U.S. patent application number 14/023283 was filed with the patent office on 2014-01-09 for system and method to obstruct propagation of electromagnetic radiation induced in implanted body electrodes.
The applicant listed for this patent is Chong Il Lee, Sergio Lara Pereira Monteiro. Invention is credited to Chong Il Lee, Sergio Lara Pereira Monteiro.
Application Number | 20140012347 14/023283 |
Document ID | / |
Family ID | 44511725 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140012347 |
Kind Code |
A1 |
Lee; Chong Il ; et
al. |
January 9, 2014 |
System and method to obstruct propagation of electromagnetic
radiation induced in implanted body electrodes
Abstract
A device to improve the safety of neuronal, heart, muscle and
organ electrical stimulation devices during MRI scanning. The
device consists of means to disconnect the electrical stimulation
device, the battery pack and controlling electronics from the
connecting wires, while, concomitantly, introducing an extra
network to dissipate the induced radio frequency energy with the
objective of preventing the build-up of electric potential (usually
called voltage in US) at the switch gap, with consequently
destruction of the switch.
Inventors: |
Lee; Chong Il; (Stanton,
CA) ; Monteiro; Sergio Lara Pereira; (Los Angeles,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lee; Chong Il
Monteiro; Sergio Lara Pereira |
Stanton
Los Angeles |
CA
CA |
US
US |
|
|
Family ID: |
44511725 |
Appl. No.: |
14/023283 |
Filed: |
September 10, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13046801 |
Mar 14, 2011 |
8565869 |
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14023283 |
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Current U.S.
Class: |
607/36 ; 607/45;
607/63 |
Current CPC
Class: |
A61N 1/3718 20130101;
A61B 5/076 20130101; A61N 1/36142 20130101; A61N 1/086 20170801;
G01R 1/06744 20130101; A61B 5/04001 20130101; G01R 1/07307
20130101; A61B 5/055 20130101; A61N 1/3752 20130101; A61N 1/0534
20130101; A61B 5/0031 20130101; G01R 1/06766 20130101 |
Class at
Publication: |
607/36 ; 607/63;
607/45 |
International
Class: |
A61N 1/37 20060101
A61N001/37; A61N 1/36 20060101 A61N001/36; A61N 1/375 20060101
A61N001/375 |
Claims
1. A system for mitigating the effects of an electromagnetic energy
induction device on an implanted electrical stimulating device, the
system comprising: a first electrical network comprising one or
more electrodes implanted at a first location, the one or more
electrodes connected in series with at least one first electrical
switch at a first location; an electrical energy storage means and
electronics controlling unit implanted at a second location,
wherein the energy storage means and electronics controlling unit
are connected in series with at least one second electrical switch
at a second location; an electrical conducting means, connecting
the one or more electrodes in series with the at least one first
electrical switch at the first location, to the electrical energy
storage means and the electronics controlling unit in series with
the at least one second electrical switch at the second location;
wherein a second electrical network comprising at least one energy
dissipating device in parallel connection with the one or more
electrodes and in parallel with the electrical energy storage means
and the electronics controlling unit, is configured to dissipate
the energy induced in the electrical stimulating device by the
electromagnetic energy induction device.
2. The system according to claim 1, wherein the electrical energy
storage means and the electronics controlling unit are implanted at
separate locations.
3. The system according to claim 1, wherein the at least one first
electrical switch is configured to provide electrical continuity
for electrical current flow, or to interrupt the electrical current
flow between the one or more electrodes and the electrical
conducting means, and the at least one second electrical switch is
configured to provide electrical continuity for electrical current
flow, or to interrupt the electrical current flow between the
electric storage means and the controlling electronics unit and the
electrical conducting means.
4. The system according to claim 3, wherein the continuity states
of the at least one first electrical switch and the at least one
second electrical switch are controlled by a human operator via
telemetry.
5. The system according to claim 3, wherein the continuity states
of the at least one first electrical switch and the at least one
second electrical switch are automatically selected by the
controlling electronics.
6. The system according to claim 1, further comprising at least one
third electrical switch configured to provide electrical continuity
for electrical current flow, or to interrupt the electrical current
flow between the energy dissipating device and the electrical
conducting means.
7. The system according to claim 1, further comprising at least one
capacitor configured to provide a small impedance for electrical AC
current flow characterized by high frequency, while configured to
provide a large impedance for electrical AC current flow
characterized by low frequency, the at least one capacitor
connected in series with the at least one energy dissipating device
and providing an electrical path from the at least one energy
dissipating device and the electrical conducting means.
8. The system according to claim 1, wherein the at least one energy
dissipation device is a resistor.
9. The system according to claim 1, wherein the electromagnetic
energy induction device is an MRI system.
10. The system according to claim 1, wherein the one or more
electrodes is/are configured to provide electrical stimulation in a
brain.
11. The system according to claim 1, wherein the one or more
electrodes is/are configured to provide electrical stimulation in a
heart.
12. The system according to claim 1, wherein the one or more
electrodes is/are configured to provide electrical stimulation in
an animal organ.
13. A method of mitigating the effects of an electromagnetic energy
induction device on an implanted electrical stimulating device
comprising at least one stimulating electrode and an electrical
energy storage means and a controlling electronics connected by
electrical connecting wires, the method comprising: providing at
least one first electrical switch in series with the at least one
stimulating electrode; providing at least one second electrical
switch in series with the electrical energy storage means and the
controlling electronics; providing at least one energy dissipating
device in electrical parallel connection with the at least one
stimulating electrode and with the electrical energy storage means
and with the controlling electronics, wherein the first electrical
switch and the second electrical switch are configured to interrupt
the electrical current flow at the command of an operator, and the
energy dissipating device is configured to dissipate the energy
induced by the induction device, thereby preventing the electrical
energy built up at the first electrical switch and second
electrical switch.
14. The method according to claim 13, further comprising a third
electrical switch configured to interrupt the electrical current
flow at the command of an operator; wherein the third electrical
switch is configured to complete a closed loop including the energy
dissipating device and the electrical connecting wires; whereby the
energy dissipating device is configured to dissipate the energy
induced by the electromagnetic energy induction device, preventing
the electric potential built up at the gap of the first switch and
the second switch.
15. The method according to claim 13, further comprising at least
one capacitor configured to offer smaller electrical resistance to
high-frequency AC currents then to low-frequency AC currents;
wherein the at least one capacitor is configured to complete a
closed loop including the energy dissipating device and the
electrical connecting wires; whereby the energy dissipating device
is configured to dissipate the energy induced by the
electromagnetic energy induction device, preventing the electric
potential built up at the gap of the first switch and the second
switch.
16. A non-transitory computer program medium for use on a computer
system for control the path of electrical energy on at least one
stimulating electrode, on an electrical energy storage means and
controlling electronics and on at least one energy dissipating
device, the computer program medium comprising a computer usable
medium having computer readable program code thereon, the computer
readable program code including: program code for controlling the
opening and closing of at least one first electrical switch and at
least one second electrical switch, wherein the at least first
electrical switch is connected in series with the at least one
stimulating electrode and the at least second electrical switch is
connected in series with energy storage medium and the controlling
electronics, whereby the first electrical switch is capable to
interrupt the flow of electrical energy into the at least one
stimulating electrode and the second electrical switch is capable
to interrupt the flow of electrical energy into the energy storage
device and the controlling electronics; whereby the at least one
energy dissipating device is configured to dissipate unwanted
energy, thereby preventing unwanted energy to flow into the
stimulating electrodes and into the energy storage device and the
controlling electronics.
17. The non-transitory computer program medium according to claim
16 wherein the unwanted energy is induced by an MRI imaging system.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Provisional
application Ser. No. 61/340,183, entitled "Device and means to
obstruct propagation of electromagnetic radiation in implanted body
electrodes" filed Mar. 15, 2010, by the present inventors which is
incorporated herein by reference in its totality. This application
is a continuation of patent application Ser. No. 13/046,801,
currently allowed. This application is related to U.S. Pat. No.
8,335,551, filed 24 Sep. 2009, and patent application Ser. No.
12/586,763, filed Sep. 28, 2009, published Apr. 1, 2010, currently
allowed, all by the present inventors. All these are incorporated
herein by reference in their totality.
FEDERALLY SPONSORED RESEARCH
[0002] Not applicable
SEQUENCE LISTING OR PROGRAM
[0003] Not applicable
BACKGROUND OF THE INVENTION
[0004] 1. Field of Invention
[0005] This invention relates to electrical stimulation of animal
cells, particularly human brain and heart electrical stimulation,
including spine and other types of neurons, other types of muscles
and organs like bladder and stomach, and in particular to the
possibility of partial obstruction of the current induced in same
by electromagnetic radiation, e.g., induced during MRI (Magnetic
Ressonance Imaging).
