This application is being filed concurrently with International Application No. ______ entitled Near-Infrared Lasers For Non-Invasive Monitoring Of Glucose, Ketones, HBA1C, And Other Blood Constituents (Attorney Docket No. OMNI0101PCT); International Application ______ entitled Short-Wave Infrared Super-Continuum Lasers For Early Detection Of Dental Caries (Attorney Docket No. OMNI0102PCT); U.S. application Ser. No. ______ entitled Focused Near-Infrared Lasers For Non-Invasive Vasectomy And Other Thermal Coagulation Or Occlusion Procedures (Attorney Docket No. OMNI0103PUSP); International Application ______entitled Short-Wave Infrared Super-Continuum Lasers For Natural Gas Leak Detection, Exploration, And Other Active Remote Sensing Applications (Attorney Docket No. OMNI0104PCT); U.S. application Ser. No. ______ entitled Short-Wave Infrared Super-Continuum Lasers For Detecting Counterfeit Or Illicit Drugs And Pharmaceutical Process Control (Attorney Docket No. OMNI0105PUSP); and U.S. application Ser. No. ______ entitled Near-Infrared Super-Continuum Lasers For Early Detection Of Breast And Other Cancers (Attorney Docket No. OMNI0107PUSP), the disclosures of which are hereby incorporated in their entirety by reference herein.
This disclosure relates to lasers and light sources for healthcare, medical, or bio-technology applications including systems and methods for using focused near-infrared light sources for non-invasive varicose vein occlusion and other thermal coagulation or occlusion procedures.
Varicose veins are very common in both women and men, and varicose veins may be painful and unattractive. For example, it has been estimated that 41% of women and 15% of men are affected by asymptomatic and visible veins on the legs. Consequently, leg vein therapy is one of the most commonly requested cosmetic procedures. Although these veins may start by being of cosmetic importance, more than half may become symptomatic, particularly if left untreated.
Varicose veins are veins that may have become enlarged and tortuous, and the term commonly refers to veins on the leg. Varicose veins are most common in the superficial veins of the legs, which are subject to high pressure when standing. Superficial vein is a term used to describe a vein that is close to the surface of the body. The term is used to differentiate veins that are close to the surface from veins that are far from the surface, which are known as deep veins. Because most of the blood in the legs is returned by the deep veins, the superficial veins, which return only about 10% of the total blood of the legs, can usually be removed or ablated without serious harm.
The heart pumps oxygen-rich blood into a large artery known as the aorta. The aorta divides into two main arteries, which continue to branch into smaller arteries delivering blood to the rest of the body. Once the oxygen has been delivered, veins carry the blood back to the heart. However, unlike arteries the veins are dependent on one-way valves to keep blood moving in an upward motion. The muscles of the legs help push the blood through the veins, while the one-way valves close and prevent the blood from falling back towards the feet. When the one-way valves fail to close properly, blood may reverse its flow. This may cause increased pressure in the veins, and over time may cause them to swell and become bulging, varicose veins.
Depending on the severity of the varicose veins, treatments may include non-surgical as well as surgical procedures. Non-surgical treatments include sclerotheraphy, elastic stockings, elevating the legs, and exercise. In sclerotheraphy procedures, a medicine may be injected into the blood vessel, causing the vessel to shrink. The traditional surgical treatment has been vein stripping to remove the affected veins. Alternative techniques are available as well, such as ultrasound-guided foam sclerotherapy, radiofrequency ablation, and endovenous laser treatment (ELT). ELT is a relatively newer, minimally invasive treatment for varicose veins. ELT uses a laser that has been fit with a laser fiber tip that is used to introduce light energy into the vein to be treated. The light energy, in turn, may damage the inner vein wall, causing the collagen fibers to contract and the vein to collapse.
As an alternative to ELT, it would be desirable to have a non-invasive treatment or method for treating varicose veins. By using appropriate wavelengths of infrared light, the penetration depth may be large enough to reach non-invasively the varicose veins. The skin may comprise water, collagen, adipose and elastin, so larger penetration depth may be achieved by avoiding absorption peaks in these constituents with appropriate selection of the infrared wavelengths. Also, by focusing the light, the intensity of the light may be lower on the skin surface and higher at the vein vessel wall and lumen, thus permitting less damage to the skin while heating the vessel. In addition, surface cooling may be used to prevent damage to the top layer of the skin by limiting the temperature rise at the skin. Hence, by using a combination of cooling and/or focused light and infrared light, it may be possible to non-invasively cause occlusion of the varicose veins without substantially damaging the skin, or at least the top layer of the skin. Moreover, this technique may be beneficially applied to other procedures such as treatment of finger or toe nails from fungal infection, treatment of hemorrhoids, laser tissue welding, dermatology treatments including treatment for acne or sebaceous hyperplasia, and non-invasive vasectomy procedures.
In one embodiment, a therapeutic system includes a light source generating an output optical beam comprising a plurality of semiconductor sources generating an input optical beam, a multiplexer configured to receive at least a portion of the input optical beam and to form an intermediate optical beam, and one or more fibers configured to receive at least a portion of the intermediate optical beam and to form the output optical beam, wherein the output optical beam comprises one or more optical wavelengths, and wherein at least a portion of the one of more fibers is a fused silica fiber with a core diameter less than approximately 400 microns. An interface device is configured to receive a received portion of the output optical beam and to deliver a delivered portion of the output optical beam to a sample, wherein the interface device comprises one or more lenses to focus at least a part of the delivered portion of the output optical beam on the sample, and wherein the interface device further comprises a surface cooling apparatus to reduce damage to a top surface of the sample. The part of the delivered portion of the output optical beam is at least partially absorbed in the sample to thermally damage at least a part of the sample, and a sample temperature in the part of the sample reaches about 65 Celsius or higher, while a cover temperature at the top surface of the sample remains less than about 65 Celsius. The output optical beam comprises a fluence less than about 250 Joules per centimeter squared.
In another embodiment, a therapeutic system includes a light source generating an output optical beam comprising one or more semiconductor sources generating an input optical beam, one or more fibers configured to receive at least a portion of the input optical beam and to form an intermediate optical beam, and a light guide configured to receive at least a portion of the intermediate optical beam and to form the output optical beam, wherein the output optical beam comprises one or more optical wavelengths. An interface device is configured to receive a received portion of the output optical beam and to deliver a delivered portion of the output optical beam to a sample, wherein the interface device comprises one or more lenses to focus at least a part of the delivered portion of the output optical beam on the sample, and wherein the interface device further comprises a surface cooling apparatus to reduce damage to a top surface of the sample. At least some of the part of the delivered portion of the output optical beam is at least partially absorbed in the sample to thermally damage at least a part of the sample, and a sample temperature in the part of the sample reaches about 65 Celsius or higher, while a cover temperature at the top surface of the sample remains less than about 65 Celsius.
