阅读说明：本技术 使用电流位置结合磁场感测的导管定位 (catheter localization using current position in combination with magnetic field sensing ) 是由 D.M.陆德温 G.弗雷森 M.巴尔-塔尔 G.科恩 M.舍施特 D.奥萨奇 于 2019-05-29 设计创作，主要内容包括：本发明题为“使用电流位置结合磁场感测的导管定位”。本发明涉及一种设备,所述设备包括接口和处理器。所述接口被配置用于与以下交换信号：(i)探针,所述探针插入患者体内并包括柔性远端组件,其中所述远端组件包括磁位置传感器和两个或更多个体内电极,以及,(ii)多个体表电极,所述多个体表电极附接到所述患者体外。所述处理器被配置为基于与所述探针交换的所述信号估计所述磁传感器在连续测量之间的空间位移,并且基于以下来估计所述远端组件在体内的位置：(i)与所述体内电极和所述体表电极交换的所述信号,(ii)所述探针的所述体内电极中的两个或更多个之间的先验已知空间关系,以及(iii)所述磁传感器的所述估计的空间位移。(The invention provides catheter localization using current position in combination with magnetic field sensing. The invention relates to a device comprising an interface and a processor. The interface is configured to exchange signals with: (i) a probe inserted into a patient and comprising a flexible distal assembly, wherein the distal assembly comprises a magnetic position sensor and two or more in-vivo electrodes, and, (ii) a plurality of body surface electrodes attached to the outside of the patient. The processor is configured to estimate a spatial displacement of the magnetic sensor between successive measurements based on the signals exchanged with the probe, and to estimate a position of the distal assembly within the body based on: (i) the signals exchanged with the in-vivo electrodes and the body-surface electrodes, (ii) an a priori known spatial relationship between two or more of the in-vivo electrodes of the probe, and (iii) the estimated spatial displacement of the magnetic sensor.)

1. An apparatus, comprising:

An interface for exchanging signals with:

(i) A probe inserted into a patient and comprising a flexible distal assembly, wherein the distal assembly comprises a magnetic position sensor and two or more in-vivo electrodes; and

(ii) A plurality of body surface electrodes attached to the exterior of the patient; and

A processor configured to estimate a spatial displacement of the magnetic sensor between successive measurements based on the signals exchanged with the probe, and to estimate a position of the distal assembly within the body based on: (i) the signals exchanged with the in-vivo and body-surface electrodes, (ii) an a priori known spatial relationship between two or more of the in-vivo electrodes of the probe, and (iii) the estimated spatial displacement of the magnetic sensor.

2. The apparatus of claim 1, wherein the processor is configured to estimate the location of the distal assembly by:

Estimating location coordinates of the in vivo electrode based on the signals;

Locally scaling the location coordinates based on the a priori known spatial relationship; and

Correcting the locally scaled position coordinates based on the spatial displacement of the magnetic sensor.

3. The apparatus of claim 1, wherein the signal received from the intra-body electrode is indicative of at least one voltage sensed by the intra-body electrode in response to a voltage applied by the body-surface electrodes.

4. the apparatus of claim 1, wherein the signals received from the body surface electrodes are indicative of electrical currents sensed by the body surface electrodes in response to at least one electrical current applied by the in vivo electrodes.

5. a method for position sensing, comprising:

Exchange signals with:

(i) A probe inserted into a patient and comprising a flexible distal assembly, wherein the distal assembly comprises a magnetic position sensor and two or more in-vivo electrodes; and

(ii) A plurality of body surface electrodes attached to the exterior of the patient;

estimating a spatial displacement of the magnetic sensor between successive measurements based on the signals exchanged with the probe; and

Estimating a position of the distal assembly within the body based on: (i) the signals exchanged with the in-vivo and body-surface electrodes, (ii) an a priori known spatial relationship between two or more of the in-vivo electrodes of the probe, and (iii) the estimated spatial displacement of the magnetic sensor.

6. The method of claim 5, wherein estimating the location of the distal assembly comprises:

Estimating location coordinates of the in vivo electrode based on the signals;

Locally scaling the location coordinates based on the a priori known spatial relationship; and

Correcting the locally scaled position coordinates based on the spatial displacement of the magnetic sensor.

