BIOMEDICAL PRESSURE SENSOR

Abstract

A biomedical pressure sensor for measuring the pressure in a fluid includes an optical fiber having at least one measurement section arranged at a distance from a distal end of the optical fiber. The biomedical pressure sensor further includes a deforming member on the outer surface of the optical fiber at the location of the measurement section that is arranged for locally deforming the optical fiber under the influence of the applied pressure of the fluid to be measured. The measurement section is arranged for measuring said local deformation of the optical fiber.

Claims

1-39. (canceled)

40. A biomedical pressure sensor for measuring the pressure in a fluid, comprising: an optical fiber having at least one measurement section arranged at a distance from a distal end of the optical fiber, and a deforming member on the outer surface of the optical fiber at the location of the measurement section that is arranged for locally deforming the optical fiber under the influence of the applied pressure of the fluid to be measured, wherein the measurement section is arranged for measuring said local deformation of the optical fiber.

41. The biomedical pressure sensor of claim 40, wherein the optical fiber is fixed to the deforming member over substantially the full length of the deforming member

42. The biomedical pressure sensor of claim 40, wherein a deforming member extends at diametrical opposite locations on the optical fiber.

43. The biomedical pressure sensor of claim 40, wherein the deforming member is a cylindrical member surrounding the optical fiber.

44. The biomedical pressure sensor of claim 40, wherein the outer surface of the deforming member is arranged to be in direct contact with the surrounding fluid.

45. The biomedical pressure sensor of claim 40, wherein the deforming member is arranged to deform the optical fiber in a substantially axial direction under the influence of the applied pressure and/or wherein the deforming member is arranged to contract under the influence of an increase in applied pressure of the fluid.

46. The biomedical pressure sensor of claim 40, wherein the deforming member comprises end surfaces perpendicular to the axial direction, wherein the measuring section extends between the two end surfaces, and wherein the biomedical pressure sensor is arranged such that end surfaces are in contact with the fluid.

47. The biomedical pressure sensor of claim 40, wherein: the optical fiber comprises a plurality of measurement sections, a deforming member is provided on the outer surface of the optical fiber at at least the locations of the measurement sections, the respective measurement sections are mutually separated at distances in the axial direction of the optical fiber, wherein each measurement section is provided with a deforming member, and wherein the respective deforming members are mutually separated at distances in the axial direction of the optical fiber, or at least two of the respective measurement sections are enclosed in a continuous deforming member that is provided on the outer surface of the optical fiber.

48. The biomedical pressure sensor of claim 40, wherein the optical fiber further comprises a reference measurement section arranged for measuring a reference deformation of the optical fiber due to a temperature of a surrounding fluid, and wherein the reference measurement section is preferably arranged in close proximity to a measurement section and/or wherein the outer surface of the optical fiber at the of the reference measurement section is in direct contact with the surrounding fluid.

49. The biomedical pressure sensor of claim 40, wherein properties a, b, ν, E of the deforming member are such that S.sub.P2λ≥0.10 fm/Pa, wherein S.sub.P2λ denotes the sensitivity of the biomedical pressure sensor, according to the formula: $S_{P2\lambda }\left(a,b,v,E\right):=\left[\frac{a^2.Math.\left(2v-1\right)+b^2{v}_{\mathrm{quartz}}}{E.Math.a^2-E.Math.b^2+E_f.Math.b^2}\right].Math.S_{\mathrm{.Math.2\lambda }}$ wherein a [m] denotes the outer radius of the deforming member, b [m] denotes the inner radius of the deforming member (and/or outer radius of the optical fiber), ν [−] denotes the Poisson's ratio of the material of deforming member, ν.sub.quartz [−] denotes the Poisson's ratio of material of the optical fiber, E [Pa] denotes the Young's modulus of the material deforming member, E.sub.f [Pa] denotes the Young's modulus of the optical fiber, and S.sub.ε2λ denotes the ratio of strain (ε) to the wavelength (λ).

50. The biomedical pressure sensor of claim 40, wherein: an outer radius of the deforming member is no less than two times an inner radius of the deforming member; the Young's modulus of the material of the deforming member is less than 10 GPa; the Poisson's ratio of the material of the deforming member is less than 0.5 and/or; the optical fiber has an outer diameter of no more than 125 μm.

