EP1682026A4

EP1682026A4 - Magnetic navigation of medical devices in magnetic fields

Info

Publication number: EP1682026A4
Application number: EP04796484A
Authority: EP
Inventors: Rogers C Ritter; Raju R Viwanathan; Roger N Hastings
Original assignee: Stereotaxis Inc
Current assignee: Stereotaxis Inc
Priority date: 2003-10-27
Filing date: 2004-10-26
Publication date: 2009-01-07
Also published as: WO2005044081A2; WO2005044081A3; EP1682026A2

Abstract

A method of turning a medical device with the assistance of an externally applied magnetic field, in a direction with a component in a plane perpendicular to the direction of the externally applied magnetic field. The method includes applying a first torque to the distal end of the medical device by creating a magnetic moment at the distal end of the medical device, and applying a second torque to the distal end of the medical device. The second torque may be created by creating a second magnetic moment in the distal portion of the device spaced from the first, by using an electrostrictive device, by using a stylette inserted into the device, by using a fluid-driven shaped tube, or otherwise.

Description

MAGNETIC NAVIGATION OF MEDICAL DEVICES LN MAGNETIC FIELDS

BACKGROUND OF THE INVENTION [0001] This invention relates to the navigation of medical devices in magnetic fields, and in particular to the navigation of medical devices in magnetic fields created by magnetic resonance imaging equipment. [0002] Systems have been developed for navigating medical devices in externally applied static magnetic fields, such as those created by magnetic resonance imaging equipment. Examples of such systems are disclosed in Kuhn, U.S Patent No. 6,216,026, Arenson, U.S. Patent No. 6,304,769, and Hastings et al., U.S. Patent No. 6,401,723, the disclosures of all of which are incorporated herein by reference. These systems employ a controllable variable magnetic moment in the medical device to orient the magnetic medical device relative to the externally applied magnetic field. One way of creating a controllable variable magnetic moment is with one or more coils in the distal end which can be selectively energized. [0003] Although these prior systems allow effective magnetic navigation in a static magnetic field, magnetic navigation of a medical device in a static magnetic field is constrained by the nature of the interaction between the magnetic moments and the external field. The torque on a dipole moment m in a homogeneous external magnetic field B is given by τ = m x B. This torque is necessarily perpendicular to the external field B and to the moment m. In navigation it is generally possible to completely vary the direction of m relative to the catheter tip, but in fixed field navigation, such as in an MRI, B cannot be changed. Thus, when the medical device is in a plane that is perpendicular to the external field B, the device cannot be deflected in the plane in which it lies, irrespective of m, because this requires a torque that is parallel to B. [0004] Another difficulty encountered with at least some prior systems for navigating in a static magnetic field of an MRI system is the inductive rf heating of wire leads powering the coils used to change the magnetic moment of the device.

SUMMARY OF THE INVENTION [0005] The present invention provides for the navigation of medical devices in the plane perpendicular to an applied magnetic field, and more specifically turning a medical device with the assistance of an externally applied magnetic field or other means, or a combination thereof, in a direction with a component in a plane perpendicular to the direction of the externally applied magnetic field. Generally the method comprises applying a first torque to the distal end of the medical device by creating a magnetic moment at the distal end of the medical device; and applying a second torque to the distal end of the medical device. This second torque can be applied by creating a second magnetic moment at the distal end of the medical device, spaced from the first. It may also be allowed by mechanically turning the distal end of the medical device, for example by turning the proximal end of the device, by rotating an element anchored to the distal end of the device, inserting a shaped stylette into the medical device, or operating one or more active elements, for example electrostrictive elements or pressure operated elements, for changing the shape of the medical device. The second torque can be applied by the reaction of the distal end portion itself to the axial rotation caused by the first torque. [0006] In another aspect of various embodiments of this invention, long electrical leads to coils (or other electrically powered elements on the distal end of the device, such as electrostrictive elements) on the distal end of the device are eliminated by providing a fiber optic conduit to a photovoltaic cell in the distal end of the medical device, which powers one or more electrically powered elements in the distal end of the device. [0007] Thus some embodiments of the method and apparatus of this invention allow a medical device being navigated in a static magnetic field to be turned in a direction in a plane perpendicular to the applied magnetic field. Other embodiments of the method and apparatus of this invention allow apparatus for changing the magnetic moment of the distal end of a medical device or powering other elements at the distal end of the device without the need for electrical leads extending the length of the device to the distal end. These and other features and advantages will be in part apparent, and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS [0008] Figure 1 is a schematic view of a medical device C being navigated in a static applied magnetic field B, lying in a plane P perpendicular to the applied magnetic field; [0009] Figure 2 is a schematic view of a medical device C in a vessel V that lies in a plane perpendicular to the applied magnetic field. [0010] Figure 3A is a longitudinal cross-sectional view of a first embodiment of a medical device constructed according to the principles of this invention; [0011] Figure 3B are views of a first alternate construction of a device constructed according to the principles of this invention; [0012] Figure 3C are views of the first alternate construction after the distal end has been twisted for cause the distal end portion to assume a helical configuration; [0013] Figure 3D is a longitudinal cross-sectional view of an alternate construction of a medical device constructed according to the principles of this invention; [0014] Figure 4 is a longitudinal cross-sectional view of a second embodiment of a medical device constructed according to the principles of this invention; [0015] Figure 5 is a longitudinal cross-sectional view of a third embodiment of a medical device constructed according to the principles of this invention; [0016] Figure 6 is a longitudinal cross-sectional view of a fourth embodiment of a medical device constructed according to the principles of this invention; [0017] Figure 7 is a side elevation view of a fifth embodiment of a medical device constructed according to the principles of this invention; [0018] Figure 8 is a longitudinal cross-sectional view of a sixth embodiment of a medical device constructed according to the principles of this invention; [0019] Figure 9 is a longitudinal cross-sectional view of a seventh embodiment of a medical device constructed according to the principles of this invention; [0020] Figure 10 is a longitudinal cross-sectional view of an eighth embodiment of a medical device constructed according to the principles of this invention; [0021] Corresponding reference numerals indicate corresponding parts throughout the several views of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0022] The present invention provides a method for navigating a medical device in an operating region in a subject's