System and method for removing energy from an electric choke, electric choke

Abstract

An electric choke and a system and method for removing energy from the electric 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 the electric choke by generating magnetic energy. The at least one inductive coupler is operable to convert the magnetic energy into electrical energy. The resistor is electrically connected to the at least one inductive coupler and is operable to dissipate the electrical energy as heat.

Description

Technical Field

[0001] Embodiments of the present invention relate generally to electrical chokes and medical imaging systems, and more particularly, to systems and methods for removing energy from electrical chokes. Background Art

[0002] MRI is a widely accepted and commercially available technology for obtaining digital visual images representing the internal structure of an object (which has a large population of atomic nuclei that are sensitive to nuclear magnetic resonance ("NMR"). Many MRI systems use superconducting magnets to scan the subject / patient by applying a strong main magnetic field to the nuclei in the subject to be imaged. The nuclei are excited by RF signals / pulses emitted by radio frequency ("RF") coils at characteristic NMR (Larmor) frequencies. By spatially interfering with the local magnetic field around the subject and analyzing the RF responses (hereinafter also referred to as "MR signals") obtained from the nuclei when the excited protons relax back to their normal state of lower energy, a graph or image of the responses of these nuclei is generated and displayed as a function of their spatial position. The image of the nuclear responses (hereinafter also referred to as "MRI image" and / or simply "image") provides a non-invasive view of the internal structure of the subject.

[0003] Many conventional MRI systems use gradient coils to generate gradient magnetic fields, which in turn provide localization / spatial encoding of atomic nuclei. These 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 of these electronic topologies / devices often 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., inductors) have ferrite cores that are susceptible to overheating when subjected to common-mode current. Specifically, 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 ferrite core overheating can be reduced by increasing the core size, many devices using ferrite cores (e.g., gradient amplifiers) have limited space. In other words, increasing the core size to improve its performance is often impractical. Furthermore, many emerging MRI technologies require higher common-mode currents and / or faster switching times than conventional ferrite cores can handle without significant risk of overheating.

[0004] Therefore, there is a need for an improved system and method for removing energy from an electrical choke. Summary of the Invention

[0005] In one embodiment, a system for removing energy from an electric 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 the electric choke by generating magnetic energy. The at least one inductive coupler is operable to convert the magnetic energy into electrical energy. The resistor is electrically connected to the at least one inductive coupler and is operable to dissipate the electrical energy as heat.

[0006] In another embodiment, an electric choke is provided. The electric choke includes one or more magnetic cores, at least one inductive coupler, and a resistor. The one or more magnetic cores are operable to generate magnetic energy. The at least one inductive coupler is operable to convert the magnetic energy into electrical energy. The resistor is electrically connected to the at least one inductive coupler and is operable to dissipate the electrical energy as heat.

[0007] In yet another embodiment, a method for removing energy from an electric choke is provided. The method includes generating magnetic energy through one or more magnetic cores of the choke; converting the magnetic energy into electrical energy through at least one inductive coupler; and dissipating the electrical energy as heat through a resistor electrically connected to the at least one inductive coupler. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0009] 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;

[0010] Figure 2 According to an embodiment of the present invention Figure 1 A schematic cross-sectional view of a magnet assembly of a magnetic resonance imaging system;

[0011] Figure 3 According to an embodiment of the present invention, Figure 1 A k-space map obtained by a magnetic resonance imaging system;

[0012] Figure 4 For the embodiment of the present invention, the Figure 1 An electrical diagram of a system for removing energy from an electric choke in a magnetic resonance imaging system;

[0013] Figure 5 To describe an embodiment of the present invention Figure 4 A diagram of the surface of the magnetic core of the system;

[0014] Figure 6 To describe an embodiment of the present invention Figure 5 A diagram of the cross-sectional area of ​​the magnetic core;

[0015] Figure 7 To describe the embodiment according to the present invention, Figure 4 A diagram of the output waveform of the H-bridge of the system;

[0016] Figure 8 To describe an embodiment of the present invention Figure 4 a graph of the temperature of one or more magnetic cores of the system over time; and

[0017] Figure 9 According to an embodiment of the present invention, the Figure 1 Diagram of a multi-level converter of a system in which an electric choke removes energy. DETAILED DESCRIPTION

[0018] Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same drawing reference numerals are used throughout the drawings to refer to the same or similar parts without repeated description.

[0019] As used herein, the terms "substantially," "generally," and "approximately" refer to conditions that are 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 "electrically in communication" mean that the referenced elements are directly or indirectly connected so that current can flow from one element to another. The connection may include a direct conductive connection, i.e., an inductive connection without an intervening capacitor, inductor, or active element, a capacitive connection, and / or any other suitable electrical connection. Intermediary components may be present. The term "real-time," as used herein, refers to a level of processing response that is perceived by a user as 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.

[0020] Furthermore, while the embodiments disclosed herein are described with respect to MRI systems, 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 understood, embodiments of imaging systems associated with the present invention may be used to analyze tissue generally and are not limited to human tissue.

[0021] Now refer to Figure 1, illustrates the major components of an MRI system 10 incorporating an embodiment of the present invention. Thus, the operation of the system 10 is controlled by an operator console 12, which includes a keyboard or other input device 14, a control panel 16, and a display screen 18. The console 12 communicates via a link 20 with a separate computer system 22, which enables the operator to control the generation and display of images on the display screen 18. The computer system 22 includes a plurality of modules that communicate with each other via a backplane 24. These modules include an image processor module 26, a CPU module 28, and a memory module 30, which may include a frame buffer for storing image data arrays. 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 include a mouse, joystick, keyboard, trackball, touch-activated screen, light wand, voice control, or any similar or equivalent input device, and may be used for interactive geometry indication. The computer system 22 and the MRI system controller 32 collectively form an "MRI controller" 36.

[0022] The MRI system controller 32 comprises a set of modules connected together via a backplane 38. These modules include a CPU module 40 and a pulse generator module 42, which is connected to the operator console 12 via a serial link 44. Via link 44, the system controller 32 receives commands from the operator indicating the scan sequence to be performed. The pulse generator module 42 operates the system components to execute the desired scan sequence and generates data indicating the timing, intensity, and shape of the generated RF pulses, as well as the timing and length of the data acquisition window. The pulse generator module 42 is connected to a set of gradient amplifiers 46 to dictate the timing and shape of the gradient pulses generated during the scan. The pulse generator module 42 also receives patient data from a physiological acquisition controller 48, which receives signals from a number of different sensors connected to the patient, such as ECG signals from electrodes attached to the patient. 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 the magnet system. The patient positioning system 52 also receives commands through the scan room interface circuit 50 to move the patient to the desired scanning position.

[0023] 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 the gradient amplifier system 46, which includes Gx, Gy, and Gz amplifiers. Each gradient amplifier excites a corresponding physical gradient coil (generally designated 54) in the gradient coil assembly to generate magnetic field gradients used to spatially encode the acquired signals. The gradient coil assembly 54 forms part of a magnet assembly 56, which also includes a polarizing magnet 58 (which, in operation, provides a uniform longitudinal magnetic field, B0, throughout a target volume 60 encompassed by the magnet assembly 56) and a whole-body (transmit and receive) RF coil 62 (which, in operation, provides a transverse magnetic field, B1, that is generally perpendicular to B0 throughout the target volume 60).

[0024] The resulting signals emitted by the excited nuclei in the patient can be sensed by the same RF coil 62 and coupled to a preamplifier 66 through a transmit / receive switch 64. The amplifier MR signals are demodulated, filtered, and digitized in the receiver portion 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 transmit mode and to connect the preamplifier 66 to the RF coil 62 during receive mode. The transmit / receive switch 64 can also enable a separate RF coil (e.g., a surface coil) to be used in transmit mode or receive mode.

