CN110857971A

CN110857971A - Radio frequency coil for medical imaging device

Info

Publication number: CN110857971A
Application number: CN201810961665.7A
Authority: CN
Inventors: 赛卡特·萨哈; 藤本昌宏; 迈克尔·P·爱德华
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2018-08-22
Filing date: 2018-08-22
Publication date: 2020-03-03

Abstract

Methods and systems are provided for a Radio Frequency (RF) coil of a Magnetic Resonance Imaging (MRI) system. In one embodiment, a radio frequency coil for a medical imaging device includes: a first conductive portion having a first end and an opposing second end; and a first plurality of notches of the first conductive portion extending across a centerline of the first conductive portion from the first end to the second end. In this way, the amount of eddy currents generated within the conductive surface of the RF coil is reduced, thereby reducing the temperature and vibration of the RF coil.

Description

Radio frequency coil for medical imaging device

Technical Field

Embodiments of the subject matter disclosed herein relate to Magnetic Resonance Imaging (MRI), and more particularly, to Radio Frequency (RF) coils for MRI systems.

Background

Magnetic Resonance Imaging (MRI) is a medical imaging modality that can produce images of the interior of a patient without X-ray radiation or other types of ionizing radiation. An MRI system is a medical imaging device that utilizes a superconducting magnet to generate a strong, uniform static magnetic field within a designated region (e.g., within a passageway shaped to receive a patient). When the patient's body (or a portion of the patient's body) is located within the magnetic field, the nuclear spins associated with the hydrogen nuclei that form water within the patient's tissue become polarized. The magnetic moments associated with these spins align along the magnetic field direction and induce a small net tissue magnetization in the magnetic field direction. The MRI system additionally includes magnetic gradient coils that produce a spatially varying magnetic field that is small in magnitude relative to the magnitude of the uniform magnetic field produced by the superconducting magnet. The spatially varying magnetic fields are configured to be orthogonal to each other in order to spatially encode the region by generating characteristic resonance frequencies of hydrogen nuclei at different locations within the patient. A Radio Frequency (RF) coil assembly is then used to generate pulses of RF energy at or near the resonant frequency of the hydrogen nuclei. The pulse of RF energy is absorbed by the hydrogen nuclei, adding energy to the nuclear spin system and modulating the hydrogen nuclei from a resting state to an excited state. When the hydrogen nuclei relax from the excited state back to the quiescent state, they release the absorbed energy in the form of an RF signal. The signal is detected by the MRI system and converted into an image by a computer using known reconstruction algorithms.

Disclosure of Invention

In one embodiment, a Radio Frequency (RF) coil for a medical imaging device includes: a first conductive portion having a first end and an opposing second end; and a first plurality of notches of the first conductive portion extending across a centerline of the first conductive portion from the first end to the second end. In this manner, the plurality of notches reduce the amount of eddy currents flowing through the first conductive segment and reduce the operating temperature of the RF coil during imaging of the patient.

It should be appreciated that the brief description above is provided to introduce in simplified form selected concepts that are further described in the detailed description. It is not meant 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 from reading the following description of non-limiting embodiments, with reference to the attached drawings, in which:

fig. 1 shows a schematic diagram of an example Magnetic Resonance Imaging (MRI) system including a Radio Frequency (RF) coil, according to an embodiment.

FIG. 2 shows a perspective view of an aperture of a gantry of an MRI system including an RF coil having a segmented end-ring, in accordance with an embodiment;

FIG. 3 illustrates a front perspective view of the RF coil of FIG. 2 in accordance with one embodiment;

FIG. 4A shows a flat view of the exterior of the RF coil of FIG. 2 in accordance with an embodiment, and FIG. 4B shows a flat view of the interior of the RF coil of FIG. 2 in accordance with an embodiment;

FIG. 5A shows an enlarged view of a conductive portion located outside of the RF coil of FIG. 2 according to one embodiment, and FIG. 5B shows an enlarged view of a conductive portion located inside of the RF coil of FIG. 2 according to one embodiment;

FIG. 6A shows relative temperatures of the conductive portion shown by FIG. 5A, and FIG. 6B shows relative temperatures of the conductive portion shown by FIG. 5B, according to one embodiment; and

fig. 7 illustrates a graph of temperature of the bore of fig. 2 during operation of the RF coil of fig. 2 in accordance with an embodiment.

Fig. 2-6B are shown generally to scale, although other relative dimensions may be used.

Detailed Description

The following description relates to various embodiments of Magnetic Resonance Imaging (MRI). In particular, systems and methods are provided for a Radio Frequency (RF) coil of an MRI system. An MRI system, such as that shown in fig. 1, includes a gantry having an aperture with an imaging volume located therein. An RF coil comprising two opposing end rings and a plurality of rungs is coupled around a perimeter of the bore to image a patient positioned within the imaging volume. As shown in fig. 3-5B, the RF coil includes a plurality of conductive portions coupled to the inner and outer surfaces of the end-ring. As shown in fig. 5A-5B, each conductive portion includes a plurality of notches extending in a transverse direction relative to a centerline of the conductive portion. The recess of each conductive portion reduces the amount of eddy currents within the conductive portion during operation of the MRI system. The reduction of the eddy current lowers the temperature of the conductive portion as shown in fig. 6A to 6B, and the amount of vibration of the RF coil can be reduced. The reduced temperature of the conductive portion results in a reduced temperature of the bore of the housing as shown in fig. 7. The reduction in temperature and vibration due to the reduced eddy currents may result in increased patient comfort and reduced power consumption by the RF coil.

