JPH0690922A - Rf coil for mri - Google Patents

Abstract

PURPOSE:To provide the constitution which is non-magnetic, can be used by high frequency power of several tens of kW, and can be subjected to fine adjustment in a QD distributor/coupler for QD (rotary magnetic field)-transmitting the high frequency power to an RF coil being signal transfer means in an MRI, and QD-adding a received signal. CONSTITUTION:The embodiment of a QD distributor/coupler for high power of 63.8MHz frequency is shown herein. As for a waveform matching cable 301 of #1/8, a high frequency coaxial cable RG-217/U of a 50OMEGA system is used. As for a capacitor 302, a non-magnetic high frequency power vacuum variable capacitor of 5kV breakdown strength, 25A current capacity, and about 5-100pF variable capacity is useful. By using the vacuum variable capacitor, fine adjustment of gain and phase between adjusting terminals can be executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is an inspection apparatus (MRI) using the NMR phenomenon for measuring nuclear magnetic resonance signals from hydrogen, phosphorus, etc. in a living body and visualizing the density distribution and relaxation time of nuclei.
In the above, relates to a QD distributor for QD-transmitting high-frequency power to the RF coil which is a signal transmitting / receiving means, or a QD coupler for QD-adding a received nuclear magnetic resonance signal.

[0002]

2. Description of the Related Art In order to improve the image quality of an MRI apparatus, it is essential to improve the performance of an RF coil which is a nuclear magnetic resonance signal measuring section.

Among them, QD conversion of the RF coil is effective in terms of theoretically improving the signal detection sensitivity by √2 times and improving the S / N ratio.
This is an important technique from the viewpoint that the high frequency heat generation of the human body can be reduced because it is only required to do 2. Further, the QD of the RF coil is also effective in terms of the uniformity of the captured image.

In the QD conversion of the RF coil, in order to generate a circularly polarized wave in the RF coil, the transmission power to two orthogonal ports is distributed and phase-shifted, and the received signal generated from the subject is circularly polarized. Receive as a wave at two ports, phase shift,
Need to add up.

The prior art is listed below.

1. Prepare two sets of distributor, coupler, and phase shifter separately and use them in combination.

2. A branch line type hybrid ring circuit in which four λ / 4 cables are combined is used, which has the functions of a distributor, a coupler, and a phase shifter.

3. Use the rat race circuit. This method is described in Journal of Magnetic Resonance (J.Magn.Reson.) Vol. 69, 236-24.
Reported on page 2 (1986).

4. A QD distribution / coupling circuit in which two λ / 8 cables and two capacitors are combined is used. For this basic configuration, refer to 1991 SMRM (Annual Meeti).
ngof the Society of Magnetic Resonance in Medicin
e) Proceedings, page 124.

[0010]

As described above, although there are some methods in the prior art, the λ / 8 described in item No. 4 is used.
A QD distribution / coupling circuit that combines two cables and two capacitors has a small number of parts and is useful.

The QD distribution / coupling circuit can be used even in a strong magnetic field, and requires a high frequency power as the field becomes higher. Therefore, it is necessary to have a structure capable of withstanding a high frequency power of several tens of kilowatts. . It is an object of the present invention to provide a QD distributor / combiner that can be used in high magnetic fields and with high frequency power.

From the viewpoint of improving operability, the QD distribution /
It is necessary to eliminate complicated cable routing between the coupling circuit and the RF coil, and it is desirable that the installation space be as small as possible. Another object of the present invention is to provide a structure of a QD distributor / combiner having a small installation space.

Further, regarding the method of adjusting the QD distribution / coupling circuit, in the prior art using the rat race circuit, the adjustment is performed by changing the cable length of the wavelength matching cable, and it is difficult to make fine adjustment after manufacturing. There was a problem. Yet another object of the present invention is to provide a QD distributor / combiner that can be finely adjusted.

Furthermore, in the transmission / reception system wiring system using the QD distribution / coupling circuit, an RF coil for both transmission and reception,
In particular, when a whole-body coil is used, a large amount of power is applied, so if the QD distribution circuit isolation becomes poor for some reason, part of the input high-frequency power may leak into the input of the preamplifier and destroy the preamplifier. There is. Another object of the present invention is to provide a wiring system for preventing preamplifier destruction by using the QD distribution / coupling circuit.

[0015]

In order to achieve the above object, a QD distribution / coupling circuit is constituted only by non-magnetic high frequency power components.

In order to achieve another purpose,
The wavelength matching cables are bundled in a loop and stored, and the QD
By directly connecting the distributor / coupler to the RF coil body,
Achieves a QD distributor / combiner with a small installation space.

In order to achieve still another object,
By using a variable capacitor, it is possible to realize a QD distributor / combiner capable of fine adjustment of gain and phase both manually and automatically.

