Abstract:
The invention provides a guidewire with a centering mechanism. The mechanism lifts the guidewire from a vessel wall and biases it towards the center of the vessel. Since the guidewire can be selectively lifted away from the vessel wall, scraping the catheter against the wall can be avoided, the tip can be guided into the correct branch of a bifurcation, and an imaging device can be used to its full potential. In certain aspects, the invention provides a guidewire with an elongated shaft with a proximal portion and a distal portion comprising a distal tip. One or more centering mechanism can be provided on a guidewire.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of, and priority to, U.S. Provisional Patent Application Ser. No. 61/774,228, filed Mar. 7, 2013, the contents of which are incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention generally relates to a guidewire for intravascular intervention, and particularly to mechanisms for centering a guidewire within a vessel. 
       BACKGROUND 
       [0003]    Some people are at risk of having a heart attack or stroke due to fatty plaque buildups in their arteries that restrict the flow of blood or even break off and block the flow of blood completely. Angioplasty is a procedure for treating sites that are affected by plaque. In this procedure, a needle is used to make an opening through a patient&#39;s skin and into a blood vessel, often the femoral artery in the patient&#39;s leg. A sheath is used to hold the opening open and a radiopaque dye is injected, allowing physician view the treatment site on x-ray and select a suitable balloon catheter and a guidewire for treatment. 
         [0004]    The guidewire is then inserted through the hole and guided through the artery until the tip just passes the treatment site. The physician guides the wire by twisting and manipulating the proximal end that sits outside the patient. With the wire in place, the balloon catheter is slid over the proximal end and pushed forward until the balloon lies within the narrowed area. The balloon is then inflated to compress the plaque or to deliver a stent. 
         [0005]    A number of problems are associated with this procedure. For example, in places where the guidewire lies against the side of the vessel, pushing the catheter over the guidewire can scrape the catheter against the vessel wall. The guidewire tends to be pushed against the vessel wall by any curve in the vessel. Specifically, the guidewire will push against the inside wall at the peak of the curve and against the outside wall at the ends of the curve. 
         [0006]    Curves also present navigational challenges. For example, where a curve in the vessel lies close to a branch-point, it can be difficult to guide the tip of the wire into the correct branch due to the strong tendency of the curve to push the wire towards one side of the vessel. 
         [0007]    Some positioning difficulties could be helped by an imaging guidewire. For example, a guidewire with an ultrasound imaging tip could help a physician navigate the vessels. However, the tendency of the guidewire to push up against the vessel wall interferes with imaging. If the imaging device is pushed into the vessel wall, it will not be useful for viewing its environment. 
       SUMMARY 
       [0008]    The invention provides a guidewire with a mechanism for centering the guidewire within a vessel. A physician can operate the mechanism to cause it to lift the guidewire from the vessel walls and bias it towards the center of the vessel. Since the guidewire can be selectively lifted away from the vessel wall, scraping the catheter against the wall can be avoided, the tip can be guided into the correct branch of a bifurcation, and an imaging device can be used to its full potential. Thus the centering mechanism improves visibility and helps maneuver the guidewire to the location where fatty plaque is narrowing the arteries. The centering mechanism also minimizes trauma to healthy tissue by keeping the catheter from scraping through the vessel walls. Since the centering mechanism helps navigate the balloon to the affected site while protecting healthy tissue, angioplasty procedures can reach a number of sites that otherwise may have been inaccessible due to complex combinations of curves and branch-points within the blood vessels. Thus, by pushing the tip away from vessel walls and helping the physician orient the guidewire in the intended direction of travel, while also improving the view offered by imaging guidewires, a guidewire centering mechanism can be valuable for treating a person who is at serious risk for heart attack or stroke. 
         [0009]    In certain aspects, the invention provides a guidewire for an intravascular procedure. The guidewire has an elongated shaft with a proximal portion and a distal portion comprising a distal tip. A centering mechanism is provided on the distal portion so that, when the distal portion is inserted into a vessel in a body, the centering mechanism can be operated to center the guidewire in the vessel. A guidewire can include a single centering mechanism, or a number of centering mechanisms disposed at different locations along the length. 
