Methods and systems for a floating cable trap

Various methods and systems are provided for a current trap. In one example, the current trap has a spiral core made of a nonconductive material, a coiled wire having a plurality of turns wound around the spiral core, and one or more tuning capacitors physically attached to the spiral core and electrically connected to the coiled wire to form a resonance circuitry with the coiled wire.

FIELD

Embodiments of the subject matter disclosed herein relate to magnetic resonance imaging, and more particularly, to a current trap for a magnetic resonance imaging system.

BACKGROUND

Magnetic resonance imaging (MRI) is a medical imaging modality that can create images of the inside of a human body without using x-rays or other ionizing radiation. MM systems include a superconducting magnet to create a strong, uniform, static magnetic field B0. Exposure of a human body, or part of a human body, to the magnetic field B0, induces polarization of hydrogen nuclear spin in tissue water. The nuclei are excited by a radio frequency signal and upon relaxation to a rest energy state, energy is released as an RF signal which may be transformed into an image.

An MM system utilizes RF coils to transmit RF excitations and/or receive MR signals. Shielded coil-interfacing cables may be used to transmit signals between the RF coils and other aspects of a processing system of the MRI system. For example, the coil-interfacing cables may transmit signals to control the RF coils and/or to receive signals from the RF coils. The coil-interfacing cables may be subjected to electro-magnetic fields and as a result, transmitter-driven common mode currents may adversely affect coil tuning, coil-to-coil coupling in phased array coils, inhomogeneity in generated images, and/or unpredictable heating of components.

Common mode traps, or baluns, providing high common mode impedances, may be used to mitigate the effect of transmitter-driven currents. Conventionally, grounded baluns may be coupled to the coil-interfacing cables to block the induced currents. However, coupling of the baluns to the coil-interfacing cables may demand a complex soldering process. The soldering process may expose conductors in the coil-interfacing cables to high temperatures, leading to degradation of the conductors.

BRIEF DESCRIPTION

In one embodiment, a current trap includes spiral core made of a nonconductive material, a coiled wire having a plurality of turns wound around the spiral core, and one or more tuning capacitors physically attached to the spiral core and electrically connected to the coiled wire to form a resonance circuitry with the coiled wire. In this way, soldering of the current trap assembly to coil-interfacing cables is not demanded and the current trap assembly may located anywhere along the cables.

DETAILED DESCRIPTION

The following description relates to various embodiments for a current trap for MRI systems. In particular, systems are provided for a floating spiral configuration for a current trap for an MRI system, such as the MM system illustrated inFIG. 1. Herein, a floating trap may be defined as a trap that may be removably coupled to cables of the MRI system by mechanical engagement and without additional processes to secure the trap to the cables, such as soldering. Furthermore, coupling the floating trap to the cables, unlike non-floating current traps, does not demand cutting of the cables, thus allowing a position of the floating trap to be readily reconfigured along the cables. As shown inFIG. 2, a current trap may be arranged along a communication cable configured to receive MR data. The current trap may be a floating trap as depicted inFIGS. 3 and 4. The current trap may be assembled by engaging a coiled wire with a spiral core, as shown inFIG. 9. The current trap may be configured to engage with cables of the MRI system by winding the cables around the spiral core, as illustrated inFIGS. 5 and 6. As illustrated inFIG. 14, the current trap may be coupled to up to four cables. A floating trap assembly is shown inFIG. 7and a cross-section of the assembly is shown inFIG. 8. The current trap may be further covered with a shield, as illustrated inFIG. 10, when the current trap is to be positioned proximate to a patient. A routine for blocking transmission-induced currents along cable of an MRI system by implementing the floating trap is depicted inFIG. 11. A schematic of an electrical circuit of the floating trap is shown inFIG. 12and a repositioning of the floating trap along a cable of an MRI system is illustrated inFIG. 13.

FIG. 1illustrates a magnetic resonance imaging (MM) apparatus10that includes a magnetostatic field magnet unit12, a gradient coil unit13, an RF coil unit14, an RF body coil unit15, a transmit/receive (T/R) switch20, an RF driver unit22, a gradient coil driver unit23, a data acquisition unit24, a controller unit25, a patient bed26, a data processing unit31, an operating console unit32, and a display unit33. The Mill apparatus10transmits electromagnetic pulse signals to a subject16placed in an imaging space18with a magnetostatic field formed to perform a scan for obtaining magnetic resonance signals from the subject16to reconstruct an image based on the magnetic resonance signals thus obtained by the scan.

