JP3137363B2 - Magnetic resonance imaging equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a magnetic resonance (MR: magn).
The present invention relates to a magnetic resonance imaging apparatus that can generate an image using a etic resonance phenomenon.

[0002]

2. Description of the Related Art Magnetic resonance phenomena occur when a zero magnetic field
Nuclei with different spin and magnetic moments
A phenomenon in which only electromagnetic waves of a frequency are resonantly absorbed and emitted.
This atomic nucleus has an angular frequency ω₀(Ω₀= 2
πν₀, Ν₀; Larmor frequency). ω₀= ΓH₀  Here, γ is the gyromagnetic ratio specific to the type of nucleus.
And H₀Is the static magnetic field strength.

An apparatus for performing a living body diagnosis using the above principle processes an electromagnetic wave of the same frequency induced after the above-described resonance absorption, and performs a signal processing to obtain a nuclear density, a longitudinal relaxation time T ₁ , and a transverse relaxation time. Diagnostic information reflecting magnetic resonance parameters such as T ₂ , flow, chemical shift and the like, for example, slice images of the subject can be obtained non-invasively.

[0004] In order to collect diagnostic information by magnetic resonance, it is possible to excite and collect signals from all parts of a subject placed in a static magnetic field. Due to clinical demands for imaging, an actual apparatus is designed to excite a specific site and collect its signal.

In this case, the specific part to be imaged is generally a slice part having a certain thickness, and an echo signal or FI from this slice part is generally used.
The magnetic resonance signal (MR signal) of the D signal is collected by performing a number of data encoding processes, and these data are collected.
The data group is subjected to image reconstruction processing by, for example, a two-dimensional Fourier transform method to generate a tomographic image (slice image) of the specific slice portion.

[0006] Such a magnetic resonance imaging apparatus includes:
Usually have A base lasing means for reducing the increase and artifacts of the S / N ratio of the data. Less than,
The conventional averaging means will be described with reference to FIG. That is, FIG. 10 shows the twice averaging means, in which one data (one phase encoded data) to be reconstructed is created from two data having the same phase encoding amount.

As data collection, the first data S1
, The second data S2 is collected by changing the phase by 180 °, and these data S1 and S2 are held. Here, the data S1 and S2 are DC components, respectively.
Are added, and an inflow section FF of FID (free induction damping) is included.

The subtraction value of these data S1 and S2 (S1-
S2) is divided by 2 which is the number of data to obtain one phase encoded data S = ((S1 -S2) / 2). In the phase encoded data S, the DC component DC and the flow-in portion FF of FID (free induction attenuation) are offset, the S / N ratio is improved, and an image suitable for diagnosis is obtained.

In addition to the two-time averaging method shown in FIG. 10 described above, there is a technique conventionally called a one-time averaging method. In the one-time averaging method, the occurrence of an artifact can be pushed out to the highest frequency region (outside the region of interest) as shown in FIG. 11 by collecting data by changing the phase amount by 180 ° for each phase encoding. Things. In FIG. 11, screen 2 of the display unit
Although the image IM appears in 3A, the artifact AF appears in both corners of the screen 23A.

[0010]

However, the averaging means in the above-mentioned conventional magnetic resonance imaging apparatus is useful because the S / N ratio is improved and unnecessary components are removed by averaging once or twice. However, in order to further improve this advantage, for example, to perform averaging three times, the above-described method cannot be adopted. Hereinafter, a problem in a case where averaging is performed three times by the same method as the above-described twice averaging will be described with reference to FIGS.
This will be described with reference to FIG.

That is, FIG. 12 shows a three-time averaging method, in which one data (one phase-encoded data) to be reconstructed is created from three data having the same phase-encoding amount. Following the acquisition, the second data S2 was acquired by changing the phase by 180 °,
Further, the phase of the first data S is changed by 180 °.
Third data S3 is collected in the same manner as 1, and these data S1, S2 and S3 are held. Here, data S
DC components DC are added to 1, S2, and S3, respectively, and a flow-in portion FF of FID (free induction damping) is included.

