News Column

Patent Application Titled "Circular Coils for Deep Transcranial Magnetic Stimulation" Published Online

September 11, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventors ZANGEN, ABRAHAM (JERUSALEM, IL); ROTH, YIFTACH (RECHELIM, IL), filed on February 21, 2013, was made available online on August 28, 2014.

The assignee for this patent application is Brainsway, Inc.

Reporters obtained the following quote from the background information supplied by the inventors: "Transcranial magnetic stimulation (TMS) is a noninvasive technique used to apply brief magnetic pulses to the brain, or to other human organs, and to thereby activate neuronal structures. The pulses are administered by passing high currents by a stimulator through an electromagnetic coil externally placed upon the patient (for example, placed on the scalp for brain treatment), inducing electrical currents in the underlying tissue, thereby producing a localized axonal depolarization. This technique has become a major tool in central nervous system research, as well as a potentially promising treatment option for various neurobehavioral and neurological disorders.

"Most known TMS coils stimulate superficial brain regions in the brain cortex, but the rate of decay of the induced magnetic and electric field as a function of distance from the coil is high. Hence the efficacy of affecting deeper neuronal structures is low. Stimulating deeper neuronal structures may be feasible if the intensity of the induced field is greatly increased. Yet operation at such increased intensity may increase the risk for seizures and for physiological damage to the tissue.

"A method for deep brain TMS with minimal stimulation of superficial regions is disclosed in U.S. Pat. No. 7,407,478, wherein deep brain stimulation is made possible while minimizing side effects. The device described therein includes a base and an extension portion, the base having individual windings for individual paths of current flow, and the extension portion designed so as to minimize unwanted stimulation of other regions of the brain.

"However, there is a need for more specifically designed coils, which can target particular areas of the brain including deep neuronal structures with minimal effect on other brain regions. Examples of specific brain regions that may be desired to be stimulated are frontal lobe regions, occipital lobe regions, parietal lobe regions, right temporal regions and left temporal regions. Other examples may include activation of brain regions including deeper brain regions in a certain circumference of the brain, such as around a particular axial slice.

"Thus, there is a need for specifically designed coils for deep TMS which are location-specific for frontal lobe, occipital lobe, parietal lobe or temporal lobe brain regions. The coils must induce the desired distribution of the electric field in the brain, and simultaneously induce electric field intensity in the relevant brain tissue which will be feasible for neuronal stimulation with available TMS stimulators for most of the population. The stimulation intensity is routinely calibrated individually for each subject based on his or her motor threshold. Hence the coil efficiency must guarantee that the motor threshold and stimulation intensity for most of the relevant population is within an acceptable range with respect to available stimulators power outputs.

"The coils design must be efficient with respect to energy consumption, coil heating rate, compact size and ease of operation."

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors' summary information for this patent application: "There is provided, in accordance with one embodiment of the present invention, a coil for transcranial magnetic stimulation. The coil includes a base portion having substantially parallel multiple stimulating elements, wherein the base portion is configured to encircle at least a portion of a first section of a body part and to provide electrical flow in a substantially circular path, and a return portion having substantially parallel multiple return elements, wherein the return portion is configured to encircle at least a portion of a second section of the body part which is different than the first section, and to provide electrical flow in a continuation of the substantially circular path of the base portion.

"In embodiments of the present invention, the base portion is complementary to the human head or head portion, or to another body organ. The base has a flexibility that allows it to conform to the relevant body organ (such as the human head or head portion).

"The base includes individual stimulating elements carrying electric current in one or more common directions, referred to herein as a 'main direction.' In this main direction, the main physiologic effect (such as neuronal stimulation) is induced in the body organ. The elements are not dense together at a narrow segment, but are rather distributed at various locations around the body organ. In some embodiments the individual elements are evenly distributed across the base. In other embodiments some or all the elements may be grouped in two or more groups with certain distances between the groups. The spacing between adjacent elements may be uniform, variable, periodic or other. In embodiments where some or all the elements are grouped in groups, the spacing between adjacent groups or between a group and an adjacent element, and the breadth of each group, may be uniform across the base, variable, periodic or other. Any combination or arrangement of elements is included within the scope of the invention, with a particular feature being that the elements are not crowded together in a narrow segment.