Although an MRI system is described by way of example, it will be appreciated that the present technique may also be useful when applied to images acquired using other imaging modalities, such as tomosynthesis, computed tomography, C-arm angiography, and the like. The present discussion of MRI imaging modalities is provided merely as an example of one suitable imaging modality.

Fig. 1 shows an MRI system 10, which includes a static field magnet unit 12 (e.g., a superconducting magnet), a magnetic gradient generator 13, a local RF coil 14, a volume RF coil 15 (which may be referred to herein as a body RF coil), a transmit/receive (T/R) switch 20, an RF signal driver 22, a gradient driver 23, a data acquisition unit 24, a controller unit 25, a patient table 26 (which may be referred to herein as a couch), a data processing unit 31, an operation console unit 32, and a display unit 33. The local RF coil 14 is a surface coil configured to be placed proximate to a surface of an anatomical structure of a subject 16 (e.g., a patient) to be scanned by the MRI system 10. The volume RF coil 15 is a coil configured to transmit RF signals (e.g., electromagnetic waves of radio frequency), and the local RF coil 14 is configured to receive RF signals. Thereby, the volume RF coil 15 and the local RF coil 14 are spatially separated from each other, but may be electromagnetically coupled to each other. In some examples, the local RF coil 14 and/or the volume RF coil 15 may transmit and receive RF signals. Example modes of operation of the coils (e.g., the local RF coil 14 and the volume RF coil 15) are described further below.

The MRI system 10 includes a patient table 26 for placing an object 16 (e.g., a patient) thereon. By moving the patient table 26, the subject 16 can be moved inside and outside the imaging volume 18. The imaging volume 18 may be positioned within a bore 19 of a gantry 17 of the MRI system 10. In some examples, the controller unit 25 may send control signals (e.g., electrical signals) to the operating console unit 32 and/or the display unit 33 to indicate a position of the patient table 26 within the imaging space 18 to an operator (e.g., a user, a technician, etc.) of the MRI system 10.

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

The display unit 33 includes a graphic display device (e.g., a computer screen), and displays an image on the graphic display device based on a control signal received from the controller unit 25. The display unit 33 displays, for example, an image on an input item, and the operator inputs operation data on the input item from the operation console unit 32. The display unit 33 also displays the slice image of the object 16 generated by the data processing unit 31.

The data processing unit 31 includes a computer and a recording medium (e.g., a hard disk drive) on which a program executed by the computer to perform predetermined data processing is recorded. The data processing unit 31 is electrically coupled with 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 spectral data by applying various image processing operations to the Magnetic Resonance (MR) signals output from the data acquisition unit 24 (described in more detail below).

The static field magnet unit 12 includes a ring-shaped superconducting electromagnet coupled to a ring-shaped vacuum vessel (e.g., the gantry 17) and positioned inside the ring-shaped vacuum vessel. The electromagnets define a cylindrical space (e.g., bore 19) around the subject 16 and generate a static magnetic field of substantially constant magnitude and direction within the cylindrical space (e.g., in the direction of the y-axis within the cylindrical space, as indicated by reference axis 199). The static magnetic field generated by the electromagnet may be referred to herein as a uniform magnetic field.

The MRI system 10 also includes a magnetic gradient generator 13 that generates additional magnetic fields (which may be referred to herein as gradient magnetic fields) in the imaging space 18 to correlate MR signals received by the local RF coils 14 with three-dimensional positional information. For example, the gradient magnetic fields generated by the magnetic gradient generator 13 may have different magnitudes (e.g., different field strengths) at different locations within the imaging space 18. The magnetic gradient generator 13 comprises a three gradient coil system. Each gradient coil system adjusts the magnitude of the gradient magnetic field in one of three perpendicular directions. For example, a first gradient coil system adjusts the magnitude of the gradient magnetic field in the frequency encoding direction, a second gradient coil system adjusts the magnitude of the gradient magnetic field in the phase encoding direction, and a third gradient coil system adjusts the magnitude of the gradient magnetic field in the slice selection direction. The frequency encoding direction, the phase encoding direction, and the slice selection direction may be defined based on input from a user (e.g., an operator) of the MRI system 10 (e.g., via the operation console unit 32). More specifically, the magnetic gradient generator 13 adjusts the magnitude of the gradient magnetic field in the slice selection direction of the subject 16 in response to an input from the operator. The local RF coil 14 then transmits RF pulses to selected slices of the subject 16 and excites the slices (e.g., excites hydrogen nuclear spins within the selected slices of the subject 16). The magnetic gradient generator 13 adjusts the magnitude of the gradient magnetic field in the phase encoding direction of the subject 16 to phase encode the MR signals transmitted by the slice excited by the RF pulse. Then, the magnetic gradient generator 13 adjusts the magnitude of the gradient magnetic field in the frequency encoding direction of the subject 16 to frequency encode the MR signals transmitted by the slice excited by the RF pulse.

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

The RF coils (e.g., the local RF coil 14 and/or the volume RF coil 15) of the MRI system 10 may transmit electromagnetic pulse signals to a subject 16 located within an imaging space 18, wherein homogeneous magnetic fields and gradient magnetic fields extend through the imaging space 18. The local RF coil 14 is shaped, for example, to enclose a region to be imaged of the subject 16. In some examples, the local RF coil 14 may be referred to as a surface coil or a receiver coil. The MRI system 10 receives MR signals from the subject 16 (e.g., via a data acquisition unit 24 coupled to the RF coils) and processes the MR signals (e.g., via a data processing unit 31) in order to construct an image of a slice of the subject 16 based on the received MR signals.

