Multi-core optical fiber and elongated device for medical intervention applications

Abstract

A multicore optical fiber (10) configured for optical shape sensing. The fiber (10) includes a cladding (12) and a plurality of cores (14, 16, 18, 20) embedded in the cladding (12). The cores (14, 16, 18, 20) each have a reflective strain-sensitive structure (21) responsive to strain in the fiber (10). The cladding (12) includes a main section (22) along a length of the fiber (10) and a distal tip section (24) disposed distal of the main section (22). The main section (22) has a first width along a first axis transverse to a longitudinal axis of the fiber (10) and a first number of cores, and the tip section (24) has a second width along a second axis parallel to the first axis and a second number of cores. The second width is reduced relative to the first width such that a bending stiffness of the tip section (24) about a bending axis orthogonal to the second axis is lower than a bending stiffness of the main section (22) about a bending axis orthogonal to the first axis. Also disclosed is an elongate device for medical intervention applications including such a multicore optical fiber.

Description

Technical Field

[0001] This invention generally relates to the field of optical shape sensing technology (also known as Fiber Optic RealShape (FORS) technology). Specifically, this invention relates to multi-core optical fibers and elongated devices including multi-core optical fibers for medical interventional applications. Background Technology

[0002] Fiber Optic True Shape (FORS) technology is a shape sensing and reconstruction technique used in elongated devices such as guidewires to enable accurate, three-dimensional, and real-time visualization of the device, allowing for effective navigation during minimally invasive endovascular procedures without X-ray guidance. Reducing X-ray radiation exposure during such procedures is beneficial for patients, physicians, and staff.

[0003] FORS technology uses a shape-sensing-enabled elongated device (such as a guidewire) and a measurement system (which typically includes a light source and an optical detector compatible with the shape-sensing-enabled elongated device) for use in surgery, as well as a signal processing unit and a user interface for viewing and tracking the visualized elongated device.

[0004] FORS-enabled devices typically include an integrated twisted multicore glass fiber with a sensor that can be configured as a distributed fiber Bragg grating (FBG) sensor. Light from a light source is used to interrogate the sensor, and the reflections are analyzed to determine the local deformation of each segment of the fiber, allowing the complete three-dimensional shape to be reconstructed. In this way, the entire shape of the elongated device can be reconstructed and visualized in real time during surgery. FORS-enabled devices can be visualized against the background of the patient's anatomy by overlaying images (such as CT scans and X-rays) acquired before or during surgery. Therefore, the number of images is significantly reduced compared to X-ray-guided surgery, which requires a new X-ray image each time the elongated device needs to be visualized, resulting in a significant reduction in X-ray dose.

[0005] The applicant of this application has developed guidewires and catheters that enable FORS, which have been successfully used in complex aortic interventional procedures, particularly fenestrated endovascular aortic aneurysm repair (FEVAR) and / or branched endovascular aortic aneurysm repair (BEVAR) and peripheral endovascular lesion repair (EVPLR).

[0006] In complex aortic procedures, the mechanical requirements for the distal segment of the guidewire used in conventional procedures do not limit the use of brittle glass fiber sensors that extend to the distal end of the slender device, because navigation is typically within large blood vessels (such as the aorta) where the guidewire navigates freely within the vessel and usually does not encounter obstructions.

[0007] In other procedures, such as various peripheral surgeries and the treatment of peripheral artery disease (PAD), using a slender device with FORS can also be beneficial in reducing radiation dose. However, in these types of surgeries, the vessel diameter is much smaller, and the navigation trajectory is often very tortuous, i.e., with many bends, and potentially requiring approaching many bifurcations to reach the target location, often involving acute angles that the slender device must traverse. Furthermore, these smaller vessels are more vulnerable and can be damaged by the tip of the slender device. Especially in PAD, angioplasty techniques require traversing the narrowed or occluded portion of the vessel. For more severe occlusions, traversing the narrowed or occluded portion of the vessel requires force, and sometimes the tip of the device prolapses, i.e., the device forms a loop and the tip folds back onto itself—a phenomenon also known as “knuckling”—resulting in very sharp bending at the tip of the device, i.e., a bending radius <1 mm. In these cases, the tip of the device must also be strong enough to withstand this deformation.

[0008] For FORS-enabled devices (such as guidewires) used in peripheral interventional procedures, the device tip must be soft and flexible enough to allow for easy navigation through sharp bends and acute-angled bifurcations. For example, the tip load of the combination of the device's internal fiber and the outer shell tip must not exceed the limits required for safe navigation (i.e., without damaging blood vessels), which is approximately 2–4 grams of force for guidewires used in peripheral procedures.

[0009] Moreover, during these procedures, the curvature of the optical fiber can become high enough to impede shape sensing, or even exceed the maximum curvature that the glass fiber can withstand, causing the glass material to fail during use, i.e., break or shatter.

[0010] Specifically, during procedures requiring navigation through complex anatomical structures and / or through narrow lesions or occlusions, the forces acting on the device's tip can cause deformation, which is too extreme for glass fibers to handle, especially when the tip forms a loop or prolapses. Glass fiber breakage not only hinders the use of FORS (Forward-of-Resistance System) techniques, but can also lead to patient safety issues if glass fragments potentially damage the internal structure of the device tip, further altering its mechanical properties.

[0011] At the same time, even in such challenging environments (involving large deformations due to the formation of rings and prolapse, resulting in sharp bending radii), the shape and orientation of the end of the slender device must still be reconstructed as accurately as possible using FORS technology, so that the need for X-ray guidance can still be avoided.

[0012] US 2012 / 099112 A1, US 11135092 B2, and US 2013 / 41670 A1 disclose optical fibers in which a portion of the cladding of the optical fiber is removed along its length. However, these optical fibers are not suitable for solving the aforementioned technical problems. Summary of the Invention

[0013] One object of the present invention is to provide a multi-core optical fiber configured for optical shape sensing, particularly for use in elongated devices for medical interventional applications, which are suitable for surgeries that must navigate through tortuous anatomical structures and / or pass through narrow lesions or occlusions, while allowing reconstruction of the shape and orientation of the end region of the optical fiber.

