Patent Publication Number: US-2009227993-A1

Title: Shaped fiber ends and methods of making same

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 12/350,835, filed on Jan. 8, 2009, the entire contents of which are herein incorporated by reference. This application claims the benefit of U.S. Provisional Application No. 61/082,721 filed on Jul. 22, 2008, the entire contents of which is incorporated herein by reference. This application is related to U.S. Provisional Patent Application No. 61/025,514 filed on Feb. 1, 2008, and U.S. Provisional Application No. 61/019,626 filed Jan. 8, 2008, the entire contents of each of which is incorporated herein by reference. This application is also related to U.S. patent application Ser. No. 11/537,258, filed on Sep. 29, 2006, published as U.S. Patent Application Publication No. 2007/0078500 A1, U.S. patent application Ser. No. 11/834,096, filed on Aug. 6, 2007, published as U.S. Patent Application Publication No. 2007/0270717 A1, and U.S. patent application Ser. No. 12/350,870, filed on Jan. 8, 2009, the contents of each of which is incorporated herein in their entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention are directed to systems and methods for the analysis and treatment of a lumen. More particularly, embodiments of the present invention relate to a balloon catheter system that is used to perform methods of analysis and angioplasty of endovascular lesions. 
     2. Description of the Related Art 
     With the continual expansion of minimally-invasive procedures in medicine, certain procedures that have been highlighted in recent years include catheter applications targeting small tightly curved lumens (e.g., coronary vessels) for diagnosis and treatment or other applications which may benefit from the use of small core diameter fibers (e.g., about 100 microns or less). One type of common procedure is a percutaneous transluminal angioplasty procedure, or “PTA” which, when applied to coronaries, is more specifically called a percutaneous coronary transluminal angioplasty procedure, or “PTCA”. These procedures utilize a flexible catheter with an inflation lumen to expand, under relatively high pressure, a balloon at a distal end of the catheter to expand a stenotic lesion. 
     The PTA and PTCA procedures are now commonly used in conjunction with expandable tubular structures known as stents and an angioplasty balloon, which is often used to expand and permanently place the stent within the lumen. An angioplasty balloon utilized with a stent is referred to as a stent delivery system. Conventional stents have been shown to be more effective than an angioplasty procedure alone in order to maintain patency in most types of lesions and also to reduce other near-term endovascular events. A risk with a conventional stent, however, is the reduction in efficacy of the stent due to the growth of the tissues surrounding the stent which can again result in the stenosis of the lumen, often referred to as restenosis. In recent years, new stents that are coated with pharmaceutical agents, often in combination with a polymer, have been introduced and shown to significantly reduce the rate of restenosis. These coated stents are generally referred to as drug-eluting stents, though some coated stents have a passive coating instead of an active pharmaceutical agent. 
     With the advent of these advanced technologies for PTA and PTCA, there has been a substantial amount of clinical and pathology literature published about the pathophysiologic or morphologic factors within an endovascular lesion that contribute to its restenosis or other acute events such as thrombosis. These features include, but are not limited to, collagen content, lipid content, calcium content, inflammatory factors, and the relative positioning of these features within the plaque. Several studies have been provided showing the promise of identifying the above factors through the use of visible and/or near infrared spectroscopy (i.e. across wavelengths ranging between about 250 to 2500 nm), including those studies referenced in U.S. Publication No. US2004/0111016A1 by Casscells, III et al., U.S. Publication No. US2004/0077950A1 by Marshik-Geurts et al., U.S. Pat. No. 5,304,173 by Kittrell et al., and U.S. Pat. No. 6,095,982 by Richards-Kortum, et al., the contents of each of which is herein incorporated by reference. However, there are very few, if any, highly safe and commercially viable applications making use of this spectroscopic data for combining the diagnosis and treatment in a PTA or PTCA procedure. Certain catheter probes, including some described in the aforementioned disclosures, include various therapeutic components but do not combine angioplasty treatments with effective, safe spectroscopic examination and diagnosis with commercially viable flexibility and dimensions for coronary vessel use (e.g., catheters having less than about 1.5 mm in outer diameter and generally having fewer than 8 fibers). 
     Catheter probes may be small enough and flexible enough for coronary use, but are neverthless very limited in the numbers and dimensions of optical components that can be packaged in the catheter probe&#39;s body and distal end. Typical technologies for delivering and/or collecting radiation along a lumen, particularly to and from those target areas peripheral to a catheter body and/or through a peripheral balloon, can require additional features including lenses, reflectors, bent fibers, and the like, which can increase the catheter probe&#39;s maximal outer diameter to suboptimal levels for coronary or other small lumen use, add prohibitive costs, and/or are not able to provide an effective and complete analysis of the target coronary vessel region. Some optical fibers developed for smaller probes include shaped ends such as “side-fire” fibers, which have their ends cleaved at an angle and may be subsequently coated so as to direct radiation to or from the fiber tip at a substantial transverse angle. However, these types of fibers still only allow distribution/collection about a limited scope of the periphery of the fiber tip, generally less than about an 83 degree circumferential scope. Shaping the interior profile of optical fiber tips has been proposed such as in, for example, U.S. Pat. No. 5,537,499 by Brekke, the entire contents of which is herein incorporated by reference. Laser and mechanical approaches for fiber-tip formation suggested by such technologies, however, are very impractical and limited for the types of fibers optimal for low profile catheter probes (e.g., with fibers having a core diameters of about 100 microns or less and having maximum outer diameters of about 125 microns or less) because of the necessary precise dimensions of the shaping tool and/or motion required by the shaping tool and/or fiber tip. 
