JPH0838445A - Nuclear magnetic resonance inspecting device - Google Patents

Abstract

PURPOSE:To regularly utilize the dynamic range of a receiving system with high efficiency even when the magnitude of input signal is fluctuated. CONSTITUTION:A digital attenuator 42 is controlled by a sequence controller 52 in such a manner that the attenuance is set large when input signal is large, and small when the input signal is small. Thus, a phase wave detecting circuit 54 or an A/D converter 43 can regularly treat signals of the same size regardless of the fluctuation of the input signal, and their dynamic ranges can be sufficiently utilized.

Description

Detailed Description of the Invention

[0001]

This invention relates to the nuclear magnetic resonance phenomenon (M
R phenomenon) is used to perform imaging and spectroscopy measurements, and
The present invention relates to improvement of a reception system of MR signals.

[0002]

2. Description of the Related Art In a nuclear magnetic resonance examination apparatus, a subject (human body) is irradiated with a pulsed RF power having a frequency matching the resonance frequency of the subject to excite the subject and generate an NMR signal generated in the subject. Data is received and collected, and the data is processed to reconstruct an image or perform a spectroscopy measurement. The magnitude of the NMR received signal varies depending on the situation. Therefore, the gain of the receiving system is
I try to adjust it before the measurement.

[0003]

However, conventionally, the gain of the receiving system is fixed after adjustment before measurement,
Inconvenience occurs because it cannot be changed during measurement. For example, in a three-dimensional imaging sequence, the amplitude value of the received signal changes greatly depending on the slice position. In this way, when the magnitude of the received signal changes during measurement, the gain of the receiving system must be set according to the maximum signal, but if this is the case, when the receiving signal is small, the dynamic range of the receiving system is small. Since it is only used, the accuracy of the collected data deteriorates.

In view of the above, the present invention makes it possible to effectively utilize the dynamic range of the receiving system to improve the accuracy of collected data and to improve the measurement accuracy such as the improvement of image quality in MR imaging. The purpose is to provide a device.

[0005]

In order to achieve the above object, according to the present invention, a magnetic field generator for generating a static magnetic field and a gradient magnetic field, an RF pulse transmitter, and an NMR signal are received and detected. Further, in a nuclear magnetic resonance examination apparatus having a receiving device for converting into digital data, a data processing device for processing data obtained from the receiving device, and a control device for controlling these, the receiving device is configured to receive the NM
It is characterized by including a high-speed variable attenuator that attenuates the R signal.

The high-speed variable attenuation type attenuator can be composed of a large number of attenuating elements and a semiconductor relay composed of a high-speed semiconductor switching element which switches these in accordance with signals from the outside.

[0007]

The receiver for receiving the NMR signal is provided with a high-speed attenuation type variable attenuator for attenuating the received NMR signal. This high-speed variable attenuation attenuator can change the attenuation at high speed, so the attenuation can be changed even during measurement, and even if the amplitude of the received signal changes during measurement, it can be followed. Attenuation can be changed. Therefore, the detection circuit after the attenuator, the A / D converter, and the like can always handle the received signal having a constant amplitude, and the dynamic range of these can be effectively utilized. Therefore, highly accurate measurement data can be obtained, and image quality can be improved when MR imaging is performed by a three-dimensional imaging sequence or the like.
The measurement accuracy can be improved.

If the high-speed variable attenuation attenuator is composed of a large number of attenuating elements and a semiconductor relay composed of a high-speed semiconductor switching element that switches these in accordance with external signals, the attenuating elements are attenuated according to external signals. Since the degree can be changed digitally (stepwise) at high speed, the attenuation degree change command can be issued from the control device during measurement to make the attenuation degree follow the change of the received signal during measurement. You can

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. A nuclear magnetic resonance examination apparatus according to one embodiment of the present invention is configured as shown in FIG. In FIG. 1, the magnet assembly 11 includes a main magnet for generating a static magnetic field and a gradient magnetic field coil for generating a gradient magnetic field that is superimposed on the static magnetic field. The gradient magnetic field is generated by X,
It is generated as the magnetic field strengths are respectively inclined in the directions of three axes of Y and Z. By selecting one of the gradient magnetic fields in the three-axis directions or by combining them, the gradient magnetic field Gs for slice selection, the gradient magnetic field Gr for reading and frequency encoding, and the gradient magnetic field Gp for phase encoding are set in arbitrary directions. It

An object (not shown) is placed in the space to which the static magnetic field and the gradient magnetic field are applied. For this subject,
An RF coil 12 is attached for irradiating the subject with RF pulses and for receiving the NMR signal generated in the subject.

A current supplied to the gradient magnetic field coil of the magnet assembly 11 is given by the gradient magnetic field controller 21.
The waveform of the pulse current corresponding to the gradient magnetic field pulse is controlled by the gradient magnetic field controller 21. The waveform data is given from the sequence controller 52 to the gradient magnetic field control device 21, whereby the gradient magnetic fields Gs, Gp, and Gr generated as pulses having a waveform required in a pulse sequence such as the spin echo method or the gradient echo method are generated. Will be made.