For example, during a state in which the subject 16 is positioned for scanning by the MRI system 10 (e.g., during a state in which the subject 16 is within the imaging space 18), spins of hydrogen nuclei within tissue of the subject 16 may coincide with an initial magnetization vector produced by a combination of the uniform magnetic field and the gradient magnetic field. The local RF coil 14 can transmit an RF pulse as an electromagnetic wave to the subject 16 based on a control signal from the controller unit 25. The RF pulses transmitted to the subject 16 generate high frequency magnetic fields within a slice of the subject 16 to be imaged (e.g., selected by an operator of the MRI system 10). The high frequency magnetic field excites the spins of the hydrogen nuclei in a slice of the object 16 and aligns the spins with a magnetization vector that changes compared to the initial magnetization vector. As the spins of the excited hydrogen nuclei in the slice of the subject 16 relax and return to coincide with the initial magnetization vector, the local RF coil 14 receives electromagnetic waves generated from the tissue of the subject 16 as MR signals.

The volume RF coil 15 may alternatively (or additionally) be used to generate high frequency magnetic fields similar to those described above with reference to the local RF coil 14. For example, the volume RF coil 15 is positioned to surround the imaging space 18 and may generate RF pulses in a direction orthogonal to the direction of the uniform magnetic field generated by the static field magnet unit 12 within the imaging space 18 so as to excite the hydrogen nuclei of the subject 16. Unlike the local RF coil 14, which may be disconnected from the MRI system 10 and replaced with a different local RF coil, the volume RF coil 15 is fixedly attached and coupled to the MRI system 10. Furthermore, local coils such as those including the local RF coil 14 may transmit signals to and/or receive signals from a local region of the subject 16 (e.g., a particular anatomy or slice of the subject 16), while the volumetric RF coil 15 may transmit signals to and/or receive signals from a larger portion of the subject 16 (e.g., the entire body of the subject 16).

An RF signal driver 22 electrically coupled to the coils (e.g., the volume RF coil 15 and/or the local RF coil 14) via the T/R switch 20 includes a gate modulator (not shown), an RF power amplifier (not shown), and an RF oscillator (not shown) for driving the local RF coil 14 and/or the volume RF coil 15 to form a high frequency magnetic field in the imaging volume 18 (as described above). The RF signal driver 22 modulates an RF signal received from the RF oscillator, which is based on a control signal from the controller unit 25, into a signal having a predetermined timing and a predetermined envelope via a gate modulator. The RF signal modulated by the gate modulator is amplified by an RF power amplifier and then output to the local RF coil 14 and/or the volume RF coil 15.

The T/R switch 20 may selectively electrically couple the local RF coil 14 and/or the volume RF coil 15 to the data acquisition unit 24 when operating in the receive mode, and the T/R switch 20 may selectively electrically couple the local RF coil 14 and/or the volume RF coil 15 to the RF signal driver 22 when operating in the transmit mode. During a state in which both the local RF coil 14 and the volume RF coil 15 are used for a single scan (e.g., during a state in which the local RF coil 14 is configured to receive MR signals and the volume RF coil 15 is configured to transmit RF signals), the T/R switch 20 may direct control signals from the RF signal driver 22 to the volume RF coil 15 while directing the received MR signals from the local RF coil 14 to the data acquisition unit 24. As noted above, the volumetric RF coil 15 may be configured to operate in a send-only mode, a receive-only mode, or a send and receive mode. The local RF coil 14 may be configured to operate in a transmit and receive mode or a receive only mode.

The data acquisition unit 24 comprises a preamplifier (not shown), a phase detector (not shown) and an analog/digital converter (not shown) for acquiring magnetic resonance signals received by the local RF coil 14 and/or the volume RF coil 15. In the data acquisition unit 24, the phase detector phase-detects the MR signal received by the local RF coil 14 and/or the volume RF coil 15 (in which the MR signal is amplified by a preamplifier) using the output from the RF oscillator of the RF signal driver 22 as a reference signal, and outputs the phase-detected analog MR signal to an analog/digital converter for conversion into a digital signal. The digital signal thus obtained is output to a data processing unit 31 electrically coupled to the controller unit 25.

The controller unit 25 includes a computer and a recording medium recording a program to be executed by the computer. The program, when executed by a computer, causes various portions of the system to perform operations corresponding to a predetermined scan. The recording medium may include, for example, a read-only memory (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 (for example, input by an operator of the MRI system 10), and further controls the patient table 26, the RF signal driver 22, the gradient driver 23, and the data acquisition unit 24 by outputting control signals to the patient table 26, the RF signal driver 22, the gradient driver 23, and the data acquisition unit 24. 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.

During a scan (e.g., imaging the subject 16 according to the above-described examples), coil interface cables (not shown) may be used to transmit signals between the RF coils (e.g., the local RF coil 14 and the volumetric RF coil 15) and other aspects of the processing system (e.g., the data acquisition unit 24, the controller unit 25, etc.), for example, to control the RF coils and/or to receive information from the RF coils. As previously mentioned, in one example, the volume RF coil 15 may transmit RF signals and the local RF coil 14 may receive MR signals. The local RF coil 14 and/or the volume RF coil 15 may include a coil for transmitting RF excitation signals ("transmitter coil") and a coil for receiving MR signals transmitted by the imaging subject ("receive coil"). In some examples, the transmitter coil and the receive coil may be the same coil (e.g., configured to both transmit RF excitation signals and receive MR signals) such that the coil is a single mechanical structure or an array of structures in which the transmit/receive mode of the coil may be switched by auxiliary circuitry (e.g., T/R switch 20). In other examples, the volume RF coil 15 and the local RF coil 14 may be separate structures physically coupled to each other via a data acquisition unit or other processing unit.

