DEVICE AND METHOD FOR DETERMINING A LOCAL PROPERTY OF A BIOLOGICAL TISSUE

Abstract

The disclosure relates to an ablation catheter for determining a local property of a biological tissue, said catheter having a flexible shaft, a data processing device, and an NMR sensor, which is arranged at the distal end of the shaft and is connected to the data processing device, wherein the NMR sensor comprises a first sensor element for generating a static magnetic field and a second sensor element for generating a magnetic alternating field, wherein the distal end of the shaft can be arranged adjacently to the point of the tissue to be measured, wherein the data processing device is designed to determine the local property of the tissue at this point on the basis of a signal of the NMR sensor transmitted to the data processing device. The disclosure also relates to a corresponding method.

Claims

1. An ablation catheter for determining a local property of a biological tissue, comprising: a flexible shaft, a data processing device, and an NMR sensor, which is arranged at the distal end of the shaft and is connected to the data processing device, wherein the NMR sensor comprises a first sensor element for generating a static magnetic field and a second sensor element for generating a magnetic alternating field, wherein the distal end of the shaft can be arranged adjacently to the point of the tissue to be measured, wherein the data processing device is designed to determine a local property of the tissue at this point on the basis of a signal of the NMR sensor transmitted to the data processing device, and wherein the data processing device is also designed to determine the progress of formation of a lesion.

2. The ablation catheter according to claim 1, wherein the first sensor element is formed as a permanent magnet or as a coil.

3. The ablation catheter according to claim 2, wherein the permanent magnet is spherical or cuboid-shaped.

4. The ablation catheter according to claim 1, wherein the second sensor element is formed as a coil.

5. The ablation catheter according to claim 1, wherein a shaft tip arranged at the distal end of the shaft has at least one recess in the form of a slot or is embodied as a helix antenna.

6. The ablation catheter according to claim 1, wherein the NMR sensor is pivotable and/or rotatable relative to the shaft by means of at least one pull cable fastened to the NMR sensor.

7. The ablation catheter according to claim 1, wherein der NMR-Sensor is mounted on a substrate which has a first portion with a higher elasticity and a second portion with a lower elasticity as compared to the first portion, wherein the first portion brings about a restoring force when the NMR sensor is pivoted relative to the shaft.

8. The ablation catheter according to claim 1, wherein the NMR sensor is designed for excitation by means of magnetic alternating field pulses, wherein a further pulse is sent after a 90 excitation pulse, which further pulse rotates the spins of the protons of the tissue through 180.

9. A method for determining a local property of a biological tissue, in which method, following excitation by an NMR sensor arranged at the distal end of a flexible shaft of an ablation catheter, adjacently to the point of the tissue to be measured, an NMR response signal of the tissue is generated and the local tissue property is determined on the basis of this NMR signal.

10. The method according to claim 9, wherein, prior to the generation of the NMR signal, the axis of an excitation cone of the NMR sensor is oriented substantially perpendicularly to the tissue surface.

11. The method according to claim 10, wherein the NMR sensor is oriented: by actuating at least one pull cable fastened to the NMR sensor, such that a pivoting and/or rotation of the NMR sensor is brought about, and/or by rotating the shaft.

12. The method according to claim 9, wherein the distal end of the shaft is displaced in the direction of the longitudinal axis of the shaft in such a way that the distal end of the shaft bears against the surface of the tissue to be measured.

13. The method according to claim 9, wherein intermittently between the determination of the local tissue property on the basis of the NMR signal, a shaft tip arranged at the distal end of the shaft is supplied with a current or a voltage is applied to the shaft tip.

14. A computer program product for determining a local property of a biological tissue, said computer program product comprising program code means for executing a computer program following implementation thereof in a data processing device, wherein the program code means are intended to execute the method according to claim 9 following the implementation in the data processing device.

Description

DESCRIPTION OF THE DRAWINGS

[0046] The present invention will be explained hereinafter on the basis of exemplary embodiments and with reference to the drawings. Here, all features described and/or shown in the drawings form the subject matter of the present invention, individually or in any combination, and also independently of their summary in the claims and the dependency references of the claims.

