JPH10179537A - Magnetic resonance imaging device and magnetic resonance imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately reduce an artifact due to an FID component and/or a DC component, eliminate a need of removing the artifact at a post-process, and allow an application even to the variable encoding method by controlling the phases of RF excited pulses and ADC in MRI involving an odd-number averaging process. SOLUTION: This device is equipped with means 30b and 32T for applying gradient magnetic field and RF pulses to a specimen along the sequence of the SE method, a receiving means 32R including an A/D converter 53 for A/D converting echo signals, a means 36 for executing the odd-number times (n) (n: integer equal to or larger than 3) of excitation, and averaging the echo signals from the receiving means 32R via the execution, and another means 30b for preliminarily controlling the phases of the RA pulses and the A/D converter 53 so as to keep the vector sum of FID or DC components in the A/D converted signals at zero or substantially zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging and a magnetic resonance imaging method,
The present invention relates to suppression of a free induction decay (FID) component and / or a direct current (DC) component having a substantially constant amplitude that causes artifacts when an MR signal is detected from a subject and an averaging process is performed an odd number of times.

[0002]

2. Description of the Related Art A magnetic resonance imaging method for medical diagnosis is an imaging method based on a magnetic resonance phenomenon of a nuclear spin in a subject, which is noninvasive and free from X-ray exposure like an X-ray apparatus. An image inside the subject can be obtained. Therefore, its usefulness has been increasingly exerted in clinical settings in recent years.

In performing magnetic resonance imaging, a high-frequency magnetic field pulse B1 is generally applied to a subject placed in a static magnetic field B0 together with a gradient magnetic field pulse for determining an imaging section. The MR signal is generated from the subject by being energized by the application of the high frequency magnetic field pulse B1. MR signals are collected while applying a gradient magnetic field pulse for adding positional information, and an actual image is reconstructed based on the collected signals.

[0004] MR signals are usually collected as spin echoes or gradient magnetic field echoes. Therefore, the FID component forming the pseudo echo contributes to the artifact on the image. In addition, a DC component generated by signal conversion of an A / D converter that samples an echo also causes an artifact. As a conventional technique for suppressing this artifact, for example, a technique described in U.S. Pat. No. 4,616,182 is known. According to the patent, in an imaging sequence using two excitation pulses (for example, a 90 ° pulse and a 180 ° pulse), the phases of the excitation pulses are controlled.

The phase control will be described in detail.
Of the excitation pulse (180 ° pulse) is alternately inverted for each sequence, and the FI
The D component is phase-encoded. By performing the Fourier transform also in the phase encoding direction, the FI
The artifact due to the D component moves from the center to the end of the reconstructed image (see FIG. 6). Usually, an important organ is set so as to appear at the center of the reconstructed image. Therefore, in most cases, the artifact at the edge of the image does not interfere with the interpretation. However, also in this case, post-processing (for example, linear interpolation) for removing artifacts on the image is performed as necessary. In addition, the first excitation pulse (90 °
Pulse) is alternately inverted for each sequence, and the phase of the detection signal is alternately inverted for each sequence.
The FID component is phase-encoded at a phase that is alternately inverted for each line. By this phase encoding, D
The C component also moves from the center to the end on the Fourier-transformed reconstructed image.

[0006] On the other hand, in magnetic resonance imaging, an averaging method for improving the S ^/ N ratio to n ^1/2 by applying an averaging process (averaging process) to n MR signals for each pixel is frequently used. I have. In the case where the averaging number N is 1 or an even number, artifact suppression due to the FID component and / or the DC component can be performed by the phase control method of the RF pulse according to the method described in the above-mentioned US patent.

