CN115856738A - Magnetic resonance system and radio frequency transmitter thereof - Google Patents
Magnetic resonance system and radio frequency transmitter thereof Download PDFInfo
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- CN115856738A CN115856738A CN202211414012.XA CN202211414012A CN115856738A CN 115856738 A CN115856738 A CN 115856738A CN 202211414012 A CN202211414012 A CN 202211414012A CN 115856738 A CN115856738 A CN 115856738A
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Abstract
The invention discloses a magnetic resonance system and a radio frequency transmitter thereof, wherein the radio frequency transmitter comprises a signal processing unit, a switch unit, a signal modulation unit and a signal amplification module; the signal processing unit is used for processing the received baseband signal, outputting a target signal to one end of the switch unit, and controlling the other end of the switch unit to be connected with the input end of the signal amplification module or the input end of the signal modulation unit according to the relation between the target frequency and the reference frequency; the signal modulation unit is used for modulating the target signal; the output end of the signal modulation unit is connected with the input end of the signal amplification module; the signal amplification module is used for amplifying an input signal to obtain a radio frequency signal of the target frequency. The invention provides two signal transmitting paths according to the relation between different target frequencies and reference frequencies, and can ensure the phase stability of radio frequency signals to the maximum extent.
Description
Technical Field
The invention relates to the technical field of magnetic resonance systems, in particular to a magnetic resonance system and a radio frequency transmitter thereof.
Background
Clinical Magnetic Resonance (MR) systems have been derived from Nuclear Magnetic Resonance (NMR) spectroscopy devices. With the advancement of industrial technology, B of MR system 0 The strength of the field (main static magnetic field) can be increased continuously. MR system canFor Magnetic Resonance Imaging (MRI), but also for Magnetic Resonance Spectroscopy (MRS) and Magnetic Resonance Spectroscopy (MRSI). With B 0 The field enhancement, in MRS-like applications, 1 h and a plurality of non 1 The application of H nuclide (multi-nuclear) has more obvious advantages in the indexes such as resolution capability, frequency resolution, signal sensitivity and the like aiming at different chemical component spectrum components of chemical shift.
Following B of the MR system 0 The increasing field strength, i.e., operating frequency, is increasingly sensitive to the stability of the signal link phase in some phase sensitive applications, such as imaging. The traditional radio frequency transmitter or signal source for generating high-frequency signals carries out superheterodyne or single sideband modulation in a multi-stage frequency mixing mode, and because the target frequency required to be supported is higher, more than one stage of frequency mixing is required, and the phase fluctuation of local oscillators at various stages can be superposed to cause phase fluctuation to be increased, thereby affecting the final signal quality or the system imaging quality.
Disclosure of Invention
The invention aims to overcome the defects that in the prior art, a radio frequency transmitter or a signal source generating a high-frequency signal carries out superheterodyne or single sideband modulation in a multi-stage mixing mode, has large phase fluctuation and poor signal quality or system imaging quality, and provides a magnetic resonance system and the radio frequency transmitter thereof.
The invention solves the technical problems through the following technical scheme:
a first aspect of the present invention provides a radio frequency transmitter of a magnetic resonance system, including a signal processing unit, a switching unit, a signal modulation unit, and a signal amplification module;
the signal processing unit is used for processing the received baseband signal, outputting a target signal to one end of the switch unit, and controlling the other end of the switch unit to be connected with the input end of the signal amplification module or the input end of the signal modulation unit according to the relation between the target frequency and the reference frequency; wherein the reference frequency is determined according to a sampling frequency of the signal processing unit;
the signal modulation unit is used for modulating the target signal; the output end of the signal modulation unit is connected with the input end of the signal amplification module;
the signal amplification module is used for amplifying an input signal to obtain a radio frequency signal of the target frequency.
Optionally, the signal processing unit includes a control unit and a digital-to-analog conversion unit;
the control unit is used for receiving the baseband signal and the control information, performing digital signal processing on the baseband signal according to the control information and outputting an intermediate frequency signal;
the digital-to-analog conversion unit is used for performing digital-to-analog conversion processing on the intermediate frequency signal and outputting the target signal;
the control unit is further used for controlling the other end of the switch unit to be connected with the input end of the signal amplification module or the input end of the signal modulation unit.
Optionally, the signal modulation unit includes a first mixer, a second mixer, and a combiner;
the first input end of the combiner is connected with the output end of the first frequency mixer, the second input end of the combiner is connected with the output end of the second frequency mixer, and the output end of the combiner is connected with the input end of the signal amplification module.
