JP6420583B2 - Magnetic resonance apparatus and program - Google Patents

Description

  The present invention relates to a magnetic resonance apparatus that performs fat suppression, and a program applied to the magnetic resonance apparatus.

  As a method for photographing a blood vessel wall, a photographing method using a black blood method is known (see, for example, Patent Document 1).

JP 2013-166040 A

  The black blood method is a method of rendering tissue surrounding blood by making the blood flowing through the blood vessel a low signal. As a method for rendering a blood vessel wall using the black blood method, for example, a method is known in which the longitudinal magnetization of blood is reduced using an MSDE (Motion Sensitized Driven Equilibrium) sequence and data is collected using a 3D gradient echo method.

In addition, when photographing a blood vessel wall, it is important that fat is not drawn as much as possible, and therefore, a fat suppression method is often used in photographing a blood vessel wall. As a fat suppression method, there is a method of using an inversion pulse for inverting the longitudinal magnetization of fat before data collection. In this method, the longitudinal magnetization of fat is reversed, and data is collected at the timing when the longitudinal magnetization of fat reaches a null point. Therefore, it is possible to collect data in which fat is suppressed. However, the longitudinal magnetization Mz of fat reversed by the inversion pulse recovers with time T1, and the longitudinal magnetization Mz of fat gradually approaches Mz = 1. Therefore, when the longitudinal magnetization of fat has a null point (or a value close to the null point), the fat suppression effect of the inversion pulse is high, but as the longitudinal magnetization of fat approaches Mz = 1, Fat suppression effect is reduced. For this reason, there exists a problem that the artifact by fat tends to appear in an image.
For these reasons, a technique for acquiring an image with reduced fat artifacts is desired.

According to a first aspect of the present invention, there is provided a scanning unit that executes a scan for collecting k-space data from an imaging region of a subject, and the imaging region based on the k-space data collected by the scanning unit. A magnetic resonance apparatus having an image creating means for creating an image,
The scanning means includes
Applying a fat suppression pulse for suppressing the MR signal of fat contained in the imaging region;
A first sequence having a first excitation pulse for exciting the imaging region after the fat suppression pulse is applied, from the imaging region excited by the first excitation pulse; Perform a first sequence to collect data in the low frequency region;
A second sequence having a second excitation pulse for exciting the imaging region such that a fat spin flip angle is smaller than a water spin flip angle, and is excited by the second excitation pulse. Performing a second sequence for collecting high-frequency data in k-space from the imaging region
The image creating means includes
The magnetic resonance apparatus creates an image of the imaging region based on the low-frequency region data and the high-frequency region data of the k space.

A second aspect of the present invention is a magnetic resonance apparatus that executes a scan for collecting k-space data from an imaging region of a subject, and for suppressing MR signals of fat contained in the imaging region A first sequence having a first excitation pulse for applying a fat suppression pulse and exciting the imaging region after the fat suppression pulse is applied, wherein the first sequence is excited by the first excitation pulse. A first sequence for collecting data in a low frequency region of k-space is executed from the imaging region, and the imaging region is excited so that the flip angle of the fat spin is smaller than the flip angle of the water spin A second sequence having a second excitation pulse for collecting data in a high frequency region of k-space from an imaging region excited by the second excitation pulse. A program which is applied to a magnetic resonance apparatus for performing the Sequence,
An image creation process for creating an image of the imaging region based on the low-frequency region data and the high-frequency region data of the k-space;
Is a program for causing a computer to execute.

  In the first sequence, data of a low frequency region having a high fat suppression effect can be collected by the fat suppression RF pulse. On the other hand, the second sequence can collect data in a high frequency region with a high fat suppression effect by the second excitation pulse. Therefore, an image with reduced fat artifacts can be obtained.

It is the schematic of the magnetic resonance apparatus of one form of this invention. It is a figure which shows the process which the processor 9 performs. It is a figure which shows schematically the imaging | photography site | part of this form. It is explanatory drawing of the normal scan SC for imaging | photography of the blood vessel wall of an imaging | photography site | part using a fat suppression method together. It is explanatory drawing of the collection order of the data of k space when performing scan SC. It is a figure which shows the data of the view of kz = 1 collected in the period P2. It is a figure which shows the scan of this form performed in order to image | photograph a blood vessel wall using a fat suppression method together. It is explanatory drawing of data collection period J1 and J2. It is explanatory drawing when collecting data in the period P1. It is explanatory drawing when collecting the data of k space in the period P2. It is explanatory drawing when collecting the data of k space in the period P3. It is explanatory drawing when collecting the data of the view of kz = -N. It is a figure which shows the example which collects the data of the low frequency area | region RL2 regarding a kz direction in the data collection period J1, and collects the data of the high frequency area | region RH21 and RH22 regarding a kz direction in the data collection period J2. The figure which shows the example which collects the data of the low frequency area | region RL3 regarding 2 directions of ky direction and kz direction in the data collection period J1, and the data of the high frequency area | region RH3 regarding 2 directions of ky direction and kz direction in the data collection period J2. It is.

  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 reception RF coil 4, and the like.