7. The method of claim 5, wherein exchanging the signals comprises receiving signals from the intra-body electrodes, the signals indicative of at least one voltage sensed by the intra-body electrodes in response to voltages applied by the body-surface electrodes.

8. The method of claim 5, wherein exchanging the signals comprises receiving signals from the body surface electrodes, the signals indicative of electrical currents sensed by the body surface electrodes in response to at least one electrical current applied by the body interior electrodes.

Technical Field

The present invention relates generally to sensing the position of an object placed within a living body, and in particular to providing correction for impedance-based position measurements.

Background

Tracking the position of in vivo objects such as insertion tubes, catheters and implants is required in many medical procedures. For example, U.S. patent application publication 2007/0016007 describes a position sensing system that includes a probe adapted for introduction into a body cavity of a subject. The probe includes a magnetic field transducer and at least one probe electrode. The control unit is configured to measure the position coordinates of the probe using the magnetic field transducer. The control unit also measures an impedance between the at least one probe electrode and one or more points on the body surface of the subject. The control unit uses the measured position coordinates to calibrate the measured impedance.

As another example, U.S. patent application publication 2014/0095105 describes an algorithm to correct and/or scale a current-based coordinate system, which may include determining one or more global transformation or interpolation functions and/or one or more local transformation functions. The global and local transformation functions may be determined by computing a global metric tensor and a plurality of local metric tensors. The tensor of metric may be computed based on a predetermined and measured distance between closely spaced sensors on the catheter.

U.S. patent application publication 2011/0319910 describes systems and methods for using shape data to improve control of a shapeable or steerable instrument. The method (comprising obtaining a plurality of local shape data) comprises using an impedance-based localization system, and wherein the shapeable instrument comprises at least one sensor, wherein the system further comprises at least one electrode, wherein the impedance-based localization system determines a voltage gradient between the sensor and the electrode. In one embodiment, a plurality of localized shape data is provided, including using an electromagnetic positioning system, and wherein the shapeable instrument includes at least one electromagnetic coil.

Disclosure of Invention

Embodiments of the invention described herein provide an apparatus comprising an interface and a processor. The interface is configured to exchange signals with: (i) a probe inserted into a patient and comprising a flexible distal assembly, wherein the distal assembly comprises a magnetic position sensor and two or more in-vivo electrodes, and, (ii) a plurality of body surface electrodes attached to the outside of the patient. The processor is configured to estimate a spatial displacement of the magnetic sensor between successive measurements based on signals exchanged with the probe, and to estimate a position of the distal assembly within the body based on: (i) signals exchanged with the in-vivo and body-surface electrodes, (ii) a priori known spatial relationship between two or more of the in-vivo electrodes of the probe, and (iii) an estimated spatial displacement of the magnetic sensor.

In some embodiments, the processor is configured to estimate the location of the distal assembly by: estimating position coordinates of the in-vivo electrode based on the signals, locally scaling the position coordinates based on a priori known spatial relationships, and correcting the locally scaled position coordinates based on spatial displacement of the magnetic sensor.

In some embodiments, the signals received from the intra-body electrodes are indicative of at least one voltage sensed by the intra-body electrodes in response to voltages applied by the body surface electrodes.

In one embodiment, the signals received from the body surface electrodes are indicative of currents sensed by the body surface electrodes in response to at least one current applied by the body interior electrodes.

There is additionally provided, in accordance with an embodiment of the present invention, a method for position sensing, including exchanging signals with: (i) a probe inserted into a patient and comprising a flexible distal assembly, wherein the distal assembly comprises a magnetic position sensor and two or more in-vivo electrodes, and (ii) a plurality of body surface electrodes attached to the outside of the patient. Based on the signals exchanged with the probe, the spatial displacement of the magnetic sensor between successive measurements is estimated. Estimating a position of the distal assembly within the body based on: (i) signals exchanged with the in-vivo and body-surface electrodes, (ii) a priori known spatial relationship between two or more of the in-vivo electrodes of the probe, and (iii) an estimated spatial displacement of the magnetic sensor.

the invention will be more fully understood from the following detailed description of embodiments of the invention taken together with the accompanying drawings, in which:

drawings

FIG. 1 is a diagram of a position tracking system including an active current position (ACL) and a magnetic induction subsystem, according to one embodiment of the present invention;

FIG. 2 is a schematic detail view of a flexible lasso catheter including a magnetic sensor and a plurality of sensing electrodes, according to an embodiment of the invention;

FIG. 3 is a schematic view of the flexible lasso catheter of FIG. 2 in a straight and deformed state, according to one embodiment of the invention; and

fig. 4 is a flow chart schematically illustrating a method for accurately mapping a cavity in a body, in accordance with an embodiment of the present invention.

