Device for determining the position of a catheter inside the body of a patient

Abstract: In a method for determining the position of a catheter inside the body of a patient from position signals transmitted by the catheter and received by position location means (10), located at a distance from the catheter, or from position signals transmitted by position location means and received by the catheter, position signals are transmitted during a calibration stage from known calibration positions (8) inside the body, or position signals, transmitted by position location means, are received at the said known calibration positions. A correction function is determined from the difference between the calibration positions derived from the received location signals and the known, true calibration positions, whereupon catheter positions, derived from received position signals, are corrected in subsequent measurement stages according to the correction function. A device for determining the position of a catheter inside the body of a patient has a transmitter or receiver (8), arranged on the catheter, means (24,26,28) for moving the catheter to different positions inside the body, position location means (10) located at a distance from the catheter and equipped with receivers for receiving position signals from the catheter transmitters or equipped with transmitters for transmitting position signals for reception by catheter receivers, and an analysis unit (32) for determining the position of the catheter from received position signals. The analysis unit is arranged to determine, in a calibration stage, with calibration transmitters in known calibration positions inside the body to transmit position signals for reception by position location means or calibration receivers in known calibration positions derived from position signals, transmitted by the position location means, a correction function from the difference between calibration positions derived from received position signals and the said known, true calibration positions for calibration transmitters or receivers. The analysis unit (32) is further arranged to use the correction function for correcting, in subsequent measurements, the catheter positions determined from received position signals.

Description: The present invention relates to a device for determining the position of a catheter inside the body of a patient from position signals transmitted by the catheter and received by a remote position location means or from position signals transmitted by the position location means and received by the catheter. Such a position location device is disclosed in US 5,042,486 and in WO 95/08130, and comprises a transmitter or receiver inside the catheter, means for advancing the catheter to different positions in the body, position location means, located at a distance from the catheter and equipped with a receiver for receiving position signals from the catheter transmitter or equipped with a transmitter for transmitting position signals for reception by the catheter receiver, and an analysis unit for determining the position of the catheter from position signals received. In determinations of the position of e.g. the tip of a catheter inside the body, e.g. in a blood vessel or a cavity of the heart, or in the imaging of internal organs by mapping, the heterogeneity and, accordingly, the varying physical properties of adjacent tissues and even the presence of other objects in or outside the body can cause distortion, to a greater or lesser degree, in position determination or geometry depiction. Thus, the effect can be considerable in the use of ultrasound because of e.g. variation in the density of tissues and the velocity of sound. When electromagnetic methods are used, the variation in e.g. electrical conductivity, relative permittivity and relative permeability can affect measurement accuracy. In non-medical applications, such as astronomy and remote sensing, corrections can be made for both constant and time-related aberrations in the atmosphere and measuring system by observing a reference object with a known shape in the ray path or close to the observed object. In the brochure "A new method for non-fluoroscopic catheter based endocardial mapping", published by Ben-Haim et al., a technique is described for endocardial mapping with a non-fluoroscopic catheter in which a number of radiographs are first taken of a heart catheter located in a number of different positions in a ventricle of a heart. The object of the present invention is make possible accurate determination of the position of a catheter inside the body without the use of ionizing radiation. This object is achieved with a device of the initially cited kind with the features set forth in claim 1. Preferred embodiments are defined in the dependent claims. In the device according to the invention, a correction function, subsequently utilized for correcting measurement data in position determination and for correcting image data in mapping, is accordingly determined. Correct position determination and correct geometry are therefore attained with use of a