JPH04200532A - MR device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

(Industrial Application Field) This invention is applicable to an MRI apparatus that performs imaging using nuclear magnetic resonance (NMR) and an MR3 apparatus that performs spectroscopy.
The present invention relates to an MR device such as an MR device.

[Conventional technology]

An MR device that utilizes the nuclear magnetic resonance phenomenon selectively excites a specific region of a subject, receives echo signals from it, and performs spectroscopy, or selectively excites a specific slice plane and performs spectroscopy. The position information in one axis direction is encoded into the frequency of the echo signal, the position information in the other axis direction is encoded into the phase of the echo signal, and the received echo signal is subjected to two-dimensional Fourier transform to obtain the position in the two axis directions. Imaging is performed by decoding information to obtain a tomographic image on the slice plane.

[Invention or problem to be solved]

However, the subject to be measured by an MR device is usually a human body, and body movements such as breathing movements are unavoidable, which causes a problem in that the echo signal phase is disturbed. . In particular, in the case of an MR imaging apparatus, disturbances in the echo signal phase due to body movement become disturbances in positional information in a specific direction encoded in the phase, causing artifacts in images. In view of the above, an object of the present invention is to provide an MR device that can detect phase shift due to body movement.

[Means to solve the problem]

In order to achieve the above object, the MR apparatus according to the present invention includes means for generating a static magnetic field, and means for selectively exciting a specific region of a subject placed in the static magnetic field to generate a spin echo signal. , means for exciting the vicinity of the selected excitation region within the same repetition time to generate an FID signal at a time different from the spin echo signal; a means for receiving the spin echo signal and the FID signal; and a means for receiving the spin echo signal and the FID signal; It is characterized by being equipped with means for monitoring the signal phase.

[For production]

Since the spin echo signal is subjected to phase encoding for imaging, even if its phase is detected, it is not possible to determine whether the phase is disturbed by body movement. On the other hand, if an FID signal is generated by exciting a region other than the region selectively excited to generate a spin echo signal and close to that region, this FID signal will require phase encoding. FI because it is not affected by
The D signal represents phase disturbance due to body movement. Therefore, the excitation that generates the FID signal is performed within the same repetition time as the excitation that generates the spin echo signal, and the generation timing of the FID signal and the generation timing of the spin echo signal are shifted. These FID signals and spin echo signals are received, and the phase of the FID signals is monitored. Since body movement can be determined by monitoring the phase of the FID signal, if it is determined that the body should not move the next day, the repeat sequence can be repeated again. Data based on signals can be collected.