In yet another embodiment, a method of therapy includes generating an output optical beam comprising generating an input optical beam from one or more semiconductor sources, forming an intermediate optical beam after propagating at least a portion of the input optical beam through one or more fibers, and guiding at least a portion of the intermediate optical beam and forming the output optical beam, wherein the output optical beam comprises one or more optical wavelengths. The method may also include receiving a received portion of the output optical beam and delivering a delivered portion of the output optical beam to a sample, focusing at least a part of the delivered portion of the output optical beam on the sample, and cooling a top surface of the sample. The method may further include absorbing at least some of the part of the delivered portion of the output optical beam in the sample, damaging thermally at least a part of the sample, and wherein a sample temperature in the part of the sample reaches about 65 Celsius or higher, while a cover temperature at the top surface of the sample remains less than about 65 Celsius.
For a more complete understanding of the present disclosure, and for further features and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:
As required, detailed embodiments of the present disclosure are described herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the disclosure that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present disclosure.
The vein anatomy in a typical human leg is illustrated in
Varicose veins may lead to unsightly bluish-purple blemishes, but they may also cause discomfort and disability. Varicose veins are abnormally dilated, tortuous, superficial veins caused by incompetent venous valves. Most commonly, the varicose vein condition may affect the lower extremities, such as the saphenous veins. Varicose vein difficulty may be due to valve defects inside the veins themselves. In particular, they may occur when the stop valves within the veins fail to propel oxygen depleted blood back to the heart from the legs. Because of the valve malfunction, blood may be allowed to pool in the leg veins, causing them to become distorted and painful and, if left untreated, may lead to ulceration and skin damage.
As an example,
One example of a laser-based treatment for varicose veins is endovenous laser treatment, or ELT. ELT may be a minimally invasive, ultrasound-guided technique used for treating varicose veins using laser energy commonly performed by an interventional radiologist or vascular surgeon. In ELT, an optical fiber may be inserted into the vein to be treated, and laser light, normally in the infrared portion of the spectrum, is shone into the interior of the vein. This may cause the vein to contract, and the optical fiber is slowly withdrawn.
One embodiment of the ELT procedure 400 is shown in
The principle of ELT may be ablation and photocoagulation of the vein interior by laser-induced thermal effects. In one embodiment, the effect on the vein 450 is illustrated in
Some of the prior techniques to treat varicose veins have attempted to heat the vessel by targeting the hemoglobin in the blood, and then having the heat transfer to the vessel wall. For these embodiments, lasers emitting wavelengths of approximately 500 nm to 1100 nm have been used. Attempts have also been made to optimize the laser energy absorption by utilizing local absorption peaks of hemoglobin at 810 nm, 940 nm, 980 nm and 1064 nm. However, the heat transfer method used in these instances may result in poor efficiency in heating the collagen in the vessel wall and damaging or destroying the endothelial cells. In some embodiments, it may also be desired to limit the heating to approximately 80-85 degrees Celsius to avoid boiling, vaporization and carbonization of tissues. In addition, blood may coagulate at about 80 degrees Celsius. Regions of blood that have coagulated and remain in the vein may prevent the vein from completely collapsing on itself. Moreover, heating the endothelial wall to 85 degrees Celsius may result in heating the vein media to approximately 65 degrees Celsius, which is known to lead to collagen contraction or shrinkage.
In various embodiments, methods to treat varicose veins by targeting the vessel wall directly with a more appropriate wavelength of laser light have been contemplated. In particular, laser wavelengths may be employed that transmit through any residual blood in the vessels, yet the laser light may be absorbed by the water and collagen of the vessel wall. For example, experiments have demonstrated that laser energy may be absorbed directly in the vessel walls using wavelengths in the range of approximately 1200 nm to 1800 nm. One advantage of this range of wavelengths is that energy may be absorbed more uniformly with less risk of hot spots, boiling, or explosions caused by blood pockets. Also, this wavelength range may lead to less pain and collateral bruising, perhaps because very little light transmits outside the vessel to cause damage.
Since in a non-invasive varicose vein treatment technique the light would have to transmit through the dermis 157, the absorption coefficient for the various skin constituents should be examined. One other consideration may be the scattering through tissue in the dermis. Although the absorption coefficient may be useful for determining the material in which light of a certain infrared wavelength will be absorbed, to determine the penetration depth of the light of a certain wavelength may also require the addition of scattering loss to the curves. In
In one embodiment, the vein or vessel walls may be modeled as smooth muscle tissue. As an example, smooth muscle tissue or tunica media may comprise protein, which may have an absorption coefficient similar to collagen (e.g., 503). Hence, by selecting wavelengths near peaks of absorption for collagen 503 in
In one embodiment, one desired goal for a non-invasive varicose vein treatment procedure is to cause coagulation (probably through a thermal process) or occlusion of the vein or vessel wall with minimal damage to the skin above. From
In a particular embodiment, wavelengths for the non-invasive procedure may be selected based on the absorption curves 500 in
A light based procedure may also be aided by several means of preserving the top layers of the skin. In one embodiment, the light could be focused to a depth of approximately the varicose veins (e.g., ultrasound imaging may be used to locate the varicose veins). By focusing the light, a funnel may be created for the light intensity, with a lower intensity on the epidermis and dermis layers and higher intensity at the varicose veins. In another embodiment, surface cooling may be added to preserve the epidermis and at least a fraction of the dermis. For example, surface cooling may be a common technique used in laser based dermatology and cosmetic surgery applications. Surface cooling methods may include a cryo-spray, air cooling, or a water/liquid cooled surface in contact with skin. The water/liquid cooled surface may be in contact surrounding the laser beam spot, or the laser beam may transmit through the surface if it is at least partially transmitting at the laser wavelength. Although two techniques for preserving the skin have been described, combinations of the two or other techniques may also be used and are intended to be covered by this disclosure.
An exemplary set-up for non-invasive varicose vein treatment 600 is illustrated in
In one embodiment, the light input 700 to the non-invasive varicose vein treatment assembly may be as shown in
Another embodiment of the non-invasive apparatus 800 is illustrated in
Another embodiment of the non-invasive apparatus 900 is illustrated in
In some instances it may be desirable to create multiple locations of focused light on the varicose vein. For example, the speed of the treatment may be increased by causing thermal coagulation or occlusion at multiple locations One way to accomplish this may be to slide the assemblies and/or the light source such as shown in
In the embodiment of
Although several embodiments of non-invasive varicose vein apparatuses are illustrated in
The lens and/or mirror assemblies may comprise one or more lenses, microscope objectives, curved or flat mirrors, lens tipped fibers, or some combination of these elements. As an example, the optics such as used in a camera may be employed in this arrangement, provided that the optics is substantially transparent at the light wavelengths being used. Moreover, reflections and losses through the optics may be reduced by applying anti-reflection coatings, and chromatic dispersion may be reduced by using reflective optics rather than refractive optics. Although a particular method of focusing the light has been described, other methods may also be used and are intended to be covered by this disclosure.
