CN116687375A - Radio frequency transmitting device, magnetic resonance imaging system and operation method - Google Patents

Abstract

The present disclosure provides a radio frequency transmitting device, a magnetic resonance imaging system and an operating method. A radio frequency transmit apparatus for a magnetic resonance imaging system comprising: a transmit coil comprising a plurality of legs extending in an axial direction, the plurality of legs being circumferentially arranged at equally spaced angles about an axis of the transmit coil, the plurality of legs comprising a plurality of first legs and a plurality of second legs arranged alternately with each other, wherein each of the plurality of first legs comprises 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 a respective one of the plurality of first legs, and a phase of a radio frequency pulse signal output by each of the plurality of radio frequency amplifiers being individually adjustable.

Description

Radio frequency transmitting device, magnetic resonance imaging system and operation method

Technical Field

The present 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 comprising such a radio frequency transmitting device, and a method of operating a radio frequency transmitting device for a magnetic resonance imaging system.

Background

Magnetic Resonance Imaging (MRI) is one application of Nuclear Magnetic Resonance (NMR) in medicine. Nuclei in a static magnetic field are excited by Radio Frequency (RF) pulses of a specific Frequency, so that spin axes of the nuclei deviate and resonance occurs. After stopping transmitting the radio frequency pulse, the excited atomic nuclei transmit echo signals, gradually release the absorbed energy in the form of electromagnetic waves, and the phase and the energy level of the electromagnetic waves are restored to the state before excitation. The echo signals emitted by the atomic nuclei are subjected to further processing such as spatial encoding, and the like, so that an image can be reconstructed.

The approaches described in this section are not necessarily approaches that have been previously conceived or pursued. Unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, the problems mentioned in this section should not be considered as having been recognized in any prior art unless otherwise indicated.

Disclosure of Invention

According to an aspect of an embodiment of the present disclosure, there is provided a radio frequency transmitting apparatus for a magnetic resonance imaging system, including: a transmit coil comprising a plurality of legs extending in an axial direction, the plurality of legs being circumferentially arranged at equally spaced angles about an axis of the transmit coil, the plurality of legs comprising a plurality of first legs and a plurality of second legs arranged alternately with each other, wherein each of the plurality of first legs comprises 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 plurality of first legs, and a phase of a radio frequency pulse signal output by each of the plurality of radio frequency amplifiers being individually adjustable.

According to another aspect of an embodiment of the present disclosure, there is provided a magnetic resonance imaging system comprising: a body coil; a gradient coil; the radio frequency system comprises the radio frequency transmitting device and the receiving device, wherein the body coil is used as a transmitting coil of the radio frequency transmitting device.

According to another aspect of the disclosed embodiments, a method of operating a radio frequency transmitting device for a magnetic resonance imaging system is presented, wherein the radio frequency transmitting device is configured as a radio frequency transmitting device according to an embodiment of the disclosure, the method comprising: and adjusting the phase of the radio frequency signal pulse output by each of the plurality of radio frequency amplifiers of the radio frequency transmitting device so as to switch to a circular polarization mode or an elliptical polarization mode.

It should be understood that the description in this section is not intended to identify key or critical features of the embodiments of the disclosure, nor is it intended to be used to limit the scope of the disclosure. Other features of the present disclosure will become apparent from the following specification.

Drawings

The above and other features and advantages of the present disclosure will become more apparent to those of ordinary skill in the art by describing in detail embodiments thereof with reference to the attached drawings, in which:

figure 1 shows a schematic diagram of a radio frequency transmitting device for a magnetic resonance imaging system according to an embodiment of the present disclosure.

