JPH10201733A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To gain plural images having different imaging conditions on one time imaging. SOLUTION: This apparatus collects NMR signal with image sequence chart of different imaging conditions slice by slice on of n times slicing in time for one time imaging (TR) by an MRI apparatus. RF pulse 11, 11A, gradient magnetic fields GS 12, 12A, GP 13, 13A, GR 14, 14A, and echo time 15, 15A are changed between sequence chart 1 for slice 1 and sequence chart 2 for slice 2 and by the changing of their slicing imaging conditions such as thickness of both slices, an imaging field, etc., can be changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging sequence performed using a magnetic resonance imaging apparatus (hereinafter, referred to as an MRI apparatus), and more particularly to an imaging sequence capable of imaging a large number of slices in a short time.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing a configuration of an MRI apparatus used for performing ordinary magnetic resonance imaging. In order to obtain a nuclear magnetic resonance signal (hereinafter referred to as an NMR signal) from a subject using an MRI apparatus, the subject is placed in a measurement space that is a uniform static magnetic field generation region, and an appropriate gradient magnetic field and high-frequency magnetic field pulse are applied. (Hereinafter referred to as an RF pulse) must be given to the subject to cause a nuclear magnetic resonance phenomenon in the body of the subject. In FIG. 5, a sequence control unit 101 is a device that generates and controls a gradient magnetic field and an RF pulse applied to a subject. The sequence control unit 101 includes a transmitter 102 that outputs an RF pulse at a predetermined timing and an irradiation coil 103 that irradiates the subject with an RF pulse in order to resonate a specific nuclide (generally, hydrogen) in the subject. And a gradient magnetic field control unit 104 for generating a gradient magnetic field for determining the resonance frequency of the NMR signal to be collected and controlling the intensity and direction, and an NMR emitted by the subject.
It controls a receiving coil 108 for detecting a signal and a receiver 107 for detecting and measuring this NMR signal. Also,
The sequence control unit 101 calculates N
The MR signal data is input, and the NMR signal data is output to the processing device 109. The processor 109 performs various calculations based on the input NMR signal data, reconstructs an image of the tomographic plane of the subject, and displays the reconstructed image on the CRT display 110.

[0003] The gradient magnetic field usually has three orthogonal axes (X axis, Y axis).
Axis, the Z axis) and their intensities are G _x , G _Y ,
It is represented by G _z . The gradient magnetic field in each axial direction is configured so that its intensity can be arbitrarily controlled by the gradient magnetic field control unit 104. The gradient magnetic field drive unit 105 excites the corresponding gradient magnetic field coils 106 in the axial direction based on the control signal output from the gradient magnetic field control unit 104, and generates gradient magnetic fields G _x , G _Y , and G _Z required for measurement. It is generated at a predetermined timing. (Other than the combination of G _X , G _Y , and G _Z , the gradient magnetic field may generate GS in the slice axis direction, GP in the phase encoding direction, and GR in the NMR signal reading direction.)

An example of a conventional imaging sequence performed using the MRI apparatus having the above configuration will be described below. FIG. 6 is an example of a conventional photographing sequence. In this imaging sequence, NMR signals of n slice tomographic planes are collected during one imaging repetition time TR, but all other imaging conditions are the same except for the position of the slice tomographic plane. That is, in FIG. 6, the NMR signal acquisition sequence of slice 1 (hereinafter referred to as slice 1)
7 and the sequence chart 8 of the slice 2, the RF pulse 11, the gradient magnetic field GS1
2, GP13, GR14, and echo time 15 are the same. As a result, only one image under the same shooting conditions could be obtained in one shooting.

FIG. 7 shows the relationship between the subject and the imaging region. In the conventional imaging method, when the subject is to be photographed from the head to the chest, a head region 21 and a neck region 2 are used.
2. Imaging was performed for each region separately in the chest region 23 and the like (the head region 21 and the neck region 22 may be performed together). Therefore, when photographing a wide photographing area, photographing is required many times.

[0006]

In the imaging sequence as described above, when imaging different parts of the subject under different imaging conditions, a plurality of imagings must be performed separately for each part and each imaging condition. I had to. For this reason, the subject is restrained for a long time, causing a great deal of pain to the subject.

In recent MRI apparatuses, the uniformity of the static magnetic field in the measurement space has been improved, and the practical use of phased array coils has made it possible to secure a wide range of imaging regions. In view of such circumstances, an object of the present invention is to provide an MRI apparatus capable of acquiring a plurality of images having different imaging conditions in one imaging.

[0008]

An MRI apparatus according to the present invention comprises:
A static magnetic field generating means for generating a static magnetic field in the measurement space, a gradient magnetic field generating means for generating a gradient magnetic field to be applied to the subject inserted in the measurement space, and a high-frequency pulse transmitting means for irradiating the subject with a high-frequency pulse, NMR signal receiving means for detecting an NMR signal emitted from the subject;
Image processing means for reconstructing an image of the tomographic plane of the subject based on the R signal; gradient magnetic field generating means, high-frequency pulse transmitting means, NMR signal receiving means, image processing An MRI apparatus having a sequence control unit for controlling means has a plurality of sequence charts having different imaging conditions in an imaging sequence in one imaging repetition time (TR) (claim 1).

