Magnetic vascular defect treatment system

Device and method for treating vascular defects by filling the defect with magnetically controlled devices. Vascular defects include aneurysms and arteriovenous malformations (AVMs), particularly in the head and neck of the patient. The magnetic devices fall into categories of ferro-fluids, magnetic objects and magnetic coils. Ferro-fluids consist of a magnetic particulate that is combined with a glue or polymer agent. The ferro-fluid is magnetically held and solidified, while the adhesive agent cures. Magnetic objects such as polyvinyl alcohol (PVA) coated magnetic particles can be injected into a vascular defect such as an AVM. The magnetic objects are attracted into pre-selected AVM branches by the application of a magnetic gradient. Magnetic coils are magnetically steered and held within an aneurysm to improve coil delivery. Large neck aneurysms are particularly assisted by this method, due to the need to steer the coil towards the center of the aneurysm and to hold the coils within the aneurysm. Various methods of magnetically controlling these devices are described to cover a broad range of new treatment approaches.

FIELD OF THE INVENTION
 The present invention relates generally to both a method and related
 apparatus for treating vascular defects such as aneurysms or arteriovenous
 malformations (AVMs) in a patient's vasculature. More particularly the
 invention is directed to a system well suited for treating vascular
 defects in vessels in the head and neck of a patient.
 BACKGROUND OF THE INVENTION
 Aneurysms are circumscribed dilations connecting directly with the lumen of
 a blood vessel. Aneurysms may result from acquired or congenital diseases
 which create a weakness in the blood vessel wall. It should be appreciated
 that aneurysms have a relatively turbulent flow of blood through the
 "neck" of the aneurysm. AVMs are inappropriately interconnected vessels
 that shunt blood from the arterial circulation to the venous flow. AVM
 defects are usually congenital. Depending on vessel size and the nature of
 the interconnections that make up the malformation, AVMs can also be
 accompanied by substantial blood flow. In both of these types of vascular
 defect the presence of blood flow complicates treatment.
 Typically aneurysms have thin walls which are vulnerable to a sudden
 rupture. If an aneurysm ruptures, the resulting hemorrhage can cause
 death. A hemorrhage can also cause both excessive pressure on nearby
 tissues and a reduction of blood flow to the tissues "downstream" of the
 aneurysm.
 Neurosurgeons have perfected certain conventional treatments for embolizing
 aneurysms in small vessels of the brain. The embolization process causes
 the aneurysm to heal in a way that removes the "pocket" from the wall of
 the vessel. In the most mature technique, the neurosurgeon accesses the
 region of the aneurysm under direct visualization through a craniotomy and
 places one or more aneurysm clips on the "neck" or opening of the
 aneurysm. This conventional open surgical approach has a high rate of
 success, but is highly invasive and undesirable for that reason. The risk
 associated with conventional approaches has encouraged the development of
 minimally invasive intravascular treatment approaches. Currently, the most
 widely used minimally invasive technique, involves placement of small
 coils of wire into the aneurysm. The coils are delivered transluminaly
 through a catheter that is navigated to the aneurysm site. Once the
 catheter is advanced into the neck of the aneurysm, multiple coils are
 released into the aneurysm. The coils dramatically reduce the blood flow
 through the aneurysm, which results in clotting within the aneurysm. The
 GDC coiling procedure can be time-consuming due to the number of coils
 that need to be inserted and released to fill or "pack" the aneurysm. The
 coiling procedures often need to be repeated because it is difficult to
 completely `pack" the aneurysm with coils. In this procedure the "neck" of
 the aneurysm helps to retain the coils. Consequently there are a
 substantial number of aneurysms which cannot be treated using coils
 because the large neck allows the first coil to escape from the aneurysm.
 This common problem is seen radiographically as the first coil curving out
 of the aneurysm and entering the associated vessel branch. Retrieving an
 repositioning coils is both difficult and time consuming.
 In additions to "coils", liquid or semi-liquid occlusive embolic materials
 have been proposed for use in treating aneurysms. These fluids include
 iron-acrylic compounds, as well as, a large collection of biocompatible
 glues and polymers. Attempts have been made to inject the occlusive
 materials directly into aneurysms to fill the cavity of the aneurysm.