In some examples (e.g., examples in which the transmitter coil and the receive coil are not the same coil), it may be desirable to configure the receive coil to be mechanically and electrically isolated from the transmitter coil in order to obtain improved image quality. In one example, the receive coil (e.g., local RF coil 14) may be configured to receive MR signals for a duration of time after the RF signals are transmitted from the transmitter coil (e.g., volume RF coil 15). However, during the time duration that the transmitter coil is transmitting the RF signal, it may be desirable to electromagnetically decouple the receive coil from the transmitter coil so that the receive coil is not resonant with the transmitter coil (e.g., so that the receive coil is not receiving the RF signal from the transmitter coil). Electromechanically decoupling (e.g., deactivating) the receive coil during transmission of the RF signal by the transmitter coil may reduce an amount of noise generated within auxiliary circuitry coupled to the receive coil and may result in improved image quality.

In some examples (as described below with reference to fig. 2-6), the volume RF coil 15 may be positioned in a birdcage device (which may be referred to herein as a birdcage coil assembly) coupled to an outer surface of the bore 19 of the gantry 17 and surrounding the imaging space 18.

Fig. 2 shows an aperture 200 of a gantry of an MRI system including an RF coil 206 (similar to the aperture 19 of the gantry 17 of the MRI system 10 shown in fig. 1 and described above). An imaging space is formed within interior 202 of bore 200 for imaging of a subject (e.g., a patient positioned on a table, such as table 26 shown in fig. 1 and described above). In the example shown in fig. 2, the bore 200 is cylindrical in shape, having a central axis 204. In other examples, the aperture 200 may have a different shape (e.g., a shape having a rectangular cross-section).

The RF coil 206 is a volume RF coil similar to the volume coil 15 shown in fig. 1 and described above. The RF coil 206 is circumferentially coupled to an outer surface 208 of the bore 200 about the central axis 204 and includes a first end ring 210 and a second end ring 212 coupled together via a plurality of rungs 214 (which may be referred to herein as legs). The first end ring 210 and the second end ring 212 are annular shaped around a perimeter of the bore 200 for imaging a patient within the interior 202 (e.g., as described above with reference to fig. 1). Each of the first end ring 210 and the second end ring 212 may be formed of a non-conductive material (e.g., an electrical insulator) and include a plurality of conductive portions 216. In one example, the first end ring 210 and the second end ring 212 can be formed of glass-reinforced epoxy, and the conductive portion can be a copper layer bonded directly to the end ring surface (e.g., adhered directly to the surface without other components therebetween). In other examples, the end-rings may be formed of different materials (e.g., silicon dioxide) and/or the conductive portions may be formed of different conductive materials (e.g., gold, platinum, etc.). For example, the end rings may each include one or more printed circuit boards, with the conductive portions being copper layers permanently adhered to the circuit board surfaces. Each conductive portion includes a plurality of notches positioned to reduce eddy currents within the conductive portion, as shown in further detail in first and

second illustrations

300 and 302 of fig. 3.

Fig. 3 shows a perspective view of an RF coil 206 decoupled from an outer surface 208 of the bore 200 of the MRI system. The first end ring 210 and the second end ring 212 of the RF coil 206 each include a first surface and an opposing second surface (which may be referred to herein as an outer surface and an inner surface, respectively). For example, the first end ring 210 includes an inner surface 304 and an outer surface 306, and the second end ring 212 includes an inner surface 308 and an outer surface 310. Although the first end ring 210 is described below as an example, the second end ring 212 is similarly configured with respect to the first end ring 210.

The first end ring 210 includes a first plurality of conductive portions 312 (which may be referred to herein as outer portions) positioned along the outer surface 306. As described above, each conductive portion of the outer portion 312 may be formed of a conductive metal (e.g., copper) bonded directly to the outer surface 306 of the first end ring 210. As shown in the first inset 300, the outer portion 312 includes a first conductive portion 314 having a first configuration and a second conductive portion 316 having a second configuration. In particular, the first conductive portion 314 includes a plurality of notches 318, the plurality of notches 318 extending from a first end 320 and a second end 322 of the first conductive portion 314 in a transverse direction relative to a centerline 324 of the first conductive portion 314 toward the centerline 324. However, the notch 318 does not extend across the centerline 324 of the first conductive portion 314. The second conductive portion 316 includes a plurality of notches 328, the plurality of notches 328 extending in a transverse direction relative to a centerline 326 of the second conductive portion 316 from a first end 330 of the second conductive portion 316 to a second end 332 of the second conductive portion 316 and across the centerline 326. The shape of the first and second

conductive portions

314, 316 is shown in further detail by fig. 5A-5B and described below.

The outer portion 312 includes a plurality of conductive portions similar to the first and second

conductive portions

314 and 316 described above (e.g., having the same shape), with portions similar to the first conductive portions 314 disposed along the entire perimeter of the outer surface 306 in an alternating arrangement with portions similar to the second conductive portions 316. Each portion similar to the first conductive portion 314 is located between two corresponding portions similar to the second conductive portion 316. In other words, each portion similar to the first conductive portion 314 is positioned such that one portion similar to the second conductive portion 316 is positioned adjacent the first end 320 and another portion similar to the second conductive portion 316 is positioned adjacent the second end 322. This arrangement repeats along the entire circumference of the outer surface 306 such that no two portions similar to the first conductive portion 314 are positioned adjacent to each other along the outer surface 306. Similarly, no two portions similar to the second conductive portion 316 are positioned adjacent to each other along the outer surface 306. In this arrangement, the outer portion 312 includes the same number of portions similar to the first conductive portion 314 as the outer portion 312 includes portions similar to the second conductive portion 316. For example, the outer portion 312 may include 16 portions similar to the first conductive portion 314 (including the first conductive portion 314) and 16 portions similar to the second conductive portion 316 (including the second conductive portion 316), wherein each portion similar to the first conductive portion 314 is adjacent to two corresponding portions similar to the second conductive portion 316. In other examples, the outer portion 312 may include a different number of portions (e.g., 32 portions similar to the first

conductive portion

314 and 32 portions similar to the second conductive portion 316).

