JPH057570A - Mri apparatus - Google Patents

Abstract

PURPOSE:To enable the prevention of degrading of an image as caused by the mixing into an RF system a noise attributed to a clock signal of a control system. CONSTITUTION:A phase relationship synchronizing means (PLL and a computer system) is included to maintain a relationship a phase of a clock signal of a control system 2 and a phase of an NMR signal for the whole view per observation. An arithmetic processing section 20 obtains a noise component attributed to a clock signal of a control system 2 from a reception data with the reception of no NMR signal and subtracts the noise component from a reception data of each view to correct the reception data. Or the arithmetic processing section 20 reconstructs an image by a Fourier transform of the reception data of each view while performing a processing a DC component to the end of the image thereby obtaining an image of a high quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MRI apparatus,
More specifically, the present invention relates to an MRI apparatus capable of preventing deterioration of image quality due to clock signal noise mixed in an RF system.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing the essential parts of an example of a conventional MRI apparatus. In this MRI apparatus 51, the control system 5
In 2, the 4 MHz signal generated by the oscillator 53 is multiplied,
A computer system is driven by generating a 32 MHz clock signal.

On the other hand, in the RF system (from the oscillator 54 to the bandpass filter BPF 6f in FIG. 3), the oscillator 5
The 10 MHz signal generated in step 4 is multiplied to create a 20 MHz signal and the frequency is divided to create a 5 MHz signal. And R
At the time of F transmission, a 1.29 MHz signal is generated by DDS based on the transmission / reception frequency switching signal from the control system 52, and this and 5 MHz signal are mixed by the mixer 5a to BP.
Generate 6.29MHz signal by F6a, and this and the above 2
The signal of 0MHz is mixed by the mixer 5b and 2 by the BPF 6b.
A signal of 6.29 MHz is generated, and the signal of 5 MHz modulated by the RF amplitude signal of the control system 52 is further mixed with the mixer 5.
An RF signal of 21.29 MHz is produced by mixing in d, and this is supplied to the RF coil 10 via an amplifier (not shown). Further, when receiving the NMR signal, a signal of 1.665 MHz is generated by DDS based on the transmission / reception frequency switching signal from the control system 52, and this signal and the signal of 5 MHz are mixed by the mixer 5a and then mixed by the BPF 6a. .665 MHz
A signal is produced, and the signal of 20 MHz is mixed with the mixer 5b to produce a signal of 26.665 MHz by the BPF 6b, which is supplied to the mixer 5e of the NMR signal receiving section.

In the NMR signal receiving section, 21.29 MHz received by the RF coil 10 and amplified by an amplifier (not shown)
Of the NMR signal of 26.665 MHz and the signal of the mixer 5
The signal of 5375MHz is made by BPF6e by mixing with e, and it is mixed with the signal of 5MHz by the mixer 5f.
A signal of 375 kHz is created by F6f, and this is input to the arithmetic processing unit 70 as received data. Arithmetic processing unit 70
Reconstructs the image by Fourier transforming the received data.

[0005]

In the above conventional MRI apparatus 51, the clock signal (32 MHz) of the control system 52 is used.
Is mixed as noise in the preceding stage of the mixer 5e of the NMR signal receiving unit, the mixer 5e mixes it with the 26.665 MHz signal to generate 5.335 MHz noise. This is not removed even by the BPF 6e because the frequency band is similar to the 5.375 MHz signal by the NMR signal.
The 5.335 MHz noise is mixed with the 5 MHz signal in the mixer 5f to generate 335 kHz noise. This is not removed even by the BPF 6f because the frequency band is close to the 375 kHz signal by the NMR signal. Therefore, noise of 335 kHz is mixed with the received data and input to the arithmetic processing unit 70.

FIG. 4 shows 375 kHz in the received data.
FIG. 3 is a conceptual diagram showing the NMR signal component of R and a noise component of 335 kHz for three different views. Control system 5
Since the two clock signals and the RF system signal are completely independent, the phase relationship between both components in each view is random.

