Method and system for navigating a catheter probe

What is claimed is:

1. A method of determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain, comprising the steps of:

inducing within said sensing coil a set of orientation signal values each representative of an orientation of said sensing coil and independent of a position of said sensing coil;

determining the orientation of said sensing coil using said induced orientation signal values;

inducing within said sensing coil a set of positional signal values each representative of the position of said sensing coil; and

determining the position of said sensing coil using said positional signal values and said determined orientation.

2. The method as recited in claim 1, wherein the step of inducing said set of orientation signal values comprises the steps of:

generating from outside said body a series of magnetic fields each penetrating at least said navigational domain and characterized substantially by a principal magnetic component in one axial dimension and relatively smaller magnetic components in two other axial dimensions.

3. The method as recited in claim 1, wherein the step of inducing said set of positional signal values comprises the steps of:

generating from outside said body a series of magnetic fields each penetrating at least said navigational domain and characterized substantially by two principal gradient magnetic components in respective axial dimensions and a relatively smaller magnetic components in a third axial dimension.

4. The method as recited in claim 3, wherein said generating step further includes the steps of:

generating said fields to provide a plurality of constant signal surfaces for the sensing coil such that an intersection between two such surfaces with components in the same axial dimensions produces a line along which said sensing coil is located;

wherein said two such surfaces are identified from among said plurality of constant signal surfaces by their ability to induce one of said positional signal values.

5. The method as recited in claim 4, further comprises the steps of:

weighting each line in accordance with a signal strength of said corresponding constant signal surface; and

determining an intersection of said weighted lines.

6. The method as recited in claim 5, wherein six constant signal surfaces are generated to produce three intersection lines.

7. A system for determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain, comprising:

first transmit means for projecting into said navigational domain magnetic energy that is sufficient to induce signal values within said sensing coil representative of an orientation of said sensing coil and independent of the position of said sensing coil;

second transmit means for projecting into said navigational domain magnetic energy that is sufficient to induce signal values within said sensing coil representative of the position of said sensing coil; and

analysis means, coupled to said first transmit means and said second transmit means, for determining the position and orientation of said sensing coil from said induced signal values.

8. A system for determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain, comprising:

first signal-inducing means for inducing within said sensing coil orientation signals that are representative of the orientation of said sensing coil;

analysis means, coupled to said first signal-inducing means, for determining the orientation of said sensing coil using said induced orientation signals and independent from a position of said sensing coil;

second signal-inducing means for inducing within said sensing coil position signals that are representative of the position of said sensing coil; and

analysis means, coupled to said second signal-inducing means, for determining the position of said sensing coil using said determined orientation and said induced position signals.

9. The system as recited in claim 8, wherein the first signal-inducing means comprises:

field generation means for successively generating magnetic field patterns projected into said navigational domain, each characterized substantially by a principal magnetic field component in one direction and relatively smaller magnetic components in two other directions.

10. The system as recited in claim 9, wherein said field generation means comprises a set of magnetic coils.

11. The system as recited in claim 10, wherein said magnetic coils are disposed in a planar top of an examination deck upon which a patient is disposed during a surgical procedure.

12. The system as recited in claim 10, wherein said magnetic coils are disposed in a planar top and in rail members edge supported by said planar top for an examination deck upon which a patient is disposed during a surgical procedure.

13. The system as recited in claim 8, wherein the second signal-inducing means comprises:

field generation means for successively generating magnetic field patterns each characterized by a first and second gradient field component in respective directions and a relatively smaller third component in another direction.

14. The system as recited in claim 13, wherein the field generation means comprises a magnetic coil assembly.

15. A method of determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain, comprising the steps of:

defining the location of said sensing coil with a set of independent location parameters; and

sequentially generating within said navigational domain a sequence of magnetic fields for inducing within said sensing coil a corresponding sequence of induced signals each defined by an induced signal expression that functionally relates said induced signal to certain ones of said location parameters, such that said set of location parameters is determinable by sequentially solving individual signal expression groups each including certain ones of said induced signal expressions and sufficient to represent a subset of said location parameters.

