JPH03210240A - Magnetic resonance imaging device - Google Patents

Abstract

(57) [Summary] 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 is directed to magnetic resonance (MR)
The present invention relates to a magnetic resonance imaging apparatus that obtains morphological information such as slice images of a subject (living body) and functional information such as spectroscopy using the phenomenon (sonance).

(Prior art) Magnetic resonance is a phenomenon in which an atomic nucleus with non-zero spin and magnetic moment placed in a static magnetic field resonantly absorbs and emits only electromagnetic waves of a specific frequency. The angular frequency ω0 (ωo111112πν
0. . ; Larmor frequency) ν.

ω0−γn.

Here, γ is the gyromagnetic ratio specific to the type of atomic nucleus,
Further, Ho is the static magnetic field strength.

This type of MHI device, which performs biological diagnosis using the above-mentioned principle, processes the electromagnetic waves of the same frequency that are generated after the above-mentioned resonance absorption, and calculates the nuclear density, longitudinal relaxation time T.
3. Transverse relaxation time T2. Diagnostic information that reflects information such as flow and chemical shift, such as slice images of a subject, can be obtained non-invasively.

Therefore, collecting diagnostic information by magnetic resonance is able to excite all parts of the subject placed in a static magnetic field and collect signals, but there are limitations in the equipment configuration and clinical problems with imaging images. Due to these demands, actual devices excite a specific region and collect its signals.

In this case, the specific region to be imaged is generally a sliced region with a certain thickness;
Magnetic resonance signals (MR multiplied signals) of echo signals and FID signals from this slice site are collected by performing a data encoding process many times, and these data groups are subjected to image reconstruction processing using, for example, a two-dimensional Fourier transform method. By doing so, an image of the specific slice region is generated.

Here, a conventional magnetic resonance imaging apparatus, particularly a receiving system, will be explained with reference to FIG.

That is, the reception system includes a reception coil section 10 including a coil and a preamplifier, and a mixer 11 that mixes an output signal from the reception coil H10 and a reference signal from a phase shifter 13, which will be described later.
A, IIB, and frequency f. An oscillator (O3C) 12 that oscillates and outputs a sinusoidal waveform signal of edible gain amplifiers 14A, 14B that amplify the outputs of the phaser 13 and the mixers 11A, 11B, and whose gains can be manually adjusted by A; and the variable gain amplifiers 14A, 14B.
A low pass filter (LPF) 15A that filters a predetermined low frequency component in the output of.

15B, A/D converters (ADCs) 16A and 16B that convert the outputs of the LPFs 15A and 15B into digital signals, and an interface 17 that transmits the outputs of the ADCs 16A and 16B to a computer (not shown). Here, mixers 11A, IIB, and an oscillator (O8C
) 12, phase shifter 13, and low-pass filter (L P
F) 15A and 15B constitute a quadrature phase detection circuit.

(The invention attempts to solve this problem.tllm) Here, if there is variation in gain between the two systems (cosine term channel and sine term channel) of the receiving system, it becomes an artifact called a ghost and is visualized, so it is necessary to install the device. The variable gain amplifiers 14A and 14B were manually adjusted during periodic inspections and as needed to adjust the gains of both channels.

However, there are problems in that it takes a lot of time to adjust both channels, and also requires a measuring device or the like, making it difficult to make adjustments easily.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic resonance imaging apparatus that allows easy adjustment of variations in gain between two receiving systems.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems and achieve the objects, the present invention has a structure in which the following means are enhanced.

That is, the present invention provides a magnetic resonance imaging apparatus having a phase detection type receiving system, which includes a signal generating means for generating a sinusoidal waveform signal, and an output of this signal generating means is provided as an input to the receiving system when the signal is not collected. means for calculating the ratio of the outputs of the two systems of the receiving system when the output of this means is given to the receiving system; The present invention is characterized by comprising a compensating means for compensating for the unbalance of the gain by calculation.

(Function) According to such a configuration, the unbalance of the gains of the two systems can be compensated by calculation simply by performing an electrical operation of inputting the output of the signal generating means to the receiving system when the signal is not collected. , is easy.

