U.S. patent application number 10/469423 was filed with the patent office on 2005-01-20 for brain electrode.
Invention is credited to Gill, Steven Streatfield.
Application Number | 20050015130 10/469423 |
Document ID | / |
Family ID | 9909720 |
Filed Date | 2005-01-20 |
United States Patent
Application |
20050015130 |
Kind Code |
A1 |
Gill, Steven Streatfield |
January 20, 2005 |
Brain electrode
Abstract
The present invention relates to an electrode (1), in particular
a deep brain stimulating (DBS) electrode or a deep brain lesioning
electrode. The present invention also relates to a method for
manufacturing the electrode (1) of the present invention and the
use of the electrode. The present invention also relates to a
directional electrode.
Inventors: |
Gill, Steven Streatfield;
(Bristol, GB) |
Correspondence
Address: |
Kenneth I Kohn
Kohn & Associates
Suite 410
30500 Northwestern Highway
Farmington Hills
MI
48334
US
|
Family ID: |
9909720 |
Appl. No.: |
10/469423 |
Filed: |
August 20, 2004 |
PCT Filed: |
February 26, 2002 |
PCT NO: |
PCT/GB02/00851 |
Current U.S.
Class: |
607/116 |
Current CPC
Class: |
Y10T 29/49224 20150115;
A61N 1/0534 20130101 |
Class at
Publication: |
607/116 |
International
Class: |
A61N 001/05 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2001 |
GB |
01049824 |
Claims
1. An electrode comprising: (a) a core comprising one or more
insulated wires having non-insulated ends; (b) an insulating sheath
around the core, wherein the non-insulated ends of the one or more
wires are exposed; and (c) one or more electrode areas formed by
depositing electrically conducting material on the surface of the
sheath, wherein the one or more electrode areas are in electrical
contact with at least one of the non-insulated ends.
2. The electrode of claim 1 wherein the core comprises a plurality
of insulated wires having non-insulated ends.
3. The electrode of claim 2, wherein each end of each insulated
wire is in electrical contact with a separate electrode area.
4. The electrode of claim 1, wherein the electrically conducting
material is deposited by jet printing, etching, photolithography,
plasma deposition, evaporation and electroplating.
5. The electrode of claim 1, wherein the electrically conducting
material is gold or platinum.
6. The electrode of claim 1, wherein the electrode is a deep brain
stimulating (DBS) or deep brain lesioning electrode.
7. A method for constructing an electrode according to claim 1
comprising: (a) coating the core of one or more insulated wires
with the electrically insulating sheath, wherein the non-insulated
ends of the one or more wires are not coated by the sheath; and (b)
depositing electrically conducting material on the surface of the
sheath to form one or more electrode areas which are in electrical
contact with at least one of the non-insulating ends.
8. The method of claim 7, wherein the one or more insultated wires
are wound around a supporting member.
9. The method of claim 8, wherein the supporting member is a
tungsten wire.
10. The method of claim 7, wherein the electrically conducting
material is deposited by jet printing, etching, photolithography,
plasma deposition, evaporation and electroplating.
11. A directional electrode comprising: (a) a core comprising one
or more insulated wires having non-insulated ends; (b) an
electrically insulating sheath around the core, wherein the
non-insulating ends of the one or more wires are exposed; and (c)
one or more electrode areas on the surface of the sheath in
electrical contact with at least one of the non-insulated ends
wherein each electrode area extends over less than half the
circumference of the electrode.
12. The directional electrode of claim 11, wherein each of the one
or more electrode areas extends over less than a quarter of the
circumference of the electrode.
13. The directional electrode of claim 12, wherein each of the one
or more electrode areas extends over about an eighth of the
circumference of the electrode.
14. The directional electrode claim 11, wherein the longitudinal
axis of the one or more electrode areas are parallel to or
perpendicular to the longitudinal axis of the electrode.
15. The directional electrode of claim 11 wherein the core
comprises a plurality of insulated wires having non-insulated
ends.
16. The directional electrode of claim 15, wherein each end of each
insulated wire is in electrical contact with a separate electrode
area.
