JP3095402B2 - Transmitter / receiver for magnetic resonance imaging apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] (Industrial application field) The present invention relates to morphological information such as slice images of a subject (living body) and spectroscopy utilizing a magnetic resonance (MR) phenomenon. The present invention relates to a transmission / reception device of a magnetic resonance imaging apparatus that obtains functional information such as a scopy.

(Prior Art) A magnetic resonance phenomenon is a phenomenon in which a nucleus having a non-zero spin and a magnetic moment placed in a static magnetic field resonatesly absorbs and emits only an electromagnetic wave of a specific frequency. Resonates at an angular frequency ω ₀ (ω ₀ = 2πν ₀ , ν ₀ ; Larmor frequency) shown in FIG.

ω ₀ = γHo where γ is the gyromagnetic ratio specific to the type of atomic nucleus, and H ₀ is the static magnetic field strength.

This type of MR imaging device (MRI device) that performs a living body diagnosis using the above principle processes the electromagnetic waves of the same frequency induced after the above-mentioned resonance absorption, and processes the nucleus density and longitudinal relaxation time. Diagnostic information reflecting information such as T ₁ , lateral relaxation time T ₂ , flow, chemical shift, etc., for example, a slice image of a subject, etc. is obtained in a non-invasive manner.

The collection of diagnostic information by magnetic resonance can excite all parts of the subject arranged in a static magnetic field and collect signals. However, there are restrictions on the device configuration and clinical demands on imaging images. For this reason, an actual apparatus excites a specific portion and collects a signal of the specific portion.

In this case, the specific part to be imaged is generally a slice part having a certain thickness, and the echo signal from this slice part and the magnetic resonance signal (MR signal) of the FID signal are often used. The data is collected by executing a data encoding process, and the data group is subjected to image reconstruction processing by, for example, a two-dimensional Fourier transform method, thereby generating an image of the specific slice portion.

In addition, this type of MRI apparatus uses permanent magnets, superconducting magnets,
A static magnetic field generator by one or a combination of normal conducting magnets,
A gradient magnetic field generating coil and its power supply, an RF coil unit including one or a combination of a transmitting (dedicated) coil, a receiving (dedicated) coil, and a transmitting / receiving (combined) coil, and transmitting to the subject from the transmitting / receiving coil unit or the transmitting coil. A transmitter that generates a transmission signal for excitation according to a magnetic resonance phenomenon, and a receiver that receives a magnetic resonance signal induced in the subject from the transmission / reception coil unit or the reception coil,
The power supply of the gradient magnetic field generating coil, the transmitter and the receiver are operated in a pulse sequence for signal collection, and the received signal is subjected to pixel reconstruction such as Fourier transform to generate an image, and necessary control and signal processing is performed. And a computer system that controls it. Note that the RF coil unit, the transmitter, and the receiver constitute a transmission / reception device.

Here, as shown in FIG. 13, the RF coil unit 100
Since the subject 22 is placed inside, the stray capacitance C _S exists, and its value differs for each subject 22 due to factors such as the size of the subject, and the overall impedance of the RF coil unit 100 fluctuates. It was a factor to make it.

On the other hand, an RF coil unit 100 of this type of MRI apparatus has a first coil and a second coil, and the first coil and the second coil are geometrically displaced by 90 °. Some have been configured. As a receiver, 90
も の There is one that performs quadrature detection using two detectors with shifted phases. This detector uses quadrature detection (QD: Quadrutur
e Detection) method. The above-described RF coil unit 100 in which the first coil and the second coil are geometrically displaced by 90 ° is called a QD coil, and there are several types of this QD coil.

FIG. 14 is a configuration diagram of a conventional transmission / reception device, in which a variation in the impedance of a QD coil caused by a variation in the stray capacitance C _S can be compensated for by a capacitance component of a resonator.

That is, the coil 10 forms a linear coil, is connected to the resonator 12, and is connected to the transmitter 18 and the receiver 20 via the transmission / reception switching circuit 16. In the coil 10, for example, the head of a human body is placed as the subject 22.

Here, the capacitance component of the resonator 12 is constituted by the respective variable capacity tuning capacitor C _T, a matching capacitor C _M of the variable displacement type.