In order to achieve another purpose, a QD distributor for transmission and a QD coupler for reception are separately prepared, and two cable wires between them are connected in series with a cross diode and λ / 4. A wiring system for preventing preamplifier destruction can be realized by connecting with a cross diode inserted in parallel with GND across a cable and turning on the diode passively or actively with DC bias.

[0019]

[Function] In order to automatically perform fine adjustment of the gain and phase of the QD distributor / coupler, a non-magnetic ultrasonic motor or the like is attached to the rotary shaft of the variable capacitor, and the shaft is rotated to control the capacitance value by computer control. It can be realized by changing it.

Further, in the wiring system for protection of the preamplifier, when a large amount of power is induced in the λ / 4 cable of the receiving system during high frequency power transmission, the cross diode inserted in parallel with the GND in the input stage of the preamplifier is passive. ON, λ
Due to the nature of the / 4 wavelength matching cable, the preamplifier side has a high impedance when viewed from the cross diode inserted in series, so that power is not supplied and the preamplifier is protected.
Further, in order to ensure this operation, a DC bias may be applied to the diode inserted in parallel with the GND at the input stage of the preamplifier in accordance with the gate signal for applying the irradiation pulse.

[0021]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an inspection apparatus using NMR which is an embodiment of the present invention. In the figure, 105 is a control device, 106 is a high frequency pulse generator, 107 is a power amplifier, 108 is a transmission / reception RF for generating a high frequency magnetic field and detecting a signal generated from a target object 120.
A coil, 109 is a preamplifier, 110 is a detector, and 111 is a signal processing device. Also, 112, 113, 11
4 are coils for generating a gradient magnetic field in the Z direction and directions perpendicular to the Z direction (X direction and Y direction) 115, 1 respectively.
16, 117 are the coils 112, 113, and
A power supply unit for driving 114 is shown. The gradient magnetic field generated by these coils causes the magnetic field distribution in the space in which the inspection target is placed to have a desired gradient. The control device 105 has a function of outputting various commands to each device at a fixed timing. The output of the high frequency pulse generator 106 is amplified by the power amplifier 107 and excites the RF coil 108. RF coil 10
The signal component received at 8 passes through the preamplifier 109,
After detection by the detector 110, the signal processing device 111 converts the image. The static magnetic field is generated by the coil 118 driven by the power supply 119. The human body 120 to be inspected is placed on a bed 121, and the bed 121 is configured to be movable on a support base 122.

According to the present invention, a QD distributor for QD transmitting the power generated by the high frequency power amplifier 108 to the RF coil 108 and an NM from the RF coil 108.
The present invention relates to a QD combiner for QD adding R signals.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows an embodiment of a QD distributor / combiner for high power at a frequency of 63.8 MHz.

In this embodiment, a 50Ω high frequency coaxial cable RG- is used as the λ / 8 wavelength matching cable 201.
217 / U is used. The capacitor 202 is a non-magnetic ceramic capacitor for high frequency power ATC-100E.
Is used.

The high frequency power is input from the terminal 210, the power is equally divided into the terminals 212 and 213 with a phase difference of 90 degrees, and is supplied to the RF coil connected to the end.

The NMR signal received by the RF coil is input from terminals 212 and 213, and QD is input to terminal 211.
It is added and output.

In this structure, the length of the cable 201 is about 370 ± 5 mm, and the capacity of the capacitor is 5 mm.
The desired characteristics, that is, the terminal 210-
Isolation between 211 and terminals 212-213 is 25 dB or more, and the phase difference is 90 degrees. Also, terminals 210-212
A transmission loss of 3 dB between the terminals 210 and 213 is obtained.

FIG. 3 shows another embodiment of the QD distributor / combiner for high power having a frequency of 63.8 MHz.

Also in this embodiment, as the λ / 8 wavelength matching cable 301, a 50Ω high-frequency coaxial cable RG-
217 / U is used. As the capacitor 302, a vacuum variable capacitor for high frequency power is used. The vacuum variable condenser is, for example, UC125 / 5/25 of EEV or COMET.
CV1C-30E, etc. of the company is useful. By using the variable capacitor, the gain and phase between the adjustment terminals can be finely adjusted.

Further, in this embodiment, a QD distributor / combiner capable of automatically adjusting the gain and the phase can be realized by changing the capacitance value of the variable capacitor by computer control.

FIG. 4 shows an embodiment of a QD coupler having a frequency of 63.8 MHz.

In this embodiment, the QD coupler is directly connected to the RF coil body by the connectors 403 and 404. The signal added with QD is the connector 405.
Is output to.

Since it is dedicated to reception, the remaining 1 port is terminated with 50Ω406.

