Patent Description:
As another example, <CIT> describes a system that records use of a structure deployed in operative association with heart tissue in a patient. An image controller generates an image of the structure while in use in the patient. An input receives data including information identifying the patient. An output processes the image in association with the data as a patient-specific, data base record for storage, retrieval, or manipulation.

<CIT> describes a robotic catheter control system that includes a proximity sensing function configured to generate a proximity signal that is indicative of the proximity of the medical device such as an electrode catheter to a nearest anatomic structure such as a cardiac wall. The control system includes logic that monitors the proximity signal during guided movement of the catheter to ensure that unintended contact with body tissue is detected and avoided. The logic includes a means for defining a plurality of proximity zones, each having associated therewith a respective proximity (distance) criterion.

<CIT> describes a radio-frequency based catheter system and method for ablating biological tissues within the body vessel of a patient that comprises a radio-frequency ("RF") generator for selectively generating a high frequency RF energy signal in a deployable catheter having an RF transmission line, an RF antenna mounted on the distal portion of the catheter, and a temperature sensor also mounted on a distal portion of the catheter for detecting temperature adjacent an ablation site. The shapeable catheter apparatus may carry one or more intracardiac electrocardiogram (ECG) electrodes to permit physicians to obtain both optimum tissue proximity and electrical conductive activities before and after tissue ablation.

<CIT> relates to methods and systems for position determination for using an intrabody probe having a plurality of electrodes to generate a plurality of different electrical fields, and to also measure, using the plurality of electrodes, a measurement set (a Ve-e measurement set) comprising a plurality of measurements of the plurality of different electrical fields while the probe remains in one position. From the Ve-e measurement.

set, spatial position coordinates for the intrabody probe are estimated within an intrabody coordinate system, using an established mapping between previously observed Ve-e measurement sets and positions in the intrabody coordinate system.

<CIT> relates to methods and systems for graphically creating a representation of an anatomical structure, such as a heart. The distal end of an elongated probe is moved within the anatomical structure, and geometric shapes are defined within a coordinate system. By defining geometric shapes, such as spheres or circles, as the distal probe end is moved within the anatomical structure, the cavity within the anatomical structure can be represented.

Embodiments of the present invention that are described hereinafter provide a radiofrequency (RF) transmission system for estimating proximity of tissue of a cavity wall of an organ of a patient to a catheter inside the cavity. A related method, which is disclosed but not claimed as such, relies on the typically higher impedance of tissue as compared to blood, especially in the low RF frequency range of several kHz. Thus, measured impedances increase as the catheter nears a cavity wall, indicating closer proximity of tissue.

In some embodiments, during an electro-anatomical mapping session of a cavity, such as a cardiac chamber, a catheter having multiple distal-electrodes is positioned in the cavity. The disclosed system measures bi-polar impedances (impedances between pairs of distal-electrodes) in one or more RF frequency ranges. A processor uses the measured impedances, along with a prior calibration process, to estimate the proximity of tissue to the catheter. The mapping involves three stages:.

A processor is configured to represent at least a portion of a cavity volume of an organ of a patient with a sphere-model. The sphere-model comprises spheres of different sizes, with the smaller spheres located closer to the surface. The processor may identify directions along which the sizes of spheres decrease monotonically. Based on intersections between the smallest spheres at the respective indicated directions, the processor calculates an estimated contour along the surface of the cavity wall.

In some embodiments, while the catheter is moved across the cardiac chamber, a position-tracking system measures various positions P of the catheter distal end. The system uses, for example, a magnetic sensor that is fitted at the distal end of the catheter. The sensor outputs, in response to externally-applied magnetic fields, position signals which are received by a processor of the position-tracking system. Based on the position signals, the processor derives catheter positions P inside the cardiac chamber.

In parallel, the system measures proximity signals, such as electrical bi-polar signals between one or more pairs of the distal-electrodes that are fitted on the distal end of the catheter. Based on the bi-polar signals, which, as noted above, are indicative of the proximity of wall tissue to the catheter, and based on the measured positions P, a processor constructs a cavity sphere-model. The sphere-model represents at least a portion of the cavity volume by a set of partially overlapping spheres {(P, ρ)}. Each sphere (P, ρ) in the model is described by (a) a known location, P, of its center, and, (b) a yet unscaled radius, ρ, which is indicative of a distance between location P and the cavity wall. In an embodiment, (i) the magnetically measured positions P are the centers P of the spheres {(P, ρ)}, and (ii) the unscaled radiuses, ρ, are derived from the electrically measured impedances, such that as impedance becomes higher ρ becomes smaller.

In the disclosed cavity representation, a sphere (P, ρ) which is located deeper inside the cavity (i.e., further away from a cavity wall) will typically be larger than a sphere located closer to a wall (i.e., deeper spheres have a larger ρ). The transition from larger to smaller diameter spheres is typically gradual and "smooth.

To scale radiuses ρ into absolute values R, (i.e., to calibrate ρ), the processor uses instances when the distal end comes into physical contact with cavity wall tissue. When an electrode pair comes in physical contact with a location T over cavity wall tissue, the processor correlates the bi-polar signals with a geometrically known distance RT between the electrode-pair and the magnetic sensor, which is at a respective location PT. Distance RT is known from the dimensions of the catheter distal end, yielding a reference sphere (PT, RT) for scaling the radiuses of set {(P, ρ)}T. In an embodiment, the scaling is performed in real time.

In some embodiments, the processor scales the radiuses of the sphere model in a certain portion of the cavity based on a location T in which the catheter is known to have made physical contact with the cavity wall (tissue). To detect physical contact at location T, the system may employ the distal electrodes and/or a dedicated sensor, such as a contact-force sensor, or other methods and means known in the art.

In an embodiment, a multiplicity of distinct calibration points T is used as the catheter moves inside the cardiac chamber. In this way, multiple sphere-models, each localized about a distinct contact location, are combined into a global sphere-model that represents a larger portion of the cardiac chamber, possibly the entire chamber.

Once calibration has conducted, i.e., after the processor constructed the calibrated sphere-model about a location T, the processor identifies a direction, in the sphere representation, along which a smooth transition occurs from larger spheres to the smallest spheres. This direction points toward the location of local wall tissue, in that the smallest spheres are those nearest to wall tissue, as explained above.

At this point the processor identifies segments defined by the smallest overlapping spheres that are approximately located on the cavity wall in the vicinity of location T.

In some embodiments, the processor further analyses the derived set of segments so as to locally map a continuous cavity wall in the vicinity of location T (e.g., by interpolating between the segments).

In an embodiment, the disclosed system and method may then generate an electro-anatomical map of the cardiac chamber. The map may be presented to a user, e.g., a physician.

The Processor is programmed in software containing a particular algorithm that enables the processor to conduct each of the processor related steps and functions outlined above.

The disclosed RF transmission system and method for estimating tissue proximity is capable of rapidly providing an electro-anatomical model of at least a portion of a cardiac cavity. Combined with minimal perturbation to cardiac tissue achieved by using low-voltage, highfrequency, electrical signals (i.e., far above any bio-physiological activation frequency), the disclosed system and method may give a physician an efficient and safe means of obtaining clinical information to support treatment decisions, such as how to inhibit an arrhythmia.

<FIG> is a schematic, pictorial illustration of an electro-anatomical mapping system <NUM>, in accordance with an embodiment of the present invention. As seen, a physician <NUM> navigates a PENTARAY® catheter <NUM> (made by Biosense-Webster, Irvine, California), seen in detail in inset <NUM>, to a target location in a heart <NUM> of a patient <NUM> by manipulating shaft <NUM> using a manipulator <NUM> near the proximal end of the catheter and/or deflection from a sheath <NUM>.

Catheter <NUM> is inserted, in a folded configuration, through sheath <NUM>, and only after sheath <NUM> is retracted does catheter <NUM> regain its intended functional shape. By containing catheter <NUM> in a folded configuration, sheath <NUM> also serves to minimize vascular trauma on its way to the target location.

<FIG> depicts a physician <NUM> using catheter <NUM>, seen in inset <NUM>, to perform electro-anatomical mapping of a cavity of heart <NUM>, having a cavity wall <NUM>, of a patient <NUM>. In some embodiments, system <NUM> determines the position and/or the proximity of catheter <NUM> to cardiac wall <NUM> tissue in a cavity of heart <NUM>, as described below.

Catheter <NUM> incorporates a magnetic sensor <NUM> on a shaft <NUM>. Catheter <NUM> further comprises one or more arms, which may be mechanically flexible, to each of which are coupled one or more distal-electrodes <NUM>, as seen in inset <NUM>. Magnetic sensor <NUM> and distal-electrodes <NUM> are connected by wires running through shaft <NUM> to various driver circuitries in a console <NUM>.

In some embodiments, system <NUM> comprises a magnetic-sensing sub-system to estimate a position of catheter <NUM> inside a cardiac chamber of heart <NUM>. Patient <NUM> is placed in a magnetic field generated by a pad containing magnetic field generator coils <NUM>, which are driven by unit <NUM>. The magnetic fields generated by coils <NUM> generate position signals in a magnetic sensor <NUM>, which are then provided as corresponding electrical inputs to a processor <NUM>, which uses these to calculate the position of catheter <NUM>.

The method of position sensing using external magnetic fields and sensor <NUM> is implemented in various medical applications, for example, in the CARTO™ system, produced by Biosense-Webster, and is described in detail in <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>, in <CIT>, and in <CIT>, <CIT>and <CIT>.

Processor <NUM>, typically a general-purpose computer, is further connected via suitable front end and interface circuits <NUM>, to receive signals from surface-electrodes <NUM>. Processor <NUM> is connected to surface-electrodes <NUM> by wires running through a cable <NUM> to the chest of patient <NUM>. In some embodiments, processor <NUM> estimates the position of catheter <NUM> inside a cavity by correlating electrical position signals received from either distal-electrodes <NUM> and/or surface-electrodes <NUM> with position-calibrated electrical signals acquired previously. The method of electrode position sensing using calibrated electrical signals is implemented in various medical applications, for example in the CARTO™ system, produced by Biosense-Webster, and is described in detail in <CIT>, <CIT>, <CIT>, and <CIT>.

In some embodiments, during a mapping procedure, distal-electrodes <NUM> acquire and/or inject radiofrequency (RF) bi-polar signals (i.e., differential electrical signals between pairs of distal-electrodes <NUM>). Signals traveling at least partially through the tissue of wall <NUM> are typically more attenuated than those traveling through the blood of heart <NUM>. A processor <NUM> receives the various RF bi-polar proximity signals via an electrical interface <NUM>, and uses bio-impedance information contained in these signals to construct an electro-anatomical proximity map <NUM> of the cavity, as further elaborated below. During and/or following the procedure, processor <NUM> may display electro-anatomical proximity map <NUM> on a display <NUM>.

In some embodiments, processor <NUM> is further configured to estimate and verify the quality of physical contact between each of distal-electrodes <NUM> and wall <NUM> (i.e., the surface of the cardiac cavity) during measurement, so as to correlate the RF bi-polar proximity indicative signals with known distances. Using the correlated bi-polar proximity signals, and the respective positions measured by sensor <NUM>, processor <NUM> constructs a cavity sphere-model which is used, for example, to map at least a portion of heart <NUM>, as described below.

In an embodiment, the processor indicates a physical contact based on signals received from one or more contact force sensors that are fitted at the distal end of catheter <NUM>. In another embodiment, the indication of physical contact is based on the frequency response of the impedances sensed by distal-electrodes <NUM>. Such a method and technique is described in <CIT>, entitled "Touch detection Based on Frequency Response of Tissue," which is assigned to the assignee of the present patent application.