         [0010]    In some embodiments, the centering mechanism uses a flexible sleeve that bows outward from an axis of the guidewire when compressed in a direction parallel to the axis. The flexible portion of the sleeve can be compressed by translating an outer sleeve along an inner core. For example, the proximal portion of the guidewire can present, to a physician, a graspable portion of the outer sleeve and of the inner core, allowing the physician to pull back the outer sleeve causing the centering mechanism to bow outwards. Moreover, the guidewire can be designed to transmit torque so that a physician can twist the proximal portion to cause the distal, inserted portion to twist. For example, torque can be transmitted by a key and keyway structure or a splined structure. 
         [0011]    In certain embodiments, the centering mechanism includes a balloon. A balloon can be included that surrounds the guidewire and inflates into a torus. Or, a balloon can be included that inflates into a spheroid lobe on one side of the guidewire. Where a centering mechanism comprises one or a number (e.g., three) lobe-shaped balloons, one, selected ones, or all of the balloons can be inflated to center the guidewire without occluding the flow of blood. Other embodiments of a centering mechanism can be provided that do not occlude the flow of blood. For example, a centering mechanism can make use of one or more struts configured to expand out from the guidewire to push the wire away from the vessel wall. A sleeve or band can be included to constrain the strut or struts against a core member. Removing the sleeve from the vicinity of the strut results in the strut expanding away from the core member. Moreover, the centering mechanism can be configured so that the sleeve can be returned to its original position to compress the strut back against the core member. 
         [0012]    A guidewire of the invention can include a centering mechanism along with other features. For example, a guidewire can include an imaging device. In some embodiments, an acoustic transducer is included for intravascular ultrasound imaging. The guidewire can be an IVUS imaging guidewire or can include an optoacoustic imaging fiber. An optoacoustic imaging fiber can use a photoacoustic transducer on an optical fiber that include one or more fiber Bragg grating to send an optical signal along the length of the fiber and guidewire while using an acoustical signal to image the tissue. The acoustic signal is received through the photoacoustic transducer and the signal information is carried out through the proximal end of the guidewire by the optical signal (e.g., as an interferometric signal). 
         [0013]    In related aspects, the invention provides a coronary intervention system that uses a catheter with a treatment device and a guidewire that includes a centering mechanism. The guidewire is configured to be inserted into a blood vessel and the catheter is configured to slide over the guidewire to carry the treatment device to a treatment site. The catheter may itself include a structure for centering the guidewire in the vessel. This way, the guidewire may be centered by both the guidewire centering mechanism and the catheter structure, thus allowing the guidewire to be centered in more than once place, or giving a physician greater control of guidewire navigation. The guidewire centering mechanism can operate through the use of a balloon, one or more struts, or a pliable material configured to bow outwards from the guidewire. In certain embodiments, the guidewire has a central core member and an outer sleeve member that can be translated relative to the core member in a direction substantially parallel to an axis of the guidewire. 
         [0014]    Aspects of the invention provide methods of performing angioplasty that include inserting a guidewire into a vessel of a patient and operating a centering mechanism disposed at a distal portion of the guidewire to bias the distal portion towards the center of the vessel. A catheter can be introduced to the treatment site by using the guidewire. These steps can be performed in any order. The guidewire centering mechanism can be employed when the catheter is already substantially advanced over the guidewire or the centering mechanism can be used when only the guidewire is substantially within the vessel, to aid in navigating the guidewire into position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  shows a catheter according to certain embodiments of the invention. 
           [0016]      FIG. 2  depicts guidewire for use with a catheter. 
           [0017]      FIG. 3  shows a centering mechanism for a guidewire. 
           [0018]      FIG. 4  shows the centering mechanism of  FIG. 3  in an expanded configuration. 
           [0019]      FIG. 5  shows a guidewire with centering mechanism being used in a vessel. 
           [0020]      FIG. 6  illustrates an un-deployed balloon for use as a centering mechanism. 
           [0021]      FIG. 7  shows a deployed balloon as a centering mechanism. 
           [0022]      FIG. 8  shows use of balloon to center a guidewire at a site within a vessel. 
