CN108241133B - System and method for common mode trap in MRI system - Google Patents

Abstract

Various methods and systems are provided for a common mode trap for a Magnetic Resonance Imaging (MRI) device. In one embodiment, a common mode trap comprises: a first conductor and a second conductor counter-wound around a length of the center conductor, the first conductor and the second conductor radially spaced a distance from the center conductor, the first and second conductors secured to a first side of the center conductor; and third and fourth conductors counter-wound around a length of the center conductor, the third and fourth conductors radially spaced from the center conductor by the distance, the third and fourth conductors secured to a second side of the center conductor opposite the first side. In this way, the density of the common mode trap conductors in the common mode trap can be increased, thereby increasing the mutual inductance between the common mode trap and the center conductor.

Description

System and method for common mode trap in MRI system

Cross Reference to Related Applications

This application is a continuation-in-part application of U.S. patent application No. 15/166,636 entitled "SYSTEMS AND METHODS FOR COMMON MODE TRAPS IN MRI SYSTEMS," filed on 27/5/2016. The entire contents of the above application are incorporated by reference herein in their entirety for all purposes.

Technical Field

Embodiments of the subject matter disclosed herein relate to Magnetic Resonance Imaging (MRI), and more particularly to a common mode trap for an MRI system.

Background

Magnetic Resonance Imaging (MRI) is a medical imaging modality that can form images of the interior of the human body without the use of X-rays or other ionizing radiation. MRI uses superconducting magnets to create a strong, uniform static magnetic field. When the human body, or a part of the human body, is placed in a magnetic field, the nuclear spins associated with the hydrogen nuclei in the tissue water become polarized, with the magnetic moments associated with these spins becoming preferentially aligned along the direction of the magnetic field, resulting in a small net tissue magnetization along this axis. The MRI system also includes gradient coils that generate small amplitude, spatially varying magnetic fields with orthogonal axes to spatially encode the MR signals by forming a signature resonance frequency at each location in the body. Radio Frequency (RF) coils are then used to generate RF energy pulses at or near the resonance frequency of the hydrogen nuclei, which add energy to the nuclear spin system. When the nuclear spins relax back to their rest energy state, they release the absorbed energy in the form of an RF signal. This signal is detected by the MRI system and converted into an image using a computer and known reconstruction algorithms.

As described above, an RF coil is used in an MRI system to transmit an RF excitation signal and receive an MR signal, i.e., an RF signal transmitted by an imaging subject. Coil interface cables may be used to transmit signals between the RF coil and other aspects of the processing system, for example, to control the RF coil and/or receive information from the RF coil. The coil interface cable may be disposed within a bore of the MRI system and subjected to electromagnetic fields generated and used by the MRI system. The cable may support transmitter driven common mode currents that produce field distortion and/or unpredictable heating of components. These field distortions may cause shadowing of the cables to appear within the image reconstructed from the received MR signals.

Typically, a balun or common mode trap providing a high common mode impedance may be utilized to mitigate the effects of the transmitter drive current. However, placing the common mode trap or blocking circuit in the proper location can be difficult, as the proper placement can vary based on the positioning of the cable or coil associated with the common mode trap. Furthermore, even if conventional common mode traps or blocking circuits are placed in place, excessive voltage and/or power dissipation may occur.

Furthermore, baluns or common mode traps that are too close to each other on the cable may become coupled due to fringing magnetic fields, resulting in detuning of the baluns, which may adversely affect the functionality of the baluns.

Disclosure of Invention

In one embodiment, a common mode trap for a Magnetic Resonance Imaging (MRI) device includes: a first conductor and a second conductor that are counter-wound around a length of the center conductor, wherein the first and second conductors are radially spaced apart from the center conductor by a first distance, wherein the first and second conductors are secured to a first side of the center conductor; and a third conductor and a fourth conductor that are counter-wound around a length of the center conductor, wherein the third and fourth conductors are radially spaced from the center conductor by a first distance, and wherein the third and fourth conductors are secured to a second side of the center conductor opposite the first side. In this way, the density of the common mode trap conductors in the common mode trap may be increased, thereby increasing the mutual inductance between the common mode trap and the center conductor arranged therein.

Specifically, technical solution 1 of the present application relates to a common mode trap for a Magnetic Resonance Imaging (MRI) apparatus, including: a first conductor and a second conductor that are counter-wound around a length of a center conductor, wherein the first and second conductors are radially spaced apart from the center conductor by a first distance, wherein the first and second conductors are secured to a first side of the center conductor; and a third conductor and a fourth conductor that are rewound around the length of the center conductor, wherein the third and fourth conductors are radially spaced from the center conductor by the first distance, and wherein the third and fourth conductors are secured to a second side of the center conductor opposite the first side.

Claim 2 of the present application is the common mode trap according to claim 1, wherein the first and second conductors orthogonally cross paths.

Claim 3 of the present application is the common mode trap of claim 1, further comprising a dielectric spacer disposed radially around the center conductor along the length, wherein the first, second, third and fourth conductors are counter-wound around the dielectric spacer.

Technical solution 4 of the present application is the common mode trap according to technical solution 1, further comprising: first and second capacitors positioned at each end of the length along the first side; and third and fourth capacitors positioned at each end along the length of the second side, wherein the first and second conductors are secured to the first and second capacitors, and wherein the third and fourth conductors are secured to the third and fourth capacitors.

Technical solution 5 of the present application is the common mode trap according to technical solution 4, further comprising:

a fifth conductor and a sixth conductor that are counter-wound around the length of the center conductor, wherein the fifth conductor and the sixth conductor are radially spaced from the center conductor by a second distance that is greater than the first distance, wherein the first and second conductors are fixed to the first capacitor and the second capacitor on the first side of the center conductor; and

a seventh conductor and an eighth conductor that are counter-wound around the length of the center conductor, wherein the seventh and eighth conductors are radially spaced from the center conductor by the second distance, and wherein the seventh and eighth conductors are secured to the third capacitor and the fourth capacitor on the second side of the center conductor.

Technical solution 6 of the present application is the common mode trap according to technical solution 4, further comprising: fifth and sixth capacitors positioned at each end of the length along a third side equidistant from the first and second sides; and seventh and eighth capacitors positioned at each end of the length along a fourth side positioned opposite the third side and equidistant from the first and second sides.

Technical solution 7 of the present application is the common mode trap according to technical solution 6, further comprising:

a fifth conductor and a sixth conductor that are counter-wound around the length of the center conductor, wherein the fifth conductor and the sixth conductor are radially spaced from the center conductor by the first distance, wherein the fifth and sixth conductors are fixed to the fifth capacitor and the sixth capacitor on the third side of the center conductor; and seventh and eighth conductors that are rewound around the length of the center conductor, wherein the seventh and eighth conductors are radially spaced apart from the center conductor by the first distance, and wherein the seventh and eighth conductors are secured to the seventh and eighth capacitors on the fourth side of the center conductor.

Claim 8 of the present application the common mode trap according to claim 1, wherein the common mode trap is tuned to provide a resonant frequency close to an operating frequency of the MRI system.

Claim 9 of the present application is the common mode trap according to claim 1, further comprising a plurality of annular disks disposed around the center conductor at regular intervals, wherein each of the conductors passes through each of the plurality of annular disks.

Technical solution 10 of the present application relates to a common mode trap assembly for a Magnetic Resonance Imaging (MRI) system, including: a center conductor having a length and configured to transmit signals between an MRI radio frequency coil and a processing element of the MRI system; and a plurality of common mode traps extending along at least a portion of the length of the center conductor, the common mode traps configured to provide an impedance to reduce a transmitter drive current of the MRI system, wherein each of the common mode traps comprises a second length and comprises a plurality of conductor pairs, each of the plurality of conductor pairs comprising a first conductor and a second conductor that are backwound around the center conductor.

Claim 11 of the present application the common mode trap assembly of claim 10, wherein each of the common mode traps comprises a first plurality of capacitors positioned at a first end of the common mode trap and a second plurality of capacitors positioned at a second end of the common mode trap, wherein the first and second common mode trap conductors of the common mode trap are secured to the first plurality of capacitors and the second plurality of capacitors.

Claim 12 of the present application is the common mode trap assembly of claim 10, wherein for each of the plurality of conductor pairs, the first conductor and the second conductor orthogonally cross paths.

Claim 13 of the present application is the common mode trap assembly according to claim 10, wherein each of the plurality of common mode traps is adjacently disposed.

Claim 14 of the present application the common mode trap assembly of claim 10, wherein each of the common mode traps comprises a dielectric spacer disposed radially around the center conductor.

Technical solution 15 of the present application relates to a method for providing a transmission cable for a Radio Frequency (RF) coil of a Magnetic Resonance Imaging (MRI) system, comprising: providing a center conductor having a length and configured to transmit signals between the RF coil and a processing element of the MRI system; and positioning a plurality of common mode trap conductor pairs around the center conductor along at least a portion of the length of the center conductor, wherein the plurality of common mode trap conductor pairs are symmetrically distributed around the center conductor, wherein each common mode trap conductor pair comprises a first common mode trap conductor helically wound around the center conductor in a first direction along the portion of the length of the center conductor and a second common mode trap conductor helically wound around the center conductor in a second direction opposite the first direction along the portion of the length.

Technical solution 16 of the present application relates to the method of claim 15, wherein a first half of the plurality of common mode trap conductor pairs is positioned at a first radial distance from a central axis of the center conductor, and wherein a second half of the plurality of common mode trap conductor pairs is positioned at a second radial distance from the central axis, the second radial distance being greater than the first radial distance.

