CN101872001B - Parallel emitting and receiving radio-frequency interface circuit and phased array emitting and receiving head coil - Google Patents

Abstract

The invention relates to a parallel transmitting and receiving radio frequency interface circuit and a phased array transmitting and receiving head coil. The phased array transmitting and receiving head coil includes an inner shell and an outer shell with transparent ends. The inner shell and the outer shell correspond to the eyes of the tester. There is a fully open window at each position, and eight phased array surface loops are arranged on the outer surface of the inner shell, with upper and lower circles, a total of eight phased array surface loops, one of which is set around the window; the parallel transmitting and receiving radio frequency interface circuit includes a Power divider, the power divider is connected with eight phase shifters, and each phase shifter linearly shifts each input RF signal, and each RF signal after phase shift passes through the input/output of a transmitting and receiving switch The terminal transmits to the eight phased array surface loops on the coil of the phased array transmitting and receiving head; the eight phased array surface loops transmit radio frequency signals and receive human hydrogen atoms to generate eight-way magnetic resonance signals, and the eight-way magnetic resonance signals pass through each transmitter respectively. The input/output end of the receiving transfer switch is input to a preamplifier; the control end of each transmitting and receiving transfer switch is connected to the control system of the scanner. The invention can be widely applied to various magnetic resonance high-field imaging systems, especially ultra-high-field imaging systems.

Description

Parallel transmitting and receiving radio frequency interface circuit and phased array transmitting and receiving head coil

technical field

The invention relates to a magnetic resonance high-field and ultra-high-field imaging system, in particular to a parallel transmitting and receiving radio frequency interface circuit and a phased array transmitting and receiving head coil suitable for the magnetic resonance high-field and ultra-high-field imaging system.

Background technique

Magnetic resonance imaging technology has developed rapidly in the past ten years. It has not only become an indispensable tool for clinical medical diagnosis, but also an "astronomical telescope" or "microscope" for directly observing the cognitive activities of the brain, which has completely changed the relationship between the brain and cognition. The face of research in the field of knowledge science. The main bottleneck restricting the development of magnetic resonance technology is the image signal-to-noise ratio, resolution and imaging speed. At present, the main way to solve this problem is to increase the strength of the main magnetic field, improve the transmitting and receiving functions of the coil, realize multi-channel parallel imaging, and increase the imaging speed. The current high-field (generally 3T) and ultra-high-field (7T and above) magnetic resonance imaging systems and parallel imaging technology are the most striking technological development trends in the field of magnetic resonance imaging.

Compared with the existing clinical mainstream 1.5T MRI system, the high-field and ultra-high-field whole-body MRI systems have greatly improved several key indicators such as signal-to-noise ratio, functional signal strength and spectral resolution. The 7T magnetic resonance imaging system can currently achieve a resolution of less than 0.1 mm, making it possible to observe more subtle body tissue structures and their functional activities. Although the high-field and ultra-high-field whole-body magnetic resonance systems have such outstanding capabilities, there are still many technical problems to be solved in order to give full play to their functions. Inhomogeneity affects the image signal-to-noise ratio of the magnetic resonance imaging system, excessive absorption of electromagnetic energy by the human body, that is, high SAR value, high difficulty of static magnetic field shimming, etc.

Contents of the invention

In view of the above problems, the object of the present invention is to provide a parallel transmitting and receiving radio frequency interface circuit and a phased array transmitting and receiving head coil with uniform radio frequency field emission, high image signal-to-noise ratio, and low electromagnetic energy emission.

In order to achieve the above object, the present invention adopts the following technical solutions: a parallel transmitting and receiving radio frequency interface circuit and a phased array transmitting and receiving head coil, characterized in that: the phased array transmitting and receiving head coil includes an inner A shell and an outer shell, the inner shell and the outer shell are provided with a fully open window corresponding to the position of the tester's eyes, and the outer surface of the inner shell is provided with eight phased array surface loops in total, upper and lower circles, One of the phased array surface loops is arranged around the window; the parallel transmitting and receiving radio frequency interface circuit includes a power divider, which divides the input single-channel radio frequency signal into eight radio frequency signals; the power divider is connected to eight shifters Each of the phase shifters linearly shifts each input RF signal, and each RF signal after phase shifting is transmitted to the phased array transmitter through the input/output end of a transmitting and receiving switch. The eight phased array surface loops on the receiving head coil make the phase shift difference between the two adjacent phased array surface loops in each circle a fixed value, and the two phased arrays corresponding to the upper and lower circles The phase difference of the radio frequency signals between the surface loops is a fixed value; the eight phased array surface loops transmit radio frequency signals and receive human hydrogen atoms to generate eight-way magnetic resonance signals, and the eight-way magnetic resonance signals are respectively passed through each of the transmitting and receiving The input/output end of the changeover switch is input to a preamplifier; the control end of each transmit-receive changeover switch is connected to the control system of the scanner, so as to receive the switch control instruction for transmission or reception outputted by the control system.

