JPH11239570A - Mri device and mr imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To guarantee the effect of a gradient magnetic field spoiler even in the case of mutually independently producing the program of a prior sequence including a pre-pulse and the gradient magnetic field spoiler and a data gathering sequence, to almost surely prevent the generation of pseudo echoes and to suppress the generation of an artifact. SOLUTION: The imaging site of a subject is scanned based on a scanning sequence including the prior sequence including a pre-saturation pulse and the gradient magnetic field spoiler in Z axis and X axis directions and the data gathering sequence. To put it concretely, the polarity of a gradient magnetic field waveform in the slice direction and read direction of the data gathering sequence is judged, the polarity of the gradient magnetic field spoiler in the Z axis and X axis directions is matched with the judged polarity and thereafter, scanning by the scanning sequence is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to magnetic resonance imaging for imaging the inside of a subject based on the magnetic resonance phenomenon of the subject. Particularly, the present invention relates to magnetic resonance imaging in which a high-frequency excitation pulse called a pre-pulse is applied to an imaging region or its vicinity before executing a sequence for collecting MR signals from the imaging region.

[0002]

2. Description of the Related Art In magnetic resonance imaging (MRI), a nuclear spin of a subject placed in a static magnetic field is magnetically excited by a high frequency signal of the Larmor frequency, and an MR signal generated by the excitation is generated. This is an imaging method for reconstructing an image.

In this magnetic resonance imaging, an imaging method in which a high-frequency excitation pulse called a pre-pulse is applied is known. The pre-pulse is a pulse used for the purpose of suppressing the MR signal from the blood flow flowing into the imaging surface or suppressing the MR signal from the fat at the imaging site. The pre-pulse is usually applied during the execution of the pre-sequence with a gradient magnetic field spoiler pulse (hereinafter, referred to as a gradient magnetic field spoiler) for diffusing nuclear spins in each gradient magnetic field direction to prevent generation of a pseudo echo. Is done. That is, as a pre-sequence, a pre-pulse is first applied to the imaging region, and then a gradient magnetic field spoiler is applied in the same direction (polarity) as the pre-pulse. Gradient magnetic field spoilers are, for example, x, y,
It is applied as a component in the z-axis direction.

The pre-sequence software program for applying the pre-pulse emphasizes versatility.
Usually, the data acquisition sequence (also referred to as the present sequence) is often produced as a separate product, that is, independently. The software programs for both sequences are installed on the MRI apparatus and cooperate to handle the scan.

[0005]

However, in the prior art, since the software program of the pre-sequence and the data acquisition sequence are independently produced as described above, the pre-sequence and the data acquisition sequence are not used when actually used in the MRI apparatus. The polarity of the gradient magnetic field spoiler and the pulse of the data acquisition sequence may be different from each other. That is, for example, in the slice direction or the readout direction, the polarity of the slice gradient magnetic field pulse or the readout gradient magnetic field pulse in the data acquisition sequence may be opposite to that of the gradient magnetic field spoiler in those directions in the pre-sequence. In this case, depending on imaging conditions such as slice thickness and readout resolution,
The time integration of the gradient magnetic field in the slice direction or the gradient magnetic field in the readout direction between the pre-sequence and the data acquisition sequence may become zero or substantially zero. That is, the nuclear spin phase dephased (dispersed) by the gradient magnetic field spoiler is rephased by the subsequent gradient magnetic field in the slice direction and / or the readout direction, and the applied gradient magnetic field spoiler becomes ineffective or its effect is greatly reduced. . The spin whose phase has returned in the rephase direction generates a pseudo echo in a subsequent sequence. This spurious echo was acquired during the execution of the data acquisition sequence and appeared as an artifact in the reconstructed image.

The present invention has been made to overcome such a conventional situation. Even when software programs of a pre-sequence including a pre-pulse and a gradient magnetic field spoiler and a data acquisition sequence are produced independently of each other. It is an object of the present invention to guarantee the effectiveness of the gradient magnetic field spoiler, to almost certainly prevent the generation of a pseudo echo accompanying the application of the pre-pulse, and to significantly suppress the generation of image artifacts caused by the pseudo echo.

