JP2011131000A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus having high accuracy for detecting a position of a site changing accordance with a body movement of a subject. <P>SOLUTION: A first candidate Xm of a diaphragmatic position is detected based on a signal intensity profile, and a second candidate Xp of the diaphragmatic position is detected based on a phase profile. After that, the maximum value Δθmax of the phase difference in the phase profile is compared with the predetermined standard value Δθt, and when the Δθmax is bigger than the Δθt, the second candidate Xp of the diaphragmatic position is determined as the diaphragmatic position X1 for the occasion when a navigator sequence NP1 is performed. Meanwhile, when the Δθmax is equal or smaller than the Δθt, the first candidate Xm of the diaphragmatic position is determined as the diaphragmatic position X1 for the occasion when the navigator sequence NP1 is performed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a magnetic resonance imaging apparatus that collects magnetic resonance signals from an imaging region of a subject.

Conventionally, various methods have been proposed for reducing body motion artifacts due to respiration in imaging with a magnetic resonance imaging apparatus. For example, a method is known in which the position of the diaphragm that is displaced with respiratory motion is detected immediately after the execution of an imaging sequence for collecting imaging region data from a subject. In this method, when the detected diaphragm position is out of a predetermined range, the data is re-acquired assuming that the imaging sequence is executed during a period when the body movement due to respiration is large. Therefore, it is possible to reduce deterioration in image quality due to body motion artifacts.
A Du method is known as a method for detecting the position of the diaphragm used in this method (see Non-Patent Document 1).

Du YP, Saranathan M, Foo TK. An accurate, robust, and computationally efficient navigator algorithm for measuringdiaphragm positions.J Cardiovasc Magn Reson. 2004; 6: 483-490.

  However, the method of Non-Patent Document 1 has a problem that when the liver signal and the blood flow signal flowing in the lung region continuously appear, the detection accuracy of the position of the diaphragm is lowered, and this problem is solved. It is hoped to do.

The first magnetic resonance imaging apparatus comprises:
A navigator sequence for collecting magnetic resonance signals from a navigator area including a predetermined part that is displaced in accordance with body movement of the subject, and an imaging sequence for collecting magnetic resonance signals from the imaging area of the subject Scanning means for performing a first scan for performing,
Means for determining a position of the predetermined portion based on a phase profile of a magnetic resonance signal obtained by performing a navigator sequence in the first scan;
A magnetic resonance imaging apparatus comprising:
The navigator sequence in the first scan has a gradient magnetic field for providing a phase difference between the magnetization of the predetermined portion and the magnetization of the body fluid flowing in the navigator region.

The second magnetic resonance imaging apparatus is
A navigator sequence for collecting magnetic resonance signals from a navigator region including a first part that is displaced in accordance with the body movement of the subject and a second part that is displaced in accordance with the body movement of the subject; Scanning means for performing a scan for performing an imaging sequence for collecting magnetic resonance signals from the imaging region of the specimen;
Means for determining a position of the first part based on a phase profile of a magnetic resonance signal obtained by performing a navigator sequence in the scan;
A magnetic resonance imaging apparatus comprising:
The navigator sequence in the scan has a gradient magnetic field for providing a phase difference between the magnetization of the first part and the magnetization of the second part.

By providing the navigator sequence with a gradient magnetic field for providing a phase difference between the magnetization of the predetermined part and the magnetization of the body fluid flowing in the navigator region, it becomes easy to distinguish the predetermined part from the body fluid, The detection accuracy of the position of a predetermined part can be improved.
Further, by providing the navigator sequence with a gradient magnetic field for providing a phase difference between the magnetization of the first part and the magnetization of the second part, the magnetization of the first part is distinguished from the second part. It becomes easy to do, and the detection accuracy of the position of the 1st part can be raised.

1 is a diagram showing a magnetic resonance imaging apparatus 1 according to an embodiment of the present invention. It is explanatory drawing of the scan performed when imaging the subject. It is a figure which shows a scanning area | region. 6 is a diagram showing an example of an MR image for region setting displayed on the display device 12. FIG. It is a figure explaining the processing flow until the position of a diaphragm is detected. It is a figure explaining the procedure of a process of navigator data. It is a position profile which shows the position of the diaphragm during navigator sequence NP1-NP. It is a figure which shows an experimental result. It is a figure which shows an example of the navigator sequence of a 90 degree-180 degree line excitation spin echo type | mold.