Wherein, the reference numerals are as follows:

10 radio frequency transmitting device

100 transmitting coil

110 first leg

First portion of first leg 111

112 second portion of the first leg

114 capacitor

114' capacitance

115 intervals

120 second leg

121 first portion of second leg

122 second portion of the second leg

126PIN diode

130 third leg

300 coaxial cable

310 inner conductor

320 outer conductor

400 radio frequency output matcher

Detailed Description

For a clearer understanding of the technical features, objects, and effects of the present disclosure, specific embodiments of the disclosure will now be described with reference to the drawings in which like reference numerals represent like parts throughout the several views.

In this document, "schematic" means "serving as an example, instance, or illustration," and any illustrations, embodiments described herein as "schematic" should not be construed as a more preferred or advantageous solution.

For simplicity of the drawing, only the portions relevant to the present disclosure are schematically shown in each drawing, which do not represent the actual structure thereof as a product. Additionally, in order to simplify the drawing for ease of understanding, components having the same structure or function in some of the drawings are shown schematically with only one of them, or only one of them is labeled.

Herein, "a" means not only "only this one" but also "more than one" case. Herein, "first", "second", etc. are used merely to distinguish one from another, and do not indicate their importance and order, and preconditions for existence of one another, etc.

During magnetic resonance imaging, the object to be examined is placed in a magnetic resonance imaging system in a relatively strong and homogeneous static main magnetic field, also called B0 field, so that the nuclear spins of the object to be examined are oriented along the static magnetic field lines. In order to trigger nuclear spin resonance, a radio frequency pulse (RF pulse) is emitted toward the object to be examined. After stopping the emission of the radio frequency pulse, the excited nuclei (e.g. hydrogen nuclei of water molecules in the human body) release the absorbed energy gradually in the form of electromagnetic waves, the phase and energy level of which are restored to the pre-excitation state, and the signals received during this process are used for the reconstruction of MR images. In order to spatially encode the received signal, a gradient magnetic field is superimposed on the static magnetic field, which gradient magnetic field is distributed in three directions in space.

Magnetic resonance imaging systems typically comprise a magnet, e.g. a tube-shaped superconducting magnet, for providing a uniform main magnetic field B0 in the direction of the magnet axis. The magnetic resonance imaging system further comprises gradient coils for generating a gradient magnetic field having a gradient in the X, Y, Z direction of the space.

The magnetic resonance imaging system further comprises a radio frequency system. In magnetic resonance at a specific field strength, the nuclei (e.g. hydrogen nuclei of water molecules in the human body) have a specific precession frequency. To resonate a nucleus having this particular precession frequency, a radio frequency pulse is applied that corresponds to the precession frequency. The transmit coil of the radio frequency system may be used to transmit radio frequency pulses of this particular frequency. The body coil of the magnetic resonance system may be used as a transmit coil.

To excite nuclei at a particular precession frequency to resonate, a quadrature radio frequency transmit coil may be employed. There are two requirements for the radio frequency pulse emitted by the orthogonal radio frequency emitting coil, one is that the pulse frequency is equal to the precession frequency of the core, and the other is that the polarization direction of the radio frequency pulse is the same as the precession direction of the core. In the case of a quadrature radio frequency transmit coil, when two currents of equal magnitude but 90 degrees out of phase are input from two coupling points, a circularly polarized radio frequency field is excited. In the related art, this can be achieved by a radio frequency system including a radio frequency generator, a radio frequency amplifier, a transmit antenna switching switch (Transmit Antenna Selector, TAS), a body coil channel selector (Body Coil Chanel Selector, BCCS), a transmit antenna level sensor (Transmit Antenna Level Sensor, TALES), and a body coil serving as a transmit coil. The radio frequency generator is used for generating radio frequency signals to be transmitted, the radio frequency amplifier is used for amplifying the radio frequency signals to be transmitted, the transmitting antenna change-over switch is used for switching and outputting the output power of the radio frequency amplifier to the body coil channel selector, and the body coil channel selector is used for dividing one path of radio frequency signals input through the transmitting antenna change-over switch into two paths of radio frequency output signals which are orthogonal (namely, 90 degrees out of phase), and outputting the two paths of radio frequency output signals to the transmitting antenna level sensor through the radio frequency output port, and outputting the two paths of radio frequency signals to two coupling points of the transmitting coil through a cable, so that a circularly polarized radio frequency field is excited to be generated. However, the rf system has a complex structure, requires a plurality of components, and can only generate a circularly polarized rf field. To achieve an elliptically polarized rf field, additional phase shifting elements are also provided in the body coil channel selector, which makes the structure of the rf system more complex.

