Abstract:
Provided are body fat measuring techniques employed to date, usually applying a certain level of force to the tissue causing narrowing of the adipose tissue layer at the time of measuring. This creates a bias in the adipose layer thickness measurement results that is not accounted for when employing these methods. Provided is a current apparatus and method offering a solution for accounting for this bias thus improving the accuracy of body fat measurements.

Description:
TECHNICAL FIELD 
       [0001]    The current method and apparatus relate to the field of devices for measuring thickness of tissue and more specifically to devices for measuring the thickness of adipose tissue. 
       BACKGROUND 
       [0002]    Obesity is a condition in which abnormal or excessive fat accumulation in adipose tissue impairs health. With all the risks associated with carrying too much body fat, there has been a growing awareness of the benefit to one&#39;s health to maintaining a healthy weight and staying within healthy Body Mass Index (BMI) ranges. Measuring one&#39;s body fat percentage as part of maintaining a healthy body weight has become prevalent. 
         [0003]    Additionally, cosmetic body shaping treatments, also termed body contouring treatments, commonly involve employing complex devices and numerous methods of treatments to reduce body adipose tissue. These devices and treatments include application of various forms of heating energy, mechanical energy and similar. In such treatments it would be useful to obtain accurate information regarding the thickness of the adipose tissue in general and specifically of the adipose tissue in the area being treated. 
         [0004]    Many methods of assessing a person&#39;s body fat and lean mass have been developed. The most common methods include underwater or hydrostatic weighing, skin fold thickness measurements (caliper), bioelectrical impedance and BMI calculation based on a subject&#39;s height and weight. 
         [0005]    Some techniques, such as that described in US Patent Application Publications No. 2003/0018257 and No. 2009/0270728 employ ultrasound to measure fat tissue thickness, relying on the varying intensity and/or reflection time of the beams reflected from the various tissue layers. US Patent Application Publication No. 2003/0018257 limits the frequency of the emitted ultrasound beams to above 10 MHz. This technique relies on the inherent density of the various tissue layers to differentiate between them and assess their thickness. 
         [0006]    Other techniques, such as that described in US Patent Application Publication No. 2010/0036246 employs ultrasound image analysis techniques to determine the type and thickness of a target tissue. 
         [0007]    The technique described by U.S. Pat. No. 5,941,825 discloses measuring body fat from two different locations on the surface of the skin to correct for the parallax error resulting from ultrasound beam emission into the tissue in an angle other than orthogonal. 
       SUMMARY 
       [0008]    The body fat measuring techniques employed to date, as known to the authors of this disclosure, apply a certain level of force to the tissue causing narrowing of the adipose tissue layer at the time of measuring. This creates a bias in the adipose layer thickness measurement results that is not accounted for when employing these methods. The current apparatus and method offer a solution for accounting for this bias thus improving the accuracy of body fat measurements. 
         [0009]    There is thus provided, in accordance with an exemplary embodiment of the current method and apparatus a method of employing an ultrasound transducer for measuring adipose tissue thickness and accounting for a certain level of force of coupling of an applicator to the skin, effecting narrowing of the tissue layers being measured. 
         [0010]    In accordance with another exemplary embodiment of the present method and apparatus, there is also provided an applicator including one or more ultrasound transducers and a resilient spacer employing a method of measuring an adipose tissue thickness and accounting for a certain level of force of coupling of the applicator to the skin, effecting narrowing of the tissue layers being measured. 
         [0011]    In accordance with yet another exemplary embodiment of the present method and apparatus, there is also provided an applicator including one or more ultrasound transducers and one or more RF electrodes employing a method of measuring an adipose tissue thickness and accounting for a certain level of force of coupling of the applicator to the skin, effecting narrowing of the tissue layers being measured, employing reflected ultrasound beam signals and adipose tissue RF impedance measurement. 
         [0012]    In accordance with still another exemplary embodiment of the present method and apparatus, there is also provided an apparatus including one or more RF electrodes divided into one or more external segments and one or more internal segments driven at the same potential and measuring separately the current through each segment to obtain differentiation between the current flowing through skin tissue and the current flowing through fat tissue. 
         [0013]    In accordance with still another exemplary embodiment of the present method and apparatus, there is also provided a method of measuring water content of adipose tissue employing reflected ultrasound beam signals and RF electrodes to measure adipose tissue conductivity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present method and apparatus will be understood and appreciated from the following detailed description, taken in conjunction with the drawings in which: 
           [0015]      FIGS. 1A and 1B  are simplified views of an exemplary embodiment of the current method and apparatus; 
           [0016]      FIGS. 2A ,  2 B,  2 C and  2 D are simplified illustrations of an exemplary method of implementation of the embodiment of  FIGS. 1C and 1D  in accordance with the current method and apparatus; 
           [0017]      FIGS. 3A and 3B  are simplified illustrations of another embodiment of the current method and apparatus; 
           [0018]      FIG. 4  is a simplified illustration of an exemplary method of implementation of the embodiment of  FIGS. 3A and 3B  in accordance with the current method and apparatus; 
           [0019]      FIGS. 5A and 5B  are simplified illustrations of received signals of portions of an ultrasound beam in accordance with another embodiment of the current method and apparatus; 
           [0020]      FIG. 6  is a simplified illustration of an embodiment of an adipose tissue thickness measuring device applicator in accordance with the current method and apparatus; 
           [0021]      FIGS. 7A ,  7 B,  7 C,  7 D,  7 E,  7 F,  7 G,  7 H and  7 I are simplified plan-view and cross-sectional view illustrations of various examples of configurations and exemplary embodiments of the apparatus of  FIG. 6 . 
           [0022]      FIG. 8  is a graph illustrating the dependence of adipose tissue impedance on a force effecting narrowing of the adipose tissue. 
