JPH10192253A - Rf coil for magnetic resonance imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a sensitivity area regardless of shape, placement, etc., of a coil, by connecting a high frequency attenuator and a high frequency phase shifter, which are independently controllable, to plural signal ports respectively and a signal synthesizer to the high frequency phase shifter. SOLUTION: Both ends of a number of linear segments 11 are connected to ring conductors 12, and this multisegment RF coil 10 is formed by a pair of segments 11 facing at 180 deg.. A high frequency attenuator 22 is connected to a signal port mounted on both ends of a capacitor inserted into each segment 11 via a preamplifier 21, and the high frequency phase shifter 23 is connected to the signal synthesizer 24. The attenuation degree of the high frequency attenuator 22 and the quantity of phase shift of the high frequency phase shifter 23 are arbitrarily and independently determined by a control signal from outside. Thereby control of a sensitivity area is enabled regardless of shape, placement, etc., of a coil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a magnetic resonance imaging apparatus for performing imaging using a magnetic resonance phenomenon, and more particularly to an RF coil used for transmitting or receiving an RF signal.

[0002]

2. Description of the Related Art Conventionally, an RF coil having a plurality of signal ports, such as a multi-segment type RF coil or a so-called multi coil, has been used as an RF coil for a magnetic resonance imaging apparatus. These are devised to improve the sensitivity uniformity and expand the sensitivity range. Signals from multiple ports (to multiple ports) are synthesized by the coil body, or after data collection, Combining.

[0003]

However, the conventional RF coil having a plurality of signal ports has a problem that the sensitivity region is generally determined by the shape or arrangement of the coil, and there is no flexibility. For this reason, a signal from a portion other than the target imaging region, for example, a moving portion may be detected in the same manner, and may cause an artifact that adversely affects the image.

SUMMARY OF THE INVENTION In view of the above, the present invention makes it possible to control a sensitivity area regardless of the shape and arrangement of a coil, and to create a dead area in which a signal from a specific part which causes an artifact is not received. It is an object of the present invention to provide an RF coil for a magnetic resonance imaging apparatus that can perform the above-described steps.

[0005]

In order to achieve the above object, in an RF coil for a magnetic resonance imaging apparatus according to the present invention, a plurality of signal ports, each of which is connected to the port and which can be independently controlled. It is characterized in that a high-frequency attenuator and a high-frequency phase shifter and a signal synthesizer connected to these high-frequency phase shifters are provided.

[0006] Respective signals from a plurality of signal ports of the RF coil are input to a signal synthesizer via a high-frequency attenuator and a high-frequency phase shifter. Therefore, signals can be synthesized after arbitrarily determining the degree of attenuation and the amount of phase shift of each signal.
In this way, since each signal can be arbitrarily superimposed or canceled out, it is possible to arbitrarily create a dead area by moving the signal superimposed part and the canceled out part, or to change the sensitivity depth. And so on.

[0007]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In the example shown in FIG. 1, the present invention is applied to a multi-segment type RF coil. This multi-segment type RF coil 10
Is connected to a ring-shaped conductor 12 by connecting both ends of a number of linear segments 11 to each other.
One coil is formed substantially by a pair of segments 11 facing each other by 80 °. The signal ports are provided at both ends of the capacitor 13 inserted in each segment 11. One signal port may be provided for one coil composed of a pair of segments 11 or one pair of segments 1
One coil may be provided and two coils may be provided for one coil.

Each port is connected to a high-frequency attenuator 22 via a preamplifier 21 and further to a high-frequency phase shifter 23. Many high-frequency phase shifters 23 are connected to a signal synthesizer 24. The high frequency attenuator 22 needs to be connected to a stage subsequent to the preamplifier 21 in order to reduce the noise figure of the received signal. The degree of attenuation of the high-frequency attenuator 22 and the amount of phase shift of the high-frequency phase shifter 23 can be independently and arbitrarily determined by an external control signal.

In this multi-segment type RF coil 10, when the total number of segments 11 is N, the signal detected in the n-th segment 11 is expressed as follows. A × cos {ωt + (2n−1) π / N} Since the signal detected in each segment 11 is basically synthesized without phase shift, the segment 11
The sensitivity distribution can be made more uniform as the number is increased.

