WO2001024685A2 - Method for navigating magnetic devices in the body - Google Patents
Method for navigating magnetic devices in the body Download PDFInfo
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- WO2001024685A2 WO2001024685A2 PCT/US2000/041063 US0041063W WO0124685A2 WO 2001024685 A2 WO2001024685 A2 WO 2001024685A2 US 0041063 W US0041063 W US 0041063W WO 0124685 A2 WO0124685 A2 WO 0124685A2
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- magnet
- source
- patient
- magnetic
- field
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Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
- A61B1/00147—Holding or positioning arrangements
- A61B1/00158—Holding or positioning arrangements using magnetic field
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
- A61B1/005—Flexible endoscopes
- A61B1/01—Guiding arrangements therefore
-
- 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
- A61B34/70—Manipulators specially adapted for use in surgery
- A61B34/73—Manipulators for magnetic surgery
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M25/00—Catheters; Hollow probes
- A61M25/01—Introducing, guiding, advancing, emplacing or holding catheters
- A61M25/0105—Steering means as part of the catheter or advancing means; Markers for positioning
- A61M25/0127—Magnetic means; Magnetic markers
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M25/00—Catheters; Hollow probes
- A61M25/01—Introducing, guiding, advancing, emplacing or holding catheters
- A61M25/0105—Steering means as part of the catheter or advancing means; Markers for positioning
Definitions
- This invention relates to a method for navigating magnetic devices in the body, and in particular to a method for safely and efficiently navigating magnetic devices in the body using a moveable source magnet outside the body
- navigation of a magnet-tipped medical device takes into account the lag between the direction of the magnetic field applied by the source magnet and actual direction of the magnet tip It is known that the magnet tip will lag the exact direction of the magnetic field at its location by some finite amount This lag is the result of a restoring torque due to the stiffness of the attached device (e g , the guidewire, catheter endoscope, or other device to which the magnetic element is associated) This creates an ambiguity between the applied magnetic field and the actual direction of the magnet tipped device that can interfere with safe and efficient navigation
- the way this turn angle ambiguity is removed is to provide a lead angle for the magnetic field which accounts for the restoring, or turn-resisting, torque of the attached medical device
- information about the restoring stiffness of the medical device to which the magnet is attached is included in a computer program controlling the navigation Information of about the desired angle of turn and the desired radius
- a second aspect of this invention it is desirable to make turns in such a way as to maintain the magnet tip of the medical device in the same plane as the initial direction and the desired final direction avoiding the problem of "coning" in which the magnet tip swings out of the plane of the turn.
- This is particularly important when the navigation is through the parenchyma, although even when navigating through body lumens, such as blood vessels maintaining plana ⁇ ty during the turn can be important
- the movement of the source magnet usually accurately aligns the tip of the medical device in the desired final direction the movement of the magnet does not necessarily move the tip in the desired plane
- Fig 1 is a schematic diagram of a system for safely and efficiently navigating in accordance with this invention
- Fig 2 is an enlarged schematic diagram of the source magnet and patient
- Fig 3 is a schematic view of the source magnet showing some of the field lines
- Fig 3A is a schematic view of the source magnet shown in Fig 3 after a rotation about Fig 4 is a schematic view of the source magnet with a polar coordinate system superimposed at the center of the source magnet,
- Fig 5 is a vertical cross-sectional view of the source magnet, illustrating the magnetic field directions useful for a turn in an axial plane
- Fig 6A is a top plan view of the source magnet, illustrating the magnetic field directions useful for a turn from an axial plane at point A in Fig 5,
- Fig 6B is a top plan view of the source magnet, illustrating the magnetic field directions useful for a turn from an axial plane at point B in Fig 5,
- Fig 7A is a perspective view of a single magnet system having three degrees of freedom, for implementing the method of the present invention
- Fig 7B is a perspective view of the system shown in Fig 7A with the surface of constant magnetic field strength superposed thereon, illustrating some of the exclusion zones around which the magnet must be maneuvered,
- Fig 7C is a perspective view of a single magnet system having five degrees of freedom, for implementing the method of the present invention
- Fig 7D is a perspective view of the single magnet system shown in Fig 7C, from a different angle
- Fig 7E is a side elevation view of the single magnet system shown in Fig 7C, showing a work envelope in which the single magnet can move above a patient around the end of the patient and below the patient
- Fig 7F is a side elevation view of the single magnet system showing the magnet behind the patient s head and showing clearance required for the rotation of the single magnet
- Fig 7G is a side elevation view of the single magnet system showing the magnet work envelope in which the single magnet can translate and rotates in an annulus around a patient s body and the sweep volume required to accommodate rotations of the single magnet in the magnet work envelope
- Fig 7H is a side elevation view of the single magnet system showing the source magnet rotated in cardiac to provide better access for the single magnet to the patient,
- Fig 71 is an end elevation view of the single magnet system showing the work envelope in which the source magnet can move in an annulus around a patient's head and showing the clearance between the work envelope of the magnet and the imaging system,
- Fig 8 is a schematic view showing the frames of reference of the source magnet, the patient, and a locator device,
- Fig 9 is representation of the approximately spheroidal shape of a surface of constant field strength for a magnet having axial symmetry
- Fig 10 is a diagram of a constant field strength surface showing several trial moves of the source magnet useful in visualizing the efficient movement of the source magnet
- Fig 11 is a schematic view a patient and a source magnet, illustrating coordinates and vectors useful in navigating,
- Fig 12 is diagram of the coordinates for the source magnet, shown in Fig 11 illustrating the planes of rotation, and
- Fig 13 is a flow chart of the navigation inverse algorithm
- Fig 14 is a cross sectional view of a typical coil source magnet 38 showing a number of its magnetic field lines, and illustrating the gradient direction in two different locations,
- Fig 15A is a cross-sectional view of an aneurysm showing the relative orientations of an applied magnetic field and an applied magnetic gradient before a gradient turn, and
- Fig 15B is a cross-sectional view of the aneurysm showing the relative orientations of an applied magnetic field and an applied magnetic gradient after a gradient turn
- a magnetic medical device is safely and efficiently navigated in the body using an externally applied magnetic field
- the navigation system 20 for implementing the methods of this invention is shown schematically in Fig 1 as comprising a computer 22 having a keyboard 24, mouse 26 and joystick 28 for inputting the physician's instructions
