Abstract:
The current method and apparatus employs ultrasound beams to precisely monitor in real time the temperature of a specific segment of tissue being treated. Additionally, the current method and apparatus also provides ultrasound thermo-control of aesthetic skin treatment sessions. Such sessions may include one or more aesthetic skin tissue treatments such as sub-dermal fat cells breakdown, lessening of the amount of sub-dermal fat, tightening of loose skin, tightening and firming of body surfaces, reduction of wrinkles in the skin and collagen remodeling.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is being filed under 35 U.S.C. 371 and claims the benefit of the filing date of United States provisional application for patent that was filed on Oct. 6, 2009 and assigned Ser. No. 61/248,997 by being a national stage filing of International Application Number PCT/IL2010/000751 filed on Sep. 15, 2010, each of which are incorporated herein by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The method and apparatus relate to the field of aesthetic body treatments and more specifically to a method and apparatus for precise real time ultrasound monitoring of aesthetic treatments applied to skin. 
       BACKGROUND 
       [0003]    Aesthetic treatment devices are operative to effect treatment to delicate skin tissue layers employing numerous therapies including thermotherapy consisting of the application of energy into the tissue in a form of light, RF, ultrasound, electrolipophoresis, iontophoresis and microwaves and any combination thereof. 
         [0004]    All currently known methods used in the art raise a subject&#39;s skin temperature above normal to about 50-60 degrees Celsius at which tissue damage may occur. It is therefore imperative to be able to precisely monitor in real time the temperature of a specific segment of tissue being treated and use the acquired information to alter the course of treatment and maintain subject&#39;s safety. 
         [0005]    In order to continuously monitor skin temperature, suitable sensors such as thermocouples or thermistors are commonly incorporated into electrodes or transducers through which the energy is applied to the skin. These sensors have limited ability to precisely monitor the effect of the treatment on the tissue being treated. The accuracy of their reading in real time as well as the dependability on the information they provide as to tissue temperature at a specific treatment area are limited. 
         [0006]    The use of the aforementioned techniques of temperature monitoring does not obviate certain potential skin damage risk since, for example, the sensor response time depends on various parameters such as heat conductivity from the skin to the sensor and heat conductivity inside the sensor. This may result in possible skin damage before the sensor reduces or cuts off the heating energy applied to the skin. To some extent, this risk can be avoided by reducing the cut-off temperature operating limit for the sources of heating energy supplying energy such as optical radiation, RF energy, and ultrasound energy. However, this would limit the heating energy transmitted to the skin and the treatment efficacy. 
         [0007]    Currently used methods employing ultrasound to determine tissue temperature changes are based on ultrasound echo reflection and ultrasound deflection and are highly influenced by attenuation and diffusivity rendering them highly inaccurate. 
         [0008]    There is therefore a need for precise real-time monitoring and control of skin tissue temperature during skin tissue heating treatments using RF, Laser or any other form of heating energy. The use of ultrasound thermometry and thermocontrol as described in the current method and apparatus provides a precise, non-invasive solution for such a need. 
       SUMMARY 
       [0009]    The current method and apparatus employs ultrasound beams to precisely monitor in real time the temperature of a specific segment of tissue being treated. Additionally, the current method and apparatus also provides ultrasound thermo-control of aesthetic skin treatment sessions. Such sessions may include one or more aesthetic skin tissue treatments such as sub-dermal fat cells breakdown, lessening of the amount of sub-dermal fat, tightening of loose skin, tightening and firming of body surfaces, reduction of wrinkles in the skin and collagen remodeling. 
         [0010]    In accordance with an exemplary embodiment of the current method and apparatus an applicator includes a housing including an ultrasound transmitter and receiver. The transmitter and receiver consist of one or more piezoelectric elements arranged in one or more spatial configurations. The transmitter emits ultrasound beams in pulse form into tissue at a Brewster&#39;s angle of incidence. The ultrasound beam pulses travelled through the tissue, generally parallel to the surface of the skin and/or along an inter-layer border between treated tissue layers, are emitted thereby at a Brewster&#39;s angle of incidence and received by the receiver. The receiver piezoelectric elements convert the received beam signals to electric pulses, which are then communicated to an apparatus controller. 
         [0011]    In another exemplary embodiment of the current method and apparatus, the housing includes one or more pairs of transceivers each consisting of a first transceiver operative to emit ultrasound beams into the tissue at a Brewster angle of incidence and a second transceiver operative to receive ultrasound beams emitted by the first transceiver, propagated through the skin substantially in parallel to the surface thereof and emitted thereby at a Brewster&#39;s angle of incidence. 
         [0012]    In yet another exemplary embodiment of the current method and apparatus, the controller is operative, in real time, to analyze the ultrasound beams for information regarding changes in propagation speed of the beams, which are indicative of temperature changes in the tissue through which the beams have travelled. The controller is also operative to compare the temperature changes to tissue treatment temperature range limits defined in a predetermined treatment protocol and determine the criticality of the changes in light of these defined range limits. The criticality may be determined, for example, by setting upper and lower temperature limits for treatment heating energy levels applied to skin during a specific treatment session. These limits may be further broken down into temperature ranges and categorized as to levels of criticality. 
         [0013]    In accordance with still another exemplary embodiment of the current method and apparatus the controller is also operative to take one or more actions based on the temperature changes and criticality thereof. For example, the controller may be provided with a treatment protocol, defining action to be taken at each level of criticality. Such actions may include changing the course of treatment by, for example, increasing or decreasing the level of treatment heating energy application, changing the duration of treatment heating energy application or stopping the treatment session altogether, recording changes and criticality thereof in a database, displaying the information on a display, printing the information on a printout or alerting a user. 
         [0014]    In accordance with yet another exemplary embodiment of the current method and apparatus the controller communicates the new determined tissue treating temperature to a power generator operative to excite oscillation of the transmitter piezoelectric elements. 
         [0015]    In accordance with still another exemplary embodiment of the current method and apparatus the applicator also employs one or more sources of heating energy in a form of at least one of a group consisting of light, RF, ultrasound, electrolipophoresis, iontophoresis and microwaves. 
         [0016]    It will be appreciated that the current method and apparatus may be employed during one or more aesthetic skin tissue treatment selected from a group consisting of sub-dermal fat cells breakdown, lessening of the amount of sub-dermal fat, tightening of loose skin, tightening and firming of body surfaces, reduction of wrinkles in the skin and collagen remodeling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The present method and apparatus will be understood and appreciated from the following detailed description, taken in conjunction with the drawings in which: 
           [0018]      FIG. 1A  and  FIG. 1B  are simplified views of an exemplary embodiment of the current method and apparatus for precise ultrasound monitoring of treated skin temperature in real time employing a Brewster&#39;s angle of incidence. 
           [0019]      FIG. 1C  is a plan view of aesthetic treatment device applicator of  FIG. 1A . 
           [0020]      FIG. 2A  is a simplified view of yet another exemplary embodiment of the current method and apparatus for ultrasound monitoring treated skin temperature in real time employing a Brewster&#39;s angle of incidence. 
           [0021]      FIG. 2B  is a plan view aesthetic treatment device applicator of  FIG. 2A . 
       
