U.S. patent application number 12/223964 was filed with the patent office on 2009-09-03 for method and apparatus for treatment of adipose tissue.
This patent application is currently assigned to SYNERON MEDICAL LTD. Invention is credited to Shimon Eckhouse, Michael Kreindel, Avner Rosenberg.
Application Number | 20090221938 12/223964 |
Document ID | / |
Family ID | 38008148 |
Filed Date | 2009-09-03 |
United States Patent
Application |
20090221938 |
Kind Code |
A1 |
Rosenberg; Avner ; et
al. |
September 3, 2009 |
Method and Apparatus for Treatment of Adipose Tissue
Abstract
The invention provides methods and apparatuses (4) for the
treatment of adipose tissue. The methods comprise application of
ultrasound energy to a region of adipose tissue, and the
apparatuses comprise at least one source of ultrasound energy (42a,
42b) configured to direct ultrasound energy through a skin surface
into the subcutaneous adipose tissue. In one embodiment, a pressure
gradient is created in the region generating relative movement
between fat cell constituents having different densities. In
another embodiment, a protrusion of skin and underlying adipose
tissue containing is formed and ultrasound energy is radiated into
the adipose tissue in the protrusion. In another embodiment, an RF
electric field is generated inside a region of adipose tissue
together with the ultrasound energy.
Inventors: |
Rosenberg; Avner; (Beit
Shearim, IL) ; Eckhouse; Shimon; (Haifa, IL) ;
Kreindel; Michael; (Zichron Ya'acov, IL) |
Correspondence
Address: |
THE NATH LAW GROUP
112 South West Street
Alexandria
VA
22314
US
|
Assignee: |
SYNERON MEDICAL LTD
Yokneam lllit
IL
|
Family ID: |
38008148 |
Appl. No.: |
12/223964 |
Filed: |
February 15, 2007 |
PCT Filed: |
February 15, 2007 |
PCT NO: |
PCT/IL2007/000211 |
371 Date: |
November 18, 2008 |
Current U.S.
Class: |
601/2 ;
606/33 |
Current CPC
Class: |
A61B 2018/0047 20130101;
A61B 2017/00026 20130101; A61N 1/0408 20130101; A61N 1/328
20130101; A61N 7/00 20130101; A61N 2007/0008 20130101; A61N
2007/0078 20130101; A61N 2007/0039 20130101; A61B 2017/00061
20130101; A61B 2090/378 20160201; A61N 1/0472 20130101; A61B
2017/00106 20130101; A61B 18/12 20130101 |
Class at
Publication: |
601/2 ;
606/33 |
International
Class: |
A61N 7/00 20060101
A61N007/00; A61B 18/18 20060101 A61B018/18 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2006 |
US |
11/335181 |
Claims
1-163. (canceled)
164. A method for treatment of adipose tissue, said method
comprising: (a) applying at least one source of moderately focused
ultrasound energy to a skin protrusion surface to generate a
pressure gradient in said tissue; (page 11, line 4) (b) enhancing
the pressure gradient at the expense of pressure amplitude at the
focusing volume by limiting the focusing of said ultrasound energy,
such that the desired effects on the adipose tissue will be
enhanced; (c) generating relative movement between said adipose
tissue ingredients such as lipid vacuole, cytoplasm fluid cells and
intercellular fluids with sufficient intensity to rupture said cell
membranes.
165. The method according to claim 164, wherein said moderately
focused ultrasound energy is confined to a view angle of less than
120 degrees.
166. The method according to claim 164, wherein said moderately
focused ultrasound energy is confined to a view angle of less than
90 degrees.
167. The method according to claim 164, wherein in order to avoid
penetration of the ultrasound energy to internal tissues and organs
below the adipose tissue, said moderately focused ultrasound energy
is radiated into a protrusion formed of said adipose tissue about
parallel to the skin surface outside the protrusion.
168. The method according to claim 167, wherein said protrusion is
formed by one of vacuum means or mechanical manipulation of the
tissue.
169. The method according to claim 168, wherein said protrusion is
formed by mechanical manipulation of the tissue.
170. The method according to claim 168, wherein said protrusion is
formed by vacuum.
171. The method according to claim 167, wherein said ultrasound
energy is transmitted through said skin protrusion.
172. The method according to claim 164, wherein said moderately
focused ultrasound energy generates a pressure gradient between 2
GPa/m to 15 GPa/m, and has a frequency lower than 1 MHz.
173. The method according to claim 164, wherein the differences
between the density of the tissue ingredients assist in generating
said relative movement between them.
174. The method according to claim 164, further comprising
controlling the negative pressure generated by said ultrasound such
that said pressure level does not cause cavitation in said tissue
ingredients.
175. The method according to claim 174, wherein a sensor comprising
a receiver tuned to half the ultrasound transmitting frequency
detects and controls appearance of cavitations in the tissue.
176. A method for delivering ultrasound energy to subcutaneous
adipose tissue, and selectively treating fat cells, said method
comprising: (a) forming a protrusion of a skin region and
underlying adipose tissue; (page 14, line 12) (b) applying to said
protrusion a moderately focused ultrasound and generating a path of
preferred RF absorption path by selectively heating with the
ultrasound, fluids (cytoplasm and intracellular fluids) located in
said adipose tissue and; (page 15, line 3 and line 14) (c) applying
RF to said tissue volume, said RF being preferentially absorbed by
the preferred RF absorption path generated by the ultrasound
application and generating additional stress by charging the cell
membranes; and wherein said RF and ultrasound at least partially
operating on the same tissue volume.
177. An applicator for treatment of adipose tissue, said applicator
comprising: (a) a manipulator, said manipulator forms a protrusion
of a region of the tissue to be treated; (b) at least one source of
moderately focused ultrasound energy to be applied to the tissue in
the protrusion to generate a high conductivity path and pressure
gradient in said adipose tissue, said pressure gradient imparts a
relative movement between said tissue ingredients such as lipid,
cytoplasm and intercellular fluids; (c) a source of RF for
application to said protrusion said RF being preferentially
absorbed by the high conductivity path generated by the ultrasound
application; and wherein said RF and ultrasound at least partially
operate on the same tissue volume.
178. The applicator according to claim 177, wherein said
manipulator forms the protrusion by mechanically manipulating the
tissue or by application of vacuum.
179. The applicator according to claim 178, wherein said protrusion
is formed by mechanically manipulating the tissue.
180. The applicator according to claim 178, wherein said protrusion
is formed by application of vacuum.
181. The applicator according to claim 177, wherein said applicator
directs moderately focused ultrasound energy into said adipose
tissue through a protruding region of the skin parallel to
non-deformed surrounding said protruding tissue region of the
skin.
182. The applicator according to claim 177, wherein said source of
moderately focused ultrasound energy provides the ultrasound energy
at an angle of 90 degrees to said protrusion.
183. The applicator according to claim 177, wherein said applicator
provides moderately focused ultrasound energy confined to a view
angle of less than 120 degrees.
184. The applicator according to claim 177, wherein said applicator
provides moderately focused ultrasound energy confined to a view
angle of less than 90 degrees.
185. The applicator according to claim 177, wherein said source of
moderately focused ultrasound energy generates a pressure gradient
between 2 GPa/m to 15 GPa/m.
186. The applicator according to claim 177, wherein said source of
moderately focused ultrasound energy has a frequency lower than 1
MHz.
187. The applicator according to claim 186, wherein said ultrasound
energy emitted by said source is transmitted through said
protruding tissue region.
188. The applicator according to claim 186, wherein said source of
the ultrasound energy is one of a group of a flat transducer,
curved transducer or a transducer with a lens.
189. The applicator according to claim 177, further comprising: (a)
at least one RF electrode (b) a skin-cooling device, and (c) a
receiver tuned to half the ultrasound transmitting frequency, said
receiver senses and detects appearance of cavitations in the
treated tissue and controls said pressure level such that it does
not cause cavitation in said lipid, cytoplasm and intercellular
fluids.
190. An applicator for treatment of adipose tissue, said applicator
comprising: (a) a manipulator, said manipulator forms a protrusion
of a region of the tissue to be treated; (b) at least one source of
moderately focused ultrasound energy radiating in a direction
parallel to undisturbed body surface (page 19 line 22) and
generating a high conductivity path and pressure gradient in said
adipose tissue, said pressure gradient imparts a relative movement
between said tissue ingredients; (c) a source of RF for application
to said protrusion said RF being preferentially absorbed by the
high conductivity path generated by the ultrasound application; and
wherein said RF and ultrasound energy absorbed in at least common
tissue volume destruct the cells by causing said cell necrosis or
apoptosis.