  The magnet 2 has a bore 21 in which the subject 13 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 13. The cradle 3a is configured to be able to move into the bore 21. The subject 13 is transported to the bore 21 by the cradle 3a.
A reception RF coil (hereinafter referred to as “reception coil”) 4 receives a magnetic resonance signal from the subject 13.

  The MR apparatus 100 further includes a transmitter 5, a gradient magnetic field power supply 6, a receiver 7, a computer 8, an operation unit 11, a display unit 12, 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. A combination of the magnet 2, the receiving coil 4, the transmitter 5, the gradient magnetic field power source 6, and the receiver 7 corresponds to the scanning means.

  The computer 8 controls the operation of each unit of the MR apparatus 100 so as to realize various operations of the MR apparatus 100 such as transmitting necessary information to the display unit 12 and reconstructing an image. The computer 8 includes a processor 9 and a memory 10.

FIG. 2 shows processing executed by the processor 9. The memory 10 stores a program executed by the processor 9. The processor 9 reads a program stored in the memory 10 and executes processing described in the program. The processor 9 configures an image creating unit 91 and the like by reading a program stored in the memory 10.
The image creating unit 91 creates an image of the imaging region based on the data received from the receiver 7.

  The processor 9 is an example that constitutes the image creating means 91, and functions as this means by executing a program stored in the memory 10.

The operation unit 11 is operated by an operator and inputs various information to the computer 8. The display unit 12 displays various information.
The MR apparatus 100 is configured as described above.

FIG. 3 is a diagram schematically showing an imaging region of this embodiment.
In this embodiment, a part including the blood vessel A in the neck of the subject is set as an imaging part. FIG. 3 shows a slab SL representing the range of the imaging region. In this embodiment, an example in which a blood vessel wall of a blood vessel A is imaged using the MR apparatus 100 will be described. When photographing a blood vessel wall, it is important that fat is not depicted as much as possible, and therefore, a fat suppression method is often used in photographing a blood vessel wall. Therefore, hereinafter, a scan executed for imaging a blood vessel wall in combination with the fat suppression method will be described. In the following description, in order to clarify the effect of the scan in this embodiment, before explaining the scan in this embodiment, the normal used for imaging a blood vessel wall together with the fat suppression method is used. The scanning will be described.

  FIG. 4 is an explanatory diagram of a normal scan SC for imaging the blood vessel wall at the imaging site together with the fat suppression method. Hereinafter, as an example of the scan SC, the scan SC will be described by taking a scan for imaging a blood vessel wall by the black blood method.

In FIG. 4, the scan SC is divided into a plurality of periods P1 to Pz.
In the period P1, an ASPIR (Adiabatic Spectral Inversion Recovery) pulse F, an MSDE sequence DIF, and a data acquisition sequence V are executed. The MSDE sequence DIF is executed once, and the data collection sequence V is executed a plurality of times.

  The ASPIR pulse F is an adiabatic pulse for reversing the longitudinal magnetization in an adiabatic manner while modulating the amplitude and phase, and is used as a fat suppression pulse for suppressing the MR signal of fat in the imaging region. . After applying the ASPIR pulse F, the MSDE sequence DIF is executed.

  FIG. 4 shows an example of the MSDE sequence DIF. The MSDE sequence DIF is executed to reduce the longitudinal magnetization of the blood a flowing through the blood vessel A (see FIG. 3). The MSDE sequence DIF has 90x pulses, 180y pulses, and -90x pulses. Further, the MSDE sequence DIF has MPG (Motion Probing Gradient). Further, the MSDE sequence DIF has a killer pulse for disappearing the transverse magnetization immediately after the -90x pulse.

  A data collection period J for collecting k-space data is provided after the MSDE sequence DIF. In the data collection period J, the data collection sequence V is executed a plurality of times. FIG. 4 shows a 3D gradient echo system sequence as an example of the data acquisition sequence V. The data acquisition sequence V has a single excitation pulse Q1 for exciting the imaging region. The data acquisition sequence V has a slice selection gradient magnetic field G1 corresponding to the excitation pulse Q1. The imaging region is excited by applying the excitation pulse Q1 and the slice selective gradient magnetic field G1. After exciting the imaging region, a gradient magnetic field such as a phase encoding gradient magnetic field and a frequency encoding gradient magnetic field is applied.

In FIG. 4, the pulse sequence executed in the period P1 is described, but the ASPIR pulse F, the MSDE sequence DIF, and the data acquisition sequence V are executed in the other periods P2 to Pz as well as the period P1.
Next, the collection order of k-space data when the scan SC of FIG. 4 is executed will be described.

FIG. 5 is an explanatory diagram of the collection order of k-space data when the scan SC is executed. In FIG. 5, the kx direction of the k space is not shown and a ky-kz plane is shown.
In the period P1, first, an ASPIR pulse F for reversing the longitudinal magnetization of fat is applied. The ASPIR pulse F can reverse the longitudinal magnetization of fat in the imaging region. After applying the ASPIR pulse F, the MSDE sequence DIF is executed. After the longitudinal magnetization of the blood is reduced by the MSDE sequence DIF, the data collection period J is started.