In another embodiment, processor <NUM> is configured to determine whether one or more flexible arms of a multi-arm distal end of catheter are in physical contact with wall <NUM> tissue based on identifying geometrical flexion of the arms. Techniques of this sort are described, for example, in <CIT>, entitled "Using a Piecewise-Linear Model of a Catheter Arm to Identify Contact with Tissue," which is assigned to the assignee of the present patent application.

Processor <NUM> is typically 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.

In particular, processor <NUM> runs a dedicated algorithm that enables processor <NUM> to perform the disclosed steps, comprising calculations of proximities and positions, calibrations, and calculating the cavity surface, as further described below.

The example illustration shown in <FIG> is chosen purely for the sake of conceptual clarity. <FIG> shows only elements related to the disclosed techniques, for the sake of simplicity and clarity. System <NUM> typically comprises additional modules and elements that are not directly related to the disclosed techniques, and thus are intentionally omitted from <FIG> and from the corresponding description. The elements of system <NUM> and the methods described herein may be further applied, for example, to control an ablation of wall <NUM> tissue of heart <NUM> using part of distal-electrodes <NUM>.

Other types of sensing and/or therapeutic catheters, such as DECANAV®, SMARTTOUCH®, and LASSO® (all produced by Biosense-Webster) may equivalently be employed.

<FIG> are side-views of a distal end of catheter <NUM> performing tissue proximity measurements, in accordance with embodiments of the present invention. The catheter distal end is immersed in the blood pool of a cardiac cavity, in the vicinity of a cavity wall <NUM> of tissue <NUM>.

<FIG> shows a focal catheter, such as the DECANAV® catheter, which comprises multiple distal-electrodes <NUM>. In an embodiment, distal-electrodes <NUM> are used to inject, and receive, bi-polar currents (shown schematically as curved arrows <NUM>) at different RF frequency ranges. As seen, some of the electrical paths pass partly in tissue, whereas others pass entirely in blood.

In an embodiment, the process is preset, in the sense that injection and receiving electrodes are selected in advance, as are the frequencies and driving voltages of the currents provided to the injection electrodes.

In some embodiments, the different electrical frequency ranges comprise the ranges of <NUM>-<NUM> and <NUM>-<NUM>. The reason for using two different frequency ranges is that impedance at the <NUM>-<NUM> range is practically insensitive to tissue <NUM>, whereas signals at the <NUM>-<NUM> range show measurable sensitivity to tissue <NUM>. Using the high frequency as reference, small changes in the low-frequency impedances, i.e., as a function of proximity of tissue, can be accurately resolved.

In an embodiment, as catheter <NUM> moves within the cardiac cavity, processor <NUM> receives impedance measurements measured between pairs of distal-electrodes <NUM>. Each impedance measurement depends on the transmitting and receiving electrodes, the injection frequencies and voltages, as well as the intervening material (blood and/or tissue). Typically, tissue has a higher impedance than blood, especially in the lower frequency range, so that impedances are generally higher if the electrodes are in close proximity to wall <NUM> of tissue <NUM>, and vice versa. The dependence of impedances on frequency and on blood and/or tissue, in an embodiment, is provided in <CIT>, cited above.

Processor <NUM> arranges the bi-polar impedances in matrices [M]. Processor <NUM> correlates each matrix [M] with a respective position P measured by position sensor <NUM> at which the bi-polar impedances are measured. A set of ordered pairs {(P, [M])} is stored by processor <NUM> in a memory <NUM>. Each bi-polar impedance signal matrix [M] is related to an unscaled wall tissue proximity p to the catheter. Hence, at this stage, the processor holds a sphere-model which comprises a set {(P, ρ)}, with radiuses ρ that are not to scale.