[0006] 2. Discussion of Prior Art
[0007] Several types of implanted devices for the purpose of
delivering electrical pulses to different parts of the body have
become practical, the most ubiquitous of which being the cardiac
pacemaker, but also including DBS (Deep Brain Stimulation) and
other neuronal stimulating devices, as for pain control, and other
stimulators in the brain and peripheral nervous system as well, and
also for other needs, as bowl control and the like. One of the
disadvantages of wearing some of these, is their propensity to
absorb electromagnetic waves, which are induced AC, which is
subsequently released as heat in localized spots in the wearer's
body, with potential for discomfort, pain, or worse, depending on
the temperature increase, or electrical interference with normal
neural signals. In heart pacemakers another type of danger exists,
which is the transfer of induced voltage on the connecting wires to
the heart, or worse, to the heart sinus pacemaker, which could
induce unwanted and erratic heart beats with the potential of
causing the heart to stop. In other words, the wirings act as an
antenna that then is the origin of current pulses along the device.
The danger also exists to totally or partly destroy the electronic
circuit that controls the device if the electromagnetic induced AC
propagates to it, with the potential of erratic electrical pulses,
with unpredictable consequences, including death too. These
implanted devices are generally composed of a battery and an
electronic circuit, which is implanted near the skin, for easy
access if a need arises for replacement, from where wires run to
the desired electrical stimulation location, as heart, brain,
spinal cord, etc. Unfortunately the connecting wires act as
antennae for external electromagnetic radiation, which in turn
cause an unwanted current to flow through the connecting wire, that
ultimately may cause either battery or electronic circuit failure,
if the pulse propagates towards the battery, or it may cause
heating on the other extremity of the connecting wire, which may
then be on or near the heart, brain, spinal cord, etc, wherever the
stimulation happens to be. This problem may be especially acute in
DBS, because the wires are longer, running from the chest to the
top of the skull then down from the top, inside the skull to the
bottom of the brain, making DBS a longer antenna for
electromagnetic radiation than heart pacemakers are, which in turn
causes more energy to be absorbed by the DBS than by the heart
pacemakers. With heart pacemakers, on the other hand, though the
wires are shorter, so the induced voltage is lower (also the
induced energy), the very nature of the device, to pace the heart,
with electrodes placed at the most efficient positions to influence
the heart beat, any electrical induced voltage is potentially
mortally dangerous because it can cause erratic heart beating.
[0008] Because of this possible danger, MRI images are often, or at
least occasionally, avoided in patients that wear one of these
implanted devices, particularly in DBS and heart pacemakers
wearers, because of the longer wires on the former, and the
rhythmic sensitivity of the latter. DBS wearers carry a longer
antenna, from the battery/electronics in the chest with a wire
running to the top of the head. Pacemakers, though having shorter
wires, are less likely to develop higher power to cause dangerous
heating but suffer from the danger of causing heart arrhythmias.
This avoidance is a problem because implanted patients are exactly
the older ones, which are the ones more likely to need imaging,
X-Ray, MRI, sonography, etc. From these, MRI is the worse, because
it subjects the patient to a radio frequency (RF), AC
electromagnetic field of frequency on the order of 50 MHz, a
frequency range used by many communications devices exactly because
the antennae are so effective in this range. Because of this, at
the very least the medical practitioners are prone to avoid
requesting an MRI imaging on patients wearing electrical
stimulating implants, particularly on a DBS wearer, who is known to
be implanted with a longer wire, more prone to absorb
electromagnetic energy created by the MRI imaging system.
[0009] This problem is widely recognized in the literature, and
much time has been devoted to its solution, yet a complete and
inexpensive solution has been eluding the designers of electrical
stimulating devices.
[0010] Mark Kroll et al. U.S. Pat. No. 7,369,898, May 6, 2008
(REF_Kroll2008), recognizes the problem and teaches a method to
prevent the controlling unit from being disturbed by the RF and
then sending erratic stimulating pulses to the stimulation site
that are not programmed in the device. Though this is an
improvement, it still fails to even address the other problem of
induced RF in the conducting wire that goes from the power pack box
to the stimulation site. It is only a partial solution. Moreover,
Kroll teaches a method that depends on the device itself
recognizing the presence of strong magnetic field, then the
presence of an RF, before it enters in a self-protective mode. This
has the disadvantage of relying on an automatic response, which can
fail to activate, as opposed to a human activated response, which
can be checked by a trained professional. Above all, Kroll's
solution, when and if it succeeds, is a protection for the battery
and electronics package only, located in the patient chest, but not
a solution for heating and unwanted electrical stimulation due to
induced currents in the connecting wires. Indeed, the very solution
proposed by Kroll indicates that though the community is aware of
the problem and have been trying to solve it for a long time, the
true solution has been eluding all, indicating the importance of an
inventive, a creative solution for this problem.
[0011] Zeijlemaker et al. (U.S. Pat. No. 7,623,930, Nov. 24, 2009)
(REF_Zeijlemaker2009) discloses a coordination between the
telemetry system and the MRI system with the view of minimizing the
possible damage, but it fails to stop the current flow due to
induced electromagnetic waves in the wires that comprise the
implant device. It also points to the eagerness of the community to
solve a serious problem that has been eluding the practitioners of
the art.
[0012] These examples show that this is a crowded field, with many
practitioners of the art trying to solve a serious problem
associated with electrical implants interaction with the RF
electromagnetic waves used in MRI imaging. Yet, in spite of so much
search and resources through in the problem, its solution has been
eluding all.
OBJECTS AND ADVANTAGES
[0013] Accordingly, several objects and advantages of my invention
are:
[0014] 1. To allow patients wearing electrically implanted devices
to receive MRI imaging with a smaller risk of complications arising
from the procedure,
[0015] 2. To decrease the level of worries by treating physician
about possible complications from MRI imaging in implanted
patients, therefore opening more options for his diagnostics and
creating the possibility of better, more professional and accurate
diagnostics,
[0016] 3. To increase the possibility that a patient wearing an
electrical stimulation device will indeed have an MRI examination
when one is needed for decisions on his/her health,
SUMMARY
[0017] We claim a method and means to substantially decrease the
electric current induced in implanted devices, as, for example, by
magnetic resonance imaging (MRI) radio frequency (RF)
electromagnetic (EM) radiation from propagating through the wires
of electrical devices implanted in patients subjected to MRI
imaging or other electromagnetic radiation. Without such blocking,
or filter, physicians are at least uneasy about requesting MRI
imaging in patients wearing such implants, resulting in diminished
information for treatment, at most unable to get an MRI imaging. In
the worst case an imaging may cause localized heating and possibly
catastrophic results, including death, or erratic heart beating,
also with the possibility of death. Our device ameliorates this
situation, substantially decreasing the probability that adverse
side effects occurs.
DRAWINGS
[0018] FIG. 1 shows a schematic representation of the
implementation of the main embodiment of this invention. Switches
SW1 (a, b, c, and d) allow current to flow into and out of the
stimulating device (FIG. 1a), or interrupt its flow (FIG. 1b).
[0019] FIG. 2 shows a schematic representation of a variation of
the implementation of the main embodiment of this invention. FIG.
2a displays the case where the current flows through the
stimulating device (normal use) and FIG. 2b displays the case where
the stimulating device is disconnected while the alternative path
through resistors R-sub-a and R-sub-d are connected in a closed
loop through switches SW2a and SW2d.
[0020] FIG. 3 shows a possible variation of the main embodiment
with extra switches SW1a and SW1b inside the picafina of our
invention, just before the beginning of the stimulating
electrodes.
[0021] FIG. 4 shows an op-amp based low pass filter of the VCVS
variety (Voltage-controlled voltage-source)
LIST OF REFERENCE NUMERALS
[0022] BAT1=battery pack/control electronics [0023] CW1 and
CW2=Control wire 1 and control wire 2
[0024] SW1a, SW1b, SW1c, SW1d, switches to turn on or off the
stimulating devices and the battery/electronics pack.
[0025] ST1=electrical stimulating device
[0026] R2a and R2d=resistances to dissipate the energy induced by
some external electromagnetic radiation in the circuit.
[0027] Wire1, wire2=two exemplary wires running from the battery
pack/electronics circuit to the stimulation electrode. The former
is located usually in the patient chest, while the latter is
typically in the lower part of the brain, the wires going from the
chest, under the skin, behind the ear, up to the top of the skull
then down the brain.
[0028] WireC, wireCloop=controlling wire to connect/disconnect
wires wire1, wire2, etc. and loops A1-A2-B2-B1-A1, etc.
[0029] WireControl1 and WireControl2=control wires used to turn
switches SW1 and SW2 on and off, as needed.