  In the data collection period J, the data collection sequence V is executed a plurality of times. In the data collection period J, view data (data on the ky axis) with kz = 0 is collected according to the ky centric order. In the ky centric order, data of grid points of ky = 0 is first collected, and then data of grid points of ky> 0 and data of ky <0 are sequentially ordered from the grid points close to the grid points of ky = 0. This figure shows ordering in which data of grid points are collected alternately. Therefore, in the first half of the data collection period J, data in the low frequency region RL in the ky direction is collected, and in the second half of the data collection period J, data in the high frequency region RH in the ky direction is collected. After collecting view data of kz = 0, the process proceeds to the next period P2.

  In the period P2, data of kz = 1 is collected according to the ky centric order. FIG. 6 shows data of a view with kz = 1 collected in the period P2. Similarly, the data collection sequence V for collecting the data of each kz view is repeatedly executed in the periods P3 to Pz until the data of all the kz views are collected. Therefore, all data on the ky-kz plane can be collected by repeatedly executing the data collection sequence V in the periods P1 to Pz.

  In the scan SC, k-space data is collected after the longitudinal magnetization of the blood is reduced by the MSDE sequence DIF. Therefore, an image having a sufficiently large contrast between blood and the blood vessel wall can be acquired. Also, fat can be suppressed by the ASPIR pulse F. Further, since the ASPIR pulse F is an adiabatic pulse, there is an advantage that it is not easily affected by the nonuniformity of B1.

  However, the longitudinal magnetization Mz of fat inverted by the ASPIR pulse F recovers T1 with time, and the longitudinal magnetization Mz of fat gradually approaches Mz = 1. Therefore, the fat suppression effect of the ASPIR pulse F is high in the first half of the data acquisition period J, but the fat suppression effect of the ASPIR pulse F is reduced in the second half of the data acquisition period J. For this reason, there exists a problem that the artifact by fat tends to appear in an image. Therefore, in this embodiment, in order to cope with this problem, the blood vessel wall is imaged together with the fat suppression method as follows (see FIG. 7).

FIG. 7 is a diagram showing a scan of this embodiment that is executed for imaging a blood vessel wall in combination with the fat suppression method.
The scan SC of this embodiment is common in that the ASPIR pulse F, the MSDE sequence DIF, and the data acquisition sequence V are executed as compared with the normal scan (see FIG. 4). However, the scan SC of this embodiment is different from the normal scan (see FIG. 4) in that, in addition to the data collection sequence V, another data collection sequence W is also executed.

  In this embodiment, after applying the ASPIR pulse F, the MSDE sequence DIF for reducing the longitudinal magnetization of blood is executed. After the MSDE sequence DIF is executed, k-space data is collected. In this embodiment, two data collection periods J1 and J2 for collecting k-space data are provided after the MSDE sequence DIF. The data collection period J1 is a period for collecting data in the low frequency region of the k space, while the data collection period J2 is a period for collecting data in the high frequency region of the k space. Hereinafter, the two data collection periods J1 and J2 will be described (see FIG. 8).

FIG. 8 is an explanatory diagram of the data collection periods J1 and J2.
In the lower left of FIG. 8, a ky-kz plane of k space in which data is collected in the data collection periods J1 and J2 is shown. In the data collection period J1, data of the low frequency region RL1 (white background portion) in the ky direction is collected. On the other hand, in the data collection period J2, data in the high frequency regions RH11 and RH12 (shaded portions) in the ky direction is collected.

  In the data collection period J1, a data collection sequence V for collecting data in the low frequency region RL1 is executed. The data collection sequence V is the same as the data collection sequence used in normal scanning.

  The data acquisition sequence V has a single excitation pulse Q1 for exciting the imaging region. The data acquisition sequence V has gradient magnetic fields applied to the z axis, the y axis, and the x axis. The z-axis, y-axis, and x-axis correspond to the SI direction, AP direction, and RL direction (see FIG. 3), respectively. A slice selection gradient magnetic field G1, a phase encoding gradient magnetic field, and a rewinder are applied to the z-axis. A phase encoding gradient magnetic field and a rewinder are applied to the y-axis. A frequency encoding gradient magnetic field is applied to the x-axis.

  The imaging region is excited by applying the excitation pulse Q1 and the slice selective gradient magnetic field G1. After exciting the imaging region, a gradient magnetic field such as a phase encoding gradient magnetic field and a frequency encoding gradient magnetic field is applied. The phase encoding gradient magnetic field of the data acquisition sequence V is adjusted so that data in the low frequency region RL1 in the ky-kz plane of the k space is acquired. In this embodiment, the data collection period J1 is provided so that the data of the low frequency region RL1 is collected when the longitudinal magnetization of fat reversed by the fat suppression pulse F reaches the null point. Therefore, due to the fat suppression effect of the fat suppression pulse F, data of the low frequency region RL1 in which the fat signal is sufficiently suppressed can be acquired in the data acquisition period J1. Note that the order of collecting data of the low frequency region RL1 in the k space during the data collection period J1 will be described later.