The magnetostatic field magnet unit12includes, for example, typically an annular superconducting magnet, which is mounted within a toroidal vacuum vessel. The magnet defines a cylindrical space surrounding the subject16, and generates a constant primary magnetostatic field.

The MM apparatus10also includes a gradient coil unit13that forms a gradient magnetic field in the imaging space18so as to provide the magnetic resonance signals received by the RF coil unit14with three-dimensional positional information. The gradient coil unit13includes three gradient coil systems, each of which generates a gradient magnetic field which inclines into one of three spatial axes perpendicular to each other, and generates a gradient field in each of frequency encoding direction, phase encoding direction, and slice selection direction in accordance with the imaging condition.

The RF coil unit14is disposed, for example, to enclose the region to be imaged of the subject16. In the static magnetic field space or imaging space18where a static magnetic field is formed by the magnetostatic field magnet unit12, the RF coil unit14may transmit, based on a control signal from the controller unit25, an RF pulse to the subject16. This excites a spin of protons in the subject16. The RF coil unit14may also receive magnetic resonance signals generated when the proton spin thus excited in the subject16returns into alignment with the initial magnetization vector. The RF coil unit14may transmit RF excitation and receive MR signal using the same RF coil.

The RF body coil unit15is disposed, for example, to enclose the imaging space18, and produces RF pulses within the imaging space18to excite the nuclei. In contrast to the RF coil unit14, which may be easily disconnected from the MR apparatus10and replaced with another RF coil unit, the RF body coil unit15is fixedly attached and connected to the MR apparatus10.

The T/R switch20can selectively connect the RF body coil unit15to the data acquisition unit24when operating in receive mode, and to the RF driver unit22when operating in transmit mode. Similarly, the T/R switch20can selectively connect the RF coil unit14to the data acquisition unit24when the RF coil unit14operates in receive mode, and to the RF driver unit22when operating in transmit mode. When the RF coil unit14and the RF body coil unit15are both used in a single scan, for example if the RF coil unit14is configured to receive MR signals and the RF body coil unit15is configured to transmit RF signals, then the T/R switch20may direct control signals from the RF driver unit22to the RF body coil unit15while directing received MR signals from the RF coil unit14to the data acquisition unit24. The coils of the RF body coil unit15may 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 unit14may be configured to operate in a transmit-receive mode or a receive-only mode.

The RF driver unit22may include a gate modulator (not shown), an RF power amplifier (not shown), and an RF oscillator (not shown). The RF driver unit22modulates, based on a control signal from the controller unit25and using the gate modulator, the RF signal received from the RF oscillator into a signal of predetermined timing having a predetermined envelope. The RF signal modulated by the gate modulator is amplified by the RF power amplifier and then output to the RF coil unit14.

The gradient coil driver unit23drives the gradient coil unit13based on a control signal from the controller unit25and thereby generates a gradient magnetic field in the imaging space18. The gradient coil driver unit23may include three systems of driver circuits (not shown) corresponding to the three gradient coil systems included in the gradient coil unit13.

The data acquisition unit24may include a preamplifier (not shown), a phase detector (not shown), and an analog/digital converter (not shown). The phase detector phase detects, using the output from the RF oscillator of the RF driver unit22as a reference signal, the magnetic resonance signals received from the RF coil unit14and amplified by the preamplifier, and outputs the phase-detected analog magnetic resonance signals to the analog/digital converter for conversion into digital signals. The digital signals thus obtained are output to the data processing unit31.

The MM apparatus10includes a table26for placing the subject16thereon. The subject16may be moved inside and outside the imaging space18by moving the table26based on control signals from the controller unit25.

The controller unit25includes a computer and a recording medium on which a program to be executed by the computer is recorded. The program when executed by the computer causes various parts of the apparatus to carry out operations corresponding to an MRI scan.

The operating console unit32may include user input devices such as a keyboard and a mouse. The operating console unit32is used by an operator, for example, to input such data as an imaging protocol and to set a region where an imaging sequence is to be executed. The data about the imaging protocol and the imaging sequence execution region are output to the controller unit25.

The data processing unit31includes a computer and a recording medium on which a program to be executed by the computer to perform data processing is recorded. The data processing unit31is connected to the controller unit25and performs data processing based on control signals received from the controller unit25. The data processing unit31is also connected to the data acquisition unit24and generates spectrum data by applying various image processing operations to the magnetic resonance signals output from the data acquisition unit24.