     SUMMARY OF THE INVENTION 
     The systems and methods of the invention provide hospitals and physicians with reliable, simplified, and cost-effective optical components for body lumen inspection devices, including catheter and endoscopic-based devices useful for diagnosing a broad range of tissue conditions. Various embodiments of the invention provide reliable control over multiple light emission paths within a multiple-fiber catheter and/or endoscopic probe while allowing the probe to remain substantially flexible and maneuverable within a body lumen. Reliance on inflexible, expensive, elaborate and/or difficult to assemble components that inhibit prior art devices is thus reduced. By improving control over light emission paths with efficient and low profile components, fewer fibers are required than with typical prior art devices. Thus, improving the flexibility and reducing the size of such a system is especially beneficial for small body vessel applications. 
     In accordance with an aspect of the invention, there are provided apparatus with fiber optical configurations for performing an optical analysis of a body lumen. In an embodiment, the tips of one or more fibers having maximum core/cladding diameters of 125 microns deliver and/or collect radiation about a circumferential perimeter of the tip of greater than about 90 degrees and, in an embodiment, of greater than about 120 degrees and, in an embodiment, of greater than about 150 degrees and, in an embodiment, of up to 360 degrees. In an embodiment, the tips of the fibers are also manufactured to distribute and/or collect radiation across a longitudinal scope of greater than about 10 degrees in the direction opposite the distal end of the one or more fibers and, in an embodiment, greater than about 30 degrees and, in an embodiment, greater than about 60 degrees. In an embodiment, the tips include a cavity or recess formed out of the terminating end of the tip. In an embodiment, the cavity is conically shaped. In an embodiment, the cavity is elliptically shaped. In an embodiment, the apparatus comprises a lumen-expanding balloon catheter having one or more delivery fibers and/or one or more collection fibers with at least one of a transmission output or a transmission input located within the balloon. In an embodiment, the at least one transmission output or transmission input are held against the inside wall of the balloon such that the transmission output or transmission input will remain proximate to the inside wall of the balloon when the balloon expands. 
     In an aspect of the invention, the tips of the one or more fibers are modified with a process that forms a cavity or recess or other desired shape in the terminating end of the tip. In an embodiment, the process includes the steps of providing a fiber end with a predetermined core/cladding profile having at least one first material with a first resistance level to an etchant and at least one second material with a second resistance level to the etchant that is greater than the first resistance level. In an embodiment, the concentration of the first material gradually decreases and the concentration of the second material gradually increases as the material&#39;s distance from the center of the fiber increases. In an embodiment, the second material comprises silica and the first material comprises a dopant. In an embodiment, the dopant comprises Germanium (Ge). In an embodiment, the dopant comprises at least one of Fluorine (F), Beryllium (Be), and Phosphorous (P). In an embodiment, the etchant comprises Hydrofluoric acid (HF). 
     In an aspect of the invention, an optical fiber tip comprises a core and a recess formed in said core at a distal end of the optical fiber tip, said recess having a vertex within said core. 
     In an embodiment, said core has a diameter of about 200 microns or less. In an embodiment, said core has a diameter of about 100 microns or less. In an embodiment, said core has a diameter of about 50 microns or less. 
     In an embodiment, said core is a graded-index core. In an embodiment, said graded-index core has a material composition with a dopant concentration profile in relation to a shape of said recess. In an embodiment, the dopant concentration profile includes a dopant concentration that has a maximum level at a center of said core. In an embodiment, said maximum level of the dopant concentration at the center of said core is about 15% of the material composition. 
     In an embodiment, said recess has a shape of a conic section. In an embodiment, said recess has the shape of a cone. 
     In an embodiment, a cross-section of said recess has a shape of an ellipse. In an embodiment, said recess has a primary vertex located proximal to a center of the core. 
     In an embodiment, said primary vertex has a maximum depth that is less than a maximum diameter of said core. In an embodiment, said maximum depth is less than 75% of the maximum diameter of said optical fiber tip. In an embodiment, said primary vertex has a maximum depth of less than about 70 microns. In an embodiment, said primary vertex has a maximum depth of less than about 50 microns. 
     In an embodiment, said recess is covered with at least one of a reflective material, a light diffusing material, and a light blocking material. In an embodiment, said at least one of a reflective material, light diffusing material, and light blocking material comprises at least one of a glass and a polymer. In an embodiment, said at least one of a reflective material, light diffusing material and light blocking material comprises at least one of a thermoplastic and thermosetting plastic. In an embodiment, said at least one of a reflective material, light diffusing, and light blocking material comprises polytetrafluoroethylene. 
     In an embodiment, the core has a terminating end and wherein an air gap is located between said vertex located within said core and said at least one of the reflective material, light diffusing material, and light blocking material. In an embodiment, said air gap has a span along the longitudinal axis of the fiber tip that is about the same as a width of said core. In an embodiment, said air gap has a span along the longitudinal axis of the fiber tip of about 50 microns or less. 
