Magnetic resonance imaging system, high-frequency power distribution unit and gradient amplifier

Abstract

The invention relates to a magnetic resonance imaging system, a high-frequency power distribution unit and a gradient amplifier. Power systems and circuits are discussed herein for generating a gradient magnetic field in a magnetic resonance imaging (MRI) system. Embodiments provide magnetic resonance imaging systems, high frequency power distribution units, and gradient amplifiers that may include the use of a plurality of gradient amplifiers that share a high frequency power distribution unit that may play a role of power distribution and power supply. The high frequency power distribution unit may allow multiple gradient amplifiers to be driven using a single power supply via a shared power bus. Gradient amplifiers may use modern semiconductor materials that provide high frequency, high voltage performance, and may be implemented by using a single semiconductor bridge.

Description

[0001] This application is a divisional application with the filing date of February 19, 2019, application number 201910124415.2, entitled "Magnetic Resonance Imaging System, High-Frequency Power Distribution Unit and Gradient Amplifier". Technical Field

[0002] The subject matter disclosed herein relates to magnetic resonance imaging (MRI) devices, and more specifically to systems that provide precise, high-power currents to drive gradient coils, for example. Background Technology

[0003] This section is intended to introduce the reader to certain aspects of the technology that may be relevant to the various aspects of this disclosure, which are described and / or claimed below. This discussion is intended to help provide the reader with background information to facilitate a better understanding of the various aspects of this disclosure. Accordingly, it is understood that these statements are to be read in this context and not as an admission of prior art.

[0004] Magnetic resonance imaging (MRI) is an imaging modality typically used to generate images (e.g., spatial maps) based on the distribution of molecules within an object. Generally, MRI images of an object (e.g., a patient) are generated by measuring the properties of the gyromagnetic material of the object, such as hydrogen nuclei. These properties are typically obtained by measuring emissions from the gyromagnetic material in the object in response to excitation from an applied electric field. The magnetic fields used for excitation generally include a strong master magnetic field, a magnetic field gradient, and a radio frequency (RF) magnetic field excitation pulse. Note that the magnetic field gradient can be used by the MRI system to provide spatial encoding to the acquired data. For this purpose, gradient coils can be used to generate a spatial gradient of the magnetic field so that the spatial coordinates of the object can be correlated with locally encoded magnetic field values. As a result of this magnetic field-based encoding, the emissions from the gyromagnetic material can contain information that can be used to inform the spatial origin of a particular emission during image reconstruction.

[0005] Magnetic field gradients can be obtained by driving specific currents into gradient coils. More specifically, these magnetic field gradients can be controlled by adjusting the current in the gradient coils responsible for generating the magnetic fields. Magnetic coils can be associated with each spatial axis, x-axis, y-axis, and z-axis, and the current in each axis coil can be independently controlled during data acquisition, resulting in varied 3D slices of the image. To generate current in the magnetic coils, magnetic coil drivers can be used. Magnetic coil drivers can include gradient power supplies capable of inducing current in the magnetic coils and gradient amplifiers (e.g., current amplifiers). Magnetic coil drivers may require very precise currents for accurate, high-resolution spatial encoding. Furthermore, the current, and the voltage required to drive the current in the magnetic coils, can be very large and variable. Therefore, power supply design in these systems can be particularly challenging due to the large current variations and large voltages typically used by amplifiers. Summary of the Invention

[0006] Certain embodiments commensurate with the scope of the previously claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather to provide only a brief overview of the possible forms of the invention. In fact, the invention may encompass various forms similar to or different from the embodiments set forth below.

[0007] In one embodiment, a magnetic resonance imaging (MRI) system is described. The MRI system may include multiple gradient coils and gradient drivers that drive the gradient coils. The gradient driver may include multiple gradient amplifiers, and each gradient amplifier can independently control the gradient coils via electrical coupling. Furthermore, each gradient amplifier employs a single semiconductor bridge to perform control. The gradient driver also includes a power distribution unit (PDU). The PDU can receive an alternating current (AC) power signal from the MRI system's main power supply and provide a DC power signal to the gradient amplifiers via a direct current (DC) bus.