Claim 17 of the present application relates to the method of claim 15, wherein the first and second common mode trap conductors are positioned radially a first distance from a central axis of the center conductor at a midpoint of the length and radially a second distance from the central axis at each end of the length, the second distance being less than the first distance.

Claim 18 of the present application relates to the method of claim 15, wherein the first and second common mode trap conductors are fixed to posts positioned at first and second ends of the length.

Technical means 19 of the present application relates to the method according to technical means 15, further comprising: providing a dielectric spacer radially along the length of the center conductor; and coupling the plurality of common mode trap conductor pairs to the dielectric spacer.

Claim 20 of the present application is directed to the method of claim 19, further comprising providing a shield radially surrounding the dielectric spacer.

It should be understood that the brief description above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. And is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

Drawings

The invention will be better understood by reading the following description of non-limiting embodiments with reference to the attached drawings, in which:

FIG. 1 is a block diagram of an MRI system according to an embodiment of the present invention.

Figure 2 is a block diagram illustrating a continuous common mode trap assembly according to an embodiment of the present invention.

Figure 3 is a perspective view of a common mode trap having two common mode trap conductors.

Figure 4 is a side view of a common mode trap with two common mode trap conductors on a curved cable.

Figure 5 is a side view of a common mode trap with two common mode trap conductors on a straight cable.

Figure 6 is a top view of a common mode trap with two common mode trap conductors on a straight cable.

Figure 7 is a perspective view of a common mode trap having four common mode trap conductors on a straight cable according to an embodiment of the present invention.

Figure 8 is a perspective view of a common mode trap having eight common mode trap conductors on a straight cable.

Figure 9 is a perspective view of a common mode trap having eight common mode trap conductors supported by washers on a flex cable according to an embodiment of the present invention.

Figure 10 is a top view of a common mode trap having eight common mode trap conductors on a straight cable according to an embodiment of the present invention.

Figure 11 is a cross-sectional view of the common mode trap of figure 10 according to an embodiment of the present invention.

Figure 12 is a cross-sectional view of a common mode trap having sixteen common mode trap conductors according to an embodiment of the present invention.

Figure 13 is a high level block diagram illustrating an example method for a common mode trap having four common mode trap conductors in accordance with an embodiment of the present invention.

Figure 14 is a high level block diagram illustrating an example method for a common mode trap having eight common mode trap conductors according to an embodiment of the present invention.

Detailed Description

The following description relates to various embodiments of a common mode trap for an MRI system. In particular, the system is provided for a high density spiral configuration in a common mode trap assembly of an MRI system (such as the MRI system depicted in fig. 1). As shown in fig. 2, a common mode trap assembly including a plurality of common mode traps may be placed on a cable for transmitting received MR data. Figures 3-6 show various views of a common mode trap having two counter-wound common mode trap conductors. In different embodiments the common mode trap may comprise more than two counter wound common mode trap conductors. For example, figure 7 shows a common mode trap with four counter-wound common mode trap conductors. As another example, figure 8 shows a common mode trap having eight counter-wound common mode trap conductors. As the complexity of the common mode trap configuration increases, various methods may be used to mechanically support and maintain the configuration of the common mode trap conductors. For example, figure 9 shows a plurality of gaskets supporting common mode trap conductors. Figures 10 and 11 show another method for arranging eight common mode trap conductors on a common mode trap. Figure 12 shows a common mode trap with sixteen counter wound common mode trap conductors. Figures 13 and 14 illustrate an example method for constructing a high density common mode trap.

Fig. 1 shows a Magnetic Resonance Imaging (MRI) apparatus 10, which includes a static magnetic field magnet unit 12, a gradient coil unit 13, an RF coil unit 14, an RF body coil unit 15, a transmit/receive (T/R) switch 20, an RF port interface 21, an RF driver unit 22, a gradient coil driver unit 23, a data acquisition unit 24, a controller unit 25, a patient bed 26, a data processing unit 31, an operation console unit 32, and a display unit 33. The MRI apparatus 10 transmits an electromagnetic pulse signal to a subject 16 placed in an imaging space 18 having a formed static magnetic field to perform a scan for obtaining a magnetic resonance signal from the subject 16 to reconstruct an image of a slice of the subject 16 based on the magnetic resonance signal thus obtained by the scan.

The static field magnet unit 12 typically comprises an annular superconducting magnet mounted within an annular vacuum vessel, for example. The magnet defines a cylindrical space around the subject 16, and generates a constant primary static magnetic field in the Z direction of the cylindrical space.

The MRI apparatus 10 further comprises a gradient coil unit 13, the gradient coil unit 13 forming a gradient magnetic field in the imaging space 18 to provide magnetic resonance signals with three-dimensional localization information received by the RF coil unit 14. The gradient coil unit 13 includes three gradient coil systems each generating a gradient magnetic field inclined to one of three spatial axes perpendicular to each other, and generates a gradient field in each of a frequency encoding direction, a phase encoding direction, and a slice selection direction according to imaging conditions. More specifically, the gradient coil unit 13 applies a gradient field in a slice selection direction of the subject 16 to select a slice; and the RF coil unit 14 transmits RF pulses to and excites selected slices of the subject 16. The gradient coil unit 13 also applies a gradient field in a phase encoding direction of the subject 16 to phase encode magnetic resonance signals from slices excited by the RF pulses. Then, the gradient coil unit 13 applies a gradient field in a frequency encoding direction of the subject 16 to frequency encode the magnetic resonance signals from the slice excited by the RF pulse.

The RF coil unit 14 is provided, for example, to surround a region to be imaged of the subject 16. In the static magnetic field space or imaging space 18 where the static magnetic field is formed by the static magnetic field magnet unit 12, the RF coil unit 14 transmits RF pulses as electromagnetic waves to the subject 16 based on a control signal from the controller unit 25, thereby generating a high-frequency magnetic field. This excites the spins of protons in the slice of the subject 16 to be imaged. When the proton spins thus excited in the slice to be imaged of the subject 16 return to being aligned with the initial magnetization vector, the RF coil unit 14 receives the generated electromagnetic waves as magnetic resonance signals. The RF coil unit 14 may transmit and receive RF pulses using the same RF coil.

The RF body coil unit 15 is provided, for example, so as to surround the imaging space 18, and generates an RF magnetic field pulse orthogonal to the main magnetic field generated by the static magnetic field magnet unit 12 within the imaging space 18 to excite nuclei. In contrast to the RF coil unit 14, which can easily be disconnected from the MR device 10 and replaced with another RF coil unit, the RF body coil unit 15 is fixedly attached and coupled to the MR device 10. Furthermore, although local coils such as those including the RF coil unit 14 may transmit signals to or receive signals from only a local region of the subject 16, the RF body coil unit 15 generally has a large coverage area and may be used to transmit signals to or receive signals from the whole body of the subject 16. The use of receive-only local coils and transmit body coils provides uniform RF excitation and good image uniformity at the expense of high RF power deposited in the subject. For transmit-receive local coils, the local coil provides RF excitation to the region of interest and receives MR signals, thereby reducing the RF power stored in the subject. It will be appreciated that the specific use of the RF coil unit 14 and/or the RF body coil unit 15 depends on the imaging application.

The T/R switch 20 may selectively electrically connect the RF body coil unit 15 to the data acquisition unit 24 when operating in a receive mode and to the RF driver unit 22 when operating in a transmit mode. Similarly, the T/R switch 20 may selectively electrically connect the RF coil unit 14 to the data acquisition unit 24 when the RF coil unit 14 is operating in the receive mode and to the RF driver unit 22 when operating in the transmit mode. When both the RF coil unit 14 and the RF body coil unit 15 are used in a single scan, for example if the RF coil unit 14 is configured to receive MR signals and the RF body coil unit 15 is configured to transmit RF signals, the T/R switch 20 may direct control signals from the RF driver unit 22 to the RF body coil unit 15 while directing MR signals received from the RF coil unit 14 to the data acquisition unit 24. The coils of the RF body coil unit 15 may be configured to operate in a transmit-only mode, a receive-only mode, or a transmit-receive mode. The coils of the local RF coil unit 14 may be configured to operate in a transmit-receive mode or a receive-only mode.

The RF driver unit 22 includes a gate modulator (not shown), an RF power amplifier (not shown), and an RF oscillator (not shown) for driving the RF coil unit 14 and forming a high-frequency magnetic field in the imaging space 18. The RF driver unit 22 modulates the RF signal received from the RF oscillator into a signal having a predetermined timing of a predetermined envelope based on a control signal from the controller unit 25 and using a gate modulator. The RF signal modulated by the gate modulator is amplified by an RF power amplifier and then output to the RF coil unit 14.

The gradient coil driver unit 23 drives the gradient coil unit 13 based on a control signal from the controller unit 25, thereby generating a gradient magnetic field in the imaging space 18. The gradient coil driver unit 23 comprises driver circuits (not shown) corresponding to three of the three gradient coil systems comprised in the gradient coil unit 13.

The data acquisition unit 24 includes a preamplifier (not shown), a phase detector (not shown), and an analog/digital converter (not shown) for acquiring magnetic resonance signals received by the RF coil unit 14. In the data acquisition unit 24, the phase detector phase-detects the magnetic resonance signal received from the RF coil unit 14 and amplified by the preamplifier using the output from the RF oscillator of the RF driver unit 22 as a reference signal, and outputs the phase-detected analog magnetic resonance signal to an analog/digital converter to be converted into a digital signal. The digital signal thus obtained is output to the data processing unit 31.

The MRI apparatus 10 includes a table 26 for placing the subject 16 thereon. The subject 16 can be moved inside and outside the imaging space 18 by moving the table 26 based on a control signal from the controller unit 25.

