JP3337797B2 - Magnetic resonance imaging equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus, and more particularly to an improvement in a quadrature phase detector for performing quadrature phase detection on a signal from a receiving coil.

[0002]

2. Description of the Related Art A magnetic resonance imaging apparatus obtains a tomographic image of a subject through quadrature phase detection and image processing of a signal obtained from a receiving coil.

Here, the quadrature detector comprises a first circuit and a second circuit connected in parallel with each other.

[0004] The first circuit is configured to detect N
The MR signal is taken out as real-part information and is converted into a digital signal after passing through a low-pass filter. The second circuit takes out the NMR signal detected by the receiving coil as imaginary-part information and goes through a low-pass filter. Later, it is converted into a digital signal. In this case, both the real part information and the imaginary part information have been detected, and the phases are shifted by π / 2. Then, image processing is performed based on each digital signal from such a quadrature phase detector, and a tomographic image is displayed via a display.

[0005]

In the magnetic resonance imaging apparatus constructed as described above, the NMR signal detected by the receiving coil has a center frequency of, for example, 10 MHz.
z, a signal having a frequency component of a band of 20 KHz. Even if hum noise is mixed in this case, 10M
By mixing with the local signal at 1 Hz.
It becomes a signal of 0 MHz ± 50 Hz and is removed by a low-pass filter at the subsequent stage.

However, a problem has been pointed out that hum noise caused by a power supply mixed in a later stage of such a detection circuit appears on an image without being removed.

That is, for image reconstruction, A / D
It is necessary to convert an analog signal into a digital signal using a converter, but in order to effectively use the A / D converter, an input voltage of about 10 V is required. For this reason, after the detection, the signal amplified to about 1 V is amplified to about 10 V. If hum noise is mixed at this time, the hum noise is also amplified as it is and image reconstruction is performed. Will be an element. Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a magnetic resonance imaging system capable of greatly reducing the influence of hum noise due to a power supply despite its simple configuration. It is to provide a device.

[0008]

In order to achieve such an object, the present invention basically provides a method for producing a nuclear magnetic material from a subject.
A first circuit for detecting real part information of a resonance signal;
A second circuit for detecting imaginary part information of the sound signal.
Magnetic Resonance Imaging System with Quadrature Phase Detector
The first circuit and the second circuit each have two systems.
And one of the two lines is a
A wiring layer is formed on the lint board, and the other is
It is characterized by being provided on the wiring layer .

[0009]

According to the magnetic resonance imaging apparatus having such a configuration, one of the main signal line and the sub signal line of each of the first circuit and the second circuit is formed on the printed circuit board. And the other is a coated single wire superimposed on the wiring layer.
As a result, the area of the closed loop formed by the main signal line and the sub signal line becomes substantially zero, and the magnetic flux due to the hum noise hardly interlinks. For this reason, if hum noise is added to either the first circuit or the second circuit after the low-pass filter, hum noise having the same phase is added to the main signal line and the sub-signal line, and these hum noises are caused by the difference. Will disappear.

On the other hand, since the NMR signals of the main signal line and the sub signal line are out of phase with each other by π, they are amplified without loss and output. Therefore, irrespective of the simple configuration, the influence of the hum noise due to the power supply can be greatly reduced.

[0011]

FIG. 3 is a schematic diagram showing an embodiment of a magnetic resonance imaging apparatus according to the present invention. This magnetic resonance imaging apparatus is roughly classified into a central processing unit (CP)
U) 1, a sequencer 2, a transmission system 3, a static magnetic field generating magnet 4, a reception system 5, and a signal processing system 6.

The CPU 1 controls each of the sequencer 2, the transmission system 3, the reception system 5, and the signal processing system 6 according to a predetermined program. Sequencer 2
Operates based on a control command from the CPU 1, and sends various commands necessary for data collection of tomographic images of the subject 7 to the transmission system 3, the gradient magnetic field generation system 21, and the reception system 5.

