Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/06—Devices, other than using radiation, for detecting or locating foreign bodies ; determining position of probes within or on the body of the patient
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/06—Devices, other than using radiation, for detecting or locating foreign bodies ; determining position of probes within or on the body of the patient
  • A61B5/061—Determining position of a probe within the body employing means separate from the probe, e.g. sensing internal probe position employing impedance electrodes on the surface of the body
  • A61B5/062—Determining position of a probe within the body employing means separate from the probe, e.g. sensing internal probe position employing impedance electrodes on the surface of the body using magnetic field
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
  • A61B6/12—Devices for detecting or locating foreign bodies
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
  • A61B6/48—Diagnostic techniques
  • A61B6/486—Diagnostic techniques involving generating temporal series of image data
  • A61B6/487—Diagnostic techniques involving generating temporal series of image data involving fluoroscopy
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
  • A61B6/50—Clinical applications
  • A61B6/503—Clinical applications involving diagnosis of heart
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
  • A61B8/08—Detecting organic movements or changes, e.g. tumours, cysts, swellings
  • A61B8/0833—Detecting organic movements or changes, e.g. tumours, cysts, swellings involving detecting or locating foreign bodies or organic structures
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B34/00—Computer-aided surgery; Manipulators or robots specially adapted for use in surgery
  • A61B34/20—Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
  • A61B2034/2046—Tracking techniques
  • A61B2034/2051—Electromagnetic tracking systems

Definitions

• the present invention relates to a method for locating a measurement and/or treatment catheter in a vessel or organ of a patient relative to a fixed catheter, also positioned- within the patient in the vicinity of the measurement and/or treatment catheter, signals then being transmitted from one of said catheters, as well as to an arrangement, comprising a measurement and/or treatment catheter, intended to be positioned in a vessel or organ of a patient, and a fixed catheter, also intended to be positioned within the patient in the vicinity of the measurement and/or treatment catheter, one of said catheters having signal transmitting means to be used for locating the measurement and/or treatment catheter relative the fixed catheter.
• US patent specification 5,042,486 describes a method for real time portrayal of a catheter in a vessel, which makes use of a transmitter for electromagnetic or acoustic waves located at the tip of the catheter. These waves are received by receiving antennas attached to the exterior surface of the patient and are converted into electrical image signals. From these signals the position of the catheter relative to external antennas is determined.
• a disadvantage of this technique is that the patient may not flex or bend or even breathe since the external antennas will then move relative to each other and to the catheter and the information will be distorted and the results unreliable and inaccurate.
• US patent specifications 5,391,199 and 5,443,489 apparatus and methods for treating cardiac arrhythmias and for ablation are described.
• Reference catheters having a receiving or sending antenna, are then introduced into the heart and the position of a mapping/ablating catheter relative the reference catheters is determined by use of an external transmitter or receiver.
• an appropriate method such as by x- ray.
• the purpose of the present invention is to propose a technique for locating a measurement and/or treatment catheter in a vessel or organ of a patient relative a fixed catheter, serving as a reference, with which technique the above dis- cussed disadvantages of the prior art solutions are eliminated.
• the signals are transmitted from two points, separated in the longitudinal direction of the catheter. In this way also the direction of the catheter can be determined.
• the sign of the phase of the received signals are determined relative to the sign of the phase of the transmitted signals in order to determine the direction of the magnetic field uniquely. In this way it is possible to determine the direction of the measurement and/or treatment catheter tip relative to the direction of the induced magnetic field B and accordingly to the direction of the fixed catheter.
• the signals are formed of ultrasonic pulses, transmitted from one of the catheters and received at the other one and the position of the measurement and/or treatment catheter is determined from the flight times of the received pulses.
• the results of the deter- mination are independent of the amplitude of the received pulses.
• the first signal received by the sensor in question will determine the shortest distance to the signal transmitting means and consequently reflections and scat- tering pose no problem.
• the ultrasonic pulses are transmitted from two points, separated in the longitudinal direction of one of the catheters and the pulses are received by sensors disposed on the other catheter in a triangular configuration, preferably positioned in the corners of an equilateral triangle, the transmitting points and the sensors being suitably positioned in different planes for improving the accuracy in the case of three sensors.
• the position of the measurement and/or treatment catheter relative to the fixed catheter can be correctly determined.