The controller unit 25 includes a computer and a recording medium on which a program to be executed by the computer is recorded. The program, when executed by a computer, causes various portions of an apparatus to perform operations corresponding to a predetermined scan. The recording medium may include, for example, a ROM, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, or a nonvolatile memory card. The controller unit 25 is connected to the operation console unit 32, and processes operation signals input to the operation console unit 32, and also controls the console 26, the RF driver unit 22, the gradient coil driver unit 23, and the data acquisition unit 24 by outputting control signals thereto. The controller unit 25 also controls the data processing unit 31 and the display unit 33 based on an operation signal received from the operation console unit 32 to obtain a desired image.

The operation console unit 32 includes user input devices such as a keyboard and a mouse. The operation console unit 32 is used by an operator to, for example, input data such as an imaging scheme and set a region where an imaging sequence is to be performed. Data on the imaging scheme and the imaging sequence execution region is output to the controller unit 25.

The data processing unit 31 includes a computer and a recording medium on which a program to be executed by the computer to perform predetermined data processing is recorded. The data processing unit 31 is connected to the controller unit 25, and performs data processing based on a control signal received from the controller unit 25. The data processing unit 31 is also connected to the data acquisition unit 24, and generates spectrum data by applying various image processing operations to the magnetic resonance signals output from the data acquisition unit 24.

The display unit 33 includes a display device, and displays an image on a display screen of the display device based on a control signal received from the controller unit 25. The display unit 33 displays, for example, an image regarding an input item with respect to which the operator inputs operation data from the operation console unit 32. The display unit 33 also displays slice images of the subject 16 generated by the data processing unit 31.

Different RF coil units may be used for different scan targets. To this end, the RF coil unit 14 may be disconnected from the MRI apparatus 10 so that a different RF coil unit may be connected to the MRI apparatus 10. The RF coil unit 14 may be coupled to the T/R switch 20, and thus to the RF driver unit 22 and the data acquisition unit 24, via the connector 17 and the RF port interface 21. Specifically, the connector 17 may be inserted into the RF port interface 21 to electrically couple the RF coil unit 14 to the T/R switch 20. The interchange of the RF coil units can be easily achieved using a single connector 17 fixedly attached to the RF coil unit 14.

During scanning, coil cross-over cables (not shown) may be used to transmit signals between the RF coils (e.g., RF coil unit 14) and other aspects of the processing system (e.g., data acquisition unit 24, controller unit 25, etc.), for example, to control the RF coils and/or to receive information from the RF coils. The coil interface cable may be disposed within the bore or imaging space 18 of the MRI apparatus 10 and subject to the electromagnetic fields generated and used by the MRI apparatus 10. The cable may support transmitter driven common mode currents that produce field distortion and/or unpredictable heating of components. The effect of the transmitter drive current can be mitigated with a balun or common mode trap that provides a high common mode impedance. Various embodiments of such common mode traps and common mode trap assemblies are further described in this specification.

Figure 2 illustrates a schematic block diagram of a continuous common mode trap assembly 200 formed in accordance with various embodiments. The common mode trap assembly 200 may be configured, for example, for use in a bore of an MRI system (e.g., the MRI apparatus 10 described above). For example, in the illustrated embodiment, the common mode trap assembly 200 is configured as a transmission cable 201, the transmission cable 201 being configured for transmitting signals between a processing unit (or controller) 250 and a receive coil 260 of the MRI system. In the illustrated embodiment, the transmission cable 201 (or common mode trap assembly 200) includes a center conductor 210 and a plurality of common mode traps 212, 214, 216. It may be noted that although the common mode traps 212, 214, and 216 are depicted as being distinct from the center conductor 210, in some embodiments the common mode traps 212, 214, 216 may be integrally formed with the center conductor 210 or as part of the center conductor 210.

The center conductor 210 in the illustrated embodiment has a length 204 and is configured to transmit signals between an MRI receive coil 260 and at least one processor (e.g., processing unit 250) of an MRI system. The center conductor 210 may comprise, for example, one or more of a ribbon conductor, a wire, or a coaxial cable bundle. The depicted length 204 of the center conductor 210 extends from a first end of the center conductor 210 (which is coupled to the processing unit 250) to a second end of the center conductor 210 (which is coupled to the MRI receive coil 260). In some embodiments, the center conductor may pass through the center opening of the common mode trap 212, 214, 216.

As shown in fig. 2, the depicted common mode traps 212, 214, 216 (which may be understood to cooperate to form a common mode trap cell 218) extend along at least a portion of the length 204 of the center conductor 210. In the illustrated embodiment, the common mode traps 212, 214, 216 do not extend along the entire length 204. However, in other embodiments, the common mode traps 212, 214, 216 may extend along the entire length 204 or substantially along the entire length 204 (e.g., along the entire length 204 except for portions at the ends configured to couple to, for example, a processor or a receive coil). The common mode traps 212, 214, 216 are arranged contiguously. As shown in fig. 2, each of the common mode traps 212, 214, 216 is contiguously disposed to at least another one of the common mode traps 212, 214, 216. As used herein, abutting may be understood to include components or aspects that are immediately adjacent or in contact with each other. For example, adjacent components may abut one another. It may be noted that in practice, in some embodiments, a small or insignificant gap may be between the abutting components. In some embodiments, an insignificant gap (or conductor length) may be understood as 1/40 that is less than the wavelength of the emission frequency in free space. In some embodiments, insignificant gaps (or conductor lengths) may be understood as 2 centimeters or less. For example, an adjoining common mode trap has no (or no significant) such intervening gap or conductor between the two: which may be susceptible to current flow from the magnetic field without the mitigation provided by the common mode trap. For example, as depicted in fig. 1, the common mode trap 212 is adjacent to the common mode trap 214, the common mode trap 214 is adjacent to the common mode trap 212 and the common mode trap 216 (and interposed between the common mode trap 212 and the common mode trap 216), and the common mode trap 216 is adjacent to the common mode trap 214. Each of the common mode traps 212, 214, 216 is configured to provide an impedance to reduce a transmitter drive current of the MRI system. In various embodiments, the common mode traps 212, 214, 216 provide a high common mode impedance. For example, each common mode trap 212, 214, 216 may include a resonant circuit and/or one or more resonant components to provide a desired impedance at or near a desired frequency or within a target frequency range. It is noted that the common mode traps 212, 214, 216 and/or the common mode trap cell 218 may also be referred to as chokes or baluns by a person skilled in the art.

In contrast to systems having separate discrete common mode traps with spaces therebetween, various embodiments (e.g., common mode trap assembly 200) have a portion over which the common mode traps extend continuously and/or contiguously such that there are no locations along the portion where common mode traps are not disposed. Thus, difficulties in selecting or implementing a particular placement location of the common mode trap may be reduced or eliminated, as all locations of interest may be included within a continuous and/or contiguous common mode trap. In various embodiments, a continuous trap portion (e.g., common mode trap cell 218) may extend along a length or a portion of a length of the transmission cable. The continuous trap sections may be formed by contiguously joined individual common mode traps or trap segments (e.g., common mode traps 212, 214, 216). Furthermore, adjoining common mode traps may be employed in various embodiments to at least one of reduce interaction with the coil elements, distribute heat over a larger area (e.g., to prevent hot spots), or help ensure that the blockage is located at a desired or needed location. Furthermore, contiguous common mode traps may be employed in various embodiments to help distribute voltage over a larger area. Additionally, in various embodiments, the continuous and/or contiguous common mode trap provides flexibility. For example, in some embodiments, the common mode trap may be formed using a continuous length of conductor (e.g., an outer conductor wrapped around a center conductor) or otherwise organized into integrally formed adjoining sections. In various embodiments, the use of a contiguous or continuous common mode trap (e.g., formed in a cylinder) provides a range of flexibility by which flexing of the component does not significantly change the resonant frequency of the structure or the component maintains frequency as it is flexed.

It may be noted that in various embodiments, the individual common mode traps or sections (e.g., common mode traps 212, 214, 216) may be constructed or formed substantially similarly to one another (e.g., each trap may be a portion of the length of a tapered wound coil), but each individual trap or section may be configured slightly differently than the other traps or sections. For example, in some embodiments, each common mode trap 212, 214, 216 is tuned independently. Thus, each common mode trap 212, 214, 216 may have a resonant frequency different from the other common mode traps of the same common mode trap assembly 200.

Alternatively or additionally, each common mode trap may be tuned to have a resonant frequency close to the operating frequency of the MRI system. As used herein, a common mode trap may be understood to have a resonant frequency close to an operating frequency when the resonant frequency defines or corresponds to a frequency band that includes the operating frequency, or when the resonant frequency is close enough to the operating frequency to provide an on-frequency blocking (on-frequency blocking) or to provide a blocking impedance at the operating frequency.

Further, additionally or alternatively, each common mode trap may be tuned to have a resonant frequency lower than the operating frequency of the MRI system (or each common mode trap may be tuned to have a resonant frequency higher than the operating frequency of the MRI system). In case each trap has a frequency lower than the operating frequency (or each trap has a frequency higher than the operating frequency), the risk of any traps cancelling each other out (e.g. since one trap has a frequency higher than the operating frequency, different traps have a frequency lower than the operating frequency) can be eliminated or reduced. As another example, each common mode trap may be tuned to a particular frequency band to provide a broadband common mode trap assembly.

In various embodiments, the common mode trap may have a two-dimensional or three-dimensional butterfly configuration to cancel magnetic field coupling and/or local distortion.