17. The directional electrode of claim 16, wherein the plurality of
electrode areas are in a staggered arrangement.
18. The directional electrode of claim 11, wherein the electrically
conducting material is gold or platinum.
19. The directional electrode of claim 11, wherein the electrode is
a deep brain stimulating (DBS) or deep brain lesioning
electrode.
20. The directional electrode of claim 11, comprising a line along
the length of the electrode in alignment with the electrode areas
for orientating the position of the electrode areas.
21. The directional electrode of claim 11, which produces a
monopolar current.
22. The directional electrode of claim 11, which produces a bipolar
current.
23. A method for constructing the directional electrode of claim
11, comprising: (a) coating the core of one or more insulated wires
with the electrically insulating sheath, wherein the non-insulated
ends of the one or more wires are not coated by the sheath; and (b)
depositing electrically conducting material on the surface of the
sheath to form the one or more electrode areas which are in
electrical contact with at least one of the non-insulating
ends.
24. The method of claim 23, wherein the one or more insulated wires
are wound around a supporting member.
25. The method of claim 24, wherein the supporting member is a
tungsten wire.
26. The method of claim 23, wherein the electrically conducting
material is deposited by jet printing, etching, photolithography,
plasma deposition, evaporation and electroplating.
27. Use of the directional electrode of claim 11 in therapy.
28. A brain electrode arranged to produce an effective field which
is offset to one side of the electrode and which has a plane of
symmetry through a plane through the longitudinal axis of the
electrode.
29. A method of making a brain electrode comprising the steps of:
arranging an elongate conductive electrode core in a mould cavity,
arranging a conductor to contact the core and to extend outside the
cavity of the mould, casting moulding material into the cavity of
the mould to form a coating on the core so that the conductor
creates a path to the core through the coating.
Description
[0001] The present invention relates to an electrode, in particular
a deep brain stimulating (DBS) electrode or a deep brain lesioning
electrode. The present invention also relates to a method for
manufacturing the electrode of the present invention and the use of
the electrode.
[0002] Stimulating and lesioning electrodes are used in a variety
of surgical procedures, in particular, DBS electrodes are used in a
variety of neurosurgical procedures.
[0003] A surgeon wishing to stimulate or lesion a particular area
of nervous tissue, can target the end of an electrode to the target
site so that a desired electrical current can be delivered.
Numerous methods are known for targeting the electrode to the
desired site including stereotactic methods.
[0004] Generally, deep brain stimulating electrodes are
manufactured by forming a coil of one or more insulated wires
having non-insulated ends on a support, welding electrode
conducting areas on to the non-insulated ends of the wires and
placing a sheath of non-conducting material over the non-conducting
parts of the electrode. It is clear that such a method for
producing an electrode is laborious and therefore expensive.
[0005] Furthermore, as numerous parts are used in the construction
of the electrode, it is possible that the overall diameter of the
electrode will vary along its length. In particular, the electrode
areas which are welded on to the electrode, especially to spot weld
points, can be proud of the rest of the surface of the electrode
leading to difficulties in inserting the electrode. A further
problem with electrodes constructed in this manner is that the
electrode has to be of a sufficient size for it to enable electrode
conducting areas to be welded onto the non-insulated ends of the
wires.
[0006] There is therefore a need in the art for an electrode which
can be constructed more efficiently and with greater accuracy.
[0007] It is becoming increasingly common for patients with
disorders of brain function, including disorders of movement,
intractable pain, epilepsy and some psychiatric disorders to be
treated with deep brain stimulation. DBS electrodes are chronically
implanted into the fine targets in the brain where electrical
stimulation will disrupt abnormal neural firing in these patients
to alleviate their symptoms. Brain targets for treating functional
disorders are usually deeply situated and of small volume. For
example, the optimum target for treating Parkinson's disease is
situated in the sub-thalamic nucleus (STN) and is a sphere of 3 to
4 mm in diameter or an ovoid of 3 to 4 mm in diameter and 4 to 5 mm
in length. Other targets such as the globus pallidus (used for
treating hyper- or hypo-kinetic disorders) or targets in the
thalamus (used for treating tremor) are usually no more than 1 to 2
mm larger.
