Robotic surgical system and method for surface modeling

A method of generating a three-dimensional model of at least a portion of a heart includes inserting an electrode within the portion of a heart, robotically moving the electrode therein, periodically detecting position information of the electrode to generate a plurality of location points defining a space occupied by the portion of the heart, and generating a three-dimensional model of the portion of the heart including position information for at least some of the plurality of location points within the portion of the heart. The plurality of location points includes at least some location points on the surface of the heart and at least some location points interior thereto. The model is generated by utilizing a surface construction algorithm such as a shrink-wrap algorithm to identify the surface points and isolate or eliminate the interior points.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The instant invention relates to robotically controlled medical devices. In particular, the instant invention relates to a robotic surgical system for navigating a medical device through a patient's body for diagnostic and therapeutic purposes.

b. Background Art

Catheters are used for an ever growing number of medical procedures. To name just a few examples, catheters are used for diagnostic, therapeutic, and ablation procedures. Typically, the user manually manipulates the catheter through the patient's vasculature to the intended site, such as a site within the patient's heart. The catheter typically carries one or more electrodes or other diagnostic or therapeutic devices, which may be used for ablation, diagnosis, cardiac mapping, or the like.

It is well known that, to facilitate manipulation of the catheter through the patient's vasculature to the intended site, portions of the catheter shaft, especially the distal regions thereof, may be made steerable. For example, the catheter may be manufactured such that the user can translate, rotate, and deflect the distal end of the catheter as necessary and desired to negotiate the tortuous paths of the patient's vasculature en route to the target site. Navigating a catheter reliably through the patient's body to a precise location, however, is an extremely tedious process requiring a substantial amount of time and skill and potentially causing a high degree of fatigue in the physician, especially where actuation forces are transmitted over large distances.

BRIEF SUMMARY OF THE INVENTION

It is thus desirable to be able to navigate a medical device accurately and precisely through a patient's body to the locations of diagnostic or therapeutic interest.

It is also desirable to be able to reduce the fatigue factor associated with navigating a medical device through a patient's body.

It is further desirable to be able to preserve the ability to manually navigate a medical device when so desired.

It is also desirable that the medical device be able to distinguish proximity or degree of contact between the medical device and a tissue surface.

It is further desirable that the medical device be usable to create a map of a geometry of the patient's body, which map may include diagnostic information, without the need to distinguish surface points from interior points during the data-gathering phase.

According to a first aspect of the invention, a method of generating a three-dimensional model of at least a portion of a heart includes the steps of: inserting an electrode within a portion of a heart; robotically moving the electrode randomly within the portion of the heart; periodically detecting position information of the electrode, thereby generating a plurality of location points that define a space occupied by the portion of the heart; and generating a three-dimensional model of the portion of the heart, the three-dimensional model including position information for at least some of the plurality of location points within the portion of the heart. The plurality of location points may include at least some location points on a surface portion of the heart and at least some location points not on the surface portion of the heart. Optionally, the plurality of location points is a cloud of location points, and the step of generating a three-dimensional model includes using a surface construction algorithm, such as a shrink-wrap algorithm, to wrap a surface around the cloud of location points. The surface construction algorithm may also distinguish a subset of the plurality of location points defining a three-dimensional surface model of the portion of the heart, thereby generating a plurality of surface location points that define a surface of the portion of the heart. Alternatively, the surface construction algorithm may eliminate location points determined to be interior to a three-dimensional surface model of the portion of the heart, thereby generating a plurality of surface location points that define a surface of the portion of the heart.

According to another aspect of the invention, a method of generating a three-dimensional model of at least a portion of a heart includes the steps of: inserting an electrode within a portion of a heart; moving the electrode within the portion of the heart using a robotic controller; periodically detecting position information of the electrode, thereby generating a plurality of location points that define a space occupied by the portion of the heart; processing the plurality of location points using a surface construction algorithm to identify a subset of the plurality of location points, which subset of location points defines a three-dimensional surface model of the portion of the heart; and outputting the identified subset of the plurality of location points. The processing step optionally includes processing the plurality of location points using a shrink-wrap algorithm to eliminate location points that are determined to be interior to the three-dimensional surface model of the portion of the heart, thereby identifying a subset of the plurality of location points that define the three-dimensional surface model of the portion of the heart. The step of moving the electrode within the portion of the heart may include moving the electrode randomly or according to a predetermined pattern. Optionally, the predetermined pattern includes a first predetermined pattern until a determination is made that the electrode is in contact with a surface of the portion of the heart and a second predetermined pattern after the electrode has made contact with the surface of the portion of the heart. In some embodiments of the invention, the second predetermined pattern is not substantially continuous along the surface of the portion of the heart.

In still another aspect of the invention, a method of generating a three-dimensional model of at least a portion of a heart includes the steps of: inserting an electrode within a portion of a heart; using a robotic controller to move the electrode randomly within the portion of the heart; detecting position information of the electrode, thereby generating a plurality of location points that define a space occupied by the portion of the heart; generating a plurality of triangles by connecting the plurality of location points; and generating a three-dimensional model of the portion of the heart including position information for a plurality of location points that describe a three-dimensional surface model of the portion of the heart. The step of generating a three-dimensional model may include processing the plurality of location points using a surface construction algorithm to eliminate location points that are determined to be interior to the three-dimensional surface model of the portion of the heart, thereby identifying a subset of the plurality of location points that define vertices for a plurality of triangles representing the three-dimensional surface model of the portion of the heart.

In still another embodiment, a system for generating a three-dimensional model of at least a portion of a heart includes: an electrode for inserting within a portion of a heart; a robotic controller for moving the electrode within the portion of the heart; a detector for detecting position information of the electrode and for generating a plurality of location points that define a space occupied by the portion of the heart; and a modeling processor for generating a three-dimensional model of the portion of the heart including position information for a plurality of location points that describe a three-dimensional surface model of the portion of the heart. Optionally, the modeling processor processes the plurality of location points to eliminate location points that are determined to be interior to the three-dimensional surface model of the portion of the heart. Alternatively, the modeling processor processes the plurality of location points to eliminate location points that are determined to be interior to the three-dimensional surface model of the portion of the heart, thereby identifying a subset of the plurality of location points defining vertices for a plurality of triangles representing the three-dimensional surface model of the portion of the heart.