Described herein are just some examples of the beneficial use of infrared laser treatment based on using focused light and/or surface cooling. However, many other medical procedures can use the infrared light consistent with this disclosure and are intended to be covered by the disclosure. For example, although non-invasive varicose vein treatment has been described in detail as one embodiment, more generally the focused infrared light may be used to thermally coagulate or occlude relatively shallow vessels non-invasively or minimally invasively while preserving or minimizing damage to the top layer of the skin or tissue. Other applications where this more general technique may be beneficial include treatment of finger or toe nails from fungal infection, treatment of hemorrhoids, laser tissue welding, dermatology treatments including treatment for acne or sebaceous hyperplasia, and non-invasive vasectomy procedures, for example.
In one embodiment, it may be advantageous to use focused infrared light for treatment of finger or toe nail fungus. Onychomycosis, or fungal infection of nails (most often on the toes) affects about 12% of Americans, according to the American Academy of Dermatology. Toenail laser treatment may offer an attractive alternative to oral medication, which carries a risk of liver damage, and a nail lacquer, which has poor efficacy. The causes for onychomycosis include dermatophytes, non-dermatophyte molds and Candida species. The nail plate may become thickened with yellowish or brownish discoloration, brittle with crumbling edges and, in addition, it is not uncommon for the nail plate to separate from the nail bed. Onychomycosis may be difficult to treat, with high rates of persistence or recurrence of fungal infection.
The fungus may grow below the fingernail or toenail, particularly near the beginning section where the nail grows from (e.g., the eponychium or lunula). For laser treatment of the fungus, the light may advantageously penetrate through the fingernail or toenail to the epidermis and dermis below the nail. Thus, it may be desirous to select a wavelength of light that may pass through the nail plate and into the nail bed, which may then result in superheating of the fungal material. It is believed that exposure of the fungi to high temperatures may inhibit their growth as well as cause cell damage, perhaps even cell death. The upper right side of
Fingernails and toenails are generally made of tough protein called keratin. In addition, the composition of the nails includes about 7-12% water. Thus, for the wavelength of light to pass the nail plate to the nail bed, it may be desirous to minimize absorption by keratin and water, as well as the scattering through the nail plate.
Beyond the absorption of keratin, the scattering through the nail plate and overall water absorption may also need to be considered. For example, scattering increases at the shorter wavelengths, since the scattering loss increases inversely as some power of the wavelength. Also, above about 2000 nm, the water absorption background increases with increasing wavelength. As an example,
Laser treatment of nail fungus has been studied at near-infrared wavelengths around 1064 nm, 870 nm, and 930 nm. These infrared laser wavelengths may be accompanied by a visible tracer beam, so the physician knows where the light is incident on the sample. However, it may be further advantageous to select a laser wavelength in one of the minima of keratin and water absorption, or near the overall minimum near about 1850 nm. In one embodiment, it may be desirable to select a wavelength near 980 nm 1404 rather than near 1064-1075 nm 1405, as further described with respect to
In yet another embodiment, it may be advantageous to use focused infrared light for treatment of hemorrhoids. A laser hemorrhoidectomy is a procedure that employs laser energy for the treatment of hemorrhoids. When this treatment is applied, a laser may be used to heat the problematic vein, which may in turn cause the vein to collapse and perhaps even disintegrate. Similar to the treatment of varicose veins, focused infrared light may damage the veins while preserving the skin above and in surrounding areas. The focusing of the light as well as possibly using surface cooling procedures may be advantageous for hemorrhoid treatments using lasers. Another advantage of laser hemorrhoidectomy treatment may be that the technique may be used to treat several affected veins at approximately the same time. Furthermore, the laser treatment procedure may minimize the risk of bleeding, which may be a problem in typical surgical procedures. Any combination of the techniques described in this disclosure may be used for the laser treatment of hemorrhoids.
As yet another example, the focused infrared light may be beneficial for laser tissue welding. Bonding of edges of human tissue is a necessary step in most surgical procedures. Current techniques of joining include suture or staple incisions, in which case the tissue bonding process may occur naturally. However, suturing or stapling incisions may introduce foreign materials that may cause inflammation or leave visible scars. On the other hand, laser assisted bonding may help improve post-operative bonding, perhaps even speeding up the healing process.
Laser tissue welding may play a more significant role in surgical methods as laparoscopic, endoscopic and micro-surgical techniques continue to develop. Laser tissue welding may utilize the energy from a laser beam to anastomose tissues, and the technique may be particularly advantageous when suturing or stapling is difficult. In many instances, the laser tissue welding technique also uses a protein solder placed over the anastomosis site. Protein solders may help create a watertight seal, decrease thermal damage, improve consistency of welds, and may even reduce operative times. In one embodiment, laser soldering with albumin based glue may cause less damage and scaring in bonded tissues. For example, experiments have been performed using a 810 nm semiconductor diode laser and two human serum albumin based biomaterials. Experimental evidence also seems to indicate that it may be beneficial to match the optical penetration depth with the thickness of the target tissue. By matching the depth of penetration to tissue thickness, transmural tissue heating may be accomplished.
The mechanisms of laser tissue welding are not precisely known, but there have been many studies that seem consistent with experimental data. Most of these speculations have laser energy being absorbed to create heat-induced changes of the media into collagen, which occurs at temperatures near about 70-80 degrees Celsius. In one example, researchers found that tissue welding resulted in a homogenizing change in the collagen with inter-digitation of the individual fibers. They speculate that the inter-digitation was the structural basis for the tissue welding effect. In another example, researchers found that laser welding led to direct collagen-to-collagen and collagen-to-elastin bonding. In yet another study, researchers report that the mechanism of welding is from the roping effect of parallel collagen fibers as well as the cross-linking that occurs at the cut ends of the collagen fibers. Thus, these studies point to the hypothesis that collagen fiber bonding, through some form of inter-digitation, roping, fusion, or other physiochemical means may be responsible for the welding effect.
