阅读说明：本技术 Mri系统中功率源和梯度放大器的同步控制 (Synchronized control of power source and gradient amplifier in MRI system ) 是由 亚什·维尔·辛格 王汝锡 胡安·安东尼奥·萨巴特 卡纳卡萨白·维斯瓦纳坦 于 2019-05-23 设计创作，主要内容包括：本发明题为“MRI系统中功率源和梯度放大器的同步控制”。在磁共振成像(MRI)系统中,梯度放大器子系统、功率源子系统和配电单元子系统的操作的同步控制是通过向梯度放大器子系统、功率源子系统和配电单元子系统的相应控制块提供线圈命令参考信号作为输入来实现的。线圈命令参考信号对应于用于MRI系统的扫描仪的至少一个梯度放大器(30、32、34)的预定梯度放大器(30、32、34)电流。(the invention relates to synchronous control of a power source and a gradient amplifier in an MRI system. In a Magnetic Resonance Imaging (MRI) system, synchronous control of the operation of the gradient amplifier subsystem, the power source subsystem and the power distribution unit subsystem is achieved by providing coil command reference signals as inputs to respective control blocks of the gradient amplifier subsystem, the power source subsystem and the power distribution unit subsystem. The coil command reference signal corresponds to a predetermined gradient amplifier (30, 32, 34) current for at least one gradient amplifier (30, 32, 34) of a scanner of the MRI system.)

1. A method for synchronizing control of a Magnetic Resonance Imaging (MRI) gradient chain (42), the MRI gradient chain (42) including a power source (48) and a gradient amplifier (50) coupled to a power output of the power source (48), the gradient amplifier (50) operatively coupled to the gradient amplifier (30, 32, 34) to energize the gradient amplifier (30, 32, 34) with coil currents, wherein the method comprises:

Monitoring an output current and an output voltage supplied from the power source (48) to the gradient amplifier (50) to generate a power source output current feedback (Il _ PS) and a power source output voltage feedback (Vo _ PS);

monitoring the coil current supplied from the gradient amplifier (50) to the gradient amplifier (30, 32, 34) to generate a coil current feedback (I _ coil);

providing a coil current reference signal (91) to a power source control block (104) and a gradient amplifier control block (106);

providing a power source output voltage reference signal (Vo _ PS reference) to the power source control block (104);

Generating a control command signal (142) for the power source (48) via the power source control block (104) using the power source output voltage feedback (Vo _ PS), the power source output voltage reference, the power source output current feedback (Il _ PS), and a coil current reference signal (91) as inputs, the control command signal (142) for the power source (48) corresponding to a desired power output by the power source (48) to the gradient amplifier (50) according to the coil current reference signal (91); and

Generating, via the gradient amplifier control block (106), a control command signal (156) for the gradient amplifier (50) using the coil current feedback (I _ coil) and the coil current reference signal (91), the control command signal (156) for the gradient amplifier (50) corresponding to a required power output by the gradient amplifier (50) to the gradient amplifier (30, 32, 34) according to the coil current reference signal (91).

2. the method of claim 1, wherein the coil current reference signal (91) is a coil current command signal indicative of currents for the gradient amplifiers (30, 32, 34) that are excited in a predetermined manner according to a pulse pattern that produces gradient magnetic fields specified by an imaging sequence.

3. The method of claim 1, wherein generating the control command signal (142) for the power source (48) (48) comprises calculating a feed-forward current control input (IFF _ PS) for the power source (48) from the coil current reference signal (91) via an electrical model (126) of the gradient amplifier (30, 32, 34), a gradient amplifier filter, and the gradient amplifier (50).

4. The method of claim 3, wherein generating the control command signal (142) for the power source (48) comprises:

generating a voltage error signal by determining a difference between the power source output voltage reference signal (Vo _ PS ref) and a voltage feedback signal for the power source (48), the power source output voltage reference signal (Vo _ PS ref) being a target voltage at an output of the power source;

Generating a current command signal from the voltage error signal using power source voltage control;

generating a current error signal by combining the current command signal and the feed forward current control input for the power source (48) and subtracting the power source output current feedback (Il _ PS); and

Generating the control command signal (142) for the power source (48) (48) from the current error signal using a power source current controller.

5. the method of claim 1, wherein generating the control command signal (156) for the gradient amplifier (50) comprises deriving a feed-forward control input for the gradient amplifier (50) from the coil current reference signal (91) via an electrical model of the gradient amplifier (30, 32, 34) and a gradient amplifier filter.