The display unit33includes a display device and displays an image and/or other information on the display screen of the display device based on control signals received from the controller unit25. The display unit33displays, for example, scanning parameters. The display unit33also displays an MR image of the subject16generated by the data processing unit31.

During a scan, coil-interfacing cables (not shown) may be used to transmit signals between the RF coils (e.g., RF coil unit14) and other aspects of the processing system (e.g., data acquisition unit24, controller unit25, and so on), for example to control the RF coils and/or to receive information from the RF coils. In some embodiments, the coil-interfacing cables are integrated into the RF coil unit14. The coil-interfacing cables may be disposed within the bore or imaging space18of the MRI apparatus10and subjected to electro-magnetic fields produced and used by the MRI apparatus10. The cables may be subject to transmitter driven common mode currents which create field distortions and/or unpredictable heating of components. Baluns or common mode traps that provide high common mode impedances may be utilized to mitigate the effect of transmitter driven currents. Various embodiments of such common mode traps and common mode trap assemblies are described further herein.

FIG. 2illustrates a block schematic diagram of a common mode trap assembly200or balun assembly200. The balun assembly200may be configured, for example, for use in the bore of an MRI system, such as the MRI apparatus10described herein above. For example, in the illustrated embodiment, the balun assembly200is configured as a transmission cable201configured for transmission of signals between a processing unit (or controller)250and a receive coil260of an MM system. In some embodiments, the transmission cable201is integrated into the receive coil260and becomes part of it. The receive coil260further includes one or more coil elements coupled to the transmission cable, as known in the art.

In the illustrated embodiment, the transmission cable201(or balun assembly200) includes a central conductor210and at least one balun212. The central conductor210in the illustrated embodiment has a length204, and is configured to transmit a signal between the MRI receive coil260and at least one processor of an MRI system (e.g., processing unit250). The central conductor210may include one or more of a ribbon conductor, a wire, or a coaxial cable bundle, for example.

The depicted balun212, as seen inFIG. 2, extends along at least a portion of the length204of the central conductor210. In the illustrated embodiment, balun212does not extend along the entire length204. However, in other embodiments, the balun212may extend along the entire length204, or substantially along the entire length204.

The balun212is configured to provide an impedance to the receive transmitter driven currents of an MM system. The balun212in various embodiments provides high common mode impedances. For example, the balun212may include a resonant circuit and/or one or more resonant components to provide a high impedance at or near a desired frequency or within a target frequency range. It may be noted that the balun212may also be referred to as a choke by those in the art.

The balun212may be tuned to have a resonant frequency near an operating frequency of the MRI system. As used herein, a balun may be understood as having a resonant frequency near an operating frequency when the resonant frequency defines or corresponds to a band that includes the operating frequency, or when the resonant frequency is close enough to the operating frequency to provide on-frequency blocking, or to provide a blocking impedance at the operating frequency.

In conventional designs, the balun has a central opening through which the central conductor passes and the balun is usually soldered to the central conductor. Such soldering process may be complex and may expose the central conductor to high temperatures. The central conductor, adapted for RF applications, may be sensitive to heat and soldering the central conductor may result in degradation of the central conductor. The present disclosure describes an implementation of a balun that may be installed without soldering or any special complex process. Additionally, the balun may be removed and reinstalled without causing any wire degradation.

The current trap302may be a generally cylindrical structure formed of two portions: a spiral core304, and a coiled wire308. The spiral core304may be formed of a rigid, durable, nonconductive (e.g., insulating) material, such as plastic, and provides a frame for the current trap302. A central tube310of the spiral core304may extend along an entire length312of the spiral core304along the central axis303. The length312of the spiral core304may be different depending on an application of the current trap302. For example, a diameter and length of a cable to which the current trap302is coupled may affect the length312of the spiral core. As an example, the length312of the spiral core304may be 3.5 cm. An inner diameter314of the central tube310may be, for example, 0.2-0.5 cm while an outer diameter316of the central tube310may be 0.4-0.7 cm. The inner diameter314and the outer diameter316may be uniform along the length312of the spiral core304. Alternatively, as shown in a cross-section800inFIG. 8, the inner diameter314may taper between a first end802and a second end806of the central tube310for plastic piece tooling. However, in other embodiments, the inner diameter314may remain uniform between the first end802and the second end806.

