阅读说明：本技术 用于从电扼流圈中移除能量的系统和方法、电扼流圈 (System and method for removing energy from an electrical choke, an electrical choke ) 是由 D·J·林克 S·沃尔特曼 R·哈拉迪莱克 T·斯特雷特 M·韦扎 M·弗里曼 于 2019-02-28 设计创作，主要内容包括：提供了一种电扼流圈以及用于从电扼流圈移除能量的系统和方法。该系统包括一个或多个磁芯、至少一个电感耦合器和电阻器。一个或多个磁芯被配置为通过生成磁能来形成电扼流圈的一部分。至少一个电感耦合器操作用于将磁能转换成电能。电阻器电连接到至少一个电感耦合器并且操作用于将电能耗散为热量。(An electrical choke and a system and method for removing energy from an electrical choke are provided. The system includes one or more magnetic cores, at least one inductive coupler, and a resistor. The one or more magnetic cores are configured to form a portion of an electrical choke by generating magnetic energy. At least one inductive coupler is operative to convert magnetic energy into electrical energy. The resistor is electrically connected to the at least one inductive coupler and is operative to dissipate the electrical energy as heat.)

1. A system for removing energy from an electrical choke, comprising:

one or more magnetic cores configured to form a portion of an electrical choke by generating magnetic energy;

at least one inductive coupler operative to convert the magnetic energy into electrical energy; and

a resistor electrically connected to the at least one inductive coupler and operative to dissipate the electrical energy as heat.

2. The system of claim 1, wherein an outer diameter of at least one of the magnetic cores is less than or equal to about 1.5 inches.

3. The system of claim 1, wherein at least one of the magnetic cores has a cross-sectional area of less than or equal to about 0.15 square inches.

4. The system of claim 1, wherein the one or more magnetic cores comprise ferrite.

5. The system of claim 1, wherein the resistor is operative to tune an impedance of the choke.

6. The system of claim 1, wherein the resistor is cooled by at least one of air and a liquid coolant.

7. The system of claim 1, wherein the electrical choke is disposed in an h-bridge.

8. The system of claim 1, wherein the electrical choke is disposed within a gradient amplifier.

9. An electrical choke, comprising:

one or more magnetic cores operable to generate magnetic energy;

at least one inductive coupler operative to convert the magnetic energy into electrical energy; and

a resistor electrically connected to the at least one inductive coupler and operative to dissipate the electrical energy as heat.

10. The electrical choke of claim 9, wherein at least one of the magnetic cores has an outer diameter less than or equal to about 1.5 inches.

11. The electrical choke of claim 9, wherein at least one of the magnetic cores has a cross-sectional area less than or equal to about 0.15 square inches.

12. The electrical choke of claim 9, wherein the one or more magnetic cores comprise ferrite.

13. An electrical choke in accordance with claim 9, wherein said resistor is operative to tune the impedance of said choke.

14. The electrical choke of claim 9, wherein the resistor is cooled by at least one of air and a liquid coolant.

15. A method for removing energy from an electrical choke, comprising:

generating magnetic energy through one or more magnetic cores of the choke;

converting the magnetic energy into electrical energy by at least one inductive coupler; and

dissipating the electrical energy as heat through a resistor electrically connected to the at least one inductive coupler.

16. The method of claim 15, further comprising:

the impedance of the choke is tuned by the resistor.

17. The method of claim 15, further comprising:

the resistor is cooled by at least one of air and a liquid coolant.

18. The method of claim 15, further comprising:

the object is scanned with a magnetic resonance imaging system comprising the electrical choke in a gradient amplifier.

19. The method of claim 15, wherein at least one of the magnetic cores has an outer diameter of less than or equal to about 1.5 inches.

20. The method of claim 15, wherein the one or more magnetic cores comprise ferrite.

Technical Field

Embodiments of the invention relate generally to electrical chokes and medical imaging systems, and more particularly, to systems and methods for removing energy from electrical chokes.

