CATHETER FOR OPTICAL COHERENCE TOMOGRAPH, AND CATHETER PRODUCTION METHOD

[0001] The present invention relates to an optical coherence tomography catheter and a method for manufacturing the optical coherence tomography catheter.

[0002] U.S. Pat. No. 6,445,939 (Patent Document 1) discloses a method for connecting a catheter for an optical coherence tomography (OCT) system, which images the inside of a cavity, to a rotary joint. An FC/APC connector is used in this method. U.S. Pat. No. 7,813,609 (Patent Document 2) describes the structure of a catheter for an OCT system. This catheter includes an interior member that rotates, a tube housing that covers the interior member, and an optical connector that provides connection to a rotary joint.

[0003] According to the OCT catheters of the related art described in Patent Documents 1 and 2, a method of assembling a connecting portion to be connected to the rotary joint includes attaching a ferrule to a proximal end of an optical fiber contained in the interior member, and polishing an end surface of the optical fiber at an end surface of the ferrule. The interior member is generally expensive, and therefore needs to be processed carefully. Therefore, the process takes a long time and the manufacturing cost is high.

[0004] Japanese Unexamined Patent Application Publication No. 2009-205100 (Patent Document 3), Japanese Unexamined Patent Application Publication No. 2011-118348 (Patent Document 4), and Japanese Unexamined Patent Application Publication No. 2008-197622 (Patent Document 5) describe so-called field-installable fusion splice single-core optical connectors. The field-installable fusion splice single-core optical connectors can be attached to an optical fiber in the field, and include a ferrule and a short-length fiber fitted to the ferrule. A ferrule-side end (a front end) of the short-length fiber is polished in advance, and a rear end of the short-length fiber is fusion-spliced to a front end of the optical fiber to be connected.

[0005] An object of the present invention is to provide an OCT catheter and a method for manufacturing the OCT catheter with which the assembly time, manufacturing cost, and the risk of breakage of a spliced portion between a short-length fiber and an optical fiber contained in an interior member can be reduced.

[0006] To achieve the above-described object, a method for manufacturing an optical coherence tomography catheter is provided. The optical coherence tomography catheter includes an interior member that contains a first optical fiber and that is to be inserted into a body, and an optical connector including a ferrule assembly, which includes a second optical fiber and a ferrule fixed to one end of the second optical fiber, and a tube, one end of which is directly or indirectly fixed to the ferrule assembly and which guides the interior member, the optical connector being connectable to a rotary joint of an optical coherence tomography system. The method includes a first step of selecting the ferrule assembly including an embedded optical fiber having a first length as the second optical fiber, cutting the first optical fiber so that a sum of lengths of the first optical fiber and the second optical fiber is equal to a predetermined length, and fusion-splicing one end of the first optical fiber and the other end of the second optical fiber together to form a spliced portion; and a second step of inserting the spliced portion into the tube. When the cutting of the optical fiber or the fusion-splicing fails in the first step, the ferrule assembly including an embedded optical fiber having a second length, which is greater than the first length, as the second optical fiber is selected, the first optical fiber is cut again, and the spliced portion is formed again.

[0007] According to another aspect of the present invention, an optical coherence tomography catheter is provided. The optical coherence tomography catheter includes (1) an interior member that contains a first optical fiber and that is to be inserted into a body; (2) an optical connector including a ferrule assembly, which includes a second optical fiber and a ferrule fixed to one end of the second optical fiber, and a tube, one end of which is directly or indirectly fixed to the ferrule assembly and which guides the interior member, the optical connector being connectable to a rotary joint of an optical coherence tomography system; and (3) a spliced portion in which the other end of the second optical fiber and one end of the first optical fiber are fusion-spliced together, the spliced portion being disposed in the tube.

[0008] According to the OCT catheter and the method for manufacturing the OCT catheter of the present invention, the assembly time, manufacturing cost, and the risk of breakage of the spliced portion between the short-length fiber and the optical fiber contained in the interior member can be reduced.