The sum of the data S1, S2 and S3 (S1−S2 + S3) is divided by 3 which is the number of data, and one phase encoded data S4 = ((S1−S2 + S3)
) / 3). This phase encoded data S4 is
Inflow part F of DC component DC and FID (free induction damping)
Although F is not canceled out and the S / N ratio is improved, as shown in FIG. 13, the artifact A is located at the center of the screen 23A where the main part of the image IM appears.
F appears, resulting in an image that is not preferable for diagnosis.

It is an object of the present invention to provide a magnetic resonance imaging apparatus capable of improving the S / N ratio and reducing artifacts even when averaging is performed three or more times an odd number of times. .

[0014]

Means for Solving the Problems The present invention has the following means in order to solve the above problems and achieve the object. That is, the first aspect of the present invention is an averaging method for acquiring magnetic resonance signals related to the same phase encoding a plurality of times and performing addition / subtraction processing on the collected signals to obtain phase encoded data related to reconstruction processing. In the magnetic resonance imaging apparatus comprising means, the averaging means,

[0015] The magnetic resonance signals according to the same phase encoding are collected n times (odd number of 3 or more) for the normal phase and the opposite phase, and one extra of the collected n magnetic resonance signals is added once. The above-mentioned addition and subtraction processing is performed.

According to a second aspect of the present invention, there is provided an average for acquiring magnetic resonance signals related to the same phase encoding a plurality of times, and adding / subtracting the collected signals to obtain phase encoded data related to a reconstruction process. A magnetic resonance imaging apparatus comprising

The magnetic resonance signals related to the same phase encoding are collected n times (odd number of 3 or more), wherein the phase of the excitation pulse is inverted for each phase encoding and n
During the data collection of an odd number of times, the data is collected by inverting the phase with that of the other data collection, and the collected n
A magnetic resonance imaging apparatus comprising: averaging means for obtaining the phase-encoded data for the reconstruction processing by performing the addition and subtraction processing on the magnetic resonance signals.

According to a third aspect of the present invention, there is provided an average for acquiring magnetic resonance signals related to the same phase encoding a plurality of times, and adding and subtracting the collected signals to obtain phase encoded data related to a reconstruction process. A magnetic resonance imaging apparatus comprising

The magnetic resonance signals according to the same phase encoding are collected n times (odd number equal to or more than 3) for the normal phase and the opposite phase, and one of the collected n magnetic resonance signals is added once. A first averaging means for performing the addition / subtraction processing to

The magnetic resonance signals according to the same phase encoding are collected n times (odd number of 3 or more), wherein the phase of the excitation pulse is inverted for each phase encoding and n
During the data collection of an odd number of times, the data is collected by inverting the phase with that of the other data collection, and the collected n
Second averaging means for obtaining the phase-encoded data for the reconstruction processing by subjecting the magnetic resonance signals to addition and subtraction processing, wherein the first averaging means and the second averaging means are selectively provided. A magnetic resonance imaging apparatus characterized in that it can be executed in

[0021]

According to the first aspect of the present invention, averaging is performed substantially even times, so that the DC component and the FID
(Free induction damping) and the inflow part is canceled out, and S /
The N ratio is improved, and an image suitable for diagnosis is obtained.

According to the second aspect of the invention, for example, 3
In the case of the first averaging, the first and second data are collected in the same manner as in the second averaging described in the related art, and the third data is collected in the same manner as in the conventional example of the first averaging. When an image is created by inverting and collecting the phase of the excitation pulse for each phase encoding and averaging these, an artifact is driven out to the highest frequency region. Therefore, the S / N ratio is improved, and an image suitable for diagnosis is obtained. According to the invention according to claim 3,
The invention according to claim 1 and the invention according to claim 2 can be selected as desired according to diagnostic conditions and the like.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic resonance imaging apparatus according to the present invention will be described below with reference to the drawings. That is, as shown in FIG. 1, the present apparatus has a magnet assembly 10 that can accommodate the subject P inside.

The magnet assembly 10 includes a static magnetic field magnet related to one or a combination of a permanent magnet, a normal conducting magnet, and a superconducting magnet, a gradient magnetic field coil, transmission of a high-frequency pulse for excitation and reception of a magnetic resonance signal. And an RF coil that performs at least one.

Assuming that the static magnetic field magnet of the magnet assembly 10 is a normal conducting magnet or a superconducting magnet,
A static magnetic field control circuit 11 for controlling the current is provided. The gradient magnetic field coil of the magnet assembly 10 is controlled by a gradient magnetic field control circuit 12 which receives a command from the system controller 13.