correction function determined by having a catheter, or the tip of a catheter, perform a known movement inside a cavity in the body at the same time as the position of the catheter is determined from position signals sent and received between the catheter and remote position location means. According to advantageous embodiments of the device according to the invention, the calibration catheter also acts as the measurement catheter and has a flexible, tubular outer sleeve enclosing a sliding and rotating mandrel in whose tip a transmitter or receiver is arranged. The distal end section of the mandrel is appropriately made of a resilient material and is pre-bent, or is a curved coil spring arranged on the distal end of the mandrel, the catheter transmitter or receiver being arranged at the free end of the curved coil spring. The mandrel's end section is alternately made of a memory alloy, and a means is provided for electrically heating the end section in order to bend it. The mandrel's end section can also be devised with a mechanical joint to permit bending of the end section. At the catheter end located outside the body, a means is provided for sliding and/or rotating the mandrel in relation to the sleeve. The end of the curved end section thereby describes a cylindrical area when the mandrel is linearly displaced and rotated at the same time. According to another advantageous embodiment of the device according to the invention, the said sliding and/or rotating means is motorized, and a transducer is arranged for automatic reading of the mandrel's movement and control of the drive motor on the basis thereof. In this manner, the mandrel's determined movement is fed back to the drive motor in order to control same and cause the mandrel to perform the desired movement. If the position location means is outside the patient's body or in the patient at a relatively long distance from the measurement catheter, compensation must be made for movement between the measurement catheter and the position location means caused by the patient's breathing or other movements. According to yet another advantageous embodiment of the device according to the invention, a reference receiver or transmitter is therefore arranged on the sleeve of the catheter to serve, in concert with the catheter transmitter or receiver, as an internal reference in compensating for the patient's breathing and other movements. An exemplifying embodiment of the device will now be described in greater detail to explain the invention, referring to an attached drawing in which FIG. 1 shows one embodiment of the device, according to the invention, with a basket catheter, and FIGS. 2 and 3 illustrate two ways to achieve a curved section on the distal end of the mandrel. FIG. 1 shows one embodiment of the device, according to the invention, with a basket catheter containing a flexible, tubular catheter sleeve 2 inside of which a mandrel 4 and a wire basket 6 are retracted during the catheter's insertion into the patient's body. A catheter transmitter 8 is arranged at the end of the mandrel 4 to transmit location signals, intended for reception by position location means in the form of a receiver unit 10, arranged at a distance from the tip of the catheter 4, preferably outside the patient's body. A catheter receiver is alternately arranged at the tip of the mandrel 4 to receive signals from the position location means 10 in the form of a transmitter unit. When the mandrel 4 is in the retracted position, the catheter transmitter or receiver 8 is in the opening of the catheter sleeve 2. When the catheter is in position inside the patient, the wire basket 6 is deployed outside the catheter sleeve 2. The basket 6 is made of e.g. metal wire, carbon fiber or a polymer material, and is resilient so it expands when deployed outside the catheter sleeve 2. When the catheter has been accordingly inserted into a cavity in the patient's body, the expanded basket 6 fills the cavity in whole or part and is affixed in same. The basket 6 therefore keeps its interior separated from body tissue, enabling the catheter tip 8 therein to describe the desired movement without touching wall tissue or any other mechanical impediment. In the "starting position", the catheter transmitter or receiver 8 is in the mouth of the catheter sleeve 2. When the tip of the catheter is in position, e.g. in the ventricle of a heart, the catheter transmitter or receiver 8 can be deployed outside the catheter sleeve 2 with the mandrel 4. The end section 12 of the mandrel 4 can be advantageously pre-bent so the catheter transmitter or receiver 8 describes a circular movement when the mandrel 4 is rotated. When the mandrel 4 is axially displaced at the same time as it is rotated on its axis, the catheter transmitter and/or receiver 8 will describe a cylindrical movement. In order to achieve the curved end section 12 of the mandrel, the end section can, as noted above, be pre-bent or alternately made of a memory alloy, such as NiTi, and means 14 provided for electrically heating the end section 16 so as to thereby bend same. See FIG. 2. According to another