JPH01221150A - Data collecting method for mri - Google Patents

Abstract

PURPOSE:To shorten a photographing time, to improve through-put, and to relieve the burden of a patient, by a gradient echo signal and a spin echo signal are generated by one pulse sequence to collect data thereof. CONSTITUTION:After one pulse sequence is completed and a restoring time elapses, the intensity of a pulse 31 of an inclining magnetic field Gy for phase encoding is changed to perform the same pulse sequence. The intensity of a Gy pulse 31 is varied by a number responding to the number of reforming picture matrixes to repeat a pulse sequence. This repetition completes one scan for collecting data necessary to formation of a picture related to a slice surface. Since, only by performing scan one time, data on a gradient echo signal and data on a spin echo signal are provided, a data collection time is reduced to a half compared with a case in which the data is obtained by an independent pulse sequence, through-put of a device is not only improved but also the burden of a patient is relieved.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method of acquiring data in MRI (imaging using nuclear magnetic resonance), and particularly to improving a pulse sequence for data acquisition.

[Conventional technology]

Traditionally, MRI pulse sequences include GE (gradient echo) method, SE (spin echo) method, and IR (
Inversion recovery) method is known.

[Problem to be solved by the invention 1] However, each of these pulse sequences is independent, and two cannot be performed simultaneously in one pulse sequence. Therefore, gradient echo signal data and spin When you want to obtain echo signal data, you have to perform scanning using two types of pulse sequences, and as a result, when you want to collect these two types of data, the data collection time (imaging time) This poses a problem in that the process becomes longer, the throughput of the device deteriorates, and the burden on the patient increases. This invention has been improved by generating two types of signals in one pulse sequence and collecting two types of data, thereby shortening imaging time, improving throughput, and reducing the burden on patients. The purpose is to provide an MRI data collection method. [Means for Solving the Problems] In order to achieve the above object, in the MRl data collection method according to the present invention, a gradient magnetic field pulse for slice selection whose magnetic field strength is gradient in a direction perpendicular to the tomographic plane is applied. Then, a gradient magnetic field pulse for phase encoding whose magnetic field strength is inclined in one direction within the tomographic plane is applied, and at the same time, a gradient magnetic field pulse for phase encoding whose magnetic field intensity is inclined in one direction within the tomographic plane is applied. A frequency encoding gradient magnetic field pulse whose magnetic field strength is tilted in a direction perpendicular to the gradient direction is applied, and then a gradient magnetic field pulse for frequency encoding with the same polarity is applied, and this latter frequency encoding gradient is applied. A sampling pulse is generated when applying a magnetic field pulse to collect data from the received signal, and after applying these gradient magnetic field pulses for phase encoding and gradient magnetic field pulses for frequency encoding, a 180° pulse is generated while applying a gradient magnetic field pulse for slice selection. Then, the same amount of unipolar and opposite polarity frequency encoding gradient magnetic field pulses as the above unipolar and opposite polarity frequency encoding gradient magnetic field pulses are sequentially applied, and then unipolar and opposite polarity frequency encoding gradient magnetic field pulses are applied sequentially. A pulse sequence in which frequency encoding gradient magnetic field pulses of opposite polarity are applied one after another, and when this last frequency encoding gradient magnetic field pulse is applied, a sampling pulse is generated to collect data from the received signal, the above-mentioned phase encoding gradient magnetic field pulse is Repeat while changing the size.

[For production]

By exciting the subject with an excitation pulse while applying a gradient magnetic field pulse for slice selection, only spins on a predetermined cross-sectional plane are selectively excited. Thereafter, positional information in one direction within the tomographic plane is encoded by applying a gradient magnetic field pulse for phase encoding in which the magnetic field strength is inclined in one direction. On the other hand, after the excitation pulse, a frequency encoding gradient magnetic field pulse whose magnetic field strength is tilted in a direction perpendicular to the gradient direction of the phase encoding gradient magnetic field is applied within the tomographic plane, and then the polarity is changed. Since the same-frequency encoding gradient magnetic field pulses are applied, the reversal of the gradient magnetic field aligns the phases of the spins and generates a gradient echo signal. At this time, data is collected from the received signal using the sampling pulse, so
Gradient echo signal data can be collected. Furthermore, after the 180° pulse, the same amount of frequency encoding gradient magnetic field pulses of one polarity and opposite polarity as the previous frequency encoding gradient magnetic field pulses of one polarity and opposite polarity are sequentially applied.
The influence of the frequency encoding gradient magnetic field pulse before the 0° pulse is canceled. In other words, since magnetization is reversed by a 180° pulse, applying a gradient magnetic field pulse of the same amount to the same polarity is the same as applying a gradient magnetic field pulse of the same amount to the opposite polarity.
°The influence of the frequency encoding gradient magnetic field pulse before the pulse is canceled. Therefore, the magnetization is reversed by the 180° pulse, and the spins become aligned in phase after a certain period of time. In addition, since frequency encoding gradient magnetic field pulses of - polarity and opposite polarity are sequentially applied, the magnetic field The phase of the spins is inverted and focused (the phases are aligned), and a spin echo signal is generated. At this time,
Since data is collected from the received signal using the sampling pulse, data on the spin echo signal can be collected. Since gradient magnetic field pulses for frequency encoding are applied when these gradient echo signals and echo signals are generated, position information in the direction in which the magnetic field strength of this gradient magnetic field is inclined is encoded. .