16. The method as recited in claim 15, wherein said sequence of magnetic fields comprises:

a series of unidirectional magnetic fields each characterized substantially by a principal magnetic field component in one direction and relatively smaller magnetic components in two other directions; and

a series of gradient magnetic fields each characterized by a first and second gradient field component in respective directions and a relatively smaller third component in another direction.

17. The method as recited in claim 16, wherein said signal expression groups include:

an orientation group including induced signal expressions each functionally related to a respective one of said unidirectional magnetic fields and an orientation of said sensing coil, and independent of a position of said sensing coil; and

a position group including induced signal expressions each functionally related to a respective one of said gradient magnetic fields, the orientation of said sensing coil, and the position of said sensing coil.

18. The method as recited in claim 17, wherein the step of sequentially solving said individual signal expression groups includes the steps of:

initially solving the induced signal expressions of said orientation group; and

next solving the induced signal expressions of said position group.

19. A system for determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain, comprising:

means for defining the location of said sensing coil with a set of independent location parameters; and

field generation means for sequentially generating within said navigational domain a sequence of magnetic fields for inducing within said sensing coil a corresponding sequence of induced signals each defined by an induced signal expression that functionally relates said induced signal to certain ones of said location parameters, such that said set of location parameters is determinable by sequentially solving individual signal expression groups each including certain ones of said induced signal expressions and sufficient to represent a subset of said location parameters.

20. The system as recited in claim 19, wherein said sequence of magnetic fields comprises:

a series of unidirectional magnetic fields each characterized substantially by a principal magnetic field component in one direction and relatively smaller magnetic components in two other directions; and

a series of gradient magnetic fields each characterized by a first and second gradient field component in respective directions and a relatively smaller third component in another direction.

21. The system as recited in claim 20, wherein said signal expression groups include:

an orientation group including induced signal expressions each functionally related to a respective one of said unidirectional magnetic fields and an orientation of said sensing coil, and independent of a position of said sensing coil; and

a position group including induced signal expressions each functionally related to a respective one of said gradient magnetic fields, the orientation of said sensing coil, and the position of said sensing coil.

22. The system as recited in claim 21, wherein said field generation means comprises:

analysis means for solving the induced signal expressions of said orientation group; and

analysis means for solving the induced signal expressions of said position group.

Description Submit all comments and votes

FIELD OF THE INVENTION

The present invention relates to catheter navigation systems and, more particularly, to a method and system for determining the position and orientation of a catheter probe being used during a surgical procedure.

BACKGROUND OF THE INVENTION

Various configurations have been proposed to guide and detect a catheter probe through the internal spaces of a patient undergoing a surgical procedure. These proposed configurations are characterized by several alternative approaches including, inter alia, procedures for solving equations to determine unknown location parameters, the generation and detection of magnetic fields, and the use of sensing devices affixed to the catheter probe.

U.S. Pat. No. 4,905,698 to Strohl, Jr. et al. discloses a locator device external to a subject for generating an electromagnetic field that projects into the subject. A catheter inserted into the subject is fitted with a sensing coil at its distal end. The phase of the voltage that is induced in the coil in response to the field is compared to the phase of the generated field. When an in-phase condition occurs, this is an indication that the locator is behind the coil; alternatively, an out-of-phase condition indicates that the locator is beyond the coil. Positions intermediate these two rough approximations of the coil position are not determined other than by a beeping indicator that signifies that this intermediate positioning has been reached.

U.S. Pat. No. 4,821,731 to Martinelli et al. discloses an electroacoustical transducer means secured to the distal end of a catheter that is inserted into a subject for generating acoustical pulses that propagate along an imaging axis and reflect from an anatomical area of interest. The acoustic echoes are converted by the transducer means into electrical signals representative of an image of the anatomical area under reflection and the relative position of the transducer means and angular orientation of the sensing/imaging axis.