alternative, a curved coil spring 18 is arranged on the distal end of the mandrel 20, the catheter transmitter or receiver 22 being arranged on the free end of the spring 18. See FIG. 3. The advantage of the latter embodiment is that the load on the material is reduced and, accordingly the risk of fatigue. The mandrel's end section can also be devised with a mechanical joint to make possible bending of the end section into the desired shape. The proximal end of the catheter is intended to be outside the patient's body, and a means 24 is arranged on this end for displacing and/or rotating the mandrel 4 in relation to the sleeve 2. This movement of the mandrel 4 can be manual, and scales 26 are arranged to permit the reading of the magnitude of the displacement and rotation. This part of the catheter can be made with dimensions facilitating manipulation of the mandrel 4 and reading of the scales 26. Movement of the mandrel 4 can also be automated with the aid of appropriate actuators arranged in an automation unit 28. These motorized actuators are accordingly connected to the mandrel 4 in order to displace and rotate it in relation to the sleeve 2, and the automation unit 28 has transducers for automatic reading of the magnitude of displacement and rotation. The read values can be fed back to the motorized actuators in order to control their operation so the desired movement of the mandrel 4 is achieved. The values read for the displacement and rotation of the mandrel 4 are sent to a unit 30 for determining the true position of the catheter's transmitter or receiver 8, and these values, with data from the receiver unit 10 representing positions for the catheter transmitter 8, are sent to an analysis unit 32. In instances in which the position location means 10 are devised as a transmitter unit for transmitting signals intended for reception by a catheter receiver 8, the signals received by the catheter receiver 8 are instead sent to the analysis unit 32. Determination of the correction function is performed as follows: The catheter transmitter or receiver 8 is made to perform a known movement, preferably a three-dimensional movement, in the space inside the basket 6 during simultaneous registration of the position of the catheter transmitter or receiver 8 with the measurement system which is to be calibrated, i.e. the catheter transmitters or receivers and position location means 10. The analysis unit 32, which appropriately consists of a computer system, compares the true movement made by the catheter transmitter or receiver 8, as determined from the scales 26 or by transducers in the automation unit 28, with movement measured with the position location means 10. A correction function, with which the measured, apparent position of the catheter tip can be translated in a subsequent measurement stage into a true position, can be calculated from the difference between the two movements. The movement can e.g. form a body with a known shape, as described by the catheter transmitter or receiver 8, whereupon the correction function is determined from the difference between this true shape and the shape determined by the position location means 10. The calibration procedure can use a balloon, instead of a wire basket, inside the catheter sleeve 2 during the catheter's insertion into the patient's body, the balloon thereupon being deployed outside the sleeve and inflated with a gas, e.g. air, or a liquid, e.g. isotonic saline solution or some other liquid with the appropriate physical properties. In certain instances, depending on the kind of position location system utilized, the use of a liquid with the right properties is particularly important in preventing distortion of wave fronts. This is especially the case if ultrasonic signals are employed for position location. When a plurality of calibration transmitters or receivers 34 is permanently arranged on the wires of the basket, the calibration stage can be performed without the need for a mandrel, carrying a transmitter or receiver, to move the transmitter or receiver to different known positions. If the wire basket 6 is sufficiently stiff, the calibration transmitters or receivers 34 will assume known positions after the basket's 6 expansion, and the correction function can be determined from the differences between these true positions and the positions measured for the transmitters or receivers 34 by the position location means 10. When calibration transmitters or receivers are permanently arranged on the wall of a balloon, of the kind described above, the same technique can obviously be used in this instance for determining the correction function. However, the balloon must be inflated with pressure sufficient for it to assume a known, well-defined shape. After calibration, the calibration catheter can be replaced with a new, special measurement catheter which is inserted into the sleeve 2. Alternately, the wire basket 6 can be arranged with an opening at its anterior end through which the mandrel 4 with its transmitter or receiver can be inserted for subsequent measurement stages. Here, the mandrel 4 and wire basket 6 are