[0008] In another embodiment, a high-frequency power distribution unit (HFPDU) is described. The HFPDU may include a power distribution unit and a power supply. The power distribution unit may have a line filter and a first rectifier. The power distribution unit may receive a three-phase AC power signal from the power supply and generate an intermediate DC signal. The power supply includes a semiconductor bridge, a high-frequency transformer, a high-speed rectifier, and a filter. The semiconductor bridge may receive the intermediate DC signal from the rectifier and generate a high-frequency AC power signal. The high-frequency AC power signal may be provided to the high-frequency transformer, which provides current insulation. Furthermore, the transformer's shield may be coupled to a safety ground. The AC power from the transformer may be provided to the high-speed rectifier to generate an output DC power signal.

[0009] In another embodiment, a gradient amplifier is described. The gradient amplifier can drive a gradient coil in an MRI system. The gradient amplifier may have a single semiconductor bridge having a first branch including a first switch and a second switch. A first terminal of the gradient coil may be coupled to the midpoint of the first branch. The single semiconductor bridge may have a second branch including a third switch and a fourth switch. A second output terminal of the gradient coil may be coupled to the midpoint of the second branch. The first and second branches are arranged in parallel with respect to an input DC bus. The first and second terminals provide signals that can be used to drive the gradient coil via, for example, a ripple filter. Attached Figure Description

[0010] These and other features, aspects, and advantages of the invention will be better understood by referring to the accompanying drawings, which characterize similar parts throughout the drawings, in which: Figure 1 This is a diagram of a magnetic resonance imaging (MRI) system employing a gradient power architecture according to an embodiment of the present disclosure; Figure 2 This is a diagram of a gradient power architecture using an integrated power supply and a gradient amplifier according to an embodiment; Figure 3 This is a diagram of a conventional gradient power architecture with isolation circuitry for gradient amplification, according to an embodiment. Figure 4A This is a diagram of a conventional isolated gradient amplifier with an H-bridge design and an isolated DC bus, according to an embodiment; Figure 4B This is a diagram of a conventional gradient amplifier with an H-bridge design and an isolated DC bus, according to an embodiment. Figure 4C yes Figure 4B The diagram shows a conventional gradient amplifier in a configuration that causes a short circuit. Figure 5 This is a diagram of an integrated power architecture with a high-frequency power distribution unit (HFPDU) and a shared DC bus to drive a gradient amplifier, according to an embodiment. Figure 6 This is a diagram of a high-frequency power distribution unit (HFPDU) according to an embodiment; and Figure 7 This is a diagram of a gradient amplifier with a single bridge design and a shared DC bus, according to an embodiment. Detailed Implementation

[0011] The following describes one or more specific embodiments. In the effort to provide a concise description of these embodiments, certain features of the actual implementation may be omitted in this specification. It should be understood that, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developer's specific objectives, such as complying with constraints related to security, systems, and business, which will vary from implementation to implementation. Furthermore, it should be understood that such development efforts may be complex and time-consuming, but remain routine tasks of design, manufacture, and production for those skilled in the art who will benefit from this disclosure.

[0012] When describing elements of various embodiments of this disclosure, the articles “a,” “an,” and “the” are intended to mean that one or more elements are present. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that additional elements may exist in addition to the listed elements.

[0013] Magnetic resonance imaging (MRI) uses systems and apparatuses to generate images by mapping specific properties of the gyromagnetic material of the object being imaged. More specifically, an MRI system uses a strong magnetic field to excite the gyromagnetic nucleus of the object and measures the radio frequency (RF) emissions from the excited gyromagnetic nucleus in response to the excitation. The magnetic field used can come from multiple magnetic field sources within the MRI system. For example, the object can be immersed in a strong, constant magnetic field from the main coil, a variable magnetic field gradient providing spatial encoding, and an RF excitation pulse that may have a frequency at or near the resonant frequency of the gyromagnetic nucleus. The variable magnetic field gradient can be used to add spatial localization to the RF emissions from the gyromagnetic nucleus. The RF excitation pulse can be applied via the RF excitation coil, and the RF excitation pulse can be precessed to excite the magnetization vector of the gyromagnetic material. Pulse sequences and specific series of applications of these magnetic fields to the object can be used to obtain appropriate data from the MRI system to generate an image of the object.

[0014] This application generally relates to systems and circuits that can be used to generate variable magnetic field gradients. Magnetic field gradients can be generated by means of gradient coils, which produce magnetization associated with spatial directions. For example, a two-dimensional MRI system may have two gradient coils (e.g., longitudinal and transverse), and a three-dimensional MRI system may have three gradient coils, one of which is associated with each spatial direction (e.g., longitudinal, axial, and transverse). Each gradient coil is controlled independently of the other gradient coils to create a strong magnetic field. Furthermore, the magnetization provided by the gradient coils can be adjusted during the data acquisition process to generate multidimensional images of the object. Thus, due to high-frequency switching, large voltage and current, and accuracy requirements, the circuits that drive gradient coils, referred to herein as gradient coil drive circuits, have stringent performance specifications.