           [0023]      FIGS. 9A ,  9 B,  9 C and  9 D are simplified illustrations of an exemplary method of implementation of the embodiment of  FIG. 6  in accordance with the current method and apparatus; 
           [0024]      FIG. 10  is a simplified illustration of the effect of RF frequency on tissue conductivity or impedance of tissue layers interposed between RF electrodes in accordance with the current method and apparatus; and 
           [0025]      FIG. 11  is a graph illustrating the frequency dependence of the conductivity or impedance of adipose, skin and muscle tissues. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    For the purpose of this disclosure the terms “fat”, “fat tissue” or “adipose tissue” as used in the present disclosure have the same meaning and are used interchangeably throughout the disclosure. It should also be understood that the apparatuses, processes and treatments disclosed below may also be applicable to other types of tissue. 
         [0027]    The term “a certain level of force” as used in the present disclosure means a level of force which may be known, previously recorded, predetermined or arbitrary, determined in real time or arrived at empirically. 
         [0028]    The term “water” as used in the present disclosure means any electrically conductive naturally or artificially occurring fluid in and around tissue such as edema, exudate, transudate, tumescent solution or fluid such as a solution of sterile dilute salt water, adrenaline, lidocaine, anesthetic material or other ingredients injected into the adipose tissue during a cosmetic body contouring procedure. 
         [0029]    The term “treatment” as used in the present disclosure means an aesthetic or cosmetic procedure of coupling to the tissue or skin energy affecting the tissue or skin appearance. 
         [0030]    The term “narrowing” as it relates to “fat”, “fat tissue”, or “adipose tissue” and used in the present disclosure means narrowing of the “fat”, “fat tissue” or “adipose tissue” layer thickness as a result of an applied level of force exerting pressure on the tissue. 
         [0031]    The terms “emitting” and “radiating” as related to ultrasound beams or ultrasound beam pulses are used interchangeably in the present disclosure and mean generation of any type of ultrasound energy from an ultrasound transducer. 
       Adipose Tissue Thickness Measurement Employing an Ultrasound Transducer 
       [0032]    Reference is made to  FIGS. 1A and 1B , which are simplified views of exemplary embodiments of the current method and apparatus.  FIG. 1A  illustrates an ultrasound transducer  100 , which communicates with a control unit  140  including, among others, a source of power  144 , and an ultrasound driver  146  coupled to a surface  102  of skin  104 . In the exemplary embodiment of  FIGS. 1A and 1B  and in accordance with the current method and apparatus, when activated, transducer  100  emits ultrasound beams in pulse form, which propagate throughout the tissue. The ultrasound beam pulses may be emitted concurrently or consecutively. Portions of the emitted beams are reflected from tissue interfaces (surfaces disposed between adjacent tissue layers having different acoustic indexes). 
         [0033]    Separation between the transmitted ultrasound beams and the received portions thereof may be achieved in the time domain by emitting the beams in pulse form, or in the frequency domain by varying the frequency within a band to isolate the reflected pulse as will be further described in detail below. 
         [0034]    In  FIG. 1A , for example, a portion of a beam emitted by transducer  100  is reflected from the skin layer  104  and adipose tissue layer  106  interface as indicated by an arrow designated reference numeral  150  and is represented by a received signal  152  received by transducer  100  at (t 1 )) measured from time of emission (t E ). Another portion of the emitted beam is reflected from a deeper adipose tissue layer  106 -muscle layer  108  interface as indicated by arrow designated reference numeral  160  and is represented by signal  162  received by transducer  100  at (t 2 )) measured from time of emission (t E ). The thickness (d 1 ) of fat tissue layer  106  may then be calculated from the time difference (t 2 −t 1 ) between received reflected beam portion signals  152  and  162  and known velocity of sound in fat tissue. 
         [0035]    This technique, which is widely used in the art, is sometimes deficient in that it does not account for the narrowing of the adipose tissue layer effected by the force of coupling of the measuring device applicator (in this case, an ultrasound transducer). This bias resulting from this unavoidable narrowing may be highly significant in soft fat layers having physical properties closer to those of fluids than to those of solids. 
         [0036]      FIG. 1B  illustrates the above described bias effect. When applied to a single selected location on the skin at a certain level of force, transducer  100  presses upon skin layer  104  creating a depression  110 . As a result, adipose tissue layer  106 , which is much more fluid in nature than skin layer  104  and muscle layer  108  escapes from the area under transducer  100  and flows to the sides, narrowing fat layer thickness from (d 1 ) to (d 2 ) and shortening the propagation and reflection time of beam portion  160  from (t 2 ) to (t′ 2 ). The skin layer, being much less fluid in nature than the fat tissue is almost unchanged, so (t′ 1 ) is very close to (t 1 ). 
         [0037]    Alternatively, the calculation may employ only ultrasound beam pulse portion  160  to receive the thickness of fat tissue layer  106  and skin layer  104  combined. In some application this may be a required quantity. Since the thickness of skin in various areas of the human body is well documented, the skin thickness at the sight of measurement may be derived from a lookup table and be subtracted from the combined fat tissue layer thickness and skin to arrive at the thickness of fat tissue layer  106  alone. 
         [0038]    Referring now to  FIGS. 2A ,  2 B,  2 C and  2 D, which are simplified illustrations of an exemplary method of implementation of the embodiment of  FIGS. 1A and 1B  in accordance with the current method and apparatus. In  FIG. 2A , transducer  200  is coupled to the surface  202  of skin layer  204  at a certain level of force indicated by an arrow  240  creating depression  210  and decreasing fat tissue layer  206  thickness to a thickness (d 3 ). Transducer  200  is activated to emit ultrasound beams in pulse form at an emission times (t E ). The recorded emitted signals are designated by the letter (E). A series of pulse signals  221  of beam pulse portions  260  reflected from fat  206 -muscle  208  interface are received and recorded, displaying a time of reception (t 221-1 , t 221-2 , t 221-3  . . . ). 