[0047] The drawings show schematically:

[0048] FIG. 1 shows a catheter according to the present invention in a view from the side,

[0049] FIG. 2 shows a device according to the present invention in a view from the side,

[0050] FIG. 3 shows a first exemplary embodiment for the primary realization of the NMR sensor of the device according to FIG. 2,

[0051] FIG. 4 shows a second exemplary embodiment for the primary realization of the NMR sensor of the device according to FIG. 2,

[0052] FIG. 5 shows a third exemplary embodiment for the primary realization of the NMR sensor of the device according to FIG. 2,

[0053] FIG. 6 shows a second exemplary embodiment of a device according to the present invention in a view from the side including the magnetic field lines of the first sensor element,

[0054] FIG. 7 shows the NMR sensor of the device according to FIG. 6 in a view from the side,

[0055] FIG. 8 shows the shaft tip of the device according to FIG. 6 including the magnetic field lines of the second sensor element in a view from the side,

[0056] FIG. 9 shows a second exemplary embodiment of a shaft tip of the device according to FIG. 6 in a view from above,

[0057] FIG. 10 shows a third exemplary embodiment of a shaft tip of the device according to FIG. 6 in a view from the side,

[0058] FIG. 11 shows the shaft tip according to FIG. 10 in a view from above,

[0059] FIG. 12 shows a third exemplary embodiment of a device according to the present invention in a view from the side including the magnetic field lines of the first sensor element,

[0060] FIG. 13 shows the NMR sensor of the device according to FIG. 12 in a view from the side,

[0061] FIG. 14 shows the shaft tip of the device according to FIG. 12 including the magnetic field lines of the second sensor element in a view from the side,

[0062] FIG. 15 shows a second exemplary embodiment of a shaft tip of the device according to FIG. 12 in a view from the side,

[0063] FIG. 16 shows the shaft tip according to FIG. 10 in a view from above,

[0064] FIGS. 17-22 show the orientation of the excitation cone by means of rotation of the NMR sensor of the device according to FIG. 9,

[0065] FIG. 23 shows a further exemplary embodiment of an NMR sensor of a device according to the present invention in a view from the side,

[0066] FIG. 24 shows the magnetic field lines of the second sensor element of the NMR sensor according to FIG. 23,

[0067] FIG. 25 shows the magnetic field lines of the first sensor element of the NMR sensor according to FIG. 23,

[0068] FIGS. 26-27 show the orientation of the excitation cone by means of rotation of the NMR sensor according to FIG. 23, and

[0069] FIG. 28 shows the excitation of the protons by means of the NMR sensor in accordance with the sin echo method in the time domain and the frequency domain.

DETAILED DESCRIPTION

[0070] The design and the operating principle of a catheter according to the present invention or of a device according to the present invention comprising a shaft will be explained hereinafter on the basis of an ablation catheter which is used for intracardiac ablation. The present invention, however, is not intended to be limited to this example. The design and the operating principle of a catheter according to the present invention all of a device according to the present invention can be transferred analogously to catheters/devices for other treatments or other tissues, wherein the determination of the local tissue property, for example the local thickness or local lesion depth, is of significance.

[0071] FIG. 1 shows an exemplary embodiment of a catheter according to the present invention with a handgrip 1, at least one electrical and/or optical signal line 2 for the transmission of signals from and/or to the at least one or sensor or sensor element, mounted on the catheter, and/or the at least one electrode, a flush line 3, a control mechanism 4, and an inner shaft 20. The inner shaft 20 as part of the device according to the present invention. For ablation, the inner shaft 20 is inserted into the body of the patient, for example along the blood vessels of the patient, until the distal end of the inner shaft 20 bears against the desired point of the heart muscle tissue which is to be ablated. In order to detect the electrical cardiac activity, at least one electrode 5 is provided at the distal end of the inner shaft 20. In the embodiment shown in FIG. 1, the electrode 5 is formed as a ring electrode. A mini electrode arranged within the distal tip of the inner shaft 20 is likewise conceivable. By means of the control mechanism 4, the distal end of the inner shaft 20 can be deflected for example via a push-pull mechanism, as is illustrated by means of the dashed arrows. Additionally, as will be described below in greater detail, the excitation cone 32, by means of a rotational movement of the control mechanism 4, can be oriented relative to the tissue to be examined and to be ablated. Alternatively to the manual control by means of the control mechanism 4, a bidirectional automated control can be applied.

