Accurate basket catheter tracking

1. A system comprising:

a catheter configured to be inserted into a body-part of a living subject, and comprising:

an insertion tube including a distal end, and a first coil-based position sensor disposed at the distal end;

a pusher including a second coil-based position sensor disposed thereon and a distal portion, and being configured to be advanced and retracted through the insertion tube; and

an expandable assembly comprising a plurality of flexible strips disposed circumferentially around the distal portion of the pusher, with first ends of the flexible strips connected to the distal end of the insertion tube and second ends of the flexible strips connected to the distal portion of the pusher, the flexible strips being configured to bow radially outward when the pusher is retracted;

at least one magnetic field radiator configured to transmit alternating magnetic fields into a region where the body-part is located, the first and second coil-based position sensors being configured to output respective first and second position signals in response to the transmitted alternating magnetic fields; and

processing circuitry configured to:

receive the first and second position signals from the first and second coil-based position sensors;

compute a distance and a relative orientation angle between the first and second coil-based position sensors responsively to the received first and second position signals; and

estimate respective positions of the flexible strips responsively to at least the computed distance and relative orientation angle, while accounting for a distortion of one or more of the flexible strips from a symmetrical disposition when the relative orientation angle has a value greater than zero.

2. The system according to claim 1 , wherein the processing circuitry is configured to compute a roll of the expandable assembly responsively to the position signal from at least one of the first or second coil-based position sensors.

3. The system according to claim 2 , further comprising a display, wherein the processing circuitry is configured to render to the display a representation of at least a part of the catheter and the body-part responsively to the estimated respective positions of the flexible strips.

4. The system according to claim 1 , wherein the processing circuitry is configured to:

compute the location and orientation coordinates for one sensor of the first and second coil-based position sensors using the position computation; and

compute the location coordinates for another sensor of the first and second coil-based position sensors subject to a constraint that the computed orientation coordinates for the other sensor will be equal to the computed orientation coordinates of the one sensor within a given tolerance.

5. The system according to claim 4 , wherein the given tolerance is approximately plus or minus two degrees.

6. The system according to claim 1 , wherein the processing circuitry is configured to:

compute initial location and initial orientation coordinates for the first and second coil-based position sensors using the position computation;

compute an average of the initial orientation coordinates of the first and second coil-based position sensors; and

compute the location and orientation coordinates for the first and second coil-based position sensors using the position computation subject to a constraint that the orientation coordinates for the first and second coil-based position sensors will be equal to the computed average of the initial orientation coordinates with a given tolerance.

7. The system according to claim 1 , wherein the processing circuitry is configured to compute the location and orientation coordinates for the first and second coil-based position sensors subject to a constraint that the computed orientation coordinates for the first and second coil-based position sensors will be equal within a given tolerance.

8. The system according to claim 1 , wherein at least one of the first and second coil-based position sensors comprises a dual-axis position sensor.

9. The system according to claim 1 , wherein at least one of the first coil-based position sensor comprises a triple-axis position sensor.

10. The system according to claim 1 , wherein the first and second coil-based position sensors are coaxial.

11. The system according to claim 1 , wherein the plurality of flexible strips comprises a plurality of electrodes.

12. The system according to claim 11 , wherein at least some of the electrodes of the plurality of electrodes are configured to detect electrophysiological signals for electro-anatomical mapping.

13. The system according to claim 11 , wherein at least some of the electrodes of the plurality of electrodes are configured to deliver ablative energy to tissue.

14. A method, comprising:

inserting a catheter into a body-part of a living subject, the catheter comprising an insertion tube, a first coil-based position sensor disposed at a distal end of the insertion tube, a pusher including a second coil-based position sensor disposed thereon, an expandable assembly including flexible strips disposed circumferentially around a distal portion of the pusher, with first ends of the strips connected to the distal end of the insertion tube and second ends of the strips connected to the distal portion of the pusher;

retracting the pusher causing the flexible strips to bow radially outward;

transmitting alternating magnetic fields into a region where the body-part is located;

outputting by the first and second coil-based position sensors respective first and second position signals in response to the transmitted alternating magnetic fields;

receiving the first and second position signals from the first and second coil based position sensors;

computing a distance and a relative orientation angle between the first and second coil-based position sensors responsively to the received first and second position signals; and

estimating respective positions of the flexible strips responsively to at least the computed distance and relative orientation angle, while accounting for a distortion of one or more of the flexible strips from a symmetrical disposition when the relative orientation angle has a value greater than zero.

15. The method according to claim 14 , further comprising:

computing a roll of the expandable assembly responsively to the position signal from at least one of the first or second coil-based position sensors; and

rendering to a display a representation of at least a part of the catheter and the body-part responsively to the estimated respective positions of the flexible strips.

16. The method according to claim 14 , further comprising:

computing the location and orientation coordinates for one sensor of the first and second coil-based position sensors using the position computation; and

computing the location coordinates for another sensor of the first and second coil-based position sensors subject to a constraint that the computed orientation coordinates for the other sensor will be equal to the computed orientation coordinates of the one sensor within a given tolerance.

17. The method according to claim 14 , further comprising:

computing initial location and initial orientation coordinates for the first and second coil-based position sensors using the position computation;

computing an average of the initial orientation coordinates of the first and second coil-based position sensors; and

computing the location and orientation coordinates for the first and second coil-based position sensors using the position computation subject to a constraint that the orientation coordinates for the first and second coil-based position sensors will be equal to the computed average of the initial orientation coordinates with a given tolerance.

18. The method according to claim 14 , further comprising computing the location and orientation coordinates for the first and second coil-based position sensors subject to a constraint that the computed orientation coordinates for the first and second coil-based position sensors will be equal within a given tolerance.

19. The method according to claim 14 , wherein the first and second coil-based position sensors are coaxial.

20. The method according to claim 14 , wherein the flexible strips comprises a plurality of electrodes.