[0014] Another object of the present invention is to provide an elongated device for medical interventional applications that is suitable for procedures that must navigate through tortuous anatomical structures and / or pass through narrow lesions or occlusions, while allowing the shape and orientation of the distal region of the elongated device to be reconstructed with sufficient accuracy using FORS technology.

[0015] In a first aspect of the invention, a multi-core optical fiber configured for optical shape sensing is provided, the multi-core optical fiber including a cladding and a plurality of cores embedded in the cladding, each core having a reflective strain-sensitive structure responsive to strain in the optical fiber, wherein the cladding includes a main segment along the length of the optical fiber and a distal end segment disposed distal to the main segment, the main segment having a first width and a first number of cores along a first axis transverse to the longitudinal axis of the optical fiber, and the end segment having a second width and a second number of cores along a second axis parallel to the first axis, wherein the second width is reduced relative to the first width such that the bending stiffness of the end segment about a bending axis orthogonal to the second axis is lower than the bending stiffness of the main segment about a bending axis orthogonal to the first axis.

[0016] This invention is based on the idea of ​​reducing the thickness of the multi-core fiber in the distal end section of a multi-core fiber along at least one axis, so that the end section of the multi-core fiber according to the invention can withstand a smaller bending radius, i.e., a higher curvature, compared to conventional multi-core fibers. The main section of the multi-core fiber is preferably optimized for high-quality shape sensing, for example, it is provided by conventional 125 μm diameter silica glass fiber, because the main section does not undergo high deformation during use. On the other hand, the distal end section of the fiber has reduced bending stiffness and can therefore be bent about at least one axis with a smaller bending radius or a higher curvature compared to the main section. The bending stiffness of the distal end section of the fiber can be reduced compared to the bending stiffness of the main section along only one axis, which may be the preferred bending direction, or along more than one axis (e.g., along two perpendicular axes), where in this case, the width of the distal end section can be reduced relative to the width of the main section along more than one axis (e.g., along two perpendicular axes).

[0017] The term “width” as used in the context of the distal end segment of an optical fiber in this disclosure should be understood as the thickness of the distal end segment, i.e., as used herein as a synonym for “thickness”. The term “width” as used in the context of the main segment of an optical fiber in this disclosure should be understood as the diameter of the main segment, i.e., as used herein as a synonym for “diameter”.

[0018] The reflective strain-sensitive structure etched into the core of the optical fiber may include a fiber Bragg grating.

[0019] In another aspect of the invention, an elongated device for medical interventional applications is provided, comprising: The main section and the distal terminal section together define a lumen along the length of the elongated device; and According to the first aspect, the multi-core optical fiber is arranged in a cavity, wherein the end section of the optical fiber is arranged in the distal terminal section of the elongated device.

[0020] Optionally, the distal end segment of the optical fiber can rotate freely within the lumen of the elongated device.

[0021] Due to the reduced width of the distal end segment of the multi-core optical fiber according to the invention, the elongated device is suitable for surgeries that must navigate through tortuous anatomical structures and / or pass through narrow lesions or occlusions, while allowing the shape and orientation of the end region of the elongated device to be reconstructed with sufficient accuracy using FORS technology.

[0022] Preferred embodiments of the invention are defined in the dependent claims. It should be understood that the claimed multi-core optical fiber and the claimed elongated device for medical applications have similar and / or identical preferred embodiments, especially those defined in the dependent claims and disclosed herein.

[0023] In an embodiment of the multi-core optical fiber according to the invention, the cladding of the end segment may have at least one flat side surface along the length of the end segment.

[0024] Flattening at least one side surface of the end section of a multi-core optical fiber reduces the bending stiffness of the end section around at least one bending axis orthogonal to the width of the end section along its reduced axis. Furthermore, flattening the side surface of the distal end section of the multi-core optical fiber is advantageous because it can be achieved using simple techniques such as laser ablation, milling, or grinding.

[0025] Preferably, the cladding of the end segment may have a first flat side surface and a second flat side surface along the length of the end segment, wherein the first flat side surface is opposite to the second flat side surface.

[0026] This embodiment allows for a further reduction in the thickness of the fiber end segment, and thus a reduction in the bending stiffness of the fiber end segment, to further reduce the minimum bending radius of the distal end segment or increase the maximum curvature of the distal end segment, without the risk of distal end segment breakage or fracture. Furthermore, this embodiment is advantageous if the distal end segment should have a preferred bending direction in two opposite bending directions around the same bending axis.

[0027] In another embodiment, the second number of fiber cores may be equal to the first number of fiber cores.

[0028] This embodiment is advantageous because, despite the reduction in the thickness of the end section, the strain sensitivity of the distal end section of the multi-core fiber is not reduced compared to the strain sensitivity of the main section. When the width of the distal end section is reduced along at least one axis, the reduction in the width of the distal end section is performed such that, in this embodiment, the fiber core in the distal end section remains intact.

[0029] In another embodiment, the second number of fiber cores is equal to or greater than 1, but less than the first number of fiber cores.

[0030] In this embodiment, the distal end section includes at least one fiber core or even only one fiber core, while the main section includes a greater number of fiber cores than the end section of the fiber. The advantage of this embodiment is that the thickness or width of the distal end section of a multi-core fiber can be made very small, such that only a small number of fiber cores (e.g., only one fiber core) remain in the distal end section. This reduces the strain sensitivity of the distal end section, but this embodiment allows for even smaller bending radii of the distal end section without the risk of distal end section breakage or fracture.

[0031] In the context of the preceding embodiment, another embodiment provides that a first subset of the core of the main segment terminates at or near the start of the end segment, and a second subset of the core of the main segment extends into the end segment.

