USOO7396326B2
`
`(12) United States Patent
`Ghiron et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,396,326 B2
`Jul. 8, 2008
`
`(54) FERROFLUIDIC COOLING AND
`ACOUSTICAL NOSE REDUCTION IN
`MAGNETIC STIMULATORS
`
`(75) Inventors: Kenneth Ghiron, Allentown, PA (US);
`Mark Edward Riehl, Doylestown, PA
`s
`s
`(US)
`(73) Assignee: Neuronetics, Inc., Malvern, PA (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 11/130,657
`(22) Filed:
`May 17, 2005
`
`(65)
`
`Prior Publication Data
`US 2006/0264692 A1
`Nov. 23, 2006
`
`(2006.01)
`(51) E" on
`(52) U.S. Cl. .............................o 600/13
`(58) Field of Classification Search ............. i.
`s.
`See application file for complete search history.
`References Cited
`U.S. PATENT DOCUMENTS
`
`(56)
`
`3,658,051 A * 4, 1972 MicaLean ..................... 600/14
`3,683,923 A
`8, 1972 Anderson ....
`... 128,303.14
`4,078.392 A
`3, 1978 Kestner ......................... 62/99
`4,601,753. A
`7, 1986 Soileau et al.
`... 75,251
`4,994.015 A
`2/1991 Cadwell ...................... 600/13
`5,078,674. A
`1/1992 Cadwell ...................... 600/13
`5,097,833 A
`3/1992 Campos ...
`... 128/421
`5,116,304 A
`5, 1992 Cadwell
`... 600/13
`5,299,569 A
`4, 1994 Wernicke et al. .............. 6O7/45
`
`
`
`1/1998 Young ........................... 600/9
`5,707,334 A
`6/2000 Klopotek ..........
`... 606/27
`6,074.385 A *
`1/2001 Ishikawa et al. ............... 600/9
`6,179,769 B1
`1/2001 Mueller .....
`... 600/13
`6,179,771 B1
`3/2001 Ives et al. - - - - - - - - -
`... 600,411
`6,198.958 B1
`T/2001 Ilmoniemi et al. .......... 600/544
`6.256,531 B1
`5/2002 Zarinetchi et al. ............. 607.61
`6,389,318 B1
`6/2002 Fischell et al. ................ 600, 13
`6,402,678 B1
`1 1/2002 John ...................
`... 607,45
`6,463,328 B1
`1 1/2002 Kirkpatricket al. ........... 607,45
`6,480,743 B1
`6,484,059 B2 11/2002 Gielen .................
`... 607,45
`6,497,648 B1
`12/2002 Rey .................
`... 600/14
`6,503,187 B1
`1/2003 Ilmoniemi et al. ............ 600, 14
`6,516.288 B2
`2/2003 Bagne ........................ 702/179
`6,560,490 B2
`5/2003 Grill et al. .................... 6O7/72
`6,567,702 B1
`5/2003 Nekhendzy et al. ........... 6O7/46
`(Continued)
`FOREIGN PATENT DOCUMENTS
`
`EP
`
`1273 320 A1
`1, 2003
`(Continued)
`OTHER PUBLICATIONS
`Baudewig, J. et al., “Functional MRI of Cortical Activations Induced
`by Transcranial Magnetic Stimulation(TMS)”. Brain Imaging
`NeuroReport, 2001, 12(16), 3543-3548.
`(Continued)
`Primary Examiner Samuel G. Gilbert
`(74) Attorney, Agent, or Firm Woodcock Washburn LLP
`(57)
`ABSTRACT
`A ferrofluid chamber has a housing that is adapted to be
`coupled to a component that generates a magnetic field of
`Sufficient strength to stimulate anatomical tissue. In addition,
`a ferrofluid is disposed within the housing for cooling the
`component.
`
`30 Claims, 6 Drawing Sheets
`
`HEAT excHAIGER 32
`
`
`
`
`
`Sound
`Absorber
`36
`
`...it isote DENSE
`stolice Aracon
`
`FERROFLUID30
`
`Chamber
`36
`
`LUMENIS EX1008
`Page 1
`
`