191. The applicator according to claim 188, further comprising: (a)
at least one RF electrode (b) a skin-cooling device, and (c) a
receiver tuned to half the ultrasound transmitting frequency, said
receiver senses and detects appearance of cavitations in the
treated tissue and controls said pressure level such that it does
not cause cavitation in said lipid, cytoplasm and intercellular
fluids.
192. A method of selective treatment of fat cells, said method
comprising: (a) forming a protrusion of a skin region and
underlying adipose tissue; (b) applying to said protrusion at an
angle of 90 degrees short pulses of moderately focused low
frequency ultrasound; (c) generating high pressure gradients and
high strain in said cell membranes and selectively heating said
cell membranes, and; (d) destructing said fat cells.
193. The method according to claim 192, wherein the length of the
pulses is between millisecond and 100 microsecond.
194. The method according to claim 192, wherein the ultrasound
frequency is below 1 MHz.
195. The method according to claim 192, wherein the differences in
viscosity of cytoplasm and the cell membranes facilitate selective
heating of said membranes.
196. The method according to claim 192, wherein the temperature of
selectively heated cells is below 44 degrees Celsius.
Description
FIELD OF THE INVENTION
[0001] The invention relates to methods and apparatuses for the
reduction of adipose (fat) tissue.
LIST OF REFERENCES
[0002] The following references are brought to facilitate
description of the background of the present invention, and should
not be construed as limiting the scope or patentabililty of the
invention:
U.S. Pat. No. 5,143,063 [0003] U.S. Pat. No. 5,158,070 [0004] US
Patent Applications Nos. 2005/0154431 and 2004/0106867 [0005] U.S.
Pat. No. 6,607,498 [0006] U.S. Pat. No. 6,113,558 [0007] U.S. Pat.
No. 6,889,090 [0008] U.S. Pat. No. 5,871,524 [0009] U.S. Pat. No.
6,662,054 [0010] S. Gabriel, R. W. Lau, and C. Gabriel, Phys. Med.
Biol. 41 (1996), pp 2251-2269 [0011] Luc Fournier and Be'la Joo's,
Physical review 67, 051908 (2003) [0012] Alster T. S. and Tanzi, E.
L., The Journal of Cosmetic and Laser Therapy. 2005; 7: 81-85
[0013] "Physical properties of tissue", by Francis A. Duck,
Academic Press Ltd., 1990, p. 138. [0014] "Physical properties of
tissue", by Francis A. Duck, Academic Press Ltd., 1990, p. 85
[0015] Herve Isambert, Phys. Rev. Lett. 80, p3404 (1998) [0016] K.
Y. Saleh and N. B. Smith, Int. J. Hyperthermia Vol. 20, NO. 1
(February 2004), pp. 7-31.
BACKGROUND OF THE INVENTION
[0017] Reduction of subcutaneous fat layers, or adipose tissue, is
an aesthetic treatment for which there is a growing demand. One
method, liposuction, is a very aggressive invasive treatment
requiring local or general anesthesia, and the subsequent healing
process is very long and painful. Methods for non-invasive local
reduction of fat are based on the delivery of electromagnetic or
sound energy through the skin into the subcutaneous adipose tissue.
The main challenge with non-invasive treatment of fat tissue is to
transfer the energy through the outer layers of the skin, and
concentrating it to the required level in the fat tissue with
minimal collateral damage to the skin layers and deeper body
tissues.
[0018] U.S. Pat. No. 5,143,063 describes a method for destruction
of fat cells (adipocytes) in subcutaneous adipose tissue, in which
radiant energy is focused into these cells. The radiant energy may
be electromagnetic in the microwave range, or ultrasound. The major
mechanism for cell destruction is the heat generated by the radiant
energy. Only at the focal volume is the energy density high enough
for cell destruction, while outside the focal volume the energy
density is lower than the damage threshold. There is no specific
selectivity for destruction of fat cells, only a geometrical
selectivity created by the focusing.
[0019] U.S. Pat. No. 5,158,070 discloses use of ultrasound pulses
of short duration that are powerful enough to tear soft tissue.
Ultrasound pulses having a frequency between 3 MHz to 10 MHz and a
pulse length of one .mu.sec to one msec are focused in the soft
tissue to effect tearing and destruction. Due to the application of
short intense pulses, mechanical, and not thermal, effects are
presumed to be responsible for the tissue destruction.
[0020] The following calculation provides an estimate for the peak
pressure of the ultrasound wave required for this cell tearing.
Assuming a plane ultrasound wave for which the cell size is much
smaller then the wavelength, the local displacement U(x) is given
by:
U(x)=U.sub.max sin(.omega.t-kx)
where U.sub.max is the maximum displacement given by:
U m ax = V m ax .omega. ##EQU00001##
V.sub.max is the maximum velocity, .omega.=2.pi.f, f is the
frequency of the ultrasound, and k is the wave vector. For a plane
wave, .omega.=kc, where c is the sound velocity at the tissue.
Taking the derivative of U with respect to x, the strains
obtained:
U x = - k V ma x .omega. cos ( .omega. t - kx ) = - V ma x c cos (
.omega. t - kx ) ##EQU00002##
[0021] The maximal strain is V.sub.max/c. The strength of a typical
cell membrane has been investigated, and it was found that
stretching a cell membrane by more then 2% causes it to tear,
leading to cell necrosis, (Luc Fournier and Be'la Joo's, Physical
review 67, 051908 (2003)). This corresponds to a strain of 0.02.
Since the sound velocity in a typical soft tissue is about 1500
m/sec, for rupturing a cell membrane, V.sub.max has to be over 30
m/sec. For a plane wave, V=P/Z, where P is the pressure and Z is
the acoustic impedance of the tissue, a typical value for Z is 1.5
MRayleigh, so that P has to be greater than 45 MPa. This number
corresponds to a very intense ultrasound, which can be achieved
with a very high degree of focusing, and which is obtainable at
frequencies in the range of a few MHz. For example, US Patent
Application No. 2005/0154431, discloses adipose tissue destruction
generated by HIFU (High Intensity Focused Ultrasound), with a
typical frequency of 1-4 MHz and a pressure of about 30 MPa, close
to the theoretical estimate of 45 Mpa obtained above.
[0022] This method of cell rupturing is also not selective for
adipose tissue cells (adipocytes) because the adipocyte membrane is
not weaker than that of other cells. Also the shape and size of the
cell did not enter in the above considerations. In this respect,
cell destruction by rupturing the cell membrane is similar to cell
destruction by heating the cells (hyperthermia). Neither method is
selective for adipocytes, and any selectivity in the method relies
on geometry i.e. very strong focusing of the radiation in the
adipose tissue. For both methods, a high degree of focusing yields
a very small focal volume where cell destruction occurs. A typical
effective focal width is a few millimeters. Therefore, the focal
volume has to be moved over the treated area. US Patent
Applications Nos. 2005/0154431 and 2004/0106867 disclose such a
system.
[0023] Another physical effect of focused ultrasound that can cause
cell lysis, is cavitations. Cavitations are small bubbles, starting
from initial small gas nucleation centers, which are driven larger
by the negative pressure phase of the ultrasound wave. The rate of
generation and growth of cavitations is an increasing function of
the amplitude of the pressure, therefore an increasing function of
the ultrasound power density. Under certain critical conditions,
the bubbles collapse violently, generating in their vicinity shock
waves and fluid jets that can destroy cells. In liquid
environments, especially in aqueous solutions, there is evidence
that collapse of cavitations causes cell necrosis and apoptosis.
U.S. Pat. No. 6,607,498 discloses focusing ultrasound energy on
adipose tissue to cause cavitations and lysis of adipose tissue.
U.S. Pat. No. 6,113,558 discloses the application of focused pulsed
ultrasound, which causes cavitations, for non-invasive treatment of
tissues. This last patent contains a list of possible applications,
which include the induction of apoptosis and necrosis, clot lysis,
and cancer treatment. This patent includes a study on the
generation of cavitations and on the optimization of pulse width
and pulse repetition rate for maximizing the cavitations. The
cavitation threshold for a non-degassed buffer solution and blood
are in the range of 1000-1500 W/cm.sup.2, while for degassed fluids
the threshold rises to 2000 W/cm.sup.2. The ultrasound frequency in
these experiments was 750 kHz. Cavitation damage is not cell
selective, and can be induced on many cell types. The cavitation
threshold is quite high, and can be expected to be much higher
inside adipose tissue, since most of the tissue volume is fat
(lipid vacuoles). As with thermal treatment and mechanical
rupturing of cells by ultrasound, also with cavitation, a high
degree of focusing is required to ensure treatment of the selected
tissue only (geometrical selectivity). There is another reason for
the importance of focusing in cavitation treatment: Cavitations
absorb ultrasound very strongly. Therefore, if cavitations are
created close to the applicator, that is between the focal region
and the ultrasound radiating transducer (for example at the skin),
then most of the ultrasound energy will be dissipated there and
will not reach the target tissue in the focal volume. To prevent
this from occurring, the focusing must be sufficient to assure an
intensity above the minimum value for cavitation at the focal
volume, while the intensity at other tissues between the transducer
and focal volume must be below the threshold for cavitation.
