DISTRIBUTED INTRAVASCULAR FIBER BRAGG PRESSURE SENSOR

Abstract

The present invention relates to a pressure sensing device (10) comprising an optical fiber (12), the optical fiber (12) comprises a central axis (L) and at least one optical fiber core (14), the at least one optical fiber core (14) having one or more reflective FBG structures, and a coating (16) surrounding the optical fiber (12), the coating (16) having mechanical properties which are radially asymmetric along the central axis (L).

Claims

1. Pressure sensing device comprising: an optical fiber comprising a central axis (L) and at least one optical fiber core, the at least one optical fiber core having one or more reflective FBG structures, and a coating surrounding the optical fiber, the coating comprising a first annular subsection extending through a first annular sector with azimuth .sub.1 and a second annular subsection extending through a second annular sector with azimuth .sub.2, wherein the mechanical properties of the first and second annular subsections are different, and wherein the azimuths .sub.1 and .sub.2 complementarily vary along a portion of the central axis (L).

2. Pressure sensing device of claim 1, wherein the pressure sensing device is adapted to determine multiple local pressures along the central axis, the local pressures exerting radial forces on the coating.

3. Pressure sensing device of claim 1, wherein the difference between thermal expansion coefficients of the first annular section and the second annular section is below 10% and the difference between Poisson ratios of the first annular section and the second annular is larger than 75%.

4. Pressure sensing device of claim 1, wherein the first and second annular subsections are disposed staggered along the central axis (L), forming at least two longitudinal sections.

5. Pressure sensing device of claim 4, wherein each of the at least two longitudinal sections encompasses at least one reflective FBG structure.

6. Pressure sensing device of claim 1, wherein the azimuths .sub.1 and .sub.2 continuously vary along at least a portion of the central axis (L).

7. Pressure sensing device of claim 1, wherein the first and second annular subsections comprise identical material chemically and/or physically treated to provide different mechanical properties of the first and second annular subsections.

8. Pressure sensing device of claim 6, wherein the first and second annular subsections comprise two different materials.

9. Pressure sensing device of claim 6, wherein the optical fiber core further comprises non-periodic structures causing random variations of the refractive index.

10. System for pressure sensing, comprising: an interventional device comprising a pressure sensing device of claim 1, and a console configured to communicate with the interventional device.

11. System of claim 10, wherein the interventional device is a guidewire or a catheter.

12. Method for determining pressure values, comprising optically determining bending of an optical fiber comprising a central axis (L) and at least one optical fiber core, the at least one optical fiber core having one or more reflective FBG structures, wherein a coating surrounds the optical fiber, the coating comprising a first annular subsection extending through a first annular sector with azimuth .sub.1 and a second annular subsection extending through a second annular sector with azimuth .sub.2, wherein the mechanical properties of the first and second annular subsections are different, and wherein the azimuths .sub.1 and .sub.2 complementarily vary along a portion of the central axis (L), and calculating pressures or a pressure difference from the bending of the optical fiber.

13. Method of claim 12, wherein the pressure is a blood pressure in a blood vessel.

14. Method of claim 12, wherein calculating the pressure difference from the bending of the optical fiber is performed by calibration measurements and/or FEM simulations.

15. Computer program comprising program code means for causing a computer to carry out the steps of the method when said computer program is carried out on the system of claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0078] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. In the following drawings

[0079] FIG. 1 shows a system for pressure sensing employing the present pressure sensing device in a blood vessel in a schematic representation;

[0080] FIG. 2 shows a schematic representation of the cylindrical coordinate system used in the present invention;

[0081] FIG. 3 shows a schematic depiction of a part of a pressure sensing device according to the present invention;

[0082] FIGS. 4a and 4b show a schematic depiction of how a non-radial symmetric coating pattern turn hydrostatic pressure into shape changes; and

[0083] FIG. 5 show a schematic depiction of a part of a pressure sensing device with different asymmetry of the coatings applied to the optical fiber.