[0015] To meet accuracy, high frequency, and high power specifications, conventional gradient power architectures often include gradient drivers with multilevel converters employing multiple cascaded semiconductor bridges. This type of design allows for high current accuracy when operating at high power while driving gradient coils. However, conventional gradient power architectures are bulky due to the large number of components used. This disclosure discusses more efficient designs for gradient power architectures. In this embodiment, an integrated gradient power supply or high-frequency power distribution unit (HFPDU) can be used, which can provide a reliable DC output to the gradient amplifier. Embodiments can also employ gradient amplifiers with a single bridge design to drive the coils, which can reduce amplifier power consumption and energy storage requirements at the amplifier input due to the shared DC bus across multiple axes. In another embodiment, a method for grounding the system is disclosed that reduces crosstalk between axes. This embodiment can employ a simplified amplifier design by reducing the number of bridges in the gradient amplifier. For this purpose, the switches and / or semiconductor bridges used in the HFPDU and / or gradient amplifier can be implemented using high-voltage, wide-bandgap devices (e.g., silicon carbide devices).

[0016] Although the devices discussed herein are provided in the context of gradient amplifiers for MRI systems, it should be understood, as appreciated in the art, that this embodiment, used for simplified high-power, high-frequency circuitry, can be used to improve other systems employing multilevel converters by simplifying semiconductor bridges. In light of the above, Figure 1 An example of an MRI system 10 is shown. The MRI system 10 includes a scanner 12 and a scanner control system 14. The scanner 12 may have a housing 20 around an aperture 22. A movable stage 24 may be used to allow a patient 26 to be placed in the aperture 22. The housing 20 of the scanner 12 may also include a main magnet 28, which can establish a main magnetic field for data acquisition. Magnetic gradient coils 30, 32, and 34 placed in the scanner 12 can provide a magnetic field gradient that can provide spatial encoding of the gyromagnetic nuclei of the patient 26 during the imaging process. An RF excitation coil 36 of the MRI system 10 can generate radio frequency (RF) pulses that are used to excite a portion of the gyromagnetic nuclei of the patient 26 during imaging. The MRI system 10 may also be provided with an acquisition coil 38, which can read out the RF signals generated by the gyromagnetic nuclei in the patient 26 as the nuclei transition from an activated state to a relaxed state. In some embodiments, the RF excitation coil 36 and the acquisition coil 38 may be substantially the same. The various coils and magnets of the scanner 12 may be powered by a main power supply 40.

[0017] Magnetic gradient coils 30, 32, and 34, associated with the x, y, and z axes, can be controlled by gradient drive circuit 42, which can independently adjust each spatial axis. Gradient drive circuit 42 can be powered by main power supply 40. As described in detail below, gradient drive circuit 42 may include gradient power supplies and amplifiers that can independently control the gradients associated with the three axes. RF excitation coil 36 can be controlled by RF drive circuit 44. Receiver circuit 48 can acquire RF signals detected by acquisition coil 38 and processed by receive array switch 46. Drive circuits 42 and 44 and receiver circuit 48 can be coupled to controller 52 via interface 50. Interface 50 may include a memory bank and / or buffers for transmitting communication between controller 52 and drive circuits 42, 44, and receiver circuit 48. Controller 52 may include a general-purpose processor, application-specific integrated circuit (ASIC), and / or programmable logic device (PLD). The controller 52 can further communicate with a storage circuit 54, which can store data acquired through the receiving circuit 48. The storage circuit 54 can also store instructions for the controller 52 in the form of an imaging protocol. The imaging protocol may include instructions for the drive circuits 42 and 44 to control gradient coils 30, 32, and 34 and the RF excitation coil 36 in specific ways, respectively. Furthermore, the scanner control system 14 may have an interface 56 allowing connection 60 between the MRI system 10 and other external devices, such as computer clusters for image reconstruction or registration, medical databases, diagnostic systems, PACS systems, displays, printers, 3D visualization interfaces, or any other device that can use MRI images or data. The storage circuit 54 can also store instructions to control gradient coils 30, 32, and 34 by adjusting the current in the coils via the gradient drive circuit 42.