In the alternating arrangement described above, each portion similar to the first conductive portion 314 is located at a respective rung of the plurality of rungs 214. For example, the conductive portion 334 at the outer surface 306 of the first end ring 210 is located at a first end 340 of the rung 338 and the conductive portion 336 at the outer surface 310 of the second end ring 212 is located at a second end 342 of the rung 338, wherein the first end 340 is opposite the second end 342 in a direction of a central axis 344 of the RF coil 206, and the rung 338 extends between the conductive portion 334 and the conductive portion 336 (e.g., between the first end ring 210 and the second end ring 212) in a direction parallel to the central axis 344. The conductive portion 334 of the outer surface 306 of the first end ring 210 is mechanically and electrically coupled (e.g., welded, fused, etc.) to the rung 338 at the first end 340, and the conductive portion 336 of the outer surface 310 of the second end ring 212 is similarly mechanically and electrically coupled to the rung 338 at the second end 342. In this configuration, current may flow between the conductive portion 334 of the first end ring 210 and the conductive portion 336 of the second end ring 212 via the rungs 338. Although the conductive portions 334 and the conductive portions 336 are described above as being coupled to the rungs 338 by way of example, each portion of the first end ring 210 that is similar to the first conductive portion 314 is similarly coupled to a corresponding portion of the second end ring 212 (where the corresponding portion is similar to the first conductive portion 314) by a corresponding rung of the plurality of rungs 214.

No portion at the outer surface 306 or the outer surface 310 similar to the second conductive portion 316 is directly coupled to the plurality of rungs 214. However, each portion similar to the second conductive portion 316 is mechanically and electrically coupled to each adjacent conductive portion. For example, a conductive portion 346 (similar to the second conductive portion 316) is mechanically and electrically coupled to two adjacent conductive portions 348 (each similar to the first conductive portion 314) along the outer surface 306 of the first end ring 210. In this configuration, the conductive portions at the outer surface 306 of the first end ring 210 are electrically coupled to each other such that current may flow through each portion (e.g., during a state in which the MRI system is operated to image a patient, as described above with reference to fig. 1).

The first end ring 210 additionally includes a second plurality of conductive portions 352 (which may be referred to herein as inner portions) positioned along the inner surface 304. As described above (and similar to the outer portion 312), each conductive portion of the inner portion 352 may be formed from a conductive metal (e.g., copper) that is directly bonded to the inner surface 304 of the first end ring 210. As shown in the second inset 302, each conductive portion of the inner portion 352 has a shape similar to the second conductive portion 316 described above. For example, the conductive portion 354 includes a plurality of notches 360, the plurality of notches 360 extending across a centerline 362 in a transverse direction relative to the centerline 362 of the conductive portion 354 from the first end 320 to the second end 322.

Although the conductive portions at the outer surface 306 are positioned in an alternating arrangement as described above, the conductive portions at the inner surface 304 do not have an alternating arrangement. Each conductive portion of inner portion 352 is shaped in the same manner (e.g., similar to second conductive portion 316) with respect to each other conductive portion of inner portion 352. Each conductive portion of the inner portion 352 is electrically and mechanically coupled (e.g., welded, fused, etc.) with each adjacent conductive portion of the inner portion 352 such that current may flow through each portion (e.g., during a state in which the MRI system is operated to image a patient, as described above with reference to fig. 1). Additionally, one or more conductive portions of the inner portion 352 may be electrically coupled with one or more conductive portions of the outer portion 312 such that current may flow to portions located at both the inner surface 304 and the outer surface 306. Although the configuration (e.g., shape, location, etc.) of the conductive portions of the first end ring 210 is described above as an example, the second end ring 212 includes a similar configuration.

By shaping the conductive portions at inner surface 304 and inner surface 308 to include a notch extending across a centerline of each conductive portion, the amount of eddy currents within each conductive portion may be reduced. For example, during operation of the MRI system, the temperature of the bore 200 (shown by fig. 2) may become high due to eddy currents generated in the conductive portions of the first end ring 210 and the second end ring 212. The electrical eddy currents are generated by the interaction between the magnetic field generated by the gradient coils (e.g., the magnetic gradient generator 13 described above with reference to fig. 1) and the conductive portions of the end-ring. The eddy currents, in combination with the static magnetic field (e.g., the B0 field generated by a static field magnet unit, such as the static field magnet unit 12 described above), may additionally cause vibration of the RF coil 206, thereby causing an increase in the acoustic noise level within the interior 202 of the bore 200. By increasing the number of conductive portions that include notches, the eddy currents are interrupted, resulting in a reduction in the temperature of the aperture 200 and/or a reduction in the amount of acoustic noise within the interior 202. In particular, increasing the number of conductive portions comprising notches extending across the centerline of each portion relative to the number of conductive portions comprising notches not extending across the centerline of each portion further reduces the generation of eddy currents.