 Typically this procedure uses a needle to pierce the wall of the aneurysm
 to place the material. There has been limited success using these fluids
 due to the tendency of the blood flow to pass the embolic material out of
 the aneurysm. This "wash out" situation presents serious complications due
 to the high probably of occluding the distal branches of the cerebral
 vasculature. Some investigators have attempted to treat aneurysms with
 liquids that denature proteins such as alcohol and the like. These
 procedures are risky as well due to the fact that the treatment occurs in
 a vessel with active blood flow and the denaturing process can occur in
 healthy tissue by accident.
 The literature has reported several studies where magnetic particles are
 combined with other materials to serve as an embolic material. The studies
 have reported improved success in treating aneurysms. In one
 representative study, a needle surrounded by a magnet was inserted through
 a burr hole in the patient's head. A stereotactic frame attached to the
 patient's head was used to direct the needle to the dome of the aneurysm.
 The mixture of magnetic particles and occlusive agent was injected through
 the needle, across the wall of the vessel. The study revealed several
 defects or shortcomings including the need for a burr hole in the skull
 and a prolonged embolization time for the occlusive agent. Complications
 also resulted from rupturing the aneurysm. In the reported study the
 magnet remained in place in the patient's head for several days to
 completely embolize the aneurysm. The reported technique was unable to
 hold a magnetic mixture in aneurysms greater than about 1-cm in diameter.
 AVMs may also be treated with embolic materials. The most frequently
 reported technique involves the use of very small polyvinyl alcohol
 particles, which are sized to occlude the smallest fistulas in the AVM.
 This technique involves "guess work" to prepare the right size particles
 that will not pass through the AVM. Also, there is limited control of the
 emboli, since the catheter placement and the direction of greatest blood
 flow dictate the delivery of the embolic particles. Visualization of the
 particles is problematic as well.
 For these reasons it is desirable to improve treatment techniques for
 vascular defects such as aneurysms and AVMs.
 SUMMARY
 The methods and devices presented in this invention can be used to treat
 vascular defects such as aneurysms and AVMs as found within the body. The
 invention is disclosed in the context of neurovascular treatments for ease
 of explanation, but the context should not be taken as a limitation in the
 scope of the invention. For example, the invention maybe used to treat
 other larger arteriovenous malformations, fistulas or aneurysms elsewhere
 in the body.
 The method of the invention involves the navigation of a catheter to a
 treatment site with or without the aid of an external magnetic field. Once
 the distal tip of the catheter is located at the treatment site, a
 magnetic device is delivered into the aneurysm. The magnetic device is
 held in position by the application of an external magnetic field.
 The term magnetic device refers to two types of embolic devices and their
 equivalents. In each case, the device carries a magnetically active
 element or particle. In one embodiment, the magnetic device is a
 macroscopic magnetically responsive occlusion device such as a coil, the
 second type of magnetic device is a "ferro-fluid" which is a viscous
 liquid containing magnetically active particulate. In either embodiment,
 magnetically active material contributes to the functional properties of
 the device.
 In general, the magnetic device may be shaped, delivered or steered by
 using magnetic fields or gradients. Magnetic fields align a magnetic
 object in the direction of the applied field, while magnetic gradients
 pull a magnetic object in the direction of the applied gradient. Magnetic
 fields and gradients can be used separately or in combination to achieve
 the desired effect. When used in combination, the magnetic field can be
 axially aligned with the gradient or transversely with the gradient. These
 two forms of gradients are often referred to as "axial" or "transverse,"
 respectively. All of the various magnetic fields and gradient
 configurations provide unique control to the magnetic device, although for
 each device and procedure it is likely that one configuration will prove
 optimal.
 In general, the externally applied magnetic field and field gradient
 assists in the positioning and retaining the magnetic device during the
 procedure. For example the applied field supplies a sufficient force to
 hold a large volume of ferro-fluid in the aneurysm or AVM and to steer and
 retain magnetically "tipped" coils in the aneurysm. A local magnetic field
 and gradient generated by the distal tip of the catheter can also
 cooperate to shape and retain the ferro-fluid or control the release of
 the magnetic device.
 The incorporated references discuss certain imaging and navigation
 techniques that may be used advantageously with the devices and methods of
 the present invention.