first retracted into the sleeve 2, whereupon only the mandrel and its transmitter or receiver protrude through the opening in the basket. After calibration, the same catheter, or some other catheter, can be used for e.g. mapping, as noted above. However, the catheter can be designed to perform a plurality of functions which may be needed in the diagnosis and/or treatment of various patient disorders. The catheter can be equipped with electrodes for sensing electrical activity in body tissue and/or electrical stimulation of body tissue, for ablation or be equipped with pressure sensors. The previously determined correction function is used here for positioning the catheter during the diagnostic and/or therapeutic procedures. The position location means, which can be devised, as noted above, as transmitters or receivers (antennae), arranged on another catheter or catheters, can be located outside the patient's body or inside her/his body. If the position location means is outside the patient's body, or inside her/his body, at a relatively long distance from the calibration and measurement catheter, compensation for movements the patient might make, e.g. in breathing, is often necessary. This can be performed by utilization of one or a plurality of reference catheters arranged in the vicinity of the catheter in question. When the reference catheter or catheters is/are in the vicinity of the measurement catheter, the reference catheter or catheters and measurement catheters do not move in relation to each other but only move jointly. Here, the position determination technique according to the invention can also be used for determining the positions of the reference catheters. Alternately, one or a plurality of reference transmitters or receivers 36 (see FIG. 1) can be permanently arranged on the catheters 2. The detected movement of the catheter transmitter or receiver 8 in relation to these reference transmitters or receivers 36 is the "true" movement of the tip of the catheter and is therefore not caused by patient movements. In this embodiment, the catheter therefore serves as its own reference. In certain applications, establishing a reference point for the catheter transmitter or receiver and the catheter in relation to the examined organ, e.g. a starting position or end position to which reference point the movement of the catheter is related, is desirable. One such reference point can be registered by biplane exposure with a fluoroscope or some other known technique. The transmitters and receivers used in the invention can comprise piezo means for ultrasonic position location signals, coils or antennae for electromagnetic position location signals or magnets and Hall-generators for magnetostatic communications systems. Since the heart, blood vessels and other organs pulsate at each heartbeat, synchronizing registration of the catheter's position to the ECG signal is often necessary so each position registration occurs in the same phase of the heart cycle. This thereby eliminates this source of error in position determination. For this reason, a synchronization unit 38 is arranged to synchronize the analysis unit 32 so it performs catheter position determinations in the same phase of the heart cycle. See FIG. 1.

Claims: A device for determining the position of a measurement catheter inside the body of a patient having a transmitter or receiver (8) arranged thereon, comprising means (24,26,28) for advancing the measurement catheter to different positions inside the body; position location means (10) located at a distance from the measurement catheter and equipped with a receiver unit for receiving position signals from the catheter transmitters (8) or equipped with a transmitter unit for transmitting position signals to be received by the catheter receiver (8); and an analysis unit (32) for determining the position of the measurement catheter from received position signals characterized in that the device comprises a calibration catheter having a number of calibration transmitters (8;34) or calibration receivers (2;34) arranged thereon; in that the analysis unit (32) is arranged to determine, in a calibration stage with the number of calibration transmitters (8;34) in a plurality of known calibration positions inside the body, to transmit position signals to be received by the position location means (10) or with the number of calibration receivers (8;34) in a plurality of known calibration positions for receiving position signals transmitted by the position location means (10), a correction function from the difference between a plurality of calibration positions derived from the received position signals and the said plurality of known, true calibration positions for the number of calibration transmitters or receivers (8;34), and the analysis unit (32) is arranged to correct, in a subsequent measurement stage and according to the correction function, the position of the measurement catheter derived from the received position signals. A device according to claim 1, characterized in that the measurement catheter and the calibration catheter are realized as a single