Given the importance of collagen in the laser tissue welding process, it may be advantageous to use wavelengths of light that are near an absorption peak in collagen. This may reduce collateral damage near and surrounding the wound healing location. Since the heat goes directly into heating the collagen, this may also reduce the power level required for the laser. The absorption coefficient for collagen 503 is shown in
The particular choice of wavelength for laser tissue welding may also be determined by attempting to match the penetration depth to the thickness of the tissue to be welded. For example,
Other modifications may also be used advantageously in the laser tissue welding process, beyond using a wavelength of light near one of the collagen absorption peaks. For example, since the collagen temperature wants to be near or about 70 degrees Celsius, a temperature monitoring system may be used to reduce the laser power when this temperature range is reached. Moreover, it may be advantageous to add a protein solder near or over the anastomosis site, such as albumin solders. When such solders are used, it may also be advantageous to perhaps add a wavelength of light excitation that is absorbed by the solder (e.g., one wavelength might correspond to the collagen, while another wavelength could correspond to the solder. Alternately, there may be a wavelength that is absorbed preferentially by both collagen and the solder). In one embodiment, the solder added could be albumin, and some of the near-infrared absorption peaks for albumin are near approximately 1.51 microns, 1.7 microns, 1.74 microns, 2.17 microns and 2.28 microns. Thus, selecting a wavelength near 1720 nm (1.72 microns) might be absorbed by collagen and albumin. Alternately, beyond the wavelength selected for heating collagen, a second wavelength could be added that falls near one of the albumin absorption peaks. Moreover, using focused light and/or surface cooling techniques may also enable effective laser tissue welding while reducing damage to the top layer, which may result in scaring or unnecessary tissue damage. Although specific embodiments of laser tissue welding are described, other methods and combinations may also be used and are intended to be within the scope of this disclosure.
Although particular examples have been discussed, other therapeutic and diagnostic medical procedures may also benefit for the use of infrared light. Other procedures may benefit from using focused infrared light that may be used to thermally coagulate or occlude relatively shallow vessels non-invasively or minimally invasively while preserving or minimizing damage to the top layer of the skin or tissue. Particularly when these procedures are external to the body, various surface cooling techniques may also be used advantageously. The discussion has been for exemplary applications, but more generally different wavelengths of light may be used, and different combinations of cooling and/or focusing may be used, and these are also covered within the scope of this disclosure.
Various embodiments of this disclosure provide a method of causing coagulation or occlusion of sections of varicose veins with minimal damage to the skin. One method of achieving this goal may be to focus the light, so that low intensity may be incident on the skin, while higher intensity of light may be incident on the varicose vein wall and lumen. Another method of achieving this goal may be to add surface cooling of the epidermis and dermis, such as using cryogenic spray or liquid-cooled surface contact—techniques that are commonly used in dermatology and cosmetic surgery. In yet another method, some combination of light focusing and surface cooling may be employed. These are provided as particular examples, but other methods of minimizing damage to the skin may also be used and are intended to be covered by this disclosure.
In a non-limiting example, a plurality of spots may be used, or what might be called a fractionated beam. The fractionated laser beam may be added to the laser delivery assembly or delivery head in a number of ways. In one embodiment, a screen-like spatial filter may be placed in the pathway of the beam to be delivered to the biological tissue. The screen-like spatial filter can have opaque regions to block the light and holes or transparent regions, through which the laser beam may pass to the tissue sample. The ratio of opaque to transparent regions may be varied, depending on the application of the laser. In another embodiment, a lenslet array can be used at or near the output interface where the light emerges. In yet another embodiment, at least a part of the delivery fiber from the infrared laser system to the delivery head may be a bundle of fibers, which may comprise a plurality of fiber cores surrounded by cladding regions. The fiber cores can then correspond to the exposed regions, and the cladding areas can approximate the opaque areas not to be exposed to the laser light. As an example, a bundle of fibers may be excited by at least a part of the laser system output, and then the fiber bundle can be fused together and perhaps pulled down to a desired diameter to expose to the tissue sample near the delivery head. In yet another embodiment, a photonic crystal fiber may be used to create the fractionated laser beam. In one non-limiting example, the photonic crystal fiber can be coupled to at least a part of the laser system output at one end, and the other end can be coupled to the delivery head. In a further example, the fractionated laser beam may be generated by a heavily multi-mode fiber, where the speckle pattern at the output may create the high intensity and low intensity spatial pattern at the output. Although several exemplary techniques are provided for creating a fractionated laser beam, other techniques that can be compatible with optical fibers are also intended to be included by this disclosure.
In a further embodiment, it may be advantageous to apply surface cooling techniques to minimize damage to the skin above the varicose veins. In a particular embodiment, the surface cooling may be accomplished by having a thermally conductive surface approximately in contact with the skin, as illustrated 904 in
In yet another embodiment, the surface cooling may be accomplished using a dynamic cooling device, such as a cryogenic spray. As an example,
Beyond the use of focused light and surface cooling, other methods may also be used to reduce the potential for pain or damage to the skin. In yet another embodiment, an optical clearing agent, OCA, may be applied to the skin to reduce the laser power necessary. The OCA may reduce skin scattering and increase transmission through the skin, thereby reducing the required power levels and the risk of skin burns. The OCA may also reduce the differences in refractive index between different skin layers and air, thereby reducing the amount of reflected light from refractive index mismatches. Examples of common OCAs include dimethyl sulfoxide, glycerol, glucose and other sugar compounds—as well as mixtures of these compounds. Also, in one embodiment the OCA may be delivered to the skin using a pneumatic jet device, such as a Madajet device made by Advanced Meditech International. For instance, the OCA may be applied near and around the spot(s) of laser irradiation.
In another embodiment, a local anesthetic may be used in the vicinity of the laser irradiation and clamp or mount. One example of a local anesthesia may be lidocaine. Many local anesthetics may be membrane stabilizing drugs, and local anesthetics may be bases and may usually be formulated as the hydrochloride salt to render them water-soluble. Beyond optical clearing agents and local anesthesia, other ointments, creams, liquids or sprays may also be applied to the skin area before, during and after the laser irradiation, and these are also intended to be covered by this disclosure.
Some preliminary experiments show the feasibility of using focused infrared light for non-invasive varicose vein procedures, or other procedures where relatively shallow vessels below the skin are to be thermally coagulated or occluded with minimum damage to the skin upper layers. In one embodiment, the penetration depth and optically induced thermal damage has been studied in chicken breast samples. Chicken breast may be a reasonable optical model for smooth muscle tissue, comprising water, collagen and proteins. Commercially available chicken breast samples were kept in a warm bath (about 32 degrees Celsius) for about an hour, and then about half an hour at room temperature in preparation for the measurements.
An exemplary set-up 1200 for testing chicken breast samples using collimated light is illustrated in
For these particular experiments, the measured depth of damage (in millimeters) versus the incident laser power (in Watts) is shown 1300 in
In one embodiment, if the penetration depth is defined as when the damage begins to approximately saturate, then for wavelengths near 980 nm 1301 the penetration depth 1306 may be defined as approximately 4 mm. For wavelengths near 1210 nm 1302 the penetration depth 1305 may be defined as approximately 3 mm, and for wavelengths near 1700 nm 1303 the penetration depth 1304 may be defined as approximately 2 mm. These are only approximate values, and other values and criteria may be used to define the penetration depth. It may also be noted that the level of damage at the highest power points differs at the different wavelengths. For example, at the highest power point of 1303 near 1700 nm, much more damage is observed, showing evidence of even boiling and cavitation. This may be due to the higher absorption level near 1700 nm (e.g., 501 in
Even near wavelengths such as described in
In another embodiment, focused infrared light has been used to preserve the top layer of a tissue while damaging nerves at a deeper level. For instance,
For a particular embodiment, histology of the renal artery is shown in
The histology with focused infrared light exposure 1650 is illustrated in
Thus, by using focused infrared light near 1708 nm in this example, the top approximately 0.5 mm of the renal artery is spared from laser damage. It should be noted that when the same experiment is conducted with a collimated laser beam, then the entire approximately 1.5 mm is damaged (i.e, including regions 1656 and 1657). Therefore, the cone of light with the lower intensity at the top and the higher intensity toward the bottom may, in fact, help preserve the top layer from damage. There should be a Beer's Law attenuation of the light intensity as the light propagates into the tissue. For example, the light intensity should reduce exponentially at a rate determined by the absorption coefficient. In these experiments it appears that the focused light is able to overcome the Beer's law attenuation and still provide contrast in intensity between the front and back surfaces.
