Abstract:
An apparatus for lowering the temperature of skin on a patient during treatment applying electromagnetic energy to the skin comprising a window of a first thermally conductive material through which electromagnetic energy can pass for placement against the epidermis of the skin. A reservoir of coolant is spaced from an edge of the window. A non-flowing second thermally conductive material connects the window and the reservoir to transfer heat from the window to the coolant in the reservoir.

Description:
TECHNICAL FIELD 
     This invention relates to electromagnetic and laser treatment devices and more particularly to a cooling apparatus for use with electromagnetic and laser devices to cool the human skin during the treatment of patients. 
     BACKGROUND 
     The method of treating cutaneous lesions with light sources such as lasers is primarily based on the principal of Selective Photothermolysis proposed by Anderson (“Selective Photothermolysis: Precise Microsurgery by Selective Absorption of Pulsed Radiation”, Science, Volume 220, April 1983). This mechanism involves the selective absorption of light by various chromophores in the body. As these chromophores absorb the light energy, they heat up and destroy the surrounding tissue. This tissue destruction can be used as an alternative therapy to sclerotherapy in a beneficial way to remove unsightly veins and other vascular lesions since these lesions typically contain one or more highly absorbent chromophores. 
     The degree of selectivity and therefore tissue damage is dependent upon the type and amount of chromophore present in the tissue, the depth of the target in the tissue, and highly dependent upon the wavelength of the light being used. Since lasers are able to provide light in very precise wavelength regimes, lasers are ideal instruments for capitalizing on this principal for treatment of various lesions. This selectivity can be very beneficial in that specific lesions containing or surrounded by a particular chromophore(s) can be targeted with specific wavelengths to provide localized heating and damage while sparing surrounding tissue lacking the chromophore(s). 
     In practice however, the light absorption of different chromophores may be similar. For example, melanin, a chromophore which is found in the epidermis of the skin, may absorb a very similar amount of light energy at some wavelengths as the target tissue (such as the hemoglobin in a vein). Therefore, when attempting to deliver sufficiently large amounts of light energy to a target area such as a vein, the melanin in the skin above the target area may absorb enough light energy to cause epidermal damage to the skin before the target area has received sufficient energy to cause sufficient damage. 
     If this epidermal layer, however, is superficially cooled just prior to and/or during the application of the laser energy, the net change in temperature of the chromophores and tissue on the surface will be less and therefore the collateral damage will be less as well. 
     It has been known for quite some time that simple cooling techniques can be used to certain advantage in conjunction with certain therapies, including RF and laser therapies. Such simplistic cooling mechanisms include, for example, applying an ice bag to the target area for a predetermined time period prior to the application of therapeutic energy to the target area. It has also been prior described to precool the target area, as described above, and alternately provide therapeutic energy to the target area and a recooling of the target area. 
     It has been known for quite sometime that various cooling techniques can be used to protect the device used to provide treatment to a patient. U.S. Pat. No. 4,832,024, issued to Boussignak et al. is one such device in which a cooling fluid is flowed in a chamber between an optical fiber and the distal emitting end of a cardiovascular catheter. Various other prior art devices provide a similar cooling of the device, sometimes together with some resultant cooling of the patient target area. U.S. Pat. No. 4,733,660 issued to Itzkan is such a device in which a coolant is flowed at the distal end of a laser system, such that the laser light is passed through the liquid coolant, which is passed across the irradiated areas of the patient under treatment. U.S. Pat. No. 3,821,510 issued to Muncheryan provides a hand held laser instrumentation device in which cooling is achieved by evaporation when a coolant is sprayed from the laser device to the superficial tissue of the patient undergoing treatment. International Patent Publication WO 97-37723 similarly provides a cooling spray directly onto the tissue of the patient. U.S. Pat. Nos. 5,814,040 and 5,820,628 also spray gas and/or liquid directly onto the skin to provide cooling. 