- a display 30 is also connected to computer 22 to allow the physician to operate the system and monitor the navigation Imaging apparatus 32 is connected to the computer, which processes the signals and displays images of the operating region on the display 30
- a controller 34 is connected to the computer for controlling an articulation mechanism 36 that moves the source magnet 38 The magnet 38 in turn creates a magnetic field in the operating region 40 of the patient, and more particularly at the operating point 42 in the operating region, to control the orientation of a magnetic medical device 44 having a magnet tip 46
- the magnetic medical device 44 may be any medical device that the physician wants to navigate in the body, for example a guide wire, a catheter, an endoscope, etc
- the medical device 44 has a magnet tip 46 associated with it that is of sufficient size and shape to be responsive to an applied magnetic field and/or gradient from the external source magnet 38 for navigating the medical device
- the magnet tip 46 may be a permanent magnet or a permeable magnet In this description, it is assumed that the magnet tip 46 is a permanent magnet, with the magnet field aligned along the longitudinal axis of the magnet
- This invention could readily adapt this invention for use with permanent magnets of other configurations, or for use with permeable magnets
- the magnetic medical device 44 is located at a particular operating point 42 within a larger operating region 40 in the patient
- the operating region 40 is the region within the patient that the external source magnet 38 can apply a sufficient magnetic field to affect the direction of the magnetic medical device 44
- the source magnet 38 may be a permanent magnet, but it is preferably an electromagnet, and more preferably a superconducting electromagnet
- the source magnet 38 may actually comprise more than one magnet
- the source magnet 38 is mounted on an articulation device 36 that can move the magnet 38
- the articulation device 36 can translate and/or rotate the source magnet
- the articulation device might permit two rotations of the source magnet, or perhaps two rotations of the magnet combined with a single translation, for example toward and away from the patient
- the articulation device might permit two rotations of the source magnet, and three translations of the source magnet in three mutually perpendicular directions
- the imaging apparatus 32 may be, for example, bi-planar fluoroscopy equipment for imaging the operating region 40 Bi-planar fluoroscopy allows the location and sometimes the location and the direction of the magnetic medical device 44 (or at least the distal end of the magnetic medical device) to be determined
- a proper turn is defined as one in which the distal end of the magnetic medical device 44 remains in the plane containing the initial direction of the magnetic medical device and the desired final direction of the magnetic medical device It is desirable to move the source magnet 38 in such away as to effect the turning of the magnetic medical device 44 in a plane
- some of these possible movements will cause the magnetic medical device 44 to sweep out of the plane of the proper turn, in a motion known as "coning" that can unnecessarily disturb surrounding tissue
- Others of these possible movements will be inefficient because of the significant movement required of the source magnet 38
- Still others of these possible movements will be prohibited by practical considerations, such as limitations on the rotation or translation of the magnet, interference with the equipment surrounding the magnet and the patient, imaging equipment, and imaging beams It is important to select a magnet motion that is both safe, / e causes a "proper" turn and efficient,
- safe and efficient navigation is achieved by taking into account the lag between the actual orientation of the medical device 44 and the orientation of the magnetic field applied by the source magnet 38
- Equation (1) will apply exactly to the moment, but only inexactly to a fixed geometrical aspect, say the axis, of an elongated permeable magnetic tip This is because m shifts with B in a permeable magnet
- the magnet tip 46 is a permanent magnet magnetized along its longitudinal axis, unless otherwise specified
- a person of ordinary skill in the art could readily calculate characteristics of a permeable tip moment, and use them in a similar fashion
- the need for a lead torque must be anticipated
- the desired angle of turn can be input, for example, using two point or three point navigation methods such as those disclosed in co-pending U S patent application Serial No 09/020,798, filed February 9, 1998 entitled "Device and Method for Specifying Magnetic Field for Surgical Applications", incorporated herein by reference, or co-
- the source magnet(s) 38 employed in magnetic navigation are designed so as to have fields which can be represented unambiguously
- the articulation mechanism 36 for moving the source magnets 38 is designed to maneuver a source magnet to a position and orientation needed to apply the required field and/or gradient at the operating point 42 where the magnet tip 46 is located
- the sometimes complex field shape of source magnet 38 generally demands a complex approach to moving the source magnet to turn magnet tip 46, including translation and/or rotation of the source magnet
- known symmetries of the source magnet 38 can reduce its complexity, cost, and weight of the articulation mechanism
- the field of a common solenoid coil has complete symmetry about its longitudinal axis, and thus rotation about the longitudinal axis does not change the field at the operating point in the patient
- a first step in calculating a safe, efficient turn is the definition of the plane in which the magnet tip remains during the turn This plane can be specified as a unit vector n perpendicular to it and determined from the equation
- n (V ⁇ x V 2 )/
- Vi represents the initial direction
- V 2 represents the desired final direction
- the proper movement of the source magnet 38 may involve translations and/or rotations
- the method incorporating "Euler angles” is a convenient and well-known tool for treating the rotations of an object such as the source magnet Goldstein, "Classical Mechanics” (Second Edition), Addison-Wesley Publishing Co. (1980), incorporated herein by reference, describes matrix operations for keeping track of vectors in such rotations It is significant that these rotations are "noncommutative", meaning that sequential rotations lead to a final direction which depends on the order of the individual component rotations, / e., the order of the rotations is important This noncommutative nature of rotational operations in mechanics must be taken into account when implementing rotations
- a source magnet 38 in the form of a simple coil, is shown with a few of its field lines, which are symmetrical about its longitudinal axis (Axis 1 )
- the initial position and orientation of tip magnet 46 is represented by vector Vi and the desired final position and orientation of the tip magnet after a 90 degree turn is represented by vector V 2 after the turn
- Each point on each field line of source magnet 38 is a magnetic field vector B, and each field line is in a plane that that contains the coil axis (Axis 1 ) and is referred to as an "axial plane "
- the magnet tip 46 will orient itself exactly along a field line at its location This implies that the initial position before a turn, and the desired final position after a turn, lie along a field line of the source magnet 38 This assumption that V lies along B is important where, for example, the imaging system used to monitor the procedure can only locate the position of the magnet tip 46, and not its orientation.
