JPH10295669A - Mr imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate an MR image free of influence of a temporary undeliberate motion of a subject. SOLUTION: An MR imaging device includes a body motion monitor device 58 and body motion sensor 59 whereby the vibration of the throat part of a subject 61 is monitored at all times, and a marking is applied to the data of that line which involves vibration, and data collection is made for all lines, and the obtained data unprocessed and the markers are recorded in a recording device 57. When a computer 51 reads later this unprocessed data to perform the image reconstructing process, the data of the line equipped with marking is excluded, and image reconstruction is made upon complementing with the data obtained through computation from the data which is in the complex conjugate relationship.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MR imaging apparatus for producing an image using an MR phenomenon (nuclear magnetic resonance phenomenon), and is particularly suitable for performing an imaging without being affected by unexpected temporary body movement. The present invention relates to an MR imaging apparatus.

[0002]

2. Description of the Related Art When an object physically moves in an MR imaging apparatus, the frequency of data acquired at that time is disturbed, and thus an artifact occurs in a reconstructed image. 2. Description of the Related Art Conventionally, there has been known an apparatus that measures an electrocardiogram, captures a respiratory movement, and collects data in synchronization with the heartbeat or the respiratory movement, thereby suppressing an artifact due to a body movement.

[0003]

However, although the conventional MR imaging apparatus which avoids the influence of the body movement can certainly cope with the periodic movement such as the movement of the heart and the movement of the respiration, In addition to such periodic movements, there are other temporary movements such as coughing, sneezing, and swallowing, and the disadvantage is that such unexpected movements cannot be dealt with. Was.

[0004] In view of the above, it is an object of the present invention to provide an MR imaging apparatus improved so that a good image can be obtained without being affected by unexpected temporary movement of a subject.

[0005]

In order to achieve the above object, an MR imaging apparatus according to the present invention comprises:
Means for generating a static magnetic field, gradient magnetic field generating means for generating a gradient magnetic field to be superimposed on the static magnetic field, RF transmitting means,
RF receiving means and controlling these gradient magnetic field generating means, RF transmitting means and RF receiving means to apply an RF excitation pulse and to generate a slice selecting gradient magnetic field pulse, a phase encoding gradient magnetic field pulse, and a readout gradient magnetic field pulse. Control means for repeating a pulse sequence for applying and receiving the generated NMR signal and acquiring data while sequentially changing the gradient magnetic field pulse for phase encoding, means for detecting the movement of the subject, and collecting when the object moves Image reconstruction processing means for performing image reconstruction processing after correcting the data of the selected line with other data.

[0006] The movement of the subject is detected, and information on which line of data is being collected when an unexpected movement has occurred is stored. Therefore, at the time of the image reconstruction processing, by correcting the data of the line collected during the movement using other data, it is possible to obtain data free from the influence of the movement. In other words, raw data space (K space)
Based on the fact that there is a complex conjugate relationship between the data located at the origin symmetric location in, instead of the data of the line collected when moving, it is symmetric about the location where it should be located and the origin. It can be determined by calculation from the data to be placed at the location. Therefore, since the data affected by the motion is removed, and the substitute data is supplemented, and the image reconstruction processing is performed, a good image free from motion artifacts can be obtained.

[0007]

Next, embodiments of the present invention will be described in detail with reference to the drawings. The MR imaging apparatus according to the present invention is configured as shown in FIG. In FIG. 1, the magnet assembly 11 includes a main magnet for generating a static magnetic field, and a gradient coil for generating gradient magnetic fields Gx, Gy, Gz superimposed on the static magnetic field. A subject 61 placed on an examination table 62 is inserted into the space to which the static magnetic field and the gradient magnetic field are applied. The subject 61 is irradiated with an RF pulse and the NM generated by the subject 61 is emitted.
An RF coil 12 for receiving the R signal is attached. Further, the subject 61 is also provided with a body movement sensor 59 for detecting the movement. here,
The body motion sensor 59 uses a vibration sensor, which is
1 attached to the throat.

A magnetic field control circuit 21 is provided as a circuit for supplying a gradient magnetic field current to the gradient coil of the magnet assembly 11. A waveform signal from the waveform generation circuit 53 is sent to the magnetic field control circuit 21. In the waveform generating circuit 53, information on each pulse waveform of the gradient magnetic fields Gx, Gy, Gz is set in advance from the computer 51. At the timing instructed by the sequence controller 52, the gradient magnetic field Gx,
Waveform signals for each of Gy and Gz are generated and sent to the magnetic field control circuit 21, whereby pulsed gradient magnetic fields Gx, Gy and Gz having a predetermined waveform are generated.

The R generated by the RF oscillation circuit 31
The F signal is sent to the amplitude modulation circuit 32, which becomes a carrier signal, and is amplitude-modulated according to the RF waveform signal sent from the waveform generation circuit 53. The RF signal after the amplitude modulation is amplified through the RF power amplifier 33 and then applied to the RF coil 12. The oscillation frequency of the RF oscillation circuit 31 is controlled by the computer 51 and the subject 61
Is matched to the resonance frequency of the body tissue. Information on the waveform of the modulation signal is given from the computer 51 to the waveform generation circuit 53 in advance. Waveform generation circuit 53
The timing of the RF oscillation circuit 31 is determined by the sequence controller 52.

[0010] NMR received by RF coil 12
The signal is sent to a phase detection circuit 42 via a preamplifier 41 and is subjected to phase detection. An RF signal from the RF oscillation circuit 31 is sent as a reference signal for the phase detection. The signal obtained by the phase detection is sampled at a predetermined sampling timing by the A / D converter 43 controlled by the sequence controller 52, and is converted into digital data. The data obtained from the A / D converter 43 is taken into the computer 51, and the computer 51 performs a two-dimensional Fourier transform to reproduce the image data of each pixel.