A spiral rib318may be disposed at an outer surface of the central tube310, protruding radially outwards from the central axis303. The spiral rib318may provide insulation between each turn of the coiled wire308, where each turn is a full 360 degree rotation around the central axis303. In other words, each turn of the coiled wire308is spaced away from adjacent turns by the spiral rib318, thereby electrically insulating each turn. The spiral core304may be fabricated, by injection molding, for example, so that the spiral rib318and the central tube310are made as one piece. The spiral rib318may have a trapezoidal cross-section, e.g., when the cross-section is taken along the y-z plane as shown inFIG. 4. Therein, a width402of the spiral rib318, defined along the z-axis, at a base404of the spiral rib318is greater than a width406of the spiral rib318at an outer edge or tip408of the spiral rib318.

A height410of the spiral rib318may be equal to or greater than a sum of a diameter322of the coiled wire308plus a diameter of each cable coupled to the current trap302. For example, as shown inFIG. 8, the height410is equal to or greater than the sum of the diameter322of the coiled wire, a diameter of a first cable716aand a diameter of a second cable716b. The spiral rib318protrudes radially outwards, away from the central tube310, and coils around the central tube310to form a plurality of layers320. The plurality of layers320are continuous with one another but are seen individually in the cross-sectional view inFIG. 4.

The height410of the spiral rib318remains substantially uniform along the length312of the spiral core304. Thus, each of the plurality of layers320are similar in shape and size. The uniform height of the spiral rib318results in a cylindrical outer geometry of the spiral core304. As shown inFIG. 4, the plurality of layers320are spaced uniformly apart along the length312of the spiral core304. A distance between each of the plurality of layers320at the base404of each layer may be a pitch412of the spiral rib318. The pitch412may be similar to, narrower, or wider than the width402of the spiral rib318at the base404of the spiral rib318.

The pitch412of the spiral rib318may be configured to accommodate winding of the coiled wire308so that the coiled wire308is inserted between each of the plurality of layers320at the base404of each of the plurality of layers320. As such, the pitch412of the spiral rib318may be similar to or larger than the diameter322(shown inFIG. 3) of the coiled wire308. The pitch412of the spiral rib318may be different according to the thickness of the coiled wire308. For example, if a thicker coiled wire308is to be inserted into the spiral core304, the pitch412of the spiral rib318may be made larger. Conversely, if a thinner coiled wire308is to be inserted, the pitch412may be made smaller. The length312of the spiral core304may also be varied if a specific pitch and a specific number of the plurality of layers320is desired. Furthermore, a helix angle α, as shown inFIG. 4, indicates an angle of a spiraling of the spiral rib318relative to the y-axis.

The coiled wire308is wound around the central tube310along the spiral rib318. In some embodiments, the coiled wire308includes a first straight section324and a second straight section326, and a central portion328, positioned between the first straight section324and the second straight section326and coiled around the central tube310of the spiral core304. In some embodiments, the coiled wire308includes only the central portion328, which forms an inductor and enables the current trap302to interact with coil-interfacing cables through electromagnetic induction. The central portion328of the coiled wire308generates an electromagnetic field when a shield current flows through the coil-interfacing cables, which impedes the shield current via a resonance circuitry of the current trap302, as described further below. The coiled wire308may be a conductor made of any appropriate conductive material, such as copper, aluminum, etc., but not ferromagnetic materials.

A length416of the central portion328, as shown inFIG. 4, may be similar to or shorter than the length312of the spiral core304. The central portion328may have a number of turns equal to or fewer than a number of spaces418in between the plurality of layers320of the spiral core304. InFIG. 4, the central portion328has six turns, corresponding to six spaces418between the plurality of layers320. However, other numbers of turns of the central portion328of the coiled wire308and of spaces418between the plurality of layers320have been contemplated, such as 4, 7, 8, etc.

As described above, the central portion328of the coiled wire308is in contact with and wraps around the central tube310of the spiral core304. The central portion328has a helical configuration and each turn of the central portion328coils around the central tube310of the spiral core304along a uniform angle relative to the y-axis, which may be equal or close to the helix angle α.

FIG. 9shows the coiled wire308being coupled to the spiral core304. The central portion328may be fed into the spaces418between the plurality of layers320by turning the coiled wire308in a rotational direction indicated by arrows904. The coiled wire308may be rotated until all turns of the central portion328are engaged in the spaces418. The engagement of the coiled wire308with spiral core304forces the turns of the coiled wire308to be spaced apart by the pitch412of the spiral core304.

