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 strips connected to the distal end of the insertion tube and second ends of the 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 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 position sensors;

compute location and orientation coordinates for the first and second position sensors using a position computation in which the location and orientation coordinates of each of the position sensors are interdependently computed in an iterative manner responsively to the respective received position signals, and subject to a constraint that the first and second position sensors are coaxial;

compute a distance between the computed location coordinates of the first position sensor and the computed location coordinates of the second position sensor; and

estimate respective positions of the flexible strips responsively to at least the computed distance.

2. The system according to claim 1 , further comprising a display, 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 position sensors; and 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.

3. 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 position sensors using the position computation; and compute the location coordinates for another sensor of the first and second 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.

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

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

6. 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 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 position sensors;

computing location and orientation coordinates for the first and second position sensors using a position computation in which the location and orientation coordinates of each of the position sensors are interdependently computed in an iterative manner responsively to the respective received position signals, and subject to a constraint that the first and second position sensors are coaxial;

computing a distance between the computed location coordinates of the first position sensor and the computed location coordinates of the second position sensor; and

estimating respective positions of the flexible strips responsively to at least the computed distance.

7. The method according to claim 6 , further comprising:

computing a roll of the expandable assembly responsively to the position signal from at least one of the first or second 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.

8. The method according to claim 6 , further comprising:

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

computing the location coordinates for another sensor of the first and second 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.

9. The method according to claim 6 , further comprising:

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

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

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

10. The method according to claim 6 , further comprising computing the location and orientation coordinates for the first and second position sensors subject to a constraint that the computed orientation coordinates for the first and second position sensors will be equal within a given tolerance.