     U.S. Pat. Nos. 5,057,104; 5,282,797; and 5,486,172 to Chess provide methods and apparatus for cooling the skin simultaneously with the delivery of laser light energy. Although lasers and cooling of the skin are involved and discussed, the devices described require a cooling fluid to reside over or be passed over the treatment site during laser treatment. This requires that the cooling medium be captured between two separate transparent windows which can impair visibility of the treatment area. Proper visualization of the treatment site is very important since many veins are smaller than 100 microns and difficult to target without excellent visibility of target site. A multi-layer fluid container assembly such as described is expensive, and can impair the ability of the practitioner to deliver the light to the appropriate target area. 
     Additionally, if not used correctly, these devices can cause relatively large refractive changes in both the incoming laser light (changing the delivered treatment spot size and therefore the treatment fluences) and in the visible light leaving the target area (making it difficult to aim the treatment beam correctly). 
     U.S. Pat. No. 5,344,418 to Ghaffari provides a system with a thermally conductive optical window which is cooled on one side by a cooled gas (carbon dioxide and Freon™ are mentioned) and in contact with the skin on the other. This system is described to be used in combination with a feedback mechanism to control laser light delivery to the treatment site. The cooling mechanism described requires the use of complex delivery equipment and expensive (and possibly) environmentally hazardous) materials. 
     U.S. Pat. No. 4,140,130 to Storm provides a RF system with a cooling electrode used to direct RF energy to the target and to keep the skin cool. However, this system also calls for the cooling fluid to flow over the target area where the energy is being delivered and relates to RF devices, not to lasers. 
     U.S. Pat. No. 3,967,627 to Brown provides a heating and cooling applicator and control and monitoring circuitry for cooling and heating areas of the body. This device is not used for laser therapy and also has the cooling fluid passing over the entire contact area to be cooled. 
     SUMMARY 
     It is an object of this invention to provide a simple device to cool the skin during treatment with electromagnetic energy, including treatment of vascular and cutaneous lesions, skin disorders, and the removal of hair. 
     It is another object of this invention to decrease the complexity of the existing art and to provide a more economical, cost-effective, and easy to use device. This is accomplished in one embodiment by using a thermodynamic property of water or other material called the “latent heat of fusion” to provide a temporary but relatively constant temperature at the treatment window. 
     It is still further an object of the present invention to provide a simpler, easier means of visualizing and cooling the target treatment zone while simultaneously delivering the electromagnetic energy. 
     It is yet another object of the invention to provide an apparatus which can be used for cooling the skin during treatment with electromagnetic energy in areas which are difficult to access with existing art such as the areas around the nose and ankles. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of one embodiment of the invention; 
     FIG. 2 a  is a perspective view of another embodiment of the invention; 
     FIG. 2 b  is a cross sectional view of the embodiment of FIG. 2 a;    
     FIG. 3 is a schematic view of the heat transfer mechanism of various embodiments. 
     FIG. 4 is a graph depicting temperature verses time for an embodiment of this invention; and 
     FIG. 5 is a view of an alternative embodiment of this invention. 
    
    
     DETAILED DESCRIPTION 
     The mechanisms for heating the desired tissues during treatment with electromagnetic energy have been described and it is now established in the practice that cooling the skin during such treatment reduces patient discomfort, allows for higher treatment fluences, and increases the efficacy of the treatment. Such treatments include a treatment of an epidermal layers of the skin, to treat skin disorders, hair removal, and the treatment of vascular and pigmented lesions. 
     FIG. 1 is a cross-sectional view depicting one embodiment of this invention. FIG. 1 depicts system  100  which includes an energy exit port  101 , such as a lens or the end of an optical fiber, at the distal end of a delivery device  120 , and a cooling device  110 . Cooling device  110  allows cooling of the skin in conjunction with exposure to electromagnetic energy, including laser energy. Such cooling may take place before, during, and/or after such exposure to electromagnetic energy. 
