JP2001070283A - Method for collecting data of mr imaging and mri instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the flow artifact without using any dummy pulse by controlling the phase encode quantity of a pulse sequence so that the echo data arranged in the phase encode directional center of the k-space can be collected in a steady state where the magnitude of vertical magnetized components is substantially constant. SOLUTION: A two-dimensional scanning depending on field echo method is adapted as pulse sequence, the operations of an inclined magnetic field power source 4 and a transmitter 8 are controlled by a sequencer 5 on the basis of the pulse sequence information of two-dimensional scanning imparted from a host computer 6, and the echo signal is collected through a receiver 8R. The data configuration is performed while advancing from the high frequency area of the frequency space to the low frequency area with the lapse of time, and the echo data of low frequency component on the k-space is excited in the state where the vertically magnetized component of a spin is laid in a steady state. According to this, the signal intensity is stabilized to enhance the image contrast, and the flow artifact by the pulsation of the heart is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MR (magnetic resonance) imaging data processing method and an MRI (magnetic resonance imaging) apparatus for imaging the inside of a subject based on a magnetic resonance phenomenon. In particular, the present invention relates to MR imaging for performing reconstruction by a Fourier transform method, and more particularly to an MR imaging in which the acquisition order of echo data is improved.

[0002]

2. Description of the Related Art In magnetic resonance imaging, a nuclear spin of a subject placed in a static magnetic field is magnetically excited by a high frequency signal of its Larmor frequency, and MR signals such as echo signals generated by the excitation are used. This is an imaging method for reconstructing an image.

[0003] In order to perform this magnetic resonance imaging, a pulse is transmitted from an RF coil to a subject based on a pulse train in which various pulses are arranged in time series according to a certain rule, that is, a pulse sequence. It is necessary to receive an echo signal (MR signal) generated by the spin magnetic resonance phenomenon through an RF coil.
The received echo signal is converted into echo data by subsequent signal processing. When the image reconstruction method is the Fourier transform method, the echo data is arranged in the frequency space (k space) corresponding to the amount of phase encoding. The arrangement data in the frequency space is further Fourier transformed and reconstructed into a real space image.

[0004] In performing such imaging, usually, a method is employed in which an echo signal is collected in a steady state in which the magnitude of the longitudinal magnetization component of the spin existing at the imaging site of the subject is constant. . One method of obtaining this steady state is to apply an RF pulse as a dummy pulse (idling pulse). That is, several (for example, about 20) dummy pulses are applied to the first part of the pulse sequence. Therefore, the magnitude of the longitudinal magnetization component of the spin is made constant by the dummy pulse.

On the other hand, as described above, echo data is arranged in k-space in accordance with the amount of phase encoding.
The data arrangement order in the k-space is determined according to the order in which the amount of phase encoding is changed. Conventionally, the variable order of the amount of phase encoding has been linear order (linear order).
r) phase encoding method, centric order (c)
An entric order) phase encoding method is known. The phase encoding method of the linear order is shown in FIG.
As shown in FIG. 7, in the k-space phase encoding direction, data is arranged in a linear order on the k-space from the high-frequency region to the low-frequency region and further to the high-frequency region. In the k-space, the frequency becomes lower as the phase encoding amount in the phase encoding direction approaches zero, which is closer to the encoding area at the center of the space. In the centric-order phase encoding method, as shown in FIG. 18, the order from a low-frequency region of k-space (the center of k-space) to a high-frequency region (region near the end in the phase-encoding direction of the same space) is used. Is a method of arranging data.

[0006]

However, the linear and centric order phase encoding methods described above have the following problems.

In the case of the linear order, the echo data is k
The phase encoding amount is controlled so that the space linearly moves from the high-frequency region to the zero-encoding region and further to the high-frequency region, but in a general abdominal imaging protocol,
Flow artifacts due to the heart beat during this control appear on other organs, which may lead to misdiagnosis.

On the other hand, in the case of the centric phase encoding method, data arranged at the center of the k-space is collected first, so that it is easily affected by eddy currents, and the influence of amplitude change of longitudinal magnetization of spins is neglected. Since it is impossible, the application of the dummy pulse, that is, the blanking is absolutely necessary.
As a result, as described above, the imaging time is lengthened.

SUMMARY OF THE INVENTION The present invention has been made to overcome the current situation encountered in the prior art, and in two-dimensional and three-dimensional MR imaging, it is possible to improve image contrast and improve cardiac contrast without using dummy pulses. It is an object of the present invention to reduce flow artifacts caused by pulsation of the image.

[0010]

In order to achieve the above-mentioned object, the present invention employs a pulse sequence without any blanking, and sets k in a steady state in which the magnitude of the longitudinal magnetization component is substantially constant.
It is based on controlling the amount of phase encoding of a pulse sequence so that echo data arranged at the center in the spatial phase encoding direction can be collected.

That is, by executing the pulse sequence, the echo data of the high frequency component in the k-space is first excited in the state of the longitudinal magnetization component in which the longitudinal magnetization component of the spin has not yet reached a steady state. This excitation has a substantially idle function. Since this high frequency component hardly contributes to the image contrast, even if it does not reach the steady state, it hardly affects the image quality. On the other hand, the echo data of the low-frequency component in the k-space is excited in a state where the longitudinal magnetization component of the spin is already in a steady state. Therefore, the signal intensity is stabilized, so that the image contrast is improved and the flow artifact due to the pulsation of the heart is reduced.

A method of controlling the amount of phase encoding according to the present invention is described as “inverse centric order (reversec order)”.
The phase encoding method (that is, data collection) of "entrical order" will be referred to.

A specific configuration of the present invention is provided as follows.

The data acquisition method for MR imaging according to the present invention is a method that includes a process of receiving an echo signal generated in a subject and arranging the data of the echo signal in a frequency space. When arranging, data is arranged while progressing over time from the high frequency region to the low frequency region of this frequency space.

Preferably, when the data is arranged in the frequency space, the data is arranged in a low frequency region of the frequency space in a steady state in which the magnitude of the longitudinal magnetization component of the spin can be regarded as constant. .

As an example, the arrangement of the data is started alternately from harmonic regions of opposite polarities centered on zero encoding in the phase encoding direction in the frequency space. Further, for example, the pulse sequence for collecting the echo signal may be an FE (field echo) method, an SE (spin echo) method, an FSE (fast SE) method, a FASE (fast Asymmetric SE) method, or an EPI (echo planar imaging). Is the law.

The pulse sequence for collecting the echo signal is a pulse sequence for collecting the echo signal by dividing the application of the refocusing RF pulse a plurality of times. The arrangement of the data may be started alternately.

Further, the pulse sequence for collecting the echo signal is a pulse sequence formed by using a half-Fourier method in combination with the fast SE method, and a first method for calculating and arranging the data in the frequency space. The arrangement of the data can be started from the harmonic region of the region other than the region of the second region and the second region forming a pair with the first region.

Further, the pulse sequence for collecting the echo signal may be a pulse sequence for performing a two-dimensional scan or a three-dimensional scan.

As still another example, a data arrangement that progresses from a high-frequency region to a low-frequency region of the frequency space over time is as follows:
It is characterized in that it stops at a part of the frequency space. In this case, after the data arrangement progressing from the high frequency region to the low frequency region in the frequency space with time, the data arrangement proceeding from the low frequency region to the high frequency region with time in the remaining region of the frequency space can be continued. it can. This data arrangement can be performed alternately with time in regions of mutually opposite polarities centered on zero encoding in the phase encoding direction in the frequency space.

On the other hand, the MRI apparatus according to the present invention receives a echo signal generated in the subject by executing a predetermined pulse sequence, and arranges the data of the echo signal in a frequency space to generate an image. The apparatus is characterized by comprising a data arranging means for arranging the data in the frequency space while moving the data from a high frequency region to a low frequency region with time when arranging the data in the frequency space.

Preferably, the data arranging means sets a phase encoding amount such that the data arranging is performed while progressing from a high frequency region to a low frequency region of the frequency space with time, and is included in the pulse sequence. Includes phase encoding direction gradient magnetic field.

More preferably, the gradient magnetic field in the phase encoding direction is set such that data is arranged in a low frequency region of the frequency space in a steady state in which the magnitude of the longitudinal magnetization component of the spin can be regarded as constant. Have been.

Further, the pulse sequence may be a FE (field echo) method, an SE (spin echo) method, an FSE
(Fast SE) method, FASE (Fast Asymmetric)
SE) method or EPI (echo planar imaging) method.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment according to the present invention will be described below with reference to FIGS.

FIG. 1 shows a schematic configuration of an MRI (magnetic resonance imaging) apparatus according to this embodiment.

This MRI apparatus uses a patient P as a subject.
Bed, a static magnetic field generator for generating a static magnetic field, a gradient magnetic field generator for adding positional information to the static magnetic field, a transmitter / receiver for transmitting and receiving high-frequency signals, control of the entire system and image reconstruction A control / arithmetic unit responsible for
The apparatus includes an electrocardiogram measurement unit that measures an ECG signal as a signal representing a cardiac phase of the subject P, and a breath-holding command unit that commands the patient P to hold his / her breath.

The static magnetic field generating section includes, for example, a superconducting magnet 1 and a static magnetic field power supply 2 for supplying a current to the magnet 1, and has a cylindrical opening (diagnostic space) into which the subject P is loosely inserted. the axial direction (Z axis direction) to generate a static magnetic field H _0. Note that a shim coil 14 is provided in this magnet portion. The shim coil 14 is supplied with a current for homogenizing a static magnetic field from a shim coil power supply 15 under the control of a host computer described later. The couch part can retreatably insert the top plate on which the subject P is placed into the opening of the magnet 1.

The gradient magnetic field generator has a gradient magnetic field coil unit 3 incorporated in the magnet 1. The gradient magnetic field coil unit 3 includes three sets (types) of x, y, and z for generating gradient magnetic fields in X, Y, and Z axis directions orthogonal to each other.
The coils 3x to 3z are provided. The gradient magnetic field section also has x,
A gradient magnetic field power supply 4 for supplying a current to the y, z coils 3x to 3z is provided. The gradient magnetic field power supply 4 supplies a pulse current for generating a gradient magnetic field to the x, y, and z coils 3x to 3z under the control of a sequencer 5 described later.

An x, y, z coil 3x from the gradient magnetic field power supply 4
By controlling the pulse current supplied to ~ 3z,
The gradient magnetic fields in the three axes X, Y, and Z directions, which are physical axes, are combined, and the slice gradient magnetic field G _S , the phase encode direction gradient magnetic field G _E , and the readout direction (frequency encode direction) gradient magnetic field G _R are orthogonal to each other. Can be arbitrarily set and changed in each logical axis direction. Slice direction, phase encoding direction, and gradient magnetic fields in the readout direction are superimposed on the static magnetic field H _0.

The transmitting and receiving unit includes an RF coil 7 disposed near the subject P in the imaging space in the magnet 1,
And a transmitter 8T and a receiver 8R, which are connected to each other. The transmitter 8T and the receiver 8R are connected to a sequencer 5 described later.
It operates under the control of. The transmitter 8T supplies the RF coil 7 with an RF current pulse having a Larmor frequency for causing nuclear magnetic resonance (NMR). The receiver 8R has R
The F-coil 7 receives an MR signal (high-frequency signal) such as an echo signal, and pre-amplifies the signal, intermediate frequency conversion,
After performing various kinds of signal processing such as phase detection, low frequency amplification, and filtering, A / D conversion is performed to generate digital amount of echo data (original data) according to the MR signal.

The control / arithmetic unit includes a sequencer (also called a sequence controller) 5, a host computer 6, an arithmetic unit 10, a storage unit 11, and a display unit 1.
2, an input device 13 and a sound generator 16. Among them, the host computer 6 has a function of instructing the sequencer 5 with pulse sequence information and controlling the operation of the entire apparatus by the stored software procedure.

The host computer 6 performs an imaging scan based on any of the following pulse sequences. This imaging scan is an MR scan for acquiring a set of echo data necessary for image reconstruction,
It is set to a dimensional scan or a three-dimensional scan. The imaging scan may be performed in combination with a breath holding method in which the patient holds his or her breath in a state of inhaling or exhaling, and an ECG gating method based on an ECG signal.

In this embodiment, the pulse sequence is a pulse train based on three-dimensional (3D) scan or two-dimensional (2D) scan, and includes, for example, an SE (spin echo) method, an FSE (fast SE) method, The FASE (Fast Asymmetric SE) method (ie, fast S
A pulse train based on an E method (an imaging method combining the half Fourier method) and an EPI (echo planar imaging) method is used. In each of these pulse trains, the "inverse centric order" phase encoding method (data collection method) according to the present invention is applied.

The sequencer 5 has a CPU and a memory, stores the pulse sequence information sent from the host computer 6, and controls the operations of the gradient magnetic field power supply 4, the transmitter 8T, and the receiver 8R according to the information. At the same time, the echo data (digital amount) of the MR signal output from the receiver 8R is input once and transferred to the arithmetic unit 10. Here, the pulse sequence information is all information necessary to operate the gradient magnetic field power supply 4, the transmitter 8T, and the receiver 8R in accordance with a series of pulse sequences, for example, x, y, z coils 3x to 3z. The intensity of the pulse current applied to the
It contains information about the application timing and the like.

The arithmetic unit 10 receives the echo data (also called original data or raw data) output from the receiver 8R through the sequencer 5, and inputs a two-dimensional or three-dimensional k-space (Fourier) on its internal memory. Echo data, also called spatial or frequency space)
The echo data is subjected to a two-dimensional or three-dimensional Fourier transform for each set to reconstruct image data in a real space. The arithmetic unit 10 can also perform a process of synthesizing data relating to the image, a difference operation process, and the like as necessary.

The storage unit 11 can store not only reconstructed image data but also image data that has been subjected to the above-described synthesizing processing and difference processing. The display 12 displays an image. In addition, the operator can input, to the host computer 6, imaging conditions desired by the operator, pulse sequences, and information regarding image synthesis and difference calculation.

A voice generator 16 is provided as an element of the breath-hold command unit. The voice generator 16 can emit a breath-hold start and a breath-hold end message as voice when instructed by the host computer 6.

Further, the electrocardiogram measuring section comprises an ECG sensor 17 which is attached to the body surface of the subject and detects an ECG signal as an electric signal. 6 and an ECG unit 18 for outputting to the sequencer 5. The measurement signal from the electrocardiograph is used by the sequencer 5 when performing an imaging scan. This gives E
Synchronization timing by the CG gate method (cardiac synchronization method) can be set appropriately, and data can be collected by performing an imaging scan of the ECG gate method based on the synchronization timing.

In the configuration of the present embodiment, the sequencer 5, the host computer 6, and the arithmetic unit 10 constitute a data arrangement unit.

Next, the operation of the imaging scan by the MRI apparatus of this embodiment will be described with reference to FIGS.

[First Example (FIGS. 2 to 4)] A first example which can be employed in this embodiment will be described with reference to FIGS.
In this embodiment, the pulse sequence shown in FIG.
It adopts a two-dimensional scan based on the E method. The sequencer 5 controls the operation of the gradient magnetic field power supply 4 and the transmitter 8T based on the pulse sequence information of the two-dimensional scan based on the FE method given from the host computer 6.

[0043] According to the two-dimensional scanning, the first 90 ° RF pulse for excitation with a slice gradient magnetic field pulse G _S is applied, selective excitation of the object is performed. Thereafter, while applying a read gradient field G _R, in (Fig. 2 applies the phase encoding gradient field G _E of applying the phase encoding method of the inverse centric order, on the waveform of the phase-encoding gradient field G _E Described in the
A substantially W-shaped arrow symbol indicates a waveform of "inverse centric order").

[0044] Further, after this, by inverting the polarity of the read gradient G _R acquiring echo signals. Gradient G _E The phase encoding, for example, the phase encoding number 128 the positive polarity side and - is assigned to the amplitude value of the polarity.
Amplitude = 0 of the magnetic field waveform G _E corresponds to the phase encoding amount = 0 k-space.

[0045] Of these, when applying a phase encoding gradient field G _E, the phase-encoding amount is controlled as shown schematically in Figure 3. That is, control is performed such that the amount of phase encoding decreases for each excitation and the polarity thereof alternately swings on the positive and negative sides. In addition, the first and second phase encoding amounts of the first excitation portion are set to the amounts that carry the highest frequency encoding in the k space, and the last 128 excitation times correspond to the phase encoding amount in the k space = 0. are doing.

For this reason, the echo data collected for each excitation is sequentially arranged at the position of the corresponding phase encoding amount in the k-space in the order schematically shown in FIG. That is, 1
The echo data collected with the second excitation is located at the top of the k-space in the amount of phase encoding, and the second echo data is located at the bottom of the k-space. Further, the echo data collected for the third time is arranged at the position of the phase encoding amount below the first time, and the echo data of the fourth time is arranged at the position of the phase encoding amount above the second time. Similarly, the echo data collected in the k-space is alternately arranged above and below in the phase encoding direction, and the echo data collected at the last 128 times is exactly arranged at the position where the phase encoding amount = 0.

As described above, two-dimensional echo data arranged corresponding to data collection in the inverse centric order is:
In the arithmetic unit 10, each data set is subjected to two-dimensional Fourier transform (reconstruction) to generate real space image data. This image data is displayed on the display unit 12 and stored in the storage unit 11.

[Second Embodiment (FIG. 5)] In the second embodiment, as shown in FIG. 5, in the pulse sequence based on the FE method shown in the first embodiment, the saturation pulse SAT and the spoiler are used before the excitation. A pulse SP is applied. By applying the saturation pulse SAT, the spin of the blood flow flowing into the imaging site is saturated in advance, and the blood flow signal collected at the imaging site is suppressed. Gradient G _E The phase encoding is applied on the basis of the reverse centric phase encoding method.

[Modifications (FIGS. 6 to 9)] Next, modifications of the above-described first and second embodiments will be described with reference to FIGS. Specifically, in the first and second embodiments described above, M
The present invention relates to a configuration for avoiding problems when an R contrast agent is used in combination.

When the MR scan is performed by using the inverse centric phase encoding method using a contrast agent, as shown in FIGS. 6 and 7, a low-frequency component of k-space (a phase encoding amount = 0 and its nearest neighbors). The imaging start time may be set so that the contrast agent reaches the scan site at approximately the time when the area is collected. When collecting in the inverse centric order in this way, while collecting before low frequency components,
The effect of the contrast agent hardly works on the signal of the high frequency component, and the signal value becomes low, which may cause blurring in the details of the image.

In order to avoid this, as shown in FIGS. 8 and 9, high-frequency components are collected in an inverse centric order up to a certain number of encodings, and the phase encoding amount of the remaining area thereafter is collected in a centric order. collect.
That is, the inverse centric order and the centric order are used together. As a result, the initial high-frequency components collected in the inverse centric order still have the effect of blanking. Since the data reflecting the effect of the contrast agent is placed in the area collected in the centric order of the second half of the shooting, high-frequency components up to a certain level are also held in high signal, preventing blurring of the image it can. In addition, since the inverse centric order and the centric order have a regular symmetry of data arrangement in k-space with respect to time, periodic artifacts related to the heart beat can be similarly dispersed and made inconspicuous. it can.

[Third Embodiment (FIG. 10)]
As shown in FIG. 10, a pulse sequence based on the SE method is used.
Thus, a two-dimensional scan pulse is applied. Encouragement
After a 90 ° RF pulse is applied, a predetermined time TE
180 ° RF pulse for refocus is applied after
It is. Thereafter, the gradient magnetic field G for phase encoding is used._EIs applied
The magnetic field waveform G _EIs the inverse centric order
Based on the phase encoding method (ie data collection method)
For example, the order of changing the amplitude value is controlled.

[Fourth Embodiment (FIGS. 11 to 13)] The fourth embodiment is an example in which a pulse sequence based on the FSE method is adopted and two-dimensional scanning is performed by using the pulse sequence.

After a 90 ° RF pulse for excitation is first applied by the sequencer 5 as shown in FIG.
A plurality of 180 ° RF pulses for refocus are sequentially applied at regular time intervals, whereby a plurality of echo signals are generated each time the spin is refocused. These echo signals are phase-encoding gradient field G _E applied in advance,
They are collected together with the application of the read gradient field G _R. After the collected echo signals are generated as echo data by the receiver 8R, they are arranged in a two-dimensional k-space by the arithmetic unit 10.

Assuming that the number of echo signals is eight, for example, the k space is filled using the echo data of eight echo signals collected for each excitation. k-space is 1
In the case of a matrix size of 28 × 128, if there is echo data for 16 excitations, data arrangement in the entire k space is completed. Therefore, k-space is divided into eight regions R1~R8 to the phase encoding direction k _pe, eight echo data due to each round of excitation of eight divided regions R1~
R8 are sequentially arranged.

[0056] In this case, gradient magnetic field _{G E} a phase-encoding
Applies the inverse centric order phase encoding method (data collection method) according to the present invention for each excitation,
The change order of the amplitude is controlled. That is, as shown in FIG. 12, the amount of phase encoding given to eight echo signals in each excitation is controlled in an inverse centric order.

As a result, as shown in FIG. 13, the echo data is arranged from the high-frequency region to the low-frequency region of the k space for each excitation. Assuming that the divided regions R1 to R8 of the k space are arranged in order from the top as shown in the figure, for each excitation, from one of the divided regions at the upper and lower ends of the k space to the other,
(R1, R8, R2, R7,..., R4, R)
5), echo data is arranged.

The thus arranged echo data is subjected to a two-dimensional Fourier transform and reconstructed into real space image data.

[Fifth Embodiment (FIGS. 14 and 15)] The fifth embodiment is an example in which a pulse sequence based on the FASE method is adopted, and three-dimensional scanning is performed by using the pulse sequence.

The FASE method is a pulse sequence of the SE system, and uses the FSE method and the half Fourier method together.
The pulse train shown in FIG. By executing this pulse sequence, echo data filling a predetermined area A of the k space is collected, and echo data of the remaining area B is obtained by calculation from the collected data and arranged.

[0061] phase-encoding gradient field G _E used in the pulse sequence of the FASE method, reverse centric order of phase encoding method (data collection method) has been employed according to the present invention. More specifically, as shown in FIG. 15, among the predetermined areas A for arranging the collected data in the k space, the target areas A above and below the phase encoding direction with the zero encoding therebetween.
For 1, A2, similarly to the embodiment described above, are set phase encoding gradient field G _E in the reverse centric ordering.

Of the above-mentioned predetermined area A, the high-frequency area A3, which is the object of the area B on which data is to be arranged by calculation, and which is opposite to this area, can collect data sequentially for each phase encoding amount. the phase encoding gradient field G _E is set to. The data of the high frequency region A3 is collected after the data collection of the target regions A1 and A2 described above.

[Sixth Embodiment (FIG. 16)]
This is an example in which a pulse sequence based on the EPI method is adopted, and two-dimensional scanning is performed using the pulse sequence.

FIG. 16 shows a pulse sequence based on the FE-based EPI method. The phase encoding gradient field G _E applied in the pulse sequence, reverse centric order of phase encoding method (data collection method) has been applied in accordance with the present invention. As a result, data arrangement is performed in the k-space in the same order as in FIGS. 3 and 4 from the high-frequency region to the low-frequency region.

As described above, according to the present embodiment, two-dimensional or three-dimensional scanning can be performed in the form of various pulse trains based on the inverse centric order.

For this reason, the echo data in the end region in the phase encoding direction, which is the high frequency region of the k space, is collected and arranged first, and the echo data in the central portion in the same direction, which is the low frequency region, is collected later. And placed. The pulse application for echo data collection in the high frequency region which hardly contributes to the image contrast, which precedes in time, also has the function of applying the conventional dummy pulse. In other words, while collecting echo data in the high-frequency region, a steady state in which the amplitude of the longitudinal magnetization component of the spin is substantially constant is achieved, and the data in the central part of the k-space reflected in the image contrast in this steady state Collection and placement takes place. Therefore, a dummy pulse to be applied at the beginning of the pulse sequence as in the related art becomes unnecessary, and the time required for this application becomes unnecessary, and the entire imaging time can be reduced.

Even when multi-slice imaging is performed using this scan method, echo data at the center of k-space, which is dominant in image contrast, is collected in a steady state of spins, so that sensitivity unevenness between multi-slices is reduced. Can be reduced.

Further, according to the scan based on the inverse centric order, the periodicity of data collection and arrangement is divided and dispersed. Can reduce or disperse the flow artifact caused by the pulsation.

Further, according to the data collection of the inverse centric order, since the echo data at the center of the k-space is collected after the eddy current is stabilized, there is an advantage that the data is hardly affected by the eddy current.

In the case of the scanning method in which the application (excitation) of an RF pulse for data collection in the high frequency region of the k-space is performed earlier in time, the MT effect can be caused. Actively available for imaging. The image contrast can be improved by utilizing the MT effect.

It should be noted that the present invention is not limited to the configuration of the above-described embodiment, and it is needless to say that the present invention can be further modified into various forms based on the gist of the claims.

[0072]

As described above, according to the data acquisition method and the MRI apparatus of the MR imaging of the present invention, when arranging echo data in the frequency space, the time elapses from the high frequency region to the low frequency region of this frequency space. During the data collection in the high frequency region, which hardly contributes to the image contrast, the pulse application performs the idling function while collecting data in the low frequency region that determines the image contrast. The longitudinal magnetization component enters a substantially constant steady state. As a result, it is possible to perform two-dimensional or three-dimensional MR imaging that improves image contrast and reduces flow artifacts due to heart beats and the like without using a dummy pulse as in the related art.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram illustrating an example of a configuration of an MRI apparatus according to an embodiment of the present invention.

FIG. 2 is a pulse sequence of a two-dimensional scan based on the FE method according to the first embodiment.

FIG. 3 is a diagram showing a change in phase encoding amount (change in inverse centric order) with time in the first embodiment.

FIG. 4 is a schematic view of a k-space for showing a data arrangement order according to an inverse centric order in the first embodiment.

FIG. 5 is a pulse sequence of a two-dimensional scan based on the FE method according to the second embodiment.

FIG. 6 is a view for explaining phase encoding of an inverse centric order and arrival timing of a contrast agent for explaining a modification of the first and second embodiments.

FIG. 7 is an explanatory diagram of a k-space based on an inverse centric order corresponding to FIG. 6;

FIG. 8 is a view for explaining the phase encoding of the combined use of the inverse centric order and the centric order and the arrival timing of the contrast agent for explaining a modification of the first and second embodiments.

FIG. 9 is an explanatory diagram of a k-space based on a combined type order corresponding to FIG. 8;

FIG. 10 is a pulse sequence of a two-dimensional scan based on the SE method according to the third embodiment.

FIG. 11 is a pulse sequence of a two-dimensional scan based on the FSE method according to the fourth embodiment.

FIG. 12 is a diagram showing a change in phase encoding amount (change in inverse centric order) for each excitation with time in the fourth embodiment.

FIG. 13 is a schematic diagram of a k-space for showing a data arrangement order according to an inverse centric order in a fourth embodiment.

FIG. 14 shows 3 based on the FASE method according to the fifth embodiment.
Pulse sequence for dimensional scan.

FIG. 15 is a schematic diagram of a k-space for showing a data arrangement order according to an inverse centric order in the fifth embodiment.

FIG. 16 shows a pulse sequence of a two-dimensional scan based on the FE-based EPI method according to the sixth embodiment.

FIG. 17 is a schematic view of a k-space for showing conventional linear-order data collection.

FIG. 18 is a schematic view of k-space for showing conventional centric order data collection.

[Explanation of symbols]

 Reference Signs List 1 magnet 2 static magnetic field power supply 3 gradient magnetic field coil unit 4 gradient magnetic field power supply 5 sequencer 6 host computer 7 RF coil 8T transmitter 8R receiver 10 arithmetic unit 11 storage unit 12 display 13 input unit

Claims (14)

[Claims] 1. Receiving an echo signal generated in a subject,
In the data acquisition method of MR imaging that involves processing of arranging the data of the echo signal in a frequency space, when arranging the data in the frequency space, the data gradually progresses from a high-frequency region to a low-frequency region of the frequency space with time. A data acquisition method for MR imaging, wherein data is arranged. 2. The data collection method according to claim 1, wherein when arranging the data in the frequency space, the magnitude of the longitudinal magnetization component of the spin is reduced in a steady state where the magnitude of the longitudinal magnetization component can be regarded as constant. A data processing method for MR imaging, wherein data is arranged in a frequency domain. 3. The data collection method according to claim 2, wherein the data arrangement is started alternately from harmonic regions having mutually opposite polarities centered on zero encoding in the phase encoding direction in the frequency space. Data acquisition method for MR imaging. 4. The data acquisition method according to claim 3, wherein the pulse sequence for acquiring the echo signal is FE.
(Field echo) method, SE (spin echo) method, F
SE (Fast SE) method, FASE (Fast Asymmetry)
a data acquisition method for MR imaging, which is an ic SE) method or an EPI (echo planar imaging) method. 5. The data collection method according to claim 3, wherein the pulse sequence for collecting the echo signal is a pulse sequence for collecting the echo signal by dividing the application of the refocus RF pulse a plurality of times. And a step of arranging the data alternately from a harmonic region in the frequency space. 6. The data collection method according to claim 3, wherein the pulse sequence for collecting the echo signal is a high-speed pulse sequence.
A pulse sequence formed by using the half Fourier method in combination with the E method, wherein a first region in which the data is obtained by calculation in the frequency space and arranged is a second region forming a pair with the first region. A data acquisition method for MR imaging, wherein the arrangement of the data is started from a harmonic region of a region other than the region. 7. The data acquisition method according to claim 3, wherein the pulse sequence for acquiring the echo signal is a pulse sequence for performing a two-dimensional scan or a three-dimensional scan. Method. 8. The data acquisition method according to claim 1, wherein a data arrangement that progresses from a high frequency region to a low frequency region of the frequency space with time is limited to a part of the frequency space. Data collection method. 9. The data collection method according to claim 8, wherein after data arrangement progressing from the high frequency region to the low frequency region of the frequency space with time, the remaining region of the frequency space is shifted from the low frequency region to the high frequency region. A data acquisition method for MR imaging, characterized by continuing data arrangement progressing over time in a region. 10. The data collection method according to claim 9, wherein the data arrangement is performed alternately with time in regions of mutually opposite polarities centered on zero encoding in the phase encoding direction in the frequency space. A data acquisition method for MR imaging, comprising: 11. An MRI apparatus that receives an echo signal generated in a subject by executing a predetermined pulse sequence and arranges the data of the echo signal in a frequency space to generate an image. An MRI apparatus comprising: a data arranging means for arranging data while arranging in a frequency space over time from a high frequency region to a low frequency region in the frequency space. 12. The MRI apparatus according to claim 11, wherein the data arranging means sets a phase encoding amount such that the data arranging is performed with time from a high frequency region to a low frequency region of the frequency space. The MRI apparatus further includes a gradient magnetic field in a phase encoding direction included in the pulse sequence. 13. The MRI apparatus according to claim 12, wherein the phase encoding direction gradient magnetic field is arranged in a low frequency region of the frequency space in a steady state in which the magnitude of the longitudinal magnetization component of the spin can be regarded as constant. An MRI apparatus characterized in that the setting is made to perform the following. 14. The MRI apparatus according to claim 11, wherein the pulse sequence is FE (field echo).
Method, SE (spin echo) method, FSE (fast SE) method,
An MRI apparatus characterized by a FASE (High-Speed Asymmetric SE) method or an EPI (Echo Planar Imaging) method.