[0032] For example, the main segment can have four cores: three outer cores and one central core, while the distal end segment retains only one or two cores. Alternatively, the main segment can have a total of seven cores: three outer cores at a wider radial distance from the fiber's central axis, one central core, and three cores located between the central and outer cores. The three outer cores can terminate at the start of the distal end segment, but the four remaining cores extending into the distal end segment allow for full-shape 3D reconstruction of the multi-core fiber.

[0033] It is advantageous if there is no or only a very small refractive index step at the transition of the fiber core from the main section to the distal end section (which may cause reflections, which in turn may degrade strain measurements). In other words, one or more fibers extending from the main section to the distal end section preferably have a continuous core.

[0034] In another embodiment, the core of a first subset of the main segment terminates at a certain angle, thereby reducing light reflection.

[0035] In this embodiment, the front surface of the fiber core of the main segment, which terminates at the beginning of the distal end segment (i.e., at the distal end of the main segment), is not orthogonal to the longitudinal axis of the optical fiber. This is advantageous because it reduces or even avoids back reflection of interrogation light that may occur at the core / air interface at the distal end of the main segment, and thus improves the signal-to-noise ratio of the shape sensing measurements.

[0036] In another embodiment, one or more of the cores in the end section may be arranged eccentrically relative to the neutral bending plane of the cladding.

[0037] This embodiment is advantageous because even though the number of cores in the distal end segment is reduced compared to the number of cores in the main segment, one or more cores in the end segment can still transmit bending information of the distal end segment due to their eccentricity relative to the neutral bending plane of the end segment cladding.

[0038] In another embodiment, the core of the main segment includes a central core disposed centered relative to the neutral bending plane of the cladding of the main segment, wherein a distal portion of the central core extends into the end segment, and the distal portion of the central core is disposed eccentrically relative to the neutral bending plane of the cladding of the end segment.

[0039] The central core in the main section of an optical fiber is typically insensitive to bending because it is centered relative to the neutral bending plane of the cladding in the main section. However, if the cladding of the terminal section has a reduced width asymmetrically relative to the neutral bending plane of the cladding in the main section, the central core is eccentrically positioned relative to the neutral bending plane of the cladding in the terminal section, making bending strain sensible even in the central core, and thus providing bending information from the terminal section.

[0040] In another embodiment, the end section of the optical fiber may have a bending stiffness about a bending axis, which is 0.05 Nmm. 2 -0.2 Nmm 2 Within the range.

[0041] The bending stiffness of the distal end section within a given range is significantly lower than that of the fiber in the main section. For example, the bending stiffness of a typical 100 μm diameter glass fiber is 0.34 Nmm. 2 Reducing the fiber width decreases the fiber's bending stiffness. For example, removing a 20 μm cladding layer that results in an 80 μm diameter will reduce the bending stiffness to 0.14 N / mm. 2 .

[0042] In addition, the end segments of multi-core optical fibers can have lengths ranging from 1 cm to 5 cm.

[0043] Preferably, the main segment and the end segment are made of a single monolithic optical fiber.

[0044] The overall configuration of the main section and the end section has the following advantages: multi-core fiber can be made from a single fiber, for example by post-processing a standard multi-core fiber, without the need to connect the two fiber components to each other.

[0045] A method for manufacturing multi-core optical fibers according to the present invention may have the following configuration: Provides standard multi-core optical fiber configured for optical shape sensing, and Post-processing is performed on the distal end section of the optical fiber that is exposed to high bending curvature to reduce the width of the distal end section along at least one axis.

[0046] Optionally, post-processing of the distal end segment may include: Laser ablation of a portion of the cladding in the end section removes a portion of the cladding material.

[0047] Optionally, laser ablation may include femtosecond laser ablation.

[0048] Femtosecond laser ablation is a technique that allows for highly precise removal of material while minimizing the heat-affected zone (typically smaller than a few micrometers) around the treated area. Therefore, this form of laser ablation is also known as "cold ablation." This type of processing is advantageous because the reflective strain-sensitive structure etched into the fiber core may decay at higher temperatures, thus reducing the sensitivity of the reflective strain-sensitive structure.

[0049] Optionally, the method may further include: after laser ablation, especially after femtosecond laser ablation, laser processing of the surface of the processed area with a laser pulse on a longer timescale at a lower flux, such that the surface is not ablated, but the thin surface layer on the cladding is melted to form a smooth outer surface of the optical fiber.

[0050] This combination of different laser processing types allows for the creation of smooth ablation surfaces on thinned parts, which improves the mechanical properties (e.g., strain at fracture) of the thinned end segments.

[0051] Furthermore, the conventional xyz manipulation stage of the laser target allows for easy processing to reduce the fiber diameter along at least one axis, thereby reducing the minimum bending radius orthogonal to that axis.

[0052] In other configurations of the method, post-processing of the distal end segment may include milling or grinding the cladding of the end segment to reduce the width of the end segment along at least one axis.

[0053] In some other configurations of this method, the distal end segment of the optical fiber can be processed by thermoforming or stretching. In this case, a reflection strain-sensitive structure (e.g., one or more fiber Bragg gratings) must be (re)written into the end segment affected by the high-temperature processing.

[0054] Alternatively, the end segment can be manufactured as a separate component and connected to the main segment of the optical fiber.

[0055] When the end segments are made from a single piece of fiber and connected to the main segment of the fiber, it is advantageous that the end segments can be pre-set with a desired cross-sectional shape, i.e., a decreasing width along at least one axis. In this way, a set of distal end segments can be kept in stock. The end segments can be processed individually by any method, including, for example, laser processing or thermoforming, or cutting from a longer fiber that is stretched differently from the main segment. The distal end segments can be connected to the main segment by splicing, wherein the common core of the main segment and the distal end segments must be aligned at the splice.