     In an embodiment, said tip is manufactured to emit or collect radiation circumferentially around approximately 90 degrees or more of the end of the fiber optics. In an embodiment, said tip is manufactured to emit or collect radiation around approximately 120 degrees or more of the circumference of said tip. In an embodiment, said tip is manufactured to emit or collect radiation around approximately 150 degrees or more of the circumference of said tip. In an embodiment, said tip is manufactured to emit or collect radiation around the entire circumference of said tip. 
     In another aspect of the invention, a catheter for placement within a body lumen comprises a flexible conduit that elongatedly extends along a longitudinal axis, the flexible conduit having a proximal end and a distal end; and at least one waveguide with a optical fiber tip having a terminating end positioned along the flexible conduit, the optical fiber tip comprising a recess in a terminating end of the optical fiber tip. 
     In an embodiment, the catheter further comprises a flexible, expandable balloon around said terminating end. In an embodiment, said flexible, expandable balloon is an angioplasty balloon. In an embodiment, said optical fiber tip is radially coupled to said angioplasty balloon. 
     In another aspect of the invention, a method of manufacturing an optical fiber tip comprises providing an optical fiber core comprising a terminating end; and forming a recess in said terminating end. 
     In an embodiment, the step of forming a recess comprises applying an etching process to the optical fiber core. 
     In an embodiment, the method further comprises forming a cladding about said optical fiber core, wherein said optical fiber core and cladding comprises a material composition, the material composition including a first material having a first level of resistance to said etching process and a second material having a second increased level of resistance to said etching process. 
     In an embodiment, said first material comprises silica. 
     In an embodiment, said second material comprises germanium. In an embodiment, said second material comprises at least one of germanium, fluorine, beryllium, phosphorous, and hydrofluoric acid. 
     In an embodiment, across at least a portion of the diameter of said optical fiber and in relation to the distance from the center of said optical fiber core, the concentration of said first material decreases and the concentration of said second material increases in relation to a predetermined shape of said recess. 
     In an embodiment, the first material is germanium, and the maximum concentration of germanium is about 15% of the material composition at the center of said optical fiber core. 
     In an embodiment, said optical fiber core comprises a graded index core fiber. 
     In an embodiment, said optical fiber tip has a core diameter of about 200 microns or less. In an embodiment, said core diameter is about 100 microns or less. In an embodiment, said core diameter is about 50 microns or less. 
     In an embodiment, said recess is formed in the shape of a conic section. In an embodiment, said recess is formed in the shape of a cone. 
     In an embodiment, said recess is formed in the shape of an ellipse. 
     In an embodiment, said recess is formed with a primary vertex located proximal to a center of the core of said optical fiber. 
     In an embodiment, said primary vertex is formed with a maximum depth from the end of said optical fiber tip that is less than the maximum diameter of the core of said optical fiber tip. In an embodiment, said maximum depth is less than 75% of the maximum diameter of said optical fiber tip. 
     In an embodiment, said primary vertex is formed with a maximum depth from the end of said optical fiber tip of less than about 70 microns. In an embodiment, said primary vertex is formed with a maximum depth from the end of said optical fiber tip of less than about 50 microns. 
     In an embodiment, the method further comprises the step of covering said recess with at least one of a reflective material and light diffusing material. 
     In an embodiment, said at least one of a reflective material and light diffusing material comprises at least one of a glass and a polymer. 
     In an embodiment, said at least one of a reflective material and light diffusing material comprises at least one of a thermoplastic and thermosetting plastic. 
     In an embodiment, said at least one of a reflective material and light diffusing material comprises polytetrafluoroethylene. 
     In an embodiment, the step of covering said recess comprises immersing said optical fiber tip in a solution of said at least one of a reflective material and light diffusing material. 
     In an embodiment, covering said recess leaves an air gap between a terminating end of the optical fiber core and said at least one of the reflective material and light diffusing material. In an embodiment, said air gap has a span along the longitudinal axis of the fiber tip that is about the same as a width of said core. In an embodiment, said air gap has a span along the longitudinal axis of the fiber tip of about 50 microns or less. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features, and advantages of the invention will be apparent from the more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1A  is an illustrative view of a fiber tip for analyzing and medically treating a lumen, according to an embodiment of the invention. 
         FIG. 1B  is an illustrative cross-sectional view of the fiber tip of  FIG. 1A , taken along section lines I-I′. 
         FIG. 1C  is an illustrative view of another fiber tip for analyzing and medically treating a lumen, according to an embodiment of the invention. 
         FIG. 1D  is an illustrative cross-sectional view of the fiber tip of  FIG. 1C , taken along section lines II-II′. 
         FIG. 2A  is an illustrative view of a treatment end of a catheter instrument for analyzing and medically treating a lumen according to an embodiment of the present invention. 
         FIG. 2B  is a cross-sectional view of the catheter of  FIG. 2A , taken along section lines I-I′ of  FIG. 2A . 
         FIG. 2C  is a cross-sectional view of the catheter of  FIG. 2A , taken along section lines II-II′ of  FIG. 2A . 
         FIG. 3A  is an illustrative view of a catheter instrument for analyzing and medically treating a lumen, according to an embodiment of the present invention. 