           [0023]      FIG. 9  shows a strut-based embodiment of a centering mechanism. 
           [0024]      FIG. 10  shows the mechanism of  FIG. 9  in a deployed state. 
           [0025]      FIG. 11  gives a perspective view of an un-deployed strut-based centering mechanism. 
           [0026]      FIG. 12  gives a perspective view of a deployed strut-based centering mechanism. 
           [0027]      FIG. 13  is a cross-sectional view taken along the dotted line shown in  FIG. 10 . 
           [0028]      FIG. 14  shows a cross sectional view of a single strut for biasing guidewire. 
           [0029]      FIG. 15  shows a centering mechanism with five struts. 
           [0030]      FIG. 16  shows a system including a guidewire and a balloon catheter. 
           [0031]      FIG. 17  shows an imaging fiber for use on a guidewire of the invention. 
           [0032]      FIG. 18  illustrates a guidewire being introduced into a vessel. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    Embodiments of the invention provide a guidewire with an expandable element that biases the guidewire to a particular location within a vessel, facilitating the precise placement of the guidewire and providing greater accuracy during subsequent catheter procedures. The expandable element can function as a centering mechanism, tending to center the guidewire within the vessel. A guidewire of the invention may also include detection elements that detect placement of the guidewire and subsequent therapy. 
         [0034]      FIG. 1  shows a catheter  101  according to certain embodiments of the invention. Catheter  101  includes a proximal portion  103  that is generally outside of a patient during use and a distal portion  105  extending to a distal tip  109  configured for insertion into a patient. Distal portion  105  may generally include a treatment device. Guidewire  201  may be seen extending from distal tip  109 . Pictured in  FIG. 1  is a stent disposed around a balloon, but any suitable treatment device may be included. A length of catheter  101  extending through distal portion  105  generally defines a catheter shaft  111  capable of being delivered over guidewire  201 . Intravascular balloon catheters are used for such procedures as balloon angioplasty, or percutaneous transluminal coronary angioplasty (PTCA). Catheter  101  generally includes a pliable material that provides flexibility or maneuverability, allowing catheter  101  to be guided to a treatment site in a patient&#39;s blood vessels. Preferably, catheter  101  has enough stiffness to allow it to be pushed to a target treatment site, and accordingly, an ability to optimize a balance of pliability versus stiffness or pushability is beneficial to medical use. Elongate shaft  111  may include any suitable material such as, for example, nylon, low density polyethylene, polyurethane, or polyethylene terephthalate (PET), or a combination thereof (e.g., layers or composites). Generally, shaft  111  will be capable of transmitting torque along an axis of the shaft. Catheter  101  may itself include a mechanism to aid in centering. For example, U.S. Pat. No. 7,547,304 to Johnson described a guidewire centering catheter tip. U.S. Pat. No. 5,660,180 to Malinowski describes an intravascular ultrasound imaging guidewire that can be centered through use of a catheter. 
         [0035]    Catheter  101  may include an angioplasty balloon or other interventional device at distal portion  105  to expand or dilate blockages in blood vessels or to aid in the delivery of stents or other treatment devices. Blockages include the narrowing of the blood vessel called stenosis. 
         [0036]    Typically, catheter shaft  111  will include a guidewire lumen so that the catheter may be advanced along guidewire  201 . A guidewire lumen in a balloon catheter is described in U.S. Pat. No. 6,022,319. An inner surface of a guidewire lumen may include features such as a silicone resin or coating or a separate inner tube made, for example, of preformed polytetrafluoroethylene (PTFE). The PTFE tube may be installed within the catheter shaft by sliding it into place and then shrinking the catheter shaft around it. This inner PTFE sleeve provides good friction characteristics. Other suitable materials for use in catheter  101  include high density polyethylene (HDPE) or combinations of material, for example, bonded in multiple layers. 
         [0037]    Catheter  101  may include coaxial tubes defining separate inflation and guidewire lumens, for example, along a portion of, or an entirety of, a length of catheter  101 . A plurality of lumens may be provided in parallel configuration or coaxial at one point and parallel at another, with a transition such as a plunging portion that traverses a wall located between the parallel and the coaxial portions (See, e.g., U.S. Pat. No. 7,044,964). Other possible configurations include one or more of a guidewire tube or guidewire lumen disposed outside of the balloon. Or the guidewire tube may be affixed to and extend along the wall of the balloon. Catheter  101  is generally introduced into vessel and advanced to a site of treatment by the use of guidewire  201 . 