Embodiments of the present disclosure provide a radio frequency transmit apparatus for a magnetic resonance imaging system, comprising a transmit coil and a plurality of radio frequency transmitters. The transmitting coil includes a plurality of legs extending in an axial direction, the plurality of legs being uniformly arranged in a circumferential direction around an 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 equally spaced angles in 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 radio frequency amplifiers is integrally provided on one of the plurality of first legs, respectively, and the phase of the radio frequency pulse signal output by each of the radio frequency amplifiers can be individually adjusted.

Compared with a radio frequency transmitting system requiring various components in the related art, the embodiment of the disclosure reduces the number of required electronic components through the plurality of radio frequency amplifiers which are integrated on the transmitting coil and can independently adjust the phase, particularly omits a BCCS module and a TX cable for transmitting radio frequency signals to the transmitting coil, reduces the manufacturing cost and improves the overall reliability of the radio frequency transmitting device. Furthermore, the phase difference of the radio frequency signals transmitted into the respective legs of the transmitting coil can be freely controlled to provide different radio frequency fields, thereby meeting the requirements of different applications. In addition, the enlarged field of view (FoV) can be excited, shadows and distortions reduced, providing the quality of magnetic resonance imaging.

Referring to fig. 1, fig. 1 shows a schematic diagram of a radio frequency transmitting device 10 for a magnetic resonance imaging system according to one embodiment of the present disclosure.

As shown in fig. 1, the radio frequency transmission device 10 includes a transmission coil 100 having a cage-like structure formed of a plurality of axially extending legs. The legs of the transmit coil 100 are arranged circumferentially about the axis of the transmit coil. The radio frequency transmitting device 10 further comprises a plurality of radio frequency amplifiers 200, the radio frequency amplifiers 200 being integrated on the transmitting coil 100.

In the embodiment shown in fig. 1, the transmitting coil 100 includes 16 legs uniformly arranged in the circumferential direction. Of the 16 legs, there are eight first legs and eight second legs, the first legs and the second legs being alternately arranged. A first leg, such as one first leg 110 or the other first leg 130 shown in fig. 1, is separated into left and right portions, i.e., first portion 111 and second portion 112, by a gap or slit 115, electrically isolating first portion 111 from second portion 112. In other embodiments, instead of the gap or slit 115, the first portion 111 and the second portion 112 may also be electrically isolated from each other by an insulator disposed therebetween.

The eight first legs are circumferentially arranged at equally spaced angles of 45 degrees about the axis of the transmit coil 100, for example one first leg 110 is spaced at an angle of 45 degrees from the other first leg 130. One radio frequency amplifier 200 (only one is illustrated in fig. 1) is integrated on each of the eight first legs, i.e. in series on such legs comprising a first portion 111 and a second portion 112 electrically isolated from each other. Therefore, the first legs of the integrated radio frequency amplifier are distributed at equal angular intervals along the circumferential direction around the axis of the transmitting coil, so that the formed radio frequency field is more uniform. The phase of the rf pulse signal output by each rf amplifier 120 can be adjusted individually. One of which is shown in fig. 1, by way of example. Each of the radio frequency amplifiers 200 forms a plurality of signal loops between the first leg and the second leg thereof, for example, one radio frequency amplifier 200 forms one signal loop with each two circumferentially adjacent legs (e.g., the circumferentially adjacent first leg 110 and the second leg 120 in fig. 1) of the transmitting coil 100, forms another signal loop with the leg circumferentially spaced from the other legs, and is integrated on one of the legs (e.g., the first leg 110). The plurality of signal loops cooperate to form a radio frequency field.