<FIG> shows an instance in which catheter <NUM> comes into contact with the cavity wall <NUM> at a contact point T. The occurrence of physical contact may be determined by any suitable sensor, for example by a force measured by a force sensor in catheter <NUM>, and/or a change of impedance between selected distal-electrodes <NUM>. (<FIG> assumes that contact is at two adjacent electrodes <NUM><NUM>.

At contact, the processor scales a respective distance ρ between the contacting tissue wall <NUM> at contact point T and location sensor <NUM> in the catheter into RT (based on catheter geometry, as explained above), yielding a calibrating sphere (PT, RT).

Based on the calibration at location T, the processor constructs a correlated pair (RT, [M]T), after which the processor scales distances ρ correlated with previous matrices [M] measured in the vicinity of contact point T, to produce a locally scaled set of spheres {(P, R)}T.

As indicated above, only the distance RT to wall <NUM> tissue, not the direction to the tissue wall, is known, and this distance defines a sphere <NUM> of radius R around a location PT of sensor <NUM>, as is illustrated in <FIG> describes how processor <NUM> determines a direction to tissue wall <NUM>.

In an embodiment, the described calibration process is repeated as catheter <NUM> touches tissue at distinct locations {T} in the chamber. The resulting local sphere-models {(P, R)}T, are subsequently used to estimate cavity wall proximity in a vicinity of each contact location TE{T}. As further described below, the disclosed calibration is valid in a region localized about a respective contact point T. Mapping an entire cavity requires multiple contact points.

The illustrations in <FIG> are brought by way of example. As another example, in some embodiments, distal end <NUM> is part of a multi-arm catheter (e.g., an arm). In another embodiment, the disclosed tissue-proximity estimation method is applied using a Basket-type catheter distal end. In an alternative to a current injection acquisition method, bi-polar electrical potentials 60a are applied between pairs of distal-electrodes <NUM> at different frequencies, and the respective impedances are then measured.

<FIG> is a schematic, pictorial illustration of a geometric construction of a localized cavity sphere-model, in accordance with an embodiment of the present invention. During, for example, an investigative electro-anatomical mapping session based on signals acquired using catheter <NUM>, processor <NUM> constructs a local set of calibrated spheres {{P, R)}T, i.e., spheres <NUM> and spheres <NUM>, in the vicinity of location T, over cavity wall <NUM>.

In an embodiment, an inclusion criteria for a sphere to be part of the local set {(P, R)}T, is based, for example, on a position P being, at most, a given distance Γ from a position PT used for scaling the radiuses. Therefore, <FIG> describes only a cavity sphere-model localized (e.g., in the Γ sense) about a given physical contact location T.

The cavity sphere-model can cover a larger portion of the cavity, and up to the entire cavity, if, for example, a sufficient number of distinct contact locations T are recorded over the entire cavity wall during calibration, and a collection of separate sphere-models (e.g., separated from each other by a distance Γ) are obtained.

For regions closer the center of the cavity, approximately equidistant from the cavity walls, a respective set of spheres <NUM> have approximately equal diameters. This is indicated schematically as a region A of <FIG>, where the circles (spheres) will typically have larger diameters than those shown.

Radiuses of spheres <NUM> at points P closer to the wall will typically be smaller than those further away from wall <NUM>, as in a shown in <FIG> as region B. The gradual transition from the larger to smaller diameter spheres defines a direction <NUM> where cavity wall <NUM> exists.

Outmost intersection segments <NUM> (shown as points <NUM>) of partially overlapping smallest spheres <NUM> estimate the location of cavity wall <NUM>. In an embodiment, processor <NUM> locally maps tissue wall <NUM>, by interpolating over segments <NUM>.

The example illustration shown in <FIG> is chosen purely for the sake of conceptual clarity. For example, some of the spheres shown may not be to exact scale, for clarity of presentation. Segments <NUM> are, in reality, curves in space that extend in directions into, and out of, the page.