The phase shifter is a coaxial cable, and the length of the coaxial cable determines the phase shift amount of the phase shifter.

The phase shift difference between the two adjacent phased array surface loops in each circle is 90°, and the phase difference of the radio frequency signal between the two phased array surface loops corresponding to the upper and lower circles is 180°.

Three pairs of the upper and lower phased array surface loops on the outer surface of the inner shell are arranged symmetrically.

The parallel transmitting and receiving radio frequency interface circuit further includes eight attenuators connected between each of the phase shifters and the transmitting and receiving switch for adjusting the amplitude of each radio frequency signal.

Each of the phased array surface loops on the coil of the phased array transmitting and receiving head includes three fixed capacitors, three adjustable capacitors and an inductor, wherein the three fixed capacitors, two adjustable capacitors and the inductor are connected in series to form a resonant circuit.

The two ends of an adjustable capacitor in the resonant circuit are connected to the transmitting and receiving switch in the radio frequency interface circuit through another adjustable capacitor; the fixed capacitor is a non-magnetic high-voltage resistant fixed capacitor, and the adjustable The capacitor is a non-magnetic and high-voltage adjustable capacitor; the inductance in the surface loop of the phased array is composed of four sections of copper skin.

The present invention has the following advantages due to the adoption of the above technical scheme: 1. The radio frequency interface circuit adopted in the present invention is evenly divided into eight radio frequency signals from the single channel radio frequency signal output by the single channel power amplifier, and linearly phases the radio frequency signals of each road. The radio frequency interface circuit receives the transmission or reception switch control signal sent by the scanner's control system. When the radio frequency interface circuit is in the transmitting state, it transmits uniform eight-way radio frequency signals with different phases to the head coil. The hydrogen atoms in the soft tissue of the human brain in the head coil are excited to make the hydrogen atoms of the human body generate nuclear magnetic resonance signals. After the eight channels of magnetic resonance signals are amplified, they are sent to the magnetic resonance imaging system for image reconstruction and post-processing. 2. Since the present invention uses a power divider to divide a single-channel radio frequency signal into eight radio frequency signals, and then carry out linear phase shifts on the eight radio frequency signals separated by the power divider through eight phase shifters, and carry out phase shift to each radio frequency signal , until the shimming of the radio frequency field is obtained, compared with the multi-channel parallel transmission system using multiple power amplifiers, the present invention adopts the power division method to save the cost of purchasing or developing expensive magnetic resonance power amplifiers, and can use lower cost Achieve the effects of multi-channel parallel transmission and RF field shimming. 3. Since the head coil of the present invention has a fully-opened window, compared with the traditional window, the fully-opened window can fully open the visual fields of the left and right eyes, which is beneficial to clear visual stimulation to the experimental subjects. 4. Since the transmitting and receiving head coil of the present invention adopts a phased array surface loop, the resonant frequency of each phased array surface loop satisfies 123.2MHz, while making each resonant loop have a high quality factor, thereby improving the image signal-to-noise ratio Favorable conditions are provided. 5. Since there is an overlapping area between two adjacent phased array surface loops of the present invention, the mutual coupling is removed through an appropriate overlapping area; between two adjacent diagonal phased array surface loops, a common capacitor is used , to achieve the role of decoupling, to ensure a high signal-to-noise ratio of the image. 6. Since the two ends of an adjustable capacitor of the resonant circuit in each phased array surface circuit of the present invention are connected to the transmitting and receiving switch in the radio frequency interface circuit through another adjustable capacitor, the phased array head coil can be adjusted To match the phase and impedance of the preamplifier, the signal-to-noise ratio of the image is further improved. 7. Since the coil frame, copper skin inductor, fixed capacitor and adjustable capacitor of the present invention are all non-magnetic mechanical materials and electronic components, and the mechanical materials are not imaged in the magnetic resonance experiment, the image signal-to-noise ratio can be further improved . The invention can be widely applied to various magnetic resonance high-field imaging systems, especially ultra-high-field imaging systems.