Figure 3 is a perspective view of a common mode trap 300 having two counter wound common mode trap conductors. The common mode trap 300 comprises an outer sleeve or shield 303, a dielectric spacer 304, an inner sleeve 305, a first common mode trap conductor 307 and a second common mode trap conductor 309.

The first common mode trap conductor 307 is helically wound around the dielectric spacer 304 or at a tapered distance from a center conductor (not shown) disposed within the aperture 318 of the common mode trap 300 in the first direction 308. Further, a second common mode trap conductor 309 is helically wound around the dielectric spacer 304, or at a tapered distance from a center conductor disposed within the bore 318 in a second direction 310 opposite the first direction 308. In the illustrated embodiment, the first direction 308 is clockwise and the second direction 310 is counterclockwise.

The conductors 307 and 309 of the common mode trap 300 may comprise a conductive material (e.g., metal) and may be shaped as, for example, a strip, a wire, and/or a cable. In some embodiments, the counter wound or outer conductors 307 and 309 may serve as return paths for current through the center conductor. Further, in various embodiments, the counter-wound conductors 307 and 309 may cross each other orthogonally (e.g., the centerline or path defined by the first common mode trap conductor 307 is perpendicular to the centerline or path defined by the second common mode trap conductor 309 as a common mode trap conductor crossing path) to eliminate, minimize, or reduce coupling between the common mode trap conductors.

It may further be noted that in various embodiments, the first common mode trap conductor 307 and the second common mode trap conductor 309 are loosely wrapped around the dielectric spacer 304 to provide flexibility and/or reduce any variation in bonding, coupling or inductance when the common mode trap 300 is bent or flexed. It may be noted that the looseness or tightness of the counter-wound outer conductor may vary depending on the application (e.g., based on the relative dimensions of the conductor and the dielectric spacer, the amount of bending or flexing required for the common mode trap, etc.). In general, the outer or reverse wound conductors should be tight enough so that they remain in the same general orientation around the dielectric spacer 304, but loose enough to allow a sufficient amount of slack or movement during bending or flexing of the common mode trap 300 to avoid, minimize, or reduce coupling or bonding of the reverse wound outer conductors.

In the illustrated embodiment, the outer shield 303 is discontinuous in the middle of the common mode trap 300 to expose a portion of the dielectric spacers 304, and in some embodiments the dielectric spacers 304 are disposed along the entire length of the common mode trap 300. By way of non-limiting example, the dielectric spacer 304 may be composed of teflon or another dielectric material. The dielectric spacer 304 acts as a capacitor and thus may be tuned or configured to provide a desired resonance. It should be understood that other configurations for providing capacitance to the common mode trap 300 are possible, and that the illustrated configuration is exemplary and not limiting. For example, a discrete capacitor may alternatively be provided to the common mode trap 300.

Further, the common mode trap 300 includes first and second columns 313, 309 (not shown) fixed to the first and second common mode trap conductors 307, 309. To this end, a first post 313 and a second post are positioned at opposite ends of the common mode trap and are fixed to the outer shield 303. The first and second legs 313, 309 ensure that the first and second common mode trap conductors 307, 309 are positioned proximate the outer shield 303 at the ends of the common mode trap 300, thereby providing a tapered butterfly configuration of the contrawound conductor as further described herein.

The tapered butterfly configuration comprises a first loop formed by a first common mode trap conductor 307 and a second loop formed by a second common mode trap conductor 309 arranged such that induced currents in the first loop 307 (currents induced due to the magnetic field) and the second loop 309 cancel each other out. For example, if the field is uniform and the first loop 307 and the second loop 309 have equal areas, the resulting net current will be zero. The tapered cylindrical arrangement of loops 307 and 309 provides improved flexibility and uniformity of resonant frequency during flexing relative to the two-dimensional arrangements typically used for common mode traps.

In general, a tapered butterfly configuration, as used herein, may be used to refer to a flux-canceling conductor configuration that includes, for example, at least two similarly-sized opposing loops that are symmetrically disposed about at least one axis and arranged such that a current induced in each loop (or set of loops) by a magnetic field tends to cancel a current induced in at least one other loop (or set of loops). For example, referring to fig. 2, in some embodiments, counter-wound conductors (e.g., conductors wound in opposite helical directions about a central member and/or axis) may be radially spaced a distance from the central conductor 210 to form common mode traps 212, 214, 216. As depicted in fig. 3 and further described in this specification, the radial distance may be tapered towards the end of the common mode trap to reduce or completely eliminate edge effects. In this way, the common mode traps 212, 214, 216 may be positioned continuously or contiguously without a significant gap therebetween.

Figure 4 is a side view 400 of a common mode trap 401 on a curved (i.e., flexed) cable or center conductor according to an embodiment of the present disclosure. As depicted, the common mode trap 401 includes an outer sleeve or shield 403 wrapped around a cable or center conductor (not shown). As depicted, the common mode trap 401 includes a first common mode trap conductor 407 and a second common mode trap conductor 409, the first common mode trap conductor 407 and the second common mode trap conductor 409 each being fixed to a first column 413 and a second column 415 positioned at a first end and a second end, respectively, of the common mode trap 401. The first and second common mode trap conductors 407, 409 are counter wound in a tapered spiral configuration around the sleeve or shield 403. The tapered helical configuration is further described in this specification in connection with fig. 5-6.

In some embodiments, the shield 403 is discontinuous in the middle of the common mode trap 401 to expose dielectric spacers 420 that may be disposed within the shield 403 along the length of the common mode trap 401, as described above. However, it should be understood that different configurations of dielectric spacers are possible, and that the depicted configuration is exemplary and not limiting.

Figure 5 is a side view 500 of a common mode trap 401 on a straight (i.e., non-flexing) cable or center conductor according to an embodiment of the present disclosure. The common mode trap 401 has a length L.

With respect to the tapered spiral configuration, it should be noted that the first and second common mode trap conductors 407, 409 are spaced apart at different radial distances or heights from the central axis 530 of the common mode trap 401. In particular, the first and second common mode trap conductors 407 and 409 are spaced apart from the central axis 530 at posts 413 and 415 by a radial distance or height H1. When the first and second common mode trap conductors 407, 409 are wrapped around the shield 403, the conductors cross orthogonally at a radial distance H2 from the central axis 530. Further, in the middle of the common mode trap 401 (i.e., near the gap where the dielectric spacer 420 is exposed), the first and second common mode traps 407, 409 orthogonally cross at a radial distance H3 from the central axis 530.

The height H1 may be configured such that the first and second common mode trap conductors 407, 409 are positioned at or substantially near the shield 403, while the height H3 may be configured such that the first and second common mode trap conductors 407, 409 are positioned at a desired distance away from the shield 403, where the conductors orthogonally cross in the middle of the common mode trap 401. That is, height H3 is significantly greater than height H1.

Further, the height H2 of the first common mode trap conductor 407 and the second common mode trap conductor 409 at their orthogonal intersection may be greater than the radial distance H1 and less than the radial distance H3. In this way the spiral configuration of the first and second common mode trap conductors tapers towards the ends of the common mode trap. However, in some examples, height H2 and height H3 may be equal such that the taper of the spiral between the orthogonal intersection of conductors 407 and 409 and posts 413 and 415 at height H2 is steeper than when height H2 is less than height H3. Such a configuration may be desirable because the impedance of the common mode trap 401 is greatest when the common mode trap conductor is spaced further away from the shield 403. However, it should be understood that the heights H1, H2, and H3 may be configured to achieve a desired impedance of the common mode trap 401 while reducing or eliminating edge effects at the ends of the common mode trap 401.

Furthermore, both eccentric crossings of the conductor are shown at the same radial distance H2, such that the taper of the spiral is symmetrical about the center of the common mode trap. However, in some embodiments, the eccentric intersection point may be positioned at a different radial distance from the central axis such that the taper of the helix is asymmetric.

The spiral topology of the common mode trap is based on two oppositely rotating spirals. The first spiral may be wound around the common mode trap according to:

wherein the content of the first and second substances,

indicating the azimuth

The radius of the helix. Similarly, the second spiral may be wound around the common mode trap according to:

according to the orthogonality condition of the two spirals, in order to achieve a minimum mutual inductance between the spirals, the relationship between the length L of the common mode trap and its maximum radius is:

if function

Is of constant value, such as R, along the entire common mode trap length L_maxThen the common mode trap topology corresponds to the previous common mode trap approach.

In addition, a function

May be chosen as a symmetric function. For example, a function

Can be symmetrical about the center of the common mode trap at a minimum radius R along the length L of the common mode trap_minAnd a maximum radius R_maxThe built-in conical shape between is defined as:

wherein the content of the first and second substances,

including the azimuth angle at which the spiral is at the maximum radius (e.g., at the center of the common mode trap where the spirals cross), and where n includes the order of the taper. As n increases from 0, the taper of the spiral towards the end of the common mode trap becomes steeper. Thus, in the design of the common mode trap, the value of the selected taper order n can be adjusted to selectively control the fringing fields, thereby increasing the number of common mode traps per unit length of cable or center conductor. This specification further describes exemplary common mode trap configurations with different taper orders n in conjunction with figure 5.

Figure 6 is a top view 600 of a common mode trap 401 on a straight cable or center conductor according to an embodiment of the present disclosure. The tapered spiral configuration of the first and second common mode trap conductors 407, 409 is evident in the varying radial distances H4, H5, H6, and H7 of the first and second common mode trap conductors 407, 409.