In this case, since the installation space is limited,
A thin high-frequency coaxial cable such as 1.5D-2V is used as the λ / 8 cable, and the cables 401 are housed in a case that is bundled in a loop to reduce the storage space.

Also, the capacitor 402 is a variable capacitor, for example, Murata ceramic trimmer capacitor CV0.
Using 1-D500, fine adjustment of gain and phase between adjustment terminals is possible.

Incidentally, the embodiment shown in FIGS.
The configuration at 3.8MHz is shown, but the desired frequency,
For example, at 21.1MHz, the cable length is 110
It is about 0 mm, and the capacitance of the capacitor is 150 pF, and the desired characteristics can be obtained. The same applies to other frequencies, and the cable length and the capacitance value of the capacitor are almost inversely proportional to the frequency used.

FIG. 5 shows an embodiment showing a wiring system of a transmission / reception system using the QD distributor / combiner described in this patent.

This wiring system is the basis of the description in Document (1). The QD distributor / combiner 501 is used for a QD type RF coil for both transmission and reception.

High frequency power is input to the terminal 510 from the high frequency power amplifier 504, and the power is supplied to the X coil 502 and the Y coil.
The coil 503 is equally divided and supplied with a phase difference of 90 degrees.

Next, the X coil 502 and the Y coil 503.
The NMR signal received in (1) is QD-added to the terminal 511, output, and guided to the preamplifier 505.

In this case, the X coil 502 and the Y coil 5
If the matching of 03 is deviated from 50Ω for some reason, the isolation between the terminals 510 and 511 is deteriorated, and a part of the high frequency power input to the terminal 510 is lost.
There is a risk that the preamplifier 505 may be leaked to the first unit and the preamplifier 505 may be destroyed.

FIG. 6 shows another embodiment showing the wiring system of the transmission / reception system using the QD distributor / combiner described in this patent. This wiring system is the same QD type RF that is used for both transmission and reception as in FIG.
Used for coils.

In this embodiment, a QD distributor for transmission and a QD coupler for reception are separately prepared in order to prevent the destruction of the preamplifier described above.

The high frequency power input from the high frequency power amplifier 611 is equally divided by the QD distributor 601 with a phase difference of 90 degrees, passes through the cross diodes 605 and 606 which are passively turned on by the power application, the X coil 603 and the Y coil. 604.

Next, the X coil 603 and the Y coil 604
Since the NMR signal received at is too weak to turn on the cross diodes 605 and 606, the QD coupler 602 outputs a Q signal via the λ / 4 cables 609 and 610.
D-added and guided to the preamplifier 612.

When high power is induced in the λ / 4 cables 609 and 610 of the receiving system during high frequency power transmission, the cross diodes 607 and 608 are passively turned on, and λ /
Due to the nature of the four-wavelength matching cable, points A and B have high impedance, so no power is supplied and the preamplifier 6
12 is protected.

In order to ensure this operation, it is sufficient to apply a DC bias to the diodes 607 and 608 in accordance with the gate signal for applying the irradiation pulse. In this case, the diodes 607 and 608 need not be cross diodes.

FIG. 7 shows another embodiment showing the wiring system of the transmission / reception system using the QD distributor / combiner described in this patent. This wiring is used for a QD type RF coil dedicated to reception, for example, a head coil and a knee coil. The NMR signals received by the X coil 702 and the Y coil 703 are QD-added, output, and guided to the preamplifier 705. The cross diode 704 is for protecting the preamplifier 705. When high power is induced in the receiving coil 702 or 703,
704 is passively turned on, and the induced power is reduced to GND.

In this case, if the QD coupler has a structure as shown in FIG. 3, it can be directly connected to the main body of the receiving coil and the signal is amplified after the QD addition, so that only one preamplifier 705 is required.

FIG. 8 shows another embodiment showing the wiring system of the transmission / reception system using the QD distributor / combiner described in this patent. This wiring is used for a QD type RF coil dedicated to reception, for example, a head coil and a knee coil. The NMR signals received by the X coil 802 and the Y coil 803 are stored in the preamplifier 80.
6 and 807, QD is added by the QD coupler 801 and output. The cross diodes 804 and 805 are
This is for protecting the preamplifiers 806 and 807. If a large amount of power is induced in the receiving coil 802 or 803, 80
4 and 805 are passively turned on, the induced power is set to GND, and the preamplifier is protected.

[0053]

As described above, according to the present invention, a QD distributor / coupler having a non-magnetic structure and capable of withstanding high frequency power of several tens of kilowatts can be manufactured with a simple structure.

Since the number of parts is small, it is 3 compared to the conventional product.
It can be manufactured at a cost of less than one-third. Further, since it is non-magnetic, the installation place is not limited, and since it can be applied to a compact structure, operability is also improved.

