Patent Application
20090163899
Tissue ablation with pulses of light energy can be used to treat a variety of ailments. For example, the catheters can be used to ablate vascular occlusions that restrict the flow of blood to tissue and organs. When these occlusions develop in vessels supplying blood to heart (e.g., coronary arteries and veins) they can cause heart attacks and angina. When they develop in vessels supplying blood to the brain (e.g., cerebral arteries and veins), they can cause strokes and other neurological problems. In tissue ablation, the pulses of light energy are used to disrupt these vascular occlusions to increase or reopen or the flow of blood through the vessel.
Tissue ablation methods to recanalize a blood vessel are minimally invasive and may include advancing a distal end of a light-guiding catheter to a position close to the occlusion. The light-guiding catheter typically has an optical fiber that can transmit light energy from a light source to the target tissue with minimal energy loss. For example, the catheter may be advanced through a patient's vasculature to the site of the occlusion and then an optical fiber may be advanced through a lumen inside the catheter to reach the occlusion. When the distal end of the fiber is in place, light pulses originating at a light source are sent through the fiber to irradiate the occlusion. A light source producing a high intensity/high energy light pulse can be highly effective at fragmenting soft tissue occlusions.
However, additional classes of occlusions such as chronic total occlusions (CTOs) have proven much harder to treat with tissue ablation. CTOs are generally calcified, fibrotic occlusions that are difficult to fragment with pulses of light energy. In response, the ablation power has been increased to more effectively disrupt these kinds of occlusions. However, attempts to increase the energy density of the light pulse have presented some technical challenges.
In order to efficiently transmit light pulses energy with increased energy density, the cross-sectional area of the optical fiber can be increased. However, for single fiber catheter systems a practical limit on the thickness of the fiber is quickly reached, because the fiber has to be capable of traveling through tortuous blood vessels to reach the target tissue. The thicker the optical fiber becomes the less flexible it becomes, making it more difficult to advance to the target.
Another approach is to divide the light pulse through a group of smaller diameter fibers that have coaxially aligned distal ends to deliver the pulse of light energy to the target tissue. Even when grouped together, the smaller fibers are more flexible than a single fiber of the same diameter and better able to navigate the bends and twists of a patient's vasculature. However, the bundled optical fibers need to be glued or bonded together at the distal tip in order to maintain position and ensure security in case of a fiber break. The presently favored bundling materials are biocompatible epoxy resins.
Unfortunately, these epoxies are not very durable under the acoustic shock conditions that are typical for Excimer laser ablation of hard, calcified target tissue (e.g., CTOs). In as little as 1000 light pulses, enough epoxy can etch from the distal tip of the light catheter to expose the distal edges and walls of the optical fibers. Exposed optical fibers are fragile and even slight force can fracture the fibers and significantly reduce the amount of light they can transmit to the target. Thus, there is a need for new ways to bundle the distal ends of optical fibers used in the light ablation of tissue. This an other issues are addressed by the present invention.
The present invention uses an optical fiber bundle with a hardened distal tip to ablate target tissue in a patient. The hardened distal tip uses materials that are harder and more durable than the epoxies used to bind individual optical fibers in conventionally bundled fiber optic tips. These materials may include metals, silicate glasses, and diamond like carbon (DLC) films, among other types of hard bonding materials. The added durability helps maintain the integrity of the tip when the fiber optic unit (e.g., a light-guiding catheter) is ablating hardened target tissue, such as a calcified chronic total occlusion (CTO). The acoustic shock that accompanies the ablating of the hardened tissue can etch the epoxy in less than 1000 light pulses. In contrast, a hardened tip using glass or metal bonding materials can still be largely intact after more than 62,000 light pulses. Thus, the hard bonded tips can be used to ablate hardened tissue for more light pulses and with less loss of mechanical integrity and transmission efficiency than conventional, epoxy bonded tips.
Embodiments of the invention include a fiber optic unit to ablate tissue with light. The unit may include a bundle of optical fibers having a bundle proximal end adaptable to a light source, and a bundle distal end though which the light exits to reach the tissue. The unit may also include hard material coatings (e.g., glass, ceramic, or metal coatings) formed around distal ends of each of the optical fibers, where the metal coatings are swaged to bond the distal ends of the optical fibers together.
Embodiments of the invention may also include methods of making an optical fiber bundle for tissue ablation having a hard bonded distal end. The methods may include providing a plurality of optical fibers that includes a light transmitting core and a polymeric coating, and stripping the polymeric coating from distal wall portions of the optical fiber. The methods may also include depositing a metal coating on the stripped distal wall portion of the optical fiber, and swaging the distal ends of the optical fibers together to form the metal bonded distal end of the bundle.