         [0039]    In  FIG. 2B  the level of force at which ultrasound transducer  200  is coupled to surface  202  is then gradually reduced, manually or automatically, as indicated by arrow  250  bringing about the reduction in the depth of depression  210  of skin layer  204  and an increase in fat tissue layer  206  thickness to a thickness (d 2 ). Pulse signals  222  continue to be recorded, now displaying a longer time gap between time of emission (t E ) of the emitted pulses (E) and time (t 222 ) of received pulse signals  222 , for example, (t 222-1 &gt;t 221-1 ), indicating the change in fat tissue layer  206  thickness from (d 3 ) to a thickness (d 2 ) affecting changes in the propagation times of reflected portions  260 . 
         [0040]    In  FIG. 2C  the process described in  FIG. 2B  is repeated. The level of force at which ultrasound transducer  200  is coupled to surface  202  is further gradually reduced, manually or automatically, as indicated by arrow  270  to a point of disengagement (end point or disengagement point) of ultrasound transducer  200  emitting surface  212  from skin  204  surface  202 . At this end point, which is as close to optimal as possible, transducer  200  is coupled to skin  204  surface  202  at a minimal level of force or, optimally, with no application of force. No noticeable depression  210  exists and measured fat layer thickness (d 1 ) is as close as possible to true thickness (d 0 ) which prevails at rest (i.e., with no contact between transducer  200  emitting surface  212  and skin  204  surface  202  as shown as  FIG. 2D ). 
         [0041]    Immediately following the end point (disengagement or zero force point) of  FIG. 2C , contact between transducer  200  emitting surface  212  and skin  204  surface  202  is broken, as illustrated in  FIG. 2D . At this instance, no reflected pulse signals are received. This implies that the time of reception (t 223-3 ) of the last recorded pulse signal  223 - 3  ( FIG. 2C ) represents the most precise indicator of thickness (d 1 ) of adipose tissue layer  206 . In other words, i.e., thickness (d 1 ) at time of measurement of pulse  223 - 3  is closest to true thickness (d 0 ) without application of pressure to the skin-zero force adipose layer thickness. 
         [0042]    In the above description, measurement of the thickness of fat tissue layer  206  may or may not include beam portion  150  ( FIGS. 1A and 1B ) reflected from the skin  204 -fat tissue layer  206  interface. In the embodiment illustrated in  FIG. 2 , the value of skin layer  204  thickness may be derived from a lookup table (as described hereinabove). 
       Adipose Tissue Thickness Measurement Employing an Ultrasound Transducer and a Spacer 
       [0043]    Referring now to  FIGS. 3A and 3B , which are simplified illustrations of another embodiment of the current method and apparatus. According to the current embodiment, the reflected ultrasound can be used to measure the spacer thickness and deduce from the spacer resilient properties the level of force at which applicator  300  is applied to surface  302 . An applicator  300  including a resilient spacer  320  attached to the emitting surface of an ultrasound transducer  330  of the type depicted in  FIG. 1  is coupled to a rigid surface  302 . Spacer  320  may be made of a resilient material selected from a group consisting of rubber, epoxy and a polymer, or have a resilient structure including a bias element such as a spring and filled with liquid acoustic transmission media. The resilient spacer may be of a known initial thickness and selected to have a known modulus of elasticity or if the resilient force is generated by a bias such as a spring, the spacer may have a known spring constant. 
         [0044]    In another embodiment, spacer  320  may also include one or more strain measuring elements ( 322 ) such as a strain gauge that communicates with a control unit  140  ( FIG. 1 ). 
         [0045]    In yet another embodiment, spacer  320  may be made of a piezoelectric material and be operative to respond to pressure effected by the level of force of applicator  300  coupling to surface  302  and respond to the level of force by producing an electrical signal to control unit  140  ( FIG. 1 ) indicating changes in the level of force. 
         [0046]    In still another embodiment, ultrasound transducer  330  itself may be operative to respond to pressure effected by the level of force of applicator  300  coupling to surface  302  and respond to the level of force by producing an electrical signal to control unit  140  ( FIG. 1 ) indicating changes in the level of force. 
         [0047]    As shown in  FIG. 3A , applicator  300 , transducer  330  and attached spacer  320  are coupled to a rigid surface  302  at a certain level of force (N) as indicated by arrow  340 . Force (N) may be a force of coupling pressed against the tissue surface exerting pressure at the location where the adipose tissue thickness is being measured. Force (N) may be applied manually by an operator or automatically by an aesthetic treatment applying device. A portion of a beam emitted by transducer  330  through resilient spacer  320  is reflected from rigid surface  302  as indicated by an arrow designated reference numeral  354  and is represented by a signal  352  received after a time period of (t 1 ) measured from time of emission (t E ). The time gap between the transmitted signal (E) and received reflected beam portion  350  signal  352  is used to calculate spacer thickness, spacer strain and force (N). 
         [0048]    The procedure described in  FIG. 3A  above and in  FIG. 3B  is a calibration stage, which may be performed by the user. Alternatively, the physical properties of the resilient spacer may be predetermined by the composition of the material selected for spacer production. Additionally, the spacer may be calibrated in production and provided pre-calibrated by the manufacturer. The calibration information may be supplied by the manufacturer with the pre-calibrated resilient spacer. 
         [0049]    In  FIG. 3B , applicator  300 , transducer  330  and attached spacer  320  are coupled to rigid surface  302  at a greater certain level of force (N′) so that (N′)&lt;(N) as indicated by an arrow designated the reference numeral  342 . A portion of a beam emitted by transducer  330  through resilient spacer  320  is reflected off rigid surface  302  as indicated by an arrow designated reference numeral  354  and is represented by a signal  352  received after a time period of (t 2 ) measured from time of emission (t E ). Time period (t 2 ) is shorter than time period (t 1 ) designating the compression of spacer  320  thickness d s  from (d s1 ) to (d s2 ). 
