Radio frequency transmit device, magnetic resonance imaging system and method of operation

Abstract

This disclosure provides a radio frequency (RF) transmitting device, a magnetic resonance imaging (MRI) system, and an operating method. The RF transmitting device for the MRI system includes: a transmitting coil comprising a plurality of legs extending axially, the plurality of legs being arranged circumferentially at equal intervals around the axis of the transmitting coil; the plurality of legs including a plurality of first legs and a plurality of second legs arranged alternately, wherein each of the plurality of first legs includes a first portion and a second portion electrically isolated from each other; and a plurality of RF amplifiers, each of the plurality of RF amplifiers being integrated on one of the plurality of first legs, and the phase of the RF pulse signal output by each RF amplifier being individually adjustable.

Description

Technical Field

[0001] This disclosure relates to the field of magnetic resonance imaging technology, and in particular to a radio frequency transmitting device for a magnetic resonance imaging system, a magnetic resonance imaging system including such a radio frequency transmitting device, and a method for operating the radio frequency transmitting device for a magnetic resonance imaging system. Background Technology

[0002] Magnetic resonance imaging (MRI) is a medical application of nuclear magnetic resonance (NMR). It uses radio frequency (RF) pulses of a specific frequency to excite atomic nuclei placed in a static magnetic field, causing the spin axes of these nuclei to deviate and resonate. After the RF pulses are stopped, the excited nuclei emit echo signals, gradually releasing the absorbed energy in the form of electromagnetic waves, restoring their phase and energy levels to their pre-excitation state. Further processing, such as spatial coding, of the echo signals emitted by the nuclei allows for the reconstruction of an image.

[0003] The methods described in this section are not necessarily methods that had been previously conceived or adopted. Unless otherwise specified, no method described in this section should be assumed to be prior art simply because it is included in this section. Similarly, unless otherwise specified, the issues mentioned in this section should not be considered to be accepted in any prior art. Summary of the Invention

[0004] According to one aspect of the present disclosure, a radio frequency transmitting device for a magnetic resonance imaging system is provided, comprising: a transmitting coil including a plurality of legs extending axially, the plurality of legs being arranged circumferentially at equal intervals around the axis of the transmitting coil, the plurality of legs including a plurality of first legs and a plurality of second legs arranged alternately to each other, wherein each of the plurality of first legs includes a first portion and a second portion electrically isolated from each other; and a plurality of radio frequency amplifiers, each of the plurality of radio frequency amplifiers being integrated on one of the first legs, and the phase of a radio frequency pulse signal output by each radio frequency amplifier being individually adjustable.

[0005] According to another aspect of the present disclosure, a magnetic resonance imaging system is provided, comprising: a body coil; a gradient coil; and a radio frequency system, the radio frequency system including the aforementioned radio frequency transmitting device and receiving device, wherein the body coil serves as the transmitting coil of the radio frequency transmitting device.

[0006] According to another aspect of the present disclosure, a method for operating a radio frequency (RF) transmitter for a magnetic resonance imaging (MRI) system is provided, wherein the RF transmitter is configured as an RF transmitter according to the present disclosure, the method comprising: adjusting the phase of RF signal pulses output by each of a plurality of RF amplifiers of the RF transmitter to switch to a circular polarization mode or an elliptical polarization mode.

[0007] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0008] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings, so that those skilled in the art can more clearly understand the above and other features and advantages of this disclosure, in which:

[0009] Figure 1 A schematic diagram of a radio frequency transmitting device for a magnetic resonance imaging system according to an embodiment of the present disclosure is shown.