In some embodiments, as shown in fig. 1, each first leg 100 includes a coaxial cable 300, the coaxial cable 300 including an inner conductor 310 and an outer conductor 320, the inner conductor 310 may be wire-shaped, and the outer conductor 320 may be sleeve-shaped and fit around the outer circumference 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-shaped inner conductor 310 passes through the sleeve-shaped outer conductor 320 and protrudes a distance, one end of the inner conductor 310 being connected to the output terminal of the radio frequency amplifier 200, and the other end being connected to the second portion 112 of the first leg 110. It is noted that the inner conductor 310 is insulated from the first portion 111 in order to avoid a short circuit. For example, the portion of the inner conductor 310 that extends from the outer conductor 320 overhangs the first portion 111 and approaches the second portion 112 after passing through the space 115, thereby connecting with the second portion 112. The surface of the portion of the inner conductor 310 extending from the outer conductor 320 may be covered with an insulator such as rubber, so that insulation can be achieved even when the inner conductor 310 contacts the first portion 111, and short-circuiting can be avoided. The inner conductor 310 is disposed coaxially with the outer conductor 320 and is electrically insulated from each other. An insulating material such as rubber is provided between the inner conductor 310 and the outer conductor 320, so that the inner conductor 310 and the outer conductor 320 are electrically insulated from each other.

By this connection, the internal conductor 310 and the external conductor 320 serve as two poles of one signal loop, so that the pulse signal emitted from the radio frequency amplifier 200 starts from the end of the internal conductor 310 connected to the radio frequency amplifier 200, passes through the internal conductor 310, the second portion 112 of the first leg 110, the second leg 120, and finally returns to the first portion 111 of the first leg 110 at the starting position and the external conductor 320 provided on the first portion 111.

The integration of the rf amplifier 200 on the transmitting coil 100 eliminates the need for long cables therebetween for transmitting rf signals, while having a lower resistance, thereby greatly reducing the energy loss in the signal loop due to impedance and reducing the power required for operation of the device.

Illustratively, as shown in fig. 1, each leg of the transmitting coil has a loop segment at both ends such that each leg is generally in the shape of an elongated "i" shape, the loop segment at the left end of the first leg 110 being connected to the loop segment at the left end of the second leg by a capacitor 114', the loop segment at the right end of the first leg 110 being connected to the loop segment at the right end of the second leg by a capacitor 114. It will be appreciated that the capacitor allows the alternating current to pass through and that the radio frequency pulse is also an alternating signal, thereby enabling the alternating signal to flow between the first leg and the second leg, forming a signal loop for the radio frequency pulse. Meanwhile, as the impedance of the capacitor to alternating current is smaller, compared with a common resistor component, the energy loss caused by impedance in a signal loop can be greatly reduced, and the power required by the operation of equipment is reduced.

According to some embodiments, each second leg 120 comprises: 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 the second leg 120 where no coaxial cable is provided. The bias power supply provides bias current, after the detuning unit receives the bias current, the detuning unit can circulate alternating current signals, after the bias power supply is turned off, the detuning unit 126 is in a disconnected state, the alternating current signals cannot pass through, so that a signal loop of radio frequency pulses is cut off, and a plurality of detuning units on a transmitting coil are simultaneously disconnected, so that detuning of the transmitting coil is realized.

Illustratively, the second leg 120 includes first and second spaced apart portions 121, 122, with the detuning unit connected between the first and second portions 121, 122 of the second leg 120. In some examples, the detuning unit is a PIN diode 126. It will be appreciated that the detuning unit is not limited to a PIN diode, as long as it is an electronic component capable of achieving an open-close switching in response to a bias current.

