Patent Description:
Various techniques were proposed for improving intra-body magnetic position sensors and their integration. For example, <CIT> describes a medical device assembly for use in a magnetic environment, including a medical device comprising a shaft having proximal and distal end portions. The device further comprises a position sensor at the distal end portion of the shaft that comprises first and second leads extending therefrom to the proximal end portion of the shaft. The device further comprises an electromechanical connector having a plurality of connection points at a first end thereof. First and second of the connection points are electrically connected to the first and second sensor leads, respectively. The connector further comprises an error loop segment electrically coupled to third and fourth connection points. The error loops segment assists in forming a compensation loop that can be used to correct for magnetic noise.

As another example, <CIT> describes a method and apparatus for determining the position and orientation of a remote object relative to a reference coordinate frame. The apparatus can be used for locating the end of a catheter or endoscope, digitizing objects for computer databases, virtual reality and motion tracking. The apparatus includes a plurality of field-generating elements for generating electromagnetic fields, a drive for applying, to the generating elements, signals that generate a plurality of electromagnetic fields that are distinguishable from one another, a remote sensor having one or more field-sensing elements for sensing the fields generated and a processor for processing the outputs of the sensing element(s) into remote object position and orientation relative to the generating element reference coordinate frame. The methods presented here can also be applied to other magnetic tracking technologies as a final "polishing" stage to improve the accuracy of their position and orientation solution.

In another field, <CIT> describes several embodiments of methods of making magnetic resonance catheter coils. At least one pair of generally parallel electrically conductive coil elements, which are electrically connected to each other, is patterned on a flexible electrically insulative base member. A catheter is provided over the coil assembly. In one embodiment, a second pair of generally parallel electrically conductive coil elements are provided in order to create a quadrature coil. In some embodiments, tuning and matching circuits and decoupling circuits may be provided. The (a) coils, (b) coil assemblies, as well as (c) catheter coils containing coil assemblies produced by these methods are also disclosed. The coils may be miniaturized so as to facilitate ready insertion within a suitable sheath, such as a probe or catheter, into a patient, including into body openings, or into blood vessels or into interior regions of the body.

For further background, <CIT> describes a medical device assembly comprises a medical device which comprises a shaft having proximal and distal end portions. The device further comprises a sensor at the distal end portion of the shaft that comprises first and second leads extending therefrom to the proximal end portion of the shaft. The device further comprises an electromechanical connector having a plurality of pins at a first end thereof. First and second of the pins are electrically connected to the first and second sensor leads, respectively, thereby forming a first partial magnetic loop between the first and second pins. The connector further comprises first and second jumpers electrically connecting the first pin and third pins, and second and fourth pins, respectively, thereby forming a second partial magnetic loop. The partial magnetic loops are configured to combine with partial magnetic loops of another connector to form a pair of magnetic noise cancellation loops.

There is provided, according to the present invention, a catheter according to claim <NUM> or <NUM>.

There is additionally provided, according to the present invention, an assembly wiring method according to claim <NUM> or <NUM>.

Embodiments of the present invention that are described herein provide improved assembly wiring methods and wiring assemblies for reducing interference that is picked-up by electrical wiring in a magnetic field. The embodiments described herein refer mainly to wiring that runs through a catheter, from a sensor at the distal end of the catheter to readout circuitry at the proximal end. The disclosed assembly wiring techniques, however, are applicable in various other systems and applications.

In some embodiments, a coil sensor included in a catheter-based position-tracking system generates differential signals in response to an alternating magnetic field. The signals are transmitted to a differential input port at a first end of a wiring assembly, and then conveyed by the wiring assembly to a differential output port at a second end of the wiring assembly. In some embodiments, an amplifier is coupled to receive the outputted differential signal at the second end of the wiring assembly.

In general, a wiring assembly may generate interfering electric potentials, for example, in response to alternating magnetic fields traversing an area encompassed by a pair of leads included in the assembly (the pair essentially acting as a single winding coil having a non-zero area). The interfering signals may distort the sensor signals and degrade the overall performance of a system using the signals, such as in a catheter-based position-tracking system using position signals generated by a magnetic sensor.

Embodiments of the present invention that are described hereinafter provide wiring configurations in which a first and second pairs of electrical leads, which convey the differential signal from a first end to a second end, and which are connected to one another at the first end and at the second end in a configuration that cancels pickup of an ambient magnetic field by the wiring assembly. As noted above, such wiring assembly can be used, for example to connect a sensor to electrical readout circuitry.