DETAILED DESCRIPTION
 FIG. 1 represents a schematic illustration of a patient 10 undergoing a
 minimally invasive procedure to treat an aneurysm 12 using the methods and
 devices of this invention. The patient's head located near a magnet system
 14. The magnet system 14 is controlled by the physician to generate and
 apply a magnetic field 16 at the treatment site.
 The externally applied magnetic fields are described and shown
 schematically herein but other incorporated references describe these
 magnet systems in great detail. For example, the incorporated reference
 describes a suitable magnet system, which could be used to apply the
 magnetic field and to also image the magnetic device in the body. However,
 for purposes of this disclosure, the primary purpose of the magnet system
 14 is to exert a well-defined and controlled magnetic field and magnetic
 gradient at the treatment site. Throughout the schematic illustrations,
 directional arrows are identified with labeling to indicate the preferred
 type of magnetic field and/or gradient for the magnetic device under
 control. These directional arrows are identified as a magnetic field 20,
 general gradient 52, axial gradient 79 and transverse gradient 81. These
 reference numerals are used throughout to identify these magnetic
 properties. Generally, the direction of the resultant attractive force
 generated by applied magnet is indicated in the figures by the direction
 of the arrow indicating the external magnetic field. The term general
 gradient 52 is used where the magnetic field direction with respect to the
 magnetic gradient direction is relatively unimportant for the process
 being described.
 When the magnet system 14 is positioned with axis 18 parallel to the
 tractive forces, as seen in FIG. 7, the configuration may be referred to
 as an "axial" gradient 79. When the position of magnet system 14 with the
 axis 18 is perpendicular to the tractive forces as seen in FIG. 6 the
 configuration may be called a "transverse" gradient 81. In general, the
 control of the forces can be achieved either mechanically by moving the
 magnet system 14 with respect to the patient 10 or electrically by
 adjusting the currents in an electromagnet. For example, an axial field
 can be converted to a transverse field by rotation and translation of the
 magnet with respect to the position of the patient as seen in FIG. 1.
 FIG. 2 shows an enlarged view of a portion of the vasculature of a patient
 containing an aneurysm 22. In practice, the physician will gain access to
 the vessel 24 and pass a catheter 26 through an introducer into the
 patient's vasculature. The catheter 26 will then be navigated using
 conventional guidewire techniques or under magnetic control as set forth
 in the incorporated references, to the treatment site. The physician will
 position the catheter 26 in the "neck" 28 of the aneurysm 22 with or
 without the aid of the magnet system. With the distal tip 30 of a catheter
 device 26 located within the neck 28 of the aneurysm, the physician can
 inject a magnetic device 32 into the cavity. In general a syringe or push
 wire (not shown) is coupled to the lumen 32 of the catheter 26, and the
 magnetic device 32 is extruded from the lumen of the catheter by the
 syringe or push wire. In FIG. 2 the catheter 26 device does not have a
 distal magnetic tip. Therefore, in this instance, the external gradient 52
 along with syringe pressure serves to "meter" the magnetic device into the
 aneurysm by the forces resulting from the exterior magnet without the
 influence of any local magnetic field. In this particular drawing, the
 magnetic device 32 is a so-called "ferro-fluid".
 The ferro-fluid type of magnetic device 32 may take any one of numerous
 formulations. In general, the material will be sufficiently viscous to be
 deliverable at reasonable flow rates trough a small catheter lumen under
 the pressure of a physician operated syringe. It has been found that the
 ferro-fluids used in experiments stiffen under the application of an
 external field. This effect must be taken into account during formulation.
 Experimentation has been preformed with carbonyl iron compounds in a
 cyanoacrylate carrier. In this combination, the iron material is in
 particulate form and the cyanoacrylate acts as a glue to solidify the
 composite material in the aneurysm. It is likely that temperature
 activated and light activated glues may be combined with magnetic
 particles to improve the solidification of the ferro-fluid. It is also
 anticipated that other diluent materials may be added to the ferro-fluid
 to modify and enhance the delivery properties of the material. Therefore,
 in this context, ferro-fluid should be understood to encompass microscopic
 particulate material, which is combined with a binder or glue agent which
 causes the ferrofluid to congeal into a solid mass after delivery. Both
 magnetic and magnitisable materials are operative and both cyanoacrylate
 and albumen based glues are operable. It is believed that the number of
 candidate materials for ferro-fluid is large and may include for example,
 hydrogels or copolymers mixed with the magnetically active particles.