         [0050]    The correlation between (d s1 ) and (d s2 ) at various levels of force may be employed to calculate the force (N) from the reflected ultrasound as well as the thickness (d) at a zero level of force. The correlation between (d s1 ) and (d s2 ) at various levels of force of coupling and the time of reception of their corresponding signals may then be derived empirically, be recorded and arranged in a database such as a lookup table. This data may be also collected for various ultrasound frequencies, various resilient spacers having various thicknesses and various moduli of elasticity, having various acoustic properties and other varying applicable factors. In actuality, this may serve as a spacer calibration process. 
         [0051]    Reference is now made to  FIG. 4 , which is a simplified illustration of an exemplary method of implementation of the embodiment of the spacer shown in  FIGS. 3A and 3B  in accordance with the current method and apparatus and in a state of compression similar to that shown in  FIG. 3B . An applicator  400  including a transducer  430  and a resilient spacer  420 , such as that shown in  FIGS. 3A and 3B , are coupled to the surface  402  of skin  404  at a certain level of force indicated by an arrow  440 , creating a depression  410  in skin  404 , compressing spacer  420  and effecting the narrowing of fat tissue layer  406  thickness to a thickness (d). 
         [0052]    A portion of a beam emitted by transducer  430  through now compressed resilient spacer  420  is reflected from spacer  420 -surface  402  of skin  404  interface as indicated by an arrow designated reference numeral  450  and is represented by a signal  452  received after a time period of (t 1 ) measured from time of emission (t E ). Another portion of the emitted beam is reflected from a deeper adipose tissue layer  406 -muscle layer  408  interface as indicated by arrow designated reference numeral  460  and is represented by signal  462  received at (t 3 )) measured from time of emission (t E ). 
         [0053]    Another beam portion  470  is reflected from the skin  404 -fat  406  interface because of acoustical impedance mismatch and is represented by signal  472 . 
         [0054]    The process described hereinabove enables the measuring of the fat layer thickness vs. level of force of coupling. During the measurement session, the caregiver or an automatic system may apply varying levels of force to the applicator. During this time, the transducer transmits a sequence of pulses, and the reception times of pulses reflected from spacer  420 -skin  404 , skin  404 -fat  406  and fat  406 -muscle  408  interfaces are recorded. The pulse signals reflected from spacer  420 -skin  404  interface or skin  404 -fat  406  interface may be used to deduce the level of force of coupling and the pulse signals reflected from fat  406 -muscle  408  interface may be used to deduce fat layer  406  thickness. This method and apparatus may be employed to obtain the value of fat thickness vs. applicator level of force of coupling. This data (i.e., fat thickness and applicator level of force of coupling) may also be used for deriving fat elastic properties and/or to obtain fat layer thickness at a specific level of force, which may be used as a reference for all measurements. Zero force point or disengagement point may also be identified by this measurement, to obtain the value of undisturbed fat tissue thickness. 
         [0055]    The acoustical properties of the spacer, specifically the acoustical impedance, may be selected to be close or identical to that of the skin to eliminate skin reflected signal isolating only the skin  404 -fat  406  interface reflected signal, or, alternatively, a spacer may be selected with an impedance as close as possible, but different than that of skin so that to sufficiently allow detection of spacer  420 -skin  404  interface reflection, so skin thickness may also be measured. 
         [0056]    When the acoustic impedance of spacer  420  is selected to match the impedance of the skin, the first reflection signal  470  will be obtained from the skin  404 -fat  406  interface. To measure spacer  420  thickness by this reflection  470  one has to assume fixed skin thickness. The acoustic impedance of the spacer  420  can be selected to be slightly different from that of the skin, to generate a reflected signal  450  from the spacer-skin interface. This reflection may be used to measure spacer thickness directly. The difference between spacer and skin impedances can be selected to be at the minimal value required to generate measureable return signal, and not much larger to prevent too much loss at the spacer-skin interface and enable enough power propagation into the deeper fat layer. 
         [0057]    Reference is now made to  FIGS. 5A and 5B , which are simplified illustrations of received signals of portions of an ultrasound beam in accordance with another embodiment of the current method and apparatus. In  FIG. 5A  the time (t ad ) of reception of a signal  502  of the portion of the beam reflected from the skin-adipose (or adipose-muscle tissue) tissue interface and measured from time of emission (t E ) may be shorter than the decay time (t d ) of the transmitted signal, depicted by line  504  and therefore might be partially/fully masked. 
         [0058]    In accordance with the current method and apparatus, a spacer, such as that described hereinabove, or a non-resilient spacer, may also be operative to delay beam portion reflections to a point in time beyond transmitted signal decay time (t d ). 
         [0059]      FIG. 5B , illustrates the effect of adding a spacer having acoustic properties operable to delay reflected beam portions in received signal in accordance with the current method and apparatus. The delayed reflected signals includes all signals of interest, such as spacer-skin, skin-fat and fat muscle interface reflection. Such an acoustic spacer may enable the isolation of a signal  502  reflected from tissue interfaces, and enhance the accuracy of thickness measurement of the desired tissue layer. 
         [0060]    A spacer of the type described in  FIGS. 3A and 3B  may also have an acoustic index matched to that of skin so that to eliminate reflection of a portion of the ultrasound beam from the surface of the skin, such as that indicated by reference numeral  450  ( FIG. 4 ). 
         [0061]    Other methods to isolate the pulse signal reflected from the adipose tissue  106 -muscle  108  interface ( FIG. 1 ), in accordance with the current method and apparatus, may also employ techniques such as Linear Frequency Modulation (FM). 