The RF pulse is generated by R from the RF oscillation circuit 34.
The F carrier signal is amplitude-modulated by the amplitude modulation circuit 33, the RF power supply 37 is driven through the amplifier 35 and the attenuator 36, and the RF power is supplied.
The subject is irradiated by supplying RF power to the coil 12. The RF oscillation circuit 34 is controlled by the sequence controller 52 and generates an RF carrier signal having a frequency corresponding to the resonance frequency of the subject. The amplitude modulation signal is a digital R waveform generated from the digital RF waveform generator 31 under the control of the sequence controller 52.
It is obtained by converting the F pulse waveform into an analog signal by the D / A converter 32.

When excited by such an RF pulse, an NMR signal is generated in the subject and the N
The MR signal is received by the RF coil 12 and sent to the digital attenuator 42 via the preamplifier 41. The digital attenuator 42 can be configured by connecting a large number of attenuating elements 61 such as resistors to which semiconductor relays 62 are connected at both ends, as shown in FIG. The semiconductor relay 62 can be controlled by a control signal from the outside to switch between passing the damping element 61 and bypassing it, whereby the damping degree can be changed stepwise. The semiconductor relay 62 is Ga
It is composed of a high-speed semiconductor switching element of about 2 to 4 nsec such as an As semiconductor switching element. As a result, for example, the maximum attenuation is 0.1 dB in 64 steps.
It is possible to obtain an attenuator capable of switching at high speed up to dB at a speed of several nsec.

The digital attenuator 42 is controlled by a sequence controller 52, and the received signal attenuated by a predetermined amount through the digital attenuator 42 is sent to a phase detection circuit 43 for phase detection. As the reference signal for this phase detection, the RF oscillation circuit 34 described above is used.
The RF signal from is transmitted. The signal obtained by the phase detection is sent to the A / D converter 45 through the anti-aliasing filter 44, sampled at a predetermined sampling timing, and converted into digital data. A
The data obtained from the A / D converter 45 is stored in the computer 51.
Is taken into. The computer 51 performs processing such as reconstructing an image from the collected digital data. The computer 51 also controls the sequence controller 52 in accordance with pulse sequences that make up various imaging scans.

In the nuclear magnetic resonance examination apparatus thus constructed, for example, a three-dimensional imaging sequence is performed. In this three-dimensional imaging sequence, FIG.
As shown in, the value of the received signal greatly changes according to the slice position (the signal value is large in the central slice,
It becomes smaller when going to the periphery). Since this change characteristic is known in advance, the sequence controller 52 holds attenuation level information that cancels the change characteristic. Then, the sequence controller 52 sets the attenuation degree of the digital attenuator 42 for each slice encode, and thus the reception gain is set to the one shown in FIG. 3B. Therefore, the signal value passed through the digital attenuator 42 is always a constant value as shown in FIG. Therefore, the signal value will be the same for every slice,
Phase detection and A / D conversion are always performed in the optimum dynamic range, the accuracy of data is improved, and an image with excellent image quality (contrast) can be obtained for any slice.

It should be noted that the above description has been made with reference to one embodiment, and the specific configuration and the like can be variously modified without departing from the spirit of the present invention.
For example, unlike the above, the receiving system may perform signal processing in the order of the anti-aliasing filter 44, the phase detection circuit 43, and the A / D converter 45. Further, it is needless to say that the present invention can be applied not only to the three-dimensional imaging sequence, but also to other imaging sequences and other measurement sequences.

[0017]

According to the nuclear magnetic resonance examination apparatus of the present invention, the dynamic range of the receiving system can always be effectively utilized by controlling the receiving gain, whereby the accuracy of collected data is improved and, as a result, the MR is obtained. You can improve the image quality of the image by imaging,
It is possible to improve the measurement accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram of a nuclear magnetic resonance inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a digital attenuator of the same embodiment.

FIG. 3 is a graph showing an example of signal values and reception gains in the same example.

[Explanation of symbols]

 11 magnet assembly 12 RF coil 21 gradient magnetic field control device 31 digital RF waveform generator 32 D / A converter 33 amplitude modulation circuit 34 RF oscillation circuit 35 amplifier 36 attenuator 37 RF power supply 41 preamplifier 42 digital attenuator 43 phase detection Circuit 44 Anti-aliasing filter 45 A / D converter 51 Computer 52 Sequence controller 61 Attenuation element 62 Semiconductor relay

Claims (1)

[Claims] 1. A magnetic field generator for generating a static magnetic field and a gradient magnetic field, an RF pulse transmitter, a receiver for receiving and detecting an NMR signal, and further converting it into digital data.
In a nuclear magnetic resonance examination apparatus having a data processing device for processing data obtained from the receiving device and a control device for controlling the data, the receiving device is a high-speed variable attenuation attenuator for attenuating a received NMR signal. A nuclear magnetic resonance examination apparatus comprising: