Patent Publication Number: US-9405078-B2

Title: Method for disposable guidewire optical connection

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. continuation patent application Ser. No. 14/191,385 filed Feb. 26, 2014, which is a divisional of U.S. patent application Ser. No. 13/598,596 filed Aug. 29, 2012, which claims priority from U.S. provisional patent application 61/529,029 filed Aug. 30, 2011, the contents of which are hereby incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The subject matter disclosed generally relates to guidewires for minimally invasive medical use. More specifically, it relates to methods and devices for terminating optical fibers within guidewires. 
     BACKGROUND 
     The use of pressure measurement guidewires has been in existence for at least the last 10 years. These pressure guidewires are most commonly used to measure the pressure distal to a lesion (stenosis), most commonly in the coronary vasculature. By calculating the ratio between the measured pressure distal to the lesion and some point more proximal, most commonly in the ascending aorta or the coronary tree root, the fractional flow reserve (FFR) is obtained. The FFR is now commonly used to assess the significance of lesion stenosis and thereby to inform the physician as to the most appropriate treatment strategy. 
     Current devices use piezo-electric pressure transducing elements mounted into a guidewire for measuring blood pressure distal to stenosis that intervene in the calculation of the FFR value. Piezo-electric transducers however suffer from lack of stability as a result of moisture induced sensor drift. Optical pressure element as described in U.S. Pat. No. 7,689,071 do not suffer from such adverse effect and they are better suited for FFR measurement such as for pressure guidewire described in U.S. patent application Ser. No. 13/389,319. 
     Pressure guidewires also must allow easy disconnection and reconnection of the guidewire to a pressure analyzer. Pressure guidewires involve the measurement of distal blood pressure, followed by the insertion of other interventional medical devices such as Percutaneous Transluminal Coronary Angioplasty (PTCA) balloon catheter over the guidewire for stenting in case of significant lesion. It is however desirable to have the ability to reliably re-connect the guidewire to the pressure analyzer for post stenting FFR assessment, or for multi-vessel lesion assessment. Current electrical connectors such as those described in U.S. Pat. Nos. 4,958,642, 4,961,433, 5,178,159, 5,240,437, 5,358,409, 5,348,481, 5,413,508, 6,196,980, 6,428,336, 7,274,956 are suited for electrical connection. Although they have the ability to provide a reliable electrical connection in dry conditions, they are typically quite sensitive to conditions where the surface of the guidewire connector contacts are contaminated with blood residues after the removal of the interventional device such as PTCA balloon catheter. 
     A selection of prior art documents is described below. They are discussed for illustrative purposes only. These documents do not necessarily represent the closest prior art. 
     U.S. Pat. No. 5,125,058 provides a method for optically connecting a guidewire mounted device to a relaying cable. The method however relies on the accuracy of the internal diameter of the guidewire, which is difficult to achieve. The guidewire mounted optical fiber interface is recessed within the guidewire, making the fiber surface polishing a difficult task. The optical portion that is devoted to be inserted into the guidewire needs to be of very small diameter, making the connector very sensitive to mechanical damage. 
     U.S. Pat. No. 5,601,087 relies on the addition to the guidewire shaft of a proximal tubing portion, often called ferrule, with accurate outside diameter for alignment purpose. The addition of such proximal tubing portion adds extra production steps to the device and represents a challenging assembly process considering the presence of optical parts. 
     U.S. Pat. No. 6,445,939 also relies on the addition of a ferrule attached to the proximal end of the guidewire shaft. It is indeed very difficult and expensive to machine such a tinny precise ferrule, and to attach it to the proximal end of the guidewire shaft. 
     U.S. Pat. No. 7,736,301 also relies on the addition of a ferrule near the proximal end of the guidewire shaft. The ferrule is, in this case, not attached to the guidewire as it is desired to allow for rotational connection, hence further increasing the requirement on the diameter tolerance of the parts. 
     Hence, there is a need for an optical guidewire connector having the ability to reliably connect a guidewire mounted optical pressure sensor to an external pressure analyzer or a similar opto-electronic device; that is disposable, and hence that is easy to produce and is low in cost of material; and that is not sensitive to the presence of moisture or blood contamination. 
     SUMMARY 
     According to an embodiment, there is described a method for terminating a first optical fiber within a proximal portion of a guidewire tubing. The guidewire tubing has an outside diameter defined as having a tolerance of 0.001″ or better. The method comprises centering the first optical fiber within the guidewire tubing. 
     According to an aspect, the method further comprises grinding, polishing, or etching the guidewire tubing to bring the outside diameter within a tolerance of ±0.001″ or better. 
     According to an aspect, a gap exists between an outside diameter of the first optical fiber and an inside diameter of the guidewire tubing, the method further comprising slipping an overlay tubing over the optical fiber to fill the gap at least in part. 
     According to an aspect, the centering comprises centering the first optical fiber relative to the outside diameter of the guidewire tubing using an alignment centering tubing device, the method further comprising using an adhesive for securing the first optical fiber in the center of guidewire proximal portion. 
     According to an aspect, the alignment centering tubing device comprises a first ferrule having an inside diameter adapted to the outside diameter of the guidewire tubing, a second ferrule having an inside diameter adapted to an outside diameter of the first optical fiber, the method further comprising concentrically aligning the first ferrule and the second ferrule. 
     According to an aspect, the aligning the first ferrule and second ferrule comprises using a split sleeve over the first ferrule and second ferrule thereby holding both ferrules coaxially. 