  After the data collection period J1, a data collection sequence W for collecting data in the high frequency regions RH11 and RH12 is executed. FIG. 8 shows an example of the data collection sequence W.

  The data acquisition sequence W has an excitation pulse Q2 for exciting the imaging region. FIG. 8 shows an example in which a SpSp (Spectral Spatial) pulse for selectively exciting water is used as the excitation pulse Q2. The SpSp pulse (excitation pulse) Q2 has a plurality of RF pulses. In the present embodiment, an example is shown in which the SpSp pulse Q2 has five RF pulses having a magnitude along a Gaussian envelope. The data acquisition sequence W has gradient magnetic fields applied to the z axis, the y axis, and the x axis. A slice selection gradient magnetic field G2, a phase encoding gradient magnetic field, and a rewinder are applied to the z-axis. A phase encoding gradient magnetic field and a rewinder are applied to the y-axis. A frequency encoding gradient magnetic field is applied to the x-axis.

  The imaging region is excited by applying the SpSp pulse Q2 and the slice selective gradient magnetic field G2. After exciting the imaging region, a gradient magnetic field such as a phase encoding gradient magnetic field and a frequency encoding gradient magnetic field is applied. The phase encoding gradient magnetic field of the data acquisition sequence W is adjusted so that data of the high frequency regions RH11 and RH12 in the ky-kz plane of the k space is acquired.

  Since the data acquisition sequence W excites the imaging region using the SpSp pulse Q2 that selectively excites the spin of water, the excitation of the fat spin is suppressed even if the imaging region is excited. Therefore, since the fat suppression effect by the SpSp pulse Q2 is exhibited, data of the high frequency regions RH11 and RH12 in which the fat signal is sufficiently suppressed can be obtained in the data collection period J2. Note that the order of collecting data of the high-frequency regions RH11 and RH12 in the k space in the data collection period J2 will be described later.

Although the pulse sequence executed in the period P1 is described in FIG. 8, the ASPIR pulse F, the MSDE sequence DIF, the data acquisition sequence V, and the data acquisition sequence in the other periods P2 to Pz as well as the period P1. W is executed.
Next, the collection order of k-space data in this embodiment will be described.

9 to 12 are explanatory diagrams of the data collection order in this embodiment. Hereinafter, FIGS. 9 to 12 will be described in order.
FIG. 9 is an explanatory diagram when data is collected in the period P1. In FIG. 9, the suffix “1”, “2”,..., “M” is added to the reference sign V in order to distinguish the data collection sequence V executed m times in the data collection period J1. . Further, in order to distinguish the data collection sequence W executed n times during the data collection period J2, the suffix “1”, “2”,.

  In the period P1, first, an ASPIR pulse F for reversing the longitudinal magnetization of fat is applied. The ASPIR pulse F can reverse the longitudinal magnetization of fat in the imaging region. After applying the ASPIR pulse F, the MSDE sequence DIF is executed. After the longitudinal magnetization of blood is reduced by the MSDE sequence DIF, the process proceeds to the data collection period J1.

In the data acquisition period J1, data acquisition sequences V1 to Vm having a single excitation pulse Q1 are executed. Further, in the data collection period J1, the phase encoding gradients of the data collection sequences V1 to Vm are collected so that data DL ₀ of m lattice points located in the low frequency region RL1 is collected on the view of kz = 0. The magnetic field is adjusted. When collecting data DL ₀ of m lattice points, data of lattice points with ky = 0 is first collected, and then lattice points with ky> 0 in order from lattice points closest to the lattice point with ky = 0. And grid point data with ky <0 are collected alternately. After executing the data collection sequences V1 to Vm, the process proceeds to the next data collection period J2.

In the data collection period J2, data collection sequences W1 to Wn having SpSp pulses Q2 that selectively excite water are executed. Also, the data collection period J2, on the view of kz = 0, the data _{DH 01} for d number of grid points located within the high frequency region RH11, located within a high frequency region RH12 (n-d) pieces of grid points as the data DH ₀₂ is collected in the phase encoding gradient magnetic field data acquisition sequence W1~Wn is adjusted. Therefore, in the data collection period J2, data (DH ₀₁ + DH ₀₂ ) of n lattice points located in the high frequency region (RH11 + RH12) are collected. When collecting data of n lattice points (DH ₀₁ + DH ₀₂ ), data of lattice points of ky> 0 and data of lattice points of ky <0 are alternately arranged in order from lattice points close to the low frequency region RL1. Collected.

  Therefore, in the period P1, the data of the view with kz = 0 is collected according to the ky centric order. After collecting view data of kz = 0, the process proceeds to the next period P2 (see FIG. 10).

FIG. 10 is an explanatory diagram when collecting k-space data in the period P2.
In the period P2, as in the period P1, after applying the ASPIR pulse F, the MSDE sequence DIF, the data acquisition sequence V, and the data acquisition sequence W are executed. Dadashi, the data collection period J1, on the view kz = 1, so that the data DL ₁ of the m grid points located within the low-frequency region RL1 is collected, phase encode of the data acquisition sequence V1~Vm The gradient magnetic field is adjusted. When collecting data DL ₁ of m lattice points, data of lattice points with ky = 0 is first collected, and then lattice points with ky> 0 in order from lattice points closest to the lattice point with ky = 0. And grid point data with ky <0 are collected alternately.

