Patent Application
20060036300
The invention relates to methods for treating adipose tissue.
Skin tissue consists of an outer epidermal layer overlying a dermal layer that is in contact with a layer of subcutaneous adipose tissue. Excess adipose tissue is responsible for such medical problems as obesity, cellulites, loose skin, and wrinkles. By destroying the adipose cells, the appearance of the outer layer of the skin can be improved. Damaged adipose tissue is evacuated from the body by the lymphatic system. The destruction of adipose tissue in the sub-dermal layer often provides the following medical and cosmetic solutions: weight reduction, cellulite reduction, loose skin reduction, deep wrinkle reduction and body re-contouring. Reduction of the fat content may also cause skin tightening. Wrinkles are created in skin due to the breakage of collagen fibers and to the penetration of fat into the dermal layer of the skin.
Most existing wrinkle treatment methods target the collagen but do not have a significant effect on deep wrinkles. Radio frequency (RF) energy has been actively used for the treatment of epidermal and dermal layers of the skin. For example U.S. Pat. No. 6,749,626 describes the use of RF energy for collagen formation in the dermis. U.S. Pat. No. 6,241,753 describes a method for collagen scar formation. U.S. Pat. Nos. 6,470,216, 6,438,424, 6,430,446 and 6,461,378 disclose methods and apparatuses for destroying the collagen matrix using RF, cooling and a special electrode structure that smoothes the skin surface. U.S. Pat. Nos. 6,453,202, 6,405,090, 6,381,497, 6,311,090, 5,871,524 and 6,425,912 describe methods and apparatuses for delivering RF energy to the skin using membrane structure. U.S. Pat. Nos. 6,453,202 and 6,425,912 describe method and apparatus for delivering RF energy to the skin using dielectric electrodes. U.S. Pat. Nos. 6,381,498, 6,377,855, 5,919,219, 5,948,011, 5,755,753 describe methods of collagen contraction using RF energy, and a reverse temperature gradient on the skin surface.
U.S. Pat. Nos. 6,378,380, 6,377,854 and 5,660,836 describe methods of lyposculptering using RF energy and external cooling to affect the collagen inside the adipose tissue.
Another method to reduce and redistribute adipose issue is skin massaging. This method is based on improving of blood circulation and increasing fat metabolism. U.S. Pat. No. 6,662,054 describes a method for skin massaging in combination with non-aggressive RF heating for increasing skin and fat metabolism.
U.S. Pat. No. 6,273,884 to Altshuler et al. discloses simultaneous application of optical energy and negative pressure to the skin in order to treat a skin defect. This method is limited by the light penetration depth, which does not exceed a 1-2 millimeters.
U.S. Pat. No. 5,143,063 describes a method based on thermal destruction of fat using the focusing of microwave or ultrasound energy in adipose tissue. But both types of energy are very expensive and its safety limitations are not clear.
The above mentioned methods attempt to solve the problems created by excess adipose tissue such as body contouring, loose skin, and deep wrinkles, by contracting the superficial collagen tissue. These methods are limited in their penetration depth. A more effective and longer lasting result would be achieved by directly affecting the adipose tissue. However, in order to reach the sub-dermal layer adipose tissue, it is necessary to deliver RF current into the fat tissue to a depth of over 2 mm without damaging the skin. Furthermore, the amount of energy and duration of the energy application should be high enough to create adipose tissue necrosis.
1. The present invention provides a method for delivering RF energy sufficiently deep below the skin surface so as to generate a heating of the deep skin layer that is strong enough to destroy fat cells. In accordance with the invention, a region of skin is deformed so that the region protrudes out from surrounding skin. The deformed skin preferably protrudes above the periphery of the region to a height of 1 to 30 mm.
One or more RF electrodes are then applied to the skin protrusion in order to direct the RF current through the skin protrusion. Deforming of the skin can be done by applying vacuum suction to the skin surface or by pinching the skin surface. Alternatively, deforming the skin can be done by applying a pressure to the periphery of the treated skin region that is higher than a pressure applied at the interior of the region.