[0010] The accompanying figure is labeled as follows:

[0011] 10 radio frequency transmitters

[0012] 100 transmitting coil

[0013] 110 First Leg

[0014] 111 First leg, first part

[0015] 112 The second part of the first leg

[0016] 114 capacitor

[0017] 114' capacitor

[0018] 115 interval

[0019] 120 Second Leg

[0020] 121 The first part of the second leg

[0021] 122 The second part of the second leg

[0022] 126PIN diode

[0023] 130 Third Leg

[0024] 300 coaxial cable

[0025] 310 Internal Conductor

[0026] 320 external conductor

[0027] 400 RF Output Matching Unit Detailed Implementation

[0028] To provide a clearer understanding of the technical features, objectives, and effects of this disclosure, specific embodiments of this disclosure will now be described with reference to the accompanying drawings, in which the same reference numerals denote the same parts.

[0029] In this document, “illustrative” means “serving as an example, illustration or description”, and any illustration or implementation described herein as “illustrative” should not be construed as a more preferred or advantageous technical solution.

[0030] To keep the drawings concise, each drawing only schematically shows the parts relevant to this disclosure, and they do not represent the actual structure of the product. Furthermore, to facilitate understanding, in some drawings, components with the same structure or function are shown only schematically, or only one is labeled.

[0031] In this article, "one" can mean not only "only one" but also "more than one". In this article, "first", "second", etc., are used only to distinguish one from another, not to indicate their importance, order, or mutual dependence.

[0032] In magnetic resonance imaging (MRI), the subject is placed in the MRI system within a relatively strong and uniform static master magnetic field, also known as the B0 field. This field causes the nuclear spins of the subject to align along the static magnetic field lines. To trigger nuclear spin resonance, a radio frequency (RF) pulse is emitted towards the subject. After the RF pulse emission stops, the excited nuclei (e.g., the hydrogen nuclei of water molecules in the human body) gradually release the absorbed energy in the form of electromagnetic waves, restoring their phase and energy levels to their pre-excitation state. The signals received during this process are used to reconstruct the MR image. To spatially encode the received signals, a gradient magnetic field, distributed in three spatial directions, is superimposed on the static magnetic field.

[0033] Magnetic resonance imaging (MRI) systems typically include a magnet, such as a tubular superconducting magnet, to provide a uniform main magnetic field B0 along the magnet's axis. MRI systems also include gradient coils to generate gradient magnetic fields with gradients in the X, Y, and Z directions of space.

[0034] Magnetic resonance imaging (MRI) systems also include radio frequency (RF) systems. In magnetic resonance with a specific field strength, nuclei (such as the hydrogen nuclei of water molecules in the human body) have a specific precession frequency. To induce resonance in nuclei with this specific precession frequency, an RF pulse with the same precession frequency needs to be applied. The transmit coil of the RF system is used to transmit this RF pulse at this specific frequency. The body coil of the MRI system can be used as the transmit coil.

[0035] To induce resonance in a nucleus at a specific precession frequency, orthogonal radio frequency (RF) transmitting coils can be used. Two requirements apply to the RF pulse emitted by the orthogonal RF transmitting coil: the pulse frequency must be equal to the nucleus's precession frequency, and the polarization direction of the RF pulse must be the same as the nucleus's precession direction. For orthogonal RF transmitting coils, when two currents of equal magnitude but with a 90-degree phase difference are input from two coupling points, a circularly polarized RF field can be generated. In related technologies, this can be achieved through an RF system including an RF generator, an RF amplifier, a transmit antenna selector (TAS), a body coil channel selector (BCCS), a transmit antenna level sensor (TALES), and a body coil used as the transmitting coil. The system comprises a radio frequency (RF) generator to generate the RF signal to be transmitted, an RF amplifier to amplify the RF signal, a transmit antenna switch to switch the output power of the RF amplifier to the body coil channel selector, and a body coil channel selector to split the RF signal input through the transmit antenna switch into two orthogonal (i.e., 90-degree phase difference) RF output signals. These output signals are then output to the transmit antenna level sensor via the RF output port, and subsequently to the two coupling points of the transmit coil via cables, thereby generating a circularly polarized RF field. However, this RF system is complex, requires numerous components, and can only generate a circularly polarized RF field. To achieve an elliptically polarized RF field, an additional phase shifting element is needed in the body coil channel selector, further complicating the RF system's structure.