[0022] The inventor of the present invention has considered applying a field-installable fusion splice single-core optical connector to a catheter for an OCT system. This eliminates the necessity of a polishing step in the assembly of the catheter. In addition, the field-installable fusion splice single-core optical connector is inexpensive, and therefore the manufacturing cost can be reduced. However, the method using the field-installable fusion splice single-core optical connector involves the following problems.

[0023] That is, OCT catheters are required to include an optical fiber having a predetermined optical path length so that interference waves can be observed. The allowable error of the optical path length is, for example, as small as ±5 mm or ±2 mm. Field-installable fusion splice single-core optical connectors include a short-length fiber having a constant length. If a spliced portion between the short-length fiber and an optical fiber contained in an interior member breaks, the length of the optical fiber contained in the interior member is slightly reduced when the optical fibers are fusion-spliced together again. Therefore, there is a risk that the error in the optical path length will be greater than the allowable error.

[0024] An OCT catheter and a method for manufacturing the OCT catheter according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, the same components are denoted by the identical reference numerals, and redundant descriptions are omitted.

[0025] FIG. 1 is a perspective view of an OCT catheter 1A according to an embodiment of the present invention, illustrating the state in which a tube housing is removed. The OCT catheter 1A includes an interior member (torque wire) 10, which is to be inserted into a body, and an optical connector 30 to be connected to a rotary joint of an OCT system. A lens 12, through which light is emitted toward the inside of the body and interference light is received, is attached to the distal end of the interior member 10. The interior member 10 contains an optical fiber (first optical fiber) that optically couples the optical connector 30 to the lens 12. A proximal end portion of the interior member 10 (portion that is not inserted into the body) is inserted into a metal tube 20, which will be described below, at one end of the metal tube 20 and is held in such a manner that the proximal end portion is movable in a longitudinal direction.

[0026] FIG. 2 is an exploded perspective view of the optical connector 30. FIG. 3 is a sectional view of the optical connector 30 in the longitudinal direction. The optical connector 30 is a so-called fusion splice SC connector. The optical connector 30 includes a ferrule assembly 31; the metal tube 20, one end of which is directly or indirectly fixed to the ferrule assembly 31 and which guides the interior member 10; a joint member 32 with which the metal tube 20 is fixed to the ferrule assembly 31; a plug housing 33 that accommodates the ferrule assembly 31 and the joint member 32, and an outer housing 34 that covers the plug housing 33. The metal tube 20 guides the interior member 10 in the longitudinal direction during, for example, a pull-back operation, and holds the proximal end portion of the interior member 10 so that the proximal end portion is not bent.

[0027] The ferrule assembly 31 includes a short-length fiber (also referred to as a second optical fiber or an embedded optical fiber) 35; a substantially columnar ferrule 36 that is fixed to one end of the short-length fiber 35 and holds the short-length fiber 35; and a tubular metal flange member 37 that is fixed to the ferrule 36. The ferrule 36 holds the short-length fiber 35 such that the short-length fiber 35 extends along the center axis of the ferrule 36. An end surface (front end surface) of the ferrule 36 is polished so as to be at an angle (for example, 8 degrees) with respect to a plane perpendicular to the center axis of the short-length fiber 35.

[0028] The short-length fiber 35 projects from the ferrule assembly 31 into the metal tube 20 by a predetermined length. The proximal end surface of the optical fiber contained in the interior member 10 is fusion-spliced to the metal-tube-20-side end surface of the short-length fiber 35. As described below, the spliced portion between the optical fiber contained in the interior member 10 and the short-length fiber 35 is disposed in the metal tube 20.

[0029] FIG. 4 is an enlarged sectional view illustrating the detailed structures of the ferrule assembly 31 and the joint member 32. FIG. 5 is a diagram illustrating the shape of the joint member 32, wherein FIG. 5(a) is a front view, FIG. 5(b) is a side view, FIG. 5(c) is a rear view, and FIG. 5(d) is a sectional side view.

