WO2008011662A1

WO2008011662A1 - A system and an element for sensing a property in an in-vivo environment

Info

Publication number: WO2008011662A1
Application number: PCT/AU2007/001017
Authority: WO
Inventors: John William Arkwright; Simon Nicholas Doe
Original assignee: Commonwealth Scientific And Industrial Research Organisation
Priority date: 2006-07-27
Filing date: 2007-07-23
Publication date: 2008-01-31

Abstract

The present invention provides a system for sensing a first property in an in-vivo environment. The system comprises a first sensing element for sensing the first property, or a quantity indicative of the first property, in the in-vivo environment and for generating a second property in response to the first property, or the quantity indicative of the first property. The system also comprises a second sensing element operatively coupled to the first sensing element for sensing the second property in the in-vivo environment and for generating a third property in response to the second property

Description

A SYSTEM AND AN ELEMENT FOR SENSING A PROPERTY IN

AN IN-VIVO ENVIRONMENT

Field of the Invention

The present invention broadly relates to a system and an element for sensing a property in an in-vivo environment .

Background of the Invention

A large number of people suffer from gastric acid reflux, which arises from reflux of stomach acid into the esophagus. Such "reflux" is discomforting and can even result in formation of tumours . Treatment often requires detailed knowledge of the reflux distribution in the esophagus. As the reflux is acidic, important information can be obtained by measuring pH values at different positions in the esophagus.

Further, many people suffer from dysphagia, which is a disorder that causes difficulty in swallowing. Diagnosis of this disease is often difficult and typically requires monitoring of pressures and/or bolus presence in the esophagus .

Any such measurements require typically a relatively large number of electrical wires or relatively thick tubes which are inserted through a patient's nose and consequently are very discomforting. Further, the measurement systems are typically only adapted to measure one property and cannot easily be converted to measure another property. In addition, measurement systems which are arranged for measuring more than one property typically combine separate measurement devices for each property and consequently are rather complicated devices. There is a need for technological advancement.

Summary of the Invention

The present invention provides in a first aspect a system for sensing a first property in an in-vivo environment, the system comprising: a first sensing element for sensing the first property, or a quantity indicative of the first property, in the in-vivo environment and for generating a second property in response to the first property, or the quantity indicative of the first property, and a second sensing element operatively coupled to the first sensing element for sensing the second property in the in-vivo environment and for generating a third property in response to the second property.

The first property may be any property in the in-vivo environment, but typically is associated with detecting the presence or transportation of bolus or sensing a pH value in the in-vivo environment.

The system typically is arranged for measuring different first properties. In this case the system may comprise a number of different first sensing elements which typically generate the same type of second property in response to the first properties. Consequently, it is possible to use a system with only one type of second sensing element for sensing different first properties which is of significant practical advantage.

The first sensing element may comprise a component for direct sensing of the first property. For example, the first property of the in-vivo environment may be a pH value and the first sensing element may comprise a material that contracts or expands in response to a change in the pH value .

Alternatively, the first sensing element may comprise a component for sensing a quantity that is indicative of the first property. For example, the first property may by is associated with the presence or transport of bolus and the first sensing element may comprise a component for sensing an impedance or a capacitance that is indicative of the presence or passing of the bolus.

The second property may for example be a movement, change in dimension or deformation that is generated by the first sensing element. The third property may be any suitable property including for example a hydraulic or pneumatic property, but typically is an electrical or optical property that changes in response to the movement, change in dimension or deformation of the first sensing element .

For example, the second sensing element may comprise an optical light guide and a Bragg grating. The or each Bragg grating typically has an optical response that depends on a strain of the Bragg grating and which changes in response to the movement, change in dimension or deformation of the first sensing element. Specifically, if the strain is increased, a wavelength of a reflected light beam will shift to longer wavelengths. Such an optical device has the significant advantage that typically only a single optical fibre is required through which light is guided to and from the or each Bragg grating and which incorporates the or each Bragg grating. Consequently, only minimal cross-sectional space is required, which reduces discomfort for the patient.