[0018] To control gradient coils to generate spatially encoded magnetic field gradients, a gradient driver may include a set of amplifiers. Figure 2 The MRI gradient power architecture 100 shown is a simplified power architecture that can be used to implement the gradient drive circuit 42. In the illustrated gradient drive circuit 42, a main power supply 40 provides the power that can be used by the gradient drive circuit 42. As an example, the main power supply can provide an alternating current (AC) signal. The voltage provided by the main power supply can have different rated voltages and / or frequencies based on geographical location or the available power grid. For example, the voltage can be 380V, 415V, 480V, etc., and the signal frequency can be 50 / 60Hz. The main power supply 40 can power several single-phase and three-phase MRI current drivers, including the gradient driver 42.

[0019] The gradient drive circuit 42 may include a high-frequency power distribution unit (HFPDU) 104 and gradient amplifiers 106A, 106B, and 106C. HFPDU 104 may be coupled to power supply 40 and may receive three phases of power supply 40. HFPDU 104 may provide DC signals to gradient amplifiers 106A, 106B, and 106C via a shared DC bus 107. In the illustrated example, gradient amplifiers 106A, 106B, and 106C are responsible for driving gradient coils 30, 32, and 34. Each amplifier may be associated with a corresponding gradient coil. In this example, gradient amplifiers 106A, 106B, and 106C may drive gradient coils 30, 32, and 34, respectively. Controller 52 may control the supplied current and voltage and ultimately control the spatially encoded magnetic field gradient during data acquisition. For this purpose, controller 52 can control the switches (e.g., switches in a semiconductor bridge) in gradient amplifiers 106A, 106B, and 106C to induce specific currents and / or voltages in gradient coils 30, 32, and 34, respectively.

[0020] As discussed above, the current and voltage driving the gradient coils can be very large and subject to rapid switching. Due to stringent performance specifications, traditional power architectures can replicate several circuits and components, including strong isolation structures in the power supply, amplifier, and gradient coils. Figure 3 , 4A The methods 4B and 4C are used to illustrate the challenges encountered in conventional power gradient architecture systems. However, it should be noted that the teachings of this application can be applied to conventional power architectures, and as... Figure 3 , 4A 4B and 4C can also be embodiments of this disclosure. Therefore, in Figure 3 The gradient power architecture 200 illustrates three drive circuits 201A, 201B, and 201C, whose outputs are electrically isolated from each other. Drive circuits 201A, 201B, and 201C can drive gradient coils 30, 32, and 34, respectively. In the provided example, power distribution unit 202 can be coupled to the power supply of the MRI system (e.g., main power supply 40) and can provide power signals to drive circuits 201A, 201B, and 201C. In an embodiment, power distribution unit 202 can be a transformer for each phase of the main power supply of the MRI system and can provide AC signals to drive circuits 201A, 201B, and 201C.

[0021] Each drive circuit can receive a power signal from the power distribution unit 202. In this example, gradient power supply 204A receives a power signal from the power distribution unit 202. The gradient power supply 204A shown generates multiple isolated DC voltages, which are provided to gradient amplifier 206A. The multiple DC voltages in gradient power supply 204A can facilitate the generation of a precise current to gradient coil 30 using a multilevel converter used in the design of gradient amplifier 206A. Similarly, gradient power supply 204B can generate multiple isolated DC voltages to gradient amplifier 206B, which can drive gradient coil 32, and gradient power supply 204C can generate multiple isolated DC voltages to gradient power amplifier 206C, which can drive gradient coil 34. Note that in this design, gradient power supply 204A is coupled to gradient amplifier 206A via multiple dedicated DC buses 207A, gradient power supply 204B is coupled to gradient amplifier 206B via dedicated DC bus 207B, and gradient power supply 204C is coupled to gradient amplifier 206C via dedicated DC bus 207C. Dedicated DC buses 207A, 207B, and 207C are decoupled from each other to prevent crosstalk between signals. Note that each isolated circuit can also have a ripple filter between the gradient amplifier and the gradient coil. Ripple filters 208A, 208B, and 208C can be incorporated in drive circuits 201A, 201B, and 201C to filter noise in the currents delivered to gradient coils 30, 32, and 34, respectively.