[0030] The flange member 37 has a cylindrical shape and extends in the axial direction of the short-length fiber 35, and one end of the flange member 37 is securely fitted to the other end portion of the ferrule 36. The short-length fiber 35 extends through the flange member 37. The flange member 37 includes a flange 37a that projects in a direction that crosses the axial direction of the short-length fiber 35. The flange 37a is brought into contact with a projection formed on the inner wall surface of the plug housing 33, so that the ferrule assembly 31 is positioned. The inner diameter of the flange member 37 is sufficiently greater than the diameter of the short-length fiber 35. The gap between the flange member 37 and the short-length fiber 35 is filled with a resin 38 that holds the short-length fiber 35. The resin 38 is composed of a resin material such as an epoxy resin or an acrylic resin.

[0031] The joint member 32 is provided to fix the metal tube 20 to the ferrule assembly 31. As illustrated in FIG. 5, the joint member 32 has a substantially cylindrical shape, and includes a front portion 32a having a first inner diameter L1 on one side thereof and a rear portion 32b having a second inner diameter L2, which is smaller than the first inner diameter L1, on the other side thereof. The other end portion of the flange member 37 is inserted into the front portion 32a, so that the joint member 32 and the flange member 37 are securely fitted together. The proximal end portion of the metal tube 20 is inserted into the rear portion 32b. (The rear portion 32b of the joint member 32, that is, a portion of the joint member 32 into which the metal tube 20 is inserted, has a constant inner diameter and a constant outer diameter. In other words, the area of the cross section of this portion that is perpendicular to the longitudinal direction is constant.) The short-length fiber 35 extends through the front portion 32a and the rear portion 32b. The joint member 32 is made of a material such as SUS304.

[0032] The length of the joint member 32 in the axial direction of the short-length fiber 35 is preferably such that the joint member 32 can be disposed in the plug housing 33. However, as long as the joint member 32 is disposed in a bonding member (member that covers the optical connector 30 that rotates at a high speed) that is bonded to the rotary joint, the joint member 32 may have a length such that the joint member 32 projects from the plug housing 33.

[0033] When the OCT catheter 1A is used, the optical connector 30 is rotated at a high speed. The rotating force is applied to the interior member 10 through the metal tube 20. Depending on the material and structure of the metal tube 20, resonance may occur at the proper angular frequency. Therefore, the joint member 32 preferably has such a length that the resonance can be prevented.

[0034] FIG. 6 is a sectional view of the optical connector 30 in the longitudinal direction according to a modification. The OCT catheter 1A further includes a tube housing 41. The tube housing 41 is a tubular body that covers the interior member 10 and the optical connector 30. One end of the tube housing 41 is fixed to the OCT system. Although the interior member 10 and the optical connector 30 are rotated with respect to the OCT system, the tube housing is stationary and does not rotate. The gap between the tube housing 41 and the interior member 10 is filled with a liquid, such as a physiological saline solution.

[0035] A support 42, which supports the interior member 10 or the metal tube 20, is disposed in the tube housing 41. In many cases, the support 42 holds the metal tube 20. In one embodiment, the support 42 is a stop valve that prevents the above-described liquid from flowing into the optical connector 30. To prevent the metal tube 20 from resonating, the length of the joint member 32 is preferably set such that the distance L between the other end 32c of the joint member 32 and the support 42 is outside a range in which the metal tube 20 resonates when the rotational speed of the optical connector 30 is within an operational rotational speed range (for example, 0 rpm to 12000 rpm).

[0036] The distance L at which the metal tube 20 resonates can be determined as follows. That is, let L be the distance between the other end 32c of the joint member 32 and the support 42, E be the flexural rigidity (Young's modulus) of the metal tube 20, I be the second moment of area of the metal tube 20, i be the order number of the resonance, ρ be the density of the metal tube 20, and A be the area of cross section of the metal tube 20 that is perpendicular to the center axis, the proper angular frequency p_i of the metal tube 20 can be determined by the following Equation (1).