    
    
     GLOSSARY 
       [0022]    The terms “transmitter”, “transceiver” and “receiver” used in the present disclosure mean devices that use piezoelectric elements to emit and/or receive ultrasound beams and may be used interchangeably, their functionality defined by their predetermined location in the apparatus and electric connection to a controller as will be described in detail hereinbelow. 
         [0023]    The term “skin” and “skin tissue” may be used interchangeably in the present disclosure and mean the tissue layer consisting of epidermis, dermis and including dermal structures such as sebaceous glands, hair follicle, hair shafts, sweat glands, etc. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0024]    Reference is now made to  FIG. 1A  which is a simplified view of an exemplary embodiment of the current method and apparatus for precise ultrasound monitoring of treated skin temperature in real time employing a Brewster&#39;s angle of incidence.  FIG. 1A  illustrates a cross-sectional view of an exemplary embodiment of an aesthetic skin treatment device applicator  100 . Applicator  100  includes an ultrasound transmitter  102  and an ultrasound receiver  104 , each consisting of one or more piezoelectric elements (not shown). The piezoelectric elements may be constructed from one or more materials selected from a group consisting of ceramics, polymers and composites. 
         [0025]    According to an exemplary embodiment of the current method and apparatus the transmitter and receiver are positioned at a predetermined distance from each other on opposing borders of an area of skin being treated  106  and at a predetermined angle relative to the surface of the skin. The angle between transmitter  102  and receiver  104  and the surface of the skin is maintained by a wedge  110  made of a sound index-matching material as known in the art. The index-matching material, such as a polymer (PVDF), liquid, cement (adhesive) or gel, has an index of refraction that closely approximates that of the medium adjacent to it, for example tissue layer  112 , and is used to reduce reflection at the surface thereof. The distance between the transmitter and receiver is dependent on the thickness of the tissue at the area to be treated. The considerations determining the distance between the transmitter and receiver and the angle at which they are positioned relative to the surface of the skin will be explained in detail herein below. 
         [0026]    Due to the physical-electrical nature of piezoelectric materials, it will be appreciated that transmitter  102  and receiver  104  may each function as a transceiver, emitting an ultrasound beam when excited by an electrical voltage received from a generator or converting a received ultrasound beam into an electrical voltage, amplified and delivered as a signal. The functionality of the transmitter  102  and receiver  104  may be dependent on the electrical circuitry configuration of apparatus  100  or controlled by a controller to determine the directionality of the transmitted ultrasound beams from transmitter  102  to receiver  104  or vice versa. 
         [0027]    In the current exemplary embodiment applicator  100  may employ one or more sources of heating energy in a form of at least one of a group consisting of light, RF, ultrasound, electrolipophoresis, iontophoresis and microwaves and delivered to the tissue by heating surfaces. The current exemplary embodiment employs one or more RF electrodes heating surfaces  108  to heat skin  112  and/or subcutaneous fat  114 . At proper treatment parameters, the applied energy heats area of skin  106 , which includes skin and subcutaneous fat. 
         [0028]    The elements of transmitter  102  and receiver  104  may be positioned in one or more predetermined configurations selected from a group consisting of two-dimensional and three-dimensional spatial configurations. Transmitter  102  and receiver  104  may also be positioned in a plurality of predetermined configurations in relation to heating surfaces  108 . For example, View-A of  FIG. 1A  as illustrated in  FIG. 1C , which is a plan view of aesthetic treatment device applicator  100  of  FIG. 1A , illustrates transmitter  102  and receiver  104  positioned perpendicular to heat delivering surfaces  108  and on opposing borders of the tissue segment to be treated. In another exemplary embodiment of the current method and apparatus transmitter  102 , receiver  104  and heat delivering surfaces  108  may be positioned on the same plane such as transmitter  102  and/or receiver  104  in-between two heating surfaces  108 . 
         [0029]    Reference is now made to  FIG. 1B , which is a simplified cross section of another exemplary embodiment of the current method and apparatus for precise ultrasound monitoring of treated skin temperature in real time employing a Brewster&#39;s angle of incidence. 
         [0030]    A transmitter  102  and a receiver  104  are positioned at a predetermined distance (L) from each other on opposing borders of an area  106  of skin tissue  112  being treated by energy delivered from heat delivery surface  108 . 