[0022] Figure 4A , 4B The diagram in the 4Cs is a visual representation provided in this article to depict the challenge, which is accompanied by, for example... Figure 3 The gradient power architecture 200 shown in the example is derived from a conventional power architecture that uses a shared DC bus. (The example is provided for further information.) Figure 4ATwo gradient amplifiers, gradient amplifier 206A and gradient amplifier 206B, are shown. In this example, each gradient amplifier receives three DC power signals via a dedicated DC bus. Gradient amplifier 206A receives two high-voltage DC signals 220A and 222A and a low-voltage DC signal 224A via a dedicated DC bus 207A. In this example, gradient amplifier 206A is constructed using three semiconductor bridges 230A, 230B, and 230C. The semiconductor bridges are cascaded to form a multilevel converter. Each semiconductor device can be powered independently and therefore can receive DC signals. As shown in this example, semiconductor bridge 230A is powered by DC signal 220A and can be coupled to output terminal 244 and to one leg of semiconductor bridge 232A. Furthermore, semiconductor bridge 232A, powered by DC signal 222A, is coupled to one leg of semiconductor bridge 234A. Semiconductor bridge 234A, powered by DC signal 224A, is coupled to output terminal 242. As understood in the art, the switches in semiconductor bridges 234A, 234B, and 234C can be switched on or off at high frequency with a variable duty cycle to control the current supplied between terminals 242 and 244. The voltage output of the gradient amplifier 206A across terminals 242 and 244 can be used to drive the current in gradient coil 30.

[0023] Figure 4A The gradient amplifier 206B is arranged in a similar manner to the gradient amplifier 206A. Three semiconductor bridges 230B, 232B, and 234B are powered by DC signals 220B, 222B, and 224B respectively via dedicated DC buses. The three semiconductor bridges are cascaded to form a multilevel converter and provide outputs to terminals 252 and 254. The voltage output between terminals 252 and 254 drives current in the second gradient coil 32. The current output in the gradient coil 32 can be controlled by frequently switching on or off the semiconductor bridges 230B, 232B, and 234B. It should be noted that... Figure 4A In the system, dedicated DC buses 207A and 207B are separate, thereby isolating DC signals 220A and 220B, 222A and 222B, and 224A and 224B. Figure 4B It shows the relationship with Figure 4A Gradient amplifiers 206A and 206B are similar to gradient amplifiers, but in contrast, these amplifiers are powered by a shared DC bus 272. As a result of using the shared bus 272, gradient amplifiers 206A and 206B exhibit coupling 273.

[0024] In fact, due to coupling 273, Figure 4BThe system shown may suffer a DC voltage surge fault during operation. Note that both gradient amplifiers 206A and 206B receive the same DC signals 274, 276, and 278 coupled via coupling 273 through a shared DC bus 272. Furthermore, note that because gradient coils 30 and 32 can be driven independently, the states of the switches in gradient amplifier 206A are independent of the states of the switches in gradient amplifier 206B. Therefore, a short circuit across the shared DC bus 272 may occur in certain states of the switches in gradient amplifiers 206A and 206B. In fact, Figure 4C The diagram illustrates the state of the switch with a short circuit 282 on the shared DC bus 272. Due to the arrangement of the switches, the short circuit 282 across gradient amplifiers 206A and 206B could cause malfunction. Therefore, as shown, when powered by the shared DC bus 272, a gradient amplifier implemented using a multilevel converter design with an H-bridge, such as... Figure 4B The gradient amplifiers 206A and 206B may be susceptible to short circuits.

[0025] Traditional power architectures such as gradient power architecture 200 may also be in Figure 3 The gradient power supplies 204A, 204B, and 204C and / or gradient amplifiers 206A, 206B, and 206C are subjected to high common-mode voltage stress. Conventional power architectures 200 utilize multilevel converters operating at high frequencies. In fact, the combined switching frequencies in gradient amplifiers 206A, 206B, and 206C can reach tens of kHz. As a result of this high-frequency switching, the second circuitry on the secondary side (i.e., the isolated DC voltage side) of the gradient power supplies 204A, 204B, and 204C, as well as the bridge and DC link capacitors of the gradient amplifiers 206A, 206B, and 206C, may be affected by high-frequency voltages relative to ground (e.g., safety ground, system ground). These high-frequency voltages can cause common-mode voltage stress in cables, transformers, capacitors, and high-speed diodes. Strict isolation requirements may be necessary to prevent damage from common-mode voltage stress. Further design complexity can lead to common-mode currents induced due to system common-mode voltage, which may also affect amplifier fidelity and potentially cause undesirable imaging artifacts. To reduce the high isolation requirements in gradient coils 30, 32, and 34, the amplifier output can be safely grounded at the midpoint in gradient filter 208.