• more than three sensors can be used and the positions and number of the transmitting points and sensors can be interchanged. Theoretically it is not possible with this method, in the case of using only three sensors on the platform, to distinguish the true catheter position from its mirror positions. However, in practice this will be no problem and such a theoretical uncertainty in the obtained results can for example be eliminated by using sensors with a certain lobe directivity.
• the distal tip of the measurement and/or treatment catheter is moved on a surface and the positions and directions of the tip are successively determined to map the surface.
• the first measuring point will result in knowledge of the position and direction of the catheter tip of the measurement and/or treatment catheter relative to the fixed catheter. Since the position and direction of the fixed catheter are unknown this information does not tell much.
• the measurement and/or treatment catheter and repeating the measurement new positions relative to the fixed catheter are obtained which can be joined by surface elements. In this way e.g. the interior surface of a heart chamber can be mapped, including the direction of the measurement and/or treatment catheter tip, and shown as a three-dimensional image on a monitor, without knowing the starting positions of the catheters.
• a fluoroscopic biplane exposure or an ultrasound imaging of the catheters is performed at one stage to determine their positions relative the patient. Then it is possible to correctly orient the obtained topological map relative to the patient.
• the signal transmitting means comprises two triaxial coil systems, or a triaxial or biaxial coil system and a single coil, separated in the longitudinal direction of the catheter. It is then possible to determine the direction of the catheter relative to the other catheter having a triaxial coil system near the tip. It is important to determine the direction of the catheter tip portion, since its transmitting or receiving means are normally situated a certain distance from the catheter tip and therefore to be able to determine the exact position of the tip from the measurements the direction of the tip portion must be known. By using two triaxial coils on the transmitting catheter the arrangement will be redundant, which can be utilized to increase the precision and accuracy of the position determination.
• the transmitting means are disposed to sequentially transmit electromagnetic signals through the different coils. This is a preferred way of energizing the coils. It would be, however, possible to energize all the coils simultaneously with different frequencies and thereafter filtering the pickup signals with bandpass filters. Such a procedure would however be more complicated.
• the signal transmit- ting means and the receiving means are situated in the distal tip portion of the respective catheter and this tip portions are rigid to avoid errors in the measuring results due to flexure of the tip portions.
• fig.l schematically shows a measurement and/or catheter and a fixed catheter introduced into the respective heart chamber
• fig.2 shows schematically the distal tip portion of a fixed catheter provided with two triaxial coils for illustrating the principle of one embodiment of the invention
• fig.3 shows the tip portion of a measurement and/or treatment catheter
• fig.4 shows a triaxial coil used in the invention
• fig.5 illustrates schematically an alternative embodiment of the invention using ultrasound technique
• fig.6 shows a helical, three-dimensional ultrasound transducer platform
• fig.7-9 illustrate alternative embodiments of platforms carrying ultrasound transducers.
• fig. 1 a part of a heart 2 is schematically shown with a measurement and/or treatment catheter 4 introduced into one of the heart chambers 6 and a fixed catheter 8 introduced into the other heart chamber 10.
• the body surface is shown at 12.
• the fixed catheter 8 is connected to a transmitter 18 through conductors 20 for energizing the transmitting means 16.
• the receiving means 14 of the measurement and/or treatment catheter 4 are through electrical conductors 22 extending inside the catheter 4 connected to a receiver 24, which in its turn is connected to a signal processor 26 for determining the position of the measurement and/or treatment catheter 4 relative the fixed catheter 8 from the received signals, as described more in detail below.
• the results can be shown on a display 28.
• the signal processor 26 also controls the transmitter 18 as indicated in the figure.
• FIG. 2 illustrates the principle of one embodiment of the invention. More precisely, in the distal tip portion 30 of a fixed catheter two triaxial coils 32, 34 are mounted, separated by a certain distance ⁇ x in the longitudinal direction of the fixed catheter 30.
• the triaxial coils 32, 34 are formed as miniature crossed coil system as illustrated in fig. 4, each coil system generating three orthogonal magnetic fields when energized. Each coil can have a diameter of 3 mm and contains 100 turns, and the distance ⁇ x between the two triaxial coil systems 32, 34 can typically be about 5 - 15 mm.
• the catheter portion 30 between the coil systems 32, 34 must be rigid such that the relative positions of the coil systems remain constant.