$\begin{array}{cc}{p}_i={\left(\frac{\mathrm{\pi }}{L}\right)}^2\sqrt{\frac{\mathrm{EI}}{\rho A}}& \left(1\right)\end{array}$

[0037] As the distance L increases, the resonant frequency decreases. In Equation (1), the range of the distance L at which the metal tube 20 resonates can be determined by substituting the operational rotation frequency of the optical connector 30 for the proper angular frequency p_i and calculating the distance L corresponding to the operational rotation frequency. The length of the joint member 32 is preferably set such that the distance L is outside the range. Since the support 42 is fixed to the tube housing 41, the support 42 is stationary during the pull-back operation of the interior member 10. Therefore, the distance L changes as the joint member 32 is moved in the axial direction in the pull-back operation. Such a change is preferably taken into consideration when determining the range of the distance L. More specifically, the distance of the joint member 32 is preferably determined so that the proper angular frequency p_i is greater than or equal to 1.25 times the operational rotation frequency, in other words, so that the operational rotation frequency is smaller than 0.8 times the proper angular frequency. More preferably, the metal tube 20 is made of a material that is not easily plastically deformed (for example, SUS304) to reduce damage to the metal tube 20 caused by the resonance.

[0038] FIG. 7 is a sectional view of the optical connector 30 in the longitudinal direction according to another modification. The tube housing 41 includes a portion having a first inner diameter D1 and a portion (narrow portion) having a second inner diameter D2 that is smaller than the first inner diameter D1 in a region between the other end 32c of the joint member 32 and the support 42. In this case, the narrow portion may be regarded as another support 41a. The distance L may be determined as the distance between the other end 32c of the joint member 32 and the support 41a.

[0039] FIG. 8 is a conceptual diagram illustrating a spliced portion S formed by fusion-splicing the proximal end of the optical fiber 14 (first optical fiber) contained in the interior member 10 and the other end of the short-length fiber 35 (second optical fiber). The OCT catheter 1A further includes the spliced portion S. The spliced portion S is disposed in the metal tube 20, and is protected by the metal tube 20 so that breakage thereof does not occur. Preferably, a protecting member for protecting a glass fiber included in the optical fiber 14 and a glass fiber included in the short-length fiber 35 is provided in a section where the glass fibers are exposed. The protecting member may have various structures, such as a tube fixed with an adhesive, a heat-shrinkable tube, or a curing agent applied by using a pen or the like.

[0040] FIG. 9 is a flowchart of a method for manufacturing the OCT catheter 1A. In a first step S10, a plurality of ferrule assemblies 31 including short-length fibers 35 having different lengths are prepared (step S11). Next, among the ferrule assemblies 31, a ferrule assembly 31 including a short-length fiber 35 having a certain length (first length) is selected (step S12). Then, the optical fiber 14 is cut so that the sum of the lengths of the optical fiber 14 and the short-length fiber 35 is equal to a predetermined length, that is, an optical path length suitable for observation of interference waves (step S13). Then, one end of the optical fiber 14 and the other end of the short-length fiber 35 are fusion-spliced together to form the spliced portion S (step S14).

[0041] In the first step S10, there is a possibility that the process of cutting the optical fiber 14 (step S13) or the fusion splicing process (step S14) will fail (No in step S15). In such a case, a ferrule assembly 31 including a short-length fiber 35 having a second length, which is longer than the first length, is selected (step S12). Then, the optical fiber 14 is cut again so that the sum of the lengths of the optical fiber 14 and the short-length fiber 35 is equal to the predetermined length (step S13), and the spliced portion S is formed again (step S14).