In some embodiments, the wiring assembly comprises a first pair of leads that is connected to a coil of a magnetic sensor. The first pair of leads may pick up interfering signals from ambient magnetic fields traversing an area encompassed by the leads. A second pair of leads of the wiring assembly, having a similar geometrical arrangement as the first pair (e.g., encompassing a same area, up to a pre-defined tolerance), is connected in an inverse-parallel configuration to the first pair of leads in order to compensate for an interfering signal generated by the first lead pair.

In the disclosed inverse-parallel connection configuration, the two pairs of leads are connected in parallel, but with their polarities reversed, as further described below. An interfering signal generated by the second lead pair is essentially the same as the interfering signal generated by the first lead pair, but with inverse polarity, and thus can be used to cancel the interfering signal inputted to readout circuitry. The two pairs of leads (i.e., four leads) are reduced by the disclosed wiring configurations into two leads that feed sensor signals to readout circuitry, such as comprising a single amplifier, with the interfering signals canceled already at the input of the amplifier.

In some embodiments, the wiring assembly comprises a first lead pair and a second lead pair, which are connected in series to feed a single amplifier. To compensate for the interfering signal generated by the first pair, the second pair of leads, having a similar geometrical arrangement as the first pair, is incorporated, in series, in a way that cancels out the induced interfering signals at the input of the amplifier. Again, an interfering signal generated in the second lead pair is essentially the same as the interfering signal generated by the first lead pair, but of inverse polarity, so an interconnection of the two pairs of leads in series cancels the interfering signals.

Heuristically, the disclosed inverse-parallel connection configuration can be treated as cancelling interfering voltages, and the in-series connection configuration can be treated as cancelling interfering currents. A particular selection of one of the two connecting schemes may depend on details of the readout circuitry, such as amplifier type.

In some embodiments, a flexible printed circuit board (PCB) is patterned with the two pairs of leads. The two pairs of leads are patterned such that the first pair and the second pair are either connected with an inverse-parallel configuration, or an in-series configuration, to feed a single amplifier. In other embodiments, the disclosed connection schemes are used to couple one or more sensors to readout circuitry comprising multiple amplifiers. Such multiple-amplifier circuitry is typically fed by numerous signals that require the disclosed pickup noise cancellation schemes, as would occur to a person skilled in the art.

The disclosed wiring configurations for the cancellation of magnetic pickup noise to avoid inputting to readout circuitry pick up noise with the signal result in higher quality output signals from readout circuitry when compared to using bulky solutions, such as "twisted-pair" insulated wires. By patterning the leads on a PCB, the disclosed techniques may be advantageous for compact electrical layouts, as is required for fitting multiple sensors at the distal end of a catheter. The disclosed lead architectures and patterning techniques may thus allow better miniaturization, as well as cost-effectiveness, of instruments such as catheters.

The disclosed technique is further advantageous over less compact solutions (e.g., twisted-pairs), as the disclosed embodiments are especially adapted for highfrequency alternating magnetic fields, in which the "twist pitch" of wires must be tight enough to ensure low pickup noise. Twisting the leads sufficiently thus becomes a demanding and expensive process, while the disclosed patterning techniques conforms more readily with such requirements.

<FIG> is a schematic, pictorial illustration of a catheter-based magnetic position-tracking and ablation system <NUM>, in accordance with an embodiment of the present invention. System <NUM> comprises a catheter <NUM>, having a shaft distal end <NUM> that is navigated by a physician <NUM> into a heart <NUM> of a patient <NUM> via the vascular system. In the pictured example, physician <NUM> inserts shaft distal end <NUM> through a sheath <NUM>, while manipulating the distal end of shaft distal end <NUM> using a manipulator <NUM> near the proximal end of the catheter. As shown in an inset <NUM>, shaft distal end <NUM> comprises a magnetic sensor <NUM> contained within the shaft distal end <NUM> and an ablation catheter <NUM>.

In the embodiments described herein, catheter <NUM> is used for ablation of tissue in heart <NUM>. Although the pictured embodiment relates specifically to the use of ablation catheter <NUM> for ablation of heart tissue, the elements of system <NUM> and the methods described herein may alternatively be applied in position-tracking of other catheter types, such as electrophysiological mapping catheters. Moreover, the disclosed assembly wiring techniques may be used to improve signal quality received from other sensors fitted at distal end <NUM>, such as contact force sensors and electrophysiological activity sensors.

