JPH06205753A - Rf signal transmitting/receiving system for mr device - Google Patents

Abstract

PURPOSE:To provide the RF signal transmitting/receiving system of an MR device driving the RF signal to the RF coil of the MR device (nuclear magnetic resonance device), having high reliability, and capable of transmitting and receiving in both the single mode and the quadrature mode. CONSTITUTION:This RF signal transmitting/receiving system of an MR device is provided with a power amplifier 10 generating the high-power RF signal, the first quadrapture hybrid 20 receiving the output of the power amplifier 10 on one input, transmission/reception switching circuits 21, 22 connected to two output signals different in phase of the first quadrapture hybrid 20, the second quadrapture hybrid 23 connected to the transmission/reception switching circuits 21, 22 and connected with its output to an RF coil 30 in the single transmission/reception mode, and the third quadrapture hybrid 26 receiving the detection signal of the RF coil 30 via the transmission/reception switching circuits 21, 22 and sending its output as the detection signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an RF signal transmission / reception system for an MR device (nuclear magnetic resonance device) for driving an RF signal to an RF coil and receiving a detection signal.

[0002]

2. Description of the Related Art An MR apparatus has been recently used as a means for visualizing anatomical information of a human body in the same manner as an X-ray CT apparatus. The MR device is a physics that emits a part of the absorbed RF energy when a specific atomic nucleus forming a biological tissue is excited by absorbing a specific radio frequency (hereinafter abbreviated as RF) under the influence of a magnetic field. It is based on a phenomenon (NMR phenomenon).

FIG. 5 is a conceptual diagram of an MR device. In the figure, reference numeral 1 is a magnet for generating a magnetic field, and 2 is an RF coil provided in the magnet 1 to which an electric power in an RF band is applied to obtain a detection signal thereof. In the case of the whole body magnet as shown in the figure, the patient 3 is placed so as to be wrapped inside the RF coil 2.

In such a state, the transmitter 4 applies power of a frequency in the RF band to the RF coil 2. The power applied to the transmitter 4 at this time is, for example, 10 KW to 20 KW.
Is used. As a result, a signal based on the NMR phenomenon from the body of the patient 3 is induced in the RF coil 2. Receiver 5
Receives the detection signal, amplifies it, and sends it to the A / D converter 6. The A / D converter 6 converts the input signal into digital data.

The computer 7 inputs the output data of the A / D converter 6, performs image processing, and displays the result on the display 8. The operator examines the lesion area of the patient while looking at the image displayed on the display 8.
Reference numeral 9 is an interface that acts as an intermediary between the computer 7 and other components (the transmitter 7, the receiver 5, and the A / D converter 6).

Next, the structure of the RF signal transmitting / receiving section will be described in detail. FIG. 6 is a conceptual diagram of a quadrature transceiver circuit. In the figure, 10 is a power amplifier which receives an RF signal and generates power for RF coil application. The output of the power amplifier 10 enters the quadrature hybrid 11 via the first changeover switch S1.

The quadrature hybrid (also referred to as a 90 ° splitter) has four terminals (connector terminals), and these terminals can be used as both input terminals and output terminals. FIG. 7 is an explanatory view of the usage state of the quadrature hybrid and shows the relationship between the input / output terminals and the phase. (A) and (b) are 1 input / 2 output modes, (c) and (d) are 2 input / 1 output modes.

For example, as shown in (a), when a signal is input to terminal 1 of these terminals, signals of which phases are 90 ° different from each other are generated at terminals 2 and 4 of the remaining three terminals. It is a thing. The remaining one terminal 3 is terminated with a resistor R. The resistor R has an impedance of 50Ω, and thus has a resistance value of 50Ω.

A second switch S2 is provided on the output side of the quadrature hybrid 11. Here, a method of connecting the first and second switches S1 and S2 will be described. The output of the power amplifier 10 is connected to the common contact of the first switch S1. The contact a of the switch S1 is connected to the quadrature hybrid 11, and the contact b is the second contact.
Is connected to the b contact of the switch S2. Switch S
The contact a of No. 2 is connected to the output terminal of the quadrature hybrid 11, and the common contact of the switch S2 is connected to the RF coil (not shown). The other output terminal of the quadrature hybrid 11 is connected to the RF coil without a switch. The operation of the circuit thus configured will be described below.