[0024] Besides ultrasound and microwave radiation, application of
RF (Radio Frequency) energy can affect both the skin and
subcutaneous layers. U.S. Pat. No. 6,889,090 discloses the
application of RF energy for skin treatment. U.S. Pat. No.
5,871,524, describes application of radiant energy through the skin
to an underlying subcutaneous layer or deeper soft tissue layers.
The main energy source is RF. A bipolar RF application, such as
described in U.S. Pat. No. 6,889,090, is preferred over unipolar
RF, since in unipolar RF currents flow through uncontrolled
channels in the body, and may cause unwanted damage.
[0025] RF energy is applied to the body through two conducting
electrodes applied to the skin between which an alternating voltage
is driven. The RF current flows according to Ohm's law through the
conducting tissues, generating heat, which can affect the tissue.
The conductivity of the skin layers is an order of magnitude larger
than that of fat tissue. Typical skin conductivity is about 0.4 S/m
and that of adipose tissue is about 0.04 S/m at RF frequencies
between 100 kHz and 10 MHz (S. Gabriel, R. W. Lau, and C. Gabriel,
Phys. Med. Biol. 41 (1996), pp 2251-2269). Therefore most of the
current flows through the skin layers, which is good for skin
treatments, for example, hair removal and skin rejuvenation.
However, it is less efficient for treatment of the deeper adipose
layers.
[0026] U.S. Pat. No. 6,662,054 discloses the application of
negative pressure (vacuum) to a region of the skin, so that this
region protrudes out of the surrounding skin, and applying RF
energy to the protrusion via electrodes. Under negative pressure,
the path between the RF electrodes is longer along the skin than
through the subcutaneous layers. Therefore, more RF energy is
delivered into subcutaneous layers than through the skin. A
commercial system based on U.S. Pat. No. 6,662,054 has proved
efficient for treatment of cellulites (TINA S. ALSTER &
ELIZABETH L. TANZI, The Journal of Cosmetic and Laser Therapy.
2005; 7: 81-85). Cellulite is clinically manifested by irregular
skin contours or dimpling of the skin. It is caused by excess
adipose tissue retention within fibrous septae. The skin
irregularity is proportional to the subcutaneous fat projected into
the upper dermis.
[0027] Most of the volume of an adipocyte is occupied by a fat
fluid drop, known as a lipid vacuole. The typical diameter of the
cell is 50-100 .mu.m. It tends to 100 .mu.m in adipose tissue of
obese people. Between the lipid vacuole and cell membrane, is
cytoplasm. Typically the width of the cytoplasm is only a few
micrometers and it is not uniform around the lipid vacuole. It can
be in the range from below 1 .mu.m in one region of the cell and
3-5 .mu.m in other regions.
[0028] The macroscopic physical properties of adipose tissue, mass
density and sound velocity, are dominated by the material of the
lipid vacuole, which occupies most of the tissue volume in mature
fat cells which are the cells to be treated in reduction of the fat
layer. The physical properties of the lipid vacuole fluid are thus
almost identical to those of fat tissue. The density of adipose
tissue is about 10% lower than that of other body tissues.
According to "Physical properties of tissue", by Francis A. Duck,
Academic Press Ltd., 1990, p. 138, the density of adipose tissue is
916 Kg/m.sup.3, while that of body fluids and soft tissue are above
1000 Kg/m.sup.3 (i.e. above the density of water). The dermis
density is about 1100 Kg/m.sup.3, while that of muscles is 1040
Kg/m.sup.3. The cytoplasm and intercellular fluid are aqueous
solutions so that their density is expected to be similar to that
of other body fluids and soft tissues, i.e. in the range of
1020-1040 Kg/m.sup.3. The velocity of sound is about 1430 m/sec in
adipose tissue, compared to 1530 m/sec for skin, at normal body
temperature. Moreover, on page 85 of the Duck reference, the slope
of the sound velocity versus temperature curve for fat is
completely different from that of other body fluids. For fat, sound
velocity decreases with increasing temperature, dropping to 1400
m/sec at 40.degree. C., while that of water and other body fluids
rises with temperature, and is about 1520 m/sec at 40.degree. C.
for water and higher for body fluids and soft tissues other than
fat.
[0029] A basic model of the electrical properties of cells at the
microscopic level can be found in Herve Isambert, Phys. Rev. Lett.
80, p 3404 (1998). The cell membrane is a poor electrical conductor
and therefore behaves essentially as a local capacitor upon the
application of an electric field across the cell. The charging of
the cell membrane under the application of external electric field
generates a stress at these membranes, yielding strain which
depends on the elastic properties of the cell, and which at
increased intensity can rupture the cell membrane, a phenomena
known as "electroporation".
SUMMARY OF THE INVENTION
[0030] The present invention provides methods and apparatuses for
the treatment of adipose (fat) tissue. As used herein, the term
"treatment of adipose tissue" includes such procedures as fat
destruction, inducing fat necrosis, inducing fat apoptosis, fat
redistribution, adipocyte (fat cell) size reduction, and cellulite
treatment.
[0031] The apparatuses of the invention include at least one
ultrasound transducer configured to be applied to a skin surface
and to radiate ultrasound energy through the skin into the
subcutaneous adipose tissue. The methods of the invention include
directing adipose tissue through the skin layer into the
subcutaneous adipose tissue.
[0032] One embodiment of the invention is based upon a new finding
that pressure gradients of ultrasound energy can lead to selective
treatment of the adipose tissue cells. Without wishing to be bound
by a particular theory, it is believed that the treatment or
destruction of adipose tissue cells by pressure gradients generated
by ultrasound energy is due to differences between the mass density
of the lipid and that of the other constituents of the adipocytes.
As explained below, a pressure gradient in adipose tissue capable
of treating or destroying the adipose tissue cells may be generated
using a moderately focused ultrasound transducer.
[0033] In another embodiment of the invention, skin and a region of
the underlying adipose tissue are made to protrude out from the
surrounding skin surface. Ultrasound energy is then directed to
adipose tissue in the protrusion. The protrusion may be formed, for
example, by applying a negative pressure (vacuum) to the skin
region or by mechanical manipulation of the skin region. The
apparatus of this aspect of the invention includes an applicator
adapted for causing a skin region to protrude above the surrounding
skin region and one or more ultrasound transducers which radiate
ultrasound energy preferably into the protrusion.
[0034] In yet another embodiment of the invention, ultrasound
energy and RF energy are directed into the adipose tissue. The
apparatus of this aspect of the invention includes an applicator
having at least one pair of RF electrodes and at least one
ultrasound transducer.
[0035] The present invention provides methods and apparatus for
treatment of adipocytes. One aspect of the invention is based upon
a new finding that pressure gradients of ultrasound energy can lead
to selective treatment of the adipose tissue cells. Without wishing
to be bound by a particular theory, it is believed that the
selective treatment of adipose tissue cells by pressure gradients
generated by ultrasound energy is due to differences between the
mass density of the lipid and that of the other constituents of the
adipocytes.
[0036] When ultrasound energy is directed to a fat cell, for
frequencies of less than about 1 MHz, the wavelength of the
ultrasound wave is about 1.5 mm, much larger than the fat cell
dimensions, which are 50-100 .mu.m. For a plane acoustic wave
propagating through the tissue having pressure amplitude P.sub.max,
angular frequency .omega. and wave vector k=2.pi./.lamda., where
.lamda. is the wavelength, the pressure p(x,t) is:
p(x,t)=P.sub.max sin(.omega.-kx) (1)
Neglecting viscosity, the movement of fluids can be calculated from
Euler's equation:
.differential. v .fwdarw. .differential. t + ( v .fwdarw.
.gradient. ) v .fwdarw. = - 1 .rho. .gradient. p ( 2 )
##EQU00003##
Where v is the velocity vector, and .rho. is the mass density of
the fluid. For small velocities (compared to the sound velocity c)
the term (v.DELTA.)v can be neglected and the velocity is
proportional to the pressure gradient. For the plane wave of
equation 1, since the motion is only in the x-direction:
.differential. v .differential. t = - 1 .rho. .differential. p
.differential. x = P ma x k .rho. cos ( .omega. t - kx ) ( 3 )
##EQU00004##
The velocity is:
v ( x , t ) = P ma x k .rho..omega. sin ( .omega. t - kx ) ( 4 )
##EQU00005##
And the local displacement of the fluid is:
U ( x , t ) = - kP ma x .rho..omega. 2 cos ( .omega. t - kx ) ( 5 )
##EQU00006##
This is the formula for a plane acoustical wave, and for such a
wave .omega.=kc and kP.sub.max is the pressure gradient.
[0037] Let .rho..sub.li be the density of the fluid of the lipid
vacuole, and .rho..sub.cy the density of the cytoplasm fluid in an
adipocyte. The respective amplitudes of the displacements can be
calculated using equation (5) and substituting the corresponding
densities:
U li = kP ma x .rho. li .omega. 2 ##EQU00007## U cy = kP ma x .rho.
cy .omega. 2 ##EQU00007.2##
And the relative movement of the two fluids is given by:
.DELTA. U = U li - U cy = kP ma x .omega. 2 ( 1 .rho. li - 1 .rho.
cy ) ( 7 ) ##EQU00008##
Numerical Example:
[0038] Taking typical values for the adipocytes, .rho..sub.li=916
Kg/m.sup.3, .rho..sub.cy=1020 Kg/m.sup.3, and taking P.sub.max=4
MPa, .omega.=2.pi.f, f=250 kHz, and c=1400 m/sec, k=.omega./c=1122
m.sup.-1, the result is .DELTA.U=0.2 .mu.m. The physical meaning is
that the cytoplasm fluid, which is a "minority" fluid in the
adipose tissue, oscillates under these conditions with respect to
the "majority" fluid, the lipid vacuole, with an amplitude of 0.2
.mu.m. The pressure of P.sub.max=4 MPa corresponds to the power
flow density of P.sup.2/2Z=6.2 MW/m.sup.2=620 W/cm.sup.2 and to a
peak pressure gradient of kP.sub.max=4.5 GPa/m
[0039] A relative displacement of 0.2 .mu.m is significant at the
scale of cellular dimensions. The cytoplasmic layer in the
adipocytes has a thickness of few micrometers, at some regions of
the cell even below 1 .mu.m. More specifically, there are regions
of the cell where over a length of 5-10 .mu.m the width of the
cytoplasm changes from below one micrometer to few micrometers. At
the narrower regions, the fluid movement of the cytoplasm is damped
by viscosity, while at the wider regions the cytoplasm is freer to
move. Under the conditions of this example, there is a difference
of displacement of about 0.2 .mu.m over a length of 5-10 .mu.m,
which means a strain of 0.04-0.02. Since the cell membrane borders
the cytoplasm, the cell membrane is also subjected to that strain,
which is above the threshold for membrane rupture.
[0040] Another effect that may be associated with the above
relative movement of adipocyte fluids is selective heating of the
cytoplasm. The viscosity will cause some of the kinetic energy to
be converted into heat. Since the cytoplasm is a minority fluid in
the fat tissue and since the lipid vacuole fluid has poor heat
conductance, the generated heat will selectively raise the
temperature of the cytoplasm and of the cell membrane bordering it,
and may lead to cell necrosis or apoptosis, directly by the local
temperature rise at the membrane, or by lowering its strength at
the elevated temperature.
[0041] For a non-plane wave, kP.sub.max in equation 7 must be
replaced by the more general pressure gradient, .DELTA.P, in
accordance with Euler's equation. It is known to use focusing of
the ultrasound energy to generate very high power densities in a
focal volume. It helps in two ways: first, it facilitates
production of high power densities by an ultrasound transducer,
and, second, it generates geometrical selectivity for the desired
effect at the focal volume. However it should be noted that
focusing, especially strong focusing, enhances the peak pressure
substantially more than the pressure gradient. As a limiting
example, a spherical transducer will generate at its center a very
high peak pressure but zero pressure gradient, a manifestation of
the fact that at the center the fluid is not moving. The focusing
may be described physically as a superposition of plane waves. The
pressure amplitude is a scalar, and at the focus the phases of the
plane waves are identical, therefore the pressure at the focus is a
scalar sum of the pressure amplitudes. However, the pressure
gradient, and the displacement which is proportional to that
gradient (by Euler's equation), are vectors, therefore their vector
summed amplitude is always smaller than the sum of the magnitudes.
More specifically, for strong focusing, the ultrasound radiation
arrives at the focus from directions with large angular deviations,
reducing the vector sum of the pressure gradient and of the fluid
displacement. Therefore, according to the invention, it is
preferred to limit the focusing in order to enhance the pressure
gradient at the expense of the pressure amplitude at the focus, so
that the selective effects on the fat cell will be obtained without
the undesired effects associated with high pressure, such as
cavitations.
[0042] Thus, in its first aspect, the present invention provides a
method for treatment of adipose tissue in a region of subcutaneous
adipose tissue comprising directing applying at least one source of
ultrasound energy to a skin surface to generate a pressure gradient
in the region, said pressure gradient generating relative movement
between fat cells constituents having different densities, the
relative movement having sufficient intensity to cause a treatment
of the fat cells.
[0043] In its second aspect, the invention provides a method for
treatment of adipose tissue in a region of subcutaneous adipose
tissue comprising: [0044] a. forming a protrusion of skin and
underlying adipose tissue containing the region; and [0045] b.
radiating ultrasound energy into the region.
[0046] In its third aspect, the invention provides a method for
treatment of fat tissue in a region of subcutaneous adipose tissue
comprising: [0047] a. radiating ultrasound energy into the region;
and [0048] b. generating an RF electric field inside the
region.
[0049] In another of its aspects, the invention provides an
apparatus for treatment of adipose tissue in a region of
subcutaneous adipose tissue comprising at least one source of
ultrasound energy configured to direct ultrasound energy through a
skin surface to generate a pressure gradient in the region, said
pressure gradient generating relative movement between fat cell
constituents having different densities with sufficient intensity
to cause treatment of the fat cells.
[0050] In another of its aspect, the invention provides an
apparatus for treatment of adipose tissue in a region of
subcutaneous adipose tissue comprising: [0051] a. a device
configured to form a protrusion of skin and underlying adipose
tissue containing the region; and [0052] b. at least one ultrasound
energy source configured to radiate ultrasound energy into the
region.
[0053] In still another of its aspects, the invention provides an
apparatus for treatment of fat tissue in a region of subcutaneous
adipose tissue comprising: [0054] a. An ultrasound energy source
configured to direct ultrasound energy through a skin surface into
a region of subcutaneous adipose tissue; and [0055] b. At least two
electrodes driven by an RF power source configures to generate RF
field inside said region of adipose tissue.
[0056] In another of its aspects, the invention provides a method
for treatment of adipose tissue in a region of subcutaneous adipose
tissue comprising: [0057] a. forming a protrusion of skin and
underlying adipose tissue containing the region; [0058] b.
radiating ultrasound energy into the region; and [0059] c.
generating an RF electric field inside the adipose tissue.
[0060] In still another of its aspects, the invention provides an
apparatus for treatment of adipose tissue in a region of
subcutaneous adipose tissue comprising: [0061] a. a device
configured to form a protrusion of skin and underlying adipose
tissue containing the region; [0062] b. at least one ultrasound
energy source configured to radiate ultrasound energy into the
region; and [0063] c. at least two RF electrodes and an RF driver
configured to produce an RF electric field inside the
protrusion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0064] In order to understand the invention and to see how it may
be carried out in practice, preferred embodiments will now be
described, by way of non-limiting examples only with reference to
the accompanying drawing's, in which:
[0065] FIG. 1 shows the "view angle" of an ultrasound transducer
and vector summation of pressure gradients;
[0066] FIG. 2 shows an apparatus for reduction of adipose tissue in
accordance with one embodiment of the invention;
[0067] FIG. 3 shows an applicator, including an ultrasound
transducer for use in the system of FIG. 1;
[0068] FIGS. 4a and 4b show pressure distribution contours
generated by a flat, uniform phase ultrasound transducer;
[0069] FIG. 5 shows an applicator configured to radiate ultrasound
energy into a body protrusion created by negative pressure;
[0070] FIG. 6 shows the applicator of FIG. 5 provided with a degree
of freedom for the ultrasound transducer to rotate and adapt to the
protrusion;
[0071] FIGS. 7a and 7b show an applicator configured to radiate
ultrasound energy into a body protrusion created by mechanical
manipulation of the skin;
[0072] FIG. 8 shows an applicator, including at least one
ultrasound transducer and at least a pair of RF electrodes;
[0073] FIG. 9 shows an applicator including at least one ultrasound
transducer and at least a pair of RF electrodes configured to
provide RF and ultrasound energy into adipose tissue at a
protrusion created by mechanical manipulation of the skin;
[0074] FIG. 10 shows an applicator including at least one
ultrasound transducer and at least a pair of RF electrodes,
configured to provide RF and ultrasound energy into the adipose
tissue at a protrusion created by negative pressure (vacuum);
and
[0075] FIG. 11 shows schematically an alternative arrangement of
the for RF electrodes with respect to the ultrasound
transducers.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0076] According to invention, based on the above considerations,
an apparatus for selective destruction of fat cells will include an
ultrasound transducer, which is moderately focused. Referring to
FIG. 1, an ultrasound transducer 21 has a focal point 22. The view
angle .alpha. of the transducer edges from the focal point
correlates with the focusing in a very general way: The larger
.alpha. the larger the focusing. The displacement and the pressure
gradient at the focus generated by waves coming from the edges of
the transducer, is the vector sum of vector 24a and vector 24b
yielding vector 25. The magnitude of the vector 25 is the magnitude
of the vector 24a multiplied by 2 cos(.alpha./2) (assuming 24a is
equal to 24b). For .alpha.=120' this factor is 1, compared to a
factor of 2 for the scalar summation of the pressure at the same
point. That is, for large .alpha. the pressure is enhanced by the
focusing much more then the pressure gradient. Therefore, to obtain
the selective fat reduction according to the invention, the angle
.alpha. is limited. Preferred values are .alpha.<120.degree.,
more preferred .alpha.<90.degree..
[0077] According to the invention, based on equation 7, for
selective destruction of fat cells it is preferred to radiate the
ultrasound at low frequencies, preferably lower than 1 MHz, more
preferred below 300 kHz. The numerical example above demonstrated
that at 250 kHz peak pressure gradient of 4.5 GPa/m is expected to
selectively damage fat cells. For moderate focusing this
corresponds to a power flow density of about 700 W/cm.sup.2, which
is lower than the threshold for cavitation, which is preferably
avoided according to the invention.
[0078] Pulsed operation is another way according to the invention
for enhancing the selective effects of the ultrasound for cell
destruction. Short pulses with high intensity generate high strain
at the cell membranes due to the high pressure gradients, while the
average power is low enough to prevent non-selective damage by
excessive heating of tissues. Also, for selectively heating of
cytoplasm and cell membranes by viscosity it is preferred to apply
short intense pulses, since this viscosity heating effect is
non-linear. Typical parameters may be: pulse length between 10
.mu.sec and 10 msec, more preferred between 100 .mu.sec and 1
msec.
[0079] The pulse repetition rate is preferably matched to the pulse
length to generate a power duty of 1% to 10%. The average power is
preferably controlled by peak power and duty, in order to control
the heating of tissues. While the basic effect is non-thermal, some
increase in temperature may be desired, since it reduces the
strength of the cells. Preferably tissue heating above normal body
temperature is kept below 44.degree. C., a temperature known as the
pain threshold. Controlled tissue heating according to the
invention can be obtained from the ultrasound energy, more
preferably, RF energy is applied to the treated volume as detailed
below.
[0080] The pulse width and pulse repetition rates are preferably
selected to be as far as possible from those optimal for
cavitations at the treated tissues. As disclosed in U.S. Pat. No.
6,113,558, there is an optimal pulse length and pulse repetition
frequency for generating cavitations, which are preferably to be
avoided. These optimal conditions for cavitations may depend on
tissue type and its conditions (such as temperature). Therefore the
specific minimum cavitations conditions may require some matching
to the treated site. A cavitations sensor may be included in the
system to assist finding the minimum cavitations conditions.
Detection of cavitations can be based on the detection of enhanced
reflections at the transmitted ultrasound frequency or by the
detection of ultrasound radiation at half the transmitted
frequency, which is a known indication of cavitations.
[0081] The differences in sound velocities between the lipid
vacuole and other fluids in the fat tissue are due to differences
in compressibility. At elevated temperature, the difference
increases. ("Physical properties of tissue", by Francis A. Duck,
Academic Press Ltd., 1990, p. 85, FIG. 4.1). For example, the sound
velocity at 40.degree. C. for fat and other body fluids is 1400 m/s
and 1520 m/s, respectively. The respective adiabatic
compressibility values are .beta.=5.6.times.10.sup.-10 and
.beta.=4.2.times.10.sup.-10. Thus, under these conditions, the fat
is more compressible than other body fluids by 30%. However, high
pressures are required to exploit this. For examples a pressure of
P=10 MPa will generate a relative volume changes
.DELTA.V/V=.beta.P=5.6.times.10.sup.-3 and
.DELTA.V/V=.beta.P=4.2.times.10.sup.-3 for the lipid and cytoplasm
respectively. The difference between the fluids is
1.4.times.10.sup.-3, which over a scale of typical cell size
(50-100 micrometers) will cause a relative movement of about 0.1
.mu.m. For comparison, the mass density difference effect yielded
movement of about 0.2 .mu.m at a lower pressure of 4 MPa.
[0082] In accordance with one aspect of the invention, at least one
ultrasound transducer configured to be applied to a skin surface,
radiates ultrasound energy through the skin into the subcutaneous
fat layers to effect relative movement between fat cell
constituents and to cause fat cell necrosis or apoptosis. According
to the invention, a flat transducer having a uniform phase over its
surface is used, or a moderately focused transducer with fixed
focus, or a phased transducer array, which can produce a moderate
focus and can be electronically scanned inside the fat tissue to
cover a larger treatment volume.
[0083] As explained above, almost all prior art high power
ultrasound applications use a very high degree of focusing, to
enhance the ratio between the wanted damage at the target tissue
and unwanted damage at the entrance layers (between transducer and
target). However, since according to the present invention the
tuning is for selective damage to fat cells, moderate focusing is
used. Moderate focusing can reduce unwanted cavitations effects
while not reducing cell rupturing. This is attributed to the fact
that cavitations depend on the pressure magnitude of the ultrasound
wave (more specifically, on the negative pressure magnitude) and
not on the pressure gradient.
[0084] In another of its aspects, the invention provides a method
and apparatus for delivering ultrasound energy to subcutaneous
adipose tissue. According to this aspect of the invention, skin and
a region of the underlying adipose tissue are made to protrude out
from the surrounding skin surface. Ultrasound energy is then
directed to adipose tissue in the protrusion. The protrusion may be
formed, for example, by applying a negative pressure (vacuum) to
the skin region or by mechanical manipulation of the skin region.
The apparatus of this aspect of the invention includes an
applicator adapted for causing a skin region to protrude above the
surrounding skin region and one or more ultrasound transducers
which radiates ultrasound energy preferably into said
protrusion.
[0085] Creating a protruding region of skin and underlying adipose
tissue and radiating the ultrasound energy preferably parallel or
close to parallel to the non-protruding skin surface, has the
advantage that the radiation is preferentially directed into the
fat tissue inside the protrusion while much less ultrasound energy
is directed into other body tissues. This reduces the risks of
unwanted damage to deep body tissues which might be much more
sensitive to ultrasound energy, such as lungs, and reduces the pain
which is known to be effected when high intensity ultrasound
radiation heats the bones. A preferred apparatus according to the
invention may include at least two ultrasound transducers with
overlapping irradiated focal volumes inside the adipose tissue. The
relative phases of the emitted radiation from said transducers may
be controlled for maximizing the pressure gradients at selected
locations inside the treated tissue.