     According to an aspect, a gap exists between an outside diameter of the first optical fiber and an inside diameter of the guidewire tubing, and wherein the centering further comprising slipping an overlay tubing over the optical fiber to fill the gap at least in part. 
     According to an aspect, the alignment centering tubing device comprises a first ferrule having an inside diameter adapted to the outside diameter of the guidewire tubing, a second ferrule having an inside diameter adapted to an outside diameter of an overlay tubing, the method further comprising concentrically aligning the first ferrule and the second ferrule. 
     According to another embodiment, there is described a method for connecting a first optical fiber within a proximal portion of a guidewire tubing, the method comprising: centering the first optical fiber within the proximal portion of the guidewire tubing; and connecting the first optical fiber to a female connector comprising a second optical fiber having a core diameter different from a core diameter of the first optical fiber. 
     According to an aspect, the method further comprises connecting the first optical fiber to a female connector comprising an alignment centering tubing device comprising a first ferrule having an inside diameter adapted to the outside diameter of the guidewire tubing, a second ferrule having an inside diameter adapted to an outside diameter of a second optical fiber for relaying an optical signal to an external signal conditioner unit, the method further comprising concentrically aligning the first ferrule and the second ferrule. 
     According to an aspect, the first ferrule and second ferrule are aligned with a split sleeve holding both ferrules coaxially. 
     According to another embodiment, there is described a female optical receiving device for connecting a first optical fiber to a second optical fiber, the first optical fiber being substantially centered within a proximal portion of a guidewire tubing, the female optical receiving device comprising a first ferrule having a longitudinal axis and an inside diameter adapted to an outside diameter of the guidewire tubing, a second ferrule having a longitudinal axis and an inside diameter adapted to an outside diameter of the second optical fiber, the longitudinal axis of the first ferrule being aligned with the longitudinal axis of the second ferrule. 
     According to an aspect, the device further comprises a split sleeve slipped and fixed over the first ferrule and the second ferrule simultaneously thereby aligning the longitudinal axis of the first ferrule and the longitudinal axis of the second ferrule. 
     According to an aspect, the second optical fiber has a core diameter different from a core diameter of the first optical fiber, the second optical fiber being fixed within the second ferrule. 
     According to another embodiment, there is described, an interface connector handle for connecting a first optical fiber to a second optical fiber, the first optical fiber being substantially centered within a proximal portion of a guidewire tubing, the second optical fiber being routed through and extending from an optical interface cable, the interface connector handle comprising a biasing assembly for urging the first optical fiber into contact with the second optical fiber. 
     According to an aspect, the handle further comprises a female optical receiving device at a distal end of the second optical fiber and wherein first optical fiber is for insertion in the female optical receiving device in order to contact the second optical fiber. 
     According to an aspect, the biasing assembly comprises a collet through which the guidewire tubing is pushed and held in place when the collet is in a closed position. 
     According to an aspect, the biasing assembly further comprises a biasing device and a connector cap through which the guidewire tubing is slid toward the female optical receiving device, the connector cap capable of movement in a direction, the biasing device exercising a counter force opposite the direction of movement of the connector cap, the counter force forcing the collet toward the closed position. 
     According to another embodiment, there is described a method for terminating a first optical fiber within a proximal portion of a guidewire tubing, the method comprising centering the first optical fiber relative to the outside diameter of the guidewire tubing using an alignment centering tubing device, the method further comprising using an adhesive for securing the first optical fiber in the center of guidewire proximal portion. 
     According to an aspect, the alignment centering tubing device comprises a first ferrule having an inside diameter adapted to the outside diameter of the guidewire tubing, a second ferrule having an inside diameter adapted to an outside diameter of the first optical fiber, the method further comprising concentrically aligning the first ferrule and the second ferrule. 
     According to an aspect, the aligning the first ferrule and second ferrule comprises using a split sleeve over the first ferrule and second ferrule thereby holding both ferrules coaxially. 
     According to another embodiment, there is provided a method for terminating an optical fiber within a proximal portion of a guidewire tubing, the guidewire tubing having an outside diameter and comprising a lumen, the method comprising centering the optical fiber relative to the outside diameter of the proximal portion of the guidewire tubing wherein the optical fiber and the inside of the lumen define an average gap there between, the average gap around the optical fiber being between 1 μm and 100 μm for allowing a substantial displacement of the optical fiber inside the lumen during the centering. 
     According to an aspect, the lumen has an inside diameter and the optical fiber has a diameter, the average gap is defined as half the difference between the inside diameter of the lumen and the diameter of the optical fiber. 
     According to an aspect, the diameter of the optical fiber is 80 μm and the inside diameter of the lumen is larger than 125 μm. 
     According to an aspect, the outside diameter and the lumen both have a central axis and an offset exists between the outside diameter central axis and the lumen central axis, wherein the centering comprises centering relative to the outside diameter thereby aligning the optical fiber on the outside diameter central axis and not on the lumen central axis. 
     According to an aspect, the offset has a maximum value equal to the average gap. 
     According to an aspect, centering comprises centering with an alignment centering tubing device. 
     According to an aspect, centering comprises centering with an alignment centering tubing device, the dimensions of which are more precise than the precision of the dimensions of the outside diameter of the proximal portion of the guidewire tubing, whereby the precision of alignment is dependent upon the precision of the dimensions of the alignment centering tubing device and upon the outside diameter of the proximal portion of the guidewire. 
     According to an aspect, centering comprises centering with an alignment centering tubing device having a precision of about 5 μm. 
     According to an aspect, the method further comprises slipping an overlay tubing over the optical fiber to fill the gap at least in part. 
     According to an aspect, the method further comprises using an adhesive for securing the optical fiber in the center of guidewire proximal portion. 
     According to an aspect, the centering comprises centering using an alignment centering tubing device. 
     According to an aspect, using the alignment centering tubing device comprises using a first ferrule having an inside diameter adapted to the outside diameter of the guidewire tubing, and a second ferrule having an inside diameter adapted to an outside diameter of the optical fiber, the method further comprising concentrically aligning the first ferrule and the second ferrule. 
     According to an aspect, the aligning the first ferrule and second ferrule comprises using a split sleeve over the first ferrule and second ferrule thereby holding both ferrules coaxially. 
     According to an aspect, the centering further comprises slipping an overlay tubing over the optical fiber to fill the gap at least in part. 
     According to an aspect, using the alignment centering tubing device comprises using a first ferrule having an inside diameter adapted to the outside diameter of the guidewire tubing, and a second ferrule having an inside diameter adapted to an outside diameter of the overlay tubing, the method further comprising concentrically aligning the first ferrule and the second ferrule. 
     According to another embodiment, there is provided a method for terminating an optical fiber within a proximal portion of a guidewire tubing, the guidewire tubing having an outside diameter defining a central longitudinal axis and comprising a lumen having an inside diameter and defining a lumen central axis being coaxial with the central longitudinal axis with an uncertainty between 1 μm and 100 μm, the method comprising centering the optical fiber relative to the outside diameter of the proximal portion of the guidewire tubing regardless of the coaxiality between the lumen and the outside diameter of the guidewire tubing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention are incorporated and constitute a part of this specification, illustrate an exemplary embodiment of the invention that together with the description serve to explain the principles of the invention. 
         FIG. 1  is a schematic diagram of the guidewire assembly connection showing a cross-section of an interface cable handle according to an embodiment; 
         FIG. 2  is a schematic diagram showing a cross-section of the proximal end of the guidewire with its optical fiber protruding therefrom according to an embodiment; 
         FIG. 3  is schematic diagram showing a cross-section of an alignment assembly device for aligning the optical fiber in the center of the proximal end of guidewire according to an embodiment; 
         FIG. 4  is schematic diagram showing a cross-section of guidewire proximal end terminated to provide connectivity according to an embodiment; 
         FIG. 5  is a schematic diagram showing a cross-section of guidewire proximal end terminated to provide connectivity according to another embodiment that comprises an overlay tubing; 
         FIGS. 6A and 6B  are schematic diagrams showing cross-sections of an alignment assembly device for aligning the optical fiber with overlay tubing in the center of the proximal end of guidewire according to another embodiment; 
         FIGS. 7A and 7B  are schematic diagrams showing cross-sections of an optical female connectivity part used to receive a guidewire proximal end and aligning respective fibers together according to an embodiment; 
         FIG. 8  is a schematic diagram showing a cross-section view of a handle which can be used in a method for holding female receiving optical parts at the end of an optical interface cable according to an embodiment; 
         FIG. 9  is a schematic diagram showing a side view of the handle of  FIG. 8 ; and 
         FIGS. 10A and 10B  are schematic diagrams showing a cross-section view of the handle of  FIG. 8  in the open position ( FIG. 10A ) and the closed position ( FIG. 10B ). 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of the embodiments, references to accompanying drawings are by way of illustration of an example by which the invention may be practised. It will be understood that other embodiments may be made without departing from the scope of the invention disclosed. 
     The system  2  for measuring FFR is shown in  FIG. 1 . It comprises a guidewire  1  instrumented with an optical pressure sensor  7  near the distal end (toward the patient). The guidewire  1  is therefore built with a hollow tubing (i.e., a guidewire tubing) for accommodating the optical fiber (not shown). The guidewire proximal end (toward the clinician) is terminated with a connectivity end for connecting to optical interface cable  5 . The optical interface cable  5  is used to relay the optical signal from signal conditioner unit  3  (e.g., an optical analyzer) to guidewire mounted optical pressure sensor  7 , and back to signal conditioner unit  3 . Guidewire  1  comprises an internal optical fiber (not shown) that carries the light signal to the optical pressure sensor  7  and back to signal conditioner unit  3 . In this respect, both optical fiber in the guidewire  1  and the optical fiber in the optical interface cable  5  need to be coaxially aligned and held in contact during use. The distal end of the optical interface cable  5  is terminated with optical alignment device  6  (also referred to herein as the female optical receiving device) that is embedded within the interface cable handle  4 . 