[0025] The MR signals picked up by the RF coil 62 are digitized by the transceiver module 68 and transmitted to the memory module 72 in the system controller 32. When the raw K-space data 74 ( Figure 3 ) array, the scan is complete. For each image to be reconstructed, the raw k-space data / profile is rearranged into a separate k-space data array, and each of these data / profiles is input to the array processor 76, which operates to Fourier transform the data into an image data array. The image data is transmitted via the serial link 34 to the computer system 22, where it is stored in the memory 30. In response to commands received from the operator console 12, the image data can be archived in a long-term storage device, or the image data can be further processed by the image processor 26, transmitted to the operator console 12, and presented on the display 18.

[0026] like Figure 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. The magnet assembly 56 includes a cryostat 80 and one or more radially aligned longitudinally spaced superconducting coils 82 that form the polarized magnet 58 ( Figure 1 The superconducting coils 82 are capable of carrying large currents and are designed to generate a B0 field within the patient / target volume 60. It should be understood 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 rest of the MRI system 10. Figure 1 ). The magnet assembly 56 may further include other components, such as a cover, a support, a suspension member, an end cap, a bracket, etc. (not shown). Although Figure 1 and 2 The embodiment of the magnet assembly 56 shown in FIG utilizes a cylindrical topography, but it should be understood that topologies other than cylindrical can be used. For example, a flat geometry in a split-open MRI system can also utilize the embodiments of the present invention described below. Figure 2 As further shown in , a patient / imaged subject 84 is inserted into the magnet assembly 56 .

[0027] Go to Figure 4 , showing that a gradient amplifier 46 ( Figure 1 ) and a system 90 for removing energy from the choke 86. It should be understood 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, can be grouped into one or more modules 100, 102, each electrically connected to common-mode bus bars 104 and 106 passing through the choke 86. The modules 100, 102 can further be electrically connected in parallel to a power supply / capacitor 108. The switches 92, 94, 96, 98 can 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.

[0028] The choke 86 may include one or more magnetic cores 108 , 110 , 112 operative to generate magnetic energy from the common-mode current flowing through the bus bars 104 , 106 , i.e., the magnetic cores 108 , 110 , 112 generate a magnetic field that stores energy from the common-mode current flowing through the bus bars 104 , 106 .

[0029] Briefly go to Figure 5 and Figure 6 , showing the direction of one of the magnetic cores 112 along Figure 5 A front view taken along the axis 114 in FIG. Figure 5 ) and sectional views ( Figure 6 ). It should be understood that although Figure 5 and Figure 6 A single core 112 is depicted, but it should be understood that the other cores 108 and 110 are similar in shape and / or function to the core 112. Thus, each core 112 may have a substantially cylindrical shape (ie, having an outer diameter 116, an inner diameter 118, and a cross-sectional area 120). Figure 6 ). As in Figure 4 As best seen in FIG. 1 , bus bars 102 and 106 pass through cores 108, 110, 112 within inner diameter 118 ( Figure 6 It should be understood that the cores 108, 110, 112 may have other shapes, including rectangular, triangular, or any other shape capable of generating a magnetic field / energy from the common mode current flowing through the bus bars 104, 106 ( Figure 4 ).

[0030] return Figure 4 , system 90 includes: magnetic cores 108, 110, 112; one or more inductive couplers 122; and a resistor 124 electrically connected to the inductive couplers 122. The inductive couplers 122 operate to convert magnetic energy generated by the magnetic cores 108, 110, 112 into electrical energy, which flows to the resistor 124, which in turn operates to dissipate the electrical energy as heat.

[0031] In an embodiment, one or more inductive couplers 122 may be provided through the inner diameter 118 of the magnetic cores 108, 110, 112 (at Figure 5 and 6 10, 112. It should be understood that the number of windings and / or inductive couplers 122, i.e., the number of wires forming the windings, can vary. For example, an embodiment of the system 90 can have from about 1 to about 10 turns. In an embodiment, the inductive coupler 122 can be made of copper and / or any other material suitable for converting magnetic energy into electrical energy / current and for transmitting the electrical energy to the resistor 124. In an embodiment, the inductive coupler 122 can be formed of about twelve (12) to about twenty-six (26) AWG or equivalent round, 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 can take any form capable of converting the magnetic energy generated by the magnetic cores 108, 110, 112 into electrical energy.