[0026] Given the challenges presented by traditional architectures such as the gradient power architecture 200, Figure 5 , 6 And 7 shows in Figure 2The features of the gradient power architecture 100 discussed herein can benefit from facilitating the use of a shared DC bus and the addition of suitable grounding points for power circuits. Therefore, the design of the gradient power architecture 200 can reduce the duplication of large and / or expensive components, lower isolation requirements, reduce electrical stress due to common-mode current leakage, and improve the space coding provided by the gradient coils 30, 32, and 34. Figure 5 As shown, the gradient power architecture 100 may employ an integrated HFPDU 104, which provides DC signals to gradient amplifiers 106A, 106B, and 106C. These DC signals may be provided by a shared DC bus 107. In some embodiments, the output DC signals in the shared DC bus 107 may have a voltage ranging from 350 to 2 kV. The HFPDU 104 may include a power distribution unit 302 and a single power supply 304.

[0027] Figure 6 An electrical diagram of an embodiment of HFPDU104 is shown. HFPDU104 includes a power distribution unit 302 and a single power supply 304. Power distribution unit 302 is coupled to the three-phase terminals of the main power supply of the MRI system (e.g., main power supply 40) and generates an intermediate DC signal supplied to power supply 304. Power distribution unit 302 may include a line-side filter 320 and a rectifier circuit 322. Power supply 304 can receive the unregulated intermediate DC signal from power distribution unit 302 and create a regulated output DC signal supplied to a gradient amplifier via DC bus 107. Power supply unit 304 includes an H-bridge 324, a high-frequency transformer 326, a high-speed rectifier 328, a filter circuit 330, a grounded Y-capacitor circuit 332, and a capacitor bank 334. As a result of this architecture, HFPDU104 avoids the use of a bulky transformer. In fact, different voltage levels and / or signal frequencies can be used to power power distribution unit 302 based on the electrical specifications of different locations.

[0028] As discussed above, power supply 304 can receive an unregulated DC signal from power distribution unit 302 and create a regulated DC signal via DC bus 107. In this example, power supply 304 may include an H-bridge 324 that provides an internal high-frequency AC signal via high-frequency transformer 326. Rectifier 328 generates a DC signal, which can be provided to DC bus 107. Filter circuitry 330 can be used to filter noise generated in rectifier 328. In gradient power circuits, capacitor bank 334 is a very expensive component due to its size and high capacitance requirements to meet peak gradient power demands. Since HFPDU 104 uses a single power supply 304, a single capacitor bank 334 is used to meet the peak gradient demands of three gradient amplifiers 106A, 106B, and 106C. Reducing the number of capacitors reduces the constraints associated with the size and heat dissipation of gradient amplifiers 106A, 106B, and 106C. Furthermore, as illustrated, since the power for the three gradient amplifiers 106A, 106B, and 106C is supplied from power supply 304, a safety ground can be added to the midpoint of capacitor bank 332. This grounding of capacitor bank 332 in the shared DC bus 107 does not increase the isolation requirements in the gradient coils. The output of HFPDU 104 can be made between terminals 342 and 344 of the shared DC bus 107.

[0029] like Figure 7 As shown, HFPDU104 can be coupled to gradient amplifiers 106A, 106B, and 106C. The electrical coupling shown is between gradient amplifiers 106A, 106B, and 106C and terminals 342 and 344 of the shared DC bus 107. Gradient amplifiers 106A, 106B, and 106C can be designed using single semiconductor bridges 350, 360, and 370, respectively. A single bridge design can be used instead of, for example... Figure 4A The H-bridge multilevel converter shown is illustrated. Individual semiconductor H-bridges 350, 360, and 370 can be implemented using switches with high-voltage, wide-bandgap devices (e.g., silicon carbide (SiC) devices). High-voltage, wide-bandgap devices allow for precise high-frequency control of extremely large currents and thus avoid the limitations of conventional power architectures (e.g., Figure 3 The power architecture 200 uses multiple H-bridges and multiple DC inputs.

[0030] The illustrated gradient amplifier 106A includes a single H-bridge 350. The single bridge 350 may include a first branch with switches 352A and 352B, and a second branch with switches 354A and 354B. The first branch controls the voltage at its midpoint. Similarly, the second branch controls the voltage at its midpoint. Terminals at the midpoint of the H-bridge 350 can be coupled to the input terminals of a ripple filter 356, and the output terminals 358A and 358B of the ripple filter 356 are coupled to the gradient coil 30. The gradient ripple filter 356 can filter high-frequency noise from the single bridge 350 and reduce the ripple component in the current flowing into the gradient coil 30.