- the magnet tip 46 is small enough to be represented approximately by a vector at a point.
- FIG 3 and 3A show two alternate ways to rotate a field vector parallel to Vi in a patient to a new direction parallel to V 2 at essentially the same point in the patient
- a translation of -Vt upward in the figure of the source magnet 38 to relocate the operating point from Bi to point B 3 will accomplish this 90 degree turn of the field at a given point in the patient.
- Fig 3A the source magnet 38 is shown rotated clockwise 90 degrees about Axis 2, which brings field point B into a position parallel to the desired direction V 2 . It may or may not be necessary to translate the source magnet 38 to bring the new location of B to the starting position of Bi, i.e , to the turning point in the patient.
- the rotation and translation of the source magnet 38 preferably occur simultaneously, retaining the proper relationship between translational speed and rotational angular velocity, so as to maintain the field direction (with the magnet tip 46 crossing from field line to field line of the source magnet 38 as necessary while the source magnet rotates and translates) so that the directional change of the field lines crossing the region between point Vi and point V 2 smoothly turn the magnet 46 as the medical device 44 progressed in feeding the magnet tip forward through the turn If the turn is very sharp, the vectors would remain nearly at a point, and only change direction
- one of the many possible movements (translation and/or rotation) of the magnet may be more efficient than the others
- one of the many possible movements (translation and/or rotation) of the magnet may be more efficient than the others
- the selected movement can not always be the most efficient turn, and structural limitations of the magnet such as placement of the cryocooler, power connections, etc , will sometimes prevent the use of the most efficient turn In such cases a proper movement will not be the most efficient, but it should at least meet the requirement of maintaining the magnet tip in the plane of the turn
- a spherical coordinate system is useful in describing the position of the location of Vi relative to the source magnet 38
- r is a vector from the center of the source magnet 38 to the operating point 42 (/ e , the location of the magnet tip 46)
- ⁇ is the polar angle from the axis of the source magnet (Axis 1) down to the line r
- ⁇ is the azimuthal angle around Axis 1 of the plane of r and Axis 1 , relative to an arbitrary fixed reference plane containing the axis
- the first type are the axial planes, which are any planes that contain both the field line and the magnet axis
- the second type are planes perpendicular to the axial plane
- This second type of plane lies on the midplane of the magnet, it is referred to as the equatorial plane
- a useful totally orthogonal system would have two other axes perpendicular to the source magnet's axis (Axis 1 ) and to each other These axes are indicated as Axis 2 and Axis 3 in Fig 4, and they lie in the equatorial plane of the source magnet 38
- Axes 2 and 3 are shown schematically in Fig 4, and could be physically implemented with a gimbal apparatus to allow the source magnet to rotate about these two axes
- a usable articulation mechanism need only have two of these three
- m is the moment of the dipole (now representing the source magnet 38) and falls along the source magnet axis (by convention the z-axis)
- r is a vector between m (at the coil center) and the operating point in the patient, and r is its magnitude
- m is located and aligned along the z-axis in the most efficient use of that coordinate system
- the dot product m r is then mr cos ⁇ , where m is the magnitude of the magnetic moment
- n a (V ⁇ x Va)/
- V a is a vector along the axis of the source magnet 38
- This plane is chosen for convenience because it contains Vi, and it is magnetically the same as any other plane containing the axis of the source magnet 38 Therefore a vector Vi located in a plane at any azimuthal angle ⁇ will satisfy equation (4) for this case
- n a happen to be parallel to Axis 2 or Axis 3 of Fig 4
- the most general rotation can be formed from a trigonometric combination of rotations about these two axes
- the axis n a were found in one case to be 45 degrees clockwise (looking down on the coil) from Axis 2, it would mean that the front of the coil between Axis 2 and Axis 3 would tilt up to perform a clockwise rotation about the n a axis Looking toward these axes, Axis 2 would rotate counterclockwise, and Axis 3 would rotate clockwise (looking along this unit vector) In this case, both axes would rotate at the same angular rates
- Fig 5 illustrates this turn in an axial plane (with Vi and V 2 separated by an exaggerated distance)
- the starting point is labeled A, and B and C identify two other points around that field line which passes through A
- A For clarity, only a single field line is shown (The circular shape shown for the field line is not intended to be a highly accurate representation of the shape of a field line from a real coil )
- the plane of turn, designated by n a is oriented out of the page
- the field line at point B is parallel to V 2 , and a simple translation of the source magnet 38 to bring point B to the location of V 2 would accomplish a turn of the magnet tip 46 in the patient
- the translation would have to be judiciously chosen on some curve in order for the field strength to remain unchanged during the turn It is desirable that the field strength remain constant to reduce variations in the direction of the magnet tip 46
- the translational path should e in the starting plane With these choices, the turn would be a proper one albeit probably not efficient
- the translational path would be determined by moving from point A to point B in the field line of equation (3) or an accurate line calculated for a real coil and then translating the source magnet in the inverse direction of that path To maintain the curve as a proper turn would involve a choice of fixed ⁇
- An obvious choice for an efficient (although perhaps not the most efficient) proper turn in this case would be a translation with ⁇ and magnitude B fixed at each step of the turn and with ⁇ changing smoothly and monotonically