【Example】

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an MR imaging apparatus according to an embodiment of the present invention, and FIG. 2 shows a pulse sequence of the embodiment. First, as shown in FIG.
2 and a receiving coil 13 are attached, and these are placed within the static magnetic field formed by the main magnet 15 and the gradient coil 14 and the gradient magnetic field formed superimposed thereon. The gradient coils 14 are refined so that they can independently generate gradient magnetic fields whose magnetic field strengths are gradient in each direction of three orthogonal axes. The gradient magnetic fields of the three orthogonal axes are respectively a gradient magnetic field Gs for slice selection, a gradient magnetic field Gr for readout (frequency encoding), and a gradient magnetic field cp for phase encoding. The gradient coil 14 has gradient magnetic fields Gs and Gr.
, Gp are supplied with current from each power source 21, 22, 23,
Gradient magnetic fields in each direction are formed. The waveforms of currents supplied by the gradient magnetic field power supplies 21 to 23 are controlled by a gradient magnetic field controller 24 so that the gradient coil 14 forms gradient magnetic field pulses with predetermined waveforms. On the other hand, the transmitting coil 12 is supplied with an RF pulse sent from a high frequency power source 33. In the frequency converter 32, the RF sine wave signal from the synthesizer 34 is used as a carrier signal, and the RF pulse is AM-modulated with a 5-inch waveform from the R, F waveform generator 31.
3. An NMR signal generated after the subject 11 is irradiated with an RF pulse from a transmitting coil 12 to excite its nuclear spins is received by a receiving coil 13 . It is also possible to use the transmitting coil 12 and the receiving coil 13 as both, and to switch between the high frequency power supply 33 on the transmitting side and the preamplifier 35 on the receiving side using a signal switcher (not shown). This received NMR signal is amplified by a preamplifier 35, then detected by a quadrature phase detector 36, and then converted into digital data by an A/D converter 37 and taken into the host computer 41. This quadrature phase detector 36 is a PSD (PhaseSens
This is a detection circuit of the itive Detector type, which mixes the reference signal sent from the synthesizer 34 and the received signal, and outputs the difference in frequency between the two signals. The sequence controller 42 is the host computer 41
Under the control of It sends information regarding the frequency (corresponding to the resonant frequency) and controls the sample timing of the A/D converter 37, etc. A console 43 having a display device and an input device such as a keyboard device is connected to the host computer 41 . The data taken into the host computer 41 is subjected to two-dimensional Fourier transform to reconstruct an image, and the resulting image is displayed on the display device of the console 43. In this embodiment, a pulse sequence as shown in FIG. 2 is employed as a pulse sequence for imaging. This pulse sequence is basically a spin echo method with some additions. First, a 90° pulse 51 is applied to change the nuclear spin to 90°.
Gradient magnetic field Gs pulse 5 for slice selection simultaneously when folding
Add 3. This selectively excites only nuclear spins within a predetermined slice plane. Next, the gradient magnetic field G for readout (frequency encoding)
The pulse 55 of r and the pulse 57 of the gradient magnetic field cp for phase encoding are added to encode the position information in one axis direction in the slice plane into the frequency, and the position information in the other axis directions in the slice plane are encoded into the frequency. encode into . Thereafter, a 180° pulse 52 is applied together with a gradient magnetic field pulse 54 for slice selection, and then a pulse 56 of a gradient magnetic field Gr for readout (frequency encoding) is applied to generate a spin echo signal 60. The above is a pulse sequence based on the normal spin echo method, but here, the frequency spectrum of the 90° pulse 51 and the frequency spectrum of the 180° pulse 52 are different as shown in FIG. ° The frequency band of pulse 52 is widened. Therefore,
1 than the slice plane selectively excited by the 90' pulse 51
The slice plane selectively excited by the 8° pulse 52 becomes thicker, and the vicinity of both sides of the slice plane selectively excited by the 90° pulse 51 is excited only by the 180° pulse 52 and becomes transversely magnetized. Therefore, an FID signal will be generated from the region excited by this 180° pulse 52. Immediately after this 180° pulse 52, a pulse 58 of a gradient magnetic field Gp for phase encoding is added, and the day phase pulse is also added to perform phase encoding on this FID signal. Immediately after this day phase pulse, an FID signal 59 occurs, which is temporally separated from the spin echo signal 60 that occurs later. Therefore, the FID signal 59 and spin echo signal 60 are received by the receiving coil 13, amplified by the preamplifier 35, and then detected by the quadrature phase detector 36. Both the FID signal 59 and the spin echo signal 60 are Perform A/D conversion using a D converter. Then, the host computer 41 performs Fourier transform on the FID signal 59 and monitors its phase state. Then, the phase of this FID signal 59 represents positional information in the gradient magnetic field Gp force direction of the subject 11, and therefore remains constant unless the subject 11 moves. When the subject 11 moves, especially when a body movement occurs in the phase encoding direction of the subject 11, the phase becomes different, and by monitoring the phase relationship, it is possible to determine whether there has been a body movement in the subject 11. It is possible to judge. Therefore, when the phase relationship of the FID signal 59 is disturbed and it can be determined that there has been a body movement, the repetition sequence (1
(view sequence), the host computer 41 controls the pulse sequence to be performed again with the same phase encode amount. By repeating each view sequence in this way and completing one scan, data can be collected from spin echo signals obtained without the influence of body movement, so an image without body movement artifacts can be reconstructed.

【Effect of the invention】

According to the MR apparatus of the present invention, phase disturbance due to body movement can be detected for each repeated sequence. Therefore, when a phase disturbance occurs, it is possible to perform the same repeated sequence again to collect data without phase disturbance due to body movement.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a time chart showing a pulse sequence according to the embodiment, and Fig. 3 is a frequency spectrum of a 90° pulse and a 180° pulse in the embodiment. It is a graph. 11... Subject, 12... Transmission coil, 13...
Receiving coil, 14... Gradient coil, 15... Main magnet, 21... Gradient magnetic field power supply for slice selection, 22
...Gradient magnetic field power supply for readout, 23... Gradient magnetic field power supply for phase encoding, 24... Gradient magnetic field control device, 3
1... RF waveform generator, 32... Frequency converter, 3
3...High frequency power supply, 34...Synthesizer, 35.
...Preamplifier, 36...Quadrature phase detector, 37...
・A/D converter, 41... host computer, 42
...Sequence controller, 43...Console, 51...90° pulse, 52...180° pulse, 53.54...Gradient magnetic field pulse for slice selection, 5
5.56... Gradient magnetic field pulse for readout (frequency encoding), 57.58... Gradient magnetic field pulse for phase encoding, 59.・. FID signal, 60... spin echo signal.

Claims (1)

[Claims] (1) means for generating a static magnetic field; means for selectively exciting a specific region of a subject placed in the static magnetic field to generate a spin echo signal; means for exciting and generating an FID signal at a time different from the spin echo signal; means for receiving the spin echo signal and the FID signal;
An MR device comprising means for monitoring an ID signal phase.