[0008] Current DBS electrodes, for example those supplied by
Medtronic Inc, Minneapolis, Minn., are of dimensions to accommodate
such volumes. For example, such electrodes have a diameter of about
1.27 mm and have 4 ring electrodes of the same diameter positioned
at their distal end. Each ring electrode has a length of 1.5 mm
with a 1.5 or 0.5 mm separation. In use, the DBS electrode is
connected to a battery driven pulse generator via a cable and the
equipment implanted subcutaneously, generally with the pulse
generator positioned below the clavicle. The frequency, amplitude
and pulse width of the stimulating current delivered to the
electrode contacts can be programmed using external induction.
[0009] A problem with the use of such electrodes is the difficulty
in accurately placing the electrode within the desired target. The
accuracy of placement is key to the effectiveness of the treatment.
For a small target such as the STN, misplacement of the electrode
by no more than 1 mm will not only result in sub-optimal
symptomatic control but may induce unwanted side effects such as
weakness, altered sensation, worsened speech or double vision (see
FIG. 4).
[0010] The established method to place an electrode into a
functional brain target is first to localise the area of abnormal
brain function. This is achieved by fixing a stereotactic reference
frame to the patient's head, which can be seen on diagnostic
images, and from which measurements can be made. The stereotactic
frame then acts as a platform from which the electrode is guided to
the target using a stereoguide that is set to the measured
co-ordinates.
[0011] However, functional neurosurgical targets are often
difficult or impossible to visualise on diagnostic images and so
their actual position may need to be inferred with reference to
visible land marks in the brain and using a standard atlas of the
brain to assist the process. Due to anatomical variation between an
individual and the atlas and even between different sides of the
same brain in an individual such differences can lead to error in
target localisation. Errors in target localisation may also result
from patient movement during image acquisition or geometric
distortion of images which can be intrinsic to the imaging methods.
Such errors may be further compounded at surgery by per-operative
brain shift. This may result from the change in head position from
that during image acquisition to the position on the operating
table, from leakage of cerebrospinal fluid when a burr hole is made
with subsequent sinking of the brain and/or from the passage of the
electrode through the brain substance. Surgeons attempt to correct
these errors by performing per-operative electrophysiological
studies on the patients undergoing functional neurosurgery who are
kept awake during the procedures. These studies include
microelectrode recording of the neural firing in the planned target
area and/or stimulation of the target area using a test electrode.
A series of passes are made through the target area with
microelectrodes and sample recordings taken. The target is defined
by its characteristic patterns of firing. Because of the jelly-like
consistency of the brain and the depth of the functional targets
within it, there needs to be a space of about 2 mm between
different microelectrode passes to prevent the electrode passing
down a previously made track. Thus, for a small target such as the
STN, it is possible for the recordings from two microelectrode
passes, 2 mm apart, to both register location within the target
structure but to find neither of them to be optimally located
centrally within the target. Likewise, if a test stimulation
electrode is passed just off the optimal target position, i.e.
.+-.1 millimetre, then a second pass to correct this error will
almost inevitably result in the electrode passing down the same
track.
[0012] If an electrode is placed exactly in the centre of a target
having a 3 mm diameter, then the distance from the electrode
surface to the edge of the target is usually under 1 mm. If the
current spreads beyond this, then side effects can be incurred. For
these reasons, given the small chance that an electrode will be
placed in the centre of a target and that a placement error of
.+-.1 mm can result in sub-optimal treatment with side effects,
which cannot readily be corrected with repositioning, there is a
need for an electrode which overcomes at least some of these
problems.
[0013] U.S. Pat. No. 5,843,148 discloses a high resolution brain
stimulation lead, wherein the electrode comprises ring segments
diagonally arranged along the circumference of the lead.
Accordingly, in theory by passing a stimulation current between
electrode contact areas (i.e. ring segment), off axis stimulation
can be achieved. Off axis stimulation refers to the generation of
an electric field that is displaced to one side of the electrode.
