CN111624539B - System and method for removing energy from an electric choke, electric choke - Google Patents

Abstract

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. The 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 electrical energy as heat.

Description

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

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 an electrical choke.

Background

MRI is a widely accepted and commercially available technique for obtaining digitized visual images representing the internal structure of an object, which has a large population of nuclei 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 RF signals/pulses emitted by radio frequency ("RF") coils at a characteristic NMR (larmor) frequency. A map or image of the responses of the nuclei as a function of their spatial location is generated and displayed by spatially perturbing the local magnetic field around the subject and analyzing the RF responses (hereinafter also referred to as "MR signals") derived from the nuclei as the excited protons relax back to their lower energy normal state. The image of the nuclear response (hereinafter also referred to as "MRI image" and/or simply "image") provides a non-invasive view of the internal structure of the subject.

Many conventional MRI systems use gradient coils to generate gradient magnetic fields, which in turn provide localization/spatial encoding of nuclei. 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 of ferrite cores can be reduced by increasing the size of the core, many devices (e.g., gradient amplifiers) that use ferrite cores have limited space. In other words, it is often impractical to increase the performance of a ferrite core by increasing the size of the ferrite core. Furthermore, many emerging MRI techniques require higher common mode currents and/or faster switching times than conventional ferrite cores can handle 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. The 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 electrical energy as heat.

In another embodiment, an electrical choke is provided. The electrical choke comprises one or more cores, at least one inductive coupler, and a resistor. One or more magnetic cores are operative to generate magnetic energy. The 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 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 the magnetic energy into electrical energy through at least one inductive coupler, and dissipating the electrical energy into 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 accompanying 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 in accordance with an embodiment of the present 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 present 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 present 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 invention;

FIG. 6 is a diagram depicting the 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 the output waveform of an h-bridge incorporating the system of FIG. 4, in accordance with an embodiment of the present invention;

FIG. 8 is a graph depicting temperature over time of one or more cores of the system of FIG. 4, in accordance with an embodiment of the invention, an

Fig. 9 is a diagram of a multilevel converter including a system for removing energy from the electrical choke of fig. 1, in accordance with 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 need not be repeated.

As used herein, the terms "substantially," "substantially," and "about" mean conditions within reasonably achievable manufacturing and assembly tolerances relative to ideal desired conditions suitable for achieving the functional purpose of the component or assembly. As used herein, "electrically coupled," "electrically connected," and "electrically communicating" mean that the referenced elements are directly or indirectly connected such that current may 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. There may be intervening components. The term "real-time" as used herein means a level of processing response that a user perceives 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.

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 embodiments 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. The console 12 communicates through a link 20 with a separate computer system 22, which computer system 22 enables an 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 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 include a mouse, joystick, keyboard, trackball, touch activated screen, light stick, voice controller, 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 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 pulser module 42, the pulser module 42 being connected to the operator console 12 by a serial link 44. Via link 44, system controller 32 receives commands from an 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 generate 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 pulser module 42 can 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 that 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 amplifier 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 the magnetic field gradients used for spatially encoding 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 ₀ within an entire target volume 60 enclosed by the magnet assembly 56) and an entire subject (transmit and receive) RF coil 62 (in operation, the entire subject (transmit and receive) RF coil 62 provides a transverse magnetic field B ₁ generally perpendicular to B ₀ in the entire target volume 60).

The resulting signals emitted by excited nuclei in the patient may be sensed by the same RF coil 62 and coupled through the transmit/receive switch 64 to a preamplifier 66. The amplified 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 a transmit mode and to connect the preamplifier 66 to the RF coil 62 during a 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 coils 62 are digitized by the transceiver module 68 and transferred to a memory module 72 in the system controller 32. When the array of raw K-space data 74 (fig. 3) has been acquired in the memory module 72, the scan is complete. 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 transferred to computer system 22 via serial link 34 where the image data is stored in memory 30. The image data may be archived in long-term storage in response to commands received from operator console 12 or may be further processed by image processor 26, transferred to operator console 12 and presented on 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 apart superconducting coils 82, the one or more superconducting coils 82 forming polarizing magnet 58 (fig. 1). Superconducting coil 82 is capable of carrying large currents and is designed to generate a B ₀ field within patient/target volume 60. It should be appreciated that magnet assembly 56 may further include terminal shields and a vacuum vessel (not shown) surrounding cryostat 80 to help isolate cryostat 80 from heat generated by the remainder of MRI system 10 (FIG. 1). The magnet assembly 56 may further include other elements such as a cover, support, suspension member, end cap, bracket, etc. (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 a topography other than cylindrical may be used. For example, flat geometries in 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) that in embodiments may be grouped into one or more modules 100, 102, each electrically connected to common mode bus bars 104 and 106 through choke 86. The modules 100, 102 may further be electrically connected in parallel with a power source/capacitor 108. The switches 92, 94, 96, 98 may be mounted to a grounded heat sink to create a capacitance from the power terminal to ground. This capacitance, in turn, causes a common mode current to flow as a result of the activation of the switches 92, 94, 96, 98.