Fig. 4A-4B each show a planar view of a different side of RF coil 206. The views shown by fig. 4A-4B are included for illustrative purposes to indicate the relative positions, numbers, and arrangements of the conductive portions of the inner portion 352 and the outer portion 312. For example, fig. 4A shows a flat view of the exterior of RF coil 206 (e.g., the side of RF coil 206 that includes exterior portion 312 and that is positioned away from outer surface 208 of bore 200 during a state in which RF coil 206 is coupled to bore 200), while fig. 4B shows a flat view of the interior of RF coil 206 (e.g., the side of RF coil 206 that includes interior portion 352 and that is positioned in coplanar contact with outer surface 208 of bore 200 during a state in which RF coil 206 is coupled to bore 200). A reference axis 499 is included for comparing the views shown by fig. 4A-4B.

As shown in fig. 4A-4B, configuring inner portion 352 to include only conductive portions having notches extending across a centerline of each portion increases the number of conductive portions of RF coil 206 similar to second conductive portion 316 relative to the number of conductive portions similar to first conductive portion 314. Because the second conductive portion 316 includes the notch 328 that extends across the centerline 326, the amount of eddy currents within the second conductive portion 316 is reduced relative to the first conductive portion 314 during operation of the RF coil 206. Similarly, because RF coil 206 includes a greater number of conductive portions similar to second conductive portion 316 relative to portions similar to first conductive portion 314, the amount and/or magnitude of eddy currents within RF coil 206 are reduced, thereby reducing the temperature and vibration of RF coil 206.

Bracket 400 shown in fig. 4A illustrates the location of first conductive portion 314 and second conductive portion 316 at outer surface 306, and bracket 402 shown in fig. 4B illustrates the location of conductive portion 354 and adjacent similar conductive portion 355 at inner surface 308 (as shown in fig. 3). The first conductive portion 314, the second conductive portion 316, the conductive portion 354, and the conductive portion 355 are each illustrated in more detail by fig. 5A-5B.

Fig. 5A-5B illustrate an axis 500 positioned about the central axis 344 of the RF coil 206 shown in fig. 3. As shown, the axis 500 extends in a direction parallel to each of the notches (e.g., the notch 318 of the first conductive portion 314, the notch 328 of the second conductive portion 316, the notch 504 of the conductive portion 355, and the notch 360 of the conductive portion 354). Axis 500 (and central axis 344) extends in a transverse direction with respect to each centerline of each conductive portion (e.g., centerline 324 of first conductive portion 314, centerline 326 of second conductive portion 316, centerline 362 of conductive portion 354, and centerline 502 of conductive portion 355). In the examples shown in fig. 2-6B and described herein, each conductive portion includes four notches. However, in alternative embodiments, one or more of the conductive portions may include a different number of notches (e.g., three, five, six, etc.). Additionally, in the examples described herein, each notch is positioned the same distance from each adjacent notch in the direction of the respective centerline (e.g., such as length 506 between notches 318 of first conductive portion 314 being the same as length 508 between notches 328 of second conductive portion 316). In alternative embodiments, one or more lengths between adjacent notches may be different than other lengths between adjacent notches. For example, at least one length between the notches 318 of the first conductive portion 314 may be different than a length between other adjacent notches 318 and/or a length between the notches 328 of the second conductive portion 316.

As mentioned above, the recess of the conductive portion reduces the temperature of the conductive portion during operation of the MRI system. Fig. 6A to 6B show relative temperatures at respective regions of the conductive portion during an operating state. Specifically, regions operating at a first temperature are indicated by a first stippling shading 600, regions operating at a second temperature lower than the first temperature are indicated by a second stippling shading 602, and regions operating at a third temperature lower than each of the first and second temperatures are indicated by a third stippling shading 604. The temperature near the centerline 324 of the first conductive portion 314 (e.g., at region 606) increases relative to the temperature near the centerline 326 of the second conductive portion 316 (e.g., at region 608). The reduction in temperature of the region 608 of the second conductive portion 316 relative to the region 606 of the first conductive portion 314 is a result of the extension of the notch 328 across the centerline 326.

As described above, since the RF coil 206 includes an increased number of portions similar to the second conductive portion 316 relative to the number of portions similar to the first conductive portion 314, the temperature of the RF coil 206 is reduced during operation of the MRI system relative to an RF coil that does not include such a configuration. Fig. 7 illustrates a graph 700, the graph 700 illustrating a difference in operating temperature of a standard RF coil that does not include a notch extending across a centerline of the conductive portion relative to the RF coil 206 described herein. In particular, curve 702 shows the temperature over time of an bore of an MRI system (e.g., bore 200 shown in fig. 2) coupled with a standard RF coil during a state of operating the MRI system (e.g., imaging a patient), and curve 704 shows the temperature over time of a bore coupled instead with RF coil 206 under the same state. In one example, the peak temperature indicated by curve 702 may be 58 degrees celsius and the peak temperature indicated by curve 704 may be 52 degrees celsius. Patient comfort may be increased by reducing the temperature of the bore and the amount of vibrational noise generated by operation of the MRI system via the RF coil 206.

Fig. 2-6B illustrate example configurations with relative positioning of various components. If shown in direct contact or directly coupled to each other, these elements may be referred to as being in direct contact or directly coupled, respectively, in at least one example. Similarly, elements shown as abutting or adjacent to one another may, at least in one example, abut or be adjacent to one another, respectively. By way of example, components that are in coplanar contact with each other may be referred to as being in coplanar contact. As another example, in at least one example, there is only one space between elements that are positioned apart from each other, and no other element may be so-called. As yet another example, elements shown above/below each other, on opposite sides of each other, or on left/right sides of each other may be referred to as such. Further, as shown, in at least one example, an uppermost element or point of an element can be referred to as a "top" of the component, and a lowermost element or point of the element can be referred to as a "bottom" of the component. As used herein, top/bottom, upper/lower, above/below may be relative to a vertical axis of the drawings and are used to describe the positioning of elements in the drawings relative to each other. Thus, in one example, elements shown above other elements are positioned vertically above the other elements. As yet another example, the shapes of elements depicted in the figures may be referred to as having those shapes (e.g., circular, rectilinear, planar, curved, rounded, chamfered, angled, etc.). Further, in at least one example, elements shown as crossing each other can be referred to as crossing elements or crossing each other. Still further, in one example, an element shown as being within another element or an element shown as being outside another element may be referred to as such.