         [0031]    Transmitter  102  is operative to emit ultrasound beams, commonly in pulse form, at an angle relative to the surface of skin to be treated  112  so that a portion of the emitted beams impinges upon skin tissue  112  at a Brewster&#39;s angle of incidence, here indicated by the Greek letter (α). In light of the principle that ultrasound beams introduced into tissue at a Brewster&#39;s angle of incidence (α) propagate generally along the border between two mediums having two different sound refraction indexes, the beam emitted by transmitter  102  follows propagation path (I), which is generally parallel to the surface of skin tissue  112 , through treated area  106  and along a distance (Lst). Skin tissue  112  emits the ultrasound beams at a Brewster&#39;s angle of incidence to be received by receiver  104 . Receiver  104  converts the received ultrasound beams to signals communicated to a controller (Not shown). 
         [0032]    During wave propagation inside the body, beams propagating through body tissues excite all particles to oscillate in all directions. Receiver  104  is, therefore, operative to receive most of the beams emitted by transmitter  102 , at any distance there from and the signal value of the received beams depends on the transmitter-receiver distance. 
         [0033]    Beams emitted into tissue layers  112 ,  114 ,  116  and  118  by transmitter  102  impinge on the surface of tissue  112  at a plurality of angles of incidence. 
         [0034]    The fastest beams, i.e., the first to be received by receiver  104 , are the beams travelled along the fastest transmitter  102 -receiver  104  distance. The first beams to be received by receiver  104 , i.e., those travelled along the fastest transmitter  102 -receiver  104  distance, are those that have impinged on the surface of tissue layer  112  at a Brewster&#39;s angle of incidence and travelled along the surface of tissue  112  parallel thereto. 
         [0035]    According to another exemplary embodiment of the current method and apparatus, the controller is operative to obtain from the ultrasound beam signals information regarding changes in propagation speed of the beams, which are indicative of the temperature changes in skin area  106  through which the beams have propagated. The controller then may compare the changes to a predetermined treatment protocol and determine the criticality of the changes, resulting in taking one or more actions based on the changes and criticality. Such actions may be, for example, one or more of the following: Record information relating to the changes and criticality in a database, display the information on a display, communicate the changes and criticality to a remote user, print the information on a printout, alert a user as to the changes based on their criticality and change the course of treatment based on the criticality. The controller is also operative to control each element in transmitter  102  and receiver  104  individually and determine the sequence of ultrasound beam pulse delivery. 
         [0036]    According to yet another exemplary embodiment of the current method and apparatus, a portion of the beams emitted by transmitter  102  penetrate skin tissue  112  layer (L 112 ) and are refracted at the tissue layer borders due to differences in the sound refraction indexes between the various tissue layers. For example, beams travelling along propagation path (II) are emitted by transmitter  102  into tissue layer  112  and are refracted by the borders between adjacent tissue layers  112  (Skin) and  114  (L 114 , Fat), refracted once again at the border between tissue layers  114  (Fat) and  116  (L 116 , Muscle), and impinge upon a deeper tissue layer border, here being a border between layers  116  (Muscle) and  118  (Bone), at a Brewster&#39;s angle of incidence (α). In this case, the beam may then propagate along the border of deep tissue layers  116  and  118 , following propagation path (II) along a distance (Lb) at the end of which it is deflected at a Brewster&#39;s angle of incidence, refracted once again along the propagation path towards the surface of skin  112  and emitted thereby. 
         [0037]    Still referring to  FIG. 1B  and in accordance with another exemplary embodiment of the current method and apparatus determination of treated skin area  106  temperature, based on the ultrasound beam signals received from receiver  104  and communicated to the controller, may be obtained as follows: 
         [0038]    The speed of sound wave propagation through various body tissues is well documented and may also be achieved empirically. It is also well documented that propagation speed of sound beams through tissue is temperature-dependent and is altered by any increase or decrease in tissue temperature. The approximated values of speed of sound in tissue at normal body temperature are as follows: 
         [0039]    Skin: Velocity (V D ) ˜1700-1800 Meters per Second (m/s) 
         [0040]    Fat: V ˜1460 m/s 
         [0041]    Muscle: V 1580 m/s; and 
         [0042]    Bone: Vb≧3000 m/s. 
         [0043]    Soft tissue: Vst ˜1540 m/s. (average) 
         [0044]    The propagation time of an ultrasound beam pulse along the path indicated by Roman numeral (I) may be calculated by employing the following formula: 
         [0000]    
       