[0036] Embodiments of this disclosure provide a radio frequency (RF) transmitting device for a magnetic resonance imaging (MRI) system, including a transmitting coil and a plurality of RF transmitters. The transmitting coil includes a plurality of legs extending axially and uniformly arranged circumferentially around the axis of the transmitting coil. The plurality of legs includes a plurality of first legs and a plurality of second legs, wherein the plurality of first legs are arranged at equal angular intervals along the circumferential direction of the transmitting coil, and each first leg includes a first portion and a second portion electrically isolated from each other. Each of the plurality of RF amplifiers is integrated onto one of the first legs, and the phase of the RF pulse signal output by each RF amplifier can be individually adjusted.

[0037] Compared to related technologies that require multiple components in their radio frequency (RF) transmission systems, the embodiments disclosed herein reduce the number of required electronic components by integrating multiple RF amplifiers on the transmit coil, each with individually adjustable phases. In particular, this eliminates the need for the BCCS module and the TX cable transmitting RF signals to the transmit coil, thus lowering manufacturing costs and improving the overall reliability of the RF transmission device. Furthermore, the phase difference of the RF signals transmitted to each leg of the transmit coil can be freely controlled to provide different RF fields, thereby meeting the needs of various applications. In addition, it can excite a magnified field of view (FoV), reduce shading and distortion, and improve the quality of magnetic resonance imaging.

[0038] refer to Figure 1 , Figure 1 A schematic diagram of a radio frequency transmitting device 10 for a magnetic resonance imaging system according to an embodiment of the present disclosure is shown.

[0039] like Figure 1 As shown, the radio frequency transmitting device 10 includes a transmitting coil 100, which has a cage-like structure and consists of multiple legs extending axially. The legs of the transmitting coil 100 are arranged circumferentially around the axis of the transmitting coil. The radio frequency transmitting device 10 also includes multiple radio frequency amplifiers 200, which are integrated on the transmitting coil 100.

[0040] exist Figure 1 In the illustrated embodiment, the transmitting coil 100 includes 16 legs evenly arranged circumferentially. Of the 16 legs, eight are first legs and eight are second legs, arranged alternately. The first legs, for example... Figure 1 The first leg 110 or the other first leg 130 shown is separated into two parts, namely the first part 111 and the second part 112, by a gap or slit 115, thereby electrically isolating the first part 111 and the second part 112. In other embodiments, instead of the gap or slit 115, the first part 111 and the second part 112 may also be electrically isolated from each other by an insulator disposed therebetween.

[0041] Eight first legs are arranged circumferentially around the axis of the transmitting coil 100 at equal intervals of 45 degrees, for example, one first leg 110 is spaced 45 degrees from another first leg 130. An RF amplifier 200 is integrated on each of the eight first legs. Figure 1 The diagram only shows one RF amplifier, which is connected in series with legs such as a first portion 111 and a second portion 112 that are electrically isolated from each other. Therefore, since the first legs of the integrated RF amplifier are arranged at equal angular intervals circumferentially around the axis of the transmitting coil, the resulting RF field is more uniform. The phase of the RF pulse signal output by each RF amplifier 120 can be adjusted individually. For example, in... Figure 1One of the radio frequency (RF) amplifiers is shown. Each RF amplifier 200 forms multiple signal loops between its first leg and second leg, for example, one RF amplifier 200 with each of every two circumferentially adjacent legs of the transmitting coil 100 (e.g., Figure 1 The first leg 110 and the second leg 120, which are adjacent in the circumferential direction, form a signal loop, and the legs that are spaced apart in the circumferential direction form another signal loop, which is integrated on one of the legs (e.g., the first leg 110). The multiple signal loops work together to form a radio frequency field.