DETAILED DESCRIPTION
Preferred Embodiment
FIGS. 1a and 1b
[0030] We start with a shorter detailed description suitable for
electronics engineers, followed by a more detailed description with
less technical terms for medical personnel and general background
readers. Such an approach is useful for the complete description of
an invention that is of interest of practitioners of two very
different fields: electronics and medicine. The first, technical
description, is written for the electrical engineer, the latter,
general description, is intended for neurosurgeons, neurologists,
medical personnel and anyone without knowledge of the electronics
circuits and electrical phenomena.
[0031] Detailed Description for Electronics Engineers.
[0032] In its main embodiment, the improvement of our invention
over prior art electrical stimulating devices, is the introduction
of isolation switches (in-line) to prevent propagation of RF
electromagnetic waves into the critical parts of the implant,
together with alternate path (or paths) in parallel with both the
stimulation device (ST1) and the battery/electronics (BAT1) which
serve to damp the electromagnetic energy induced in the connecting
wires. It is of note that without the alternate path to form a
closed circuit with most of the connecting wire, opening a switch
leading to the stimulating device (ST1) or to the
battery/electronics box (BAT1) is likely to cause electric
potential increase at the gap with a consequent spark and
destruction of the switch. The alternative paths to dump the
unavoidable induced EM wave that necessarily is induced in the
existing wires is an integral part of the invention we disclose.
The latter (the bypass network) are necessary to forestall the
destruction of the former (the in-line switches) due to the fast
increase in voltage at the switch gap, though our invention is not
dependent on any theory that explains the mechanism of destruction,
which is added here only for completeness.
[0033] Electrical stimulating devices can be generally seen as
three main components, but this arbitrary division is made here as
only a simplifying subdivision to drive the attention to the parts
that are important for the invention. The first component is a
battery and other electrical energy source and the controlling
electronics (BAT1), which are usually together in a sealed box
implanted in the patient's chest, near the skin for easier access;
the second are the stimulating electrodes (ST1), which are made in
any necessary shape appropriate for the situation, which for the
main embodiment we are considering to be a DBS (Deep Brain
Stimulator); and finally, the third component are the wires
connecting the former to the latter.
[0034] Referring to FIGS. 1 (a and b), the reader can see switches
SW1c and SW1d which are near the battery pack BAT1 and switches
SW1a and SW1b, which are near the stimulating electrodes, which in
this case are brain stimulating electrodes, as used in DBS (Deep
Brain Stimulation), as an example only, the principle being valid
for other electrical stimulation as well. Switches SW1 (a, b, c,
and d) are controlled by telemetry, either directly, or indirectly
via commands received from the electronics command unit in BAT1,
which receives commands by telemetry. The telemetry control is made
with specially designed equipment that can be controlled either by
the patient himself or by a neurologist, a nurse, or any other
medically trained person. The electronics for this is not shown in
the drawings, it being standard technology in use in many other
applications. In particular existing DBS, heart pacemakers and the
like do use telemetry devices to adjust the parameters of the
stimulating electrical pulse, so the telemetry part is old art, not
part of our invention. Our device uses additional commands not used
by existing art, say, to open/close SW1, but these are obvious
extensions for the people with experience in the arts of software
and/or digital hardware design, so they will not be discussed here.
It is worth to point out that current art of DBS use telemetry to
select the parameters appropriate to each patient, as voltage
level, for example. A trained person, capable of acting on the
controls of the device, is able, using some telemetry control, to
turn the switches on and off as needed.
[0035] In the main embodiment these switches are semiconductor
switches activated by an electronics circuit which contains some
logic and perhaps some digital addressing too. Consequently each of
the switches needs to be connected to an electrical power. The main
embodiment of our invention works with SW1 of the type known as
normally open switches: without power they go into the open state.
To turn all off, the BAT1 command unit has only to turn SW1c and
SW1d off, which automatically turns off SW1a and SW1b because they
lose power. Persons with knowledge in the art of electronics are
aware that normally-open switches are not the only possible option,
normally-closed switches being also possible, as well as mechanical
switches, three-state switches, and more. A semiconductor,
normally-open switch is suggested here only as a concrete case, it
not being our intention to limit our invention to this option.
[0036] Referring still to FIGS. 1a and 1b, resistances R-sub-a and
R-sub-d are to provide and alternative path to the induced current
in the wires after switches SW1 (a, b, c and d) are opened. R-sub-a
and R-sub-d can be considered as a resistive load for the isolated
network. The value of the resistances R-sub-a and R-sub-d are such
that their impedances (resistances) is much larger than the total
impedance from SW1a to SW1b through the network branch that
includes the stimulating device, that is, the total impedance from
a through SW1a, the wire connecting SW1a to the stimulating device
ST1, the impedance of ST1, the impedance of the wire that connects
this latter to SW1b, and finally the impedance of SW1b. Saying it
in other words, the value of the resistance R-sub-a is much larger
than the total value of the impedance in parallel with R-sub-a
which contains the stimulating device ST1. For the main embodiment
ST1 is a Deep Brain Stimulating (DBS) device, which has a typical
impedance of Z-sub-ST1=1 k-Ohms, in which case R-sub-a should have
a resistance R-sub-a=1000 k-Ohms=1 M-Ohms. Considering that Joule's
law for resistive devices,
P=V*2/R,
[0037] states that for a fixed potential difference the dissipated
power is inversely proportional to the resistance, with these
recommended values the power dissipated in R-sub-a would be 1/1000,
or 0.1% of the total power dissipated in ST1, which is negligible.
In battery lifetime, taking into consideration that the implanted
battery usually lasts 3 years, and considering that 3 years is
approximately 1,000 days, this means that the extra 1/1000 power
dissipated in the parallel resistor R-sub-a would decrease the
battery lifetime from 3 years to a lifetime of 2 years, 11 months
and 30 days (instead of 31 days), a perfectly acceptable
degradation.
[0038] If R-sub-d is also 1 M-Ohm, the parallel combined resistance
of R-sub-a and R-sub-b is R-par=500 Ohms, the total "lost" power
would be 1/500 of the total, and the total average lifetime of the
battery would decrease from a typical 3 years to 2 years, 11 months
and 29 days, still very acceptable. These are approximate values
for the DBS case, other stimulating devices have similar
parameters, and the invention is not bound to work only with these
values, as will be appreciated by persons with skills in the art of
electronics. Moreover, the value of R-sub-a and R-sub-d can be
different than 1 M-Ohm, as needed for each case, this particular
value of 1 M-Ohm being an exemplary case only, not intended to
limit our invention.
[0039] The switches SW1a and SW1b should be as close as possible to
the stimulating device ST1, which, in the DBS case of the main
embodiment, indicates that SW1a and b should preferentially be at
the top of the skull, and switches SW1c and SW1d should be as close
as possible to the battery pack/electronics controlling unit BAT1,
which, in the normal arrangement for DBS means that SW1c and d
should be, in the main embodiment, in the chest, just at the exit
of the box which contains the battery and the electronics
controlling unit.
[0040] To turn switches SW1 off, the battery pack/electronics
control package in BAT1 turns off, upon telemetry command, switches
SW1c and SW1d, which in turns automatically starves SW1a and SW1b
of power, which causes these latter to go into the off state too
(assuming that they are of the normally-open type switches). After
the MRI session is finished, to turn the stimulating device on
again the telemetry control commands the control package in BAT1 to
turn power on for SW1c and SW1d, which either automatically, or
after another command, turns on the two switches close to ST1: SW1a
and SW1b, after what the electrical stimulating device is ready for
operation again.
[0041] In the main embodiment, switches SW1 (a, b, c and d) are
semiconductor switches, as a bipolar or a FET transistor, which
uses less space in the implanted device, which must by necessity be
small, but semiconductor switches is not a restriction to our
invention, because any other type of switch that can be
manufactured on the appropriate size and with bio-compatible
materials is within the scope of the invention. The necessary
electronics, as transistors, etc., easily fit in the space:
REF_DieSize. In particular, switches SW1c and SW1d, which are
located near the battery pack/electronics (BAT1) can easily be
other technology, as mechanical switches, etc., for robustness,
given that they can be inside or at the exit port of the battery
BAT1, with more space available.
[0042] It will not escape the persons with knowledge in the art of
electronics that the same principles apply to other electrical
stimulation, as heart stimulation (heart pacemakers), neural
stimulators (as for pain control), physiological electrical
stimulators (as for bowel movement control, bladder control, etc.),
and devices to cause muscle contraction, as in artificial limbs,
etc. all of which causes problems with MRI imaging because all of
them needs a relatively long wire, which acts as an antenna for the
MRI RF radiation.
[0043] Detailed Description for General Background Readers.