[Embodiment 1] Referring to a pulse sequence diagram according to an embodiment of the present invention, first, while applying a pulse 41 of a gradient magnetic field Gz whose magnetic field strength is inclined in the Z direction, an excitation pulse of, for example, 90° is applied. A pulse 11 is generated to excite the subject. This Z direction is a direction perpendicular to the slice plane to be imaged, and the 90° pulse 11 gives a pulsed high-frequency signal having the same frequency component as the rotation frequency of the atomic nucleus (for example, a hydrogen nucleus) located on this slice plane. It is. In this way, by applying a high-frequency signal of a specific frequency to a subject placed in a magnetic field whose magnetic field strength is inclined in the Z direction, it is possible to identify a region of magnetic field strength corresponding to that frequency, that is, a region perpendicular to the Z direction. It is possible to selectively excite only the slice plane. Thereafter, a pulse 31 of a gradient magnetic field Gy whose magnetic field strength is inclined in one direction within the slice plane (hereinafter referred to as the Y direction) is applied, and position information in the Y direction is encoded into a phase. On the other hand, after disturbing the phase of the spins by applying a pulse 21 to the gradient magnetic field Gx whose magnetic field strength is inclined in the direction perpendicular to the Y direction (this is the X direction) in this slice plane, the polarity is changed. Inverted Gx pulse 2
When the zero-inverted gradient magnetic field Gx pulse 22 giving 2 becomes about the same amount as the first gradient magnetic field pulse 21, the phases of the spins become aligned and a gradient echo signal 51 is generated. When this echo signal is generated, the gradient magnetic field Gx pulse 22
is being applied, the position information in the X direction is encoded into frequency. Therefore, data regarding the gradient echo signal 51 can be collected by generating a sampling pulse and sampling the received signal around the time when the gradient echo signal 51 is generated. Next, the pulse 42 of the gradient magnetic field Gz for slice selection is again applied.
While applying 180° pulse 12 having the same frequency component as above, the magnetization is reversed by 180° on the same slice plane as ''. Thereafter, a pulse 23 having the same polarity and the same amount as the pulse 22 is applied to the gradient magnetic field Gx, and further, the polarity is reversed and a pulse 24 having the same polarity and the same amount as the pulse 21 is applied. Then,
Since the magnetization is reversed by 180° in 180° pulse 12, Gx pulses of the same polarity and the same amount will act on opposite polarities by the same amount, and the Gx before 180° pulse 12
The influence of pulse 21.22 is canceled by this Gx pulse 23.24. After the application of the 180" pulse 12, the spins become aligned in phase and a spin echo signal 52 is generated.
G to encode directional position information into frequency.
Apply the x pulse 26, but before applying the Gx pulse 26, the polarity of which is opposite to that of the Gx pulse 26 for dispersing the phase.
A pulse 25 is applied, and the phase disturbed by this Gx pulse 25 is brought into alignment by applying a Gx pulse 26. Then, around the time when this spin echo signal 52 is generated, a sampling pulse is generated to sample the received signal, and data regarding the spin echo signal 52 is collected. Since one pulse sequence ends in this way, after the recovery time has elapsed, the phase encoding gradient magnetic field G
The same pulse sequence is performed again by changing the size of the y pulse 31. If the above pulse sequence is repeated by changing the size of the Gy pulse 31 by a number corresponding to the number of reconstructed image matrices, the above slice 1 for collecting the data necessary to reconstruct the image on the surface.
Scanning ends. Here, data related to gradient echo signals and data related to spin echo signals can be obtained by performing only one scan, so the data acquisition time is halved compared to the case where these are obtained by independent pulse sequences.
This not only improves the throughput of the device, but also reduces the burden on the patient (subject). Effects of the Invention According to the MHI data collection method of the present invention, it is possible to generate a gradient echo signal and a spin echo signal and collect their data in one pulse sequence, thereby reducing the imaging time. It is possible to shorten the time, improve the throughput of the device, and reduce the burden on the patient.

[Brief explanation of the drawing]

The figure is a time chart showing a pulse sequence of an embodiment of the present invention. 11.12...RF excitation pulse, 21-26...Gradient magnetic field pulse for frequency encoding, 31...Gradient magnetic field pulse for phase encoding, 41.42...
- Gradient magnetic field pulse for slice selection, 5101. Gradient echo signal, 52... Spin echo signal.

Claims (1)

[Claims] (1) Excite the subject with an excitation pulse while applying a gradient magnetic field pulse for slice selection in which the magnetic field strength is tilted in a direction perpendicular to the tomographic plane, and then the magnetic field strength is tilted in one direction within the tomographic plane. At the same time, applying a gradient magnetic field pulse for frequency encoding whose magnetic field strength is inclined in a direction perpendicular to the gradient direction of the gradient magnetic field for phase encoding in the tomographic plane. Then, the polarity is changed and the same frequency encoding gradient magnetic field pulse is applied.
When this latter frequency encoding gradient magnetic field pulse is applied, a sampling pulse is generated to collect data from the received signal, and after the application of these phase encoding gradient magnetic field pulses and frequency encoding gradient magnetic field pulse, a slice selection gradient magnetic field pulse is generated. 1 while applying
Excite the subject with an 80° pulse, then sequentially apply frequency-encoding gradient magnetic field pulses of unipolar and opposite polarity in the same amount as the above-mentioned unipolar and opposite-polarity frequency-encoding gradient magnetic field pulses, and then A pulse sequence in which frequency encoding gradient magnetic field pulses of one polarity and the opposite polarity are sequentially applied, and when this last frequency encoding gradient magnetic field pulse is applied, a sampling pulse is generated and data is collected from the received signal, the above-mentioned phase encoding gradient MRI characterized by repeating magnetic field pulses while changing the magnitude
data collection methods.