Also, the data collection period J2, on the view kz = 1, the data _{DH 11} for d number of grid points located within the high frequency region RH11, located within a high frequency region RH12 (n-d) pieces of grid points as the data DH ₁₂ is collected in the phase encoding gradient magnetic field data acquisition sequence W1~Wn is adjusted. Therefore, in the data collection period J2, data (DH ₁₁ + DH ₁₂ ) of n lattice points located in the high frequency region (RH11 + RH12) are collected. When collecting data of n lattice points (DH ₁₁ + DH ₁₂ ), lattice point data of ky> 0 and lattice point data of ky <0 are alternately arranged in order from the lattice point close to the low frequency region RL1. Collected.

  Therefore, in the period P2, the data of the view with kz = 1 is collected according to the ky centric order. After collecting the view data of kz = 1, the process proceeds to the next period P3 (see FIG. 11).

FIG. 11 is an explanatory diagram for collecting k-space data in the period P3.
In the period P3, as in the period P1, after applying the ASPIR pulse F, the MSDE sequence DIF, the data acquisition sequence V, and the data acquisition sequence W are executed. However, in the data collection period J1, data collection sequences V1 to Vn are collected so that data DL- ₁ of m lattice points located in the low frequency region RL1 is collected on the view of kz = -1. The phase encoding gradient magnetic field is adjusted. When collecting data DL ₋₁ of m lattice points, data of lattice points with ky = 0 is collected first, and then lattice points with ky> 0 in order from lattice points closest to the lattice point with ky = 0. Point data and grid point data with ky <0 are collected alternately.

Further, in the data collection period J2, on the view with kz = −1, d lattice point data DH- ₁₁ located in the high frequency region RH11 and (nd) pieces of data DH- ₁₁ located in the high frequency region RH12. The phase encoding gradient magnetic fields of the data acquisition sequences W1 to Wn are adjusted so that the lattice point data DH- ₁₂ is acquired. Therefore, in the data collection period J2, data (DH- ₁₁ + DH- ₁₂ ) of n lattice points located in the high frequency region (RH11 + RH12) are collected. When collecting data of n lattice points (DH ₋₁₁ + DH ₋₁₂ ), data of lattice points of ky> 0 and data of lattice points of ky <0 are sequentially obtained from the lattice points close to the low frequency region RL1. Collected alternately.

  Therefore, in the period P3, the data of the view of kz = −1 is collected according to the ky centric order. After collecting view data of kz = −1, the process proceeds to the next period P4.

  In the period P4, view data of kz = 2 is collected. After the data of kz = 2 is collected, the process proceeds to a period P5, and the data of the view of kz = -2 is collected. Similarly, data is collected in order from the kz view close to kz = 0 (see FIG. 12).

FIG. 12 is an explanatory diagram when collecting view data of kz = −N.
The view data of kz = −N is collected during the period Pz.
In the period Pz, as in the period P1, after applying the ASPIR pulse F, the MSDE sequence DIF, the data acquisition sequence V, and the data acquisition sequence W are executed. However, in the data collection period J1, the data collection sequences V1 to Vm are collected so that the data DL- _N of m lattice points located in the low frequency region RL1 is collected on the view of kz = -N. The phase encoding gradient magnetic field is adjusted. When collecting data DL- _N of m lattice points, data of lattice points with ky = 0 is collected first, and then lattice points with ky> 0 in order from the lattice points closest to the lattice point with ky = 0. Point data and grid point data with ky <0 are collected alternately.

Further, in the data collection period J2, on the view of kz = −N, data DH− _N1 of d lattice points located in the high frequency region RH11 and (n−d) pieces of data located in the high frequency region RH12. The phase encoding gradient magnetic fields of the data acquisition sequences W1 to Wn are adjusted so that the grid point data DH- _N2 is acquired. Therefore, in the data collection period J2, data (DH _−N1 + DH _−N2 ) of n lattice points located in the high frequency region ( _RH11 + _RH12 ) are collected. When collecting data of n lattice points (DH _−N1 + DH _−N2 ), data of lattice points with ky> 0 and data of lattice points with ky <0 are sequentially obtained from lattice points close to the low frequency region RL1. Collected alternately.
Therefore, in the period Pz, the data of the view of kz = −N is collected according to the ky centric order.

  In this way, all data on the ky-kz plane can be collected. After collecting the k-space data, the image creating means 91 (see FIG. 2) performs image reconstruction based on the data of the low-frequency region RL1 of the k-space and the data of the high-frequency regions RH11 and RH12. An image of the part can be acquired.