When the common contacts of the switches S1 and S2 are both connected to the b side, the power amplifier 10 is directly connected to the RF coil without the quadrature hybrid 11.
This mode is called single transmission / reception mode. Next, when the common contact of the switches S1 and S2 is connected to the a side, the output of the power amplifier 10 is connected to the quadrature hybrid 11. As a result, Quadrature Hybrid 11
RF signals whose phases are different from each other by 90 ° are taken out from and are applied to the RF coil. This mode is called the quadrature transmission / reception mode.

The single transmission / reception mode and the quadrature transmission / reception mode can be selectively used as necessary.
The quadrature transmission / reception mode has a property that power efficiency is twice as high as that of the single transmission / reception mode.

In such a configuration, the switches S1 and S2 are
You cannot use a relay for. The reason is that this circuit is placed in a strong magnetic field, so that the exciting coil of the relay cannot be excited well. Therefore, when the RF transceiver circuit is placed in a strong magnetic field, a diode switch circuit as shown in FIG. 8 is used.

In FIG. 8, the same parts as those in FIG. 6 are designated by the same reference numerals. In the figure, C1 to C6 are capacitors, L1 to L6 are inductors, and D1 to D4 are pin diodes. The capacitors C1 to C6 are all decaps, and the impedances XL of the inductors L1 to L6 are XL >> 50Ω.

A bias voltage B1 is applied to the anode of the diode D1 via the inductor L2, a bias voltage B2 is applied to the cathode of the diode D2 via the inductor L3, and a cathode of the diode D3 is applied to the cathode of the diode D3. The bias voltage B3 is applied, and the bias voltage B4 is applied to the anode of the diode D4 via the inductor L5.

The output of the power amplifier 10 is a capacitor C
1 is connected to the common connection point of the diodes D1 and D2, the anode of the diode D1 and the cathode of the diode D3 are connected via capacitors C2 and C4, and the cathode of the diode D2 is connected via the capacitor C3 to the quadrature hybrid 11 It is connected to the. One output of the quadrature hybrid 11 is connected to the anode of the diode D4 via the capacitor C5, and the diode D3
The common connection point of D4 and D4 is connected to the RF coil via the capacitor C6.

The inductor L1 is composed of diodes D1 and D2.
Of the diodes D3 and D4 and the ground. The inductor L6 is connected between the common connection point of the diodes D3 and D4 and the ground. Explaining the operation of the circuit configured in this way,
It is as follows. (During single transmission) At this time, diodes D1 and D3
A bias is applied to B1 and B3 so that a forward current flows. Further, the diodes D2 and D4 are reverse biased to B2 and B4 so as to cut off the output of the power amplifier 10. As a result, the signal flow changes from power amplifier → C1 → D1 → C2 → C4 → D3 → C6, and the output of the power amplifier 10 is directly connected to the RF coil in the single transmission mode. (When transmitting quadrature) At this time, diode D2
B2 and B4 are biased so that a forward current flows through D4. Further, the diodes D1 and D3 are connected to B1 and B3 so as to cut off the output of the power amplifier 10.
Reverse bias to. As a result, the signal flow is as follows: power amplifier → C1 → D2 → C3 → quadrature hybrid 11 → C5 → D4 → C6 or power amplifier → C1 → D
2 → C3 → quadrature hybrid 11 → RF coil, the output of the power amplifier 10 is converted by the quadrature hybrid 11 into two signals having a phase difference of 90 °, and the quadrature transmission mode is established in which the output signal is connected to the RF coil.

[0017]

As mentioned above, RF is used.
It is impossible to use a relay as a switch for switching the signal transmission / reception mode between the single transmission / reception mode and the quadrature transmission / reception mode in a strong magnetic field. In order to perform the switching operation even in a strong magnetic field, it is necessary to have a diode switch configuration using pin diodes as shown in FIG. However, it is 10K in 50Ω system
A diode that switches a large power of W to 20 KW is expensive and has a problem of low reliability. Also, a high voltage reverse bias was required.

The present invention has been made in view of the above problems, and an object thereof is to provide an RF signal transmission / reception system for an MR device which is highly reliable and can perform transmission / reception in both single mode and quadrature mode. I am trying.