U.S. Pat. No. 4,642,786 to Hansen discloses a magnetic position and orientation measurement system that determines the location of an object in space with various configurations, each characterized by the attachment of a retransmitter to the object consisting of passive resonant circuits. The retransmitter is in a predetermined position and orientation with respect to the object. A magnetic field is generated at a resonant frequency of the retransmitter which then retransmits a magnetic field for subsequent reception. The position and orientation of the object may be calculated based upon the induced signals as developed by the reception of the retransmitted magnetic field. The original transmission and reception may be implemented with an integrated transceiver, separate transmitter and receiver elements, or a single transmitter and an array of receiver coils.

U.S. Pat. No. 4,317,078 to Weed et al. discloses how the location of a magnetically sensitive element may be determined by moving a magnetic field source along specified reference axes to induce signals in the sensor so as to identify a set of null points representative of certain flux linkage values. The null point locations are used to calculate the sensor position.

U.S. Pat. No. 3,868,565 describes a system where a magnetic field is generated which rotates about a known pointing vector. The generated field is sensed along at least two axes by a sensor attached to the object to be located or tracked. Based upon the relationship between the sensed magnetic field components, the position of the object relative to the pointing vector can be computed.

U.S. Pat. No. 4,173,228 to Van Steenwyk et al. discloses a catheter locating system that includes a sensor attached to the distal end of the catheter. An electromagnetic field is projected into the body cavity with magnetic probe coils. The field is detected by the sensor, which generates an induced signal whose magnitude and phase are representative of field strength, separation of sensor and probe coils, and relative orientation of sensor and probe coils. The probe coil undergoes linear and rotational movement to identify orientations and locations of the probe coil where minima and maxima occur in the measured signal induced in the sensor. This information is representative of the position and orientation of the sensor.

U.S. Pat. No. 5,211,165 to Dumoulin et al. discloses a modified catheter device that includes a small RF transmit coil attached to its distal end. The transmit coil is driven by an RF source to create an electromagnetic field that induces electrical signals in an array of receive coils distributed around a region of interest. Alternatively, the receive coils can be placed on the invasive device and the transmit coils are distributed outside the patient. A minimum of one transmit coil and three receive coils is necessary to precisely determine the location of the invasive device. A series of equations is developed to solve for the unknowns x-y-z-.phi.-.theta..

PCT Application No. WO94/04938 to Bladen et al. describes how the location and orientation of a single sensing coil may be determined from induced signals developed in response to a sequence of applied magnetic fields emanating from three groups of field generators each including three mutually orthogonal coils.

The positioning methodology developed by Bladen et al. involves calculating the distance from the sensing coil to each group of field generators as a function of the induced voltage developed in the sensing coil by the field generator. The distance calculation is used to define the radius of a sphere centered on the respective field generator. The intersection (i.e., overlap) of the spheres is used to calculate an estimate of the sensor position, using the spherical radius extending from the known location of the field generators as the estimate for each generator.

The orientation algorithm of Bladen et al. develops general equations for induced voltage including the entire set of unknown variables (x-y-z location and .phi.-.theta. orientation). The algorithm specifically solves for the orientation parameters by substituting the measured induced voltage and the computed x-y-z coordinates into the general induced voltage equation, and then reduces the equations to the unknown variables .phi.-.theta..

In an alternative orientation algorithm described by Bladen et al., the induced voltage is treated as a vector quantity, allowing the angle between the magnetic field at the generator and the radial vector joining the sensor to the generator to be calculated with a dot product computation. The angle between the radial vector and the sensor axis can be determined from the computed field angle using the dipole equations that define the generator fields. This sensor angle and the radial position as determined by the position algorithm together define the sensor position for use in the alternative orientation algorithm. These values are used to compute the angular orientation .phi. and .theta..

OBJECTS OF THE INVENTION

It is a general object of the present invention to obviate the above-noted and other disadvantages of the prior art.

It is a more specific object of the present invention to provide a catheter navigation system capable of determining the location of a catheter probe.

It is a further object of the present invention to develop a catheter navigation system employing a sensing coil affixed to the end of a catheter probe for generating induced voltage signals that are sufficient to describe the position and orientation of the sensing coil.

It is a further object of the present invention to develop a methodology for generating magnetic fields that are sufficient to create a series of soluble mathematical expressions describing the position and orientation of the sensing coil.