  In this embodiment, after applying the fat suppression pulse F, the longitudinal magnetization of blood is reduced by the MSDE sequence DIF, and k-space data is collected. Data collection in the k space is performed in two data collection periods J1 and J2. In the data collection period J1, data of the low frequency region RL1 in the k space is collected. In this embodiment, the data collection period J1 is provided so that the data of the low frequency region RL1 is collected when the longitudinal magnetization of fat reversed by the fat suppression pulse F reaches the null point. Therefore, it is possible to collect data in a low frequency region in which the fat signal is sufficiently suppressed by the fat suppression effect of the fat suppression pulse F.

  However, since the T1 recovery of fat progresses with time, the longitudinal magnetization of fat gradually increases and approaches 1. Therefore, since the degree of T1 recovery is greater in the data collection period J2 than in the data collection period J1, the fat suppression effect of the ASPIR pulse F is reduced in the data collection period J2. For this reason, the ASPIR pulse F exhibits a sufficient fat suppression effect for the data in the low frequency region RL1 collected during the data collection period J1, but the data in the high frequency region collected during the data collection period J2. There is a problem that a sufficient fat suppression effect cannot be exhibited. Therefore, in this embodiment, in order to cope with this problem, in the data collection period J2, the high frequency regions RH11 and RH12 are used using the data collection sequence W (see FIG. 8) having the SpSp pulse Q2 that selectively excites the spin of water. Is collecting data. Since the data collection sequence W excites the imaging region using the SpSp pulse Q2 that selectively excites the spin of water, the excitation of the fat spin is suppressed even if the imaging region is excited. Therefore, during the data collection period J2, the fat suppression effect by the SpSp pulse Q2 is exhibited, so that data of the high frequency regions RH11 and RH12 in which the fat signal is sufficiently suppressed can be obtained.

  In the present embodiment, fat suppression of data in the low frequency region RL1 is performed using the ASPIR pulse F, but fat suppression of data in the high frequency regions RH11 and RH12 is performed using the SpSp pulse Q2. Since the SpSp pulse Q2 is easily affected by B1 nonuniformity, collecting data of the high frequency regions RH11 and RH12 using the SpSp pulse Q2 may cause shading due to nonuniform B1 in the image of the imaging region. . However, in this embodiment, fat suppression of data in the low frequency region is performed using the ASPIR pulse F that is strong against the influence of B1 nonuniformity. Therefore, since the influence of non-uniform B1 is sufficiently reduced in the low-frequency region data, an image with reduced shading can be obtained.

  Note that, if the area of the low frequency region RL1 is too large, the number of data sampling in the data collection period J1 increases, so that it is conceivable that the fat suppression effect of the ASPIR pulse F decreases during the data collection period J1. Therefore, it is desirable to set the area of the low frequency region RL1 in consideration of the duration of the fat suppression effect of the ASPIR pulse F.

  In general, the time width of the SpSp pulse Q2 used in the data acquisition sequence W is longer than the time width of the excitation pulse Q1 used in the data acquisition sequence V. Therefore, the repetition time TRw of the data acquisition sequence W may be longer than the repetition time TRv of the data acquisition sequence V due to the difference in time width between the pulses Q1 and Q2. However, if the repetitive time changes during the scan, it causes image quality degradation. Therefore, when the time width of the SpSp pulse Q2 is longer than the time width of the excitation pulse Q1, it is preferable to set the values of the repetition times TRv and TRw so that the repetition time TRv becomes the same value as the repetition time TRw. .

  In this embodiment, data in the low frequency region RL1 related to the ky direction is collected in the data collection period J1, and data in the high frequency regions RH11 and RH12 related to the ky direction is collected in the data collection period J2. However, the area in which data is collected in the data collection period J1 is not limited to the low frequency area RL1, and data in a different area from the low frequency area RL1 may be collected. Similarly, the area in which data is collected in the data collection period J2 is not limited to the high frequency areas RH11 and RH12, and data in a different area from the high frequency areas RH1 and RH12 may be collected. Two other examples of areas in which data is collected in the data collection periods J1 and J2 are shown below (see FIGS. 13 and 14).

  FIG. 13 is a diagram illustrating an example in which data in the low frequency region RL2 in the kz direction is collected in the data collection period J1, and data in the high frequency regions RH21 and RH22 in the kz direction is collected in the data collection period J2. FIG. 13 shows an example of collecting data in the period P1.

In the data collection period J1, on the view of ky = 0, so that the data DL ₀ of the m grid points located within the low-frequency region RL2 is collected, phase-encoding gradient field data acquisition sequence V1~Vm is Adjusted. When collecting data DL ₀ of m lattice points, data of lattice points of kz = 0 is collected first, and then lattice points of kz> 0 in order from lattice points close to the lattice point of kz = 0. And data of lattice points of kz <0 are collected alternately.

Also, the data collection period J2, on the view of ky = 0, the data _{DH 01} for d number of grid points located within the high frequency region RH21, located within a high frequency region RH22 (n-d) pieces of grid points as the data DH ₀₂ is collected in the phase encoding gradient magnetic field data acquisition sequence W1~Wn is adjusted. Therefore, in the data collection period J2, data (DH ₀₁ + DH ₀₂ ) of n lattice points located in the high frequency region (RH21 + RH22) are collected. When collecting data of n lattice points (DH ₀₁ + DH ₀₂ ), data of lattice points of kz> 0 and data of lattice points of kz <0 are alternately arranged in order from lattice points close to the low frequency region RL1. Collected.

  Therefore, in the period P1, the data of the view with ky = 0 is collected according to the kz centric order.

  In FIG. 13, the data executed in the period P1 is described. However, in the other periods P2 to Pz, the data of each ky view is collected according to the kz centric order as in the period P1. Accordingly, data of all views on the ky-kz plane can be collected.

In the data collection period J1, it is possible to obtain data of the low frequency region RL2 in which the fat signal is sufficiently suppressed by the ASPIR pulse F. In the data collection period J2, data of the high frequency regions RH21 and RH22 in which the fat signal is sufficiently suppressed can be obtained by the SpSp pulse Q2 (see FIG. 8) of the data collection sequence W. Furthermore, since the fat suppression of the data of the low frequency region RL2 is performed using the ASPIR pulse F which is strong against the influence of B1 nonuniformity, an image with sufficiently reduced shading can be obtained.
Next, FIG. 14 will be described.

  FIG. 14 shows that data in the low frequency region RL3 in the two directions of the ky direction and the kz direction is collected in the data collection period J1, and data in the high frequency region RH3 in the two directions of the ky direction and the kz direction is collected in the data collection period J2. It is a figure which shows an example.

  FIG. 14 shows a method (radial fan beam) for collecting data radially from the center of the ky-kz plane. In the data collection period J1, the data collection sequences V1 to Vm are collected so that the data DL of m lattice points located in the low frequency region RL3 are collected in order from the lattice point close to the center C of the ky-kz plane. The phase encoding gradient magnetic field is adjusted.

  In the data collection period J2, the phase encode gradient magnetic fields of the data collection sequences W1 to Wn are adjusted so that the data DH of n lattice points located in the high frequency region RH3 are collected.

  In FIG. 14, the data executed in the period P1 is described. However, in the other periods P2 to Pz, data is collected by the radial fan beam as in the period P1. Therefore, data of the low frequency region RL3 and the high frequency region RH3 on the ky-kz plane can be collected.

  In the data collection period J1, data of the low frequency region RL3 in which the fat signal is sufficiently suppressed can be obtained by the ASPIR pulse F. Further, in the data collection period J2, the data of the high frequency region RH3 in which the fat signal is sufficiently suppressed can be obtained by the SpSp pulse Q2 (see FIG. 8) of the data collection sequence W. Furthermore, since the fat suppression of the data in the low frequency region RL3 is performed using the ASPIR pulse F which is strong against the influence of B1 nonuniformity, an image with sufficiently reduced shading can be obtained. In FIG. 14, since it is not necessary to collect data of lattice points located outside the high frequency region RH3, the scan time can be shortened.

  In addition, although the example which collects data by radial fan beam is shown in FIG. 14, it is also possible to collect data according to the elliptical centric order which collects data spirally from the center of a ky-kz plane.

  In this embodiment, an ASPIR pulse (adiabatic pulse) that performs spin flipping adiabatically is used to suppress fat. However, another fat suppression pulse such as a STIR (Short TI Inversion Recovery) pulse may be used instead of the ASPIR pulse. The ASPIR pulse is an inversion pulse with a flip angle set to 180 °. However, if the fat can be suppressed, the flip angle is not necessarily set to 180 °, and the flip angle may be set to 170 °, for example.

  In the present invention, the SpSp pulse (see FIG. 8) that selectively excites water is used as the excitation pulse of the data acquisition sequence W. However, the excitation pulse of the data acquisition sequence W is not limited to the SpSp pulse as long as the imaging region can be excited so that the fat spin flip angle is smaller than the water spin flip angle. Alternatively, other excitation pulses may be used.

  In this embodiment, an MSDE sequence for suppressing blood signals is executed. However, the present invention is not limited to the example of executing the MSDE sequence. For example, when it is not necessary to suppress the blood signal, the data acquisition sequences V and W may be executed without applying the MSDE sequence after applying the ASPIR pulse F.

  In this embodiment, the data collection sequence V is executed m times in the data collection period J1, but m may be m ≧ 2 or m = 1. In the present embodiment, the data collection sequence W is executed n times in the data collection period J2, but n may be n ≧ 2 or n = 1.

  In this embodiment, data arranged at one grid point is collected by one data collection sequence V, and data arranged at one grid point is collected by one data collection sequence W. However, data arranged at a plurality of grid points may be collected by one data collection sequence V, or data arranged at a plurality of grid points may be collected by one data collection sequence W. .

  In this embodiment, data is collected using a 3D gradient echo sequence, but data may be collected using another 3D sequence. Further, instead of the 3D sequence, the data of the imaging region may be collected using a 2D sequence for collecting slice plane data.