         [0062]    It is well known in the art that in echo systems, such as an ultrasound echo system, the range resolution is related to the transmitted bandwidth. The transmitted bandwidth is inversely proportional to the pulse width. As described in  FIGS. 5A and 5B  hereinabove beams in short pulse mode are radiated and reflected. However, instead of using real short pulses, virtual pulses or equivalent to short pulses may be formed by continuous or stepwise transmission of frequencies covering the same bandwidth as the real or virtual pulse. Standard transform techniques may then be employed by computerized processing to transform the results from frequency domain to time domain and isolate the virtual pulse reflected from the adipose tissue from the frequency dependent reflections. 
         [0063]    When employing the Linear Frequency Modulation (FM) technique, the transmitted frequency of the radiated pulses is scanned linearly within a frequency band and the returned signal is mixed with the transmitted signal. The resulting frequency difference is directly proportional to the tissue thickness range. 
         [0064]    Employing the aforementioned techniques, the following considerations may also be included when selecting the frequency range (or equivalently, pulse length): 
         [0065]    a) Since typical sound velocity (v) in tissue is 1500 m/sec, an added fat thickness (d) of, for example, 1 mm of will increase the delay of the return signal by 1.33 microseconds [(d/v)×2=(0.001/1500)×2=1.33 microseconds]. Therefore for a resolution better than 1 mm the pulse front rise time must be of the order of 1 microsecond, which means that the spectral content of the pulse should have a bandwidth above about 200 kHz. 
         [0066]    b) Considering the attenuation of the acoustic wave in the fat layer and to prevent excessive loss in reflected signal intensity, it is advisable to use frequencies lower than a few MHz, since attenuation in tissue is proportional to frequency. To reduce attenuation frequency lower then 3 MHz or lower than 1 MHz may be used. 
         [0067]    c) Still another consideration in selecting frequency range (or equivalently, pulse length) is avoiding too many details in the reflection. The reflection of interest is that reflected from fat-muscle interface. Hence, it is desirable to weaken reflections from small irregularities in the tissue. Lower frequencies will average these irregularities reflections with no effect on the fat-muscle reflection. In one embodiment employed in accordance with the current method and apparatus, the ultrasound frequency may be scanned between 200 kHz and 2 MHz. In another embodiment, the ultrasound may be transmitted in pulsed mode, pulse signal rise time being between few tens to few hundreds of nanoseconds, more specifically the pulse signal rise time being between 50 nsec to 500 nsec, the pulse signal width being between 0.1 to 10 microseconds. Alternatively, the transducer area may be large enough to generate a broad beam which averages non-uniformities in the fat tissue. Since typical collagen structures within the fat layer are a few mm in size, the transducer radiating aperture width may be selected to be larger than 5 mm, or, more specifically larger than 10 mm. 
       Adipose Tissue Thickness Measurement Employing Ultrasound and RF Impedance Measurement 
       [0068]    Reference is now made to  FIG. 6 , which is a simplified illustration of an embodiment of an adipose tissue thickness measuring device applicator in accordance with the current method and apparatus. An adipose tissue thickness measuring device applicator  600  includes one or more ultrasound transducers  620  and one or more RF electrodes  630 . 
         [0069]    Applicator  600  is connected to a control unit  640 , which includes a power source  644 . Power source  644  is connected to an ultrasound driver  646  and RF generator  648 . Control unit  640  also contains a processor  650  for monitoring impedance and controlling various functions of the system. Processor  650  may also be operative to calculate from the impedance measured between the electrodes the level of narrowing of adipose tissue effected by the coupling of applicator  600  as will be described below. 
         [0070]    Control unit  640  may also have an input device, such as a keypad  652  that allows an operator to input to processor  648  selected values of parameters of the measurement and/or treatment, such as the frequency, pulse duration and intensity of the ultrasound and RF energy to be directed to the adipose tissue. 
         [0071]    Applicator  600  is connected to control unit  640  via a harness  642  cables  654  to supply power to ultrasound transducer  620  and RF electrodes  630 . 
         [0072]    Ultrasound transducers  620  and one or more RF electrodes  630  may be coupled at a certain level of force to a surface  602  of a skin layer  604 . Alternatively and optionally, all or part of ultrasound transducer  620  may also be operative to operate as an RF electrode or electrodes, by covering its surface with electrically conducting layer or grid which has a low attenuation of ultrasound waves as will be explained in detail below. Alternatively, in a mono-polar configuration, a separate return electrode may be employed. Optionally, ultrasound transducer  620  may also include a resilient or rigid spacer and operate as in the embodiments described in detail hereinabove. 
         [0073]    In the current embodiment, RF electrodes  630  are employed to enable measuring of electrical impedance of a tissue segment, mainly adipose tissue layer  606  volume  610 , disposed between electrodes  604  as a real time indicator of the coupling force effecting narrowing and affecting measured thickness of adipose tissue layer  606 , as will be described in detail hereinbelow. 
         [0074]    Electrodes  630  placed, for example, on the surface  602  of skin  604  may be employed to determine the electrical impedance of the adipose tissue volume  610  disposed between electrodes  630  by applying a certain RF voltage between the electrodes and measuring the current between them. The current path in the tissue can be from the electrode, through the skin back to the other electrode, from the skin to the fat and back to the skin and to the other electrode, or in the path electrode-skin-fat-muscle-fat-skin-electrode. The current division between these paths depends on the tissue properties and on the electrodes configuration. At a frequency of about 1 MHz the resistance of the fat is about ten times that of the skin, and the resistance of the muscle is about half that of the skin. The larger the separation between the electrodes, the larger the portion of current flowing in the paths which includes the fat and the muscle. 
         [0075]      FIGS. 7A ,  7 B,  7 C,  7 D,  7 E,  7 F,  7 G,  7 H and  7 I are simplified illustrations of various examples of configurations and exemplary embodiments of the apparatus of  FIG. 6  as viewed from the direction indicated by arrow (W). One or more RF electrodes  730  may be disposed on one or more sides of an ultrasound transducer  720 . For example, and as shown in  FIG. 7A , which is a simplified illustration of an exemplary embodiment in accordance with the current method and apparatus, one or more RF electrodes  730  are disposed on opposite sides of an ultrasound transducer  720 . 