`

`US 7,396,326 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
`6,571, 123 B2
`5/2003 Ives et al. ................... 600,544
`6,629,935 B1
`10/2003 Miller et al. ...
`... 600,558
`6,641,520 B2 * 1 1/2003 Bailey et al.
`... 6009
`6,663,556 B2 12/2003 Barker ...........
`... 600/14
`6,827,681 B2 12/2004 Tanner et al. ...
`... 6009
`6,849,040 B2
`2/2005 Ruohonen et al. .
`... 600/14
`6,978,179 B1
`12/2005 Flagget al. .......
`... 607,45
`2001/0031906 A1 10, 2001 Ishikawa et al. ..
`... 600/13
`2002fOO13612 A1
`1/2002 Whitehurst ....
`... 607,45
`2002fOO872O1 A1
`7/2002 Firlik et al. ....
`... 607,45
`2002/009 1419 A1
`7/2002 Firlik et al. ....
`... 607,45
`2002/0103515 A1
`8/2002 Davey et al. ...
`... 607.66
`2003,0004392 A1
`1/2003 Tanner et al. ..
`... 6009
`2003/0023159 A1
`1/2003 Tanner .......
`600,417
`2003/0028072 A1
`2/2003 Fischell et al.
`... 600/13
`2003/0050527 A1
`3/2003 Fox et al. ..........
`... 600/13
`2003/0073899 A1
`4/2003 Ruohonen et al. .
`... 600,417
`2003, OO88274 A1
`5, 2003 Gliner et al. ......
`... 607.3
`2003/0097.161 A1
`5, 2003 Firlik et al. ....
`... 607,72
`2003/O125786 A1
`7/2003 Gliner et al. ......
`... 607,116
`2003/030706 A1
`7/2003 Sheffield et al. ...
`... 607,46
`2003. O195588 A1 10, 2003 Fischell et al. .
`... 670/55
`2003/0204135 A1 10/2003 Bystritsky ...
`600/407
`2004/0010177 A1
`1/2004 Rohan et al. ...
`... 6009
`2004/OO77921 A1
`4/2004 Becker et al. ..
`... 6009
`2004/O127942 A1
`7/2004 Yomtov et al. .
`... 607.3
`2004/O153129 A1
`8, 2004 Pless et al. .....
`... 607.62
`2005, 0021104 A1
`1/2005 DiLorenzo ..
`... 607,45
`2005, 0124848 A1
`6, 2005 Holzner ......
`6009
`2005/0216071 A1
`9, 2005 Devlin et al. ...
`... 607,48
`2005/0228209 A1 10, 2005 Schneider et al. .
`... 600/13
`2005/0256539 Al 11/2005 George et al. .................. 607/2
`
`
`
`FOREIGN PATENT DOCUMENTS
`
`WO
`WO
`WO
`WO
`WO
`WO
`WO
`WO
`WO
`WO
`WO
`WO
`
`WO99,64884
`
`WOO1-97906 A2
`WO O2/O9811
`A1
`WO O2/032504
`A2
`WO O2/O85449
`A2
`WO O2/O85454
`A1
`WO O2/O89.902
`A2
`WO O2/O94997
`A2
`WOO3,035.162
`A2
`WO 04/082759
`A2
`WO 04/100765
`A2
`WO 05/OOO401
`A1
`
`12/1999
`12/2001
`2, 2002
`4/2002
`10, 2002
`10, 2002
`11, 2002
`11, 2002
`5, 2003
`9, 2004
`11, 2004
`1, 2005
`
`WO
`
`WO 05/065768 A1
`7/2005
`OTHER PUBLICATIONS
`Bohning, D.E. et al., “ATMS Coil Positioning/Holding System for
`MR Image-Guided TMS Interleaved with fMRI”, Clinical
`Neurophysiology, 2003, 114, 2210-2219.
`Bohning, D.E. Ph.D. et al., “Combined TMS/fMRI Study of inten
`sity-Dependent TMS over Motor Cortex”. Society of Biological
`Psychiarty, 1999, 45, 385-394.
`Bohning, D.E. Ph.D. et al., “Bold-fMRI Response to Single-Pulse
`Transcranial Magnetic Stimulation (TMS)”, Journal of Magnetic
`Resonance Imaging, 2000, 11, 569-574.
`George, M.S. et al., “A Controlled Trial of Daily Left Prefrontal
`Cortex TMS for Treating Depression'. Society of Biological Psychia
`try, 2000, 48,962-970.
`Grafman, J. Ph.D., "TMS as a Primary Brain Mapping Tool”
`Transcranial Magnetic Stimulation in Neuropsychiatry, 2000, 115
`140.
`Lisanby, S.H. et al., “Sham TMS: Intracerebral Measurement of the
`Induced Electrical Field and the Induction of Motor-Evoked Poten
`tials”. Society of Biological Psychiatry, 2001, 49, 460-463.
`Lorberbaum, J.P., M.D. et al., “Safety Concerns of TMS'.
`Transcranial Magnetic Stimulation in Neuropsychiatry, 2000, 141
`161.
`Loo, C.K. et al., “Transcranial Magnetic Stimulation (TMS) in Con
`trolled Treatment Studies: Are Some "Sham' Forms Active?', Soci
`ety of Biological Psychiatry, 2000, 47,325-331.
`Nahas, Z. et al., “Unilateral Left Prefrontal Transcranial Magnetic
`Stimulation(TMS) Produces Intesity-Dependent Bilateral Effects as
`Measured by Interleaved BOLD fMRI”. Society of Biological Psy
`chiatry, 2001, 50, 712-720.
`Nahas, Z. et al., “Left Prefrontal Transcranial Magnetic
`Stimulation(TMS) Treatment of Depression in Bipolar Affective Dis
`order: A Pilot Study of Acute Safety and Efficacy”, BiPolar Disor
`ders, 2003, 5, 40-47.
`Pridmore, S., “Substituition of Rapid Transcranial Magnetic Stimu
`lation Treatments for Electroconvulsive Therapy Treatments in a
`Course of Electroconvulsive Therapy'. Depression and Anxiety,
`2000, 12, 118-123.
`Ruohonen, J., “Electroencephalography Combined with TMS'.
`BioMag Laboratory, Helsinki University Central Hospital. http://
`www.biomag.helsinki.fi/tims. TMSEEG.html, Oct. 6, 1999, 22 pages.
`Hess, C.W. et al., “Magnetic Stimulation of the Human Brain: Influ
`ence of Size and Shape of the Stimulating Coil”. Motor Distrubances
`II, 1990, 3, 31-42.
`Wassermann, E.M., “Repetitive Transcranial Magnetic Stimulation:
`An Introduction and Overview', CNS Spectrums, The International
`Journal of Neuropsychiatric Medicine, Jan. 1997, 7 pages.
`* cited by examiner
`
`LUMENIS EX1008
`Page 2
`
`

`

`U.S. Patent
`
`Jul. 8, 2008
`
`Sheet 1 of 6
`
`US 7,396,326 B2
`
`
`
`Cable to TMS
`Stimulator
`20
`
`Strain Relief
`
`
`
`Ferromagnetic
`Core
`12
`
`Flat Wire Windings
`14
`
`Insulating
`Material
`16
`
`Figure 1
`
`LUMENIS EX1008
`Page 3
`
`

`

`U.S. Patent
`
`Jul. 8, 2008
`
`Sheet 2 of 6
`
`US 7,396,326 B2
`
`201
`
`200
`
`Create Magnetic Field
`
`
`
`
`
`
`
`2O3
`
`205
`
`2O7
`
`Circulate Ferrofluid
`
`Heat Ferrofluid
`
`Cool Ferrofluid
`
`Figure 2
`
`LUMENIS EX1008
`Page 4
`
`

`

`U.S. Patent
`
`Jul. 8, 2008
`
`Sheet 3 of 6
`
`US 7,396,326 B2
`
`SOUNDASORBER
`34
`
`
`
`CONVEN
`
`HEATECHANGER
`32
`
`s (A
`/
`
`FERROFLUID
`30
`
`Figure 3
`
`LUMENIS EX1008
`Page 5
`
`

`

`U.S. Patent
`
`Jul. 8, 2008
`
`Sheet 4 of 6
`
`US 7,396,326 B2
`
`
`
`Sound
`AbSOrber
`36
`
`HEAT excHAIGER 32
`
`... it ORE DENSE
`1 STRONGERATTRACTION
`
`FERROFLUID30
`
`Chamber
`36
`
`LUMENIS EX1008
`Page 6
`
`

`

`U.S. Patent
`
`Jul. 8, 2008
`
`Sheet 5 of 6
`
`US 7,396,326 B2
`
`Heat Exchanger 32
`Ferrofluid 30
`Permanent magnet 50
`
`
`
`Chamber 36
`
`
`
`
`
`
`
`Patient 52
`
`Figure 5
`
`LUMENIS EX1008
`Page 7
`
`