[0032] 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 embodiments, the resistor 124 may be wire wound, thin film, ceramic, surface mounted, through hole, cold plate mountable, etc. In embodiments, the resistor 124 may be cooled by a gas, solid, and / or liquid coolant 126 (e.g., air, forced air, water, liquid nitrogen, ice, dry ice, etc.). It should also be understood that the resistor 124 may be used to tune the impedance of the choke 86, i.e., changing the resistance of the resistor 124 may change the impedance of the choke 86. In such embodiments, the resistor 124 may be manually controllable or controllable by a controller (e.g., the MRI controller 36 ( Figure 1 )) controlled variable resistor.

[0033] Figure 7 Shown in FIG is a diagram depicting a system 90 ( Figure 4 ) of H bridge 88( Figure 4 ) is a graph of the output waveform of . It will be understood that axes 128, 130 and 132 represent voltage (v), current (amperes) and time (ns), respectively, wherein lines 134, 136 and 138 represent the measured voltage, current and ideal square wave, respectively. Figure 7 As can be seen in FIG. 1 , embodiments of system 90 provide a significant reduction in “ringing” (eg, the edges of square wave 138 generally represented by arrow 140 ) in voltage 134 and current 136 following a change of state.

[0034] Go to Figure 8 , depicting a gradient amplifier 46 ( Figure 1 ) within four different H-bridges 88 ( Figure 4 ) of the magnetic cores 108, 110, 112 ( Figure 4 ) versus time. Specifically, axes 142 and 144 represent temperature in C° and time in minutes, respectively; lines 146, 148, 150, and 152 represent the gradient amplifier 46 ( Figure 1 ) of the cores in different h-bridges; and lines 154 and 156 represent the bus bars 104, 106 ( Figure 4 ) temperature. As can be seen between t = 0 min and t = 30 min, when the system 90 ( Figure 4) is activated / in place, the temperature of the cores 146, 148, 150, 152 remains below 60°C; when the system 90 is deactivated / removed between t=30min and t=42min, the temperature of the cores 146, 148, 150, 152 soars to over 100°C; and when the system 90 is reactivated / placed between t=42min and t>=75min, the temperature of the cores 146, 148, 150, 152 returns to below 60°C.

[0035] It should be understood that by removing the electric choke 86 ( Figure 4 ) removes energy, embodiments of the system 90 provide magnetic cores 108, 110, 112 of reduced size. For example, embodiments of the system 90 may provide magnetic cores 108, 110, 112 having an outer diameter 116 (less than or equal to about 1.5 inches) Figure 5 and Figure 6 ), 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 cores 108, 110, 112, the cores 108, 110, 112, which are traditionally made of ferrite, can themselves be made of materials that were previously impractical due to the risk of overheating.

[0036] In addition, if Figure 9 As shown in FIG, 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 should be understood that embodiments of the present invention may be incorporated into a multi-level converter having N (e.g., four (4)) H-bridges.

[0037] Finally, it should also be understood that the 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 achieve the results described herein. For example, as previously described, the systems 10 and / or 90 may include at least one processor and system memory / data storage structures that may include random access memory (RAM) and read-only memory (ROM). The at least one processor of the systems 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 appropriate combinations of magnetic, optical, and / or semiconductor memory and may include, for example, RAM, ROM, a flash drive, an optical disk (such as a compact disk), and / or a hard disk or drive.

[0038] In addition, a software application that adapts the controller to perform the methods disclosed herein can be read from a computer-readable medium into the main memory of at least one processor. As used herein, the term "computer-readable medium" 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 the devices described herein) for execution. Such media can take many forms, including but not limited to non-volatile media and volatile media. Non-volatile media include, for example, optical disks, magnetic disks, or optical magnetic disks, such as memory. Volatile media include dynamic random access memory (DRAM), which typically constitutes main memory. Common forms of computer-readable media include, for example, floppy disks, flexible disks, hard disks, magnetic tape, any other magnetic media, CD-ROMs, DVDs, any other optical media, RAM, PROMs, EPROMs or EEPROMs (electronically erasable programmable read-only memories), FLASH-EEPROMs, any other memory chips or cassettes, or any other medium that can be read by a computer.