         FIG. 3B  is a block diagram illustrating an instrument deployed for analyzing and medically treating the lumen of a patient, according to an embodiment of the present invention. 
         FIG. 4A  is an illustrative schematic view of a fiber tip being formed in an etchant solution according to an embodiment of the invention. 
         FIG. 4B  is an illustrative cross-sectional view of the fiber tip of  FIG. 4A , taken along section lines I-I′, while placed in an etchant solution according to an embodiment of the invention. 
         FIG. 4C  is an illustrative schematic view of the fiber tip of  FIG. 4A  after extraction from an etchant solution. 
         FIG. 4D  is an illustrative schematic view of a portion of an outer protective layer being removed from the fiber tip of  FIGS. 4A-4C . 
         FIG. 5A  is an illustrative chart of a dopant concentration of a graded index fiber core in an embodiment of the invention. 
         FIG. 5B  is an illustrative cross-sectional view of a fiber tip formed from a fiber core with a dopant concentration according to the chart of  FIG. 5A  in an embodiment of the invention. 
         FIG. 6A  is another illustrative chart of dopant concentration of a graded index fiber core in an embodiment of the invention. 
         FIG. 6B  is an illustrative cross-sectional view of a fiber tip formed from a fiber core with a dopant concentration according to the chart of  FIG. 6A  in an embodiment of the invention. 
         FIG. 7A  is an illustrative cross-sectional view of a fiber tip having an end coated with a reflective material according to an embodiment of the invention. 
         FIG. 7B  is an illustrative perspective view of the fiber tip of  FIG. 7A  taken along reference line I-I′. 
         FIG. 7C  is an illustrative view of a fiber tip with an air gap spaced between a reflective coating and the core of the tip. 
         FIG. 8A  is an illustrative cross-sectional view of a fiber tip positioned adjacent a reflective surface according to an embodiment of the invention. 
         FIG. 8B  is an illustrative perspective view of the fiber tip and reflective surface of  FIG. 8A  taken along reference line II-II′. 
         FIG. 9  is an illustrative perspective view of a fiber tip adjacent a flat reflective surface according to an embodiment of the invention. 
         FIG. 10  is an illustrative perspective view of a fiber tip adjacent a concave reflective surface according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     The accompanying drawings are described below, in which example embodiments in accordance with the present invention are shown. Specific structural and functional details disclosed herein are merely representative. This invention may be embodied in many alternate forms and should not be construed as limited to example embodiments set forth herein. 
     Accordingly, specific embodiments are shown by way of example in the drawings. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the claims. Like numbers refer to like elements throughout the description of the figures. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element is referred to as being “on,” “connected to” or “coupled to” another element, it can be directly on, connected to or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise,” “comprises,” “comprising,” “include,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
       FIG. 1A  is an illustrative view of a fiber tip  45 A for analyzing and medically treating a lumen, according to an embodiment of the present invention.  FIG. 1B  is an illustrative cross-sectional view of the fiber tip  45 A of  FIG. 1A , taken along section lines I-I′. Fiber tip  45 A includes a conically-shaped recess  55 A formed in a core about which radiation entering and exiting fiber tip  45 A may be incident on, such as along exemplary sample trace arrows  42 . In an embodiment, fiber tip  45 A is adopted as a light delivery/collection end of one or more fibers in an optical probe such as a catheter probe of which embodiments are further described herein. The conically-shaped recess  55 A allows radiation to be distributed or collected about a substantially wider directional scope than a conventional fiber end, wherein radiation, for example, optical radiation such as light (e.g., along trace lines  42 ) is refracted or reflected at various angles after becoming incident upon the recess  55 A. In other embodiments, the recess  55 A can have other shapes, such that a vertex is located within the core of the tip  45 A. In other embodiments, recess  55 A can have other shapes that comprise higher order polynomial curves. In other embodiments, the recess has a curved surface, the curved surface having a vertex within the core. 
     A fiber with a recessed tip in accordance with an embodiment of the invention permits the recess  55 A to allow light  43  passing through the fiber in a direction of the fiber to be collected from or distributed or otherwise redirected in directions substantially transverse to the direction of the light  43  passing through the fiber. For example, the angle θ defining the conical shape of recess  55 A can be increased so as to allow distribution and/or collection of radiation across a range of directions relative to the longitudinal direction of the fiber, for example, the directions being greater than about 10 degrees and up to about 120 degrees off-axis from the longitudinal axis of the fiber. The conically-shaped recess  55 A also allows light to be distributed/collected up to a full 360 degree periphery about the fiber tip circumference. In various embodiments, the fibers with recesses in accordance with those described herein have cores with maximum diameters of about 100 microns or less (and total maximum outer diameters of 125 microns or less). These embodiments thereby significantly increase the effective numerical aperture and control over transmission to/from low diameter fibers without the need for bending the fiber and/or adding separate optical components such as, for example, lenses, reflectors, and the like. 