The current trap302may further include one or more tuning capacitors that form a resonance circuitry with the coiled wire308which functions as an inductor in the circuitry. A printed circuit board (PCB)702may carry the tuning capacitors, as shown in a perspective view700and in the cross-section view800ofFIG. 8, taken along line A-A′ ofFIG. 7. The PCB702may carry a set of tuning capacitors704, each tuning capacitor spaced apart from the other tuning capacitors704and arranged on an outward facing surface of the PCB702, e.g., a surface of the PCB702facing away from the spiral core304of the current trap302. The current trap302may be tuned by coupling a probe to the PCB702to adjust the impedance to block a target frequency, such as 127.7 MHz, before the current trap assembly703is coupled to the coil-interfacing cable. In other words, the current trap assembly703may be pre-tuned during manufacturing and provided to a user as a tuned, ready-to-use device.

The PCB702may be coupled to the first end802(as shown inFIG. 8) of the central tube310of the spiral core304by an adhesive. It will be appreciated that the PCB702may be similarly coupled to the second end806of the central tube310of the spiral core304without affecting a tuning capacity of the set of tuning capacitors704. The PCB702may include a slot706, as shown inFIG. 7extending from an outer edge705of the PCB702towards the central axis303and terminating at a rounded end710disposed between the outer edge705of the PCB702and the central axis303. The rounded end710of the slot may align with the first section324of the coiled wire308along the z-axis, allowing the first section324of the coiled wire308to extend through the rounded end710. The rounded end710may be lined with a conductive material, such as a copper gasket, and functions as a first electrical connection end for the set of capacitors704. In some embodiments, the rounded end710is made in contact with the first section324of the coiled wire308via soldering, to electrically couple the set of tuning capacitors704of the PCB702to the coiled wire308at one end.

The PCB702may also have a central aperture718aligned with the central axis303and extending entirely through a thickness of the PCB702, as shown inFIG. 8, where the thickness is defined along the z-axis. A bus wire functions as a second electrical connection end for the set of capacitors704and passes through the central aperture718of the PCB702. The bus wire continues to pass through the central tube310from the first end802all the way to the second end806and is made in contact with the second section326of the coiled wire308via soldering, to electrically couple the set of tuning capacitors704of the PCB702to the coiled wire308at another end.

The PCB702may be configured as a circular disc as shown inFIGS. 7 and 8. A variety of conductive tracks, pads and other features may be etched into laminated sheets of copper and electrical components, such as the set of tuning capacitors704, may be soldered on to the PCB702. The set of tuning capacitors704may be spaced away from one another. In some embodiments, the inductor formed by the coiled wire308is connected to the set of capacitors704by connecting two ends of the coiled wire308to two ends of the capacitor set704respectively, as described above.

One or more cables may be wound around the spiral core304and stacked on top of the coiled wire308to form a floating trap assembly.FIGS. 7 and 8show two cables716wound around the spiral core304and stacked on top of the coiled wire308. An equivalent electrical circuit diagram of this floating trap assembly is shown inFIG. 12. The inductor1206(e.g., central portion328of coiled wire308) and the tuning capacitor(s)704form a resonance circuitry. Cables1202and1204(e.g., coil-interfacing cables in an MRI system) are coupled to the inductor1206via electromagnetic interaction. The resonance circuitry has a high impedance to shield currents generated in cables1202and1204and can reduce the shield currents through the electromagnetic coupling with cables1202and1204.

The cables716may be coil-interfacing cables, curving around a first end707of the spiral rib318and extending through the slot706, as shown inFIGS. 6-8. Each of the cables716may include a shield. The shield may be a common conductive layer, formed of a material such as braided strands of metal, a spirally wound metallic tape, a conducting polymer, etc., that circumferentially surrounds each of the cables716. As such, the shield encloses one or more insulated conductors, e.g., wires, of each of the cables716. Implementing each of the cables716with the shield may reduce electrical noise which may otherwise degrade electrical signals transmitted by the cables716. The shield may also decrease electromagnetic radiation which may cause electromagnetic interference with other electrical devices.

The conductive nature of the shield may result in an increased likelihood of generation of shield currents on the cables716, which may cause localized heating of the cables716, distortion of MRI images, and adversely affect coil tuning. Thus equipping the MM system with at least one floating trap assembly703may circumvent the issues described above.