(Problems to be Solved by the Invention) In the above-described compensating means, each time compensation is required, that is, every time the subject changes, two tuning capacitors C _T and matching capacitors C _M in the example of FIG. 14 are used. It is necessary to adjust the variable capacitor. In order to make this adjustment, it is necessary only to add an impedance detector, a driving means (motor, etc.) for the variable capacitance type capacitor, and a switching device for inserting the additional system into the circuit of FIG. On the other hand, the adjustment work is complicated and time-consuming, and as a result, the examination efficiency is reduced and the patient suffers more.

Although the above is a consideration of the coil impedance fluctuation accompanying the change in the stray capacitance when the subject is changed, the coil impedance fluctuation may occur in other cases. That is, the coil 10
Must match the frequency of the magnetic resonance signal to be received. In this case, the frequency of the magnetic resonance signal changes according to the static magnetic field strength even for the same nuclide, and differs depending on the type of nuclide even for the same static magnetic field strength. Generally, it has a wide band of several megahertz to tens of megahertz.

Therefore, when the static magnetic field strength or the nuclide to be imaged is changed, the above-described compensation must be performed each time.
The same problem as described above, that is, every time compensation is required, that is, each time the static magnetic field strength or the nuclide to be imaged is changed,
In the example of the figure, it is necessary to adjust two variable capacitance capacitors, which are the tuning capacitor C _T and the matching capacitor C _M. In order to perform this adjustment, the impedance detector and the driving means of the variable capacitor (motor, etc.)
In addition to the need for a switch or the like for adding an additional system and inserting the additional system into the circuit shown in FIG. 14, the operation for adjustment is complicated and time-consuming, and as a result, the inspection efficiency is reduced. The patient suffered more pain.

Therefore, the object of the present invention is that no adjustment work is required,
An object of the present invention is to provide a transmission / reception device of a magnetic resonance imaging apparatus capable of practically compensating for a coil impedance variation accompanying a variation of a stray capacitance for each subject.

Another object of the present invention is to provide a magnetic recording apparatus in which even if the static magnetic field strength and the nuclide to be imaged are changed, once the adjustment is performed, no adjustment work is required thereafter, and the coil impedance fluctuation can be practically compensated. An object of the present invention is to provide a transmission / reception device for a resonance imaging device.

[Structure of the Invention] (Means for Solving the Problems) The present invention has a structure in which the following means are taken in order to solve the above problems and achieve the object. That is, the transmitting and receiving device of the magnetic resonance imaging apparatus according to claim 1 of the present invention includes a first coil, a second coil geometrically displaced by 90 ° with respect to the first coil, Transmitting means for transmitting a signal, the first and second signals
Receiving means for receiving an output signal from the coil of
A first signal control means provided corresponding to the first coil, wherein the high frequency signal output from the transmission means is distributed to first and second signals, and the first signal is phase-shifted. Is supplied to one of the first and second coils after shifting by 90 °, and a second signal is supplied to the other of the first and second coils by a first signal control means. , A second signal control means provided corresponding to the second coil, wherein an output signal from the first coil and an output signal from the second coil are output from one of the two coils. And a second signal control unit that combines the signals after shifting the phase by 90 ° and outputs the combined signals to the receiving unit.

A transmission / reception apparatus for a magnetic resonance imaging apparatus according to a second aspect of the present invention is the transmission / reception apparatus according to the first aspect, wherein the transmission / reception apparatus is provided between the first coil and the first signal control means and the second Characterized in that impedance conversion means is provided between the coil and the second signal control means.

Further, a transmission / reception device of the magnetic resonance imaging apparatus according to claim 3 of the present invention is the apparatus according to any one of claims 1 and 2, and the first and second signal control means include a broadband 90構成 さ れ る It is characterized by being composed of a hybrid circuit.

(Embodiment) Hereinafter, a first embodiment of a transmission / reception apparatus of a magnetic resonance imaging apparatus according to the present invention will be described with reference to FIG. 1 in which the same parts as those in FIG. .

In the present embodiment, as a transmitting / receiving coil unit, a first coil 10A and a second coil
STR as shown in FIG. 2 which is a QD coil 10 having 10B
(Slotted Tube Resonator) A coil 200, a cross elliptical coil (not shown), a saddle coil, a bird gauge coil, a surface QD coil (not shown), or the like can be used.