6. the method of claim 5, wherein generating the control command signal (156) for the gradient amplifier (50) comprises:

Generating a current error signal by determining a difference between the coil current reference signal (91) and the coil current feedback (I _ coil);

generating a feedback-derived control signal from the current error signal using a gradient amplifier current controller; and

generating the control command signal (156) for the gradient amplifier (50) by combining the feedback derived control signal and the feedforward control input derived from the coil current reference signal (91) for the gradient amplifier (50) to produce a desired voltage output at the gradient amplifier (30, 32, 34).

7. The method as recited in claim 1, wherein the MRI gradient chain (42) further includes a power distribution unit configured to receive power input from a grid or utility and provide power to the power source (48), and wherein the method further includes:

Monitoring an output voltage of the power supplied from the power distribution unit to the power source (48) to generate a power distribution unit output voltage feedback;

Sensing at least one of an output current or an inductor current of the power distribution unit to generate power distribution unit current feedback;

Providing the coil current reference signal (91) to a power distribution unit control block; and

Generating, via the power distribution unit control block, a control command signal for the power distribution unit using the power distribution unit output voltage feedback, a power distribution unit output voltage reference corresponding to a target output voltage of the power distribution unit, the power distribution unit current feedback, and the coil current reference signal (91), the control command signal for the power distribution unit corresponding to a desired power output by the power distribution unit to the power source (48) in accordance with the coil current reference signal (91).

8. The method of claim 7, wherein generating the control command signal for the power distribution unit comprises:

generating a voltage error signal by determining a difference between the output voltage reference signal for the power distribution unit and the power distribution unit output voltage feedback;

Generating a feedback-derived control command signal from the voltage error signal using a power distribution unit voltage controller;

Generating a current error signal by adding and subtracting the power distribution unit current feedback from the current command signal and a feed-forward control input for the power distribution unit derived from the coil current reference signal (91); and

Generating the control command signal for the power distribution unit from the current error signal using a power distribution unit current controller.

9. A Magnetic Resonance Imaging (MRI) system comprising:

A power source (48) configured to receive power from a power distribution unit;

a gradient amplifier (50) coupled to an output of the power source (48) and a gradient amplifier (30, 32, 34) of a scanner of the MRI system, wherein the gradient amplifier (50) is configured to provide a coil current to the gradient amplifier (30, 32, 34) using power received from the power source (48) and thereby generate a gradient magnetic field;

A power source control block (104) configured to control the power source (48) using a power source control command signal;

A gradient amplifier control block (106) configured to control the gradient amplifier (50) using gradient amplifier control command signals; and

A synchronization control platform configured to provide a synchronization reference signal to the power source control block (104) and the gradient amplifier control block (106) such that the control of the power source (48) and the gradient amplifier (50) is synchronized by the synchronization reference signal.

10. the MRI system of claim 9, wherein the synchronization reference signal is a coil current command signal indicative of currents excited in a predetermined manner for the gradient amplifiers (30, 32, 34).

11. The MRI system of claim 10, wherein the power source control block (104) includes an electrical model of the gradient amplifier (30, 32, 34), the gradient amplifier filter, and the gradient amplifier (50), and wherein the electrical model is configured to generate a feed-forward control signal for the power source (48) from the coil current command signal.

12. The MRI system of claim 11, wherein the power source control block (104) includes a power source voltage controller configured to generate a feedback-derived control signal for the power source (48) from a voltage error signal produced by subtracting a power source voltage feedback signal measured at an output of the power source (48) from a reference voltage for the power source (48).

13. The MRI system of claim 12, wherein the power source control block (104) is configured to combine the feed-forward control signal with the feedback-derived control signal for the power source (48) and subtract a power source output current feedback (Il _ PS) signal to produce a power source current error signal, and wherein the power source control block (104) includes a power source current controller configured to generate a control command signal (142) for the power source (48) (48).

14. The MRI system of claim 10, wherein the gradient amplifier control block (106) includes an electrical model of the gradient amplifier (30, 32, 34) and a gradient amplifier filter, and wherein the electrical model is configured to generate a feed-forward control signal for the gradient amplifier (50) from the coil current command signal.

15. the MRI system of claim 14, wherein the gradient amplifier control block (106) comprises a gradient amplifier current controller, and wherein the gradient amplifier current controller is configured to generate a feedback-derived control signal from a current error signal produced by subtracting a coil current feedback (I _ coil) signal measured at an output of the gradient amplifier (50) from the coil current command signal.

Background

Generally, Magnetic Resonance Imaging (MRI) examination is based on the interaction between a main magnetic field, a Radio Frequency (RF) magnetic field, and a time-varying magnetic gradient field, in which a gyromagnetic material has nuclear spins within an object of interest, such as a patient. Certain gyromagnetic materials (such as hydrogen nuclei in water molecules) have a characteristic behavior in response to an external magnetic field. The precession of the spins of these nuclei can be influenced by manipulating the field to produce RF signals that can be detected, processed, and used to reconstruct a usable image.