The coupling of the PCB702to the current trap302allows the floating trap assembly703to be tuned away from an MM system and independent of the MM system. Use of the floating trap assembly703may therefore be expedited by precluding a time-consuming tuning procedure. The tuning procedure may be performed during manufacturing of the floating trap assembly703where the set of tuning capacitors704may be adjusted to provide an impedance of the floating trap assembly703that blocks a resonant frequency of a shield current carried by the cables716. Alternatively, the floating trap assembly703may be configured to block a range of frequencies to enable the floating trap assembly703to be used across a variety of systems with varying resonance frequencies to be impeded.

The cable(s)716may be wound around the spiral core304of the current trap302through the spaces418between the plurality of layers320of the spiral core304, the spaces418shown inFIG. 4. The cable(s)716may be arranged so that the cables716are stacked along the y-axis within each of the spaces418. The stacking of the cables716is shown in greater detail inFIGS. 5, 6 and 8. A side view500and a perspective view600of the current trap302coupled to the cables716is depicted inFIGS. 5 and 6, respectively. Similar toFIGS. 3-4, a section (e.g., indicated by bracket306inFIG. 3) of the spiral rib318of the spiral core304is removed for clarity. The cables716may be similar in diameter to the diameter322of the coiled wire308or may have diameters different from the coiled wire308or from one another in other examples.

A configuration of the cables716, when coupled to the spiral core304, may be similar to the configuration of the coiled wire308. A first region502and a second region504of the cables716, which are not coupled to the spiral core304, may extend away from the spiral core304along the z-axis. The cables716may follow a similar geometry to the coiled wire308wrapping around the central portion328of the coiled wire308through the spaces418between the plurality of layers320along the helix angle α, as shown inFIG. 4and extending away from the spiral core304at the first and second regions502,504, in opposite directions.

The stacking of the cables716and the coiled wire308along the spiral core304is further depicted in the cross-section800ofFIG. 8. The cables716include the first cable716aand the second cable716b, as shown in a first dashed region816. The first cable716ais positioned directly adjacent to the coiled wire308, in between the coiled wire308and the second cable716b, as shown in the first and second regions502,504of the cables716inFIG. 6. In other words, no other cables or objects are disposed between the first cable716aand the coiled wire308along an entire length of the coiled wire308.

As the cables716wind through the spiral core304, the relative positioning of the first cable716a, as shown inFIG. 8, is maintained in contact with the coiled wire308along the length312of the spiral core304. In the first dashed region816ofFIG. 8, the coiled wire308and the cables716are stacked along the y-axis, e.g., along a radial direction perpendicular to the central axis303, with the first cable716aon top of the coiled wire308and the second cable716bon top of the first cable716a. While the stacking of the coiled wire308and the cables716may be angled with respect to the y-axis, e.g., following the helix angle α as shown inFIG. 4, the coiled wire308and the cables716do not align parallel with the central axis303at any point along the spiral core304.

A second dashed region818shows an arrangement of the coiled wire308and the cables716in an opposite side of the spiral core304from the first dashed region816. The first cable716ais positioned directly below the coiled wire308along the y-axis and the second cable716bis positioned directly below the first cable716a. Thus the relative positioning of the first cable716aand second cable716bis maintained along the spiral core304and around the spiral core304.

Dimensions of the spaces418between the plurality of layers320of the spiral core304may be configured to accommodate cable diameters that differ from the diameter322of the coiled wire308. The pitch412of the spiral rib318may be similar to the diameter322of the coiled wire308. A width of the spaces418may increase along the y-axis towards the tip408of the spiral rib318(which are also tops408of the plurality of layers320) so that a width820of the spaces418at the tops408of the spaces418is wider than the pitch412of the spiral core304. The increase in width of the spaces418in a radial direction away from the central axis303enables a diameter822of each of the cables716, which may be larger than the diameter322of the coiled wire308, to fit within the spaces418. However, the width820of the spaces418is maintained less than two times the diameter822of the cables716so that the cables may not shift.

The height410of the spiral rib318may be equal to or greater than a sum of the diameter322of the coiled rib308and the diameters822of the cables716. Furthermore, the height410may be varied to accommodate more cables716than shown inFIGS. 5-7. The current trap302may be configured to couple to up to four cables716, the cables716stacked similarly to the first and second cables716a,716b, as shown inFIG. 8, along the radial direction perpendicular to the central axis303. An example of a current trap coupled to four cables is depicted inFIG. 14.