[0042] In some embodiments, such as Figure 1 As shown, each first leg 100 includes a coaxial cable 300, which includes an inner conductor 310 and an outer conductor 320. The inner conductor 310 may be wire-like, and the outer conductor 320 may be sleeve-like and fitted around the outer periphery of the inner conductor 310. The coaxial cable 300 is disposed on the first leg 110, wherein the outer conductor 320 is disposed on the first portion 111 of the first leg 110, and the wire-like inner conductor 310 passes through the sleeve-like outer conductor 320 and extends a certain distance. One end of the inner conductor 310 is connected to the output terminal of the RF amplifier 200, and the other end is connected to the second portion 112 of the first leg 110. It should be noted that, in order to avoid short circuits, the inner conductor 310 is insulated from the first portion 111. For example, the portion of the inner conductor 310 extending from the outer conductor 320 is suspended on the first portion 111, and approaches the second portion 112 after passing through the gap 115, thereby connecting with the second portion 112. Alternatively, the surface of the portion of the inner conductor 310 extending from the outer conductor 320 can be covered with an insulating material such as rubber, thus achieving insulation even if the inner conductor 310 comes into contact with the first portion 111, preventing short circuits. The inner conductor 310 and the outer conductor 320 are coaxially arranged and electrically insulated from each other. An insulating material such as rubber is provided between the inner conductor 310 and the outer conductor 320, thereby electrically insulating the inner conductor 310 and the outer conductor 320 from each other.

[0043] With this connection method, the inner conductor 310 and the outer conductor 320 form two poles of a signal loop, so that the pulse signal emitted from the radio frequency amplifier 200 starts from the end of the inner conductor 310 connected to the radio frequency amplifier 200, passes through the inner conductor 310, the second part 112 of the first leg 110, the second leg 120, and finally returns to the first part 111 of the first leg 110 at the starting position and the outer conductor 320 disposed on the first part 111.

[0044] The integration of the RF amplifier 200 onto the transmitting coil 100 eliminates the need for a long cable between the two for transmitting RF signals. At the same time, the lower resistance significantly reduces energy loss in the signal loop due to impedance, thereby reducing the power required for device operation.

[0045] For example, such as Figure 1 As shown, each leg of the transmitting coil has loop-shaped portions at both ends, making each leg roughly an elongated "I" shape. The loop-shaped portions at the left ends of the first leg 110 and the second leg are connected by a capacitor 114', and the loop-shaped portions at the right ends of the first leg 110 and the second leg are connected by a capacitor 114'. It can be understood that the capacitor allows alternating current to pass through, and since the radio frequency pulse is also an alternating signal, this allows the AC signal to flow between the first and second legs, forming a signal loop for the radio frequency pulse. Simultaneously, because the capacitor has low impedance to alternating current, compared to general resistive components, it can significantly reduce energy loss caused by impedance in the signal loop, reducing the power required for device operation.

[0046] According to some embodiments, each second leg 120 includes a detuning unit connected to a bias power supply (not shown) and located on either the first leg 110 or the second leg 120, for example, on a second leg 120 without a coaxial cable. The bias power supply provides a bias current, which, after the detuning unit receives the bias current, allows AC signals to flow. When the bias power supply is turned off, the detuning unit 126 is in an off state, preventing AC signals from passing through, thereby cutting off the signal loop of the radio frequency pulse. Multiple detuning units on the transmitting coil simultaneously disconnect, achieving detuning of the transmitting coil.

[0047] Exemplarily, the second leg 120 includes a spaced-apart first portion 121 and second portion 122, with a detuning unit connected between the first portion 121 and the second portion 122 of the second leg 120. In some examples, the detuning unit is a PIN diode 126. It is understood that the detuning unit is not limited to a PIN diode, but can be any electronic component capable of switching between open and closed states in response to a bias current.

[0048] It should be noted that in this embodiment, a first leg is uniformly arranged at 45-degree intervals in the circumferential direction in each leg of the transmitting coil and an RF amplifier 200 is arranged on the first leg. However, it is not limited to this. The first legs can also be arranged at other angles and at equal intervals in the circumferential direction of the transmitting coil. For example, the first legs can be arranged at 90-degree intervals and an RF amplifier can be arranged on each first leg, so that the other legs are constructed as second legs.