`

`U.S. Patent
`
`Jul. 8, 2008
`
`Sheet 6 of 6
`
`US 7,396,326 B2
`
`Heat Exchanger 32
`
`Ferrofluid 30
`
`One way valve 60A
`
`Magnetic material 62
`
`Winding 54
`
`
`
`
`
`
`
`Chamber 36
`
`
`
`One way valve 60B
`
`Patient 52
`
`Figure 6
`
`LUMENIS EX1008
`Page 8
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`

`

`US 7,396,326 B2
`
`1.
`FERROFLUIDC COOLING AND
`ACOUSTICAL NOISE REDUCTION IN
`MAGNETC STIMULATORS
`
`FIELD OF THE INVENTION
`
`The invention relates to the field of magnetic stimulation.
`Specifically, the invention relates to cooling a magnetic
`stimulation device. In addition, the invention relates to acous
`tically insulating Such a magnetic stimulation device.
`
`10
`
`BACKGROUND OF THE INVENTION
`
`2
`etc.), which add to the cost and complexity of the magnetic
`device. Furthermore, the additional moving parts add to the
`potential for a device malfunction.
`An additional consideration of magnetic devices is acous
`tical noise generated by the magnetic coil of a magnetic
`device as the coil is energized. For example, when the coil is
`energized, it creates a strong magnetic field that, in many
`applications, rapidly changes in intensity. The changing mag
`netic field causes windings of the coil to experience hoop
`stresses that intermittently stress the windings, which causes
`a sharp acoustic click.
`Such noise is especially pronounced in magnetic stimula
`tion devices, as the therapeutic magnetic fields are created by
`pulsing the stimulation device's coil. Such noise is problem
`atic for patients, as the stimulation device is typically located
`in close proximity to the patients head, and therefore the
`noise from the stimulation device may be uncomfortable. In
`addition, a health practitioner who is repeatedly exposed to
`Such noise may be adversely affected. A conventional solu
`tion, placing earplugs in the patient’s ears, is undesirable
`because it is an additional step to perform in the therapeutic
`process and does not solve the problem of the noise caused by
`the device in the treatment facility (e.g., physicians office,
`hospital, etc.). In addition, the use of earplugs is undesirable
`because Some psychiatric or young patients may be uncoop
`erative, and therefore the use of earplugs unnecessarily com
`plicates the procedure.
`Thus, a conventional Solution for the reduction of acousti
`cal noise is the placement of noise reduction material around
`all or part of a magnetic device. Alternatively, a chamber
`containing a partial vacuum may be formed around the mag
`netic device, because a partial vacuum contains very few
`particles that may propagate a mechanical (sound) wave.
`However, such noise reduction techniques have the disadvan
`tage of adversely affecting heat transfer for cooling. For
`example, the best noise reduction materials are fabricated to
`contain air pockets that do not transfer noise well. However,
`Such air pockets also have the characteristic being poor con
`ductors of heat. The same is true to an even greater extent in
`the case of a vacuum. Thus, if Such a noise reduction tech
`nique is used, the magnetic stimulation device cannot be
`adequately cooled. Attempting to mitigate Such a dilemma by
`placing acoustical material, or forming a partial vacuum,
`around a cooling system that is itself arranged around a mag
`netic device is undesirable because of the added size, cost and
`complexity of the resulting device.
`Conventionally, ferrofluids have been used to cool audio
`speaker systems, which is a lower Voltage application when
`compared to a magnetic stimulation device or other high
`voltage magnetic device. A ferrofluid is a fluid with sus
`pended ferromagnetic particles. The ferromagnetic particles
`can be influenced by the magnetic field created by the speaker
`So as to enhance fluid convection between the speaker and a
`heat sink to cool the speaker. An additional benefit of ferrof
`luids is that they can be used to cool a device while still