Detailed Description

SUMMARY

Some medical procedures require accurate spatial mapping of the patient's anatomy, such as the anatomy of the left atrium of the heart. For example, such mapping may be performed using sensing electrodes (also referred to as intra-body electrodes) fitted to a flexible distal end assembly of a medical instrument (e.g., a catheter). The sensing electrodes are used in impedance position tracking methods. In this method, the position of the distal end of the catheter can be estimated by measuring the impedance between the sensing electrode and a surface electrode attached to the patient's skin. In principle, impedance-based techniques are sufficient to derive the position of the sensing electrode, e.g. in the heart. However, in practice, the resulting position accuracy is often insufficient.

In the description below, a pure active current localization (PureACL) impedance based system and technique manufactured by Biosense-Webster is used as an example of an impedance based position tracking system, and a catheter using such sensing electrodes is referred to as a "PureACL catheter". The surface electrode is hereinafter referred to as "ACL patch".

in some embodiments, to improve the positioning accuracy of impedance-based measurements (such as that of the PureACL system), a calibration catheter is first inserted into the heart. The calibration catheter includes a magnetic position sensor and sensing electrodes similar to those of the PureACL catheter. The calibration catheter is used to generate a calibration map in which accurate position measurements of the magnetic sensor are correlated with less accurate PureACL (impedance-based) measurements.

A PureACL catheter subsequently inserted into the heart uses the calibration map to provide the physician with the correct position of its distal end in the heart using only sensing electrodes (i.e. using a method based on PureACL impedance).

in many practical cases, the accuracy of magnetic calibration purelacl position sensing can be further improved using a "local scaling" process. In some embodiments, such a process, hereinafter referred to as "independent current location" (ICL), is applied in order to further improve the accuracy of the magnetically calibrated purelacl location. The ICL procedure is applicable to a catheter having a plurality of sensing electrodes disposed on its distal end. Using known spatial relationships between two or more electrodes (e.g., at one or more known distances between electrodes located at up to about 1cm from each other), and possibly other inputs, the ICL procedure can scale the relative positions of the multiple electrodes to precisely fit the shape of the distal end of the purelacl catheter, ultimately providing a highly accurate electrode location.

The assumption used in ICL (i.e. the actual distance between adjacent electrodes is equal to the known distance) is valid as long as the distal end of the catheter is sufficiently rigid to withstand very local deformations. If this assumption is invalid (i.e., if the distal end of the catheter deforms more than an allowable amount), the local scaling procedure does not provide the desired accuracy.

In practice, the flexible distal assembly does deform during mapping, but over the entire assembly dimension. Since the magnetically calibrated purelacl and ICL methods provide accurate position only when the distal assembly is undeformed, the deformation results in errors in the sensing electrode position derived from the magnetically calibrated purelacl and ICL methods. The error is particularly large at the edges of the mapped volume, which are less completely surrounded by the surrounding ACL tiles than in the middle of the mapped volume.

Embodiments of the present invention described hereinafter provide position sensing systems and methods in which magnetic sensors of a magnetic position tracking system are coupled to a flexible distal end assembly. The magnetic sensor measures its own displacement between successive measurements (e.g., between its new measurement position minus its previous measurement position). The measurement displacement is used as a correction to the latest purelacl and ICL measurement positions of the sensing electrode. As described above, such correction is needed because less accurate impedance based position measurements may not capture changes in the position of the sensing electrode.

in some embodiments of the invention, a magnetic sensor (i.e., a position sensor of a magnetic position tracking system) is coupled to a base section of a flexible distal end assembly of a catheter. As an example, a flexible purefacl lasso catheter is provided that includes a flexible base section and a helical end section. A magnetic sensor is coupled to the base section.

The sensing electrodes may be distributed over the base section and/or over the helical end section. When the base section is deformed during the mapping process, the actual position of the sensing electrode is displaced (e.g., due to bending, deflection, and/or torsion of the flexible base section) relative to the position derived using purelacl and ICL.