Closer to the pillar 413, the first and second common mode trap conductors 407, 409 are spaced apart from the central axis 530 of the common mode trap 401 by a radial distance H4. At the same time, near the exposed portion of the dielectric spacer 420, closer to the orthogonal intersection of the conductors 407 and 409, the first conductor 407 and the second conductor 409 are spaced a radial distance H5 from the central axis 530 of the common mode trap 401. In some embodiments, radial distance H4 is less than radial distance H5. As such, the helical configuration of the first and second conductors 407, 409 tapers towards the post 413.

Similarly, toward the post 415, the first and second conductors are spaced a radial distance H7 from the central axis 530, while closer to the center intersection, the conductors are spaced a radial distance H6 from the central axis 530. Radial distance H6 may be greater than radial distance H7, thereby tapering the helical shape of first conductor 407 and second conductor 409 toward post 415.

In some embodiments, radial distances H4 and H7 are equal, and radial distances H5 and H6 are equal. In this way the taper of the conductor may be symmetrical about the middle of the common mode trap 401. However, in other embodiments, the radial distance may be configured differently such that the taper of the spiral is asymmetric.

Figure 7 is a perspective view 700 of a common mode trap 701 having four common mode trap conductors on a straight cable or center conductor 702 according to an embodiment of the present invention. Specifically, the common mode trap 701 includes common mode trap conductors 710, 711, 712, and 713. Similar to the common mode trap described above in connection with fig. 3-6, the common mode trap 701 may include a shield 703 at least partially surrounding the center conductor 702 and a dielectric spacer 704, which dielectric spacer 704 may be partially exposed as depicted in some examples.

As depicted, the common mode trap conductor is configured in a counter-wound pair of common mode trap conductors. For example, the common mode trap conductors 710 and 711 terminate at points 716 and 718 and are counter-wound in a spiral configuration such that the common mode trap conductor 711 is wound in a clockwise direction around the center conductor 702 and the common mode trap conductor 710 is wound in a counterclockwise direction around the center conductor 702. A pair of common mode trap conductors 710 and 711 thus form a first common mode trap conductor pair 715. The first pair of common mode trap conductors 715 is therefore similar to and functions similarly to the pair of common mode trap conductors 407 and 409 of the common mode trap 401 described above. For example, the common mode trap conductors 710 and 711 cross orthogonally three times in the depicted spiral configuration.

Similarly, the common mode trap conductors 712 and 713 terminate at points 717 and 719 and are counter-wound in a spiral configuration such that the common mode trap conductor 712 is wound in a clockwise direction around the center conductor 702 and the common mode trap conductor 713 is wound in a counter-clockwise direction around the center conductor 702. The pair of common mode trap conductors 712 and 713 thus form a second pair of common mode trap conductors 720.

The second pair of common mode trap conductors 720 may be similar to the first pair of common mode trap conductors 715 except that they are positioned opposite the first pair of common mode trap conductors 715. To this end, the terminations 716 and 718 are positioned on the opposite side of the center conductor 703 from the terminations 717 and 719.

It should be noted that the common mode trap 701 may have the same length L as the common mode trap 401 described above. Thus, the number of common mode trap conductors of the common mode trap 701 (also referred to herein as the density of the common mode trap) is twice the density of the common mode trap 401 described above. In other words, the density of the common mode trap 701 is increased relative to the density of the common mode trap 401. By increasing the density of the common mode trap, the mutual inductance of the common mode trap 701 and the center conductor 702 is increased. In particular, the mutual inductance between the common mode trap 701 and the center conductor 702 is twice the mutual inductance between the common mode trap 401 and the center conductor disposed therein. In turn, the common mode trap 701 provides a higher impedance on the center conductor 702, thereby improving the invisibility of the center conductor 702 to external electromagnetic radiation.

As depicted, the common mode trap pairs 715 and 720 are connected to a surface of the center conductor 702, and the center conductor 702 may be encased in a dielectric spacer 704 that provides capacitance to the conductors. This configuration, in which the common mode trap conductor is symmetrically counter wound and directly connected to the dielectric spacer surrounding the center conductor, may be referred to in this specification as a connected dither balun. Other configurations are also described in this specification, such as floating dither baluns, in which the common mode trap conductor is connected to a capacitor or dielectric material located remotely from the center conductor.

Figure 8 is a perspective view 800 of a common mode trap 801 having eight common mode trap conductors on a straight cable or center conductor 802. In particular, the common mode trap 801 includes common mode trap conductors 810, 811, 812, 813, 820, 821, 822, and 823.

Similar to the common mode trap 701 described above, the common mode trap conductors 810, 811, 812, 813, 820, 821, 822, and 823 are configured in pairs. Specifically, the common mode trap conductors 810 and 811 are counter-wound in the helical configuration described above to form a first pair 816 of common mode trap conductors, while the common mode trap conductors 812 and 813 are similarly counter-wound in the helical configuration and form a second pair 817 of common mode trap conductors. As depicted, the first common mode trap conductor pair 816 is positioned a first radial distance 807 away from the central axis of the center conductor 802, and the second common mode trap conductor pair 817 is positioned a second radial distance 808 away from the central axis of the center conductor 802, wherein the first radial distance 807 is greater than the second radial distance 808.

Similarly, the common mode trap conductors 820 and 821 are rewound in a spiral configuration to form a third common mode trap conductor pair 826, and the common mode trap conductors 822 and 823 are rewound in a spiral configuration to form a fourth common mode trap conductor pair 827. The third pair of common mode trap conductors 826 is positioned a first radial distance 807 from the central axis of the center conductor 802 and the fourth pair of common mode trap conductors 827 is positioned a second radial distance 808 from the central axis of the center conductor 802.

The common mode trap 801 thus comprises four common mode trap conductor pairs arranged symmetrically around the central conductor 802. The density of the common mode trap 801 is thus twice that of the common mode trap 701 described above.

The pair of common mode trap conductors 816 and 817 terminate at first 814 and second 815 capacitors positioned at opposite ends of the common mode trap 801. Similarly, the common mode trap conductor pair 826 and 827 terminates at a third capacitor 824 and a fourth capacitor 825 located at opposite ends of the common mode trap 801. As depicted, the first capacitor 814 and the second capacitor 815 are positioned on opposite sides of the center conductor 802 from the third capacitor 824 and the fourth capacitor 825.

Various methods described herein for supporting a common mode trap conductor in a common mode trap are available. For example, figure 9 is a perspective view 900 of a common mode trap 901 having eight common mode trap conductors mechanically supported by a plurality of annular discs or washers 910 on a straight cable or center conductor 902 in accordance with an embodiment of the present invention. The common mode trap 901 may be similar to the common mode trap 801 in that the common mode trap 901 may include four common mode trap conductor pairs (depicted as dashed lines), with two of the common mode trap conductor pairs being positioned at a first radial distance away from the central axis of the center conductor 902 and the remaining two common mode trap conductor pairs being positioned at a second, smaller radial distance away from the central axis of the center conductor 902.

Plurality of washers 910 includes a first washer 911, a second washer 912, a third washer 913, a fourth washer 914, a fifth washer 915, a sixth washer 916, a seventh washer 917, an eighth washer 918, and a ninth washer 919. As depicted, the plurality of gaskets 910 may be evenly and regularly distributed along the common mode trap 901. As an illustrative and non-limiting example, each of the plurality of washers 910 may include an annular disc composed of a plastic material.

Furthermore, each gasket comprises a plurality of conductor apertures through which the common mode trap conductor may pass. For illustration, fig. 9 also includes a front view 930 of an exemplary washer 931 having an inner radius 932 and an outer radius 933. Washer 931 defines an aperture 934, and a center conductor may be disposed through aperture 934. Furthermore, the gasket 931 comprises a plurality of conductor apertures through which the common mode trap conductor may pass. Specifically, the gasket 931 includes a first pair of conductor apertures 935, a second pair of conductor apertures 936, a third pair of conductor apertures 937, and a fourth pair of conductor apertures 938.

As depicted, the first and fourth pairs of conductor apertures 935, 938 may be relatively positioned adjacent an outer edge of the gasket 931 defined by an outer radius 933, while the second and third pairs of conductor apertures 936, 937 may be relatively positioned adjacent an inner edge of the gasket 931 defined by an inner radius 932. With reference to the common mode trap conductor pair described above in connection with fig. 8, the common mode trap conductor pair 816 and 826 at the first radial distance 807 may pass through the outer conductor apertures 935 and 938. Similarly, the common mode trap conductor pair 817 and 827 at the second radial distance 808 can pass through the inner conductor apertures 936 and 937.

Each washer of the plurality of washers 910 may be rotated 90 degrees relative to each adjacent washer. For example, the gasket 911 is positioned at the end of the common mode trap 901 in an arbitrarily defined orientation of zero degrees. At the same time, the washer 912 is rotated 90 degrees relative to the washer 911 such that the conductor orifice of the washer 912 is oriented 90 degrees relative to the conductor orifice of the washer 911. Further, washer 913 is rotated 90 degrees relative to washer 912 such that the conductor aperture of washer 913 is oriented 90 degrees relative to the conductor aperture of washer 912, but zero degrees relative to the conductor aperture of washer 911. This rotational configuration is repeated for each washer of the plurality of washers 910 such that washers 911, 913, 915, 917, and 919 are aligned with each other and washers 912, 914, 916, and 918 are aligned with each other. Each pair of conductor apertures is configured to force orthogonal crossing of common mode trap conductors passing therethrough. In this way, the symmetry of the common mode trap configuration, and hence the effectiveness of the common mode trap in combating external electromagnetic radiation, may be maintained, while still providing flexibility of the common mode trap on the center conductor.