"The individual elements in the base carrying current in the main direction are all or mostly tangential to the relevant body organ (such as a portion of a human skull), at all or a substantial part of their path. In order to optimize the efficacy of activation in deeper brain regions, it is desirable to minimize the non-tangential components of the induced electric field. Since the induced electric field orientation is in general parallel to the orientation of the elements carrying alternating currents, it is desirable to minimize the portions of coil elements which are non-tangential to the body organ (such as a human skull), especially in the base and its vicinity.

"Coil elements carrying electric current in a direction opposite to the one or more main directions, are placed remote from the base. These elements are referred to herein as 'return elements.' In some embodiments, the return elements are located adjacent to other body organs or other portions of a body organ (such as other head regions), relative to the base. These return elements are termed 'contacting return elements.' In other embodiments, the return elements are located at a certain distance from the body and are not configured to contact the body. These return elements are termed 'protruding return elements.' In some embodiments, some of the return elements are contacting and some of them are protruding.

"The stimulating elements encircle a body organ (such as a human head or head portion). In some embodiments, the coil includes a single base which conforms to the head or other body organ in a certain region. In some embodiments, the base is adjacent to the frontal cortical region, while in other embodiments, the base is adjacent to the occipital region, temporal region or parietal region of the skull. In some embodiments, the base includes multiple portions, wherein each portion conforms to a different region of the body organ, such as the head. Spacing between adjacent elements may be different within one base portion than within another base portion.

"Return elements are located remote from the base or from specific portions of the base. In some embodiments, return elements surround the body part (such as the head) as a continuation and in a similar plane to the base elements. For example, in some embodiments, the base elements may be adjacent to a frontal head region and the return elements may be adjacent to an occipital head region. Connecting elements connecting stimulating elements to return elements may run along the temporal lobe on the right and left hemispheres, for example. In some embodiments, return elements may run in a different plane than stimulating elements. For example, stimulating elements of the base may be adjacent to occipital head regions, while return elements run along parietal head regions. In some embodiments, return elements contact head regions which are remote from stimulating elements. In some embodiments, all stimulating elements and/or all return elements are contacting elements, while the spacing between elements and the density of elements may vary in different regions. In some embodiments, return elements are protruding elements. In yet other embodiments, some of the return elements are contacting and some are protruding. Similarly, connecting elements may be contacting, protruding, or partially contacting and partially protruding.

"The definition of the base relates to the functional elements of the coil carrying electric currents. However, there is no limitation regarding other elements of the device, such as mechanical components, cases and covers. Thus, certain elements of the base may be encased in a case containing additional coil elements such as return elements and other elements.

"The coil must induce the desired distribution of the electric field in the brain, and simultaneously induce an electric field intensity in the relevant brain tissue which is high enough to induce neuronal stimulation.

"Several features of the coil are important in order to achieve the above goals. These include:

"1. Arrangement of the base portion elements. This arrangement must be optimized for each coil design and each specific goal. An interplay between two competing ideals may take place: Better depth penetration profile, namely higher relative electric field in the deeper target brain region compared to superficial region, on one hand, and higher absolute electric field intensity in the target brain region on the other hand. As a non-limiting example, suppose a base portion contains two groups of elements with a certain distance d between them. Increasing d will improve the depth penetration profile but may reduce the absolute field intensity in the target brain region. The intensity must be such that it will enable induction of the desired physiological effect in the target neural structures in the majority of the population with stimulators available in the market. Hence the distance d--as well as other configuration parameters--must be optimized for each coil design.