As described above, in the MRI apparatus 51, the 375 kHz NMR signal component and 335 kHz of the received data are received.
Since the phase relationship of the noise component of kHz is random,
The noise component cannot be removed and appears as an artifact in the image, degrading the image quality.

Therefore, the present invention is to provide an MRI apparatus capable of preventing the deterioration of the image quality caused by the noise caused by the clock signal of the control system being mixed into the RF system.

[0009]

The MRI apparatus of the present invention comprises a phase relation synchronizing means for keeping the relation between the phase of the clock signal of the control system and the phase of the NMR signal constant for all views in one observation. What is done is a characteristic of the configuration.

In the above configuration, the received data is corrected by obtaining the noise component caused by the clock signal of the control system from the received data when the NMR signal is not received, and subtracting the noise component from the received data of each view. It is preferable to further include reception data correction means.

Further, in the above structure, the received data of each view is Fourier transformed to reconstruct the image, and the DC component is processed to remove the DC component at the edge of the image.
It is preferable to further include a component removing means.

[0012]

In the MRI apparatus of the present invention, the phase relation synchronizing means controls the relation between the phase of the clock signal of the control system and the phase of the NMR signal so as to be constant in every view. As a result, the phase relationship between the NMR signal component and the noise component in the received data becomes constant in every view,
Only the noise component is measured without the NMR signal component,
By subtracting it from the received data of each view, the noise component can be removed and an image without artifacts can be obtained. Further, for example, by using the Chopletson technique, the artifacts caused by the noise component can be driven to the edge of the image, so that the deterioration of the image can be substantially prevented. Also,

[0013]

The present invention will be described in more detail with reference to the embodiments shown in the drawings. The present invention is not limited to this. FIG. 1 shows an MR according to an embodiment of the present invention.
It is a block diagram which shows the I apparatus 1. In this MRI apparatus 1, the control system 2 multiplies the signal of 10 MHz generated by the oscillator 3 to produce a signal of 20 MHz, and multiplies the signal by 1.6 by a PLL to produce a clock signal of 32 MHz. Driving the system.

On the other hand, in the RF system (from the oscillator 3 to the bandpass filter BPF 6f in FIG. 1), the signal of 10 MHz generated in the oscillator 3 is multiplied to produce a signal of 20 MHz and the signal is divided to generate a signal of 5 MHz. create. Then, at the time of RF transmission, a 1.29 MHz signal is produced by DDS based on the transmission / reception frequency switching signal from the control system 2, and this and the 5 MHz signal are mixed by the mixer 5a, and the BPF 6a.
6.29MHz signal is generated by this, and this and 20MHz
The signal of 6 is mixed by the mixer 5b, and 26.2 by the BPF 6b.
A signal of 9 MHz is produced, and the 5 MHz signal modulated by the RF amplitude signal of the control system 2 is mixed by the mixer 5d to produce an RF signal of 21.29 MHz, which is supplied to the RF coil 10. When receiving the NMR signal, a DDS signal of 1.665 MHz is produced based on the transmission / reception frequency switching signal from the control system 2. This signal and the 5 MHz signal are mixed by the mixer 5a and mixed by the BPF 6a. .665 MHz signal is generated, and this and the 20 MHz signal are mixed by the mixer 5b, and the BPF 6b outputs 26.665M.
Create a Hz signal, and use this for the mixer 5e of the NMR signal receiver.
Supply to.

In the NMR signal receiving section, the NMR signal of 21.29 MHz received by the RF coil 10 and the above 26.6 are received.
The signal of 65 MHz is mixed by the mixer 5e to make a signal of 5.375 MHz by the BPF 6e, the signal of 5 MHz is mixed with the signal of 5 MHz by the mixer 5f, and the signal of 375 kHz is made by the BPF 6f, and this is input to the arithmetic processing unit 20 as received data. . The arithmetic processing unit 20 performs a Fourier transform on the received data to reconstruct an image.