       FIG. 2  shows a first embodiment of the proximal portion  10  of the guidewire  1  such that after some further processing as detailed with reference to  FIG. 3  herein below, it can be connectorized to an optical interface cable  5  (see  FIG. 7A ). Guidewire proximal portion outside diameter  13  of the guidewire  1  has an accurate and precise diameter. 
     The first optical fiber  11  can be aligned in the center of the guidewire tubing  12  relative to the outside diameter  13  with a positioning apparatus having the ability to mechanically position the first optical fiber  11  in the center of the guidewire  1 , i.e., concentric with the surface of the outside diameter  13  of the guidewire proximal portion  10 . The position of the first optical fiber  11  relative to the guidewire tubing  12  is measured by methods such as those available from Beta LaserMike, Dayton, Ohio. 
     The optical fiber alignment method shown in  FIG. 3  is a preferred method because its compactness does not require a high level of mechanical stability for the assembly apparatus, while also being a self-alignment method. The alignment assembly device  20  (also known as an alignment centering tubing device) is made of a first alignment ferrule  21 , tubing or similar device having a precise internal diameter  22  adapted to receive the guidewire proximal portion  10 . By way of example, the first alignment ferrule  21  is preferably made with a commercial optical fiber alignment ferrule, either made of ceramic, zirconium, glass, stainless steel or other material providing adequate support and alignment accuracy. In the following, it is understood that ferrule is either a ferrule, a tubing or other similar device made of ceramic, zirconium, glass, stainless steel or other adequate material. Commercial ferrules for optical fibers are made with tolerances on eccentricity and hole diameter of the order of ±1 micron. A preferred outside diameter of such ferrules is typically of 1.25 mm, although it can be of other diameters such as 2.5 mm. The second alignment ferrule  23  is used to receive the first optical fiber  11  and it is therefore selected to have an internal diameter  24  that matches the diameter of the optical fiber cladding. Both ferrules are then coaxially aligned with the use of a split sleeve  25 . 
     Proper centering of the first optical fiber  11  within the guidewire proximal portion  10  is therefore possible considering the guidewire proximal portion outside diameter  13  is accurate. The guidewire proximal portion  10  shall have a guidewire proximal portion outside diameter  13  with a tolerance better than ±0.001″ (25 μm), and preferably it shall have a tolerance better than ±0.0005″ (12.5 μm). One preferred method of obtaining a diameter with an accuracy of ±0.0005″ or better is to grind the guidewire proximal portion  10  of the guidewire tubing  12  outer surface using a center-less grinder or other types of grinders known by those skilled in the art to be appropriate for this task. It is also obvious for those skilled in the art that other methods such as electro-etching can be used for the same purpose. The first optical fiber  11  is then aligned in the axial center of the outside diameter of the guidewire tubing  12 , and fixed in place using an adhesive  14 . 
     Conventional optical fiber alignment methods, as found in U.S. Pat. No. 5,187,761 for example, relies on the use of high precision ferrules, or similarly high precision tubing, for centering the optical fiber. Using such conventional methods, the optical fiber is centered by sitting against the inside diameter of the ferrule. Proper centering of the optical fiber depends on the tolerance of the outside diameter of the ferrule, the tolerance of the inside diameter of the ferrule, the tolerance of the concentricity of the outside diameter relative to the inside diameter of the ferrule, and on the tolerance of the inside diameter of the ferrule relative to the outside diameter of the fiber. Centering of the fiber depends on all above factors and therefore, off-axis centering of the optical fiber is the addition of all above mentioned tolerance errors. 
     A tolerance of 0.001″, or more stringent tolerance of 0.0005″ or 0.0002″, is achievable for the outside diameter of a guidewire, for example by center-less grinding or other methods described above. However, stringent tolerance of the inside diameter coupled to stringent tolerance of the concentricity of the inside diameter relative to the outside diameter of a guidewire is difficult to achieve. Although such accurate component is achievable, as found in U.S. Pat. No. 5,601,087 for example, it is achievable only with the addition of precise component combined to the guidewire construction, such component adding to the cost and complexity of the guidewire. 
     The currently described alignment method relies solely on the outside diameter of the guidewire, coupled to the tolerance of the alignment ferrule  21  (or equivalent) in the alignment assembly device  20 , which can be in the order of 1 μm, or in the order of 5 microns or other desired tolerance. Assuming the tolerances of parts  21  and  23  used for making the alignment device shown in  FIG. 3  are 1 micron, which is typical for such components, the optical fiber would be center relative to the outside diameter of the guidewire proximal portion with a maximum error of 5 microns (the addition of tolerance on inside and outside diameters of both alignment ferrules and the tolerance on the outside diameter of the optical fiber) plus the tolerance on the outside diameter of guidewire. The error caused by the alignment device, in view of the tolerance of the outside diameter of the guidewire, is typically negligible considering the tolerance on the outside diameter of the guidewire. 
     Given the high precision on the alignment ferrule  21 , the fiber does not need to be pre-centered (or almost centered) by the use of a tight lumen in which the optical fiber is confined, as found in U.S. Pat. No. 5,187,761, for example. The optical fiber  11  is rather loose in a lumen which is considerably larger than the fiber. 
     Because the fiber is loose, there is defined a gap  32  between the first optical fiber  11  and the internal surface  26  of the guidewire proximal portion  10 . Because the fiber  11  may be off the central axis of the lumen when it is centered relative to the outside diameter  13 , the gap, g(φ), is a variable dependent on the angle φ around the fiber  11 . The average gap G is defined as the angular mean of the gap around the fiber in the lumen at the guidewire proximal portion  10 , which can be formalized as: 
     