Optionally, the radio frequency transmitter further comprises a clock generating unit for providing clock signals for the first mixer and the second mixer; wherein the clock signal provided by the clock generation unit for the first mixer and the clock signal provided by the clock generation unit for the second mixer are in quadrature.
Optionally, the target signal includes a first analog sub-signal and a second analog sub-signal which are orthogonal, and the switching unit includes a first switch and a second switch;
one end of the first switch is used for receiving the first analog sub-signal, and one end of the second switch is used for receiving the second analog sub-signal.
Optionally, the control unit is specifically configured to, when the target frequency is less than or equal to the reference frequency, control the other end of the first switch to be connected to the input end of the signal amplification module, and control the other end of the second switch to be grounded;
the control unit is specifically configured to control the other end of the first switch to be connected to the input end of the first mixer and control the other end of the second switch to be connected to the input end of the second mixer when the target frequency is greater than the reference frequency.
Optionally, the signal modulation unit further includes a radio frequency amplifier, connected in series between the output end of the combiner and the input end of the signal amplification module, and configured to amplify the power of the signal output by the combiner.
Optionally, the control unit is further configured to output a disable enable signal to the radio frequency amplifier if the target frequency is equal to or less than the reference frequency; and outputting a turn-on enable signal to the radio frequency amplifier when the target frequency is greater than the reference frequency.
Optionally, the radio frequency transmitter further includes a filtering unit connected in series between the signal modulating unit and the signal amplifying module, where the filtering unit includes a multiplexer and a plurality of filters connected in series, and different filters are used for filtering signals with different frequencies;
the control unit is further configured to control the gating end of the multi-way switch according to the control information, so that a path between the filter corresponding to the control information and the signal modulation unit is conducted.
A second aspect of the invention provides a magnetic resonance system comprising a radio frequency transmitter of the magnetic resonance system of the first aspect.
On the basis of the common knowledge in the field, the above optional conditions can be combined randomly to obtain the preferred embodiments of the invention.
The positive progress effects of the invention are as follows: two signal transmitting paths are provided according to the relation between different target frequencies and reference frequencies, and the phase stability of the radio frequency signals can be ensured to the maximum extent. Specifically, the method comprises the following steps: when the signal processing unit controls the other end of the switch unit to be connected with the input end of the signal amplification module, the signal processing unit and the signal amplification module are directly connected in sequence to form a first signal transmitting path; when the signal processing unit controls the other end of the switch unit to be connected with the input end of the signal modulation unit, the signal processing unit, the signal modulation unit and the signal amplification module are sequentially connected to form a second signal transmitting path.
Drawings
Fig. 1 is a schematic structural diagram of a radio frequency transmitter of a magnetic resonance system according to an embodiment of the present invention.
Fig. 2 is a schematic structural diagram of a radio frequency transmitter of another magnetic resonance system according to an embodiment of the present invention.
Fig. 3 is a schematic structural diagram of a radio frequency transmitter of another magnetic resonance system according to an embodiment of the present invention.
Fig. 4 is a schematic structural diagram of a filtering unit according to an embodiment of the present invention.
Fig. 5 is a schematic structural diagram of a radio frequency transmitter of a magnetic resonance system according to an embodiment of the present invention.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the invention thereto.
For a pure direct radio frequency transmission architecture, the output of a DAC (Digital to Analog Converter) can be directly output by a first-stage amplification drive, for a higher radio frequency working frequency, according to the nyquist sampling theorem, the sampling clock of the DAC needs to be at least 2 times of the radio frequency, and for the DAC and a logic device such as an FPGA (Field Programmable Gate Array) interfaced with the DAC, the working speed requirement is extremely high. For example, for the application of multiple nuclide parallel emission, the requirement of the FPGA is an ultra-high interface rate, but the logic resource of the FPGA occupies a little, and the overall design is extremely inconsistent. When the operating frequency is high to a certain extent (for example, the operating frequency is greater than or equal to 1.5 GHz), the DAC sampling rate or the data refresh rate above 3GSPS cannot be supported by the mainstream DAC chip technology. Even if an ultra-high-end DA chip is available, the cost is extremely expensive, and the same high-end FPGA with multiple channels and an ultra-high-speed serial interface is required to be matched. In a word, the power consumption, the volume and the cost of the whole machine are not dominant.