Background

MRI is a widely accepted and commercially available technique for obtaining digitized visual images representing the internal structure of a subject, which has a large population of atomic nuclei that are sensitive to nuclear magnetic resonance ("NMR"). Many MRI systems use superconducting magnets to scan a subject/patient by applying a strong main magnetic field to nuclei in the subject to be imaged. Nuclei are excited by radio frequency ("RF") signals/pulses emitted by an RF coil at a characteristic NMR (larmor) frequency. By spatially perturbing the local magnetic field around the subject and analyzing the RF response (hereinafter also referred to as "MR signal") obtained from the nuclei as the excited protons relax back to their lower energy normal state, a map or image of these nuclear responses as a function of their spatial position is generated and displayed. Images of nuclear responses (hereinafter also referred to as "MRI images" and/or simply "images") provide a non-invasive perspective of the internal structure of the subject.

Many conventional MRI systems use gradient coils to generate gradient magnetic fields, which in turn provide localized/spatial encoding of the nuclei. The gradient coils are often driven by gradient amplifiers, which are typically based on power switching electronic topologies/devices, such as metal oxide semiconductor field effect transistors ("MOSFETs") and/or insulated gate bipolar transistors ("IGBTs"). Many such electronic topologies/devices typically have fast switching edges that require common-mode filtering to improve amperage output fidelity and system electromagnetic compatibility ("EMC") performance. However, many common mode filters (e.g., electrical chokes) have ferrite cores that are susceptible to overheating when subjected to common mode currents, i.e., the higher and/or longer the common mode current flows through the ferrite core, the more heat is generated in the ferrite core. While the risk of overheating the ferrite core may be reduced by increasing the size of the core, many devices that use ferrite cores (e.g., gradient amplifiers) have limited space. In other words, it is generally impractical to increase the performance of a ferrite core by increasing its size. Furthermore, many emerging MRI techniques require higher common mode currents and/or faster switching times than can be handled by conventional ferrite cores without significant risk of overheating.

Accordingly, there is a need for an improved system and method for removing energy from an electrical choke.

Disclosure of Invention

In one embodiment, a system for removing energy from an electrical choke is provided. The system includes one or more magnetic cores, at least one inductive coupler, and a resistor. The one or more magnetic cores are configured to form a portion of an electrical choke by generating magnetic energy. At least one inductive coupler is operative to convert magnetic energy into electrical energy. The resistor is electrically connected to the at least one inductive coupler and is operative to dissipate the electrical energy as heat.

In another embodiment, an electrical choke is provided. The electrical choke includes one or more cores, at least one inductive coupler, and a resistor. The one or more magnetic cores are operative to generate magnetic energy. At least one inductive coupler is operative to convert magnetic energy into electrical energy. The resistor is electrically connected to the at least one inductive coupler and is operative to dissipate the electrical energy as heat.

In yet another embodiment, a method for removing energy from an electrical choke is provided. The method includes generating magnetic energy through one or more magnetic cores of a choke; converting magnetic energy into electrical energy by at least one inductive coupler; and dissipating the electrical energy as heat through a resistor electrically connected to the at least one inductive coupler.

Drawings

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

figure 1 is a block diagram of a magnetic resonance imaging system including a system for removing energy from an electrical choke in accordance with an embodiment of the present invention;

figure 2 is a schematic cross-sectional view of a magnet assembly of the magnetic resonance imaging system of figure 1, according to an embodiment of the invention;

figure 3 is a diagram of k-space acquired by the magnetic resonance imaging system of figure 1 in accordance with an embodiment of the invention;

figure 4 is an electrical diagram of a system for removing energy from an electrical choke included in the magnetic resonance imaging system of figure 1 in accordance with an embodiment of the invention;

FIG. 5 is a diagram depicting a surface of a magnetic core of the system of FIG. 4, in accordance with an embodiment of the present invention;

FIG. 6 is a diagram depicting a cross-sectional area of the magnetic core of FIG. 5, in accordance with an embodiment of the present invention;

FIG. 7 is a graph depicting an output waveform of an h-bridge incorporating the system of FIG. 4, in accordance with embodiments of the present invention;

FIG. 8 is a graph depicting temperature of one or more magnetic cores of the system of FIG. 4 over time, in accordance with embodiments of the present invention; and

fig. 9 is a diagram of a multilevel converter including a system for removing energy from the electrical choke of fig. 1, according to an embodiment of the invention.