For example, the second sensing element may be of the type disclosed in the applicant's PCT international patent application numbers PCT/AU2006/000308, PCT/AU2006/000309 and PCT/AU2006/000310, which hereby are incorporated by- reference .

The first sensing element and the second sensing element may be removably coupled to each other. For example, the first sensing element may comprise a coupling for retrospective coupling to the second sensing element. Such a system has the practical advantage that it can be used for measuring different properties using the same interrogation method. For example, the second sensing element by itself may be an element for measuring a pressure in the in-vivo environment. If a suitable first sensing element is coupled to the second sensing element, the system may then be arranged for measuring another property in the in-vivo environment . In one specific embodiment the system comprises a kit that enables in-vivo measurement of pressure and/or a pH value and/or measurements associated with the presence or transportation of bolus.

Further, the system may comprise a plurality of the first sensing elements and a series of the second sensing elements. In this case it is possible to conduct measurements at a series of positions and typically simultaneously. One or more second sensing elements for measuring a pressure may be coupled to respective first sensing elements and one or more other second sensing elements for measuring a pressure may not be coupled to respective first sensing elements. Such a system makes it possible to measure a pressure in the in-vivo environment at those second sensing elements which are not coupled to first sensing element and measure another property at those second sensing elements which are coupled to a respective first sensing element .

The first and second sensing elements typically are arranged and in use coupled to each other so that the or each second sensing element is exclusively sensitive to the second property that the or each first sensing element generates in response the first property or quantity indicative of the first property.

The first sensing element typically is attachable to the second sensing element. In a specific embodiment the first sensing element is provided in form of a sleeve that fits over a portion of the second sensing element. Alternatively, the first sensing element may have any suitable shape and may be attachable to the second sensing element by means of an adhesive or any mechanical connection. The first sensing element may also be shaped so that it can be clipped onto a portion of the second sensing element.

The first sensing element typically has a first sensing surface via which the first property of the in- vivo environment can be sensed by the first sensing element. The first sensing element typically also has a second sensing surface via which the second property can be sensed by the second sensing element .

The first sensing element typically has a plurality of side portions and the first and second sensing surfaces typically are not positioned on the same side portion of the first sensing element. For example, the first and second surfaces may form parts of opposite side portions.

The second sensing element typically has a third sensing surface for sensing the second property. In one specific embodiment, the first and second sensing elements are shaped so that, when the first sensing element is coupled to the second sensing element, the second sensing surface is positioned over the third sensing surface. For example, the second sensing surface may be in contact with - Q - the third sensing surface. Alternatively, a gap may be defined between the second sensing surface and the third sensing surface. The gap typically is filled with a fluid. The first and second sensing elements typically are arranged for insertion into a body lumen, such as the esophagus and may at least partially be positioned in a catheter. For example, the second sensing elements may be positioned in the catheter and the first sensing elements may project through windows of the catheter. Alternatively, the second sensing elements may be positioned on the catheter so that a generated deformation, change in dimension or movement can be sensed by a respective second sensing element through a wall of the catheter. Further, a wall portion of a catheter may be positioned between the first sensing element and the second sensing element .

The present invention provides in a second aspect a method of sensing a first property in an in-vivo environment, the method comprising: sensing the first property, or the quantity indicative of the first property, generating a second property in response to the first property, or a quantity indicative of the first property, sensing the second property in the in-vivo environment and generating a third property in response to the second property.

The step of generating the second property typically comprises converting the first property into a movement, change in dimension or deformation. The first property may be, or may relate to, any property in the invivo environment, but typically is associated with detecting the presence or transportation of bolus or a pH value in the in-vivo environment .

The step of sensing the first property may include sensing the first property directly or indirectly by sensing a quantity that is indicative of the first property.

The present invention provides in a third aspect a sensing element for sensing a property, or a quantity indicative of the property, in an in-vivo environment, the sensing element being arranged for coupling to another in- vivo sensing element and comprising: a medium that changes a colour in response to the sensed property or the quantity indicative of the property, and a sensing surface via which the change in colour can be sensed in the in-vivo environment by the other in-vivo sensing element.

The present invention provides in a fourth aspect a sensing element for sensing a property, or a quantity indicative of the property, in an in-vivo environment, the sensing element being arranged for coupling to another in- vivo sensing element and comprising: a medium that deforms or changes a dimension in response to the sensed property or the quantity indicative of the property, and a sensing surface via which the deformation or change in dimension can be sensed in the in-vivo environment by the other in-vivo sensing element.

The present invention provides in a fifth aspect a sensing element for sensing a property, or a quantity indicative of the property, in an in-vivo environment, the sensing element being arranged for coupling to another in- vivo sensing element and comprising: an optical medium that changes its birefringence in response to the sensed property or the quantity indicative of the property, and a sensing surface via which the change in birefringence can be sensed in the in-vivo environment by the other in-vivo sensing element.

The sensing elements according to the third, fourth or fifth aspects of the present invention typically comprise a mount for mounting the sensing element to the other in-vivo sensing element. The property, or the quantity indicative of the property, typically relates to an impedance, capacitance or pH value in the in-vivo environment, or an a parameter associated with ingested material

The invention will be more fully understood from the following description of specific embodiments of the invention. The description is provided with reference to the accompanying drawings .

Brief Description of the Drawings

Figure 1 (a) and (b) shows a system for sensing a property in an in-vivo environment according to a specific embodiment of the present invention, Figures 2 (a) and (b) show an apparatus for pressure sensing according to an embodiment of the present invention and Figure 2 (c) shows an alternative component of the apparatus for pressure sensing, Figure 3 shows a unit for sensing a property in an in-vivo environment according to a specific embodiment of the present invention,

Figure 4 shows a unit for sensing a property in an in-vivo environment according to another specific embodiment of the present invention and

Figure 5 shows a unit for sensing a property in an in-vivo environment according to a further specific embodiment of the present invention.

Detailed Description of Specific Embodiments

Referring initially to Figure 1 (a) , a system for sensing a property in an in-vivo environment according to a specific embodiment of the present invention is now described. The system 100 comprises a light source 102 which in this embodiment is a broadband light source commonly referred to as a "white" light source even though the light that is emitted by the light source 102 may have any wavelength range . The light is directed via optical circulator 104 to sensor units 106 and 107. In a variation of this embodiment the circulator 104 may be replaced by an optical coupler, an optical splitter or an optical beam splitter. The sensor units 106 and 107 are arranged for measuring a first property in an in-vivo environment, such as transport of bolus through a body lumen, a pressure or a pH value for characterising reflux in the esophagus. Each sensor unit 106 comprises a first sensing element 106 (a) and a second sensing element 106 (b) . In this embodiment, the first sensor elements 106 (a) are arranged to convert the first property, or a quantity indicative of the first property, into a swelling or deformation. For example, the quantity may be an ionic concentration or an electrical impedance indicative of the presence of bolus. Alternatively, the property may be a pH value, which may be measured directly. Each second sensor element 106 (b) detects the deformation or movement in form of a pressure, which in this embodiment is converted into an indicative optical signal.

The second sensor elements 106 (b) are positioned in a catheter (not shown) for insertion into the human body. The first sensor elements 106 (a) are positioned on the catheter and over the second sensor elements 106 (b) . The catheter may also have windows through which the first sensor elements 106 (b) project. Further, the sensor units 106 and 107 typically comprise an X-ray opaque material, such as a metallic material, for locating in the human body.

In this embodiment the system 100 comprises a series of the second sensor elements 106 (b) . Sensor unit 107 does not comprise a first sensor element 106 (a) and only comprises sensor element 106 (b) for in-vivo pressure measurement .

Each second sensor element 106 comprises a Bragg grating 108 which is formed in an optical fibre 110. Each Bragg grating 108 is in this embodiment positioned in association with an enclosure 112. Each enclosure 112 has a movable wall portion which is provided in the form of a diaphragm (not shown) . In this embodiment, the optical fibre 110 is rigidly connected at end-portions 113 and 115 of a respective enclosure 112 so that a respective Bragg grating 108 is positioned between two end portions. Each Bragg grating is positioned on or near a respective diaphragm such that an external pressure change effects movement of the diaphragm which in turn will apply a strain to the Bragg grating 108. The strain causes a change of an optical property of the Bragg grating 108, such as a change of an optical path length, which influences an optical response of the Bragg grating 108 to light guided to the Bragg grating 108. Consequently it is possible to sense change in a pressure and a chosen property from analysing the optical response from the Bragg gratings.

In this embodiment each Bragg grating 108 has a slightly different refractive index variation so that each Bragg grating 108 has an optical response that has a slightly different spectral response. The light that is produced by light source 102 and that is directed to the Bragg gratings 108 therefore causes three unique responses from the Bragg gratings 108 which are directed via the optical circulator 104 to optical analyser 114 for optical analysis. Such a procedure is commonly referred to as wavelength division multiplexing (WDM) . The Bragg grating may also effect optical responses which overlap in wavelength or frequency space as long as sufficient information is known about each Bragg grating to allow the signals to be successfully deconvolved.

As in this embodiment each Bragg grating 108 causes a different response, it is possible to associate a particular response with a position along the apparatus 106. The combined response from the Bragg gratings is wavelength division multiplexed and the optical analyser 114 uses known wavelength division de-multiplexing techniques to identify the responses from the respective grating positions. Suitable software routines are used to determine a pressure or pressure distribution from the optical responses received from the Bragg gratings. Pressure measurements typically include calibrating the apparatus .

In a variation of this embodiment at least some of the Bragg gratings 108 may be identical and consequently, if the strain conditions are the same, their optical response will also be the same. In this case a pulsed light source may be used to guide light to the Bragg gratings and the positions of the Bragg gratings may be estimated from a time at which the responses are received by the optical analyser 114.

In one particular example the reflectivity of each Bragg grating 108 is chosen so that each response has, at the location of the optical analyser 114, approximately the same intensity. It will be appreciated that in a further variation of this embodiment the apparatus may be arranged so that responses from respective Bragg gratings can be analysed by receiving light that is transmitted through the Bragg gratings 108. For example, in this case the system 100 typically is arranged so that light is guided from the light source 102 through the Bragg gratings 108 and then directly to the optical analyser 114.

In this embodiment each Bragg grating 108 is written into an optical fibre and spliced between fibre portions 110. It will be appreciated, that in alternative embodiments the Bragg gratings 108 and the fibre portions 110 may be integrally formed from one optical fibre. The same optical fibre may be used for writing respective refractive index variations for each grating so that spaced apart Bragg gratings are formed separated by fibre portions. In this embodiment the enclosures 112 comprise a rigid material while the fibre portions 110 are relatively flexible. Consequently the apparatus is an articulated device. Figure 1 (b) shows the system 100 as also shown in Figure 1 (a) , but the optical fibre 110 is bent between the enclosures 112 of the articulated device.

Figures 2 (a) and (b) show schematically a second sensor element in more detail . The second sensor element 120 comprises in this embodiment an optical fibre 122, a Bragg grating 124 and an enclosure 126 which includes a body 128, a diaphragm 130 and an anvil 132. The optical fibre 122 is attached to the body 128, which is composed of a rigid material, at attachment regions 127 and 129 so that the Bragg grating 124 is positioned between the attachment regions 127 and 129. In this embodiment attachment is effected using a suitable adhesive but a person skilled in the art will appreciate that various other means may be used to secure the Bragg grating 124 to the body 128. The enclosure 126 encloses a volume 134 and is arranged so that a change in external pressure will change the enclosed volume 134 by deflecting the diaphragm 130 and the anvil 132. This results in a force on the Bragg grating 124 between the attachment regions and from one side which increases a distortion of the Bragg grating 124. In this embodiment the Bragg grating 124 is distorted into the enclosed volume 134. This arrangement prevents that an axial force acting on fibre 122 external to the enclosure and the attachment regions 127 and 129 affects the optical response of the Bragg grating 124.

Figure 2 (c) shows an enclosure 133 which is a variation of the enclosure 126 shown in Figure 2 (a) . The enclosure 133 has two portions 135 and 137 for securely fixing a fibre containing the Bragg grating and two recesses 139 and 141 for coupling the Bragg grating in a flexible manner. The flexible coupling portions reduce bending forces at the portions 135 and 137 on the coupled Bragg grating.

It is to be appreciated that the apparatus shown in Figure 2 has only one of many possible designs. For example, the apparatus may not necessarily have an anvil but the Bragg grating may be mechanically distorted into the enclosed volume without an anvil and in contact with the diaphragm. Further, the second sensor elements 106 (b) and 120 may not necessarily comprise enclosures, but may be positioned in a catheter in which fluidal communication is possible between adjacent second sensor elements. In addition, the Bragg grating may be distorted outwardly.

The applicant's PCT international patent application numbers PCT/AU2006/000308 , PCT/AU2006/000309 and PCT/AU200S/000310 disclose pressure sensing elements and for further details reference is being made to these PCT international applications.

Figure 3 shows a sensing unit according to a specific embodiment of the present invention in more detail. The unit 300 comprises a first sensing element 302 and a second sensing element 304. The first sensing element 302 and the second sensing element 304 are in contact. For example, the sensing unit 300 may be arranged so that the first sensing element 302 may be clipped over the second sensing element 304. In this embodiment the first sensing element 302 can be retrospectively fitted to a respective second sensing element 304 and can also be removed.

The second sensing element 304 is of a type similar to the second sensing element 120 shown in Figure 2 and discussed above. The second sensing element 304 comprises a Bragg grating (not shown) and a diaphragm (also not shown) , over which the first sensing element 302 is positioned. For example, a system for in-vivo measurement of a property may comprise a series of such sensing units 302 which may comprise one optical fibre in which the Bragg gratings are written.

The first sensing element 302 comprises in this embodiment a polymeric material formed from a cross-linked copolymeric hydrogel and comprises PMAA (poly (methacrylic acid)) with poly (ethylene glycol) dimethacrylate. The polymeric material is positioned on a silicon substrate. Alternatively, the polymeric material may comprise diethanolamine derivatized poly (vinylbenzyl chloride) or may be formed from poly (methacrylic acid-co- methacryloxyethyl glucoside) and poly (methacrylic acid-g- ethylene glycol) hydrogels. The polymeric material expands or contracts in response to a change in pH value and the first sensing element 302 is arranged so that the expansion or contraction results in a deformation of the sensing element 302. The deformation effects a sideway force on the diaphragm of the second sensing element . The change in sideway force results in a change of strain of the Bragg grating which in turn can be sensed by a change in an optical response of the second sensing element 304.

In an alternative embodiment the first sensing element 302 is arranged for sensing a change in impedance or conductivity or bolus presence which also results in a deformation of a portion of the second sensing element 302.

The embodiment as shown in Figure 4 shows a sensing unit 400 that is related to the sensing unit 300 shown in Figure 3 and discussed above. In this embodiment, however, the sensing unit 400 comprises a cylindrical first sensing element 402 that is fitted around the second sensing element 304.

Figure 5 shows a unit for sensing a property in an in-vivo environment according to a further specific embodiment of the present invention. The unit 500 comprises a first sensing element 402 also shown in Figure 4 and described above. The unit 500 further comprises a second sensing element 504 which differs from the previously described second sensing elements as it is not an optical sensing element and generates another suitable property in response to a deformation of the first sensing element 402. For example, the second sensing element 504 may be an electrical device which may comprise a piezoelectric sensor that generates a voltage in response to a detected deformation of the first sensing element 402. Alternatively, the second sensing element may be a pneumatic or hydraulic device that is arranged to detect a deformation of the first sensing element 402.

The sensing units 300 400 and 500 may be positioned partially in a catheter. For example, a sensing system may comprise a series of sensing units 300 or 400 and the second sensing elements 304 may be positioned in the catheter. The first sensing elements 302 and 402 may be positioned on the catheter and over respective second sensing elements. A wall portion of the catheter may be positioned between the second and first sensing elements. Alternatively, the catheter may comprise windows through which the first sensing elements project. The first sensing elements may also be positioned in the catheter, but the catheter may comprise windows which expose sensing surfaces of the first sensing elements.