In another embodiment, experiments have also been conducted on dermatology samples with surface cooling, and surface cooling was shown to preserve the top layer of the skin during laser exposure. In this particular example, the experimental set-up 1700 is illustrated in
In this embodiment, the light is incident on the sample 1704 through a sapphire window 1711. The sapphire material 1711 is selected because it is transparent to the infrared wavelengths, while also being a good thermal conductor. Thus, the top layer of the sample 1704 may be cooled by being approximately in contact with the sapphire window 1711. The laser light 1712 used is near 1708 nm from a cascaded Raman oscillator (described in greater detail herein), and one or more collimating lenses 1713 are used to create a beam with a diameter 1714 of approximately 2 mm. This is one particular embodiment of the sample surface cooling arrangement, but other apparatuses and methods may be used and are intended to be covered by this disclosure.
Experimental results obtained using the set-up of
In summary, experiments verify that infrared light, such as near 980 nm, 1210 nm, or 1700 nm, may achieve penetration depths between approximately 2 mm to 4 mm or more. The top layer of skin or tissue may be spared damage under laser exposure by focusing the light, applying surface cooling, or some combination of the two. These are particular experimental results, but other wavelengths, methods and apparatuses may be used for achieving the penetration and minimizing damage to the top layer and are intended to be covered by this disclosure. In an alternate embodiment, it may be beneficial to use wavelengths near 1310 nm if the absorption from skin constituents (
Infrared light sources can be used for diagnostics and therapeutics in a number of medical applications. For example, broadband light sources can advantageously be used for diagnostics, while narrower band light sources can advantageously be used for therapeutics. In one embodiment, selective absorption or damage can be achieved by choosing the laser wavelength to lie approximately at an absorption peak of particular tissue types. Also, by using infrared wavelengths that minimize water absorption peaks and longer wavelengths that have lower tissue scattering, larger penetration depths into the biological tissue can be obtained. In this disclosure, infrared wavelengths are defined as wavelengths in the range of approximately 0.9 microns to 10 microns, more preferably wavelengths between about 0.98 and 2.5 microns.
As used throughout this disclosure, the term “couple” and or “coupled” refers to any direct or indirect communication between two or more elements, whether or not those elements are physically connected to one another. In this disclosure, the term “damage” refers to affecting a tissue or sample so as to render the tissue or sample inoperable. For instance, if a particular tissue normally emits certain signaling chemicals, then by “damaging” the tissue is meant that the tissue reduces or no longer emits that certain signaling chemical. The term “damage” and or “damaged” may include ablation, melting, charring, killing, or simply incapacitating the chemical emissions from the particular tissue or sample. In one embodiment, histology or histochemical analysis may be used to inspect and determine whether a tissue or sample has been damaged.
As used throughout this disclosure, the term “spectroscopy” means that a tissue or sample is inspected by comparing different features, such as wavelength (or frequency), spatial location, transmission, absorption, reflectivity, scattering, refractive index, or opacity. In one embodiment, “spectroscopy” may mean that the wavelength of the light source is varied, and the transmission, absorption or reflectivity of the tissue or sample is measured as a function of wavelength. In another embodiment, “spectroscopy” may mean that the wavelength dependence of the transmission, absorption or reflectivity is compared between different spatial locations on a tissue or sample. As an illustration, the “spectroscopy” may be performed by varying the wavelength of the light source, or by using a broadband light source and analyzing the signal using a spectrometer, wavemeter, or optical spectrum analyzer.
As used throughout this document, the term “fiber laser” refers to a laser or oscillator that has as an output light or an optical beam, wherein at least a part of the laser comprises an optical fiber. For instance, the fiber in the “fiber laser” may comprise one of or a combination of a single mode fiber, a multi-mode fiber, a mid-infrared fiber, a photonic crystal fiber, a doped fiber, a gain fiber, or, more generally, an approximately cylindrically shaped waveguide or light-pipe. In one embodiment, the gain fiber may be doped with rare earth material, such as ytterbium, erbium, and/or thulium. In another embodiment, the infrared fiber may comprise one or a combination of fluoride fiber, ZBLAN fiber, chalcogenide fiber, tellurite fiber, or germanium doped fiber. In yet another embodiment, the single mode fiber may include standard single-mode fiber, dispersion shifted fiber, non-zero dispersion shifted fiber, high-nonlinearity fiber, and small core size fibers.
As used throughout this disclosure, the term “pump laser” refers to a laser or oscillator that has as an output light or an optical beam, wherein the output light or optical beam may be coupled to a gain medium to excite the gain medium, which in turn may amplify another input optical signal or beam. In one particular example, the gain medium may be a doped fiber, such as a fiber doped with ytterbium, erbium, and/or thulium. In another embodiment, the gain medium may be a fused silica fiber or a fiber with a Raman effect from the glass. In one embodiment, the “pump laser” may be a fiber laser, a solid state laser, a laser involving a nonlinear crystal, an optical parametric oscillator, a semiconductor laser, or a plurality of semiconductor lasers that may be multiplexed together. In another embodiment, the “pump laser” may be coupled to the gain medium by using a fiber coupler, a dichroic mirror, a multiplexer, a wavelength division multiplexer, a grating, or a fused fiber coupler.
As used throughout this document, the term “super-continuum” and/or “supercontinuum” and/or “SC” refers to a broadband light beam or output that comprises a plurality of wavelengths. In a particular example, the plurality of wavelengths may be adjacent to one-another, so that the spectrum of the light beam or output appears as a continuous band when measured with a spectrometer. In one embodiment, the broadband light beam may have a bandwidth of at least 10 nm. In another embodiment, the “super-continuum” may be generated through nonlinear optical interactions in a medium, such as an optical fiber or nonlinear crystal. For example, the “super-continuum” may be generated through one or a combination of nonlinear activities such as four-wave mixing, the Raman effect, modulational instability, and self-phase modulation.