     The shape of a recess of a fiber tip in accordance with an embodiment of the invention can be configured in order to provide a particular distribution/collection profile. For example,  FIG. 1C  is an illustrative view of another fiber tip for analyzing and medically treating a lumen, according to an embodiment of the present invention.  FIG. 1D  is an illustrative cross-sectional view of the fiber tip of  FIG. 1C , taken along section lines II-II′. Accordingly, the shape of the recess of the fiber tip shown in  FIGS. 1C and 1D  is different than the conical shape of  FIGS. 1A and 1B , permitting the fiber tip shown in  FIGS. 1C and 1D  to correspond to a different distribution/collection profile. However, the recess  55 B shown in  FIGS. 1C and 1D  can have other shapes with a recess having a vertex located within the core of the tip  45 B. In other embodiments, recess  55 B can have other shapes that comprise higher order polynomial curves. In other embodiments, the recess  55 B has a curved surface, the curved surface having a vertex within the core. In an embodiment, a recess  55 B is configured in an elliptically-shaped manner which can allow more light to be distributed between the longitudinal/side direction than that of a more angularly sharper recess (e.g., such as that of  FIGS. 1A-1B ). In an embodiment, a fiber tip recess is adapted in relation to a fiber&#39;s core/cladding components to provide a desired optical profile such as, for example, those described in further detail herein below. 
     Formed tips according to various embodiments of the invention can increase the directional scope (aperture) in which light is delivered and collected and, in particular, those directions transverse to the longitudinal axis of the catheter&#39;s treatment end. The formed tips are particularly beneficial for near-field type scanning around the circumferential periphery of the tips and, in an embodiment, are adapted for use in fibers that are maintained in close peripheral contact to the outside edge of an angioplasty-type balloon system such as described further herein. The embodiment is particularly advantageous in that it may avoid the need for many of the additional components (e.g., reflectors, lenses, etc. . . . ) common to typical optical fiber catheter probes while allowing for delivery and collection of radiation across a wide area. In an embodiment, the potential loss of power associated with the removal of a core and cladding from the fiber is mitigated by the close proximity in which various embodiments position the tips  45 A,  45 B in relation to targeted tissue and/or fluids 
       FIG. 2A  is an expanded illustrative view of the treatment end of a catheter instrument incorporating fiber tips  45  in accordance with an embodiment of the present invention.  FIG. 2B  is a cross-sectional view of the catheter of  FIG. 2A , taken along section lines I-I′ of  FIG. 2A .  FIG. 2C  is a cross-sectional view of the catheter of  FIG. 2A , taken along section lines II-II′ of  FIG. 2A . In an embodiment, a flexible outer covering  30  can operate as an inflatable balloon and is attached at its proximal end about a catheter sheath  20 . An inner balloon  50 , fibers  40 , and a guidewire sheath  35  extend through an opening  22  at a distal end of catheter sheath  20  and into inner balloon  50 . In an embodiment, a proximal end of inner balloon  50  is attached to the interior of catheter sheath  20  with glue  52  placed between inner balloon  50  and catheter sheath  20 . An intervening lumen  63  formed between catheter sheath  20  and guidewire sheath  35  can be used to transfer fluid media to inner balloon  50  from a fluid source (e.g., liquid/gas source  156  of  FIGS. 3A-3B ). A separate lumen  67  can be used to transfer fluid to and from the area between outer covering  30  and inner balloon  50  (e.g., as in an angioplasty balloon). 
     In an embodiment, both inner balloon  50  and lumen  67  are supplied simultaneously by the same fluid source. Inner balloon  50  is initially filled with fluid and will continue to expand against outer covering  30  as fluid pressure between inner balloon  50  and guidewire sheath  35  and the fluid pressure between the outer covering  30  and inner balloon  50  equalize, resulting in the distal end acting as an angioplasty balloon while substantially maintaining the delivery and collection ends  45  of fibers  40  against the inside wall of outer covering  30 . Fiber tips  45  can be in accordance with, for example, those of  FIGS. 1A-1D  so as to allow distribution and/or collection of radiation (e.g., along exemplary trace lines  42 ) about the periphery of outer covering  30  and an adjacent lumen wall. In an embodiment, fiber tips  45  include two delivery ends  45 D for delivering radiation and two collection ends  45 R for receiving radiation. 
     In an embodiment, radiation can also be directed/collected between fiber tips  45  by way of the balloon interior (e.g., along exemplary trace lines  47 ,  48 , and  49 ) so as to obtain and monitor information about the distance between fiber tips  45  (and balloon  30 ) and sheath  35  and thus provide information about the level and uniformity of expansion of balloon  30 . In an embodiment, preliminary readings are taken of signals received through light reflected from sheath  35  and the corresponding measured sizes of balloon  30 . This information can then later be used during deployment to provide estimates of the level of expansion of balloon  30 . In an embodiment, a source/type of radiation of a wavelength range distinct from that used for examining the lumen wall is used to monitor the level of expansion of balloon  30 . In an embodiment, the sheath  35  can include material coating so as to reflect, enhance, and/or modify signals directed to the sheath from fiber tips  45 , after which a distinct signal is received corresponding to the level of expansion of balloon  30 . In an embodiment, inner balloon  50  may include a reflective coating (e.g., as shown and described in reference to  FIG. 3A ) for aiding in the distribution and collection of radiation between fiber ends  45  and the lumen wall. In an embodiment, the reflective coating can be manufactured to allow selected radiation to pass through (e.g., as in a bandpass filter or through a small gap in the reflective coating) toward sheath  35 . 