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

FIG. 1 is a diagram showing a magnetic resonance imaging apparatus 1 according to an embodiment of the present invention.
A magnetic resonance imaging (MRI) apparatus 1 includes a magnetic field generator 2, a table 3, a cradle 4, a receiving coil 5, and the like.

  The magnetic field generator 2 includes a bore 21 in which the subject 13 is accommodated, a superconducting coil 22, a gradient coil 23, and a transmission coil 24. The superconducting coil 22 applies a static magnetic field B0, and the gradient coil 23 applies a gradient magnetic field in the frequency encoding direction, the phase encoding direction, and the slice selection direction. The transmission coil 24 transmits an RF pulse. In this embodiment, the superconducting coil 22 is used, but a permanent magnet may be used instead of the superconducting coil 22.

  The cradle 4 is configured to be movable from the table 3 to the bore 21. The subject 13 is transported to the bore 21 by the cradle 4.

  The receiving coil 5 is attached from the chest to the abdomen of the subject 13. The reception coil 5 receives a magnetic resonance signal generated from the subject 13 when an imaging sequence and a navigator sequence described later are executed.

  The MRI apparatus 1 further includes a sequencer 6, a transmitter 7, a gradient magnetic field power supply 8, a receiver 9, a central processing unit 10, an input device 11, and a display device 12.

  Under the control of the central processing unit 10, the sequencer 6 receives information for executing a navigator sequence for obtaining the position of the diaphragm and an imaging sequence for collecting image data of the subject 13, the transmitter 7 and Send to gradient magnetic field power supply 8. Specifically, under the control of the central processing unit 10, the sequencer 6 sends RF pulse information (center frequency, bandwidth, etc.) of the navigator sequence and the imaging sequence to the transmitter 7, and information on the gradient magnetic field (gradient). The intensity of the magnetic field) is sent to the gradient magnetic field power supply 8.

  The transmitter 7 outputs a drive signal for driving the transmission coil 24 based on the information sent from the sequencer 6.

  The gradient magnetic field power supply 8 outputs a drive signal for driving the gradient coil 23 based on the information sent from the sequencer 6.

  The receiver 9 processes the magnetic resonance signal received by the receiving coil 5 and transmits it to the central processing unit 10.

  The central processing unit 10 implements various operations of the MRI apparatus 1 such as transmitting necessary information to the sequencer 6 and the display unit 12 and reconstructing an image based on a signal received from the receiver 9. The operation of each part of the MRI apparatus 1 will be summarized. The central processing unit 10 is configured by, for example, a computer. The central processing unit 10 is an example of a means for obtaining the position of a predetermined part described in the means for solving the problem, and functions as this means by executing a predetermined program.

  The input device 11 inputs various commands to the central processing unit 10 in response to the operation of the operator 14. The display device 12 displays various information.

  A combination of the magnetic field generator 2, the sequencer 6, the transmitter 7, and the gradient magnetic field power supply 8 corresponds to the scanning means described in the means for solving the problem.

  Next, scanning executed when the subject 13 is imaged in the present embodiment will be described.

  FIG. 2 is an explanatory diagram of a scan executed when the subject 13 is imaged, and FIG. 3 is a diagram showing a scan area.

In the present embodiment, after the pre-scan is executed, the main scan is executed.
The pre-scan is a scan executed to determine an allowable range AW (see FIG. 7) of the diaphragm position described later. The allowable range AW of the diaphragm position will be described later.

In the pre-scan, the navigator sequence NP _i (i = 1 to r) is executed. The navigator sequence NP _i is a sequence executed to detect the position of the diaphragm. FIG. 2 shows a cylindrical gradient echo type navigator sequence as an example of the navigator sequence NP _i . xgrad represents a gradient magnetic field applied in the x-axis direction, ygrad represents a gradient magnetic field applied in the y-axis direction, zgrad represents a gradient magnetic field applied in the z-axis direction, and RF represents a high-frequency pulse.