     Port  101  emits electromagnetic energy, such as laser energy,  102 , which is generated in any convenient manner well known to those of ordinary skill in the art. Energy  102  is directed to a patient target area through cooling window  104  of cooling device  110 , which in operation is placed against the area of the patient to be treated. Cooling window  104  is in direct contact with the patient&#39;s skin, or in contact with the skin via a liquid, gel, or membrane. Cooling window  104  is constructed of a material which is tough yet inexpensive, and provides good thermal conductivity and low absorption of energy  102 . Preferably, the material used to construct window  104  is not hydroscopic. Suitable materials for window  104  include many glasses known to those in the laser industry including quartz, including polymorphic glass, undoped YAG, diamond, and sapphire, for example being largely transparent to a variety of electromagnetic energy  102 , for example laser energy in the wavelength range between about 0.2 to 3.5 microns. In certain embodiments, a range of 400 to 1100 nanometers is used. If desired, window  104  is coated on one or both sides with an anti-reflective coating. Preferably, window  104  allows excellent visualization during the procedure, is scratch resistant and is small enough to treat highly contoured areas, such as those on the face and nose. 
     Surrounding window  104  is a thermally conductive material  103  which, in the embodiment of FIG. 1, is thermally coupled to a thermal reservoir  105 . Thermal reservoir  105  acts as a heat sink and comprises, for example, a mass of thermally conductive material, if desired the same material used to form thermally conductive material  103 . In another embodiment, thermal reservoir  105  is a cavity containing coolant medium which is chilled prior to the use of cooling device  110 . In one embodiment, thermal reservoir  105  contains a fluid such as water and/or ice; carbon dioxide, hydrocarbons, fluorocarbon, chlorofluorocarbons, air, nitrogen, Freon™, gels, or other cooling solids and/or liquids and/or gasses, which is cooled to a desired temperature or, if desired, frozen prior to use of cooling device  110 . In operation, window  104  absorbs very little energy  102  passing through it to the patient&#39;s skin. By way of example, if sapphire is used as the material for window  104 , and window  104  is formed to a thickness of approximately 1 to 20 mm, only about less then one percent of laser energy is absorbed by window  104 . This small amount of heat absorbed by window  104  is readily absorbed by thermally conductive material  103  surrounding window  104  so that the temperature of window  104  is not increased. More importantly, since window  104  absorbs very little energy from energy beam  102  such that its temperature does not rise to any significant degree during treatment of the patient, window  104  serves to conduct heat away from the patient&#39;s skin in the treatment area, thereby preventing discomfort to the patient and enhancing treatment efficacy by allowing a longer treatment period. 
     The size of thermal reservoir  105  is made to any convenient size consistent with convenient operator utilization and a desired amount of thermal cooling effect based upon the type of material forming thermal reservoir  105 . For greater cooling ability, thermal reservoir  105  contains a material capable of changing state, such as, for example, water, which may be frozen prior to the treatment of the patient. During treatment of the patient, this frozen coolant contained within thermal reservoir  105  acts as an excellent coolant device and absorbs significant amounts of heat as the state changes from solid to liquid and the latent heat of fusion is absorbed by the coolant material during this change of state. Alternatively, gas such as air, nitrogen, CO 2 , or a cryogenic gas is used as the coolant material. In other embodiments, a gas is used which is cooled to a liquid or solid state, allowing the latent heat of vaporization and/or the latent heat of fusion to be used in achieving the desired cooling effect. 
     The present invention has been designed specifically to cool the surface of the skin before, during and after laser exposures. Like other active cooling devices used in dermatology, the present invention significantly lowers the temperature of the epidermis and the dermal-epidermal junction. The lower temperature facilitates higher treatment fluences and reduces the thermal damage to non-target tissue, which significantly reduces side effects such as transitory hyper- or hypo-pigmentation. The present invention significantly reduces the pain experienced by patients. Unlike other cooling technologies, this embodiment of the present invention does not require the use of expensive cryogenic canisters or chillers and does not use cumbersome hoses to provide cooling. FIG. 3 shows a magnified cross sectional view of a cooling tip in contact with skin with arrows indicating the flow of heat from the epidermis, to the sapphire window and the cooling reservoir. 