A display device 54, a keyboard 55, a mouse 56, a recording device 57, and a body movement monitoring device 58 are connected to the computer 51. The display device 54 displays the reconstructed MR image and the like. Input and setting of an imaging sequence, imaging parameters, and the like are performed by a keyboard 55, a mouse 56, and the like. The recording device 57 is composed of a magneto-optical disk device or the like,
The collected raw data and the image data after reconstruction are recorded. The body movement monitoring device 58 constantly monitors the movement of the subject 61 (in this case, vibration in the throat) via the body movement sensor 59. Examinee 6 by body motion monitor device 58
When it is determined that 1 has moved (coughed, sneezed, or swallowed), information on the fact is sent to the computer 51, and the computer 51 marks which line of data is being collected.

In the MR imaging apparatus configured as described above, for example, a pulse sequence by the field echo method as shown in FIG. 2 is performed. At the same time as the application of the RF pulse 71, a gradient magnetic field pulse (here, a Gz pulse) 72 for slice selection is applied to selectively excite one location in the Z direction. After that, a gradient magnetic field pulse (G
A y-pulse) 73 is added, and a read-out (and frequency encoding) gradient magnetic field pulse (Gx pulse) 74 is added to generate a resonance signal 75. Such a pulse sequence is repeated while sequentially changing the Gy pulse.

The data collected one line at a time for each phase encoding amount is arranged in a raw data space (K space) 81 as shown in FIG. In the raw data space 81, the horizontal direction is the frequency encoding direction, and the vertical direction is the phase encoding direction. The raw data collected in this way is the subject 61
Are recorded in the recording device 57 irrespective of the movement of the recording device.

It is assumed that the subject 61 sneezes at a certain point in time during the data collection and detects that. If the data of the line at the time of sneezing is collected, the marker section 82 corresponding to the line is collected.
Is marked. Such a marker section 82 is also recorded by the recording device 57.

After all the raw data and markings have been recorded in the recording device 57, they are read out by the computer 51. Then, the computer 51 excludes the data of the marked line, and instead, the position where the data of this line should be arranged is the line to be arranged at a position symmetrical to the origin in the raw data space. The data obtained by calculation using the fact that these data have a complex conjugate relationship are arranged from the data of (1). After the raw data space is completely filled in this way, an image is obtained by performing an image reconstruction operation in the computer 51.

In this way, since the data of the line collected during the temporary movement is excluded and the image is reconstructed after supplementing with data calculated from data having a complex conjugate relationship, data having a complex conjugate relationship is obtained. As long as is normally acquired, a good image as shown in FIG. 4A without any artifact due to the influence of motion can be obtained. By the way, if an image is reconstructed by using the data of the line collected during the temporary movement as it is, an image having an artifact due to the movement as shown in FIG.

In the above description, the vibration of the throat of the subject 61 is constantly monitored by the body movement sensor 59 and the body movement monitoring device 58, so that it is possible to detect which line has been collected during the imaging. However, various sensors and the like can be used in addition to this configuration depending on the part where the body movement is detected and the type of the body movement to be detected. In addition, as a method of correcting the line at the time of movement, various known methods can be used other than the calculation method based on the complex conjugate relationship.

In addition, it goes without saying that the specific configuration and the like can be variously changed without departing from the spirit of the present invention. For example, the pulse sequence is not limited to the above-described field echo method, and another method such as a spin echo method can be used.

[0019]

As described above, according to the MR imaging apparatus of the present invention, even if there is a temporary unexpected movement, it is possible to obtain a good image which is not affected by the movement. Therefore, giving the instruction to not move does not put pressure on the patient,
The burden on the patient is reduced.

[Brief description of the drawings]

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

FIG. 2 is a time chart showing a pulse sequence used in the embodiment.

FIG. 3 is a diagram showing a raw data space and a marker unit.

FIG. 4 is a diagram showing an example of a reconstructed image.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Magnet assembly 12 RF coil 21 Magnetic field control circuit 31 RF oscillation circuit 32 Amplitude modulation circuit 33 RF power amplifier 41 Preamplifier 42 Phase detection circuit 43 A / D converter 51 Computer 52 Sequence controller 53 Waveform generation circuit 54 Display device 55 Keyboard 56 Mouse 57 Recording device 58 Body motion monitoring device 59 Body motion sensor 61 Subject 62 Examination table 71 RF excitation pulse 72 Slice selection gradient magnetic field pulse 73 Phase encoding gradient magnetic field pulse 74 Reading gradient magnetic field pulse 75 Resonance signal 81 Raw Data space 82 Marker section

Claims (1)

[Claims] A means for generating a static magnetic field; a gradient magnetic field generating means for generating a gradient magnetic field so as to be superimposed on the static magnetic field;
F transmitting means, RF receiving means, and controlling these gradient magnetic field generating means, RF transmitting means and RF receiving means,
A pulse sequence for applying an excitation pulse, applying a slice selection gradient magnetic field pulse, a phase encoding gradient magnetic field pulse, and a readout gradient magnetic field pulse, and receiving the generated NMR signal to acquire data is referred to as the phase encoding gradient pulse. Control means that repeats while sequentially changing the magnetic field pulse, means for detecting the movement of the subject, and image reconstruction processing means for correcting the data of the line collected at the time of movement with other data and then performing image reconstruction processing An MR imaging apparatus comprising: