JPH0751244A - Mri device and mr imaging method - Google Patents

Abstract

PURPOSE:To harmonize the reduction of the TE and the compensation of the phase shift of an MR signal by the speed, by selecting to add a partial GMN pulse whose time width is smaller than the GMN pulse by a GMN pulse addition selecting means. CONSTITUTION:When a designation is made to compensate the phase shift of an MR signal by the speed, in the system in which an echo signal obtained by the receiver coil of a magnet assembly 5 is input to a computer 2 through a phase detector 10 and an AD converter 11, the image is reconstructed depending on the obtained data of the echo signal, and it is displayed in a display device 12, a pulse sequence a GMN pulse is added is provided in a full compensation. On the other hand, in the condition of a partial compensation, a pulse sequence to which a partial GMN pulse is added is produced. That is, after the bipolar inclination pulses (S1+S2), and (R1+R2) of a slice shaft Gz, the partial GMN bipolar inclination pulses (Sp and Rp) from which the time width of the GMN bipolar inclination pulse is reduced are added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MRI apparatus and an M
More specifically, the present invention relates to an MRI apparatus and an MR imaging method that can coordinate the shortening of TE and the compensation of the phase shift of the MR signal due to the velocity.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional MRI apparatus which uses a GMN (Gra) for compensating a phase shift of an MR signal due to a velocity.
It is a flowchart of a GMN pulse addition selection process which selects whether to add a dient moment nulling) pulse. In step 61, the user specifies whether or not to compensate the phase shift of the MR signal due to the velocity. If no compensation is specified, the process proceeds to step 62. When the compensation is designated, the process proceeds to step 63.

In step 62, a pulse sequence without GMN pulse is created. FIG. 7 illustrates a pulse sequence of the gradient echo method without adding a GMN pulse. In the pulse sequence of this gradient echo method, the hatched portion S1 of the slice axis Gz
And S2 have opposite polarities, equal amplitude-time products, and are bipolar gradient pulses. Furthermore, the hatched portions R1 and R2 of the frequency encode axis Gx have opposite polarities,
The amplitude and time products are the same, and it is a bipolar gradient pulse.

In step 63, a pulse sequence to which a GMN pulse is added is created. FIG. 8 illustrates a pulse sequence of the gradient echo method with the GMN pulse added. In the gradient echo method pulse sequence, after the bipolar gradient pulse (S1 + S2) of the slice axis Gz, the bipolar gradient pulse (S
A GMN bipolar gradient pulse Sf obtained by folding back 1 + S2) with respect to time is added. Hatching part S1
And S4 have the same polarity and amplitude-time product, and the hatched portions S2 and S3 have the same polarity and amplitude-time product. Further, before the bipolar gradient pulse (R1 + R2) on the frequency encode axis Gx, the bipolar gradient pulse (R1
A GMN bipolar gradient pulse Rf obtained by folding back 1 + R2) with respect to time is added. Hatched part R1
And R3 have the same polarity and the same amplitude-time product, and the hatched portions R2 and R4 have the same polarity and the same amplitude-time product.

In the pulse sequence shown in FIG. 7 in which the GMN pulse is not added, the artifact due to the flow cannot be suppressed, but the TE can be shortened by the amount in which the GMN pulse is not added. On the other hand, in the pulse sequence to which the GMN pulse shown in FIG. 8 is added, the artifact due to the flow can be suppressed, but the TE cannot be shortened due to the GMN pulse. Therefore, generally, when TE reduction is emphasized, no compensation is designated, and when suppression of artifacts due to flow is emphasized, compensation is designated.

[0006]

As described above, in the conventional MRI apparatus, the shortening of TE and the suppression of the artifact due to the flow are the alternative choices. However, this has a problem that it is not possible to cope with the case where the TE is appropriately shortened and the artifacts due to the flow are moderately suppressed. Therefore, an object of the present invention is to provide an MRI apparatus and an M-type apparatus which can coordinate the shortening of TE and the compensation of the phase shift of the MR signal due to the speed.
An R imaging method is provided.

[0007]

The MRI apparatus of the present invention is a GMN for compensating a phase shift of an MR signal due to velocity.
In the MRI apparatus having a GMN pulse addition selecting means for selecting whether to add a pulse to at least one axis of a slice axis, a phase encode axis and a frequency encode axis or not to add the GMN pulse, the GMN pulse addition selecting means, It is a feature of the configuration that it is possible to select to add a partial GMN pulse having a time width smaller than that of the GMN pulse.