[0086] In another of its aspects, the present invention provides a
method and apparatus for treating subcutaneous adipose tissue. The
method comprises directing ultrasound energy and RF energy to the
adipose tissue. The apparatus of this aspect of the invention
includes an applicator having at least one pair of RF electrodes
and at least one ultrasound transducer. Applicant's co-pending U.S.
patent application Ser. No. 11/189,129 discloses the combination of
high frequency ultrasound energy and RF energy in skin rejuvenation
treatments. That application discloses generating a path of higher
RF conductivity by heating of selected tissue volume by focused
ultrasound, and applying RF to the body which will preferentially
flow through the high conductivity path. However the situation with
adipose tissue is much more complex, due to the large differences
in the mechanical, electrical and thermal properties of the
majority lipid vacuole fluid and the minority cytoplasm and
intercellular fluids. The total electrical conductivity inside the
tissue is composed from direct, Ohmic conductivity of the
intercellular fluid, and the Ohmic conductivity of the fluids
inside the cells in series with the capacitance of the cell
membrane (which is a poor conductor). Since in mature adipose
cells, most of the cell volume is filled with the poorly conducting
fluid of the lipid vacuole, most of the current flows in the narrow
channels of the cytoplasm and the intercellular fluid. Thus,
although both RF energy and ultrasound energy are known to be
poorly absorbed in fat tissue, most of the absorbed energy goes to
the very thin layers of fluids between the lipid vacuoles, which
occupy a very small fraction of the fat tissue volume. While on
average, a relatively small amount of energy is absorbed in the
adipose tissue, the specific energy transferred to the small
volumes of cytoplasm and intercellular fluid may be high. The fact
that the cell membrane borders these fluids makes the energy
investment in these fluids very effective for destruction of the
cell membrane, followed by cell necrosis or apoptosis. Selective
heating of these fluids can be achieved by exploiting the
difference in the cell fluid properties, as discussed above. The RF
energy and the ultrasound energy combine in these specific fluids
of the fat tissue, so the desired effects are enhanced without
increasing the danger of collateral damage which might be produced
in other tissues, especially at the skin through which the energy
is delivered, if the energy of a single type is increased to obtain
the same effect. The combination of ultrasound energy and RP energy
is more effective in several ways. The heating of tissue by
ultrasound increases the RF conductivity, so that more energy is
delivered by the RF, and the total heating reduces the cell
strength. In adipose cells, these effects are concentrated mainly
in the thin layers of the cytoplasm, so it is more effective for
destruction of fat cells and the selectivity is enhanced by the
combination. The combination of ultrasound and RF energy also
increases the strain on the fat cell membrane, since both
ultrasound and RF induce such strain on fat cells. The ultrasound
wave generates a strain at the fat cell membranes as discussed
above. The electric fields of the RF also generate strain due to
charging of the membranes (see, for example, Herve Isambert,
Supra). Simultaneous application of RF and ultrasound on the same
tissue volume yields a combined strain. In the adipose tissue both
effects concentrate at the thin cytoplasm and the adjacent membrane
of the adipocytes. That combination may reduce the intensity
required from each energy source, so that the risk of collateral
damage may be reduced.
[0087] In a preferred embodiment of this aspect of the invention,
at least one ultrasound transducer and at least two RF electrodes
are applied to the protuberance. A region of skin and underlying
adipose tissue to be treated is made to protrude above the
surrounding skin surface. The RF energy may be applied prior to or
during formation of the protuberance to pre-heat the tissue. The RF
energy may be applied prior to and/or at least partially
simultaneously with the ultrasound energy. When this protrusion is
created, the transducers are driven to radiate ultrasound energy
into the protruding tissues. RF energy is applied to the tissue via
the at least two electrodes, which are either conductive for direct
injection of current to the skin, or insulted by a thin layer of
insulating material for capacitive coupling of energy to the
tissue.
[0088] Application of RF and ultrasound energies to a protruding
region of skin allows treatment of subcutaneous adipose tissue and
cellulites.
[0089] FIG. 2 shows an apparatus 4 for applying ultrasound to
subcutaneous adipose tissue in accordance with one embodiment of
the invention. An applicator 3, to be described in detail below,
contains one or more ultrasound transducers. The applicator is
adapted to be applied to the skin of an individual 5 in a region of
skin and underlying adipose tissue to be treated. The applicator 3
is connected to a control unit 1 via a harness 2. The control unit
1 includes a power source 8. The power source 8 is connected to an
ultrasound driver 6. The control unit 1 contains a processor 9 for
monitoring and controlling various functions of the system. The
control unit 1 has an input device, such as a keypad 10 that allows
an operator to input to the processor 9 selected values of
parameters of the treatment, such as the frequency, pulse duration
and intensity of the ultrasound energy to be directed to the
adipose tissue.
[0090] The applicator 3 may optionally contain one or more pairs of
RF electrodes in addition to the ultrasound transducers. In this
case, the power supply 8 is connected to an RF generator 15 that is
connected to the RF electrodes in the applicator 3 via wires in the
cable 2. When RF electrodes are included in the applicator 3, the
processor 9 may monitor the electrical impedance between electrodes
and determined the temperature distribution in the vicinity of the
target from the impedance measurements. The system 1 may optionally
includes cooling means for cooling the skin surface during
treatment. For example, the control unit may contain a
refrigeration unit 12 that cools a fluid such as ethanol or water
for cooling the applicator 3. The cooled fluid flows from the
refrigeration unit 12 to the applicator via a first tube in the
harness 2, and flows from the applicator 3 back to the
refrigeration unit via a second tube in the harness 2.
[0091] The control unit may also include a vacuum pump 18 for
evacuating an interior chamber in the applicator 3, in order to
cause a region of the skin surface to protrude above the surround
surface. The pump 18 is connected to an interior chamber of the
applicator 3 by a vacuum hose in the cable 2, as explained
below.
[0092] In accordance with one aspect of the invention, the
applicator 3 is configured to deliver ultrasound energy to a region
of subcutaneous adipose tissue that so as to generate a pressure
gradient in the region that ruptures selectively fat cells in the
in the region.
[0093] FIG. 3 shows an embodiment 3a of the applicator 3. The
applicator 3a includes at least one ultrasound transducer 37. The
transducer is connected through a cable, preferably a coaxial cable
in the harness 2 to the ultrasound driver 6 in the control unit 1.
In use, the ultrasound transducer is attached to the skin surface
27, preferably with ultrasound gel or other ultrasound transmitting
material, and generates a focal volume 33 extending around focal
point 22 inside the subcutaneous adipose tissue 35. According to
one aspect of the invention, the view angle .alpha. 23 is limited
to maximize the ratio of pressure gradient to pressure at the focal
volume. Preferred values are .alpha.<120.degree., more preferred
.alpha.<90.degree.. The control unit 1 drives the ultrasound
transducer at an intensity to which produces at the focal volume
pressure gradient between 0.5 GPa/m to 50 GPa/m, more preferred
between 2 GPa/m to 15 GPa/m. Preferably, the ultrasound radiation
is at a frequency lower than 1 MHz, more preferred below 300 kHz.
Pulsed operation of the transducer is preferred, preferred pulse
lengths being between 10 .mu.sec and 10 msec, more preferred
between 100 .mu.sec and 1 msec. The pulse repetition rate is
preferably matched to the pulse length to generate a power duty of
1% to 10%.
[0094] The ultrasound transducer of the embodiments 3a may be flat
with uniform phase over its radiating surface. This embodiment has
the advantage of simplicity both of the transducer and the driving
electronics. A flat, uniform phase transducer generates a pressure
distribution, which has a maximum at a focal region, where the
pressure can reach more than 1.5 times that on the transducer
surface. FIG. 4 shows a specific example for a flat transducer with
a 20.times.20 mm radiating area. In the diagrams of FIG. 4, the
x-axis is parallel to the transducer surface while the z-axis is
normal to the transducer surface. The origin is at the center of
the transducer. Dimensions are in mm. FIG. 4(a) is calculated for
ultrasound frequency of 180 kHz, and 4(b) for 250 kHz. The contour
numbers are pressures, normalized to a unit pressure on the
transducer surface. Since the focusing is very small, contours of
pressure gradients at the focal region (not shown) are very close
to the pressure contours. The choice of the ultrasound frequency
controls the distance from the transducer face to the maxima, and
which thus determines the depth of treatment. In FIG. 4(a), the
region 29a of maximum pressure has an amplitude of 1.68, and is
located between z=10 mm to z=20 mm. For a frequency of 250 kHz with
the same radiating area, the maximum pressure is 1.66 and moves to
a region 29b between z=16 mm and z=32 mm, further from the
transducer face, as shown in FIG. 4(b). It is also preferred to
select the thickness of the layer between the radiating surface and
the skin so that the skin surface is at a region of minimum of
radiation intensity. Human skin is typically 1.5-2.5 mm thick.
Referring again to FIG. 4(a), contours of minimum pressure are at a
distance of up to about 4 mm from the radiating surface. By coating
the transducer face with a layer of material having acoustical
impedance close to that of human tissues and having a thickness of
about 4 mm, a ratio of about 1.66 between the maximum pressure in
the subcutaneous adipose tissue and maximum pressure at the skin is
obtained.