On the other hand, the averaging number N may be set to an odd number (for example, 3) in order to optimize the scanning time. At this time, the phase control of the RF pulse for suppressing the artifact due to the FID component and / or the DC component is generally complicated. For example, it is assumed that the averaging number N = 3, and the sequence is a spin echo method using a 90 ° pulse (flip pulse) and a 180 ° pulse (flop pulse). In order to control the phase of the RF excitation pulse, usually, 0 ° -0 ° -0 °... Type, 0 ° -180 ° -0
° ... type, random phase type, etc. are used. Now, the phase of the flip pulse is

(Equation 1) And in accordance with that of the ADC (A / D converter),

(Equation 2) It shall be changed to. The first bracket is for phase encoding PE = 0, and the second bracket is for phase encoding PE = 1.
Respectively. As a result, the phases of the RF pulse, echo, FID component, and ADC become as shown in FIG. 7, for example, so that even-numbered FIDs (eg, “2” times when the number of averaging = 3) out of the odd-numbered times Component, DC
Ingredients can be canceled. (Refer to the portion surrounded by the dotted line in FIG. 7.) The FID component and the DC component for the remaining one time are calculated in the same manner as the suppression method in the above-mentioned US patent.
Artifacts captured as short-wavelength components in the direction of PE in the k-space in the PE direction, reconstructed and moved to the end are post-processed on the image.

[0008]

As described above, in order to suppress the artifacts in the above-described averaging process of the odd number of times, the FID component and the DC component due to the remaining one sequence without being canceled are required. Post-processing is performed in response to this. However, since this post-processing involves an increase in the calculation load of the processing device and a deterioration in image quality, it is a technique that should be avoided as much as possible.

When the variable encoding method is performed together with the averaging process in order to increase the speed of MR imaging, “0” is set to the region in each phase encoding direction on the k-space where no MR signal is collected. Compensating zero-filling is performed to achieve k-space data placement. When Fourier transform is performed on the k-space data on which the zero filling is performed, an artifact caused by the FID component and the DC component is as follows.
Unlike the method described in the above-mentioned U.S. Patent, although the degree varies depending on the spatial position, it generally spreads over the entire image in real space. When the artifact has spread over the entire real space image in this way, it is almost no longer possible to remove the artifact by post-processing.

The present invention has been made in view of such a problem of the conventional artifact suppression method, and controls the phases of an RF excitation pulse and an ADC when performing magnetic resonance imaging with an averaging process an odd number of times. It is a main object of the present invention to accurately reduce artifacts caused by the FID component and / or the DC component and eliminate the need for post-processing removal.

When performing magnetic resonance imaging with an averaging process of an odd number of times using the variable encoding method, artifacts due to the FID component and the DC component can be accurately detected only by controlling the phases of the RF excitation pulse and the ADC. Another object is to eliminate the need for post-treatment removal.

[0012]

In order to achieve the above object, a magnetic resonance imaging apparatus of the present invention provides a subject placed in a static magnetic field with a gradient magnetic field pulse and an RF pulse along an echo sequence pulse sequence. Applying means for applying; receiving means including an A / D converter for A / D converting an echo signal obtained in response to the application of the gradient magnetic field pulse and the RF pulse; and odd number n (n ≧ 3) And the signal processing means for performing the averaging process on the echo signal obtained from the receiving means by executing the excitation along with the pulse sequence, while being included in the output signal of the A / D converter. The phase in which the RF pulse and the phase of the A / D converter are controlled in advance so that the vector sum of the unnecessary component causing the artifact becomes zero or substantially zero. And a control means.

For example, the pulse sequence is a sequence of the SE method. In this case, the unnecessary components are a FID component serving as a pseudo echo and a DC component of the A / D converter.

Preferably, the RF pulse comprises a flip pulse and a flop pulse, and the phase control means controls the phase of the flip pulse and holds the phase of the flop pulse at a constant value. Is desirable. Further, it is preferable that the phase control means is means for controlling the phase of the A / D converter so as to match the phase of the echo signal. For example, the phase control means changes the phase of the flip pulse for each excitation by a phase difference Δ
Includes phase difference control means for controlling so as to shift by a value determined by θ = 2mπ / N (m is an integer, N is the number of averaging).

Preferably, the receiving means has a circuit configuration of a digital receiver including the A / D converter.

For example, the pulse sequence is a sequence of the FE method. In that case, the unnecessary component is A
This is the DC component of the / D converter.

Further, for example, the signal processing means can be formed as a means for further performing zero filling processing in k-space based on a variable encoding method.