[0072] At the distal end of the inner shaft 20 (see FIG. 2), an electrically conductive shaft tip 25 is provided, which is connected to an electrical circuit. The connections are disposed on the inner side of the shaft tip 25 and are guided through the inner shaft 20. For the ablation, the shaft to 25 is exposed to an electrical high-frequency current via a signal line 2. As a result of the contact of the shaft tip 25, the high-frequency current also passes into the heart muscle tissue bearing against the shaft tip 25 and is hereby destroyed.

[0073] In order to assess the progress of the lesion formation or the ablation, the catheter according to the invention has an NMR sensor at the distal end of the inner shaft 20. This NMR sensor 30 is connected to a data processing device 40 (for example a (micro)processor or a computer) arranged outside the body of the patient. The assessment of the progress of the ablation is implemented by the NMR sensor 30 and is controlled by the data processing device 40. Before the treatment is started and at the end of each treatment step, the NMR sensor 30 is activated by the data processing device 40 and excites, in an excitation cone 32, the protons of the heart muscle tissue 50 disposed in the excitation cone 32. By superimposing a static magnetic field and a magnetic alternating field, the spins of the protons are oriented and brought out of their state of equilibrium. The NMR signal emitted by the protons as they return to the state of equilibrium is detected by the NMR sensor 30 and transmitted to the data processing device 40. This device, on the basis of the difference between amplitude and phase of the NMR signal before the onset of the ablation and the last-measured NMR signal, calculates in particular the difference in the amplitude, for example the reduction in the thickness of the heart muscle tissue at the point disposed in the excitation cone 32, and on this basis also calculates the lesion depth. As soon as a sufficient lesion depth is reached, the treatment at this point can be terminated and as applicable continued at another point. The limit value for the amplitude and/or phase change of the NMR signal at which the treatment is terminated can be defined experimentally.

[0074] The catheter according to the present invention thus enables a precise assessment of the progress of the lesion formation or the ablation in a simple way.

[0075] As has already been explained above, the NMR sensor 30 has a first sensor element 34, which generates a static magnetic field, and a second sensor element 35, which produces a magnetic alternating field. Here, the field lines of the static magnetic field of the first sensor element 34 and the field lines of the magnetic alternating field of the second sensor element 35 must be arranged perpendicularly to one another at least in the excitation cone 32. Three fundamental exemplary embodiments for the realization of the first and second sensor element are shown with reference to FIGS. 3 to 5.

[0076] In the exemplary embodiment according to FIG. 3, the first sensor element 34 is embodied as a coil, the magnetic field lines of which run parallel to the (longitudinal) axis 22 of the inner shaft 20. The second sensor element 35 is likewise embodied as a coil, wherein the magnetic field lines of this coil run perpendicularly to the axis 22. In an alternative exemplary embodiment, both the first sensor element 34 and the second sensor element 35 can each be embodied as a coil, wherein in this case the magnetic field lines of the first sensor element run perpendicular to the axis 22 of the inner shaft 20, and the magnetic field lines of the second sensor element run parallel to the axis 22 of the inner shaft 20.

[0077] In the exemplary embodiments shown in FIGS. 4 and 5, the first sensor element 34 is embodied as a permanent magnet. By contrast, the second sensor element 35 is embodied as a coil. In the exemplary embodiment shown in FIG. 4, the magnetic field lines of the first sensor element 34 run perpendicularly to the axis 22 of the inner shaft 20, and in the exemplary embodiment shown in FIG. 5 parallel to the axis 22 of the inner shaft 20. Accordingly, the magnetic field lines of the second sensor element 35 in the exemplary embodiment shown in FIG. 4 run parallel, and in the exemplary embodiment shown in FIG. 5 run perpendicular to the axis 22 of the inner shaft 20.

[0078] The exemplary embodiment shown in FIGS. 6 and 7 corresponds to the principle shown in FIG. 5, wherein the first sensor element 34 is spherical. The second sensor element 35 is a coil which is wound around the spherical first sensor element and which for example is made from neodymium. The arrangement formed of first sensor element 34 and second sensor element 35 is shown in FIG. 7. The first sensor element for example has a diameter of 2 mm. The magnetic flux density of the first sensor element is for example 1 T at the surface. The magnetic field lines of the first sensor element 34 are shown in FIG. 6, whereas the magnetic field lines of the second sensor element are shown in FIG. 8 (see dashed lines).

