JP3647444B2 - MRI equipment - Google Patents

Description

  The present invention relates to an MRI (Magnetic Resonance Imaging) apparatus, and more particularly to an MRI apparatus capable of preventing image quality deterioration due to the influence of eddy current and residual magnetization caused by a phase encoding gradient.

FIG. 27 shows a pulse sequence of a conventional high-speed SE (Spin Echo) method.
In this pulse sequence Kp, an excitation pulse R and a slice gradient ss are applied. Next, the first inversion pulse P1 and the slice gradient ss are applied, the phase encode gradient gy (i) is applied to the warp axis, and then the NMR signal is received from the first echo SE1 while applying the lead gradient rr. Thereafter, a rewind gradient gyr (i) having the same time integral value as that of the encode gradient gy (i) and having the opposite polarity is applied to the warp axis. Next, the second inversion pulse P2 and the slice gradient ss are applied, the encode gradient gy (i + 1) is applied to the warp axis, and then the NMR signal is received from the second echo SE2 while applying the read gradient rr, Thereafter, a rewind gradient gyr (i + 1) having the same time integral value as that of the encode gradient gy (i + 1) and opposite polarity is applied to the warp axis. Next, the third inversion pulse P3 and the slice gradient ss are applied, the encode gradient gy (i + 2) is applied to the warp axis, and then the NMR signal is received from the third echo SE3 while applying the read gradient rr, Thereafter, a rewind gradient gyr (i + 2) having the same time integral value as the encode gradient gy (i + 2) and opposite polarity is applied to the warp axis. Thus, after repeating the transmission of the inversion pulse to the reception of the NMR signal M times, the killer gradient Kil is applied. Thereafter, this is repeated N times with a repetition time TR, and NMR signals obtained by performing (M × N) different phase encoding on the warp axis are collected.
Note that p = 1, 2,..., N. In FIG. 27, M = 3, but usually M ≧ 4 is often used to shorten the scan time. Further, there is a relationship of i = (p−1) M + 1, and (i), (i + 1), and (i + 2) in the encode gradients gy (i), gy (i + 1), and gy (i + 2) in FIG. 27 are phase encode numbers. Represents.

  The killer gradient Kil is a gradient pulse for spoiling the transverse magnetization, and conventionally its polarity is constant.

FIG. 28 shows a data collection trajectory in the k-space by the pulse sequence Kp.
In the case of the echo train of M = 3, the k-space Ksp is divided into three segments Sg1, Sg2, and Sg3. Then, data (eg, tc1) of the first segment Sg1 is collected by the first echo SE1, data (eg, tc2) of the second segment Sg2 is collected by the second echo SE2, and data of the third segment Sg3 is collected by the third echo SE3. Collect data (eg tc3).
FIG. 28 shows p = 1, and the position on the phase axis of the data is determined by the phase encode gradients gy (1), gy (2), gy (3), and the rewind gradients gyr (1), gyr (2). , Gyr (3), the phase encoding amount is returned to “0”.
Since the data in the vicinity of the phase encoding amount “0” determines the contrast of the image, the time TEeff until the second echo SE2 shown in FIG. 27 is an effective echo time.

FIG. 29 shows a pulse sequence of a conventional 3D (three-dimensional) high-speed SE method.
In this pulse sequence Kp ′, an excitation pulse R and a slice gradient ss are applied. Next, a rewind gradient gzr (0) having the same phase integral gradient and time integral value applied to the slice axis immediately before and having the opposite polarity is superimposed on the crusher gradient and applied to the slice axis, and the first inversion pulse is applied. P1 and the slice gradient are applied, and the phase encode gradient gz (i) is superimposed on the crusher gradient and applied to the slice axis. Further, the phase encode gradient gy (i) is applied to the warp axis. Next, the NMR signal is received from the first echo SE1 while applying the lead gradient rr, and then the rewind gradient gyr (i) having the same time integral value as the warp axis encode gradient gy (i) and the opposite polarity is applied. The phase encode gradient gz (i) of the slice axis and the rewind gradient gzr (i) having the same time integral value and opposite polarity are superimposed and applied to the crusher gradient. Next, the second inversion pulse P2 and the slice gradient are applied, and the phase encode gradient gz (i + 1) is superimposed on the crusher gradient and applied to the slice axis. Further, a phase encode gradient gy (i + 1) is applied to the warp axis. Next, the NMR signal is received from the second echo SE2 while applying the lead gradient rr, and then the rewind gradient gyr (i + 1) having the same time integral value as the encode gradient gy (i + 1) of the hoop axis is applied. Then, a rewind gradient gyr (i + 1) having the same time integral value and opposite polarity with the phase encode gradient gz (i + 1) of the slice axis is superimposed and applied to the crusher gradient. Next, the third inversion pulse P3 and the slice gradient are applied, and the phase encode gradient gz (i + 2) is superimposed on the crusher gradient and applied to the slice axis. Further, the phase encode gradient gy (i + 2) is applied to the warp axis. Next, the NMR signal is received from the third echo SE3 while applying the lead gradient rr, and then the rewind gradient gyr (i + 2) having the same polarity as the encode gradient gy (i + 2) of the warp axis and the opposite polarity is applied. . Thus, after repeating the transmission of the inversion pulse P to the reception of the NMR signal M times (here, M = 3), the killer gradient Kil is applied. Thereafter, this is repeated at a repetition time TR, and NMR signals obtained by performing phase encoding on the slice axis and the warp axis are collected.

In the high-speed SE method such as the pulse sequences Kp and Kp ′ in FIGS. 27 and 29, the amplitude of the phase encode gradients gy (i), gy (i + 1), and gy (i + 2) on the warp axis is shortened in order to shorten the repetition time TR. Is made as large as possible, and the time width tgy is shortened accordingly. Similarly, in the 3D high-speed SE method such as the pulse sequence Kp ′ in FIG. 28, the amplitudes of the phase encode gradients gz (i), gz (i + 1), gz (i + 2) on the slice axis are increased as much as possible. Accordingly, the time width tgz is shortened.
However, the eddy current is generated as the amplitude of the gradient pulse is increased and the time width is shortened. Further, residual magnetization is generated as the amplitude is increased. When an eddy current or residual magnetization is generated, artifacts are generated on the image due to the influence thereof, and the image quality is deteriorated.
In particular, in an MRI apparatus using a permanent magnet, image quality deterioration due to residual magnetization generated in the magnetic shunt plate becomes a problem.

  On the other hand, for example, Japanese Patent Laid-Open No. 6-245917 proposes a technique for canceling the influence of residual magnetization by applying an offset gradient, and a technique for correcting a phase shift due to residual magnetization of the magnetic shunt plate by calculation. ing.