FIG. 2 shows an example in which the present invention is applied to a so-called multi-coil. As shown in FIG.
The multi-coil 30 is formed by arranging a plurality of planar surface coils 31 in a plane so as to partially overlap each other. Each coil 31
Is connected to a high-frequency attenuator 22 via a preamplifier 21 and further connected to a high-frequency phase shifter 23. Many high-frequency phase shifters 23 are connected to a signal synthesizer 24. Generally, in this multi-coil 30, a coil 31
It is possible to widen the sensitivity distribution by increasing.

The high frequency attenuator 22 is configured, for example, as shown in FIG. The circuit in FIG. 3 can be basically regarded as a π-type resistance attenuation network formed by the resistance components of the PIN diodes 41, 42, and 43 connected in π-type. The resistance is changed by the DC bias current flowing through the PIN diodes 41, 42, and 43 to change the attenuation rate. The coils 44 to 47 are choke coils for blocking AC components, and the capacitors 48 to 51 are coupling capacitors for blocking DC. The DC bias currents applied to the attenuation rate control signal input terminals 52, 53 cause the PIN diodes 41, 42
Is Rp and the resistance of the PIN diode 43 is Rs, the attenuation rate B (dB) can be expressed by the following equation. B = 20 log {(1 + k) / (1-k) Rs} (dB)

As shown in FIG. 4, for example, the high-frequency phase shifter 23 includes inductances 61 to 64 and a capacitor 65.
To 68, the variable capacitance diodes 69 and 70, and the resistor 7
1, 72. A reverse bias voltage is applied to the variable capacitance diodes 69 and 70 by the control voltage from the phase control signal input terminal 73, and the capacitance is changed according to the control voltage to adjust the amount of change in the phase of the input RF signal. Output.

As described above, as shown in FIGS. 1 and 2, signals of a plurality of signal ports are respectively transmitted to the high-frequency attenuator 22.
And the high frequency phase shifter 23, the signal is synthesized by the signal synthesizer 24, so that the magnitude and phase of the signal from each segment can be determined irrespective of the shape and positional relationship of the coil segments. Therefore, the multi-segment RF coil 10 shown in FIG. 1 can cope with an elliptical magnetic field, and the multi-coil 30 shown in FIG. 2 can arbitrarily superimpose or cancel signals from each of the plurality of surface coils 31. Therefore, the dead zone can be arbitrarily created by moving the signal overlapping portion and the canceling portion, or the sensitivity depth (the size of the sensitive region in the direction perpendicular to the surface of the surface coil 31) can be varied. And so on. Since the sensitivity region can be controlled in this way, it is useful when, for example, it is desired to emphasize only a signal near the surface of the subject and perform imaging, or to remove the influence of an artifact from a specific part.

Note that the present invention is not limited to the above example, but is applicable to other types of RF coils and the like. Further, the specific circuit configuration of the high-frequency attenuator 22 and the high-frequency phase shifter 23 may have another configuration. In addition, it goes without saying that various changes can be made without departing from the spirit of the present invention.

[0015]

As described above, according to the RF coil for a magnetic resonance imaging apparatus of the present invention, the magnitude and phase of the signal from each segment are determined irrespective of the shape and positional relationship of each segment of the coil. Can be arbitrarily overlapped or canceled out, so that the sensitivity region can be controlled, and the sensitivity depth can be adjusted or a dead region can be created.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an embodiment of the present invention.

FIG. 2 is a schematic perspective view showing another embodiment.

FIG. 3 is a circuit diagram showing a circuit example of a high-frequency attenuator.

FIG. 4 is a circuit diagram showing a circuit example of a high-frequency phase shifter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Multi-segment type RF coil 11 Segment 12 Ring type conductor 13 Capacitor 21 Preamplifier 22 High frequency attenuator 23 High frequency phase shifter 24 Signal synthesizer 30 Multi coil 31 Planar surface coil 41-43 PIN diode 52, 53 Attenuation rate control Signal input terminal 69, 70 Variable capacitance diode 73 Phase control signal input terminal

Claims (1)

[Claims] 1. A high-frequency attenuator and a high-frequency phase shifter respectively connected to each of a plurality of signal ports, each of which can be independently controlled, and a signal combiner connected to these high-frequency phase shifters. An RF coil for a magnetic resonance imaging apparatus.