During an imaging sequence, time-varying gradient fields are generated by applying currents to a series of gradient coils. The gradient coils are energized via gradient amplifiers connected to a power source. The gradient amplifier is typically a power converter with a high bandwidth for controlling the gradient magnetic field with high accuracy. Energy storage components (e.g., capacitors) are some key components in the circuit structure of the gradient amplifier, as the energy storage components act as buffers between the power source and the gradient amplifier. Such energy storage components may be used to provide stored energy to the inductive components of the gradient coil. Unfortunately, the energy storage components add to the cost, weight, and volume of the gradient amplifier. Reducing weight and volume is one of the challenging tasks in compact gradient amplifier design. Accordingly, there is a need to reduce reliance on or use such energy storage components in a more efficient manner.

disclosure of Invention

The present disclosure includes a method for synchronizing control of a Magnetic Resonance Imaging (MRI) gradient chain. The MRI gradient chain includes a power source and a gradient amplifier coupled to a power output of the power source, the gradient amplifier being operatively coupled to the gradient coil to energize the gradient coil with a coil current. The method includes monitoring an output current and an output voltage supplied from a power source to a gradient amplifier to generate a power source output current feedback and a power source output voltage feedback; monitoring a coil current supplied to the gradient coil from the gradient amplifier to generate a coil current feedback; providing a coil current reference signal to a power source control block and a gradient amplifier control block; providing a power source output voltage reference signal to a power source control block; generating, via a power source control block, a control command signal for the power source using the power source output voltage feedback, the power source output voltage reference, the power source output current feedback, and the coil current reference signal as inputs, the control command signal for the power source corresponding to a desired power output by the gradient amplifier to the power source according to the coil current reference signal; and generating, via a gradient amplifier control block, control command signals for the gradient amplifiers corresponding to the required power output by the gradient amplifiers to the gradient coils in accordance with the coil current reference signals using the coil current feedback and the coil current reference signals.

the present disclosure also includes a Magnetic Resonance Imaging (MRI) system, comprising: a power source configured to receive power from a power distribution unit; a gradient amplifier coupled to an output of the power source and a gradient coil of a scanner of the MRI system. The gradient amplifier is configured to provide coil currents to the gradient coils using power received from the power source and thereby generate gradient magnetic fields. The system further comprises: a power source control block configured to control a power source using a power source control command signal; a gradient amplifier control block configured to control the gradient amplifier using a gradient amplifier control command signal; and a synchronization control platform configured to provide a synchronization reference signal to the power source control block and the gradient amplifier control block such that control of the power source and the gradient amplifier is synchronized by the synchronization reference signal.

the present disclosure also includes a Magnetic Resonance Imaging (MRI) method performed by the MRI system. The method comprises the following steps: acquiring magnetic resonance data from a subject of interest using a scanner of the MRI system, the magnetic resonance data being acquired using a pulse sequence, wherein gradient coils of the scanner are pulsed with gradient coil currents; controlling provision of gradient coil current to the gradient coils by controlling operation of a gradient amplifier subsystem operatively coupled to the gradient coils, a power source subsystem configured to provide power to the gradient amplifier subsystem, and a power distribution unit subsystem configured to provide power to the power source subsystem; and synchronously controlling operation of the gradient amplifier subsystem, the power source subsystem and the power source subsystem by providing coil command reference signals as inputs to respective control blocks of the gradient amplifier subsystem, the power source subsystem and the power distribution unit subsystem. The coil command reference signal corresponds to a predetermined gradient coil current for at least one of the gradient coils of the scanner.

drawings

these and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates one embodiment of a Magnetic Resonance Imaging (MRI) system having a power source and a gradient amplifier with synchronized control;

FIG. 2 shows an embodiment of a synchronization subsystem in a gradient chain of the MRI system of FIG. 1;

FIG. 3 illustrates an embodiment of a control scheme for synchronizing control of the Power Distribution Unit (PDU), Power Source (PS), and Gradient Amplifier (GA) of FIG. 2;

FIG. 4 shows the response of the PS output voltage and the output inductor current of the PS when the PDU, PS, and GA of FIG. 2 use unsynchronized control;

FIG. 5 shows the response of the PS output voltage and the output inductor current of the PS when the PDU, PS, and GA of FIG. 2 use synchronous control; and is

Fig. 6 shows the response of the PS output voltage and the output inductor current when the PDUs, PS and GA of fig. 2 use synchronous control and the capacitances at the PS output and GA input are reduced.