The MR imaging method of the present invention is the MR imaging method of applying a bipolar gradient pulse to at least one of a slice axis, a phase encode axis and a frequency encode axis, before or after the bipolar gradient pulse. Instead of adding a GMN bipolar gradient pulse that is symmetrically folded back with respect to time, a partial GMN bipolar gradient pulse having a shorter time width of the GMN bipolar gradient pulse is added as a structural feature.

[0009]

In the MRI apparatus of the present invention, the GMN pulse addition selecting means for selecting whether or not to add the GMN pulse for compensating the phase shift of the MR signal due to the velocity applies the partial GMN pulse having a smaller time width than the GMN pulse. I made it possible to select. For this reason, it becomes possible to select an intermediate value between the reduction of TE and the suppression of the artifact due to the flow, and the TE can be shortened moderately and the artifact due to the flow can be suppressed moderately. become.

In the MR imaging method of the present invention, the M including the bipolar gradient pulse is included in the pulse sequence.
In the R imaging method, the bipolar gradient pulse is folded back and forth symmetrically in time with respect to G.
A partial GMN bipolar gradient pulse with a reduced duration of the MN bipolar gradient pulse is applied before or after the bipolar gradient pulse. For this reason, TE is shortened and artifacts due to flow are suppressed, not
It becomes possible to select an intermediate value between them, so that TE can be shortened moderately and also artifacts due to the flow can be suppressed moderately.

[0011]

The present invention will be described in more detail with reference to the embodiments shown in the drawings. The present invention is not limited to this. FIG. 1 shows an MR according to an embodiment of the present invention.
It is a block diagram of I device 1. Calculator 2 is a console 13
Based on the instructions from, control the whole operation. The sequence controller 3 operates the gradient magnetic field driving circuit 4 based on the stored sequence, and causes the gradient magnetic field coil of the magnet assembly 5 to generate a gradient magnetic field. Further, the gate modulation circuit 7 is controlled to modulate the RF pulse generated by the RF oscillation circuit 6 into a predetermined waveform, and the RF pulse is applied from the RF power amplifier 8 to the transmission coil of the magnet assembly 5.

The echo signal obtained by the receiving coil of the magnet assembly 5 is input to the phase detector 10 via the preamplifier 9 and further to the computer 2 via the AD converter 11. The computer 2 reconstructs an image based on the echo signal data obtained from the AD converter 11, and displays the image on the display device 12.

In FIG. 2, in the MRI apparatus 1 described above, a GMN pulse for compensating the phase shift of the MR signal due to the velocity is not added, a GMN pulse is added, or a partial GM is used.
It is a flow diagram of GMN pulse addition selection processing which selects whether to add N pulses. In step 21, M depending on speed
The user specifies whether to compensate the phase shift of the R signal. If no compensation is specified, the process proceeds to step 22. When the compensation is designated, the process proceeds to step 23.

In step 22, a pulse sequence without GMN pulse is created. For example, the pulse sequence shown in FIG. 7 described above is created.

In step 23, the user specifies whether to perform full compensation or partial compensation. When full compensation is designated, the process proceeds to step 24. When the partial compensation is designated, the process proceeds to step 25.

In step 24, a pulse sequence to which a GMN pulse is added is created. For example, as shown in FIG.
Create the pulse sequence shown in.

In step 25, a pulse sequence to which a partial GMN pulse is added is created. FIG. 3 illustrates a pulse sequence of the gradient echo method to which a partial GMN pulse is added. In this pulse sequence, the bipolar gradient pulse (S1
A partial GMN bipolar gradient pulse Sp is added after + S2). This partial GMN bipolar gradient pulse Sp is the bipolar gradient pulse (S
1 + S2) is returned with respect to time, and the time width of the GMN bipolar gradient pulse Sf (FIG. 8) is shortened. The hatched portions S1 and S4 'have the same polarity, and the amplitude-time product is 1: 0.5, for example. Further, the hatched portions S2 and S3 'have the same polarity, and the amplitude-time product is, for example, 1: 0.5. Furthermore, the frequency encode axis Gx
The partial GMN bipolar gradient pulse Rp is added before the bipolar gradient pulse (R1 + R2). This partial GMN bipolar gradient pulse Rp
Is a shortened time width of the GMN bipolar gradient pulse Rf (FIG. 8) obtained by folding the bipolar gradient pulse (R1 + R2) with respect to time. Hatch part R
1 and R3 ′ have the same polarity, and the amplitude-time product is, for example, 1:
It is 0.5. The hatched portions R2 and S4 'have the same polarity, and the amplitude-time product is, for example, 1: 0.5.