       
         
           
             G 
             = 
             
               
                 
                   1 
                   
                     2 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     π 
                   
                 
                 ⁢ 
                 
                   
                     ∫ 
                     0 
                     
                       2 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       π 
                     
                   
                   ⁢ 
                   
                     
                       g 
                       ⁡ 
                       
                         ( 
                         ϕ 
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                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ⅆ 
                       ϕ 
                     
                   
                 
               
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                   r 
                   l 
                 
                 - 
                 
                   
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                     f 
                   
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     As seen from the formula, the average gap is also equal to the difference between the inside radius of the lumen, r l , and the outside (clad) radius of the fiber  11 , r f . 
     A large average gap implies that the tolerance on the dimensions of the guidewire tubing  12  can be relaxed because there is more space for the fiber to undergo a displacement within the lumen during the alignment or centering. This weakened constraint implies a lower cost. 
     According to an embodiment, the optical fiber  11  has a diameter of 80 μm and the lumen has an inside diameter of 250 μm, thereby creating a gap  32  having an average value of 85 μm all around the fiber. Using these numbers, if the inside diameter of the lumen and the outside diameter of the guidewire are exactly coaxial, the gap will be 80 μm all around the fiber. However, as detailed below, coaxiality is not a requirement in the currently described optical fiber alignment method. It means that the gap can be 70 μm on one side of the fiber and 100 μm on the other side, for example. The optical fiber  11  is centered relative to the outside diameter  13 , but the lumen inside the guidewire tubing  12  can be offset. 
     Alignment assembly device  20  shown in  FIG. 3  is therefore used to center the first optical fiber  11  in the guidewire tubing  12 . The optical guidewire is prepared by letting the first optical fiber  11  protrude out of the guidewire tubing  12 . The required amount of adhesive  14  is then provided to fill the gap between the first optical fiber  11  and the internal surface  26  of the guidewire proximal portion  10 , and left uncured. The guidewire proximal portion  10  with protruding first optical fiber  11  is then inserted into the first alignment ferrule  21  and pushed such that the first optical fiber  11  enters into the second alignment ferrule  23 . Depending on specific alignment assembly device  20 , the guidewire proximal portion  10  can be pushed close to or in intimate contact with the second alignment ferrule  23 , hence minimizing optical fiber misalignment that may be caused by the first optical fiber  11  bending outside second alignment ferrule  23 . The adhesive  14  is then cured according to known adhesive curing methods. 
     An alternative method consists in inserting the guidewire proximal portion  10  within the first alignment ferrule  21  and pushed such that the first optical fiber  11  enters into the second alignment ferrule  23  with no adhesive yet. The required amount of adhesive  14  for filling the gap between the first optical fiber  11  and the internal surface  26  of the guidewire proximal portion  10  is then provided, followed by a curing step of the adhesive  14 . This alternative method helps in preventing the adhesive  14  from also filling the gap between the guidewire proximal portion  10  and the internal surface of the first alignment ferrule  21 , allowing an easy removal of the guidewire assembly after the adhesive  14  is cured. 
     Once the adhesive  14  is cured, the guidewire with centered first optical fiber  11  is retrieved from the alignment assembly device  20  to be terminated as shown in  FIG. 4 . The guidewire optical termination surface  31  of the guidewire is polished such that the first optical fiber  11  can be connected to the interface cable optical fiber (not shown here). Although the guidewire optical termination surface  31  can be polished on a hard surface, it is preferred to polish the guidewire proximal portion  10  on a soft polishing surface such that the optical fiber termination is provided with the ability to form a physical contact with the interface cable optical fiber. 