Further, regarding the adjusting method, it becomes possible to easily perform fine adjustment after manufacturing, which is impossible in the conventional technique.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an inspection apparatus using NMR that is an embodiment of the present invention.

FIG. 2 is a configuration diagram of an embodiment of the present invention.

FIG. 3 is a configuration diagram of an embodiment of the present invention.

FIG. 4 is a configuration diagram of an embodiment of the present invention.

FIG. 5 is a wiring diagram of an embodiment of the present invention.

FIG. 6 is a wiring diagram of an embodiment of the present invention.

FIG. 7 is a wiring diagram of an embodiment of the present invention.

FIG. 8 is a wiring diagram of an example of the present invention.

[Explanation of symbols]

105 ... Control device, 106 ... High-frequency pulse generator, 10
7 ... Power amplifier, 108 ... RF coil, 109 ... Preamplifier, 110 ... Detector, 111 ... Signal processing device, 112,
113, 114, 118 ... Coil, 115, 116, 1
17, 119 ... Driving power source, 120 ... Human body, 121 ... Bed, support stand ... 122 Support stand, 201 ... Cable, 202
... capacitors, 210, 211, 212, 213 ... terminals, 301 ... cables, 302 ... variable capacitance capacitors,
310, 311, 312, 313 ... Terminal, 401 ... Cable, 402 ... Variable capacitor, 403, 404, 4
05 ... connector, 406 ... 50Ω terminator, 501 ... QD
Distributor / combiner, 502 ... X coil, 503 ... Y coil,
504 ... High frequency power amplifier, 505 ... Preamplifier, 51
0,511 ... Terminal, 601 ... QD distributor, 602 ... QD
Coupler, 603 ... X coil, 604 ... Y coil, 60
5,606,607,608 ... Cross diode, 60
9,610 ... λ / 4 cable, 611 ... High frequency power amplifier, 612 ... Preamplifier, 613, 614 ... 50Ω terminator, 701 ... QD coupler, 702 ... X coil, 703 ...
Y coil, 704 ... Cross diode, 705 ... Preamplifier, 706 ... 50Ω terminator, 801, ... QD coupler, 8
02 ... X coil, 803 ... Y coil, 804, 805 ...
Cross diode, 806, 807 ... Preamplifier, 80
8 ... 50Ω terminator.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location G01R 33/38 9219-2J G01N 24/04 E 9219-2J 24/08 D 8203-2G G01R 33 / 22 N

Claims (9)

[Claims] 1. A static magnetic field, a gradient magnetic field and a high frequency magnetic field, each magnetic field generating means, a signal detecting means for detecting a nuclear magnetic resonance signal from an inspection object, a computer for calculating a detection signal of the signal detecting means, and A QD for transmitting high-frequency power QD (Quadrature Detection) in an RF (Radio Frequency) coil, which is a signal detection unit in an inspection apparatus using nuclear magnetic resonance having an output unit for calculation by a computer Power distributor (hereinafter, QD distributor) and QD for adding nuclear magnetic resonance signals to QD
An R for MRI, which has a signal coupler (hereinafter, QD coupler), and the QD distributor and the QD coupler are composed of two wavelength matching cables and two sets of capacitors.
F coil. 2. The wavelength matching cable according to claim 1, wherein a coaxial cable (hereinafter, λ / 8 cable) having a length of ⅛ of a wavelength of a desired high frequency signal is used for MRI. RF coil. 3. An RF coil for MRI, wherein the λ / 8 cable according to claim 2 is bundled in a loop to reduce the storage space. 4. An RF coil for MRI, comprising a QD distributor and a QD coupler capable of finely adjusting gain and phase by using a variable capacitor as the capacitor according to claim 1. 5. The two wavelength-matching cables according to claim 1 and two sets of components such as capacitors are non-magnetic Q
MR having D distributor and QD coupler
RF coil for I. 6. An MRI characterized in that the QD distributor and the QD coupler according to claim 1 are directly connected to an RF coil body.
RF coil. 7. An RF coil for MRI, characterized in that the QD coupler according to claim 1 is directly connected to the output of a preamplifier through a cross diode for preamplifier protection. 8. A QD distributor and a QD distributor capable of automatically adjusting the gain and phase by changing the capacitance value of the variable capacitor according to claim 4 by computer control.
An RF coil for MRI, which has a D coupler. 9. In the transmission / reception system wiring system using a QD distributor and a QD coupler according to claim 1, a QD distributor for transmission and a QD coupler for reception are separately prepared, and the QD distributor and It is characterized by having a wiring system to prevent the destruction of the preamplifier by connecting two sets of QD couplers across λ / 4 and turning on the diodes passively or actively by DC bias. RF coil for MRI.