A technical effect of the present disclosure is to reduce the amount and magnitude of eddy currents within conductive portions of an RF coil via a plurality of notches extending toward a centerline of each conductive portion. By reducing the amount of eddy current, the temperature of the RF coil is reduced, and the amount of vibration of the RF coil is reduced. The reduced temperature and vibration results in a reduced temperature of the bore of the MRI system and reduces the acoustic noise level within the bore, thereby increasing patient comfort. Another technical effect of the present disclosure is to increase the electrical power efficiency of the RF coil. By reducing eddy currents, the reduced amount of electrical energy is converted to thermal energy within electrically conductive portions of the RF coil, thereby more efficiently generating the RF signal.

In one embodiment, a Radio Frequency (RF) coil for a medical imaging device includes: a first conductive portion having a first end and an opposing second end; and a first plurality of notches of the first conductive portion extending across a centerline of the first conductive portion from the first end to the second end. In a first example of the RF coil, the RF coil further includes: a second conductive portion having a third end and an opposing fourth end; a second plurality of notches formed at the third end, wherein each notch of the second plurality of notches extends toward the fourth end and does not cross a centerline of the second conductive portion; and a third plurality of notches formed at the fourth end, wherein each notch of the third plurality of notches extends toward the third end and does not cross a centerline of the second conductive portion. The second example of the RF coil optionally includes the first example, and further includes wherein a centerline of the first conductive portion and a centerline of the second conductive portion are positioned parallel to each other. The third example of the RF coil optionally includes one or both of the first example and the second example, and further includes wherein the first conductive portion is one of a first plurality of conductive portions positioned along a first circumferential surface of an end-ring of the RF coil. A fourth example of the RF coil optionally includes one or more or each of the first through third examples, and further includes a second plurality of conductive portions positioned along a second circumferential surface of the end-ring, the second circumferential surface being opposite the first circumferential surface in a radial direction of the end-ring. A fifth example of the RF coil optionally includes one or more or each of the first through fourth examples, and further includes wherein the first plurality of conductive portions includes a second conductive portion positioned adjacent to the first conductive portion along the first circumferential surface, the second conductive portion including a second plurality of notches and a third plurality of notches positioned opposite each other across a centerline of the second conductive portion. A sixth example of the RF coil optionally includes one or more or each of the first through fifth examples, and further includes wherein each of the second plurality of conductive portions has the same shape as the first conductive portion. A seventh example of the RF coil optionally includes one or more or each of the first through sixth examples, and further includes wherein the first circumferential surface forms an outer perimeter of the end-ring and the second circumferential surface forms an inner perimeter of the end-ring. An eighth example of the RF coil optionally includes one or more or each of the first through seventh examples, and further includes wherein the first circumferential surface and the second circumferential surface are each formed of a dielectric material, wherein each of the first plurality of conductive portions is directly bonded to the first circumferential surface, and wherein each of the second plurality of conductive portions is directly bonded to the second circumferential surface.

In another embodiment, a Radio Frequency (RF) coil for a medical imaging device includes: a first plurality of conductive portions positioned along a first surface of the first end ring; and a plurality of notches formed by a first conductive portion of the first plurality of conductive portions and extending across a centerline of the first conductive portion. In a first example of the RF coil, the RF coil further includes a second plurality of conductive portions located at the first surface, wherein each conductive portion of the second plurality of conductive portions includes a second plurality of notches that do not extend across a centerline of any of the conductive portions of the second plurality of conductive portions, and wherein each conductive portion of the second plurality of conductive portions is positioned in an alternating arrangement with each conductive portion of the first plurality of conductive portions. The second example of the RF coil optionally includes the first example, and further includes wherein the first end-ring is one of a plurality of end-rings of the RF coil. A third example of the RF coil optionally includes one or both of the first example and the second example, and further including wherein the plurality of end rings includes exactly a first end ring and a second end ring, wherein the first end ring and the second end ring are coupled together by a plurality of rungs. A fourth example of the RF coil optionally includes one or more or each of the first through third examples, and further includes a second plurality of conductive portions positioned along a second surface of the first end ring, the second surface opposite the first surface, and wherein each conductive portion of the second plurality of conductive portions includes a second plurality of notches extending across a centerline of each conductive portion of the second plurality of conductive portions. A fifth example of the RF coil optionally includes one or more or each of the first through fourth examples, and further includes wherein the first plurality of conductive portions includes a different second conductive portion including a second plurality of notches that do not extend across a centerline of the second conductive portion. A sixth example of the RF coil optionally includes one or more or each of the first through fifth examples, and further includes wherein the first conductive portion and the second conductive portion are positioned adjacent to each other along the first surface.