In the navigator sequence NP _i , when an RF pulse is transmitted, a region is linearly selected by applying a gradient magnetic field so that the polarities alternately and continuously change in the y direction and the z direction. In the present embodiment, slice selection is performed on a linear navigator region Rna (see FIG. 3) that straddles the liver 13a, the diaphragm 13b, and the lung 13c. Thereafter, a reading gradient magnetic field is applied in the x direction, and navigator data is collected. The navigator sequence NP _i has bipolar gradients G1 and G2 in ygrad. The bipolar gradients G1 and G2 are gradient magnetic fields for providing a phase difference φ between the magnetization of the liver 13a and the diaphragm 13b and the magnetization of the blood 13d flowing on the lung 13c side. The phase difference φ is given by the following equation.
φ = γA · Ti · v (1)
Where γ: Gyromagnetic ratio
A: Area of each lobe of bipolar gradients G1 and G2
Ti: Time from the center of the gradient G1 lobe to the center of the gradient G2 lobe
v: Blood flow velocity

For example, considering the blood flow flowing at a blood flow velocity v = 10 cm / s, the phase difference φ≈180 degrees can be obtained by setting the area A = 3900 us · G / cm and the time Ti = 3 ms. The reason why the bipolar gradients G1 and G2 are provided in the navigator sequence NP _i will be described later.

In this scan, an imaging sequence IS _j (j = 1 to n) for collecting imaging data of an area (hereinafter referred to as “imaging area”) Rim (see FIG. 3) that is actually imaged, and the position of the diaphragm Navigator sequence NM _j (j = 1 to n) is detected. The navigator sequence NM _j is the same sequence as the navigator sequence NP _i executed in the pre-scan.

  Below, the operation | movement at the time of imaging the test subject 13 using the magnetic resonance imaging apparatus 1 of this embodiment is demonstrated.

  First, the operator 14 acquires an MR image for region setting used for setting the navigator region Rna and the imaging region Rim. The operator 14 operates the input device 11 to acquire a region setting MR image and inputs a scan execution command for acquiring the region setting MR image. When this execution command is input, a scan for acquiring a region setting MR image is executed, and the region setting MR image is displayed on the display device 12 (see FIG. 4).

FIG. 4 is a diagram illustrating an example of an MR image for region setting displayed on the display device 12.
The display device 12 displays a region setting MR image 121. In FIG. 4, a coronal image is displayed as the region setting MR image 121. The operator 14 operates the input device 11 to set the navigator region Rna in the region setting MR image 121. In the present embodiment, a linear area extending over the liver 13a, the diaphragm 13b, and the lung 13c is set as the navigator area Rna.

  Further, the operator 14 operates the input device 11 to set slices SL1 to SLz for setting the imaging region Rin in the MR image 121 for region setting. By inputting the slices SL1 to SLz, the range of the slices SL1 to SLz is set as the imaging region Rim.

  The region setting MR image 121 used for setting the navigator region Rna and the imaging region Rim may be an axial section or a sagittal section in addition to the coronal section.

  After setting the navigator area Rna and the imaging area Rim, the operator 14 inputs an execution command for executing the pre-scan and the main scan. When this execution command is input, a pre-scan and a main scan are executed (see FIG. 2). Hereinafter, the operation of the MRI apparatus in the pre-scan and the operation of the MRI apparatus in the main scan will be described in order.

(1) Operation of MRI apparatus 1 in prescan In navigator sequence NP _i (i = 1 to r) is executed in prescan (see FIG. 2). In this case, MRI device 1, based on the navigator data collected by executing the navigator sequence NP _i, detects the position of the diaphragm at the time when the navigator sequence NP _i is executed. Hereinafter, a processing flow when the MRI apparatus 1 detects the position of the diaphragm will be described.

  FIG. 5 is a diagram illustrating a processing flow until the position of the diaphragm is detected. 5 will be described with reference to FIG.

  First, in step S1, a navigator sequence NP1 is executed (see FIG. 6A). By executing the navigator sequence NP1, navigator data is collected from the navigator region Rna. After the navigator sequence NP1 is executed, the process proceeds to step S2.

