed, safety shutter  32  is positioned to terminate delivery of the treatment beam to the patient S. An encoder attached to the shaft of the shutter motor detects the position of the safety shutter. The microcontroller  40  monitors the position of the safety shutter  32  and in the event of a discrepancy can terminate laser exposure by closing the safety shutter. Others ways of terminating exposure include disabling the high voltage power supply to prevent charging of the main charging capacitor or disabling the discharge of the main charging capacitor (thus preventing the firing of the flash lamp). 
         [0028]    Details of the X, Y scanner assembly  20  will next be discussed in connection with  FIGS. 4-7B . In general, the X, Y scanner  20  is operable to move the scanning mirror  34  ( FIG. 2 ) in two orthogonal directions to produce a pattern of treated regions on the skin. 
         [0029]    Referring to  FIG. 4 , the scanner  20  includes an x-motion scanning unit  60  for scanning the light across the tissue surface in a first direction (arbitrarily labeled the “x” direction), and a y-motion scanning unit  58  for moving the light in a second direction that is preferably orthogonal to the x-direction. Although various scanner configurations may be used for this purpose, one suitable scanner uses a pair of stepper motors operable to move a single mirror relative to two axes. This scanner is differentiated from prior scanners in part for its single moving mirror design, use of stepper motors for precise movement and miniature size. 
         [0030]      FIG. 5  shows a side view of scanning mirror  34  mounted on a rectangular mirror mount  46 . Mount  46  is attached to the face of mirror  34  that is opposite to the reflective surface  48  used by the mirror to reflect laser light onto tissue. This figure schematically illustrates general movement of the mirror and mount during scanning. One direction of movement, referred to here as y-direction movement, involves using a first stepper motor to pivot the mount in a forward and backward direction as indicated by arrows “y”. The second form of movement, referred to here as the x-direction movement, involves using a second stepper motor to pivot the mount laterally as indicated by arrows “x”. 
         [0031]    Components of the scanner  20  are shown in  FIGS. 6A and 6B . Scanner includes a base  50  fixed within the handpiece. Base  50  is a u-shaped piece defining an opening  52 . A yoke  54  is mounted within the opening  52 . Yoke  54  is mounted to the base by pins  56  and is pivotable about the pins to produce y-direction movement of the mirror. Mirror mount  46 , which carries mirror  34 , is coupled to the yoke  54 . 
         [0032]    Y-movement scanning unit  58  is mounted to the base  50 . X-movement scanning unit  60  is mounted to the yoke  54 . 
         [0033]    In general, the y-movement scanning unit  58  has components that abut the yoke  54  to produce forward/backward pivoting of yoke  54  about pins  56 , causing corresponding movement of mount  46  and mirror  34 . See the arrows marked “y”. The x-movement scanning unit pivots the mount  46  back and forth as indicated by arrows “x” to produce side to side movement of the mirror  34 . 
         [0034]    Details of the Y-movement scanning unit  58  will be described with reference to  FIGS. 7A through 7B . The unit  58  includes a stepper motor  62  that produces rotation of shaft  64 . A cam  66  having a central mount  68  is coupled to the shaft  64 . Cam  66  includes a cam bearing  70  and a spring saddle  72 . Cam bearing  70  is positioned in contact with a cam follower bearing  74  ( FIGS. 6A and 7B ) on the yoke  54 . 
         [0035]    The cam  66  and shaft  64  are coupled such that the mount  68  is laterally offset from the shaft  64 . Thus, activation of the motor to rotate the shaft  64  produces eccentric rotation of the cam. A useful way to visualize the movement of the cam is to picture an automobile wheel being rotated about an axel that is laterally offset from the center of the wheel. The eccentric movement of the cam  66  results in cyclic movement of the cam bearing  70  towards and away from the cam follower bearing  74  with which the cam bearing  70  is in contact. As a result, the yoke  54  (as well as all components carried by the yoke) pivots back and forth about the pins  56 , moving the mirror  34  as indicated by arrows “y” in  FIGS. 6A and 7A . Spring saddle  72  aids in maintaining contact between the cam follower bearing  74  and the cam bearing  70  throughout scanning. 