Detailed Description

one or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the present disclosure, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Further, any numerical examples in the following discussion are intended to be non-limiting, and thus additional numbers, ranges, and percentages are within the scope of the disclosed embodiments.

As mentioned above, the energy storage (capacitance) is one of the key factors in the circuit design of the gradient amplifier. For example, a capacitor is attached at each input dc port of the gradient amplifier and is also connected to the output of the power source. The accumulator provides stored energy to the gradient coil inductor during high slew rate (high di/dt) transients. In accordance with the present disclosure, it is now recognized that it is possible to reduce the required capacitance values in these energy storage elements of the gradient amplifier by synchronizing the control of the different subsystems of the MR gradient chain. Reducing the capacitance value may be considered to allow smaller energy storage elements, or more efficient use of such elements. Furthermore, the GA will still be able to ensure accurate gradient field control and will have a higher power density.

According to the present disclosure, synchronous control is achieved at least in part by communication of real-time input of coil current reference values to controllers for GA and PS. Communication and control synchronization may be performed by a common control platform for the PS and GA, and in certain embodiments, the common control platform also controls Power Distribution Units (PDUs). For example, the power source is connected to the grid through a low frequency transformer or another power source converter in its front end. The front end power handling is a PDU. Such a PDU has some energy storage elements connected at the output of the PDU and the input of the PS. The energy storage elements may have active control means.

The embodiments described herein may be implemented as at least a portion of a Magnetic Resonance Imaging (MRI) system, where a particular imaging routine (e.g., a diffusion MRI sequence) is initiated by a user (e.g., a radiologist). Thus, the MRI system may perform data acquisition, data construction, and, in some cases, image synthesis. Thus, referring to fig. 1, a magnetic resonance imaging system 10 is schematically shown as including a scanner 12, scanner control circuitry 14, and system control circuitry 16. According to embodiments described herein, the MRI system 10 is generally configured to perform MR imaging, such as an imaging sequence for diffusion imaging.

The system 10 also includes a remote access and storage system or device, such as a Picture Archiving and Communication System (PACS)18, or other device, such as a remote radiology device, so that data acquired by the system 10 may be accessed on-site or off-site. In this manner, MR data can be acquired and then processed and evaluated either onsite or offsite. While the MRI system 10 may include any suitable scanner or detector, in the illustrated embodiment, the system 10 includes a whole-body scanner 12 having a housing 20 through which an aperture 22 is formed. The table 24 is movable into the aperture 22 to allow a patient 26 to be positioned therein to image a selected anatomical structure within the patient.

The scanner 12 includes a series of associated coils for generating controlled magnetic fields for exciting gyromagnetic materials within the anatomy of the subject being imaged. In particular, main magnet coils 28 are provided for generating a main magnetic field B0 generally aligned with the bore 22. A series of gradient coils 30, 32 and 34 allow the generation of controlled magnetic gradient fields for positionally encoding specific gyromagnetic nuclei within the body of the patient 26 during an examination sequence. A Radio Frequency (RF) coil 36 is configured to generate radio frequency pulses for exciting specific gyromagnetic nuclei within the patient. In addition to the coils attributed to the scanner 12, the system 10 also includes a set of receive coils 38 (e.g., a coil array) configured to be placed (e.g., abutted) proximal to the patient 26. For example, the receive coils 38 may include a neck/chest/waist (CTL) coil, a head coil, a unilateral spine coil, and the like. Generally, the receive coil 38 is placed near or at the top of the patient 26 in order to receive the weak RF signal (weaker relative to the transmit pulse generated by the scanner coil) generated by certain gyromagnetic nuclei within the patient 26 as they return to a relaxed state.

The various coils of the system 10 are controlled by external circuitry to generate the required fields and pulses, and to read emissions from the gyromagnetic material in a controlled manner in the illustrated embodiment, a main power source 40 provides power to a main field coil 28 to generate a main magnetic field B _o the illustrated system 10 further includes a gradient chain 42(MRI gradient chain) that is typically used to provide power to the gradient coils 30, 32, and 34 to produce gradient magnetic fields (e.g., G _x, G _y, G _z). the illustrated embodiment of the gradient chain includes a power input 44 (e.g., power from a utility or grid), a Power Distribution Unit (PDU)46, a Power Source (PS)48, and a drive circuit 50 that together provide power to pulse the gradient field coils 30, 32, and 34. the drive circuit 50 may include amplification and control circuitry for supplying current to the coils, the current being defined by the sequence of digitized pulses output by the scanner control circuitry 14. as shown in the figures, PDU46, PS48, and the driver circuit 50 (including one or more Gradient Amplifiers (GA)) are connected to the scanner control circuitry 14 for synchronization as further described below.