[0019]

According to the present invention for solving the above-mentioned problems, there is provided a power amplifier which generates a high-power RF signal, and a first input which receives an output of the power amplifier.
Quadrature hybrid, and a transmission / reception switching circuit connected to the two output signals of the first quadrature hybrid having different phases, and in the single transmission / reception mode, these transmission / reception switching circuits are connected, and the output is connected to the RF coil. The second quadrature hybrid to be connected and the detection signal of the RF coil are received via a transmission / reception switching circuit,
It is characterized in that it is constituted by a third quadrature hybrid whose output is taken out as a detection signal.

[0020]

[Function] An RF coil with a quadrature hybrid and one with no quadrature hybrid are prepared. An RF coil with a quadrature hybrid is used in the single transmission / reception mode, and an RF coil without a quadrature hybrid is used in the quadrature transmission / reception mode. Further, in the single transmission / reception mode and the case of the quadrature transmission / reception mode, the detection signal input to the third quadrature hybrid is switched by the switch to enable the phase inversion. With such a configuration, it is possible to provide a highly reliable RF signal transmission / reception system for an MR device capable of transmitting and receiving in both single mode and quadrature mode.

[0021]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. The same parts as those in FIG. 6 are designated by the same reference numerals. In the figure, 10 is a power amplifier that generates a high-power RF signal, 20 is a first quadrature hybrid that receives the output of the power amplifier 10 at its one input, 2
1 and 22 are 2 of the first quadrature hybrid 20
It is a transmission / reception switching circuit that receives signals having different phases and transfers them to the RF coil, and also receives a detection signal from the RF coil.

Reference numeral 23 is a second quadrature hybrid which receives the outputs of these transmission / reception switching circuits 21 and 22 in the single transmission / reception mode and whose outputs are connected to the RF coil. 24 and 25 are the transmission / reception switching circuits 21 and 22.
A preamplifier for amplifying the detection signal by receiving the output of
These preamplifiers 24, 25 (transmission / reception switching circuit 21,
This is a changeover switch for changing over the output of 22) by a changeover signal to perform phase inversion.

26 receives the output of the changeover switch 40,
It is a third quadrature hybrid whose output is taken out as a detection signal. One terminal of each of the first to third quadrature hybrids 20, 23 and 26 is grounded by a resistor R. The resistance value of the resistor R is set to 50Ω for impedance matching. 30 is RF
It is a coil.

Here, the RF coil 30 and the second quadrature hybrid 23 are integrated. That is,
Second quadrature hybrid 23 and RF coil 30
Are integrated and are used in the single transmission / reception mode. In the quadrature transmission / reception mode, the quadrature hybrid 23 is not attached and only the RF coil 30 having two terminals is used.

Next, the structure of the changeover switch 40 will be described in detail. The changeover switch 40 has two switch parts. a is a common contact of the first switch section, b,
c is a contact corresponding to the common contact a. The b contact enters the first input of the third quadrature hybrid 26, c
The contact is in the second input. d is a common contact of the second switch portion, and e and f are contacts corresponding to the common contact d. The e-contact enters the first input of the third quadrature hybrid 26 and the f-contact enters the second input. The operation of the system configured as described above will be described below. (In single transmission / reception mode) At this time, as shown in FIG. 1, the RF coil 30 with the second quadrature hybrid 23 is used. The output of the power amplifier 10 enters the first quadrature hybrid 20, from which two signals 90 ° out of phase with each other are obtained.
These two RF signals enter the second quadrature hybrid 23 via the transmission / reception switching circuits 21 and 22.

Upon receiving the two signals having different phase differences, the quadrature hybrid 23 synthesizes these two signals into one signal and outputs it. Since one combined signal is applied from the quadrature hybrid 23 to the RF coil 30, the single transmission mode is set.

NMR detected from a subject (not shown)
The signal enters the second quadrature hybrid 23,
The detection signals input to the quadrature hybrid 23 are output from the two output terminals as signals having a phase difference of 90 °. These detection signals are amplified by the preamplifiers 24 and 25 via the transmission / reception switching circuits 21 and 22, and then enter the changeover switch 40.

At this time, in the changeover switch 40, the common contact a is connected to the c contact and the common contact d is connected to the e contact by the changeover signal, and the cross connection is made. Therefore, the third
From the quadrature hybrid 26, the sum of the two signals is extracted and output. Here, common contacts a and b
The reason why each is cross-connected will be described.