         [0038]      FIG. 2  depicts guidewire  201 . Guidewire  201  generally has a proximal portion  213  and a distal portion  209  terminating at distal tip  205 . Guidewire  201  includes a mechanism to bias a location of guidewire  201  away from a vessel wall when guidewire  201  is inserted therein. Guidewires are discussed in U.S. Pat. No. 5,439,139; U.S. Pat. No. 3,789,841; U.S. Pat. No. 6,059,738; and U.S. Pat. No. 6,423,012 
         [0039]      FIG. 3  shows a centering mechanism  215  according to certain embodiments of the invention. Here, mechanism  215  includes a pliable polymer sheath  219  fixed to a core member  221  near a distal tip  205  of guidewire  201 . The other end of sheath  219  is fixed to a sleeve member  217  disposed around core member  221 . Sleeve member  217  is configured to translate longitudinally relative to core member  221 , in a direction substantially parallel to an axis of guidewire  201 . 
         [0040]      FIG. 4  shows the centering mechanism  215  of  FIG. 3  in an expanded configuration. When sleeve member  217  is translated in a direction towards distal tip  205 , relative to core member  221 , polymer sheath  219  bows outward from guidewire  201 . Preferably, sheath  219  includes a polymer with elasticity, such as a urethane or PTFE polymer. An operator can center guidewire  201  by pushing sleeve  217  inwards towards a patient away from a proximal end of guidewire  201 . If sheath  219  includes enough elasticity, it will tend to return to a non-expanded state of its own disposition. Sheath  219  can be substantially contiguous so that in its expanded state it tends to occlude blood flow. In other embodiments, sheath  219  can include slits parallel to an axis of guidewire  201  so that when it expands, separate strips of the polymer bow outwards and allow blood to flow past centering mechanism  215  even while deployed. 
         [0041]      FIG. 5  shows centering mechanism  215  being deployed to center distal portion  209  of guidewire  201  near a treatment site  151 . Here, distal tip  109  of catheter  101  is shown being used to introduce balloon  107 . As can be seen in  FIG. 5 , distal tip  109  is kept away from the vessel walls to prevent damage to the tissue. An expandable pliable sheath is thus one mechanism for a centering mechanism. Other embodiments are provided. 
         [0042]      FIGS. 6 and 7  illustrate use of an inflatable balloon  225  at a distal portion  209  of guidewire  201  as a centering mechanism. Guidewire  201  includes balloon inflation lumen  227  (shown here disposed within guidewire  201 —lumen  227  could also be provided as a tube along a side of guidewire  201 ). Forcing an inflation fluid (e.g., air, gas, water, saline, etc.) through inflation lumen inflates the balloon as shown in  FIG. 7 . 
         [0043]      FIG. 8  shows use of balloon  225  as centering mechanism  215  to center guidewire  201  in a site within a vessel  151 . Distal tip of a catheter  109  is again illustrated to show that it is kept away from the vessel wall by centering mechanism  215 . 
         [0044]      FIG. 9  shows a strut-based embodiment of a centering mechanism  215  of the invention. Here, guidewire  201  includes a central core  221  surrounded by outer sleeve  217 . Outer sleeve  217  compresses one or more of strut  235  against the side of core  221 . Strut  235  can include a springy material or a shape-memory material (e.g., steel, iron, nitinol, etc.) that tends to bias strut  235  away from core  221 . Sleeve  217  can include one or more aperture  237 . When sleeve  217  is translated relative to core  221 , aperture  237  is positioned over strut  235 . Strut  235  is then released and expands away from core  221  under its own dispositional bias. 
         [0045]      FIG. 10  shows centering mechanism  215  with struts  235  in a deployed state, expanded away from core  205 . 
         [0046]      FIGS. 11 and 12  give perspective views of a centering mechanism  215  including a plurality of struts  235  in the compressed and expanded states, respectively. While shown here using a sleeve  217  with aperture  237 , sleeve  217  could also operate to compress one or more of strut  235 , and to allow them to expand, by having a terminal edge disposed in a vicinity of the strut or struts. Pull back on sleeve  217  can cause a terminal end of sleeve  217  to be removed from strut or struts  235 , allowing them to expand. Sleeve  217  could then be pushed forward to compress strut or struts  235 . Other arrangements are also possible and within the scope of the invention. For example, a terminus of sleeve  217  may have a straight (circular) edge, or may have a scalloped or slotted appearance, with individual recess for individual ones of strut  235 . 
         [0047]      FIG. 13  is a cross-sectional view of a centering mechanism  215  including a plurality of struts  235  taken along the dotted line shown in  FIG. 10 . While shown in  FIG. 13  as including three of strut  235 , centering mechanism  215  can include any number of strut  235 . In fact, in certain embodiments, a single one of strut  235  provides a mechanism for biasing guidewire  201  away from a vessel wall in one direction. 
         [0048]      FIG. 14  shows a cross sectional view of a single strut  235  for biasing guidewire  201  away from a vessel wall. Strut  235  as depicted in  FIG. 14  may be operated substantially as described above with regards to  FIGS. 9 and 10 . Biasing a guidewire  201  away from a vessel wall may be particularly beneficial for a guidewire that is configured to transmit torque from one end to another. For example, an operator may view guidewire  201  via x-ray angiography and see that it needs to be pushed away from a vessel wall. The operator may twist the proximal end until the single strut  235  appears on the angiograph as oriented towards the wall. The operator may then deploy centering mechanism  215  to bias guidewire  201  towards a center of the vessel. Accordingly, embodiment of the invention that include a sheath surrounding a core can optionally include a structure for transmitting torque from one portion of guidewire  201  to another. Any suitable torque transmitting mechanism may be employed. In certain embodiments, torque is transmitted by a key and keyslot mechanism or by a spline mechanism. 
         [0049]    As shown in  FIG. 14 , sleeve  217  includes bosses  241  defining a keyslot and core  221  includes a key  245  that fits therein. One of skill in the art will recognize that variations are possible such as placing one or more key or keyslot on either of core  221  and sleeve  217 . Additionally or alternatively a surface of core  221 , sleeve  217 , or both can be splined. 
         [0050]      FIG. 15  shows a centering mechanism  215  for a guidewire  201  that includes five of strut  235 . The centering mechanism  215  is depicted from the proximal perspective with each of strut  235  mounted to core  221  at a proximal end of strut  235 . Thus a mounted, butt-end of each strut  235  is seen, with a elongated member of each strut extending away from the view, into the page, and biased away from core  221 . 
         [0051]    Struts  235  can be assembled on guidewire by any suitable means including, for example, welding, co-molding, clamping, banding, or adhesives. In some embodiments, a portion of strut  235  is swaged into the material of core  221 . A band (e.g., metal or a polymer) may also be strapped around the bases of struts  235 . Adhesives or spot welds may be additionally used, as desired. Thus a guidewire  201  of the invention includes a mechanism  215  for centering the guidewire within a vessel. 
         [0052]      FIG. 16  shows a cross-sectional view through distal portion  105  of catheter  101 . Running through catheter  101  is catheter shaft  111  defining guidewire lumen  117  extending to distal tip  109 . Inflation channel  119  may generally be disposed along guidewire lumen  117  along a length of catheter shaft  111 . Balloon  107  surrounds inflation lumen  113  which is in fluid communication with inflation channel  119 . Guidewire  201  may optionally include one or more of imaging device  135 . Balloon  107  may be any suitable balloon known in the art such as, for example, an angioplasty balloon. Balloon  107  is configured to be expandable, and may be used to deliver stent  161  or to open an obstructed vessel. Balloon  107  generally includes a strong flexible material and exhibits a narrow profile in an un-inflated state. Any suitable material may be used for balloon  107  including, for example, polyolefins such as polyethylene, polyvinyl chloride, polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) and copolyesters, polyether-polyester block copolymers, polyamides, polyurethane, poly(ether-block-amide) and the like. Balloons are described in U.S. Pat. No. 7,004,963; U.S. Pub. 2012/0071823; and U.S. Pub. 2008/0124495, the contents of each of which are incorporated by reference. Materials for balloon catheters are described in U.S. Pat. No. 5,820,594. Balloon catheters are described in U.S. Pat. No. 5,779,731 and U.S. Pat. No. 5,411,016. 