Another control circuit 52 is provided for regulating the operation of the RF coil 36. The circuit 52 includes switching means for alternating between active and passive modes of operation in which the RF coil 36 transmits and does not transmit signals, respectively. The circuitry 52 also includes amplification circuitry configured to generate the RF pulses. Similarly, the receive coil 38 is connected to a switch 54 that can switch the receive coil 38 between receive and non-receive modes. Thus, the receive coils 38 resonate with the RF signals generated from the relaxed gyromagnetic nuclei within the patient 26 in the receive mode, and they do not resonate with the RF energy from the transmit coils (i.e., coils 36) to prevent undesired operation in the non-receive mode. In addition, the receive circuitry 56 is configured to receive data detected by the receive coils 38 and may include one or more multiplexing and/or amplification circuits.

It should be noted that although the scanner 12 and control/amplification circuitry described above are shown coupled by a single line, many such lines may be present in a practical example. For example, a single wire may be used for control, data communication, power transmission, and the like. In addition, appropriate hardware may be provided along each type of line to properly process data and current/voltage. Indeed, various filters, digitizers, and processors may be disposed between the scanner and either or both of the scanner and system control circuits 14, 16.

As shown, the scanner control circuitry 14 includes interface circuitry 58 that outputs signals for driving the gradient field coils and the RF coils, and for receiving data indicative of the magnetic resonance signals generated during an examination sequence. The interface circuit 58 is coupled to a control and analysis circuit 60. The control and analysis circuit 60 executes commands for the drive circuit 50 and the circuit 52 based on a defined protocol selected via the system control circuit 16. In the illustrated embodiment, the control and analysis circuitry 60 of the scanner control circuitry 14 is communicatively coupled to the elements of the gradient chain 42 (including the PDU46, the PS48, and the driver circuitry 50) to achieve control synchronization. In certain embodiments, for example, the control and analysis circuitry 60 may transmit a common reference signal to the elements of the gradient chain 42 to synchronize their control. The common reference signal may be, for example, a coil current reference for one or more of the gradient coils. More specifically, the driver circuit 50 may include a GA for each gradient coil, and the control and analysis circuit 60 may suitably transmit the reference current for the particular gradient coil to the gradient chain 42. More details regarding such control are set forth below.

The control and analysis circuitry 60 is also operative to receive the magnetic resonance signals and perform subsequent processing prior to transmission of the data to the system control circuitry 16. The scanner control circuitry 14 also includes one or more memory circuits 62 that store configuration parameters, pulse sequence descriptions, inspection results, and the like during operation.

Interface circuitry 64 is coupled to control and analysis circuitry 60 for exchanging data between scanner control circuitry 14 and system control circuitry 16. In certain embodiments, the control and analysis circuitry 60, while shown as a single unit, may include one or more hardware devices. The system control circuitry 16 includes interface circuitry 66 that receives data from the scanner control circuitry 14 and transmits data and commands back to the scanner control circuitry 14. The control and analysis circuitry 66 may include a CPU in a general purpose or application specific computer or workstation. The control and analysis circuitry 66 is coupled to the memory circuitry 70 to store program code for operation of the MRI system 10 and to store processed image data for later reconstruction, display and transmission. The program code may execute one or more algorithms that, when executed by the processor, are configured to perform reconstruction of the acquired data.

Additional interface circuitry 72 may be provided for exchanging image data, configuration parameters, etc. with external system components, such as the remote access and storage device 18. Finally, the system control and analysis circuitry 66 may be communicatively coupled to various peripherals to facilitate operator interface and to generate hard copies of the reconstructed images. In the illustrated embodiment, these peripheral devices include a printer 74, a monitor 76, and a user interface 78, including, for example, a keyboard (e.g., integral with the monitor 76), a mouse, a touch screen, and the like.

Fig. 2 depicts a schematic diagram of an embodiment of the synchronized control of the different subsystems in the gradient chain 42 of the MRI system 10. In the illustrated embodiment, the subsystems include a PDU subsystem 82, a PS subsystem 84, and a GA subsystem 86, all of which are controlled using a synchronous control platform 88. In certain implementations, each of these subsystems may have its own dedicated controller, such as a proportional integral or proportional integral derivative controller communicatively coupled to the synchronous control platform 88.

In accordance with the present disclosure, the synchronization control platform 88 may be implemented as part of the scanner control circuitry 60 and/or as part of the system control circuitry 66, for example. By way of non-limiting example, scanner control circuitry 60 and/or system control circuitry 66 may include one or more sets of instructions stored in memory 62 and/or memory 70 that are executable by the respective control circuitry (e.g., the corresponding processor or processors) to implement at least a portion of the synchronization control process described herein. For example, synchronization control platform 88 may be implemented, at least in part, using one or more software packages stored in memory 62 and/or memory 70.