body to which a static magnetic field is applied. As used herein a medical device means any medical device that is navigated in the body, including but not limited to guide wires, catheters, endoscopes, etc. The static magnetic field can be applied with a source magnet that is part of a dedicated magnetic navigation system, or the magnetic field can be applied with a magnet from a magnetic resonance imaging system. [0023] As shown in Figure 1, when a medical device C lies in a plane P perpendicular to the direction of the applied magnetic field B, it is not possible to move the medical device in the direction indicated by arrow X in the plane P purely by changing the magnetic moment at the distal tip of the medical device. Moreover, it is not possible to move in any arbitrary direction having a component in the plane P purely by changing the moment m. The problem of being unable to navigate in the "forbidden" plane is illustrated in more detail in Figure 2, where the device C lies an a vessel V and it is desired to turn the device C into a branch D, with both V and C in the plane of the page, which is perpendicular to the field B. As shown in Figure 2, the magnetic field direction B is into the paper, as represented by the X's. Thus the turn in direction R is in the plane perpendicular to the magnetic field direction, and cannot be accomplished simply by changing the magnetic moment at the distal end of the device C. Indeed, the magnetic moment interacting with the external magnetic field generally causes the device tip to move out of the plane P defined by V and D. Means to accomplish effective turns of the tip within the plane P require that the tip be moved, however slightly, back into the plane, at which point there will be at least a small component of the bent tip that is along the field direction. The requisite change in m and tip orientation or displacement can then be calculated (by computer). One aspect of this invention is to have computer optimization of a succession of such small turn combinations so that the complete turn is made optimally for the given geometry. The degree of "adverse lever arm" in using the combination motion depends on the daughter vessel size and on the closeness of the "parent-daughter" plane to the forbidden plane. [0024] A first embodiment of a medical device for navigation in a static magnetic field constructed in accordance with the principles of this invention is indicated generally as 20 in Figure 3A. As shown in Figure 3A, the device 20 is preferably an elongate device having a proximal end 22, a distal end 24, and comprising a generally tubular sidewall 26 with a lumen 28 extending therethrough. The distal end 24 of the medical device 20 preferably includes at least one element 30 for selectively creating a magnetic moment at the distal end of the medical device to orient the distal end of the medical device relative to a static magnetic field applied to the operating region in which the device 20 is being navigated by an external source magnet or magnets. The element 30 may be any of a variety of elements for selectively creating a magnetic moment, but in this preferred embodiment the element 30 comprises at least one electromagnetic coil, and more preferably at least three mutually perpendicular coils. These coils can be arranged on a cubic substrate or simply embedded in the wall of the medical device. The coils can be powered via leads 32, which preferably comprise a pair of leads for separately powering each coil. [0025] The distal end 24 of the medical device 20 may include a second element 34, spaced a distance d from first element 30, for selectively creating a second magnetic moment at the distal end of the medical device 20 to orient the distal end of the medical device relative to a static magnetic field applied to the operating region by the external source magnet or magnets. The element many be any of a variety of elements for selectively creating a magnetic moment, but in this preferred embodiment the element comprises electromagnetic coils, and in particular an electromagnetic coil unit. The coil unit preferably comprises at least three mutually perpendicular coils. These coils can be arranged on a cubic substrate or simply embedded in the wall of the medical device. The coils can be powered via leads 36, which preferably comprise a pair of leads for separately powering each coil. The leads 32 and 36 can either extend through the lumen 28 as shown, extend through a separate lumen (not shown), or be embedded in the wall 26. [0026] The distance d between the elements 30 and 34 is preferably sufficient, given the properties of the medical device, to allow the device to flex between the elements. [0027] The two elements 30 and 34 allow the distal end portion 24 of the medical device 20 to be turned out of the plane perpendicular to the field B, and then turned in the desired direction. The operation of the elements 30 and 34 can be controlled by computer to optimize the efficiency of the turn according to the physical properties of the device (the wall stiffness and the spacing d) and the particular turn that is desired. The turn with component in the forbidden plane is possible with this device because the two moments 30 and 34 created magnetically can react so as to create a mechanical torque between them, which is not subject to the limit of the torque on the magnetic moments themselves. This can be seen from the fact that different torques out of the forbidden plane, when coupled by a flexible mechanical member, can be arranged to have appropriate out-of-plane moments cancel mechanically, so that the complete device can have a turning component in the plane. [0028] If L is the supported length of device (this depends on the particular medical application) where the device freely extends (measured back from the distal tip); d is the spacing between the elements 30 and 34; E is the Young's modulus of the material of the device; and I is the bending moment of area; and a magnetic moment of magnitude m produced by the most distal element 30 causes the device tip to move out of the plane P shown in Fig. 1 by an amount z. Then in order to move the tip back into this plane, the second element 34 is preferably controlled so as to produce a magnetic moment whose magnitude is ni_! = βm(l + α), where α=(EI/(L-d)) (d/L)(z/L) and β is a number in the range 1/5 < β < 5. [0029] It is desirable to know the orientation of the elements 30 and 34 prior to energizing its coils. This can be conveniently done by moving the distal end of the medical device, and using the coils comprising the elements 30 and 34 to measure the static field B and thereby determine their orientation relative to the known orientation of the field B. For example it is possible to temporarily energize one of the coils in the element 30 and measure the response of the other two coils, and repeat this for each of the other coils, and thereby determine the orientation of the element 30, and thus the orientation of the distal end portion of the device surrounding the element 30. It is also possible to energize some or all of the more proximal element 34 to induce a movement of the element 30, and simultaneously measure the effect on the coils of element 30, and thereby determine the orientation of the element 30, and thus the orientation of the distal end portion of the device surrounding the element 30. It is also possible to mechanically move the elements 30 and 34 by advancing, retracting or turning the proximal end of the medical device, measuring the effect on the coils of element 30, and thereby determine the orientation of the element 30, and thus the orientation of the distal end portion of the device surrounding the element 30. The movement of the element can be a small single impulse or a small repetitive "dithering" of the element. [0030] Where the coils are not provided on a substrate, but are instead laminated on, or embedded