FIG. 14shows a detailed view1400of a section of a current trap1402having a spiral core1404similarly configured to the spiral core304shown inFIGS. 3-9. A space1406between adjacent threads1408of the spiral core1404receives a coiled wire1410and four cables1412. The cables1412are stacked on top, relative to the y-axis, of the coiled wire1410and on top of one another.

The floating trap assembly703may have several advantages over a conventional balun (e.g., non-floating). The coil-interfacing cables of the Mill system may be wrapped around the spiral core of the floating trap assembly without cutting the cables. Thus soldering of the floating trap assembly to the cables is not demanded, mitigating exposure of the cables to high temperature. As the floating trap assembly is a portable unit that is not anchored to any other structures, the floating trap assembly may be positioned anywhere along the cables without cutting the cables and may therefore be placed in convenient locations along the cables that allow the floating trap assembly to be readily accessed.

An example of how a floating trap assembly may be reconfigured along at least one coil-interfacing cable is depicted in a schematic diagram1300inFIG. 13. The current trap1302may be coupled to a cable1304extending between a processing unit1306and a receive coil1308of an MRI system. The current trap1302may be arranged at a first location1310, closer to the processing unit1306than the receive coil1308, and connected to the cable1304by winding the cable1304around a spiral core of the floating trap assembly1302on top of a coiled wire of the current trap1302.

The floating trap assembly may be re-located to a second location1312along the cable1304by unwinding the cable1304from the spiral core of the current trap1302and moving the current trap1302along the cable, closer to the receive coil1308. The current trap1302may be coupled to the cable1304by winding the cable1304around the spiral core of the current trap1302. Furthermore, the floating trap assembly may be readily re-positioned to any point along the cable1304between the processing unit1306and the receive coil1308.

Referring toFIG. 10, a shielded current trap1002is depicted in a perspective view1000. Similar to the unshielded current trap shown inFIGS. 3-4, the shielded current trap1002may have a coiled wire1004coupled to a bus wire1014which functions as an electrical connection end for tuning capacitor(s). Additionally, the shielded current trap1002may be configured as a floating current trap. It will be appreciated that while the bus wire1014ofFIG. 10is not depicted inFIGS. 3-9for brevity, the bus wire1014may be similarly coupled to the current trap302ofFIGS. 3-9.

In addition to components of the unshielded current trap, the shielded current trap1002further comprises a shield1020enclosing the cables1018. The shield1020is a hollow cylinder that encloses the spiral core, the coiled wire, and the cable. The shield1020may be formed of an electromagnetically insulating material such as plastic coated with an outer layer of copper tape. Furthermore, the shield1020may be provided as a sheet of the electromagnetically insulating material with a mechanism for coupling parallel edges of the sheet to one another. In this way, the cables1018may be first coiled around the spiral core and then the shield1020may be wrapped around the spiral core and maintained in the cylindrical geometry around the spiral core by fastening the parallel edges of the shield1020to one another. Implementing the shielded current trap1002with the shield1020may reduce the exposure of a patient to electromagnetic radiation.

FIG. 11is a high-level block diagram illustrating an example method1100for blocking transmission-induced currents on one or more central conductors (e.g., coil-interfacing cables) by coupling the central conductors to a floating trap assembly, such as the floating trap assembly703ofFIGS. 7 and 8, according to an embodiment of the disclosure. Prior to engagement with the central conductors, the floating trap assembly may be tuned to a resonance frequency that is equal or close to an operating frequency of an MRI system via tuning capacitors coupled to a printed circuit board of the floating trap assembly. The one or more central conductors may be successively wrapped around the floating trap assembly, as shown inFIGS. 5-8.

Method1100begins at1102. At1102, RF energy generated at a body coil of the MRI system is transmitted to the central conductors. The signal transmission generates a shield current which is carried along the shields of the central conductors at1104. At1106, the floating trap assembly traps the RF current at the central conductors. For example, a high impedance of the floating trap assembly, where the resonant frequency is pre-set (e.g., tuned) to the operating frequency of the MM system, reduces the shield current.

The technical effect of the disclosure may include improved performance of MM systems due to reduced interaction between transmission cables and coil elements. Another technical effect of the disclosure may include achieving desired impedance of a floating trap assembly via a single floating trap. Yet another technical effect of the disclosure may include positioning the floating trap assembly anywhere along the transmission cables. Yet another technical effect of the disclosure may include reducing a coil surface temperature relative to a feed board of an MRI system.