         [0076]    In  FIG. 7B , which is a cross-sectional view illustration of another exemplary embodiment, one or more RF electrodes  730  are located at any one or more sides of one or more ultrasound transducers  720  such as, for example, that depicted in  FIG. 7A . In  FIG. 7B , electrodes  730  are equipotential. Current sensors  732  communicate with RF electrodes  730  and measure the current at each electrode. A current detected by sensors  732 - 1  communicating with RF electrodes  730 - 1  is indicative of a current flowing through fat layer  706  along path  750 , while a current detected by sensors  732 - 2  communicating with RF electrodes  730 - 2  is indicative of current flowing through skin layer  704  along path  752 . 
         [0077]      FIG. 7C  is a cross-section view illustration of yet another exemplary embodiment in accordance with the current method and apparatus in which ultrasound transducers  720  also serve as RF electrodes as will be explained in detail below. Current sensors  736  communicating with ultrasound transducers  720  electrodes and current sensors  732  on RF electrodes  730  measure the current at each electrode. A current detected by sensors  732  communicating with RF electrodes  730  is indicative of a current flowing through fat layer  706  along path  750 , while a current detected by sensors  736  communicating with the RF electrodes of transducers  720  is indicative of current flowing through skin layer  704  along path  752 . 
         [0078]      FIG. 7D , which is a plan view simplified illustration of still another exemplary embodiment in accordance with the current method and apparatus, one or more RF electrodes  730  may be attached to the emitting surface of transducer  720 . RF electrodes  730  may be made of a conductive material acoustically matched (i.e., acoustically transparent) to transducer  720  or a spacer (not shown) as described hereinabove. RF electrodes  730  may be in the form of thin electrically conducting layer such as a mesh as shown in  FIG. 7D  having one or more current sensors  732  dispersed, for example, along mesh intersections. 
         [0079]    In another exemplary embodiment each one or more RF electrode  730  may be made of a distinct mesh made of a conductive material, acoustically matched and attached to the emitting surface of transducer  720  or a spacer (not shown) at separate locations as shown in  FIG. 7E . 
         [0080]    In  FIG. 7F , which is a plan view simplified illustration of yet another embodiment in accordance with the current method and apparatus, at least two RF electrodes  730  and  738  may be arranged concentrically around ultrasound transducer. 
         [0081]    Alternatively, each RF electrode may be divided into one or more external segments and one or more internal segments driven at the same potential and having the current flowing through each segment measured separately to obtain differentiation between the current flowing through skin tissue and the current flowing through fat tissue. 
         [0082]    It will be appreciated by persons skilled in the art that the electrodes depicted in  FIG. 7F  need not be only circular and may be of any other suitable geometrical shape such as a square, rectangle, hexagon, etc. 
         [0083]      FIG. 7G  is a cross-section view simplified illustration of still another exemplary embodiment of the current method and apparatus.  FIG. 7G  illustrates a mono-polar electrical configuration of an ultrasound transducer  722  that also serves as an RF electrode similar to that depicted in  FIG. 7D  and a single RF electrode  730  concentrically surrounding ultrasound transducer/electrode  722  in a configuration similar to that of  FIG. 7F . Both transducer/electrode  722  and electrodes  730  are equipotential and connected to a return electrode  734  located elsewhere on the body. Current sensors  732  and  736  measure the current flowing through each of transducer/electrode 722  and electrode  730 . 
         [0084]    A current detected by sensor  736  communicating with transducer/electrodes  722  is indicative of a current flowing through fat layer  706  along path  750 , while a current detected by sensor  732  communicating with RF electrode  730  is indicative of current flowing through skin layer  704  along path  752 . 
         [0085]      FIG. 7H  is a cross-section view simplified illustration of another exemplary electrical configuration of a pair of ultrasound transducer/electrode  722  and RF electrode sets in which each set includes an ultrasound transducer  722  that also serves as an RF electrode and a single RF electrode  730  concentrically surrounding ultrasound transducer/electrode  722  in a configuration similar to that of  FIG. 7F . 
         [0086]    Each pair of RF electrodes and transducer/electrodes (i.e., pair  730 - 1 / 730 - 2  and pair  722 - 1 / 722 - 2 ) are equipotential. The configuration may also include a separate return electrode (not shown) positioned elsewhere on the body. 
         [0087]    Current sensors  736  communicating with ultrasound transducers/electrodes  722  and sensors  732  on RF electrodes  730  measure the current at each electrode. A current detected by sensors  736  communicating with transducers/electrodes  722  is indicative of a current flowing through fat layer  706  along path  750 , while a current detected by sensors  732  communicating with RF electrodes  730  is indicative of current flowing through skin layer  704  along path  752 . 
         [0088]    In  FIG. 7I , which is illustrates yet another exemplary embodiment of the current method and apparatus, RF electrode  730  is arranged concentrically about ultrasound transducer/electrode  722  of the type, for example, depicted in  FIG. 7D  above. 
         [0089]    In any of the ultrasound transducer  720 / 722  one or more RF electrodes  730  configurations described above, transducer  720 / 722  and electrode  730  may abut each other, be positioned in propinquity to each other or be at a distance from each other. 
         [0090]    It will be appreciated by persons skilled in the art that the current method and apparatus are by no means limited to the exemplary embodiments and configuration examples or combination thereof set forth hereinabove. 
         [0091]    It has been found experimentally, and as shown in  FIG. 8 , which is a graph illustrating the dependence of adipose tissue impedance on a force effecting narrowing of the adipose tissue, that when coupling an apparatus/applicator, such as fat thickness measuring device applicator  600  ( FIG. 6 ) or a body aesthetic treatment device applicator, to the skin, an inverse correlation exists between impedance of the tissue below the apparatus/applicator-skin contact area and the force of coupling (N) effecting narrowing of the tissue. 