 Throughout this specification, the term ferro-fluid is used to denote a
 material which is magnetically active and which is injected into the
 aneurysm or vascular defect. It should also be understood that other
 materials may be present in high concentrations to improve the delivery or
 reactive characteristics of the ferro-fluid. Embolization times and or
 solidification times of solidifying or adhesive agents vary considerably.
 Agents with shorter solidification times are most suitable. To improve the
 predictability of the solidification time, an agent could be mixed with
 the magnetic particles and activated with an external source. The external
 source could consist of ultra-violet light or radio frequency source.
 However, this method is not limited to a particular source used to
 activate the agent.
 The ferro-fluid embodiments illustrated in FIGS. 2, 4, 5, 6, 7, have
 microscopic magnetic particulate. Larger particles may be used as well but
 the geometry of the occlusion process differs from that associated with
 smaller particles as discussed in connection with FIG. 3.
 FIG. 3 shows a catheter 26 device for delivering discrete magnetic objects
 or particles typified by particle 50. The discrete objects may be as large
 as the catheter lumen 42. These particles may be sequentially inserted
 into the aneurysm. An external magnetic field 52 attracts and groups the
 individual objects, causing a single solid object 54 to form. Retention of
 the solid object 54 type of magnetic device, in the aneurysm reduces or
 prohibits blood flow through the aneurysm, causing it to clot. The shape
 of the magnetic objects can be spherical as shown or they may be
 cylindrical. However, many other shapes that are easily passed through a
 catheter device could be used as well. These magnetic devices may be
 coated with an adhesive forming a large particulate ferro-fluid. Given the
 relatively large volume of each device, the distribution of magnetic
 material may be non-uniform in the particle. Alternatively, the magnetic
 portion of the device may be concentrated and symmetrically placed. For
 example, the magnetic portion may be a small sphere of Hiperco coated with
 a thick layer of hydrogel or the like. For use in treating AVMs as seen in
 FIG. 17 the magnetic devices may have a coating such as polyvinyl alcohol
 (PVA) enclosing a magnetically active material such as magnetite or
 Hiperco.
 FIG. 17 shows a catheter delivering PVA coated magnetic particles into an
 AVM 56. In this particular procedure, the magnet gradient 52 attracts the
 magnetic devices typified by particle 58 along a path that lodges the
 particle in the branch 60 selected by the physician. In this instance, the
 external magnetic gradient is used along with blood flow in the vessel to
 direct the magnetic devices to the desired branch after they have left the
 distal tip of the catheter 26.
 FIG. 4 shows another instance of a ferro-fluid type of magnetic device 32
 used to fill an aneurysm 22, under the influence of an external magnetic
 gradient 52. However, in this instance the catheter body 26 includes a
 magnetically active distal tip 29. This tip 29 may be the most distal
 segment of the catheter body or it may be near the distal tip. In either
 event, the magnet or magnetic material 29 serves to constrict and control
 the flow of ferro-fluid out of the lumen 30. In this procedure, the flow
 of blood around the interior of the aneurysm is insufficient to overcome
 the tractive force holding the magnetic device 32 in the cavity and there
 is little risk of the material escaping from the cavity. Depending upon
 the glue or adhesive system used to prepare the ferrofluid, the external
 magnet remains on and in position long enough to allow the ferro-fluid to
 "set up" and become a solid mass. Once the ferro-fluid material has set,
 the magnet may be removed.
 FIG. 5 shows a catheter device 26 similar to that of FIG. 4 but the
 relationship between the magnetic forces differs. In this embodiment the
 magnet structure 29 at the tip is relatively stronger than the applied
 force. In this situation the external magnetic field is "weaker" than the
 magnetic gradient 52 as in FIG. 4. In this instance, the ferro-fluid 32 is
 attracted to the distal magnetic tip structure 29 and forms a bloom 19
 around the tip. The catheter would remain in place until the ferro-fluid
 32 forms a solid or adheres to the aneurysm wall. Using this method, it
 may be important to ensure that the ferro-fluid does not bond or adhere to
 the catheter tip. However, other methods could be incorporated to leave
 the distal magnet in the aneurysm following the injection of the
 ferro-fluid surrounding the magnet. In addition, the externally applied
 magnetic gradient 52 could be eliminated with the distal magnet 29
 supplying the entire attractive force to keep the ferro-fluid within the
 aneurysm.