[0044] Before we describe our invention to the readers that are
familiar with the medical aspects of the invention but not familiar
with the electronics aspects of it, we want to remind the readers
that the devices used in current art, whether used for DBS,
stimulation for epilepsy or other neurological malfunctions, heart
pacemaking, spinal stimulation, etc. generally contain a
sophisticated electronics circuit inside the same box that houses
the battery pack (BAT1). This electronics circuit is capable of
adjusting the parameters of the electrical stimulation upon command
send by telemetry (action at a distance, as radio waves). For DBS,
which is the example used for the main embodiment, the controlling
circuits can adjust the stimulating voltage (or current), the pulse
frequency and duration, and more. Our device makes use of some
extra commands to be added to this existing set in the current art.
It should therefore be clear to persons without electronics
experience that the possibility of turning on/off the switches SW1
(a, b, c and d) is a simple extension of current art.
[0045] During MRI imaging the patient is put inside a strong and
homogeneous magnet field, over which there is a slowly space
varying magnetic field, and to an electromagnetic (EM) wave of a
frequency on the order of 50 MHz, the actual value depending on the
strength of the magnetic field. From now on we will refer to this
as the RF field or as the 50 MHz wave, though 50 is only an
approximate value. The 50 MHz frequency used for MRI is similar in
value to the frequency that is used for communications, and is
approximately half the frequency used for FM and traditional TV
transmission. FM radio reception is affected by the passage of
people in front of the radio (if the radio is using its own
antenna, and not an external antenna), a fact that can easily be
observed walking in front of an inexpensive FM radio receiver, as a
bedside clock-radio, which works around 100 Mhz. This signal
variation indicates that the FM frequency is capable of interacting
with the human body--else there would be no change due to the
appearance of a human near the radio; AM does not change as one
walks around the radio, because our bodies do not interact with the
frequency used for AM, which is around 1 MHz. MRI uses a slightly
lower frequency than FM, that is also capable of interacting with
the human body. By controlling this EM wave and measuring it after
it interacts with the patient, that is, how much of it is absorbed,
an image of the atoms inside the body, according to each atom's
environment (or the cell structure), can me constructed. Since
different tissues have different combinations of atoms and
different environment around the same atom, the effect of each
tissue on the EM wave is different and measuring this slight
changes an image can be made. The EM wave in itself causes no harm
to the patient, as it is of a frequency similar to the waves used
in communications, a little lower in frequency than the frequency
used for FM radio. Some fire, police and other similar services use
frequencies near the frequencies used by MRI, at 30 MHz (VHF low),
but this information is put here only for completeness, and its
accuracy and completeness should not be considered against our
invention, because it is independent of our invention and is only
included for general understanding of radio frequency EM waves.
[0046] The patient undergoing the imaging cannot wear any
ferromagnetic metal as iron, because these would be attracted by
the strong magnetic field. Any other non-magnetic metal, as copper,
aluminum, titanium, even if it is not attracted by the strong
magnetic field, causes another adverse effect, as it functions as
an antenna for the RF radio frequency wave used for the imaging.
The long wire, acting as an antenna, does the same job as an
ordinary radio antenna, capturing the radio waves existing in its
environment. It happens that metals are far more effective in
absorbing electromagnetic waves than human tissues, this being why
antennas are usually made with metallic wires, and consequently
most of the 50 MHz power used for the image is absorbed by the
wires from the battery pack/electronics to the implanted device.
Given that the imaging 50 MHz power is very large, the induced
voltage and current in the wires can be enough to either destroy
the battery pack/electronics or else to heat up the device enough
to cause tissue damage. In other words, since the MRI imaging
machine bombard the patient with strong, powerful radio frequency
waves, as needed for a better imaging, it follows that stronger
currents can appear in the wires. This is similar to having a radio
near the transmitting antenna and far from it, an effect that one
can see driving away from a city: eventually the signal fades away,
because the signal strength becomes too low to be captured, the
induced voltage too low, or conversely, eventually a station
appears on the radio as one approaches a city, because the signal
increases in intensity, the induced voltage in the antenna
increases its value. It follows that DBS implanted patients may be
subjected to induced voltages, and then to the induced currents
caused by the induced voltage, in the long wire that runs under the
skin from the battery and electronics BAT1, usually implanted in
his/her chest, up and along the neck to the top of his/her skull
then down again to the base of the brain inside the skull. Indeed,
this is a several feet long wire, which acts as a good antenna for
the approximately 50 MHz frequency waves used in MRI imaging. It
happens that the radio frequency waves used in imaging are quite
powerful, as the requirement is to interact with weakly interacting
body molecules, which in turn means that the radio waves induced in
the wire running under the skin may deposit uncomfortably large
electrical energy, with the potential of causing heat, including in
the brain. The problem of induced radio waves EM energy is not
present in normal situations as the patient walks around town,
because the normal energy level of the existing radio waves is
quite low. It is only the concentration of radio EM energy inside
the confined space of the MRI device that can be potentially
dangerous. As an exemplary situation we can mention the production
of light by fluorescent lamps just standing alone in the air but
near a powerful radio transmitting antenna; the high EM fields
existing in the close vicinity of the transmitting antenna is
enough to cause the fluorescent lamp to produce light without the
normal connection with the standard electrical power. A coil near a
high-voltage transmission line is able to power some devices, a
practice that found its way to the legislature, laws having been
passed to forbid the practice because it is a way to capture the
electrical energy from the air without paying for it. Analogously
to the car approaching and receding a town, in principle one can do
the same capture of the electrical energy at any home in town, but
in town the 60 Hz wave is lower voltage, too weak to be practical
to capture it from the air.
[0047] Regarding the total power radiated by the RF imaging coils,
it depends on the particular MRI system that is used, but it can
easily be around 50 ordinary pressing irons set for full
heat--quite a lot of heat indeed!
[0048] It is not possible to prevent the induction of EM waves in
the wires. Shortening the wires would improve the situation,
because the energy induced is proportional to the length of it,
among other factors, which could be achieved placing the battery
and controlling electronics in the head, nearer to the point of
stimulation. But other limitations, among them space in the head,
prevent, or make it difficult, to lodge the battery and electronics
in the head. In other situations, as heart pacemaker, for example,
the points of insertion of the wire for the heart pacemaker, which
typically is in the artery/vein near the clavicle also determine a
relatively long wire for heart pacemaker too. So far a solution for
the length of the wire has not been found and a long wire
inevitably captures more EM waves. This has been the conundrum
faced by physicians that need MRI images of patients implanted with
DBS devices. Our invention seeks to ameliorate this problem of EM
waves induced in the long wires that lead from the battery located
in the chest to the DBS electrodes ST1 implanted in the brain.
[0049] It is not possible to prevent the EM induction (the antenna
effect, so to say) in the wires, so it is necessary to accept that
electric energy will be induced into and then run through the wires
when a wearer of electrical implanted devices is undergoing MRI, or
otherwise is near any high power EM radiation. Our invention
discloses the use of switches that can be closed or opened under
the control of the electronics in the battery pack/electronics box
BAT1, which can interrupt the current flow along the wires running
from the battery pack to the brain, as in FIGS. 1a and 1b. Just
opening the circuit would work, but a safety device is added to our
invention, because the possibility that the EM wave induced on the
wires could rise the electric potential (the voltage) on the
switches, enough to cause them to arc (that is, for a spark to jump
across the contacts and the switch going into conducting mode, even
if only temporarily). To forestall this electrical energy
accumulation on the switches SW1, our invention also discloses a
closed loop that is used to dissipate the energy induced on it, as
described in the sequel. FIGS. 1a and 1b display the two
situations. The wires running from the battery BAT1 to the
stimulating electrode ST1 carry the stimulation signal from the
battery pack/controlling electronics BAT1 to the brain, and SW1a,
SW1b, SW1c and SW1d can be closed or opened by telemetry or some
other action-at-a-distance, to close or open the electrical path
from the connecting wire to the battery pack BAT1 and to the
stimulating electrode ST1. The resistors R-sub-a and R-sub-d are
also part of the circuit. The resistance of R-sub-a and R-sub-d are
of such a value that it is far more difficult for the stimulating
current signal sent by BAT1 to go through them then to go through
the stimulating device ST1. In our main embodiment we disclose a
value of 1000 larger electrical resistance for R-sub-a/R-sub-d than
for the stimulating device ST1. The typical resistance of a
DBS-type ST1, as used in current art, is around 1 k-Ohms, so
R-sub-a and R-sub-d are 1000 k-Ohms=1 M-Ohms resistances. The
equation that describes the power usage by resistive electrical
devices is the Joule's law, which says that for a fixed electric
potential (voltage) the power used is inversely proportional to the
resistance, as 1000 times higher resistance, 1000 times less power.