Embodiments of the invention may still further include methods to ablate target tissue with light. The methods may include providing a fiber optic unit that includes a bundle of optical fibers having a bundle proximal end adapted to a light source and a bundle distal end though which the light exits to reach the tissue. The hard coating (e.g., metal coating) formed around distal ends of each of the optical fibers are swaged to bond the distal ends of the optical fibers together. The methods may also include advancing the bundle's distal end to a position proximate to the target tissue, and transmitting the light through the optical fibers to ablate the target tissue.
Embodiments of the invention may yet still further include a fiber optic unit having a glass-fused distal tip to ablate tissue with light. The unit may include a bundle of optical fibers having a bundle proximal end adaptable to a light source, and a bundle distal end though which the light exits to reach the tissue. A glass coating may be formed around distal ends of each of the optical fibers, wherein the glass coatings are fused to bond the distal ends of the optical fibers together.
Embodiments of the invention may yet also include methods of making an optical fiber bundle for tissue ablation having a glass fused distal end. The methods may include providing a plurality of optical fibers, where each fiber includes a fused-silica light transmitting core surrounded with a polymeric coating. The method may further include stripping the polymeric coating from distal wall portions of the optical fiber, and heating the stripped distal ends of the optical fibers to fused them together into the glass fused distal end of the optical fiber bundle.
Embodiments of the invention may also include methods of making an optical fiber bundle for tissue ablation having a hardened distal end. The methods may include providing a plurality of optical fibers comprising a fused-silica light transmitting core surrounded with a polymeric coating. The methods may also include stripping the polymeric coating from distal wall portions of the optical fiber, and depositing a hardening material on the stripped distal ends of the optical fibers. The methods may still also include curing the deposited hardening material to form the hardened distal end of the optical fiber bundle.
Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the invention. The features and advantages of the invention may be realized and attained by means of the instrumentalities, combinations, and methods described in the specification.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings wherein like reference numerals are used throughout the several drawings to refer to similar components. In some instances, a sublabel is associated with a reference numeral and follows a hyphen to denote one of multiple similar components. When reference is made to a reference numeral without specification to an existing sublabel, it is intended to refer to all such multiple similar components.
Fiber optic bundles having hard bonded distal tips are described. The tips may be part of a fiber optic unit that delivers pulses of light energy to ablate target tissue in a patient (e.g., a light-guiding catheter).
The metal used in the coatings may be a biocompatible metal or alloy of metals. For example, gold and platinum are known biocompatible metals that have been approved for use in medical devices that make direct contact with a patient's circulatory system. Thus, examples of the metals used in the coatings include gold, platinum, and alloys of the two metals. Additional metals may include silver, copper, and iron, among other metals.
The metal coatings 104 are formed on the cylindrical walls of the optical fibers starting at the distal ends of the fibers. They may extend about 1 mm to about 3 mm down the length of the fibers towards their proximal ends. The thickness of the metal coating 104 may be about 1 μm to about 30 μm. The optical fibers 102 themselves may be made from a light transmitting material such as quartz or bonded silica, and may have a diameter of about 50 μm.
The outer circumference of the distal tip of the unit may be surrounded by a metal band 106. The band may extend about 1 mm to about 3 mm down the length of the fibers towards their proximal ends, and may terminate with the metal coatings on the optical fibers 102. The band may be made from the same type of metal or alloy as the metal coating 104, or may be made from a different metal.
The distal tip of the bundle is ringed by a band of radiopaque material 206 that adds additional integrity to the tip. The band may be made from the same hardened material that coats 204 the optical fibers 202, or from a different metal. For example, the band 206 may be made from a biocompatible metal or metal alloy such as gold and/or platinum. The thickness of the band 206 may be about 0.01 mm to about 0.02 mm (e.g., 0.012 mm).
Referring now to
The metal bonded distal end shown in
The proximal end of the optical fiber bundle 712 may be adapted to a light source 714 that generates the light energy pulses transmitted by the bundle. Examples of light sources include flash lamps and lasers. For example, the light source 714 may be an Excimer laser, such as a XeCl Excimer laser that outputs laser light pulses at about 308 nm.
