JPH0558103U - Blocking circuit for receiving coil of MR device - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to preferably block the coupling between the transmitting coil and the receiving coil even when the amplitude of the RF excitation pulse is small. A resonance circuit for receiving an NMR signal is formed in a receiving coil 3 of an MR device by interposing a first capacitor C1 and a second capacitor C2. The resonance coil L1 and the anti-parallel connected silicon diode D are connected to the first capacitor C1.
The parallel resonance type blocking circuit 201 is formed by connecting the series circuits 1a and D1b in parallel. The second capacitor C2 has an anti-parallel connection Schottky barrier diode D2.
The auxiliary blocking circuit 1 is formed by connecting a and D2b in parallel. [Effect] The disturbance of the RF pulse waveform can be almost eliminated.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to a receiving coil blocking circuit for an MR device, and more particularly to a receiving coil blocking circuit for an MR device useful for improving decoupling characteristics between a transmitting coil and a receiving coil.

[0002]

[Prior Art]

 FIG. 8 is a schematic diagram of an example of a conventional MR device. In this MR device 501, power is supplied from the transmission unit 102 to the transmission coil 103 via the coaxial cable A1, and the RF pulse is given to the patient K from the transmission coil 103. Then, the NMR signal from the patient K is received by the receiving coil 3, and is sampled by the receiving unit 104 via the coaxial cable A2.

As shown in FIG. 9, a first capacitor C1 and a second capacitor C2 are provided in the receiving coil 3 to form an NMR signal receiving resonance circuit. A series circuit of a resonance coil L1 and two anti-parallel connected silicon diodes D1a and D1b is connected in parallel to the first capacitor C1. The first capacitor C1, the resonance coil L1, and the silicon diodes D1a and D1b form a parallel resonance type blocking circuit 201 for preventing formation of a resonance circuit for receiving an NMR signal.

Since the silicon diodes D1a and D1b are turned off with respect to a weak NMR signal, the parallel resonance type blocking circuit 201 does not function, and the NMR by the receiving coil 3, the first capacitor C1 and the second capacitor C2. A resonant circuit for signal reception is formed. On the other hand, since the silicon diodes D1a and D1b are turned on for a strong RF pulse, the parallel resonance type blocking circuit 201 functions to receive the NMR signal by the receiving coil 3, the first capacitor C1 and the second capacitor C2. Eliminates the formation of resonant circuits.

[0005]

[Problems to be solved by the device]

 FIG. 10A is a waveform diagram of the RF pulse supplied from the transmitter 102. When the amplitude of the RF pulse is higher than the predetermined level ± H1, the parallel resonance type blocking circuit 201 functions as described above, and blocks the coupling between the transmission coil 103 and the reception coil 3. However, when the amplitude of the RF pulse is smaller than the predetermined level ± H1, since the voltage applied to the silicon diodes D1a and D1b is also small, the silicon diodes D1a and D1b do not turn on, and the transmission coil 103 and the reception coil 3 are separated. There is a problem that the waveform of the RF pulse is distorted as a result of coupling, as shown in FIG. Such a problem becomes remarkable when a small-diameter coil, a low-frequency coil, or the like is used as the transmission coil 103, or when scanning is performed at a low flip angle.

Therefore, an object of the present invention is to provide a receiving coil blocking circuit of an MR device capable of suitably blocking the coupling between the transmitting coil and the receiving coil even when the amplitude of the RF excitation pulse is small. ..

[0007]

[Means for Solving the Problems]

 A receiving coil blocking circuit of an MR device according to the present invention forms a resonance circuit for receiving an NMR signal in a receiving coil of the MR device by interposing a first capacitor and a second capacitor, and the first capacitor includes , A resonant coil and a series circuit of anti-parallel connected silicon diodes are connected in parallel to form a parallel resonant blocking circuit, and at least a Schottky barrier diode connected in anti-parallel is connected in parallel to the second capacitor. The structural feature is that an auxiliary blocking circuit is formed. In the above structure, a capacitor or coil may be connected in series with the Schottky barrier diode.

[0008]

[Action]

 In the receiving coil blocking circuit of the MR device of the present invention, the Schottky barrier diode having a small shoulder voltage is turned on and the auxiliary blocking circuit functions even if the level of the RF pulse is small and the silicon diode is not turned on. Then, since the second capacitor does not function, the receiving coil deviates from the resonance with respect to the RF pulse, and the transmitting coil and the receiving coil do not couple with each other. The current flowing through the Schottky barrier diode is small because the level of the RF pulse is small, and the Schottky barrier diode is not damaged.

When the level of the RF pulse is increased, the silicon diode is turned on and the parallel resonance type blocking circuit functions, so that the decoupling of the transmission coil and the reception coil is maintained. Further, since the parallel resonance type blocking circuit suppresses the current flowing through the receiving coil to a small value, the current flowing through the Schottky barrier diode is also small and the Schottky barrier diode is not damaged.

Since the level of the NMR signal is sufficiently smaller than the shoulder voltage of the Schottky barrier diode, the auxiliary blocking circuit does not function at the time of receiving the NMR signal and does not hinder the reception of the N MR signal.

[0011]

【Example】

 -First Embodiment- Fig. 1 is a schematic view of an MR device according to the present invention. In this MR device 101, power is supplied from a transmitter 102 to a transmission coil 103 via a coaxial cable A1, and an RF pulse is applied to a patient K from a transmission coil 103. Then, the NMR signal from the patient K is received by the receiving coil 3, and is sampled by the receiving unit 104 via the coaxial cable A2.