Additionally or alternatively, the synchronization control platform 88 may be implemented as one or more hardware controllers communicatively coupled to the PDU subsystem 82, the PS subsystem 84, and the GA subsystem 86 and the scanner control circuitry 60 and/or the system control circuitry 66. By way of non-limiting example, such hardware may include appropriate input and output communication features (e.g., communication ports), and one or more appropriately configured controllers having memory with stored instructions or programmed logic circuits.

The power flow in the embodiment shown in fig. 2 is generally from left to right. As shown, PDU46 is connected to power source input 44, in this case the grid (utility). PDU46 may be a low frequency transformer with taps on the primary to service different input voltage conditions, or it may be another power conversion stage with or without isolation. In embodiments where PDU46 is isolated, it may include a high frequency transformer. In embodiments where PDU46 is implemented as a power conversion stage, the power flowing out of grid 44 can be controlled by controlling the output current of PDU46, which is denoted as Il _ PDU in fig. 2, as measured by PDU output current sensor 90.

Control of the PDU output may be performed based on a synchronization reference signal 91 that is provided to the PS subsystem 84 and the GA subsystem 86 in addition to the PDU subsystem 82. In certain implementations, the synchronization reference signal is a target drive current (e.g., a current command signal) for one or more of the gradient coils 30, 32, 34.

In the embodiment of fig. 2, the PDU subsystem 82 includes a power storage block 92, denoted as an "ES cap," which represents one or more passive capacitive elements (capacitors). The DC bus voltage (V _ DC) of the PDU subsystem 82 is controlled by the PDU converter (if present) or is dependent on load and grid conditions. In such embodiments, the PDU converter may be communicatively coupled to the synchronization control platform 88 to receive, for example, reference signals for synchronization with the PS subsystem 84 and the GA subsystem 86.

It should be noted that in some systems, PDU46 may be an uncontrolled low frequency transformer and therefore may not be part of the synchronization control scheme described herein. In other words, certain embodiments of the present disclosure may synchronize the control of the PS subsystem 84 and the GA subsystem 86 without controlling the PDU 46.

As shown in FIG. 2, the PS subsystem 84 includes different blocks depicting each of the power sources for the gradient coils 30, 32, 34. In particular, the PS subsystem 84 includes a first power source 48A (denoted as PS-X) for the X-gradient field coil 30, a second power source 48B (denoted as PS-Y) for the Y-gradient field coil 32, and a third power source 48C (denoted as PS-Z) for the Z-gradient field coil 34.

the output of the PS subsystem 84 (which may be a single output or multiple isolated outputs from each power source 48) is provided as an input to a GA subsystem 86. The output of the PS subsystem 84 may be controlled based on a synchronization reference signal 91 provided by the synchronization control platform 88, a measured output voltage of the PS subsystem 84 (denoted as Vo _ PS as a feedback control component), and a current through an output inductor of the PS subsystem 84 (Il _ PS as a feedback control component). For example, I1_ PS may be measured by PS output inductor current sensor 94. In certain implementations, there may be a respective PS output current sensor associated with each of the power sources 48 to measure their respective outputs.

The illustrated GA subsystem 86 includes, among other things, a first gradient field amplifier 50A (shown as GA-X) for the X-gradient field coil 30, a second gradient amplifier 50B (shown as GA-Y) for the Y-gradient field coil 32, and a third gradient amplifier 50C (shown as GA-Z) for the Z-gradient field coil 34. The gradient amplifier 50 receives power from the power source 48 and controls the drive currents of the gradient coils 30, 32, 34 during the imaging pulse sequence.

The output from each gradient amplifier 50 (shown as Icoil in fig. 2) is measured by a corresponding GA output coil current sensor 96. In addition to the synchronous reference signal 91, the respective outputs of the gradient amplifiers 50 may each be controlled using Icoil as feedback.

An embodiment of a control scheme 100 for synchronizing the control of PDUs 46, PS48 and GA50 is schematically shown in fig. 3. In particular, a control scheme 100 for a single gradient amplifier providing current to a single gradient coil of the MRI system 10 is shown. However, it should be noted that the illustrated control scheme 100 may be performed in combination for the gradient coils 30, 32, 34. As shown in the control scheme 100, power is provided by PDU46 and storage capacitor 92 to PS48, PS48 in turn provides power output to GA50, and GA50 provides power to the gradient coils 30, 32, 34. Thus, the lines shown between ES cap 92, PDU46, PS48, and GA50 generally represent high voltage, high power connections between power converters, passive components, or inductive loads. The lines extending from these power transmission lines are feedback lines (e.g., lines from sensors) provided to the control block, as described below.