An advantage of the present invention is a reduced exposure to radiation for both the patient and the physician, since the present invention reduces the time required to navigate the catheter to a target location and minimizes the need for fluoroscopy to locate the catheter within the patient.

Another advantage of the present invention is the ability to easily switch between automated robotic control and manual control of the catheter.

Still another advantage of the present invention is the ability to remotely interact with the robotic surgical system controlling the catheter.

DETAILED DESCRIPTION OF THE INVENTION

Robotic Surgical System

FIG. 1schematically illustrates an embodiment of a robotic surgical system10for robotic manipulation and control of a medical device12. Medical device12is preferably a catheter, which may be any type of catheter, including, by way of example only and without limitation, an ablation catheter, a guide wire catheter, an introducer catheter, a probe, or a stylet. It should be understood, however, that any other therapeutic, diagnostic, or assistive medical device may be controlled by robotic surgical system10without departing from the scope of the present invention. Such other devices include, but are not limited to, syringes, electrophoresis devices, iontophoresis devices, transdermal pharmaceutical delivery devices, myoblast delivery devices, stem cell delivery devices, ablation devices, stents, and pacemaker leads, which may be carried on or delivered by a catheter. It should further be understood that robotic surgical system10may be used to manipulate and control more than one medical device12in accordance with the quick installation and removal feature described herein. Accordingly, the terms “medical device,” “probe,” “therapeutic device,” and “catheter” are used interchangeably herein.

Robotic surgical system10generally includes a track14, a catheter holding device16, a translation servo mechanism18, a catheter deflection control mechanism20, a deflection servo mechanism22, and a controller24operatively coupled to at least one of translation servo mechanism18and deflection servo mechanism22. Translation and deflection servo mechanisms18,22may be any type of device for providing mechanical control at a distance, including continuous motors, stepper motors, hydraulic actuators, pulley systems, and other devices known to those of ordinary skill in the art. Catheter deflection control mechanism20and deflection servo mechanism22are collectively referred to herein as a “catheter deflection mechanism.”

Catheter holding device16includes a catheter receiving portion26. Catheter receiving portion26is configured to receive catheter12by installing a catheter control handle28, located near a proximal end30of catheter12, into catheter receiving portion26. Preferably, catheter receiving portion26is adapted for quick installation and removal of any type of catheter12(or, as noted above, another medical device), thereby facilitating the installation of device12for control by robotic surgical system10and removal of device12for manual control (e.g., user manipulation of catheter control handle28). Accordingly, catheter control handle28may be secured in catheter receiving portion26by a frictional fit or with one or more quick-release fasteners. Alternatively, the inner surface of catheter receiving portion26and the outer surface of catheter control handle28may include mating threaded portions to permit catheter control handle28to be screwed into catheter holding device16. In other embodiments of robotic surgical system10, catheter control handle28is clamped or strapped in place in catheter receiving portion26. An adapter may also be used to facilitate the reception of catheter control handle28within catheter receiving portion26.

One embodiment of catheter holding device16is illustrated inFIGS. 2 and 3with catheter control handle28placed, but not secured, therein. Catheter holding device16includes a base plate32and a plurality of upstanding support plates34. Support plates34support cams36, which are connected to pulley systems38.

Catheter control handle28is received downwardly through an opening40into the catheter receiving portion26and onto belts40of pulley systems38. As catheter control handle is urged downwardly, belts40rotate upper and lower pulleys38a,38bin the direction of arrows a. This, in turn, urges cams36downwards via links42and draws upper pulleys38a,38btowards one another via links44, while simultaneously wrapping the belts40about catheter control handle28. Catheter control handle28is thereby secured within catheter receiving portion26as shown inFIGS. 4 and 5. To remove catheter control handle28from catheter holding device16, the user need only release cams26, which reverses the process described above and opens catheter receiving portion26.

Catheter holding device16is translatably associated with track14. The phrase “translatably associated with” encompasses all types of relative lateral motion between catheter holding device16and track14. For example, catheter holding device16may slide relative to track14. Alternatively, catheter holding device16may move laterally along a screw mechanism46, such as a worm gear, a lead screw, or a ball screw, attached to track14. Preferably, catheter holding device16has a translation range relative to track14(i.e., the lateral distance that catheter holding device16can travel relative to track14between extremes) of at least about 5 cm, the approximate width of a human heart. More preferably, the translation range of catheter holding device16relative to track14is at least about 10 cm.

In the preferred embodiment of the invention, a carriage48is translatably mounted on track14via screw mechanism46. Catheter holding device16is mounted on carriage48such that catheter holding device16translates relative to track14with carriage48. For example, base plate32may be fixedly or removably mounted on carriage48. Alternatively, catheter holding device16may be integrally formed with carriage48as a single assembly (i.e., base plate32and carriage48may be a single, unitary component). Likewise, in some embodiments of the invention, catheter holding device16may be translatably mounted directly on track14without an intervening carriage.

Translation servo mechanism18is operatively coupled to catheter holding device16and adapted to control translation of catheter holding device16relative to track14in order to adjust the lateral position of catheter holding device16along track14. Preferably, translation servo mechanism18is operatively coupled to carriage48in order to move carriage48, and therefore catheter holding device16mounted thereon, laterally along track14. In the embodiment shown inFIG. 1, translation servo mechanism18drives screw mechanism46, thereby moving carriage48laterally therealong.

Deflection servo mechanism22is operatively coupled to and adapted to control catheter deflection control mechanism20. In the preferred embodiment of the invention, deflection servo mechanism22is operatively coupled to catheter deflection control mechanism20such that deflection servo mechanism22can rotate catheter deflection control mechanism20. Either or both of deflection servo mechanism22and catheter deflection control mechanism20may be mounted on carriage48in order to simplify the transmission system linking deflection servo mechanism22and catheter deflection control mechanism20. In some embodiments of robotic surgical system10, catheter deflection control mechanism20is incorporated in catheter holding device16, for example by utilizing pulley systems38, and in particular belts40, as further described below. One of ordinary skill in the art will appreciate, however, that catheter deflection control mechanism20may also be separated from catheter holding device16without departing from the spirit and scope of the present invention.

Controller24is adapted to control at least one of translation servo mechanism18and deflection servo mechanism22in order to navigate catheter12received in catheter holding device16. It should also be noted that the use of multiple controllers to control translation servo mechanism18and deflection servo mechanism22is regarded as within the scope of the present invention. Throughout this disclosure, the term “controller” refers to a device that controls the movement or actuation of one or more robotic systems (that is, the component responsible for providing command inputs to the servo mechanisms). One of ordinary skill in the art will understand how to select an appropriate controller for any particular mechanism within robotic surgical system10. Further, the term “controller” should be regarded as encompassing both a singular, integrated controller and a plurality of controllers for actuating one or more robotic systems.

As shown inFIG. 6, catheter12is preferably a steerable catheter including at least one pull wire50extending from catheter control handle28near proximal end30of catheter12to a distal end52of catheter12. Pull wires50may be coupled to at least one pull ring54, also located near distal end52of catheter12. When placed in tension, pull wires50deflect distal end52of catheter12into various configurations. As one of skill in the art will understand, additional pull wires50will enhance the deflection versatility of distal end52of catheter12. For example, a single pull wire50with a single point of attachment to pull ring54will permit distal end52of catheter12to deflect on a single axis, and perhaps in only one direction, for example upwards relative toFIG. 6. By adding a second pull wire50(as shown inFIG. 6), or by looping a single pull wire50to have two points of attachment56to pull ring54, distal end52of catheter12may be deflected in two directions, for example both upwards and downwards relative toFIG. 6. A catheter12with four pull wires50attached to pull ring54at about 90° intervals can deflect in four directions, for example upwards, downwards, and into and out of the plane of the paper relative toFIG. 6.

One or more catheter deflection actuators58may be provided on catheter control handle28to selectively tension one or more pull wires50, thereby controlling the direction and degree of deflection of distal end52of catheter12. In some embodiments, one or more knobs may be provided, rotation of which selectively tension one or more pull wires50. It should be understood, however, that catheter deflection actuators58may take many other forms, including, but not limited to, sliders and switches, without departing from the spirit and scope of the present invention. Additionally, it is contemplated that rotating catheter control handle28itself may selectively tension pull wires50and deflect distal end52of catheter12.

Returning toFIG. 1, when catheter control handle28is received within catheter receiving portion26, catheter12translates relative to track14with catheter holding device16, thereby providing a first degree of freedom permitting catheter12to be advanced into and retracted from a patient's body. Additionally, catheter12is operatively coupled to catheter deflection control mechanism20such that actuation of catheter deflection control mechanism20causes distal end52of catheter12to deflect, thereby providing a second degree of freedom to catheter12. In particular, catheter deflection actuator58may be operatively coupled to catheter deflection control mechanism20such that catheter deflection control mechanism20can actuate catheter deflection actuator58to selectively tension one or more pull wires50and deflect the distal end52of catheter12by a desired amount in a desired direction.

In some embodiments of the invention, rotating catheter deflection control mechanism20will rotate catheter deflection actuator58in turn, thereby selectively tensioning one or more pull wires50within catheter12. The transmission system between catheter deflection control mechanism20and catheter deflection actuator58may be a frictional fit provided, for example, by rubberized coatings surrounding catheter deflection control mechanism20and catheter deflection actuator58. Alternatively, catheter deflection control mechanism20and catheter deflection actuator58may be coupled with mating gear teeth or knurling.

Referring specifically to the embodiment of catheter holding device16depicted inFIGS. 2-5, when catheter12is secured in catheter receiving portion26, belts40frictionally engage catheter control handle28. They may also engage catheter deflection actuator58. Thus, if pulley system38is driven by deflection servo mechanism22, belts40may rotate catheter control handle28, catheter deflection actuator58, or both, in order to selectively tension one or more pull wires50and deflect distal end52of catheter12.

It should be understood that the particular configurations of catheter deflection control mechanism20and catheter deflection actuator58described above are merely exemplary and can be modified without departing from the spirit and scope of the invention. For example, if catheter deflection actuator58is a slider rather than a knob, catheter deflection control mechanism20may be suitably modified, or even replaced as a modular unit, to actuate a slider. This facilitates the quick connect/disconnect operation of robotic surgical system10by allowing easy installation and interconnection between off-the-shelf medical devices of varying construction and robotic surgical system10.

As described above, the inclusion of additional pull wires50in catheter12increases the number of directions in which distal end52of catheter12can deflect. This is referred to herein as “deflection versatility.” Where relatively few pull wires50(e.g., fewer than about four pull wires50) are used, however, compensation for lost deflection versatility may be had by rotating catheter12about its axis. For example, in a catheter using only a single pull wire50with a single point of attachment to pull ring54, permitting the catheter to deflect only in one direction, the catheter may be deflected in the opposite direction simply by rotating it 180° about its axis. Similarly, a catheter that can deflect in two directions 180° apart can be deflected in the directions midway therebetween by rotating the catheter900about its axis.

Accordingly, in some embodiments of the invention, catheter receiving portion26is rotatable. An example of such a rotatable catheter receiving portion is catheter receiving portion26defined by pulley system38depicted inFIGS. 2-5. A rotation servo mechanism60is operatively coupled to rotatable catheter receiving portion26and adapted to control rotatable catheter receiving portion26. Thus, pulley system38may be driven by rotation servo mechanism60, thereby engaging belts40to rotate catheter12about its axis.

If desired, rotation servo mechanism60may be mounted on carriage48or affixed to catheter holding device16such that rotation servo mechanism60translates relative to track14with catheter holding device16. This arrangement creates a fixed-distance relationship between rotation servo mechanism60and catheter holding device16, which can simplify the transmission system coupling rotation servo mechanism60to catheter holding device16.

When installed in catheter holding device16, catheter12rotates with catheter receiving portion26, thereby providing a third degree of freedom to catheter12and compensating for low deflection versatility attributable to a relatively lower number of pull wires50. Catheter receiving portion26is preferably rotatable at least about 360° about its axis, such that catheter12received therein is also rotatable at least about 360° about its axis, thereby facilitating deflection of distal end52of catheter12in substantially any direction, significantly enhancing the deflection versatility of the distal end52of the catheter12. Catheter receiving portion26may also be designed to rotate about 720° or more about its axis.

Rotating catheter12by rotating catheter receiving portion26may cause inadvertent deflection of distal end52of catheter12. As one skilled in the art will recognize from this disclosure, as catheter receiving portion26and catheter12rotate, catheter deflection actuator58may remain stationary, rather than rotating with catheter control handle28, if the torque applied by rotation servo mechanism60is insufficient to overcome the inertia of catheter deflection control mechanism20. That is, catheter deflection actuator58may bind against catheter deflection control mechanism20, causing relative rotation between catheter control handle28and catheter deflection actuator58. This relative rotation may result in uncommanded tensioning of one or more pull wires50, inadvertently deflecting distal end52of catheter12.

To maintain a substantially constant deflection as catheter12rotates, therefore, controller24may be operatively coupled to both rotation servo mechanism60and deflection servo mechanism22. Controller24is adapted to control at least one of deflection servo mechanism22and rotation servo mechanism60, and preferably to simultaneously control both deflection servo mechanism22and rotation servo mechanism60, to maintain a substantially constant deflection of distal end52as catheter receiving portion26and catheter12rotate. For example, as controller24commands rotation servo mechanism60to rotate catheter receiving portion26, controller24may simultaneously command deflection servo mechanism22to actuate catheter deflection control mechanism20to counter-rotate, thereby substantially eliminating relative rotation between the catheter deflection actuator58and catheter control handle28, helping to maintain a substantially constant deflection of catheter12. Alternatively, as controller24commands rotation servo mechanism60to rotate catheter receiving portion26, it may simultaneously command deflection servo mechanism22to decouple catheter deflection control mechanism20from catheter deflection actuator58, thereby permitting catheter deflection actuator58to rotate freely with catheter control handle28. In either case, controller24may be configured to eliminate the need to couple deflection servo mechanism22and rotation servo mechanism60through a mechanical transmission system such as a differential. Further, though described herein as a single controller adapted to control the translation, deflection, and rotation servo mechanisms18,22,60, multiple controllers may be used without departing from the spirit and scope of the present invention.

An introducer62, preferably a steerable introducer, and most preferably an Agilis™ steerable introducer, may be provided as part of robotic surgical system10. A proximal end64of introducer62is preferably stationary, while a distal end66of introducer62extends into a patient (not shown for clarity) to a location proximate a target site (the term “target” is used herein to refer to a location at which treatment or diagnosis occurs). Introducer62may be steerable via a robotic control system68including at least one servo mechanism70adapted to control distal end66of introducer62in at least one degree of freedom. Preferably, robotic control system68includes three servo mechanisms70adapted to control distal end66of the introducer62in three degrees of freedom (translation, deflection, and rotation), resulting in a total of six degrees of freedom for robotic surgical system10, and at least one controller72adapted to control servo mechanisms70. Similar control principles may be applied to steerable introducer62as are described herein with respect to robotic surgical system10and medical device12.

One of ordinary skill in the art will appreciate that the deflection of distal end52of catheter12is a function not only of the input to catheter deflection actuator58(i.e., the selective tensioning of one or more pull wires50), but also of the extent to which catheter12is advanced beyond a generally rigid sheath, such as introducer62. That is, the further distal end52of catheter12is advanced beyond distal end66of introducer62, the greater the deflection of distal end52of catheter12will be for a given input at catheter deflection actuator58.

It is therefore desirable to calibrate the deflection of distal end52of catheter12in terms of both catheter deflection control mechanism inputs and extensions of catheter12beyond distal end66of introducer62. By robotically actuating catheter deflection control mechanism20between extremes (e.g., commanding a complete rotation of catheter deflection actuator58) and measuring the resulting deflection of distal end52of catheter12(e.g., using a localization system), catheter deflection control mechanism inputs may be correlated with deflections of distal end52for a given extension of catheter12beyond distal end66of introducer62. A similar process may be performed for a multiple different extensions of catheter12beyond distal end66of introducer62, resulting in a family of calibration curves relating catheter deflection control mechanism inputs to deflections of distal end52of catheter12. Each curve corresponds to a particular extension of catheter12beyond distal end66of introducer62; the amount of extension of catheter12beyond distal end66of introducer62may be derived, at least in part, from the amount of translation of catheter holding device16relative to track14.

To create a substantially sterile field around catheter12outside the patient's body, an expandable and collapsible tubular shaft74substantially surrounds at least a portion of catheter12, such as the region of catheter12between catheter holding device16and proximal end64of introducer62. Preferably, shaft74is sterilized before use along with other relevant components of robotic surgical system10. As catheter holding device16translates to advance catheter12into the patient (i.e., to the right inFIG. 1), tubular shaft74collapses upon itself. Contrarily, as catheter holding device16translates to retract catheter12from the patient (i.e., to the left inFIG. 1), tubular shaft74expands. Preferably, tubular shaft74is assembled from a plurality of telescoping tubular elements76. It is contemplated, however, that tubular shaft74may alternatively be an accordion-pleated or other expandable and collapsible structure.

As depicted inFIGS. 7 and 8, robotic surgical system10may be employed to robotically navigate catheter12into and through the patient and to one or more sites, which may be target sites, within the patient's body by actuating one or more of translation servo mechanism18, deflection servo mechanism22, and rotation servo mechanism60(if present) via controller24. Robotic surgical system10may operate automatically according to a computerized program as executed by controller24(FIG. 7). It is also contemplated that the user, who may be a surgeon, cardiologist, or other physician, may control robotic surgical system10through an appropriate set of controls78, such as a three-dimensional joystick (e.g., a joystick with three input axes), a steering yoke, or another suitable input device or collection of such devices permitting the user to robotically steer catheter12(FIG. 8).

As described above, catheter12can be quickly and easily disconnected from catheter holding device16. Thus, if the user desires to manually control catheter12at any point during the procedure, the user may disconnect catheter12from the catheter holding device16as described above. The user may navigate catheter12manually for as long as desired, and then replace it into catheter holding device16and resume robotic control.FIG. 9illustrates the user manually operating catheter12after having removed it from catheter holding device16.

In some embodiments of the invention, multiple robotic surgical systems controlling multiple medical devices may be employed during a procedure. For example, a first robotic surgical system may control an ultrasonic imaging transducer, while a second robotic surgical system may control an ablation catheter. A single controller, or multiple cooperating controllers, may coordinate the multiple medical devices and the multiple robotic surgical systems, for example in conjunction with a single localization system, or alternatively by utilizing data from the ultrasonic imaging transducer to control the movement of the ablation catheter.