51. A catheter comprising: a biomedical sensor for measuring the pressure in a fluid, wherein the biomedical pressure sensor comprises an optical fiber having at least one measurement section arranged at a distance from a distal end of the optical fiber, wherein the biomedical pressure sensor further comprises a deforming member on the outer surface of the optical fiber at the location of the measurement section that is arranged for locally deforming the optical fiber under the influence of the applied pressure of the fluid to be measured and wherein the measurement section is arranged for measuring said local deformation of the optical fiber, wherein the catheter is an elongated member surrounding the optical fiber over at least the largest part of the optical fiber in the axial direction, and wherein the catheter is arranged to be inserted in a body.

52. The catheter of claim 51, wherein an inner surface of the catheter is in direct contact with the optical fiber and an outer surface of the catheter is arranged to be in direct contact with the fluid to be measured, and wherein the deforming member is formed integrally with the catheter.

53. The catheter of claim 51, wherein the elongated solid member is made from at least two materials, and wherein at least the deforming member is made from a first material and wherein the remainder of the elongated solid member is made from a material different from the first material.

54. The catheter of claim 51, wherein the catheter further comprises an elongated tubular sheath, wherein the biomedical pressure sensor is substantially enclosed by the elongated tubular sheath and the catheter is arranged such that the measurement section is able to measure a pressure in an environment surrounding the catheter at the location of the measurement section, and wherein a peripheral wall of the elongated tubular sheath comprises an opening at at least the location of the measurement section.

55. The catheter of claim 54, wherein the elongated tubular sheath comprises a plurality of tubular sections, wherein an end of a first tubular section is arranged at a distance from an end surface of the deforming member at a first end and wherein an end of a second tubular section is arranged at a distance from an end surface of the deforming member at a second end.

56. The catheter of claim 55, wherein said first and second tubular sections are connected through a third tubular section such that the end of the first tubular section and a first end of the third tubular section and the end of the second tubular section and a second end of the third tubular section at least partially overlap, and wherein a peripheral wall of the third tubular section is fluid permeable.

57. The catheter of claim 51, wherein an outer diameter of the catheter is 8 Fr or less.

58. A method for measuring pressure of a fluid, comprising: providing a biomedical pressure sensor for measuring the pressure in the fluid, wherein the biomedical pressure sensor comprises an optical fiber comprising at least one measurement section arranged at a distance from a distal end of the optical fiber, wherein the biomedical pressure sensor further comprises a deforming member on the outer surface of the optical fiber at the location of the measurement section arranged for locally deforming the optical fiber under the influence of the applied pressure of the fluid to be measured and wherein the measurement section is arranged for measuring said local deformation of the optical fiber; projecting light in one end of the optical fiber; and measuring the light reflected.

59. The method of claim 58, further comprising inserting the biomedical pressure sensor in a human or animal body.

Description

[0039] The present invention is further illustrated by the following Figures, which show a preferred embodiment of the device and method according to the invention, and are not intended to limit the scope of the invention in any way, wherein:

[0040] FIG. 1 is a perspective view of an embodiment of the pressure sensor according to the invention.

[0041] FIG. 2 is a cross-sectional view of an embodiment of the pressure sensor according to the invention.

[0042] FIGS. 3a and 3b show in a perspective and a cross-sectional view a preferred embodiment of the sensor according to the invention.

[0043] FIGS. 4 and 5 show the results of one-to-one comparisons between a pressure sensor according to the invention and an electrical pressure sensor.

[0044] FIG. 6 shows the cross-section of an embodiment of a pressure sensor within a solid catheter according to the invention.

[0045] FIG. 7 schematically shows the test-setup for evaluating the cross-talk between the different measurement sections of the pressure sensor shown in FIG. 6.

[0046] In FIG. 1 a pressure sensor 1 is schematically shown. An optical fiber 2 is enclosed by a cylindrical member 3, that is formed by gluing (or fixing by means of any suited method) two parts 3a,3b around the optical fiber 2. The cylindrical member 3 shown in FIG. 1 acts as the deforming member and essentially covers the measurement section, comprising a grating (not visible in FIG. 1), that is present on the optical fiber 2. The pressure sensor 1 as shown is suitable for direct use. By placing it in a fluid of which the pressure needs to be determined, the fluid comes into direct contact with the full outer surface of the part of the sensor that is submerged. The fluid, and thereby also its associated pressure, is direct distributed on the full outer circumferential surface 32 and on both end surfaces 31 of the deforming member 3. The pressure leads to, depending on the material used for the deforming member, to a contraction or expansion in the longitudinal, or axial, direction 1 of the deforming member 3. As the optical fiber 2 is fixed to the deforming member 3 over substantially the full length of the deforming member 3, the contraction and or expansion leads to a substantially equal deformation in the measurement section of the optical fiber 2. This change of length is detected through the changing wavelengths that are reflected by the Fiber Bragg Grating. A suitable measurement unit can be configured to this end.

[0047] FIG. 2 again shows that the optical fiber 2 is enclosed by a cylindrical member 3. In this cross-sectional view, the grating 4 of the fiber Bragg grating making up the measurement section can clearly be identified. The cylindrical member 3 fully encloses the grating 4, thereby ensuring that the measurement section, and thus the grating 4, is uniformly deformed by the pressure applied. The optical fiber 2 and cylindrical member 3 are enclosed by a catheter 100 that forms the housing of the pressure sensor 1. The catheter 100 is constructed from multiple sections. The catheter is mostly made up of the main sections 101 that enclose parts of the optical fiber 2 that are spaced apart from the measurement sections, which are encapsulated by the cylindrical members 3. Around the location of the cylindrical member 3, the sensor 1 is enclosed by a fluid permeable section 102. Such permeable section 102 is either made from a permeable material, or is provided with holes for enabling direct contact between the fluid of which the pressure is to be determined and the cylindrical member 3. Overlapping regions 105 between the main sections 101 and permeable section 102 allow for connecting these by means of a glue layer 103, or any suitable method for connecting the sections. The catheter 100 is thus made from a series of interconnected sections of tubular sheath. Note that, apart from the here shown catheter, different types of housings can be placed around the pressure sensor 1, or around the deforming member 3. A main purpose of such a housing is for instance to shield the more fragile part of the sensor, or to provide for a better and safer way of handling the pressure sensor 1.

[0048] It is furthermore noted that the outer diameter d.sub.1 of the main section 101 is substantially equal, or only slightly larger, than the outer diameter d.sub.3 of the cylindrical member 3. The inner diameter d.sub.2 of the permeable section 102 is somewhat larger than the outer diameters d.sub.1 and d.sub.3. Due to this construction, the cylindrical member 3 is free to move with respect to the inner wall 104 of the permeable section 102. Also, as the main sections 101 are spaced at a distance from the end surfaces 31 of the cylindrical member 3, the cylindrical member is, in general, free to move with respect to the catheter 100. In addition, the sections 101, 102 making up the catheter 100 can easily be assembled and connected. Due to the fact that diameters d.sub.1 and d.sub.3 only slightly differ, the cylindrical member 3 can only be fixed to the optical fiber 2 during assembly, as main sections 101 cannot slide over the cylindrical members 3. Hence, when assembling the catheter (from left to right) one first needs to slide optical fiber into (left) main section 101, fix the cylindrical member 3 to the optical fiber 2 at the location of the grating 4 and after this mount the (right) main section 101 and permeable section 102 before fixing all the sections 101, 102 together for obtaining the assembled catheter comprising the pressure sensor 1.

[0049] As the optical fiber 2 is connected (not shown) at a distance from the grating 4 (making up the measurement section), the influence, due to connecting forces introduced into the fiber 2, on the pressure measurements is minimized.

[0050] Note that even though the deforming member is, in the current example, a cylindrical member 3, different types of shapes, such as a sphere, cuboid, hexagonal prism, triangular prism, etc. are also possible. The catheter can similarly be formed from tubular sections with different, corresponding, cross-sections.

[0051] FIGS. 3a and 3b show cross-sections of a catheter 100 comprising the pressure sensor 1. The permeable section 102 comprises multiple openings 106, wherein an opening 106 can either be formed by, for instance, circular holes or slits extending in the axial direction of the permeable section 102 over substantially the full length of the cylindrical member 3.

[0052] The sensitivity of the pressure sensor 1 is for a large part determined by the outer diameter d.sub.0 of the optical fiber 2, and more specifically, by the ratio between outer diameter d.sub.0 of the fiber 2 (which corresponds to the inner diameter of the cylindrical member 3) and the outer diameter d.sub.3 of the cylindrical member 3, such that d.sub.3/d.sub.n should be maximized for optimizing the sensitivity. The outer diameter d.sub.3 is in turn limited by the maximum allowable outer diameter d.sub.4 of the permeable section 102. Hence, the optimal design requires an as small as possible gap 6 between the outer diameter d.sub.3 and the inner diameter d.sub.2, such that d.sub.3/d.sub.0 can be maximized, while still ensuring that the cylindrical member 3 is free to move within the catheter 100. In addition, the fluid of which the pressure needs to be measured has to be able to flow around the full circumference of the cylindrical member 3, such that the pressure is uniformly transferred to the cylindrical member 3.