As used throughout this disclosure, the terms “optical light” and/or “optical beam” and or “light beam” refer to photons or light transmitted to a particular location in space. The “optical light” and or “optical beam” and/or “light beam” may be modulated or unmodulated, which also means that they may or may not contain information. In one embodiment, the “optical light” and/or “optical beam” and/or “light beam” may originate from a fiber, a fiber laser, a laser, a light emitting diode, a lamp, a pump laser, or a light source.
As used throughout this document, the terms “near”, “about”, and the symbol “˜” are used to designate approximate center wavelengths with a range that may depend on the particular application. For example, in one embodiment “about 1720 nm” refers to one or more wavelengths of light with a wavelength value anywhere between approximately 1680 nm and 1760 nm. In another embodiment, the term “near 1720 nm” refers to one or more wavelengths of light with a wavelength value anywhere between approximately 1700 nm and 1740 nm. Similarly, as used throughout this document, the term “near 1210 nm” may refer to one or more wavelengths of light with a wavelength value anywhere between approximately 1170 nm and 1250 nm. In one embodiment, the term “near 1210 nm” refers to one or more wavelengths of light with a wavelength value anywhere between approximately 1190 nm and 1230 nm.
Different light sources may be selected for the infrared based on the needs of the application. Some of the features for selecting a particular light source include power or intensity, wavelength range or bandwidth, spatial or temporal coherence, spatial beam quality for focusing or transmission over long distance, and pulse width or pulse repetition rate. Depending on the application, lamps, light emitting diodes (LEDs), laser diodes (LD's), tunable LD's, super-luminescent laser diodes (SLDs), fiber lasers or super-continuum sources (SC) may be advantageously used. Also, different fibers may be used for transporting the light, such as fused silica fibers, plastic fibers, mid-infrared fibers (e.g., tellurite, chalcogenides, fluorides, ZBLAN, etc), photonic crystal fibers, or a hybrid of these fibers.
In one embodiment, LED's can be used that have a higher power level in the infrared wavelength range. LED's produce an incoherent beam, but the power level can be higher than a lamp and with higher energy efficiency. Also, the LED output may more easily be modulated, and the LED provides the option of continuous wave or pulsed mode of operation. LED's are solid state components that emit a wavelength band that is of moderate width, typically between about 20 nm to 40 nm. There are also so-called super-luminescent LEDs that may even emit over a much wider wavelength range. In another embodiment, a wide band light source may be constructed by combining different LEDs that emit in different wavelength bands, some of which could overlap in spectrum. One advantage of LEDs as well as other solid state components is the compact size that they may be packaged into.
In yet another embodiment, various types of laser diodes may be used in the infrared wavelength range. Just as LEDs may be higher in power but narrower in wavelength emission than lamps and thermal sources, the LDs may be yet higher in power but yet narrower in wavelength emission than LEDs. Different kinds of LDs may be used, including Fabry-Perot LDs, distributed feedback (DFB) LDs, distributed Bragg reflector (DBR) LDs. A plurality of LDs may be spatially multiplexed, polarization multiplexed, wavelength multiplexed, or a combination of these multiplexing methods. Also, the LDs may be fiber pig-tailed or have one or more lenses on the output to collimate or focus the light. Another advantage of LDs is that they may be packaged compactly and may have a spatially coherent beam output. Moreover, tunable LDs that can tune over a range of wavelengths are also available. The tuning may be done by varying the temperature, or electrical current may be used in particular structures such as distributed Bragg reflector LDs. In another embodiment, external cavity LDs may be used that have a tuning element, such as a fiber grating or a bulk grating, in the external cavity.
In another embodiment, super-luminescent laser diodes may provide higher power as well as broad bandwidth. An SLD is typically an edge emitting semiconductor light source based on super-luminescence (e.g., this could be amplified spontaneous emission). SLDs combine the higher power and brightness of LDs with the low coherence of conventional LEDs, and the emission band for SLD's may be 5 nm to 100 nm wide, preferably in the 60 nm to 100 nm range. Although currently SLDs are commercially available in the wavelength range of approximately 400 nm to 1700 nm, SLDs could and may in the future be made the cover a broader region of the infrared.
In yet another embodiment, high power LDs for either direct excitation or to pump fiber lasers and SC light sources may be constructed using one or more laser diode bar stacks. As an example,
Brightness may be increased by spatially combining the beams from multiple stacks 1903. The combiner may include spatial interleaving, wavelength multiplexing, or a combination of the two. Different spatial interleaving schemes may be used, such as using an array of prisms or mirrors with spacers to bend one array of beams into the beam path of the other. In another embodiment, segmented mirrors with alternate high-reflection and anti-reflection coatings may be used. Moreover, the brightness may be increased by polarization beam combining 1904 the two orthogonal polarizations, such as by using a polarization beam splitter. In a particular embodiment, the output may then be focused or coupled into a large diameter core fiber. As an example, typical dimensions for the large diameter core fiber range from diameters of approximately 100 microns to 400 microns or more. Alternatively or in addition, a custom beam shaping module 1905 may be used, depending on the particular application. For example, the output of the high power LD may be used directly 1906, or it may be fiber coupled 1907 to combine, integrate, or transport the high power LD energy. These high power LDs may grow in importance because the LD powers can rapidly scale up. For example, instead of the power being limited by the power available from a single emitter, the power may increase in multiples depending on the number of diodes multiplexed and the size of the large diameter fiber. Although
Each of the light sources described above have particular strengths, but they also may have limitations. For example, there is typically a trade-off between wavelength range and power output. Also, sources such as lamps, thermal sources, and LEDs produce incoherent beams that may be difficult to focus to a small area and may have difficulty propagating for long distances. An alternative source that may overcome some of these limitations is an SC light source. Some of the advantages of the SC source may include high power and intensity, wide bandwidth, spatially coherent beam that can propagate nearly transform limited over long distances, and easy compatibility with fiber delivery.
Supercontinuum lasers may combine the broadband attributes of lamps with the spatial coherence and high brightness of lasers. By exploiting a modulational instability initiated supercontinuum (SC) mechanism, an all-fiber-integrated SC laser with no moving parts may be built using commercial-off-the-shelf (COTS) components. Moreover, the fiber laser architecture may be a platform where SC in the visible, near-infrared/SWIR, or mid-IR can be generated by appropriate selection of the amplifier technology and the SC generation fiber. But until now, SC lasers were used primarily in laboratory settings since typically large, table-top, mode-locked lasers were used to pump nonlinear media such as optical fibers to generate SC light. However, those large pump lasers may now be replaced with diode lasers and fiber amplifiers that gained maturity in the telecommunications industry.
In one embodiment, an all-fiber-integrated, high-powered SC light source 2000 may be elegant for its simplicity (
The SC generation 2007 may occur in the relatively short lengths of fiber that follow the pump laser. Exemplary SC fiber lengths may range from a few millimeters to 100 m or more. In one embodiment, the SC generation may occur in a first fiber 2008 where the modulational-instability initiated pulse break-up occurs primarily, followed by a second fiber 2009 where the SC generation and spectral broadening occurs primarily.