The influence of remanent magnetization due to the phase encoding gradient becomes noticeable particularly when the sequence of the high-speed SE method is executed by an MRI apparatus using a permanent magnet.
This will be described with reference to FIGS.
As shown in FIG. 30, a residual magnetization of intensity ΔGY (i) is generated by the phase encode gradient gy (i) of the warp axis, and the residual magnetization causes a phase shift in the first echo SE1. Similarly, the phase shift is generated for the second echo SE2 and the following.
Further, the rewind gradient gyr (i) cannot return the phase encoding amount to “0”, which affects the phase of the second echo SE2 and the phase of the third echo SE3. The same applies to the rewind gradient gyr (i + 1) or less, and the phase encoding amount cannot be returned to “0”, and the subsequent echo phase is affected.
Furthermore, it is necessary to make the phase of the stimulated echo STE (Stimulated Echo) generated at the same time as the spin echo coincide with the phase of the spin echo, but these phases do not coincide. FIG. 30 shows the second echo SE2 that is the most important for determining the contrast of the image and the second stimulated echo STE2 that occurs at the same time, but the intensity ΔGY caused by the phase encoding gradient gy (i). Since the phase of the second echo SE2 is shifted due to the influence of the residual magnetization (i), the second stimulated echo STE2 is not affected (from the first inversion pulse P1 to the second inversion pulse P2). Because the section is longitudinally magnetized), the phases will not match. As a result, interference occurs, and ghost artifacts, shading artifacts, and ringing artifacts occur on the image.

Further, as shown in FIG. 31, the residual magnetization of intensity ΔGZ (i) is generated by the phase encode gradient gz (i) of the slice axis, and the residual magnetization causes a phase shift in the first echo SE1. Similarly, the phase shift is generated for the second echo SE2 and the following.
In addition, the phase encode amount cannot be returned to “0” due to the rewind gradient gzr (i), which affects the phase of the second echo SE2 and the phase of the third echo SE3. The same applies to the rewind gradient gzr (i + 1) or less, and the phase encoding amount cannot be returned to “0”, and the subsequent echo phase is affected.
Further, the phase of the second echo SE2 that is most important for determining the contrast of the image and the second stimulated echo STE2 that occurs at the same time do not coincide with each other, resulting in artifacts on the image.

However, the conventional technique proposed in Japanese Patent Laid-Open No. 6-245917 has a problem that is not sufficient to prevent image quality deterioration due to the effect of eddy current and residual magnetization caused by the phase encoding gradient. .
SUMMARY OF THE INVENTION An object of the present invention is to provide an MRI apparatus that can prevent image quality deterioration due to the influence of eddy currents and residual magnetization caused by a phase encoding gradient.

In a first aspect, the present invention provides an MRI apparatus comprising an RF pulse transmission means, a gradient magnetic field application means, and an NMR signal reception means, wherein an RF pulse is transmitted by the RF pulse transmission means, and the gradient magnetic field application The phase encode gradient is applied to the warp axis by the means, the NMR signal is received by the NMR signal receiving means, and then the phase encode gradient and the time integral value are equal to the basic component having the same polarity and the opposite polarity by the gradient magnetic field applying means. A rewind gradient to which a warp axis correction component for correcting the influence of eddy current or residual magnetization caused by the gradient is added is applied to the warp axis, or the rewind gradient corresponding to the basic component and the warp axis correction component are applied. An MRI apparatus is provided that applies an auxiliary rewind gradient to a warp axis. In addition, in the above “adding”, it may be added as an amplitude, a time width, or both an amplitude and a time width.
In the MRI apparatus according to the first aspect, “(basic component having the same phase encode gradient and time integral value and opposite polarity) + (warp axis correcting component for correcting the influence of eddy current or residual magnetization caused by the phase encode gradient)” The rewind gradient consisting of "" is applied to the warp axis, or the rewind gradient consisting of (basic component with the same phase integral gradient and time integral value and opposite polarity) and the effect of eddy current or remanent magnetization due to the phase encode gradient A supplemental rewind gradient consisting of a warp axis correction component for correcting) is applied to the warp axis.
The basic component returns the phase encode amount to “0” (original rewind), and the warp axis correction component cancels the influence of eddy current or residual magnetization caused by the phase encode gradient. For this reason, it is possible to prevent the deterioration of the image quality of the image due to the influence of eddy current or residual magnetization caused by the phase encoding gradient.
In a second aspect, the present invention relates to an MRI apparatus comprising an RF pulse transmitting means, a gradient magnetic field applying means, and an NMR signal receiving means, wherein an RF pulse is transmitted by the RF pulse transmitting means, and the gradient magnetic field application is performed. By means, a phase encode gradient obtained by adding a warp axis correction component for correcting the influence of eddy current or residual magnetization caused by the phase encode gradient to the basic component of the phase encode gradient of the warp axis determined from the scan parameter is applied to the warp axis. Alternatively, a phase encode gradient corresponding to the basic component and an auxiliary phase encode gradient corresponding to the warp axis correction component are applied to the warp axis, and after receiving the NMR signal by the NMR signal receiving means, the gradient magnetic field application Means that the basic component of the phase encode gradient and the time integral value are equal and opposite in polarity. Provides an MRI apparatus wherein applying a gradient to the warp axis. In addition, in the above “adding”, it may be added as an amplitude, a time width, or both an amplitude and a time width.
In the MRI apparatus according to the second aspect, a phase consisting of “(basic component of phase encode gradient determined from scan parameters) + (warp axis correction component for correcting the effect of eddy current or residual magnetization caused by phase encode gradient)” Apply the encode gradient to the warp axis, or the phase encode gradient consisting of (the basic component of the phase encode gradient determined from the scan parameters) and the warp axis correction to correct the effect of eddy current or residual magnetization caused by the phase encode gradient A supplemental phase encoding gradient consisting of component) is applied to the warp axis.
Phase encoding is performed by the basic component (original phase encoding), and the influence of eddy current or residual magnetization caused by the phase encoding gradient is canceled by the warp axis correction component. For this reason, it is possible to prevent the deterioration of the image quality of the image due to the influence of eddy current or residual magnetization caused by the phase encoding gradient.