         [0053]    In some embodiments, the balloon includes artificial muscle (electro-active polymer). Electro-active polymers exhibit an ability to change dimension in response to electric stimulation. The change may be driven by electric field E or by ions. Exemplary polymers that respond to electric fields include ferroelectric polymers (commonly known polyvinylidene fluoride and nylon 11, for example), dielectric EAPs, electro-restrictive polymers such as the electro-restrictive graft elastomers and electro-viscoelastic elastomers, and liquid crystal elastomer composite materials. Ion responsive polymers include ionic polymer gels, ionomeric polymer-metal composites, conductive polymers and carbon nanotube composites. Common polymer materials such as polyethylene, polystyrene, polypropylene, etc., can be made conductive by including conductive fillers to the polymer to create current-carrying paths. Many such polymers are thermoplastic, but thermosetting materials such as epoxies, may also be employed. Suitable conductive fillers include metals and carbon, e.g., in the form of sputter coatings. Electro-active polymers are discussed in U.S. Pat. No. 7,951,186; U.S. Pat. No. 7,777,399; and U.S. Pub. 2007/0247033, the contents of each of which are incorporated by reference. 
         [0054]    In some embodiments, guidewire  201  includes imaging fiber  129  extending from a proximal portion  103  of catheter  101 . At proximal portion  103 , imaging fiber  129  may be operably coupled to a control unit (not pictured) via an optical coupler. Imaging device  135  may include any suitable imaging technology known in the art. In certain embodiments, device  101  uses optical-acoustic transduction to perform ultrasound imaging using imaging fiber  129  and imaging device  135 . 
         [0055]      FIG. 17  shows an imaging fiber  129  configured for optical-acoustic imaging. Along fiber  129 , a cladding surrounds fiber core  131 . Light  137  is transmitted from the control unit down a length of fiber  129 . Within fiber core, fiber Bragg grating  149  partially reflects light  137 . Also, where included, terminal fiber Bragg grating  141  reflects light. Additionally, blazed fiber Bragg grating  145  reflects light in a direction substantially radial to an axis of fiber  129 . The radial portion of the path of light  137  extends to photoacoustic transducer  135 . When light  137  impinges on photoacoustic transducer  135 , phonons are generated, leading to thermal strain of photoacoustic transducer  135 . Thus, photoacoustic transducer  135  uses incoming light  137  as an energy source to generate a longitudinal pressure wave  139 . When distal portion  105  is in a patient&#39;s vessel, pressure wave  139  can be used for ultrasonic imaging of material in the vessel, plaque, the vessel wall, surrounding tissue, other material, or a combination thereof. Parts of wave  139  that bounce back constitute the return signal that will contribute to the ultrasonic image data. Imaging fibers and methods of making them are discussed in U.S. Pat. No. 8,059,923, the contents of which are incorporated by reference for all purposes. 