Further, the R of the magnet assembly 10
The F coil includes a transmission system including a high-frequency oscillator 14, a gate circuit 15, and a power controller 16, and a diplexer circuit 17,
A preamplifier 18, a phase detection circuit 19 including an A / D converter 19a, a one-dimensional preprocessing means 2 which is a main part of the apparatus of the present embodiment.
0, and is driven for transmission and reception by a receiving system comprising the waveform memory 21. The data obtained by the receiving system is transmitted to the image creation unit 2
2, where a slice image or the like is created and displayed on the display unit 23.

The details of the one-dimensional preprocessing means 20 are shown in FIG. That is, the one-dimensional preprocessing means 20 includes a first program memory 20a, a second program memory 20b,
It comprises a switch 20c, a programmable signal calculator 20d, and a buffer memory 20e.

In each of the above-mentioned components, the system controller 13 is capable of executing the pulse sequence shown in FIG. 3, for example, and supplies the switching signal ES to the switch 20c of the one-dimensional preprocessing means 20. It has become. FIG. 3 shows a waveform diagram relating to the data collection process of the i-th phase encoded data, and one phase encoded data is obtained from three data. Here, the pulse sequence is 90 °-
The spin echo method is 180 ° pulse sequence is intended to be an example, 90 ° to selective excitation with an excitation pulse and slice gradient G _S, following the application of the phase encoding gradient G _E and the read gradient field G _R , by applying a 180 ° excitation pulse and the slice gradient field G _S, acquiring echo signals first one by the application of the read gradient G _R. Next, the second echo is collected. The 90 ° excitation pulse for collecting the second echo was in phase with the 90 ° excitation pulse for collecting the first echo signal. Sometimes the phases are reversed. Next, when collecting the third echo, the 90 ° excitation pulse is in positive phase.

The first one-dimensional preprocessing means 20 shown in FIG.
The program memory 20a of FIG. 4 holds the three-time averaging method shown in FIG. 4 in the form of a computer program, and the second program memory 20b of FIG.
The three-time averaging method shown in FIGS. 6 and 7 is held in the form of a computer program.

Hereinafter, the three-time averaging method shown in FIG. 4 will be described. That is, it is assumed that the switch 20c has been switched to the first program memory 20a in FIG. 2, and the excitation pulse for collecting the first echo signal and the third echo signal in accordance with the pulse sequence shown in FIG. And the excitation pulse for collecting the second echo signal is applied in the opposite phase.

The signal collected by the application of the excitation pulse is digitized by the A / D converter 19a and stored in the buffer memory 20e as three data for obtaining one phase encoded data. For three data S1, S2, S3 as shown in FIG. 4, (S1-S2
) / 2 = S4, (S3-S2) / 2 = S5, and data S4 and S5 are obtained. In this case, the second data S2 is used twice. Then, (S4 + S5) / 2 is obtained by the programmable signal calculator 20d.
= S. This S is data related to this phase encoding.

This data S is (S1 -2S2 + S3) /
4, the averaging is performed substantially an even number of times, so that the direct current component and the flow-in portion of the FID (free induction damping) are offset, and the S / N ratio is improved. An image suitable for diagnosis is obtained.

In the above description, the three data S1, S2,
In order to obtain S3, instead of collecting excitation pulses in the normal phase and in the opposite phase, that is, inverting the phase, a method of inverting the sign of the amplitude of the excitation pulse may be used.

Next, the three-time averaging method shown in FIGS. That is, in FIG.
Is switched to the second program memory 20b, and the excitation pulse for collecting the first echo signal and the second echo signal is switched in phase every encoding according to the pulse sequence shown in FIG. Applied.
The signal collected by the application of the excitation pulse is A / D
The data is digitized by the converter 19a and stored in the buffer memory 20e as three data for obtaining one phase encoded data.

Then, the programmable signal operation unit 20d
, The addition and subtraction corresponding to each of these three data S1, S2 and S3 are performed. The reconstructed image using the phase-encoded data obtained in this way can be one in which the artifact has been driven out to the highest frequency region (outside the region of interest).