[0056] In an embodiment of the elongated device according to the invention, a strip may be arranged along the inner wall of the terminal section of the housing, the strip having a thickness in the direction of the thickness axis and a width in the direction of the width axis, the thickness being less than the width, and the multi-core optical fiber according to the invention is arranged relative to the strip such that the second axis is parallel to the thickness axis.

[0057] In this embodiment, the thinning axis of the multi-core optical fiber coincides with the thin axis of the strip that provides mechanical stability at the distal end of the elongated device. The difference in bending resistance between the thick and thin axes of the strip will cause a preferred bending direction at the end of the device, causing the optical fiber to bend only around the thinner dimension. For example, a strip with a width dimension three times larger than its thickness dimension has 81 times greater bending resistance in the width direction than in the thickness direction, making the optical fiber safer to prevent accidental bending in the wrong direction (i.e., the direction consistent with the thicker dimension of the optical fiber). In this embodiment, it is advantageous if the distal end portion of the optical fiber does not rotate freely within the cavity of the elongated device, because the housing of the elongated device has a preferred bending direction due to the strip. Therefore, in this embodiment, the distal end section of the optical fiber can be fixed. Attached Figure Description

[0058] These and other aspects of the invention will become apparent from the embodiments described below, and will be illustrated with reference to the embodiments described below. In the following figures: Figure 1 A length of an example of a multi-core optical fiber is shown; Figure 2 An embodiment of a multi-core optical fiber is shown according to... Figure 3 Side view of arrow II in the image, where... Figure 2 The fiber core of the multi-core optical fiber is omitted in the text; Figure 3 It shows Figure 2 A front view of a multi-core optical fiber, showing the fiber core; Figure 4 An embodiment of a multi-core optical fiber is shown according to... Figure 5 Side view of arrow IV in the image, where... Figure 4 The fiber core of a multi-core optical fiber is not shown in the diagram. Figure 5 It shows Figure 4 A front view of the multi-core optical fiber; and Figure 6 A side view of an embodiment of an elongated device including a multi-core optical fiber is shown. Detailed Implementation

[0059] Figure 1 A length of multi-core optical fiber 10 configured for use in FORS technology is shown. The multi-core optical fiber 10 includes a cladding 12 and a plurality of cores 14, 16, 18, and 20. Core 14 is a central core arranged on and along the central axis of the optical fiber 10, and cores 16, 18, and 20 are outer cores arranged radially separated from the central core 14. The outer cores 16, 18, and 20 are spirally wound around the central core 14. The outer cores 16, 18, and 20 are angularly spaced from each other around the longitudinal central axis of the optical fiber 10. For a quantity of three outer cores, the angular spacing between adjacent cores is typically 120°. The multi-core optical fiber 10 may have fewer than four cores or more than four cores. For example, the multi-core optical fiber 10 may include seven cores, including three radially outer cores, one central core, and three other cores located in intermediate radial positions between the three outer cores and the central core.

[0060] Each of the fiber cores 14, 16, 18, and 20 includes a reflective strain-sensitive structure 21, which in Figure 1 The multi-core fiber 10 is illustrated exemplarily with respect to fiber core 20. The reflective strain-sensitive structure may include one or more fiber Bragg gratings (FBGs). The reflective strain-sensitive structure 21 (e.g., one or more FBGs) responds to strain in the fiber 10. The multi-core fiber 10 can sense strain, which may be axial, bending, or torsional strain, thereby enabling 3D shape reconstruction of the multi-core fiber 10 to be performed using optical interrogator systems known in the art. When the multi-core fiber 10 is used in elongated devices such as guidewires or conduits, 3D shape reconstruction of the elongated device can thus be provided.

[0061] It has been demonstrated that typical multi-core fibers with cladding diameters in the range of, for example, 100 μm–125 μm, provide good strain sensitivity and are therefore well-suited for FORS (Form-of-Right) techniques. In interventional medical applications, such as peripheral surgery and the treatment of peripheral artery disease, slender devices equipped with multi-core fibers and enabling Fiber-of-Right-Shape (FORS), especially FORS-enabled guidewires, are beneficial for reducing radiation dose. However, in these types of procedures, the diameter of the vessels is very small, and the navigation trajectory is often very tortuous (i.e., with many bends), and it is potentially necessary to approach many bifurcations to reach the target location, often involving slender devices and acute angles through which the multi-core fibers must therefore traverse. Furthermore, these smaller vessels are more vulnerable and can be damaged by the ends of slender devices. Especially in PADs, angioplasty techniques require traversing narrowed or occluded portions of the vessel. For more severe occlusions, this often requires force, and sometimes the end of the guidewire prolapses, i.e., the wire forms a loop and the end folds back onto itself; this phenomenon is also known as “joint flexion,” which results in very sharp bending at the end of the device, for example, a bending radius <1 mm.

[0062] Wang, Jian-Bo et al.'s "An Effective Guideline Looping Technique for the Recalalization of Occlusive Segments of Infrapopitual Vessels" (Korean Journal of Radiology 11 (2010), pp. 441-448) describes this transluminal angioplasty technique. As described herein, a hydrophilic guidewire is inserted into a proximal branch of the vessel, and then a 'U' shape is formed by continuously rotating and advancing the guidewire. The looped guidewire is then advanced into and onto the occluded segment of the vessel, after which a catheter is passed along the guidewire across the occluded segment. The guidewire described herein is not equipped with an optical fiber.

[0063] When an elongated device (such as a guidewire) includes an optical fiber extending to the distal end of the elongated device, and when the optical fiber undergoes loop formation as described above, the curvature of the optical fiber can become too high, thus hindering shape sensing, or when the curvature of the optical fiber becomes even higher than the maximum curvature that the glass fiber can withstand, this causes the glass material of the optical fiber to fail, i.e., the optical fiber may break or shatter.