in, the distal end portion of the medical device, in addition to creating a moment at the distal end of device, and magnetically sensing orientation, the coils can also function as strain gauges, measuring the bend of the device, and thus facilitating the determination of the configuration of the distal end portion of the device. Thus, by measuring changes in the resistance of coils, the bending of the device can be measured, and the configuration of the device determined. [0031] This position information can be used to provide automated closed loop navigation. Once the components of the static magnetic field along the axes of the three orthogonal coils adjacent the tip of the device are determined, the orientation of the coils relative to the static field can be computed. The currents required to change the orientation of the coils can be calculated and applied to the coils. The catheter can be advanced, and the process repeated until the catheter tip reaches its desired destination. [0032] Another method to determine the orientation is to place a series of MR- visible markers along the device in known orientations relative to one or more of the elements 30 and 34, and to extract the device orientation from appropriate image processing [0033] Rather than using two elements 30 and 34, it should also be possible to apply an axial twist to the distal end portion of the device with just element 30 (or a plurality of coils if not provided as a single element). In this case, the portion of the device adjacent the distal end is constructed to assume the shape of a helix upon axial twisting of the distal end of the device. This mechanically causes the distal tip of the device to turn in a direction with some component in a plane perpendicular to the direction of the applied magnetic field, although because of the helical configuration of the distal end portion, the device is no longer in the original plane. However, it many circumstances this motion, with a component in the "forbidden" plane is still useful for navigation, even though the device has moved out of its original plane. In navigations in chambers in the body, such as the heart, this three dimensional movement can be useful. In navigations through body lumens, such as blood vessels, the physical restraint of the lumen can help retain the device in the original plane as it turns. This is shown in the comparison of Figure 3B before application of axial twist, with Figure 3C after application of axial twist. [0034] In an alternative construction of the first embodiment shown in Fig. 3D, a deformable element 40 can be provided in the distal end of the device. The element 40 is preferably sufficiently flexible, that it readily bends under the torques that can be created by the elements 30 and 34, yet is sufficiently stiff that it substantially resists bending under the resilience of the device itself. Thus, that element 30 or the elements 30 and 34 can be used to create a bend in the element 40 and when the elements are deenergized, the element 40 can retain the distal end portion of the device in its bent configuration mechanically straightened out or straightened out by the application of appropriate currents in the element 30 or elements 30 and 34 to straighten the distal end of the device and thus the element 40. A heating element or other device can be provided to facilitate returning the element 40 to its unbent configuration. Thus the user can temporarily fix the configuration of the distal end of the device, and use this configuration in navigation, including navigation in the "forbidden" plane, and then readily reshape the distal end of the device. The element 40 can be incorporated into any of the embodiments of this invention, if desired. [0035] A second embodiment of a medical device for navigation in a static magnetic field constructed in accordance with the principles of this invention is indicated generally as 120 in Figure 4. As shown in Figure 4, the device 120 is preferably an elongate device having a proximal end 122, a distal end 124, and comprising a generally tubular sidewall 126 with a lumen 128 extending therethrough. The distal end 124 of the medical device 120 preferably includes at least one element 130 for selectively creating a magnetic moment at the distal end of the medical device to orient the distal end of the medical device relative to a static magnetic field applied to the operating region in which the device 120 is being navigated by an external source magnet or magnets. The element 130 may be any of a variety of elements for selectively creating a magnetic moment, but in this preferred embodiment the element 130 comprises at least one electromagnetic coil, and more preferably at least three mutually perpendicular coils. These coils can be arranged on a cubic substrate or simply embedded in the wall of the medical device. The coils can be powered via leads 132, which preferably comprise a pair of leads for separately powering each coil. The leads 232 can either extend through the lumen 228 as shown, extend through a separate lumen (not shown), or be embedded in the wall 226. [0036] In operation, the element 130 is powered via leads 132 to turn the distal end 124 of the medical device 120 out of the "forbidden" plane perpendicular to the direction of the applied magnetic field. The proximal end 122 of the medical device 120 is then rotated as indicated by arrow 134 (about the axis of 120) to turn the distal end 124 of the device in the desired direction. This rotation can be either manually performed or implemented and driven by computer control. The operation of the element 130 can be controlled by computer. It is desirable to know the orientation of the element 130 prior to energizing its coils. This can be conveniently done by moving the distal end of the medical device, and using the coils comprising the element 130 to measure the static field B and thereby determine their orientation relative to the know orientation of the field B. [0037] It is desirable to know the orientation of the element 130 prior to energizing its coils. This can be conveniently done by moving the distal end of the medical device, and using the coils comprising the element 130 to measure the static field B and thereby determine their orientation relative to the know orientation of the field B. For example it is possible to temporarily energize one of the coils in the element 130 and measure the response of the other two coils, and repeat this for each of the other coils, and thereby determine the orientation of the element 130, and thus the orientation of the distal end portion of the device surrounding the element 130. It is also possible to mechanically move the element 130 by advancing, retracting or turning the proximal end of the medical device, measuring the effect on the coils of element 130, and thereby determine the orientation of the element 130, and thus the orientation of the distal end portion of the device surrounding the element 130. The movement of the element can be a small single impulse or a small repetitive "dithering" of the element. [0038] Where the coils are not provided on element 130, but are instead laminated on, or embedded in, the distal end portion of the medical device, in addition to creating a moment at the distal end of device, and magnetically sensing orientation, the coils can also function as strain gauges, measuring the bend of the device, and thus facilitating the determination of the configuration of the distal end portion of the device. Thus, by measuring changes in the resistance of coils, the bending of the device can be measured, and the configuration of the device determined. [0039] Another method to determine the orientation is to place a series of MR-visible markers along the device in known orientations relative to the element 130, and to extract the device orientation from appropriate image processing. [0040] A third embodiment of a medical