 FIG. 6 illustrates the application of a transverse gradient 81 to the
 ferro-fluid 32 as it exits the catheter 26. In this instance, the magnetic
 field and the magnetic gradient are perpendicular resulting in a force,
 which tends to cause the ferro-fluid to form layers or lamella in the
 aneurysm 22. With the application of a transverse gradient 81 at the
 aneurysm, the ferro-fluid 32 forms into structured layers or lamella as
 typified by layer 27. In this instance, the layers, typified by layer 27,
 adhere to one another and align with the field of the external magnet. It
 is preferred to align the layers perpendicular to the neck of the aneurysm
 to sufficiently "pack" the aneurysm and to prevent the material from
 forming in the nearby vessel branch.
 FIG. 7 illustrates the application of an axial gradient 79 to the
 ferro-fluid 32 as it exits the catheter 26. In this instance, the magnetic
 field and the magnetic gradient are parallel resulting in a force, which
 tends to cause the ferro-fluid to form peaks in the aneurysm 22. These
 appear as columns of closely spaced structures in the aneurysm typified by
 structure 66. Utilizing this method, a smaller volume of ferro-fluid can
 effectively reduce the blood flow into the aneurysm, causing a clot to
 form. The choice between the use of a "transverse" or "axial" gradient or
 some intermediate field is essentially a medical choice driven in part by
 the volume and shape of the aneurysm as well as the relative size of the
 "neck".
 FIG. 18 illustrates the use of a ferro-fluid type magnetic device 61 to
 treat an AVM 59. In this instance, the catheter 26 ejects a stream of
 ferro-fluid that is magnetically solidified forming a "toothpaste-like
 string" 61 which is advanced into the branch 60 where occlusion occurs.
 Once again the external field 52 can both direct and retain the
 ferro-fluid in a structured form while the adhesive material in the
 ferro-fluid composition sets up. Using this approach, an adhesive or
 polymer agent can be administered to the AVM without concern for the agent
 passing through the AVM and appearing in the general circulation.
 The various ferro-fluid embodiments allow the physician to fill the
 vascular defect with a selectable amount of material that typically
 adheres to or conforms to the shape of the defect. That is, the
 granularity of the particulate is so fine that an excellent match between
 the shape of the defect and the shape of the treatment device can be
 achieved, along with a matching of volume as well. Coil systems do not
 possess this feature.
 FIG. 9 shows a problem present with prior-art, coil placement systems. It
 is common to have the coil 40 curl up and pass out of the neck 41 of the
 aneurysm 22 reentering the vasculature near the neck as seen by the
 position of the distal tip 44 of the coil 40. In this prior-art system,
 the physician will retract the coil 40 back into the catheter 26 and try
 to twist and reposition the catheter to prevent the reoccurrence of the
 event. The physician may also retract and replace the coil with a smaller
 diameter coil to enable proper coil delivery.
 FIG. 8 shows a coil type magnetic device that includes a magnetic or
 magnetically active tip structure 70 mounted on a coil 72. The coil may be
 platinum or another non-magnetic material. The coil is temporarily
 attached to a push wire 74. The push wire is used to advance the coil from
 the distal opening of a catheter to retrieve the coil back into the
 catheter. This form of magnetic device may be biased into a straight form
 as seen in the drawing or it may be biased into a preformed curve shape,
 which may be advantageously used to direct the device into aneurysms.
 Typically coils are biased into curvilinear shapes to assist in placement.
 This particular construction is well suited for magnetically winding a
 coil using an external magnetic field in aneurysms.
 FIG. 10 shows a magnetic device of FIG. 8 being pushed out of a catheter
 26. The externally applied field 20 aligns the tip of the coil towards the
 center of the aneurysm, permitting the coil to be tightly wound into the
 aneurysm. This is shown in the drawing by the decreasing radius of the
 coil. This feature overcomes the "first coil" problem explained in
 connection with FIG. 9.