[0007]

In order to achieve the above object, according to the MRI apparatus of the present invention, a pre-sequence including a pre-pulse applied to a subject and a gradient magnetic field spoiler applied in a physical axis direction after the pre-pulse is applied. And scanning the imaging region of the subject based on a scan sequence including a data acquisition sequence executed after the execution of the pre-sequence, and making the polarity of the gradient magnetic field spoiler coincide with the polarity of the gradient magnetic field waveform of the data acquisition sequence. It is characterized by having polarity control means.

[0008] As a preferred example, the polarity control means includes:
A determination unit configured to determine the polarity of the gradient magnetic field waveform in the logical axis direction of the data acquisition sequence; and an adjustment unit configured to adjust the polarity of the gradient magnetic field spoiler to the determined polarity. In this case, for example, it is preferable that the determination unit determines a polarity of a main waveform of the gradient magnetic field waveform in the logical axis direction of the data acquisition sequence. Further, the logical axis direction in which the determination unit determines the polarity is a slice direction and a readout direction, and the gradient magnetic field spoiler whose polarity is adjusted by the adjustment unit is a physical axis direction corresponding to the slice direction and the readout direction. Good.

As a further preferred example, there is a configuration in which the imaging site is an oblique surface oblique on the physical axis coordinates. At this time, for example, a means may be provided for obliquely causing the gradient magnetic field spoiler in the physical axis direction to correspond to the oblique degree of the oblique surface.

As another example, the pre-pulse may be formed by a pre-saturation pre-saturation pulse.

As another example, the pre-sequence and the data collection sequence are stored in storage means as program data on software produced independently of each other. By independently producing both sequences in this way, the versatility of the pre-sequence is enhanced, and it can be applied to various data acquisition sequences.

On the other hand, an MRI imaging method according to the present invention provides a pre-sequence including a pre-pulse applied to a subject and a gradient magnetic field spoiler applied in the physical axis direction after the pre-pulse is applied, and data acquisition executed after the execution of the pre-sequence In a method of scanning the imaging region of the subject based on a scan sequence including a sequence, the polarity of the gradient magnetic field waveform in the logical axis direction of the data acquisition sequence is determined, and the polarity of the gradient magnetic field spoiler is adjusted to the determined polarity. After that, a scan according to the scan sequence is executed.

Thus, for example, the polarity of the gradient magnetic field spoiler in the preliminary sequence in the slice direction and the readout direction is adjusted to the polarity of, for example, the main waveform of the gradient magnetic field waveform in the data acquisition sequence before scanning. For this reason, it is possible to avoid a state in which the integrated area of the gradient magnetic field spoiler and the subsequent waveform for data collection becomes zero, and the effect of the gradient magnetic field spoiler (spreading action of the spin phase) is hardly reduced. The generation of the accompanying pseudo echo can be reliably prevented or suppressed.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First Embodiment A first embodiment of the present invention will be described with reference to FIGS.

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

This MRI apparatus comprises a bed on which a subject P is placed, 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, and a transceiver for transmitting and receiving high-frequency signals. And a control / arithmetic unit for controlling the whole system and reconstructing an image, and an electrocardiographic measuring unit for measuring an ECG signal as a signal indicating a cardiac phase of the subject P.

The static magnetic field generator includes, for example, a superconducting magnet 1 and a static magnetic field power supply 2 for supplying a current to the magnet 1, and a cylindrical opening (diagnostic space) into which the subject P is loosely inserted. A static magnetic field H ₀ is generated in the axial direction (Z-axis direction).
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 controller 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. This gradient magnetic field coil unit 3 has X and X as physical axes orthogonal to each other.
It includes three sets (types) of x, y, and z coils 3x to 3z for generating gradient magnetic fields in the Y and Z axis directions. The gradient magnetic field unit further includes a gradient magnetic field power supply 4 for supplying a current to the x, y, z coils 3x to 3z. This gradient power supply 4
Under the control of the sequencer 5, which will be described later, a pulse current for generating a gradient magnetic field is supplied to the x, y, z coils 3x to 3z.

