JP6208464B2 - Magnetic resonance equipment - Google Patents

Description

  The present invention relates to a magnetic resonance apparatus for imaging a region including a blood vessel.

  A 3D gradient echo type black blood imaging method is known as a method for imaging a blood vessel wall.

JP 2012-254361 A

In the 3D gradient echo black blood imaging method, the spin of the entire region is reversed by an IR pulse, and when the longitudinal magnetization of the blood spin becomes near null, the 3D gradient echo method is used. MSDE (Motion Sensitized Driven
There is a method in which a blood flow signal is attenuated by an Equilibrium method and imaged by a 3D gradient echo method. However, in any method, the blood flow signal may not be sufficiently suppressed due to the blood inflow effect (Inflow effect).
Therefore, a method that can sufficiently suppress the blood flow signal is desired.

One aspect of the present invention is a magnetic resonance apparatus that excites a slab having an imaging region including a blood vessel and acquires an image of the imaging region,
The slab is
A first region adjacent to the imaging region and including a blood vessel;
A second region adjacent to the imaging region on the opposite side of the first region and including a blood vessel;
The excitation pulse for exciting the slab is
The magnetic resonance apparatus is configured to realize an excitation profile in which a flip angle in the first region and the second region is larger than a flip angle in the imaging region.

  In addition to the inflow effect of blood flowing from the first region into the imaging region, the inflow effect of blood flowing from the second region into the imaging region can be suppressed, so that an image in which blood signals are sufficiently reduced Can be obtained.

It is the schematic of the magnetic resonance apparatus of one form of this invention. It is a figure which shows an example of the normal scan performed in order to image | photograph a blood vessel wall. It is explanatory drawing of the scan SC implemented with this form. It is explanatory drawing when slab SL is excited. It is explanatory drawing when performing the Fourier transformation of a slice direction. It is a figure which shows the example which provided gradient pulse Gx1, Gx2, and Gx3 for every excitation pulse x1, x2, and x3. It is a figure which shows another example of an excitation profile.

  Hereinafter, although the form for inventing is demonstrated, this invention is not limited to the following forms.

FIG. 1 is a schematic view of a magnetic resonance apparatus according to one embodiment of the present invention.
A magnetic resonance apparatus (hereinafter referred to as “MR apparatus”) 100 includes a magnet 2, a table 3, a receiving coil 4, and the like.

  The magnet 2 has a bore 21 in which the subject 11 is accommodated. The magnet 2 includes a superconducting coil, a gradient coil, an RF coil, and the like.

The table 3 has a cradle 3 a that supports the subject 11. The cradle 3a is configured to be able to move into the bore 21. The subject 11 is transported to the bore 21 by the cradle 3a.
The receiving coil 4 receives a magnetic resonance signal from the subject 11.

  The MR apparatus 100 further includes a transmitter 5, a gradient magnetic field power source 6, a receiver 7, a control unit 8, an operation unit 9, a display unit 10, and the like.

The transmitter 5 supplies current to the RF coil, and the gradient magnetic field power source 6 supplies current to the gradient coil.
The receiver 7 performs signal processing such as detection on the signal received from the receiving coil 4.

  The control unit 8 transmits necessary information to the display unit 10 and reconstructs an image based on data received from the receiver 7 so as to realize various operations of the MR device 100. Control the operation of each part. The control unit 8 includes an image generation unit 81 and the like. The image generating unit 81 generates an image of an imaging region R3 (see, for example, FIG. 3) described later.

The operation unit 9 is operated by an operator and inputs various information to the control unit 8. The display unit 10 displays various information.
The MR apparatus 100 is configured as described above.

  In this embodiment, a scan for imaging the blood vessel wall is executed. Hereinafter, in order to clarify the difference between the scan executed in the present embodiment and the normal scan, first, an example of the normal scan executed for imaging the blood vessel wall will be described.

FIG. 2 is a diagram illustrating an example of a normal scan executed for imaging a blood vessel wall.
The scan SC is a scan for executing blood vessel wall imaging of a 3D gradient echo system. In the scan SC, the sequence A is repeatedly executed. The repetition time of the sequence A is indicated by “TR”. The sequence A includes a preparation unit P and a data collection unit Q.

The preparation unit P is executed to attenuate the blood flow signal. FIG. 2 shows a sequence by the MSDE method as an example of a specific sequence of the preparation unit P. For convenience of explanation, only one axis of the gradient magnetic field is shown.
After the blood flow signal is attenuated by the preparation unit P, the data collection unit Q is executed.