Detailed Description

Reference will now be made in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts, and the description will not be repeated.

As used herein, the terms "substantially," "substantially," and "about" refer to conditions within reasonably achievable manufacturing and assembly tolerances relative to ideal desired conditions suitable for achieving the functional purpose of a component or assembly. As used herein, "electrically coupled," "electrically connected," and "in electrical communication" mean that the referenced elements are directly or indirectly connected such that an electrical current may flow from one element to another. The connection may comprise a direct conductive connection, i.e., an inductive connection, a capacitive connection and/or any other suitable electrical connection without intervening capacitive, inductive or active components. Intervening components may be present. The term "real-time" as used herein refers to a level of processing responsiveness that a user feels is sufficiently immediate or that enables a processor to keep up with external processes. The term "MR data" as used herein refers to data derived from MR signals, such as raw K-space and/or image space.

Further, while the embodiments disclosed herein are described with respect to an MRI system, it should be understood that embodiments of the present invention may be applicable to any device that utilizes/includes an electrical choke. Still further, as will be appreciated, embodiments of imaging systems related to the present invention may be used to analyze tissue in general, and are not limited to human tissue.

Referring now to FIG. 1, the major components of an MRI system 10 incorporating an embodiment of the present invention are shown. Thus, operation of the system 10 is controlled by an operator console 12, which operator console 12 includes a keyboard or other input device 14, a control panel 16, and a display screen 18. Console 12 communicates via link 20 with a separate computer system 22, which computer system 22 enables an operator to control the generation and display of images on display screen 18. The computer system 22 includes a plurality of modules that communicate with each other through a backplane 24. These modules include an image processor module 26, a CPU module 28, and a memory module 30, which memory module 30 may include a frame buffer for storing an array of image data. The computer system 22 communicates with a separate system controller or control unit 32 via a high-speed serial link 34. The input device 14 may comprise a mouse, joystick, keyboard, trackball, touch-activated screen, light wand, voice controller, or any similar or equivalent input device and may be used for interactive geometry prescription. The computer system 22 and the MRI system controller 32 together form an "MRI controller" 36.

The MRI system controller 32 includes a set of modules connected together by a back plate 38. These modules include a CPU module 40 and a pulse generator module 42, with the pulse generator module 42 being connected to the operator console 12 by a serial link 44. Through link 44, the system controller 32 receives commands from the operator to indicate the scan sequence to be performed. The pulse generator module 42 operates the system components to perform the desired scan sequence and generates data indicative of the timing, intensity, and shape of the generated RF pulses and the timing and length of the data acquisition window. The pulse generator module 42 is connected to a set of gradient amplifiers 46 to indicate the timing and shape of the gradient pulses generated during the scan. The pulse generator module 42 may also receive patient data from a physiological acquisition controller 48, which physiological acquisition controller 48 receives signals from a plurality of different sensors connected to the patient, such as ECG signals from electrodes attached to the patient. And finally, the pulse generator module 42 is connected to a scan room interface circuit 50, which receives signals from various sensors associated with the condition of the patient and magnet system. The patient positioning system 52 also receives commands through the scan room interface circuit 50 to move the patient to the desired scan position.

The pulse generator module 42 operates the gradient amplifiers 46 to achieve the desired timing and shape of the gradient pulses generated during the scan. The gradient waveforms generated by the pulse generator module 42 are applied to a gradient amplifier system 46 having Gx, Gy and Gz amplifiers. Each gradient amplifier excites a corresponding physical gradient coil (generally designated 54) in the gradient coil assembly to produce magnetic field gradients which are used to spatially encode acquired signals. The gradient coil assembly 54 forms part of a magnet assembly 56, the magnet assembly 56 further comprising a polarizing magnet 58 (in operation, the polarizing magnet 58 provides a uniform longitudinal magnetic field B throughout a target volume 60 enclosed by the magnet assembly 56₀) And a whole-body (transmit and receive) RF coil 62 (in operation, the whole-body (transmit and receive) RF coil 62 is provided generally perpendicular to B throughout the target volume 60₀Transverse magnetic field B₁)。

The resulting signals emitted by the excited atomic nuclei in the patient may be sensed by the same RF coil 62 and coupled through a transmit/receive switch 64 to a preamplifier 66. The amplifier MR signal is demodulated, filtered and digitized in the receiver section of the transceiver 68. The transmit/receive switch 64 is controlled by a signal from the pulse generator module 42 to electrically connect the RF amplifier 70 to the RF coil 62 during the transmit mode and to connect the preamplifier 66 to the RF coil 62 during the receive mode. The transmit/receive switch 64 may also enable a separate RF coil (e.g., a surface coil) to be used in either the transmit mode or the receive mode.

The MR signals picked up by the RF coil 62 are digitized by the transceiver module 68 and transferred to a memory module 72 in the system controller 32. The scan is complete when an array of raw K-space data 74 (fig. 3) has been acquired in the memory module 72. For each image to be reconstructed, the raw K-space data/material is rearranged into a separate K-space data array, and each of these data/materials is input to an array processor 76, which array processor 76 operates to fourier transform the data into an image data array. The image data is transmitted to the computer system 22 via the serial link 34 where it is stored in the memory 30 at the computer system 22. In response to commands received from the operator console 12, the image data may be archived in long-term storage, or the image data may be further processed by the image processor 26, transferred to the operator console 12, and presented on the display 18.

As shown in fig. 2, a schematic side view of a magnet assembly 56 according to an embodiment of the present invention is shown. The magnet assembly 56 is cylindrical with a central axis 78. Magnet assembly 56 includes a cryostat 80 and one or more radially aligned, longitudinally spaced superconducting coils 82, the one or more superconducting coils 82 forming polarizing magnet 58 (fig. 1). Superconducting coil 82 is capable of carrying high currents and is designed to produce B within patient/target volume 60₀A field. It should be appreciated that the magnet assembly 56 may further include terminal shields and a vacuum vessel (not shown) surrounding the cryostat 80 to help isolate the cryostat 80 from heat generated by the remainder of the MRI system 10 (fig. 1). The magnet assembly 56 may further include other elements such as covers, supports, suspension members, end caps, brackets, and the like (not shown). While the embodiment of the magnet assembly 56 shown in fig. 1 and 2 utilizes a cylindrical topography, it should be understood that topographies other than cylindrical may be used. For example, flat geometries in split-open (split-open) MRI systems may also utilize embodiments of the present invention described below. As further shown in fig. 2, a patient/imaged subject 84 is inserted into the magnet assembly 56.

Turning to fig. 4, an electrical choke 86 forming part of an h-bridge 88 of at least one of the gradient amplifiers 46 (fig. 1) and a system 90 for removing energy from the choke 86 are shown. It should be appreciated that the h-bridge 88 includes a switching topology defined by one or more switches 92, 94, 96, 98 (e.g., MOSFETs and/or IGBTs), which in embodiments may be grouped into one or more modules 100, 102, each electrically connected to common mode bus bars 104 and 106 through the choke 86. The modules 100, 102 may further be electrically connected in parallel with a power supply/capacitor 108. The switches 92, 94, 96, 98 may be mounted to a grounded heat sink to create a capacitance from the power supply terminal to ground. This capacitance in turn causes a common mode current to flow due to the activation of the switches 92, 94, 96, 98.

Choke 86 may include one or more magnetic cores 108, 110, 112, the one or more magnetic cores 108, 110, 112 operative to generate magnetic energy from the common mode current flowing through bus bars 104, 106, i.e., magnetic cores 108, 110, 112 generate a magnetic field that stores energy from the common mode current flowing through bus bars 104, 106.