Consequently the fixed resistors R-sub-a and R-sub-d use
1/1,000=0.1% of the total power delivered by the battery, a very
small amount of the total power delivered by the BAT1. Battery
lifetime is important for implanted devices, because when the
battery runs out, another small surgery needs to be performed to
change it; a small surgery to change a box implanted just under the
skin, but a surgery nonetheless. Assuming a lifetime of 3 years for
the battery, which is typical, and considering that 3 years is
approximately 1,000 days, the addition of the 2 resistors, each
using 1/1000 of the power used by the stimulating device ST1,
subtracts 2 days of operation (one for each resistor), therefore
decreasing the total lifetime of the battery from 3 years to 2
years, 11 months and 29 days (on a 31 days month)--a very
negligible and eminently acceptable decrease in battery
lifetime.
Operation of the Invention
[0050] Operation of the Invention for Electrical Engineers.
[0051] In the main embodiment of our invention, during normal
operation, switches SW1 (a, b, c, and d) are set to the conductive,
or closed state (see FIG. 1a). In this state the main path from the
electrical power source to the stimulating device is the normal
path offered by the wires that run through d-a and b-c. Resistors
R-sub-a and R-sub-d are in parallel with the circuit of interest
(ST1) but their values, being as it is suggested, 1,000 larger than
the device impedance along implanted stimulating device ST1,
represents only a minimal perturbation of the system that can
safely be disregarded--at least as far as energy drain is
concerned. The electrical power source is usually a battery, and is
a battery for the main embodiment, but not necessarily so. This
normal operation is any situation in which the patient is not
subjected to very high power of radio frequency. When the patient
knows that he/she is going to enter an environment of high power
radio frequency, as happens during MRI imaging, the patient
him/herself, or a nurse, an M.D., or any other trained personnel,
using a telemetry instrument which works together with the
implanted electronics in the patient's chest, in a similar way as a
remote control of a TV or similar device, sends a command to the
electronics in the battery pack/electronics box BAT1 located in the
patient chest to turn off (to the non-conductive or open state)
switches SW1 (a, b, c and d). Though the main embodiment discloses
switches SW1 (a, b, c, and d) as under control of the electronics
in the box indicated as BAT1 (several figures), this is not the
only possibility, it being also possible that SW1 answers to direct
commands from the telemetry, or any other combination. In this
state, the current that is induced in the connecting wires cannot
reach the stimulating device ST1 and the battery pack BAT1 because
it is blocked by the interrupted paths at SW1. The induced current
on the connecting wires would then circulate on the only available
closed path, which is through R-sub-a and R-sub-d (FIG. 1b),
dissipating the induced EM energy on R-sub-a and R-sub-d.
[0052] In the main embodiment switch SW1 is controlled by a digital
command that is sent by the electronics/control command unit in
BAT1 in the same wire as the power wire, and which is separated
from the standard power to ST1 by a high frequency pass filter
followed by a digital decoder which checks if the digital sequence
matches the command to open the switches SW1c and SW1d. If there is
a match the switches are turned off, which starves SW1a and SW1b of
power, which then turns these off too, because in the main
embodiment SW1 (a, b, c and d) are of the normally open type.
[0053] The main embodiment of our invention uses four switches
(SW1a, b, c and d) in line with two wires that run from the
battery/electronics box BAT1 to the stimulating electrodes ST1,
that is, from the chest to the top of the head and from there into
the brain: popularly known as plus and minus, more correctly known
as positive and return or positive and ground or better, live and
ground or return. In actuality there are several such wires
carrying current to the stimulator device, so there exists a
plurality of wires wire1, wire2, etc, each of which contains two
switches SW1a and b, SW1c and d, etc. along its length, capable of
opening its path. Switches SW1, in the main embodiment, are
controlled by the controlling electronics, which is, in the main
embodiment, packaged with the battery BAT1 in the patient's chest.
The extra wires that connect R-sub-2 create a loop to dissipate the
energy induced in the wires that lead to the stimulating device
ST1. The introduction of the closed loop is crucial for the
invention, for without it the electric potential difference (often
called voltage in US) would increase on the switches SW1a, b, etc.
by the induced EMF effect, as described by Maxwell's equations,
eventually causing arcing, possible destruction of the switches,
and potential harm to the patient. From this controlling
electronics, which is capable of receiving controlling signals by
radio waves or some other type of telemetry, a wire with a command
runs to the switches SW1a, SW1b, etc. In the main embodiment this
is the same as the power wire, separated by a high=frequency filter
to select the command for SW1a, b, etc. The command may be, for
example, f=100 kHz to turn switch on (completing the connection),
and 10 kHz to turn the switch off (disconnecting the connection),
and the switches should latch once set in any state. It is also
possible to have separate command wires for this control, but the
main embodiment uses the same as the power wire to save space in an
implanted device. In the normal situation for brain stimulation,
that is, current running through SW1a, b, c and d, to the
stimulating electrodes in the brain ST1, CW1 is set to the on (or
conducting state), while during MRI imaging CW1 is set to the off
state. In the former situation (stimulation working) almost all the
electrical current, as set by the controlling electronics in the
battery pack/electronics control BAT1 in the patient chest, is
directed to the stimulating electrode ST1 in the brain, while in
the latter situation (during MRI imaging) there is no possible
electrical current path to the implanted electrodes, while an
alternative path is available to dissipate the energy in the
resistances along the loop a-b-c-d-a through dumping resistors
R-sub-a and R-sub-d.
[0054] Operation of the Invention for General Background
Readers.
[0055] Varying electromagnetic fields always induce currents on
wires which are in their space. This is why antennas pick up radio
signals, and why transformers work as they do. This is an
unavoidable result. Therefore, the wires that carry the power or
other electrical signals to the stimulating device are certain to
"absorb" electrical energy from the approximately 50 MHz imaging
radio frequency wave used for the MRI imaging. This "absorbed", or
induced electric current, is capable to cause harm to the wearer of
implanted electrical devices, because the imaging radio frequency
wave carry power equivalent to 20 or more pressing irons (20 kW or
more), which is a lot of heat. Since this induced power cannot be
prevented, our invention discloses a set of switches SW1 (a, b, c,
and d) to disconnect the battery+electronics in box BAT1, and the
stimulating device ST1, of the wires that connect them. In the main
embodiment the switches SW1 (a, b, c, and d) are semiconductor
switches. SW1 (a, b, c, and d) etc. are controlled by signals sent
over the power wires, blocked from the switches by a high-frequency
passing filter, that is a frequency filter that only allows high
frequencies to pass, which is able to pass to types of signals, at
two different frequencies f1=10 kHz and f2=100 kHz, one to turn SW1
on, the other to turn SW1 off.
[0056] Once SW1 is off, the continuous path through the stimulating
device ST1 and through the battery/electronics box BAT1 is open
(that is, not available to electrical conduction), which causes
that the only closed path for current flow is the path that goes
through resistors R-sub-a and R-sub-d, which then dumps the induced
EM radiofrequency induced on the connecting wires.
[0057] Without the alternative path through R-sub-a and R-sub-d,
the electric potential (known as voltage in US) would increase with
the possibility of arcing and destruction of switches SW1, besides
opening ST1 and BAT1 to destruction by the high current induced by
the induced radio frequency signal. With the available path through
R-sub-a and R-sub-d, these act as energy dump, dissipating the
energy induced in the wires that are part of the implanted
device.
Description and Operation of Alternative Embodiments
[0058] Several alternative embodiments are possible. For example,
it is possible to have one single switch in each stimulating wire,
say near the skull, SW1a, omitting the second switch SW1b, on the
return wire, because once the path is broken no current can flow
through stimulating electrodes ST1. Likewise for the battery
pack/electronic circuit, it is possible to omit SW1d, keeping only
SW1c, for the same reason. Redundancy may be preferable to offer
more protection, this being why the main embodiment contains
redundancy, a common practice in all branches of engineering, but
redundancy is not necessary for the operation of the basic
principle of this invention, which is to break the path for induced
current while opening an alternative path to dissipate the energy
induced by the high frequency external EM field.
[0059] Another alternative embodiment is to use filters F1a, F1b,
etc and F2a, F2d, etc., passive or active filters, in lieu of the
switches SW1a, SW1b, etc. and in line with R-sub-a, R-sub-b etc.,
or in lieu of these. The word "filter" is used in the art of
electronics engineering to mean "frequency selective device",
devices that provide an easy flow for some frequencies and a
difficult flow for other frequencies (see definitions).