     The optical connectorization method shown in  FIG. 4  is however not optimal. The relatively large amount of adhesive  14  used to fill the gap  32  between the first optical fiber  11  and the internal diameter of the guidewire tubing  12  makes such optical connection susceptible to optical fiber misalignment during assembly and over time. As the amount of adhesive  14  increases during assembly, the risk of having the adhesive  14  unevenly distributed increases, which in turn increases the risks of unevenly pulling the first optical fiber  11  off the axial center. In use, all adhesives have the tendency to swell over time, especially when in presence of moisture and with temperature change. A relatively large amount of adhesive  14  therefore makes the optical termination more unstable. 
     The termination shown in  FIG. 5  is a variation of the one shown in  FIG. 4 , where the gap between the first optical fiber  11  and the internal surface  26  of the guidewire proximal portion  10  is partially filled with an overlay tubing  36 . In an embodiment, the overlay tubing  36  is selected to precisely match the first optical fiber  11 . The amount of adhesive  14  holding the fiber in the center of the guidewire proximal portion  10  is significantly reduced, hence long term stability of the optical connection is assured. 
     The optical connection illustrated in  FIG. 5  can be terminated using the same optical assembly device shown in  FIG. 3 . The overlay tubing  36  in this case would just barely extend further than the guidewire proximal portion  10  during assembly. 
     For those cases where the overlay tubing  36  is very precise, it may however be desirable to use the alignment assembly device  27  shown in  FIG. 6A , where the second alignment ferrule  41  has an internal diameter adapted to receive the overlay tubing  36 . However, misalignment errors caused by tolerances of inner diameter  37  and outer diameter  38  of the overlay tubing  36  add up to the final coaxial positioning error of the first optical fiber  11  relative to the outside diameter  13 , potentially leading to sub-optimal concentricity between the first optical fiber  11  and the outside diameter  13 . It has been found that the optical fiber provides adequate stiffness for aligning concentrically with the guidewire when aligned with set-up and alignment method shown in  FIG. 3 . A preferred method consists in using an overlay tubing that does not precisely fit over the first optical fiber  11 . 
       FIG. 6B  illustrates such a preferred assembly method and alignment assembly device  20  using an overlay tube  39  that does not precisely fit over the first optical fiber  11 . The concentric alignment of the first optical fiber  11  within the guidewire proximal portion  10  is assured by inserting the first optical fiber  11  in a second alignment ferrule  23  having an internal diameter matching the outside diameter of the first optical fiber  11 , while the overlay tube  39  purpose is mainly for filling the gap  32  (shown in  FIG. 4 ). 
     The method as described above allows the use of guidewires with accuracy requirement on the outside diameter only, as opposed to other methods known in the prior art where outside diameter, inside diameter and concentricity must be considered. For example, in U.S. Pat. No. 5,187,761 (Mehadji et al.), although it relates to conventional optical connection and is not related to a guidewire, the method described therein reports the use of very accurately defined endpieces, with a tolerance of about 0.5 μm (0.00002″) or less on the outside diameter. The lumen inside such endpieces must also have an internal diameter defined with a high accuracy of about the same value, 0.5 μm (0.00002″) or less. The coaxiality or concentricity between the central longitudinal axis of both the outside and the inside diameters must be maintained with a precision of about 0.5 μm (0.00002″) or less, too. The necessity of a high accuracy on the outside diameter, the inside diameter and their concentricity would be very difficult and costly if implemented for the optical connection relating to a guidewire. The difficulty of implementing such accurate components for the optical connection of a guidewire device is increased by the fact that a guidewire has an outside diameter much smaller than conventional optical connector devices as those described in U.S. Pat. No. 5,187,761. A guidewire outside diameter is typically in the range of 0.0014″ (350 microns), 0.0018″ (457 microns) or 0.035″ (890 microns). Another difficulty resides in the material used to build a guidewire. Guidewire are built using stainless steel or other metallic materials, while accurate ferrules and other components for the implementation of the optical connectivity conventional methods, as described in U.S. Pat. No. 5,187,761, use ceramic, glass, zirconium or the like, which materials are very difficult to join to stainless steel or other metallic based materials. Such high cost and assembly complexity are prohibitive when considering the guidewire is to be used only once, such as the pressure guidewire used for medical purposes. 