In one embodiment, one or two meters of standard single-mode fiber (SMF) after the power amplifier stage may be followed by several meters of SC generation fiber. For this example, in the SMF the peak power may be several kilowatts and the pump light may fall in the anomalous group-velocity dispersion regime—often called the soliton regime. For high peak powers in the dispersion regime, the nanosecond pulses may be unstable due to a phenomenon known as modulational instability, which is basically parametric amplification in which the fiber nonlinearity helps to phase match the pulses. As a consequence, the nanosecond pump pulses may be broken into many shorter pulses as the modulational instability tries to form soliton pulses from the quasi-continuous-wave background. Although the laser diode and amplification process starts with approximately nanosecond-long pulses, modulational instability in the short length of SMF fiber may form approximately 0.5 ps to several-picosecond-long pulses with high intensity. Thus, the few meters of SMF fiber may result in an output similar to that produced by mode-locked lasers, except in a much simpler and cost-effective manner.
The short pulses created through modulational instability may then be coupled into a nonlinear fiber for SC generation. The nonlinear mechanisms leading to broadband SC may include four-wave mixing or self-phase modulation along with the optical Raman effect. Since the Raman effect is self-phase-matched and shifts light to longer wavelengths by emission of optical photons, the SC may spread to longer wavelengths very efficiently. The short-wavelength edge may arise from four-wave mixing, and often times the short wavelength edge may be limited by increasing group-velocity dispersion in the fiber. In many instances, if the particular fiber used has sufficient peak power and SC fiber length, the SC generation process may fill the long-wavelength edge up to the transmission window.
Mature fiber amplifiers for the power amplifier stage 2006 include ytterbium-doped fibers (near 1060 nm), erbium-doped fibers (near 1550 nm), erbium/ytterbium-doped fibers (near 1550 nm), or thulium-doped fibers (near 2000 nm). In various embodiments, candidates for SC fiber 2009 include fused silica fibers (for generating SC between 0.8-2.7 μm), mid-IR fibers such as fluorides, chalcogenides, or tellurites (for generating SC out to 4.5 μm or longer), photonic crystal fibers (for generating SC between 0.4 and 1.7 μm), or combinations of these fibers. Therefore, by selecting the appropriate fiber-amplifier doping for 2006 and nonlinear fiber 2009, SC may be generated in the visible, near-IR/SWIR, or mid-IR wavelength region.
The configuration 2000 of
In one embodiment, one example of the SC laser that operates in the short wave infrared (SWIR) is illustrated in
In this particular 5 W unit, the mid-stage between amplifier stages 2102 and 2106 comprises an isolator 2107, a band-pass filter 2108, a polarizer 2109 and a fiber tap 2110. The power amplifier 2106 uses a 4 m length of the 12/130 micron erbium/ytterbium doped fiber 2111 that is counter-propagating pumped using one or more 30 W 940 nm laser diodes 2112 coupled in through a combiner 2113. An approximately 1-2 meter length of the combiner pig-tail helps to initiate the SC process, and then a length of PM-1550 fiber 2115 (polarization maintaining, single-mode, fused silica fiber optimized for 1550 nm) is spliced 2114 to the combiner output.
If an approximately 10 m length of output fiber is used, then the resulting output spectrum 2200 is shown in
Although one particular example of a 5 W SWIR-SC implementation has been described, different components, different fibers, and different configurations may also be used consistent with this disclosure. For instance, another embodiment of the similar configuration 2100 in
In an alternate embodiment, it may be desirous to generate high power SWIR SC over 1.4-1.8 microns and separately 2-2.5 microns (the window between 1.8 and 2 microns may be less important due to the strong water and atmospheric absorption). For example, the top SC source of
In one embodiment, the top of
In yet another embodiment, the bottom of
Even within the all-fiber versions illustrated such as in
For therapeutic applications, it may be desirable to generate laser power with high spectral density in a narrower wavelength range. As an alternative to multiplexed laser diodes such as in
In one embodiment, a specific example of the infrared fiber laser operating at approximately 1708 nm is shown in detail in
The bottom of
As an example, the inner grating set 2478 can be designed to provide high reflectivity near 1630 nm. The reflectivity can be in the range of about 70% t to 90%, but in this particular embodiment can be closer to 98%. The outer grating set 2479 and 2480 can be designed to reflect light near 1708 nm (i.e., the desired longer signal wavelength). The first fiber Bragg grating 2479 can have high reflectivity, for example in the range of 70 to 90 percent, but more preferably is closer to 98%. The second fiber Bragg grating 2480 also serves as the output coupler, and hence should have a lower reflectivity value. As an example, the reflectivity of grating 2480 can be in the range of 8% to 50%, and is preferably closer to 12%.
Moreover, to remove the residual shifted pump light from the first or intermediate orders of Raman shifting, WDM couplers can be used surrounding the oscillator, such as 2481 and 2482. In this particular embodiment, the WDM couplers 2481 and 2482 are 1550/1630 couplers (i.e., couplers that pass light near 1550 nm but that couple across or out wavelengths near 1630 nm). Such couplers can help to avoid feedback into the pump fiber laser 2450 as well as minimize the residual intermediate orders in the longer signal wavelength 2476. It may also be beneficial to add an isolator between the pump fiber laser 2450 and the cascaded Raman oscillator 2475 to minimize the effects of feedback. Although one specific example is provided for the cascaded Raman oscillator 2475, any number of changes in the components or values or additional components can be made and are intended to be covered in this disclosure.
In yet another embodiment, a specific example of the infrared fiber laser operating at approximately 1212 nm is shown in detail in
The pump fiber laser can be formed by using a set of gratings 2554 and 2556 around the gain fiber 2551. In one embodiment, the fiber Bragg gratings 2554 and 2556 can have reflecting at a wavelength near 1105 nm. The reflectivity of 2554 can be in the range of 70% to 90%, and in this particular embodiment can be closer to 98%. The second fiber Bragg grating 2556 can also serve as the output coupler, and hence may have a lower reflectivity value. As an example, the reflectivity of grating 2556 can be in the range of 5% to 50%, but is preferably closer to 10% in this embodiment. Other elements may also be inserted into the linear resonator cavity, such as additional taps. Although one particular example of a pump fiber laser 2550 is described, any number of changes in elements or their positions can be made consistent with this disclosure.
The bottom of
As an example, the inner grating set 2578 can be designed to provide high reflectivity near 1156 nm. The reflectivity can be in the range of 70% to 90%, and in this particular embodiment can be closer to 99%. The outer grating set 2579 and 2580 can be designed to reflect light near 1212 nm (i.e., the desired longer signal wavelength). The first fiber Bragg grating 2579 can have high reflectivity, for example in the range of 70% to 90%, but in this embodiment is closer to 99%. The second fiber Bragg grating 2580 can also serve as the output coupler, and hence may have a lower reflectivity value. As an example, the reflectivity of grating 2580 can be in the range of 8% to 50%, but is closer to 25% in this embodiment.