device for navigation in a static magnetic field constructed in accordance with the principles of this invention is indicated generally as 220 in Figure 5. As shown in Figure 5, the device 220 is preferably an elongate device having a proximal end 222, a distal end 224, and comprising a generally tubular sidewall 226 with a lumen 228 extending therethrough. The distal end 224 of the medical device 220 preferably includes at least one element 230 for selectively creating a magnetic moment at the distal end of the medical device to orient the distal end of the medical device relative to a static magnetic field applied to the operating region in which the device 220 is being navigated by an external source magnet or magnets. The element 230 many be any of a variety of elements for selectively creating a magnetic moment, but in this preferred embodiment the element 230 comprises at least one electromagnetic coil, and more preferably at least three mutually perpendicular coils. These coils can be arranged on a cubic substrate or simply embedded in the wall of the medical device. The coils can be powered via leads 232, which preferably comprise a pair of leads for separately powering each coil. The leads 232 can either extend through the lumen 228 as shown, extend through a separate lumen (not shown), or be embedded in the wall 226. [0041] A flexible cable 234 preferably extends through the lumen 228, and is anchored adjacent the distal end 224 of the medical device 220. The cable 234 is preferably sufficiently flexible so as not to unduly interfere with the flexing and navigation of the medical device 220, but has sufficient torsional stiffness so that rotation of the cable 234 rotates the distal end 224 of the medical device. Thus in operation, the element 230 is energized via the leads 232 and turned out of the forbidden plane, and then the cable 234 can be turned to turn the distal end 224 of the medical device 220 in the desired direction. The operation of the element 230 can be controlled by computer. It is desirable to know the orientation of the element 230 prior to energizing its coils. This can be conveniently done by moving the distal end of the medical device, and using the coils comprising the element 230 to measure the static field B and thereby determine their orientation relative to the known orientation of the field B. Likewise the turning of cable 234 may also be computer-controlled, with or without the use of feedback-control methods. [0042] The orientation of the element 230 can be conveniently determined by moving the distal end of the medical device, and using the coils comprising the element 230 to measure the static field B and thereby determine their orientation relative to the know orientation of the field B. For example it is possible to temporarily energize one of the coils in the element 230 and measure the response of the other two coils, and repeat this for each of the other coils, and thereby determine the orientation of the element 230, and thus the orientation of the distal end portion of the device surrounding the element 230. It is also possible to mechanically move the element 230 by advancing, retracting or turning the proximal end of the medical device, measuring the effect on the coils of element 230, and thereby determine the orientation of the element 230, and thus the orientation of the distal end portion of the device surrounding the element 230. The movement of the element can be a small single impulse or a small repetitive "dithering" of the element. [0043] Where the coils are not provided on element 230, but are instead laminated on, or embedded in, the distal end portion of the medical device, in addition to creating a moment at the distal end of device, and magnetically sensing orientation, the coils can also function as strain gauges, measuring the bend of the device, and thus facilitating the determination of the configuration of the distal end portion of the device. Thus, by measuring changes in the resistance of coils, the bending of the device can be measured, and the configuration of the device determined. [0044] Another method to determine the orientation is to place a series of MR-visible markers along the device in known orientations relative to the element 230, and to extract the device orientation from appropriate image processing [0045] A fourth embodiment of a medical device for navigation in a static magnetic field constructed in accordance with the principles of this invention is indicated generally as 320 in Figure 6. As shown in Figure 6, the device 320 is preferably an elongate device having a proximal end 322, a distal end 324, and comprising a generally tubular sidewall 326 with a lumen 328 extending therethrough. The distal end 324 of the medical device 320 preferably includes at least one element 330 for selectively creating a magnetic moment at the distal end of the medical device to orient the distal end of the medical device relative to a static magnetic field applied to the operating region in which the device 320 by an external source magnet or magnets. The element 330 many be any of a variety of elements for selectively creating a magnetic moment, but in this preferred embodiment the element 330 comprises at least one electromagnetic/ coil, and more preferably at least three mutually perpendicular coils. These coils can be arranged on a cubic substrate or simply embedded in the wall of the medical device. The coils can be powered via leads 332, which preferably comprise a pair of leads for separately powering each coil. The leads 332 can either extend through the lumen 328 as shown, extend through a separate lumen (not shown), or be embedded in the wall 326. [0046] The distal end 324 of the medical device 320 preferably includes at least one bending element, such as electrostrictive bending elements 334, connected by leads 336. The electrostrictive elements may be piezoelectric materials which change shape upon the application of a potential, or electrostrictive polymers which change length, or any other element which creates mechanical action upon application of electrical current or potential. There are preferably a plurality of electrostrictive bending elements 334 and corresponding leads 336 disposed circumferentially around the distal end of the medical device 320. In the preferred embodiment there are at least four elements 334. These elements can be used individually or in groups to achieve the desired configuration. These elements can also be used in opposed pairs for example one element on one side of the device 320 constricting and one element on the other side of the device expanding to bend the device 320 in the desired direction. [0047] In operation, the element 330 allows the distal end portion 324 of the medical device 20 to be turned out of the plane perpendicular to the field B, and then the electrostrictive elements 334 used to turn the distal end 324 in the desired direction. Alternatively, the distal end 324 of the medical device 320 can be bent using one or more of the elements 324, and then the element 330 can be operated to turn the distal end 324 in the desired direction. The operation of the elements 330 can be controlled by computer. Likewise the electrostrictive elements 334 can also be computer-controlled. It is desirable to know the orientation of the elements 330 prior to energizing their coils. This can be conveniently done by moving the distal end of the medical device, and using the coils comprising the element 330 to measure the static field B and thereby determine their orientation relative to the known orientation of the field B. An alternate method can be based on the use of suitable MR-visible markers in the device together with image processing. [0048] The orientation of the element 330 can be conveniently determined by moving the distal end of the medical device, and using the coils comprising the element 330 to measure the static field B