In a third aspect, the present invention provides the MRI apparatus having the above-described configuration in which an RF pulse is transmitted by the RF pulse transmitting unit, a phase encoding gradient is not applied to the warp axis, and a read gradient is read by the gradient magnetic field applying unit. An NMR signal is received by the NMR signal receiving means while being applied to the shaft, and an RF pulse is transmitted by the first phase information obtaining means for obtaining first phase information from the received NMR signal and the RF pulse transmitting means. The phase encode gradient is not applied to the warp axis, and the equivalent magnetic field gradient is applied to the lead axis by the gradient magnetic field applying means, and the equivalent phase encode gradient is equal to the time integral value. A polar equivalent rewind gradient is applied to the lead axis, and then the gradient is applied to the lead axis by the gradient magnetic field applying means. A second phase information acquisition means for receiving an NMR signal by the NMR signal reception means while applying, and acquiring second phase information from the received NMR signal; and the first phase information and the second phase information. And a warp axis correction component calculating means for obtaining the warp axis correction component from the above.
In the MRI apparatus according to the third aspect, the warp axis correction component is obtained as follows.
(1) Transmit an RF pulse, receive no NMR signal while applying a read gradient to the lead axis without applying a phase encode gradient to the warp axis, and obtain first phase information from the received NMR signal .
(2) An RF pulse is transmitted, no phase encode gradient is applied to the warp axis, and an equivalent phase encode gradient having the same time integral value as the phase encode gradient is applied to the lead axis, and the equivalent phase encode gradient and the time integral value are applied. Is applied to the lead axis, and an NMR signal is received while applying the read gradient to the lead axis, and second phase information is obtained from the received NMR signal.
(3) A warp axis correction component is obtained from the first phase information and the second phase information.
The first phase information is phase information when there is no influence of eddy current or residual magnetization caused by the phase encoding gradient. The second phase information is phase information when an effect of eddy current or residual magnetization caused by the phase encoding gradient is equivalently applied to the lead axis. Therefore, if the first phase information and the second phase information are compared, the influence of eddy current or residual magnetization caused by the phase encoding gradient can be quantitatively known. Therefore, the warp axis correction component for canceling it can be obtained quantitatively.

In a fourth aspect, the present invention provides the MRI apparatus configured as described above, wherein an RF pulse is transmitted by the RF pulse transmitting means, a phase encoding gradient is applied to the warp axis by the gradient magnetic field applying means, and then the gradient magnetic field is applied. The present phase information acquisition means for receiving the NMR signal by the NMR signal receiving means while applying the read gradient to the lead axis by the applying means, and acquiring the current phase information from the received NMR signal, and the RF pulse transmitting means An RF pulse is transmitted, a phase encode gradient whose time width is expanded and amplitude is reduced by the gradient magnetic field applying means is applied to the warp axis, and then the NMR is applied while applying a read gradient to the lead axis by the gradient magnetic field applying means. Ideal phase that receives the NMR signal by the signal receiving means and obtains ideal phase information from the received NMR signal Providing a distribution obtaining unit, an MRI apparatus wherein from the phase information and phase information of the ideal that it has and a warp-axis correction component calculating means for determining the warp-axis correction component of the current.
In the MRI apparatus according to the fourth aspect, the warp axis correction component is obtained as follows.
(1) An RF pulse is transmitted, a phase encode gradient is applied to the warp axis, an NMR signal is received while a read gradient is applied to the lead axis, and current phase information is acquired from the received NMR signal.
(2) An RF pulse is transmitted, a phase encode gradient with an expanded time width and reduced amplitude is applied to the warp axis, an NMR signal is received while applying a read gradient to the lead axis, and an ideal is obtained from the received NMR signal. Get phase information.
(3) A warp axis correction component is obtained from the current phase information and ideal phase information.
The current phase information is phase information including the influence of eddy current or residual magnetization caused by the phase encoding gradient. The ideal phase information is phase information when there is no influence of eddy current or residual magnetization caused by the phase encoding gradient. Therefore, by comparing the current phase information with the ideal phase information, the effect of eddy current or residual magnetization caused by the phase encoding gradient can be quantitatively known. Therefore, the warp axis correction component for canceling it can be obtained quantitatively.

In a fifth aspect, the present invention transmits an excitation RF pulse by the RF pulse transmitting means, then transmits an inverted RF pulse by the RF pulse transmitting means, and then sets the phase encoding gradient to the warp axis by the gradient magnetic field applying means. And then receiving the NMR signal by the NMR signal receiving means while applying the read gradient to the lead axis by the gradient magnetic field applying means, and repeating M times from the transmission of the inverted RF pulse to the reception of the NMR signal, An MRI that applies a killer gradient by the gradient magnetic field applying means, repeats N times from the transmission of the excitation RF pulse to the application of the killer gradient, and collects (M × N) differently phase-encoded NMR signals In the apparatus, the gradient magnetic field applying means applies when repeating the transmission of the inverted RF pulse to the reception of the NMR signal M times. Times of to have the same Gokusei the polarity of the sum of the phase encoding gradient, to provide an MRI apparatus characterized by switching the polarity of the killer gradient.
In the MRI apparatus according to the fifth aspect, the polarity of the killer gradient is switched so as to be the same as the polarity of the sum of the plurality of phase encode gradients applied by the corresponding pulse train.
Conventionally, since the polarity of the killer gradient is constant, it only functions as a spoiler. However, if the polarity of the killer gradient is switched so that it has the same polarity as the sum of the phases of the multiple phase encode gradients applied by the corresponding pulse train, the effect of canceling the effects of eddy current or residual magnetization caused by the phase encode gradient Can also be played. For this reason, it is possible to prevent the deterioration of the image quality of the image due to the influence of eddy current or residual magnetization caused by the phase encoding gradient.

In a sixth aspect, the present invention transmits an excitation RF pulse by the RF pulse transmitting means, then transmits an inverted RF pulse by the RF pulse transmitting means, and then sets the phase encoding gradient to the warp axis by the gradient magnetic field applying means. In the MRI apparatus that receives the NMR signal by the NMR signal receiving means while applying or applying to the warp axis and the slice axis and then applying the read gradient to the lead axis by the gradient magnetic field applying means, the phase encoding gradient causes The transmission phase of the inverted RF pulse by the RF pulse transmission means is changed or the detection phase of the phase detection by the NMR signal reception means is changed so as to suppress the zero-order phase component generated by the influence of the residual magnetization. An MRI apparatus is provided.
The influence of the residual magnetization caused by the phase encoding gradient includes a zero-order phase component that is applied uniformly without depending on the location, and a primary phase component that changes linearly depending on the location. The zero-order phase component mainly generates ghost artifacts, and the first-order phase component mainly generates shading artifacts.
Here, since the zero-order phase component appears as an overall phase shift of the NMR signal, the transmission phase of the inverted RF pulse by the RF pulse transmitting means is changed, or the phase detection by the NMR signal receiving means is detected. It can be restored by changing the phase. As a result, ghost artifacts can be suppressed.