The transmission system 3 has a high-frequency transmitter 8, a modulator 9, and an irradiation coil 11 as a high-frequency coil. The modulator 9 amplitude-modulates a high-frequency pulse from the high-frequency transmitter 8 according to a command from the sequencer 2. The amplitude-modulated high-frequency pulse is amplified through the high-frequency amplifier 10 and supplied to the irradiation coil 11, so that the subject 7 is irradiated with a predetermined pulse-shaped electromagnetic wave.

The static magnetic field generating magnet 4 is for generating a uniform static magnetic field around the subject 7 in a predetermined direction. An irradiation coil 11 is provided inside the static magnetic field generating magnet 4.
Besides, a gradient magnetic field coil 13 for generating a gradient magnetic field,
The receiving coil 14 of the receiving system 5 is provided. The gradient magnetic field generation system 21 controls the gradient magnetic field power supply 12 that supplies a current to the gradient magnetic field coil 13, a gradient magnetic field power supply 12 that supplies a current to the gradient magnetic field coil 13, and a gradient magnetic field power supply 12 that can apply a gradient magnetic field independently in Cartesian coordinate axis directions orthogonal to each other. And a sequencer 2.

The receiving system 5 has a receiving coil 14 as a high-frequency coil, an amplifier 15 connected to the receiving coil 14, a quadrature detector 16 and an A / D converter 17, and an NMR signal from the subject 7 When the receiving coil 14 detects the signal,
The signal is converted into a digital quantity via an amplifier 15, a quadrature phase detector 16, and an A / D converter 17, and is converted into two series of collected data sampled by the quadrature phase detector 16 at a timing instructed by the sequencer 2. The data is converted and sent to the central processing unit 1.

The signal processing system 6 has an external storage device such as a magnetic disk 20 and an optical disk 19 and a display 18 composed of a CRT or the like.
1, the CPU 1 executes processing such as signal processing and image reconstruction, and displays a desired cross-sectional image of the subject 7 on the display 18 as well as a magnetic disk 20 of an external storage device. To be recorded.

FIG. 2 shows the receiving coil 14 and the amplifier 1
5, quadrature detector 16, A / D converter 17, and C
FIG. 3 is a detailed diagram showing a PU1 extracted. Here, FIG.
In the figure, the circuit surrounded by the dotted line is a circuit mounted on the printed circuit board 50. In the figure, an NMR signal detected by a receiving coil 14 is amplified by an amplifier 15 and then input to a power splitter 23.

The power splitter 23 outputs the NMR signal as its input into two NMR signals without any change, one of which is used as real part information in a complex number and the other is used as imaginary part information. It has become.

The NMR signal used as the real part information is:
The signal is input to the mixer 24 and frequency-converted by the mixer. That is, the so-called local signals output from the high-frequency oscillator 8 constitute two signals whose phases are shifted by π / 2 by the phase shifter 25, respectively. A signal having a phase difference of 0 among these signals is input to the mixer 24, and a signal having a phase difference of −π / 2 is input to the imaginary part circuit 26.

The output from the mixer 24 includes a high-frequency component and a low-frequency component, and the low-pass filter 27 at the next stage extracts only the low-frequency component required for image reconstruction. Has become. Then, the signal composed of the low frequency component is input to the AF amplifier 28, and after being amplified by the AF amplifier 28, the A / D converter 1
7 and is input to the CPU 1.

On the other hand, the NMR signal used as the imaginary part information from the power splitter 23 is input to the imaginary part circuit 26, and its output is digitized by the A / D converter 17 and input to the CPU 1. Has become.

As described above, a local signal is input to the mixer 24 from the phase shifter 25. Further, the signal composed of low frequency components is A
The signal is input to an F amplifier 28, amplified by the AF amplifier 28, digitized by the A / D converter 17, and input to the CPU 1. Thus, the CPU 1 can reconstruct an image from each of the above-described signals and obtain a tomographic image.