For a pure analog domain single-sideband modulation architecture, the clock generation unit may be configured to support a local oscillator output frequency F from a direct current DC to a high frequency LO . At this time due to F LO The span is large, and extremely many filter paths are required to be matched for switching, so that the number of selectable paths is large. For a pure analog domain single sideband modulation architecture, the frequency synthesizer module can also be configured to support from F DAC 2 to high frequency F LO Output, simultaneously with the DAC output frequency F at the same high frequency 1 Lower sideband modulation is carried out, and finally lower working frequency F is output RF ＝|F LO -F 1 L. But, another serious problem is faced when the random jitter of the system clock is Δ t. The phase fluctuation superimposed after DAC and mixer is 2 pi (F) LO +F 1 )Δt＞＞2πF RF Δt。
The other scheme is to perform fundamental frequency filtering on the digital clock signal output by the clock generation unit to ensure that no spurious signal is introduced when the digital clock signal is used as a local oscillator signal to participate in frequency mixing. However, generally, high-frequency local oscillators or clock signals appear in a differential form, and then, a plurality of links such as a balun (a radio frequency transformer for converting a differential signal to a single-ended signal), a filter, a multi-way switch, a radio frequency amplifier for gain compensation and the like are needed. Each system channel needs two local oscillator signals, and each local oscillator signal needs to be added with the device. This solution requires the introduction of more peripheral circuits, increasing cost, power consumption and bulk.
The embodiment provides a method for combining two processing modes of direct radio frequency emission and analog single-sideband modulation aiming at all potential applications of magnetic resonance multi-coreThe framework which can be realized by the simplest electronic components and ensures lower phase jitter combines the respective advantages of the two frameworks, can improve the output frequency of a magnetic resonance system radio frequency transmitter to the maximum extent under the condition of hardly introducing a redundant circuit and ensures the stability of the phase. Specifically, the present embodiment does not require the DAC to output an excessive high frequency signal, and switches to the direct radio frequency transmission path when the target frequency is not high; when the target frequency is too high, the difference with the target frequency can be made up by a local oscillator frequency mixing link in the analog single-sideband modulation channel. In this embodiment, the frequency of the two orthogonal local oscillator signals must be greater than half of the sampling rate of the DAC, i.e. F LO >F DAC And/2, the number of filter paths available for switching is greatly reduced.
The present embodiment provides a radio frequency transmitter of a magnetic resonance system, as shown in fig. 1, including a signal processing unit, a switching unit, a signal modulating unit, and a signal amplifying module.
The signal processing unit is used for processing the received baseband signal, outputting a target signal to one end of the switch unit, and controlling the other end of the switch unit to be connected with the input end of the signal amplification module or the input end of the signal modulation unit according to the relation between the target frequency and the reference frequency.
The reference frequency is determined according to the sampling frequency of the signal processing unit, and may be one half of the sampling frequency of the signal processing unit. The target frequency is the expected frequency of the radio frequency signal output by the radio frequency transmitter, can be specifically set by a user, and is sent to the signal processing unit through upper computer software.
The signal modulation unit is used for modulating the target signal; and the output end of the signal modulation unit is connected with the input end of the signal amplification module. In a specific implementation, the signal modulation unit may perform modulation processing on the target signal in a frequency mixing manner, so as to obtain a signal with a higher frequency.
The signal amplification module is used for amplifying an input signal to obtain a radio frequency signal of the target frequency. In a specific implementation, the signal amplification module may be a gain amplifier, configured to amplify a gain of the input signal. Because the gains of the processing links in front of the signal amplification module for different working frequency signals have obvious differences, the signal amplification module is adapted to signals with different amplitudes, and the amplitude range of the target signal output by the signal processing unit is ensured to be matched with the amplitude dynamic range of small signal power required to be output by the radio frequency transmitter to the maximum extent as far as possible.
Specifically, the gain control in the gain amplifier may also be performed according to control information issued by upper computer software via the control unit according to B 0 And analyzing the field intensity mark and the nuclide information corresponding to each emission channel. The gain amplifier may be a variable gain amplifier, or may include a fixed gain amplifier and a digitally controlled attenuator. The fixed gain amplifier is used for amplifying the gain of an input signal by a fixed multiple, and further realizes the stepping or superposition of gain attenuation by controlling the numerical control attenuator.
In this embodiment, two signal transmission paths are provided according to the relationship between different target frequencies and reference frequencies, so that the phase stability of the radio frequency signal can be ensured to the maximum extent. Specifically, the method comprises the following steps: when the signal processing unit controls the other end of the switch unit to be connected with the input end of the signal amplification module, the signal processing unit and the signal amplification module are directly connected in sequence to form a first signal transmitting path; when the signal processing unit controls the other end of the switch unit to be connected with the input end of the signal modulation unit, the signal processing unit, the signal modulation unit and the signal amplification module are sequentially connected to form a second signal transmitting path.