One terminal of the first resonator 12A is connected to the terminal of the first coil 10A of the QD coil 10, and one terminal of the second resonator 12B is connected to the terminal of the second coil 10B. One terminal of the 90 ° phase shifter 24 is connected to the other terminal of the first resonator 12A. The other terminal of the 90 ° phase shifter 24 and the second
The other terminals of the resonator 12B are connected to two input terminals of a combiner 14, respectively. The combined output terminal of the combiner 14 is connected to a transmitter 18 and a receiver 20 via a transmission / reception switching circuit 16.
In the QD coil 10, for example, the head of a human body is placed as the subject 22.

Here, the capacitance components of the first resonator 12A and the second resonator 12B are respectively a variable capacitance type tuning capacitor C _T and a variable capacitance type matching capacitor C _M.
It is composed of

The transmission / reception switching circuit 16 is capable of performing bidirectional switching using, for example, a PIN diode as a high-frequency switching element. The transmission mode and the reception mode are alternately set and controlled at high speed by a pulse sequence controller (not shown).

Further, a system including the first coil 10A and the first resonator 12A is referred to as a first channel, and the second coil 10B
And a system including the second resonator 12B is referred to as a second channel.

The above is the configuration of the transmission / reception apparatus. As the magnetic resonance imaging apparatus, in addition to the transmission / reception apparatus, a static magnetic field generator (not shown), a gradient magnetic field generating coil and a power supply thereof, a power supply of the gradient magnetic field generating coil and transmission Container 18
And a computer system that performs pulse sequence operation for the receiver 20 for signal collection, performs image reconstruction such as Fourier transform on the received signal to generate an image, and performs necessary control and signal processing. This computer system has a pulse sequence controller,
The control of the transmission / reception switching circuit 16 and the control of the transmitter 18 and the receiver 20 are performed as described above.

According to the transmission / reception apparatus of the magnetic resonance imaging apparatus according to the present embodiment configured as described above, the transmission / reception apparatus is used as follows. That is, when installed in the first, second resonator 12A, 12B tuning capacitor C _T of the capacitor C _M for matching QD coil 10, also assumed to be adjusted when appropriate. Here, the first coil 10A and the second coil 10B of the QD coil 10 are arranged symmetrically with respect to the subject, that is, the distance between the first coil 10A and the subject and the second coil 10A. 10B,
The distance between the subjects is the same, and the first coil 10
Since the A and the second coil 10B have the same structure, the change in the impedance in the first channel and the change in the impedance in the second channel are almost the same each time the subject changes.

In this case, since the 90 ° phase shifter 24 has a function of shifting the phase by 90 °, when the first channel is viewed through the 90 ° phase shifter 24 from the first channel side of the combiner 14, the reflected wave is:
Since the phase is shifted by 90 ° in the forward path, and the phase is shifted by 90 ° in the return path, the reflected wave returns by 180 ° due to both.

In other words, the reflected waves cancel each other out because the reflected waves are 180 ° out of phase. That is, there is no reflected wave. In other words, it is matched to 50Ω.

Therefore, if the coil impedance fluctuates due to the stray capacitance fluctuation for each subject 22,
1, the impedance matching of the entire first and second channels can be achieved without adjusting the capacitance components of the second resonators 12A and 12B. In this case, the transmission / reception switching circuit 16
The transmission mode and the reception mode are alternately set in conjunction with a pulse sequence for acquiring image data, and when the transmission mode is set, a transmission signal from the transmitter 18 is transmitted to the QD coil 10.
When a transmission signal (high-frequency pulse) for excitation is applied to the subject 22 and the reception mode is set,
The magnetic resonance signal received by the QD coil 10 is guided to the receiver 20.

As described above, according to the present embodiment, the tuning capacitor C _T and the matching capacitor C _{M of} the first and second resonators 12A and 12B are set when the QD coil 10 is installed or at an appropriate time.
Is adjusted, even if the coil impedance fluctuates in accordance with the stray capacitance of each subject 22, even if the coil impedance fluctuates, the impedance detector, the driving means of the variable capacitor (motor, etc.), Predetermined impedance matching is performed without adding a switch or the like and without requiring an operation for adjustment. Thereby, the inspection efficiency is improved.

Next, a second embodiment of the present invention will be described with reference to FIG.

