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LASER SKIN PERFORATOR
BACKGROUND OF THE INVENTION
1. Field of the Invention 5 This invention relates to lasers and laser systems, and, in
one aspect to a laser-device for producing a hole in skin through which blood may be withdrawn. In one particular aspect this invention relates to modifying the output profile of a laser beam to produce improved skin perforators. 10
2. Description or Related Art
Capillary blood sampling is a process for obtaining blood samples from the sub-dermal capillary beds of patients. A common method is to produce a small wound in the patient's 15 skin using a sharp needle or small blade, called a blood lancet. Lancets are commonly used once and discarded. The lancet procedure produces a sharp, blood infected waste product which represents a risk to patients and health care workers, and which must be disposed of under carefully 2Q controlled conditions. In addition, the use of disposable blood lancets requires the health care providing organization to maintain a large inventory of disposable lancets. Certain lancet designs include an exposed point which produce significant fear and apprehension in patients who anticipated 25 a painful experience. Although modem designs have attempted to eliminate such apprehension, reduction of patient discomfort would significantly increase the usefulness of new capillary sampling techniques.
Lasers typically have a light source for optical excitation, 30 an active laser material, and a set of reflecting mirrors. Most solid state lasers have a design with a rod of laser crystal or glass material optically pumped by a high intensity lamp or set of LED arrays, with mirrors placed a distance from, or in contact with, or coated onto, the surfaces of the laser rod. 35 One mirror has either a hole or a reduced reflectance relative to the other. Light is injected from the lamp or LED array into the laser material initiating the discharge of photons from dopants in the rod. These photons travel between the two mirrors producing light amplification. The amplified 40 laser beam escapes the system through the hole or area of reduced reflectance. As an active medium various lasant materials are used to produce different wavelengths of laser light. These materials include, but are not limited to, rareearth-doped oxide and fluoride laser crystals and glasses, 45 e.g. yttrium-aluminum-garnet (YAG). Such crystals and glasses will be doped with impurities to fix the resultant wavelength of the laser. These traditional laser designs have precise mirrored surfaces. The reflective surfaces are usually made by coating the surfaces with several thin layers of 50 dielectric material. If separate mirrors are used, they are placed precisely with respect to the optical axis of the laser rod and with respect to each other. The reflective mirror surfaces can be also produced by coating them onto the polished faces of a laser crystal. 55
Modal distribution is a property of projected light. A projection mode can be characterized by an angular direction vector in which light beams may travel with respect to some normal angle. The normal angle is defined usually as 0 degrees with respect to the optical axis of a system. The 60 modal distribution of a system can be characterized by a set of angular vectors in which light travels upon output from the system. A low order distribution is one in which most of the energy in a light beam travels parallel or near to parallel with the optical axis. Most commonly available laser 65 devices are designed to have a low order distribution of modes; i.e., most devices are designed so that light energy
travels only in the 0th order mode (parallel to the normal vector) or within a small set of angular vectors surrounding the normal vector. A higher order distribution is one in which energy light travels at greater angles with respect to the optical axis.
Laser perforators are disclosed in U.S. Pat. No. 5,165,418, in Japanese patent 4,314,428, and in PCT patent application US93/10279. Certain lasers of the type described in these publications will typically exhibit a low order distribution of modes with radiant energy concentrated toward the center of the beam and, thus, the holes, or wounds, produced are relatively deep and penetrating with respect to the thickness of the skin. Such wounds are the shape of a champagne glass with a broad entrance wound and a longer slender stem. Blood is found to be available from the upper bowl portion of the wound, but little blood escapes from the lower portion, or stem, of the wound. A variety of low-order mode distribution lasers have been developed and are used in medical applications, such as eye surgery, tissue necrosis, and sensor probes.
There has long been a need to produce capillary blood samples without the production of hazardous waste products. There has long been a need to eliminate the use of disposable implements for performing such procedures while reducing worker exposure to infectious disease. There has long been a need to reduce patient discomfort and pain associated with capillary blood collection.
SUMMARY OF THE PRESENT INVENTION
The present invention provides evenly distributed laser energy across a wound site, producing a more closely regulated wound with respect to diameter and depth. Obtaining access to capillary blood with this system provides a less painful sensation to the patient and better control of the wound profile with respect to previously disclosed laserbased skin perforators. Evenly distributed energy across a greater set of modal vectors produces a more controlled wound profile. In certain embodiments of the present invention, control over the mode distribution of the laser beam is achieved by the following: a) optimization of the geometry of laser active element; b) optimization of the laser resonator geometry; c) use of external spatial filters; or d) use of optical fibers and waveguides. Projecting the laser beam with high mode distribution on the skin according to the present invention produces an upper wound profile with a relatively broad bowl portion without production of the lower, less useful, portion of a wound. Such laser perforator systems also produce less pain among subjects. Incorporation of mode distribution allows greater control of a wound profile and collection of blood, while producing less pain in subjects. Any suitable laser may be used according to the present invention; including, but not limited to, solid-state lasers, gas lasers, dye lasers, diode lasers, and diode-pumped solid-state lasers. In one aspect the output laser beam has an energy level ranging between about 0.1 to about 2 Joules and in one particular aspect the energy level is about 1 Joule. In certain aspects a pulsed laser beam is used with a pulse width ranging between 50 and 500 microseconds.
According to the present invention, a laser perforator system is designed to control the mode distribution of output laser beam or has apparatus for the mode distribution of a laser beam, including but not limited to, a hollow waveguide, a solid optical fiber waveguide, spatial filters, specific laser active element geometries, and specific laser active element materials.