and thereby determine their orientation relative to the known orientation of the field B. For example it is possible to temporarily energize one of the coils in the element 330 and measure the response of the other two coils, and repeat this for each of the other coils, and thereby determine the orientation of the element 330, and thus the orientation of the distal end portion of the device surrounding the element 330. It is also possible to mechanically move the element 330 by advancing, retracting or turning the proximal end of the medical device or actuating the electrostrictive elements 334, measuring the effect on the coils of element 330, and thereby determine the orientation of the element 330, and thus the orientation of the distal end portion of the device surrounding the element 330. The movement of the element can be a small single impulse or a small repetitive "dithering" of the element. [0049] Where the coils are not provided on element 330, but are instead laminated on, or embedded in, the distal end portion of the medical device, in addition to creating a moment at the distal end of device, and magnetically sensing orientation, the coils can also function as strain gauges, measuring the bend of the device, and thus facilitating the determination of the configuration of the distal end portion of the device. Thus, by measuring changes in the resistance of coils, the bending of the device can be measured, and the configuration of the device determined. [0050] Another method to determine the orientation is to place a series of MR-visible markers along the device in known orientations relative to the element 330, and to extract the device orientation from appropriate image processing. [0051] A fifth embodiment of a medical device for navigation in a static magnetic field constructed in accordance with the principles of this invention is indicated generally as 420 in Figure 7. As shown in Figure 7, the device 420 is preferably an elongate device having a proximal end 422, a distal end 424, and comprising a generally tubular sidewall 426 with a lumen 428 extending therethrough. The distal end 424 of the medical device 420 preferably includes at least one element 430 for selectively creating a magnetic moment at the distal end of the medical device to orient the distal end of the medical device relative to a static magnetic field applied to the operating region in which the device 420 is being navigated by an external source magnet or magnets. The element 430 may be any of a variety of elements for selectively creating a magnetic moment, but in this preferred embodiment the element 330 comprises at least one electromagnetic coil, and more preferably at least three mutually perpendicular coils. These coils can be arranged on a cubic substrate or simply embedded in the wall of the medical device. The coils can be powered via leads 332, which preferably comprise a pair of leads for separately powering each coil. The leads 432 can either extend through the lumen 428 as shown, extend through a separate lumen (not shown), or be embedded in the wall 426. [0052] The distal end 424 of the medical device 420 preferably includes at least one bending element, such as electrostrictive twisting elements 434, connected by leads 436. There is preferably a plurality of electrostrictive torsional elements 434 and corresponding leads 436 disposed circumferentially around the distal end of the medical device 420. In the preferred embodiment there are at least four elements 434. These elements can also be used in opposed pairs for example one element on one side of the device 420 constricting and one element on the other side of the device expanding to bend the device 420 in the desired direction. [0053] In operation, the element 430 allows the distal end portion 324 of the medical device 420 to be turned out of the plane perpendicular to the field B, and then the electrostrictive elements 434 used to turn the distal end 424 in the desired direction. Alternatively, the distal end 424 of the medical device 420 can be bent using one or more of the elements 424, and then the element 430 can be operated to turn the distal end 424 in the desired direction. [0054] The operation of the elements 430 and that of the electrostrictive torsional elements 434 can be controlled by computer. It is desirable to know the orientation of the elements 430 prior to energizing their coils. This can be conveniently done by moving the distal end of the medical device, and using the coils comprising the element 430 to measure the static field B and thereby determine their orientation relative to the know orientation of the field B. An alternate method of orientation determination can be based on the use of suitable MR-visible markers in the device together with image processing. [0055] The orientation of the element 430 can be conveniently determined by moving the distal end of the medical device, and using the coils comprising the element 430 to measure the static field B and thereby determine their orientation relative to the know orientation of the field B. For example it is possible to temporarily energize one of the coils in the element 430 and measure the response of the other two coils, and repeat this for each of the other coils, and thereby determine the orientation of the element 430, and thus the orientation of the distal end portion of the device surrounding the element 430. It is also possible to mechanically move the element 430 by advancing, retracting or turning the proximal end of the medical device or actuating the electrostrictive elements 434, measuring the effect on the coils of element 430, and thereby determine the orientation of the element 430, and thus the orientation of the distal end portion of the device surrounding the element 430. The movement of the element can be a small single impulse or a small repetitive "dithering" of the element. [0056] Where the coils are not provided on element 430, but are instead laminated on, or embedded in, the distal end portion of the medical device, in addition to creating a moment at the distal end of device, and magnetically sensing orientation, the coils can also function as strain gauges, measuring the bend of the device, and thus facilitating the determination of the configuration of the distal end portion of the device. Thus, by measuring changes in the resistance of coils, the bending of the device can be measured, and the configuration of the device determined. [0057] Another method to determine the orientation is to place a series of MR-visible markers along the device in known orientations relative to the element 430, and to extract the device orientation from appropriate image processing. [0058] A sixth embodiment of a medical device for navigation in a static magnetic field constructed in accordance with the principles of this invention is indicated generally as 520 in Figure 8. As shown in Figure 8, the device 520 is preferably an elongate device having a proximal end 522, a distal end 524, and comprising a generally tubular sidewall 526 with a lumen 528 extending therethrough. The distal end 524 of the medical device 520 preferably includes at least one element 530 for selectively creating a magnetic moment at the distal end of the medical device to orient the distal end of the medical device relative to a static magnetic field applied to the operating region in which the device 520 is being navigated by an external source magnet or magnets. The element 530 many be any of a variety of elements for selectively creating a magnetic moment, but in this preferred embodiment the element 530 comprises at least one electromagnetic coil, and more preferably at least three mutually perpendicular coils. These coils can be arranged on a cubic substrate or simply embedded in the wall of the medical device. The coils can be powered via leads 532, which preferably comprise a pair of leads for separately powering each coil. The