DETAILED DESCRIPTION OF THE INVENTION

[0084] With reference to FIG. 1, a system for pressure sensing 30 will be described. The system 30 allows determining blood pressure in a blood vessel. The system comprises the present pressure sensing device 10 configured to be insertable into a blood vessel 50. The system 30 further comprises an interventional device 32. The interventional device 32 may be a catheter, a guidewire or the like. At least a portion of the interventional device 32 is suitable for being introduced into a blood vessel 50 of a patient. The interventional device 32 comprises an elongated shaft 34 which may have a length of more than 1 m. The tip 36, such as an atraumatic tip, of the interventional device 32 is adapted for reciprocating movement in the blood vessel 50 without injuring the same.

[0085] The system 30 further comprises a workstation or console 60, to which the interventional device 32 may be connected for communication, in particular optical communication of one or more console components. A part of length of the interventional device 32 are configured to be insertable into a blood vessel 22.

[0086] FIG. 2 shows a schematic representation of the cylindrical coordinate system used in the present invention. The axial dimension of the optical fiber is the length L, which goes from proximal to distal. Forces, stress, strain and other vectors that are (approximately) parallel to the length are called longitudinal in the present application. Forces and other vectors that are (approximately) perpendicular to the axis are called radial. Properties and forces can vary with the azimuth angle . Properties that are independent of the azimuth are radial symmetric.

[0087] FIG. 3 shows a part of a pressure sensing device 10 according to the present invention. The pressure sensing device 10 comprises an optical fiber core 14 with at least one longer or multiple shorter FBGs written in. Alternatively, the fiber may contain multiple fiber cores with their own FBGs. If a single-core fiber is used, the core is preferably offset from the neutral axis. The fiber core 14 is coated with coatings that are in direct pressure contact with the blood stream. The coating is not axially symmetric. Rather, a plurality of longitudinal sections 20 along the length of the device each exhibit first annular subsection 22, i.e. portion, preferably one-half, of each longitudinal section 20 (for example the azimuthal angle 0<180) coated with a first coating material and second annular subsection 24 (azimuthal angle 180<360) coated with a second coating material. At other locations along the length of the device the coatings may be reversed or the fiber may be coated with just one axially symmetric coating 26. Preferably the accumulated length L.sub.O of the device with the original order of both coatings is equal to the accumulated length L.sub.I of the device with the reversed coating. The first coating material and the second coating material have different values of the Poisson's number and/or the Young's modulus. Ideally, the first coating material is a kind of rubber, with a Poisson's number v.sub.10.49 and the second coating material has Poisson's number v.sub.2 of about 0.2 or below. Ideally the first coating and the second coating have similar thermal expansion coefficients CTE.sub.1 and CTE.sub.2, wherein a deviation of CTE.sub.1 and CTE.sub.2 is 10% referred to the lowest value of CTE.sub.1 and CTE.sub.2. Furthermore, the fiber core(s) 14 are connected to an optical interrogator (shown by reference numeral 38), preferably an FGB interrogator. The other side of fiber core(s) 14 extents towards or is an atraumatic tip.

[0088] FIGS. 4a and 4b show a schematic depiction of how a non-radial symmetric coating pattern turn hydrostatic pressure into shape changes. As may be derived from FIG. 4a, the hydrostatic pressure of the blood exerts a radial force (stress) 70, 72 on the coating 16. This force causes a compression (axial strain) of the coating in the radial direction coupled with an expansion (transversal stress) in the longitudinal direction. The ratio of stress (or pressure) to strain is given by the Young's modulus while the ratio of transverse strain to axial strain is given by the Poisson's number of the coating material. In general, the hydrostatic pressure on the device 10 inside the blood vessel is independent of the azimuthal angle , i.e. radially symmetric. If the coating is also radially symmetric the resulting expansion in the longitudinal direction will be radially symmetric as well and the device and the fiber will simply expand in length according to equation (2) above. This is the case in the areas covered by the axially symmetric coating 26. But in the first annular subsections 22 covered with the first coating material and the second annular subsections 24 covered with the second coating material, the coating is not radially symmetric. The first coating will deform different from the second coating. As a result the device 10 will locally bend or deform (indicated by reference numeral 18), which is shown in FIG. 4b. This local change in shape can be read out via an optical interrogator 38 and be used to reconstruct the hydrostatic pressure. This reconstruction can be computationally difficult because thermal effect and additional strain can influence the reading. But if the first coating and the second coating have a similar or even a corresponding thermal expansion coefficient, then the bending effect is independent of temperature. Compensating for strain can be done by using optical shape sensing algorithms. An exact value for the bending effect caused by hydrostatic pressure for the device described in this embodiment is best performed using numerical simulations as indicated above with respect to equations (3) to (5). For a polymer coating E.sub.1=E.sub.2=3 GPa, with v.sub.1=0.49 and v.sub.2=0.2 and a coating thickness h=75 m a curvature of