Furthermore, by rotating the lead, different volumes of tissue
around the lead circumference may be stimulated. The major problem
with this device is that the diagonal geometry of the ring segment
results in a complex electric field which will spiral around the
portion of the diameter of the electrode and is necessarily
elongated along the axis of said electrode. The proposed
configuration would therefore not form an off axis electric field
that is suitable for treating a desired target. Furthermore, this
device does not enable one skilled in the art to adjust the volume
of tissue being stimulated in both the axial plane and the
horizontal plane independently. Instead, on rotating the electrode,
the volume of tissue stimulated varies in both the horizontal and
axial planes, making interpretation of patient's responses
extremely difficult. Furthermore, the complex geometry of the
proposed electrode would be difficult to construct and vulnerable
to mechanical failure.
[0014] There is therefore a need for an electrode which overcomes
at least some of the problems associated with the prior art
electrodes.
[0015] In a first embodiment of the present invention there is
provided an electrode having a proximal and distal end comprising a
core comprising:
[0016] (a) one or more insulated wires extending from the proximal
end to the distal end wherein the one or more insulated wires have
non-insulated ends, present at the proximal and distal ends;
[0017] (b) an insulating sheath around the core, wherein the
non-insulated ends of the one or more wires are not covered by the
insulating sheath; and
[0018] (c) one or more electrode conducting areas formed by
depositing electrically conducting material on the surface of the
sheath, wherein the one or more electrode conducting areas are in
electrical contact with at least one of the a non-insulated ends of
the one or more insulated wires.
[0019] The term "electrode" refers to any electrical conducting
lead for enabling the production of an electric field at a desired
site. Preferably the electrode is a DBS or deep brain lesioning
electrode. Such electrodes are well known to those skilled in the
art. The one or more insulated wires are arranged so that an
electric current can be passed from the proximal end of the
electrode to the distal end of the electrode. Preferably a separate
electrode conducting area is formed for the end of each one or more
insulated wires at the distal end of the electrode. By making an
electrical connection to the corresponding end of the wire at the
proximal end, the electrode conducting area will be electrically
charged. Preferably electrode conducting areas are present at one
or both ends of the electrode.
[0020] The term "insulated" as used herein means electrically
insulated. The insulated wires used in the electrode of the present
invention can be any insulated wires. Preferably the insulated
wires are made from gold, a gold alloy or a platinum/iridium
alloy.
[0021] It is further preferred that the core of the electrode
comprises a plurality of the insulated wires. It is particularly
preferred that the core comprises 3 or 4 insulated wires.
[0022] The insulating sheath can be made from any non-conductive
material, preferably a plastics material. In particular, it is
preferred that the insulating sheath is made from polyurethane.
[0023] The purpose of the electrode of the present invention is to
produce an electric field at a desired target site. The electrode
has a proximal end which, in use, is connected to an electricity
source. The proximal end is preferably connected to the electricity
source by the one or more electrode conducting areas present at the
proximal end of the electrode. Preferably each electrode conducting
area at the proximal end is connected to an electrode conducting
area at the distal end of the electrode via an insulated wire.
Electrode conducting areas at the distal end are positioned, during
use, at the target site and an electric field is produced.
Depending on the electrical connections made at the proximal end,
the electric field will be generated by corresponding electrode
conducting areas present at the distal end. Accordingly, it is
possible to produce an electric field with different electrode
conducting areas and furthermore it is possible to generate either
a mono-polar or bi-polar electric field. Altering the connections
of an electrode to an electric source is well known to those
skilled in the art. In particular, the technical manual for
Medtronic's DBS leads 3389 and 3387 clearly discusses changing
electrical connections at the proximal end of an electrode to
change the electric field generated at the distal end of the
electrode.
[0024] The electrode of the first embodiment of the present
invention is preferably less than 2 mm in diameter, more preferably
less than 1.5 mm in diameter, most preferably 1.27 mm in diameter.
The electrode can be of any length and is preferably between about
10 cm and 30 cm in length. The length of the electrode will vary
depending on the distance of the desired target from an accessible
surface of the patient.
[0025] The electrode conducting areas formed on the electrode can
be any desired shape. Preferably the electrode conducting areas are
formed as annular rings around the electrodes. For producing a
directional electric field areas such as squares or rectangles can
be formed on a part of the circumference of the electrode.