     To fully appreciate the advantages of the present invention compared to other active cooling devices, it is important to understand how it works. One embodiment of the present invention utilizes the large latent heat of fusion of water (79.71 calories/gram) to maintain the skin at a constant low temperature for long periods of time. Because it requires so much energy to melt ice, the 13.1 grams of ice in the reusable tips have more heat capacity than 1.0 liters of liquid water at 0 degrees Celsius. As the ice melts, the temperature of the reservoir in the present invention is maintained at 0 degrees Celsius. for an average of 20 minutes under normal operating conditions. This allows the window of the present invention to maintain a constant temperature of 15° C. or lower, for 20 minutes, while being traced over the skin at a rate of 1 cm/second, in a 25° C. room, with 100 watts of laser light directed through the sapphire window. When used in this manner, most of the heat removed by the present invention is not from the laser light absorbed at tissue, but rather from ordinary body heat (approximately 0.2 to 1 calorie/second are transferred from the epidermis to the sapphire window). After 20 minutes have elapsed, the cooling tip can be easily replaced with another frozen cooling tip. Thus, the four cooling tips supplied with the present invention provide 1 hour and 20 minutes of cooling that can be “recharged” by placing them in a freezer for 30 minutes and thus, allowing continuous laser treatment. FIG. 4 shows the temperature of the window in one embodiment of the present invention which does not utilize any pipping or flowing of the coolant, over a 30 minute time interval. The constant temperature during the 4-24 minute time period is due to the presence of ice in the reservoir of this embodiment. Only after all the ice in the reservoir has melted does the temperature begin rising to room temperature. 
     In one embodiment, one or more temperature sensors are placed in thermal contact with one or more of window  104 , thermally conductive material  103 , and thermal reservoir  105 . In one such embodiment, the temperature sensor is made of color changing liquid crystals or the like. 
     In one embodiment, system  100  includes, if desired, a bracket  106  such that the cooling device including cooling window  104  is attached to the distal end  101  of the delivery system, thereby allowing easy operator manipulation. In one embodiment bracket  106  is detachable from one or both of delivery system  120  and cooling device  110 , to permit cooling device  110  to be easily removed for precooling, or use on other delivery systems. 
     In certain embodiments, a good thermal bond is made between cooling window  104  and surrounding thermally conductive material  103 . Smooth surfaces to provide for a press or snap fit of window  104  into surrounding thermally conductive material  103  enhance thermal conductively therebetween. In alternative embodiments, thermal epoxy, brazing, or soldering is used to secure cooling window  104  to thermally conductive material  103  and provide good heat transfer therebetween. In alternative embodiments, thermally conductive material  103  is plated with a low allergic reaction material, such as gold plated copper. 
     FIG. 2 a  is a perspective view of an alternative embodiment of the present invention. Electromagnetic energy system  200  of FIG. 2 a  includes electromagnetic energy delivery device  220  which receives energy, for example, laser energy, via optical fiber  221  and emits energy  202  from its distal end. Energy  202  is directed to a patient target area through cooling window  204  of cooling device  210 . At least surrounding cooling window  204  is thermally conductive material  203  which conducts thermal energy from the patient&#39;s treatment area as such heat is absorbed by cooling window  204 . The heat thus absorbed by cooling window  204  and by thermally conductive material  203  is conducted to thermal reservoir  205  contained within handpiece  290 . Handpiece  290  of cooling device  210  is, if desired, attached to electromagnetic energy delivery device  220  such that system  200  is conveniently manipulated as a single unit. In one embodiment, this attachment is provided as a detachable engagement such that cooling unit  210  and electromagnetic energy deliverable device  220  can be separating for cleaning, maintenance, or the precooling of cooling device of  210  prior to use in a medical procedure. In one embodiment of this invention, cooling device  210  includes hand piece  290  which is detachably connected to cooling tip  289  via a detachable connection  291 . 