  In step S2, a one-dimensional inverse Fourier transform is performed on the navigator data collected from the navigator region Rna. After performing the one-dimensional inverse Fourier transform, the process proceeds to step S3.

  In step S3, the position of the diaphragm 13b of the subject 13 is detected based on the navigator data. Since step S3 has sub-steps S31 to S37, each sub-step will be described in turn.

  First, in sub-step S31, a signal intensity profile of navigator data obtained from the navigator area Rna is created (see FIG. 6B).

FIG. 6B is a diagram showing a signal intensity profile.
The horizontal axis of the signal intensity profile indicates the position X in the head-to-tail direction of the navigator region Rna, and the vertical axis indicates the signal intensity SM of the navigator data. In the signal intensity profile of FIG. 6B, the left side with a high signal intensity corresponds to the liver side, and the right side with a low signal intensity corresponds to the lung side. After creating the signal signal strength profile, the process proceeds to sub-step S32.

  In sub-step S32, in the signal intensity profile shown in FIG. 6B, the position Xm where the intensity changes abruptly is detected as the first candidate for the position of the diaphragm 13b. In the present embodiment, the position Xm at which the intensity changes rapidly is detected by the Du method, but another method other than the Du method may be used. After detecting the first candidate Xm at the position of the diaphragm 13b, the process proceeds to sub-step S33.

  In sub-step S33, a phase profile of navigator data obtained from the navigator region Rna is created (see FIG. 6C).

FIG. 6C shows a phase profile.
The horizontal axis of the phase profile indicates the position X in the head-to-tail direction of the navigator region Rna, and the vertical axis indicates the phase P of the navigator data. Referring to the phase profile, there is a position Xp where the phase changes abruptly. As described above, the navigator sequence NP _i has the bipolar gradients G1 and G2 for providing the phase difference φ between the magnetization of the liver 13a and the diaphragm 13b and the magnetization of the blood 13d flowing on the lung 13c side. Therefore (see FIG. 2), the position Xp where the phase changes abruptly is considered to be highly likely to be the position of the diaphragm 13b. Therefore, in the present embodiment, the position Xp where the phase P changes abruptly is detected as the second candidate for the position of the diaphragm 13b. Detection of the position Xp at which the phase P changes rapidly is performed in sub-steps S34 to S36. Below, each substep is demonstrated.

  In sub-step S34, a range to be analyzed for detecting the position Xp where the phase P changes rapidly is set with respect to the horizontal axis of the phase profile. In the present embodiment, a range Δx is set as a range to be analyzed in order to detect the position Xp where the phase P changes rapidly. Note that an analysis for detecting the position Xp where the phase P changes suddenly over the entire range of the phase profile may be performed without setting the range Δx. However, since the position Xp at which the phase P changes suddenly may appear at a position far away from the actual position of the diaphragm, when the analysis is performed over the entire range of the phase profile, the detected position Xp is , It may not necessarily correspond to the actual position of the diaphragm. Therefore, in the present embodiment, the range to be analyzed for detecting the position Xp where the phase P changes rapidly is limited to the range Δx. In the present embodiment, the range Δx is a range of a predetermined length Δx (for example, 3 cm) from the first candidate Xm at the position of the diaphragm 13b to the liver side. After setting the range Δx, the process proceeds to sub-step S35.

In sub-step S35, first, as shown in FIG. 6 (d), in the range [Delta] x, consider the position of two adjacent pixels _{X k} and _{X k + 1 (k = 1~m} -1), at the position _{X k} A phase difference Δθk between the pixel and the pixel at the position X _{k + 1} is calculated. After calculating the phase difference Δθk, the maximum value Δθmax of the phase difference Δθk is obtained. In FIG. 6 (d), the pixel at position _{X p,} the phase difference Δθp between the pixel at position _{X p + 1,} the maximum value Derutashitamax. Accordingly, the pixel position Xp at which the phase difference Δθp appears is the position Xp at which the phase P changes rapidly. This position Xp is detected as a second candidate for the position of the diaphragm 13b. After the second candidate at the position of the diaphragm 13b is detected, the process proceeds to sub-step S36.