In some examples, floating capacitors (not shown), such as capacitors 814, 815, 824, and 825 described above in connection with fig. 8, may be embedded in the gaskets 911 and 919 at the ends of the common mode trap 901. In other examples, the common mode trap 901 may include a dither balance transformer connected such that the common mode trap conductor is connected to a dielectric spacer (not shown) encasing the center conductor 802. Such examples are illustrative and not restrictive, and it should be understood that any suitable configuration for providing capacitance to the common mode trap 901 may be utilized.

The configuration of the plurality of gaskets (including the number of gaskets and the configuration of the conductor apertures of each gasket) may depend on the specific configuration of the common mode trap. For example, the plurality of gaskets 910 of the common mode trap 901 are configured to support a non-tapered spiral design of common mode trap conductors, wherein two common mode trap conductor pairs are positioned at different radial distances on two opposite sides of the common mode trap. However, in some examples, the common mode trap conductor pairs may be distributed differently around the center conductor. For example, four additional pairs of common mode trap conductors identical to the four pairs of common mode trap conductors depicted in fig. 7 and 8 may be positioned within the common mode trap and oriented 90 degrees with respect to the four pairs of common mode trap conductors depicted in fig. 7 and 8, such that the common mode trap includes 16 common mode trap conductors (eight common mode trap conductors at a first radial distance and eight common mode trap conductors at a second radial distance). Thus, each gasket may include eight additional conductor apertures distributed appropriately to accommodate additional common mode trap conductor pairs.

Still further, in some examples, the common mode trap conductor may taper towards an end of the common mode trap as described above in connection with fig. 5 and 6. In such an example, the inner radius and the outer radius of one or more of the plurality of washers may be adjusted to accommodate a gradual decrease in the radial distance of the common mode trap conductor along the length of the common mode trap.

Another method for mechanically supporting or forming the common mode trap conductor is to integrate the common mode trap conductor and, in some examples, the corresponding floating capacitor in a PVC-like hose ideally comprising teflon. The center conductor or cable can be easily disposed within the hose to provide a common mode trap to the center conductor. The hose may be flexible to allow bending of the centre conductor without disturbing the function of the common mode trap. Another method of forming a common mode trap conductor is to weave a wire around a sleeve that can be placed over the center conductor. Another method may include providing a post coupled to the shield to which the common mode trap conductor is coupled, as described above in connection with fig. 4-6.

Figure 10 illustrates a top view 1000 of a common mode trap 1001 with eight common mode trap conductors on a straight cable or center conductor 1002 according to an embodiment of the present invention. Figure 11 shows a cross-sectional view 1100 of one end of a common mode trap 1001 according to one embodiment.

The common mode trap 1001 includes four posts positioned at each end of the common mode trap 1001. As depicted in the cross-sectional view 1100, for example, the posts 1010, 1020, 1030, and 1040 are regularly distributed around the circumference of the center conductor 1002 at the first end of the common mode trap 1001; similarly, columns 1011, 1021, and 1031 corresponding to columns 1010, 1020, and 1030, respectively, and an eighth column (not shown) corresponding to column 1040 are regularly distributed around the circumference of the center conductor 1002 at a second, opposite end of the common mode trap 1001, as depicted in top view 1000.

Two common mode trap conductors are fixed to each column of the common mode trap 1001. For example, a first common mode trap conductor 1012 and a second common mode trap conductor 1013 are helically fixed to the first column 1010 around the center conductor 1002 along the length of the common mode trap 1001 and to the second column 1011. The third and fourth common mode trap conductors 1022, 1023 are fixed to the third column 1020 helically around the center conductor 1002 along the length of the common mode trap 1001 at a first end of the common mode trap 1001 and to the fourth column 1021 at a second, opposite end of the common mode trap 1001, as depicted. The fifth and sixth common mode trap conductors 1032, 1033 are fixed to the fifth column 1030 at first ends and to the sixth column 1031 at second ends. The seventh common mode trap conductor 1042 and the eighth common mode trap conductor 1043 are fixed to the seventh column 1040 and at a second end to the eighth column. As described above and depicted in fig. 10, each pair of common mode trap conductors is counter-wound in a spiral configuration. Additionally, in some examples, the common mode trap conductor may taper towards the first and second ends, but it should be understood that in other examples, the common mode trap conductor may maintain a constant radial distance from the central axis of the center conductor 1002 throughout the length of the common mode trap 1001.

In some examples, the density of the common mode trap may be increased relative to the density of the common mode trap described above. For example, figure 12 shows a cross-sectional view 1200 of one end of a common mode trap 1201 having sixteen common mode trap conductors on a center conductor 1202, according to one embodiment. Similar to the common mode traps 801 and 901 described above, the common mode trap 1201 includes a plurality of common mode trap conductor pairs coupled to capacitors in a floating configuration. However, in contrast to the common mode traps 801 and 901, the common mode trap 1201 comprises two additional capacitors at each end of the common mode trap, which capacitors are regularly distributed around the circumference of the common mode trap, similar to the distribution of the columns of the common mode trap 1001. The common mode trap 1201 thus includes eight capacitors, including a first capacitor 1210, a second capacitor 1220, a third capacitor 1230 and a fourth capacitor 1240, and corresponding capacitors (not shown) at opposite ends (not shown) of the common mode trap 1201.

As depicted, two pairs of common mode trap conductors are fixed to each capacitor, including a first pair of common mode trap conductors at a first radial distance from the central axis of the center conductor 1202 and a second pair of common mode trap conductors at a second radial distance from the central axis of the center conductor 1202, wherein the first and second radial distances are different. For example, the first common mode trap conductor 1212 is fixed to the first capacitor 1210 and spirals clockwise around the center conductor 1202 at a first radial distance along the length of the common mode trap 1201, while the second common mode trap conductor 1213 is fixed to the first capacitor 1210 and spirals counterclockwise around the center conductor 1202 at the first radial distance along the length of the common mode trap 1201. The first common mode trap conductor 1212 and the second common mode trap conductor 1213 thus form a first common mode trap conductor pair. Meanwhile, a third common mode trap conductor 1214 is fixed to the first capacitor 1210 and spirals clockwise around the center conductor 1202 at a second radial distance greater than the first radial distance along the length of the common mode trap 1201, while a fourth common mode trap conductor 1215 is fixed to the first capacitor 1210 and spirals counterclockwise around the center conductor 1202 at the second radial distance along the length of the common mode trap 1201. The third common mode trap conductor 1214 and the fourth common mode trap conductor 1215 thereby form a second common mode trap conductor pair.

Similarly, a fifth common mode trap conductor 1222 and a sixth common mode trap conductor 1223 are secured to the second capacitor 1220, thereby forming a third common mode trap conductor pair that spirals in a counter-wound configuration along the length of the common mode trap 1201 at the first radial distance. At the same time, a seventh common mode trap conductor 1224 and an eighth common mode trap conductor 1225 are fixed to the second capacitor 1220, thereby forming a fourth pair of common mode trap conductors that spiral in a counter-wound configuration along the length of the common mode trap 1201 at the second radial distance. Further, a ninth common mode trap conductor 1232 and a tenth common mode trap conductor 1233 are secured to the third capacitor 1230, thereby forming a fifth common mode trap conductor pair that spirals in a counter-wound configuration along the length of the common mode trap 1201 at the first radial distance. At the same time, an eleventh common mode trap conductor 1234 and a twelfth common mode trap conductor 1235 are secured to the third capacitor 1230, thereby forming a sixth pair of common mode trap conductors that spiral in a counter-wound configuration along the length of the common mode trap 1201 at the second radial distance. Further, a thirteenth common mode trap conductor 1242 and a fourteenth common mode trap conductor 1243 are fixed to the fourth capacitor 1240, thereby forming a seventh common mode trap conductor pair that spirals in a counter-wound configuration along the length of the common mode trap 1201 at the first radial distance. At the same time, a fifteenth common mode trap conductor 1244 and a sixteenth common mode trap conductor 1245 are secured to the fourth capacitor 1240, thereby forming an eighth common mode trap conductor pair that spirals in a counter-wound configuration along the length of the common mode trap 1201 at the second radial distance. Similar to the examples described above, each common mode trap conductor pair is fixed to a corresponding capacitor (not shown) at opposite ends of the common mode trap 1201.

Thus, the density of the common mode trap 1201 may comprise sixteen common mode trap conductors and the mutual inductance between the common mode trap and the center conductor is increased relative to common mode traps having a lower density. However, the mutual inductance between the common mode trap and the center conductor does not increase linearly with the density of the common mode trap. Conversely, as the density increases, the improvement in mutual inductance begins to diminish gradually. Thus, there is a trade-off between the increase in mutual inductance and the complexity of the higher density common mode trap, as it becomes more difficult to maintain symmetry between the common mode trap conductor pairs as more common mode trap conductor pairs are added to the common mode trap.

Figure 13 is a high-level block diagram illustrating an example method 1300 for a common mode trap in accordance with an embodiment of the present invention. Method 1300 begins at 1305. At 1305, method 1300 includes providing a center conductor. The center conductor may be configured, for example, substantially similar to center conductor 210 described above. For example, the center conductor may include a transmission cable of the MRI machine configured to couple the RF coil to the one or more processing elements.

At 1310, method 1300 includes disposing a dielectric spacer around the center conductor. In particular, the dielectric spacer may be disposed radially around the center conductor and may extend along at least a portion of the length of the center conductor. For example, the dielectric spacer may have a through hole or aperture preformed therethrough that is sized to receive the center conductor and may be secured in place to the outer sleeve of the center conductor at one or more locations. The dielectric spacers may be configured, for example, substantially similar to the dielectric spacers 304 described above. Further, an outer sleeve or shield may be provided around the dielectric spacer. In some examples, the outer sleeve may be discontinuous to expose at least a portion of the dielectric spacer.