The catheter embodiment shown has three proximal branches: The first branch 810 is adaptable to a light source 814 such as an Excimer laser. The second branch 812 is adaptable to a fluid source such as saline, a dye, or chemical solution to modify the tissue composition or absorption of light energy, among other fluids. For example, the second branch 812 may be coupled to a fluid pump 816 that pumps fluid from a fluid reservoir through the catheter lumen. The fluid can exits from the lumen's distal end to reach the area of the target tissue. When the fluid includes a dye, it may stain the target tissue to increase its absorption of the ablative light pulses. When the fluid includes a chemical solution, it may help dissolve hard components in the target tissue (e.g., calcium deposits). The pump action may also be reversed to vacuum ablated fragments of target tissue into the distal opening of the lumen.
The third proximal branch 815 is capable of receiving a tool (e.g., a guidewire) that gets advanced through the inner lumen. For example, the guidewire can be inserted into the third proximal branch, and advanced through the distal opening of the lumen and into a patient's body. When the distal end of the guidewire reaches a desired location inside the patient, the distal end of the catheter may be advanced over the guidewire until it is in position to ablate the target tissue.
The polymeric coating is stripped from the distal ends of the optical fibers 904. The amount of coating that is stripped typically ranges from about 1 mm to about 3 mm of the length of the fiber. A metal coating may then be deposited on the cylindrical walls of the fiber tips 906. The coating may be deposited by physical vapor deposition (PVD)or chemical vapor deposition (CVD) of the metal on the exposed surfaces of the fibers, among other deposition methods. PVD processes may include metal sputtering (e.g., electron-beam sputtering, ion-beam sputtering, pulsed laser sputtering, etc.). CVD processes may include reacting and/or decomposing a gaseous or liquid precursor metal-organic precursor on the fiber optic surface to deposit the hardening material.
Fibers coated with metal may then be swaged to formed a metal bonded distal end of the optical fiber bundle 908. The swaging may be done by pressing the ends of the fibers in a tool or die. A metal band may be placed around the distal tip and swaged with the optical fibers. The swaging process puts more fiber in densely packed tip configuration, which allows the tip to deliver a higher energy light pulse to the target tissue. In some cases, the swaging alone is enough to bond the individual metal tips into the metal bonded bundle tip. In additional cases, heat may be applied during or after the swaging to aid in fusing of the bundle tip 910.
Optionally, a radiopaque band may be placed around the silica-fused distal tip. The radiopaque band may be made from a radiopaque material such as a metal. The metal may be a biocompatible metal or alloy such as gold or platinum, among other metals. The radiopaque band can help maintain the radiopacity of the catheter during imaging, as well as protect the optical fibers at the periphery of the bundle distal tip.
The deposited hardening material may then be cured 1108 to form the hardened distal tip 1110 of the optical fiber bundle. Curing methods may be as simple as cooling the tip to ambient temperature to allow the molten fused silica to solidify and harden. In additional embodiments, curing may involving a heating or annealing step following the chemical vapor deposition of silica on the fiber tips. Similar to the methods described above, a radiopaque band may be optionally formed around the hardened distal tip.
When the distal tip of the bundle reaches a position proximate to the target tissue (e.g., contacting the target tissue) light may be transmitted through the optical fibers and into the target tissue 1206. One or more pulses of transmitted light energy may be used to ablate a portion of the target tissue 1208. If necessary, the distal tip of the bundle may be further advanced toward remaining target tissue 1210 after a portion of the tissue has been ablated away. This process of ablating the target tissue and advancing the distal tip for further ablation may be repeated several cycles until the target tissue has been removed (or the vessel has been recanalized). The ablation light may be pulsed ultraviolet laser light generated by an Excimer laser (e.g., a XeCl Excimer laser lasing at around 308 nm).
Experiments were conducted to observe the durability of metal bonded optical fiber bundles and compare their durability to conventionally bundled tips bonded with epoxy. These experiments included firing pulses of XeCl Excimer laser light from bundled fiber optic units into an ex-vivo Plaster of Paris (i.e., calcium sulfate hemihydrate) target. The target is meant to simulate hard, calcified tissue like the types found in chronic total occlusions. The bonded distal ends of the fiber optic bundles are positioned proximate to the Plaster of Paris target and the XeCl Excimer laser is fired multiple times before an SEM image is made of the distal tip to examine any ablative damage caused by the acoustic shock and cloud of ablated target material.
In comparison,
A similar effect is seen in
Having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention.
Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.
As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a process” includes a plurality of such processes and reference to “the optical fiber” includes reference to one or more optical fibers and equivalents thereof known to those skilled in the art, and so forth.
Also, the words “comprise,” “comprising,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups.