Turning briefly to fig. 5 and 6, a front view (fig. 5) and a cross-sectional view (fig. 6) of one of the cores 112 taken along axis 114 in fig. 5 are shown. It should be understood that while fig. 5 and 6 depict a single magnetic core 112, it should be understood that the other magnetic cores 108 and 110 are similar in shape and/or function to the magnetic core 112. Accordingly, each magnetic core 112 may have a substantially cylindrical shape with an outer diameter 116, an inner diameter 118, and a cross-sectional area 120 (fig. 6). As best seen in fig. 4, the bus bars 102 and 106 pass through the magnetic cores 108, 110, 112 (fig. 6) within an inner diameter 118. It should be understood that the magnetic cores 108, 110, 112 may have other shapes, including rectangular, triangular, or any other shape capable of generating a magnetic field/energy from common mode current flowing through the bus bars 104, 106 (fig. 4).

Returning to fig. 4, the system 90 includes: magnetic cores 108, 110, 112; one or more inductive couplers 122; and a resistor 124 electrically connected to the inductive coupler 122. The inductive coupler 122 is operative to convert magnetic energy generated by the magnetic cores 108, 110, 112 into electrical energy that flows to a resistor 124, which resistor 124 is in turn operative to dissipate the electrical energy as heat.

In an embodiment, one or more inductive couplers 122 may be conductive wires passing through the inner diameter 118 (best seen in fig. 5 and 6) of the magnetic cores 108, 110, 112, e.g., the inductive couplers 122 may be windings passing through all of the magnetic cores 108, 110, 112. It should be understood that the number of windings and/or inductive couplers 122, i.e., the number of wires forming the windings, may vary. For example, embodiments of the system 90 may have about 1 turn to about 10 turns. In an embodiment, inductive coupler 122 may be made of copper and/or any other material suitable for converting magnetic energy into electrical energy/current and for transferring electrical energy to resistor 124. In an embodiment, the inductive coupler 122 may be formed from about twelve (12) to about twenty-six (26) AWG or equivalent circular, flat, or stranded wire. Although the figures herein depict the inductive coupler 122 as a winding passing through the inner diameter 118 of the magnetic cores 108, 110, 112, it should be understood that the inductive coupler 122 may take any form capable of converting magnetic energy generated by the magnetic cores 108, 110, 112 into electrical energy.

The resistor 124 may be a heating coil and/or any other type of device capable of converting/dissipating electrical energy into heat. For example, in an embodiment, the resistor 124 may be a wire wrap, a film, a ceramic, a surface mount, a through hole, a cold plate mountable, and the like. In an embodiment, the resistor 124 may be cooled by a gaseous, solid, and/or liquid coolant 126 (e.g., air, forced air, water, liquid nitrogen, ice, dry ice, etc.). It should also be understood that resistor 124 may be used to tune the impedance of choke 86, i.e., changing the resistance of resistor 124 may change the impedance of choke 86. In such embodiments, the resistor 124 may be a variable resistor that may be manually controlled or may be controlled by a controller, such as the MRI controller 36 (fig. 1).

Shown in fig. 7 is a graph depicting the output waveform of h-bridge 88 (fig. 4) that incorporates system 90 (fig. 4). It should be understood that axes 128, 130 and 132 represent voltage (v), current (amps) and time (ns), respectively, with lines 134, 136 and 138 representing the measured voltage, current and the ideal square wave, respectively. As can be seen in fig. 7, embodiments of system 90 provide a significant reduction in "ringing" (e.g., the edges of square wave 138 generally represented by arrow 140) in voltage 134 and current 136 after a state change.