[0042] In the first step S10, the optical path length of the optical fiber 14 and the short-length fiber 35 or the fusion-spliced state of the spliced portion S may be inspected (step S16). Also when the inspection result shows that the optical path length of the optical fiber 14 and the short-length fiber 35 is outside the allowable error range or that the fusion-spliced state is not satisfactory, a ferrule assembly 31 including a short-length fiber 35 having the second length, which is longer than the first length, is selected (step S12). Then, the optical fiber 14 is cut again so that the sum of the lengths of the optical fiber 14 and the short-length fiber 35 is equal to the predetermined length (step S13), and the spliced portion S is formed again (step S14).

[0043] After the first step S10, in a second step S20, the spliced portion S is inserted into the metal tube 20, and the metal tube 20 is attached to the ferrule assembly 31 by using the joint member 32. After that, the ferrule assembly 31 is placed in the plug housing 33, and the outer housing 34 is attached. Thus, the OCT catheter 1A is completed.

[0044] The advantageous effects of the above-described OCT catheter 1A and the method for manufacturing the OCT catheter 1A will be described. According to the OCT catheter 1A and the assembly method thereof, an optical fiber having a ferrule-side end surface that is polished in advance may be used as the short-length fiber 35, and it is not necessary to directly polish the optical fiber 14 contained in the interior member 10. Therefore, the assembly process can be easily carried out in a short time. In addition, a component of an SC optical connector may be used as the ferrule assembly 31 including the short-length fiber 35, so that the manufacturing cost may be reduced.

[0045] In addition, in the OCT catheter 1A, the spliced portion S is disposed in the metal tube 20. In the method for manufacturing the OCT catheter 1A, the spliced portion S is inserted into the metal tube 20 in the second step S20. Thus, the spliced portion S is effectively protected by the metal tube 20, and the risk of breakage of the spliced portion S can be reduced.

[0046] When a component of an SC optical connector is simply used as the ferrule assembly 31, the following problem occurs. FIG. 10 is a conceptual diagram illustrating the problem, and schematically illustrates the interior member 10, the metal tube 20, and the ferrule assembly 31. As illustrated in FIG. 10(a), assume that the short-length fiber 35 and the optical fiber 14 are fusion-spliced together to form the spliced portion S. If the fusion splicing process fails, the optical fiber 14 needs to be cut and fusion-spliced again to the short-length fiber 35 of another ferrule assembly 31. However, if the optical fiber 14 becomes too short as a result of the process of cutting the optical fiber 14, as illustrated in FIG. 10(b), the sum of the optical path lengths of the optical fiber 14 and the short-length fiber 35 becomes smaller than the predetermined length. Such an interior member 10 cannot be used. The interior member 10 is very expensive, and it is preferable to avoid the situation where the interior member 10 becomes unusable. The above-described problem also occurs when the process of cutting the optical fiber 14 fails.

[0047] Accordingly, in the manufacturing method of the present embodiment, when the process of cutting the optical fiber 14 or the fusion splicing process fails in the first step S10, a ferrule assembly 31 including a longer short-length fiber 35 is selected. Then, the optical fiber 14 is cut and the spliced portion S is formed again. Accordingly, as illustrated in FIG. 10(c), the sum of the optical path lengths of the optical fiber 14 and the short-length fiber 35 may be set to the predetermined length, and the interior member 10 can be used continuously.

[0048] In addition, in the OCT catheter 1A, the optical connector 30 includes the tubular flange member 37, one end of which is fixed to the ferrule 36 such that the short-length fiber 35 extends therethrough, and the tubular joint member 32, one end of which is fitted to the other end of the flange member 37. The metal tube 20 is inserted into and fixed to the joint member 32 at the other end of the joint member 32. Since the OCT catheter 1A is structured as described above, the metal tube 20 can be securely fixed and does not easily come into contact with the spliced portion S, so that the risk of breakage of the spliced portion S can be further reduced.

