JPS6384538A - Magnetic resonance imaging apparatus - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a magnetic resonance imaging apparatus, and particularly to a magnetic resonance imaging apparatus that collects and images magnetic resonance signals of a plurality of nuclides. Regarding green equipment.

(Prior art) As is already well known, magnetic resonance imaging (MHI) is a technique in which a population of unique spins and associated nuclear magnetic efficiencies are distributed in a uniform static magnetism of 1 meter (assumed to have an intensity of Ha). When placed, the energy of a high-frequency magnetic field that rotates at an angular velocity determined by ω0-γHa (γ is called the gyromagnetic ratio and is a constant unique to the type of atomic nucleus) in a plane perpendicular to the direction of the static magnetic field. This is a method that makes it possible to obtain chemical and physical microscopic information about molecules using resonance absorption.

This magnetic resonance imaging method is used to identify specific atomic nuclei (
Examples of methods for imaging the spatial distribution of hydrogen atoms (for example, hydrogen nuclei in water and fat) include the Yakuaki reconstruction method by Lauterbur, Kumar, and Welti.

The Fourier method by Ernst et al. and the spin warp method by Hutcheson et al., which is a variation thereof, have been devised.

In such a magnetic resonance imaging apparatus, it is useful for the same apparatus to have a function of collecting and imaging magnetic resonance signals of a plurality of nuclides, such as hydrogen nuclei (IH) and carbon nuclei (13G). In order to collect magnetic resonance signals of multiple nuclides, it is necessary to apply a predetermined high-frequency magnetic field having the same frequency as the magnetic resonance frequency of each nuclide to the subject.

The B-frequency magnetic field is created by supplying high-frequency pulses from a high-frequency pulse generator to a probe coil via a four-phase switch, an SSB modulator, etc. to obtain a predetermined pulse sequence.

Here, the high-frequency pulse generator is constructed using an extremely high-precision frequency synthesizer in order to accurately match its frequency to the magnetic resonance frequency that depends on the strength of the static magnetic field, and is very expensive. Therefore, it is not preferable to prepare the same number of such high-frequency pulse generators as the number of nuclides, as this will lead to a significant increase in the cost of the device.

(Problems to be Solved by the Invention) As described above, in the conventional technology, when attempting to obtain magnetic resonance signals of multiple nuclides, the equipment becomes large-scale and extremely expensive.

An object of the present invention is to provide a magnetic resonance imaging apparatus that can obtain magnetic resonance signals of a plurality of nuclides with a simple configuration.

[Structure of the Invention] (Means for Solving the Problems) The present invention adopts a superheterodyne system in a transmitting circuit that supplies high-frequency pulses corresponding to the magnetic resonance frequencies of multiple nuclides to a probe coil, and uses a common It is characterized in that a high frequency pulse corresponding to the magnetic resonance frequency of each nuclide is generated by frequency converting the output of the high frequency pulse generator using a plurality of frequency conversion means having different conversion ratios.

In addition, if the magnetic resonance signals of multiple nuclides need to be collected in a time-sharing manner rather than simultaneously, the superheterodyne method is adopted not only for the transmitting circuit but also for the receiving circuit for collecting the magnetic resonance signals of multiple nuclides. The magnetic resonance signals detected from inside the subject by the probe coil are converted to the same intermediate frequency by the frequency conversion means, and then processed by the common signal processing means.

(Function) In the transmitting circuit, a common high-frequency pulse generator generates a high-frequency pulse of a certain frequency, and this pulse is used to convert a plurality of local oscillation frequencies by appropriately controlling a 4-phase switch, an SSB modulator, etc. By inputting it to the frequency conversion means, a high frequency pulse having the same frequency as the magnetic resonance frequency of each nuclide is created. The 4-phase switch or the SSB modulator may be provided after the plurality of frequency conversion means.

On the receiving side, when collecting magnetic resonance signals of multiple nuclides simultaneously, the magnetic resonance signals detected from within the subject are processed individually; however, when collecting in a time-sharing manner, the magnetic resonance signals are detected from within the subject. The magnetic resonance signals thus obtained are converted to the same intermediate frequency by the frequency conversion means, and then processed by the common signal processing means. The common signal processing means includes some or all of an intermediate frequency amplifier, a quadrature phase detection circuit, a DC amplifier, a low-pass filter, an A/D converter, and the like.