In variations of the described embodiment the first sensing element may not necessarily be arranged for generating a deformation in response to a response to a sensed property of the in-vivo-environment . For example, the first sensing element alternatively may be arranged for generating a change in colour, a change in capacitance, or a change in optical birefringence, which is then detected by a suitable second sensing element.

Specific examples for first sensing elements include:

• A first sensing element that generates a colour change in response to a change in the property in the in-vivo environment. For example, the colour change may be generated by the same principles as that in a Litmus test . The second sensing element may be a suitable in-vivo spectrometer or may include and endoscope (typically with suitable overlay at end- portion) . • A first sensing element that deforms (swells and/or changes shape) in response to a change in the property in the in-vivo environment. Such a sensing element typically is a bimorph element. For example, the first sensing element may transform a change in pH value in the in-vivo environment into a swelling and/or change in shape. The first sensing element 302 is an example of such a bimorph sensing element (see above . The second sensing element may be an in-vivo pressure sensing element . • A first sensing element that detects a change in capacitance or impedance of the invivo-environment at two contacts in response to a change in the property in the in-vivo environment. In this example the second sensing element is a suitable electrical device that receives an electrical signal indicative of the change in capacitance or impedance. • A first sensing element that changes an optical birefringence in response to a change in the property in the in-vivo environment. For example, the first sensing element may in this example comprise a component that squeezes a birefringent optical fibre in response to a change in property. This may be effected by a suitable bimorph component. The second sensing element may be any suitable optical sensing element that receives an optical signal indicative of the change in birefringence.

In any one of the above examples of first sensing elements the property typically is one of a pH value, a presence or passing of bolus or presence or passing of an imbibed substance .

The reference that is being made to the applicant's PCT international patent application numbers PCT/AU2006/000308, PCT/AU2006/000309 and

PCT/AU2006/000310, does not constitute an admission that the applications form a part of the common general knowledge in Australia or in any other country.

Although the invention has been described with reference to particular examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. For example, second sensing elements which are coupled to first sensing elements may not necessarily comprise a moveable wall portion such as the diaphragm. Those second sensing elements may also be in direct contact with respective Bragg gratings (or may contact the Bragg gratings via an anvil or another element, which is typically relatively hard and does not function as a diaphragm) . In addition, the apparatus may also comprise any number of optical fibres with Bragg gratings. For example, the apparatus may be arranged so that adjacent each Bragg grating for pressure sensing one or more further Bragg gratings are positioned. The one or more further Bragg gratings may not be used for measuring a pressure, but may be used to detect a change in optical period resulting from a change in local temperature, which can then be used to correct the pressure sensing of the apparatus for temperature related effects .

Claims

The Claims :

1. A system for sensing a first property in an in-vivo environment, the system comprising: a first sensing element for sensing the first property, or a quantity indicative of the first property, in the in-vivo environment and for generating a second property in response to the first property, or the quantity indicative of the first property, and a second sensing element operatively coupled to the first sensing element for sensing the second property in the in-vivo environment and for generating a third property in response to the second property.

2. The system of claim 1 wherein the first property is associated with detecting the presence or transportation of bolus in the in-vivo environment

3. The system of claim 1 wherein the first property is a pH value in the in-vivo environment.

4. The system of any one of the preceding claims wherein the first sensing element comprises a component for direct sensing of the first property.

5. The system of any one of claims 1 - 3 wherein the first sensing element comprises a component for sensing a quantity that is indicative of the first property.

6. The system of any one of the preceding claims wherein the second property is a movement, change in dimension or deformation that is generated by the first sensing element .

7. The system of any one of the preceding claims wherein the third property is an optical property.

8. The system of any one of claims 1 to 6 wherein the third property is an electrical property.

9. The system of any one of the preceding claims wherein the first sensing element and the second sensing element are removably coupled to each other.