         
           
             
               τ 
               1 
             
             = 
             
               L 
               
                 V 
                 D 
               
             
           
         
       
     
         [0000]    Wherein (τ 1 ) is the time from ultrasound beam pulse emission by transmitter  102  to reception of the pulse by receiver  104 , L is the distance between transmitter  102  and receiver  104  and (V D ) is the velocity of the beam along path (I). 
         [0045]    Changes in treated tissue temperature may be determined in real time by comparison to known sound beam propagation speeds in non-heated various body tissues as brought hereinabove and sound beam propagation speed values at various tissue temperatures received empirically and recorded. 
         [0046]    The propagation time of an ultrasound beam along the path indicated by Roman numeral (II) may be calculated employing the following formula: 
         [0000]    
       
         
           
             
               τ 
               2 
             
             = 
             
               
                 
                   
                     2 
                      
                     
                       L 
                       
                         S 
                          
                         
                             
                         
                          
                         t 
                       
                     
                   
                   
                     V 
                     
                       S 
                        
                       
                           
                       
                        
                       t 
                     
                   
                 
                 + 
                 
                   
                     L 
                     B 
                   
                   
                     V 
                     B 
                   
                 
               
               = 
               
                 
                   
                     2 
                      
                     
                       L 
                       
                         S 
                          
                         
                             
                         
                          
                         t 
                       
                     
                   
                   
                     V 
                     
                       S 
                        
                       
                           
                       
                        
                       t 
                     
                   
                 
                 + 
                 
                   
                     L 
                     - 
                     
                       2 
                        
                       h 
                        
                       
                           
                       
                        
                       tan 
                        
                       
                           
                       
                        
                       α 
                     
                   
                   
                     V 
                     B 
                   
                 
               
             
           
         
       
     
         [0047]    Wherein (τ 2 ) is the time from emission of the pulse by transmitter  102  to reception of the pulse by receiver  104 , (Lst) is the distance of beam propagation trough layers of soft tissue (Lst=L 112 +L 114 +L 116 ), (L B ) is the distance of beam propagation along the bone surface layer, (L) is the distance between transmitter  102  and receiver  104 , (h) is the thickness of the tissue layers measured from the border between bone surface layer  118  and skin layer  112 , (Vst) is the velocity of the beam propagation through soft tissue, (V B ) is the velocity in the bone  118 , (α) is Brewster&#39;s angle and wherein 
         [0000]    
       
         
           
             
               Sin 
                
               
                   
               
                
               α 
             
             = 
             
               
                 
                   V 
                   St 
                 
                 
                   V 
                   B 
                 
               
               . 
             
           
         
       
     
         [0048]    It will be appreciated from the above expression that the time ((τ 2 ) of propagation of a sound beam travelling along path (II) depends on the thickness of the tissue layers in treated area  106 , between the surface of skin tissue  112  and the muscle  116 -bone  118  border. Sound propagation speed along bone (V B &gt;3000 m/s) is more than twice the propagation speed of sound within soft tissue, hence in cases where tissue thickness (h) is small as compared with L, a sound beam travelling along path (II) and travelling distance L B  at a speed (Vb) may be received by receiver  104  before or at the same time as a sound beam travelling along path (I) and travelling distance L at a much slower speed (V D ). This may result in the sound beam travelling along path (II) masking the signal received from the sound beam travelling along path (I). This places the condition that the sound beam travelling along path (I) is received before the sound beam travelling along path (II) or that (τ 1 )&lt;(τ 2 ). This may be achieved by using the following expression: 
         [0000]    
       
         
           
             
               L 
               
                 V 
                 D 
               
             
             ≤ 
             
               
                 
                   2 
                    
                   h 
                    
                   
                     
                       1 
                       + 
                       
                         
                           tan 
                           2 
                         
                          
                         α 
                       
                     
                   
                 
                 
                   V 
                   
                     S 
                      
                     
                         
                     
                      
                     t 
                   
                 
               
               + 
               
                 
                   L 
                   - 
                   
                     2 
                      
                     h 
                      
                     
                         
                     
                      
                     tan 
                      
                     
                         
                     
                      
                     α 
                   
                 
                 
                   V 
                   B 
                 
               
             
           
         
       
     
       Therefore: 
       [0049]    
       
         
           
             h 
             ≥ 
             
               
                 L 
                  
                 
                   ( 
                   
                     
                       1 
                       
                         V 
                         D 
                       
                     
                     - 
                     
                       1 
                       
                         V 
                         B 
                       
                     
                   
                   ) 
                 
               
               
                 2 
                  
                 
                   ( 
                   
                     
                       
                         
                           1 
                           + 
                           
                             
                               tan 
                               2 
                             
                              
                             α 
                           
                         
                       
                       
                         V 
                         St 
                       
                     
                     - 
                     
                       
                         tan 
                          
                         
                             
                         
                          
                         α 
                       
                       
                         V 
                         B 
                       
                     
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    and the distance (L) between transmitter  102  and receiver  104  may be determined according to the thickness (h). 
         [0050]    Reference is now made to  FIG. 2A , which is a cross-sectional view of another exemplary embodiment of an aesthetic skin treatment device applicator  200  in which the heating energy delivery surface  208  is an RF matrix and is defined by opposing ultrasound transmitter  202  and ultrasound receiver  204 . View A, as illustrated in  FIG. 2B , is a plan view aesthetic treatment device applicator  200  of  FIG. 2A . 
         [0051]    It will be appreciated by persons skilled in the art that the present method and apparatus are not limited to what has been particularly shown and described hereinabove. Rather, the scope of the invention includes both combinations and sub-combinations of various features described hereinabove as well as modifications and variations thereof which would occur to a person skilled in the art upon reading the foregoing description and which are not in the prior art.