Turning to FIG. 8, a graph depicting the temperature of the magnetic cores 108, 110, 112 (FIG. 4) of four different h-bridges 88 (FIG. 4) within the gradient amplifier 46 (FIG. 1) over time is shown, in accordance with an embodiment of the present invention. Specifically, axes 142 and 144 represent temperature in degrees C and time in minutes, respectively; lines 146, 148, 150, and 152 represent the temperature of the magnetic cores in the different h-bridges of the gradient amplifier 46 (FIG. 1), respectively; and lines 154 and 156 represent the temperature of the bus bars 104, 106 (fig. 4) of the h-bridge corresponding to line 146. As can be seen between t-0 min to t-30 min, when the system 90 (fig. 4) is activated/in place, the temperature of the magnetic cores 146, 148, 150, 152 is kept below 60 ℃; when the system 90 is deactivated/removed between t-30 min and t-42 min, the temperature of the magnetic cores 146, 148, 150, 152 ramps up to over 100 ℃; and when system 90 is reactivated/repositioned between t 42min to t 75min, the temperature of magnetic cores 146, 148, 150, 152 returns to below 60 ℃.

It should be appreciated that by removing energy from the electrical choke 86 (fig. 4), embodiments of the system 90 provide a magnetic core 108, 110, 112 that is reduced in size. For example, embodiments of the system 90 may provide the magnetic cores 108, 110, 112 with an outer diameter 116 (fig. 5 and 6) of less than or equal to about 1.5 inches, and/or a cross-sectional area 120 of less than or equal to about 0.15 square inches. Additionally, due to the lower temperatures within the magnetic cores 108, 110, 112, the magnetic cores 108, 110, 112 themselves, which are traditionally made of ferrite, may be made of materials that were previously impractical due to the risk of overheating.

Additionally, as shown in fig. 9, embodiments of the system 90 may be incorporated into a multi-level converter 158. Although the multi-level converter 158 is depicted herein as a two (2) level converter, it is understood that embodiments of the present invention may be incorporated into a multi-level converter having N (e.g., four (4)) h-bridges.

Finally, it should also be understood that systems 10 and/or 90 may include the necessary electronics, software, memory, storage, databases, firmware, logic/state machines, microprocessors, communication links, displays or other visual or audio user interfaces, printing devices, and any other input/output interfaces to perform the functions described herein and/or to achieve the results described herein. For example, as previously described, systems 10 and/or 90 may include at least one processor and system memory/data storage structures, which may include Random Access Memory (RAM) and Read Only Memory (ROM). At least one processor of system 10 and/or 90 may include one or more conventional microprocessors and one or more auxiliary coprocessors (such as math coprocessors, etc.). The data storage structures discussed herein may include suitable combinations of magnetic, optical, and/or semiconductor memory, and may include, for example, RAM, ROM, flash drives, optical disks (such as compact disks), and/or hard disks or drives.

Additionally, a software application that adapts the controller to perform the methods disclosed herein may be read into the main memory of the at least one processor from a computer readable medium. The term "computer-readable medium" as used herein refers to any medium that provides or participates in providing instructions to at least one processor of system 10 and/or 90 (or any other processor of a device described herein) for execution. Such a medium may take many forms, including but not limited to, non-volatile media and volatile media. Non-volatile media includes, for example, optical, magnetic, or opto-magnetic disks, such as memory. Volatile media include Dynamic Random Access Memory (DRAM), which typically constitutes a main memory. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, a RAM, a PROM, an EPROM or EEPROM (electrically erasable, programmable read-only memory), a FLASH-EEPROM, any other memory chip or cartridge, or any other medium from which a computer can read.

Although in an embodiment execution of sequences of instructions in a software application causes at least one processor to perform the methods/processes described herein, hardwired circuitry may be used in place of or in combination with software instructions to implement the methods/processes of the present invention. Thus, embodiments of the invention are not limited to any specific combination of hardware and/or software.

It is to be further understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects of the above-described embodiments) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope.

For example, in one embodiment, a system for removing energy from an electrical choke is provided. The system includes one or more magnetic cores, at least one inductive coupler, and a resistor. The one or more magnetic cores are configured to form a portion of an electrical choke by generating magnetic energy. At least one inductive coupler is operative to convert magnetic energy into electrical energy. The resistor is electrically connected to the at least one inductive coupler and is operative to dissipate the electrical energy as heat. In certain embodiments, at least one of the magnetic cores has an outer diameter less than or equal to about 1.5 inches. In certain embodiments, the cross-sectional area of at least one of the magnetic cores is less than or equal to about 0.15 square inches. In certain embodiments, one or more of the magnetic cores comprise ferrite. In some embodiments, the resistor operates to tune the impedance of the choke. In certain embodiments, the resistor is cooled by at least one of air and liquid coolant. In certain embodiments, an electrical choke is disposed in the h-bridge. In certain embodiments, the electrical choke is disposed within the gradient amplifier.