2 Magnet 3 Table 3a Cradle 4 Receiving coil 5 Transmitter 6 Gradient magnetic field power supply 7 Receiver 8 Computer 9 Processor 10 Memory 11 Operation unit 12 Display unit 13 Subject 21 Bore 91 Image creation means 100 MR apparatus

Claims (19)

Scanning means for executing a scan for collecting k-space data from the imaging region of the subject, and image creating means for creating an image of the imaging region based on the k-space data collected by the scanning means A magnetic resonance apparatus comprising:
The scanning means includes
Applying a fat suppression pulse for suppressing the MR signal of fat contained in the imaging region;
A first sequence having a first excitation pulse for exciting the imaging region after the fat suppression pulse is applied, from the imaging region excited by the first excitation pulse; Perform a first sequence to collect data in the low frequency region;
The first sequence is executed at a timing further away from the fat null point in time than the first sequence, and excites the imaging region so that the fat spin flip angle is smaller than the water spin flip angle. A second sequence having two excitation pulses, the second sequence for collecting high-frequency region data of k-space from the imaging region excited by the second excitation pulse,
The image creating means includes
A magnetic resonance apparatus that creates an image of the imaging region based on data in a low frequency region and data in a high frequency region of the k space.   The magnetic resonance apparatus according to claim 1, wherein the fat suppression pulse is an adiabatic pulse.   The magnetic resonance apparatus according to claim 1, wherein the fat suppression pulse is an inversion pulse.   The magnetic resonance apparatus according to claim 1, wherein the second excitation pulse includes a plurality of RF pulses that selectively excite water in the imaging region. The first sequence and the second sequence are:
5. The 3D sequence according to claim 1, wherein the phase encoding gradient magnetic field is applied to the first axis and the second axis, and the frequency encoding gradient magnetic field is applied to the third axis. Magnetic resonance device. The scanning means includes
Performing the first sequence during a first data collection period;
Executing the second sequence in a second data collection period;
The magnetic resonance apparatus according to claim 5. The scanning means includes
Collecting data of m lattice points located in the low frequency region in the ky direction of the ky-kz plane during the first data collection period;
The magnetic resonance apparatus according to claim 6, wherein data of n lattice points located in the high frequency region with respect to a ky direction of a ky-kz plane is collected during the second data collection period. In the first data collection period, data of a first lattice point among the m lattice points is first collected, and then the m pieces are sequentially arranged from a lattice point close to the first lattice point. Collect the data of the remaining grid points of
8. The magnetic resonance apparatus according to claim 7, wherein in the second data collection period, data of the n lattice points are collected in order from lattice points close to the low frequency region.   The magnetic resonance apparatus according to claim 8, wherein the first lattice point is a lattice point with ky = 0.   10. The magnetic resonance apparatus according to claim 7, wherein the m lattice points and the n lattice points are located in the kz view having the same number. 11. The scanning means includes
Collecting data of m lattice points located in the low-frequency region in the kz direction of the ky-kz plane during the first data collection period;
The magnetic resonance apparatus according to claim 6, wherein data of n lattice points located in the high-frequency region with respect to a kz direction of a ky-kz plane is collected during the second data collection period. In the first data collection period, data of a second lattice point among the m lattice points is first collected, and then the m pieces are sequentially arranged from a lattice point close to the second lattice point. Collect the data of the remaining grid points of
12. The magnetic resonance apparatus according to claim 11, wherein in the second data collection period, data of the n lattice points are collected in order from lattice points close to the low frequency region.   The magnetic resonance apparatus according to claim 12, wherein the second lattice point is a lattice point of kz = 0. The m lattice points and the n lattice points are located in the same number ky view.
The magnetic resonance apparatus according to any one of claims 11 to 13. The high frequency region has a first high frequency region and a second high frequency region,
The magnetic resonance apparatus according to claim 1, wherein the low frequency region is located between the first high frequency region and the second high frequency region. The scanning means includes
Collecting data of m lattice points located in the low-frequency region in the ky-kz plane in the ky direction and the two directions in the kz direction during the first data collection period;
The magnetic resonance apparatus according to claim 6, wherein data of n lattice points located in the high-frequency region with respect to the two directions of the ky-kz plane is collected during the second data collection period. The scanning means includes
The magnetic resonance apparatus according to claim 16, wherein data of the m lattice points and the n lattice points are collected in order from the lattice point close to the center of the ky-kz plane.   The magnetic resonance apparatus according to claim 1, wherein the scanning unit executes a third sequence for reducing longitudinal magnetization of blood. A magnetic resonance apparatus for performing a scan for collecting k-space data from an imaging region of a subject, applying a fat suppression pulse for suppressing an MR signal of fat contained in the imaging region, A first sequence having a first excitation pulse for exciting the imaging region after a suppression pulse is applied, from the imaging region excited by the first excitation pulse, to a low frequency in k-space A first sequence for collecting region data is executed, and is executed at a timing further away from the fat null point in time than the first sequence, and the fat spin flip angle is the water spin flip. A second sequence having a second excitation pulse for exciting the imaging region so as to be smaller than an angle, and is excited by the second excitation pulse. A program which is applied to a magnetic resonance apparatus for performing the second sequence for collecting data in a high frequency region of the k-space from the imaging region,
An image creation process for creating an image of the imaging region based on the low-frequency region data and the high-frequency region data of the k-space;
A program that causes a computer to execute.

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