The choke 86 may include one or more magnetic cores 108, 110, 112, the one or more magnetic cores 108, 110, 112 being 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 magnetic fields that store energy from the common mode current flowing through the 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 the axis 114 in fig. 5 are shown. It should be appreciated that while fig. 5 and 6 depict a single magnetic core 112, it should be appreciated that the other magnetic cores 108 and 110 are similar in shape and/or function to the magnetic core 112. Thus, each 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 appreciated 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 a 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 couplers 122. The inductive coupler 122 operates to convert magnetic energy generated by the magnetic cores 108, 110, 112 into electrical energy that flows to the resistor 124, which resistor 124 in turn operates to dissipate the electrical energy as heat.

In an embodiment, one or more of the inductive couplers 122 may be conductive wires passing through the inner diameter 118 (best seen in fig. 5 and 6) of the cores 108, 110, 112, e.g., the inductive couplers 122 may be windings passing through all of the cores 108, 110, 112. It should be appreciated that the number of windings and/or inductive couplers 122, i.e., the number of wires forming the windings, may vary. For example, an embodiment of system 90 may have from about 1 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 delivering electrical energy to resistor 124. In an embodiment, the inductive coupler 122 may be formed from about twelve (12) to about twenty six (26) AWGs or equivalent round, flat or stranded wires. 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.

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, a film, a ceramic, a surface mount, a via, a mountable cold plate, or 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 appreciated 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 a variable resistor that is manually controllable or controllable by a controller, such as the MRI controller 36 (fig. 1).

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

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

It should be appreciated that by removing energy from the electrical choke 86 (fig. 4), embodiments of the system 90 provide for reduced-size magnetic cores 108, 110, 112. For example, embodiments of the system 90 may provide that the magnetic cores 108, 110, 112 have 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 temperature within the magnetic cores 108, 110, 112, the magnetic cores 108, 110, 112 themselves, which are conventionally made of ferrite, may be made of materials that were previously impractical due to the risk of overheating.

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

Finally, it should also be appreciated that system 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 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 a system memory/data storage structure, which may include Random Access Memory (RAM) and Read Only Memory (ROM). At least one processor of 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 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 adapted to 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 systems 10 and/or 90 (or any other processor of the devices described herein) for execution. Such a medium may take many forms, including but not limited to, non-volatile media and volatile media. Nonvolatile media includes, for example, optical, magnetic or magneto-optical disks, such as memory. Volatile media includes 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, RAM, PROM, 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. The 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 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, at least one of the magnetic cores has a cross-sectional area less than or equal to about 0.15 square inches. In certain embodiments, the one or more magnetic cores comprise ferrite. In some 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. In some 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 comprises one or more magnetic cores, at least one inductive coupler, and a resistor. One or more magnetic cores are operative to generate magnetic energy. The 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 electrical energy as heat. In certain embodiments, the at least one magnetic core has an outer diameter less than or equal to about 1.5 inches. In certain embodiments, the cross-sectional area of the at least one magnetic core is less than or equal to about 0.15 square inches. In certain embodiments, the one or more magnetic cores comprise ferrite. In some 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.

Still 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 the magnetic energy into electrical energy through at least one inductive coupler, and dissipating the electrical energy into heat through a resistor electrically connected to the at least one inductive coupler. In certain 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 at least one magnetic core has an outer diameter less than or equal to about 1.5 inches. In certain embodiments, the one or more 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 may reduce 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 total amount of wires 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 electronic topologies as compared to conventional chokes.

In addition, and as described above, some embodiments of the present invention enable previously impractical materials to be used in the core of an electrical choke by removing heat from the core of the electrical choke. It should 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 the use of forced air, cold plates, and/or heat sinks to cool/dissipate energy, and/or to release space near the magnetic core that includes the cold plates near the magnetic core. In addition, some embodiments of the present invention require less space for the magnetic core than conventional chokes, which in turn makes the choke according to embodiments of the present invention available for previously impractical applications.

In addition, 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 limitation of the appended claims is written in a device-plus-function format and is not intended to be so interpreted unless and until such claim limitation explicitly uses the phrase "means for..then there is no further structural functional statement.

This written description uses examples to disclose 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 skilled in the art. These 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-described invention without departing from the spirit and scope thereof, it is intended that all matter of the above description shown in the accompanying drawings shall be interpreted as illustrative only of the inventive concept and not as limiting the invention.

Claims (20)

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 for receiving electrical energy transferred from the at least one inductive coupler and dissipating the electrical energy as heat.

2. The system of 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 of claim 1, wherein at least one of the magnetic cores has a cross-sectional area of less than or equal to 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 operative 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 for receiving electrical energy transferred from the at least one inductive coupler and dissipating the electrical energy as heat.

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

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

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

13. The electrical choke of claim 9, wherein the resistor is operative to tune an impedance of the 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 said magnetic energy into electrical energy by at least one inductive coupler and transferring the electrical energy to a resistor electrically connected to said at least one inductive coupler, and

The electrical energy is dissipated as heat through the resistor.

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 subject 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 1.5 inches.

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