  The data collection unit Q is a sequence for collecting data from the slab SL. The slab SL is set so as to cross the blood vessel. In FIG. 2, two blood vessels A and B are shown as blood vessels crossing the slab SL. Blood flowing into the slab SL from the outside (I side) of the slab SL flows into the blood vessel A, while blood flowing into the slab SL from the outside (S side) of the slab flows into the blood vessel B. ing.

  The data acquisition unit Q has an excitation pulse x for exciting the slab SL. The slab SL is excited by the excitation pulse x, and the echo signal S is collected. Based on the collected echo signal S, an image including information on the blood vessel wall is reconstructed.

  In the scan SC, the blood flow signal is attenuated by the preparation unit P and the data collection unit Q is executed, so that an image with a reduced blood flow signal can be acquired. However, even if the blood flow signal is attenuated by the preparation unit P, the blood flow signal may not be sufficiently suppressed due to the blood inflow effect (Inflow effect). Therefore, in this embodiment, the scan SC is performed so that the blood flow signal can be sufficiently suppressed. The scan SC in this embodiment will be described below.

FIG. 3 is an explanatory diagram of the scan SC implemented in this embodiment.
The preparation unit P has the same sequence as in FIG. 2, but the data collection unit Q has a sequence different from that in FIG. FIG. 3 is an enlarged view of a different part of the data collection unit Q.

  The data acquisition unit Q shown in FIG. 2 excites the slab SL by the excitation pulse x, but the data acquisition unit Q of this embodiment excites the slab SL by the excitation pulses x1, x2, and x3.

  The slab SL has three regions R1, R2, and R3. A central region R3 of the slab SL is an imaging region to be imaged. On the other hand, regions R1 and R2 on both sides adjacent to the imaging region R3 are regions that are not imaged.

  The excitation pulse x1 is a pulse for exciting the region R1, and the excitation pulse x2 is a pulse for exciting the region R2. The excitation pulse x3 is a pulse for exciting the imaging region R3.

  The flip angle of the excitation pulse x1 is α. The flip angle of the excitation pulse x2 is the same value α as that of the excitation pulse x1. On the other hand, the flip angle of the excitation pulse x3 is β. The flip angle α is set to a value larger than the flip angle β. Further, gradient pulses G1 and G2 are applied in the slice direction. Hereinafter, how the slab SL is excited using the excitation pulses x1, x2, and x3 will be described with reference to FIG.

FIG. 4 is an explanatory diagram when exciting the slab SL.
4A is a diagram illustrating excitation pulses x1, x2, and x3 and gradient pulses G1 and G2 included in the data acquisition unit Q of the present embodiment, FIG. 4B is a diagram illustrating a slab SL, and FIG. c) is a diagram schematically showing an excitation profile representing a relationship between each region and a flip angle when the slab SL is excited by an excitation pulse.

First, the gradient pulse G1 is applied and the excitation pulse x1 is applied. The excitation pulse x1 is a pulse for exciting the region R1 of the slab SL. The flip angle α of the excitation pulse x1 is, for example, α = 90 °. The blood a in the blood vessel A flows outside the slab SL at the time point t0 before the excitation pulse x1 is applied, but flows through the region R1 of the slab SL at the time point t1 when the excitation pulse x1 is applied. The spin of the blood a is tilted by the flip angle α while flowing through the region R1 due to the excitation pulse x1. Therefore, even if the blood a before flowing into the slab SL has a large longitudinal magnetization, the longitudinal magnetization of the blood a becomes small while flowing through the region R1 of the slab SL.
After the excitation pulse x1, the next excitation pulse x2 is applied.

  The excitation pulse x2 is a pulse for exciting the region R2 of the slab SL. The blood b in the blood vessel B flows outside the slab SL at time t0, but flows through the region R2 of the slab SL at time t2 when the excitation pulse x2 is applied. The spin of the blood b is tilted by the flip angle α while flowing through the region R2 due to the excitation pulse x2. Therefore, even if the blood b before flowing into the slab SL has a large longitudinal magnetization, the longitudinal magnetization of the blood b becomes small while flowing through the region R2 of the slab SL. After applying the excitation pulse x2, the next excitation pulse x3 is applied.

  The excitation pulse x3 is a pulse for exciting the imaging region R3 of the slab SL. The flip angle α of the excitation pulse x3 is smaller than the flip angle β of the excitation pulses x1 and x2, for example, β = 10 °.

  Thus, in this embodiment, the region R1, the region R2, and the imaging region R3 of the slab SL are excited in order. After applying the excitation pulse x3, the gradient pulse G2 is applied. The gradient pulse G2 is a rephase pulse for correcting the phase shift of the spin in the imaging region R3 excited by the excitation pulse x3.