[0039] 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, hard-wired circuitry may be used in place of or in combination with software instructions to implement the methods / processes of the present invention. Accordingly, embodiments of the present invention are not limited to any specific combination of hardware and / or software.

[0040] It should be further understood that the above description is intended to be illustrative and not restrictive. For example, the above embodiments (and / or aspects of the above embodiments) can be used in combination with each other. In addition, without departing from the scope of the present invention, many modifications can be made to adapt specific circumstances or materials to the teachings of the present invention.

[0041] For example, in one embodiment, a system for removing energy from an electric 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 the electric choke by generating magnetic energy. The at least one inductive coupler is operable to convert the magnetic energy into electrical energy. The resistor is electrically connected to the at least one inductive coupler and is operable to dissipate the electrical energy as heat. In certain embodiments, the outer diameter of at least one of the magnetic cores is less than or equal to approximately 1.5 inches. In certain embodiments, the cross-sectional area of ​​at least one of the magnetic cores is less than or equal to approximately 0.15 square inches. In certain embodiments, the one or more magnetic cores include ferrite. In certain embodiments, the resistor is operable to tune the impedance of the choke. In certain embodiments, the resistor is cooled by at least one of air and a liquid coolant. In certain embodiments, the electric choke is disposed in an H-bridge. In certain embodiments, the electric choke is disposed within a gradient amplifier.

[0042] Still other embodiments provide an electric choke. The electric 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. The at least one inductive coupler is operative to convert the 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 approximately 1.5 inches. In certain embodiments, the cross-sectional area of ​​the at least one magnetic core is less than or equal to approximately 0.15 square inches. In certain embodiments, the one or more magnetic cores include ferrite. In certain embodiments, the resistor is operative to tune the impedance of the choke. In certain embodiments, the resistor is cooled by at least one of air and a liquid coolant.

[0043] Still other embodiments provide a method for removing energy from an electric choke. The method includes generating magnetic energy through one or more magnetic cores of the choke; converting the magnetic energy into electrical energy through 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 includes tuning the impedance of the choke through the resistor. In some embodiments, the method further includes cooling the resistor through at least one of air and a liquid coolant. In some embodiments, the method further includes scanning the object using a magnetic resonance imaging system, the magnetic resonance imaging system including the electric choke in a gradient amplifier. In some embodiments, the outer diameter of at least one magnetic core is less than or equal to approximately 1.5 inches. In some embodiments, the one or more magnetic cores include ferrite.

[0044] Thus, by removing heat from the magnetic core of an electrical choke, some embodiments of the present invention can provide a choke core that is reduced in size. It will be appreciated that reducing the size of the magnetic core can, in turn, reduce the size of the choke, thereby making a smaller and more efficient choke. In some embodiments, reducing the size of the choke can reduce the total amount of wires compared to conventional chokes, which in turn can reduce the amount of electromagnetic radiated interference ("EMI") emitted by the choke. Thus, some embodiments of the present invention can provide increased switching frequencies and / or edge rates in electronic topologies compared to conventional chokes.

[0045] Additionally, and as mentioned above, by removing heat from the core of the electric choke, some embodiments of the present invention enable previously impractical materials to be used in the core of the electric choke. It should be understood that some of these materials are significantly cheaper and / or more abundant than traditional ferrites.

[0046] Furthermore, in some embodiments, placing the resistor at a distance from the magnetic core (e.g., near a fan) allows for the use of forced air, a cold plate, and / or a heat sink to cool / dissipate energy, and / or frees up space near the magnetic core, including a cold plate near the magnetic core. Additionally, some embodiments of the present invention require less space for the magnetic core than conventional chokes, which in turn allows chokes according to embodiments of the present invention to be used in applications that were previously impractical.