The control scheme 100 includes a PDU control block 102, a PS control block 104, and a GA control block 106. The control features associated with each of the control blocks may be implemented, for example, at least in part in the scanner control circuitry 60 and its associated memory 62, the system control circuitry 66 and its associated memory 70, and the controllers within the gradient chain 42, as discussed below.

the illustrated control scheme uses a synchronization reference signal 91, in this embodiment an Icoil reference signal or a coil current reference signal (e.g., a target signal for the current provided to the gradient coils 30, 32, 34) as an input to each of the control blocks 102, 104, 106. For example, the synchronization reference signal 91 may be provided to an electrical model of each of the control blocks 102, 104, 106 to generate feed-forward control inputs for controlling respective outputs of the PDU46, PS48, and GA 50. The signals are command signals from a host computer or computing system (e.g., scanner control circuitry 60 and/or system control circuitry 66), where a particular pulse sequence, etc., may be selected by an operator or radiologist to perform a given scan. The electrical model of each of the control blocks 102, 104, 106 may be, for example, an electrical model stored on memory 62 and/or memory 70. The feed-forward inputs generated from the electrical model may be provided to respective controllers (e.g., logic circuits) associated with particular portions of the gradient chain 42 (e.g., PDU46, PS48, or GA 50).

Further, by way of example, the operations described herein in which signals are combined, subtracted, etc., may be performed using logic circuitry and/or using software associated with scanner control circuitry 60 and/or system control circuitry 66. Additionally or alternatively, the operations described herein may be implemented using logic circuitry associated with a particular feature of the gradient chain 42 (e.g., PDU46, PS48, or GA 50).

Referring now to PDU control block 102, the V _ DC reference is a set point for the voltage output of PDU46 (e.g., a voltage reference signal for power distribution unit 46), and V _ DC is a feedback signal for the output DC voltage of PDU46 (e.g., a voltage feedback signal for PDU 46). Operation 108 determines a voltage error signal 110 between the V _ DC reference and the V _ DC feedback signal. The error signal 110 goes to a Proportional Integral (PI) voltage controller 112 (denoted as PI _ V _ PDU), which may be implemented as a PI controller associated with PDU 46. The error signal 110 is used by a PDU voltage controller 112 to generate a PDU feedback derived control signal 114.

at operation 118, a feed forward control signal (IFF _ PDU) calculated in real time from the electrical model 116 of the gradient amplifier filter, the coils 30, 32, 34, GA50 and PS48 is added to the PDU feedback derived control signal 114. Operation 118 also subtracts the current feedback signal (Il _ PDU, generated by current sensor 90) from the sum of the PDU feedback derived control signal 114 and the IFF _ PDU signal, producing a current error signal 120. In embodiments where PDU46 is an isolated high frequency PDU, the Il _ PDU feedback signal is the output inductor current. In embodiments where PDU46 is not isolated, Il _ PDU may be the equivalent input current of PDU 46. The current error signal 120 goes to a proportional-integral (PI) current controller 122(PI _ I _ PDU), which may be implemented as a PI controller associated with PDU 46. The PDU current controller 122 uses the current error signal 120 to derive a PDU control command signal 124 that indicates the voltage required by the system as produced by the power converter of the PDU 46.

As shown, the ES cap 92 and PDU46 provide power output to the input of PS 48. As described above, control of the PS48 is also accomplished using the Icoil reference signal 91 provided to the gradient coils 30, 32, 34, the gradient amplifier filters, and the electrical model 126 of the gradient amplifier 50. The electrical model 126 outputs a feed forward control signal (IFF _ PS) for PS48, which is processed as discussed below.

The PS control block 104 also uses as input the Vo _ PS reference signal, which is the set point for the output voltage of PS48 (e.g., the voltage reference signal for PS48 corresponds to the target voltage at the output of PS 48). The voltage feedback signals for the output voltage (Vo _ PS) of PS48 and the Vo _ PS signal are used to generate the error signal 128 at operation 130. For example, the difference between the Vo _ PS feedback signal and the Vo _ PS reference signal may correspond to the error signal 128. In embodiments where there are multiple ports for PS48, the Vo _ PS feedback signal may be a function (e.g., a weighted sum or similar function) of the respective output voltages of these ports.

The error signal 128 may be used as an input to a PS voltage controller 132(PI _ V _ PS) configured to generate a PS feedback-derived control signal 134 for the PS 48. In the PS control block 104, at operation 136, the PS feedback derived control signal 134 is added to a feedforward control signal IFF _ PS (e.g., a feedforward current control signal) that is calculated in real time from the electrical model 126. The PS voltage controller 132 may be implemented as a PI controller associated with PS48, for example.