Robotic surgical system10facilitates precise and accurate navigation of medical device12within the patient's body. In addition, since medical device12is manipulated primarily robotically, the physician will experience considerably less fatigue during the surgical procedure. Furthermore, robotic control permits a substantially increased degree of complexity in the control and actuation mechanisms that may be incorporated into medical device12over those that may be used in a medical device12intended solely for human control, enabling an increase in the versatility of medical device12.

Contact Sensing

FIG. 10schematically illustrates a surgical system80equipped to sense contact between a probe, such as catheter12, and a tissue surface82, such as a cardiac wall. Probe12includes a sensor or instrument84carried thereon, preferably at distal end52of probe12, for measuring the value of a parameter (referred to herein as P) of tissue surface82either periodically (that is, with a relatively fixed interval between measurements) or episodically (that is, with a variable interval between measurements). Preferably, sensor84is an electrophysiology sensor capable of measuring one or more electrophysiology characteristics, including, but not limited to, impedance, phase angle, electrogram amplitude, optical feedback, and ultrasonic feedback.

To facilitate precise determination of the distance traveled by probe12between measurements of the tissue parameter (referred to herein as Δs), a precisely calibrated system is utilized. The precisely calibrated system may be a robotically controlled system to move probe12within the patient's body, such as robotic surgical system10described herein. It is also contemplated that measurements of the position of probe12within the patient's body may be made using a using a precisely locally- or universally-calibrated positional feedback (i.e., localization) system86in conjunction with a location or position electrode88carried on probe12. Preferably, the positional feedback system is the Ensite NavX™ system of St. Jude Medical, Inc., which includes pairs of electrodes90defining measurement axes by which the position of probe12may be measured. One of ordinary skill in the art will appreciate that other localization systems, such as the CARTO navigation system from Biosense Webster, Inc., may also be employed. Only one pair of electrodes90is illustrated; one of skill in the art will appreciate that additional pairs of electrodes90may be used if additional measurement axes are desired.

A processor monitors the value of the tissue parameter measured by sensor84as probe12moves within the patient's body. The processor may be incorporated in a computer system92. For purposes of this disclosure, a single processor within computer system92will be referred to, though it is contemplated that multiple computer systems92and/or multiple processors within a single computer system92may be used to practice the various aspects of the present invention. Further, one or more processor functions described herein may be integrated in a single processor without departing from the scope of the present invention.

As described above, probe12may be moved by a robotically-controlled system capable of precise movements on the order of less than about 5 mm, more preferably on the order of less than about 2 mm, and most preferably on the order of less than about 1 mm. Alternatively, the movements of probe12are precisely measured by a positional feedback system86with a margin of error of less than about 5 mm, preferably less than about 2 mm, and more preferably less than about 1 mm. For a given, precisely determined Δs (e.g., as precisely moved by robotic surgical system10or precisely measured by positional feedback system86), a corresponding amount and rate of change in the tissue parameter between measurements can be anticipated for a situation where there is no change in the proximity or degree of contact between probe12and tissue surface82.

The processor monitors the tissue parameter for an indicator of proximity or degree of contact between probe12and tissue surface82and indicates a change in the proximity or degree of contact between probe12and tissue surface82based on the monitored tissue parameter. In particular, the processor reports the change in either proximity or degree of contact based on either the amount of change in the tissue parameter or the rate of change in the tissue parameter between measurements, and preferably between successive measurements, thereof. The term “proximity” refers to the relationship between probe12and tissue surface82when probe12is not in contact with tissue surface82; it is, in lay terms, a measure of how close probe12is to tissue surface82. The term “degree of contact” refers to the relationship between probe12and tissue surface82when probe12is in contact with tissue surface82; it is, in lay terms, a measure of how hard probe12is pressing into tissue surface82.

A contact sensing method is illustrated in the high-level flowchart ofFIG. 11. Probe12is navigated into the patient's body and into meaningful proximity with tissue surface82in step100. The term “meaningful proximity” refers to probe12being sufficiently close to tissue surface82such that sensor84can capture useful electrophysiology information about surface82, and thus encompasses both contact and non-contact relationships between probe12and tissue surface82.

Once inside the patient's body, probe12is moved using a calibrated system, such as robotic surgical system10, moved and located using a calibrated system, such as positional feedback system86, or both. As probe12moves, the tissue parameter at distal end52of probe12is measured, either periodically or episodically, using sensor84(steps102,104, and106). An amount of change (ΔP) in the measured tissue parameter between successive measurements (Pnand Pn+1) is calculated in step108. The processor then indicates a change in proximity or degree of contact between probe12and tissue surface82based upon the amount of change in the measured tissue parameter in step110. That is, the processor provides the user and/or controller24controlling robotic surgical system10with an indication of either “change” or “no change” in the proximity or degree of contact based upon the amount of change in the measured tissue parameter. If desired, the process may be repeated as probe12continues to move through the patient's body by setting Pn=Pn+1(step112) and moving probe12to a new location (step104) where a new Pn+1is measured (step106).

A number of algorithms may be used to identify the change in proximity or degree of contact between probe12and tissue surface82in step110. In a first algorithm, illustrated inFIG. 12a, the amount of change in the measured tissue parameter (ΔP) is compared to a predetermined range of values ranging from a lower limit (LL) to an upper limit (UL) in step114a. (InFIGS. 12athrough12o, absolute values are used in order to account for potential negative values of ΔP.) A change is indicated when the amount of change in the measured parameter falls outside the predetermined range of values (step116a); no change is indicated when the amount of change in the measured parameter falls within the predetermined range of values (step118a).

The predetermined range of values (that is, either or both of UL and LL) may be user selectable, and may correspond generally to the anticipated amount of change in the measured tissue parameter between measurements when there is no change in the proximity or degree of contact between probe12and tissue surface82for a given Δs. “Predetermined” is used herein to refer to values that are set in advance of applying the contact sensing algorithm; for example, the values (i.e., UL and LL) may be based upon a percentage variation in the anticipated change in the measured tissue parameter, which percentage may also be user selectable.