Specifically, FIG. 5 and FIG. That is, as shown in FIG. 6, the first phase encoded data is obtained by adding the first data in the normal phase, subtracting the second data in the negative phase, and adding the third data in the normal phase. As a result, data after averaging for obtaining the first phase encoded data is obtained.

Next, the second phase encoded data is obtained by adding the first data in the normal phase, subtracting the second data in the negative phase, and subtracting the third data in the negative phase.
Averaged data for obtaining the second phase encoded data is obtained. Further, as in the case of the first phase encoded data, the third phase encoded data is obtained by adding the first data in the normal phase, subtracting the second data in the negative phase, and converting the third data into the normal phase. , The data after averaging for obtaining the third phase encoded data is obtained.

By reconstructing an image using the first phase encoded data, the second phase encoded data, the third phase encoded data,... Obtained as described above, the image has an artifact removed to the highest frequency region (outside the region of interest). It can be. In addition to FIG. 5, the method shown in FIG. 7 may be used. In the above description, the sign of the amplitude of the excitation pulse may be reversed instead of the method of reversing the phase.

In the above description, the one-dimensional preprocessing means 20 is composed of a first program memory 20a, a second program memory 20b, a switch 20c, a programmable signal calculator 20d, and a buffer memory 20e. However, as shown in FIG.
With a first program memory 20a, a switch 20c, a programmable signal calculator 20d, and a buffer memory 20e.
And one-dimensional preprocessing means 20 as shown in FIG.
To a second program memory 20b, a switch 20c, a programmable signal calculator 20d, and a buffer memory 20e.
May be configured. In addition, various modifications can be made without departing from the scope of the present invention.

[0040]

According to the present invention, the following means are provided to solve the above-mentioned problems and achieve the object.
That is, the first aspect of the present invention is an averaging method for acquiring magnetic resonance signals related to the same phase encoding a plurality of times and performing addition / subtraction processing on the collected signals to obtain phase encoded data related to reconstruction processing. In the magnetic resonance imaging apparatus comprising means, the averaging means,

The magnetic resonance signals related to the same phase encoding are collected n times (odd number of 3 or more) for the normal phase and the negative phase, and one extra of the collected n magnetic resonance signals is added once. Wherein the addition and subtraction processing is performed.
According to this configuration, averaging is performed substantially an even number of times, so that the direct current component and the flow-in portion of FID (free induction damping) are offset, and the S / N ratio is improved, which is suitable for diagnosis. Image is obtained.

According to a second aspect of the present invention, there is provided an average for acquiring magnetic resonance signals related to the same phase encoding a plurality of times, and adding and subtracting the collected signals to obtain phase encoded data related to a reconstruction process. A magnetic resonance imaging apparatus comprising

The magnetic resonance signals related to the same phase encoding are collected n times (odd number of 3 or more), wherein the phase of the excitation pulse is inverted for each phase encoding and n
During the data collection of an odd number of times, the data is collected by inverting the phase with that of the other data collection, and the collected n
Averaging means for obtaining the phase encoded data according to the addition and subtraction processing and the reconstruction processing for the magnetic resonance signals,

A magnetic resonance imaging apparatus characterized by comprising:
In the case of round averaging, the first and second data are collected by the same method of double averaging as described in the background and the art, and the third data is the same as in the conventional example of single averaging. When the image is generated by inverting the phase of the excitation pulse for each phase encoding and adding and averaging these, an artifact is removed to the highest frequency region. Therefore, the S / N ratio is improved, and an image suitable for diagnosis is obtained.

According to a third aspect of the present invention, there is provided an average for acquiring magnetic resonance signals related to the same phase encoding a plurality of times, and adding / subtracting the collected signals to obtain phase encoded data related to a reconstruction process. A magnetic resonance imaging apparatus comprising

The magnetic resonance signals related to the same phase encoding are collected n (odd number of 3 or more) times for the normal phase and the negative phase, and one extra of the collected n magnetic resonance signals is added once. A first averaging means for performing the addition / subtraction processing to

The magnetic resonance signal related to the same phase encoding is collected n times (odd number of 3 or more), in which the phase of the excitation pulse is inverted for each phase encoding and n
During the data collection of an odd number of times, the data is collected by inverting the phase with that of the other data collection, and the collected n
Second averaging means for obtaining the phase-encoded data related to the reconstruction processing by performing the addition and subtraction processing on the magnetic resonance signals,

The first averaging means and the second averaging means
Wherein the averaging means can be selectively executed by the magnetic resonance imaging apparatus. According to this configuration, the invention according to claim 1 and the invention according to claim 2 Can be selected as desired according to diagnostic conditions and the like.