         [0036]    X-axis scanning unit  60  includes a stepper motor  76  carried by the yoke  54 . Stepper motor  76  includes a shaft  78  coupled to the mirror mount  46 . Activation of the motor  76  pivots the mirror  34  side to side relative to the axis of the shaft  78 . 
         [0037]    Each of the stepper motors  62 ,  76  is preferably provided with an anti-backlash spring  86   a,    86   b  coupled to its shaft, to prevent backlash of the shaft when the polarity of the input to the motor is reversed. 
         [0038]    Referring to  FIG. 8 , the console may include a user interface  80  allowing a user to select one or more treatment parameters. For example, a user might have the option to scroll through and select from a menu of available treatment patterns using pattern select keys  82 . Similarly, the degree by which spots in the treatment pattern overlap or are spaced apart may be selected using overlap/spacing keys  84 . A selected pattern/spacing may produce distinct spaced-apart treatment spots, or overlapped spots, or a continuous “painting” of the skin surface. Other input keys may be used to select pulse width, fluence, pulse duration etc. 
         [0039]    In an exemplary embodiment, operational and treatment parameters might, but are not limited to, the following: 
         [0040]    Wavelength: 2790 nm 
         [0041]    Output power: up to 20 W 
         [0042]    Pulse Energy: Up to 1 J per pulse 
         [0043]    Pulse Duration: 100-600 μsec 
         [0044]    Repetition Rate: Up to 20 Hz 
         [0045]    Spot Size: Approx 5 mm 
         [0046]    Maximum Pattern Size: 3 cm×3 cm 
         [0047]    Treatment fluence range approx 2-5 J/cm 2    
         [0048]    Ablation depth: 20-50 μm 
         [0049]    Subsequent damage (e.g. coagulation depth): additional 30-50 μm beyond the ablation depth. 
         [0050]    During use of the disclosed treatment apparatus, the user selects the appropriate treatment parameters. Next, the handpiece  12  ( FIG. 2 ) is positioned such that the distance guide  38  is in contact with the skin of a patient. With the distance guide in contact with the skin, the laser is activated such as by depressing a footswitch. The user maintains the handpiece position while the scanner steps the treatment beam in the X and Y directions as discussed to create the desired treatment pattern. 
         [0051]    As illustrated in  FIG. 9 , skin treatment using the disclosed laser operating at a wavelength of 2.79 μm allows three effects to be achieved. First, application of the treatment beam ablates approximately 20-50 μm, and preferably approximately 30-50 μm, of the epidermis (region A in  FIG. 9 ) at a temperature in the range of approximately greater than 90° C., and more preferably greater than approximately 100° C. Residual heat (in the range of approximately 70-90° C. and preferably approximately 80° C.) coagulates an additional 30-50 μ of the epidermis (region B), creating a natural dressing for the skin. This natural dressing peels from the skin in approximately 3-5 days. The residual heat raises the temperature of a portion of the dermis (region C) to a temperature in the range of approximately 45-65° C. (and preferably approximately 55° C.), which promotes generation of new collagen within the dermis. 
         [0052]    The disclosed apparatus and associated methods have been described in connection with resurfacing and/or rejuvenating skin for treatment of dermatological conditions such as improvement of facial texture by eliminating fine lines, wrinkles, and/or scars, or for eliminating discoloration caused by photo damage. However, the method and apparatus may also be used to treat for other applications and/or to treat other biological tissue. 
         [0053]    While various embodiments have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention. This is especially true in light of technology and terms within the relevant art(s) that may be later developed. Additionally, it is contemplated that the features of the various disclosed embodiments may be combined in various ways to produce numerous additional embodiments. Thus, the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. 
         [0054]    Any and all patents, patent applications and printed publications referred to above, including those relied upon for purposes of priority, are incorporated by reference.