At 1315, method 1300 includes winding two common mode trap conductors in opposite directions around a dielectric spacer at a radial distance to form a first pair of common mode trap conductors on a first side of a center conductor. In particular, the first common mode trap conductor may be helically wound around the dielectric spacer in a first direction (e.g., clockwise) at a radial distance that may or may not be tapered, while the second common mode trap conductor may be helically wound around the dielectric spacer in a second direction (e.g., counterclockwise) at a radial distance that may or may not be tapered. As an illustrative, but non-limiting example, each end of the common mode trap conductor may be fixed to a post or capacitor positioned at each end of the common mode trap. Note that as depicted in the examples described in this specification, a "side" of a cylindrical center conductor may be understood as an axis parallel to the center axis of the center conductor, which extends along the outer surface of the center conductor. As a non-limiting example, the first and second common mode trap conductors may comprise strip conductors or wires. The helical shape of the first common mode trap conductor may be tapered such that the ends of the first and second common mode trap conductors are substantially close to the ends of the dielectric spacer, while the middle portion of the first common mode trap conductor is spaced apart from the dielectric spacer by a radial distance.

At 1320, the method 1300 includes winding two common mode trap conductors in opposite directions at a radial distance around the dielectric spacer to form a second pair of common mode trap conductors on a second side of the center conductor opposite the first side. In particular, the third common mode trap conductor may be wound in a first direction around the dielectric spacer at a tapered or non-tapered radial distance, while the fourth common mode trap conductor may be wound in a second direction around the dielectric spacer at a tapered or non-tapered radial distance. For example, the fourth common mode trap conductor may be wound in a helix having a similar pitch to the helix defined by the third common mode trap conductor, but in a different direction (e.g., clockwise and counterclockwise). It should be noted that the first and second common mode trap conductors and the third and fourth common mode trap conductors may be sufficiently loosely wound around the dielectric spacer such that the common mode trap conductors will not bond or couple to each other if the center conductor and the dielectric spacer are bent or flexed. The spiral formed by the second pair of common mode trap conductors may be tapered as described above.

At 1325, the method 1300 includes coupling a transmission cable formed by the center conductor, the dielectric spacer, and the first and second common mode trap conductor pairs to a component of the MRI system within a bore of the MRI system. For example, the transmission cable is coupled to at least one processing component (e.g., a T/R switch and/or a data acquisition system) and an RF coil of the MRI system. In particular, one end of the transmission cable is connected to the processing component and the other end of the transmission cable is connected to the RF coil. Thus, the transmission cable may be used for example to transmit signals from the receiving coils to the processing means for image reconstruction. As another example, the transmission cable is disposed within or as part of the RF coil. Method 1300 may then end.

As another example, figure 14 is a high-level block diagram illustrating an example method 1400 for a common mode trap in accordance with an embodiment of the present invention. The method 1400 begins at 1405. At 1405, method 1400 includes providing a center conductor. The center conductor may be configured, for example, substantially similar to center conductor 210 described above. For example, the center conductor may include a transmission cable of the MRI machine configured to couple the RF coil to the one or more processing elements.

At 1410, method 1400 includes disposing four capacitors around the center conductor. In particular, two capacitors may be provided on opposite sides of the center conductor at each end of the common mode trap, for example as described above in connection with figure 8.

At 1415, the method 1400 includes winding two common mode trap conductors in opposite directions about a center conductor at a first radial distance to form a first pair of common mode trap conductors on a first side of the center conductor. In particular, the first common mode trap conductor may be helically wound around the center conductor in a first direction (e.g., clockwise) at a first radial distance that may or may not be tapered, while the second common mode trap conductor may be helically wound around the center conductor in a second direction (e.g., counterclockwise) at a first radial distance that may or may not be tapered. As an illustrative and non-limiting example, the ends of the common mode trap conductor may be fixed to a first capacitor positioned at one end of the common mode trap and a second capacitor positioned at the other end of the common mode trap. As a non-limiting example, the first and second common mode trap conductors may comprise strip conductors or wires. The helical shape of the first and second common mode trap conductors may be tapered such that the ends of the first and second common mode trap conductors are substantially close to the ends of the dielectric spacer, while the middle portions of the first and second common mode trap conductors are spaced apart from the dielectric spacer by a radial distance.

At 1420, the method 1400 includes winding two common mode trap conductors in opposite directions around the center conductor at a second radial distance greater than the first radial distance to form a second pair of common mode trap conductors on a first side of the center conductor. In particular, the third common mode trap conductor may be wound in a first direction around the center conductor at a tapered or non-tapered radial distance, while the fourth common mode trap conductor may be wound in a second direction around the center conductor at a tapered or non-tapered radial distance. For example, the fourth common mode trap conductor may be wound in a helix having a similar pitch to the helix defined by the third common mode trap conductor, but in a different direction (e.g., clockwise and counterclockwise). The third and fourth common mode trap conductors are coupled to the first and second capacitors. It should be noted that the first and second common mode trap conductors and the third and fourth common mode trap conductors may be sufficiently loosely wound around the dielectric spacer such that the common mode trap conductors will not bond or couple to each other if the center conductor and the dielectric spacer are bent or flexed. The spiral formed by the second pair of common mode trap conductors may be tapered as described above.

At 1425, the method 1400 includes winding two common mode trap conductors in opposite directions at a first radial distance around the center conductor to form a third common mode trap conductor pair coupled to third and fourth capacitors on a second side of the center conductor opposite the first side.

Similarly, at 1430, the method 1400 includes winding two common mode trap conductors in opposite directions about the center conductor at a second radial distance to form a fourth pair of common mode trap conductors coupled to the third and fourth capacitors on a second side of the center conductor.

At 1435, the method 1400 includes coupling a transmission cable formed by the center conductor, the capacitor, and the common mode trap conductor pair to a component of the MRI system within a bore of the MRI system. For example, the transmission cable is coupled to at least one processing component (e.g., a T/R switch and/or a data acquisition system) and an RF coil of the MRI system. In particular, one end of the transmission cable is connected to the processing component and the other end of the transmission cable is connected to the RF coil. Thus, the transmission cable may be used for example to transmit signals from the receiving coils to the processing means for image reconstruction. As another example, the transmission cable is disposed within or as part of the RF coil. The method 1400 may then end.

Technical effects of the present disclosure may include improved performance of an MRI system due to reduced interaction between transmission cables and coil elements. Another technical effect of the present disclosure may include improving thermal distribution, for example, by distributing heat generated by a common mode trap over a larger area and/or reducing, minimizing, or preventing hot spots. Yet another technical effect of the present disclosure may include ensuring that a common mode blockage or notch is provided at all appropriate locations along a transmission cable. Another technical effect of the present disclosure may include improved flexibility of the common mode trap assembly. Yet another technical effect of the present disclosure may include rotation of the common mode traps relative to each other. Another technical effect of the present disclosure may include tapering of the common mode trap conductor. Yet another technical effect of the present disclosure may include improved mutual inductance between the common mode trap component and the center conductor.

In one embodiment, a common mode trap for a Magnetic Resonance Imaging (MRI) device includes: a first conductor and a second conductor that are counter-wound around a length of the center conductor, wherein the first and second conductors are radially spaced apart from the center conductor by a first distance, wherein the first and second conductors are secured to a first side of the center conductor; and a third conductor and a fourth conductor that are counter-wound around a length of the center conductor, wherein the third and fourth conductors are radially spaced from the center conductor by a first distance, and wherein the third and fourth conductors are secured to a second side of the center conductor opposite the first side.

In a first example of the common mode trap, the first and second conductors orthogonally cross the path. In a second example, which optionally includes the common mode trap of the first example, the common mode trap further comprises a dielectric spacer disposed radially around the center conductor along the length, wherein the first, second, third and fourth conductors are counter-wound around the dielectric spacer. In a third example of the common mode trap, optionally including one or more of the first and second examples, the common mode trap further comprises: first and second capacitors positioned at each end along a length of the first side; and third and fourth capacitors positioned at each end along a length of the second side, wherein the first and second conductors are secured to the first and second capacitors, and wherein the third and fourth conductors are secured to the third and fourth capacitors. In a fourth example of the common mode trap, which optionally includes one or more of the first to third examples, the common mode trap further comprises: a fifth conductor and a sixth conductor that are counter-wound around a length of the center conductor, wherein the fifth and sixth conductors are radially spaced from the center conductor by a second distance that is greater than the first distance, wherein the first and second conductors are secured to the first and second capacitors on a first side of the center conductor; and a seventh conductor and an eighth conductor that are counter-wound around a length of the center conductor, wherein the seventh and eighth conductors are radially spaced a second distance from the center conductor, and wherein the seventh and eighth conductors are secured to the third and fourth capacitors on a second side of the center conductor. In a fifth example of the common mode trap, which optionally includes one or more of the first to fourth examples, the common mode trap further comprises: fifth and sixth capacitors positioned at each end of the length along a third side equidistant from the first and second sides; and seventh and eighth capacitors positioned at each end of the length along a fourth side positioned opposite the third side and equidistant from the first and second sides. In a sixth example of the common mode trap, which optionally includes one or more of the first to fifth examples, the common mode trap further comprises: a fifth conductor and a sixth conductor that are counter-wound around a length of the center conductor, wherein the fifth and sixth conductors are radially spaced apart from the center conductor by a first distance, wherein the fifth and sixth conductors are secured to fifth and sixth capacitors on a third side of the center conductor; and a seventh conductor and an eighth conductor that are counter-wound around a length of the center conductor, wherein the seventh and eighth conductors are radially spaced from the center conductor by a first distance, and wherein the seventh and eighth conductors are secured to seventh and eighth capacitors on a fourth side of the center conductor. In a seventh example of the common mode trap, optionally including one or more of the first to sixth examples, the common mode trap is tuned to provide a resonant frequency close to an operating frequency of the MRI system. In an eighth example of the common mode trap, which optionally includes one or more of the first to seventh examples, the common mode trap further includes a plurality of annular disks disposed at regular intervals around the center conductor, wherein each of the conductors passes through each of the plurality of annular disks.