Description of drawings

Fig. 1 is a schematic block diagram of a parallel transmitting and receiving radio frequency interface circuit of the present invention

Fig. 2 is the structural representation of transmitting and receiving head coil of the present invention

Fig. 3 is the distribution schematic diagram of phased array surface circuit on the casing of transmitting and receiving head coil of the present invention

Fig. 4 is the circuit connection schematic diagram of the phased array surface loop on the casing of the transmitting and receiving head coil of the present invention

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

As shown in FIG. 1 , the present invention includes a parallel transmitting and receiving radio frequency interface circuit 1 and a set of phased array transmitting and receiving head coils 2 arranged on the head of a human body. The parallel transmitting and receiving radio frequency interface circuit 1 divides the single-channel radio frequency signal A output from the single-channel power amplifier into eight identical radio frequency signals, and performs linear phase shift on the eight radio frequency signals respectively, and makes the phase shifts of the eight radio frequency signals sequentially differ by a certain amount value until the emitted RF field reaches uniformity. At the same time, the parallel transmitting and receiving radio frequency interface circuit 1 sends eight radio frequency signals to the phased array transmitting and receiving head coil 2, so as to excite the hydrogen atoms in the soft tissue of the human brain in the phased array transmitting and receiving head coil 2, so that the hydrogen atoms in the human body Generate magnetic resonance signals. The coil 2 of the phased array transmitting and receiving head feeds the generated eight-way magnetic resonance signal back to the parallel transmitting and receiving radio frequency interface circuit 1, and the parallel transmitting and receiving radio frequency interface circuit 1 amplifies the eight-way magnetic resonance signal to B, and then sends it to the magnetic resonance imaging The system performs image reconstruction and post-processing.

The parallel transmitting and receiving radio frequency interface circuit 1 of the present invention includes a power divider 11 , eight phase shifters 12 , eight attenuators 13 , eight transmitting and receiving switches 14 and eight preamplifiers 15 . in:

The input end of the power splitter 11 is connected to the output end of the single-channel power amplifier, so as to equally divide the single-channel radio frequency signal A output from the single-channel power amplifier into eight identical radio frequency signals. In this embodiment, the power divider 11 adopts an octagonal Wilkinson power divider circuit, which is composed of high-frequency non-magnetic discrete components, and its working center frequency is 123.2 MHz. The 8 output ports are respectively connected with high-power heat dissipation isolation resistors to prevent the signal from being reflected and coupled to other channels when the impedance of the output end is mismatched, which will affect the power division result.

The input end of each phase shifter 12 is connected to the output end of the corresponding power divider 11, so as to perform linear phase shift on the eight RF signals separated by the power divider 11, so as to obtain a uniformly distributed RF field. In the present embodiment, what phase shifter 12 has adopted is coaxial cable, and the phase shift amount of each coaxial cable is determined by its length, such as: the cable length of every 90 ° phase shift amount is about 41cm ( This length includes the connector adapter for the coaxial cable). The radio frequency signal output by each phase shifter 12 is input into a transmitting and receiving switch 14 after being adjusted by an attenuator 13 . Compared with the multi-channel parallel transmission system using multiple power amplifiers, the present invention saves the cost of purchasing or developing expensive magnetic resonance power amplifiers by adopting the power division method, and can achieve multi-channel parallel transmission and radio frequency field uniformity at a lower cost. field effect.

The control end of each transmitting and receiving changeover switch 14 is connected to the control system (not shown in the figure) of the scanner for receiving the switching control command U for transmitting or receiving outputted by the control system. The input/output end of each transmitting and receiving changeover switch 14 is connected to the phased array transmitting and receiving head coil 2, and the output end of each transmitting and receiving changeover switch 14 is connected with the input end of a preamplifier 15 respectively, and each preamplifier 15 The output terminals of the two are respectively connected to the magnetic resonance imaging system, and are used to amplify the magnetic resonance signal B generated by the phased array transmitting and receiving head coil 2 and input it into the magnetic resonance imaging system. The preamplifier 15 also has a decoupling function, so that the signal-to-noise ratio of the image output by the magnetic resonance imaging system can be improved. In this embodiment, the operating frequency of the transmitting and receiving switch 14 is 123.2 MHz, and the timing of the parallel transmitting and receiving radio frequency interface circuit 1 is controlled by the high and low levels of the magnetic resonance system. What the preamplifier 15 adopts is the 3T preamplifier with low noise figure and high gain provided by Siemens.