In the present embodiment, one first leg is uniformly provided in each leg of the transmitting coil at an angle of 45 degrees in the circumferential direction and the radio frequency amplifier 200 is provided on the first leg, but the present invention is not limited thereto, and the first legs may be equally provided in the circumferential direction of the transmitting coil at other angles, for example, the first legs may be provided at intervals of 90 degrees and the radio frequency amplifier may be provided on each first leg so that the other legs are configured as second legs.

In the magnetic resonance imaging process, the transmitting radio frequency signal and the receiving magnetic resonance signal are respectively and alternately carried out at different time points, so that the mutual interference between the transmitting radio frequency signal and the receiving magnetic resonance signal is avoided, and the imaging precision is reduced. For this purpose, during reception of the magnetic resonance signals, the bias power supply is turned off, the detuning unit is put in an off-state, and the signal loop is detuned, so that the radio frequency transmission is turned off, and interference with reception of the magnetic resonance signals is avoided.

In order to achieve detuning, it is often necessary in the prior art to provide a PIN diode on each leg of the transmit coil. Compared with the prior art, the embodiment of the disclosure can only set the PIN diode on the second leg 120 among the two legs of one signal loop, namely set the PIN diode on the leg without the radio-frequency amplifier, only set the PIN diode on half of the legs of the transmitting coil, thereby saving half of the PIN diodes and greatly reducing the cost.

According to some embodiments, a radio frequency output matcher 400 is provided between the output end of each radio frequency amplifier 200 and the transmitting coil 100 (specifically, the first leg of the radio frequency amplifier is integrated) for reducing the reflection coefficient of the radio frequency amplifier, thereby improving the power output efficiency. Illustratively, as shown in fig. 1, a radio frequency output matcher 400 is provided between the left side of the radio frequency amplifier 200 and the right side of the transmitting coil 100. At this time, the inner conductor 310 of the coaxial cable is connected to the radio frequency output matching unit 400. It can be appreciated that by adding an electronic component such as the rf output matcher 400, the reflection coefficient of the rf amplifier can be reduced, thereby improving the power output efficiency.

According to some embodiments, the transmit coil 100 is a body coil. In some examples, the body coil 100 serves as both a transmit coil and a receive coil to receive magnetic resonance signals. In other examples, the body coil 100 acts as a transmit coil and the local coil acts as a receive coil.

According to some embodiments, the legs of the transmit coil 100 are all connected to each other by a capacitor, thereby avoiding the circulation of dc signals other than ac signals in the cage coil and enabling independent control of each rf amplifier.

According to another aspect of the disclosed embodiments, there is provided a magnetic resonance imaging system comprising: a body coil; a gradient coil; and a radio frequency system comprising a radio frequency transmitting device according to any of the above embodiments and a receiving device, wherein the body coil is used as a transmitting coil of the radio frequency transmitting device.

According to some embodiments, the magnetic resonance imaging system further comprises: a water cooling system for a gradient coil, wherein the water cooling system is further used for cooling a plurality of radio frequency amplifiers of a radio frequency transmitting device integrated on the transmitting coil. In this way, no additional cooling system for the radio frequency amplifier may be necessary.

According to some embodiments, a local coil arranged on the object to be examined is used as a receiving coil of the receiving means. For example, a local coil disposed on the abdomen, head, elbow, or knee of a human body is used as the receiving coil.

According to another aspect of the disclosed embodiments, there is provided 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 of the above embodiments, the method comprising: the phase of the radio frequency signal pulse output by each of the plurality of radio frequency amplifiers of the radio frequency transmitting device is adjusted to switch to a circular polarization mode or an elliptical polarization mode.

An operator of the magnetic resonance imaging system can independently adjust the output phase of each radio frequency amplifier according to practical application conditions, such as the shape of an imaging part, and the like, namely, a circular polarization mode or an elliptical polarization mode is selected, so that the transmitting coil generates a circularly polarized or elliptically polarized radio frequency field. For example, when scanning the abdomen, it is possible to switch to the elliptical polarization mode; when scanning the head, it can switch to circular polarization mode.