Each time the base section deforms, the magnetic sensor provides an indication of its new position (i.e. its displacement from its previously indicated position), e.g. caused by the deformation. The indication is used to correct the magnetically calibrated derived electrode position based on electrical impedance in a continuous manner.

In this specification, the terms "flexible purefacl catheter", "flexible distal assembly", "flexible base section", and "flexible catheter" are used interchangeably.

In some embodiments, the magnetic sensor provides an indication of its own displacement relative to its previously indicated position, with a spatial accuracy of 1 mm. This displacement indication is added to the successive positions derived using purelacl and ICL methods, which results in a correct derived position of the sensing electrode.

The disclosed systems and methods provide highly accurate spatial and electrophysiological mapping capabilities. These capabilities are obtained by combining compact magnetic sensor displacement sensing with relatively low cost and simplicity, characterized by purelacl and ICL impedance based position sensing. Furthermore, the inherent compactness of magnetic sensors opens the way to construct compact and flexible sensing and/or ablation catheters.

description of the System

FIG. 1 is a diagram of a position tracking system 20 including an active current position (ACL) and a magnetic induction subsystem, according to one embodiment of the present invention. The system 20 is used to determine the position of a flexible purefacl catheter, such as lasso catheter 50, which is seen in inset 25 fitted at the distal end of the shaft 22. As described above, purelacl catheter 50 contains sensing electrodes (also referred to as intracorporeal electrodes, as shown in fig. 2) similar to those of purelacl calibration catheters, but need not include the same magnetic field sensors.

The physician 30 navigates the lasso catheter 50 to a target location in the heart 26 of the patient 28 by manipulating the shaft 22 and/or deflecting from the sheath 23 using the manipulator 32 near the proximal end of the catheter. The lasso catheter 50 is inserted while being folded through the sheath 23, and only after the sheath 23 is retracted, the lasso catheter 50 resumes its intended functional shape. By including the lasso catheter 50 in the collapsed configuration, the sheath 23 also serves to minimize vascular trauma along the approach to the target location.

typically, lasso catheter 50 is used for diagnostic or therapeutic treatments, such as spatial mapping of the heart and mapping of corresponding potentials in the heart prior to performing ablation of cardiac tissue. Other types of catheters or other in-vivo devices may alternatively be used with system 20 for other purposes, by themselves or in conjunction with other therapeutic devices, such as ablation catheters.

As described above, lasso catheter 50 includes multiple sensing electrodes. These sensing electrodes are connected to drive circuitry in console 24 by wires passing through shaft 22. The console 24 includes a processor 41 (typically a general purpose computer) with appropriate front end and interface circuitry 44 for receiving signals from the purelacl patch 49. The processor 41 is connected by wires through the cable 39 to a PureACL patch 49, which PureACL patch 49 is attached to the chest skin of the patient 26.

In some embodiments, processor 41 accurately determines the position coordinates of the sensing electrodes at lasso catheter 50 that fits within heart 26. Processor 41 determines the position coordinates based on the measured impedance between the sensing electrodes (on the catheter) and the ACL patch 49 (i.e., using the pureac and ICL methods described above) among other inputs. Console 24 drives display 27, which displays the distal end of the catheter position within the body.

Electrode position sensing methods using the ACL in the system 20 are implemented in various medical applications, such as in the carto (tm) system produced by Biosense Webster corporation of Irvine, California, and described in detail in U.S. patents 7,756,576, 7,869,865, and 7,848,787, the disclosures of which are incorporated herein by reference.

The console 24 also includes a magnetic induction subsystem. The patient 28 is placed in a magnetic field generated by a pad containing magnetic field generator coils 42 driven by a unit 43. The magnetic field generated by coil 42 generates a position signal in magnetic sensor 51 which is further provided as a corresponding electrical input to processor 41 which uses these to calculate the displacement of the sensing electrode due to deformation of catheter 50 to correct the position of sensing electrodes PureACL and ICL derivation.

In some embodiments, processor 41 is further configured to estimate the location of lasso catheter 50 (i.e., the flexible distal component of catheter 50) within the body based on: (i) the current injected by the sense electrodes, (ii) the a priori known distance between adjacent sense electrodes, and (iii) an indication of the spatial displacement provided by the magnetic sensor 51, as explained below.