The proximal end of catheter <NUM> is connected to a control console <NUM>. Console <NUM> comprises a processor <NUM>, typically a general-purpose computer, with suitable front end and interface circuits <NUM> for receiving signals from catheter <NUM>, as well as for applying energy via catheter <NUM> to ablate tissue in heart <NUM> and for controlling the other components of system <NUM>. Console <NUM> also comprises a driver circuit <NUM>, configured to drive magnetic field generators <NUM>.

During a navigation of shaft distal end <NUM> in heart <NUM>, console <NUM> receives signals from magnetic sensor <NUM> in response to magnetic fields from external field generators <NUM>, for example, for the purpose of measuring the position of ablation catheter <NUM> in the heart and, optionally, presenting the tracked position on a display <NUM>. Magnetic field generators <NUM> are placed at known positions external to patient <NUM>, e.g., below a patient table <NUM>. These position signals are indicative of the position of ablation catheter <NUM> in the coordinate system of the position-tracking system. In some embodiments, the wiring assembly (not shown) that conveys the signals from sensor <NUM> to console <NUM> is configured to, according one of the disclosed assembly wiring methods, cancel pickup noises due to the magnetic fields irradiated from generators <NUM>.

This method of position sensing using external magnetic fields is implemented in various medical applications, for example, in the CARTO™ system, produced by Biosense Webster Inc. (Irvine, California) and is described in detail in <CIT>, <CIT>, <CIT>, <CIT>,<CIT>and<CIT>, in <CIT>, and in <CIT>, <CIT> and <CIT>.

Processor <NUM> typically comprises a general-purpose computer, which is programmed in software to carry out the functions described herein. The software may be downloaded to the computer in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory.

<FIG> are schematic block diagrams of wiring assemblies <NUM> and <NUM> configured to cancel magnetic pickup noises, in accordance with embodiments of the present invention. Each of the shown wiring configurations comprise two pairs of leads connected to each other in a way that cancels magnetic pickup noises.

In both embodiments shown in <FIG>, a first lead pair <NUM> and a second lead pair <NUM>, both of which can be viewed as a single winding coil, encompass a same area, up to a preset tolerance. Thus, ambient alternating magnetic field lines <NUM> induct very similar interfering signals in both lead pairs. Note that, in <FIG>, the crossing zones of lead pairs <NUM> encompass a very small area compared with the total area encompassed, and thus has a negligible effect on the values of inducted pickup signals.

As seen in <FIG>, lead pair <NUM> couples magnetic sensor <NUM> to electrical readout circuitry <NUM>, essentially a single amplifier. The second pair of leads, lead pair <NUM>, is connected in an inverse-parallel configuration to lead pair <NUM>, between inputs 60a and 60b of the amplifier. The disclosed coupling is realized using a differential input port <NUM> at a first end of wiring assembly <NUM> and a differential output port <NUM> at a second end of wiring assembly <NUM>, respectively.

At the second end, lead pair <NUM> is electrically shorted to the respective lead pair <NUM>, at output points 60c and 60d of sensor <NUM>. Thus, an interfering signal generated in lead pair <NUM> is essentially the same as the interfering signal generated in lead pair <NUM>, but with inverse polarity. In this way, interfering signals (i.e., voltages) between inputs 60a and 60b are canceled out.

<FIG> shows an embodiment, in which second lead pairs <NUM> is connected, in series, to lead pair <NUM> at a point 60e, and the two pairs of leads form, in series, an interconnect between sensor <NUM> and inputs 60a and 60b of electrical readout circuitry <NUM>. An interfering current inducted in lead pair <NUM> is essentially the same as the interfering current inducted in lead pair <NUM>, but with inverse polarity, thus canceling out the opposing interfering currents, resulting in zero interfering signals between amplifier inputs 60a and 60b. The disclosed coupling is realized using a differential input port <NUM> at a first end of wiring assembly <NUM> and a differential output port <NUM> at a second end of wiring assembly <NUM>, respectively.

The schematic diagrams shown in <FIG> are chosen purely for the sake of conceptual clarity. The schematic geometrical schemes of connecting lead pairs aiming at achieving cancellation of interfering signals by encompassing a similar effective area is brought by way of example. Other designs are possible, for example, one comprising overlaying one pair of leads on top of the other. Various types of magnetic sensors may be used, such as sensors based on coils which utilize a Faraday effect, sensors based on micro-electro-mechanical devices that utilize a Lorentz force, and others.