In other algorithms, the amount of change in the measured tissue parameter is compared to a change threshold, with the change indication based upon whether or not the measured tissue parameter crosses the change threshold. For example, as shown inFIG. 12b, the change threshold may correspond generally to the maximum anticipated amount of change in the measured tissue parameter between successive measurements for a given Δs (ΔPMAX). Thus, no change in proximity or degree of contact would be indicated when the amount of change is less than the change threshold, and a change in proximity or degree of contact would be indicated when the amount of change is greater than the change threshold. It is also contemplated that the algorithm may be modified as shown inFIG. 12c, such that the threshold corresponds generally to the minimum anticipated amount of change in the measured tissue parameter between successive measurements for a given Δs (ΔPMIN), which would reverse the conditions for indicating change or no change in proximity or degree of contact. The change threshold may be user selectable, and may be calculated as a percentage variation in the anticipated amount of change in the measured tissue parameter for a given Δs, which percentage may itself be user selectable.

In still other algorithms, the change in proximity or degree of contact is indicated based upon a rate of change in the measured tissue parameter with respect to either the time between measurements (ΔP/Δt) or the distance traveled by probe12between measurements (ΔP/Δs). The rate of change may also be calculated as a derivative of the measured tissue parameter with respect to time (dP/dt) or probe distance traveled (dP/ds). The rate of change may be calculated as a first derivative of the tissue parameter, a second derivative of the tissue parameter, or any further derivative of the tissue parameter. One of skill in the art will recognize that any of these variables may be calculated from the amount of change in the measured tissue parameter and the time between measurements or the precisely determined distance traveled by probe12between measurements. The decision processes for indicating change in proximity or degree of contact based upon rate of change variables are substantially analogous to the algorithms described with respect to the amount of change in the measured tissue parameter (i.e., comparison to a predetermined range of values or comparison to a rate of change threshold). These alternative algorithms are illustrated inFIGS. 12d-12o.

FIG. 13ais a representative chart of the measured tissue parameter as a function of time (t) or probe distance traveled (s), whileFIG. 13billustrates the derivative of the curve ofFIG. 13a. Initially, in region120, there is no change in proximity or degree of contact, so P varies only slightly. ΔP is thus quite small, so ΔP/Δt, ΔP/Δs, dP/dt, and dP/ds vary slightly about zero (dP/dt and dP/ds are illustrated inFIG. 13b).

When a change in proximity or degree of contact occurs, such as at point122, P experiences a substantial change in a very short interval of time or probe distance traveled. ΔP/Δt and ΔP/Δs are thus quite large, and the curve ofFIG. 13billustrating the derivative of the measured tissue parameter exhibits a corresponding spike124before returning to varying slightly about zero in region126. A second spike128corresponds to a point130where another change in proximity or degree of contact occurs.

The contact sensing methods described above are useful in monitoring for a change indicative of probe12making contact with tissue surface82, a change indicative of probe12breaking contact with tissue surface82, or a change indicative of a change in the degree of contact between probe12and tissue surface82. In the lattermost case, the method may provide an indicator of whether probe12is beginning to break contact with tissue surface82or is potentially being traumatically driven into tissue surface82. This information may be used by the user and/or robotic surgical system10(e.g., controller24) as feedback to adjust the movement of probe12to maintain a particular degree of contact with tissue surface82on an ongoing basis in order to improve the quality or efficiency of the medical treatment. For example, in an ablation procedure for the treatment of atrial fibrillation, one of ordinary skill will readily appreciate that a spike in a derivative of the tissue parameter, as shown inFIG. 13b, may indicate that the ablation catheter has broken contact with the cardiac surface and is therefore no longer creating a substantially continuous lesion and that appropriate corrective action is necessary to bring the ablation catheter back into contact with the cardiac surface. As another example, in a surface modeling procedure, the spike may indicate that the modeling probe has broken contact with the surface being modeled such that the collection of geometry points should be suspended in order to avoid capturing erroneous data.

Surface Modeling

FIG. 14illustrates a system150for generating a three-dimensional model of at least a portion of the patient's body. Though system150will be described in the context of generating a three-dimensional model of the patient's heart chamber152, it should be understood that system150and the method disclosed herein may also be employed to map the volume and tissue surface of any internal organ or other portion of the patient's body in which the user is interested.

Modeling system150includes electrode154for insertion into a portion of the patient's heart and a controller (once again denoted as controller24, though an additional controller or controllers could be used) for robotically moving electrode154within the portion of the heart either randomly, pseudo-randomly, or according to one or more predetermined patterns. The term “predetermined pattern” is used to mean any pattern that is not random or pseudo-random, whether that pattern is computer- or user-dictated. Further, with reference to the phrase “within a portion of a heart,” it should be appreciated that this does not refer to the movement of electrode154within the tissue itself (which could be traumatic), but rather to the movement of electrode154within a space that is interior to the patient's body (such as movement within the open space that defines heart chamber152).

Electrode154may be a position, location, or mapping electrode, with the terms being used interchangeably herein. Controller24may be incorporated in robotic surgical system10described herein, in which case electrode154may be carried on catheter12, preferably at or near distal end52of catheter12such that electrode154may be brought into contact with tissue surface82of heart chamber152. It is also contemplated that electrode154may be located more proximally along catheter12, for example adjacent to electrode88. In the latter configuration, the relationship between electrode154and distal end52may be used to derive position information for distal end52from position information for electrode154. It should be understood that carrying electrode154on a non-catheter probe, utilizing an alternative robotic control system to move electrode154, and manually moving electrode154are all regarded as within the scope of the invention. It should further be understood that the use of both individual and multiple electrodes to practice the various aspects of the present invention is contemplated (i.e., electrode88and electrode154may be the same electrode).

Positional feedback system86detects position information of electrode154within heart chamber152. Position detector86preferably includes a plurality of paired electrodes90defining measurement axes for locating electrode154within the patient's body by utilizing the electrical potentials measured by electrode154. An example of a suitable positional feedback system86is disclosed in U.S. application Ser. No. 11/227,006, filed 15 Sep. 2005 (the '006 application) and U.S. provisional application No. 60/800,848, filed 17 May 2006 (the '848 application), both of which are hereby expressly incorporated by reference as though fully set forth herein. The terms “position detector,” “positional feedback system,” “mapping system,” and “navigation system” are used interchangeably herein.