Laser light projected into the interior of a hollow waveguide (such as a capillary tube, miniature metal tube, or optical fiber) is reflected from the walls of the waveguide producing a modal distribution which expands along the length of the waveguide. Optical fiber waveguides generate 5 expanded modal distributions of light beams. Optical fibers are designed so that light reflecting from the walls is effectively retained within the fiber. It is possible to launch light into the fiber in such a way as to generate higher order modes. Bends in the optical fiber may be used to generate or i0 reject specific portions of the modal distribution, especially higher order modes, allowing control of the output distribution.
Spatial filters reduce the amount of energy traveling in particular cross sectional areas of a laser beam. Usually, low 15 order modes are reduced by filtering the center of the beam. The use of spatial filtering, however, reduces the overall energy of a beam, reducing the energy efficiency of a system.
It is common knowledge that one design feature of laser devices is the modal distribution of the output beam. In 20 virtually all cases of laser design the designer tries to produce a very low order distribution of modes, including designs of value in other fields which produce a single mode output. It is not obvious that one should reverse the objectives of common laser design practices in order to produce 25 a more useful laser perforator. Modal distribution of laser output may be manipulated by changes in the geometry of the laser active element. For example the laser element described in U.S. patent application Ser. No. 08/204,560, entitled LASER, filed on Mar. 1, 1994 and co-owned with 30 the present invention (incorporated herein by reference for all purposes, full copy appended hereto) describes a solid state laser crystal geometry which produces an output with a multi-mode distribution. In general, the inclusion of reflective surfaces into the laser cavity which are not orthogonal 35 to the optical axis of the laser system design, will produce increased order of modal distribution.
It has been found that certain laser materials naturally produce higher order mode distribution. For example, a laser constructed with erbium-doped Yttrium Scandium Alumi- 40 num Garnet (YSAG) active element has a higher order distribution than the same laser built with erbium-doped YAG (YAG:Er).
In certain embodiments the present invention discloses 45 devices as discussed above with apparatus for producing a laser output beam with a ring profile; in one aspect a hollow cylindrical rod accomplishes this. A system according to this invention includes such apparatus and a laser light source.
The present invention recognizes and addresses the pre- 50 viously mentioned problems and long-felt needs and provides a solution to those problems and a satisfactory meeting of those needs in its various possible embodiments and equivalents thereof. To one of skill in this art who has the benefits of this invention's realizations, teachings, disclo- 55 sures, and suggestions, other purposes and advantages will be appreciated from the following description of preferred embodiments, given for the purpose of disclosure, when taken in conjunction with the accompanying drawings. The detail in these descriptions is not intended to thwart this 60 patent's object to claim this invention no matter how others may later disguise it by variations in form or additions of further improvements.
In one aspect the present invention discloses a laser perforator for perforating skin with a perforation to permit 65 blood under a surface of the skin to flow out, the perforator having a laser light source for producing an output laser
beam, and a mode distribution means for intercepting the output laser beam to control distribution of laser energy of the output laser beam across the perforation of the skin. In another aspect such a laser perforator has a laser light source for producing an output laser beam having an energy level between about 0.1 to about 2.0 Joules, a mode distribution means for controlling mode distribution of the output laser beam across the perforation of the skin, the mode distribution means including a cylindrical laser rod to produce ring mode distribution of the output laser beam, the cylindrical laser rod having a 90 degree annular corner reflector to produce a ring mode distribution of the output laser beam, a doughnut lens for focusing the output laser beam, with the perforation ranging in diameter between about 0.1 to about 2.0 millimeters, in depth between about 0.5 to about 4.0 millimeters, and ranging in width between about 0.05 to about 0.2 millimeters. The present invention teaches a method for perforating skin for blood sampling to produce a perforation to permit blood under a surface of the skin to flow out, the method including, comprising, or consisting of producing a laser beam from a laser, the beam having an energy level and a plurality of energy modes, distributing the energy modes of the beam by mode distribution means for evenly distributing the energy modes, producing an output beam with an evenly distributed mode distribution, and directing the output beam to the skin and producing a perforation through the skin through which the blood flows. In another embodiment the present invention discloses a laser perforator for perforating skin with a perforation to permit blood under a surface of the skin to flow out, the perforator having a laser light source for producing an output laser beam, and a mode distribution means for producing a ring shaped profile of the output laser beam. In one such perforator the ring has a diameter ranging between about 0.1 to about 2.0 millimeters and a slit perforation is produced ranging in depth between about 0.5 to about 4.0 millimeters and ranging in width between about 0.05 to about 0.2 millimeters.
A more particular description of embodiments of the invention briefly summarized above may be had by references to the embodiments which are shown in the drawings which form a part of this specification. These drawings illustrate certain preferred embodiments and are not to be used to improperly limit the scope of the invention which may have other equally effective or legally equivalent embodiments.
DESCRIPTION OF THE DRAWINGS
FIG. 1A is a graph demonstrating low order mode distribution for a prior art laser perforator.
FIG. IB is a schematic representation of a dermal wound produced by a laser with a mode distribution as in FIG. 1A.
FIG. 2A is a graph of high order mode distribution for a laser according to the present invention and
FIG. 2B shows schematically a dermal wound produced by such a laser.
FIG. 3A is a schematic view of a laser-based skin perforation system according to the present invention.
FIG. 3B is a detail view of the wound-site produced by the perforator system of FIG. 3A.
FIG. 3C shows the modal distributions at plane A—A of FIG. 3A.
FIG. 3D shows the modal distribution at plane B—B of FIG. 3A.