Preferably each electrode conducting area extends over less than
half, more preferably less than a quarter and most preferably
between about an eighth and a sixteenth of the circumference of the
electrode by restricting the size of electrode conducting area. By
restricting the area of the electrode conducting area it is
possible to produce a directional electrical field as is discussed
in greater detail below.
[0026] Preferably the electrode conducting area is positioned on
the electrode so that its longitudinal axis is parallel to or
perpendicular to the longitudinal axis of the electrode. By
ensuring that the electrode conducting area is so orientated it is
possible for the surgeon to determine the effects of moving the
electrode with greater ease.
[0027] Preferably the electrode conducting areas are rectangular in
shape and the longitudinal axis of the rectangle is parallel to the
longitudinal axis of the electrode. It is further preferred that
the rectangles are about 1.5 to 3 mm in length and about 0.2 to 0.5
mm in width. If there is more than one electrode conducting area
present on the electrode the electrode conducting areas are
preferably arranged in a line parallel to the longitudinal axis of
the electrode (See FIG. 5). Alternatively, it is preferred that
each electrode conducting area is staggered along the length of the
electrode (see FIG. 6A). By ensuring that the electrode conducting
areas are staggered, it again allows greater flexibility to the
surgeon for producing the electric field at different positions
along the length of the electrode on which the electrode conducting
areas are positioned.
[0028] The electrically conducting material can be any material
suitable for forming an electrode conducting area including metals,
polymers etc. Preferably the electrically conducting material is
gold or platinum.
[0029] The one or more electrode conducting areas can be formed by
any method. Preferably, the electrode conducting areas are formed
by depositing electrically conducting material of the surface of
the sheath. There are numerous methods well known to those skilled
in the art for depositing electrically conducting material on the
surface of various materials. Preferably the electrically
conducting material is deposited by jet printing, etching,
photolithography, plasma deposition, evaporation, electroplating,
or any other suitable technique.
[0030] Jet printing techniques are well known to those skilled in
the art. For example, in U.S. Pat. No. 5,455,998, an ink jet head
for depositing conductive ink onto a desired surface is disclosed.
U.S. Pat. No. 5,114,744 discloses a method for applying a
conductive material to a substrate using an ink jet. Furthermore,
WO 99/43031 discloses a method for depositing by ink jet printing
an electrode layer onto a device.
[0031] Etching methods for depositing electrically conducting
material are also well known to those skilled in the art. In
particular, such methods are described in Plasma Etching in
Microtechnology, Universiteit Twente, Fluitman and Elwenspoek,
ISBN: 103650810x. See also Jansen et al, Journal of Micromechanics
and Microengineering, 14-28, 1996.
[0032] Photolithography techniques are also well known to those
skilled in the art and are described in Geiger et al, VLSI, Design
Techniques for Analogue and Digital Circuits, Chapter 2, 1990.
[0033] WO 90/33625 describes a process for depositing a conductive
layer on a substrate comprising depositing ink on the substrate by
means of lithographic printing to form a seeding layer and then
depositing an electrically conducting layer.
[0034] There are numerous deposition techniques including
evaporation, sputtering and vapour deposition. All these methods
are described in VLSI Design Techniques for Analogue and Digital
Circuits (supra).
[0035] Electroplating techniques are well known to those skilled in
the art and have been used for depositing electrically conductive
material at a desired site on numerous materials.
[0036] A further method by which it is possible to deposit
electrically conducting material is by using conductive spray
paint. Conductive spray paint may be used in combination with an
ink jet printing head. Furthermore, companies such as Precision
Painting, Anaheim, Calif., have been applying electrically
conductive coatings such as copper and nickel to a variety of
objects. Accordingly, such methods can be used in order to provide
an electrically conducting material to a desired substrate.
[0037] By depositing electrically conducting material on the
surface of the sheath, the electrode can be produced easily and
inexpensively as it is no longer necessary to weld the electrically
conducting parts to the non-insulated ends of the wires.
[0038] The electrode of the first embodiment of the present
invention is robust as it does not comprise welded contacts.