[0079] In order to avoid the formation of shielding circuit currents in the metal shaft tip 25, said shaft tip has a cross slot 26, which passes through the shaft tip 25. The slot of the cross slot for example has a width of 0.1 mm (see FIG. 9). Alternatively, a continuous spiraled slot 27 is provided laterally on the shaft tip 25. The axis of the spiral, as can be inferred from FIGS. 10 and 11, runs at an angle of at least 70 to the axis 22 of the inner shaft 20. The spiraled slot 27 likewise has a width of 0.1 mm, for example.

[0080] The exemplary embodiment shown in FIGS. 12 and 13 corresponds to the principle shown in FIG. 4 of the arrangement of the first and second sensor element, wherein in this exemplary embodiment as well the first sensor element 34 is formed as a spherical neodymium permanent magnet. The second sensor element 35 is a coil which is wound around the spherical first sensor element 34. The arrangement formed of first sensor element 34 and second sensor element 35 is shown in FIG. 13. The first sensor element for example has a diameter of 2 mm. The magnetic flux density of the first sensor element 34 is for example 1 T at the surface. The magnetic field lines of the first sensor element 34 are shown in FIG. 12, whereas the magnetic field lines of the second sensor element 35 are shown in FIG. 14 (see dashed lines).

[0081] In order to avoid the formation of shielding circuit currents in the metal shaft tip 25 in the exemplary embodiment shown in FIG. 12, said shaft tip, as shown in FIGS. 15 and 16, is embodied as a helix antenna 29. The number of helix turns is limited by the length of the metal catheter tip and lies preferably in the range of from 5 to 10 turns. In the region of the tapering catheter tip, the turns of the helix antenna 29 can be formed in an equiangular or equidistant manner (Archimedes spiral) in order to increase the bandwidth of the antenna. The thickness of the wire or helix antenna is for example between 0.05 mm and 0.5 mm.

[0082] In order to orientate the NMR sensor 30 of the exemplary embodiment shown in FIG. 6 such that the axis of the excitation cone 32 runs approximately perpendicularly to the surface of the heart muscle tissue at the point to be examined, four pull cables 37 are fastened to the periphery of the first sensor element 34. This is shown in FIG. 17. The four pull cables 37 are arranged at the periphery of the first sensor element 34 in such a way that they each enclose an angle of 90 with the adjacent pull cable 37. By pulling suitably on one or more pull cables 37, the movably mounted NMR sensor 30 can be rotated and/or pivoted (see arrows P1 and P2) about the center point or another point, preferably lying on the axis 22 of the inner shaft 20, within the first sensor element 34 and therefore in relation to the axis 22. The NMR sensor 30 can be mounted, for example, by means of a spherical shell element (not shown), wherein the NMR sensor is arranged in the spherical shell segment. Examples of an orientation of this kind in relation to the heart muscle tissue 50 are shown in FIGS. 18 to 20. In the variant of FIG. 18 the excitation cone 32 runs substantially parallel to the axis 22 of the inner shaft 20. In the constellation of FIG. 19, the axis of the excitation cone 32 runs for example at an angle of 30 to the axis of the excitation cone 32. FIG. 20 shows that, as a result of this manipulation, the excitation cone 32 can be pivoted relative to the axis of the inner shaft 20 such that the axis of the excitation cone encloses an angle of approximately 70 with the axis 22 of the inner shaft.

[0083] A similar manipulation can also be achieved by means of an arrangement in which only two pull cables 37 are provided, which are fastened to the periphery of the first sensor element 34, more specifically in a mutually opposed arrangement. An exemplary embodiment of this kind is shown in FIGS. 21 and 22. The arrow F arranged at one pull cable 37 represents the force (value and direction) which is applied by pulling on the pull cable 37 in order to rotate or pivot the NMR sensor 30 (see arrow P1) relative to the axis 22. In order to achieve the orientation of the excitation clone 32 in any (three-dimensional) direction, the inner shaft 20 can be rotated additionally about its axis 22.