The sum of the PS feedback derived control signal 134 and the IlFF _ PS signal is used to generate a current error signal 138 by subtracting the current feedback signal (Il _ PS). As described above, Il _ PS is the feedback signal generated by PS output current sensor 94 and may be the output inductor current of PS 48. Further, in embodiments where there are multiple such current feedback signals, the actual feedback signal provided to operation 136 is a function of these multiple currents. The current error 138 is provided to a PS current controller (PI _ I _ PS)140 configured to generate a PS control signal 142 indicative of the system required voltage generated by the power converter of PS 48. PS current controller 140 may be implemented as a PI controller associated with PS48, for example.

In fig. 3, referring to the GA control block 106, at operation 146, a current error 144 is generated using the Icoil reference signal 91 and an Icoil feedback signal (e.g., a coil current feedback signal). The current error 144 is provided to a GA current controller 148(PI _ GA), which may be implemented as a proportional-integral (PI) controller associated with the GA 50. The GA current controller 148 generally helps to make the coil current follow the coil current reference value. The output of the GA current controller 148 is a feedback derived control signal 150 that is added to a feed forward control signal (Vff GA) for the gradient amplifier, which is calculated in real time by an electrical model 152 of the gradient amplifier and the gradient coils 30, 32, 34. At operation 154, the sum of these two commands forms an overall control command 156 that indicates the total voltage required by the gradient coils 30, 32, 34 produced by the power converter of the GA 50. It should be noted that this type of control for GA50 helps GA50 achieve a high accuracy along Icoil reference signal 91, minimizing the error between the reference signal and the actual current in gradient coils 30, 32, 34.

To demonstrate some of the effects of synchronous control according to the present invention, fig. 4-6 depict PS output voltages and output inductor currents generated in response to the use of a particular control strategy. In particular, fig. 4 depicts the PS output voltage and the PS inductor current generated using a strategy in which PS48 and GA50 are independently controlled without synchronization. As shown, when Icoil increases from zero to 1300A (e.g., as in a gradient pulse), a voltage dip of 75V is observed in the output voltage of PS 48. This output voltage is connected to the input of the power electronic bridge of GA 50. To account for this voltage sag, in this particular embodiment, each DC input of GA50 has a total capacitance of 7mF (e.g., one or more capacitors that provide a capacitance of 7 mF), so that a fast pulse of gradient coils 30, 32, 34 can be maintained. As can be seen from fig. 4, the PS inductor current profile does not rise fast enough to keep up with the voltage drop of the PS48 output voltage.

On the other hand, fig. 5 depicts the PS output voltage and output inductor current generated in response to using a synchronous control strategy, where the Icoil reference signal is used to synchronize the control of PS48 and GA 50. Here, for the same gradient coil current command as used in fig. 4 (zero to 1300A flat top profile), the voltage dip of the PS output voltage is reduced to 32V, and the output inductor current rises very quickly to reduce the voltage drop of the output voltage of PS 48. In this embodiment, the capacitance on each DC port of GA50 is kept at 7 mF.

because the voltage sag is significantly reduced when performing synchronous control, the capacitance requirements in the DC-link of GA50 can also be reduced. For the same gradient coil current command (1300A flat top) shown in fig. 4 and 5, using a 3mF capacitance on each DC port of the amplifier, the output voltage has a voltage dip of 75V. Comparing fig. 4 and fig. 6, after reducing the DC capacitance in GA50 from 7mF to 3mF, it can be seen that the voltage dip in the output voltage of PS48 is substantially the same, which means that synchronous control can be used to reduce the capacitance requirement in GA 50. It can also be seen that the PS inductor current profile follows the Icoil current command more closely than the PS inductor current profile shown in fig. 4.

In view of the foregoing, it will be appreciated that numerous technical advantages and technical effects may be achieved when implementing synchronous control of PDUs 46, PS48, and GA 50. For example, such synchronous control allows the power required by GA50 to be controlled faster to meet the Icoil current command. In practice, the control of PS48 does not depend solely on feedback control based on the voltage of the DC link, which is slow compared to the feed forward control scheme proposed herein. In practice, the PS48 may be programmed with load commands, and the PS48 will be momentarily ready to meet the power requirements of the inductive load (e.g., gradient coils 30, 32, 34). In addition, because the capacitance requirements of the gradient amplifier are reduced, the gradient amplifier may use smaller or fewer capacitors, thereby reducing its weight and volume. The control platform can also be simplified for the gradient chain 42. The dither frequency between the power source 48 and the gradient amplifier 50 may also be reduced due to more efficient use of the energy storage feature.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.