In a seventh aspect, the present invention provides the MRI apparatus configured as described above, wherein an RF pulse is transmitted by the RF pulse transmitting means, and a phase encoding gradient is not applied to the warp axis and slice axis, but the phase is applied by the gradient magnetic field applying means. An equivalent phase encode gradient having the same encode gradient and time integral value is applied to the lead axis, an equivalent rewind gradient having the same equivalent phase encode gradient and the time integral value having the same polarity and opposite polarity is applied to the lead axis, and then the gradient magnetic field application The NMR signal is received by the NMR signal receiving means while applying the read gradient to the lead axis by the means, the phase information is obtained from the received NMR signal, and the 0th order phase component is obtained from the phase information. An MRI apparatus characterized by comprising an acquisition means.
In the MRI apparatus according to the seventh aspect, the zeroth-order phase component is obtained as follows.
(1) An RF pulse is transmitted, no phase encode gradient is applied to the warp axis and slice axis, and an equivalent phase encode gradient having the same time integral value as the phase encode gradient is applied to the lead axis. An equivalent rewind gradient having the same integral value and a reverse polarity is applied to the lead axis, and then an NMR signal is received while applying the read gradient to the lead axis, and phase information is obtained from the received NMR signal.
(2) A zero-order phase component is obtained from the phase information.
The phase information is phase information when an effect of eddy current or residual magnetization caused by the phase encoding gradient is equivalently applied to the lead axis. Therefore, by obtaining the phase at the gradient center, the zero-order phase component of the influence of eddy current or residual magnetization caused by the phase encode gradient can be quantitatively known.

In an eighth aspect, the present invention provides an MRI apparatus configured as described above, wherein the NMR signal obtained when the phase encode gradient and the rewind gradient are applied to the warp axis, and the phase encode gradient and the rewind gradient are not applied to the warp axis. The MRI apparatus further comprises a zero-order phase component acquisition means for obtaining the zero-order phase component from the obtained NMR signal.
In the MRI apparatus according to the eighth aspect, the zero-order phase component is obtained as follows.
(1) Apply a phase encode gradient and a rewind gradient to the warp axis to obtain the current NMR signal.
(2) An ideal NMR signal is obtained without applying a phase encode gradient and a rewind gradient to the warp axis.
(3) The 0th order phase amount is obtained from the phase at the gradient center of the 1D Fourier transform in the read direction of the current NMR signal, and the 0th order phase amount from the phase at the gradient center of the 1D Fourier transform in the read direction of the ideal NMR signal. And the zero-order phase component of the influence of eddy current or residual magnetization is obtained from the difference between the two.
By taking the difference between the zeroth-order phase component when the phase encode gradient and the rewind gradient are applied, and the zero-order phase component when the phase encode gradient and the rewind gradient are not applied, the zeroth-order phase component of the influence of the eddy current or residual magnetization caused by the phase encode gradient and the rewind gradient is quantitatively determined. I can know.
Since the phase encode gradient and the rewind gradient are added to the warp axis, the effect of eddy current or residual magnetization is superimposed on the zero-order phase component. Therefore, in order to prevent this, it is preferable to use a phase encode gradient and a rewind gradient that have been corrected for the effects of eddy currents or residual magnetization according to the first aspect or the second aspect.

In a ninth aspect, the present invention provides an MRI apparatus comprising an RF pulse transmitting means, a gradient magnetic field applying means, and an NMR signal receiving means, and after applying an excitation pulse by the RF pulse transmitting means, the RF pulse An inversion pulse is transmitted by the transmitting means, a phase encoding gradient is applied to the slice axis by the gradient magnetic field applying means, an NMR signal is received by the NMR signal receiving means, and the phase encoding gradient and time integration are performed by the gradient magnetic field applying means. Apply a rewind gradient to the slice axis by adding a slice axis correction component that corrects the influence of eddy current or residual magnetization caused by the phase encoding gradient to the basic component of equal and opposite polarity, or equivalent to the basic component And the auxiliary rewind gradient corresponding to the slice axis correction component are marked on the slice axis. It provides an MRI apparatus characterized by repeating only encode the number of slice axis direction to.
In the MRI apparatus according to the ninth aspect, “(basic component having the same phase encode gradient and time integral value and opposite polarity) + (slice axis correction component for correcting the effect of eddy current or residual magnetization caused by the phase encode gradient)” Apply a rewind gradient consisting of "" to the slice axis, or a rewind gradient consisting of (a fundamental component with the same phase integral gradient and time integral value and opposite polarity) and the effect of eddy current or residual magnetization due to the phase encode gradient A supplemental rewind gradient consisting of a slice axis correction component) is applied to the slice axis.
The phase encode amount is returned to “0” by the basic component (original rewind), and the influence of eddy current or residual magnetization caused by the phase encode gradient is canceled by the slice axis correction component. For this reason, it is possible to prevent the deterioration of the image quality of the image due to the influence of eddy current or residual magnetization caused by the phase encoding gradient.

In a tenth aspect, the present invention provides the MRI apparatus configured as described above, wherein an RF pulse is transmitted by the RF pulse transmitting means, a phase encoding gradient is not applied to the slice axis, and a read gradient is read by the gradient magnetic field applying means. An NMR signal is received by the NMR signal receiving means while being applied to the shaft, and an RF pulse is transmitted by the first phase information obtaining means for obtaining first phase information from the received NMR signal and the RF pulse transmitting means. The phase encode gradient is not applied to the slice axis, and a differential gradient corresponding to the difference between the basic component of the phase encode gradient and the subsequent rewind gradient is applied to the lead axis by the gradient magnetic field applying means, and the phase encode gradient and time integration are applied. Equivalent phase encoding gradient with equal value and equivalent with time integral value equal to basic component of said rewind gradient The winding gradient is applied to the lead axis, and then the NMR signal is received by the NMR signal receiving means while the read gradient is applied to the lead axis by the gradient magnetic field applying means, and second phase information is received from the received NMR signal. And a slice axis correction component calculation unit for obtaining the slice axis correction component from the first phase information and the second phase information. An MRI apparatus is provided.
In the MRI apparatus according to the tenth aspect, the slice axis correction component is obtained as follows.
(1) An RF pulse is transmitted, a phase encode gradient is not applied to the slice axis, an NMR signal is received while a read gradient is applied to the read axis, and first phase information is acquired from the received NMR signal. .
(2) An RF pulse is transmitted, a phase encode gradient is not applied to the slice axis, and a differential gradient corresponding to the difference between the basic components of the phase encode gradient and the subsequent rewind gradient is applied to the lead axis, and the phase encode gradient Equivalent phase encode gradient with the same time integral value and equivalent rewind gradient with the same time integral value as the basic component of the rewind gradient is applied to the lead axis, and the NMR signal is received while applying the lead gradient to the lead axis, and the reception The second phase information is acquired from the NMR signal obtained.
(3) A slice axis correction component is obtained from the first phase information and the second phase information.
The first phase information is phase information when there is no influence of eddy current or residual magnetization caused by the phase encoding gradient. The second phase information is phase information when an effect of eddy current or residual magnetization caused by the phase encoding gradient is equivalently applied to the lead axis. Therefore, if the first phase information and the second phase information are compared, the influence of eddy current or residual magnetization caused by the phase encoding gradient can be quantitatively known. Therefore, the slice axis correction component for canceling it can be obtained quantitatively.

  According to the MRI apparatus of the present invention, it is possible to prevent image quality deterioration due to the influence of eddy current or residual magnetization caused by the phase encoding gradient. In particular, it is useful for improving the image quality of an MRI apparatus using a permanent magnet.

  Hereinafter, the present invention will be described in more detail with reference to embodiments shown in the drawings. Note that the present invention is not limited thereby.

-First embodiment-
FIG. 1 is a block diagram of an MRI apparatus according to the first embodiment of the present invention.
In the MRI apparatus 100, the magnet assembly 1 has a space portion (hole) for inserting the subject therein, and a permanent magnet that applies a constant main magnetic field to the subject so as to surround the space portion. 1p, a gradient magnetic field coil 1g for generating a gradient magnetic field of the slice axis, the warp axis, and the lead axis, a transmission coil 1t for providing an RF pulse for exciting spins of nuclei in the subject, A receiving coil 1r for detecting an NMR signal is arranged. The gradient magnetic field coil 1g, the transmission coil 1t and the reception coil 1r are connected to a gradient magnetic field drive circuit 3, an RF power amplifier 4 and a preamplifier 5, respectively.

  The sequence storage circuit 8 operates the gradient magnetic field drive circuit 3 based on the stored pulse sequence in accordance with a command from the computer 7, generates a gradient magnetic field from the gradient coil 1 g of the magnet assembly 1, and performs gate modulation. The circuit 9 is operated, and the carrier wave output signal of the RF oscillation circuit 10 is modulated into a pulse signal having a predetermined timing and a predetermined envelope shape, which is added as an RF pulse to the RF power amplifier 4 and power amplified by the RF power amplifier 4 Thereafter, it is applied to the transmission coil 1t of the magnet assembly 1 to selectively excite the target slice region.

The preamplifier 5 amplifies the NMR signal from the subject detected by the receiving coil 1 r of the magnet assembly 1 and inputs it to the phase detector 12. The phase detector 12 uses the carrier wave output signal of the RF oscillation circuit 10 as a reference signal, phase-detects the NMR signal from the preamplifier 5, and provides it to the A / D converter 11. The A / D converter 11 converts the analog signal after phase detection into a digital signal and inputs it to the computer 7.
The computer 7 reads data from the A / D converter 11, performs image reconstruction calculation, and generates an image of a target slice area. This image is displayed on the display device 6. The computer 7 is also responsible for overall control such as receiving information input from the console 13.

FIG. 2 is a flowchart showing warp axis correction component acquisition processing in the MRI apparatus 100.
In step S1, data sy0 (k) is collected by the pulse sequence A0 shown in FIG. In this pulse sequence A0, an excitation pulse R and a slice gradient ss are applied, then an inversion pulse P and a slice gradient ss are applied, and then an NMR signal is received from the echo SE while applying a read gradient gxw, and data sy0 Collect (k). Note that no phase encode gradient is applied to the warp axis.
In step S2, the data sy0 (k) is subjected to a one-dimensional Fourier transform in the read direction, and the result is defined as SY0 (x).
In step S3, the first-order gradient dy0 of the phase term (Arctan {SY0 (x)}) of the Fourier transform result SY0 (x) is obtained (obtained by applying the least square method or the like). Further, the phase amount b0 = Arctan {SY0 (0)} at the gradient center is obtained. This phase amount b0 is the phase amount at the gradient center when there is no residual magnetization.

  Steps S1 to S3 described above are processes for obtaining the influence (deviation of the echo center of the echo signal SE) that the gradient magnetic fields gx1 and gxw are caused mainly by eddy currents.

In step S4, data syi (k) is collected by the pulse sequence Aj shown in FIG. In this pulse sequence Aj, an excitation pulse R and a slice gradient ss are applied, and then an equivalent phase encode gradient gy (i) having a time integration value equal to the phase encode gradient gy (i) of the encode number i determined by the scan parameter is read. Applied to the axis, and after the time ty (lengthened as much as possible to improve accuracy), the equivalent phase encode gradient gy (i) and the equivalent rewind gradient gyr (i) having the same time integral value and opposite polarity are applied to the lead axis To do. Next, an inversion pulse P and a slice gradient ss are applied, and then an NMR signal is received from the echo SE while applying a read gradient gxw, and data syi (k) is collected. Note that no phase encode gradient is applied to the warp axis. Here, step S4 may be repeated for all encoding numbers i (in this case, j = i), but step S4 is repeated for appropriately selected encoding numbers i in order to shorten the time (in this case j ≠). i), the data of the encoding number not selected may be obtained by interpolation. In the simplest case, step S4 is executed only for the encoding number that gives the maximum phase encoding gradient (in this case, only j = 1), and the data of the other encoding numbers are calculated in proportion to the encoding gradient. Also good.
In step S5, the data syi (k) is subjected to a one-dimensional Fourier transform in the read direction, and the result is defined as SYi (x).
In step S6, the first-order gradient dyi of the phase term (Arctan {SYi (x)}) of the Fourier transform result SYi (x) is obtained (using the least square method or the like). In addition, the phase amount bi = Arctan {SYi (0)} at the gradient center is obtained, and the phase amount difference (bi−b0) is calculated. This phase difference (bi−b0) is a zeroth-order phase component that is uniformly applied without depending on the location due to the influence of residual magnetization caused by the phase encode gradient gy (i).
The above steps S4 to S6 are processes for determining the influence that the phase encode gradient gy (i) is caused mainly by the residual magnetization.

In step S7, the magnitude ΔGY (i) of the effect of eddy current and residual magnetization caused by the equivalent phase encoding gradient gy (i) is calculated from (dyi−dy0).
dy0 represents the phase around when there is no phase encoding gradient. On the other hand, dyi represents the phase around when there is an equivalent phase encoding gradient gy (i). Originally, since the equivalent phase encoding gradient gy (i) is canceled by the equivalent rewind gradient gyr (i), (dyi−dy0) = 0 should be satisfied. However, if (dyi−dy0) ≠ 0, the magnitude of the difference represents the magnitude of the effect of eddy current and residual magnetization caused by the equivalent phase encoding gradient gy (i). Therefore, the magnitude ΔGY (i) of the eddy current and residual magnetization caused by the equivalent phase encoding gradient gy (i) can be calculated from (dyi−dy0).
That is, when the interval of the lead gradient gxw is a_gxw, and the echo center shift time due to the effect of eddy current and residual magnetization caused by the equivalent phase encoding gradient gy (i) is ty0,
γ · ΔGY (i) · ty = γ · a_gxw · ty0 (where γ is the gyromagnetic ratio)
There is a relationship
ΔGY (i) = a_gxw · ty0 / ty
Is established.

  In step S8, the correction coefficient αi (the magnitude of the influence of eddy current and residual magnetization per unit phase encoding amount) is obtained by the following equation.

In step S9, from the basic component gy (i) of the phase encode gradient determined by the scan parameter and the correction coefficient αi,
qi = αi · gy (i) (where qi ≦ 1.0)
To obtain the warp axis correction component qi.

FIG. 5 is a flowchart showing imaging data collection processing of the MRI apparatus 100.
In step S10, a new rewind gradient gyr (i) ′ is obtained from the basic component gy (i) of the phase encode gradient determined by the scan parameter and the warp axis correction component qi.
gyr (i) ′ = 0.01 · gy (i) + qi
In step S11, imaging data is acquired by the pulse sequence Bp of the fast SE method using the new rewind gradient gyr (i) ′ shown in FIG. At this time, the detection phase in the phase detector 12 is adjusted so as to cancel the phase amount difference (bi−b0), or the transmission phases of the corresponding inversion pulses P1, P2, and P3 are adjusted.
By performing imaging using the imaging data collected as described above, it is possible to prevent image quality deterioration due to the influence of eddy current or residual magnetization caused by the phase encoding gradient of the warp axis.

-Second Embodiment-
The second embodiment is a modification of the first embodiment. The warp axis correction component qi is acquired in the same manner as the first embodiment, but shown in FIG. 7 instead of the pulse sequence Bp of FIG. Imaging data is collected by the pulse sequence Cp.
That is, as shown in FIG. 7, the rewind gradient gyr (i) corresponding to the basic component gy (i) is applied, and the auxiliary rewind gradient gqr (i) corresponding to the warp axis correction component qi is used as the warp axis. Apply.
Thus, even when imaging is performed using the collected data for imaging, it is possible to prevent image quality deterioration due to the influence of eddy current or residual magnetization caused by the phase encoding gradient.

-Third embodiment-
The third embodiment is a modification of the first embodiment. The warp axis correction component qi is acquired in the same manner as the first embodiment, but the basic component gy (i) of the phase encode gradient determined by the scan parameter is obtained. And a warp axis correction component qi, a new phase encode gradient gy (i) ′ is obtained, and, as shown in FIG. 8, a fast SE method pulse sequence Dp using this new phase encode gradient gy (i) ′ is obtained. Collect imaging data.
Thus, even when imaging is performed using the collected data for imaging, it is possible to prevent image quality deterioration due to the influence of eddy current or residual magnetization caused by the phase encoding gradient.

-Fourth Embodiment-
The fourth embodiment is a modification of the first embodiment. The warp axis correction component qi is acquired in the same manner as the first embodiment. As shown in FIG. 9, the basic component gy (i) is obtained. Is applied with a phase encode gradient gy (i) corresponding to, and an auxiliary phase encode gradient gq (i) corresponding to the warp axis correction component qi is applied to the warp axis. collect.
Thus, even when imaging is performed using the collected data for imaging, it is possible to prevent image quality deterioration due to the influence of eddy current or residual magnetization caused by the phase encoding gradient.

-Fifth embodiment-
In the fifth embodiment, the warp axis correction component acquisition process of FIG. 10 is performed instead of the warp axis correction component acquisition process of FIG.
FIG. 10 is a flowchart illustrating warp axis correction component acquisition processing according to the fifth embodiment.
In step V1, the i-th phase encode gradient gy (i) B having a phase encoding amount equal to the i-th phase encode gradient gy (i) determined by the scan parameter and an amplitude that allows the influence of eddy current and residual magnetization to be negligible is used. Data sBi (k) is collected from the first echo by the pulse sequence F1p shown in FIG.
In step V2, the data sBi (k) is subjected to a one-dimensional Fourier transform in the read direction, and the result is set as SBi (x).
In step V3, the value SBi (0) at x = 0 of the Fourier transform result SBi (x) is set as ideal phase information φi. This ideal phase information φi represents a phase offset component (0th-order phase component) when there is no influence of eddy current or residual magnetization caused by the phase encoding gradient.

In Step V4, data sBi ′ (k) is collected from the first echo by the pulse sequence F1p ′ shown in FIG. 12 using the i-th phase encoding gradient gy (i) determined by the scan parameter.
In step V5, the data sBi ′ (k) is one-dimensional Fourier transformed in the read direction, and the result is SBi ′ (x).
In step V6, the value SBi ′ (0) at x = 0 of the Fourier transform result SBi ′ (x) is set as the current phase information φi ′. This current phase information φi ′ represents a phase offset component (0th-order phase component) when there is an influence of eddy current or residual magnetization caused by the phase encoding gradient.

  In step V7, a warp axis correction component qi to be added to match the current phase information φi ′ with the ideal phase information φi is calculated based on the magnet characteristics of the permanent magnet MRI apparatus.

In step V8, warp axis correction components q (i + 1) to q (i + M-1) are obtained from the second echo to the Mth echo in the same manner as in steps V1 to V7.
FIG. 13 and FIG. 14 show pulse sequences F2p and F2p ′ for the second echo.
15 and 16 show pulse sequences F3p and F3p ′ for the third echo.

  Even if the imaging data collection shown in FIGS. 5 to 9 is performed using the warp axis correction component qi obtained as described above, and imaging is performed using the imaging data, the eddy current caused by the phase encoding gradient or It is possible to prevent the deterioration of the image quality due to the influence of the residual magnetization.

-Sixth Embodiment-
In the sixth embodiment, the influence of eddy current or residual magnetization caused by the phase encoding gradient is suppressed by switching the polarity of the killer gradient.
17 and 18 show a pulse sequence of the sixth embodiment.
In the pulse sequence Gp of FIG. 17, an excitation pulse R and a slice gradient ss are applied.
Next, the first inversion pulse P1 and the slice gradient ss are applied, the phase encode gradient gy (i) is applied to the warp axis, and then the NMR signal is received from the first echo SE1 while applying the lead gradient rr. Thereafter, a rewind gradient gyr (i) having the same time integral value as that of the encode gradient gy (i) and having the opposite polarity is applied to the warp axis. Next, the second inversion pulse P2 and the slice gradient ss are applied, the encode gradient gy (i + 1) is applied to the warp axis, and then the NMR signal is received from the second echo SE2 while applying the read gradient rr, Thereafter, a rewind gradient gyr (i + 1) having the same time integral value as that of the encode gradient gy (i + 1) and opposite polarity is applied to the warp axis. Next, the third inversion pulse P3 and the slice gradient ss are applied, the encode gradient gy (i + 2) is applied to the warp axis, and then the NMR signal is received from the third echo SE3 while applying the read gradient rr, Thereafter, a rewind gradient gyr (i + 2) having the same time integral value as the encode gradient gy (i + 2) and opposite polarity is applied to the warp axis. In this way, the process from the transmission of the inversion pulse to the reception of the NMR signal is repeated M (here, M = 3) times. Next, a killer gradient Kil is applied, which has the same polarity as the sum of the phase encode gradients gy (i), gy (i + 1), and gy (i + 2) (in this case, positive).

  Next, in the pulse sequence Gq of FIG. 18, the process from the transmission of the excitation pulse R to the rewind gradient gyr (j + 2) is performed as in FIG. Next, a killer gradient Kil is applied, which has the same polarity (here, negative) as the sum of the phase encode gradients gy (j), gy (j + 1), and gy (j + 2).

  As described above, when the polarity of the killer gradient Kil is switched so as to be the same as the polarity of the sum of the M phase encode gradients applied when M is repeated from the transmission of the inverted RF pulse to the reception of the NMR signal, The effect of eddy current or residual magnetization caused by the phase encoding gradient can be canceled by the killer gradient Kil. For this reason, it is possible to prevent the deterioration of the image quality of the image due to the influence of eddy current or residual magnetization caused by the phase encoding gradient.

-Seventh embodiment-
FIG. 19 is a flowchart showing the 0th-order phase component acquisition process in the MRI apparatus 100.
In step R1, as shown in FIG. 20, data sy0 (k) of the second echo SE2 is collected by a pulse sequence H0 that does not apply a phase encode gradient and a rewind gradient to the warp axis.
In step R2, the data sy0 (k) is subjected to a one-dimensional Fourier transform in the read direction, and the result is defined as SY0 (x).
In step R3, the zero-order phase amount b0 = Arctan {SY0 (0)} is obtained. The zeroth-order phase amount b0 is a phase amount at the gradient center when there is no residual magnetization.

In step R4, as shown in FIG. 21, data syj (k) of the second echo SE2 is collected by a pulse sequence Hj in which the phase encode gradient gy (i) and the rewind gradient gyr (i) ′ are applied to the warp axis. Here, the rewind gradient gyr (i) ′ is a new rewind gradient gyr (i) ′ obtained from the basic component gy (i) of the phase encode gradient determined by the scan parameter and the warp axis correction component qi.
In step R5, the data syi (k) is subjected to a one-dimensional Fourier transform in the read direction, and the result is defined as SYi (x).
In step R6, the zero-order phase amount bj = Arctan {SYi (0)} is obtained. This zero-order phase amount bj is the phase amount at the center of the gradient when there is residual magnetization.
In step R7, a zero-order phase component bi = b0-bj is obtained.
If the 0th-order phase component bi acquired as described above is used in step S12 in FIG. 5, ghost artifacts can be suppressed.

-Eighth embodiment-
In the eighth embodiment, image quality deterioration due to the influence of eddy current or residual magnetization caused by the phase encode gradient of the slice axis in the 3D high-speed SE method is prevented.

FIG. 22 is a flowchart showing slice axis correction component acquisition processing in the MRI apparatus 100.
In step L1, data sz0 (k) is collected by the pulse sequence I0 shown in FIG. In this pulse sequence I0, an excitation pulse R and a slice gradient ss are applied, then an inversion pulse P and a slice gradient ss are applied, and then an NMR signal is received from the echo SE while applying a read gradient gxw, and data sz0 Collect (k). Note that no phase encode gradient is applied to the warp axis and slice axis.
In step L2, the data sz0 (k) is one-dimensional Fourier transformed in the read direction, and the result is SZ0 (x).
In step L3, a first-order gradient dz0 of the phase term (Arctan {SZ0 (x)}) of the Fourier transform result SZ0 (x) is obtained (obtained by applying a least square method or the like). Further, the phase amount b0 = Arctan {SZ0 (0)} at the gradient center is obtained. This phase amount b0 is the phase amount at the gradient center when there is no residual magnetization.
The above steps L1 to L3 are processes for obtaining the influence (deviation of the echo center of the echo signal SE) that the gradient magnetic fields gx1 and gxw are caused mainly by the eddy current.

In step L4, data szi (k) is collected by the pulse sequence Ij shown in FIG. In this pulse sequence Ij, a slice gradient ss is applied to the excitation pulse R and the lead axis, and then the difference between the phase encode gradient gz (i) and the rewind gradient gzr (i) of the slice axis of the encode number i determined by the scan parameter is obtained. A corresponding differential gradient dd is applied to the lead axis, then an equivalent phase encoding gradient gz (i) equal to the phase encoding gradient gz (i) of the slice axis is applied to the lead axis, and an inversion pulse P and a slice gradient ss are applied. Then, an equivalent rewind gradient gzr (i) equal to the slice axis rewind gradient gzr (i) is applied to the lead axis, and after time tz, the NMR signal is received from the echo SE while applying the read gradient gxw, and the data szi (k ). Note that no phase encode gradient is applied to the warp axis. Here, step L4 may be repeated for all encoding numbers i (in this case, j = i), but step L4 is repeated for appropriately selected encoding numbers i in order to shorten the time (in this case j ≠). i), the data of the encoding number not selected may be obtained by interpolation.
In step L5, the data szi (k) is subjected to a one-dimensional Fourier transform in the read direction, and the result is set to SZi (x).
In step L6, the first-order gradient dzi of the phase term (Arctan {SZi (x)}) of the Fourier transform result SZi (x) is obtained (using the least square method or the like). Further, the phase amount bi = Arctan {SZi (0)} at the gradient center is obtained, and the phase amount difference (bi−b0) is calculated. This phase difference (bi−b0) is a zeroth-order phase component that is uniformly applied without depending on the location due to the influence of the residual magnetization caused by the phase encoding gradient gz (i).
The above steps L4 to L6 are processes for determining the influence that the phase encode gradient gz (i) is caused mainly by the residual magnetization.

In step L7, the magnitude ΔGZ (i) of the influence of eddy current and residual magnetization caused by the phase encode gradient gz (i) is calculated from (dzi−dz0).
dz0 represents the phase around when there is no phase encoding gradient. On the other hand, dzi represents the phase around when there is a phase encoding gradient gz (i). Originally, since the phase encode gradient gz (i) is canceled by the rewind gradient gzr (i), (dzi−dz0) = 0 should be satisfied. However, if (dzi−dz0) ≠ 0, the magnitude of the difference represents the magnitude of the influence of eddy current and residual magnetization caused by the phase encoding gradient gz (i). Therefore, the magnitude ΔGZ (i) of the influence of eddy current and residual magnetization caused by the phase encode gradient gz (i) can be calculated from (dyi−dy0).
That is, when the amplitude of the lead gradient gxw is a_gxw and the echo center shift time due to the influence of eddy current and residual magnetization caused by the phase encode gradient gz (i) is tz0,
γ · ΔGZ (i) · tz = γ · a_gxw · tz0 (where γ is the gyromagnetic ratio)
There is a relationship
ΔGZ (i) = a_gxw · tz0 / tz
Is established.

  In step L8, the correction coefficient βi (the magnitude of the influence of eddy current and residual magnetization per unit phase encoding amount) is obtained by the following equation.