On the other hand, in order to achieve the above object, the magnetic resonance imaging method of the present invention applies a gradient magnetic field pulse and an RF pulse to a subject placed in a static magnetic field in accordance with an echo sequence pulse sequence. The A / D converter performs A / D conversion of an echo signal obtained in response to the application of the gradient magnetic field pulse and the RF pulse, receives a signal, and further excites an odd number of times (n is an integer of 3) by the pulse. A method of performing the averaging process on the echo signal after the A / D conversion obtained by executing the A / D conversion in accordance with the sequence, and further, an unnecessary component causing an artifact included in the A / D conversion signal. The RF pulse and the phase of the A / D converter are controlled in advance so that the vector sum of the RF pulse is zero or substantially zero.

Since the present invention is configured as described above, the RF pulse for excitation and the phase of the A / D converter are set in advance for each excitation during the odd averaging processing in which the number of averaging is 3 or more. Controlled. This phase control is equivalent to a vector of the phase of the FID component and / or the phase of the DC component of the A / D converter, which are equivalent in phase and are pseudo echoes, at the data addition stage of the averaging process. The sum is controlled to be zero or substantially zero (at least, the directions of the respective vectors have angular differences that cancel each other out). Therefore, the FID component and / or D
The C component is satisfactorily reduced, and almost no artifacts due to these unnecessary components appear on the MR image. Therefore, a special post-treatment for post-removal can be eliminated. Similar effects can be obtained when the variable encoding method is used together.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the accompanying drawings.

The magnetic resonance imaging apparatus shown in FIG.
A bed portion on which the subject P is placed, a magnet portion for generating a static magnetic field,
The system includes a gradient magnetic field unit for adding position information to the static magnetic field, a transmitting / receiving unit for transmitting / receiving a high-frequency signal, and a control / calculation unit for performing system control and image reconstruction.

The magnet portion is, for example, a superconducting magnet 21.
And a static magnetic field power supply 22 for supplying a current to the magnet 21, and generates a static magnetic field H ₀ in the axial direction (Z-axis direction) of the cylindrical opening (diagnostic space) into which the subject P is loosely inserted. Let it.
The couch portion is configured such that the top plate 25 on which the subject P is placed can be inserted into the opening of the magnet 21 so as to be retractable.

The gradient magnetic field unit includes a gradient magnetic field coil unit 28 incorporated in the magnet 21. The gradient magnetic field coil unit 28 includes three sets (types) of x, y, and z coils in the X, Y, and Z axis directions. The gradient magnetic field further includes x,
A gradient magnetic field power supply 29 for supplying a current to the y and z coils and a gradient magnetic field sequencer 30a in the sequencer 30 for controlling the power supply 29 are provided. The gradient magnetic field sequencer 30a includes a computer, and receives a command signal of a pulse sequence for collecting MR signals from a controller 35 (comprising a computer) that manages the entire apparatus. Accordingly, the gradient magnetic field sequencer 30a controls the application and strength of each of the gradient magnetic fields in the X, Y, and Z directions according to the commanded pulse sequence, and the gradient magnetic fields can be superimposed on the static magnetic field H _0. ing.

The transmitting / receiving section includes an RF coil 31 disposed near the subject P in the imaging space inside the magnet 21, a transmitter 32T and a receiver 32R connected to the coil 31,
An RF sequencer 30b (computer mounted) in the sequencer 30 for controlling the operations of the transmitter 32T and the receiver 32R is provided. The transmitter 32T and the receiver 32R supply a current pulse having a Larmor frequency for exciting nuclear magnetic resonance (NMR) to the RF coil 31 under the control of the RF sequencer 30b, while the RF coil 31 receives the current pulse. An MR signal (high-frequency signal) is received and subjected to various kinds of signal processing to form a corresponding digital signal. Transmitter 32T and receiver 32R
Are components that form part of the gist of the present invention, and details thereof will be described later.

