Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-02-17
2001-07-24
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06266551
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to systems for medical diagnosis and treatment, and specifically to medical catheters whose location can be detected.
BACKGROUND OF THE INVENTION
Various methods and devices have been described for determining the position of a probe or catheter tip inside the body using electromagnetic fields, such as in U.S. Pat. No. 5,042,486 and PCT patent publication No. WO 94/0938, whose disclosures are incorporated herein by reference. Other electromagnetic tracking systems, not necessarily for medical applications, are described in U.S. Pat. Nos. 3,644,825, 3,868,565, 4,017,858, 4,054,881 and 4,849,692, whose disclosures are likewise incorporated herein by reference.
U.S. Pat. No. 5,391,199, filed Jul. 20, 1993, which is assigned to the assignee of the present patent application and whose disclosure is incorporated herein by reference, describes a system that incorporates a catheter, which includes a position measuring device that can determine the position of the catheter in three dimensions, but not its orientation.
PCT patent application No. PCT/US95/01103, which is likewise assigned to the assignee of the present patent application and whose disclosure is incorporated herein by reference, describes a catheter system including means for determining the six-dimensions of position and orientation of the catheter's distal tip. This system uses a plurality of non-concentric coils adjacent to a locatable site in the catheter, for example near its distal tip. Preferably three orthogonal coils are used. These coils generate signals in response to externally applied magnetic fields, which allow for the computation of six position and orientation coordinates, so that the position and orientation of the catheter are known without the need for imaging the catheter.
U.S. Pat. No. 5,383,874 (Jackson et al.) describes a system for identifying and monitoring catheters, including identification means carried within the handle of the catheter body. In one embodiment of the invention of this patent, the handle includes a solid-state microchip pre-programmed with a digital value representing the catheter's identification code and other operational and functional characteristics of the catheter. The handle is connected by a cable to a control console, which reads data from the microchip. In one disclosed embodiment, the microchip may record the number of times the catheter has been used. Digital data storage in the catheter handle adds multiple digital signal wires to the catheter.
SUMMARY OF THE INVENTION
The coils of the '103 patent application and other systems for electromagnetic detection of catheter position and orientation are generally located in the catheter at a small distance proximal to the catheter's distal tip, since the distal tip is typically occupied by an electrode or other functional element. Therefore, the position and orientation detection system must be calibrated to take into account the displacement of the distal tip of the catheter relative to the location of the coils. Because of manufacturing variations, this displacement generally varies from one catheter to another.
Furthermore, the coils used to generate position signals may not be precisely orthogonal. For purposes of computing the position and orientation of the catheter, the axes of the coils define the respective axes of a coordinate system that is fixed to the catheter tip, and the directions of these axes must be known relative to the catheter. If these axes deviate from orthogonality, the respective degrees of deviation must be known and corrected for in the position and orientation computation.
Additionally, the relative gains of the coils determine the strengths of the respective position signals that the coils generate in response to externally-applied fields. Since these signal strengths are used in computing the position and orientation of the catheter, deviations of the gains from their expected values will lead to inaccuracy in the computed position and orientation. Therefore, the respective gains of the coils must be known and corrected for in the position and orientation computation.
It would, therefore, be desirable to pre-calibrate the catheter, preferably at the time of manufacture, so as to measure and compensate for variations in the positions, orientations and gains of coils used to generate position signals.
Preferably the calibration data should be recorded in such a way as to alleviate the need for recalibration and manual entry of calibration data before each use.
It is, therefore, an object of the present invention to provide a method of calibrating a device that is used to determine the position and orientation of a catheter, wherein the calibration information is retained in the catheter.
A further object of the present invention is to provide means for convenient electronic storage and recall of calibration information regarding a catheter.
In one aspect of the present invention, this calibration information is stored digitally in a microcircuit whose location is easily accessible to signal processing circuits and computing apparatus, so that the catheter need not contain digital signal wires, and digital electronic signals transmitted from the microcircuit to the signal processing circuits and computing apparatus do not interfere with low-level analog signals conveyed by wires from the distal end of the catheter to the circuits.
In preferred embodiments of the present invention, a device used to determine the position and orientation of a catheter inside the body comprises a plurality of coils adjacent to the distal end of the catheter. The catheter further comprises an electronic microcircuit adjacent to the proximal end of the catheter, which microcircuit stores information relating to the calibration of the device.
Preferably the microcircuit comprises a read/write memory component, such as an EEPROM, EPROM, PROM, Flash ROM or non-volatile RAM, and the information is stored in digital form.
In preferred embodiments of the present invention, this calibration information includes data relating to the relative displacement of the distal tip of the catheter from the coils. In some other preferred embodiments of the present invention, the calibration information also includes data relating to deviation of the coils from orthogonality, or data relating to the respective gains of the coils, or a combination of these data.
In some preferred embodiments of the present invention, in which the catheter is electrically isolated from signal processing and computing apparatus, the calibration information includes data relating to isolation circuitry in the catheter. Preferably, the catheter is isolated by at least one inductive element, such as an isolation transformer, adjacent to the proximal end of the catheter or in a handle associated with the catheter. Alternatively, the catheter may be isolated by one or more opto-isolaters, or other types of isolation circuitry known in the art. Such inductive elements and other isolation circuitry typically introduce non-linearities in signals conveyed thereby. Such non-linearities may lead to significant distortions particularly in analog signals conveyed by wires from the distal end of the catheter to the signal processing circuits. Therefore, the calibration information preferably includes data relating to signal non-linearities introduced by the inductive elements and/or other isolation circuitry.
In a preferred embodiment of the invention, the catheter is a wireless catheter which is not physically connected to the signal processing and/or computing apparatus. Rather, a transmitter/receiver is attached to a proximal end of the catheter. The transmitter/receiver communicates with the signal processing and/or computer apparatus using wireless communication methods, such as IR (infra red), RF or acoustic transmissions. One benefit of this type of configuration is that the catheter, which is inserted into the (electrically sensitive) heart can easily be made electrically floati
Ben-Haim Shlomo
Fenster Maier
Fried Shlomo
Osadchy Daniel
Biosense Inc.
Capezzuto Louis J.
Lateef Marvin M.
Mantis Mercader Eleni
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