leads 532 can either extend through the lumen 528 as shown, extend through a separate lumen (not shown), or be embedded in the wall 526. [0059] The medical device 520 preferably includes at least one two sections 534 and 536 of differing flexibility. The more proximal section 534 is preferably stiffer than the more distal section 536. The medical device 520 is adapted for use with a stylette, such as stylette 538, which has a specially shaped, resilient distal tip 540. The stylette 538 is adapted to be inserted into the lumen 528, but because of the greater stiffness of the proximal end, as the shaped tip 540 of the stylette 538 passes through the proximal portion of the lumen, the shape remains unchanged. However, as the tip 540 of the stylette 538 passes through the distal portion of the lumen 528 in distal section 536, the distal portion of the medical device 520 bends to generally conform to the shaped tip 540. [0060] In operation, the element 530 allows the distal end portion 524 of the medical device 520 to be turned out of the plane perpendicular to the field B, and then the stylette 538 can be used to turn the distal end 524 in the desired direction. Alternatively, the distal end 324 of the medical device 320 can be bent using the stylette 538, and then the element 530 can be operated to turn the distal end 524 in the desired direction. [0061] The operation of the elements 530 can be controlled by computer. It is desirable to know the orientation of the elements 530 prior to energizing its coils. The orientation of the element 530 can be conveniently determined by moving the distal end of the medical device, and using the coils comprising the element 530 to measure the static field B and thereby determine their orientation relative to the know orientation of the field B. For example it is possible to temporarily energize one of the coils in the element 530 and measure the response of the other two coils, and repeat this for each of the other coils, and thereby determine the orientation of the element 530, and thus the orientation of the distal end portion of the device surrounding the element 530. It is also possible to mechanically move the element 530 by advancing, retracting or turning the proximal end of the medical device or inserting the stylette, measuring the effect on the coils of element 530, and thereby determine the orientation of the element 530, and thus the orientation of the distal end portion of the device surrounding the element 530. The movement of the element can be a small single impulse or a small repetitive "dithering" of the element. [0062] Where the coils are not provided on element 530, but are instead laminated on, or embedded in, the distal end portion of the medical device, in addition to creating a moment at the distal end of device, and magnetically sensing orientation, the coils can also function as strain gauges, measuring the bend of the device, and thus facilitating the determination of the configuration of the distal end portion of the device. Thus, by measuring changes in the resistance of coils, the bending of the device can be measured, and the configuration of the device determined. [0063] Another method to determine the orientation is to place a series of MR-visible markers along the device in known orientations relative to the element 530, and to extract the device orientation from appropriate image processing. [0064] A seventh embodiment of a medical device for navigation in a static magnetic field constructed in accordance with the principles of this invention is indicated generally as 620 in Figure 9. As shown in Figure 9, the device 620 is preferably an elongate device having a proximal end 622, a distal end 624, and comprising a generally tubular sidewall 626 with a lumen 628 extending therethrough. The distal end 624 of the medical device 620 preferably includes at least one element 630 for selectively creating a magnetic moment at the distal end of the medical device to orient the distal end of the medical device relative to a static magnetic field applied to the operating region in which the device is being navigated by an external source magnet or magnets. The element 630 may be any of a variety of elements for selectively creating a magnetic moment, but in this preferred embodiment the element 630 comprises at least one electromagnetic coil, and more preferably at least three mutually perpendicular coils. These coils can be arranged on a cubic substrate or simply embedded in the wall of the medical device. The coils can be powered via leads 632, which preferably comprise a pair of leads for separately powering each coil. The leads 632 can either extend through the lumen 628 as shown, extend through a separate lumen (not shown), or be embedded in the wall 626. [0065] An expansible tube 634 (similar to a Bourdon tube pressure gauge) extends through the lumen 228, and is anchored adjacent the distal end 224 of the medical device 620. The tube has a wound configuration, and upon changes in the applied fluid pressure the wound portion 636 can wind or unwind, changing the shaped of distal end portion of the medical device 620. [0066] Thus in operation, the element 630 is energized via the leads 632 and turned out of the forbidden plane, and then the expansible tube 634 is pressurized or depressurized to turn the distal end 624 of the medical device 620 in the desired direction. The operation of pressure turning the tip is that of a bending (pressure release) or unbending (pressure increase) of a Bourdon tube. Alternatively, the expansible tube 634 is pressurized or depressurized to turn the distal end 624 of the medical device 620 out of the "forbidden" plane, and then the element 630 is energized via the leads 632 to turn the device in the desired direction. [0067] The operation of the element 630 can be controlled by computer. It is desirable to know the orientation of the element 630 prior to energizing its coils. The orientation of the element 630 can be conveniently determined by moving the distal end of the medical device, and using the coils comprising the element 630 to measure the static field B and thereby determine their orientation relative to the know orientation of the field B. For example it is possible to temporarily energize one of the coils in the element 630 and measure the voltage induced in the other two coils as they move through the static field B, and repeat this for each of the other coils, and thereby determine the orientation of the element 630, and thus the orientation of the distal end portion of the device surrounding the element 630. Furthermore, it is possible to determine the voltage induced in the energized coil by comparing the measured coil voltage to the TR drip across the known resistance of the coil. Thus, one or more coils may be energized, while the voltages induced in all three coils due to movement of the catheter tip in the static field B is determined. The static field in an MRI is sufficiently large that only small, "virtual" movements of the tip are required to induce a measurable voltage in the coils. It is also possible to mechanically move the element 630 by advancing, retracting or turning the proximal end of the medical device or actuating the tube 634, measuring the voltage induced in the coils of element 630, and thereby determine the orientation of the element 630, and thus the orientation of the distal end portion of the device surrounding the element 630. In addition to using the coils in element 630 as induction sensors, a variety of other magnetic sensor structures can be added adjacent element 630 to measure the three components of the static field B along the three orthogonal axes of the coils in element 630. For example, miniature Hall Effect solid state magnetic sensors may be used to measure the static field. Alternatively, Giant Magneto-Resistance (GMR) sensors, available for example from Honeywell Solid State Electronic Center, Plymouth