• the extreme tip of the portion 30 may be flexible, precurved or maneuverable in order to facilitate introduction of the catheter to the desired position.
• the coils 32, 34 in the fixed catheter 30 are preferably driven sequentially, for typically 33 ⁇ s each, by a current of about 10 mA and a frequency of 300 kHz. With a sampling rate for the measurement cycle of 5 kHz, dynamic registration of the probe tip up to about 1 kHz can be obtained.
• Coil 11 (the coil in position 1 with its axis parallel to the 1-axis) and coil 12 (the coil in position 2 with its axis parallel to the 1-axis) are excited sequentially.
• the resulting magnetic fields in point A are
• N ⁇ denotes the number of turns of the coil
• I the current to the coil
• d 2 the diameter of the coil.
• angles ⁇ and ⁇ appear from the figure and ri and r 2 denote the distances between point A and position 1 and 2 respectively.
• the quantities Bn , B ⁇ 2 and ot 11 - ⁇ 12 are measured with the receiving coil system and the four unknown quantities , r 2 , Qll and ⁇ 2 can be calculated from the above four equations. The solution of these equations will consequently give the position of the point A as an undetermined point on the concentric circle C.
• the coil 22 and the corresponding measurements are redundant but it is desirable to use it to increase the accu- racy of the position determination.
• the sign of the phase of the signal induced in the receiving coil system is measured relative to the phase of the excited transmitting coils the direction of the catheter relative to the magnetic field B and accordingly to the fixed ca theter is uniquely determined.
• a minimum requirement for determining the desired position and direction of the measurement and/or treatment catheter is realized by a configuration using three coils on the fixed catheter.
• One preferred embodiment includes the use of one crossed biaxial coil system and a single coil separated along the catheter as described above.
• other configurations are possible, e.g. a single orthogonal triaxial coil system or three single coils arranged in a suitable configuration.
• the present invention it is possible not only to determine position and direction of the catheter but also velocity and amplitude of the catheter tip. If the movement of the catheter tip shall be determined with a frequency limit of 1 kHz it will be necessary to sample with a frequency exceeding 2 kHz, e.g. 5 kHz. If at least 10 cycles are needed for forming average values and if 3 - 6 transmitting coils are used for sequential excitation a signal frequency of 150 - 300 kHz is needed.
• the invention can be used to e.g. map the interior surface of a heart chamber in the following way as indicated above.
• the fixed and the measurement and/or treatment catheters are both positioned somewhere inside the heart, c.f. figure 1. No fluoroscopic investigation is performed and the position and direction of the catheters are unknown.
• the distal tip of the measurement and/or treatment catheter is moved on a surface inside the heart and the positions of the tip are successively determined to map the surface.
• the distance and orientation of the measurement and/or treatment catheter relative to the unknown position and orientation of the fixed catheter is obtained.
• new relative positions are ob- tained which can be joined by surface elements.
• the interior surface of the heart chamber in which the measurement and/or treatment catheter is positioned is mapped and can be shown together with the direction of the measurement and/or treatment catheter tip on a monitor as a simulated three-dimensional representation without knowing the starting positions of the catheters.
• Pairs of measurement and/or treatment and fixed catheters should preferably be calibrated together at the manufacture since a perfect orthogonality between the coils is in practice difficult to obtain.
• the calibration is preferably performed in an isotonic salt solution if the frequency used makes this necessary.
• One way of performing the calibration would be to let a robot move the measurement and/or treatment catheter relative to the fixed catheter in a number of positions and angles and deliver all the measured and calculated corrections on a diskette which is supplied with the catheter set to be inserted in the workstation at the clinic.
• a simple last calibration for the current amplitude to the transmitting coils can be made at the clinic, putting the catheters in a simple fixture.
• a measurement and/or treatment catheter 38 is then provided with transmitting means in the form of two ultrasound transducers 40, 42 in positions 1 and 2.
• a fixed catheter 44 is provided with at least three sensors 46, 48, 50 in the form of three ultrasound transducers in the positions 3 , 4 and 5 in the tip portion.
• the tip portion of the fixed catheter 44 must, when in position, be curved in a controlled and stable manner to serve as a triangular platform for the transducers 46, 48 and 50 in the case of three transducers.
• the transducers 46, 48, 50 must not be in line and the receiving transducers 46, 48, 50 and the transmitting transducer 40, 42 are preferably situated in different planes in order to improve the position determination accuracy.