     The method described herein enables the use of a guidewire tubing  12 , where tolerance on the outside diameter only determines the capability of the system to center the optical fiber. More specifically, as described above, the tolerance on the outside diameter is 25 μm (0.001″) or less. Therefore, in the centering method described herein, there is no requirement on the accuracy of the inside diameter of the guidewire tubing  12 . It is rather preferably considerably larger than the optical fiber  11  such that the fiber  11  is loose in the lumen of the guidewire tubing  12 . 
     Furthermore, in the centering method described herein, there is no need for the central longitudinal axes of the inside and outside diameters of the guidewire tubing  12  to be coaxial. The only condition is that the uncertainty on the coaxiality, i.e., the maximum coaxial offset, must be smaller than the difference between the lumen inner radius and the fiber radius. The reason for this is to allow the fiber to be centered even though the inside diameter (lumen) is not coaxial. If the lumen is too far off axis, the center of the outside diameter will no more be located inside the lumen. 
     A large uncertainty on the coaxial offset is correlated with a lower cost. Therefore, it is advantageous to have a large uncertainty on the coaxial offset, i.e., a large gap  32  (difference between the lumen inner radius and the fiber  11  radius). 
     This is contrary to what is taught in U.S. Pat. No. 5,187,761, in which the fiber is substantially pre-centered when it is embedded in the lumen with a tight and well defined inside diameter. Instead, in the present invention, the fiber  11  is loose in the lumen since the lumen is large, and it needs to be centered thereafter. 
     After having the fiber  11  in the lumen of the guidewire and protruding therefrom as described above, centering needs to be done because the fiber is loose in the lumen. The alignment device holds the fiber firmly in place in the central axis relative only to the outside diameter (the centering relative to the inside diameter is irrelevant as long as the fiber is inside the lumen). Adhesive  14 , or adhesive  14  and an overlay tubing  36  can be applied to hold the centered fiber in place permanently after the guidewire is withdrawn from the centering device. 
     High precision (order of magnitude of 1 μm) is provided by the alignment device rather than by the dimensions of the guidewire tubing  12 . Transferring the high precision requirement from the guidewire dimensions to the alignment assembly device  20  reduces cost overall, because the alignment assembly device  20  is reusable while the guidewires are not (if they are used in a medical or surgical context). This is enabled by a loosened requirement on inside and outside diameter concentricity characterized by a large gap  32 . This is characterized by a difference in outer diameter of the fiber  11  and inside diameter of the lumen of the guidewire tubing  12  ranging from about 2 μm to 200 μm, preferably around 170 μm (i.e., the fiber  11  has a diameter of 80 μm and the lumen has an inside diameter of approximately 250 μm). The corresponding average gap between the fiber  11  and the lumen is the half of that difference, i.e., it ranges between 1 μm and 100 μm, 
     The above embodiments describe various methods and devices for making an optical connection at the proximal end of an optical guidewire. There is however also a need for a female part receiving the guidewire optical connection to provide an optical connection with the optical interface cable  5  for relaying the optical signal to a signal conditioner unit  3  (see  FIG. 1 ). 
       FIGS. 7A and 7B  show the optical parts used to construct such a female optical receiving device  6 . The female optical receiving device  6  is built in a way very similar to the alignment assembly device  20  shown in  FIG. 3 . The first ferrule  51  herein is also used to receive the guidewire  1 , with the inner diameter  52  adapted to receive the guidewire proximal portion  10 . First ferrule  51  and second ferrule  53  are aligned and held together using split sleeve  54 . The second ferrule  53  is however selected to receive the second optical fiber  55  routed through the optical interface cable  5  (see  FIGS. 1 and 8 ). By way of an example, the optical interface cable  5  comprises the second optical fiber  55  having a core diameter of 62.5 μm and a cladding diameter of 125 μm. In this case, the second ferrule  53  is selected with a diameter of 126 μm or 127 μm. The second optical fiber  55  is bonded inside the second ferrule  53  and polished so as to provide an adequate optical surface  56  compatible with the guidewire optical termination. 
       FIG. 7B  shows the female optical receiving device  6  with the guidewire proximal portion  10  engaged within the first ferrule  51 . The optical connection will take place with minimal losses provided that the first optical fiber  11  is coaxially aligned with the second optical fiber  55 , and provided that the faces of both first optical fiber  11  and second optical fiber  55  are in intimate contact. 