- Vi is in an axial plane but V 2 is perpendicular to that plane so that rotation about a different virtual axis n 2 is necessary Since n a still defines the starting plane, the vector axis of rotation, n 2 , is perpendicular to both Vi and n a
- n 2 (Vi x n a )/
- Figs 6A and 6B Two turns for this second general case are illustrated in Figs 6A and 6B, which are views looking down on the axis of the source magnet 38
- a first turn of the second prototypical case is illustrated in Fig 6A where the starting location is shown as a projection of point A of Figure 5 onto this view
- the field rotation is shown as n 2 , out of the paper
- FIG. 6B A second turn of the second prototypical case is illustrated in Fig 6B, where Vi is again in the axial plane, but now is located as point B of Fig 5, / e , pointing into the paper in this view Now n 2 points away from the coil
- This turn is the simplest, and is accomplished purely by rotating the coil about the axis from the center of the magnet out to the location of Vi For generality, this is shown as different from Axis 2 or Axis 3
- Such an axis is established trigonomet ⁇ cally in the same manner as described above (A prior pure rotation about the coil axis could establish one of these as the turn axis without disturbing the magnet tip, but with some simpler articulation mechanisms, such a rotation might have been considered generally unnecessary and therefore not available)
- the procedure works in the reference frame of the source magnet after the desired vector in the patient coordinate frame is transformed, and then calculates and transforms each necessary field vector into the patient frame Sometimes this can be done automatically with search methods and equations
- the procedure can involve steps in purely rotating a field vector through a turn from Vi to V 2 in the patient frame, using operations in the source magnet frame and taking care that these operations take into account when a rotation in that frame will in addition require a translation of the source magnet 38 in the patient frame
- An external locating means can be provided to connect the location and orientation of the frame of reference of the source magnet to the patient frame
- a locating means is disclosed in Van Steenwyk et al U S Patent No 4 173,228, issued November 6 1979, for Catheter Locating Device incorporated herein by reference
- unp ⁇ med coordinates (x, y, z) will designate the patient frame, and primed coordinates (x', y', z
- the transformation problem has five degrees of freedom (although, depending upon the application, it is not necessary that the articulation device must have all of these degrees of freedom)
- the translation of a vector between two reference frames has 3 components, and the rotation of a vector has 2 components (polar and azimuthal angles)
- the field vectors to be transformed need not be rotated around an axis which is collinear with their own directions
- the operating position location in each frame of reference can be specified as a vector relative to the origin in that frame of reference, and a positional transformation in a given frame is then a vector addition or subtraction (There is no need to rotate the position vectors except when dealing with exclusion zones )
- the field vectors must in general be rotated and translated
- the location vector is simply a vector from a fixed origin in that frame out to the operating point (where the magnet tip 46 is located)
- the origin for the location vector will change each time the source magnet is translated as described below Fig 8 shows frame axes in these frames plus the locator frame
- the origin of the patient frame could be at the operating point 42 where the magnet tip 46 is located, and would move as that point moved
- a locator system operating throughout the duration of the procedure would maintain information about the locations of (0, 0, 0) and (0', 0', 0') relative to its own fixed frame (0", 0", 0"
- Fig 9 illustrates a surface 100 of constant field strength for a source magnet 38, along with a few vectors 102 on each of several "latitude planes" 104 It is seen that on a given latitude plane the axial symmetry of the magnet assures that the field line vectors 102 make a constant angle with the surface 100, and also with the magnet axis Each field line lies in a plane which contains the magnet axis Thus changes in field direction, on the constant field surface, require some component of motion along a longitudinal line
- the movements of the source magnet for a proper turn are preferably first carried out
- the movement of the source magnet to effect the turn from Vi to V 2 is determined This is conveniently done with a computer processor
- the angle by which the direction of the magnet tip 46 varies from the plane containing Vi and V 2 is then determined If this amount does not exceed a predetermined threshold for acceptable deviation, e g , 5 degrees, then the articulation mechanism 36 can be operated by controller 34 under the direction of the computer processor 22 to make the determined movement of the source magnet 38 If the turn from Vi to V 2 is small, for example, 10 degrees or less it is likely that only one step of the turn is needed, as any coning during the turn will be small enough that it generally will not interfere with navigation However if the amount by which the direction of the magnet tip 46 vanes from the plane of Vi and V 2 by more than the predetermined threshold, then the turn is broken up into a number of sub-turns Of course, sub-turns could be used automatically, without testing whether they are needed
- One method of determining these intermediate vectors is to make an even-sized division of the angle of turn, constraining each individual vector to be in the plane formed by Vi and V n
- Other methods of determining these intermediate vectors include unequal divisions of the turn angle based upon where the magnet tip direction deviates from the desired plane of the turn by more than the predetermined threshold, or some lesser value
- V ⁇ ', V 2 ', , Vn' will not lie in a plane, even if V ⁇ , V 2 , ,V n d ⁇ d
- Each pair of angles, Vi', V 2 ', or V 2 ',V 3 ', etc will form a plane, which can be determined as in equation (2) above Resulting rotations Vi to V 2 , or V 2 to V 3 , etc will not generally lie in a single plane, but since these are small rotations they will have acceptable individual coning, by decision of step 2 above Choice of the starting vector in the patient plane, however, will assure that the overall turn is nearly planar
- the processor 22 determines a movement of the magnet for each of the sub- turns
- the magnet makes a rotation from V, to V,+ ⁇ the point on the constant field surface will in general move, ; e , translate relative both to (0', 0', 0 ) and to (0, 0, 0)
- the magnet rotation needed to make this small turn will not in general be uniquely determined, which is common with inverse problems
- the processor will calculate such a translation for the small angle rotation V, to V,+ ⁇ , using a series of trial rotations in a plane tangent to the surface at the initial point, in the neighborhood of the vector V, , as shown in Fig 10
- each vector associated with a rotation shown in this frame corresponds to a rotation and translation of the point in the patient reference frame That is, as the field vector position in the magnet frame changes from P, to P,+ ⁇ due to rotation in the magnet frame, the reverse transformed position in the patient frame will need in addition to translate if the original rotation in the patient frame [Goldstein equation (4-46)] is
- the processor selects from the trial rotations one which is most efficient, i.e , the trial which requires the smallest translation of the magnet to accomplish the (partial) turn in the patient frame without a translation in the patient frame
- a weighting algorithm can be developed based upon the "costs" of certain rotations over other rotations, certain translations over other translations, and of rotations over translations
- the exclusion sheet will be dynamic, i e a joint overlap of sheets for the patient region and for the magnet region will be needed to prevent interference
- the processor 22 will then cause the articulating mechanism 36 to turn and/or translate the source magnet 38 successively through the angles from V 2 ' , V n ', which will turn the angle in the patient from through V 2 , V n - ⁇ to V n .
- Fig 11 is a diagram showing a patient, a single magnet source of external magnetic field, the location for a small magnet tip to be guided in a medical procedure, and the definition of a few of the coordinates and vectors to execute the above-described type of navigation in one preferred embodiment
- a magnetic field B is to be applied with given magnitude and orientation to create a turn
- Fig 12 shows additional useful parameters and defines coordinates for the single magnet and field point (the operating point represented by position vector r') at which the field vector B is to be specified, and which is to be provided by the articulated magnet It also shows planes which make the geometric attributes of this motion easier to visualize
- the magnet position in this three degree-of-freedom problem is uniquely specified by the offset z 0 (distance of the center of the coil from the closest point of patient anatomy), and the polar and azimuth angles made by the magnet symmetry axis z relative to the translated patient coordinate system (x, y, z') system
- this method shows how to make the search for one degree of freedom trivial by using an analytical expression for one of the variables
- This method takes advantage of the fact that the field vector B must lie in the plane defined by the vectors z m and p m , due to the cylindrical symmetry of the source magnet (either a coil magnet or a permanent magnet)
- the y-z plane is horizontal, x is vertical, y is horizontal to the patient's right, and z is along the patient body axis
- a second set of coordinates is used, where x, y, z' with origin 0' is displaced along z by an amount z 0 from the patient origin 0 shown in Fig 11
- the x,y,z and x,y,z' planes are vertical and are perpendicular to the patient body axis, at the top of the patient's head and through the magnet center, respectively
- the operating point 42 (or P) is at r' in the x, y, z' coordinate system ⁇ 0 , ⁇ 0 are the spherical polar coordinates of B in a system with polar axis along z', and azimuthal angle measured from the x,z' plane
- B is shown both at its true location P and at the origin 0' where these angles can be shown clearly
- ⁇ a , ⁇ a are the polar and azimuthal angles of the magnet axis z m in the same spherical polar coordinate system as the patient frame, with the polar axis along z and the azimuth measured in the x,y plane and relative to the x-axis
- Zm, p are the cylindrical coordinates of the operating point 42 in an axially symmetric magnet coordinate system, corresponding to the vectors z m , p m
- the field point at x, y, z', specified as the vector r', is identified as P
- the point of intersection of a line parallel to the z- axis and passing through P with the line of projection of r' on the x, y plane, is identified as A
- the polar angle of r' in patient coordinates is identified as ⁇ '
- the polar angle of r' in magnet coordinates is identified as ⁇
- the point on the z-axis at z 0 + z is identified as K
- the first, O'APK is a parallelogram which forms a plane perpendicular to the x, y plane and going through both the z-axis and the field point P r' falls in this plane
- ⁇ a is a precession angle of the magnet axis the azimuthal rotation about z (measured from the x,z plane) of the line of the projection of vector z m representing the magnet axis, on the x-y plane
- the method searches magnet azimuth and magnet offset, computes a polar angle that insures that the B vector lies in a plane containing the magnet axis and the field point vector, selects an offset that insures the correct magnitude of B, and completes the azimuth search when the computed and specified B vectors are aligned in space
- Example A The derivation and details of this Example A are as follows The vectors r', z m , and B are given in their polar representations by
- angles of the position vector r are given in terms of its Cartesian coordinates by
- the polar and azimuth angles ⁇ a and ⁇ a of the magnet axis are unknowns to be determined.