As shown in Figure 2, the phased array transmitting and receiving head coil 2 of the present invention includes an inner shell 21 and an outer shell 22 with both ends transparent, and the inner shell 21 and the outer shell 22 are equipped with a rectangular shape corresponding to the position of the tester's eyes. Window 23, after the tester can put the phased array transmitting and receiving head coil 2 on the head, the tester's eyes can observe the visual image through the window 23, and the corresponding brain functional area of the tester will be stimulated in the functional magnetic resonance experiment. Generate excitation and corresponding fMRI signals. The structure of the viewing window 23 of the present invention is different from the traditional viewing window, which has a partition in the middle to separate the visual fields of the left and right eyes. And the present invention removes the partition in the middle, makes the field of vision of left and right eyes fully open, helps to carry out clear visual stimulation to the experimental subject.

As shown in Figure 3, the outer surface of the inner shell 21 in the phased array transmitting and receiving head coil 2 of the present invention is provided with a total of eight phased array surface loops 24 in the upper and lower circles, such as ch1, 2 in Figure 3 , 3, 4, 5, 6, 7 and 8, that is, four pairs of upper and lower phased array surface loops 24, such as ch7 and 3, ch8 and 4, ch5 and 1, ch6 and 2 in Fig. 3 . Among them, three pairs of upper and lower phased array surface loops 24, such as ch7 and 3, ch8 and 4, ch6 and 2 in Figure 3 are symmetrically arranged, and the remaining pair of upper and lower phased array surface loops 24, as shown in Figure The window 23 is surrounded by ch5 in 3 and the lower phased array surface loop 24 in 1, so that the pair of upper and lower phased array surface loops 24 are asymmetrically arranged as ch5 and 1 in FIG. 3 .

Since there is a mutual coupling effect between adjacent two phased array surface loops 24 and between two adjacent diagonal phased array surface loops 24, the present invention combines the adjacent two phased array surface loops 24 Some areas overlap, but do not touch each other, the purpose is to remove the mutual inductance between them, achieve decoupling effect, and then effectively improve the signal-to-noise ratio and imaging range of the magnetic resonance image. For the coupling effect between the two phased array surface loops 24 of adjacent diagonal lines, the present invention realizes by setting some common electric capacity C1 ', C2 ', C3 ', C4, C5, C6, C7 and C8; Similarly, The phased array surface loop 24 surrounding the window 23 and the corresponding asymmetric phased array surface loop 24 in the other circle are decoupled through a common capacitor C9, thereby further improving the signal-to-noise ratio and the magnetic resonance image. Imaging range, to better serve functional magnetic resonance experiments and cognitive science experiments.

As shown in Figure 4, each phased array surface loop 24 in the phased array transmitting and receiving head coil 2 of the present invention includes three fixed capacitors C1, C2 and C3, three adjustable capacitors Cf, Cp and Cs, and an inductor L1 . Among them, the fixed capacitors C1, C2, and C3, the adjustable capacitors Cf, Cp, and the inductor L1 form a resonant circuit, and the two ends of the adjustable capacitor Cp are connected to the transmit-receive conversion in the parallel transmit-receive RF interface circuit 1 through the adjustable capacitor Cs The switch 14 is used to receive eight phase-shifted radio frequency signals output from the parallel transmitting and receiving radio frequency interface circuit 1. The eight radio frequency signals are divided into upper and lower groups, which are used to drive the upper and lower circles of eight phased array surface circuits respectively. 24. The phase shift difference between two adjacent phased array surface loops 24 in each circle is 90°, and the two phased array surface loops 24 corresponding to the upper and lower circles (for example: ch7 and 3, ch8 in Fig. 3 The phase difference of the RF signal between 4, ch5 and 1, ch6 and 2) is 180°. The fixed capacitors C1, C2 and C3 cooperate with the adjustable capacitor Cf to tune the frequency of the loop, and Cp and Cs are used to tune the impedance matching and phase of the phased array surface loop 24 respectively. Inductor L1 is composed of four sections of copper skin, and the resonant frequency of this resonant circuit is 123.2MHz. In this embodiment, C1, C2 and C3 are non-magnetic and high-voltage fixed capacitors, and Cf, Cp and Cs are non-magnetic and high-voltage adjustable capacitors.

During the work of the present invention, the power splitter 11 in the parallel transmitting and receiving radio frequency interface circuit 1 divides the single-channel radio frequency signal A output from the single-channel power amplifier into eight road radio frequency signals, which are delivered to each phase shifter 12 respectively, and each phase shifter The phaser 12 linearly shifts each input radio frequency signal to obtain a uniform emission field. Simultaneously, the transmitting and receiving switch 14 in the parallel transmitting and receiving radio frequency interface circuit 1 works according to the switch control signal U for transmitting or receiving sent by the control system of the scanner. When the transmitting and receiving switch 14 receives the switching control signal U for transmitting, parallel The transmitting and receiving radio frequency interface circuit 1 is in the transmitting state, and transmits uniform eight-way radio frequency signals with different phases to the resonant circuit in the phased array surface circuit 24 on the phased array transmitting and receiving head coil 2 through the transmitting and receiving changeover switch 14. The hydrogen atoms in the soft tissue of the human brain in the coil 2 of the transmitting and receiving head are excited, so that the hydrogen atoms of the human body generate magnetic resonance signals; when the transmitting and receiving switch 14 receives the received switch control signal U, the parallel transmitting and receiving radio frequency interface circuit 1 is in the In the receiving state, the resonant circuit in each phased array surface circuit 24 on the coil 2 of the phased array transmitting and receiving head sends eight-way magnetic resonance signals generated by the excitation of hydrogen atoms in the human body to each transmitting and receiving switch 14, and transmits them in parallel. After the eight preamplifiers 15 in the receiving radio frequency interface circuit 1 amplify to B, it is sent to the magnetic resonance imaging system for image reconstruction and post-processing.

Above-mentioned each embodiment is only for illustrating the present invention, wherein the structure of each component, connection mode etc. all can be changed to some extent, every equivalent conversion and improvement carried out on the basis of the technical solution of the present invention, all should not be excluded from the present invention. outside the scope of protection of the invention.

Claims (6)

1. magnetic resonance High-Field imaging system; It is characterized in that: it comprises parallel emitting and receiving radio-frequency interface circuit and phased array emitting and receiving head coil; Said phased array emitting and receiving head coil comprises an inner casing and the shell that two ends are penetrating; The position of the corresponding tester's eye of said inner casing and shell all offers the form of a standard-sized sheet, and the outside surface of said inner casing is provided with upper and lower two circles totally eight phased array surface loops, and one of them said phased array surface loop is around said form setting;

Said parallel emitting and receiving radio-frequency interface circuit comprises that a power splitter, eight phase shifters, eight attenuators, eight emissions receive switch and eight prime amplifiers; The input end of said power splitter connects the output terminal of single channel power amplifier, being divided into the octuple radiofrequency signal from the single channel radiofrequency signal of said single channel power amplifier output; The output terminal of said power splitter connects the input end of eight said phase shifters; Each road radiofrequency signal that each said phase shifter will be imported is carried out linear phase shift; Input one said emission receives switch after dephased each road radiofrequency signal is regulated amplitude through a said attenuator; Each said emission receives the I/O end of switch with eight phased array surface loops on emission of radio frequency signals to the said phased array emitting and receiving head coil; Make that the phase shift difference between the adjacent two phased array surface loops is a definite value in every circle, the phase differential of radiofrequency signal is a definite value between the corresponding two phased array surface loops of upper and lower two circles; Said eight phased array surface loop emitting radio frequency signals also receive human body hydrogen atom generation octuple magnetic resonance signal, and said octuple magnetic resonance signal is imported a prime amplifier through the I/O end of each said emission reception switch respectively; The control end that each said emission receives switch all connects the control system of scanner, with the emission that receives said control system output or the switching controls instruction of reception.

2. magnetic resonance High-Field imaging system as claimed in claim 1 is characterized in that: said phase shifter is a concentric cable, and the length of said concentric cable determines the phase-shift phase of said phase shifter.

3. magnetic resonance High-Field imaging system as claimed in claim 2; It is characterized in that: the phase shift difference in every circle between the adjacent said two phased array surface loops is 90 °, and the phase differential of radiofrequency signal is 180 ° between the said two phased array surface loops of upper and lower two circle correspondences.

4. magnetic resonance High-Field imaging system as claimed in claim 1 is characterized in that: two phased array surface loops of the wherein three pairs of upper and lower two circle correspondences on the outside surface of said inner casing are for being symmetrical set.

5. like claim 1 or 2 or 3 or 4 described magnetic resonance High-Field imaging systems; It is characterized in that: each said phased array surface loop comprises three fixed capacities, three tunable capacitors and an inductance on the said phased array emitting and receiving head coil, and three fixed capacities wherein, two tunable capacitors and an inductance are connected into a resonant tank.

6. magnetic resonance High-Field imaging system as claimed in claim 5 is characterized in that: the two ends of the tunable capacitor in the said resonant tank receive switch through the emission that another said tunable capacitor of the series connection of an end wherein connects in the said radio-frequency interface circuit; Said fixed capacity is the high pressure resistant fixed capacity of no magnetic, and said tunable capacitor is the high pressure resistant tunable capacitor of no magnetic; Inductance is made up of four sections copper sheets in the said phased array surface loop.

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