<FIG> is a schematic, pictorial drawing of a wiring assembly implemented on a flexible printed circuit board (PCB) <NUM>, in accordance with embodiments of the present invention. PCB <NUM> is patterned with two pairs of leads. A coil <NUM> of a magnetic sensor is connected to first patterned lead pair <NUM>. As seen, both lead pair <NUM> and lead pair <NUM> encompass an area penetrated by ambient magnetic field lines <NUM>. The second pair of leads (i.e., lead pair <NUM>) is patterned on PCB <NUM> such a way that lead pair <NUM> and lead pair <NUM> encompass a same area, up to a preset tolerance.

In an embodiment, electrical readout circuitry <NUM> is connected on PCB <NUM> to lead pairs <NUM> and <NUM> in an inverse-parallel configuration in order to receive signals from sensor <NUM> that are free of interference by magnetic pickup noises that may be otherwise generated by the two pairs of leads. In another embodiment, electrical readout circuitry <NUM> is connected on PCB <NUM> by an in-series configuration of lead pairs <NUM> and <NUM>, that cancels out, at the input of electrical readout circuitry <NUM>, magnetic pickup noises that may be generated by the two pairs of leads. In some embodiments, PCB <NUM> is fitted in a distal end of catheter <NUM> that is used for position tracking.

The example shown in <FIG> is chosen purely for the sake of conceptual clarity. In alternative embodiments, the arrangement, identity, and number of components patterned or placed on PCB <NUM> may vary. The shape of PCB <NUM> and of lead pairs <NUM> and <NUM> may be different, as will occur to a person skilled in the art. For example, the two pairs of leads can be patterned one on top of the other, with a patterned insulating layer between them to prevent shorting the two pairs of leads.

<FIG> are graphs that compare magnetic pickup noise with and without noise cancelling wiring assembly, in accordance with the embodiment shown in <FIG>. Specifically, the figures show pickup noises without and with a second pair of leads connected in an inverse-parallel configuration to the first pair of pairs.

<FIG> shows a spectrum of input noise generated by lead pair <NUM>. As seen, the input noise is mostly white noise. The pickup noise peak is seen at a frequency of about <NUM>. As seen in <FIG>, when not compensated (e.g., by the embodiment seen in <FIG>), pickup noise amplitude 70a at <NUM> has a value of -<NUM> dBV, about <NUM> dBV higher than the white noise. <FIG> shows a spectrum of input noise generated by lead pairs <NUM> and <NUM>, which are connected in an inverse-parallel configuration with each other. <FIG> shows pickup noise amplitude 70b, which results from an inverse-parallel connection scheme. As seen, pickup noise amplitude 70b has a value of -<NUM> dBV, which is about <NUM> dBV lower than the uncompensated pickup noise amplitude 70a.

The graphs shown in <FIG> are brought, by way of example, to demonstrate empirically the pickup cancellation effect by an inverse-parallel connection scheme. Other measurements can be made, as well as other analysis methods applied, to demonstrate the efficacy of either one of the two connection schemes shown in <FIG>.

Although the embodiments described herein mainly address cardiac catheters, the methods and systems described herein can also be used in other applications, such as in neurology and otolaryngology. In general, the methods and schemes described herein can also be used with any systems that utilize magnetic sensors, and in particular with navigation systems.

Claim 1:
A catheter comprising:
a wiring assembly (<NUM>), the wiring assembly (<NUM>) configured to run through the catheter from a sensor (<NUM>) at a distal end of the catheter to readout circuitry at a proximal end of the catheter, and which is suitable for reducing magnetic pickup in magnetic position-tracking systems, the wiring assembly comprising:
a differential input port (<NUM>), configured to receive a differential signal from the sensor (<NUM>) at a first end of the wiring assembly;
a differential output port (<NUM>), configured to output the differential signal at a second end of the wiring assembly; and
a pair of electrical leads (<NUM>) and a second pair of leads (<NUM>), which are configured to convey the differential signal from the first end of the wiring assembly to the second end of the wiring assembly, the second pair of leads (<NUM>) connected to the pair of electrical leads (<NUM>) at the first end of the wiring assembly and at the second end of the wiring assembly,
wherein the second pair of lead (<NUM>) is inverse-parallel connected to the pair of electrical leads to cancel pickup of an ambient magnetic field by the pair of electric leads (<NUM>),
wherein the pair of electrical leads (<NUM>) and the second pair of leads (<NUM>) each encompass a same area, up to a preset tolerance.