An x, y, z coil 3x from the gradient magnetic field power supply 4
By controlling the ratio and magnitude of the pulse current supplied to .about.3z, the gradient magnetic fields in the three axes X, Y, and Z are combined, and the slice gradient magnetic field Gs, the phase encode direction gradient magnetic field Ge, and the readout are read out. The direction (frequency encoding direction) gradient magnetic field Gr can be arbitrarily set or changed. Slice direction, phase encoding direction and readout direction are logic-axis directions perpendicular to each other, the gradient of each direction are superimposed on the static magnetic field H _0.

The transmission / reception unit includes a high-frequency coil 7 disposed near the subject P in the imaging space in the magnet 1, and a transmitter 8T and a receiver 8R connected to the coil 7.
The transmitter 8T and the receiver 8R supply an RF current pulse having a Larmor frequency for exciting magnetic resonance (MR) to the high-frequency coil 7 under the control of a sequencer 5 described later, and the high-frequency coil 7 The received MR signal (high-frequency signal) is received and subjected to various kinds of signal processing to form a corresponding digital signal.

Further, the control / arithmetic unit includes a sequencer 5,
Controller 6, arithmetic unit 10, storage unit 1
1, a display 12, an input device 13, and a sound generator 16.

The controller 6 has a computer. The controller 6 instructs the sequencer 5 with pulse sequence information according to a software procedure stored in the computer, and matches the operation timing of the control block of the entire apparatus including the sequencer 5. It has a function to control those controls while making it work.

The sequencer 5 has a CPU and a memory, stores pulse sequence information sent from the controller 6, and performs a series of operations of the gradient magnetic field power supply 4, the transmitter 8R, and the receiver 8T according to the information. Control. Here, the pulse sequence information is all information necessary to operate the gradient magnetic field power supply 4, the transmitter 8R, and the receiver 8T according to a series of pulse sequences, and for example, x, y, z coils 3x to 3z. And information on the intensity of the pulse current to be applied to the device, the application time, the application timing, and the like.

This pulse sequence may be a two-dimensional scan or a three-dimensional scan,
The form of the pulse train includes an SE (spin echo) method, an FE (field gradient echo) method,
Any pulse train such as the FSE (Fast SE) method and the FASE (Asymmetric Fast SE) method may be used.

In the MRI apparatus, as will be described later, under the control of the controller 6, the sequencer 5 applies a presaturation (pre-saturation) pulse as a prepulse and three directions of X, Y and Z axes as physical axes. A pre-sequence including a gradient spoiler is applied prior to the data acquisition sequence (this sequence). In this case, the Z-axis and the X-axis are transmitted through the pre-processing of FIG.
The polarity of the axis gradient spoiler is adjusted to match the waveform polarity of the data acquisition sequence.

The pre-sequence program data is produced independently of the data collection sequence in order to ensure its versatility. The program data of both sequences is installed in the storage unit 11 in advance, for example.

The arithmetic unit 10 receives the digital data of the MR signal from the receiver 8R and inputs the original data (also called raw data) to a Fourier space (also called k-space or frequency space) formed by a built-in memory. ) And two-dimensional or three-dimensional Fourier transform processing for reconstructing the original data into a real space image.

The storage unit 11 can store image data to which original data and reconstructed image data have been applied. The display 12 displays an image. Information such as scan conditions and pulse sequences can be input to the controller 6 via the input device 13.

The voice generator 14 can emit a breath-hold start and a breath-hold end message as voice when instructed by the controller 6.

Further, the electrocardiogram measuring section is provided with an ECG sensor 17 which is attached to the body surface of the subject and detects an ECG signal as an electric signal. And an ECG unit 18 for outputting to the sequencer 5. The measurement signal from the electrocardiograph is used by the controller 6 as a timing signal when the scan sequence is executed. As a result, the synchronization timing for ECG synchronization can be appropriately set, and an ECG-gated scan based on the set synchronization timing can be performed to collect MR original (raw) data.

Next, the operation of the MRI apparatus according to the present embodiment will be described with reference to FIGS.

The sequence executed in this embodiment is shown in FIG.
As shown in (1), it consists of a pre-sequence followed by a data acquisition sequence (this sequence). The pre-sequence includes pre-saturation (pre-excitation) pulses as pre-pulses and gradient magnetic field spoilers (end spoilers) SPx, SPy applied in three directions of X, Y, and Z axes as physical axes to be applied after application of the pre-saturation pulse. ,
SPz. The gradient magnetic field spoiler may be applied in only two specific directions or one specific direction.

The data acquisition sequence includes a slice gradient magnetic field Gs applied in the Z-axis direction, a readout gradient magnetic field Gr applied in the X-axis direction, and a phase encoding gradient magnetic field Ge applied in the Y-axis direction. . In this embodiment,
The physical axes of the X, Y, and Z axes are made coincident with the logical axes of the slice direction, the readout direction, and the phase encode direction, and a so-called “oblique-free” imaging method is used for the imaging slice.

The controller 6 executes a predetermined main program (not shown) for scanning, and executes the processing shown in FIG. 2 as a part of the processing. This process
Z axis and X applied during execution of the pre-sequence
The outline of the polarity control of the gradient magnetic field spoilers SPz and SPx in the axial direction (slice direction and readout direction) is shown.

The controller 6 reads an imaging condition (including a command in each direction of slicing, reading, and phase encoding) instructed by the operator, and, based on the imaging conditions, allows the operator to slice, read, and perform phase encoding for data collection. The gradient magnetic field data in each logical axis direction is calculated (steps 51 and 52). Next, the controller 6
Vector data of the gradient magnetic field in the physical axis direction corresponding to the calculated gradient magnetic field data in the logical axis direction is calculated (step 53). In the case of this embodiment, as shown in FIG. 4, the physical axis coordinates of the apparatus and the logical axis coordinates to which the gradient magnetic field is applied are made to match, so that the logical axis (instructed gradient field direction for data collection) and the physical axis ( The directions of the gradient magnetic fields generated by the x, y, and z coils are corresponded, and vector data x, y, and z of the gradient magnetic field in each physical axis direction are created. The vector data x, y, z are temporarily stored in a memory file (step 54).

At an appropriate timing, the controller 6
The vector data x, y, and z of the gradient magnetic field in each physical axis direction are read from the memory file (step 55). Next, from the vector data x, y, and z, the polarities of the gradient magnetic fields Gz and Gr in the Z-axis and X-axis directions (ie, the gradient magnetic field for slice Gs and the gradient magnetic field for readout Gr during data acquisition) are determined. Judgment (Step 5
6). Each gradient magnetic field G in the slice direction and the readout direction
The s and Gr do not always have the same polarity (direction) over time. In fact, as shown in FIG. 3, in the + direction (for example, above the zero level in FIG. 3) and-(in FIG. (Below the zero level).

For this reason, the polarity determined in step 56 is the main waveform (WF in FIG. 3) responsible for slice excitation in the change waveform of the gradient magnetic field Gz in the Z-axis direction (slice direction).
s) and the change waveform of the gradient magnetic field Gr in the X-axis direction (readout direction) becomes the polarity (-polarity) of the main waveform (WFr in FIG. 3) responsible for reading the echo signal. Since the vector data x, y, z are formed based on the polarities of these "main waveforms", their polarities are uniquely determined from the vector data x, y, z.

The gradient magnetic field Gy in the Y-axis direction (phase encoding direction) is determined to have a positive polarity here, since the phase encoding gradient magnetic field Ge has both negative and positive polarities.

When the main polarity of the gradient magnetic field in the slice direction and the readout direction for data acquisition is determined in this way, the polarity information is notified to the sequencer 5 (step 57). As a result, the sequencer 5 accesses the memory file storing the pre-sequence software program already installed, and rewrites the polarities of the gradient magnetic field spoilers SPz and SPx in the Z-axis direction and the X-axis direction (step 58). .

Therefore, the controller 6 and the sequencer 5 execute the above-described polarity control procedure, and as shown in FIG. 3, the main waveform WF in the slice direction is obtained.
The polarity of the gradient magnetic field spoiler SPz in the Z-axis direction matches the polarity of the gradient magnetic field spoiler SPz in the readout direction, and the polarity of the main waveform WFr in the readout direction matches the polarity of the gradient magnetic field spoiler SPx in the X-axis direction. Become.

When the sequencer 5 completes the pre-sequence including the gradient magnetic field spoiler whose polarity has been adjusted as described above and the data acquisition sequence (this sequence) for acquiring image data as shown in FIG. Perform a scan.

More specifically, the sequencer 5 operates the gradient magnetic field power supply 4 and the transmitter 8T to execute the preliminary sequence first.

In the pre-sequence, as shown in FIG. 3, gradient magnetic fields Gz and Gz in the Z-axis direction and the X-axis direction for selecting a slice different from a target imaging slice.
x is applied from the z coil 3 z and the x coil x, and a presaturation pulse is applied from the high frequency coil 7. Thereby, as shown in FIG. 5, the presaturation slice PLpre is selectively excited, and the nuclear spin in the slice flips, for example, 90 degrees. At this time, the gradient magnetic field Gz in the Z-axis direction and the X-axis direction
In most cases, Gx and Gx are negligible compared to various gradient magnetic fields described below.

Thereafter, as a latter half of the pre-sequence, the gradient magnetic field power supply 4 is driven to drive the Z-axis, X-axis and Y-axis.
Axial gradient magnetic field spoilers SPz, SPx, and SP
Apply y. The polarities of these spoilers are determined by the above-described adjustment processing (see FIG. 2) so that those in the Z-axis direction and the X-axis direction are negative directions, and the main waveform WFs of the gradient magnetic field for slicing and the gradient magnetic field for reading in the data acquisition sequence. Each of them coincides with that of the main waveform WEr. By applying these spoiler pulses, the presaturation slice PLp excited by the presaturation pulse
The phase of the nuclear spin of re is dispersed and becomes a state of being dispersed.

Further, the gradient magnetic field power supply 4, the transmitter 8T, and the receiver 8R are driven by the sequencer 5, and the data acquisition sequencer is continuously executed.

In this data collection sequence, first,
Along with the slice gradient magnetic field Gs (in the Z-axis direction), for example, 90
° An excitation pulse is applied. This gradient magnetic field for slice G
s is applied with a waveform WFs falling to the negative polarity side. The desired imaging slice to be selectively excited by the waveform WFs is set, for example, at the surface position of Plime shown in FIG. Next, + for compensating for the dephase effect of this waveform WFs
The gradient magnetic field Gs for rephase, the polarity of which is reversed in the direction, the gradient magnetic field Gr for reading in the + direction (X-axis direction), and a predetermined amount of the gradient magnetic field Ge for phase encoding (Y-axis direction) are applied.

Next, in order to collect echo signals based on the FE method, the sequencer 5 inverts the polarity of the read gradient magnetic field Gr from the + direction to the-direction, and applies a waveform WFr which continues for a predetermined read period. Thereby, the echo signal is frequency-encoded in the time axis direction, and the high-frequency coil 7
And collected via the receiver 8R. Digital amount of echo data (raw data) corresponding to one phase encoding output from the receiver 8R is sent to the arithmetic unit 10, and is arranged in a frequency (k) space formed of a memory space.

A series of sequences including the above-described pre-sequence and data acquisition sequence are executed a predetermined number of times while changing the amount of phase encoding. As a result, the echo data arranged in the frequency space in the arithmetic unit 10 is subjected to, for example, two-dimensional Fourier transform, and is reconstructed as a real space image of the desired imaging slice PLime shown in FIG.

As can be seen from the waveform shown in FIG. 3, in the present embodiment, the gradient magnetic field spoiler S in the Z-axis direction and the X-axis direction is used.
The polarities of Pz and SPx are matched with the main waveform WFs of the slice gradient magnetic field Gs and the polarity of the main waveform WFr of the readout gradient magnetic field Gr, respectively. For this reason,
The spoiler SPz in the Z-axis direction and the waveform WFs do not cancel each other due to the same polarity, and the spoiler SPx in the X-axis direction
And the waveform WFr do not cancel each other due to the same polarity.

FIG. 6 shows a conventional sequence corresponding to this. This sequence is the same as that of FIG. 3 except for the polarities (+ polarities) of the gradient magnetic field spoilers SPz and SPx in the Z-axis direction and the X-axis direction. In the conventional case, the above-described polarity adjustment was not performed, and no such idea or idea was conceived.
The situation shown in the table frequently occurred. That is, as pointed out in the above-described problem of the conventional technique, depending on the imaging conditions such as the slice thickness and the reading direction resolution, the polarities of the spoiler SPz in the Z-axis direction and the waveform WFs of the gradient magnetic field for slicing are opposite to each other. There is a mutual range (see a range Rz in FIG. 6), and a range in which the polarities of the spoiler SPx in the X-axis direction and the waveform WFr of the read gradient magnetic field are opposite to each other and cancel each other (see a range Rx in FIG. 6). was there. As a result, the effectiveness of the spoilers SPz and SPx was reduced, and a pseudo echo was generated, which contributed to an artifact.

On the other hand, in the present embodiment, such a situation that such waveforms cancel each other can be reliably eliminated by the polarity adjustment in advance. For this reason, the gradient magnetic field spoiler SP
The subsequent data acquisition sequence can be performed in a spin phase state reliably dispersed by z and SPx, and the gradient magnetic field spoilers SPz and SPx can exhibit their original functions. Therefore, a pseudo echo accompanying the application of the presaturation pulse hardly occurs, and the original echo signal can be accurately collected. Therefore, image artifacts due to the pseudo echo can be reliably eliminated or reduced, and a high-quality MR image can be provided. . In addition, since the desired region is pre-saturated with the presaturation pulse, artifacts due to blood flow and body movement can be accurately removed.

Second Embodiment A second embodiment will be described with reference to FIGS. The hardware configuration of the MRI apparatus according to this embodiment is the same as or similar to that of the first embodiment (the same applies to the following embodiments).

In this MRI apparatus, as shown in FIG. 7, a gradient magnetic field in an appropriate axial direction among the physical axes of X, Y and Z is set so as to “oblique” only the imaging slice scanned in the data acquisition sequence. It is characterized by setting and adjusting the polarity of the gradient magnetic field spoiler in the pre-sequence.

In the case of this embodiment, the operation information of the operator includes information indicating that the imaging slice is oblique, and this information is recognized by the controller 6. The controller 6 and the sequencer 5 adjust the polarities of the gradient magnetic field spoilers SPz and SPx in the Z-axis direction and the X-axis direction by performing the above-described processing of FIG. 2 (steps 54 to 58 in FIG. 2).

In this process, as a result of obliquely observing the imaging slice, a gradient magnetic field waveform applied in the physical axis directions of the Z axis and the X axis is obtained, for example, as shown in FIG. That is, the components of the gradient magnetic field waveform in one logical axis direction (slice direction or readout direction) include a plurality of physical axes (Z axis or X axis).
Axis). Therefore, when determining the polarity of the gradient magnetic field spoilers SPz and SPx on the physical axes of the Z axis and the X axis (Step 55 in FIG. 2), the value (waveform area) of the gradient magnetic field waveform of the corresponding physical axis in the data acquisition sequence is determined. Judge the polarity of the large waveform and match the polarity of the gradient magnetic field spoiler to this.

For example, in the case of the example shown in FIG. 8, the gradient magnetic field spoiler SPz in the Z-axis direction has the polarity of the negative waveform WFz at the time of echo reading, and the gradient magnetic field spoiler SPx in the X-axis direction.
Is adjusted to the polarity of the waveform WFx in one direction of the slice.

Other scanning operations are the same as those described above.

Even when the imaging slice is obliquely obtained, the same operation and effect as in the first embodiment can be obtained, and the oblique slice image is pre-processed by the spoil function for the original spin of the gradient magnetic field spoiler. Artifacts accompanying the application of the saturation pulse can be effectively removed.

Third Embodiment A third embodiment will be described with reference to FIGS.

In the MRI apparatus according to this embodiment, FIG.
X, Y, Z so that the imaging slice scanned in the data acquisition sequence is “oblique” as shown in FIG.
The gradient magnetic field in the appropriate axial direction of the physical axes is set, and the strength of the gradient magnetic field spoiler in the pre-sequence is set to a value that `` obliquely '' corresponds to this, and the polarity of the gradient magnetic field spoiler is set. It is characterized by adjustment.

Also in this embodiment, the operation information of the operator includes information for obliquely causing both the imaging slice and the gradient magnetic field spoiler, and this is recognized by the controller 6. The controller 6 and the sequencer 5 perform the same processing as the processing of FIG. 2 described above, and thereby the gradient magnetic field spoiler S in the Z-axis direction and the X-axis direction.
The polarities of Pz and SPx are adjusted (steps 54 to 5 in FIG. 2).
8).

In this process, as a result of obliquely observing the imaging slice and the gradient magnetic field pulse, a gradient magnetic field waveform to be applied in the physical axis directions of the Z axis and the X axis is obtained, for example, as shown in FIG. In this case, since the oblique direction of the gradient magnetic field spoiler, the slice direction, and the reading direction are oblique, the polarities of the gradient magnetic field spoiler always match.

The scanning operation is the same as that of each of the embodiments described above.

In this manner, the same operation and effect as those of the first and second embodiments can be obtained. In particular, not only the imaging slice but also the gradient magnetic field spoiler is matched in polarity and oblique, so that the generation of the pseudo echo accompanying the application of the presaturation pulse can be more accurately reduced or suppressed.

The present invention can be further implemented in various modes. For example, the directions of the physical axes of the pre-sequence and the directions of the logical axes of the data acquisition sequence may be completely different. For example, when the cervical spine is imaged axially, a signal from the throat or the like is suppressed by a presaturation pulse.

Further, in each of the embodiments described above, one presaturation pulse is applied as a prepulse (corresponding to this, one gradient magnetic field spoiler in each physical axis direction is also provided).
Although the configuration of the pre-sequence is adopted, in the case of the MRI apparatus proposed in the present invention, a plurality of pre-pulses are applied in time series (according to this, the gradient magnetic field in each physical axis direction is applied every pre-pulse application). Spoilers are also applied one by one.)
In this manner, the polarity of the gradient magnetic field spoiler may be set to match that of the gradient magnetic field in the data acquisition sequence in the same manner as in the above-described embodiment. One example of this is shown in FIG.
1 shows a scan sequence. In the figure, pre-saturation pulses 1 and 2 are applied, and after each application, gradient magnetic field spoilers SPz1, SPx1, and SPy1 (Sy1) obliquely oblique according to the oblique state of the data acquisition sequence.
Pz2, SPx2, SPy2) are applied, and the polarities of these spoilers are matched with the pulse polarities of the data acquisition sequence as in the third embodiment.

Furthermore, in the above embodiment, the data acquisition sequence is described as an imaging sequence by the single slice method, but this may be configured as a sequence based on the multi slice method.

Further, in each of the above embodiments, the polarity control of the present invention is performed in both the slice direction and the physical axis direction corresponding to the readout direction. Control may be performed.

Further, the pre-pulse of the present invention can be applied to a pre-pulse produced independently of the data acquisition sequence, and the pre-pulse is not necessarily limited to a pre-saturation (pre-saturation) pulse.
Fat suppression pulse to perform fat suppression, MT (magnetizatio
n transfer) pulse.

The pre-pulse is a slice selection pulse (slice gradient magnetic field) as in the above-described embodiment.
A configuration in which the slice selection pulse is applied at the same time or a configuration in which such a slice selection pulse is not applied at the same time may be used.

[0072]

As described above, according to the MRI apparatus and the MR imaging method of the present invention, the polarity of the gradient magnetic field waveform in the logical axis direction of the data acquisition sequence is determined, and the polarity of the gradient magnetic field spoiler is determined according to the determined polarity. Since the polarity is matched, the time integration of the gradient magnetic field spoiler and the gradient magnetic field pulse for data acquisition can be performed even if the software program of the pre-sequence including the pre-pulse and the gradient magnetic field spoiler and the data acquisition sequence are produced independently of each other. At least in the imaging time domain, it does not become zero, it can suppress or prevent the decrease in the effectiveness of the gradient magnetic field spoiler, almost certainly prevent the occurrence of pseudo echoes due to the application of pre-pulses, and greatly suppress or reduce the artifacts appearing in the image Eliminates and provides high-quality MR images, contributing to improved diagnostic performance Who, it is possible to maintain the versatility due to it is a software program that pre-sequence is independent.

[Brief description of the drawings]

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

FIG. 2 is a schematic flowchart representatively showing a polarity control process of the gradient magnetic field spoiler in the embodiment.

FIG. 3 is a waveform diagram of a scan sequence according to the first embodiment.

FIG. 4 is a view for explaining a positional relationship between scan logical axis coordinates and gantry physical axis coordinates in the first embodiment;

FIG. 5 is a diagram illustrating a positional relationship between an imaging slice and a presaturation slice.

FIG. 6 is a waveform diagram of a scan sequence according to a conventional example compared to the scan sequence of the first embodiment.

FIG. 7 is a view for explaining the positional relationship between logical axis coordinates of scanning and physical axis coordinates of a gantry in the second embodiment.

FIG. 8 is a waveform chart of a scan sequence according to the second embodiment.

FIG. 9 is a diagram illustrating a positional relationship between scan logical axis coordinates and gantry physical axis coordinates according to the third embodiment.

FIG. 10 is a waveform chart of a scan sequence according to the third embodiment.

FIG. 11 is a waveform chart of a scan sequence according to a modified embodiment.

[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 controller 7 high frequency coil 8T transmitter 8R receiver 10 arithmetic unit 11 storage unit 12 display 13 input device

Claims (9)

[Claims] 1. A method according to claim 1, further comprising: a pre-sequence including a pre-pulse applied to the subject and a gradient spoiler in a physical axis direction applied after application of the pre-pulse; and a scan sequence including a data acquisition sequence executed after the execution of the pre-sequence. An MRI apparatus configured to scan an imaging region of a sample, comprising: a polarity control unit configured to match a polarity of the gradient magnetic field spoiler with a polarity of a gradient magnetic field waveform of the data acquisition sequence. 2. The invention according to claim 1, wherein said polarity control means determines a polarity of a gradient magnetic field waveform in a logical axis direction of said data acquisition sequence, and said gradient magnetic field spoiler is adapted to said determined polarity. An MRI apparatus comprising: an adjusting unit that adjusts the polarity of the MRI. 3. The MRI apparatus according to claim 2, wherein the determination unit determines a polarity of a main waveform of a gradient magnetic field waveform in a logical axis direction of the data acquisition sequence. 4. The invention according to claim 2, wherein the logical axis directions in which the determining means determines the polarity are a slice direction and a reading direction, and the gradient magnetic field spoiler whose polarity is adjusted by the adjusting means is in the slice direction and the reading direction. The MRI device that is the corresponding physical axis direction. 5. The MRI apparatus according to claim 1, wherein the imaging site is an oblique surface oblique on the physical axis coordinates. 6. The MRI apparatus according to claim 5, further comprising: means for obliquely causing the gradient magnetic field spoiler in the physical axis direction to correspond to the degree of obliqueness of the oblique surface. 7. The MRI apparatus according to claim 1, wherein the pre-pulse is a pre-saturation pre-saturation pulse. 8. The MRI apparatus according to claim 1, wherein the pre-sequence and the data collection sequence are stored in storage means as program data on software produced independently of each other. 9. A method according to claim 1, further comprising: a pre-sequence including a pre-pulse applied to the subject and a gradient magnetic field spoiler in a physical axis direction applied after the pre-pulse is applied; and a scan sequence including a data acquisition sequence executed after the execution of the pre-sequence. M to scan the imaging part of the sample
In the R imaging method, the polarity of the gradient magnetic field waveform in the logical axis direction of the data acquisition sequence is determined, the polarity of the gradient magnetic field spoiler is adjusted to the determined polarity, and thereafter, scanning by the scan sequence is performed. A featured MR imaging method.