Still other embodiments provide an electrical choke. The electrical choke includes one or more magnetic cores, at least one inductive coupler, and a resistor. The one or more magnetic cores are operative to generate magnetic energy. At least one inductive coupler is operative to convert magnetic energy into electrical energy. The resistor is electrically connected to the at least one inductive coupler and is operative to dissipate the electrical energy as heat. In certain embodiments, the outer diameter of the at least one magnetic core is less than or equal to about 1.5 inches. In certain embodiments, the cross-sectional area of at least one magnetic core is less than or equal to about 0.15 square inches. In certain embodiments, one or more of the magnetic cores comprise ferrite. In some embodiments, the resistor operates to tune the impedance of the choke. In certain embodiments, the resistor is cooled by at least one of air and liquid coolant.

Yet other embodiments provide a method for removing energy from an electrical choke. The method includes generating magnetic energy through one or more magnetic cores of a choke; converting magnetic energy into electrical energy by at least one inductive coupler; and dissipating the electrical energy as heat through a resistor electrically connected to the at least one inductive coupler. In some embodiments, the method further comprises tuning the impedance of the choke through a resistor. In certain embodiments, the method further comprises cooling the resistor with at least one of air and a liquid coolant. In certain embodiments, the method further comprises scanning the subject with a magnetic resonance imaging system comprising an electrical choke in a gradient amplifier. In certain embodiments, the outer diameter of the at least one magnetic core is less than or equal to about 1.5 inches. In certain embodiments, one or more of the magnetic cores comprise ferrite.

Thus, by removing heat from the core of the electrical choke, some embodiments of the invention may provide a core of the choke that is reduced in size. It will be appreciated that reducing the size of the core in turn reduces the size of the choke, thereby making a smaller and more efficient choke. In some embodiments, reducing the size of the choke may reduce the overall amount of wire as compared to conventional chokes, which in turn may reduce the amount of electromagnetic radiation interference ("EMI") emitted by the choke. Thus, some embodiments of the invention may provide increased switching frequency and/or edge rate in an electronic topology compared to conventional chokes.

Additionally, and as described above, some embodiments of the present invention enable previously impractical materials to be used in the magnetic core of an electrical choke by removing heat from the magnetic core of the electrical choke. It will be appreciated that some of these materials are significantly cheaper and/or more abundant than conventional ferrites.

Further, in some embodiments, placing the resistor at a distance from the magnetic core (e.g., near the fan) allows for the use of forced air, cold plates, and/or heat sinks to cool/dissipate energy, and/or to free space near the magnetic core including the cold plates near the magnetic core. In addition, some embodiments of the invention require less space for the core than conventional chokes, which in turn makes chokes according to embodiments of the invention useful for previously impractical applications.

Additionally, while the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting and are merely exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reading the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms "including" and "in which" are used as the plain-english equivalents of the respective terms "comprising" and "in which". Furthermore, in the appended claims, terms such as "first," "second," "third," "upper," "lower," "bottom," "top," and the like are used merely as labels, and are not intended to impose numerical or positional requirements on their objects. Furthermore, no limitations in the appended claims are intended to be construed as such, unless and until such claim limitations expressly use the phrase "means for.

This written description uses examples to disclose several embodiments of the invention, including the best mode, and also to enable any person skilled in the art to practice embodiments of 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.

As used herein, an element or step recited in the singular and proceeded with the word "a" or "an" should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to "one embodiment" of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments "comprising," "including," or "having" an element or a plurality of elements having a particular property may include other such elements not having that property.

Since certain changes may be made in the above invention without departing from the spirit and scope thereof, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative only of the concepts of the invention and not as limiting the invention.