If the common contacts a and b of the changeover switch 40 are
Consider a case in which the common contacts a are connected to the b contacts and the common contacts d are connected to the f contacts, respectively, without cross-connecting. In this case, the quadrature hybrid 26 adds the two input signals. Since the phase difference between the two signals is 180 ° different, the addition result is 0. Therefore, no output appears at the output terminal of the quadrature hybrid 26. Therefore, the result of addition of the two signals is doubled in amplitude by cross connection.

FIG. 2 is a diagram showing a signal flow during single transmission / reception according to the present invention. However, the signal level is ignored. In the figure, α, β, γ indicate phases, and β = π /
Set to 2. The signal of 2 sin ωt from the power amplifier 10 enters the first quadrature hybrid 26, and sin (ωt) from the quadrature hybrid 20.
+ Α1) and sin (ωt + α1 + β) are output. These signals enter the transmission / reception switching circuits 21 and 22, undergo a phase change, and their outputs are sin (ωt + α2).
), Sin (ωt + α2 + β).

These signals enter the second quadrature hybrid 23 and are combined into one signal 2sin (ωt +
It is output as α 3) and is applied to the RF coil 30.
The detection signal 2 sin ωt is taken out from the RF coil 30 and enters the second quadrature hybrid 23. The two signals output from the quadrature hybrid 23 are sin (ωt + γ1) and sin (ωt + γ1), respectively.
1 + β).

As a result of these signals entering the transmission / reception switching circuits 21 and 22, their output signals are sin (ωt + γ2).
), Sin (ωt + γ2 + β). These two signals are cross-connected and input to the third quadrature hybrid 26. The signals at the input stage of the quadrature hybrid 26 are sin (ωt + γ3) and s, respectively.
in (ωt + γ3 + β). As a result of adding these signals inside the quadrature hybrid 26, the output becomes 2 sin (ωt + γ4). (In quadrature transmission / reception mode) At this time, unlike the configuration shown in FIG. 1, the second quadrature hybrid 2
The RF coil 30 with 3 is not used. Therefore, the outputs of the transmission / reception switching circuits 21 and 22 are directly output to the RF coil 3.
Will be applied to zero. The output of the power amplifier 10 enters the first quadrature hybrid 20, from which two signals 90 ° out of phase with each other are obtained. These two RF signals are transmitted and received by the transmission / reception switching circuit 21,
It is applied to the RF coil 30 via 22.

NMR detected from a subject (not shown)
The signals are extracted as two phase difference signals, and these detection signals are amplified by the preamplifiers 24 and 25 via the transmission / reception switching circuits 21 and 22, and then enter the changeover switch 40.

At this time, the changeover switch 40 is in phase connection with the common contact a connected to the b contact and the common contact d connected to the f contact according to the changeover signal. Therefore, the third
From the quadrature hybrid 26, the sum of the two signals is extracted and output.

FIG. 3 is a diagram showing a signal flow when transmitting and receiving a quadrature according to the present invention. However, the signal level is ignored. In the figure, α, β, and γ indicate phases, and β =
π / 2. The signal of 2 sin ωt from the power amplifier 10 enters the first quadrature hybrid 26, and sin from the quadrature hybrid 20 respectively.
(Ωt + α1) and sin (ωt + α1 + β) are output. These signals enter the transmission / reception switching circuits 21 and 22,
A phase change occurs, and the outputs are sin (ωt +
α2) and sin (ωt + α2 + β).

These signals are applied to the RF coil 30. From the RF coil 30, the detection signal sin (ωt + γ1
), Sin (ωt + γ1 + β) are extracted. As a result of these signals entering the transmission / reception switching circuits 21 and 22, the output signals are sin (ωt + γ2) and sin (ωt), respectively.
+ Γ2 + β). These two signals are input to the third quadrature hybrid 26. As a result of adding these signals inside the quadrature hybrid 26, the output becomes 2 sin (ωt + γ3).