[0031] Similarly, the illustrated gradient amplifier 106B includes a single bridge 360. The single H-bridge 360 ​​may include a first branch with switches 362A and 362B, and a second branch with switches 364A and 364B. Terminals at the midpoints of the first and second branches of the H-bridge 360 ​​can be coupled to the input terminals of a ripple filter 366, and the output terminals 368A and 368B of the ripple filter 366 are coupled to the gradient coil 32. The gradient ripple filter 366 can block high-frequency noise from the single bridge 360 ​​and reduce the ripple component in the current flowing into the gradient coil 32 to avoid affecting the magnetic field generated by the gradient coil 32.

[0032] The gradient amplifier 106C employs a similar design, featuring a single H-bridge 370. The single H-bridge 370 may include a first branch with switches 372A and 372B, and a second branch with switches 374A and 374B. Terminals at the midpoints of the first and second branches of the H-bridge 370 can be coupled to the input terminals of a ripple filter 376, and the output terminals 378A and 378B of the ripple filter 376 are coupled to the gradient coil 34. The gradient ripple filter 376 can block high-frequency noise from the single bridge 370 and reduce the ripple component in the current flowing into the gradient coil 34.

[0033] The technical advantages of the embodiments presented herein generally include a reduction in the complexity of power circuitry used in MRI systems. Using an integrated HFPDU with a single power supply allows for more compact power circuitry for the gradient subsystem of an MRI apparatus. The HFPDU also provides DC isolation and insulation, facilitating compliance with the Mode of Patient Protection (MOPP) guidelines. Furthermore, the absence of cross-bridge connections in the gradient amplifier allows for the integration of a DC bus, further reducing the amount of wiring and insulation required in the system. A shared DC bus further allows for the use of a single capacitor bank, rather than multiple capacitor banks as in conventional designs.

[0034] It should be noted that, due to the advantages described above, the reduction and simplification in size, thermal stress, and common-mode voltage stress in the gradient amplifier allows the amplifier to be arranged within the scanning chamber. In fact, a single cable can be used to connect the HFPDU located outside the scanning chamber in the equipment room to the gradient amplifier, which can then be arranged within the scanning chamber. This architecture also allows for flexible packaging of the individual components due to the reduced size. For example, each gradient amplifier can be deployed in a separate package (e.g., a chassis). Alternatively, the gradient amplifiers can share a single chassis, which can be located within the scanning chamber. In some systems, the gradient amplifiers can be housed in the same chassis or package as the HFPDU.

[0035] Additionally, the midpoint of the capacitor bank located at the HFPDU output can be connected to a safety ground. This safety grounding arrangement reduces the switching stress on the secondary-side diode rectifier discussed above, as the amplifier's switching does not affect the common-mode voltage at the terminals. This modification eliminates the potential for insulation failure in the secondary diodes and the high-frequency transformer. Finally, it should be noted that by employing the described method and system, the gradient ripple filter becomes more effective and essentially becomes primarily differential due to the reduced common-mode current disturbance in this design.

[0036] This written description uses examples to disclose the invention, including the best mode, and enables any person skilled in the art to implement the invention, including making and using any device or system and performing any covered methods. The scope of patent protection for this invention is defined by the claims and may include other examples known to those skilled in the art. Such other examples are intended to fall within the scope of the claims if they have structural elements that are indistinguishable from the literal language of the claims, or if they include equivalent structural elements that are not substantially indistinguishable from the literal language of the claims.