Furthermore, by depositing the electrically conducting material
using the methods described above, it is possible to produce the
electrode conducting areas precisely and in virtually any size and
shape. Furthermore, the electrically conducting material can be
deposited as a thin coating ensuring that the diameter of the
electrode does not increase significantly and therefore does not
affect the insertion of the electrode. The electrodes can also be
made very small (less than 1 mm in diameter) because it is not
necessary to spot weld electrode conducting areas on to the
electrode.
[0039] In a further preferred embodiment the electrode according to
the first embodiment of the present invention may have a flexible
distal end allowing the distal end to be bent, using for example a
J wire, so that it can be moved to a desired position.
[0040] The present invention also relates to a method for
constructing an electrode according to the first embodiment of the
present invention comprising:
[0041] coating a core comprising one or more insulated wires with
an electrically insulating sheath, wherein the non-insulated ends
of the one or more wires are not coated by the sheath;
[0042] and depositing electrically conducting material on the
surface of the sheath to form one or more electrode areas which are
in electrical contact with at least one of the non-insulating ends
of the one or more insulated wires.
[0043] Preferably, the core is formed by winding the one or more
insulated wires around a supporting member. Preferably the
supporting member is a tungsten wire. The supporting member is
removed one the electrode is formed.
[0044] The electrically conducting material can be deposited by any
method, including jet printing, etching photolithography, plasma
deposition, evaporation and electroplating.
[0045] The present method is a simple and efficient method for the
production of electrodes and allows greater flexibility in the
production of the electrode conducting area on the electrode.
[0046] The method of the present invention can be automated to
further reduce the cost of producing the electrode.
[0047] In the second embodiment of the present invention, there is
provided a directional electrode having a proximal end and a distal
end comprising:
[0048] (a) a core comprising one or more insulated wires extending
from the proximal end to the distal wherein the one or more
insulated wires have non-insulated ends present at the proximal and
distal ends;
[0049] (b) an electrically insulating sheath around the core,
wherein the non-insulating ends of the one or more wires are not
covered by the insulating sheath; and
[0050] (c) one or more electrode areas in electrical contact with
at least one of the non-insulated ends of the wire, wherein each
electrode area extends over less than half the circumference of the
electrode.
[0051] The term "directional electrode" refers to an electrode
which produces an electric field that it is not uniformly formed
around the circumference of the electrode. Instead the electric
field is displaced to one side of the electrode. By having an
electric field displaced to one side of the electrode, it is
possible to change the position of the electric field by rotating
the electrode. This has the advantage that when the electrode is
placed in a sub-optimal position, it is possible to rotate the
electrode and thereby alter the position where the electric field
is produced relative to the target tissue, resulting in increased
flexibility of the system and enabling the production of an
electric field at an optimal position relative to the desired
tissue.
[0052] By ensuring that the electrode conducting area extends over
less than half the circumference of the electrode, it ensures that
the electric field is displaced to one side of the electrode.
Preferably, the electrode conducting area extends over less than a
quarter, more preferably between about an eighth and a sixteenth of
the circumference of the electrode. The smaller the electrode
conducting area, the greater displacement of the electric field
generated. However, if the electrode conducting area becomes too
small (less than a sixteenth) it is possible that the electric
field becomes toxic and causes tissue death using conventional
current supply levels. Accordingly, the amount of displacement
required can be altered by using different electrode areas having
different sizes. The directional electrode of the present invention
may therefore comprise different sized electrode conducting areas
which can be used in order to displace the electric field to
different degrees.
[0053] It may be desirable to have a small electrode conducting
area (e.g. less than a sixteenth of the circumference) when it is
desired to cause tissue death in a defined area.
[0054] As indicated above for the electrode of the first embodiment
of the present invention, the electrode conducting area can be any
shape. It is also preferred that the longitudinal axis of the one
or more electrode conducting areas are parallel or perpendicular to
the longitudinal axis of the electrode.
[0055] Preferably the one or more electrode areas are rectangular
in shape and are about 1.5 to 3 mm in length and 0.2 to 0.5 mm in
width.