With this configuration, an NMR signal acquisition sequence with different imaging conditions can be executed in one TR.
It is possible to acquire an image in which the imaging conditions such as the slice thickness and the imaging field of view are changed within one TR. As a result, an image covering a wide photographing area can be acquired in one photographing sequence, so that photographing time can be reduced.

In the MRI apparatus of the present invention, one TR
Has a plurality of sequence charts each having a different slice thickness (claim 2), a sequence chart having a different field of view (claim 3), and a sequence chart having a different echo time (claim 4). . In these configurations, the slice thickness, the field of view, and the echo time can be changed in a single imaging sequence.

In the MRI apparatus of the present invention, one TR
(5) has a plurality of sequence charts with different NMR signal acquisition matrices in the imaging sequence of (5). With this configuration, the NMR signal acquisition matrix can be changed in one imaging sequence.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a first embodiment of the photographing sequence of the present invention. FIG. 2 shows the relationship between the subject and the imaging region when the present invention is applied. In order to execute the imaging sequence of the present invention, an MRI apparatus having the configuration shown in FIG. However, details of the sequence control unit 101 are different from those of the related art.

As shown in FIG. 1, in the first embodiment of the present invention, NMR signals for n slices are collected during one imaging repetition time TR, but the sequence chart differs for each slice. Are collecting NMR signals. In other words, NMR signals are collected in different sequence charts in slice 1 and slice 2.
The same applies to other slices. Sequence chart 1 for slice 1 and sequence chart 2 for slice 2
And RF pulses 11 and 11A, gradient magnetic field G
S12 and 12A, gradient magnetic fields GP13 and 13A, gradient magnetic fields GR14 and 14A, and echo times 15 and 15A are different from each other. That is, in both sequence charts, different waveforms, output values, RF pulses of application time, and gradient magnetic fields GS, GP, GR are applied. By changing the waveforms, output values, application times, etc. of these RF pulses and gradient magnetic fields GS, GP, GR, the imaging conditions such as slice thickness, imaging field of view, NMR signal acquisition matrix, and echo time during imaging are changed. can do. In other words, slice thickness, field of view,
In order to change the imaging conditions such as the NMR signal acquisition matrix and the echo time, the sequence control unit 101 changes the RF pulse and the waveforms, output values, and application times of the RF pulses and the gradient magnetic fields GS, GP, and GR for each sequence chart. May be used to control the MRI apparatus. At this time, if a high-frequency coil for transmitting and receiving high-frequency signals having a large imaging area such as a phased array coil is used, imaging of a large imaging area can be performed during one TR.

In applying this embodiment, the relationship between the imaging conditions to be set and the RF pulse and the gradient magnetic field (described in the second, third, and fourth embodiments below) is described by the sequence controller 101. A sequence chart for each slice in the imaging sequence can be created by storing the data as data in a storage unit and externally designating the imaging conditions for each slice during imaging. On the basis of this imaging sequence, the sequence controller 101 controls the transmitter 102, the gradient magnetic field controller 104, and the receiver 10 of the MRI apparatus.
7 will be controlled. As a result, RF for each slice
At least one of the pulse 11, the gradient magnetic fields GS12, GP13, and GR14 is different in a different sequence chart.
MR signals can be collected, and images with different imaging conditions can be acquired for each slice.

FIG. 2 shows the relationship between the subject and the imaging area according to the present invention. In order to make the above embodiment effective, the imaging region 24 is expanded to include the head, neck, and chest. At this time, as the irradiation coil 103 and the reception coil 108, a phased array coil having a wide imaging area so as to cover the imaging area 24 is used.

FIG. 3 shows a second embodiment of the photographing sequence according to the present invention. This embodiment is an example of an imaging sequence having a different slice thickness for each slice. In FIG. 3, comparing the sequence chart 3 of slice 1 with the sequence chart 4 of slice 2, RF pulse 11
B, 11C waveform, application time, gradient magnetic field GS12
The output values of B and 12C are different. In the imaging sequence, the slice thickness can be changed by changing the waveform and application time of the RF pulse or the output value of the gradient magnetic field.
This is applied to the sequence chart of FIG.

Generally, in order to increase the slice thickness, there are three ways of reducing the wave number of the RF pulse, shortening the application time of the RF pulse, and reducing the output value of the gradient magnetic field GS. There is a way. Therefore, these three methods alone or in combination control the slice thickness. In the embodiment of FIG. 3, the RF pulse 11B of the sequence chart 3 of the slice 1 has a small wave number and the gradient magnetic field GS
Since the output value of 12B is small, the slice thickness of slice 1 is larger than the slice thickness of slice 2.