Claims

1. A magnetic resonance imaging system, comprising: Multiple gradient coils; as well as A gradient driver configured to drive the plurality of gradient coils, the gradient driver comprising: A plurality of gradient amplifiers, wherein each of the plurality of gradient amplifiers is electrically coupled to a gradient coil of the plurality of gradient coils, and wherein each gradient amplifier includes a respective single semiconductor bridge; and A high-frequency power distribution unit is configured to receive an AC power signal from the main power supply of the magnetic resonance imaging system and generate a DC power signal to the plurality of gradient amplifiers via a shared DC bus, the shared DC bus including a first terminal and a second terminal, wherein the high-frequency power distribution unit includes: A power distribution unit, which receives the AC power signal from the main power supply and generates an intermediate power signal; A power supply that receives the intermediate power signal from the power distribution unit and provides the DC power signal to the shared DC bus, wherein the power supply includes a single capacitor bank and a grounded Y-capacitor circuit, the two ends of the single capacitor bank being connected to a first terminal and a second terminal of the shared DC bus, respectively, and the grounded Y-capacitor circuit being configured to be coupled to the safety ground of the magnetic resonance imaging system, wherein the safety ground is added to the midpoint of the grounded Y-capacitor circuit, the grounded Y-capacitor circuit including a first capacitor and a second capacitor, the first capacitor being connected between the first terminal of the shared DC bus and the safety ground, and the second capacitor being connected between the second terminal of the shared DC bus and the safety ground.

2. The magnetic resonance imaging system as described in claim 1, wherein, The plurality of gradient coils includes an axial gradient coil, a longitudinal gradient coil, and a transverse gradient coil.

3. The magnetic resonance imaging system as described in claim 2, wherein, The plurality of gradient amplifiers includes a first gradient amplifier electrically coupled to the axial gradient coil, a second gradient amplifier electrically coupled to the longitudinal gradient coil, and a third gradient amplifier electrically coupled to the transverse gradient coil.

4. The magnetic resonance imaging system as described in claim 1, wherein, Each individual semiconductor bridge of each gradient amplifier includes a first branch and a second branch, the first branch including a first pair of switches and the second branch including a second pair of switches.

5. The magnetic resonance imaging system as described in claim 4, wherein, Each of the first pair of switches and the second pair of switches includes a high-voltage wide-bandgap device.

6. The magnetic resonance imaging system as described in claim 5, wherein, The high-voltage wide-bandgap device includes a silicon carbide device.

7. The magnetic resonance imaging system as claimed in claim 1, wherein, The power supply for magnetic resonance imaging includes a transformer configured to isolate the intermediate power signal from the DC power signal.

8. The magnetic resonance imaging system as claimed in claim 7, wherein, The transformer's shielding is electrically coupled to the ground of the magnetic resonance imaging system.

9. The magnetic resonance imaging system as claimed in claim 1, wherein, The magnetic resonance imaging system includes a scanning chamber and an equipment chamber, wherein the HFPDU is located in the equipment chamber, and wherein the plurality of gradient amplifiers are located in the scanning chamber.

10. The magnetic resonance imaging system of claim 1, wherein, The magnetic resonance imaging system includes a first package, which includes the plurality of gradient amplifiers.

11. The magnetic resonance imaging system of claim 10, wherein, The first package includes the HFPDU.

12. The magnetic resonance imaging system as claimed in claim 1, wherein, The magnetic resonance imaging system includes multiple packages, and each package includes its own gradient amplifier.

13. A high-frequency power distribution unit, comprising: A power distribution unit, comprising a line filter and a first rectifier, wherein the power distribution unit is configured to receive a three-phase AC power signal from a mains power supply and generate an intermediate DC power signal; and A power supply, comprising a semiconductor bridge, a high-frequency transformer, a high-speed rectifier, and a filter, wherein the power supply is configured to: receive the intermediate DC power signal; generate a high-frequency second AC power signal using the semiconductor bridge; and generate an output DC power signal isolated from the second AC power signal using the high-frequency transformer, the high-speed rectifier, and the filter, wherein the shield of the high-frequency transformer is electrically coupled to a ground connection point, wherein the power supply includes a single capacitor bank and a grounded Y-capacitor circuit, the two ends of the single capacitor bank being respectively connected to a first terminal and a second terminal of the shared DC bus, the grounded Y-capacitor circuit being configured to be coupled to a safety ground, the power supply being configured to provide the output DC power signal to the shared DC bus and then to multiple gradient amplifiers of a magnetic resonance imaging system, wherein the shared DC bus includes a first terminal and a second terminal, the safety ground being added to the midpoint of the grounded Y-capacitor circuit, the grounded Y-capacitor circuit including a first capacitor and a second capacitor, the first capacitor being connected between the first terminal of the shared DC bus and the safety ground, and the second capacitor being connected between the second terminal of the shared DC bus and the safety ground.

14. The high-frequency power distribution unit as described in claim 13, wherein, The three AC power signals include a nominal voltage and a nominal frequency. The nominal voltage includes 380V, 415V or 480V, and the nominal frequency includes 50Hz or 60Hz. The output DC power signal is between 350V and 2kV.

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