Moreover, to remove the residual shifted pump light from the first or intermediate orders of Raman shifting, WDM couplers can be used surrounding the oscillator, such as 2581 and 2582. In this particular embodiment, the WDM couplers 2581 and 2582 are 1100/1160 couplers (i.e., couplers that pass light near 1100 nm but that couple across or out wavelengths near 1160 nm). Such couplers can help to avoid feedback into the pump fiber laser 2550 as well as minimize the residual intermediate orders in the longer signal wavelength 2576. It may also be beneficial to add an isolator between the pump fiber laser 2550 and the cascaded Raman oscillator 2575 to minimize the effects of feedback. Although one specific example is provided for the cascaded Raman oscillator 2575, any number of changes in the components or values or additional components can be made and are intended to be covered in this disclosure.
The laser beam output that may be used in the healthcare, medical or bio-technology applications can have a number of parameters, including wavelength, power, energy or fluence, spatial spot size, and pulse temporal shape and repetition rate. Some exemplary ranges for these parameters and some of the criteria for selecting the ranges are discussed herein. These are only meant to be exemplary ranges and considerations, and the particular combination used may depend on the details and goals of the desired procedure.
Whereas it may be advantageous in a diagnostic procedure to use a broadband laser such as a super-continuum source, for various therapeutic procedures the wavelength for the laser may be selected on the basis of a number of considerations, such as penetration depth or absorption in a particular type of tissue or water. In yet another embodiment, it may be advantageous to have the laser wavelength fall in the so-called eye-safe wavelength range. For instance, wavelengths longer than approximately 1400 nm can fall within the eye safe window. So, from an eye safety consideration there may be an advantage of using the wavelength window near 1720 nm rather than the window near 1210 nm. Thus, some of the considerations in selecting the laser wavelength range from selective tissue absorption, water absorption and scattering loss, penetration depth into tissue and eye safe operation.
Another parameter for the laser can be the energy, fluence, or pulse power density. The fluence is the energy per unit area, so it can have the units of Joules/cm2. As an example, in dermatological applications or applications through the skin it may be advantageous to use fluences less than approximately 250 J/cm2 to avoid burning or charring the epidermis layer. For example, therapeutic procedures may benefit from having fluences in the range of approximately 30 to 250 J/cm2, preferably in the range of 50 to 200 J/cm2. In another embodiment, it may even be advantageous to use lower fluence levels for therapeutic procedures to impart less pain to patients, for example in the range of approximately 30 J/cm2 or less. These types of fluence levels may typically correspond to time averaged powers from the laser exceeding approximately 10 W, preferably in the power range of 10 W to 30 W, but perhaps as high as 50 W or more. Although particular fluence and power ranges are provided by way of example, other powers and fluences can be used consistent with this disclosure.
Although the output from a fiber laser may be from a single or multi-mode fiber, different spatial spot sizes or spatial profiles may be beneficial for different applications. For example, in some instances it may be desirable to have a series of spots or a fractionated beam with a grid of spots. In one embodiment, a bundle of fibers or a light pipe with a plurality of guiding cores may be used. In another embodiment, one or more fiber cores may be followed by a lenslet array to create a plurality of collimated or focused beams. In yet another embodiment, a delivery light pipe may be followed by a grid-like structure to divide up the beam into a plurality of spots. These are specific examples of beam shaping, and other apparatuses and methods may also be used and are consistent with this disclosure.
Also, various types of damage mechanisms are possible in biological tissue. In one embodiment, the damage may be due to multi-photon absorption, in which case the damage can be proportional to the intensity or peak power of the laser. For this embodiment, lasers that produce short pulses with high intensity may be desirable, such as the output from mode-locked lasers. Alternative laser approaches also exist, such as Q-switched lasers, cavity dumped lasers, and active or passive mode-locking. In another embodiment, the damage may be related to the optical absorption in the material. For this embodiment, the damage may be proportional to the fluence or energy of the pulses, perhaps also the time-averaged power from the laser. For this example, continuous wave, pulsed, or externally modulated lasers may be used, such as those exemplified in
Particularly in the example when the damage may be related to the optical absorption, it may be beneficial to also consider the thermal diffusion into the surrounding tissue. As an example, the thermal diffusion time into tissue may be in the millisecond to second time range. Therefore, for pulses shorter than about several milliseconds, the heat may be generated locally and the temperature rise can be calculated based on the energy deposited. On the other hand, when longer pulses that may be several seconds long are used, there can be adequate time for thermal diffusion into the surrounding tissue. In this example, the diffusion into the surrounding tissue should be considered to properly calculate the temperature rise in the tissue. For these longer pulses, the particular spot exposed to laser energy will reach closer to thermal equilibrium with its surroundings. Moreover, another adjustable parameter for the laser pulses may be the rise and fall times of the pulses. However, these may be less important when longer pulses are used and the damage is related to the energy or fluence of the pulses.
Beyond having a pulse width, the laser output can also have a preferred repetition rate. For pulse repetition rates above around 10 MHz, where multiple pulses fall within a thermal diffusion time, the tissue response may be more related to the energy deposited or the fluence of the laser beam. The separation between pulses or a sub-group of pulses may also be selected so that the tissue sample can reach thermal equilibrium between pulses. Also, the pulse pattern may or may not be periodic. In one embodiment, there may be several pulses used per spot, where the pulse pattern is selected to obtain a desired thermal profile. The laser beam may then be moved to a new spot and then another pulse train delivered to that spot. In one embodiment, there can be several seconds of pre-cooling, the laser can be exposed on the tissue for several seconds, and then there may also be post-cooling. Although particular examples of laser duration and repetition rate are described, other values may also be used consistent with this disclosure. For example, depending on the application and mechanisms, the pulse rate could range all the way from continuous wave to 100's of Megahertz.
Although the present disclosure has been described in several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present disclosure encompass such changes, variations, alterations, transformations, and modifications as falling within the spirit and scope of the appended claims.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the disclosure. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the disclosure. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.
This application claims the benefit of U.S. provisional application Ser. No. 61/747,492 filed Dec. 31, 2012, the disclosure of which is hereby incorporated in its entirety by reference herein. This application is related to U.S. provisional application Ser. Nos. 61/747,477 filed Dec. 31, 2012; Ser. No. 61/747,481 filed Dec. 31, 2012; Ser. No. 61/747,485 filed Dec. 31, 2012; Ser. No. 61/747,487 filed Dec. 31, 2012; Ser. No. 61/747,472 filed Dec. 31, 2012; Ser. No. 61/747,553 filed Dec. 31, 2012; and Ser. No. 61/754,698 filed Jan. 21, 2013, the disclosures of which are hereby incorporated in their entirety by reference herein.
Number | Date | Country | |
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61747492 | Dec 2012 | US |