Surgery – Instruments – Light application
Reexamination Certificate
1998-05-12
2001-05-22
Dvorak, Linda C. M. (Department: 3736)
Surgery
Instruments
Light application
Reexamination Certificate
active
06235015
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the use of a scanned beam of light to provide a method and apparatus for hair depilation. In particular, this invention relates to the use of a scanned beam of light to provide selective coagulation of targeted structures while limiting coagulation of nontargeted structures.
BACKGROUND OF THE INVENTION
Permanent or long term hair removal for cosmetic reasons has been accomplished by various methods. For example, hair can be removed by heating the hair and the hair follicle to a high enough temperature that results in coagulation. It is known that blood is coagulated when heated to temperatures on the order of 50-70° C. Heating of the epidermis, the hair and the hair follicle to temperatures on the same order of magnitude will cause coagulation in the epidermis as well as the hair follicle and will result in permanent or long term removal of the hair with the unwanted result of scarring.
One common method of hair removal without scarring, often called electrolysis, is based on the use of “electric needles” that applies electric current to each hair through the needle. The current heats the hair and not the epidermis, causes its carbonization and also causes coagulation of the tissue adjacent to the hair as well as some coagulation of the micro-vessels that feed the hair follicle. While the electric needle method can remove hair permanently or long term without scarring, its use is practically limited because the treatment is painful and the procedure is generally tedious and lengthy.
Light can also be used effectively to remove hair. For example, prior art methods of hair removal involve the application of pulsed light. R. A. Harte, et al., in U.S. Pat. No. 3,693,623, and C. Block, in U.S. Pat. No. 3,834,391, teach hair removal by coagulating individual hairs with a light coupled to the individual hair by an optical fiber at the immediate vicinity of the hair. Similarly, R. G. Meyer, in U.S. Pat. No. 3,538,919, removes hair on a hair by hair basis using energy from a pulsed laser. A similar invention using small fibers is described in U.S. Pat. No. 4,617,926 to A. Sutton.
A wide variety of lasers have been used in dermatological applications for treatment of such conditions as vascular lesions (e.g. hemangiomas), pigmented lesions (e.g., nevi), tattoo removal, lentigines, cafe-au-lait macules, and other skin conditions and lesions. Through the principles of selective photothermolysis, specific wavelengths of light are known to be absorbed to a greater or lesser degree in certain skin pigments, tattoo inks, heme (blood pigment) or other chromophores. Wavelength selection also allows the targeting of these pigments and related structures at various depths within the dermis based on the magnitude of total absorption and light scattering as a function of depth.
Selective coagulation by wavelength absorption requires that the light energy used has a wavelength that is preferentially absorbed by the target structure or tissue. It also requires that a high enough power be used to cause tissue damage and that the heat be absorbed in the target structures faster than it is dissipated to surrounding tissue.
U.S. Pat. No. 4,388,924 to H. Weissman, et al. discloses a system wherein a narrow, focused beam of light is aimed at the epidermis adjacent to the hair such that an extension of the beam intersects the hair root at an angle relative to the skin's surface. A pulse, disclosed as a short pulse of less than 400 milliseconds but more than 10 milliseconds, passes through the skin and is selectively absorbed in the hair root destroying its blood supply.
The Weissman patent discloses apparatus which employs a manually controlled two-axis positioning system supporting the focusing system that is connected to a laser light source, preferably argon, by a flexible fiber optic bundle. The argon beam has most of its energy in the wavelength range of 482-520 nanometers. The Weissman patent further discloses that light of that wavelength passes through relatively light human skin without any appreciable absorption yet is highly absorbed in a dark hair root. Thus, the Weissman patent discloses selective coagulation by light absorption as a function of wavelength. The thermal energy produced upon absorption of the light energy within the hair root causes coagulation of the blood vessels and destroys the hair root. The hair body is generally vaporized in the process. Finally, Weissman claims that the process is relatively painless to the patient because of the low degree of absorbency and short pulse within the dermis.
The above prior art techniques suffer from a number of limitations. First, techniques for irradiating an individual hair follicle are time consuming and, therefore, not generally practical for removing hairs other than from a very small region or from a region having few hairs situated therein. The procedure can also be painful, particularly if a needle-like element is inserted in the hair follicle to facilitate light energy reaching the bulge and the root or papilla, which are the parts of the hair follicle which must be destroyed in order to prevent regrowth of the hair. Furthermore, it is difficult to get sufficient energy at the wavelength described to the required portions of the follicle to cause destruction thereof without also causing significant damage to the surrounding tissue and, thus, causing pain and injury to the patient.
Using the principles of selective coagulation by wavelength absorption or photothermolysis, certain laser wavelengths at short pulse durations (several picoseconds through several milliseconds) have been shown to have therapeutic benefits for specific types of lesions or treatments. For example, the flash-lamp-pumped, pulsed dye laser radiation at 585 nm is selectively absorbed by hemoglobin in capillary beds and small blood vessels and is used to treat vascular lesions such as hemangiomas. While shorter wavelengths (e.g., 532 nm) are also selectively absorbed by blood and can be used, they do not penetrate as deeply in the lesion as the 580-590 nm units and are sometimes less effective in thicker lesions. The Q-switched ruby (694 nm), alexandrite (755 nm) and neodymium: YAG (1064 nm) lasers have increasingly longer wavelengths, are deeper-penetrating and are absorbed preferentially by melanin rather than hemoglobin. These pulsed lasers are therefore used to treat pigmented lesions (e.g., nevus of Oti) and tattoo inks of dark colors. The CO
2
laser, in contrast to the above lasers, is absorbed by the water content in tissue and is therefore non-selective by colors. One example of CO
2
laser use in dermatology is for superficial skin vaporization (cosmetic skin resurfacing) using a high-energy, short-pulsed output or a scanned continuous-output laser beam.
High-power diode lasers can now produce radiation at wavelengths of 650-700 nm, 730-1000 nm and 1880-1960 nm. Diodes are available in a wide choice of wavelengths and are efficient converters of electrical energy to light. Some diode laser outputs can be pulsed (e.g., picosecond to nanosecond) like the above solid state lasers but they cannot practically produce the very high peak power (e.g., 20-1,000 kilowatts) needed to achieve selective coagulation by wavelength absorption without unwanted tissue injury.
Treatment of pigmented skin lesions based on selective coagulation by wavelength absorption or photothermolysis has been performed using the Q-switched ruby laser, the Q-switched Nd: YAG laser and the Q-switched alexandrite laser. With these lasers, a high peak power output with a very short duration selectively vaporizes melanin-containing cells. That is, the melanin-containing cells are vaporized with minimal damage to underlying, overlying or adjacent cells. These laser types have a pulse duration too short for optimal effects on larger cellular structures such as hair follicles.
U.S. Pat. No. 5,344,418 to S. Ghaffari discloses an optical system for treatment of skin disorders resulting from blood vessels in the dermis which minimizes damage
Cekoric, Jr. Thomas
Mead, III Douglass S.
Applied Optronics Corporation
Dvorak Linda C. M.
Eitan Pearl Latzer & Cohen-Zedek
Harris-Ogugua S.
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