[0049] In magnetic resonance imaging (MRI), the transmission of radio frequency (RF) signals and the reception of magnetic resonance (MRI) signals alternate at different times to avoid mutual interference and reduced imaging accuracy. Therefore, during MRI signal reception, the bias power supply is turned off, disconnecting the detuning unit and detuning the signal circuit, thus shutting off RF transmission and preventing interference with the received MRI signal.

[0050] To achieve detuning, existing technologies typically require a PIN diode on each leg of the transmitting coil. In contrast, embodiments of this disclosure can place the PIN diode only on the second leg 120, which is one of the two legs in a signal loop. This means placing the PIN diode on the leg without an RF amplifier, requiring only half the number of legs of the transmitting coil, thus saving half the number of PIN diodes and significantly reducing costs.

[0051] According to some embodiments, an RF output matching unit 400 is provided between the output of each RF amplifier 200 and the transmitting coil 100 (specifically, the first leg of the integrated RF amplifier) ​​to reduce the reflection coefficient of the RF amplifier, thereby improving power output efficiency. For example, as... Figure 1 As shown, an RF output matching unit 400 is positioned between the left side of the RF amplifier 200 and the right side of the transmitting coil 100. The internal conductor 310 of the coaxial cable is connected to the RF output matching unit 400. It can be understood that by adding this electronic component, the RF output matching unit 400, the reflection coefficient of the RF amplifier can be reduced, thereby improving the power output efficiency.

[0052] According to some embodiments, the transmitting coil 100 is a body coil. In some examples, the body coil 100 serves as both a transmitting coil and a receiving coil to receive magnetic resonance signals. In other examples, the body coil 100 serves as a transmitting coil, and the body coil serves as a receiving coil.

[0053] According to some embodiments, multiple legs of the transmitting coil 100 are interconnected by capacitors, thereby preventing DC signals other than AC signals from flowing in the cage coil and enabling independent control of each RF amplifier.

[0054] According to another aspect of the present disclosure, a magnetic resonance imaging system is provided, comprising: a body coil; a gradient coil; and a radio frequency system, the radio frequency system including a radio frequency transmitting device and a receiving device according to any of the above embodiments, wherein the body coil serves as the transmitting coil of the radio frequency transmitting device.

[0055] According to some embodiments, the magnetic resonance imaging system further includes a water-cooling system for the gradient coil, wherein the water-cooling system also cools multiple radio frequency amplifiers integrated on the transmit coil of the radio frequency transmitting device. In this way, it is not necessary to set up an additional cooling system for the radio frequency amplifiers.

[0056] In some embodiments, a local coil arranged on the object to be inspected serves as a receiving coil of the receiving device. For example, a local coil arranged on the abdomen, head, elbow, or knee of a human body serves as a receiving coil.

[0057] According to another aspect of the present disclosure, a method for operating a radio frequency (RF) transmitter for a magnetic resonance imaging (MRI) system is provided, wherein the RF transmitter is configured as the RF transmitter according to any of the above embodiments, the method comprising: adjusting the phase of RF signal pulses output by each of a plurality of RF amplifiers of the RF transmitter to switch to a circular polarization mode or an elliptical polarization mode.

[0058] Operators of magnetic resonance imaging (MRI) systems can individually adjust the output phase of each radio frequency amplifier based on the specific application, such as the shape of the imaging site. This involves selecting either circular or elliptical polarization mode to generate a circularly or elliptically polarized radio frequency field in the transmit coil. For example, when scanning the abdomen, elliptical polarization mode can be used; when scanning the head, circular polarization mode can be used.

[0059] According to another aspect of the present disclosure, a non-transitory computer-readable storage medium storing a computer program is provided, wherein the computer program, when executed by a processor, implements the method according to any of the above embodiments.

[0060] According to another aspect of the embodiments of this disclosure, a computer program product is provided, comprising a computer program, wherein the computer program, when executed by a processor, implements the method described according to any of the above embodiments. Program code for implementing the methods of this disclosure may be written in any combination of one or more programming languages. This program code may be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus, such that when executed by the processor or controller, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may be executed entirely on a machine, partially on a machine, partially on a remote machine as a standalone software package, or entirely on a remote machine or server.

[0061] In the context of this disclosure, a computer-readable storage medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A computer-readable medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination thereof.

[0062] While embodiments or examples of this disclosure have been described with reference to the accompanying drawings, it should be understood that the methods, systems, and devices described above are merely exemplary embodiments or examples, and the scope of this disclosure is not limited by these embodiments or examples, but rather by the claims and their equivalents. Various elements in the embodiments or examples may be omitted or substituted with their equivalents. Furthermore, the steps may be performed in a different order than that described in this disclosure. Moreover, various elements in the embodiments or examples may be combined in various ways.

Claims

1. A radio frequency transmitting device for a magnetic resonance imaging system, comprising: A transmitting coil comprising a plurality of legs extending axially and uniformly arranged circumferentially around the axis of the transmitting coil, the plurality of legs including a plurality of first legs and a plurality of second legs, wherein the plurality of first legs are arranged at equal angular intervals circumferentially around the transmitting coil, and each first leg includes a first portion and a second portion electrically isolated from each other; and Multiple radio frequency amplifiers are provided, each of which is integrated on the first leg, and the phase of the radio frequency pulse signal output by each radio frequency amplifier can be adjusted individually.

2. The radio frequency launch of claim 1, wherein, Each of the plurality of first legs further includes: A coaxial cable comprising an inner conductor and an outer conductor that are coaxially arranged and electrically insulated from each other, wherein the outer conductor is connected to a first portion of a first leg, and the inner conductor is connected between the output of the RF amplifier and a second portion of the first leg.

3. The radio frequency transmitting device according to claim 1 or 2, wherein, A first portion of each of the plurality of first legs is connected via a first capacitor to a first end of an adjacent second leg, and a second portion of each of the first legs is connected via a second capacitor to a second end of an adjacent second leg.

4. The radio frequency transmitting device according to claim 1 or 2, wherein, Each of the plurality of second legs includes: A detuning unit for detuning the transmitting coil, wherein the detuning unit includes a PIN diode connected in series between the first and second portions of the second leg.

5. The radio frequency transmitting device according to claim 1 or 2, wherein, An RF output matching unit is provided between the output terminal of each of the plurality of RF amplifiers and the transmitting coil to reduce the reflection coefficient of the RF amplifiers.

6. The radio frequency transmitting device according to claim 1 or 2, wherein the transmitting coil comprises 2n legs arranged at equal intervals along the circumference, wherein, n is a natural number. Among them, the 2n-1th leg along the circumference is the first leg, and the 2nth leg is the second leg.

7. The radio frequency transmitting device according to claim 6, wherein, n is 2 or 8.

8. The radio frequency transmitting device according to claim 1 or 2, wherein, The transmitting coil is a body coil.

9. The radio frequency transmitting device according to claim 1 or 2, wherein, The multiple legs are interconnected via capacitors.

10. A magnetic resonance imaging system, comprising: Body coil; Gradient coil; as well as A radio frequency system, the radio frequency system comprising a radio frequency transmitting device and a receiving device according to any one of claims 1 to 9, wherein the body coil serves as the transmitting coil of the radio frequency transmitting device.

11. The magnetic resonance imaging system according to claim 10, further comprising: The water cooling system is used for the gradient coil, wherein the water cooling system is also used to cool the multiple radio frequency amplifiers integrated on the transmitting coil of the radio frequency transmitting device.

12. A method of operating a radio frequency transmitting device for a magnetic resonance imaging system, wherein, The radio frequency transmitting device is configured as the radio frequency transmitting device according to any one of claims 1 to 9. The method includes: The phase of the radio frequency signal pulses output by each of the multiple radio frequency amplifiers of the radio frequency transmitting device is adjusted to switch to circular polarization mode or elliptical polarization mode.

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