[0060] This option would obviate the necessity of switches to open
the circuit leading to the stimulating device ST1 and the
battery/electronics pack BAT1. This option would use low-pass
filters (filters that pass low frequencies only) to close the path
for the RF higher frequencies induced by the MRI equipment, to both
the stimulating device ST1 and the battery/electronics pack BAT1. A
low-pass filter (that allows passage of only low frequencies) is a
permanently blocking switch SW1 for the higher frequency induced
currents that cause the damage during MRI. Likewise, a
high-frequency pass filter is a constantly unimpeded path to allow
the flow of the induced RF (high frequency, around 50 MHz), to flow
through the loop composed of resistors R-sub-a and R-sub-d. For
example, a low-pass filter F1 could permanently connect the wires
that connect BAT1 to ST1 in place of the switches SW1 (a, b, c and
d), this filter designed to have low impedance Z1-low (low
resistance, or conductive state) to the low frequency used by the
stimulation signal (usually around 10 kHz, but the exact value is
not part of this invention but it is old art, as practiced by
neurologists), while having high impedance Z1-high (high
resistance, or non-conductive state) for the high frequency
characteristic of the induced radio frequency signals, e.g., used
by imaging MRI, which is of the order of 50 MHz, depending on the
static magnetic field, which is typically of the order of 2 to 5
Tesla. Such a filter F1, in the positions where SW1 are located in
the main embodiment, would allow the desired stimulating frequency
(=.about.10 kHz) to flow into the neuron stimulator ST1, while
permanently blocking most of the energy at the much higher
frequencies (=.about.50 MHz) created by MRI imaging systems. Such
an alternative embodiment may also have a different set of filters
F2 (high-pass filters, that pass the high frequencies) could be
added in series with R-sub-a and R-sub-d, such that
[0061] Z1-low<<Z2-low<<R-sub-a (at low frequencies)
[0062] Z1-high>>Z2-high<<R-sub-a (at high
frequencies),
[0063] Where low frequencies above means around 10 kHz, which
corresponds to the 200 Hz stimulating signal of 100 microsecond
pulsewidth, corresponding to a 10 kHz frequency, and high
frequencies means 50 MHz, which are the stimulating frequencies and
the imaging frequencies, respectively. Note here that the actual
stimulating frequency used by existing art is 200 Hz (200 square
pulses per second), but with 100 microsecond wide pulses, which
corresponds to a frequency of 10 kHz. It can be proved
mathematically that to pass a 100 microsecond pulse every 200 times
per second (200 Hz), it takes a filter that is easy for 10 kHz.
[0064] In this case the low frequency signal (approximately 10 kHz)
would find a much easier path (through Z1-low) to the stimulating
electrode ST1 than through the alternative parallel path through
Z2-low and R-sub-a, while the opposite would happen with the RF
high frequency induced signal at approximately 50 MHz by the MRI
system, which would find an easier path through R-sub-a and
R-sub-d, via Z2, than to the stimulating electrode ST1. In this
alternative embodiment most of the desired signal would still go to
the electrode ST1 while most of the undesirable RF signal would
still be dissipated in Ra, via Z2, etc, instead of depositing its
energy in the electrode ST1 or in the battery pack/electronics
BAT1.
[0065] It is also possible to have other combinations of frequency
filters (usually known in the electronics art simply as filters)
and the main embodiment. For example, it is possible to have the
main embodiment and filters F2 described above in series with
R-sub-a and R-sub-d, with high impedance for low-frequencies
(around 10 kHz) and low impedance for high-frequencies (around 50
MHz). Such an addition would make the main embodiment more robust,
with less wasted energy on the dumping resistors R-sub-a and
R-sub-d.
[0066] It is also possible to have some of the switches SW1 as
described in the main embodiment, while others being substituted by
the filters F1 described above, for example, have SW1c and SW1d
(the left side of FIG. 1), substituted by filters F1c and F1d.
[0067] Many other combinations are possible, as the persons with
skills in the art will see, which are still in the scope of our
invention.
[0068] Persons with skills in the art of medicine but not in the
art of electronics can look at filters as a permanent selective
switch that blocks certain signals while allowing other signals to
proceed, the selection being made according to the frequencies of
the signals. Persons with skills in the art of medicine but not in
the art of electronics can appreciate that such a filtering is what
occurs in all radio receivers, which separates a station
transmitting at a certain frequency from another station
transmitting at another different frequency. Frequency filters are
common in the art of electronics and are a developed field.
[0069] Another possible alternative embodiment shown in FIGS. 2a
and 2b, is to use switches SW1 as in the main embodiment and
switches SW2a and SW2d, in series with resistors R-sub-a and
R-sub-d. This latter switches would be in the on, or conductive
state when SW1 is in the off, or non-conductive state, and
vice-versa. During normal stimulation, which is the case all the
time except during MRI imaging situations, all SW1 are in the on
state (conductive state), allowing current to flow through
stimulating device ST1 and/all SW2 are in the off state
(non-conductive state), blocking this alternative path through
R-sub-a and R-sub-d. Conversely, during MRI imaging, all SW1 would
be turned, by telemetry, to the off (or non-conductive) state, and
all SW2 would be turned, by telemetry, to the on (or conductive)
state, thereby isolating both the stimulating device ST1 and the
battery/electronics box BAT1, while connecting the alternative
network a-b-c-d-a, through resistors R-sub-a and R-sub-d, where the
induced RF energy is dissipated.
[0070] Another possibility is to have filters with impedances Z1
(in the path to ST1) and Z2 (in the path of R-sub-a and R-sub-d) as
above, and also switches SW2 in series with Z2. Such switches SW2
would then be of the type normally opened switches (normally not
conducting), which would go into the closed state (conducting
state) upon receiving a digitally-coded signal, for example,
short-short-short-long-long-long-short-short-short, which would
open a conductive path to filters Z2 and R-sub-a, R-sub-d, etc.
Such a variation would cause a much larger impedance (resistance)
to the alternative energy-dumping path through R-sub-a, R-sub-d,
etc. when the patient is in the normal state, at which times it
would be preferable not to have R-sub-a, R-sub-d, etc.
[0071] Several possible alternatives are possible. One such
possible variation is that the loop wires, e.g., the wire
connecting points a to b, where R-sub-a and R-sub-d are located,
are made of such an alloy as to offer a substantially larger
resistance per unit length (resistivity), than the total resistance
of the loop wire that goes from the battery to the stimulating
device. For example, the total resistance of the wire connecting a
to b can be 1000 times larger than the total resistance of the
stimulating wire that goes from the battery to the stimulating
device. Such wire with such a distributed resistance, 1000 times
larger than the stimulating wire, would dissipate one thousand
times less electrical energy than the stimulating wire, because the
power dissipated is, according to Watt's power dissipation
equation, P=delta-V/R*2.
[0072] Another possibility is to have said resistors R-sub-a and
R-sub-d connected in cross: R-sub-a connected from point a to point
c and R-sub-d connected from point d to point b. Such a connection,
which would make an "X" in FIG. 1, still keeping the general
objective of offering an alternative path to any current induced by
RF in the connecting wires.
[0073] Another possibility is to have said resistors R-sub-a and
R-sub-d connected in parallel with said connecting wires from point
b to point c and said return wire from point a to point d: R-sub-a
connected from point a to point d and R-sub-d connected from point
b do point c. Such a connection would be in parallel with
connecting wires that carry the electrical current from the
electrical energy source/electronics circuit to the stimulating
electrodes.
[0074] Another possibility is to have several power carrying wires
at different voltages (or current) levels, which opens the
possibility of having different stimulating electrodes at different
voltages (or current) levels. In this case each separate power
carrying wire has its individual switch SW1.
[0075] Another possibility is to have a plurality of wires for use
as control wires as normally used in digital electronics. These
control wires could select one or another possible combination of
functions at the stimulating device ST1.
[0076] Another possibility is to have a plurality of wires for use
as address wires, as normally used in digital electronics. These
address wires could select one of a plurality of electrodes at the
stimulating device ST1. In this case the stimulating device has the
appropriate decoder associated with each stimulating electrode (or
pad), which is selected or deselected according to its own address,
using the normal practices of digital addressing.
[0077] Another possibility is to have the plurality of control
wires and address wires as a single wire which convey the
information for the stimulating device ST1 in a serial fashion, as,
for example, USB serial connection. In this case the minimum wire
number is one (plus return wire which may be common with all other
wires due to the device working at low frequencies). In this case
there exists a serial to parallel converter in the stimulating
device ST1.
[0078] Another possibility is to have switches SW1 inside the
stimulating device instead of outside it as in FIG. 1. This
possibility is shown in FIG. 3.
[0079] Another possibility is to have one or a plurality of
dedicated wires (not shown) to control switches SW1 and SW2 (and
others).
[0080] Other alternatives that are possible for the VCVS filter
displayed in FIG. 4. For example a Chebychev filter is another type
of active filter, as are a Sallen-and-Key filter, a Butterworth
filter, a Bessel filter, and so on. Indeed, any active filter would
do a similar frequency blocking still using small size capacitors.