MN 55441, can be used to measure the three components of the static field B along the three coil axes. It is noted that the magnetic fields generated by currents flowing in coils is much smaller than the static field B, so that the field sensors can be co-located with the coils, or displaced a small distance from the coils, without significant influence on the static field measurement. For example, the static field B may have magnitude of 3 Tesla, while the energized coils will produce a field less than about 0.1 Tesla at the center of these coils. The movement of the element can be a small single impulse or a small repetitive "dithering" of the element. [0068] Where the coils are not provided on element 630, but are instead laminated on, or embedded in, the distal end portion of the medical device, in addition to creating a moment at the distal end of device, and magnetically sensing orientation, the coils can also function as strain gauges, measuring the bend of the device, and thus facilitating the determination of the configuration of the distal end portion of the device. Thus, by measuring changes in the resistance of coils, the bending of the device can be measured, and the configuration of the device determined. [0069] Another method to determine the orientation is to place a series of MR-visible markers along the device in known orientations relative to the element 630, and to extract the device orientation from appropriate image processing. [0070] An eighth embodiment of a medical device for navigation in a static magnetic field constructed in accordance with the principles of this invention is indicated generally as 720 in Figure 10. As shown in Figure 10, the device 720 is preferably an elongate device having a proximal end 722, a distal end 724, and comprising a generally tubular sidewall 726 with a lumen 728 extending therethrough. The distal end 724 of the medical device 720 preferably includes at least one element 730 for selectively creating a magnetic moment at the distal end of the medical device to orient the distal end of the medical device relative to a static magnetic field applied to the operating region in which the device 720 is being navigated by an external source magnet or magnets. The element 730 many be any of a variety of elements for selectively creating a magnetic moment, but in this preferred embodiment the element 730 comprises at least one electromagnetic coil, and more preferably at least three mutually perpendicular coils. These coils can be arranged on a cubic substrate or simply embedded in the wall of the medical device. The coils can be powered via a fiber optic lead 732, which conducts high energy light to a photovoltaic converter cell 734 to create electric power for the coils which is conducted to the coils via short lead 736. The use of a fiber optic lead 732 and photovoltaic cell 734 eliminates the need for long wire lead, which are sometimes subject to heating in the rf field of an MRI system. . The fiber optic lead 732 can either extend through the lumen 728 as shown, extend through a separate lumen (not shown), or be embedded in the wall 726. This construction can be applied to any of the preceding embodiments one through seven. [0071] There is preferably a photovoltaic cell for each electrically operated element, and a fiber optic line for each photovoltaic cell. Alternatively, a single fiber optic line can be provided that provides optic signals and optic power to control the distribution of light among a plurality of photovoltaic cells, or which controls the distribution of electric power among a plurality of electrical elements. For example the fiber optic can conduct information signals to operate an optical or electrical switch. Alternatively, a distribution device such as a filter can be used to distribute light based upon wavelength. -[0072] This structure can be used to transmit power to the coils in any of the other embodiments of this invention, as well as transmit signals from any of the coils in any of the other embodiments of this invention. This structure can also be used to transmit power to electrostrictive elements in those embodiments using electrostrictive elements.

Claims

What is claimed is: 1. A method of turning a medical device with the assistance of an externally applied magnetic field, in a direction with a component in a plane perpendicular to the direction of the externally applied magnetic field, the method comprising: applying a first torque to the distal end of the medical device by creating magnetic moment adjacent the distal end of the medical device; applying a second torque to the distal portion of the medical device. 2. The method according to claim 1 wherein the magnetic moment is created by the application of an electric current to coils adjacent the distal end of the medical device. 3. The method according claim 1 wherein the second torque is applied by creating a second magnetic moment spaced from the point of application of magnet moment applying the first torque. 4. The method according to claim 1 wherein the second torque is applied by rotating the proximal end of the medical device. 5. The method according to claim 1 wherein the second torque is applied by rotating an element attached to the distal end of the medical device. 6. The method according to claim 5 the element is flexible element extending through a lumen in the device, and having an end secured to the distal end of the medical device. 7. The method according to claim 1 wherein the second torque is applied by energizing at least one electrostritive element the medical device. 8. The method according to claim 1 wherein the second torque is applied by inserting a shaped stylette into a lumen in the medical device. 9. The method according to claim 1 wherein the application of one of the first and second torques bends the medical device to orient the distal end portion of the medical device in a non-zero angle with respect to a plane perpendicular to the direction of the applied magnetic field.

10. A method of turning a medical device with the assistance of an externally applied magnetic field, in a direction with a component in a plane perpendicular to the direction of the externally applied magnetic field, the method comprising: applying a first torque to the distal end of the medical device by creating magnetic moment adjacent the distal end of the medical device; applying a second torque to the distal portion of the medical device. 11. A method of turning a medical device with the assistance of an externally applied magnetic field, in a direction with a component in a plane perpendicular to the direction of the externally applied magnetic field, the method comprising: applying a first torque to the distal end of the medical device by creating magnetic moment at the distal end of the medical device; applying a second torque to the distal portion of the medical device; changing the first torque as the second torque is applied to cause the medical device to move in a direction having a component in a plane perpendicular to the direction of the externally applied magnetic field. 12. The method according to claim 11 wherein the magnetic moment is created by the application of an electric current to coils adjacent the distal end of the medical device. 13. The method according to claim 12 wherein the second torque is applied by means of a magnetic moment at a location that is separated by a flexible length of device from the location of application of the first torque at the distal end of the device. 14. The method according to claim 12 wherein the second torque is applied by rotating the proximal end of the medical device. 15. The method according to claim 12 wherein the second torque is applied by rotating an element attached to the distal end of the medical device. 16. The method according to claim 12 wherein the second torque is applied by inserting a shaped element into the medical device.