Thus, according to the present invention, it is possible to provide a magnetic resonance imaging apparatus capable of improving the S / N ratio and reducing artifacts even when averaging is performed three or more times an odd number of times. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a magnetic resonance imaging apparatus according to the present invention.

FIG. 2 is a detailed block diagram of a one-dimensional preprocessing unit in FIG. 1;

FIG. 3 is a waveform diagram of a pulse sequence that can be executed in the present embodiment.

FIG. 4 is a diagram showing an averaging technique executed by a program stored in a first program memory shown in FIG. 2;

FIG. 5 is a diagram showing an averaging technique executed by a program stored in a second program memory shown in FIG. 2;

FIG. 6 is a diagram showing what the symbols shown in FIG. 5 mean.

FIG. 7 is a diagram showing an averaging technique different from that shown in FIG. 5 executed by a program stored in a second program memory shown in FIG. 2;

FIG. 8 is a detailed block diagram of the one-dimensional preprocessing means in FIG. 1 different from that shown in FIG. 2;

9 and 8 of the one-dimensional preprocessing means in FIG. 1;
Detailed block diagram different from the one shown in FIG.

FIG. 10 is a diagram showing an example of a conventional averaging technique.

FIG. 11 is a view showing the operation of the averaging technique shown in FIG. 10;

FIG. 12 is a diagram showing another example of the conventional averaging technique.

FIG. 13 is a view showing the operation of the averaging technique shown in FIG. 12;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Magnet assembly, 11 ... Static magnetic field control circuit, 12 ... Gradient magnetic field control circuit, 13 ... System controller, 14 ... High frequency oscillator, 15 ... Gate circuit, 16 ...
Power controller, 17: diplexer circuit, 18: preamplifier 18, 19: display unit.

──────────────────────────────────────────────────続 き Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) A61B 5/055 JICST file (JOIS)

Claims (3)

(57) [Claims] An averaging means for collecting magnetic resonance signals related to the same phase encoding over a plurality of times and performing addition / subtraction processing on the collected signals to obtain phase encoded data related to reconstruction processing. In the magnetic resonance imaging apparatus, the averaging means collects the magnetic resonance signals related to the same phase encoding n times (odd number equal to or more than 3) in the positive phase and the negative phase, and the collected n magnetic resonance signals A magnetic resonance imaging apparatus characterized in that the addition / subtraction processing is performed one extra time for one of them. 2. An averaging means for collecting magnetic resonance signals related to the same phase encoding a plurality of times and performing addition / subtraction processing on the collected signals to obtain phase encoded data related to reconstruction processing. A magnetic resonance imaging apparatus comprising:
(Odd or more than 3) times, in which the phase of the excitation pulse is inverted for each phase encoding, and the data is obtained by inverting the phase during the odd number of data acquisitions out of n times with the other data acquisitions. A magnetic resonance imaging apparatus, comprising: averaging means for acquiring the obtained n magnetic resonance signals and performing the addition and subtraction processing on the collected n magnetic resonance signals to obtain phase encoded data for reconstruction processing. 3. An averaging means for collecting magnetic resonance signals related to the same phase encoding a plurality of times, and performing addition / subtraction processing on the collected signals to obtain phase encoded data related to reconstruction processing. In the magnetic resonance imaging apparatus, the magnetic resonance signals according to the same phase encoding are collected n times (odd number equal to or more than 3) for the positive phase and the negative phase, and one of the collected n magnetic resonance signals is collected. Is a first averaging means for performing the addition / subtraction processing one extra time, and n for the magnetic resonance signal related to the same phase encoding.
(Odd or more than 3) times, in which the phase of the excitation pulse is inverted for each phase encoding, and the data is obtained by inverting the phase during the odd number of data acquisitions out of n times with the other data acquisitions. And a second averaging means for adding and subtracting the collected n magnetic resonance signals to obtain phase-encoded data relating to the reconstruction processing, wherein the first averaging means and the second averaging means Wherein the averaging means can be selectively executed.