 FIG. 11 shows a method for magnetically holding coils in an aneurysm. This
 magnetic coil device 78, is formed from a magnetiseable material such as
 "Hiperco" or 400 series Stainless Steel in a form similar to the coil 72
 of FIG. 8. This magnetic device 78 is held in the dome of the aneurysm by
 the magnetic gradient 52 of the applied field. In this instance, the wire
 of the coil has an affinity for itself and the complex form taken by the
 wire is three-dimensional and essentially fills the entire dome of the
 aneurysm 22. This method for magnetically holding coils within an aneurysm
 is particularly useful for treating aneurysms with large necks. Standard
 coils cannot be held within large neck aneurysms without applying a
 balloon to close off the neck. The balloon method presents a greater risk
 that can be obviated by the use of magnetically held coils. Once a number
 of coils are inserted into the aneurysm, the interlocked coils are
 mechanically maintained in the aneurysm without the need for a sustained
 magnetic gradient. It is important to note that this approach allows for
 the reconstruction of a vascular defect that may not be treatable with
 more conventional coiling and clipping techniques.
 FIG. 12 shows a number of coil type magnetic devices used to treat an
 aneurysm 22. Coil 84 and coil 82 are within the catheter 26 while coil 80
 has been detached into the aneurysm 22. Winding multiple coils allows for
 the use of preloaded fixed length devices. The application of an external
 gradient creates sufficient force 52 that the coil 80 is detached from the
 remaining sequence of coils by overcoming the force of attraction between
 the magnet on coil 83 on coil 80. Using this approach, a number of coils
 can be inserted into an aneurysm and individually released without the
 need to load a new coil with push wire into the catheter between each coil
 release. This process speeds the treatment of a vascular defect.
 FIG. 13 shows a use of a torque by an external magnetic field to detach a
 coil 80 from the complementary coil 82. In this instance the catheter 26
 retains the coil 82 and resists the motion induced in magnet 70 by the
 external field 20.
 FIG. 14 shows a use of a magnetic gradient 52 to detach a coil 80 from the
 push wire 74. In this instance, the catheter 26 retains the coil 80
 allowing the coupling force between magnet 70 and the push wire to be
 overcome by the gradient force 52 from the externally applied magnet.
 FIG. 15 and FIG. 16 should be considered together as they illustrate the
 same procedure. In FIG. 15 a coil 80 is magnetically wound, crossing the
 neck 25 of the aneurysm several times. In FIG. 16, the view shows the
 cross-section of the neck 25 and aneurysm 22 as seen from inside the
 vessel 23. By placing one large loop in the aneurysm crossing the neck
 several times, the neck 25 is almost completely blocked off without
 "filling" the aneurysm in the conventional sense. It is believed that the
 reduction in blood flow into and out of the aneurysm due to this blockage
 will be sufficient to encourage the formation of an embolism without the
 necessity of completely filling the aneurysm with coils.
 FIG. 19 is a schematic view of a magnetically actuated detachment mechanism
 used to uncouple a magnetic device, such as coil 72, from a push wire 73.
 In this magnetic device, the push wire terminates in a cap 71 that is
 positioned near a first cantilevered latch arm 77 and a second latch arm
 36 near the coil 72. A magnet 75 is positioned for rotational motion near
 the cap 71.
 FIG. 20 shows an external magnetic field indicated by arrows 20 acting on
 the magnet 75 tilting it to force the latch arms to expand releasing the
 coil 72. Although this mechanism is shown on a push wire to coil
 connection, it can be used on a sequence of coils as seen in FIG. 12.
 FIG. 21 shows an external energy source 47 delivering energy 48 to a
 ferro-fluid 32. The gradient 52 retains the bolus of ferro-fluid in the
 aneurysm 22 while the energy 48 catalyses the reaction to solidify the
 ferro fluid 32. The catheter 26 is retracted so that it does not adhere to
 the ferrro-fluid.
 It should be apparent that many modifications to the devices and delivery
 system are within the scope of this disclosure, and that these changes can
 be made without departing from the scope of the claims.