By detecting the position of electrode154multiple times as electrode154is moved within heart chamber152, position detector86generates a plurality, or cloud, of location points defining the space occupied by heart chamber152. Positional feedback system86need not determine whether a particular location point is a surface point or an interior point during the position detection step; the interior points will be resolved during subsequent processing. That is, the cloud of location points is generated indiscriminately, advantageously reducing the overhead and time required to collect the data set from which the three-dimensional model is generated. Thus, the cloud of location points preferably includes at least some location points on the surface of heart chamber152(“surface points”) and at least some location points not on the surface of heart chamber152(“interior points”). The cloud of location points may be stored in a storage medium, such as a hard drive or random access memory (RAM), which may be part of computer system92.

A modeling processor, which may be part of computer system92, generates a three-dimensional model of heart chamber152from the cloud of location points. The three-dimensional model includes position information for a plurality of surface points describing a three-dimensional surface model of heart chamber152. That is, after the cloud of location points is generated, the modeling processor identifies, isolates, and either disregards or eliminates the interior points by applying a surface construction or surface modeling algorithm to the plurality of location points. Preferably, the surface modeling algorithm employed is a shrink-wrap algorithm, though numerous other surface modeling algorithms are contemplated, including, but not limited to, convex hull algorithms (e.g., Qhull), alpha shapes, Hoppe's software, CoCone, and Paraform. The three-dimensional surface model may optionally be output as a graphical representation of heart chamber152on a display154, which may also be part of computer system92, or another output device. Further, the three-dimensional surface model may optionally be stored in a storage medium.

In use, electrode154is inserted within heart chamber152, for example by advancing electrode154into heart chamber152on catheter12controlled by robotic surgical system10. Next, electrode154is robotically moved within heart chamber152. As described above, movement of electrode154within heart chamber152may be random, pseudo-random, or according to a predetermined pattern. Optionally, the predetermined pattern may include two distinct components: a first predetermined pattern until a determination is made that electrode154is in contact with tissue surface82of heart chamber152, and a second predetermined pattern after electrode154has made contact with surface82of heart chamber152. The contact sensing methodology described herein may be employed to determine when electrode154has made contact with surface82of heart chamber152; to this end, it is contemplated that electrode154may function as sensor84. The second predetermined pattern need not be substantially continuous along surface82of heart chamber152; that is, electrode154may occasionally break contact with surface82of heart chamber152while following the second predetermined pattern such that electrode154“bounces” rather than “skates” along surface82of heart chamber152.

For example, in some embodiments of the invention, electrode154may first measure a few initial location points in a region of heart chamber152. Electrode154may then incrementally approach surface82of heart chamber152; the contact sensing methodology described herein, or another suitable contact sensing methodology, may be utilized to determine when electrode154has contacted surface82. A location point may be collected from surface82of heart chamber152. A section of a model of surface82of heart chamber152may then be constructed from the initial location points and the surface location point, and electrode154may then be moved small distances, such as about 5 mm anti-normal to surface82and about 5 mm laterally to an unsampled region. This process may then be repeated as necessary to complete the cloud of location points.

As electrode154is moved within heart chamber152, position information of electrode154is detected in order to generate the plurality of location points defining the space occupied by heart chamber152. If electrode154is located at or near distal end52of catheter12, position information may be stored directly; if electrode154is located more proximally, position information may be derived from the relationship between electrode154and distal end52prior to being stored. Detection of position information may be periodic (that is, with a relatively constant interval between successive measurements) or episodic (that is, with a variable interval between successive measurements). Detection may also be event-driven (for example, upon sensing a particular electrophysiological characteristic with sensor84).

The three-dimensional model of heart chamber152is then generated from the plurality of location points by utilizing a surface construction algorithm, such as a shrink-wrap algorithm, to wrap or otherwise construct a surface around the plurality of location points. The three-dimensional model includes position information for at least some of the plurality of location points within heart chamber152, preferably those location points describing a three-dimensional surface model of heart chamber152. The model may be generated by processing the plurality of location points using a surface construction algorithm to identify and output the subset of the plurality of location points defining the three-dimensional surface model, and thus surface82of heart chamber152. Interior points may be eliminated or simply disregarded by the surface construction algorithm. The subset of location points may define vertices for a plurality of triangles representing the three-dimensional surface model of heart chamber152, and the triangles themselves may be generated by interconnecting the vertices. Once generated, the three-dimensional model may be presented as a graphical representation on display156, permitting the user to interact intuitively with the model through input devices158, which may include, but are not limited to, a mouse, trackball or other pointing device160; a two- or three-dimensional joystick or control yoke162; and a keyboard or keypad164. Input devices158may be coupled to computer system92. Optionally, one or more of input devices158may also serve as controls78permitting the user to robotically steer catheter12.

As one of ordinary skill in the art will understand from the foregoing description, the present invention facilitates improved collection of location points. For example, manually controlled catheters may tend to follow repetitive or stereotypical patterns during sampling, and thus may not collection location points throughout the volume of the heart chamber. The robotically-controlled catheter of the present invention, however, is less susceptible to this shortcoming, in that it is capable of achieving the necessary control vectors to reach substantially all of the volume of the heart chamber. Further, the robotically-controlled catheter may be programmed to avoid repeat sampling of regions or to exclude repeatedly sampled location points, in the event that it is necessary to travel through a particular region more than once. As a result, the not only may the plurality of location points be improved, but also the time required to create the three-dimensional model may be reduced.

Diagnostic Data Mapping

Modeling system150may also be utilized to generate a diagnosis map for surface82of heart chamber152through the addition of an instrument for measuring physiological information, and preferably an instrument for measuring electrophysiology information, such as sensor84. It should be understood that, though described herein as separate components, one or more of sensor84, electrode88, and electrode154may optionally be combined into a single component carried on probe12. Sensor84measures electrophysiology information at a point on surface82of heart chamber152that is in meaningful proximity to probe12. The diagnosis map contains information about the physiological characteristics of surface82, for example the tissue impedance at various locations on surface82.

As described above, controller24moves probe12to a plurality of locations within heart chamber152, including into meaningful proximity with a plurality of surface points. A contact sensor, such as a force transducer, or the contact sensing methodology disclosed herein, may be employed to identify proximity or degree of contact between probe12and surface82of heart chamber152, though, as one of ordinary skill in the art will appreciate, contact sensing is not necessary if the geometry of heart chamber152is already known, since proximity and contact information between probe12and surface82can be derived from the known geometry and positional feedback system86.