In an alternative embodiment, as shown in fig. 2, the signal processing unit includes a control unit and a digital-to-analog conversion unit. The control unit is used for receiving the baseband signal and the control information, performing digital signal processing on the baseband signal according to the control information, and outputting an intermediate frequency signal. The digital-to-analog conversion unit is used for performing digital-to-analog conversion processing on the intermediate frequency signal and outputting the target signal; the control unit is further used for controlling the other end of the switch unit to be connected with the input end of the signal amplification module or the input end of the signal modulation unit.
In specific implementation, the control unit may receive a baseband signal and control information sent by upper computer software. The control unit can be connected with upper computer software through a high-speed optical fiber after parallel-serial conversion and photoelectric conversion processing are carried out in the control unit. The high-speed optical fiber can greatly save system wiring space relative to electrical connection, electromagnetic interference caused by long-distance electrical interconnection does not exist, and cost can be reduced.
The control information may include a frequency word and/or a control word, and the control unit processes the baseband signal according to the frequency word and the control word to obtain an intermediate frequency signal. Specifically, the control unit performs digital signal processing on the baseband signal in a digital up-conversion and interpolation filtering manner by combining envelope information and frequency words to obtain an intermediate frequency signal. The control information may further include information such as the species of nuclear species and/or the field strength of the magnetic resonance system corresponding to each transmit channel. The control unit is specifically configured to determine control signals to the digital-to-analog conversion unit, the switch unit, the signal modulation unit, and the signal amplification module according to control information, where in specific implementation, the control information preferentially includes the nuclide species and the field strength.
The control Unit may be a programmable logic device, and may be in a specific form of an FPGA (field programmable gate array), a DSP (Digital Signal Processing), a CPU (Central Processing Unit), an MCU (micro control Unit), or the like, and may include resources such as a logic gate circuit, a register, a hard core multiplier-adder, a storage module, a phase-locked loop, a high-speed serial-parallel conversion module, and the like therein.
In a specific implementation, the Digital-to-Analog conversion unit may be a TDAC (Tx-chain Digital-to-Analog Converter Module), and includes a base DAC Module for directly converting a Digital quantity into an Analog quantity, where the number of DAC modules is an integer multiple of 2, and may be, for example, 2, 4, 6, and the like. Each pair of DAC modules ultimately outputs a pair of quadrature analog signals I and Q. In some chips integrated with the TDAC function, a buffering processing link BF is further included, which is used to perform digital processing, such as serial-to-parallel conversion, interpolation filtering, digital up-conversion, and the like, on the intermediate frequency signal before performing digital-to-analog conversion. In addition, the chip integrating the TDAC function may further include a PLL (Phase Locked Loop) for converting the input clock signal DAC _ CLK into the internal buffer processing link BF and the clocks with different frequencies required by the DAC module processing, including the sampling frequency of the DAC module.
In specific implementation, the signal modulation unit may have a single-sideband modulation structure, or may also have a super-heterodyne structure or other structures.
In an embodiment where the signal modulation unit has a single-sideband modulation structure, as shown in fig. 3, the signal modulation unit includes a first mixer M1, a second mixer M2, and a combiner M3, a first input end of the combiner M3 is connected to an output end of the first mixer M1, a second input end of the combiner M3 is connected to an output end of the second mixer M2, and an output end of the combiner is connected to an input end of the signal amplification module.
In an alternative embodiment, as shown in fig. 3, the radio frequency transmitter further includes a clock generation unit for providing clock signals, i.e. local oscillation signals, to the first mixer M1 and the second mixer M2. The clock signal provided by the clock generation unit for the first mixer M1 and the clock signal provided by the clock generation unit for the second mixer M2 are orthogonal, that is, the phases of the two clock signals are different by 90 °. In particular, the frequency and phase relationship of the two clock signals may be determined by the control unit from the species of nuclear species and the field strength in the control information. In this embodiment, the clock generating unit directly outputs the high-frequency and high-swing digital signal in the form of an approximate square wave to provide local oscillation signals for the first mixer and the second mixer, so as to complete single-sideband modulation, and peripheral driving circuits such as a radio frequency amplifier and a filter do not need to be additionally provided for the local oscillation circuit, thereby reducing the volume and power consumption to the maximum extent.