(Example of actual pain) An embodiment of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 2 is a block diagram showing the overall configuration of magnetic resonance signal collection according to an embodiment of the present invention. In the figure, a static magnetic field generating coil 2 is energized by an excitation power source 3, and generates a uniform static magnetic field in an image area of a living body 1 to be examined. On the other hand, a transmission circuit 5 controlled by a pulse sequencer 4 outputs a high frequency pulse modulated in a 5-inch shape or a Gaussian shape, and is applied to a probe coil 8 via a duplexer 7. A high frequency magnetic field (rotating magnetic field) for inducing magnetic resonance is formed. Transverse magnetization caused by the application of this high-frequency magnetic field is induced at both ends of the coil 8 as a magnetic resonance signal. In this example, a common coil 8 is used as a transmitting coil for generating a high-frequency magnetic field and a receiving coil for detecting a magnetic resonance signal.

The magnetic resonance signal induced in the probe coil 8 is input to the receiving circuit 6 via the duplexer 7, and image reconstruction data is taken from the receiving circuit 6 into the electronic computer 7. The electronic computer 7 controls the pulse sequencer 4 via the interface 1o, and supplies the image signal obtained by image reconstruction to the display device [11].

Determination of the slice plane of the subject 1 and phase encoding (conversion from position information within the subject 1 to the phase of the magnetic resonance signal)
This is performed by switching the gradient magnetic field and applying it in a pulsed manner.

The switching timing of this gradient magnetic field is controlled by the pulse sequencer 4.

On the other hand, the strength and pulse shape of the gradient magnetic field are controlled by a gradient magnetic field controller 12. That is, X by the gradient magnetic field controller 12.

Power amplifier 13 for gradient magnetic fields in y and two directions.
14 and 15 and drive the gradient magnetic field generating coil 16 using these power amplifiers 13 to 15, a gradient magnetic field having a predetermined intensity and time variation is generated in the vicinity of the imaging region of the subject 1.

Note that since this apparatus collects and images magnetic resonance signals of a plurality (n) of nuclides, the duplexer 7 and the probe coil 8 are provided for each rJl.

FIG. 1 shows in detail the transmitting circuit 5, receiving circuit 6, n duplexers 7a to 7n, and probe coils 88 to 8n.

In FIG. 1, a transmission circuit 5 converts high-frequency pulses from a common high-frequency pulse generator 21 into the same frequency as the magnetic resonance frequency of n nuclides using n sets of mixers 25a to 25n, which are frequency conversion means. The structure is as follows. That is, in the transmitting circuit 5, the output of the high frequency pulse generator 21 is supplied to the 4-phase switch 22. 4 phase switch 2
2 is 0°.

It has four types of phase shifters, 90°, 180°, and 270°, and is controlled by the pulse sequencer 4 shown in FIG.
) method, modified CP method, CPMG (Carr Purc
This circuit selectively outputs the outputs of four types of phase shifters according to a sequence such as the elleibooi G11l method. The output of this four-phase switch 22 is modulated by an SSB modulator 23, and then passed through a switch 24 to a mixer 25a.
-25n selectively.

The mixers 25a to 25n each generate a local high frequency oscillation H26.
By supplying high-frequency signals of different frequencies from a to 26n, the high-frequency pulse input from the SSB modulator 23 is converted into a high-frequency pulse having the same frequency as the magnetic resonance frequency of each nuclide. The high frequency pulses frequency-converted in this manner are further shaped into a 5-inch shape, etc., amplified by high frequency amplifiers 27a to 27n, and then supplied to probe coils 8a to 8n via duplexers 7a to 7n, respectively. As a result, the probe coils 8a to 8b
A high-frequency magnetic field that excites different nuclides within the subject 1 is generated.

On the other hand, magnetic resonance signals detected by the probe coils 8a to 8n are input to the receiving circuit 6 via duplexers 78 to 7n. In the receiving circuit 6, the duplexers 7a-
The magnetic resonance signals from 7n are supplied to mixers 28a to 28n, which are frequency conversion means. Like the mixers 25a to 25n, the mixers 28a to 28n are connected to the local high frequency oscillator 26.
By supplying ancient frequency signals from a to 26n,
Converts the input magnetic resonance signal to the same intermediate frequency. The intermediate frequency signal thus obtained is selectively taken out via the switch 29, amplified by the intermediate frequency amplifier 30, and then quadrature-phased by the quadrature phase detection circuit 31 using the high frequency pulse from the high frequency pulse generator 21 as a reference wave. It undergoes phase detection and becomes a video band signal. Quadrature phase detection circuit 31
The output of A is amplified by a DC amplifier 32, and low-frequency noise components are removed by a low-pass filter 33.
The data is converted into a digital signal by the /D converter 34, and taken in as image reconstruction data to the electronic computer 9 in FIG. 2 via the interface 35 and stored.