That is, the second embodiment shows an example of a detailed example of the first embodiment. The combiner 14 and the 90 ° phase shifter 24 in the first embodiment are replaced by a high-frequency impedance converter. It comprises a 38 and 90 ° phase shifter 24.
Here, the high-frequency impedance converters 38 are 50
Two systems having an impedance of Ω are combined and converted into one system having an impedance of 50 Ω.

The operation of the configuration of the second embodiment will be described below. That is, the tuning capacitor C _T and the matching capacitor C _M of the first and second resonators 12A and 12B are used when the QD coil 10 is installed or at an appropriate time, for example, by a standard human equivalent phantom or the like. Assume that impedance matching adjustment of 50Ω has been made. Here, the first coil 10A and the second coil 10B of the QD coil 10 are arranged symmetrically with respect to the subject, that is, the distance between the first coil 10A and the subject and the second coil 10A. 10B, the interval between subjects is the same,
Moreover, since the first coil 10A and the second coil 10B have the same structure, when the impedance in the first channel changes, the change is almost the same as the change in the impedance in the second channel.

Here, a case will be described in which the subject 22 changes and the coil impedance fluctuates with the stray capacitance of each subject 22. In this case, assuming that the impedance of the first channel at the illustrated point is Z _A1 , Z _A1 = (50 + ΔR) + jΔI Similarly, assuming that the impedance of the first channel at the illustrated point is Z _A2 , Z _A2 = ( 50 + ΔR) + jΔI Here, ΔR and ΔI represent the real component and the imaginary component of the deviation width of each impedance from 50Ω. The real number component ΔR is ΔR≪50.

Assuming that the impedance of the first channel at the illustrated point is Z _A3 , Z _A3 = Z _A1 = (50 + ΔR) + jΔI On the other hand, the reflected wave of the second channel at the illustrated point is a 90 ° phase shifter. As a result of the shift by 24, the vehicle is shifted by 90 °, and the route is again shifted by 90 °, so the total shift is 180 °.

Therefore, the impedance Z _B4 of the second channel at the illustrated point is as follows.

Z _B4 = (50 + ΔR) −jΔI This is a complex conjugate relationship of Z _A1 .

Therefore, the combined impedance Z 'of Z _A3 and Z _B4 is as follows.

_{Z '= Z A3 + Z B4} = [(50 + ΔR) + jΔI] + [(50 + ΔR) -jΔI] = 100 + 2ΔR the synthetic impedance Z, since a half by the high-frequency impedance converter 38, it When Z ₅ next become that way.

Z ₅ = Z ′ / 2 = (100 + 2ΔR) / 2 = 50 + ΔR ≒ 50 Therefore, if the coil impedance fluctuates due to the stray capacitance fluctuation for each subject 22, the imaginary component is canceled and the real component It can be seen that only the change is affected (usually ΔI≫ΔR). Thus, first, second resonator 12A, 12B capacitors C _T for tuning, just keep adjusting the capacitor C _M for matching coil impedance even with the variation in the stray capacitance of each object 22 Even if a change occurs, the deviation of the impedance is suppressed to a level that does not pose a problem in practical use.
That is, predetermined impedance matching is performed without adding an impedance detector, a driving means (motor or the like) for a variable capacitance type capacitor, a switching device, or the like, and without requiring an operation for adjustment. .

Next, a third embodiment of the present invention will be described with reference to FIG.

That is, the third embodiment is a specific example of the first embodiment, and includes a transmission / reception switch 16A between the first channel and the first channel and the transmitter 18 and the receiver 20. ,
26B, a 90 ° hybrid 26A, 26B, and a resistor 28A, 28B interposed, where the 90 ° hybrid 26A, 26B
B is the same as that in the second embodiment, and can have a 90 ° phase function and a zero ° output combining function. The resistance values of the resistors 28A and 28B are the same as the impedance of the QD coil 10 (for example, 50Ω).

According to this configuration, the impedance of the first channel or the second channel can be phased by 90 ° at the time of transmission or reception, and the impedance of the first channel and the impedance of the second channel can be combined.
The same operation and effect as those of the embodiment can be obtained.

FIG. 5 shows a modification of FIG. 4 described above. That is,
The configuration shown in FIG. 5 is a balun having an impedance of 50Ω for each channel in FIG.
This is a configuration in which 29A and 29B are interposed, and the operation and characteristics are basically the same as those shown in FIG.

Next, a fourth embodiment of the present invention will be described with reference to FIG.

That is, in the fourth embodiment, the QD coil 10 in the configuration of the first embodiment is dedicated to transmission, the transmission / reception switch 16 is removed, and the reception coil 30 and the resonator 32 are added. Are connected to the receiver 20.

According to this configuration, the impedance of the first channel or the second channel can be phase-shifted by 90 ° at the time of transmission, and the impedance of the first channel and the second channel can be combined. The same operation and effect as the first embodiment can be obtained.

Next, a fifth embodiment of the present invention will be described with reference to FIG.

That is, in the fifth embodiment, the QD coil 10 in the configuration of the first embodiment is used only for reception, the transmission / reception switch 16 is removed, and the transmission coil 34 and the resonator 34 are added. Are connected to the transmitter 18.

According to this configuration, the impedance of the first channel or the second channel can be phased by 90 ° during reception, and the impedance of the first channel and the second channel can be combined. The same operation and effect as the first embodiment can be obtained.

The above-described examples of FIGS. 1 to 7 have a configuration in which even if the subjects are exchanged, the coil impedance variation due to the variation of the stray capacitance for each subject can be compensated for without any adjustment work. FIGS. 8 to 12 show examples in which the phase is set to 90 over a wide band even when the static magnetic field strength and the nuclide to be imaged are changed.
90 ゜ on the outbound trip, 90 ゜ on the return trip, 18 in total
When the phase is shifted by 0 °, the reflected waves cancel each other out, there is no reflected wave, and matching is achieved. Therefore, once the adjustment is performed at a certain frequency, there is no need for the adjustment work thereafter, and the configuration is such that the coil impedance fluctuation can be compensated in practical use.

The sixth embodiment shown in FIG. 8 corresponds to the first embodiment shown in FIG. 1, and includes a 90 ° phase shifter 24 and a combiner 14 having a normal frequency band characteristic in FIG. Wideband hybrid that combines the functions of a combiner and a 90 ° phase shifter in place of
114 is used. Here, in the first embodiment, the stray capacitance fluctuates every time the subject changes, but in the present embodiment, the frequency of the magnetic resonance signal is the static magnetic field even if the nuclide is the same. It varies depending on the strength, and even if the static magnetic field strength is the same, it differs depending on the type of nuclide. Therefore, two variable capacitance capacitors, a tuning capacitor C _T and a matching capacitor C _M , are used. The points that need to be adjusted are the same, the difference being that in this example, the bandwidth is a few megahertz to a few tens of megahealth. Therefore, in this embodiment, a wide-band hybrid 114 having both functions of a combiner and a 90 ° phase shifter is used instead of the 90 ° phase shifter 24 and the combiner 14 having the ordinary frequency band characteristic in FIG. is there.

 Similarly, examples of FIGS. 9 to 12 will be described below.

The seventh embodiment shown in FIG. 9 corresponds to the third embodiment shown in FIG. 4, and is different from the 90 ° hybrids 26A and 26B of the ordinary frequency band characteristic shown in FIG. The configuration uses 90 ° hybrids 126A and 126B.

The modification of the seventh embodiment shown in FIG. 10 corresponds to the modification of the third embodiment shown in FIG. 5, and has a normal frequency band characteristic 90 ° hybrid 26A shown in FIG. ,
The configuration is such that broadband 90 ° hybrids 126A and 126B are used instead of 26B.

The eighth embodiment shown in FIG. 11 corresponds to the fourth embodiment shown in FIG. 6, and includes a 90 ° phase shifter 24 and a combiner 14 having a normal frequency band characteristic in FIG. Wideband hybrid that combines the functions of a combiner and a 90 ° phase shifter in place of
114 is used.

The ninth embodiment shown in FIG. 12 corresponds to the fifth embodiment shown in FIG. 7, and includes a 90 ° phase shifter 24 and a combiner 14 having a normal frequency band characteristic in FIG. Wideband hybrid that combines the functions of a combiner and a 90 ° phase shifter in place of
114 is used.

The present invention is not limited to the above embodiments, but can be implemented with various modifications without departing from the spirit of the present invention.