`performing noise reduction, because a ferrofluid typically
`does not Support shear waves. Furthermore, a mismatch in
`Sound Velocity may also cause the reflection of Some of the
`Sound waves.
`Unfortunately, even the ferrofluid solution used in connec
`tion with speakers has disadvantages that may render it
`unsuitable for use with high Voltage magnetic devices, such as
`a magnetic stimulation device. For example, the ferrofluid
`used in connection with speaker cooling, while a dielectric
`when exposed to normal speaker-level Voltages, may be
`unable to maintain dielectric isolation at the higher Voltage
`
`25
`
`30
`
`35
`
`40
`
`45
`
`Magnetic devices are used in many applications, such as in
`magnetic stimulation devices, speakers and so forth. Mag
`15
`netic devices tend to generate heat because of resistive losses
`in the coil(s) that generate magnetic fields(s), and the amount
`of heat generated is proportional to the amount of power
`consumed by the device. Thus, high-voltage magnetic
`devices that consume large amounts of power, such as those
`used in magnetic stimulation therapy, can become very hot
`when in operation. The environment in which the magnetic
`device operates—or the operating characteristics of the
`device itself may dictate that the device operate under a
`certain temperature threshold. For example, in magnetic
`stimulation therapy, the temperature of a magnetic stimula
`tion device used to generate a therapeutic magnetic field
`should be kept below approximately 41.5° C. to stay within
`certain regulatory requirements (e.g., FDA guidelines). If a
`magnetic stimulation device is to be operated attemperatures
`exceeding 41.5°C. Such regulatory requirements dictate that
`the device manufacturer and/or health practitioner must meet
`additional guidelines to prove that operation of the device is
`safe. These additional requirements increase complexity of
`operation and overall cost, and are best avoided when pos
`sible.
`Conventionally, a magnetic stimulation device used for
`Such therapy is used until it reaches a threshold temperature,
`and then the therapy is temporarily halted until the stimula
`tion device cools. Such an arrangement therefore adds to the
`time required to perform a treatment, which is undesirable for
`both the patient and the health practitioner. Alternatively, a
`second magnetic stimulation device may need to be used (i.e.,
`swapped with the first device when the first device reaches the
`threshold temperature) so as to continue the therapy without
`interruption while the first, overheated stimulation device
`cools. This arrangement is also undesirable because of the
`added expense associated with the purchase and maintenance
`of an additional magnetic stimulation device. Furthermore,
`additional time is required of the patient and health practitio
`ner, as the second magnetic device will need to be set-up
`and/or calibrated to perform magnetic stimulation therapy on
`the patient. Because the set-up and/or calibration steps pro
`vide opportunities for operator error, requiring the operator to
`perform such steps multiple times may decrease the overall
`safety level of the treatment.
`Conventional cooling Solutions typically involve the use of
`air or fluid cooling mechanisms. An air cooling mechanism
`may involve a fan that rapidly circulates cooled or room
`temperature air past the magnetic device. A fluid cooling
`mechanism may involve the circulation of a cool fluid past the
`magnetic device, where the fluid cools the device and is
`heated in the process, and then to a cooling mechanism, after
`which the fluid is returned to the magnetic device. Both
`mechanisms have several drawbacks. For example, both
`mechanisms require additional moving parts (e.g., fans, cool
`ing mechanisms such as a refrigeration or heat exchange unit,
`
`50
`
`55
`
`60
`
`65
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`LUMENIS EX1008
`Page 9
`
`