[0095] A curved transducer and/or transducer with a lens which
produces stronger fixed focusing can be applied according to the
invention. Another embodiment will have the transducer 37 made as a
phased array, with a multi-channel phased driver in the control
unit 1. An example of a phased array ultrasound system, with a
detailed description of high intensity phased array technology as
known in the art can be found in the paper by K. Y. Saleh and N. B.
Smith, Int. J. Hyperthermia Vol. 20, NO. 1 (February 2004), pp.
7-31. An apparatus based on a phased array is more complicated both
in the transducer and in the driving electronics. However it has
the following advantages:
[0096] a. Control of degree of focusing.
[0097] b. Control of depth and position of focal volume.
[0098] c. Possible scanning of focal volume inside a selected
volume of tissue.
[0099] At least one element of the array, or any additional small
transducer in the non-array embodiments, may be a sensor comprising
a receiver that is tuned to half the transmitting frequency to
detect generation of cavitations in the body tissue, and/or tuned
to the transmitted frequency to detect enhanced reflectivity from
hard body tissue or from cavitations. According to the output of
this sensor, the control unit 1 varies the radiated ultrasound
properties (pulse length, repetition rate and intensity) to
minimize their unwanted effects. A phased array embodiment also
enables positioning the focal volume away from the hard tissue
and/or reducing the focusing to reduce cavitations.
[0100] The embodiment 3a of the applicator has the advantage of
simplicity, however, since focusing is limited, there is a risk
that residual ultrasound energy will enter deeper into the body and
hit sensitive tissue such as lungs and effect unwanted damage.
Also, if this residual ultrasound energy were to hit bones, it
might cause pain. To reduce these risks, the embodiments 3b to 3g
may be used. These embodiments exploit the very high flexibility of
fat tissue, and based on generating a protrusion out of the body
surface and attaching at least one ultrasound transducer to that
protrusion. This transducer radiates preferably in a direction
parallel to the undisturbed body surface. or at least as close as
possible to that optimal angle. Under these conditions, the adipose
tissue inside the protrusion is exposed preferentially, while much
less radiation arrives at deeper body tissue. These embodiments can
be based on mechanical manipulations and/or on application of
negative pressure (vacuum) as detailed below.
[0101] FIG. 5 shows the embodiment 3b of the applicator 3. The
applicator 3b is shown in cross-section in FIG. 5 and includes a
hollow dome 40 having an interior chamber 41. At least one
ultrasound transducer 42a and possibly more transducers, such as
42b, are located in the interior chamber 41. The dome 40 is applied
to the skin and a negative pressure is generated in the interior
chamber 41 by pumping the air out through port 44 by the vacuum
pump 18 located in the control unit 1 that is connected to the
interior chamber by a vacuum hose 46 in the harness 2. Due to the
negative pressure, body tissue 45 including skin and subcutaneous
tissue 35, is sucked into volume 41, thus protruding above the
surrounding skin surface. This suction applies the skin surface
onto the ultrasound transducers 42a and 42b. The transducers are
connected through cables 48a and 48b in the harness 2 to the
ultrasound driver 6 in the control unit 1. The cables may include
coaxial cables for driving the transducers and optionally for
sending output signals from sensors located in the applicator 3b,
such as temperature sensors or ultrasound sensors, to the processor
9 in the control unit 1 for processing by the processor 9.
[0102] The ultrasound transducers 42a and 42b have focal volumes
47a and 47b located preferably in the protruding portion of the
adipose tissue layer 35. The ultrasound transducer may be of any
type described above for embodiment 3a. A flat, uniform phase
transducer, having the radiation pattern as detailed in FIG. 4, is
applied with proper selection of dimensions and frequency to obtain
maximum intensity inside the adipose tissue at the protrusion. Any
fixed focus transducer can also be applied with the focal volume
preferably at that region. According to a preferred embodiment, the
transducer 42a (and also 42b if included) will be a phased array as
described for applicator 3a. The phased array will either focus the
radiation at the optimal region of the protrusion, or scan the
adipose tissue inside the protrusion. Although phased array is more
complicated, it has the advantages of optimal delivery of energy
into the adipose tissue at the protrusion with minimal residual
energy going to other tissues.
[0103] In a preferred embodiment, at least two transducers 42a, 42b
are used so that their volumes of maximum intensity 47a and 47b
overlap. Preferably the phases of the transducers are controlled,
and matched in a way that maximizes the ultrasound intensity in the
overlapping volumes or to maximize the pressure gradients there.
The transducer 42a (and the transducer 42b and as well as any other
transducers when present) is preferably oriented in the interior
chamber 41 so that the direction of ultrasound radiation from the
transducer is close to being parallel to the skin surface outside
the protrusion. In this orientation, penetration of the ultrasound
energy to internal tissues and organs below the subcutaneous
adipose layer is reduced or eliminated. Another embodiment will
create this preferred direction of radiation by building a
transducer which radiates at an angle to its surface. That angle
can be fixed and produced by inserting a material with appropriate
sound velocity in front of the transducer, or by a variable
radiation angle from a phased array, controlled by unit 1.
[0104] A pressure sensor may be included inside the interior
chamber 41. In this case, the control unit 1 may be configured to
drive the ultrasound transducers 42a and 42b when the measured
pressure is within a predetermined range. The propagation of
ultrasound radiation from the transducer into the tissue can be
monitored by measuring the electrical impedance of the transducer,
that is, by measuring the AC voltage and current on the transducer.
Variations in power transmission from the transducer are manifested
by changes in the voltage-current relation on the transducer.
[0105] The radiating area of each of the transducers 42a and 42b
may be, for example, between 5.times.5 mm to 50.times.50 mm, more
preferably between 10.times.20 mm to 20.times.40 mm, depending on
the volume of tissue to be treated.
[0106] FIG. 6 shows an embodiment 3c of the applicator 3 in which
the transducers 42a and 42b are allowed a degree of freedom so that
they can acquire an orientation that conforms to the skin surface
in the protrusion. In the embodiment of FIG. 6, at least one
ultrasound transducer, or the two ultrasound transducers 42a and
42b are mounted on hinges 52a and 52b respectively, and displaced
towards the center by respective springs 55a and 55b. The
electrical cables 48a and, 48b are flexible, so that the
transducers are free to rotate about the hinges 52a and 52b.
Negative pressure is created inside the interior chamber 41 as
explained above with reference to FIG. 5. As the tissue is sucked
into the interior chamber 41, it pushes the transducers 42a and 42b
against the force of springs 55a and 55b, thus causing them to
rotate on the hinges 52a and 52b against the force of the springs
55a and 55b. The direction of maximum acoustical radiation (beam
direction) of the transducer 42a is indicated in FIG. 6 by ray 58,
creating an angle .beta. with the normal 57 to the non-protruding
skin surface. As explained above with reference to FIG. 5, the
angle .beta. is preferably as close as possible to 90.degree. (i.e.
the radiation is close to being parallel to the non-protruding skin
surface). In embodiment 3c, the angle .beta. depends on the
properties of the tissues at the treatment site and on the
controllable parameters, such as the negative pressure amplitude,
its application time and the spring constants of the springs 55a
and 55b. The closer the angle .beta. is to 90.degree., the lower
the amount of energy that traverses the adipose tissue 35 and
enters other tissues deeper inside the body.
[0107] The ultrasound transducer(s) of embodiment 3c can be any of
those applicable to embodiment 3a and 3b. When a phased array is
used, the phase of each element is controlled by an electronic
driving circuit in the control unit 1, so that the focal volume can
be aimed easily by the electronic control of the array at a desired
region inside the adipose tissue. When the transducers 42a and 42b
in the embodiment 3c of the applicator 3 are phased arrays, an
angle encoder can be associated with each of the hinges 52a and 52b
to determine the orientation of the transducers 42a and 42b. The
desired focal point can then be determined according to their
orientation, and the control unit 1 will phase the array to bring
the focal volume to that position inside the fat tissue. The time
scale of vacuum pumping is between 50 msec and 1 sec, which is also
the time scale of variation of the angles of the transducers, while
the focal point can be shifted within a few tens of microseconds to
the desired location. Another important advantage of a phased array
is the ability to scan a selected volume within the adipose tissue,
by electronically controlling the phase of the array elements. The
electronic scanning is fast, and can cover a large volume within
the typical pumping time. Also, the degree of focusing can be
controlled by the electronics.
[0108] In another embodiment, the generation of the protrusion of
skin and underlying adipose tissue is done by mechanical
manipulation of the skin surface. This embodiment avoids the need
to vacuum system as is required when the protrusion is formed by
negative pressure.