A particular case may be better with a particular active filter,
and the difference between any two filters may be larger or
smaller, depending on the case, but the particular active filter
type is unimportant for this invention but only that it is a
frequency selective device.
[0081] Another possible alternative for the main embodiment is to
have active filters placed at more places along the wires, for
example, every 10 cm. along any wire, or any other spacing. Such
multiple filters would contribute for the prevention of pulse
propagation along the wire on a multiplicative manner, besides
preventing any current build-up on the wires. Given that the
filters would use power only when activated, which is expected to
be rarely, there would be no power disadvantage associated with
such a scheme, while offering better filtering and imaging RF
blocking.
[0082] Another possible alternative for the main embodiment is to
have active filters and switches together all the time. In such an
alternative embodiment the high frequency induced signal would
always see a difficult path to the stimulator ST1 and to the
battery pack/electronics BAT1, on top of which the electrical path
would be opened (disconnected) during MRI imaging.
[0083] Another possible alternative embodiment is for stimulating
devices which uses one connecting wire only, using the body of the
wearer as a return path. Some stimulating devices are of this type.
In this case there exists one wire only, and only SW1a and SW1c. In
this case R-sub-a and R-sub-d connect each wire extremity to the
body of the wearer, which forms the return path. As it will be
appreciated by electrical engineers, connecting the four switches
as said does offer some degree of protection to both the battery
pack BAT1 and the stimulating device ST1.
[0084] One of the improvements of our invention over prior art
electrical stimulating devices, is the introduction of one or
several switches, in-line (along the path) of the pertinent wires,
which are capable of opening the conductive electrical path on the
wires going from the battery pack/electronics located on the chest
to the top of the head and implanted electrode, therefore
interrupting the path of the radio frequency waves induced by the
MRI or other processes. Such switches, which can be located in a
plurality of places along the electrical path are controlled by
telemetry or some action at a distance, using radio control or the
like. These controls, action-at-a-distance can act either on the
controlling electronics housed in BAT1, which would in turn issue
the appropriate commands, carried by wires or by radio signals, to
the switches, or they can act directly on the switches themselves.
Moreover, our invention discloses switches which are capable of
being turned on or off, or to direct the electrical current one
path or another, or to disconnect the wire altogether, acting upon
external commands, which are send by telemetry, using the existing
methods of telemetry to control and adjust the prior art devices,
many of which are capable of being adjusted to the needs of each
patient using an external programmer.
[0085] Accordingly, prior to an MRI imaging session, a trained
technician, nurse, or medical doctor, can disconnect the normal,
low impedance pathway for electrical stimulation, causing that an
alternative available circuit containing a network of simple
resistors (as R-sub-a, R-sub-d, etc.), or a network of simple
resistors and high-pass filters, that is, filters that allow high
frequency to pass with little opposition, is available for the
unavoidable induced RF to dissipate the induced energy in the wires
that connect the electrical stimulation device. The high-pass
filters can be made with either passive or active devices.
[0086] An active filter (op-amp based) is better than a passive
(RC, RLC) filter because it offers sharper transitions from
passing-to-blocking frequencies. Active filters rely on an external
power supply, which in most cases is no problem, but in the case of
an implanted device, which runs on the power of an implanted
battery, which needs surgery for replacement, the energy used by an
active filter is a serious disadvantage. Indeed, given that every
electrical engineer is aware of the superiority of active filters
over passive ones, the inventors suggest, but this is not known for
sure, and should not therefore be used against the invention, that
the use of active filters were never introduced before due to their
power consumption. This invention discloses a solution to this
problem, as seen in the sequel. Moreover, in the majority of cases,
such an active filter consumes power for no reason, because it is
only needed if the patient undergoes an MRI imaging procedure,
which happens only infrequently. Besides, even when a particular
patient is subjected to an MRI procedure, the imaging procedure
lasts for less than one hour, an insignificant time when compared
with the years during which the active filter consumes the precious
battery power. The solution we propose is to have one or a series
of active filters, which are powered on demand by the standard
telemetry (radio commands) sent to the battery/electronics pack;
when not undergoing MRI imaging, or any other potentially EM
exposure, the active filter is disconnected from the circuit,
therefore not using the precious battery power. Immediately before
an MRI imaging, the active filter is turned on and connected to the
circuit as needed, providing a better blocking filter for the EM RF
frequency used by the imaging procedure, offering a better
protection than a passive RC or RLC filter would.
[0087] Another advantage of a active filter is their sizes. Active
filters can be designed to work with small valued capacitors. Also
op-amps can mimic the electrical characteristics of inductors,
effectively creating an inductor-in-a-chip, which is of a size
compatible with an implanted device.
[0088] Description of Alternative Embodiments for
Non-Engineers.
[0089] It is not possible to prevent the EM induction (the antenna
effect, so to say) in the wires, so it is necessary to accept that
electric energy will enter (penetrate) the wires of the electrical
stimulating devices, then travel to the stimulating device ST1 and
battery pack/electronics BAT1. Our invention discloses the use of
selective switches that may block the electrical current, and
filters that substantially blocks the propagation of such electric
energy along the wires, and also of filters and alternative routes
(networks) that bypass the deposited electric energy to less
harmful locations in the body, as muscles. Our invention also
discloses the introduction of switches SW1 and SW2 (a, b, c, etc.)
located at strategic points in the circuit so as to eliminate or at
least to minimize the damage caused by such induced currents.
Induced currents can occur during MRI imaging and also in any other
situation where the patient is exposed to electromagnetic
radiation, the power of it increasing the danger of the consequent
harm to the patient.
[0090] One possible technology to make electrical filters to
selective block the flow of some currents but not others, is the
use of active filters, which are built with amplifiers known as
op-amps. The op-amps themselves drain electric power, which is at a
premium in an implanted device whose battery requires surgery for
replacement. This power drain on the battery, if continuous, would
put the use of active filters or any other active circuit out of
the realm of the possibility. Our invention discloses a system of
switches that turns the active circuits off unless they are needed,
that is, unless the patient is entering a situation that requires
high frequency protection. Our invention discloses a system that
drains power for its operation only when the patient needs the
protection from radio frequency EM radiation from magnetic
resonance imaging (MRI).
[0091] FIG. 3 shows an active filter constructed with an op-amp
(operational amplifier) of the VCVS variety. Op-amps are fully
functional amplifiers built in a chip, sometimes several in a chip,
offering high gain, with which it is possible to built a variety of
circuits, including frequency filtering circuits, or circuits that
oppose the flow of AC at some frequencies only, while allowing AC
current at other frequencies to pass. Active filters are more
selective than passive filters, the former using external electric
power to function, the latter using no external power to function.
The former is based on transistors or their equivalents, the latter
is based on resistors, capacitors and coils. The actual op-amp is
very small; even with ancient, 80's technology, a 741 op-amp with
24 transistors, comfortably fits on a pin head, that is, on an area
500 micrometers in side. The full circuit, including the resistors
and capacitors, can be made together in an area that is barely
visible to the human eye with 80's technology, or to an area or 5
by 5 micrometers with Pentium 4 manufacturing technology of 2004.
Note that 5 by 5 micrometers is well smaller than what is visible
to the naked eye. It is therefore perfectly feasible to have some
such op-amp based circuits spaced along the connecting wire, such
filters being so designed as to substantially block the 50 or so
MHz AC induced by the MRI imaging system.
CONCLUSION, RAMIFICATIONS, AND SCOPE OF INVENTION
[0092] In the main embodiment and in its variations disclosed, the
switches in line with the stimulation carrying wires are placed
before, or outside the stimulating electrodes that reside in the
brain. This is not necessary, it being also possible to have some
interrupting switches in the stimulating electrode too.
[0093] The electronic switches can be implemented from transistors,
as bipolar transistors, FETs, etc., or a specially designed
commercial switch as the Fairchild Semiconductor FSA2259
(Low-Voltage 0.8 Ohm Dual-SPDTAnalog Switch, see
REF_Semiconductor_Switch) or any other standard, off-the-shelf
commercially available semiconductor switch, offered by many
semiconductor company. Semiconductor switch is an established
branch of electronics which is not part of this invention. If a
commercial switch is used, it is understood that what would be used
is the die, not the packaged chip, which is much too large for the
application in question.
[0094] The switches can be closed or opened from a distance. The
switches SW1, SW2, etc. can be controlled either by the electronics
circuitry together with the battery pack or by direct telemetry,
that is, from an outside command via radio, or infrared, etc.
signals. The controlling commands can be digital or analog, without
changing the scope of the invention.