FIG. 4 shows a third embodiment of the photographing sequence according to the present invention. This embodiment is an example of an imaging sequence having a different imaging field of view for each slice. Generally, to change the field of view, the amount of magnetic field of the gradient magnetic field (product of the output value and the application time) applied to each axis is changed. When reducing the size, increase the magnetic field amount. To change the magnetic field amount of the gradient magnetic field, change the application time while keeping the output value constant,
The output value is changed while keeping the application time constant. In FIG. 4, the sequence chart 5 of slice 1 and slice sequence 2
Compared to the sequence chart 6 of FIG.
(Phase encoding) 13B, 13C, GR (read)
The magnetic field amounts of 14B and 14C are different. Therefore, in both sequences, the imaging field of view in the phase encoding and readout directions of the gradient magnetic field changes, and slice 1 is replaced by slice 2
In contrast, the field of view in the phase encode direction is small, and the field of view in the readout direction is large.

A fourth embodiment of the photographing sequence according to the present invention will be described with reference to FIG. This embodiment is an example of an imaging sequence having a different NMR signal acquisition matrix for each slice. In FIG. 1, between the sequence chart 1 of slice 1 and the sequence chart 2 of slice 2, the gradient magnetic fields GP13 and 13A and the gradient magnetic fields GR14 and 14A have different waveforms, output values, and application times as described above. NMR signal acquisition matrix
This corresponds to the number of times the signal is sampled, and this can be changed by changing the number of times of application of the gradient magnetic field, the application time, and the like. Therefore, in FIG. 1, the gradient magnetic field GP1
The NMR signal collection matrix in the phase encoding direction can be changed by changing the number of times of application of 3,3A, and the NMR signal collection matrix in the readout direction can be changed by changing the application time of the gradient magnetic fields GR14, 14A. Can be changed.

In FIG. 1, since the gradient magnetic fields GR14 and 14A have different waveforms, output values and application times between the sequence chart 1 of the slice 1 and the sequence chart 2 of the slice 2, the echo times 15 and 1 are different.
5A is different. As described above, in order to change the echo time, the waveform, output value, and application time of the gradient magnetic field GR may be changed. By changing the echo time, images having different contrasts can be obtained. Therefore, by selecting an appropriate echo time for each part, an image having an optimum contrast can be obtained for each part.

[0021]

As described above, according to the present invention, 1
A plurality of images having different photographing conditions can be acquired in each photographing. As a result, the number of times of imaging conventionally performed for different imaging conditions can be reduced, so that the imaging time can be shortened and the time for restraining the subject can be reduced.

[Brief description of the drawings]

FIG. 1 is a first embodiment of an imaging sequence according to the present invention.

FIG. 2 is a diagram showing a relationship between a subject and an imaging region according to the present invention.

FIG. 3 is a second embodiment of the photographing sequence of the present invention.

FIG. 4 is a third embodiment of the photographing sequence of the present invention.

FIG. 5 is a block diagram showing a configuration of an MRI apparatus.

FIG. 6 shows an example of a conventional photographing sequence.

FIG. 7 is a diagram showing a conventional relationship between a subject and an imaging region.

[Explanation of symbols]

 1,2,3,4,5,6,7,8 Sequence chart 11,11A, 11B, 11C RF pulse 12,12A, 12B, 12C Gradient magnetic field GS 13,13A, 13B, 13C Gradient magnetic field GP 14,14A, 14B, 14C Gradient magnetic field GR 15, 15A, 15B, 15C Echo time 21, 22, 23, 24 Imaging area 101 Sequence control unit 102 Transmitter 103 Irradiation coil 104 Gradient magnetic field control unit 105 Gradient magnetic field drive system 106 Gradient magnetic field coil 107 Receiver 108 Receiving coil 109 Processing unit 110 CRT display

Claims (5)

[Claims] 1. A static magnetic field generating means for generating a static magnetic field in a measurement space, a gradient magnetic field generating means for generating a gradient magnetic field applied to a subject inserted into the measurement space, and a high frequency for irradiating a high frequency pulse to the subject Pulse transmitting means, nuclear magnetic resonance signal receiving means for detecting a nuclear magnetic resonance signal emitted from the subject, image processing means for reconstructing an image of a tomographic plane of the subject based on the nuclear magnetic resonance signal, One time in a magnetic resonance imaging apparatus including a sequence control unit for controlling the gradient magnetic field generating means, the high-frequency pulse transmitting means, the nuclear magnetic resonance signal receiving means, and the image processing means in accordance with an imaging sequence at the time of tomographic imaging of a subject. Wherein a plurality of nuclear magnetic resonance signal acquisition sequences having different imaging conditions are included in the imaging sequence at the imaging repetition time (TR). Air resonance imaging device. 2. The magnetic resonance imaging apparatus according to claim 1, wherein a plurality of nuclear magnetic resonance signal acquisition sequences having different slice thicknesses are included in one imaging sequence in one TR. 3. The magnetic resonance imaging apparatus according to claim 1, wherein a plurality of nuclear magnetic resonance signal acquisition sequences having different imaging fields of view are included in one imaging sequence in one TR. 4. The magnetic resonance imaging apparatus according to claim 1, wherein a plurality of nuclear magnetic resonance signal acquisition sequences having different echo times are included in one imaging sequence in one TR. 5. A magnetic resonance imaging apparatus according to claim 1, wherein a plurality of nuclear magnetic resonance signal acquisition sequences having different nuclear magnetic resonance signal acquisition matrices are included in one imaging sequence in one TR. Imaging device.