Further, in addition to the controller 35 described above, the control / arithmetic unit includes an arithmetic unit 36 for inputting digital data of the MR signal formed by the receiver 32R and calculating image data and spectrum data. Unit 37 for storing images, display 3 for displaying images
8 and an input device 39. Arithmetic unit 36
Performs processing such as placement of measured data in, for example, a two-dimensional Fourier space formed by a built-in memory, zero-filling processing when performing a variable encoding method, and Fourier transform for image reconstruction.

The controller 35 controls the operation contents and operation timing of the gradient magnetic field sequencer 30a and the RF sequencer 30b while synchronizing them.
In the present embodiment, in particular, the RF sequencer 30b has a function of controlling the phase of an RF pulse and an ADC, which will be described later, and can output a control signal for phase control according to the excitation order associated with the odd-number averaging process. .

FIG. 2 shows a block configuration of the transmitter 32T and the receiver 32R. As shown in FIG.
Frequency f1 satisfying Larmor frequency f0 = f1 + f2
Oscillating section 41 for oscillating high frequency signals of f2 and f2
And a phase control circuit 43, a frequency conversion circuit 44, an amplitude modulation circuit 45, and a high-frequency power amplification circuit 46 on the output side of the oscillation units 41 and 42. The oscillating units 41 and 42 are configured to oscillate a high frequency signal of a predetermined frequency in response to a timing signal supplied from the RF sequencer 30b.

The phase control circuit 43 is a circuit used at the time of the CPMG method and the averaging process used at the time of multi-echo imaging, and can control the phase of the high-frequency signal f1 (RF pulse) output from one of the oscillators 41. It has a circuit configuration. Specifically, the phase of the high-frequency signal f1 output from the oscillating unit 41 can be changed within a range of 0 to 360 ° according to the control signal supplied from the RF sequencer 30b. In particular, the changeable phase values are determined in advance as, for example, 0 °, 120 °, and 240 °, and the phase control is performed so that an arbitrary value can be selected from the phase values according to the control signal. The circuit of the circuit 43 may be configured. The accuracy of the phase control (change, selection) by the phase control circuit 43 is desirably about 1 ° or less.

The frequency conversion circuit 44 generates a high frequency signal of the Larmor frequency f0 from the two high frequency signals f1 and f2, and sends the high frequency signal to the amplitude modulation circuit 45. The amplitude modulation circuit 45 is a circuit for determining a power condition and a slice characteristic of an excitation high-frequency pulse, and generally has a Gaussian function, a sink function, and a function waveform such as a square wave.
The input high frequency signal of the Larmor frequency f0 is modulated.
The modulated high-frequency signal is sent to the high-frequency power amplifier circuit 46 where it is power-amplified and then supplied to the RF coil 31.

On the other hand, as shown in FIG. 2, the receiver 32R employs a digital receiver system capable of high-frequency sampling and high-speed data processing. That is, the input stage receives the MR received by the RF coil 31.
A DC cut capacitor 51 that receives a signal (here, an echo signal) is provided. On the output side of the capacitor 51, an amplifier 52 and an A / D converter (ADC) 53 are provided in this order. For this reason, the received echo signal passes through the capacitor 51, and after its DC component is removed, is amplified by the amplifier 52 and input to the ADC 53.

The ADC 53 has a circuit configured to convert an input echo signal from an analog amount to a digital amount. At the time of conversion by the ADC 53, a DC (direct current) component is usually mixed in the converted output, though the degree varies. Since this DC component causes an artifact on the reconstructed image, the phase of the ADC 53 is controlled in accordance with the phase control of the RF pulse. To this end, the ADC 53 always matches the phase of the echo signal based on the control signal received from the RF sequencer 30b. The digital echo data converted by the ADC 53 is sent to the arithmetic unit 36,
For example, it is reconstructed into image data.

Next, the operation and effect of this embodiment will be described.

In the magnetic resonance imaging here, signal acquisition by the spin echo (SE) method is performed by averaging processing with the averaging number = “3”, and also by using the variable encoding method. In this signal collection, the phase of the flop pulse is fixed at 0 ° and the phase of the flip pulse is 0 ° −120 ° −240 in order to reduce artifacts caused by the DC component by the ADC 53 and the FID component serving as a pseudo echo. The phase control of the RF pulse and the ADC is performed in a pattern that differs by 120 ° for each of the three excitations. This phase control command is issued from the RF sequencer 30b. The phase of the flop pulse may be fixed to a value other than 0 °.