• FIG. 6 Another preferred embodiment of the arrangement according to the invention can be realized by e.g. a double-curved, helical tip portion, see figure 6, which shows a helical three-dimensional ultrasound transducer platform 41, formed on a catheter distal end and having more than three transducers 43, 45, 47, 49 carried on the platform 41.
• the catheter distal end portion can be formed of e.g. a memory alloy for forming the catheter distal end portion to a platform 41 of desired shape after introduction into the vessel or organ in question.
• the tip portion denoted by D in figure 5, must be rigid such that the relative position of the transducers 40 and 42 is not changed. If it is not of interest to be able to deter- mine the direction of the tip portion of the catheter 38 only one transducer of this catheter, e.g. 40 is needed and the tip portion may be completely flexible, which is an advantage .
• Short ultrasound pulses are segmentally from the transducers 40, 42 and the flight times of these pulses to the transducers 46, 48 and 50 are measured, these flight times being a direct measure of the distance to the transmitting and receiving transducers. To improve the accuracy of the measurement more than three transducers can be used on the platform.
• the frequency of the ultrasound signals is preferably in the range of 10 - 30 MHz.
• the position is, in the case where only three transducers are utilized on the platform, or more than three sensors positioned in the same plane, not uniquely determined since also the mirrored position is possible. In practice this will, however, pose no problem, as discussed above.
• An advantageous feature of this method recites in the fact that the measurements is independent of the amplitude of the ultrasonic signals. Instead of transmitting short pulses with constant frequency from the transducers 40, 42 they can be excited to transmit a modulated pulse train with successively changing frequency, so called chirped pulse train, or other kinds of modulation according to previously known techniques.
• Fig. 7-9 show alternative embodiments of the platform for the transducers .
• the transducers 52, 54 and 56 are mounted on two wires 58, 60 which can be pushed out of the mouth 62 of the catheter 64 after insertion of the catheter 64 into the body vessel or organ in question.
• Figures 8 and 9 show a loop and a basket catheter 66 and 68 respectively with transducers 70, 72, 74 and 76, 78, 80, 82, 84, 86 mounted on wires 88, 90 and 92, 94, 96, 98 respectively forming a loop and a basket which can be retracted into the catheters 66, 68 for insertion of the catheters and pushed out of the catheter mouths 100, 102 when the catheters 66, 68 have reached their positions.
• the wires 92, 94, 96, 98 are arranged about 90 degrees apart, so that the sensors 76, 78, 80, 82, 84, 86 span a three-dimensional volume .
• the wires 58, 60, 88, 90, 92, 94, 96 and 98 can be precurved or alternatively formed of e.g. NiTi memory alloys and provided with suitable heating means for expanding the wires to desired shapes forming a platform for the transducers 52, 54, 56, 70, 72, 74, 76, 78, 80, 82, 84.
• the relative positions of all the transducers 46, 48, 50 and 52, 54, 56 and 70, 72, 74 and 76, 78, 80, 82, 84 respectively can, if necessary, be determined by measuring the distances from each transducer to all the other transducers on the platform in the way described above. It is O 98/00060
• the transmitting means of the catheters then comprises coils fed with a constant electric current or permanent magnets and the receiving means comprise e.g. Hall- elements or similar devices sensing magnetic DC fields from which the relative position can be determined.
• the current to the transmitter coils can be switched on and off to determine and correct for the interfering magnetic fields from the difference thus obtained.
• transmitting means ca be mounted as well on the fixed reference catheter as on the measurement and treatment catheters and vice versa for the receiving means .

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Cited By (10)

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Citations (4)

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• 1996
  • 1996-06-28 SE SE9602574A patent/SE9602574D0/xx unknown
• 1997
  • 1997-05-28 EP EP97924482A patent/EP0959762A1/en not_active Withdrawn
  • 1997-05-28 IL IL12661797A patent/IL126617A/en not_active IP Right Cessation
  • 1997-05-28 US US09/180,337 patent/US6266552B1/en not_active Expired - Lifetime
  • 1997-05-28 WO PCT/SE1997/000915 patent/WO1998000060A1/en not_active Application Discontinuation
  • 1997-05-28 JP JP50402698A patent/JP3853370B2/ja not_active Expired - Fee Related

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