<FIG> is a flow chart that schematically illustrates a method for electro-anatomical mapping of a cardiac cavity, which is described herein for illustrative purposes, but is not claimed as such.

In some embodiments, the steps of this algorithm are carried out by software with which processor <NUM> is programmed.

The process begins with physician <NUM> moving catheter <NUM>, which is equipped with magnetic sensor <NUM>, inside a cardiac cavity to acquire multiple magnetic position signals and bi-polar electrical proximity signals, at a proximity data acquisition step <NUM>.

In parallel, catheter <NUM>, which comprises means to detect physical contact with the cardiac cavity wall, occasionally indicates to processor <NUM> of a physical contact that catheters <NUM> make with wall tissue, at an acquire physical contact indication step <NUM>.

Based on the position signals and respective proximity signals, and using the dedicated algorithm, processor <NUM> calculates positions and respective relative (i.e., unscaled) proximities, at a position and unscaled proximity calculation step <NUM>. Next, processor <NUM> represents a portion of the cardiac cavity with spheres {(P, ρ)}T, at a local sphere-model construction step <NUM>.

Next, based on indication of physical contact in the vicinity, i.e., at step <NUM>, processor <NUM> calibrates the sphere-model into a model of spheres of known radius, {(P, R)}T, at a calibration step <NUM>.

Next, based on the local scaled sphere-model {(P, R)}T, processor <NUM> estimates a direction at which wall tissue is located, by determining a direction <NUM> along which radiuses R become smaller, at a wall tissue direction estimation step <NUM>.

Then, processor <NUM> estimates locations of intersecting segments <NUM> of the smallest spheres {(P, R)}T, so as to estimate the location of cavity wall <NUM>, at a tissue wall identification step <NUM>. Based on cavity wall <NUM> identification step, processor <NUM> estimates proximity (i.e., distance) of cavity wall tissue <NUM> from catheter <NUM>.

As noted above, the estimated tissue proximity is local. To produce an anatomical map of the cavity, the process described in steps <NUM>-<NUM> is typically repeated N times as the catheter moves inside the cavity. Next, at a cavity mapping step <NUM>, based on the N collected proximities, processor <NUM> calculates a surface of the cardiac cavity. The calculated surface is stored in memory <NUM>, at a storing step <NUM>. Finally, at a cavity map displaying step <NUM>, processor <NUM> presents to physician <NUM> the calculated surface (e.g., proximity map <NUM> of at least a portion of the cavity) on display <NUM>.

The example flow chart shown in <FIG> is chosen purely for the sake of conceptual clarity. In alternative embodiments, for example, an entire cavity is mapped with acquisition steps <NUM>-<NUM> repeating at multiple distinct locations T over the cardiac cavity wall, and with modeling steps <NUM>-<NUM> repeating, until a sufficient portion of the cavity wall is electro-anatomical mapped. In an embodiment, the processor interpolates over intersecting segments <NUM> in order to derive a locally continuous cavity wall.

Although the embodiments described herein mainly address cardiac applications, the methods and systems described herein can also be used in other medical applications, such as in neurology and nephrology.

Claim 1:
A system (<NUM>), comprising:
an interface (<NUM>), configured to receive, from a probe (<NUM>) that comprises electrodes (<NUM>) and is positioned inside a cavity in an organ of a patient, (i) proximity signals indicative of proximity of the electrodes to a wall of the cavity, and (ii) position signals indicative of positions of the electrodes within the cavity; and
a processor (<NUM>), configured to:
represent at least a portion of a volume of the cavity by a sphere model comprising multiple spheres, based on the proximity signals and the position signals, wherein the sphere-model comprises partially overlapping spheres of different sizes, with the smaller spheres located closer to the wall of the cavity;
calculate an estimated contour of the wall of the cavity based on the sphere-model; and
present the estimated contour of the wall to a user; and
characterised in that the proximity signals comprise bi-polar electrical signals, exchanged between the electrodes at a plurality of radiofrequency ranges.