The sequencer 30 operates, for example, according to a pulse sequence based on the SE method shown in FIG. That is, the RF sequencer 30b first transmits 90 ° as a flip pulse to the transmitter 32T.
Pulse, then 18 as a flop pulse
A 0 ° pulse is sequentially applied to the RF coil 31. At this time, the phases of the 90 ° pulse and the 180 ° pulse are also controlled by the RF sequencer 30b for each excitation as shown in FIGS. Thus, the subject is irradiated with the RF magnetic field pulses corresponding to the 90 ° pulse and the 180 ° pulse. In parallel with the application of the RF pulse, the gradient magnetic field sequencer 30a, which is not shown in FIG. 3 (a), has a slice direction, a phase encode direction, and a read direction at appropriate timings in the sequence of the SE method. The gradient magnetic field pulse in each axis direction is supplied to the gradient magnetic field coil unit 28.
The subject is irradiated through the

The application phases of the 90 ° pulse and the 180 ° pulse as the RF pulse and the phase of the transverse magnetization at that time, which change during the transmission, are expressed as shown in FIGS. At the time of the first excitation, as shown in FIG. 9B, the phase of the 90 ° pulse is controlled to 0 ° by the RF sequencer 30b, and the phase of the transverse magnetization at that time is 2 °.
Since the phase of the 180 ° pulse is set to 0 °, the phase of the reversed transverse magnetization at that time is 90 °.
Becomes At the time of the second excitation, as shown in FIG.
Since the phase of the 90 ° pulse is controlled to 120 °, the phase of the transverse magnetization at that time is 30 °, and the phase of the 180 ° pulse is set to 0 °, so the phase of the inverted transverse magnetization at that time is set. = 330 °. Further, at the time of the third excitation, as shown in FIG.
Since it is controlled to 240 °, the phase of the transverse magnetization at that time =
Since the phase of the 180 ° pulse is set to 0 °, the phase of the reversed transverse magnetization at that time = 21
0 °.

According to the present method, the phase of the flip pulse shifts at an equal angle Δθ (= 120 °), so that the steady state of the transverse magnetization does not collapse.

At each RF excitation by the execution of the pulse sequence, the RF coil 31 echoes (ech) due to phase focusing of the magnetization spins in response to the application of the 180 ° pulse.
o) A signal is received. This echo signal is received by the receiver 32R.
And is converted into a digital signal by the configuration of the digital receiver circuit described above. The phase of the ADC 53 responsible for the conversion to the digital signal is always controlled by the RF sequencer 30b to be the same as the phase of the echo (main echo) signal.

In a time zone for signal collection based on A / D conversion, an FID component as a pseudo echo is normally received via the RF coil 31. Since this FID component is transverse magnetization generated by a flop (180 °) pulse, the flip (90)
°) Not affected by pulses. Therefore, the phase of the FID component corresponds to the phase of the 180 ° pulse = 0 °, and is always 270 ° as shown in FIGS. In other words, since the main echo represented by the solid line SE in FIG. 3 is a signal that has undergone magnetization spin rotation by 90 pulses and 180 pulses, its phase is the same as that at the time of applying the 180 ° pulse, and the first to third times 90 °, 330 in excitation order
° and 210 °, and the phases are shifted by “−120 °”.

Now, since the phase of the ADC 53 is controlled in accordance with that of the main echo, the phase of the ADC 53 is
As shown in the order of the first to third excitations, as shown in FIG.
°, 330 °, and 210 °. As a result, AD
In the converted signal of C53, there is no phase difference between the phase of the ADC 53 and the phase of the main echo, which is equivalent to the phase of the FID component being relatively shifted by 120 ° every three excitations (the maximum in FIG. 3). (See right column and FIG. 4).

In this case, the phase of the ADC 53 is set to 9
Since the operation is performed with a shift of 120 ° for each excitation from 0 °, 330 °, and 210 °, the phase of the DC component mixed with the conversion signal of the ADC 53 is also shifted by 120 °.