[0053] In FIG. 4 and FIG. 5 results of a one-to-one comparison between a traditional electro-mechanical pressure sensor and the optical pressure sensor 1 according to the invention are shown. The results were recorded at approximately 10 kHz and band pass filtered between approximately 1 and 100 Hz. In the test-setup the pulsating rhythm of a heart-beat has been simulated, whereby simultaneous pressure measurements have been performed using these to pressure sensors. The pressure sensor 1, according to FIG. 1, was fitted with a FBG in the 50 μm optical fiber 2. The cylindrical deforming member 3 had a 1 mm outer diameter and was manufactured by gluing two ABS parts around the optical fiber 2. FIG. 4 shows the results for the sensor 1 without a housing. For the results shown in FIG. 5, the optical sensor was fitted with a housing as shown in FIG. 2. Both figures show an excellent correspondence with the electro-mechanical reference measurements.

[0054] FIG. 6 shows, in a cross-sectional view, an embodiment of the pressure sensor 201 according to the invention. The basic ingredients of the sensor are the same as in the earlier embodiment. In this embodiment the optical fiber 2 comprising two grating sections 41, 42; and a deforming member, which is a continuous cylindrical member 10 encapsulating both grating sections 41, 42 and, at least, the part of the optical fiber 2 that is in between the first grating section 41 and the second grating section 42. The continuous cylindrical member 10 thus forms the deforming members for both grating sections 41, 42. The pressure sensor 201 can be placed in a tubular sheath, forming the housing, as has been shown in FIGS. 1-3. However, the continuous cylindrical member 10 can also be extended over substantially the full length of the optical fiber 2, thereby also serving as the housing (or catheter) 300. This obviously leads to a less complex production process, as the catheter 300 can in this case be disposed on the optical fiber 2 through, for instance, an extrusion process. Thereby, the cylindrical member 10 essentially acts as a deforming member, housing and catheter at the same time. The cylindrical member 10 is, when in use, thus in direct contact with the fluid of which the pressure is to be determined. In that case it is vital that, for at least the biomedical application, the material of which the cylindrical member 10 is made, is suited to for safe use in the body. Such a material is for instance non-toxic and can be easily sterilized.

[0055] FIG. 7 shows the test-setup 500 that has been used to verify that the sensor 201 shown in FIG. 6 experiences only limited, to virtually no, cross-talk between the first 41 and second 42 grating section. A fluid flows from inlet 503 to outlet 504, thereby passing through choke 505 for generating the pressure difference between low pressure chamber 507 and high pressure chamber 506. Cavities 501 and 502 have been fitted with pressure sensors for taking reference measurements. Optical pressure sensor 201 is fitted in the setup such that the second grating section 42 is located in the low pressure chamber 507 and first grating section 41 is located in the high pressure chamber 506. The optical fiber 2 and the grating sections 41, 42 have all been enclosed in the continuous cylindrical member 10, which forms the solid catheter. The results (not shown) have shown that accurate pressure measurements, with negligible cross-talk between the different measurement sections, can be obtained using the optical pressure sensor 201.

[0056] The sensor shown in FIG. 7 can also be produced using different materials. Instead of encapsulating the outer surface of the optical fiber 2 in a single material, as was shown for instance in FIG. 6, one can decide to make the deforming members 41, 42 from a second, different material than the remainder of the cylindrical member 10. In such a way, one can optimize for the material properties of the deforming members 41, 42, while being less constrained due to other, for instance, practical reasons, such as costs or manufacturability over long lengths. Alternatively, one can first manufacture the deforming member 41, 42 on the optical fiber 2, after which the remainder of the optical fiber is packaged in a second, different material. Hereby it is even possible to package the deforming member 41, 42 in the second, different material. In case the material for the deforming members 41, 42 is not suitable for direct use in medical applications, these sections can be shielded using the second, different material from which the remainder of the cylindrical member 10 is made. This packaging, or covering, operation can easily be performed by, for instance, an extrusion process. If the second, different material is, for instance, a transparent material, one can easily verify the location of the deforming members 41, 42, and thus the measurement sections, over the full length of the pressure sensor 201. Even the deforming members 41, 42 can be made from different materials if desired.

[0057] Note that this use of different materials for different purposes can be applied to all of the embodiments shown. Also, the present invention is not limited to the embodiment shown, but extends also to other embodiments falling within the scope of the appended claims.