- the polar and azimuth angles of the B vector, ⁇ 0 and ⁇ 0 are specified by the user, or are calculated from its Cartesian representation.
- the polar angle ⁇ a can be computed mathematically in terms of the other angles by imposing the condition that the B vector lie in the Zm-r'-pm plane. This condition is necessitated by the symmetry of the coil. It is stated mathematically as the null dot product of B with a vector perpendicular to that plane
- ⁇ a tan- 1 ⁇ [sin ⁇ ' s ⁇ n ⁇ 0 sin ( ⁇ '- ⁇ 0 )]/[cos ⁇ 0 sin ⁇ 'sin ( ⁇ '- ⁇ a )+
- B(r') B p (pm, Zm)pm/pm + B z (p m ,Z m )Z m /Zm (13)
- the specified and computed unit vectors are obtained from equations (7) and (13) by dividing by the specified field magnitude and field magnitude computed by Equation (18), respectively When their dot product is equal to unity, within the specified accuracy, the azimuth search is complete
- Fig 13 is a flow chart of a program which executes the algorithm just presented to provide the inverse calculation for articulating a magnet having axial symmetry
- a preferred embodiment of a more general search which allows an incremental proper rotation of a field vector is presented below in example (B)
- An outline of an embodiment for a general 5- degree-of-freedom search is also presented below in example (C)
- One versed in the art will see how to modify these to provide inversion algorithms to articulate a magnet with any number of degrees of freedom greater than 3
- the azimuthal rotation might be limited to 360°
- the polar rotation limited to 180°
- the Z-axis translation might be limited to 8 5 inches to about 14 5 inches Motion is selected to avoid possible problem with navigation due to rotational stops in azimuthal direction
- Navigation in accordance with this invention can be conducted in such a way as to use the source magnets to pull the medical device in addition to orienting the distal end of the medical device
- Magnetic force is generated by the rate of change of magnetic field strength with position This is commonly called a "magnetic gradient" even though a vector magnetic field does not have a gradient in the usual mathematical sense
- a magnetic field is a vector field, and a gradient operates only on a scalar field, that is a scalar function of position What is usually meant by gradient is not gradient of the magnetic field, but the gradient of a scalar product of the magnetic moment vector m of the tip, and the magnetic field vector B at its location, i e , (m B) What is intended here, and generally in magnetic work, is the application of the force equation
- Fig 14 shows a cross section containing the axis of a typical coil source magnet 38 with a number of its magnetic field lines
- the arrows on the field lines show the direction of the magnetic field B at points along each line
- the gradient of the field is shown in two locations, at points A and B, by double arrows
- the directions of the arrows show the
- m B becomes simply the arithmetic product of the magnitudes of the two vectors mB
- a small magnet tip 46 on a magnetic medical device is not totally free rather it is somewhat restrained by the device with which it is associated, as well as any surrounding tissue with which it is in contact
- catheters, guidewires, and electrodes etc all have inherent stiffness that would restrain the alignment of the magnet tip with the field direction, in which case the product m ⁇ B will be somewhat smaller than mB, which is the maximum possible value
- a free magnet tip 46 at point A will be oriented with its moment aligned along the field which is along the axis of the source magnet 38, and the magnet will be pulled along the same direction This is the "longitudinal gradient" or alternatively the “longitudinal field " It is also sometimes called an "axial gradient "
- the free magnet tip 46 will have its moment m aligned along B and therefore parallel to the magnet axis, but the gradient will pull the magnet tip towards the source magnet
- a magnetic pulling force could be applied after navigation of a magnet tip to a given location, for pulling magnetic embolic materials into an aneurysm (The magnetic medical device may or may not be removed from the area before applying the pulling force)
- Either a transverse or longitudinal gradient may be used
- the computer processor 22 which controlled the initial navigation will have information not only about the orientation of the magnet tip 46, but about the orientation of the source magnetic field and gradient That is the processor will have information whether, at the operating point 42 the gradient is transverse or longitudinal
- the physician will, at the start of the procedure, input the desired method of using the gradient, and therefore at the completion of navigation (and after removal of the magnet tip if necessary) the source magnet 38 will be oriented so that the gradient is in the desired direction
- the processor 22 will have information about the current state of the magnetic field and gradient Given the desired state of the relative directions of magnetic field and gradient, the processor can determine and direct a movement of the source magnet for the purpose of changing the direction of the gradient relative to the direction of the field, or vice versa This relative movement between gradient direction and field direction is called a "gradient turn"
- Fig 15A shows a cross section of an aneurysm with a magnetic field B represented by field lines pointing away from the back wall of the aneurysm, and a magnetic gradient represented by a double arrow, pointing toward the back wall of the aneurysm
- a magnetic field B represented by field lines pointing away from the back wall of the aneurysm
- a magnetic gradient represented by a double arrow
- Fig 14 shows a gradual change in the spacing of lines moving from a longitudinal gradient at point A to a transverse gradient at point B That is, there can be a gradual change in the gradient of the scalar product m .