As shown in FIG. 2, the receiving coil 3 includes a first capacitor C1 and a second capacitor C2, which form a resonance circuit for receiving an NMR signal. A series circuit of a resonance coil L1 and two anti-parallel connected silicon diodes D1a and D1b is connected in parallel to the first capacitor C1. The first capacitor C1, the resonance coil L1, and the silicon diodes D1a and D1b form a parallel resonance type blocking circuit 201 for preventing formation of a resonance circuit for receiving an NMR signal.

Two Schottky barrier diodes D2a and D2b connected in antiparallel are connected in parallel to the second capacitor C2. The two Schottky barrier diodes D2a and D2b form an auxiliary blocking circuit 1 for preventing formation of a resonance circuit for receiving an NMR signal.

When receiving the NMR signal, since the NMR signal is weak, both the silicon diodes D1a and D1b and the Schottky barrier diodes D2a and D2b are off, and the parallel resonant blocking circuit 201 and the auxiliary blocking circuit 1 function. Instead, as shown in FIG. 3, a resonance circuit for receiving an NMR signal is formed by the receiving coil 3, the first capacitor C1, and the second capacitor C2.

At the time of transmitting the RF pulse, when the RF pulse is small, the silicon diodes D1a and D1b are turned off and the parallel resonant blocking circuit 201 does not function, but the Schottky barrier diodes D2a and D2b are turned on and the auxiliary blocking circuit is turned on. 1 functions, and only the receiving coil 3 and the first capacitor C1 are provided as shown in FIG. In this circuit, the transmitter coil 103 and the receiver coil 3 are in a decoupling state because they do not resonate with the RF pulse. The current flowing through the Schottky barrier diodes D2a and D2b is small because the level of the RF pulse is small, and does not damage the Schottky barrier diodes D2a and D2b.

At the time of transmitting the RF pulse, when the RF pulse is large, both the silicon diodes D1a and D1b and the Schottky barrier diodes D2a and D2b are turned on, and the parallel resonance type blocking circuit 201 and the auxiliary blocking circuit 1 also function, as shown in FIG. As shown in FIG. 5, the parallel resonance type blocking circuit 201 does not function the receiving coil 3, and the transmitting coil 103 and the receiving coil 3 are in the decoupling state. Further, since the parallel resonance type blocking circuit 201 suppresses the current flowing through the receiving coil 3 to be small, the current flowing through the Schottky barrier diodes D2a, D2b is also small, and the Schottky barrier diodes D2a, D2b are not damaged.

FIG. 6A is a waveform diagram of the RF pulse supplied from the transmitter 102. When the amplitude of the RF pulse is higher than the predetermined level ± H1, the parallel resonance type blocking circuit 201 functions as described above, and blocks the coupling between the transmission coil 103 and the reception coil 3. Further, when the amplitude of the RF pulse is larger than the predetermined level ± h1, the auxiliary blocking circuit 1 functions as described above to block the coupling between the transmission coil 103 and the reception coil 3. Therefore, as shown in FIG. 11B, the waveform distortion of the RF pulse can be almost eliminated.

-Second Embodiment- FIG. 7 is a view of a second embodiment of the present invention corresponding to FIG. In the second embodiment, the auxiliary blocking circuit 1 of FIG. 2 is replaced with an auxiliary blocking circuit 11 in which anti-parallel connection Schottky barrier diodes D2a and D2b are connected in series with a third capacitor C3. The other structure is similar to that shown in FIG. When the auxiliary blocking circuit 11 functions, the receiving coil 3, the first capacitor C1, the second capacitor, and the third capacitor become one resonance circuit. The resonance frequency can be adjusted by changing the third capacitor.

[0019]

[Effect of the device]

 According to the receiving coil blocking circuit of the MR device of the present invention, since the transmitting coil and the receiving coil are decoupled even when the level of the RF pulse is low, the disturbance of the waveform of the RF pulse can be almost eliminated.

[Brief description of drawings]

FIG. 1 is a schematic view of an MR device according to the present invention.

FIG. 2 is an explanatory diagram of a blocking circuit according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of an operation when receiving an NMR signal.

FIG. 4 is an explanatory diagram of an operation when the RF pulse level is low.

FIG. 5 is an explanatory diagram of an operation when the level of the RF pulse is high.

FIG. 6 is a waveform diagram of an RF pulse according to the present invention.

FIG. 7 is an explanatory diagram of a blocking circuit according to a second embodiment of the present invention.

FIG. 8 is a schematic view of an example of a conventional MR device.

FIG. 9 is an explanatory diagram of an example of a conventional blocking circuit.

FIG. 10 is a waveform diagram of a conventional RF pulse.

[Explanation of symbols]

 1 Auxiliary Blocking Circuit 3 Receiver Coil 101 MR Device 102 Transmitter 103 Transmitter Coil 104 Receiver C1 First Capacitor C2 Second Capacitor L1 Resonant Coil D1a, D1b Silicon Diode D2a, D2b Schottky Barrier Diode 201 Parallel Resonant Blocking Circuit

Claims (1)

[Scope of utility model registration request] 1. A resonance coil for receiving an NMR signal is formed in a reception coil of an MR device by interposing a first capacitor and a second capacitor, and the resonance coil and an antiparallel-connected silicon are connected to the first capacitor. A series resonance circuit of diodes is connected in parallel to form a parallel resonance type blocking circuit, and an Schottky barrier diode connected in anti-parallel is at least connected in parallel to the second capacitor to form an auxiliary blocking circuit. Blocking circuit for the receiver coil of the device.