Bend-responsive catheter

Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation

Reexamination Certificate

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C128S899000

Reexamination Certificate

active

06272371

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to cardiac diagnostic and therapeutic systems, and specifically to invasive medical probes that may be used to map the interior surfaces of the heart.
BACKGROUND OF THE INVENTION
Position-responsive cardiac catheters are known in the art. Such catheters are generally inserted percutaneously and fed through one or more major blood vessels into a chamber of the heart. A position-sensing device in the catheter, typically near the catheter's distal end, gives rise to signals that are used to determine the position of the device (and hence of the catheter) relative to a frame of reference that is fixed either externally to the body or to the heart itself. The position-sensing device may be active or passive and may operate by generating or receiving electrical, magnetic or ultrasonic energy fields or other suitable forms of energy known in the art.
U.S. Pat. No. 5,391,199, which is incorporated herein by reference, describes a position-responsive catheter comprising a miniature sensor coil contained in the catheter's distal end. The coil generates electrical signals in response to externally-applied magnetic fields, which are produced by field-generator coils placed outside the patient's body. The electrical signals are analyzed to determine three-dimensional position coordinates of the coil.
PCT patent publication number WO96/05768, filed Jan. 24, 1995, which is assigned to the assignee of the present application and whose disclosure is incorporated herein by reference, describes a position-responsive catheter comprising a plurality of miniature, preferably non-concentric sensor coils fixed in its distal end. As in the U.S. Pat. No. 5,391,199 patent, electrical signals generated by these coils in response to an externally-applied magnetic field are analyzed so as to determine, in a preferred embodiment, six-dimensional position and orientation coordinates of the coils.
Multiple position-sensing devices may be placed in a known, mutually-fixed spatial relation at or adjacent to the distal end of a catheter, as described, for example, in PCT patent application no. PCT/IL97/00009, which is assigned to the assignee of the present application and whose disclosure is incorporated herein by reference. This application describes a catheter having a substantially rigid structure at its distal end, to which one or more position sensors are fixed. The sensors are used to determine the position and orientation of the structure, preferably for use in mapping electrical activity in the heart. Although the structure itself is substantially rigid, the remainder of the catheter is generally flexible, and the position sensors do not provide coordinate information regarding any points on the catheter proximal to the structure.
PCT publication WO95/04938, which is also incorporated herein by reference, describes a miniature magnetic field sensor coil and method of remotely determining the coil's location. The sensor coil may be used to determine the spatial configuration or course of flexible endoscope within the body of a subject in one of two ways: (1) By passing the coil through an internal lumen of the endoscope, for example, the endoscope's biopsy tube, and externally tracking the coil's location while the endoscope is held stationary; or (2) By distributing a plurality of the coils, preferably about a dozen, along the length of the endoscope and determining all of the coils' locations. The position coordinates determined with respect to each location of the coil (when a single coil is used) or to all the coils (when the plurality of coils are used) are taken together to interpolatively reconstruct the spatial configuration of the endoscope within the intestines of the subject, for example, and thereby estimate the corresponding spatial configuration of the intestines.
The accuracy of this endoscope in estimating the spatial configuration of the intestines depends on having a relatively large number of position measurements and/or of coils. Passing the coil (or other sensor element) through a lumen in the endoscope is time consuming and physically not practical for use in thin probes, such as cardiac catheters that must be passed through blood vessels. Using a large number of coils, however, undesirably increases the weight and cost of the catheter and reduces its flexibility.
U.S. Pat. No. 5,042,486, whose disclosure is further incorporated herein by reference, describes a method of locating a catheter within the body of a subject, generally within a blood vessel, by tracking the position of an electromagnetic or acoustic transmitter or receiver in the tip of the catheter. The position readings are registered with a previously acquired X-ray image of the blood vessel. This method is practical, however, only when the catheter is moving within a vessel or other physiological structure that defines a narrow channel within which the catheter's movement is constrained.
PCT publication WO 92/03090, whose disclosure is also incorporated herein by reference, describes a probe system, such as an endoscope, including sensing coils mounted at spaced positions along the probe. An array of antennas in a vicinity of the probe are driven by AC electrical signals, so as to induce corresponding voltage signals in the sensing coils. These signals are analyzed to determine three-dimensional coordinates of the coils. The locations of points along the probe, intermediate a pair of the sensing coils, may be determined by interpolation between the respective coordinates of the coils.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a generally flexible catheter, for insertion into the body of a subject, wherein the course and/or position of the catheter within the body are determined using a minimal number of sensors fixed to the catheter.
It is a further object of the present invention to provide a catheter having a distal portion that assumes a predetermined shape or curvature, dependent on a force is applied thereto, and a method of determining the course of the distal portion within the body.
In one aspect of the present invention, the entire course of the distal portion is determined by measuring position coordinates of two points on the portion and using the coordinates to find the shape or curvature of the portion.
In another aspect of the present invention, the entire course of the distal portion is determined by measuring position coordinates of a point on the portion and measuring the curvature of the portion.
It is yet another object of the current invention that the course of the catheter may be determined within body cavities in which the catheter is free to move in three dimensions, and not only within constraining lumens as in the prior art.
In preferred embodiments of the present invention, a flexible catheter, having a distal end for insertion into the body of a subject, comprises first and second sensors, fixed at known, respective positions along a generally distal portion of the length of the catheter, in a known relation to one another and to the distal end. The distal portion of the catheter is sufficiently resilient so as to assume a predetermined, curved form when a force is applied thereto. At least one of the sensors is a position sensor, which generates signals responsive to the position coordinates thereof. The outputs of the first and second sensors are processed jointly to determine the curvature of the portion of the catheter, so as to find the positions of a plurality of points along the length of the distal portion, inside the subject's body.
Preferably, the at least one position sensor comprises a magnetic-field-responsive coil, as described in the above-mentioned U.S. Pat. No. 5,391,199 patent, or more preferably, a plurality of such coils, as described in the above-mentioned PCT publication WO96/05768. The plurality of coils enables six-dimensional position and orientation coordinates to be determined. Alternatively, any suitable position sensor k

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