         [0056]    In some embodiments, this return signal impinges on photoacoustic transducer  135 . The energy of return signal causes a vibration or deformation of photoacoustic transducer  135 . This results in a change in length of light path  137 . In some embodiments, the primary change in length of light path  137  is in the radial portion extending between photoacoustic transducer  135  and fiber core  131 , substantially perpendicular to an axis of fiber  129 . However, deformations in geometry of cladding  133  may result in a change of length of light path  137  in, for example, the region between fiber Bragg grating  149  and blazed fiber Bragg grating  145 . Depending on a desired embodiment, one may be favored over the other by cladding a portion of fiber  129  in a material with different rigidity or changing proportions of the depicted elements. Light reflected by blazed fiber Bragg grating from photoacoustic transducer  135  and into fiber core  131  combines with light that is reflected by either fiber Bragg grating  149  or  141  (either or both may be including in various embodiments). The light from photoacoustic transducer  135  will interfere with light reflected by either fiber Bragg grating  149  or  141  and the light  137  returning to the control unit will exhibit an interference pattern. This interference pattern encodes the ultrasonic image captured by imaging device  135 . The light  137  can be received into photodiodes within a control unit and the interference pattern thus converted into an analog electric signal. This signal can then be digitized using known digital acquisition technologies and processed, stored, or displayed as an image of the target treatment site. An incoming optical acoustical signal impinging on diodes creates an analog electrical signal which can be digitized according to known methods. Methods of digitizing an imaging signal are discussed in Smith, 1997, T HE  S CIENTIST AND  E NGINEER &#39;S G UIDE TO  D IGITAL  S IGNAL  P ROCESSING , California Technical Publishing (San Diego, Calif.), 626 pages; U.S. Pat. No. 8,052,605; U.S. Pat. No. 6,152,878; U.S. Pat. No. 6,152,877; U.S. Pat. No. 6,095,976; U.S. Pub. 2012/0130247; and U.S. Pub. 2010/0234736, the contents of each of which are incorporated by reference for all purposes. 
         [0057]    In related embodiments, imaging fiber  129  operates without a blazed fiber Bragg grating and detects a change in path length between fiber Bragg gratings  149  and  141  associated by a strain induced on fiber  129  by the impinging sonic return signal. In some embodiments, separate imaging fibers  129  are used to send and to receive an ultrasonic image. Methods of optic-acoustic imaging using fiber Bragg gratings for use with the invention are discussed in U.S. Pat. No. 8,059,923 and U.S. Pub. 2008/0119739, the contents of which are incorporated by reference in their entirety. 
         [0058]    The invention includes methods of providing an array of imaging fibers  129  that can be disposed around guidewire  201  and further provides methods of creating a plurality of image detectors  135  that are all oriented in a desired direction. In some embodiments, a plurality of substantially featureless optical fibers are arrayed in a sheet substantially parallel to one another. The sheet of fibers may be positioned on a sheet of material that may optionally have an adhesive on the surface. Additionally or alternatively, a cementing material may be applied to the sheet-like array of fibers. The fibers  129  may be arrayed in substantially straight lines (e.g., by combing prior to application of adhesive or cement) or may be in other conformations. For example, introducing a wavy or zigzag pattern into a portion of the fibers  129  may give them slack, or “play”, that allows image detectors to stay in place as guidewire  201  bends or twists. Once the fibers are so arrayed and held in place, the fiber Bragg gratings may then be formed in all of them. The fiber Bragg gratings may be formed by an inscribing method using a UV laser and may be positioned through the use of interference or masking. Inscribing and use of fiber Bragg gratings are discussed in Kashyap, 1999, F IBER  B RAGG  G RATINGS , Academic Press (San Diego, Calif.) 458 pages; Othonos, 1999, F IBER  B RAGG  G RATINGS : F UNDAMENTALS AND  A PPLICATIONS IN  T ELECOMMUNICATIONS AND  S ENSING , Artech (Norwood, Mass.) 433 pages; U.S. Pat. No. 8,301,000; U.S. Pat. No. 7,952,719; U.S. Pat. No. 7,660,492; U.S. Pat. No. 7,171,078; U.S. Pat. No. 6,832,024; U.S. Pat. No. 6,701,044; U.S. Pub. 2012/0238869; and U.S. Pub. 2002/0069676, the contents of each of which are incorporated by reference. 
         [0059]    Detectors  135  can then be introduced by grinding a channel into the surface of all of the fibers. If done with the fibers un-cemented, the fibers can be rolled over and the grinding continued so that each fiber has an annular channel extending around the fiber. Fiber Bragg grating  149 ,  141 , both, others, or a combination thereof can be formed, as well as any desired number of blazed fiber Bragg grating  145  in each fiber  129  (see  FIG. 17 ). A channel or cutaway can be formed for image detector and may optionally be filled with a photoacoustic transducer material. Suitable photoacoustic materials can be provided by polydimethylsiloxane (PDMS) materials such as PDMS materials that include carbon black or toluene. Imaging fibers and methods of making them are discussed in U.S. Pat. No. 8,059,923, the contents of which are incorporated by reference for all purposes. Once the sheet-like array is bound together (e.g., the adhesive has set), the sheet can be applied to a surface—for example, wrapped around catheter shaft  111 . 