In some embodiments, processor 41 is further configured to receive a position signal from magnetic sensor 51 indicative of the position of the distal end of catheter 50 in order to calculate the displacement in space of catheter 50 due to its deformation. The position sensing method using an external magnetic field is implemented in various medical applications, for example, in the carto (tm) system produced by Biosense Webster Inc (Diamond Bar, Calif), and described in detail in U.S. patent nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612, and 6,332,089, PCT patent publication WO 96/05768, and U.S. patent application publications 2002/0065455 a1, 2003/0120150 a1, and 2004/0068178 a1, the disclosures of which are all incorporated herein by reference.

The processor 41 is typically programmed in software to perform the functions described herein. The software may be downloaded to the computer in electronic form over a network, for example, the software may alternatively or additionally be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory.

For simplicity and clarity, FIG. 1 only shows the elements relevant to the disclosed technology. System 20 generally includes additional modules and elements that are not directly related to the disclosed technology and, therefore, are intentionally omitted from fig. 1 and the corresponding description. The elements of system 20 and methods described herein may be applied to position sensing and/or control ablation using a variety of multi-electrode catheters, such as multi-arm catheters (e.g., manufactured by biosense-Webster). Acquiring position signals may also be accomplished by applying voltage gradients using ACL patch electrodes 49 or other skin attachment electrodes, and measuring potential voltages with one or more sensing electrodes on catheter 50. (e.g., using techniques manufactured by Biosense Webster, Inc. (European, Calif.)). The interface circuit 44 may generally be configured to exchange signals with an intrabody probe and/or a body surface electrode.

Catheter localization using current location in combination with magnetic sensing

FIG. 2 is a schematic detail view of a flexible lasso catheter 50 comprising a magnetic sensor 51 and a plurality of sensing electrodes 52 and 520 according to an embodiment of the invention. The sensing electrode is also referred to herein as an intrabody electrode, and these two terms are used interchangeably. As shown in FIG. 2, a lasso catheter 50 is mounted at the distal end of the shaft 22. The flexible lasso catheter 50 comprises a flexible base section 53 to which a magnetic sensor 51 is coupled. Two sensing electrodes 520 are positioned on the base section 53, close to the magnetic sensor 51. A plurality of sensing electrodes 52 are circumferentially distributed on a lasso guidewire 54. In the fully expanded state of the catheter 50, the lasso guidewire 54 lies in a plane perpendicular to the longitudinal axis defined by the distal end of the shaft 22.

The catheter configuration depicted in fig. 2 was chosen purely for conceptual clarity. Indeed, the lasso guidewire 54 may include one or more windings about the longitudinal axis defined by the distal end of the shaft 22, or fewer than a single winding. In alternative embodiments, other flexible catheters may be fitted at the distal end of the shaft 22, such as a mapping catheter including multiple arms. The magnetic sensor 51 may include one or more magnetic sensors. Only a simplified fiber segment is shown, wherein all other elements of the magnetic sensor 51 are omitted for clarity.

FIG. 3 is a schematic view of the flexible lasso catheter of FIG. 2 in a straight and deformed state according to one embodiment of the invention.

The base section 53 of the lasso conduit 50 can be seen in the undeformed state 46 and also in the deformed state 47. States 46 and 47 illustrate two successive states of the position of the measuring electrode 52. When the noose base section 53 is undeformed, its undeformed direction 66 is parallel to the direction of the longitudinal axis defined by the distal end of the shaft 22. When the base section 53 is deformed, the base section 53 (and its lasso wire 54) points in a different direction, the deformation direction 67.

As shown in fig. 3, deformation of the base section 53 causes a position change displacement 550 of the magnetic sensor. The position of sensing electrode 520 also changes substantially the same displacement 550. For example, by applying purelacl and ICL methods to the signals from the electrodes 520 on the base section 53, one can attempt to derive the deformation direction 67 without using the disclosed techniques. However, the resulting position is only accurate to about 7mm at the edges of the mapped volume. Using embodiments of the present invention improves the accuracy at the edges of the mapped volume to about 1mm, as explained below.

The positions of sensing electrodes 52A, 52B, and 52C also change (very approximately) to positions 52A, 52B, and 52C, respectively, by displacement 550. Thus, displacement 550 serves as a correct measure of displacement 55A, 55B, and 55C, which characterizes most of the positional changes that electrodes 52A, 52B, and 52C experience due to exemplary deformations.