SUMMARY OF THE INVENTION

In one aspect of the present invention, an improved method of determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain comprises the steps of:

inducing within said sensing coil a set of orientation signal values each representative of an orientation of said sensing coil and independent of a position of said sensing coil;

determining the orientation of said sensing coil using said induced orientation signal values;

inducing within said sensing coil a set of positional signal values each representative of the position of said sensing coil; and

determining the position of said sensing coil using said positional signal values and said determined orientation.

In another aspect of the present invention, an improved system for determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain comprises:

first transmit means for projecting into said navigational domain magnetic energy that is sufficient to induce signal values within said sensing coil representative of an orientation of said sensing coil and independent of the position of said sensing coil;

second transmit means for projecting into said navigational domain magnetic energy that is sufficient to induce signal values within said sensing coil representative of the position of said sensing coil; and

analysis means, coupled to said first transmit means and said second transmit means, for determining the position and orientation of said sensing coil from said induced signal values.

In another aspect of the present invention, an improved method of determining the location of a magnetically-sensitive, electrically conductive sensing coil affixed to a distal end of a catheter probe partially inserted into a body cavity within a navigational domain comprises the steps of:

defining the location of said sensing coil with a set of independent location parameters; and

sequentially generating within said navigational domain a sequence of magnetic fields for inducing within said sensing coil a corresponding sequence of induced signals each defined by an induced signal expression that functionally relates said induced signal to certain ones of said location parameters, such that said set of location parameters is determinable by sequentially solving individual signal expression groups each including certain ones of said induced signal expressions and sufficient to represent a subset of said location parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a perspective view of a patient-supporting examination deck in accordance with a preferred embodiment of the present invention;

FIGS. 2A-C schematically illustrate a series of magnetic coil sets for generating uniform fields in the x-, y-, and z-directions, respectively, in accordance with a preferred embodiment of the present invention, and which are configured within the deck of FIG. 1;

FIGS. 3 schematically illustrates a magnetic coil assembly for determining the positional coordinates of the sensing coil in accordance with a preferred embodiment of the present invention, and which is configured within the deck of FIG. 1;

FIG. 4 is a flow diagram describing the location algorithm in accordance with the present invention;

FIG. 5 schematically depicts the magnetic coil assembly of FIG. 3 to illustrate representative field patterns generated during an excitation period;

FIG. 6 is a trace representatively illustrating surfaces of constant signal from the sensing coil, as generated by the magnetic assembly of FIG. 3;

FIG. 7 shows an upper plan schematic view of the magnetic assembly of FIG. 3;

FIG. 8 schematically illustrates a perspective view of a patient-supporting examination deck in accordance with another embodiment of the present invention; and

FIGS. 9A-D schematically illustrate a series of magnetic coil assemblies configured in the deck and rails of FIG. 8 for determining the orientation and position of the sensing coil in accordance with another embodiment of the present invention.

Throughout the drawings the same or similar elements are identified by the same reference numeral.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a method and system for determining the location of a catheter or endoscopic probe inserted into a selected body cavity of a patient undergoing a surgical procedure. The location data is obtained from electrical measurements of voltage signals that are induced within a sensing coil affixed to the distal end of the catheter probe. These induced voltage signals are generated by the sensing coil in response to prespecified electromagnetic fields that project into the anatomical region of interest which contains all prospective locations of the catheters probe. The electrical measurements of the induced signals provide sufficient information to compute the angular orientation and the positional coordinates of the sensing coil, and hence the catheter probe, which collectively define the location of the sensing coil. The present invention is operative as the patient is disposed on a patient-supporting examination deck.

As used herein, "sensing coil" refers to an electrically conductive, magnetically sensitive element that is responsive to time-dependent magnetic fields for generating induced voltage signals as a function of and representative of the applied time-dependent magnetic field. The sensing coil is adaptable for secure engagement to the distal end of a catheter probe.

As used herein, "navigational domain" refers to a fully enclosed spatial region whose internal volume substantially encloses the complete prospective range of movement of the sensing coil. The navigational domain may be defined by any geometrical space but preferably takes the form of a spherical volume. Under surgical operating conditions, the navigational domain will correspond to an anatomical region of the recumbent patient where surgical viewing or investigation is desired (e.g., a diseased area of tissue or an organ).

As used herein, "last navigational point" (hereinafter "the LNP") refers to the most recently determined location of the sensing coil before another iteration of the location algorithm is performed.

As used herein, "uniform field" refers to a magnetic field having a large magnetic field component in a specified axial dimension and relatively smaller magnetic field components in the other axial dimensions, and characterized by substantially uniform field values throughout the navigational domain. In the x-y-z coordinate system used herein, where the uniform fields of interest are the x-directed, y-directed, and z-directed fields, the induced voltage signals developed by such fields in the sensing coil are designated V.sub.x, V.sub.y and V.sub.z, respectively. The term "undirectional field" is used interchangeably with "uniform field" when appropriate.

As used herein, "undirectional coils" refer to a magnetic assembly that is operative to generate a uniform field (as defined above) within the navigational domain. A distinct magnetic assembly is employed for each uniform field. Although the unidirectional coils described herein are preferably implemented with a collection of appropriately designed magnetic coils, this implementation should not be construed as a limitation of the present invention. Rather, the unidirectional coils may be constructed from any magnetic configuration that is sufficient to generate the uniform fields.

As used herein, "gradient field" refers to a time-dependent magnetic field having non-zero field components (i.e., components with a high spatial gradient) in two of the three axial dimensions for the coordinate system of interest (e.g., x-y-z system), and a substantially zero component in the remaining axial dimension. For mathematical purposes, a substantially zero component is generated when its value is small compared to the net vector resulting from the other two field components.

As used herein, "constant signal surface" or "constant voltage surface" refers to a surface contour along which at every possible point of location for the sensing coil the same induced voltage is developed in the sensing coil.

As used herein, "delta coils" refer to a magnetic assembly for generating a gradient field (as defined above) within the navigational domain. As will become more apparent hereinafter, the delta coils will typically be described in the context of delta coil pairs including a long coil set and a short coil set each generating gradient fields with components in the same axial dimensions but whose magnetic field patterns are different. Each of the long and short coil sets may be considered to generate a family of constant signal or constant voltage surfaces from the sensing coil within the navigational domain. Although the delta coils are preferably implemented with an array of appropriately designed magnetic coils (discussed below), this preferred implementation should not serve as a limitation of the present invention as it should be apparent to those skilled in the art that other magnetic configurations may be used to adequately generate the gradient fields.

As used herein, "magnetic look-up-table" (alternatively referenced as "the LUT") refers to a database including the magnetic field values at every x-y-z coordinate position within the navigational domain for the unidirectional coils and delta coils used by the present invention. Accordingly, input data consisting of an x-y-z coordinate and a magnetic field identifier, which designates a selected magnetic coil assembly, is indexed within the database to a corresponding set of magnetic field values constituting the output data. For the x-y-z coordinate system, the output data is represented by the magnetic field variables H.sub.x H.sub.y H.sub.z where the subscript indicates the axial dimension along which the magnetic field value is being reported. The database is created through a computational analysis of the magnetic field patterns generated by the magnetic coil configurations used herein. The mathematical model to develop the necessary formulae defining the field patterns may be developed, for example, from near field electromagnetic theory. An instructive text for facilitating such an analysis is "Field and Wave Electromagnetics" 2nd edition Addison Wesley (1989) by D. K. Cheng, herein incorporated by reference. The database may be stored in any type of facility including, inter alia, read-only memory, firmware, optical storage, or other types of computer storage. Additionally, the database information may be organized into any type of format such as a spreadsheet. It should be apparent to those skilled in the art that any suitable technique may be used to ascertain or record the magnetic field values for the magnetic coil assemblies used herein.

Separation of Variables Methodology

The mathematical construct underlying the present invention is a methodology termed separation of variables. In accordance with this methodology, appropriate equations are developed to isolate unknown variables in such a manner that renders the equations uniquely soluble. There are five unknown variables (.phi.-.theta.-x-y-z) that define the location and orientation of the sensing coil. A typical approach to solving for these variables would be to develop a series of coupled