[0049] The OCT catheter 1A includes the tube housing that covers the interior member and the optical connector and that is stationary when the interior member and the optical connector rotate, and a support that is attached to an inner section of the tube housing and that supports the tube. The length of the joint member 32 is set such that the distance L between the other end 32c of the joint member 32 and the support 42 is outside the range in which the metal tube 20 resonates when the rotational speed of the optical connector 30 is within the operational rotational speed range. Thus, vibration due to resonance of the metal tube 20 can be prevented and burden on the subject can be reduced.

[0050] FIG. 11 is a conceptual diagram illustrating another example of a structure for fixing the ferrule assembly 31 to the metal tube 20 as a modification of the above-described embodiment. In this modification, the gap between the flange member 37 and the short-length fiber 35 is not filled with a resin, and the metal tube 20 is inserted into and fixed to the flange member 37. One end of the metal tube 20 is in contact with the other end surface of the ferrule 36. Also in this case, similar to the above-described embodiment, the assembly process can be easily carried out in a short time. In addition, the manufacturing cost can be reduced. Furthermore, since the spliced portion S is disposed in the metal tube 20, the spliced portion S is effectively protected by the metal tube 20, and the risk of breakage of the spliced portion S can be reduced.

[0051] The flange member 37 included in the ferrule assembly 31 for an SC connector is short, and therefore there may be a case in which the metal tube 20 cannot be securely fixed to the flange member 37. When the metal tube 20 cannot be securely fixed, there is a risk that the metal tube 20 will become unstable during high-speed rotation of the OCT catheter 1A. In such a case, the ferrule assembly 31 and the metal tube 20 may be fixed to each other by using the joint member 32 as in the above-described embodiment.

[0052] FIG. 12 is a conceptual diagram illustrating the shape of a joint member 43 as another modification of the above-described embodiment. FIG. 12(a) is a sectional side view of the joint member 43, FIG. 12(b) is a sectional view taken along line XIb-XIb, and FIG. 12(c) is a sectional view taken along line XIc-XIc. The optical connector 30 may include the joint member 43 instead of the joint member 32. The joint member 43 includes a rear portion 43b into which the metal tube 20 is inserted. The area of a cross section A2 of the rear portion 43b at the other-end side (FIG. 12(c)), the cross section A2 being perpendicular to the axial direction of the metal tube 20, is smaller than the area of a cross section A1 of the rear portion 43b at the one-end side (FIG. 12(b)), the cross section A1 being perpendicular to the axial direction of the metal tube 20. More specifically, a tapered portion 43c having an outer diameter that gradually decreases from one end toward the other end is disposed between the one end and the other end of the rear portion 43b. A portion 43d between the tapered portion 43c and the one end has an outer diameter D1, and a portion 43e between the tapered portion 43c and the other end has an outer diameter D2 (<D1).

[0053] In the metal tube 20, stress concentration occurs and maximum bending stress is applied at the boundary between the portion held by the joint member and the portion that is not held (that is, in a region near the other end of the joint member). In this modification, the flexural rigidity of the rear portion of the joint member decreases toward the other end, so that the stress concentration on the metal tube 20 can be reduced and damage to the metal tube 20 can be reduced accordingly.

[0054] The shape of the joint member according to the present modification is not limited to that illustrated in FIG. 12. FIG. 13 is a conceptual diagram illustrating a joint member 44 having another shape according to the present modification, and is a sectional side view of the joint member 44 in the axial direction. The joint member 44 includes a rear portion 44b including a tapered portion 44c that extends to the other end of the joint member 44. Also in this case, the effects of the present modification can be obtained.

[0055] The OCT catheter and the method for manufacturing the OCT catheter according to preferred embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and various changes may be made without departing from the scope thereof. For example, in the above-described embodiments, the optical connector is a fusion splice SC connector. However, the optical connector may instead be a fusion splice connector other than the fusion splice SC connector. In addition, although a metal tube is described as an example of a tube that guides the interior member in the above-described embodiments, the tube may instead be made of other materials, such as a resin.