- the navigation program implemented by the processor contains either an equation or a lookup table for the source magnetic field B of the magnet in the source magnet coordinate system
- the location of the magnet tip 46 in the patient coordinate system is transformed into the source magnet coordinate system as described in earlier, so that B is known at the operating point 42 in the patient coordinate system from a further inverse transformation
- the force F from equation (1) is determined from this information knowing m, for the current source magnet position and orientation, and for a series of trial rotations and translations
- the only additional requirement is knowledge of, or an assumption of the direction of m during the gradient turn From these trial calculations, the choice of a gradient turn of the source magnet is made in the same manner as was described for a safe navigation turn above If, due to limitations in accuracy, there is significant error in assumed change in the direction of m, it may or may not be necessary for a locator or imaging system to measure the change in direction and update the processor
- the system 200 comprises a patient bed 202 for supporting the patient, an imaging system 204 for providing images of the operating region within a patient on the patient bed 202, and a magnet system 206 for projecting magnetic fields and gradients into the operating region in a patient on the patient bed 202
- the imaging system 204 comprises a C-arm apparatus 208, mounting two pairs of imaging beam source 210 and imaging plates 212, which are preferably mutually perpendicular
- the C-arm apparatus includes a generally L-shaped support 214 that is mounted on base 216 for pivoting about a generally vertical axis, an intermediate support 218 that is mounted on L-shaped support for rotation about a generally horizontal axis, and a C- shaped bracket 220 that is mounted on the intermediate support for rotation about the central axis of the C-shaped bracket
- the magnet system 206 comprises a source magnet 222 and an articulation device
- the source magnet is preferably a superconducting electromagnet, with associated cryocooler 226
- the housing conventionally used is omitted to show the configuration of the magnet
- the articulation device 224 provides movement of the magnet 222 with three degrees of freedom (two rotations and one translations)
- the articulation device 224 comprises a base 228 that is mounted on tracks 230 for translation toward and away from the patient bed, thereby allowing translation of the magnet 222 toward and away from the operating region within a patient on the patient bed 202 (i e along the z axis as described above)
- the articulation device 224 includes a C-shaped arm 232 that is mounted on the base 228 for rotation about a first generally horizontal axis, which allows a first rotation of the magnet 222
- the magnet 222 is also mounted to the C-shaped arm 232 for rotation about a second axis generally perpendicular to the first generally horizontal axis, which allows a second rotation of the magnet
- Fig 7B shows the system 200 with a surface 234 of constant field strength projected around the magnet 222
- the cryocooler 226 projects through the surface 234
- Rotations and translations that would attempt to bring this exclusion zone to the operating region within the patient must be prohibited, because the cryocooler would strike the patients
- Other rotations and translations that would bring this exclusion zone into contact with other structures in the operating room for example with the imaging system 204 or the articulation device 224, or interfere with the imaging beams from the imaging system 204, must also be prohibited as described below
- Another embodiment of system for carrying out navigations in accordance with the methods of this invention is indicated generally as 300 in Figs 7C through 71
- the system 300 comprises a patient bed 302 for supporting the patient, an imaging system 304 for providing images of the operating region within a patient on the patient bed 302 patient, and a magnet system 306 for projecting magnetic fields and gradients into the operating region in a patient on the patient
- the imaging system 304 comprises a C-arm apparatus 308, mounting two pairs of imaging beam source 310 and imaging plates 312, which are preferably mutually perpendicular
- the C-arm apparatus includes a generally L-shaped support 314 that is mounted on base 316 for pivoting about a generally vertical axis, an intermediate support 318 that is mounted on L-shaped support for rotation about a generally horizontal axis, and a C- shaped bracket 320 that is mounted on the intermediate support for rotation about the central axis of the C-shaped bracket
- the magnet system 306 comprises a source magnet 322 and an articulation device 324 for translating and rotating the source magnet 322
- the source magnet 322 is preferably a superconducting electromagnet with associated cryocooler 326, the magnet is surrounded by a housing 328
- the articulation device 324 provides movement of the magnet 322 with five degrees of freedom (three rotations and two translations)
- the articulation device 324 comprises a base 330 that is mounted on tracks 332 for translation toward and away from the patient bed 302, thereby allowing translation of the magnet 322 toward and away from the operating region within a patient on the patient bed 302 (i.e., along the z axis as described above)
- a turntable 334 is mounted on the base 330 for rotation about a generally horizontal axis
- the turntable 334 has a track 336 extending diametrically across it for slidably mounting a support arm 338, so that the support arm can translate within the track
- the magnet is mounted on the end of the
- Fig 7E shows the system 300 with a work envelope 350 surrounding the patient, defining the volume in which the articulation device 324 can translate the magnet 322
- Fig 7F shows the system 300 illustrating the range of motion of magnet, illustrating a maximum 360 degree rotation of the magnet 322 about the C-shaped 340 (not shown in Fig 7F), and a maximum 180 degree rotation of the C-shaped arm 340, relative to the support arm 338
- Fig 7G shows the system 300 illustrating a magnet work envelope 352 within which the magnet 322 can be translated and the sweep volume 354 that must be clear to accommodate the cryocooler 324 as the C-shaped support arm 340 and the magnet 322 rotate for a given translational position of the magnet in the work envelope 352