`

`US 7,396,326 B2
`
`3
`levels used in connection with a magnetic stimulation device.
`As a result, arcing or other problems may occur.
`Therefore, what is needed is a ferrofluidic cooling appara
`tus, system and method for high Voltage applications. More
`particularly, what is needed is an apparatus, System and
`method for convectively circulating a ferrofluid to cool a high
`Voltage magnetic device. Even more particularly, what is
`needed is an apparatus, system and method of using a ferrof
`luid to cool such a high Voltage magnetic device while also
`mitigating acoustical noise.
`
`SUMMARY OF THE INVENTION
`
`In view of the foregoing shortcomings and drawbacks, an
`apparatus, system and method for cooling a magnetic device
`using a ferrofluid is described. According to an embodiment,
`a ferrofluid chamber has a housing that is adapted to be
`coupled to a component that generates a magnetic field of
`Sufficient strength to stimulate anatomical tissue. In addition,
`a ferrofluid is disposed within the housing for cooling the
`component.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`5
`
`10
`
`15
`
`4
`herein focuses on magnetic devices that are used in connec
`tion with magnetic stimulation of anatomical tissue, it will be
`appreciated that Such discussion is so limited solely for pur
`poses of explanation and clarity. Thus, it will be understood
`that an embodiment is equally applicable to any application of
`a magnetic device in any field of endeavor. Thus, the present
`discussion of magnetic devices should not be construed as
`limiting embodiments of the invention to medical or other
`applications.
`Therefore, and turning now to the context of electrical
`stimulation of the anatomy, certain parts of the anatomy (e.g.,
`nerves, tissue, muscle, brain) act as a conductor and carry
`electric current when an electric field is applied. The electric
`field may be applied to these parts of the anatomy transcuta
`neously by applying a time varying (e.g., pulsed) magnetic
`field to the portion of the body. For example, in the context of
`TMS, a time-varying magnetic field may be applied across
`the skull to create an electric field in the brain tissue, which
`produces a current. If the induced current is of sufficient
`density, neuron action potential may be reduced to the extent
`that the membrane Sodium channels open and an action
`potential response is created. An impulse of current is then
`propagated along the axon membrane that transmits informa
`tion to other neurons via modulation of neurotransmitters.
`Such magnetic stimulation has been shown to acutely affect
`glucose metabolism and local blood flow in cortical tissue. In
`the case of major depressive disorder, neurotransmitter dys
`regulation and abnormal glucose metabolism in the prefrontal
`cortex and the connected limbic structures may be a likely
`pathophysiology. Repeated application of magnetic stimula
`tion to the prefrontal cortex may produce chronic changes in
`neurotransmitter concentrations and metabolism so that
`depression is alleviated.
`In a similar fashion, non-cortical neurons (e.g., cranial
`nerves, peripheral nerves, sensory nerves) may also be stimu
`lated by an induced electric field. Techniques have been
`developed to intentionally stimulate peripheral nerves to
`diagnose neuropathologies by observing response times and
`conduction velocities in response to a pulsed magnetic field
`induced stimulus. Discomfort and/or pain may result if the
`induced electric field applied to a peripheral or cranial nerve
`is very intense or focused on a small area of such a nerve. This
`discomfort may be diminished by intentionally over-stimu
`lating the sensory nerves in the affected nerve bundle so that
`they can no longer respond to external pain stimuli, or by
`reducing the intensity and focus of the induced electric field
`that is causing the pain sensation.
`As noted above, it should be appreciated that transcutane
`ous magnetic stimulation is not limited to treatment of
`depression. In addition to depression, the transcutaneous
`magnetic stimulation methods and apparatus of the invention
`may be used to treat a patient such as a human Suffering from
`epilepsy, Schizophrenia, Parkinson's disease, Tourette's Syn
`drome, amyotrophic lateral Sclerosis (ALS), multiple Sclero
`sis (MS), Alzheimer's disease, attention deficit/hyperactivity
`disorder, obesity, bipolar disorder/mania, anxiety disorders
`(e.g., panic disorder with and without agoraphobia, Social
`phobia also known as Social anxiety disorder, acute stress
`disorder and generalized anxiety disorder), post-traumatic
`stress disorder (one of the anxiety disorders in DSM), obses
`sive compulsive disorder (also one of the anxiety disorders in
`DSM), pain (such as, for example, migraine and trigeminal
`neuralgia, as well as chronic pain disorders, including neuro
`pathic pain, e.g., pain due to diabetic neuropathy, post-her
`petic neuralgia, and idiopathic pain disorders, e.g., fibromy
`algia, regional myofascial pain syndromes), rehabilitation
`following stroke (neuro plasticity induction), tinnitus, stimu
`
`FIG. 1 is a diagram illustrating an example magnetic stimu
`lation device in which aspects of the invention may be imple
`mented;
`FIG. 2 is a flowchart illustrating an example method of