[0056] The core, insulating wires and electrically insulating
sheath of the directional electrode are as defined for the
electrode according to the first embodiment of the present
invention.
[0057] As for the first embodiment of the present invention, it is
preferred that the electrically conducting material, is gold or
platinum.
[0058] It is further preferred that the directional electrode of
the present invention comprises a mark at the proximal end of the
electrode in alignment with the electrode areas for orientating the
position of the electrode areas. Preferably the mark is a line
along the length of the electrode. The line does not have to be
continuous along the length of the electrode and is used by the
surgeon in order to be able to determine the position of the
electrode conducting areas.
[0059] It is preferred that the directional electrode according to
the second embodiment of the present invention is a DBS electrode
or a deep brain lesioning electrode.
[0060] As for the electrode of the first embodiment of the present
invention, the directional electrode can be used to produce
mono-polar current or bi-polar current.
[0061] The directional electrode of the second embodiment of the
present invention can be constructed by any method, including the
method used to construct the electrode according to the first
embodiment of the present invention or via the prior art method
comprising welding the electrode conducting areas into place on the
electrode.
[0062] The present invention further provides a method for
constructing the directional electrode according to the second
embodiment of the present invention comprising:
[0063] coating a core of one or more insulated wires having
non-insulated ends with an electrically insulating sheath, wherein
the non-insulated ends of the one or more wires are not coated by
the sheath; and
[0064] depositing electrically conducting material on the surface
of the sheath to form the one or more electrode areas which are in
electrical contact with a non-insulating end of the one or more
insulated wires.
[0065] Preferably electrically conducting material is deposited by
jet printing, etching, photolithography, plasma deposition,
evaporation or electroplating according to the method described in
respect of the electrode according to the first embodiment of the
present invention.
[0066] The present invention also provides the use of the
directional electrode of the second embodiment of the present
invention for use in therapy. Preferably the therapy is the
surgical treatment of abnormalities of brain function, including
abnormalities of movement such as Parkinson's disease, Chorea,
tremor, multiple sclerosis and cerebral palsy; abnormalities of the
mind including depression and obsessive compulsive states, chronic
pain syndromes and epilepsy. The directional electrode can also be
used to lesion brain tumours, especially in eloquent areas.
[0067] In use, the electrode is usually inserted over a supporting
wire to provide the required stiffness needed to insert the
electrode into the brain of a patient. Alternatively, and provided
a plug is not inserted into the end of the electrode, the electrode
can be inserted over a guide wire and passed down the guide wire to
the desired position.
[0068] Embodiments of the present invention will now be described
by way of example only and with reference to the accompanying
drawings, in which:
[0069] FIG. 1 shows a core of an electrode comprising four
insulated wires wound on a tungsten wire support.
[0070] FIG. 2 shows a mould half for producing an insulating sheath
around a core.
[0071] FIG. 3 shows (A) an electrode with protruding non-insulated
wire ends, (B) an electrode having electrode conducting areas at
one end, (C) an electrode having electrode conducting areas at both
ends, (D) a cross section of the end of an electrode having a bung
inserted in the end of the electrode.
[0072] FIG. 4 shows a schematic view of a desired target site and
shows optimal and sub-optimal positions of an electrode.
[0073] FIG. 5 shows the distal end of a directional electrode
comprising four electrode conducting areas arranged in a line.
[0074] FIG. 6 shows (A) the distal end of a directional electrode
comprising four electrode conducting areas in a staggered
arrangement, (B) shows a sectional view of the electrode through
line x-x.
EXAMPLES
Example 1
[0075] Constructing an Electrode
[0076] An electrode (1) having a proximal end and a distal end is
constructed by winding four platinum/iridium alloy insulated wires
(diameter of 0.10 mm) onto a tungsten wire (5) in order to form the
structure shown in FIG. 1. Thus the ends of each platinum/iridium
wire extend radially away from the tungsten wire and are spaced
apart along the length of the tungsten wire. This structure forms
the core (3) of the electrode (1). The core (3) is then inserted
into a mould (7) and a polyurethane sheath (9) cast around the core
(3). The tungsten wire (5) is held under tension in the mould (7).