In a specific implementation, the clock generating unit may further provide a clock signal to the control unit, the digital-to-analog converting unit, and the signal modulating unit. Wherein the clock generation unit may comprise a phase locked loop PLL synchronized with a reference clock of the system input. The control unit is used for processing the baseband signal based on the clock signal provided by the clock generation unit and the control information. The digital-to-analog conversion unit is used for performing digital-to-analog conversion on the intermediate frequency signal based on the clock signal provided by the clock generation unit. The clock generation unit internally comprises configurations of driving, fanning out and delaying of clock signals and local oscillation signals. The above functions are generally realized by a chip with high integration level, and such a chip is generally built in with a voltage-controlled oscillator (VCO) with ultra-high frequency, and can flexibly generate different local oscillation frequencies F meeting the needs of the magnetic resonance system by frequency division LO . And the chip can generally support high-swing high-speed differential level standard, such as digital integrated circuit interface standard HSTL (2V) PP )。
In an alternative embodiment, as shown in fig. 3, the target signal includes a first analog sub-signal I and a second analog sub-signal Q which are orthogonal, and the switching unit includes a first switch S1 and a second switch S2. One end of the first switch S1 is configured to receive the first analog sub-signal I, and one end of the second switch S2 is configured to receive the second analog sub-signal Q. The first switch S1 and the second switch S2 may be single-pole double-throw switches.
In an optional embodiment, the control unit is specifically configured to control the other end of the first switch S1 to be connected to the input end of the signal amplification module and control the other end of the second switch S2 to be grounded, when the target frequency is less than or equal to the reference frequency. The control unit, the digital-to-analog conversion unit and the signal amplification module are sequentially connected to form a first signal transmitting path.
The control unit is further configured to control the other end of the first switch S1 to be connected to the input terminal of the first mixer M1 and the other end of the second switch S2 to be connected to the input terminal of the second mixer M2, if the target frequency is greater than the reference frequency. The control unit, the digital-to-analog conversion unit, the first or second mixer, the combiner and the signal amplification module are sequentially connected to form a second signal transmitting path.
In this embodiment, when the target frequency is less than or equal to the reference frequency, it indicates that the target frequency is low, and the digital-to-analog conversion unit can satisfy the nyquist sampling theorem, and switches to the first signal transmission path to directly transmit signals without outputting signals with too high frequencies by the digital-to-analog conversion unit; and under the condition that the target frequency is greater than the reference frequency, the target frequency is higher, in order to enable the digital-to-analog conversion unit to meet the Nyquist sampling theorem, the digital-to-analog conversion unit is switched to the second signal transmission channel, and the signal modulation unit compensates the signal, so that the frequency of the transmitted signal can reach the target frequency. That is, when the output is relatively low frequency, the digital-to-analog conversion unit is used for directly sampling and outputting, and when the output is relatively high frequency, the digital-to-analog conversion unit is used for outputting in a mode of matching with one-stage single sideband modulation, so that the phase stability is ensured to the maximum extent.
In another optional embodiment, the control unit is specifically configured to control the other end of the first switch S1 to be connected to the input end of the signal amplification module when a difference between the reference frequency and the target frequency is greater than or equal to a preset value; and controlling the other end of the second switch S2 to be grounded. The control unit is further configured to, when the difference between the reference frequency and the target frequency is smaller than the preset value, connect the other end of the first switch S1 to the input end of the first mixer M1, and control the other end of the second switch S2 to be connected to the input end of the second mixer M2. The preset value is greater than or equal to 0, and can be specifically set according to actual conditions.
In an optional implementation manner, the signal modulation unit further includes a radio frequency amplifier, which is connected in series between the output end of the combiner and the input end of the signal amplification module, and is configured to amplify the power of the signal output by the combiner. In this embodiment, the rf amplifier is a fixed gain amplifier, and is used to compensate for signal power loss introduced by passive rf modules such as an rf switch (including the first switch S1 and the second switch S2), a reconstruction filter, and a mixer (including the first mixer M1 and the second mixer M2).
In an optional embodiment, the control unit is further configured to output a disable enable signal to the radio frequency amplifier if the target frequency is equal to or less than the reference frequency; and outputting a turn-on enable signal to the radio frequency amplifier when the target frequency is greater than the reference frequency. In this embodiment, when the target frequency is equal to or lower than the reference frequency, that is, when the first signal transmission path is switched, the radio frequency amplifier is disabled by outputting a disable enable signal to the radio frequency amplifier, so that power consumption of the radio frequency transmitter of the magnetic resonance system can be reduced.
In order to filter spurious signals caused by higher harmonics, in an optional embodiment, the radio frequency transmitter further includes a filtering unit connected in series between the signal modulating unit and the signal amplifying module, where the filtering unit includes a multiplexer and a plurality of filters connected in series, and different filters are used for filtering signals with different frequencies. The control unit is further configured to control the gating end of the multi-way switch according to the control information, so that a path between the filter corresponding to the control information and the signal modulation unit is conducted.