"2. Location of the return portions relative to the base portion. The distance between the portions must be optimized for each design: Too short a distance will lead to reduction of the total induced electric field in the target brain region, due to the effect of the return elements. Too long a distance will require long connecting coil elements and their effect must be taken into account. Furthermore, the coil size must be optimized for easy location, navigation and placement over the head.

"3. Location of the return portions relative to the brain. The return elements affect closer brain regions. The location of the return portions must consider their effect on any brain structure and the design must lead to minimal undesired side effects such as motor activation or pain.

"4. The type of the return elements. Return elements may be either contacting or protruding as defined above. The ratio between contacting and protruding return elements is very important in various aspects and must be optimized for each specific coil design. In general, protruding elements induce electrostatic charge accumulation on the brain surface. This leads to reduction in the absolute electric field induced in the target brain regions, and also reduction in the relative intensity of the electric field in deeper brain regions compared to superficial regions. On the other hand, contacting elements may increase the effect in adjacent brain regions. Hence a delicate optimization must be performed in each case.

"5. The distance of protruding return elements from the head, in coils containing protruding return elements. Longer distance reduces the direct effect of the return elements on the brain, but increases the charge accumulation due to the presence of longer non-tangential coil elements which are connected to the return elements and move them away from the head. A delicate optimization must be performed in each case to account for this effect.

"6. The overall coil inductance. The number, length, configuration and packing parameters of the coil windings must be planned to lead to coil inductance in the desired range. Usually the desired range for TMS coils inductance is between 15 and 30 microHenri. Too high inductance may reduce coil efficacy, increase pulse width and is often associated with increased coil resistance, energy consumption and coil heating. Too small inductance may lead to fast rate of change of the electric current which may damage stimulator components.

"Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

"The above and further advantages of the present invention may be better understood by referring to the following description in conjunction with the accompanying drawings in which:

"FIG. 1 is a schematic illustration showing principles of stimulation for circular coils, in accordance with embodiments of the present invention;

"FIGS. 2A-2C are schematic illustrations of a base portion of the circular coil of FIG. 1, in accordance with embodiments of the present invention;

"FIGS. 3A and 3B are schematic illustrations of base portions and return portions of the circular coil of FIG. 1, wherein the base and return portions have various configurations in accordance with embodiments of the present invention;

"FIG. 4 is an illustration of a return portion of the circular coil of FIG. 1, in accordance with embodiments of the present invention;

"FIG. 5 is an illustration of anatomical sections of a head;

"FIG. 6 is a perspective illustration of a coil which is an example of the circular coil of FIG. 1, in accordance with embodiments of the present invention;

"FIG. 7 is a perspective illustration of a coil which is an example of the circular coil of FIG. 1, in accordance with embodiments of the present invention;

"FIG. 8 is a perspective illustration of a coil which is an example of the circular coil of FIG. 1, in accordance with embodiments of the present invention;

"FIG. 9 is an illustration of electric field distribution maps of the coil of FIG. 6, as measured in a human head phantom model;

"FIG. 10 is an illustration of electric field distribution maps of the coil of FIG. 7 as measured in a human head phantom model; and

"FIG. 11 is an illustration of electric field distribution maps of the coil of FIG. 8 as measured in a human head phantom model.

"It will be appreciated that for simplicity and clarity of illustration, elements shown in the drawings have not necessarily been drawn accurately or to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity or several physical components may be included in one functional block or element. Further, where considered appropriate, reference numerals may be repeated among the drawings to indicate corresponding or analogous elements. Moreover, some of the blocks depicted in the drawings may be combined into a single function."

For more information, see this patent application: ZANGEN, ABRAHAM; ROTH, YIFTACH. Circular Coils for Deep Transcranial Magnetic Stimulation. Filed February 21, 2013 and posted August 28, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=1769&p=36&f=G&l=50&d=PG01&S1=20140821.PD.&OS=PD/20140821&RS=PD/20140821

Keywords for this news article include: Brainsway, Brainsway Inc., Magnetic Field Therapy, Risk and Prevention, Seizures, Transcranial Magnetic Stimulation.

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