         [0092]    The physical explanation is as follows: The resistance to current flowing though skin layer  604  ( FIG. 6 ) is constant since there is no narrowing of skin layer  604  ( FIG. 6 ) between electrodes  630  ( FIG. 6 ) during the application of force of coupling. On the other hand, the applied level of force of coupling effects narrowing of fat layer  606  ( FIG. 6 ) making the effective fat layer thickness (d) smaller (i.e., narrower). 
         [0093]    The narrowing of fat layer  606  effected by the increasing force of application (N) brings about a decrease in the resistance/impedance to current flowing along the path through fat layer  606  and through fat  606  and muscle  608 . 
         [0094]    Changes in the recorded impedance to a current flowing through tissue layers  604 ,  606  and  608 , or in the current itself (e.g., employing current sensors), are reflective of the changes in thickness (d) or narrowing of fat layer  606 . 
         [0095]    Measuring changes in tissue impedance concurrently or intermittently with ultrasound measurement of adipose tissue layer thickness (d), employing the methods and devices described hereinabove, may provide a more accurate indication of the force of coupling (N) of fat thickness measuring device applicator  600  or of a body contouring device applicator, to the skin at any certain time. 
         [0096]    Additionally, measuring changes in tissue impedance concurrently or intermittently with ultrasound measurement of adipose tissue layer thickness (d), employing the methods and devices described hereinabove, may also enable to extract from the thickness and impedance data one or more physical properties of the adipose tissue such as adipose tissue thickness dependence on force, adipose tissue thickness at zero force and adipose tissue electrical properties including adipose tissue conductivity and/or permittivity. 
         [0097]    For example, applicator  600  may be coupled to surface  602  of skin  604  employing a method similar to that described in  FIG. 2  hereinabove and shown in  FIGS. 9A ,  9 B,  9 C and  9 D, which are simplified illustrations of another exemplary method of implementation of the embodiment of  FIG. 6  in accordance with the current method and apparatus: 
         [0098]    In  FIG. 9A , applicator  900 , including transducer  920  and RF electrodes  930  is coupled to the surface  902  of skin layer  904  at a certain level of force (N 1 ), indicated by an arrow  950 , creating depression  910  and compressing fat tissue layer  906  to a thickness (d 3 ). Transducer  920  is activated to emit ultrasound beams into the tissue. The received reflected beam signals are then recorded. Concurrently, the impedance of adipose tissue layer  906  between RF electrodes  930  is measured, in this example, as being (Ω 1 ). 
         [0099]    In  FIG. 9B  the level of force at which applicator  900  is coupled to surface  902  is then gradually reduced, manually or automatically, as indicated by arrow  960  to a level of force (N 2 ) bringing about the reduction in the depth of depression  910  of skin layer  904  and an increase in fat tissue layer  906  thickness to a thickness (d 2 ). Transducer  920  is activated to emit ultrasound beams into the tissue and the received reflected beam signals are then recorded. Concurrently, the impedance of adipose tissue layer  906  between RF electrodes  930  is measured and recorded, at this point in time, as being, for example, (Ω 2 ). 
         [0100]    In  FIG. 9C  the process described in  FIG. 9B  is repeated. The level of force at which applicator  900  is coupled to surface  902  is then gradually reduced, manually or automatically, to a level of force (N 3 ) as indicated by arrow  970  up to a point of disengagement (end point or zero force point) of Transducer  920  emitting surface and of RF electrodes  930  from surface  902 . At this end point, which is as close to optimal as possible, applicator  900  is coupled to surface  902  at a minimal level of force (N 3 ) or, optimally, with no application of force (N=0). No or barely noticeable depression  910  exists. Transducer  920  is activated to emit ultrasound beams into the tissue and the received reflected beam signals are then recorded. Concurrently, the impedance of adipose tissue layer  906  between RF electrodes  930  is measured and recorded, at this point in time, as being, for example, (Ω 3 ). The measured fat layer thickness (d 1 ) is as close as possible to true thickness (d 0 ) which prevails at rest (with no contact between applicator  900  and skin  904  surface  902  as shown in  FIG. 9D ). 
         [0101]    Immediately following the end point of  FIG. 9C , contact between applicator  900  transducer  920  and RF electrodes  930  and skin  904  surface  902  is broken, as illustrated in  FIG. 9D . At this instance, the measured impedance is infinitely high due to break of electrical contact between RF electrodes  930  and skin  904  surface  902  implying that the last recorded impedance value (Ω 3 ) represents the most precise indicator of thickness (d 1 ) of adipose tissue layer  906  (i.e., thickness (d 1 ) at time of measurement of impedance value (Ω 3 ) is closest to true thickness (d 0 ) at a zero level of force). 
         [0102]    It will be appreciated by those skilled in the art that the steps depicted in  FIGS. 9A ,  9 B and  9 C may occur at any point along the graph shown in  FIG. 8  and that every pair of measured values (N) and (Ω) may be sampled periodically and compared to any other pair of measured values (N) and (Ω) along the graph, such as the previous or next pair of values (N) and (Ω), to monitor changes in fat tissue impedance and derive thickness of adipose tissue layer  906  while reducing the level of applicator  900  coupling force (N) to arrive at the thickness of adipose tissue layer  906  at zero level of force. 
         [0103]    Additionally, further experimentation may enable setting up a look up table to which the measured pairs of values (N) and (Ω) may be compared to derive the level of narrowing and thickness of adipose tissue layer  906  at any certain level of applicator  900  coupling pressure (N). 
         [0104]    The selection of measured pairs of values (N) and (Ω) to be compared may be predetermined, determined in real time or determined following the treatment session. 