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

According to another aspect of the disclosed embodiments, there is provided a computer program product comprising a computer program, wherein the computer program, when executed by a processor, implements a method according to any of the above embodiments. Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program code may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus such that the program code, when executed by the processor or controller, causes the functions/operations specified in the flowchart and/or block diagram to be implemented. The program code may execute entirely on the machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

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

Although embodiments or examples of the present disclosure have been described with reference to the accompanying drawings, it is to be understood that the foregoing methods, systems, and apparatus are merely illustrative embodiments or examples and that the scope of the present disclosure is not limited by these embodiments or examples but is defined by the claims and their equivalents. Various elements of the embodiments or examples may be omitted or replaced with equivalent elements thereof. Furthermore, the steps may be performed in a different order than described in the present disclosure. Further, various elements of the embodiments or examples may be combined in various ways.

Claims (12)

1. A radio frequency transmission device for a magnetic resonance imaging system, comprising:

a transmit coil comprising a plurality of legs extending in an axial direction, the plurality of legs being uniformly circumferentially arranged about an axis of the transmit coil, the plurality of legs comprising a plurality of first legs and a plurality of second legs, wherein the plurality of first legs are angularly equally spaced along the circumference of the transmit coil, and each first leg comprises a first portion and a second portion electrically isolated from each other; and

and each radio frequency amplifier in the plurality of radio frequency amplifiers is respectively and integrally arranged on the first leg, and the phase of a radio frequency pulse signal output by each radio frequency amplifier can be independently adjusted.

2. The radio frequency transmission device of claim 1, wherein each of the plurality of first legs further comprises:

a coaxial cable comprising an inner conductor and an outer conductor coaxially disposed and electrically insulated from each other, wherein the outer conductor is connected on a first portion of a first leg and the inner conductor is connected between an output of the radio frequency amplifier and a second portion of the first leg.

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

4. The radio frequency transmission device of claim 1 or 2, wherein each of the plurality of second legs comprises:

a detuning unit for detuning the transmit coil, wherein the detuning unit comprises a PIN diode connected in series between a first portion and a second portion of a second leg.

5. The radio frequency transmitting apparatus according to claim 1 or 2, wherein a radio frequency output matcher is provided between the respective output ends of the plurality of radio frequency amplifiers and the transmitting coil for reducing the reflection coefficient of the radio frequency amplifiers.

6. The radio frequency transmitting device as claimed in claim 1 or 2, wherein the transmitting coil comprises 2n legs arranged at equally spaced angles in the circumferential direction, wherein n is a natural number,

wherein the 2n-1 th leg in the circumferential direction is the first leg and the 2 n-th leg is the second leg.

7. The radio frequency transmission device of claim 6, wherein n is 2 or 8.

8. The radio frequency transmission device of claim 1 or 2, wherein the transmission coil is a body coil.

9. The radio frequency transmission device of claim 1 or 2, wherein the plurality of legs are connected to each other by a capacitance.

10. A magnetic resonance imaging system comprising:

a body coil;

a gradient coil; and

radio frequency system comprising a radio frequency transmitting device according to any of claims 1 to 9 and a receiving device, wherein the body coil is used as a transmitting coil of the radio frequency transmitting device.

11. The magnetic resonance imaging system of claim 10, further comprising:

a water cooling system for the gradient coil, wherein the water cooling system is further used for cooling a plurality of radio frequency amplifiers of the radio frequency transmitting device integrated on the transmitting coil.

12. A method of operating a radio frequency transmission device for a magnetic resonance imaging system, wherein the radio frequency transmission device is configured as a radio frequency transmission device according to any one of claims 1 to 9,

the method comprises the following steps:

and adjusting the phase of the radio frequency signal pulse output by each of the plurality of radio frequency amplifiers of the radio frequency transmitting device so as to switch to a circular polarization mode or an elliptical polarization mode.