[0095] The switches of the main embodiment and its variations can
be operated by radio command, as disclosed in the main embodiment
but also by other types of telemetry, as infrared, ultrasound,
etc., as is obvious to the persons familiar with the art. Radio
command was used only as a possible example, it not being intended
to be a limitation of the invention.
[0096] The extra wires (wires WireControl1 and WireControl2) to
control the switches SW1 and SW2 can be replaced by a digital code
which can be send by the existing wires that send the pulses to the
implant. This is similar to a radio controlled garage door opener,
some of which send a particular digital sequence which is
recognized by the garage door opener mechanism that acts
accordingly. In this case the digital signal is sent by the wire,
the same wire that carries the electrical stimulation pulse. It is
also possible that instead of the switches be under control of the
battery pack/electronics box, they are under direct control of an
external device, in this case much like a garage door opener. In
either case, the switches would contain a digital signal decoder to
detect the digital signal with the instruction to open or to close
each switch. These signals are common electronics circuits, widely
used by many common devices, and are not part of this invention,
which simply can be made with any of the existing prior art.
SEQUENCE LISTING
[0097] Not applicable.
DEFINITIONS
[0098] AC=Alternating current. Electric current characterized by a
back-and-forth, or to-and-from motion. The standard electric power
is AC, at the standard frequency of 60 Hz. Cf DC
[0099] Active filter=In electronics, a filter, or device to select
some frequencies to be accepted, while rejecting others that are
rejected, which uses at least one, usually more, active devices, as
transistors, op-amps and the like, which uses an external electric
power source to function. Cf passive filter.
[0100] AM=Amplitude modulation, e.g. REF_Horowitz.
[0101] DC=Direct current. Electric current that flows in one
direction only along a wire.
[0102] EM=Electromagnetic.
[0103] Filter=The word "filter" is used in the art of electronics
engineering to mean "frequency selective device", devices that
provide an easy flow for some frequencies and a difficult flow for
other frequencies. Usage defines low-pass filters (which means
low-frequency pass filters) as a filter that provides an easy path
for low frequencies, and correspondingly a difficult path for high
frequencies, with the equivalent modifications for high-pass
filters (which means high-frequency pass filters) being a filter
that provides an easy flow for higher frequencies and a difficult
flow for low frequencies. In either case the frequency of
transition from one case to the other is characteristic of the
particular situation, and the steepness of the transition as well.
There exists also band-pass filters, which provides a low, easy
path for frequencies within a certain range, while providing a
difficult path (that is, blocking) lower and higher frequencies
outside the selected range. Electronics engineers distinguish
between passive filters (made with passive devices, as R, L and C),
and active filters (made with active devices, as op-amps). The
latter have sharper transition curves from low-to-high impedance at
the transition frequency.
[0104] FM=Frequency modulation, e.g. REF_Horowitz.
[0105] MRI=Magnetic Resonance Imaging. A modality of imaging in
which the protons, mostly in hydrogen are the major responsible for
the imaging signal. It is carried or produced placing the object to
be imaged inside a strong magnetic field then directing RF
radiation to it and measuring how much is absorbed and transmitted
as a function of the magnetic field.
[0106] Passive filter=In electronics, a filter, or device to select
some frequencies to be accepted, while rejecting others that are
rejected, which uses exclusively passive elements, as resistors,
capacitors, inductors and the like. A passive filter needs no
external power to function. Cf. active filter.
[0107] Radiation=a widely used term with many meanings, here used
as EM (electromagnetic) radiation only. Note that "radiation" is
often used as a short for "ionizing radiation", as gamma rays,
which can cause cancer. The frequencies used in this case are
non-ionizing, so radiation used in this context is not
cancer-causing agent.
[0108] RF=Radio frequency. General term for EM (q.v.) frequencies
above audio frequencies, that is, above 20 kHz, but generally much
above this. Normally the term applies to frequencies starting at
the low end of the AM range (650 kHz) going to at least the upper
end of FM and TV frequencies, some few hundreds MHz or more. THz is
generally not considered RF anymore, but microwave.
[0109] Telemetry--used in the context of implanted devices for DBS
means the transmission of information using EM waves or any similar
action-at-a-distance physical phenomenon, to send instructions to
modify the state of operation of the device. Typically the
instructions are send to the microcontroller embedded in the
battery/electronics pack located in the chest, but nothing forbids
other receiving units in other locations.
REFERENCES
[0110] Medtronic MRI 2002,
http://www.medtronic.com/downloadablefiles/UC198877001EN.pdf, pg.
8, 37 ff. [0111] REF_Horowitz Horowitz and Hill "The Art of
Electronics" Cambridge University Press 2.sup.nd ed. (1989) [0112]
REF_DieSize The Prescott, which is the codename of a 2004 version
of the Pentium 4, sports 125 million transistors in 122 mm2, or
about 1 million transistors per mm2. The popular 741 op-amp is made
of 24 transistors, which scales to an area of 5 by 5 micrometers,
invisible to the naked eye! http://techreport.com/articles.x/6213/1
Not only is the 90 nm process smaller, but Intel is also
manufacturing Prescott using seven layers of copper interconnects,
instead of the six used at 130 nm. All told, the changes shrink the
Pentium 4's die size to 122 mm2, from 145 mm2 for Northwood--this
despite the fact Prescott's transistor count is 125 million, over
twice Northwood's 55 million transistors. Number of transistors
throughout IC history, particularly microprocessors
http://en.wikipedia.org/wiki/Transistor_count [0113]
REF_Semiconductor_Switch
1. Fairchild Semiconductors
[0114] http://www.fairchildsemi.com/pf/FS/FSA2259.html
FSA2259
Low-Voltage 0.8 ohm Dual-SPDTAnalog Switch
General Description
[0115] The FSA2259 is a high-performance, dual, Single Pole Double
Throw (SPDT) analog switch that features low RON of 0.8 W (typical)
at 3.0V VCC. The FSA2259 operates over a wide VCC range of 1.65V to
4.3V and is designed for break-before-make operation. The select
input is TTL-level compatible. The FSA2259 features very low
quiescent current even when the control voltage is lower than the
VCC supply. This feature suits mobile handset applications by
allowing direct interface with baseband processor general-purpose
I/Os with minimal battery consumption.
Features
[0116] 0.8 W Typical On Resistance (RON) for +3.0V Supply [0117]
0.40 W Maximum RON Flatness for +3.0V Supply [0118] -3 db
Bandwidth: >50 MHz [0119] Low ICCT Current Over an Expanded
Control Input Range [0120] Packaged in 10-Lead UMLP (1.4.times.1.8
mm) [0121] Power-Off Protection on Common Ports [0122] Broad VCC
Operating Range: 1.65 to 4.3V [0123] HBM JEDEC: JESD22-A114 [0124]
I/O to GND: 8.5 kV [0125] Power to GND: 16.0 kV 2. Pericom is a
source for ASS (Application Specific Switches)
http://www.pericom.com/pdf/presentations/switch_ov.pdf [0126] REF
Kroll2008 U.S. Pat. No. 7,369,898 Kroll, et al. May 6, 2008 System
and method for responding to pulsed gradient magnetic fields using
an implantable medical device [0127] REF_Zeijlemaker2009
Zeijlemaker et al. "Controlling telemetry during magnetic resonance
imaging", U.S. Pat. No. 7,623,930, Nov. 24, 2009 [0128] Medtronic's
New MRI Compatible Pacemaker Gets CE Mark
Tuesday, Jun. 23, 2009
[0129] http://medgadget.com/archives/2009/06/medtronic.html [0130]
Positive Results for Medtronic's MRI-Safe Pacemaker
Thursday, May 14, 2009
[0131]
http://medgadget.com/archives/2009/05/positive_results_for_medtroni-
cs_mrisafe_pacemaker.html [0132]
http://www.medtronic.com/physician/mri_safety/index.html# [0133]
http://www.medtronic.com/physician/mri_safety/clinicalControversy.html
[0134]
http://www.medtronic.com/physician/mri_safety/safeDesign.html
[0135]
http://coolmristuff.wordpress.com/2009/01/05/medtronic-mri-pacing--
system-shows-promise-2/
Medtronic MRI Pacing System Shows Promise
[0136] http://wwwp.medtronic.com/Newsroom/NewsReleaseDetails.do?
itemID=1245340154210&lang=en_US [0137] advisa clinical trial:
http://clinicaltrials.gov/ct2/show/study/NCT00839384 European news
clip http://wwwp.medtronic.com/Newsroom/NewsReleaseDetails.do?
itemId=1245340154210&lang=en_US [0138] 1. Gimbel J and Kanal E.
Can patients with implantable pacemakers safely undergo magnetic
resonance imaging? J Am Coll Cardiol. 2004;43:1325-1327.
* * * * *
References