In the MRI apparatus 1, the clock signal of the control system 2 is regarded as noise by the mixer 5 of the NMR signal receiving section.
If mixed in the previous stage from e, the above-mentioned 26.66 is mixed by the mixer 5e.
Mixing with the 5 MHz signal results in 5.335 MHz noise. This is not removed even by the BPF 6e because the frequency band is similar to the 5.375 MHz signal by the NMR signal. The 5.335 MHz noise is mixed with the 5 MHz signal in the mixer 5f to generate 335 kHz noise. This is not removed even by the BPF 6f because the frequency band is close to the 375 kHz signal by the NMR signal. Therefore, noise of 335 kHz is mixed in the received data and input to the arithmetic processing unit 20.

The control system 2 controls so that the relationship between the start timing of the pulse sequence and the phase of the clock signal in each view is always constant. Then,
Since the clock signal and the RF system signal are produced from the same oscillator 3, the relationship between the start timing of the pulse sequence and the phase of the RF system signal in each view is always constant. As a result, as shown in FIG. 2, the phase relationship between the 375 kHz NMR signal component and the 335 kHz noise component in the received data is constant in all views.

As described above, in the MRI apparatus 1, the 375 kHz NMR signal component and the 335 kHz of the received data are received.
Since the phase relationship of the noise component of Hz is constant, the arithmetic processing unit 20 can remove the noise component. That is, the arithmetic processing unit 20 separates the NM from the original observation.
Received data is obtained without an R signal component. Next, the original observation is performed, and the received data is subtracted from the obtained received data of each view. Then, the received data of each view after the subtraction is Fourier transformed to reconstruct the image. Since the image obtained by this is reconstructed from the received data from which the noise component caused by the clock signal of the control system 2 is removed, it is a high quality image without artifacts. Alternatively, the arithmetic processing unit 20
Although the received data including the noise component is used, the phase of the excitation pulse (90 ° pulse) is inverted for each view, and the signal excited in the negative phase is inverted and reconstructed to obtain the DC component ( The process of moving the baseline component) to the edge of the image (field of view) is performed. Since the phase relationship between the NMR signal component and the noise component is constant, the noise component is DC
Since it is considered as a component, the artifact caused by the clock signal of the control system 2 is driven to the edge of the image, and the original image is not spoiled.

As a process for driving the DC component to the edge of the image, in addition to the Chopper's method, the PLL and the computer system correspond to the phase relation synchronizing means.
Further, the arithmetic processing unit 20 uses the phase relation synchronizing means or DC.
It corresponds to a component removing means.

[0020]

According to the MRI apparatus of the present invention, it is possible to prevent the deterioration of the image quality due to the clock signal noise of the control system mixed in the RF system, and it is possible to obtain a high quality image.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of an MRI apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of received data of each view in the device of FIG.

FIG. 3 is a main part configuration diagram of an example of a conventional MRI apparatus.

FIG. 4 is an explanatory diagram of received data of each view in the device of FIG.

[Explanation of symbols]

1 MRI device 2 control system 3 oscillator 5a Mixer 6a bandpass filter 10 RF coil 20 arithmetic processing unit PLL phase-locked loop DDS Direct Digital Synthesizer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G06F 15/66 B 8420-5L 7831-4C A61B 5/05 390 9118-2J G01N 24/02 N

Claims (3)

[Claims] 1. The relationship between the phase of the clock signal of the control system and the phase of the NMR signal is shown for all views in one observation.
An MRI apparatus comprising a phase relationship synchronizing means for maintaining a constant value. 2. The MRI apparatus according to claim 1, wherein the NMR
The apparatus further comprises reception data correction means for correcting the reception data by obtaining a noise component caused by the clock signal of the control system from the reception data in the state where the signal is not received and subtracting the noise component from the reception data of each view. An MRI apparatus characterized in that 3. The MRI apparatus according to claim 1, further comprising DC component removing means for performing a Fourier transform on the received data of each view to reconstruct an image and for removing a DC component at the edge of the image. An MRI apparatus characterized in that