In the pulse sequence to which the partial GMN pulse shown in FIG. 3 is added, TE can be shortened moderately, and artifacts due to the flow can be suppressed moderately. Therefore, the MRI apparatus 1
According to this, it is possible to respond more flexibly than ever according to the diagnosis site and the purpose of diagnosis.

FIG. 4 is a partial GM according to the present invention.
It is explanatory drawing which generalized N pulse Sp. For the purpose of shortening TE as much as possible, bipolar gradient pulse (S1 + S
The amplitude of the hatched portion S2 in 2) is set to the hatched portion S1.
The amplitude G is set to m times, and the time width is set to 1 / m times the time width T1 of the hatched portion S1. Along with this, the amplitude of the partial GMN pulse Sp is multiplied by m, and the time width is 1 / m.
Doubled. Even if modified in this way, it is equivalent to the bipolar gradient pulse (S1 + S2) and the partial GMN bipolar gradient pulse Sp of FIG. 3, and is included in the scope of the present invention.

Now, assuming that the time width of the partial GMN bipolar gradient pulse Sp is 2T in FIG. 4, T2 = (1 + 1 / m) T1 T3 = (1 + 1 / m) T1 + T T4 = (1 + 1 / m) T1 + 2T. At this time, the phase shift amount θ of the nuclear spin moving at a constant velocity v is represented by (Equation 1).

[0021]

[Equation 1]

FIG. 5 is a graph of the phase shift amount θ.
T = 0 corresponds to the case where no GMN bipolar gradient pulse is added. Also, T = (1 + m) ^1/2 T1 / 2m
Corresponds to the case where the GMN bipolar gradient pulse Sf is added. And 0 <T <(1 + m) ^1/2 T1 / 2m
Corresponds to the case where the partial GMN bipolar gradient pulse Sp is added.

[0023]

According to the MRI apparatus and the MR imaging method of the present invention, it becomes possible to apply a partial GMN pulse having a shorter time width than the GMN pulse applied by the GMN method, so that the TE is shortened and the speed is reduced. MR by
The compensation for the phase shift of the signal can be coordinated.
Therefore, it is possible to respond more flexibly than before according to the diagnosis site and the purpose of diagnosis.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an MRI apparatus of the present invention.

FIG. 2 is a flow chart of GMN pulse addition selection processing in the MRI apparatus of FIG.

FIG. 3 is a pulse sequence diagram with a partial GMN bipolar gradient pulse added.

FIG. 4 is a general illustration of a partial GMN bipolar gradient pulse.

FIG. 5 is a characteristic diagram of a time width and a phase shift amount of a partial GMN bipolar gradient pulse.

FIG. 6 is a flow chart of GMN pulse addition selection processing in a conventional MRI apparatus.

FIG. 7 is a pulse sequence diagram without adding a GMN bipolar gradient pulse.

FIG. 8 is a pulse sequence diagram in which a GMN bipolar gradient pulse is added.

[Explanation of symbols]

1 MRI apparatus 2 computer 3 sequence controller Gx slice axis Gy phase encode axis Gz frequency encode axis Sp, Rp partial GMN bipolar gradient pulse Sf, Rf GMN bipolar gradient pulse

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location 8105-2J G01N 24/08 510 Y

Claims (2)

[Claims] 1. A GMN pulse addition for selecting whether to add a GMN pulse for compensating a phase shift of an MR signal due to velocity to at least one of a slice axis, a phase encode axis and a frequency encode axis, or not to add the GMN pulse. An MRI apparatus having a selecting means, wherein the GMN pulse addition selecting means enables selection to add a partial GMN pulse having a time width smaller than that of the GMN pulse. 2. An MR imaging method of applying a bipolar gradient pulse to at least one of a slice axis, a phase encode axis and a read axis, wherein the bipolar gradient pulse is folded back symmetrically with respect to time before or after the bipolar gradient pulse. GMN
Instead of adding a bipolar gradient pulse, the partial GM in which the time width of the GMN bipolar gradient pulse is shortened
MR characterized by applying N bipolar gradient pulses
Imaging method.