- Fig 7H shows the system 300 illustrating a rotation of the magnet 322 to provide access for the magnet to project the desired magnet field and/or gradient in the operating region in a patient on the patient bed 302
- Fig 71 shows the system 300 and illustrates the clearance between the work envelope around in the patient in which the magnet 322 moves and the support for the imaging system
- the magnetic navigation method of the present invention may be employed, there will be congestion in the region surrounding the patient, making it difficult to articulate a source magnet in ways desired to provide guiding fields in all needed directions and at required magnitudes
- the magnet and its accoutrements cannot be translated or rotated in such a way that they impinge upon the patient or any of surrounding medical equipment, including for example the patient bed and the imaging equipment, or interfere with the imaging beams
- the processor 22 can control the movement of the source magnet 38 so that the interference does not occur, and can even anticipate interferences for a planned path of a number of turns for the navigated object
- the processor 22 can determine the necessary safe and efficient steps, or component parts of a step, in a path of navigation Each such step requires rotation and/or translation of the source magnet, and the processor calculates these by transforming the desired step, in the patient reference frame, to its geometrical counterpart in the source magnet reference frame, and calculates efficient and safe source magnet motions to accomplish the field changes in the patient reference frame, as described herein The following steps can be implemented to avoid these interferences
- the geometric "edge” of the patient, imaging equipment, etc on the side facing the source magnet 38 can be thought of as a somewhat complex "sheet”
- This sheet can be defined in the coordinates of the patient reference frame by a set of vectors from the origin of that frame to appropriate points on the "patient sheet”
- the number and distribution of these vectors can vary depending on the complexity of the sheet and the desired geometrical resolution in its description Nevertheless, they can be stored in the processor memory, for example as a look-up table, or instead as a set of equations for geometrical objects
- a ' source magnet sheet can be described in the articulatable (moveable) magnet reference frame as a set of vectors in those coordinates
- the processor 22 can test for overlap or touching of the two sheets by transforming either one to the reference frame of the other Moreover, the processor can determine (and present on a display if desired) the closest distances if there is not yet an interference
- "trial” moves shown as P, and P n , etc are rotations and/or translations of the source magnet 38 which will be able to make a given direction change of the field B in the patient (given sufficient number of degrees of freedom) at the point operating point 42 where the magnet tip 46 is to be navigated, while maintaining a constant field magnitude B
- each of these vectors P corresponds to the same or nearly the same turn of B in the patient and they differ only in the way they use the excess degrees of freedom of the articulation mechanism 36 (A result of this will be a change in the "efficiency of the turn which can be defined as the amount of turning and translating of the source magnet to provide such a safe and correct (planar) turn of the vector B in the patient )
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP00978896A EP1223883A4 (en) | 1999-10-04 | 2000-10-03 | Method for safely and efficiently navigating magnetic devices in the body |
AU16306/01A AU1630601A (en) | 1999-10-04 | 2000-10-03 | Method for safely and efficiently navigating magnetic devices in the body |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US15761999P | 1999-10-04 | 1999-10-04 | |
US60/157,619 | 1999-10-04 |
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WO2001024685A2 true WO2001024685A2 (en) | 2001-04-12 |
WO2001024685A3 WO2001024685A3 (en) | 2001-08-30 |
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Application Number | Title | Priority Date | Filing Date |
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PCT/US2000/041063 WO2001024685A2 (en) | 1999-10-04 | 2000-10-03 | Method for navigating magnetic devices in the body |
Country Status (3)
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EP (1) | EP1223883A4 (en) |
AU (1) | AU1630601A (en) |
WO (1) | WO2001024685A2 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2009029523A1 (en) * | 2007-08-24 | 2009-03-05 | Boston Scientific Scimed, Inc. | Magnetically steerable catheter assembly |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5681260A (en) * | 1989-09-22 | 1997-10-28 | Olympus Optical Co., Ltd. | Guiding apparatus for guiding an insertable body within an inspected object |
US6157853A (en) * | 1997-11-12 | 2000-12-05 | Stereotaxis, Inc. | Method and apparatus using shaped field of repositionable magnet to guide implant |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2001522623A (en) * | 1997-11-12 | 2001-11-20 | ステリオタクシス インコーポレイテツド | Movable magnetic guidance system and device and method of using same for magnetic assisted surgery |
US6014580A (en) * | 1997-11-12 | 2000-01-11 | Stereotaxis, Inc. | Device and method for specifying magnetic field for surgical applications |
-
2000
- 2000-10-03 EP EP00978896A patent/EP1223883A4/en not_active Withdrawn
- 2000-10-03 WO PCT/US2000/041063 patent/WO2001024685A2/en active Application Filing
- 2000-10-03 AU AU16306/01A patent/AU1630601A/en not_active Abandoned
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5681260A (en) * | 1989-09-22 | 1997-10-28 | Olympus Optical Co., Ltd. | Guiding apparatus for guiding an insertable body within an inspected object |
US6157853A (en) * | 1997-11-12 | 2000-12-05 | Stereotaxis, Inc. | Method and apparatus using shaped field of repositionable magnet to guide implant |
Non-Patent Citations (1)
Title |
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See also references of EP1223883A2 * |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2009029523A1 (en) * | 2007-08-24 | 2009-03-05 | Boston Scientific Scimed, Inc. | Magnetically steerable catheter assembly |
US8394091B2 (en) | 2007-08-24 | 2013-03-12 | Boston Scientific Scimed, Inc. | Magnetically steerable catheter assembly |
Also Published As
Publication number | Publication date |
---|---|
AU1630601A (en) | 2001-05-10 |
EP1223883A2 (en) | 2002-07-24 |
WO2001024685A3 (en) | 2001-08-30 |
EP1223883A4 (en) | 2007-10-17 |
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