Preferably, a processor, which may be part of computer system92, causes probe12to automatically move into meaningful proximity with a plurality of surface points, for example by providing instructions to controller24incorporated in robotic surgical system10to actuate one or more of servo mechanisms18,22,60to translate, deflect, and/or rotate probe12. It is also contemplated that the user may robotically steer probe12to the plurality of points via a suitable input device158, such as joystick162.

Sensor84detects electrophysiological information for at least some of the surface points, and preferably for each surface point. The processor associates the measured electrophysiological information with the position information for the surface point at which it was measured. As one of skill in the art should appreciate from this disclosure, the position information may be already known (e.g., through application of the surface modeling methodology disclosed herein) or may be gathered concurrently with the detection of electrophysiological information. Once position and electrophysiological information for the plurality of surface points has been gathered and associated as a plurality of surface diagnostic data points, the processor generates the diagnosis map of heart chamber152therefrom.

The diagnosis map may optionally be combined with the three-dimensional surface model of heart chamber152generated by the modeling processor or with another model of heart chamber152(e.g., an MRI- or CT-generated model). For example, the diagnosis map may be superimposed upon the three-dimensional surface model. If desired, the resultant three-dimensional diagnosis model, including both position information and physiological information, can be output on display156as a graphical representation. In addition, the diagnosis map or three-dimensional diagnosis model may be stored in a storage medium, which, as noted above, may be part of computer system92.

An electrophysiology processor, which also may be incorporated within computer system92, processes the measured electrophysiology information in order to identify one or more surface points that are potential treatment sites. By way of example only, the electrophysiology processor may identify surface points having abnormal impedance as potential targets for tissue ablation in the diagnosis and treatment of cardiac arrhythmia. The electrophysiology processor may be coupled to display156such that the one or more identified potential treatment sites, or other indicia of the measured physiological or electrophysiological information, may be presented to the user by superimposition on the graphical representation of the three-dimensional model. For example, the potential treatment sites may be flagged on display156with a special icon or coloration. Alternatively, contour lines may be added to the graphical representation to illustrate the physiological and/or electrophysiological data included in the diagnosis map.FIG. 15illustrates a graphical representation of heart chamber152including both flagged potential treatment sites168and contour lines170.

The user may employ a user interface166, including display156and input devices158, to select one or more of the identified potential treatment sites as target points (also referred to herein as “treatment points”), for example by pointing to and clicking on the treatment site as superimposed on the graphical representation. In order to permit the user to intuitively designate target points, display156may be a touchscreen. User interface166is preferably coupled to controller24, and thus to probe12, such that, upon selecting one or more target points with user interface166, controller24may cause probe12to be relocated thereto for further diagnosis (e.g., the collection of additional electrophysiology information at the target site) or treatment (e.g., the delivery of a therapeutic compound or ablative energy to the target site). It is also contemplated that controller24may operate to automatically navigate probe12to one or more identified potential treatment sites for further diagnosis or treatment without intervention or target point selection by the user (i.e., controller24may be responsive directly to the electrophysiology processor).

In use, electrode154, which is preferably mounted on medical device12, is inserted within heart chamber152. (Recall that this term does not embrace embedding electrode154in cardiac tissue.) Robotic controller24is used to move electrode154within heart chamber152either randomly, pseudo-randomly, or according to one or more predetermined patterns, and into meaningful proximity with a plurality of surface points on tissue surface82of heart chamber152in order to measure electrophysiology information thereat.

Assuming a known geometry of heart chamber152, for example as generated by the surface modeling methodology disclosed herein, electrophysiology information is measured and associated with the pre-existing position information for a plurality of surface points. If the geometry is unknown, the diagnosis mapping and surface modeling processes may be combined such that, as electrode154moves within heart chamber152, both position information and electrophysiology information are measured, thereby simultaneously generating a plurality of location points defining the space occupied by heart chamber152, at least some of which are surface points, and electrophysiology information for those surface points. The plurality of location points may be processed as described herein or according to another surface construction algorithm to generate the three-dimensional surface model of heart chamber152. The measured electrophysiology information is associated with the position information for at least some of the plurality of surface points in order to generate the diagnosis map. It is also contemplated that electrophysiology measurements may be taken after generating the plurality of location points, rather than simultaneously therewith, and either before or after applying the surface construction algorithm to generate the surface model.

The diagnosis map can be generated from the resulting plurality of surface diagnostic data points. The plurality of surface diagnostic data points may also be used to generate a three-dimensional surface model of heart chamber152including both position and electrophysiology information for the plurality of surface points. The diagnosis map and/or surface model may optionally be stored in a storage medium, either individually or as a composite, or presented as a graphical representation on display156, either with or without an accompanying three-dimensional model of heart chamber152.

Once the diagnosis map is generated, it may be used as an intuitive interface for the user to select one or more target points, for example by using an input device158to point and click on the graphical representation of the three-dimensional model of heart chamber152with the diagnosis map superimposed thereon. Medical device12may subsequently be navigated to the target points so selected in order to provide treatment, such as ablation of tissue, or for further diagnosis, such as making additional electrophysiology measurements. It is contemplated that the user selecting the one or more target points may be remote from robotic surgical system10. For example, an expert physician in one city may access the three-dimensional model of heart chamber152via a computer network, such as the Internet, and select the target points, which may then be delivered to robotic surgical system10in a second city for execution.

Although several embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention. For example, the robotic surgical system10may be modified to incorporate additional servo mechanisms and controllers operating on additional degrees of freedom.

Further, though the contact sensing methodology has been described in connection with a robotically controlled medical device, it could also be implemented in a manually controlled medical device. It should also be understood that, rather than utilizing absolute values in the various contact sensing algorithms described herein, the thresholds or limits may be appropriately adjusted to compensate for negative values of ΔP, for example by taking the opposite of all thresholds or limits and reversing the comparator (i.e., changing <to >) upon detecting that ΔP is less than zero.

In addition, one of ordinary skill in the art will appreciate that, though the devices and methods disclosed herein have been described in connection with the treatment of atrial fibrillation, and in particular in connection with the creation of lesions of ablated tissue, they may be used to administer other therapies or to perform other diagnostic procedures.

Further, the devices and methods disclosed herein are capable of use both epicardially and endocardially.

All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader's understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other.