  After exciting the slab SL, the phase encode gradients Gs and Gp and the frequency encode gradient Gf are applied to collect the echo signal S (see FIG. 3).

  Similarly, the preparation unit P and the data collection unit Q are alternately executed to collect the echo signal S. When all the echo signals S necessary for image reconstruction are collected, the scan SC is terminated.

  The image generation unit 81 (see FIG. 1) performs Fourier transformation in the slice direction on the data obtained from the slab SL, and generates an image of the imaging region R3. FIG. 5 is an explanatory diagram when performing Fourier transform in the slice direction. The image generation means performs a Fourier transform in the slice direction over the region R1, the imaging region R3, and the region R2. However, the data in the regions R1 and R2 on both sides of the imaging region R3 is discarded because it causes the wrapping in the slice direction. Therefore, no aliasing appears in the image of the imaging region R3, and high-quality blood vessel wall imaging can be performed. As long as an image of the imaging region R3 can be generated, the region in which the Fourier transform in the slice direction is executed is not limited to FIG. For example, a Fourier transform in the slice direction may be performed on a part of the region R1, the imaging region R3, and a part of the region R2.

  In this embodiment, the imaging region R3 is excited by the excitation pulse x3, but before the imaging region R3 is excited, an excitation pulse x1 that excites the region R1 and an excitation pulse x2 that excites the region R2 are applied. Since the flip angle α of the excitation pulse x1 is larger than the flip angle β of the excitation pulse x3, the longitudinal magnetization of the blood a becomes sufficiently small while the blood a of the blood vessel A flows through the region R1. Accordingly, blood a having a small longitudinal magnetization flows into the imaging region R3. Further, since the flip angle α of the excitation pulse x2 is also larger than the flip angle β of the excitation pulse x3, the longitudinal magnetization of the blood b becomes sufficiently small while the blood b in the blood vessel B flows through the region R2. Therefore, blood b having a small longitudinal magnetization flows into the imaging region R3. Thus, in this embodiment, the longitudinal magnetization of blood a and b can be reduced before blood a and b flow into imaging region R3. Accordingly, not only the inflow effect of blood a flowing into the imaging region R3 from the region R1 but also the inflow effect of blood b flowing into the imaging region R3 from the region R2 opposite to the region R1 can be suppressed. It is possible to obtain an image with a sufficiently reduced signal.

  Further, since the gradient pulse G2 corrects the spin phase shift generated in the imaging region R3, a higher quality image can be obtained. Although the gradient pulse G2 cannot correct the phase shift of the spin that occurs in the regions R1 and R2, the data in the regions R1 and R2 are discarded as folded portions, so that the spins generated in the regions R1 and R2 are discarded. Even if the phase shift is not corrected, a high-quality image can be obtained.

  In this embodiment, three excitation pulses x1, x2, and x3 are applied while the gradient pulse G1 is applied. However, a gradient pulse may be provided for each of the excitation pulses x1, x2, and x3. FIG. 6 shows an example in which gradient pulses Gx1, Gx2, and Gx3 are provided for each of the excitation pulses x1, x2, and x3. Also in FIG. 6, since the excitation profile shown in FIG. 4C can be realized, the inflow effect of blood can be suppressed, and an image with a sufficiently reduced blood signal can be acquired. However, in FIG. 6, each gradient pulse Gx1, Gx2, and Gx3 requires a rise time and a fall time of the gradient, and thus has a drawback that the repetition time TR is extended. Therefore, it is preferable to apply one gradient pulse G1, as shown in FIG. 4A, rather than providing a gradient pulse for each of the excitation pulses x1, x2, and x3. By using the gradient pulse G1, the rise time and the fall time of the gradient as shown in FIG. 6 are not required, so that the extension of the repetition time TR can be sufficiently shortened.

  In this embodiment, the flip angle of the excitation pulse x1 and the flip angle of the excitation pulse x2 are the same value (α). However, if the flip angles of the excitation pulses x1 and x2 are larger than the flip angle of the excitation pulse x3, the flip angle of the excitation pulse x1 and the flip angle of the excitation pulse x2 may be different values.

  In this embodiment, the excitation pulses x1 and x2 are applied before the excitation pulse x3. However, the excitation pulse x1 or x2 may be applied after the excitation pulse x3. However, when the excitation pulse x1 or x2 is applied after the excitation pulse x3, it may be difficult to sufficiently suppress the inflow effect of blood flowing from the region R1 or R2 into the imaging region R3. Therefore, it is preferable to apply the excitation pulses x1 and x2 before the excitation pulse x3. When the excitation pulses x1 and x2 are applied before the excitation pulse x3, the longitudinal magnetization of the blood in the regions R1 and R2 can be reduced before the excitation pulse x3 is applied, and therefore, from both the regions R1 and R2. The inflow effect of blood flowing into the imaging region R3 can be sufficiently suppressed, and an image with a sufficiently reduced blood signal can be acquired.

  In this embodiment, the blood flow signal is suppressed by using the excitation pulses x1 and x2, but instead of the excitation pulses x1 and x2, a saturation pulse for saturating the magnetization of the blood in the regions R1 and R2 is used. It is also conceivable to suppress blood flow signals. However, when the saturation pulse is used, it is necessary to apply a large crusher pulse for erasing the transverse magnetization caused by the saturation pulse, which causes a problem that the repetition time TR becomes considerably long. On the other hand, in this embodiment, since the crusher pulse for erasing the transverse magnetization is unnecessary, the extension of TR can be sufficiently shortened.

  In this embodiment, three excitation pulses x1, x2, and x3 are used to realize the excitation profile shown in FIG. However, by performing inverse Fourier transform on the excitation profile shown in FIG. 4C, the RF pulse intensity information and phase information are obtained, and an RF pulse represented by a complex number having such information is designed, and this complex number is represented by this complex number. RF pulses that have been performed may be used in place of the excitation pulses x1, x2, and x3.

  In this embodiment, the excitation profile shown in FIG. 4C is realized. However, if the flip angle in the regions R1 and R2 is larger than the flip angle in the imaging region R3, the excitation profile is not limited to FIG. FIG. 7 shows another example of the excitation profile.

  In FIG. 7A, the flip angle in the imaging region R3 is a constant value, but the flip angle in the regions R1 and R2 is set to increase as the distance from the imaging region R3 increases.

  FIG. 7B is set so that the flip angle increases as the distance from the center position C in the slice direction of the imaging region R3 increases.

  7A and 7B, since the flip angle in the regions R1 and R2 is larger than the flip angle in the imaging region R3, it is possible to reduce the blood signal flowing into the imaging region R3.

  In the present embodiment, the case of photographing the neck is described, but the present invention can also be applied to the case of photographing another part other than the neck.

2 Magnet 3 Table 3a Cradle 4 Receiving coil 5 Transmitter 6 Gradient magnetic field power supply 7 Receiver 8 Control unit 9 Operation unit 10 Display unit 11 Subject 21 Bore 22 Superconducting coil 23 Gradient magnetic field coil 24 RF coil 81 Image generating means 100 MR apparatus

Claims (9)

A magnetic resonance apparatus for executing a sequence including a preparation unit for attenuating a blood flow signal and a data collection unit for collecting data from a slab including a blood vessel ,
The slab is
An imaging region including blood vessels;
A first region adjacent to the imaging region and including a blood vessel;
A second region adjacent to the imaging region on the opposite side of the first region and including a blood vessel;
The data acquisition unit of the sequence has an excitation pulse for exciting the slab, and the excitation pulse is
A magnetic resonance apparatus configured to realize an excitation profile in which a flip angle in the first region and the second region is larger than a flip angle in the imaging region. In the excitation pulse for exciting the slab,
A first excitation pulse for exciting the first region;
A second excitation pulse for exciting the second region;
A third excitation pulse for exciting the imaging region;
The magnetic resonance apparatus according to claim 1, wherein: Applying a first gradient pulse for selecting the first region, the second region, and the imaging region;
The magnetic resonance apparatus according to claim 2, wherein the first excitation pulse, the second excitation pulse, and the third excitation pulse are applied while the first gradient pulse is being applied.   The magnetic resonance apparatus according to claim 2 or 3, wherein the first excitation pulse and the second excitation pulse are applied before the third excitation pulse.   5. The magnetic resonance apparatus according to claim 3, wherein a second gradient pulse for correcting a phase shift of a spin in the imaging region is applied. The excitation pulse is represented by a complex number,
The magnetic resonance apparatus according to claim 1, wherein the excitation pulse represented by a complex number includes intensity information and phase information obtained by performing an inverse Fourier transform on the excitation profile.   The magnetic resonance apparatus according to claim 1, further comprising an image generation unit configured to generate an image of the imaging region. The first region, the imaging region, and the second region are aligned in the slice direction;
The image generating means includes
The magnetic resonance apparatus according to claim 7, wherein Fourier transform in the slice direction is executed over the imaging region to generate an image of the imaging region. The image generating means includes
Performing a Fourier transform of the slice direction over at least a portion of the first region, the imaging region, and at least a portion of the second region;
The magnetic resonance apparatus according to claim 8, wherein at least a part of data in the first area and at least a part of data in the second area are discarded as a folded part.

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