In another embodiment, a Radio Frequency (RF) coil for a medical imaging device includes: a first annular end ring coupled to a second annular end ring by a plurality of rungs, each of the first and second annular end rings including a first plurality of conductive portions; and a first plurality of notches formed by the first plurality of conductive portions and extending along an entire width of each of the first plurality of conductive portions. In a first example of an RF coil, each rung of a plurality of rungs extends from a first annular end ring to a second annular end ring in a direction parallel to a central axis of the coil, and each notch of a first plurality of notches extends in a circumferential direction around the central axis. The second example of the RF coil optionally includes the first example, and further includes wherein the first plurality of conductive portions are positioned along the first perimeter and the second perimeter of each of the first annular end ring and the second annular end ring. The third example of the RF coil optionally includes one or both of the first example and the second example, and further includes: a second plurality of conductive portions positioned along the first perimeter of each of the first and second end annular ends, wherein each of the first plurality of conductive portions is positioned in an alternating arrangement with each of the second plurality of conductive portions; and a second plurality of notches formed by the second plurality of conductive portions and extending partially along an entire width of each of the second plurality of conductive portions.

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. Furthermore, unless explicitly stated to the contrary, embodiments "comprising," "including," or "having" one or more elements having a particular property may include additional such elements not having that property. The terms "including" and "in which" are used as plain-language equivalents of the respective terms "comprising" and "in which". 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 relevant 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.

The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to "an" element or "a first" element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.

Claims

1. A Radio Frequency (RF) coil for a medical imaging device, comprising:

a first conductive portion having a first end and an opposing second end; and

a first plurality of notches of the first conductive portion, the first plurality of notches extending across a centerline of the first conductive portion from the first end to the second end.

2. The RF coil of claim 1, further comprising:

a second conductive portion having a third end and an opposing fourth end;

a second plurality of notches formed at the third end, wherein each notch of the second plurality of notches extends toward the fourth end and does not cross a centerline of the second conductive portion; and

a third plurality of notches formed at the fourth end, wherein each notch of the third plurality of notches extends toward the third end and does not cross a centerline of the second conductive portion.

3. The RF coil of claim 2 wherein a centerline of the first conductive portion and a centerline of the second conductive portion are positioned parallel to each other.

4. The RF coil of claim 1 wherein the first conductive portion is one of a first plurality of conductive portions positioned along a first circumferential surface of an end ring of the RF coil.

5. The RF coil of claim 4 further comprising a second plurality of conductive portions positioned along a second circumferential surface of the end ring, the second circumferential surface being opposite the first circumferential surface in a radial direction of the end ring.

6. The RF coil of claim 5 wherein the first plurality of conductive portions includes a second conductive portion positioned adjacent the first conductive portion along the first circumferential surface, the second conductive portion including a second plurality of notches and a third plurality of notches positioned opposite each other across a centerline of the second conductive portion.

7. The RF coil of claim 6 wherein each conductive portion of the second plurality of conductive portions has the same shape as the first conductive portion.

8. The RF coil of claim 7 wherein the first circumferential surface forms an outer perimeter of the end ring and the second circumferential surface forms an inner perimeter of the end ring.

9. The RF coil of claim 8 wherein the first circumferential surface and the second circumferential surface are each formed of a dielectric material, wherein each conductive portion of the first plurality of conductive portions is directly bonded to the first circumferential surface, and wherein each conductive portion of the second plurality of conductive portions is directly bonded to the second circumferential surface.

10. A Radio Frequency (RF) coil for a medical imaging device, comprising:

a first plurality of conductive portions positioned along a first surface of a first end ring; and

a plurality of notches formed by a first conductive portion of the first plurality of conductive portions and extending across a centerline of the first conductive portion.

11. The RF coil of claim 10, further comprising a second plurality of conductive portions at the first surface, wherein each conductive portion of the second plurality of conductive portions includes a second plurality of notches that do not extend across a centerline of any of the conductive portions of the second plurality of conductive portions, and wherein each conductive portion of the second plurality of conductive portions is positioned in an alternating arrangement with each conductive portion of the first plurality of conductive portions.

12. The RF coil of claim 10 wherein the first end-ring is one of a plurality of end-rings of the RF coil.

13. The RF coil of claim 12, wherein the plurality of end rings comprises the first end ring and a second end ring, wherein the first end ring and the second end ring are coupled together by a plurality of rungs.

14. The RF coil of claim 10, further comprising a second plurality of conductive portions positioned along a second surface of the first end ring, the second surface opposite the first surface, and wherein each conductive portion of the second plurality of conductive portions includes a second plurality of notches extending across a centerline of each conductive portion of the second plurality of conductive portions.

15. The RF coil of claim 14 wherein the first plurality of conductive portions includes a second, different conductive portion, the second conductive portion including a second plurality of notches that do not extend across a centerline of the second conductive portion.

16. The RF coil of claim 15 wherein the first and second conductive portions are positioned adjacent to each other along the first surface.

17. A Radio Frequency (RF) coil for a medical imaging device, comprising:

a first annular end ring coupled to a second annular end ring by a plurality of rungs, each of the first and second annular end rings including a first plurality of conductive portions; and

a first plurality of notches formed by the first plurality of conductive portions and extending along an entire width of each of the first plurality of conductive portions.

18. The RF coil of claim 17, wherein each rung of the plurality of rungs extends from the first annular end ring to the second annular end ring in a direction parallel to a central axis of the coil, and wherein each notch of the first plurality of notches extends in a circumferential direction around the central axis.

19. The RF coil of claim 18 wherein the first plurality of conductive portions are positioned along a first perimeter and a second perimeter of each of the first annular end ring and the second annular end ring.

20. The RF coil of claim 19, further comprising:

a second plurality of conductive portions positioned along the first perimeter of each of the first and second annular end rings, wherein each portion of the first plurality of conductive portions is positioned in an alternating arrangement with each portion of the second plurality of conductive portions; and

a second plurality of notches formed by the second plurality of conductive portions and extending partially along an entire width of each of the second plurality of conductive portions.