In another embodiment, a common mode trap assembly for a Magnetic Resonance Imaging (MRI) system includes: a central conductor having a length and configured to transmit signals between an MRI radio frequency coil and a processing element of an MRI system; and a plurality of common mode traps extending along at least a portion of a length of the center conductor, the common mode traps configured to provide an impedance to reduce a transmitter drive current of the MRI system, wherein each common mode trap comprises a second length and comprises a plurality of conductor pairs, each conductor pair of the plurality of conductor pairs comprising a first conductor and a second conductor looped around the center conductor.

In a first example of the common mode trap assembly, each common mode trap includes a first plurality of capacitors positioned at a first end of the common mode trap and a second plurality of capacitors positioned at a second end of the common mode trap, wherein the first and second common mode trap conductors of the common mode trap are fixed to the first plurality of capacitors and the second plurality of capacitors. In a second example optionally including the common mode trap assembly of the first example, the first conductor and the second conductor orthogonally cross paths for each of the plurality of conductor pairs. In a third example of the common mode trap assembly, optionally including one or more of the first and second examples, each of the plurality of common mode traps is disposed contiguously. In a fourth example of the common mode trap assembly, which optionally includes one or more of the first through third examples, each common mode trap includes a dielectric spacer disposed radially around the center conductor.

In yet another embodiment, a method for providing a transmission cable for a Radio Frequency (RF) coil of a Magnetic Resonance Imaging (MRI) system includes: providing a center conductor having a length and configured to transmit signals between an RF coil and a processing element of an MRI system; and positioning a plurality of common mode trap conductor pairs around the center conductor along at least a portion of the length of the center conductor, wherein the plurality of common mode trap conductor pairs are symmetrically distributed around the center conductor, wherein each common mode trap conductor pair comprises a first common mode trap conductor helically wound around the center conductor in a first direction along the portion of the length of the center conductor and a second common mode trap conductor helically wound around the center conductor in a second direction opposite the first direction along the portion of the length.

In a first example of the method, a first half of the plurality of common mode trap conductor pairs is positioned at a first radial distance from a central axis of the center conductor and a second half of the plurality of common mode trap conductor pairs is positioned at a second radial distance from the central axis, the second radial distance being greater than the first radial distance. In a second example of the method, which optionally includes the first example, the first and second common mode trap conductors are positioned radially a first distance from a central axis of the center conductor at a midpoint of the length and a second distance from the central axis at each end of the length, the second distance being less than the first distance. In a third example of the method, which optionally includes one or more of the first and second examples, the first and second common mode trap conductors are fixed to posts positioned at first and second ends of the length. In a fourth example of the method, which optionally includes one or more of the first through third examples, the method further comprises: providing a dielectric spacer radially along a length of the center conductor; and coupling the plurality of common mode trap conductor pairs to the dielectric spacer. In a fifth example of the method, which optionally includes one or more of the first through fourth examples, the method further comprises providing a shield radially surrounding the dielectric spacer.

As used herein, an element or step recited in the singular and proceeded with the word "a" or "an" should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to "one embodiment" of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments "comprising," "including," or "having" an element or a plurality of elements having a particular property may include additional such elements not having that property. The terms "comprising" and "wherein" are used as the plain-language equivalents of the respective terms "comprising" and "wherein". Furthermore, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements or a particular positional order on their objects.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims (20)

1. A common mode trap for a Magnetic Resonance Imaging (MRI) device, comprising:

a first conductor and a second conductor that are counter-wound around a length of a center conductor, wherein the first and second conductors are radially spaced apart from the center conductor by a first distance, wherein the first and second conductors are secured to a first side of the center conductor; and

a third conductor and a fourth conductor that are rewound around the length of the center conductor, wherein the third and fourth conductors are radially spaced apart from the center conductor by the first distance, and wherein the third and fourth conductors are secured to a second side of the center conductor that is opposite the first side.

2. The common mode trap of claim 1, wherein the first and second conductors orthogonally cross paths.

3. The common mode trap of claim 1, further comprising a dielectric spacer disposed radially around the center conductor along the length, wherein the first, second, third and fourth conductors are rewound around the dielectric spacer.

4. The common mode trap of claim 1, further comprising: first and second capacitors positioned at each end of the length along the first side; and third and fourth capacitors positioned at each end along the length of the second side, wherein the first and second conductors are secured to the first and second capacitors, and wherein the third and fourth conductors are secured to the third and fourth capacitors.

5. The common mode trap of claim 4, further comprising:

a fifth conductor and a sixth conductor that are counter-wound around the length of the center conductor, wherein the fifth conductor and the sixth conductor are radially spaced from the center conductor by a second distance that is greater than the first distance, wherein the first and second conductors are fixed to the first capacitor and the second capacitor on the first side of the center conductor; and

a seventh conductor and an eighth conductor that are counter-wound around the length of the center conductor, wherein the seventh and eighth conductors are radially spaced from the center conductor by the second distance, and wherein the seventh and eighth conductors are secured to the third capacitor and the fourth capacitor on the second side of the center conductor.

6. The common mode trap of claim 4, further comprising: fifth and sixth capacitors positioned at each end of the length along a third side equidistant from the first and second sides; and seventh and eighth capacitors positioned at each end of the length along a fourth side positioned opposite the third side and equidistant from the first and second sides.

7. The common mode trap of claim 6, further comprising:

a fifth conductor and a sixth conductor that are counter-wound around the length of the center conductor, wherein the fifth conductor and the sixth conductor are radially spaced from the center conductor by the first distance, wherein the fifth and sixth conductors are fixed to the fifth capacitor and the sixth capacitor on the third side of the center conductor; and

a seventh conductor and an eighth conductor that are rewound around the length of the center conductor, wherein the seventh and eighth conductors are radially spaced apart from the center conductor by the first distance, and wherein the seventh and eighth conductors are secured to the seventh capacitor and the eighth capacitor on the fourth side of the center conductor.

8. The common mode trap of claim 1, wherein the common mode trap is tuned to provide a resonant frequency near an operating frequency of the MRI system.

9. The common mode trap of claim 1, further comprising a plurality of annular disks disposed at regular intervals around the center conductor, wherein each of the conductors passes through each of the plurality of annular disks.

10. A common mode trap assembly for a Magnetic Resonance Imaging (MRI) system, comprising:

a center conductor having a length and configured to transmit signals between an MRI radio frequency coil and a processing element of the MRI system; and

a plurality of common mode traps extending along at least a portion of the length of the center conductor, the common mode traps configured to provide an impedance to reduce a transmitter drive current of the MRI system, wherein each of the common mode traps comprises a second length and comprises a plurality of conductor pairs, each of the plurality of conductor pairs comprising a first conductor and a second conductor that are backwound around the center conductor.

11. The common mode trap assembly of claim 10, wherein each of the common mode traps comprises a first plurality of capacitors positioned at a first end of the common mode trap and a second plurality of capacitors positioned at a second end of the common mode trap, wherein the first and second conductors of the common mode trap are secured to the first and second plurality of capacitors.

12. The common mode trap assembly of claim 10, wherein for each of the plurality of conductor pairs, the first conductor and the second conductor orthogonally cross paths.

13. The common mode trap assembly of claim 10, wherein each of the plurality of common mode traps are disposed contiguously.

14. The common mode trap assembly of claim 10, wherein each of the common mode traps comprises a dielectric spacer disposed radially around the center conductor.

15. A method for providing a transmission cable for a Radio Frequency (RF) coil of a Magnetic Resonance Imaging (MRI) system, comprising:

providing a center conductor having a length and configured to transmit signals between the RF coil and a processing element of the MRI system; and

positioning a plurality of common mode trap conductor pairs around the center conductor along at least a portion of the length of the center conductor, wherein the plurality of common mode trap conductor pairs are symmetrically distributed around the center conductor, wherein each common mode trap conductor pair comprises a first common mode trap conductor helically wound around the center conductor in a first direction along the portion of the length of the center conductor and a second common mode trap conductor helically wound around the center conductor in a second direction opposite the first direction along the portion of the length.

16. The method of claim 15, wherein a first half of the plurality of common mode trap conductor pairs is positioned at a first radial distance from a central axis of the center conductor, and wherein a second half of the plurality of common mode trap conductor pairs is positioned at a second radial distance from the central axis, the second radial distance being greater than the first radial distance.

17. The method of claim 15, wherein the first and second common mode trap conductors are positioned radially a first distance from a central axis of the center conductor at a midpoint of the length and a second distance from the central axis at each end of the length, the second distance being less than the first distance.

18. The method of claim 15, wherein the first and second common mode trap conductors are fixed to posts positioned at first and second ends of the length.

19. The method of claim 15, further comprising: providing a dielectric spacer radially along the length of the center conductor; and coupling the plurality of common mode trap conductor pairs to the dielectric spacer.

20. The method of claim 19, further comprising providing a shield radially surrounding the dielectric spacer.

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