Such changes in sensing electrode position between lasso states 46 and 47 may not be captured by the less accurate impedance-based position measurements of purelacl and ICL. To correct the position, the displacement 550 is measured by the magnetic sensor 51. It should be noted that in a similar manner, when the deformed state of like state 47 transitions to the undeformed state of like state 46, the magnetic sensor 51 will indicate the opposite displacement-550. Using displacement 550 as an input, processor 41 may verify the correctness of the electrode position or correct the less accurately measured position of the flexible distal end assembly (derived from purelacl and ICL).

A particular type of deformation of the base section 53 shown in fig. 3 is in-plane deflection. This variation is depicted by way of example only. In general, the deformation of the base section 53 of the lasso catheter 50 may include any deformation in space, such as a combination of bending and/or deflection (relative to the longitudinal axis) and torsion (about the longitudinal axis).

The magnetic sensor 51 is configured to provide an indication of deformation of the base section 53. Processor 41 uses the indication to calculate a general displacement in space 550.

In one embodiment, the lasso catheter 50 is deformed within a certain plane in space (e.g., the deformation shown in fig. 3). Exemplary forms of this bending may occur, for example, due to catheter structure (e.g., the rigid nature of base section 53) or due to the nature of the anatomy being probed. In such cases, the measurement of the deformation is substantially one-dimensional, and a simplified magnetic sensor may be assembled and/or a simplified magnetic sensing method employed.

Fig. 4 is a flow chart schematically illustrating a method for accurately mapping a cavity (e.g., a heart cavity) in a body, in accordance with an embodiment of the present invention. Fig. 4 may illustrate the position measurement of sensing electrode 55 in deformed state 47.

At the start of the mapping process, processor 41 calculates the position 62 of sensing electrode 52 at purelacl step 60. As shown in inset 61, the position is calculated at a given body position relative to an arbitrary origin 58. The measurements appear to be insensitive to deformation of the lasso catheter 50 because the calculated electrode position 62 extends about the previous undeformed direction 66 (i.e., about the electrode position in the undeformed state 46) relative to the origin 58.

Next, the processor 41 calculates a local scaling factor for the electrode position using an ICL local scaling process in an ICL step 63. The results are shown in inset 64, where the now derived positions 65 of the sensing electrodes are more compactly distributed about the undeformed direction 66 relative to the arbitrary origin 58. The spatial distribution is now corrected to reflect the local distribution of the electrodes 55 on the lasso 50, but the electrode positions 65 are still inaccurate compared to their actual positions. I.e., the impedance-based measurement is insensitive to deformation of the flexible distal end assembly of the lasso catheter 50.

To correct for such errors, the magnetic sensor 51 provides displacement of the flexible distal end assembly between subsequent measurements (i.e., between its position in state 46 and the current measurement position in state 47). The change in position measured by the magnetic sensor is given as a displacement 550, at a magnetic sensing step 68. Processor 41 corrects electrode position 65 by adding displacement 550. As seen in inset 69, the resulting calculated electrode position 70 is now correctly derived to expand about the magnetic deformation direction 67 relative to the arbitrary origin 58 (in the exemplary deformation in fig. 3, the electrode position 70 is corrected by being shifted downward by a distance 550 relative to the electrode position 65).

when the physician 30 moves the lasso catheter to a new location in the cavity, the process repeats itself, looping back to the ACL step 60, at a repositioning step 71, until the physician 30 receives a complete mapping of the cavity, for example, the cavity of the left atrium of the heart.

The exemplary flow chart shown in fig. 4 was chosen solely for the sake of conceptual clarity. In alternative embodiments, the order of the steps may be changed (e.g., ACL and magnetic sensing steps may occur in parallel), and additional steps may be used, such as magnetic sensing of catheter position. For clarity, few ICL methods have been proposed. The ICL method typically comprises more algorithm steps than presented. For example, the actual position may be determined by the ICL method by averaging the local scaling factors for each of the body voxels through which the catheter has passed.

although the embodiments described herein relate primarily to cardiac applications, the methods and systems described herein may also be used in other applications, such as gastroenterology, otorhinolaryngology, neurology.

It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art. Documents incorporated by reference into this patent application are considered an integral part of the application, except that definitions in this specification should only be considered if any term defined in these incorporated documents conflicts with a definition explicitly or implicitly set forth in this specification.