[0064] These technical problems are solved by a new design of the multi-core fiber embodiment described below.

[0065] Figure 2 and Figure 3 An embodiment of a multi-core optical fiber is shown, wherein in Figure 2 and Figure 3 In and Figure 1 Elements that are the same as, similar to or equivalent to the elements in the text are used with Figure 1 The same reference numerals are used to mark the figures.

[0066] Figure 2 and Figure 3 A multi-core optical fiber 10 is shown, comprising a cladding 12 and multiple cores 14, 16, 18, and 20 embedded within the cladding 12. For simplicity, Figure 2 Fiber cores 14, 16, 18, and 20 are not shown. Fiber core 14 is a central core extending longitudinally along the central axis of the cladding 12, and fiber cores 16, 18, and 20 are outer cores arranged at a certain radial distance from the central core 14. Fiber cores 14, 16, 18, and 20 are equipped with reflective strain-sensitive structures responsive to strain in the optical fiber 10, as referenced above. Figure 1 The aforementioned strain-sensitive structure can be a fiber Bragg grating.

[0067] Cladding 12 includes a proximal main segment 22 along the length of optical fiber 10 and a distal end segment disposed on the distal side of the main segment 22. The distal end segment 24 has a distal end 26. The term "distal" segment refers to a segment of optical fiber 10 that is the leading segment of the optical fiber in use when the optical fiber is advanced (with an instrument equipped with the optical fiber), such as in medical applications. Correspondingly, the term "proximal" segment refers to the tail segment of the optical fiber.

[0068] Main segment 22 may have the following characteristics: Figure 1 The structure shown. Main segment 22 has an axis X along the longitudinal axis transverse to the optical fiber 10. M Width W M In the context of the main segment 22 in this disclosure, the term "width" should be understood as the diameter of the main segment 22, i.e., used herein as a synonym for "diameter". Furthermore, the main segment 22 has a first number of fiber cores, which in this embodiment are four fiber cores 14, 16, 18, and 20. Figure 3 In the center, circle 28 symbolizes the spiral winding arrangement of cores 16, 18, and 20 (i.e., the outer core), for example... Figure 1 As shown.

[0069] During use in interventional procedures (such as peripheral procedures, such as the treatment of peripheral artery disease), the distal terminal segment 24 with high curvature (i.e., small radius of curvature) can be exposed along the axis X. M axis X T With width W T The term “width” as used in the context of the distal end segment 24 in this disclosure should be understood as the thickness of the distal end segment 24, i.e., as used herein as a synonym for “thickness”. Thickness W TThe size relative to the diameter W of the main segment 22 M The size is reduced so that the end segment 24 is orthogonal to the axis X. T The bending axis Y T The bending stiffness is lower than that of the main section 22 around the bending axis Y. M Parallel and with axis X M Orthogonal bending axis Y M The bending stiffness. Bending axis Y T and Y M Perpendicular to Figure 2 The drawing plane in the middle.

[0070] exist Figure 2 In one embodiment, the width or thickness of the end segment 24 is determined only along one axis (i.e., axis X). T The length of the end segment 24 decreases along the axis X perpendicular to the axis X. T The thickness of the axis can be the same as the diameter of the main section 22 along that axis.

[0071] exist Figure 3 In the middle, lines 31, 33 and dashed lines 30, 32 show the outer perimeter or surface of the main section 22, and lines 31, 33 and 34, 35 show the outer perimeter or surface of the end section 24.

[0072] Alternatively, the end segment 24 may have a width or thickness that decreases along more than one axis; for example, the width of the end segment 24 may also be along a path perpendicular to axis X. T The axis decreases.

[0073] In this embodiment, the end segment 24 has a corresponding Figure 3 The two flat side surfaces of lines 34 and 35 in the optical fiber 10. The flat surfaces 34 and 35 are opposite to each other with respect to the longitudinal central axis of the optical fiber 10, and specifically, they can be parallel to each other.

[0074] exist Figure 2 and Figure 3 In one embodiment, the end segment 24 has a preferred bending direction, i.e., around the bending axis Y. T The end segment 24 surrounds the curve perpendicular to the bending axis Y. T The stiffness of the bending axis is approximately the same as the higher bending stiffness of the main section 22. Figure 2 In the middle, the end section 24 surrounds the bending axis Y T The bends in two opposite directions are shown by dashed lines.

[0075] Furthermore, in this embodiment, the terminal segment 24 has the same number of cores as the main segment 22, that is, all cores 14, 16, 18, 20 extend into the distal terminal segment 24, preferably to the distal end 26 of the terminal segment 24.

[0076] exist Figure 2 and Figure 3 In one embodiment, the distal end segment 24 is flattened so that it is symmetrical with respect to the longitudinal central axis of the cladding 12.

[0077] Figure 4 and Figure 5 Another embodiment of optical fiber 10 is shown, wherein Figure 4 and Figure 5 fiber 10 and Figure 1 , Figure 2 and Figure 3 The same, similar, or equivalent elements of the optical fiber 10 in the middle are used with Figure 1 , Figure 2 and Figure 3 The same reference numerals are used to mark the figures.

[0078] In the following text, only descriptions will be provided. Figure 4 and Figure 5 The embodiments in the example are relative to Figure 2 and Figure 3 Differences between the embodiments in the text.

[0079] Figure 4 and Figure 5 The end segment 24 of the optical fiber 10 has a length along the axis X T thickness W T ,and Figure 2 and Figure 3 The thickness W of the distal end segment 24 of the optical fiber 10 T In comparison, this thickness W T This is further reduced. Therefore, the distance between the flat surfaces 34 and 35 of the distal end segment 24 is less than [the distance between them]. Figure 2 and Figure 3 The distance in the distal end segment 24 of optical fiber 10. Furthermore, as... Figure 4 and Figure 5 As shown, the distal end segment 24 is asymmetrical with respect to the longitudinal central axis of the cladding 12 of the main segment.