same catheter wherein the measurement catheter transmitter or receiver (8) is adapted to act in the calibration stage as a sole calibration transmitter or receiver, and in that the analysis unit (32) is arranged to determine the correction function derived from the received position signals from the sole calibration transmitter or receiver (8) located in the plurality of known calibration positions. A device according to claim 2, characterized in that the catheter contains a flexible, tubular outer sleeve with a sliding and rotating mandrel arranged therein and has the transmitter or receiver (8) arranged at the tip of same. A device according to claim 3, characterized in that the distal end section of the mandrel is made of a resilient material and is pre-bent. A device according to claim 3, characterized in that the catheter transmitter or receiver is arranged on the free end of a curved coil spring whose other end is attached to the distal end of the mandrel. A device according to claim 3, characterized in that the end section of the mandrel consists of a memory alloy, and means are arranged to electrically heat the end section in order to bend it. A device according to claim 3, characterized in that the end section of the mandrel is devised with a mechanical joint so the end section can be bent. A device according to any of claims 3-7, characterized in that means are provided at the end of the catheter outside the body for sliding and/or rotating the mandrel in relation to the sleeve. A device according to claim 8, characterized in that the said sliding and/or rotation means has scales showing the magnitude of sliding and rotation. A device according to claim 8 or 9, characterized in that the said sliding and/or rotation means is motorized. A device according to claim 10, characterized in that a transducer is arranged for automatic reading of the mandrel's movement and controlling the drive motor in accordance therewith. A device according to any of claims 3-11, whereby the catheter is intended for insertion into a cavity in a patient's body, characterized in that the catheter is devised as a basket catheter with an expanding, deployable wire basket (6) , arranged inside the outer catheter sleeve, and in that the sole calibration transmitter or receiver (8) is movably arranged in the space enclosed by the basket when the basket has expanded. A device according to any of claims 3-11, whereby the catheter is intended for insertion into a cavity in a patient's body, characterized in that the catheter has a balloon, deployable outside the catheter sleeve, which expands when filled with gas or a liquid, and in that the sole calibration transmitter or receiver (8) is movably arranged in the space inside the balloon. A device according to claim 12 or 13, characterized in that the basket and balloon can be collapsed from their expanded positions and retracted back into the catheter sleeve after the calibration stage in order to allow the catheter tip to make contact with body tissue. A device according to claim 1, whereby the calibration catheter is intended for insertion into a cavity in a patient's body, characterized in that the calibration catheter is devised as a basket catheter with an expanding, deployable wire basket (6), arranged inside an outer catheter sleeve (2), and the number of calibration transmitters or receivers (34) is permanently arranged on the basket wall. A device according to claim 1, whereby the calibration catheter is intended for insertion into a cavity in a patient's body, characterized in that the calibration catheter has a balloon, deployable outside an outer catheter sleeve, which expands when filled with gas or a liquid, and the number of calibration transmitters or receivers is permanently arranged on the wall of the balloon. A device according to any of claims 1-16, characterized in that the calibration catheter is equipped with electrodes for stimulating and/or sensing electrical activity in body tissue and/or for ablation and/or is equipped with pressure sensors. A device according to any of claims 1-17, characterized in that the transmitters and receivers consist of piezo means for ultrasonic position signals, or a coil or antenna for electromagnetic position signals, or a magnet or Hall-generator for magnetostatic communications systems. A device according to any of claims 1-15, characterized in that a synchronization unit (38) is arranged to synchronize the analysis unit (32) so it always performs determinations of catheter positions in the same phase of the heart cycle. A device according to any of the claims 1-19 characterised in that at least one reference transmitter or receiver is provided for generating a signal dependent on movements of the patient for use within the analysis unit (32) in determining the positions of one or both the measurement and the calibration catheter.

Inventors: PFEIFFER GEORG, SLETTENMARK BRUNO, PFEIFFER, GEORG, SLETTENMARK, BRUNO
Applicants: SIEMENS AG, SIEMENS AKTIENGESELLSCHAFT
Application year: 1997
Main classification: A61B5
IPC codes: A61B19, A61M25, A61B5, A61N1, A61B8, A61B18, G01B17, G01B21