[0047] In addition, although the sizes and types of materials described herein are intended to define the parameters of the present invention, they are by no means limiting and are merely exemplary embodiments. After reading the above description, many other embodiments will be apparent to those skilled in the art. Therefore, the scope of the present invention should be determined with reference to the appended claims and 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 corresponding terms "comprising" and "wherein." Furthermore, in the appended claims, terms such as "first," "second," "third," "upper," "lower," "bottom," "top," etc. are used merely as labels and are not intended to impose numerical or positional requirements on their objects. Furthermore, claims that are not written in a means-plus-function format are not intended to be so interpreted unless and until such claim limitations explicitly use the phrase "means for..." followed by a functional statement without further structure.

[0048] This written description uses examples to disclose several embodiments of the invention, including the best mode, and also to enable one of ordinary skill in the art to practice the 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 one 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 language of the claims.

[0049] As used herein, elements or steps listed in the singular and beginning with the word "one" or "an" should be understood as not excluding a plurality of said elements or steps, unless such exclusion is explicitly stated. In addition, reference to "one embodiment" of the present invention is not intended to be interpreted as excluding the existence of other embodiments that also include said features. In addition, unless explicitly stated otherwise, embodiments that "comprise," "include," or "have" an element or multiple elements having a particular attribute may include other such elements that do not have that characteristic.

[0050] As certain changes could be made in the above invention without departing from the spirit and scope thereof, all matter described above shown in the accompanying drawings shall be interpreted merely as examples illustrating the concepts of the invention and shall not be construed as limiting the invention.

Claims

1. A system for removing energy from an electric choke, comprising: one or more magnetic cores configured to form a portion of an electric choke by generating magnetic energy; at least one inductive coupler operative to convert the magnetic energy into electrical energy; as well as A resistor is electrically connected to the at least one inductive coupler and is configured to receive the electrical energy transmitted from the at least one inductive coupler and dissipate the electrical energy as heat.

2. The system according to claim 1, wherein: At least one of the magnetic cores has an outer diameter less than or equal to 1.5 inches.

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

4. The system according to claim 1, wherein: The one or more magnetic cores include ferrite.

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

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

7. The system according to claim 1, wherein: The electrical inductor is arranged in an H-bridge.

8. The system according to claim 1, wherein: The electrical choke is arranged in the gradient amplifier.

9. An electric choke comprising: one or more magnetic cores operative to generate magnetic energy; at least one inductive coupler operative to convert the magnetic energy into electrical energy; as well as A resistor is electrically connected to the at least one inductive coupler and is configured to receive the electrical energy transmitted from the at least one inductive coupler and dissipate the electrical energy as heat.

10. The electric choke according to claim 9, characterized in that At least one of the magnetic cores has an outer diameter less than or equal to 1.5 inches.

11. The electric choke according to claim 9, characterized in that At least one of the magnetic cores has a cross-sectional area less than or equal to 0.15 square inches.

12. The electric choke according to claim 9, characterized in that The one or more magnetic cores include ferrite.

13. The electric choke according to claim 9, characterized in that The resistor is operative to tune the impedance of the choke.

14. The electric choke according to claim 9, characterized in that The resistor is cooled by at least one of air and a liquid coolant.

15. A method for removing energy from an electric choke, comprising: generating magnetic energy through one or more magnetic cores of the choke; converting the magnetic energy into electrical energy through at least one inductive coupler and transmitting the electrical energy to a resistor electrically connected to the at least one inductive coupler; as well as The electrical energy is dissipated as heat through the resistor.

16. The method according to claim 15, further comprising: The impedance of the choke is tuned by the resistor.

17. The method according to claim 15, further comprising: The resistor is cooled by at least one of air and a liquid coolant.

18. The method according to claim 15, further comprising: The object is scanned using a magnetic resonance imaging system comprising the electrical choke in a gradient amplifier.

19. The method according to claim 15, characterized in that At least one of the magnetic cores has an outer diameter less than or equal to 1.5 inches.

20. The method according to claim 15, wherein The one or more magnetic cores include ferrite.

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