[0109] FIG. 7 shows an example of an embodiment 3d of the
applicator 3 which delivers a mechanical manipulation of a skin
surface in order to generate a protruding region of skin tissue and
underlying adipose tissue. The applicator 3d includes a base
element 300, which may be connected to a handle (not shown).
Grooves 301 and 302 are provided inside the base element 300 in
which bars 303 and 304, respectively, can move laterally. Rods 305
are 306 are attached to the bars 303 and 304, respectively. Plates
307 and 308 are connected to the lower end of the rods 305 are 306,
respectively. The lower surface of these plates is preferably rough
or covered with a suitable high-friction material 309 in order to
enhance friction and reduce slippage over the skin. Ultrasound
transducers 311 and 312 are attached to plates 307 and 308
respectively through hinges 313 and 314 respectively so as to be
free to rotate about the hinges. The springs 315 and 316 displace
the transducers, 311 and 312, respectively towards the skin surface
27. At the upper end of the rods 305 and 306, rods 317 and 318,
respectively, are connected. The rods 317 and 318 are driven by an
actuator 319.
[0110] The embodiment 3d has two ultrasound transducers, arranged
symmetrically. This is by way of example only and a non-symmetrical
mechanical manipulator with only one transducer or more than two
transducers may be used as required in any application.
[0111] The embodiment 3d of the applicator 3 is used to create a
protrusion of a skin surface as follows. The plates 309 and 310 are
applied onto the skin surface 27 at a site to be treated, as shown
in FIG. 7a. The actuator 319 pulls the rods 305 and 306 inwards
together with the plates 307 and 308 and the transducers 311 and
312. As shown in FIG. 7b, due to the high coefficient of friction
between the layer 309 and the skin surface, the body tissue 320 is
pushed upwards so as to form a protrusion 330. The springs 313 and
314 are designed so that the moment they exert on the transducers
311 and 312 is low enough to allow the transducers to rotate about
the hinges 313 and 314, respectively, so as to allow formation of
the protrusion, while at the same time, ensuring good coupling of
ultrasound energy from the transducers 311 and 312 to the skin
surface 27. After the protrusion has been formed, the transducers
311 and 312 radiate ultrasound energy into the body tissue, to
effect reduction of the fat in focal volumes 47a and 47b in the
subcutaneous adipose tissue 35. The ultrasound transducers may be
contained inside the plates 307 and 308. In this case, it is
desirable to allow a degree of freedom of movement to these plates,
so as to allow them to conform to the protrusion as it forms,
either freely, or by forcing them to rotate simultaneously with the
lateral motion.
[0112] The plates 307 and 306 and/or the transducers 311 and 312
may be curved in any desired shape in order to obtain a protrusion
having a desired shape. The transducers 311 and 312 of the
embodiment 3d may be any of those applicable for the other
embodiments, 3a-3c, that is, planar transducers, fixed focus
transducers or phased array transducers. If a phased array is used,
in a similar way to embodiment 3c (FIG. 6), a position encoder is
preferably added to hinges 313 and 314, and the focal position
electronically matched to the orientation of the transducers.
[0113] The apparatus 4, with the applicator 3b or 3c or 3d, may be
configured to deliver ultrasound energy to a region of subcutaneous
adipose tissue so as to generate a pressure gradient in the region
that ruptures cells in the in the region. Since this effect is
obtained using moderate focusing of the ultrasound radiation in a
volume of subcutaneous adipose tissue to be treated, when the
overlying skin surface is made to protrude above the surrounding
surface, a larger power may be applied with lower risk to internal
organs and tissues.
[0114] Ultrasound energy may be delivered to the skin together with
RF energy; as explained above. FIG. 8 shows schematically an
embodiment 3e of the applicator 3 in which an ultrasound transducer
71 is located between two RF electrodes 72 and 73. The transducer
and RF electrodes are supported by an insulating housing 77.
Application of the applicator 3e to the skin surface 27, applies
both the ultrasound transducer 71 and the RF electrodes 72 and 73
to the skin surface 27, to obtain good coupling of the RF and
ultrasound energies to the skin surface. An electrically conductive
ultrasound conductive gel may be applied to the skin prior to the
treatment. The ultrasound transducer is driven through cable 74 in
the harness 2, while cables 75 and 76 supply the RF voltage to the
electrodes from the RF generator 15 in the control unit 1.
[0115] FIG. 9 shows an embodiment 3f of the applicator 3 in which
RF electrodes have been incorporated into the embodiment 3d of FIG.
7. For example, in FIG. 9, RF electrodes 341 and 342 are located
adjacent to the transducers 311 and 312. The RF electrodes are
driven through cables 75 and 76, which are included in harness 2
(not shown). The RF electrodes can be incorporated into the plates
307 and 308 or on the transducers 311 and 312. In the later
embodiment, a thin film of electrically conducting material having
negligible ultrasound attenuation is preferably applied to each
transducer face touching the skin 27, and connected to the RF power
supply 15 in control unit 1.
[0116] FIG. 10 shows another embodiment 3g of the applicator 3 in
which a pair of RF electrodes 81 and 82 has been added to the
embodiment 3b of FIG. 5. The RF electrodes 81 and 82 are located at
the sides of the dome 40, so they can contact the skin. The RF
electrodes 81 and 82 are driven by the RF driver 15 in the control
unit 1 by cables 83 and 84 in the harness 2. The electrodes 81 and
82 and the cables 83 and 84 are electrically insulated from the
housing and from the ultrasound transducers. The housing 40 is
preferably made of insulating material. The high conductivity
contour through the skin layer 85 is longer and takes less energy
than in the planar embodiment 3e shown FIG. 8, so a higher electric
field 86 is created in the deep adipose tissue. The electric field
heats the minority fluids in the adipose tissue and generates
strain on the adipose tissue cell membranes, as explained above.
Preferably the applicators 3f and 3g are designed to make the
regions of maximum electric field and maximum ultrasound intensity
at least partially overlap within the adipose tissue, to maximize
the combined effects of the RF and the ultrasound energies. A pair
of RF electrodes can similarly be added to applicator 3c.
[0117] The applicator 3g has RF electrodes parallel to the
ultrasound transducers. It is also possible according to the
invention to locate the RF electrodes at other positions, which
provide at least partial overlap of the RF electric field and the
ultrasound radiation within the adipose tissue. FIG. 11 shows
schematically another possible arrangement of the RF electrodes and
the ultrasound transducers in side view (FIG. 11a), and in top view
(FIG. 11b). For simplicity, FIG. 11 shows only one pair of RF
electrodes 91 and 92, and a pair of ultrasound transducers 93 and
94.
[0118] Preferred RF parameters, for all the embodiments, are: RF
frequency between 100 kHz and 50 MHz, more preferred between 500
kHz and 5 MHz. Applied RF voltages are between 10V peak to 1000 V
peak, more preferred between 30V peak to 300V peak for a distance
of 10 mm between electrodes, and higher voltage for greater
electrode spacing. The RF electrode spacing may be between 5 mm to
50 mm and their length may be between 5 mm to 50 mm. Preferably,
the ultrasound transducer covers most of the area between the
electrodes. The ultrasound transducer may be flat with uniform
phase where the depth of treatment is controlled by the frequency,
or a fixed focus transducer or a phased array transducer with the
capability of scanning the focal volume, as in embodiments 3a-3d.
Preferably, the RF energy is applied in pulses, typically between
10 .mu.sec 500 msec, more preferred between 1 msec to 100 msec.
Preferably the RF and ultrasound pulses overlap at least
partially.
[0119] Monitoring the contact between the RF electrodes and the
body may be done by measuring the voltage across the electrodes and
the current, and calculating from that the impedance between the
electrodes. Based on experience with a certain electrode structure,
a range of impedances can be defined that are sufficient for the
application of the RF power. As in the previous embodiments,
coupling of the ultrasound energy to the body can be monitored by
measuring the transducer impedance.
[0120] The applicator embodiments 3b-3g are independent of any
specific physical model for the destruction of fat cells. However,
it is advantageous in all embodiments to apply the ultrasound
energy in a way that maximizes the selective destruction of fat
cells, as was done with embodiment 3a, namely, to exploit the
unique structure of fat cells to effect relative movement between
the adipose cell constituents, leading to strain and selective
heating at the cell boundary, following by damage to the cell
membrane which cause cell necrosis or apoptosis.
[0121] Any of the above embodiments may be adapted for delivering
infra-red (IR) energy to the skin surface. Delivering of IR
illumination to the skin enhances the aesthetic treatment, so that
fat, cellulites and skin can be treated simultaneously. The IR
illumination can be applied to skin regions not covered by the
ultrasound transducer or the RF electrodes.
* * * * *