10. The system of any one of the preceding claims wherein the first sensing element comprises a coupling for retrospective coupling to the second sensing element.

11. The system of any one of the preceding claims comprising a plurality of first sensing elements and a series of second sensing elements.

12. The system of claim 11 wherein one or more second elements for measuring a pressure are coupled to respective first sensing elements and one or more other elements for measuring a pressure is not coupled to respective first sensing elements.

13. The system of any one of the preceding claims wherein the first sensing element is attachable to the second sensing element.

14. The system of any one of the preceding claims wherein the first and second sensing elements are arranged and in use coupled to each other so that the or each second sensing element is exclusively sensitive to the second property that the or each first sensing element generates in response the first property or quantity indicative of the first property.

15. The system of any one of the preceding claims wherein the first sensing element is provided in form of a sleeve that fits over a portion of the second sensing element.

16. The system of any one of claims 1 to 14 wherein the first sensing element is shaped so that it can be clipped onto a portion of the second sensing element .

17. The system of any one of the preceding claims wherein the first and second sensing elements are arranged for insertion into a body lumen.

18. The system of any one of the preceding claims wherein the system comprises a catheter and the or each second sensing element is positioned in a catheter and the or each first sensing element project through windows of the catheter.

19. The system of any one of the claims 1 to 17 wherein the system comprises a catheter and the second sensing elements is positioned on the catheter.

20. The system of any one of the claims 1 to 17 the system comprises a catheter and wherein a wall portion of the catheter is positioned between the first and the second sensing element .

21. The system of any one of the preceding claims being arranged for measuring different first properties and comprising a plurality of different first sensing elements which in use generate the same type of second property in response to the first properties.

22. A method of sensing a first property in an in-vivo environment, the method comprising: sensing the first property, or a quantity indicative of the first property, generating a second property in response to the first property, or the quantity indicative of the first property, sensing the second property in the in-vivo environment and generating a third property in response to the second property.

23. The method of claim 22 wherein the step of generating the second property comprises converting the first property into a movement, change in dimension or deformation.

24. The method of claim 22 or 23 wherein the first property is associated with detecting the presence or transportation of bolus in the in-vivo environment.

25. The method of claim 22 or 23 wherein the first property is a pH value in the in-vivo environment.

26. The method of any one of claims 22 to 25 wherein the step of sensing the first property includes sensing the first property directly.

27. The method of any one of claims 22 to 25 wherein the step of sensing the first property includes sensing the first property indirectly by sensing a quantity that is indicative of the first property.

28. A sensing element for sensing a property, or a quantity indicative of the property, in an in-vivo environment, the sensing element being arranged for coupling to another in-vivo sensing element and comprising: a medium that changes a colour in response to the sensed property or the quantity indicative of the property, and a sensing surface via which the change in colour can be sensed in the in-vivo environment by the other in-vivo sensing element .

29. A sensing element for sensing a property, or a quantity indicative of the property, in an in-vivo environment, the sensing element being arranged for coupling to another in-vivo sensing element and comprising : a medium that deforms or changes a dimension in response to the sensed property or the quantity indicative of the property, and a sensing surface via which the deformation or change in dimension can be sensed in the in-vivo environment by the other in-vivo sensing element.

30. A sensing element for sensing a property, or a quantity indicative of the property, in an in-vivo environment, the sensing element being arranged for coupling to another in-vivo sensing element and comprising: an optical medium that changes its birefringence in response to the sensed property or the quantity indicative of the property, and a sensing surface via which the change in birefringence can be sensed in the in-vivo environment by the other in-vivo sensing element.

31. The sensing element of any one of claims 28 to 30 comprising a mount for mounting the sensing element to the other in-vivo sensing element .

32. The sensing element of any one of claims 28 to 30 wherein the quantity indicative of the property relates to an impedance in the in-vivo environment

33. The sensing element of any one of claims 28 to 30 wherein the quantity indicative of the property relates to a capacitance in the in-vivo environment .

34. The sensing element of any one of claims 28 to 30 wherein the property relates to a pH value in the in-vivo environment .