[0084] The movement of the excitation cone is brought about preferably by means of the control mechanism 4.

[0085] FIG. 23 shows a further exemplary embodiment of an NMR sensor 30, which has weaker non-linear behavior as compared to the above-described exemplary embodiments with the spherical permanent magnet. The first sensor element 34 is formed by a horse shoe-shaped permanent magnet, which is preferably made of neodymium. The first sensor element 34 for example has a width B of the base of 2 mm and a height H of the arms 34a of 1 mm to 2 mm. The magnetic field lines of the first sensor element are shown in FIG. 25 and run perpendicularly to the axis 22 of the inner shaft 20. In order to keep the opening angle of the excitation cone 32 as small as possible, the second sensor element 35 is embodied as a coil which is arranged between the arms 34a of the horseshoe-shaped first sensor element 34. In a preferred exemplary embodiment the second sensor element 35 has a ferromagnetic, non-electrically conductive coil core 35a, which increases the attained field strength. The magnetic field lines of the second sensor element 35 are shown in FIG. 24 and run parallel to the axis 22 of the inner shaft 20.

[0086] As is shown in FIGS. 26 and 27, the NMR sensor 30 is mounted on a substrate that is resilient at least in regions. The substrate comprises a first portion 38, which has a higher elasticity, and a second portion 39, which has a lower elasticity, wherein the first portion 38 and the second portion 39 are arranged side by side transversely to the longitudinal axis of the inner shaft 20. A pull cable 37 is also fastened to the outer side of an arm 34a of the first sensor element 34. By pulling on the pull cable (see the direction of the force F indicated by an arrow in FIG. 27), for example by means of the control mechanism 4, the NMR sensor is pivoted about an axis arranged perpendicular to the image of FIG. 27 (see arrow P1) and therefore also relative to the longitudinal axis of the shaft 20, such that the excitation cone can be oriented in relation to a tissue surface. As applicable, the inner shaft 20 is additionally rotated about its axis 22, in order to provide the orientation in any spatial direction. The resilient first portion 38 of the substrate causes a restoring force and causes the NMR sensor 30 to pivot back into the starting position shown in FIG. 26 when the tensile force F on the pull cable 37 is reduced.

[0087] On account of the relatively strong and non-linear static magnetic field gradient of a first sensor element 34 formed as a spherical solid-state magnet, the excited spins will de-phase within a short period of time. This circumstance can be counteracted by means of spin echo methods, in which for example a further pulse is sent after a 90 excitation pulse, which further pulse returns the spins of the protons through 180 (see FIG. 28). Each magnetic field pulse is a broadband pulse over a frequency range of for example 1 kHz to 20 MHz The excitation with the pulses A and B as well as the NMR signal C from the tissue are shown in FIG. 28 at the top in the time domain and at the bottom in the frequency domain.

[0088] The present invention uses the known NMR technology in order to determine, in a simple and economical manner, the progress of a treatment or the size of a lesion, in particular the depth thereof in the tissue. With the solution according to the present invention, by means of the design of the NMR sensor 30, the NMR excitation can be limited to an excitation cone 32 having a small opening angle. The depth of the observation field can be influenced via the magnetic field parameters.

It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points.

LIST OF REFERENCE NUMERALS

[0089] 1 handgrip of the catheter [0090] 2 signal line [0091] 3 flush line [0092] 4 control mechanism [0093] 5 electrode [0094] 20 inner shaft [0095] 22 axis (longitudinal axis) of the inner shaft [0096] 25 shaft tip [0097] 26 cross slot [0098] 27 spiralled sot [0099] 29 helix antenna [0100] 30 NMR sensor [0101] 32 excitation cone [0102] 34 first sensor element [0103] 34a arm of the horseshoe magnet [0104] 35 second sensor element [0105] 35a coil core [0106] 37 pull cable [0107] 38 first portion of the substrate [0108] 39 second portion of the substrate [0109] 40 data processing device [0110] 50 heart muscle tissue [0111] A,B excitation pulse [0112] BR width [0113] C NMR signal [0114] F force [0115] H height [0116] P1 arrow 1 [0117] P2 arrow 2 [0118] f display in frequency domain [0119] t display in time domain