The ends (4) of the insulated wires protrude from the sheath (9)
formed around the core (3) and are then cut flush to the surface of
the sheath (9). By cutting the ends (4) of the wires so that they
are flush to the surface of the sheath (9), the metallic core of
the wires will be exposed on the surface of the sheath (see FIG.
3A).
[0077] Electrode conducting areas (11) are then formed on the
sheath (9) and in contact with the metallic surface of each of the
cut wires. The electrically conducting material used is platinum.
The platinum is deposited as a ring around the electrode (1) on the
sheath (9) of the electrode (1) to form an electrode conducting
area (11) as a ring around the electrode (1). FIGS. 3B and C
clearly show the formation of the electrode conducting areas (11)
on the proximal and distal ends of the electrode (1).
[0078] In this example the platinum is deposited by depositing ink
on the sheath (9) by lithographic printing thereby forming a
seeding layer, and depositing platinum by electroless deposition
(see WO 00/33262).
[0079] Once the electrode conducting areas (11) are formed on the
sheath (9), the tungsten wire (5) is removed and a plug (15) is
inserted in the distal end of the electrode (1) (see FIG. 3D).
[0080] On inserting the electrode into the brain of a patient, a
tungsten wire is inserted into the electrode to provide the
electrode with sufficient rigidity for insertion.
[0081] In use, the proximal end of the electrode (1) is connected
to a pulse generator. The electrode (1) can then be used to produce
a mono-polar electrical field or a bipolar electrical field (4) at
the distal end of the electrode (1) depending on the electrical
contacts made with the generator.
[0082] The resulting electrode (1) can be used in a variety of
surgical procedures, in particular in a variety of neurosurgical
procedures.
Example 2
[0083] Method of Constructing a DBS Directional Electrode
[0084] An electrode (1) is constructed in accordance with the
method described in Example 1 except that the platinum material
deposited in order to form the electrode conducting areas (11) at
the distal end of the electrode is deposited in four discrete
rectangles on one side of the electrode (1) (see FIG. 5). Each
electrode conducting area (11) is approximately 1.5 mm long and 0.5
mm in width. The width constitutes 45.degree. of the electrode's
circumference as the electrode's diameter is 1.27 mm. A gap of 0.5
mm is formed between each electrode conducting area (11). The
proximal end of the electrode (1) has electrode conducting areas
(11) formed as rings in accordance with the method disclosed in
Example 1. The electrode (1) also comprises a line (13) running
along the length of the electrode (1) which is aligned with the
electrode conducting areas (11) and serves as an indicator of the
orientation of the electrode conducting areas (11).
Example 3
[0085] Method of Constructing a DBS Directional Electrode with
Staggered Electrode Conducting Areas
[0086] In another example, the electrode conducting areas (11) are
formed at the distal end of the electrode (1) in a staggered
arrangement (see FIG. 6A). The electrode conducting areas (11) are
about 3 mm in length and 0.5 mm in width and each electrode
conducting area (11) is separated from its neighbour by 0.2 mm.
[0087] Use of the Directional Electrode
[0088] A directional DBS electrode (1) made according to Example 2
or Example 3 is inserted into the brain of a patient so that the
distal end of the electrode (1) is placed at the desired target.
The target is stimulated to confirm accurate localisation and the
electrode (1) is rotated in order to ensure that the optimum
position of the electrode conducting areas (11) is obtained. The
indicated line (13) on the electrode (1) will assist with this
orientation. The DBS electrode (1) is now fixed to the patient's
skull and connected to a generator that is implanted subcutaneously
in the patient. Generally, the electrode of Example 2 will be used
to produce a bipolar electric current and the electrode of Example
3 will be used to produce a monopolar electric current.
[0089] If the electrode (1) position proves to be sub-optimal post
operatively, then it is possible to try the alternative electrode
conducting areas (11) in order to see if the position can be
optimised by utilising one of the alternative electrode conducting
areas (11).
[0090] The directional electrode (1) enables the surgeon to be able
to alter the position of producing an electrical current by simply
rotating the electrode (1) by utilising other electrode conducting
areas (11) formed on the distal end of the electrode (1).
* * * * *