[00007]$\frac{}{.Math.P}=1.Math.0^{-6}.Math..Math.m.Math.\text{/}.Math.N.Math..Math.\mathrm{or}$$1.3.Math..Math.{10}^{-04}.Math.\frac{1}{\mathrm{mmHg}.Math.m}$

is obtained.

[0089] FIG. 5 shows a schematic depiction of a part of a pressure sensing device with different asymmetry of the coatings applied to the optical fiber. This embodiment is similar to FIG. 3 but uses a different asymmetry of the coatings applied to the first annular subsection 22 and the second annular subsection 24 of the optical fiber core 14. According to FIG. 3 the two different coatings are applied in an alternating manner along the circumference of the fiber. In this way the azimuthal starting positions of the respective coating sections are a multiple of , as illustrated in diagram A. As a result of the symmetry of the forces applied to the optical fiber core 14 this case the fiber will locally bend as illustrated in FIGS. 4b and will show an in-plane oscillatory behavior. This symmetry can be destroyed by not simply alternating both coating materials, but also by applying subsequent coating sections at an azimuthal angle different than it (diagram B). As a consequence the coating materials start to spiral around the longitudinal axis. Due to the asymmetry of the forces now being applied to the FBG, the fiber shape will now oscillate in 3D-space, taking on the shape of a helix. Since the FBG is now allowed to expand in 3D space, instead of in a 2D plane, it is expected that the resulting strain and curvature as a function of applied pressure is larger as compared to case A, increasing the pressure sensitivity of the device. Diagram C illustrates the situation where the azimuthal starting position of the coating sections changes continuously as a function of longitudinal position along the fiber: both coating sections do not change position in a discrete manner, but rather spiral around the optical fiber core 14 in a continuous way.

[0090] The present invention may therefore provide a pressure sensing device for an intravascular device, like a guidewire or microcatheter, containing an optical fiber with one or more fiber Bragg gratings wherein the mechanical properties (especially the Young's modulus or the Poisson ratio) of the device are not radially symmetric on all points along the length of the catheter but vary with the azimuthal angle of the fiber as a function of axial position L;

[0091] so that hydrostatic pressure will exert radial forces on the device and the FBGs which can be detected to determine local hydrostatic pressure;

[0092] especially where those radial forces will lead to a local radial deformation (bending) of the device and/or the included fiber that can be detected;

[0093] especially where the mechanical properties are balanced in such a way that only hydrostatic pressure will lead to such a deformation (bending) but not thermal effects or strain. This can be done e.g. by using materials with similar thermal expansion coefficients and similar Young's modulus but different Poisson ratio;

[0094] especially where optical shape sensing methods are used to detect the deformations;

[0095] especially where the radial asymmetries are limited to certain measurement points along the length of the device;

[0096] especially where the radial asymmetries consist of one set of material parameters over half the radius (e.g. 0<180) and a second set of material parameters over the second half (e.g. 180<360;

[0097] especially where the radial asymmetries are staggered in such a way that local deformations mostly cancel each other out and do not lead to a strong deformation of the whole device, especially if this is done by alternating asymmetries by 180;

[0098] especially where the asymmetry in the material parameters is in the form of a coating of the optical fiber. The asymmetry can be induced by either (1) physically applying the coating to the fiber in an asymmetric way, or (2) treating a symmetrically applied coating by e.g. light irradiation in an asymmetric way;

[0099] where optical shape sensing technology is used to read-out information on local pressure and where both hydrostatic pressure and device position is shown to the user.

[0100] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0101] In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0102] A computer program may be stored/distributed on a suitable non-transitory medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0103] Any reference signs in the claims should not be construed as limiting the scope.