In one preferred embodiment of the invention, a bipolar RF system is used. In this embodiment, the distance between the two electrodes preferably exceeds 4 mm. As the distance between the electrodes increases, the electrical current divergence is stronger so that deeper layers of tissue can be heated.
In another preferred embodiment, a uni-polar RF system is used. In this embodiment, the area of the RF electrode preferably has an area exceeding 5 mm2. With a large electrode size the divergence of the electrical current is low at depths up to the electrode size.
Necrosis of tissue is a function of temperature of the tissue and the time duration during which the temperature is maintained. The range of temperatures in which adipose tissue necrosis can be achieved varies from 45° C. and up to 100° C., when boiling of water occurs. The practical duration of RF energy application can vary from 0.01 up to 10 sec. During this time, RF energy can be delivered continuously or in a pulsed manner. Longer pulses of treatment may limit the total treatment time.
The density of an RF current is always higher around the surface of the RF electrode applied to the skin surface. In order to avoid overheating the skin, the skin may be cooled. Cooling may be applied prior the RF energy application or/and simultaneously. The surface of the skin can be cooled using a cooled liquid or by cooling of the electrode surface. The cooling depth (d) depends on the cooling application time (t), and can be estimated from the following equation:
d=√{square root over (4αt)},
where α is the diffusivity of the tissue, which is similar to liquid and is about 1.4×10−7 m2/s. Thus, with a cooling duration longer then 2.5 sec, all layers of the skin up to about 2 mm below the surface will be cooled, so that the temperature of the adipose layer will be higher than the temperature of the dermis and epidermis. In most cases, the thickness of the dermis over the adipose layer does not exceed 1 mm. In this case, a cooling time of 1.5 sec is enough to cool the skin.
The RF electrodes may be made from metal or a semi-conductive material.
In one embodiment the electrodes are covered with a dielectric material. A liquid or gel medium can be used for electrical and thermal coupling between the applicator and the body surface.
The RF current may be combined with optical energy where the RF energy is used for heating a deeper layer while the light is used for subcutaneous fat distruction. Infrared light in the range of 700 nm to 1500 nm is preferably used in order to penetrate inside the tissue to a depth of about two millimeters. A diode laser produces optical radiation in this range and can be used in combination with RF energy. In another embodiment, filtered broad-spectrum light produced by a flash lamp can be used.
The parameters of the RF may be adjusted for selective destruction of adipose tissue, which is less effected by cooling by blood perfusion due to the lower blood vessel contents of adipose tissue. The selective destruction of adipose tissue may be combined with collagen restructuring inside the skin.
The method of the invention may be used, for example, to achieve a reduction in body weight, cellulite reduction, loose skin reduction, wrinkle treatment, body surface tightening, skin tightening, and collagen remodeling. Thus, in its first aspect, the invention provides a method of lipolysis comprising, for each of one or more regions of skin:
In its second aspect, the invention provides a method of lipolysis comprising, for each of one or more regions of the skin:
In its third aspect, the invention provides a method of lipolysis comprising, for each of one or more regions of the skin:
In its fourth aspect, the invention provides a method of lipolysis comprising, for each of one or more regions of skin:
In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
Referring first to
The applicator 100 further includes RF electrodes 121 and 122 that are embedded in the body 103 and are configured to apply RF energy to the region of skin to be treated. Cooling elements 111, 112 are attached to the electrodes 121, 122 and the body 103 to provide cooling of the skin surface. In the embodiment of
The skin is made to protrude into the chamber 104 using vacuum suction applied through the inlet 151. The skin protrusion is thus between the two electrodes 121 and 122.
Using the system of the invention to treat subcutaneous adipose tissue, the following exemplary parameter values of RF energy may be used:
The parameters of optical source 407 shown in the