In Step L9, from the basic component gz (i) of the phase encode gradient determined by the scan parameter and the correction coefficient βi,
wi = βi · gz (i)
To obtain the slice axis correction component wi.

FIG. 25 is a flowchart showing an imaging data collection process.
In step L10, a new rewind gradient gzr (i) ′ is obtained from the basic component gz (i) of the phase encode gradient determined by the scan parameter and the slice correction component wi.
gzr (i) ′ = gz (i) + wi
In step L11, imaging data is acquired by a pulse sequence Jp of the 3D high-speed SE method using the rewind gradient gzr (i) ′ of the new slice axis shown in FIG. At this time, it is preferable to simultaneously use the new rewarping gradient gyr (i) ′ of the warp axis in the first embodiment described above. Further, the detection phase in the phase detector 12 is adjusted so as to cancel the phase amount difference (bi−b0), or the transmission phases of the corresponding inversion pulses P1, P2, and P3 are adjusted.
Note that, as described with reference to FIGS. 7 to 9, an auxiliary rewind gradient or auxiliary phase encoding gradient of the slice axis may be used.

  By performing imaging using the imaging data collected as described above, it is possible to prevent image quality deterioration due to the influence of eddy current or residual magnetization caused by the phase encode gradient of the slice axis.

It is a block diagram which shows the MRI apparatus of 1st Embodiment of this invention. It is a flowchart which shows the warp axis correction component acquisition process in 1st Embodiment. FIG. 3 is an exemplary diagram of a pulse sequence used in the warp axis correction component acquisition process of FIG. 2. It is another example figure of the pulse sequence used by the warp axis correction component acquisition process of FIG. It is a flowchart which shows the data collection process for imaging in 1st Embodiment. FIG. 6 is an exemplary diagram of a pulse sequence used in the imaging data collection process of FIG. 5. It is an illustration figure of the pulse sequence used by the data collection process for imaging of 2nd Embodiment. It is an illustration figure of the pulse sequence used by the data collection process for imaging of 3rd Embodiment. It is an illustration figure of the pulse sequence used by the data collection process for imaging of 4th Embodiment. It is a flowchart which shows the warp axis correction component acquisition process in 5th Embodiment. It is an illustration figure about the 1st echo of the pulse sequence used by the warp axis correction component acquisition process of FIG. It is another illustration figure about the 1st echo of the pulse sequence used by the warp axis correction component acquisition process of FIG. It is an illustration figure about the 2nd echo of the pulse sequence used by the warp axis correction component acquisition process of FIG. It is another illustration figure about the 2nd echo of the pulse sequence used by the warp axis correction component acquisition process of FIG. It is an illustration figure about the 3rd echo of the pulse sequence used by the warp axis correction component acquisition process of FIG. It is another example figure about the 3rd echo of the pulse sequence used by the warp axis correction component acquisition processing of FIG. It is an illustration figure of the pulse sequence used by the data collection process for imaging in 6th Embodiment. It is another illustration figure of the pulse sequence used by the data collection process for imaging in 6th Embodiment. It is a flowchart of the 0th-order phase component acquisition process in 7th Embodiment. FIG. 20 is an exemplary diagram of a pulse sequence used in the 0th-order phase component acquisition process of FIG. 19. FIG. 20 is another exemplary diagram of a pulse sequence used in the 0th-order phase component acquisition process of FIG. 19. It is a flowchart which shows the slice axis correction component acquisition process in 8th Embodiment. FIG. 23 is a view showing an example of a pulse sequence used in the slice axis correction component acquisition process of FIG. 22. It is another example figure of the pulse sequence used by the slice axis | shaft correction component acquisition process of FIG. It is a flowchart which shows the data collection process for imaging in 8th Embodiment. FIG. 26 is a view showing an example of a pulse sequence used in the imaging data collection process of FIG. 25. It is a pulse sequence diagram of a conventional high-speed SE method. It is explanatory drawing of the data collection locus | trajectory in k-space. It is a pulse sequence diagram of a conventional 3D high-speed SE method. It is explanatory drawing of the problem of the conventional high-speed SE method. It is explanatory drawing of the problem of the conventional 3D high-speed SE method.

Explanation of symbols

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 MRI apparatus 1 Magnet assembly 1p Permanent magnet 7 Computer 8 Sequence memory circuit

Claims (4)

An excitation RF pulse is transmitted by the RF pulse transmission means, an inverted RF pulse is then transmitted by the RF pulse transmission means, a phase encoding gradient is then applied to the warp axis by the gradient magnetic field application means, and then the gradient magnetic field application means The NMR signal is received by the NMR signal receiving means while applying the read gradient to the lead axis, and after repeating M times from the transmission of the inverted RF pulse to the reception of the NMR signal, the killer gradient is applied by the gradient magnetic field applying means. In the MRI apparatus for collecting NMR signals subjected to (M × N) times of different phase encoding by repeating N times from transmission of the excitation RF pulse to application of the killer gradient,
The polarity of the killer gradient is such that the gradient magnetic field applying means has the same polarity as the polarity of the sum of the M phase encode gradients applied when M is repeated from the transmission of the inverted RF pulse to the reception of the NMR signal. An MRI apparatus characterized by switching between. An excitation RF pulse is transmitted by the RF pulse transmitting means, then an inverted RF pulse is transmitted by the RF pulse transmitting means, and then a phase encoding gradient is applied to the warp axis by the gradient magnetic field applying means, or the warp axis and the slice axis are applied. In the MRI apparatus that receives and then receives the NMR signal by the NMR signal receiving means while applying the lead gradient to the lead axis by the gradient magnetic field applying means,
The transmission phase of the inverted RF pulse by the RF pulse transmission means is changed or the phase at the NMR signal reception means is changed so as to suppress the zero-order phase component generated by the influence of residual magnetization caused by the phase encoding gradient. An MRI apparatus characterized by changing a detection phase of detection. The MRI apparatus according to claim 2,
The RF pulse is transmitted by the RF pulse transmission means, and the phase encode gradient is not applied to the warp axis and the slice axis, and the equivalent phase encode gradient having the same time integral value as the phase encode gradient is applied to the lead axis by the gradient magnetic field applying means. Then, an equivalent rewind gradient having the same phase integral gradient and the same time integral value and opposite polarity is applied to the lead axis, and then the NMR signal receiving means applies the read gradient to the lead axis by the gradient magnetic field applying means. An MRI apparatus comprising: a zero-order phase component acquisition unit that receives an NMR signal, acquires phase information from the received NMR signal, and obtains the zero-order phase component from the phase information.   The MRI apparatus according to claim 2, wherein the NMR signal obtained when the phase encode gradient and the rewind gradient are applied to the warp axis and the NMR signal obtained when the phase encode gradient and the rewind gradient are not applied to the warp axis; The MRI apparatus further comprises a 0th-order phase component acquisition means for obtaining the 0th-order phase component from

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