JPH03210239A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To form an image with high definition by offsetting an offset error component of a reception system analog circuit by using a signal detected with a detecting means for detecting an output of a reception system digital circuit at the time when a magnetic resonance signal is not detected. CONSTITUTION:At the time of non-collection of data, digital/analog converters DACs 16A, 16B are operated and offset error components included in detectors 12A, 12B and analog/digital converters ADCs 13A, 13B are inputted to differential amplifiers 15A, 15B. Accordingly, as for outputs of the ADCs 13A, 13B, they become outputs whose offset error components are offset. In such a manners, as for the outputs of the ADCs 13A, 13B at the time of collection of data, they are only magnetic resonance signals, therefore, the image with high definition and without no artifact can be offered.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates 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 sonancc) phenomenon.

(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 ω shown in (ω.−2πν0.ν0
; Larmor frequency).

ω0纏γH0 Here, γ is the gyromagnetic ratio specific to the type of atomic nucleus,
Further, H 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 induced after the above-mentioned resonance absorption, and calculates the nuclear density, longitudinal relaxation time, T.
1. Transverse relaxation time T2. flow.

Diagnostic information that reflects information such as chemical shifts, such as slice images of a subject, is obtained non-invasively.

Collecting diagnostic information by magnetic resonance can excite all parts of a subject placed in a static magnetic field and collect signals, but there are limitations in the equipment configuration and clinical requirements for imaging images. Therefore, in an actual device, a specific part is excited and its signal is collected.

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 the ECONI signal and FID signal 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 transposition method. By doing so, an image of the specific slice region is generated.

Here, the receiving system will be explained with reference to FIG. That is, the configuration of the receiving system includes a receiving coil 10, an amplifier 1 consisting of a preamplifier and a main amplifier, detectors 12A and 12B for cosine term components constituting a quadrature phase detector, and a detector 12A.

Analog/digital converters (ADCs) 13A and 13B that convert the output of 12B into digital signals, and ADC1
It is comprised of an interface 14 for introducing the outputs of 3A and 13B into a computer (not shown).

(Problem to be Solved by the Invention) In a conventional receiving system having such a configuration, the amplifier 11 and the detector 12A are analog circuits.

12B had an offset error, which caused deterioration in image quality due to artifacts.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic resonance imaging apparatus that eliminates offset errors in a receiving system and makes it possible to obtain high-quality images without artifacts.

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

That is, the present invention provides a magnetic resonance imaging apparatus that generates a magnetic resonance phenomenon in a subject placed in a static magnetic field, collects magnetic resonance signals induced by the phenomenon, and obtains image information. It is equipped with a detection means for detecting the output of the reception system digital circuit when no magnetic resonance signal is being detected, and a cancellation means for canceling the offset error component of the reception system analog circuit using the signal detected by the detection means. It is characterized by what it did.

(Function) According to such a configuration, since the output of the receiving digital circuit does not include an offset error component, only the magnetic resonance signal is output from the receiving digital circuit during magnetic resonance signal acquisition. High quality images without artifacts can be provided.

(Embodiment) An embodiment of the magnetic resonance imaging apparatus according to the present invention will be described below with reference to FIGS. 1 and 2, in which the same parts as in FIG. 3 are given the same numbers.

Figure 1 shows ADC13A, 13 as a receiving system analog circuit.
FIG. 2 is a block diagram showing a first embodiment in which the offset error component of B can be canceled out, and FIG. 2 shows detectors 1.2A, 12B and ADC 13A as reception system analog circuits.

13B is a block diagram showing a second embodiment in which an offset error component of 13B can be canceled out. FIG.

In the first embodiment, the detectors 12A, 12B and the ADC 13
Differential amplifiers 15A and 15B are inserted between A and 13B, and the outputs of the ADCs 13A and 13B are passed through DACs (digital/analog converters) 16A and 16B to the differential amplifier 15A.

The configuration is such that the input is 15B. Here, DAC1
6A and 16B operate in conjunction with the operation of a pulse sequencer (not shown) when data is not being collected, and their outputs are input to the differential amplifiers 15A and 15B, and do not operate when data is being collected. Therefore, the input values of the differential amplifiers 15A and 15B are held at the values when data is not collected.

In the second embodiment, the amplifier 11 and the ADC 13A.

13B, insert differential amplifiers 15A and 15B,
The outputs of ADCs 13A and 13B are passed through DACs (denotal/analog converters) 16A and 16B to differential amplifier 15.
It is configured with human power of A and 15B. Here, D.A.
C16A and 16B operate in conjunction with the operation of a pulse sequencer (not shown) when data is not being collected, and input their outputs to differential amplifiers 15A and 15B.
Furthermore, it does not operate when data is being collected, and therefore, the values at the time when data is not being collected are held as inputs to the differential amplifiers 15A and 15B.

According to the first embodiment configured in this way, when data is not collected, the DACs 16A and 16B operate to correct the offset error of the detectors 12A and 12B and the ADCs 13A and 13B in the differential amplifiers 2ii 15A and 15B. Ingredients are made manually. Therefore, the outputs of the ADCs 13A and 13B are those in which the offset error components have been canceled out.

As described above, ADC13A at the time of data collection.

The output of the 13B is only a magnetic resonance signal, so it is possible to provide a high-quality image without artifacts.

According to the second embodiment configured in this manner, when data is not collected, the DACs 16A and 16B operate and the offset error components of the ADCs 13A and 13B are input to the differential □ amplifiers 15A and 15B. . Therefore, A.D.
The outputs of C13A and 13B are those in which the offset error components are canceled.

As described above, ADC13A at the time of data collection.

The output of the 13B is only a magnetic resonance signal, so it is possible to display high-quality images without artifacts.

Although the control signals for operating the DACs 16A and 16B are said to operate in conjunction with the pulse sequence when data is not being collected, they can be selected as appropriate, such as immediately before data collection or during periodic inspections. . The compensation process described above may be executed in a computer (not shown), or a processor dedicated to the compensation process may be provided, and the compensation process may be performed by the processor.

The present invention is not limited to the above embodiments, but can be implemented with various modifications without departing from the gist of the present invention.

〔Effect of the invention〕

As described above, the present invention includes a detecting means for detecting the output of the receiving digital circuit when no magnetic resonance signal is being detected, and a detecting means for detecting the output of the receiving analog circuit using the signal detected by the detecting means. By providing a canceling means for canceling the offset error component, the output of the receiving system digital circuit does not include the offset error component.
At the time of collecting magnetic resonance signals, the receiving system digital circuit outputs only magnetic resonance signals, so that it is possible to provide a magnetic resonance imaging apparatus that can provide high-quality images without artifacts.

[Brief explanation of drawings]

1 and 2 are block diagrams showing the configuration of an embodiment of the magnetic resonance imaging device according to the present invention, and FIG. 3 is a block diagram showing the configuration of a conventional example. 10... Receiving coil; 11...Amplifier, 12A. 12B...Detector, 13A, 13B...ADC (analog/digital converter), 14A, 14B...Detector, 15A, 15B...Differential amplifier, 16A 16B...DAC (digital/analog conversion 5).

Claims (1)

[Claims] In a magnetic resonance imaging apparatus that generates a magnetic resonance phenomenon in a subject placed in a static magnetic field and collects magnetic resonance signals induced by the phenomenon to obtain image information, the magnetic resonance signals are detected. The present invention is characterized by comprising a detection means for detecting the output of the reception system digital circuit when the reception system is not in use, and a canceling means for canceling the offset error component of the reception system analog circuit using the signal detected by the detection means. Magnetic resonance imaging device.