         [0105]    Reference is now made to  FIG. 10 , which is a simplified illustration of the effect of RF frequency on tissue conductivity or impedance of tissue layers interposed between RF electrodes in accordance with the current method and apparatus. An adipose tissue thickness measuring device applicator  1000  such as that shown in  FIG. 6 , includes one or more ultrasound transducers  1020  and one or more RF electrodes  1030  disposed on opposite sides of ultrasound transducer  1020 . Alternatively, a separate return electrode may be employed in a mono-polar configuration. 
         [0106]    Ultrasound transducers  1020  and one or more RF electrodes  1030  may be coupled at a certain level of force to a surface  1002  of a skin layer  1004 . Alternatively and optionally, ultrasound transducer  1002  may also be operative to operate as an electrode. Additionally and optionally, ultrasound transducer  1002  may also include a spacer and operate as described in detail hereinabove. 
         [0107]    As discussed hereinabove, electrodes  1030  placed, for example, on the surface  1002  of skin  1004  may be employed to determine the electrical impedance of the adipose tissue segment  1010  disposed between electrodes  1030  by applying a known voltage between electrodes  1030 . The current flows in the tissue as explained hereinabove, along current paths indicated by arrows designated reference numeral  1050 ,  1052 ,  1054 . Measuring the total current at the electrode-skin surface coupling points enables to determine the conductivity or impedance of adipose tissue segment  1010 . 
         [0108]    The probing current, when generated between electrodes  1030  follows the path of least impedance. As shown in  FIG. 11 , which is a graph illustrating the comparative frequency dependence of the conductivity of adipose, skin and muscle tissues [based on “Compilation of the Dielectric Properties of Body Tissues at RF and Microwave Frequencies”, Camelia Gabriel, PhD and Sami Gabriel, MSc., Physics Department, King&#39;s College London (http://niremf.ifac.cnr.it/docs/DIELECTRIC/Home.html)], the conductivity of adipose, skin and muscle tissues varies in accordance with the frequency of the probing current. 
         [0109]    As illustrated in  FIG. 11 , at high RF frequencies, such as 100 MHz, the conductivity of wet skin is much higher than that of fat tissue allowing most of the current to flow through the skin tissue following the path indicated by reference numeral  1052  ( FIG. 10 ). A very small flow of current will reach muscle layer  1008 , following path  1054 , being impeded by fat layer  1006 . 
         [0110]    At an RF frequency of approximately 50 KHz the conductivity of wet skin and adipose tissue are approximately the same allowing the probing current to flow, evenly distributed, through both tissue layers, following both paths  1050  and  1052  and also through muscle in path  1054  ( FIG. 10 ). At frequencies below 50 KHz, the conductivity of wet skin drops dramatically below that of fat tissue allowing most of the probing current to flow through adipose tissue layer  1006  following path  1050  and a significant part through path  1054 . 
         [0111]    In accordance with the frequency dependence of the conductivity of adipose, skin and muscle tissues, when employing impedance measurement as an indicator for the level of coupling force effecting adipose tissue narrowing, such as in the exemplary method of implementation described in  FIG. 9  hereinabove, the employed RF frequency is commonly in the range between 1 KHz and 1 MHz. More commonly the employed RF frequency is in the range between 5 KHz and 500 KHz and most commonly, the employed RF frequency is in the range between 10 KHz and 100 KHz. 
         [0112]    In another embodiment, in accordance with the current method and apparatus, the measurement can be done employing several frequencies, to acquire more information on the tissue properties. One frequency may be selected from the lower end of range of frequencies, for example, about 10 kHz, to get the resistance of fat path  1050 , and another frequency may be selected from at the higher end of range of frequencies, for example 1 MHz of 100 kHz to get the resistance of skin path  1052 . 
       Measurement of Water Content of Adipose Tissue Employing Ultrasound and RF Impedance 
       [0113]    In yet another embodiment in accordance with the current method and apparatus, an adipose tissue thickness measuring device applicator, such as that shown in  FIG. 6  may also include a mechanism operative to measure conductivity or permittivity of adipose tissue between the RF electrodes and may be employed as, for example, in the exemplary method of implementation described in  FIG. 9  to provide information regarding the water content of adipose tissue. 
         [0114]    Conductivity information may be received from the measurements of the impedance between the RF electrodes together with the adipose tissue thickness and skin thickness optionally derived from the ultrasound measurements. For example, a volume  610  ( FIG. 6 ) of adipose tissue layer  606  may be analyzed accounting for adipose tissue layer  606  thickness (d) and known or expected conductivity values such as those shown in  FIG. 11 . An increase in conductivity above an expected conductivity value for the measured adipose tissue thickness (d) may indicate natural or induced infiltration of electrically conductive fluid, such as water, into the adipose tissue. The ratio between the expected conductivity value and measured conductivity value difference and the conductivity value at a measured adipose tissue layer thickness (d) may provide a quantitative indication of the water content in the tissue. 
         [0115]    As described in  FIGS. 6 ,  10  and  11  above, the same considerations for selecting an optimal frequency range may also be applied for obtaining the tissue water content. At a lower frequency the skin conductivity is lower, hence the impedance measured between the electrodes may be indicative of fat conductivity and therefore of the tissue water content as well. According to another embodiment measurement at more than one frequency is made to obtain data on tissue layer conductivities and calculate their water content by comparison to a known database such as a database of adipose tissue electrical properties. These measurements may be made at various forces on the applicator. The measured fat thickness together with the electrical resistance may be applied for isolating the fat dependent part of the conductivity and for obtaining a more accurate data on the water content. 
         [0116]    In still another embodiment in accordance with the current method and apparatus and with reference to  FIGS. 7A ,  7 B,  7 C,  7 E,  7 F,  7 G and  7 H, employing internal and external electrodes driven at the same potential and measuring separately the current through each electrode enables to obtain differentiation between measurements of the current flowing through skin tissue and the current flowing through fat tissue. 
         [0117]    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 disclosure 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.