The main echo digitized in this way is sent to the arithmetic unit 36 and subjected to Fourier transform after averaging processing and zero filling processing by a variable encoding method. As a result, an MR image is reconstructed.

At the time of the averaging process, the main echo data for three excitations is added for each identical position in the k space. In this case, the processing is performed with “the phase of the main echo = the phase of the ADC”, and the main echoes are equivalently treated as the same phase. Therefore, three main echoes are added as they are and averaged. As a result, the SN ratio is improved in accordance with the averaging number. On the other hand, the FID for each excitation
Since the phases of the components are equivalently shifted from each other by 120 °, such addition becomes a vector sum, and most of them are surely canceled. Thereby, the FID component is satisfactorily reduced to “zero” or “a value close to zero”. In addition, since the DC components of each excitation are similarly shifted from each other by 120 °, the addition of the averaging process is a vector addition, and the added value is similarly “zero” or “a value close to zero”.
become.

As described above, the phases of the RF pulse and the ADC are controlled so that the phase of only the main echo matches, and the phases of the FID component and the DC component of the ADC become vector sum = 0 during the averaging process. I have. This allows
Even in the case of the imaging of the SE method involving the odd number averaging processing in which the number of averaging is 3 or more, unlike the conventional method, the DC component and the FID component can be surely reduced, and the MR image with significantly less artifact can be obtained without post-processing. Can be provided. Even when the variable encoding method is added to the processing of the echo data, the DC component and the FID component are surely reduced as compared with the conventional phase control method. Therefore, as shown in FIG. Can be reliably prevented. That is, in the case of the variable encoding method as in the related art, it is possible to prevent a situation in which the artifact component is diffused throughout the image so that the post-processing is no longer effective. Therefore, the present phase control method can be applied to the variable encoding method without any problem, and it is possible to provide a high-quality MR image with reduced or unnecessary calculation amount such as post-processing such as linear interpolation and reduced artifacts.

In the above embodiment, the case where the number of averaging in the averaging process is "3" has been described. However, the number of averaging in the averaging process according to the phase control of the present invention is, for example, five. Even seven times can be suitably applied. In that case, the phase of the flip pulse may be shifted by an angle difference Δθ determined by Δθ = “360 ° / averaging number” for each excitation.

Further, the phase control according to the present invention can be applied to the averaging process of an even number of times in the same manner (in the case of an even number of times, the conventional method can cope with the averaging process). If the apparatus configuration allows the operator to freely determine whether the number of averaging is to be an even number or an odd number, if the method of the present invention is applied to the averaging number = even number, RF The phase control of the pulse and the ADC can be unified with that of the present invention, and the software processing required for the phase control and the averaging process can be unified, which is convenient.

Further, the pulse sequence capable of performing the phase control of the present invention is not limited to the above-described SE method, but can be applied to the FE method. In the case of the FE method, ADC D
Similarly, the C component can be canceled, and the artifact caused by the DC component can be accurately reduced.

[0047]

As described above, according to the magnetic resonance imaging apparatus and the magnetic resonance imaging method of the present invention, a gradient magnetic field pulse and an RF pulse are applied to a subject along a pulse sequence of an echo sequence, and the application of the gradient magnetic field pulse and the RF pulse is performed. A / D-converts the echo signal obtained in response to the signal A / D by the A / D converter, and further executes an odd number of n (n ≧ 3 integer) excitations along the pulse sequence. The A / D-converted echo signal is subjected to averaging processing for imaging, and unnecessary components (for example, unnecessary components that cause artifacts included in the A / D-converted signal)
R is set so that the vector sum of the FID component or the DC component of the A / D converter which is a pseudo echo is set to zero or substantially zero.
Since the F pulse (for example, the flip pulse of the pulse sequence of the SE method) and the phase of the A / D converter are controlled in advance,
Artifacts due to the FID component and / or the DC component can be accurately reduced, and it is not necessary to remove the artifacts by post-processing. Therefore, the computational load of post-processing can be reduced, and high-quality MR
Can provide images. Further, the averaging process using an odd number of times using the variable encoding method can be similarly suitably performed, and the same operation and effect can be exhibited.