[Effects of the Invention] As described above, according to the present invention, the reflected wave generated by the “shift” when the frequency is changed after performing the coil adjustment at a certain frequency is converted into the first signal for controlling the phase of the signal.
And can be eliminated by the second signal control means. This achieves broadband matching and eliminates the need for readjustment.

In addition, the first and second signal control means include first and second signal control means.
Since it is provided corresponding to the coil (channel) of
When the direction of the rotating magnetic field is reversed between the transmission of the high-frequency signal (RF excitation pulse) and the reception of the magnetic resonance signal, such transmission and reception can be effectively performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing the configuration of a first embodiment of a transmission / reception device of a magnetic resonance imaging apparatus according to the present invention, FIG. 2 is a perspective view of an STR coil as an example of a QD coil in the embodiment, and FIG. FIG. 4 is a diagram illustrating a configuration of a second embodiment of the transmission / reception device of the magnetic resonance imaging apparatus according to the present invention. FIG. 4 is a diagram illustrating a configuration of a third embodiment of the transmission / reception device of the magnetic resonance imaging device according to the present invention. FIG. 5 is a diagram showing the configuration of a modification of the third embodiment shown in FIG. 4, and FIG. 6 is a fourth diagram of the transmitting / receiving device of the magnetic resonance imaging apparatus according to the present invention.
FIG. 7 is a diagram showing the configuration of a fifth embodiment of the transmission / reception device of the magnetic resonance imaging apparatus according to the present invention, and FIG. 8 is a diagram showing the transmission / reception of the magnetic resonance imaging device according to the present invention. FIG. 9 is a diagram showing a configuration of a sixth embodiment of the device.
FIG. 9 is a diagram showing the configuration of a transmission / reception device of a magnetic resonance imaging apparatus according to a seventh embodiment of the present invention, and FIG.
FIG. 11 is a diagram showing the configuration of a modification of the seventh embodiment shown in FIG. 11, FIG. 11 is a diagram showing the configuration of an eighth embodiment of the transmission / reception device of the magnetic resonance imaging apparatus according to the present invention, and FIG. FIG. 13 is a diagram showing the configuration of a ninth embodiment of the transmission / reception device of the magnetic resonance imaging apparatus according to the present invention, FIG. 13 is a diagram showing the stray capacitance generated between the QD coil and the subject, and FIG. FIG. 2 is a diagram illustrating a configuration of a transmitting / receiving device of the device. 10 QD coil, 10A first coil, 10B second coil, 12A first resonator, 12B second resonator,
14 ... Synthesizer, 16 ... Transceiver, 16A ... Transceiver, 16B ... Transceiver, 18 ... Transmitter, 20 ... Receiver, 24 ... 90 、 Phase, 26A ... First 90 ° hybrid, 26B... Second 90 ° hybrid, 28A... First resistor, 28B... Second resistor, 29A, 29B... Balun, 30... Receiving coil, 32. , 34 ... transmitting coil, 36 ... resonator, 114 ... wide-band 90 ° hybrid, 126A ... first
Wideband 90 ° hybrid, 126B ... the second wideband 90 ° hybrid.

Claims (3)

(57) [Claims] A first coil; a second coil geometrically displaced by 90 ° with respect to the first coil; transmitting means for transmitting a high-frequency signal; Receiving means for receiving an output signal from the second coil; and first signal control means provided corresponding to the first coil, wherein the high-frequency signal output from the transmission means is transmitted to the first signal control means. And a second signal, and the first signal is shifted in phase by 90 ° before being supplied to one of the first and second coils, and a second signal is supplied to the first and second coils. First signal control means for supplying one of the two coils, and second signal control means provided corresponding to the second coil, wherein an output signal from the first coil and the second signal control means are provided. The output signal from the second coil and the output signal from one of the two coils. Transceiver of a magnetic resonance imaging apparatus which phase was synthesized from likeness 90 DEG, characterized by comprising a second signal control means for outputting to the receiving means. 2. An impedance balance / unbalance conversion means is provided between the first coil and the first signal control means and between the second coil and the second signal control means. The transmission / reception device according to claim 1, wherein: 3. The transmission / reception apparatus according to claim 1, wherein said first and second signal control means comprise a wide-band 90 ° hybrid circuit.