[0080] Furthermore, the number of fiber cores in the terminal section 24 is reduced compared to the number of fiber cores in the main section 22. In this embodiment, in Figure 4At least one fiber core exemplarily shown for fiber core 20 terminates at the beginning of end segment 24 or near the beginning of end segment 24, while fiber cores 14, 16, 18 extend into the distal end segment 24 and terminate at the distal end 26 of end segment 24.

[0081] Figure 5 The width or thickness W of the end segment 24 in other embodiments is shown by dashed line 45. T It can be further reduced so that cores 16 and 18 also terminate at the beginning of end section 24 or near the beginning of end section 24, while only the central core 14 extends into the distal end section 24 and terminates at the distal end 26 of end section 24.

[0082] Like fiber cores 20 and / or 16, 18, the fiber cores terminating at the distal end of the main segment 22 preferably terminate at an angle relative to the longitudinal axis of the fiber 10 to reduce reflections at the front surface of the terminated fiber core back into the fiber core, such as... Figure 4 The example shown is for fiber core 20.

[0083] In this embodiment, the fiber cores 14, 16, and 18 in the distal end segment 24 are arranged eccentrically relative to the neutral bending plane of the cladding of the end segment 24. The neutral bending plane of the end segment 24 is a central plane that is between and parallel to surfaces 34 and 35.

[0084] In another embodiment, the width or thickness W of the end segment 24 T It can be further reduced, as shown on surfaces 44 and 45, such that only one core exists in the end section 24, specifically a central core 14. Preferably, the central core 14 is arranged eccentrically relative to the neutral bending plane of the cladding 12 of the end section 24, wherein the neutral bending plane is an intermediate plane located between and parallel to surfaces 44 and 45 of the end section 24. This means that even the central core 14, which is insensitive to bending deformation in the main section 22, becomes sensitive to bending deformation in the end section 24.

[0085] It can also reduce the width or thickness W of the distal end segment 24. T This causes surfaces 35 and 45 to form the outline of the distal end segment 24. In this case, cores 16 and 18 extend into the distal end segment and are arranged eccentrically relative to the neutral bending plane of the end segment 24, wherein the neutral bending plane is the intermediate plane between surfaces 45 and 35 of the distal end segment 24 and parallel to the intermediate plane between surfaces 45 and 35 of the distal end segment 24.

[0086] Having width or thickness W T The bending stiffness of the end section 24 can be 0.05 N / mm. 2-0.2 Nmm 2 Within this range. For example, a typical 100 μm diameter glass fiber has a thickness of 0.34 Nmm. 2 The bending stiffness. Along axis X in end segment 24. T Reducing the thickness will decrease the bending stiffness of the end segment 24. For example, it will result in a width W of 80 μm. T Reducing the thickness or width of the 20 μm cladding will decrease the bending stiffness to 0.18 Nmm. 2 .

[0087] Preferably, the length of the end segment 24 in all the above embodiments is in the range of 1 cm to 5 cm.

[0088] In the following text, embodiments of the method for producing multi-core optical fiber 10 will be described.

[0089] A standard or conventional multi-core optical fiber is provided. The reduced width W of the end segment 24. T This can be achieved by post-processing the far-end section of a conventional multi-core optical fiber (by laser ablation of the cladding 12 in the far-end section 24, thereby removing the cladding material in the cladding 12 in the far-end section 24).

[0090] Laser ablation can be performed as femtosecond laser ablation. Femtosecond laser ablation is a technique that allows for highly precise removal of material while minimizing the heat-affected zone (typically smaller than a few micrometers) around the treated area (where the material is removed). Therefore, this form of laser ablation is also known as "cold ablation." For example... Figures 2 to 5 In the multi-core fiber of fiber 10, "cold ablation" is advantageous because the reflective strain-sensitive structure (especially in the form of a fiber Bragg grating etched inside fiber 10) may decay at higher temperatures, thereby reducing the sensitivity of the fiber Bragg grating.

[0091] Optionally, the surface of the treated area (e.g., surfaces 34, 35 or 44, 45) can be further laser-treated with longer timescale laser pulses at lower flux, so that the surface is not ablated, but the thin surface layer of cladding 12 is melted and forms a smooth outer surface of fiber 10.

[0092] This combination of different laser processing types allows for the achievement of a smooth ablation surface on the thinned distal end segment 24, which improves the mechanical properties of the thinned distal end segment (e.g., strain at fracture).

[0093] The conventional xyz manipulation stage of the laser target allows for easy manipulation to reduce the width of fiber 10 along one axis, thereby reducing the minimum bending radius orthogonal to that axis, such as... Figures 2 to 5The situation in the embodiments.

[0094] Alternatively, other processing techniques can be used to shape the distal end segment 24, such as milling or grinding, or higher-temperature processing steps, such as thermoforming or stretching, after which a reflective strain-sensitive structure (e.g., a fiber Bragg grating) must be (re)written into the distal end segment of the fiber 10 affected by the high-temperature processing to allow strain sensing using the FBG.

[0095] Alternatively, the distal end segment 24 may be composed of a cross-section having a desired shape (i.e., having a reduced width W). T The fiber is made from individual optical fibers or single optical fibers (with a cross-section). The distal end segment 24 can then be spliced ​​onto a standard optical fiber used to form the main segment 22 of the optical fiber 10. Specifically, a single optical fiber with an eccentric core to allow the export of bending information (preferably in the preferred bending direction) can be spliced ​​onto the main segment 22.

[0096] The distal end segment 24 can be processed individually by any method, including, for example, laser processing or thermoforming or cutting from a long fiber that has been stretched differently, as long as the core in the distal end segment 24 is aligned with the corresponding core in the main segment 22 of the fiber 10.