[Brief description of the drawings]

FIG. 1 is a block diagram of a magnetic resonance imaging apparatus according to one embodiment of the present invention.

FIG. 2 is a block diagram showing an outline of a transmitter and a receiver.

FIG. 3 is an explanatory diagram illustrating each state of an RF pulse, an echo signal, a FID component serving as a pseudo echo, and a phase of an ADC when signal collection is performed by an SE method with an averaging number = 3.

FIG. 4 is a diagram illustrating a phase difference of an FID component associated with three excitations based on a phase of an ADC.

FIG. 5 is a diagram illustrating a conventional inconvenience used for explaining features of the present invention.

FIG. 6 is a diagram showing a conventional example of a method for suppressing an artifact caused by an FID component and a DC component.

FIG. 7 is a view for explaining a conventional phase control method according to a method for suppressing an artifact caused by an FID component and a DC component.

[Explanation of symbols]

 Reference Signs List 30 sequencer 30a gradient magnetic field sequencer 30b RF sequencer (applying means / phase controlling means) 31 RF coil 32T transmitter (applying means) 32R receiver (receiving means) 35 controller 36 arithmetic unit (signal processing means) 41, 42 oscillator ( Phase control means) 43 phase control circuit (phase control means) 53 A / D converter

Claims (11)

[Claims] An object placed in a static magnetic field is subjected to a gradient magnetic field pulse and RF along an echo sequence pulse sequence.
A pulse applying means, and an echo signal obtained in response to the application of the gradient magnetic field pulse and the RF pulse are represented by A
Receiving means including an A / D converter for performing A / D conversion;
(N an integer of 3) excitation in accordance with the pulse sequence, and a signal processing unit for performing an averaging process on the echo signal obtained from the reception unit by the execution. A phase in which the phase of the RF pulse and the phase of the A / D converter is controlled in advance so that the vector sum of unnecessary components causing an artifact included in the output signal of the A / D converter is set to zero or substantially zero. A magnetic resonance imaging apparatus comprising a control unit. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the pulse sequence is an SE method sequence. 3. The undesired component is a FI which becomes a pseudo echo.
3. The magnetic resonance imaging apparatus according to claim 2, wherein the magnetic resonance imaging apparatus includes a D component and a DC component of the A / D converter. 4. The RF pulse comprises a flip pulse and a flop pulse, and the phase control means controls the phase of the flip pulse and holds the phase of the flop pulse at a constant value. Magnetic Resonance Imaging Equipment 5. The magnetic resonance imaging apparatus according to claim 4, wherein said phase control means is means for controlling a phase of said A / D converter to match a phase of said echo signal. 6. The phase difference control means for controlling the phase of the flip pulse by a value determined by a phase difference Δθ = 2mπ / N (m is an integer, N is an averaging number) for each excitation. 6. The magnetic resonance imaging apparatus according to claim 4, further comprising control means. 7. The magnetic resonance imaging apparatus according to claim 1, wherein the receiving unit has a circuit configuration of a digital receiver including the A / D converter. 8. The magnetic resonance imaging apparatus according to claim 1, wherein the pulse sequence is a sequence of an FE method. 9. The A / D converter according to claim 6, wherein the unnecessary component is
The magnetic resonance imaging apparatus according to claim 8, which is a C component. 10. The magnetic resonance imaging apparatus according to claim 1, wherein the signal processing unit is a unit that further performs a zero-filling process on a k-space based on a variable encoding method. 11. An object placed in a static magnetic field is subjected to a gradient magnetic field pulse and R
An F pulse is applied, an A / D converter converts an echo signal obtained in response to the application of the gradient magnetic field pulse and the RF pulse, and a signal is received.
(N an integer of 3) excitation in accordance with the pulse sequence, and applying the averaging process to the echo signal after A / D conversion obtained by the execution, wherein the A / D Magnetic resonance imaging in which the RF pulse and the phase of the A / D converter are controlled in advance so that the vector sum of unnecessary components causing an artifact included in the converted signal is set to zero or substantially zero. Method.