Here, the terminals A and B of the mixer 24 are
The mixer 24 is connected through a transmission transformer. Therefore, the terminal A and the terminal B have an opposite phase relationship, and this relationship is maintained up to the input terminal of the AF amplifier 28. Since the AF amplifier 28 has a differential input, the common mode component of the hum noise induced on the signal line C is canceled by the input and does not appear at the output.

Thus, the common mode component of the hum noise can be prevented from affecting the image. In this embodiment, the following configuration is provided as a measure against the normal mode component of the hum noise. It has become.

FIG. 1 is an explanatory diagram showing the configuration on the printed circuit board 50 at the signal line C in the circuit shown in FIG. In the figure, for example, a wiring pattern 29 is connected to a terminal A of the mixer 24 and a terminal B of the mixer 24 is connected.
, A covered single wire 30 is laid so as to overlap with the wiring pattern 29.

In the circuit thus configured, the magnetic flux of the hum noise linked between the closed loop formed by the wiring pattern 29 and the coated single wire 30 can be reduced. Between the closed loop formed by the wiring pattern 29 and the coated single line 30, only the solder resist film 50A formed on the surface of the printed circuit board 50 and the outer coating of the coated single line 30 are formed, and the hum guided to the signal line C is formed. The normal mode component of noise depends only on the thickness of the resist film and the outer coating. This makes it possible to greatly reduce the influence of hum noise due to the power supply.

In this embodiment, the wiring pattern 29 and the coated single wire 30 are overlapped with each other and
Has alternately meandered surfaces through the through hole 40. Thereby, for example, the printed circuit board 50
The hum noise generated by the wiring on the front surface of the device is canceled by the hum noise generated by the wiring on the rear surface. For this reason, there is an effect that the normal mode component of the hum noise can be further reduced.

As described above, according to the magnetic resonance imaging apparatus shown in such an embodiment, each of the main signal line and the sub signal line of the first circuit and the second circuit has:
One of them is a wiring layer formed on a printed circuit board, and the other is a coated single wire superimposed on the wiring layer. As a result, the area of the closed loop formed by the main signal line and the sub signal line becomes substantially zero, and the magnetic flux due to the hum noise hardly interlinks.

Therefore, when hum noise is applied to either the first circuit or the second circuit after the low-pass filter, hum noise having the same phase is added to the main signal line and the sub-signal line. Will disappear due to the difference.

On the other hand, since the NMR signals of the main signal line and the sub signal line are out of phase with each other by π, they are amplified without loss and output. Therefore, irrespective of the simple configuration, the influence of the hum noise due to the power supply can be greatly reduced.

In the above-described embodiment, the superimposed wiring of the wiring layer 29 formed on the printed circuit board 50 and the covering single line 30 is formed in a meandering manner via the through hole 40.
It goes without saying that the present invention is not limited to this. This is because the effect of the present invention can be obtained even if the printed circuit board 50 is formed only on one surface.

[0032]

As is apparent from the above description,
ADVANTAGE OF THE INVENTION According to the magnetic resonance imaging apparatus by this invention, despite the simple structure, the influence of the hum noise by a power supply can be reduced significantly.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a main part showing an embodiment of a magnetic resonance imaging apparatus according to the present invention.

FIG. 2 is a circuit diagram showing details of a receiving system incorporated in the magnetic resonance imaging apparatus according to the present invention.

FIG. 3 is a schematic configuration diagram showing one embodiment of a magnetic resonance imaging apparatus according to the present invention.

[Explanation of symbols]

 29 wiring layer 30 coated single wire 40 through hole 50 printed circuit board

Claims (1)

(57) [Claims] 1. Real part information of a nuclear magnetic resonance signal from a subject is
A first circuit for detection and imaginary part information of the nuclear magnetic resonance signal are detected.
A quadrature detector configured with a second circuit
In the magnetic resonance imaging apparatus obtained, the first circuit and the second circuit each include two lines.
And one of the two lines is a print base.
A wiring layer is formed on the board, and the other
A magnetic resonance imaging apparatus, which is disposed above .