`cooling a magnetic device in accordance with an embodiment
`of the invention; and
`FIGS. 3-6 are diagrams illustrating example configurations
`involving ferrofluidic cooling of a magnetic device in accor
`dance with an embodiment of the invention.
`
`25
`
`30
`
`DETAILED DESCRIPTION OF ILLUSTRATIVE
`EMBODIMENTS
`
`35
`
`The subject matter of the present invention is described
`with specificity to meet statutory requirements. However, the
`description itself is not intended to limit the scope of this
`patent. Rather, the inventors have contemplated that the
`claimed Subject matter might also be embodied in other ways,
`to include different steps or elements similar to the ones
`described in this document, in conjunction with other present
`or future technologies. Moreover, although the term “step'
`may be used herein to connote different aspects of methods
`employed, the term should not be interpreted as implying any
`particular order among or between various steps herein dis
`closed unless and except when the order of individual steps is
`explicitly described.
`Magnetic Device Overview
`As is well known to those skilled in the art, the magnitude
`of an electric field induced on a conductor is proportional to
`the rate of change of magnetic flux density across the con
`ductor. When an electric field is induced in a conductor, the
`electric field creates a corresponding current flow in the con
`ductor. The current flow is in the same direction of the electric
`field vector at a given point. The peak electric field occurs
`when the time rate of change of the magnetic flux density is
`the greatest and diminishes at other times. During a magnetic
`pulse, the current flows in a direction that tends to preserve the
`magnetic field (i.e., Lenz’s Law).
`As may be appreciated, various devices may take advan
`tage of the above principles to induce an electric field, and
`Such devices may be used in a variety of applications. For
`example, magnetic devices may be used for electrical stimu
`lation of the anatomy, and the like. While the discussion
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`lation of implanted neurons to facilitate integration, Sub
`stance-related disorders (e.g., dependence, abuse and with
`drawal diagnoses for alcohol, cocaine, amphetamine,
`caffeine, nicotine, cannabis and the like), spinal cord injury
`and regeneration/rehabilitation, stroke, head injury, sleep
`deprivation reversal, primary sleep disorders (primary insom
`nia, primary hypersomnia, circadian rhythm sleep disorder),
`cognitive enhancements, dementias, premenstrual dysphoric
`disorder (PMS), drug delivery systems (changing the cell
`membrane permeability to a drug), induction of protein Syn
`thesis (induction of transcription and translation), Stuttering,
`aphasia, dysphagia, essential tremor, and/or eating disorders
`(such as bulimia, anorexia and binge eating).
`Example Magnetic Stimulation Device
`A ferromagnetic core may be used in connection with a
`magnetic device to produce a magnetic field. In some
`embodiments, such a magnetic field may be for purposes of
`carrying out transcutaneous magnetic stimulation Such as, for
`example, Transcranial Magnetic Stimulation (TMS), Repeti
`tive TMS (rTMS), Magnetic Seizure Therapy (MST), reduc
`tion of peripheral nerve discomfort and so forth. Again,
`although some of the examples that follow may be discussed
`in connection with TMS and rTMS embodiments for the
`purposes of explanation and clarity, any type of transcutane
`ous magnetic stimulation, including all of those listed above,
`may be performed according to an embodiment of the inven
`tion. In addition, and as noted above, embodiments of the
`invention are not limited to transcutaneous magnetic stimu
`lation, as an embodiment may be used in connection with
`magnetic devices that generate a magnetic field for any pur
`pose.
`Furthermore, embodiments of the invention are not limited
`to the use of ferromagnetic core magnetic stimulation
`devices, as other core materials may be used such as, for
`example, air. The discussion herein therefore describes a fer
`romagnetic core magnetic stimulation device solely for pur
`poses of explanation and clarity. In an embodiment, a ferro
`magnetic core may be approximately hemispherical, and in
`another embodiment the ferromagnetic core may include a
`highly saturable magnetic material having a magnetic Satu
`ration of at least 0.5 Tesla. In some embodiments, a ferromag
`netic core may be shaped to optimize the magnetic field
`distribution in the treatment area. Treatment areas for other
`forms of treatment (e.g., reduction of discomfort in peripheral
`nerves, etc.) may be more or less deep than is the case for
`TMS.
`FIG. 1 illustrates an example magnetic device 10, or “coil.”
`that may be used in connection with an embodiment of the
`invention. Device 10 comprises a ferromagnetic core 12 sur
`rounded by windings 14. An insulative material 16 may be
`interposed between core 12 and windings 14. Device 10 also
`includes a cable 20 for connecting device 10 to a control
`system (not shown in FIG. 1 for clarity). Cable 20 may be
`covered by a housing 18 for protection and strain relief.
`Ferromagnetic core 12 can be fabricated from various fer
`romagnetic materials such as, for example, 3% grain oriented
`silicon Steel or vanadium permendur (also known as Super