       FIG. 8  shows an interface connector handle  4  which can be used in a method for holding the female optical receiving device  6 . A second optical fiber  55  is connected to the female optical receiving device  6  on one side, and runs through the optical interface cable  5  on the other side. The female optical receiving device  6  is held in the center of the interface connector handle  4  and pushed against a surface  68  with the help of a spring  67 . The guidewire proximal portion  10  (see  FIG. 7B ) is inserted through the conical entrance  66  of the connector cap  61 , it is pushed through the collet  63  then inside the female optical receiving device  6  such that the guidewire optical termination surface  31  (see  FIG. 4 ) and the optical surface  56  (see  FIG. 7A ) of the second optical fiber  55  are in contact. The user can then tighten the connector cap  61 . Connector cap proximal end  62  therefore pushes on collet  63  which results in closing such collet  63  by counter force exerted by spring  65  through seat  70 . It is understood that spring  65  can be replaced by similar device such as rubber tube or other biasing device. The action of pushing the tightening collet  63  into seat  70  has the effect of closing the tightening collet  63  onto the guidewire proximal portion  10 , firmly holding it in place. 
     According to an embodiment, the interface connector handle  4  comprises a biasing assembly (not number) for urging the first optical fiber  11  into contact with the second optical fiber  55 . The biasing assembly may comprise collet  63  through which the guidewire  1  is pushed and held in place when the collet  63  is in a closed position. The biasing assembly may further comprise a biasing device (spring  65 ) and connector cap through which the guidewire tubing is slid toward the female optical receiving device, the connector cap  61  capable of movement in a direction. The biasing device exercises a counter force opposite the direction of movement of the connector cap  61  and the counter force forces the collet  63  toward the closed position. 
     One aspect of the method using interface connector handle  4  is to assure and maintain a good physical contact between both the optical interface of guidewire  1  and the optical interface of female optical receiving device  6 . Physical contact is assured by the displacement of the guidewire proximal portion  10  provided upon tightening the connector cap  61 . Upon tightening connector cap  61 , collet  63  first closes and grips the guidewire proximal portion  10 , forcing guidewire optical termination surface  31  (see  FIG. 4 ) to push against the optical surface  56  of the second optical fiber  55  (see  FIG. 7A ). This action is illustrated in  FIGS. 10A and 10B . 
       FIG. 10A  shows the connector handle in an open position and  FIG. 10B  shows the connector handle in a closed (downward) position, where one can see the downward position in  FIG. 10B  of both the collet  63  and the female optical receiving device  6 . The downward displacement of guidewire  1  pushing against female optical receiving device  6  is provided by the pitch of the sliding rail  72  and its interaction with protrusion  71  (see  FIG. 9 ). The downward displacement of the guidewire  1  against the female optical receiving device  6  translates into contacting pressure between both optical termination interfaces (guidewire optical termination surface  31  (see  FIG. 4 ) and the optical surface  56  of the second optical fiber  55  (see  FIG. 7A ). The force is provided by the spring  67  that is pushing against female optical receiving device  6 . The spring  67 , applies its pressure on the female optical receiving device  6  through a flange  69  that is mounted on the second ferrule  53  (see  FIG. 7A ). The pressure between the optical interfaces assures a good physical contact and therefore a good optical connection. 
     The above method of exerting a mutual pressure on the optical termination surfaces of both a guidewire and an optical receiving device is described by way of an example. Other methods of imposing a relative movement between the guidewire and the optical receiving device are understood to be within the scope of the present description. For example, there may exist a method for moving the internal receiving device apart from the guidewire prior to guidewire insertion, followed by a release after the guidewire is tightened within a connector handle. 
     The quality of the optical connection is related to the relative centering of both optical fiber axis where they interface. One method for reducing the tolerance on this centering is to use a second optical fiber  55  in the optical interface cable  5  with a core diameter different from the core diameter of the optical fiber (not shown) of the guidewire  1 . Although this approach is not always possible, there are optical measuring methods that are well suited for such a strategy. For instance, the pressure sensor described in U.S. Pat. No. 7,689,071 and associated signal conditioning unit described in U.S. Pat. No. 7,259,862 are well suited for the implementation of such a strategy. 
     While preferred embodiments have been described above and illustrated in the accompanying drawings, it will be evident to those skilled in the art that modifications may be made without departing from this disclosure. Such modifications are considered as possible variants comprised in the scope of the disclosure.