     FIG. 2 b  depicts a cross sectional view of one embodiment of this invention similar to that shown in perspective view of FIG. 2 a , with common reference numerals. As shown in FIG. 2 b , electromagnetic energy delivery device  220  includes electromagnetic energy exit port  201 , such as a lens or an optical fiber. The connection between the electromagnetic energy delivery device  220  and hand piece  290  is shown by reference numeral  250 . As shown in FIG. 2 b , hand piece  290  in this embodiment includes a thermal reservoir  205  which contains a cooling medium. In one embodiment, this cooling medium is self contained, and is cooled prior to use of cooling device  290 . In this embodiment, the material contained within thermal reservoir  205  is formed of any convenient material capable of absorbing thermal energy, including various metals or the like. Alternatively, thermal reservoir  205  contains a liquid, such as water, or a gas such as air, nitrogen, CO 2 , or cryogenic gas. As previously described, in certain embodiments material contained within thermal reservoir  205  is capable of changing state, thereby allow the latent heat fusion and/or the latent heat vaporization to be used to absorb thermal energy from the patient&#39;s skin via cooling window  204  and thermally conductive material  203 . 
     In one embodiment, as depicted in FIG. 2 b , an inlet port  271  and an outlet port  272  are used to circulate cooling material (i.e. liquid or gas) either directly into thermal reservoir  205 , or to a chamber surrounding thermal reservoir  205 , in order to allow cooling medium to be circulated to handpiece  290 , in turn gathering thermal energy absorbed from a patient&#39;s skin. If desired, this cooling material is chilled and recirculated, for example by use of a chiller or thermoelectric cooler and pump system. Alternatively, cooling material is simply obtained from a cool source and disposed of after absorbing heat from cooling device  290 . 
     FIG. 3 is a schematic representation of heat from a patent&#39;s tissue being absorbed by thermal window  304  and transmitted to thermally conductive material  303  for absorption by thermal reservoir  305 . 
     As shown in FIG. 3, heat is absorbed from the patient&#39;s tissue by window  304  and conducted by thermal conductive material  303  to reservoir  305  containing coolant. As depicted in FIG. 3, in accordance with the teachings of the present invention, a simple and cost effective mechanism is provided for cooling patient&#39;s skin before, during, and/or after electromagnetic energy treatment, without the need for expensive and complex equipment, such as described in the prior art. Thus, no small and expensive tubes are required to pump coolant to regions directly surrounding the window. In contrast, in accordance with the teachings of this invention, a simple and cost effective structure is provided which adequately removes heat absorbed from the patient&#39;s tissue by the window, by simple thermal conductivity through non-flowing thermally conductive material to a coolant reservoir. The coolant reservoir contains adequate cooling capability to allow effective use in medical procedures without the need for expensive cooling arrangements. 
     In one embodiment of this invention, as depicted in FIG. 5, coolant is flowed through a small region  401  of device  400 , in order to remove heat from window  404  via thermally conductive material  403 . As shown in FIG. 5, even though a flowing coolant is used in this embodiment, the cost effectiveness is maintained by providing that the coolant flows only through a small portion  401  of the device, and not in a highly machined and expensive piping system surrounding window  404 . 
     In one embodiment of this invention, as depicted in FIG. 5, coolant is flowed through a small region  401  of device  400 , in order to remove heat from window  404  via thermally conductive material  403 . Device  400  can be made from gold plated copper. As shown in FIG. 5, even though a flowing coolant is used in this embodiment, the cost effectiveness is maintained by providing that the coolant flows only through a small portion. 401  of the device, and not in a highly machined and expensive piping system surrounding window  404 . Specifically, handle  406  of device  400  is provided with one or more channels for providing a flow path not adjacent to, and thus spaced from, an edge of window  404 . Coolant enters Such one or more channels through an inlet port  407  and exits handle  406  through an outlet port  408 . 
     All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     The invention now being fully described, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the appended claims.