       FIG. 3A  is an illustrative view of a catheter instrument  10  for analyzing and medically treating a lumen, according to an embodiment of the present invention.  FIG. 3B  is a block diagram illustrating an instrument  100  deployed for analyzing and medically treating the lumen of a patient, according to an embodiment of the present invention. The catheter assembly  10  includes a catheter sheath  20  and at least two fibers  40 , including one or more delivery fiber(s) connected to at least one source  180  and one or more collection fiber(s) connected to at least one detector  170 . Catheter sheath  20  includes a guidewire sheath  35  and guidewire  145 . The distal end of catheter assembly  10  includes an inner balloon  50  and a flexible outer covering  30 . In an embodiment, inner balloon  50  and outer covering  30  function as a lumen expanding balloon (e.g., an angioplasty balloon). 
     Delivery and collection ends  45  of fibers  40  are positioned between the inner balloon  50  and outer covering  30 . Inner balloon  50  can include a reflective surface  80  facing outwardly so as to improve light delivery and collection to and from delivery/collection ends  45 . The reflective surface  80  can be applied, for example, as a thin coating of reflective material such as gold paint or laminate or other similar material known to those of skill in the art. Outer covering  30  is comprised of a material translucent to radiation delivered and collected by fibers  40  such as, for example, translucent nylon or other polymers. The delivery and collection ends  45  are preferably configured to deliver and collect light about a wide angle such as, for example, between about at least a 120 to 180 degree cone around the circumference of each fiber, from a direction outward toward targeted tissues/fluids such as exemplified in  FIGS. 1A-1D  and  2 C. Various methods for forming such delivery and collection ends are described in more detail herein below. Various such embodiments in accordance with the invention allow for diffusely reflected light to be readily delivered and collected between fibers  40  and tissue surrounding the distal end of catheter  10 . 
     The proximate end of balloon catheter assembly  10  includes a junction  15  that connects various conduits between catheter sheath  20  to external system components. Fibers  40  can be fitted with connectors  120  (e.g. FC/PC type) compatible for use with light sources, detectors, and/or analyzing devices such as spectrometers. Two radiopaque marker bands  82  are fixed about guidewire sheath  35  in order to help an operator obtain information about the general location of catheter  10  in the body of a patient (e.g. with the aid of a fluoroscope). 
     The proximal ends of fibers  40  are connected to a light source  180  and/or a detector  170  (which are shown integrated with an analyzer/processor  150 ). Analyzer/processor  150  can be, for example, a spectrometer which includes a processor  175  for processing/analyzing data received through fibers  40 . A computer  152  connected to analyzer/processor  150  can be used to operate the instrument  100  and to further process spectroscopic data (including, for example, through chemometric analysis) in order to diagnose and/or treat the condition of a subject  165 . Input/output components (I/O) and viewing components  151  are provided in order to communicate information between, for example, storage and/or network devices and the like and to allow operators to view information related to the operation of the instrument  100 . 
     Various embodiments provide a spectrometer (e.g., as analyzer/processor  150 ) configured to perform spectroscopic analysis within a wavelength range between about 250 and 2500 nanometers and include embodiments having ranges particularly in the near-infrared spectrum between about 750 and 2500 nanometers. Further embodiments are configured for performing spectroscopy within one or more subranges that include, for example, about 250-930 nm, about 1100-1385 nm, about 1600-1850 nm, and about 2100-2500 nm. Various embodiments are further described in, for example, previously cited and co-pending U.S. application Ser. No. 11/537,258 (entitled “SYSTEMS AND METHODS FOR ANALYSIS AND TREATMENT OF A BODY LUMEN”), and U.S. application Ser. No. 11/834,096 (entitled “MULTI-FACETED OPTICAL REFLECTOR”), the entire contents of each of which is herein incorporated by reference. 
     Junction  15  includes a flushing port  60  for supplying or removing fluid media (e.g., liquid/gas)  158  that can be used to expand or contract inner balloon  50  and, in an embodiment, an outer balloon formed by flexible outer covering  30 . Fluid media  158  is held in a tank  156  from which it is pumped in or removed from the balloon(s) by actuation of a knob  65 . Fluid media  158  can alternatively be pumped with the use of automated components (e.g. switches/compressors/vacuums). Solutions for expansion of the balloon are preferably non-toxic to humans (e.g. saline solution) and are substantially translucent to the selected light radiation. 
       FIG. 4A  is an illustrative schematic view of a fiber tip being formed in an etchant solution according to an embodiment of the invention.  FIG. 4B  is an illustrative cross-sectional view of the fiber tip of  FIG. 4A , taken along section lines I-I′, while placed in an etchant solution according to an embodiment of the invention.  FIG. 4C  is an illustrative schematic view of the fiber tip of  FIG. 4A  after extraction from an etchant solution.  FIG. 4D  is an illustrative schematic view of a portion of the outer protective layer being removed from the fiber tip of  FIGS. 4A-4C . 