In sub-step S36, the maximum value Δθmax is compared with a predetermined reference value Δθt, and the position of the diaphragm 13b is selected from the two candidates (Xm and Xp) for the position of the diaphragm 13b based on the comparison result. Determine the candidates to be adopted. In the present embodiment, the reference value Δθt is a value that can be obtained empirically, for example, as a phase difference between the magnetization of the liver or diaphragm and the magnetization of blood flowing to the lung side. The value of the reference value Δθt is, for example, 30 degrees. When Δθmax> Δθt, the second candidate Xp at the position of the diaphragm 13b detected using the phase profile is more likely to be the position of the diaphragm than the first candidate Xm at the position of the diaphragm 13b detected using the intensity profile. Is determined to be high, and the second candidate Xp at the position of the diaphragm 13b is determined as the diaphragm position X1 when the navigator sequence NP1 is executed. On the other hand, in the case of Δθmax ≦ Δθt, the first candidate Xm of the position of the diaphragm 13b detected using the intensity profile is more in the position of the diaphragm than the second candidate Xp of the position of the diaphragm 13b detected using the phase profile. It is determined that the possibility is high, and the first candidate Xm at the position of the diaphragm 13b is determined as the diaphragm position X1 when the navigator sequence NP1 is executed. In the present embodiment, it is assumed that Δθmax> Δθt. Therefore, the diaphragm position X1 = Xp is determined.
As described above, the flow ends.

  5 and 6, the procedure for obtaining the diaphragm position X1 when the navigator sequence NP1 is executed has been described. However, the diaphragm positions X2 to Xr when the other navigator sequences NP2 to NPr are executed are described. Is also obtained according to the flow shown in FIG. Therefore, the position of the diaphragm when the navigator sequences NP1 to NPr are executed can be obtained (see FIG. 7).

FIG. 7 is a position profile showing the position of the diaphragm while the navigator sequences NP1 to NPr are being executed.
The horizontal axis of the position profile represents the navigator sequences NP1 to NPr, and the vertical axis represents the diaphragm positions X1 to Xr when the navigator sequences NP1 to NPr are executed.

  The central processing unit 10 determines the maximum exhalation position Xe, which is the position of the diaphragm 13b when the subject 13 has exhaled, based on the position profile. As a method for determining the maximum expiratory position Xe, for example, a method of determining, as the maximum expiratory position Xe, a position where the coordinate is maximum (minimum depending on how the coordinates are taken) in the position profile. Can be considered.

  After determining the maximum exhalation position Xe, based on the maximum exhalation position Xe, an allowable range AW of the position of the diaphragm when the body movement due to breathing of the subject is small is set. The width of the AW is, for example, in a range of ± 2 mm with the maximum exhalation position Xe as the center.

  As described above, the allowable range AW of the position of the diaphragm when the body movement due to breathing of the subject is small is set.

  When the allowable range AW of the diaphragm position is set, the pre-scan shifts to the main scan (see FIG. 6A).

(2) Operation of the MRI apparatus 1 in the main scan In the main scan, first, the imaging sequence IS _j (j = 1 to n) is executed, and immediately thereafter, the navigator sequence NM _j is executed. When the navigator sequence NM _j is executed, the diaphragm position X ′ _j when the navigator sequence NM _j is executed is calculated in the same procedure as the flow shown in FIG. When the diaphragm position X ′ _j is included in the allowable range AW of the diaphragm position shown in FIG. 7, it is determined that the imaging data collected in the imaging sequence IS _j was collected while the body movement due to respiration was small. And used as data for filling the k-space. On the other hand, when the diaphragm position X ′ _j deviates from the allowable range AW of the diaphragm position shown in FIG. 7, it is determined that the imaging data collected in the imaging sequence IS _j was collected while body movement due to respiration was large. In the next imaging sequence IS _{j + 1} , the data is re-acquired.
The main scan is executed as described above.

According to this embodiment, the navigator sequence NP _i in the pre-scan and the navigator sequence NM _j in the main scan have a phase difference φ between the magnetization of the liver 13a and the diaphragm 13b and the magnetization of the blood 13d flowing toward the lung 13c. Bipolar gradients G1 and G2 are provided (see FIG. 2). Therefore, by referring to the phase profile, it becomes easy to distinguish between the diaphragm and the blood flowing in the lung side region, and there is an effect that the detection accuracy of the position of the diaphragm can be improved. Experiments were performed to demonstrate that this effect was obtained. The experimental conditions are as follows.
(1) Ti = 300us (refer to formula (1))
(2) A = 2000us · G / cm (See formula (1))
(3) Δx = 4 cm (see FIG. 6C)
(4) Δθt = 0.2 rad (see sub-step S36 in FIG. 5)

FIG. 8 is a diagram showing experimental results.
FIG. 8A shows the position of the diaphragm determined based only on the signal intensity profile, and FIG. 8B shows the position of the diaphragm determined based on both the signal intensity profile and the phase profile. FIG.

  Referring to FIG. 8, it can be seen that the amplitude of the curve C representing the position of the diaphragm is more stable and the detection accuracy is higher in FIG. 8B than in FIG. 8A.

  In the present embodiment, the bipolar gradients G1 and G2 are applied to the gradient magnetic field ygrad (see FIG. 2). However, the bipolar gradients G1 and G2 may be applied to the gradient magnetic field xgrad or may be applied to the gradient magnetic field zgrad. The bipolar gradients G1 and G2 may be applied to two or more gradient magnetic fields among the gradient magnetic fields xgrad, ygrad, and zgrad.

  In the present embodiment, bipolar gradients G1 and G2 are applied in order to provide a phase difference φ between the magnetization of the liver 13a and the diaphragm 13b and the magnetization of the blood 13d flowing on the lung 13c side. However, if the phase difference φ can be provided between the magnetization of the liver 13a and the diaphragm 13b and the magnetization of the blood 13d flowing in the lung 13c, the bipolar gradients G1 and G2 may be applied multiple times. A different gradient magnetic field different from the bipolar gradients G1 and G2 may be applied.

  In the present embodiment, a cylindrical gradient echo type navigator sequence is shown as an example of the navigator sequence (see FIG. 2). However, in the present invention, the navigator sequence is not limited to the cylindrical gradient echo type, and may be another navigator sequence. An example of another navigator sequence will be described below (see FIG. 9).

FIG. 9 is a diagram showing an example of a 90 ° -180 ° linearly excited spin echo navigator sequence.
The navigator sequence shown in FIG. 9 has a 90 ° RF pulse and a 180 ° RF pulse. The 90 ° RF pulse is an RF pulse for exciting the first slice by 90 °, and the 180 ° RF pulse is an RF pulse for exciting the second slice that intersects the first slice by 180 °. . The position of the diaphragm can be detected by collecting spin echoes generated from the intersection between the first slice and the second slice.

In the navigator sequence shown in FIG. 9, two gradient magnetic fields Ga and Gb are applied to zgrad. The two gradient magnetic fields Ga and Gb are gradient magnetic fields for providing a phase difference φ between the magnetization of the liver 13a and the diaphragm 13b and the magnetization of the blood 13d flowing toward the lung 13c. In FIG. 9, since the 180 ° RF pulse is transmitted between the gradient magnetic field Ga and the gradient magnetic field Gb, the gradient magnetic fields Ga and Gb have the same polarity. In FIG. 9, the gradient magnetic fields Ga and Gb are positive in polarity, but may be negative in polarity. Since the two gradient magnetic fields Ga and Gb can provide a phase difference φ between the magnetization of the liver 13a and the diaphragm 13b and the magnetization of the blood 13d flowing toward the lung 13c, the detection accuracy of the position of the diaphragm is increased. Can do.
As described above, the present invention can be applied to various navigator sequences.

  In carrying out the present invention, the present invention is not limited to the above-described embodiment, and various modifications can be employed.

  In the present embodiment, pre-scanning is performed before the main scanning. However, the present invention can also be applied when no pre-scan is performed. For example, when the allowable range AW (see FIG. 7) of the diaphragm position is known in advance, the main scan may be performed without performing the pre-scan.

  In this embodiment, the position of the diaphragm is detected using the intensity profile and the phase profile. However, the present invention is not limited to this, and the position of the diaphragm may be detected using only the phase profile.

