Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-07-14
2001-01-23
Getzow, Scott M. (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06178353
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to implantable devices, and more particularly to implantable medical devices having a permanent magnet therein that aligns an external (non-implanted) coupling device with the implantable device so that an electromagnetic signal may be optimally coupled between the two devices.
It is known in the art for an implantable medical device, e.g., implantable cochlear stimulator (ICS), to have a permanent magnet placed therein. An external (non-implanted) device, e.g., a headpiece of an ICS system, also has a permanent magnet placed therein. Both the external device and the implantable device may have coils mounted therein to allow power and information to be electromagnetically coupled, e.g., inductively coupled, between the two devices. Optimum signal and power coupling occurs when the implanted coil in the implantable device and the external coil in the external device are properly aligned. The magnetic attraction between the two permanent magnets, one located in the implantable device (typically in the center of the implant coil) and the other located in the external device (also typically located in the center of the external coil), magnetically hold the external device in a proper position so that the needed alignment between the two devices is maintained. See, e.g., U.S. Pat. Nos. 4,352,960 (Dormer et al.) and 4,726,378 (Kaplan), both of which patents are incorporated herein by reference.
It is also known in the art to replace one of the magnets, e.g., the magnet in the implant device, with a “keeper”. A keeper is generally made from a material which is not magnetic, per se, i.e., is not magnetized, but which provides a low reluctance magnetic path for magnetic flux. The use of a keeper advantageously improves the resistance of the implant system to MRI magnetic fields, in the event such MRI fields should be applied to the patient. That is, should MRI (magnetic resonance imaging) be conducted on the patient having the implant, the magnet in the implant becomes demagnetized and distorts the MRI image. A keeper, if used in place of the implant magnet, is not damaged by the MRI and distorts the MRI image less.
Disadvantageously, when power and signals must be electromagnetically transferred between the implant device and the external device, placing a magnet or keeper within the coils used for the power and signal transmission absorbs power and reduces the efficiency of the system. Here, system efficiency is defined as the ratio of input power delivered to a transmission coil input to output power recoverable at a receiving coil. What is needed, therefore, is a system that allows magnetic attraction to maintain a proper alignment between an implantable device and an external device without having the magnetic elements absorb large amounts of power, thereby making the system more efficient. What is further needed is such a system that is compatible with MRI, i.e., that allows MRI to be conducted when necessary without harming the implant device and without significantly distorting the MRI image.
SUMMARY OF THE INVENTION
The present invention addresses the above and other needs by laminating and/or sectionalizing the magnet and/or keeper used in both the implant device and external device so as to reduce the electrical energy absorbed by both the implant device and the external device. In order to avoid being damaged by MRI, it is preferred that the implant device employ a sectionalized or laminated “keeper”, while the external device employ a laminated or sectionalized magnet, or a magnet comprising small electrically-isolated magnetic particles. The use of such laminated, sectionalized or particle-ized components advantageously creates a very high electrical resistance path across the boundaries of the laminations, sections, or paticles, thereby reducing the magnitude of eddy currents that would otherwise flow transversely through the keeper in the presence of a magnetic flux passing through the keeper or magnet. The reduction of eddy currents, in turn, reduces energy loss.
In accordance with one aspect of the invention, an implantable medical device includes a receiving coil adapted to be electromagnetically coupled with a transmitting coil of an external device, and a magnetic element responsive to a magnetic field. The magnetic element holds the implantable medical device in a desired position that aligns the receiving coil with the transmitting coil for efficient power and signal transfer between the receiving and transmitting coils. Also included are means for reducing energy loss within the magnetic element as power and signal transfers occur between the receiving and transmitting coils. Thus, the implantable medical device operates with less loss relative to the amount of energy coupled into the receiving coil.
In accordance with another aspect of the invention, a medical device system is provided that includes an implantable part and an external (non-implanted) part. The implantable part and the external part each have a coil therein through which power may be inductively coupled from the external part to the implantable part when the respective coils are aligned. The system includes a first magnetic element in the external part, and a second magnetic element in the implanted part adapted to be magnetically attracted to the magnetic element in the external part. This magnetic attraction aligns the respective coils for efficient power and signal transfer. Moreover, as a key element of the system, at least the second magnetic element has electrical resistance blocking means therein for minimizing the formation and/or flow of eddy currents in the second magnetic element when in the presence of a magnetic field. Thus, with eddy currents minimized or eliminated, the transfer of power into the implantable part may be made more efficient.
In accordance with yet a further aspect of the invention, there is provided a method for reducing power losses associated with the transfer of energy into an implantable medical device from an external device via inductive coupling. For such method, it is understood that the implantable medical device has a first magnetic element therein adapted to be magnetically attracted to a second (non-implanted) magnetic element. The method includes the steps of: (1) positioning the first magnetic element relative to an implanted coil within the implantable medical device so that when the first magnetic element is maximally magnetically attracted to the second magnetic element, the implanted coil is aligned with an external coil for efficient inductive coupling; and (2) configuring the first (implanted) magnetic element so as to minimize the formation of eddy currents therein when the second magnetic element is in the presence of a magnetic field.
It is thus an object of the present invention to provide an ICS system that efficiently transfers signals and power between an external portion and an implanted portion.
It is another object of the present invention to provide an implant device that reduces the amount of energy lost to the magnet or keeper, thereby increasing the efficiency of the implant device.
It is a further object of the invention to provide an implantable cochlear stimulator (ICS) system having sectionalized, laminated, or particle-ized magnets and/or keepers in an external portion and in an implantable portion, which magnets and/or keepers are used to hold the external portion in proper alignment with the implant portion when the ICS system is in use, and wherein the sectionalized or laminated magnets and/or keepers, or other magnetic elements made from small electrically-isolated magnetic particles, reduce the amount of energy lost in the magnets or keepers, thereby making energy transfer between the two components more efficient.
REFERENCES:
patent: 5690693 (1997-11-01), Wang et al.
patent: 6067474 (2000-05-01), Schulman et al.
Griffith Glen A.
Malmgren Richard P.
Advanced Bionics Corporation
Getzow Scott M.
Gold Bryant R.
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