In the magnetic resonance imaging apparatus described above, the high frequency pulse generator 21 is constructed using a highly accurate and highly stable frequency synthesizer, and is generally large in circuit size and expensive. However, in the present invention, the transmission circuit 5 uses a superhetero gain method to convert the frequency of the high-frequency pulse from the high-frequency pulse generator 21 to obtain a high-frequency pulse having the same frequency as the magnetic resonance frequency of each nuclide. Even though magnetic resonance signals of n nuclides are obtained, only one expensive high-frequency pulse generator is required, and the cost of the entire device can be greatly reduced.

Further, in the above embodiment, the superhetero gain method is also used in the receiving circuit 6, and after converting the magnetic resonance signals of each nuclide into the same intermediate frequency signal, signal processing including quadrature phase detection is performed. Therefore, the receiving circuit 6
The configuration can be PJIN, which also contributes to reducing the cost of the device.

Note that the present invention is not limited to the above embodiments,
For example, in the embodiment, a case has been described in which multiple nuclides are selectively excited and their magnetic resonance signals are collected sequentially, but it is also possible to simultaneously excite multiple nuclides and collect their magnetic resonance signals simultaneously. . In that case, for example, the switch 24 in the transmitter circuit 5 in FIG. It is sufficient to remove the intermediate frequency amplification 5530 and provide the same number of circuits as the number of nuclides.

In addition, in the transmitting circuit 5, a four-phase switch 22 and S
Although the SB modulator 23 is commonly used for a plurality of nuclides, it may be provided for each nuclear ridge. In addition, the present invention can be implemented with various modifications without departing from the scope of the invention.

[Effects of the Invention] According to the present invention, it is possible to provide a magnetic resonance imaging apparatus capable of collecting and imaging magnetic resonance signals of a plurality of nuclides with a commercially inexpensive configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main part configuration of a magnetic resonance imaging apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the overall configuration of the magnetic resonance imaging apparatus. 1... Subject, 2... Static magnetic field generating coil, 3...
Excitation power supply, 4... Pulse sequencer, 5... Transmission circuit, 6... Receiving circuit, 7, 7a to 7n... Duplexer, 8.8a to 8n... Probe coil, 9...
・Electronic computer, 10... I10 boat, 11... Display device, 12... Gradient magnetic field controller, 13-15
...Power amplifier, 16...Gradient magnetic field generation coil, 2
DESCRIPTION OF SYMBOLS 1... High frequency pulse generator, 22... 4 phase switcher, 23... SSB modulator, 24... Switcher, 25a
~25n...Mixer (frequency conversion means), 26a~2
6n...Local high frequency oscillator, 27a-27n...High frequency amplifier, 28a-28n...Mixer (frequency conversion means), 29...Switcher, 30...Intermediate frequency amplifier, 31... Quadrature phase detection circuit, 32... DC amplifier, 33... Low pass filter, 34... A/D converter, 35... I10 boat.

Claims (2)

[Claims] (1) A high-frequency magnetic field is applied to the specimen placed in a uniform static magnetic field by a probe coil that supplies high-frequency pulses corresponding to the magnetic resonance frequencies of multiple nuclides, and the gradient magnetic field is switched. In a magnetic resonance imaging apparatus that collects and images magnetic resonance signals of a plurality of nuclides detected by a probe coil from inside a subject by applying pulses, The transmission circuit that supplies high-frequency pulses to the probe coil includes a common high-frequency pulse generator and a plurality of frequency conversion means that converts the output of the high-frequency pulse generator at different conversion ratios and outputs the high-frequency pulses. A magnetic resonance imaging device characterized by: (2) A high-frequency magnetic field is applied to the specimen placed in a uniform static magnetic field by a probe coil that supplies high-frequency pulses corresponding to the magnetic resonance frequencies of multiple nuclides, and the gradient magnetic field is switched. In a magnetic resonance imaging apparatus that collects and images magnetic resonance signals of a plurality of nuclides detected by a probe coil from inside a subject by applying pulses, The transmitting circuit that supplies high-frequency pulses to the probe coil includes a common high-frequency pulse generator and a plurality of frequency conversion means that converts the output of the high-frequency pulse generator at different conversion ratios and outputs the high-frequency pulses. and a receiving circuit for collecting magnetic resonance signals of the plurality of nuclides,
Magnetic resonance characterized by having a frequency conversion means for converting magnetic resonance signals detected from inside a subject by a probe coil into the same intermediate frequency, and a common signal processing means for processing the output of this frequency conversion means. Video equipment.