In a specific implementation, the multi-way switch may be connected in series between the filter and the signal modulation unit, or the filter may be connected in series between the multi-way switch and the signal modulation unit, or two multi-way switches may be included, as shown in fig. 4, in n filters FLT, two ends of each filter are connected to the multi-way switch, which is a multi-way switch MS1 and a multi-way switch MS2, respectively. The multiplexer may also be referred to as a multiplexer or a data selector. The control unit can control the gating end of the multi-way switch according to the nuclide species in the control information so as to enable a channel between the filter corresponding to the nuclide species and the signal modulation unit to be conducted, and a signal with a frequency corresponding to the nuclide species can be obtained through corresponding filtering.
In a specific implementation, the first switch or the filtering unit may be connected to the signal amplification module through a third switch, one end of the third switch is connected to the signal amplification module, and the control unit controls the other end of the third switch to be connected to the other end of the first switch or the output end of the filtering unit according to the control information. It should be noted that, when the target frequency is less than or equal to the reference frequency, the control unit controls the other end of the first switch to be connected to the signal amplification module through the third switch, and controls the other end of the second switch to be grounded. And under the condition that the target frequency is greater than the reference frequency, the control unit controls the other end of the first switch to be connected with the input end of the first mixer, controls the other end of the second switch to be connected with the input end of the second mixer, and controls the other end of the third switch to be connected with the output end of the filtering unit. The third switch may also be a single pole double throw switch.
Fig. 5 is a schematic diagram showing a specific structure of a radio frequency transmitter of a magnetic resonance system. As shown in fig. 5, the radio frequency transmitter of the magnetic resonance system includes a control unit FW, a digital-to-analog conversion unit TDAC, a first switch S1, a second switch S2, a first mixer M1, a second mixer M2, a combiner M3, a radio frequency amplifier G0, a multi-way switch MS1, n filters FLT, a multi-way switch MS2, a third switch S3, a variable gain amplifier VGA, and a clock generation unit CLK _ SYN.
The clock generation unit CLK _ SYN is configured to provide a clock signal SYS _ CLK for the control unit FW and a clock signal DAC _ CLK for the digital-to-analog conversion unit TDAC. The sampling frequency of the digital-to-analog conversion unit TDAC is F DAC With reference frequency of F DAC /2. The clock signal provided by the clock generation unit CLK _ SYN to the first mixer M1 and the second mixer M2, i.e., the local oscillator signal, has a frequency F LO The phase difference between them is 90 DEG, and the target frequency is F RF . The clock generation unit CLK _ SYN alsoFor receiving a reference signal SYS REF for synchronizing the respective clock signals inside the radio frequency transmitter.
The control unit FW receives a baseband signal BB carrying a transmission waveform envelope and control information INFO sent by upper computer software, and finally generates a radio frequency small signal with specific frequency and amplitude through a series of control instruction analysis and signal processing operations and outputs the radio frequency small signal to a later-stage broadband Power Amplifier (WBPA). The WBPA is a high power output stage that ultimately applies radio frequency power to the subject of the magnetic resonance system to excite the magnetic flux on the subject and thereby induce resonance signals for subsequent processing by the receive chain and reconstruction software. Wherein the control information comprises frequency words, phase words, nuclide information corresponding to each emission channel, and B 0 The information of field intensity mark, etc. is used for processing the baseband signal according to the nuclide information corresponding to each transmitting channel and outputting intermediate frequency signal whose frequency is F 0 . The digital-to-analog conversion unit TDAC comprises a buffer processing link BF and two DAC modules (DAC 0 and DAC 1), the buffer processing link BF carries out digital processing such as serial-parallel conversion, interpolation filtering and digital up-conversion on the intermediate frequency signal, the DAC0 and DAC1 respectively carry out digital-to-analog conversion on the signal output by the BF, orthogonal analog signals I and Q are output, and the frequency of the analog signals I and Q is F 1 . Wherein, F 0 Is not always equal to F 1 ，F 1 Must be less than F DAC /2. One end of the first switch S1 is used for receiving the analog signal I, one end of the second switch S2 is used for receiving the analog signal Q, and one end of the third switch S3 is used for connecting the input end of the variable gain amplifier VGA.
If F RF ≤F DAC And/2, controlling the other end of the first switch S1 to be connected with the variable gain amplifier VGA through a third switch S3, controlling the other end of the second switch S2 to be grounded, and outputting the analog signal I after being amplified by the variable gain amplifier VGA.
If F RF ＞F DAC /2, then controlling the other end of the first switch S1 to be connected to the input of the first mixer M1, controlling the other end of the second switch S2 to be connected to the input of the second mixer M2, and controlling the other end of the third switch S3 to be connected to the filtering unitThe outputs of the elements are connected. The intermediate frequency signal enters an IQ-modulated signal processing link after being output by TDAC, specifically: the analog signal I is mixed by the first mixer M1, the analog signal Q is mixed by the second mixer M2, and the mixed signals are added by the combiner to obtain the frequency F LO ±F 1 Of the signal of (1). Specifically, the method comprises the following steps:
if F LO >F RF >F DAC And/2, configured to down-convert, the signal at the input of the radio frequency amplifier G0 is:
cos(2πF LO t)cos(2πF 1 t)+sin(2πF LO t)sin(2πF 1 t)＝cos(2π(F LO -F 1 )t)；
if F LO <F RF >F DAC And/2, configured to up-convert, the signal at the input of the rf amplifier G0 is:
sin(2πF LO t)cos(2πF 1 t)+cos(2πF LO t)sin(2πF 1 t)＝sin(2π(F LO +F 1 )t)。
and the signal output by the radio frequency amplifier G0 is filtered by the filtering unit and then output.
If F RF ≤F DAC And/2, the control unit can also output a disable enable signal SHDN to the radio-frequency amplifier G0 according to the control information so as to disable the radio-frequency amplifier G0.
If F RF ＞F DAC And/2, the control unit outputs a conduction enabling signal to the radio frequency amplifier G0 so that the radio frequency amplifier G0 can work normally.
The switch states of the first switch S1, the second switch S2, and the third switch S3 may be logically analyzed by the control unit FW according to control information issued by the upper computer software and then given. F RF And F DAC The relation of/2 can be generated by upper computer software according to system configuration information to generate a bit zone bit to be transmitted to the control unit FW, and an information analysis and distribution mechanism of the control unit FW controls the signal trend of each transmitting channel according to the control information from the upper computer software.
It should be noted that the radio frequency transmitter of the magnetic resonance system shown in figure 5 may include one or more transmit channels. All transmit channels may share a control unit and a clock generation unit. Aiming at the emission channels corresponding to different nuclide types, the adopted filtering unit, the signal modulation unit, the signal amplification module and the switch unit are independent. In a specific implementation, a reconstruction filter may be further disposed between the digital-to-analog conversion unit and the switching unit, and is used for restoring the smoothed target signal.
Table 1 serves as an example of a frequency planning for a radio frequency transmitter of a magnetic resonance system. Wherein No LO represents the selection of the first signal transmission channel, in this case F LO It is not effective. Selecting a 16-bit digital-to-analog conversion unit TDAC, wherein the application parameters are as follows: sampling frequency F DAC =1200MSPS, input parallel data rate F DIN The rate of the serial bus protocol is 150 × 2 × 16 × 10/8=6gbps if the serial bus protocol corresponds to 1 channel of 8B/10B encoded serial bus protocol, where the protocol is 1I/Q channel, i.e. 2 DAC modules. If the rf transmitter of the mr system includes 4 independent transmit channels, the control unit only needs to select a device including at least 4 high-speed serial buses supporting 6Gbps.
TABLE 1
For the four F types of 720MHz/960MHz/660MHz/1320MHz LO Corresponding to 2-4 filters FLT for retaining F LO Nearby F RF Fundamental frequency component, and depth suppression (2k + 1) F LO Nearby spurious signal components. Wherein k is an arbitrary natural number.
The embodiment also provides a magnetic resonance system which comprises the radio frequency transmitter. In a specific implementation, the magnetic resonance system may further include a power amplifier, a coil, and a radio frequency receiver, wherein a radio frequency signal output by the radio frequency transmitter is amplified by the power amplifier and then transmitted to the coil, and an acquired signal transmitted by the coil is transmitted to the radio frequency receiver, so that reconstruction of a magnetic resonance image may be achieved.
The magnetic resonance system in this embodiment adopts the radio frequency transmitter, so that the phase stability of the radio frequency signal can be ensured to the maximum extent, and the probability of artifacts appearing in the reconstructed magnetic resonance image can be reduced, thereby improving the quality of the magnetic resonance image.
While specific embodiments of the invention have been described above, it will be appreciated by those skilled in the art that this is by way of example only, and that the scope of the invention is defined by the appended claims. Various changes and modifications to these embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention, and these changes and modifications are within the scope of the invention.
Claims (10)
1. The radio frequency transmitter of a magnetic resonance system is characterized by comprising a signal processing unit, a switch unit, a signal modulation unit and a signal amplification module;
the signal processing unit is used for processing the received baseband signal, outputting a target signal to one end of the switch unit, and controlling the other end of the switch unit to be connected with the input end of the signal amplification module or the input end of the signal modulation unit according to the relation between the target frequency and the reference frequency; wherein the reference frequency is determined according to a sampling frequency of the signal processing unit;
the signal modulation unit is used for modulating the target signal; the output end of the signal modulation unit is connected with the input end of the signal amplification module;
the signal amplification module is used for amplifying an input signal to obtain a radio frequency signal of the target frequency.
2. The radio frequency transmitter of the magnetic resonance system as set forth in claim 1, wherein the signal processing unit includes a control unit and a digital-to-analog conversion unit;
the control unit is used for receiving the baseband signal and the control information, performing digital signal processing on the baseband signal according to the control information and outputting an intermediate frequency signal;
the digital-to-analog conversion unit is used for performing digital-to-analog conversion processing on the intermediate frequency signal and outputting the target signal;
the control unit is further used for controlling the other end of the switch unit to be connected with the input end of the signal amplification module or the input end of the signal modulation unit.
3. The radio frequency transmitter of the magnetic resonance system as set forth in claim 2, wherein the signal modulation unit includes a first mixer, a second mixer, and a combiner;
the first input end of the combiner is connected with the output end of the first frequency mixer, the second input end of the combiner is connected with the output end of the second frequency mixer, and the output end of the combiner is connected with the input end of the signal amplification module.
4. The radio frequency transmitter of claim 3, further comprising a clock generation unit for providing clock signals to the first mixer and the second mixer; wherein the clock signal provided by the clock generation unit for the first mixer and the clock signal provided by the clock generation unit for the second mixer are in quadrature.
5. The radio frequency transmitter of claim 4, wherein the target signal comprises a first analog sub-signal and a second analog sub-signal that are orthogonal, the switching unit comprising a first switch and a second switch;
one end of the first switch is used for receiving the first analog sub-signal, and one end of the second switch is used for receiving the second analog sub-signal.
6. The radio frequency transmitter of claim 5, wherein the control unit is specifically configured to control the other end of the first switch to be connected to the input terminal of the signal amplification module and the other end of the second switch to be grounded, if the target frequency is equal to or lower than the reference frequency;
the control unit is specifically configured to control the other end of the first switch to be connected to the input end of the first mixer and control the other end of the second switch to be connected to the input end of the second mixer when the target frequency is greater than the reference frequency.
7. The rf transmitter of claim 3, wherein the signal modulation unit further comprises an rf amplifier connected in series between the output of the combiner and the input of the signal amplification module for amplifying the power of the output signal of the combiner.
8. The radio frequency transmitter of claim 7, wherein the control unit is further configured to output a disable enable signal to the radio frequency amplifier if the target frequency is less than or equal to the reference frequency; and outputting a turn-on enable signal to the radio frequency amplifier when the target frequency is greater than the reference frequency.
9. The radio frequency transmitter of claim 2, further comprising a filtering unit connected in series between the signal modulating unit and the signal amplifying module, the filtering unit including a plurality of filters and a plurality of multi-way switches connected in series, different filters being used for filtering signals of different frequencies;
the control unit is further configured to control the gating end of the multi-way switch according to the control information, so that a path between the filter corresponding to the control information and the signal modulation unit is conducted.
10. A magnetic resonance system comprising a radio frequency transmitter of the magnetic resonance system as claimed in any one of claims 1-9.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202211414012.XA CN115856738A (en) | 2022-11-11 | 2022-11-11 | Magnetic resonance system and radio frequency transmitter thereof |
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| CN202211414012.XA CN115856738A (en) | 2022-11-11 | 2022-11-11 | Magnetic resonance system and radio frequency transmitter thereof |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117526585A (en) * | 2024-01-03 | 2024-02-06 | 成都市易冲半导体有限公司 | Phase demodulation circuit, wireless power transmitting end and wireless charging system |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117526585A (en) * | 2024-01-03 | 2024-02-06 | 成都市易冲半导体有限公司 | Phase demodulation circuit, wireless power transmitting end and wireless charging system |
| CN117526585B (en) * | 2024-01-03 | 2024-03-29 | 成都市易冲半导体有限公司 | Phase demodulation circuit, wireless power transmitting end and wireless charging system |
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