`mendur). The material is chosen to have, for example, a high
`saturation level, a sharp-knee B-H curve (i.e., quickly
`Switches from Saturated to non-saturated States), low eddy
`current losses, and a practical cost. The core material may be
`fabricated into many electrically isolated layers to minimize
`eddy current losses. The orientation of the lamination may be
`Such as to disrupt the eddy currents (i.e., perpendicular to the
`direction of induced current flow whenever possible). Also, if
`the material has a grain orientation, it may be directed parallel
`to the induced magnetic flux. In one embodiment, the ferro
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`magnetic core is according to U.S. Pat. Nos. 6,132.361 and
`5,725,471, each of which is hereby incorporated by reference
`in their entireties.
`In one embodiment, patient treatment typically includes
`applying a magnetic field to the patient using a coil con
`structed with an approximately hemispherical ferromagnetic
`core. The strength of the field and switching rate is sufficient
`to produce stimulation of the target area in a manner that is
`appropriate to the type of treatment being administered. As
`noted above, the generation of a magnetic field having the
`approximate strength for therapeutic treatment or other pur
`poses also generates heat and noise. Therefore, an embodi
`ment that provides an apparatus, system and method for miti
`gating Such heat and/or noise using a ferrofluid is discussed
`below.
`Ferrofluidic Convection and Cooling
`Generally, a ferrofluid is a Suspension of Small magnetic
`particles that may be, for example, approximately 10 nm in
`size. Such a small particle size may be selected to assure that
`settling of the particles does not occur during a time period
`that is appropriate for an application in which the ferrofluid is
`used. In addition, one or more Surfactants may be used to
`ensure continued Suspension of the magnetic particles in the
`fluid, which may be, for example, oil, water, etc. Each particle
`may have a permanent magnetic moment, and may be com
`prised from magnetic materials such as, for example, iron
`oxide compounds or the like. In the absence of an external
`magnetic field, the magnetic moments of the individual par
`ticles within the ferrofluid are not aligned with each other.
`When a magnetic field is applied, the magnetic moments
`align with the applied magnetic field. This alignment often is
`called “Superparamagnetic' as the fluid behaves as a para
`magnet with magnetic moments that are the size of the indi
`vidual magnetic particles.
`It will be appreciated that an increase in temperature of a
`ferrofluid decreases its magnetization in an applied field. For
`example, at higher temperatures, the Saturation moment of a
`ferrofluid, as well as its initial susceptibility, are reduced. The
`relationship between the magnetization of a ferrofluid and an
`applied magnetic field is called the Langevin function, which
`is known to those of skill in the art.
`Natural convection is a phenomenon caused by the change
`in volume of liquid with temperature. Hot fluids are less
`dense, and therefore a fluid exposed to a heat source will
`expand and rise. Cool fluid distant from a heat source will
`move to replace the hot fluid. In this way, heat is mechanically
`transported away from a heat Source.
`In the case of ferrofluid convection, a ferrofluid is placed in
`a magnetic field gradient where the magnetic field is greatest.
`As noted above, a cool ferrofluid has a higher magnetic Sus
`ceptibility than a hot ferrofluid and therefore is preferentially
`drawn to the areas of greatest magnetic field. In an embodi
`ment, the area of the cool ferrofluid greatest magnetic field
`may be proximate a magnetic device (e.g., a magnetic stimu
`lation device, or the like) when such a magnetic device is in
`operation. Therefore, ferrofluid that is proximate the mag
`netic device may be heated, which reduces the ferrofluids
`magnetic susceptibility and also causes the ferrofluid to
`expand in volume. As a result, cool ferrofluid (e.g., ferrofluid
`that is further away from the magnetic device), which has a
`higher magnetic Susceptibility and is more dense, is drawn to
`the magnetic device. Thus, it will be appreciated that mag
`netic and thermal convection of the ferrofluid may be estab
`lished by the increasing and decreasing of the magnetic Sus
`ceptibility and volume of the ferrofluid. Details relating to the
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`fabrication of ferrofluid-filled chambers is assumed to be
`knownto those of skill in the art, and such details are therefore
`omitted herein for clarity.
`In addition, ferrofluids may be used to reduce unwanted
`noise in solenoids and other devices. This is because a ferrof
`luid is not a good Supporter of transverse sound waves. Also,
`an interface between a ferrofluid and an adjacent object (e.g.,
`a magnetic device or the like) may reduce noise produced by
`the magnetic device. This is because of the difference of
`Sound Velocities at Such an interface, as is known to one of
`skill in the art. Furthermore, the ferrofluid may provide vibra
`tional damping. Thus, it will be appreciated that a ferrofluid
`that is being used to cool a magnetic device may also reduce
`noise produced