(Embodiment) An embodiment of the magnetic resonance imaging apparatus according to the present invention will be described below with reference to FIG. 1, in which the same parts as in FIG. 2 are denoted by the same reference numerals.

This embodiment includes a receiving coil section 10 and a mixer 11A.

11B is provided with a changeover switch 18 that can be operated by two people and has one output. The negative input of the changeover switch 18 is the receiving coil section 10, and an oscillator 19 is provided as the other input. This oscillator 19 generates a sine wave waveform signal f with a frequency of IKHz higher than the frequency fO of the oscillation output of the quadrature phase detection circuit.
It is preferable to do so. In addition, mixers 11A, IIB
and low-pass filters (LPF) 15A, 15B, an amplifier 2O is installed instead of the n-bag gain amplifiers 14A, 14B.
A and 20B are provided.

In addition, the interface 17 calculates the ratio k (cosine term channel/sine term channel) of both channels when the output of the oscillator 19 is manually operated by the changeover switch 18 by detecting the peak value, and calculates the ratio k so that this ratio k becomes 1. ,
H is an arithmetic unit that multiplies the sine term channel by k and compensates for the unbalance of the gains of the two systems through arithmetic operations.

According to this embodiment configured in this way, when the output of the oscillator 19 is input to both channels when signals are not collected,
The ratio of both channels includes the gain a of the mixer 11A of the cosine term channel, the gain of the amplifier 2OA, and the LPF 15A.
is multiplied by the gain C of the sine term channel mixer 1.
Gain a′ of 1B, gain b′ of amplifier 20B, and LPF15
The value obtained by multiplying B by the gain C′, k−(a
xbxc)/(a = xb″XC″).

Then, when the output of the receiving coil unit 10 is inputted to both channels during signal collection, by multiplying the sine term channel by k, two outputs of gain-compensated ER+kXEl can be obtained for both channels. .

As described above, according to this embodiment, the gain compensation data k can be calculated by operation by switching the switch 18 during periodic inspection, installation, etc., prior to signal collection. During signal acquisition, the gain-compensated 2
You can get the channel signal. Therefore, an image without ghost artifacts can be obtained. Moreover, it is convenient because it can be implemented using software without using any measuring equipment.

Note that the ratio calculation and compensation calculation described above may be executed within a computer, or a dedicated processor may be used. Further, the amplifiers 2OA, 20B and the variable gain amplifiers 14A, 14B may be used together, or the variable gain amplifiers 14A, 14B may be used as fixed types.

In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As described above, the present invention includes a signal generating means for generating a sinusoidal waveform signal, a means for supplying the output of the signal generating means as an input to a receiving system when the signal is not collected, and a calculating means for calculating the ratio of the outputs of the two systems of the receiving system when the outputs are applied to the receiving system; and calculating an unbalance of the gains of the two systems of the receiving system based on the value obtained by the calculating means. By providing the compensating means for compensating, the unbalance of the gains of the two systems can be compensated by calculation simply by performing an electrical operation of inputting the output of the signal generating means to the receiving system when the signal is not collected.

Therefore, according to the present invention, it is possible to provide a magnetic resonance imaging apparatus in which variations in the gains of the two receiving systems can be precisely adjusted.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the main parts of an embodiment of a magnetic resonance imaging apparatus according to the present invention, and FIG. 2 is a block diagram showing the structure of the main parts of a conventional example. 10... Receiving coil section, IIA, 11B... Mixer, 12... Oscillator (O20), 13... Phase shifter, 1
5A. 15B...Low pass filter (LPF), 16A. 16B... A/D converter (ADC), 17... Interface, 18... Changeover switch, 19...
Oscillator (O20), 2OA, 20B...Amplifier.

Claims (1)

[Claims] A magnetic resonance imaging apparatus having a phase detection type receiving system, comprising: a signal generating means for generating a sinusoidal waveform signal; a means for supplying the output of the signal generating means as an input to the receiving system when the signal is not collected; a calculation means for calculating the ratio of the outputs of the two systems of the reception system when the output is given to the reception system; and a calculation means for calculating the unbalance of the gains of the two systems of the reception system based on the value obtained by the calculation means. 1. A magnetic resonance imaging apparatus comprising: compensation means for compensating by calculation.