FIG. 4 is a block diagram showing the configuration of another embodiment of the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals. The difference between this embodiment and the embodiment shown in FIG.
The F coil 31. In this embodiment, the RF coil 31
Is a single transmission / reception coil, and has a transmission port and a reception port independently. The transmission port and the reception port are 2 of the quadrature hybrid 23, respectively.
It is connected to each of the two terminals. In this case, since the output end from the quadrature hybrid 23 and the input end from the RF coil 31 are different, the phase of the reception output from the quadrature hybrid 23 is not inverted, so the changeover switch 40 is unnecessary. If there is the changeover switch 40, the connection can be handled by making the same in-phase connection as in the case of quadrature transmission / reception.

In the above-mentioned embodiment, the case where the changeover switch 40 is provided in front of the third quadrature hybrid 26 is taken as an example. However, the present invention is not limited to this, and may be provided after the third quadrature hybrid 26. Then, the two outputs of the quadrature hybrid can be switched by a switching signal from the outside and taken out as a detection signal.

[0039]

As described above in detail, according to the present invention, by eliminating the switching in the part where power is applied, the MR device having high reliability and capable of transmitting and receiving both in the single mode and the quadrature mode. The RF signal transmitting / receiving system can be provided.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a signal flow during single transmission / reception according to the present invention.

FIG. 3 is a diagram showing a signal flow during quadrature transmission / reception according to the present invention.

FIG. 4 is a configuration block diagram showing another embodiment of the present invention.

FIG. 5 is a conceptual diagram of an MR device.

FIG. 6 is a conceptual diagram of a quadrature transceiver circuit.

FIG. 7 is a diagram illustrating a usage state of a quadrature hybrid.

FIG. 8 is a diagram showing another example of a quadrature transceiver circuit.

[Explanation of symbols]

 10 power amplifier 20 quadrature hybrid 21 transmission / reception switching circuit 22 transmission / reception switching circuit 23 quadrature hybrid 24 preamplifier 25 preamplifier 26 quadrature hybrid 30 RF coil 40 changeover switch

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location 9219-2J G01N 24/04 D 9219-2J E

Claims (6)

[Claims] 1. A power amplifier (10) for generating a high-power RF signal, a first quadrature hybrid (20) for receiving the output of the power amplifier (10) at one input thereof, and the first quadrature hybrid (20). A transmission / reception switching circuit (2) connected to two output signals of the quadrature hybrid (20) having different phases.
1) and (22), and a second quadrature hybrid (23) connected to the transmission / reception switching circuits (21) and (22) in the single transmission / reception mode and the output of which is connected to the RF coil (30). And a third quadrature hybrid (26) which receives the detection signal of the RF coil (30) via transmission / reception switching circuits (21) and (22) and whose output is taken out as a detection signal. RF signal transmission / reception system of the device. 2. The transmission / reception switching circuits (21), (22)
Between the third quadrature hybrid (26),
The RF signal transmission / reception system for an MR device according to claim 1, further comprising a changeover switch (40) for phase inversion. 3. In the quadrature transmission / reception mode, the second quadrature hybrid (23) is not attached to the R.
An RF signal transmitting / receiving system for an MR device according to claim 1, wherein an F coil (30) is used. 4. The transmission / reception switching circuit (21) in the quadrature transmission / reception mode,
The output of (22) is output to the third quadrature hybrid (2
6) In-phase connection, and in the single transmission / reception mode, the outputs of the transmission / reception switching circuits (21), (22) are cross-connected to the third quadrature hybrid (26). An RF signal transmission / reception system for the MR device described. 5. The switch (40) when the RF coil (30) having terminals divided into a transmission port and a reception port is used in a single transmission / reception mode.
3. The RF of the MR apparatus according to claim 2, wherein the outputs of the transmission / reception switching circuits (21) and (22) are connected in phase to the third quadrature hybrid (26).
Signal transmission / reception system. 6. A power amplifier (10) for generating a high-power RF signal, a first quadrature hybrid (20) for receiving the output of the power amplifier (10) at its one input, and the first quadrature hybrid (20). A transmission / reception switching circuit (2) connected to two output signals of the quadrature hybrid (20) having different phases.
1) and (22), and a second quadrature hybrid (23) connected to the transmission / reception switching circuits (21) and (22) in the single transmission / reception mode and the output of which is connected to the RF coil (30). A third quadrature hybrid (26) for receiving the detection signal of the RF coil (30) via the transmission / reception switching circuits (21), (22), and the third quadrature hybrid (26). An RF signal transmission / reception system for an MR device, which is configured to receive an output and select one of these two outputs according to a mode type.