         [0060]    Other imaging modalities may be included in system  101 . Imaging device  135  can employ any suitable imaging modality known in the art. Suitable imaging modalities include intravascular ultrasound (IVUS), optical coherence tomography (OCT), optical-acoustical imaging, and others. For ultrasound imaging, catheter  101  may include an ultrasound transducer as imaging device  135 . Ultrasonic imaging catheters are discussed in U.S. Pat. No. 5,054,492 to Scribner; U.S. Pat. No. 5,024,234 to Leary; and U.S. Pat. No. 4,841,977 to Griffith. Systems for IVUS are discussed in U.S. Pat. No. 5,771,895; U.S. Pub. 2009/0284332; U.S. Pub. 2009/0195514 A1; U.S. Pub. 2007/0232933; and U.S. Pub. 2005/0249391, the contents of each of which are hereby incorporated by reference in their entirety. OCT systems and methods are described in U.S. Pub. 2011/0152771; U.S. Pub. 2010/0220334; U.S. Pub. 2009/0043191; U.S. Pub. 2008/0291463; and U.S. Pub. 2008/0180683, the contents of each of which are hereby incorporated by reference in their entirety. In certain embodiments, catheter  101  makes use of a combination of optical and acoustic signal propagation for imaging capabilities. 
         [0061]      FIG. 18  illustrates a guidewire  201  with centering mechanism  215  being introduced into a treatment site  151  of a vessel so that catheter body  111  can be used to deliver balloon  107  to the treatment site. As shown in  FIG. 18 , as catheter  101  approaches treatment site  151  (such as a region of a blood vessel affected by atherosclerotic plaque), a physician can view site  151  on a monitor of an associated medical imaging instrument (not pictured). Using, for example, IVUS or optical-acoustic imaging, the vessel wall is viewed to monitor for the location of atherosclerotic plaques. Monitoring a position of catheter  111  may also be optionally combined with use of standard x-ray angiographic techniques. When balloon  107  is positioned at the target treatment site, it is inflated to open a passageway that will allow blood to flow past the stenosized (narrowed) portion of the vessel after the balloon is deflated. Balloon  107  may also be optionally used to deploy a stent. Such vascular intervention procedures by catheter are often performed in specialized clinical environments known as cath labs. Cath labs and associated imaging instrumentation (e.g., IVUS and OCT instruments) are known in the art. For example, IVUS is discussed in U.S. Pat. No. 8,289,284; U.S. Pat. No. 7,773,792; U.S. Pub. 2012/0271170; U.S. Pub. 2012/0265077; U.S. Pub. 2012/0226153; and U.S. Pub. 2012/0220865. Optical-acoustic imaging structures (e.g., for imaging fiber  129 ) are discussed in U.S. Pat. No. 8,059,923; U.S. Pat. No. 7,660,492; U.S. Pat. No. 7,527,594; U.S. Pat. No. 6,261,246; U.S. Pat. No. 5,997,523; U.S. Pub. 2012/0271170 and U.S. Pub. 2008/0119739. The contents of each of these patents and publications are incorporated by reference in their entirety for all of their teachings and for all purposes. As shown in  FIG. 8 , use of a centering mechanism  215  allows for centering of guidewire  201  in the vessel, thus preventing balloon  107  or another portion of catheter  101  from scraping the vessel wall. 
       INCORPORATION BY REFERENCE 
       [0062]    References and citations to other documents, such as patents, patent applications, patent publications, journals, books, papers, web contents, have been made throughout this disclosure. All such documents are hereby incorporated herein by reference in their entirety for all purposes. 
       EQUIVALENTS 
       [0063]    Various modifications of the invention and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the full contents of this document, including references to the scientific and patent literature cited herein. The subject matter herein contains important information, exemplification and guidance that can be adapted to the practice of this invention in its various embodiments and equivalents thereof.