     In an embodiment, the process for forming a fiber tip  345  occurs (as shown in  FIG. 4A ) by placing the end of a fiber  340  in a bath  200  including an etchant  220 . Fiber tip  345  includes a core  310 , a cladding layer  320 , and a protective outer layer  330 . In an embodiment, the etchant  220  comprises Hydrofluoric Acid (HF). An organic solvent  210  (e.g., silicone) can be included in the bath so as to control formation of a meniscus  215  and to prevent inadvertent exposure of portions of fiber  340  to the etchant. In an embodiment, a second material of the fiber tip such as pure silicon has a level of resistance to the etchant  220  and a first material such as a dopant (e.g., germanium) has a different level of resistance to the etchant. In an embodiment, portions of the core have different resistance levels to the etchant, the resistance levels of portions of the core dependent on the concentrations of the first and second materials. For example, a portion of the fiber tip  345  proximal to the center of the fiber tip can comprise approximately 15% of the first material, where the fiber tip  345  has the least amount of resistance to the etchant, and a portion of the fiber tip  345  proximal to an outer surface of the fiber tip can comprise approximately 0% of the first material, where the fiber tip has the greatest resistance to the etchant. Depending on the fiber type and the desired profile/shape of tip  345  (e.g., such as those shown and described in reference to  FIGS. 5-6 ), the materials of a first and second resistance can be mixed at different concentrations within different locations of the core. In an embodiment, the core  310  is formed utilizing a process such as activated chemical vapor deposition such that fine layers of core material are applied about the circumference of the core  310  with the desired concentrations of first and second materials (e.g., dopant and silica, respectively,) for providing the desired resistance levels relative to specific distances from the center of the core. In an embodiment, a layer of the core material applied during the process is about 0.004 inches thick. Fiber  340  is shown held in bath  200  of etchant solution for a predetermined amount of time. In an embodiment, fiber  340  has a graded index core with a diameter of between about 50 and 100 microns and is held in the etchant  220  for a period between about 4 minutes to 15 minutes or more. Fiber  340  can also be moved and repositioned in the etchant to affect the shape of tip  345 . As illustrated in  FIG. 4B , etchant solution  220  gradually removes material from the cladding/core interior of fiber tip  345 , forming a shaped recess  355  within the cladding/core interior. In various embodiments, general techniques for applying etchant solutions to fiber tips for forming pointed or sharpened ends are adapted for forming recessed tips as described herein. Some techniques for etching pointed or sharpened tip ends are described in P. K. Wong et al., “Optical Fiber Tip Fabricated By Surface Tension Controlled Etching,” CM Ho—Proc. of Hilton Head (2002), Lazarev, et al., “Formation of fine near-field scanning optical microscopy tips. Part I. By static and dynamic chemical etching,” Rev. Sci. Instrum. 74, 3684 (2003), U.S. Pat. No. 6,905,623 by Wei at al., the entire contents of each of which is herein incorporated by reference. 
     After application of the etchant solution  220  to tip  345  to form the desired shape of the recess  355 , fiber tip  345  is removed from the solution (as shown in  FIG. 4C ) and subsequently cleaned of etchant and solvent. In an embodiment, the tip can be additionally polished so as to remove imperfections along the outer periphery of the fiber tip. 
     In an embodiment, the outer protective layer  330  is removed from a portion of tip  345  so as to allow radiation to travel between the core of fiber  340  and locations transverse the longitudinal axis of fiber tip  345 . In an embodiment, the removal process uses a laser  350  (as shown in  FIG. 4D ) to cut a thin slice through layer  330 , after which the portion  330 ′ of layer  330  distal to the slice can be removed from tip  345 , as shown by arrows. In various embodiments, laser, chemical, and/or mechanical processes known to those of ordinary skill in the art can be used to remove the portion  330 ′ of outer layer  330  without undue damage to the interior core/cladding of fiber tip  345 . 
     In an embodiment, the formed tips are applied to fibers having graded index cores with maximum core diameters of about 100 microns or less and, in an embodiment, are of about 50 microns or less. In an embodiment, the maximum outer diameters of the fibers are of about 125 microns or less and in an embodiment, are of about 70 microns or less with appropriately sized layers of cladding and protective outer material (e.g., polyimide). Fibers with preferable core sizes between about 50 to 100 microns in various embodiments of the invention can be facilitated with generally thinner than typical overcladding/protective layers because the fibers will generally remain highly protected within the catheter components such as those described herein. Fibers with cores having diameters as small as about 9 microns for use with various embodiments of the invention can be obtained with various requested properties (e.g., low profile overcladding/jackets, doping profiles) from, for example, Yangtze Optical Fiber and Cable Co., Ltd. of Wuhan, China (See http://www.yofcfiber.com) and OFS Specialty Photonics (See http://www.specialtyphotonics.com) having offices in Avon, Conn. and Somerset, N.J., and/or manufactured in accordance with various known methods such as, for example, those described in U.S. Pat. No. 7,013,678, U.S. Pat. No. 6,422,043, and U.S. Pat. No. 5,774,607, the contents of each of which is herein incorporated by reference. 
     A dopant that can be used in a graded-index embodiment of the invention comprises Germanium (Ge) while the remaining component of a fiber consists essentially of silica. In an embodiment, the dopant comprises at least one of Fluorine (F), Beryllium (Be), and Phosphorous (P). In an embodiment, the change in the index of refraction across the diameter of the fiber core ranges between about 1.458 and 1.49 wherein the maximum index of refraction occurs in the center of the fiber core and varies approximately in proportion to the dopant concentration. In an embodiment, the maximum dopant concentration is about 15% of the material composition of the fiber at the center of a fiber and is gradually reduced to a concentration of 0% of the material composition of the fiber, for example, as presented in  FIGS. 5A and 6A . 
       FIG. 5A  is an illustrative chart of the dopant concentration of a graded index fiber core in an embodiment of the invention. In an embodiment, the dopant concentration is configured to provide an etched core including the shape of a conic section (i.e., that of the intersection between a plane and a cone). For example,  FIG. 5B  is an illustrative cross-sectional view of a fiber tip  355 A formed from a graded index fiber core with a dopant concentration having an elliptical profile such as according to the chart of  FIG. 5A . In an embodiment of the invention, a wet etching process such as described above is applied to form the fiber tip  355 A and produce a recess within the core having cross-sections in the shape of an ellipse. 
       FIG. 6A  is another illustrative chart of dopant concentration of a graded index fiber core in another embodiment of the invention.  FIG. 6B  is an illustrative cross-sectional view of a fiber tip  355 B formed from a fiber core with a dopant concentration having a linear profile such as according to the chart of  FIG. 6A . In an embodiment of the invention, a wet etching process such as described above is applied to a fiber tip so as to provide a cone-shaped shaped recess  355 B. 
     The core&#39;s graded indexing can be adjusted to provide a particular desired optical configuration. In various embodiments of the invention, the fiber tip can be cleaved at various angles prior to etching so as to also help configure the tip to a desired optical configuration (e.g., and help concentrate delivered/collected radiation along various axis). 
       FIG. 7A  is an illustrative cross-sectional view of a fiber tip having an end coated with a reflective and/or light diffusing material according to an embodiment of the invention.  FIG. 7B  is an illustrative perspective view of the fiber tip of  FIG. 7A  taken along reference line I-I′. A coating  340  is added to the recess  355 , which promotes distribution/collection of radiation along various axes transverse to the longitudinal axis of fiber tip  45 . The coating  340  can be added by applying a reflective (e.g., gold, silver) spray coating to recessed surface of the tip  45  (after masking off the other surfaces of tip  45 ) or filling in the recess with a reflective material such as a highly reflective polymer or metallic material including, for example, those that can be shaped/molded and/or later hardened with curing. In an embodiment, the reflective material is applied prior to removal of an outer protective jacket (e.g., jacket  330 ,  330 ′ of  FIGS. 4B and 4D ). In this manner, the jacket may serve to protect aspects of the tip  345  from contamination by the coating  340 . 
       FIG. 7C  is an illustrative view of a fiber tip  50  with an air gap  347  spaced between a reflective coating  345  and the core  310  of the tip  50 . In an embodiment, such an air gap  347  provides a greater change between indices of refraction across the outer boundary of the core  310  where light enters or exits, thus increasing the level light is directed off-axis from the longitudinal path  346  of the fiber core  310 . In an embodiment, the width  312  of the gap is approximately the width of the fiber core  310 . In an embodiment, the height  314  of the gap is approximately the same as the width of the fiber core  310 . In an embodiment, the width  312  and height  314  of the gap  3  are about 50 microns or less. 
       FIG. 8A  is an illustrative cross-sectional view of a fiber tip  45  positioned adjacent a reflective surface  80  according to an embodiment of the invention.  FIG. 8B  is an illustrative perspective view of the fiber tip  45  and reflective surface  80  of  FIG. 8A  taken along reference line II-II′. In an embodiment, a reflective surface  80  is placed adjacent a fiber tip  45  so that tip  45  is positioned between reflective surface  80  and targeted body tissue/fluids such as those described herein with regard to  FIG. 3A . Placement of surface  80  in this manner can help direct more radiation between tip  45  and targeted body tissue/fluids. In an embodiment, a small translucent area can be made in surface  80  so as to allow some radiation to pass between tip  45  and inner components of a catheter such as exemplary transmission paths  47 ,  48 , and  49  shown in  FIG. 2C . In an embodiment, the reflective surface is shaped in a convex manner with respect to outside body tissue/fluids (as shown in  FIG. 8B ) so as to allow a wider circumferential scope of radiation to be delivered/collected. 
       FIG. 9  is an illustrative perspective view of a fiber tip  45  adjacent a flat reflective surface  82  according to an embodiment of the invention. A flatter surface can concentrate the scope of delivered/collected radiation in a bearing more direct to body tissue/fluids than a convex surface would. In an embodiment, one or more customized distinct reflective surfaces can be arranged adjacent to individual fiber tips such as flat rectangular pieces attached to an inner balloon (e.g., see co-pending U.S. Application No. 61/019,626, filed on Jan. 8, 2008, the entire contents of which has been incorporated by reference above).  FIG. 10  is an illustrative perspective view of a fiber tip  45  adjacent a concave reflective surface  85  according to another embodiment of the invention. A more concave surface with respect to bodily tissue/fluids can help concentrate and/or evenly distribute radiation directed between a fiber tip  45  and the targeted tissue/fluids. 
     It will be understood by those with knowledge in related fields that uses of alternate or varied forms or materials and modifications to the methods disclosed are apparent. This disclosure is intended to cover these and other variations, uses, or other departures from the specific embodiments as come within the art to which the invention pertains.