[0097] In the above embodiments, the outer cores 16, 18, and 20 are preferably twisted into a helix. In this case, the remaining outer cores (such as cores 16, 18, etc.) in the distal end section Figure 5 The effective length will span less than one full twist length, thus limiting the length of the distal end segment 24 according to the twist in the original fiber.

[0098] Alternatively, individual fiber sensor segments with a reduced number of cores can be spliced ​​to the main segment 22 of a multi-core fiber, wherein the cores in the distal end segments may or may not be twisted.

[0099] Figure 6 An embodiment of an elongated device for medical applications is shown, designated by general reference numeral 100. The elongated device 100 includes a longitudinal lumen 102 and a housing 104 surrounding the lumen. The housing has a main section 106 and a distal terminal section 108. The bending stiffness of the terminal section 108 is lower than that of the main section 106 of the housing 104. Figures 2 to 5 One of those shown and as described above, a multi-core optical fiber 10 is arranged in the cavity 102, wherein the end segment 24 of the optical fiber 10 is arranged in the distal end segment 108 of the housing 104.

[0100] exist Figures 2 to 5 In the embodiment, the distal end segment 24 has a preferred bending direction, that is, in Figure 2 and Figure 4 In the drawing plane. To further support this preferred bending direction, a strip 110 can be arranged along the inner wall of the terminal section 108 of the housing 104, the strip 110 having a thickness axis (parallel to the plane). Figure 6 The thickness of element 10 in the drawing plane direction and its width in the width axis direction (perpendicular to the thickness axis) of strip 110, wherein the thickness of element 10 is less than its width, and multi-core fiber 10 is arranged relative to the strip such that the axis X T ( Figure 2 , Figure 4 Parallel to the thickness axis of element 110, or in other words, the distal end section 24 faces the wider side of element 110. The difference in bending resistance in the thickness and width directions of the strip 110 will cause a preferred bending direction of the distal end section 108 of the device 100 around the width axis of element 110, such that the distal end section 24 of the fiber 10 bends only around the thinnest dimension (e.g., the thinnest dimension orthogonal to the distal end section 24). For example, a strip with a width dimension three times larger than its thickness dimension has 81 times greater bending resistance in the width direction than in the thickness direction, making the distal end section 24 of the fiber 10 more intact to avoid accidental bending in the wrong direction (i.e., the direction consistent with the thicker dimension of the distal end section 24, perpendicular to the thickness axis). Figure 2 and Figure 4 The plane in the drawing is curved.

[0101] While it is preferred that the distal end segment 24 rotates freely within the lumen 102 of the elongated device 100, this rotatability of the distal end segment 24 is not required when providing the tape 110 (which provides a preferred bending direction by itself). In contrast, it is advantageous in this case when the distal end segment 24 of the optical fiber 10 is fixed within the lumen 102 of the device 100.

[0102] Below, example values ​​and ranges of preferred bending stiffness for the distal end section 24 for some interventional applications, as well as the thickness W of the distal end section 24, will be provided. T The relevant values ​​and ranges.

[0103] In the first-order approximation, the distal end segment of the guidewire is in Nmm 2 Bending stiffness, expressed in units, is approximately 1 / 10 of the tip load in grams (tip load is a physician-perceived conversion of the "softer / harder" feel of the guidewire tip and is calculated in grams). Typically, the tip load for coronary navigation (non-penetrating) guidewires ranges from 0.5 grams to 2-3 grams: for coronary (anterior) navigation: 0.5-1 gram, therefore bending stiffness is 0.05-0.1 Nmm. 2Within the range; for coronary artery tortuous anatomy navigation: 1.5-3 grams, therefore the bending stiffness is 0.15-0.3 Nmm. 2 Within the range.

[0104] Overall, end load is related to guidewire diameter, with, for example, a 0.035” guidewire being much stiffer than a 0.018” guidewire, and a 0.018” guidewire being stiffer than a 0.014” guidewire.

[0105] For example, a 0.018” diameter navigation guidewire has a typical end load of 1-4 grams (0.1-0.4 Nmm). 2 (Bending stiffness), which is suitable for various peripheral surgeries (e.g., peripheral angiography, angioplasty, thrombectomy, plaque resection, embolization).

[0106] Considering the total bending stiffness of the guidewire tip is 0.05-0.4 Nmm 2 Therefore, the bending stiffness of the optical fiber arranged in the guide wire must be less than the bending stiffness of the end of the guide wire. Typically, the bending stiffness of the optical fiber is no more than half of the bending stiffness of the end of the guide wire.

[0107] The bending stiffness (EI) of a circular cross-section glass optical fiber is as follows:

[0108] For optical fibers with diameters of 125 micrometers and 100 micrometers, the bending stiffness of the fiber is almost equal to (for a diameter of 100 micrometers) or even higher (for a diameter of 125 micrometers) the ideal bending stiffness of the end of a guide wire consisting of an optical fiber and a sheath (usually a coil or other flexible structure type).

[0109] Due to various reasons, including geometric constraints, the coil typically has a bending stiffness equal to that of the fiber inside it. This means that the stiffness required for the fiber to achieve a competitive end load relative to other guidewires without fibers is approximately half the total end bending stiffness of the guidewires; that is, the fiber bending stiffness is in the range of 0.025–0.02 N / mm². 2 Within the range. The table below shows the thickness W in the thinned distal end section (e.g., distal end section 24, having a thickness W on one axis). T Bending stiffness in the preferred bending direction (starting with a typical 125 or 100 micrometer diameter optical fiber):

[0110] The results in the table above demonstrate that, using the principle of thinning the distal end segment (e.g., distal end segment 24) of a conventionally sized optical fiber according to the present invention, the clinically required thickness of approximately 0.025-0.02 Nmm can be achieved. 2 The range.

[0111] Another important reason for reducing the diameter of optical fibers is to allow the fibers to withstand the most abrupt bends without breaking. There are several reasons why the guidewire may experience sharp bends.

[0112] The typical value of fiber strength under dynamic bending conditions during the duration of a typical clinical operation (up to several hours) is about 3 GPa (see Figure 8 in M. Matthewson's "Fiber Optics Reliability and Testing SPIECritical Reviews of Optical Science and Technology" (Volume CR50, pp.3-31, 1993).

[0113] Bending stress and fiber thickness (or W in the distal end segment 24) T The ratio of W to the radius of curvature is proportional. Therefore, a smaller W... T This will allow for a smaller bending radius.

[0114] For a standard 125-micron fiber, a stress limit of 3 GPa translates to a bending radius of approximately 2.9 mm, which is insufficient to produce a 180-degree bend when prolapsed within a typical peripheral blood vessel with a diameter of approximately 2 to 3 mm.

[0115] Thinning will allow for a bending radius of less than 1.5 mm, ensuring that prolapse within small blood vessels of less than 3 mm will not damage the fiber. The table below shows a series of thicknesses W for the distal end segment 24 of the fiber. T Critical bending radius R:

[0116] Desired thinning thickness W at the distal end segment T (Linearly) depends on the minimum radius of curvature that needs to be achieved during the procedure (typically as low as 2-3 mm in peripheral vessels).

[0117] Although the invention has been described and illustrated in detail in the accompanying drawings and the foregoing description, such description and illustration are to be regarded as illustrative or exemplary rather than restrictive; the invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments will be understood and implemented by those skilled in the art in the course of practicing the claimed invention, through a study of the drawings, the disclosure, and the appended claims.

[0118] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude multiple. A single element or other unit can perform the functions of several items recited in the claims. The mere fact that some measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used advantageously.

[0119] Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. A multi-core optical fiber configured for optical shape sensing, comprising: The cladding (12) and a plurality of fiber cores (14, 16, 18, 20) embedded in the cladding (12), each of the fiber cores (14, 16, 18, 20) having a reflective strain-sensitive structure (21) responsive to strain in the optical fiber (10), wherein the cladding (12) comprises a main segment (22) along the length of the optical fiber (10) and a distal end segment (24) disposed distal to the main segment (22), the main segment (22) having a first width and a first number of fiber cores along a first axis transverse to the longitudinal axis of the optical fiber (10), and the end segment (24) having a second width and a second number of fiber cores along a second axis parallel to the first axis, wherein the second width is reduced relative to the first width such that the bending stiffness of the end segment (24) about a bending axis orthogonal to the second axis is lower than the bending stiffness of the main segment (22) about a bending axis orthogonal to the first axis.

2. The multi-core optical fiber according to claim 1, wherein, The cladding (12) of the end segment (24) has at least one flat side surface (34, 35, 44, 45) along the length of the end segment (24).

3. The multi-core optical fiber according to claim 2, wherein, The cladding (12) of the end segment (24) has a first flat side surface (34, 44) and a second flat side surface (35, 45) along the length of the end segment (24), wherein the first flat side surface (34, 44) is opposite to the second flat side surface (35, 45).

4. The multi-core optical fiber according to any one of claims 1 to 3, wherein, The second number of fiber cores (14, 16, 18, 20) is equal to the first number of fiber cores (14, 16, 18, 20).

5. The multi-core optical fiber according to any one of claims 1 to 3, wherein, The second number of fiber cores (14, 16, 18) is equal to or greater than 1, but less than the first number of fiber cores (14, 16, 18, 20).

6. The multi-core optical fiber according to claim 5, wherein, The first subset of the cores (16, 18, 20) of the main section (22) terminates at the beginning of the end section (24) or near the beginning of the end section (24), and the second subset of the cores (14, 16, 18, 20) of the main section (22) extends into the end section (24).

7. The multi-core optical fiber according to claim 6, wherein, The first subset of the fiber cores (14, 16, 18, 20) of the main segment (22) terminates at a certain angle, thereby reducing the reflection of light.

8. The multi-core optical fiber according to any one of claims 1 to 7, wherein, One or more of the cores (14, 16, 18) of the end segment (24) are arranged eccentrically relative to the neutral bending plane of the cladding (12).

9. The multi-core optical fiber according to any one of claims 1 to 8, wherein, The cores (14, 16, 18, 20) of the main section (22) include a central core (14) centrally arranged relative to the neutral bending plane of the cladding (12) of the main section (22), wherein a distal portion of the central core (14) extends into the end section (24), and the distal portion of the central core (14) is eccentrically arranged relative to the neutral bending plane of the cladding (12) of the end section (24).

10. The multi-core optical fiber according to any one of claims 1 to 9, wherein, The end section (24) has a bending stiffness about the bending axis, the bending stiffness being 0.05 Nmm. 2 -0.2 Nmm 2 Within the range.

11. The multi-core optical fiber according to any one of claims 1 to 10, wherein, The length of the end segment (24) is in the range of 1 cm to 5 cm.

12. The multi-core optical fiber according to any one of claims 1 to 11, wherein, The main section (22) and the end section (24) are made of a single monolithic optical fiber.

13. The multi-core optical fiber according to any one of claims 1 to 11, wherein, The end segment (24) is made as a separate component and is connected to the main segment (22) of the optical fiber (10).

14. An elongated device for medical interventional applications, comprising: The main section (106) and the distal terminal section (108), together defining a lumen (102) along the length of the elongated device (100); and According to any one of claims 1 to 13, the multi-core optical fiber (10) is arranged in the cavity (102), wherein the end section (24) of the optical fiber (10) is arranged in the distal end section (108) of the elongated device (100).

15. The elongated device according to claim 14, wherein, The elongated device further includes a strip (110) arranged along the inner wall of the terminal section (108), the strip element (110) having a thickness in the direction of the thickness axis and a width in the direction of the width axis, the thickness being less than the width, and the multi-core optical fiber being arranged relative to the strip (110) such that the second axis is parallel to the thickness axis.

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