17. The method of claim 16 where the shaped element has an effective stiffness that is larger in value than that of the distal portion of the medical device and smaller in value than that of the proximal portion of the medical device. 18. The method according to claim 11 wherein the second torque is applied by rotating the proximal end of the medical device. 19. The method according to claim 11 wherein the second torque is applied by rotating an element attached to the distal end of the medical device. 20. A method of turning a medical device with the assistance of an externally applied magnetic field, in a direction with a component in a plane perpendicular to the direction of the externally applied magnetic field, the method comprising: applying an electric current to at least one coil to create a magnetic moment at the distal end of the medical device to apply a first torque at the distal end of the medical device by creating magnetic moment at the distal end of the medical device; and applying a second torque to the distal portion of the medical device. 21. The method of claim 20 wherein the second torque is applied by means of a magnetic moment at a location that is separated by a flexible length of device from the location of application of the first torque at the distal end of the device. 22. The method according to claim 20 wherein the second torque is applied by rotating the proximal end of the medical device. 23. The method according to claim 20 wherein the second torque is applied by rotating an element attached to the distal end of the medical device. 24. A method of turning a medical device with the assistance of an externally applied magnetic field, in a direction with a component in a plane perpendicular to the direction of the externally applied magnetic field, the method comprising: magnetically applying a first torque to the distal end of the medical device based upon a magnetic moment created in the distal end of the medical device and the applied magnetic field; mechanically applying a second torque to the distal portion of the medical device, the combined first and second moments acting on the distal portion of the medical device to cause it to turn in a direction with a component in the plane perpendicular to the applied magnetic field. 25. A method of turning a medical device with the assistance of an externally applied magnetic field, in a direction with a component in a plane perpendicular to the direction of the externally applied magnetic field, the method comprising: magnetically applying a first torque to the distal end of the medical device based upon a magnetic moment created in the distal end of the medical device and the applied magnetic field; magnetically applying a second torque to the distal portion of the medical device at a second location separated from the location of application of the first torque by a flexible length of device, based upon a magnetic moment created at the second location and the applied magnetic field; the combined first and second moments acting on the distal portion of the medical device to cause it to turn in a direction with a component in the plane perpendicular to the applied magnetic field. 26. A medical device for navigation in a static magnetic field, the device comprising a first element for selectively applying a first magnetic moment to the medical device, and a second element, spaced from the first for selectively applying a second magnetic moment. 27. The medical device according to claim 26 wherein the portion of the medical device between the first and second elements is sufficiently flexible to allow the medical device to bend. 28. A medical device for use in a magnetic field, the device having a proximal end and a distal end, an electrically powered element at the distal end, a photovoltaic cell electrically connected to the electrically powered element, and a fiber optic lead extending from the proximal end to the photovoltaic cell to provide light to the photovoltaic cell to power the electrically powered element.

29. The medical device for use in a magnetic field according to claim 29 wherein there are a plurality of electrically powered elements and at least one photovoltaic cell for each electrically powered element. 30. The medical device for use in a magnetic field according to claim 29 wherein the electrically powered element is at least one coil. 31. An elongate medical device adapted for navigation in a static field, the device comprising: an elongate body having a distal end; a plurality of magnetically actuable elements adjacent the distal end for creating a magnetic moment at the distal end of sufficient direction and magnitude to rotate the distal end of the device about its longitudinal axis; the portion of the elongate body adjacent the distal end being configured to assume a generally helical configuration upon rotation of the distal end, to thereby change the orientation of the distal end. 32. The elongate medical device according to claim 31 wherein the plurality of magnetically actuable elements comprise magnet coils. 33. The elongate medical device according to claim 31 wherein there are three magnet coils. 34. The elongate medical device according to claim 31 wherein the device is a medical catheter. 35. A method of magnetically navigating the distal end of an elongate medical device in an operating region relative to an externally applied static magnetic field, in a direction with a component in a plane perpendicular to the static magnetic field, the method comprising magnetically twisting the distal end of the device to cause the portion of the device adjacent the distal end of the medical device to assume a generally helical configuration and orient the distal end of the device in a direction with a component in a plane perpendicular to static magnetic field. 36. A method of magnetically navigating the distal end of an elongate medical device in an operating region relative to an externally applied static magnetic field, in a direction with a component in a plane perpendicular to the static magnetic field, the method comprising: creating a magnetic moment at the distal end of the medical device which causes the distal end of the medical device to rotate about its longitudinal axis to cause the portion of the medical device adjacent the distal end of the medical device to assume a generally helical configuration and orient the distal end of the device in a direction with a component in a plane perpendicular to static magnetic field. 37. The method according to claim 36 wherein creating a magnetic moment at the distal end of the medical device comprises energizing at least one of a plurality of coils adjacent the distal end to create a magnetic moment in a selected direction. 38. A method of navigating the distal end of an elongate medical device in a static magnetic field, the method comprising: selectively energizing at least one of a plurality of coils on the distal end of the medical device to create a magnetic moment in a selected direction at the distal end of the medical device in a desired direction relative to the static magnetic field; measuring a property of at least one of the plurality of coils to determine the configuration of the distal end of the medical device. 39. The method according to claim 38 wherein the resistance of the coils varies with the configuration of the distal end of the medical device, and wherein the step of measuring a property of the coil comprises measuring the resistance of at least one of the plurality of coils. 40. The method according to claim 38 wherein the step of measuring a property of the coil comprises measuring the voltage induced in the coil due to its movement relative to the static magnetic field. 41. A method of navigating the distal end of an elongate medical device in a static magnetic field, the method comprising: selectively energizing at least one of a plurality of coils on the distal end of the medical device to create a magnetic moment in a selected direction at the distal end of the medical device in a desired direction relative to the static magnetic field; selectively temporarily energizing one of the plurality of coils and measuring the effect on at least one of the plurality of coils to determine the orientation of the distal end of the medical device. 42. A method of navigating the distal end of an elongate medical device in a static magnetic field, the method comprising: measuring the three components of the static magnetic field along the axes of three orthogonal coils adjacent the tip of the device; computing the orientation of the coils relative to the static field; computing and applying coil currents required to change the orientation of the coils; advancing the catheter by an increment; repeating until the catheter tip reaches its desired destination.