In the present embodiment, in the main scan, the navigator sequence NM _j is performed immediately after the imaging sequence IS _j is performed. However, the order of each sequence in the main scan is not limited to this. For example, the imaging sequence IS _j may be performed immediately after the navigator sequence NM _j is performed.

  In the present embodiment, the allowable range AW of the diaphragm position when the body movement due to breathing of the subject is small is determined based on the maximum exhalation position Xe, but is not limited to this. For example, the allowable range AW of the position of the diaphragm when the body movement due to breathing of the subject is small may be determined based on the maximum inspiration position that is the position of the diaphragm 13b when the subject 13 has finished breathing. .

  In this embodiment, the predetermined portion that is displaced along with the body movement of the subject is the diaphragm, but of course, the present invention is not limited to this, and any other portion may be used as long as it is a portion that is displaced along with the body movement of the subject. There may be. For example, it may be a liver, a body surface, a heart, or the like. In this embodiment, the body fluid flowing in the navigator region is blood, but body fluid other than blood (for example, cerebrospinal fluid) may be used.

  In the present embodiment, the navigator region Rna is provided in a region straddling the liver 13a, the diaphragm 13b, and the lung 13c (see FIG. 3), but is not limited to this region. For example, the navigator region may be provided so as to straddle the liver 13a, the diaphragm 13b, and the heart 13e. In this case, the navigator sequence may be provided with a gradient magnetic field G for providing a phase difference between the magnetization of the diaphragm 13b (and the liver 13a) and the magnetization of the heart 13e. Since there is a large difference between the displacement speed when the diaphragm 13b (and the liver 13a) is displaced and the displacement speed when the heart 13e is displaced, the gradient profile G can be included in the phase profile by providing the navigator sequence with the gradient magnetic field G. The position Xp ′ where the phase changes abruptly appears. Therefore, the position of the diaphragm 13b can be obtained by detecting the position Xp ′. In this case, the central processing unit 10 functions as an example of a means for obtaining the position of the first part described in the means for solving the problem. As described above, in the present invention, the first part (for example, the diaphragm 13b) that is displaced by the body movement of the subject is distinguished from the second part (for example, the heart 13e) that is displaced by the body movement of the subject. It can also be applied to.

DESCRIPTION OF SYMBOLS 1 MRI apparatus 2 Magnetic field generator 3 Table 4 Cradle 5 Receiving coil 6 Sequencer 7 Transmitter 8 Gradient magnetic field power supply 9 Receiver 10 Central processing unit 11 Input device 12 Display device 13 Subject 14 Operator 21 Bore 22 Superconducting coil 23 Gradient coil 24 Transmitting coil

Claims (12)

A navigator sequence for collecting magnetic resonance signals from a navigator area including a predetermined part that is displaced in accordance with body movement of the subject, and an imaging sequence for collecting magnetic resonance signals from the imaging area of the subject Scanning means for performing a first scan for performing,
Means for determining a position of the predetermined portion based on a phase profile of a magnetic resonance signal obtained by performing a navigator sequence in the first scan;
A magnetic resonance imaging apparatus comprising:
The magnetic resonance imaging apparatus, wherein the navigator sequence in the first scan includes a gradient magnetic field for providing a phase difference between the magnetization of the predetermined part and the magnetization of the body fluid flowing in the navigator region. The means for obtaining the position of the predetermined part is
The magnetic resonance imaging apparatus according to claim 1, wherein a phase difference between adjacent pixels in the phase profile is calculated, and a position of the predetermined part is obtained based on the calculated phase difference. The means for obtaining the position of the predetermined part is
First detection means for detecting a first candidate for the position of the predetermined portion based on a signal intensity profile of a magnetic resonance signal obtained by performing a navigator sequence in the first scan;
Second detection means for detecting a second candidate for the position of the predetermined part based on the phase profile;
Determining means for determining one of the first candidate and the second candidate as the position of the predetermined part;
The magnetic resonance imaging apparatus according to claim 1, comprising: The second detection means includes
4. The magnetic resonance according to claim 3, wherein a phase difference between adjacent pixels in the phase profile is calculated, and a position of a predetermined pixel when the calculated phase difference reaches a maximum value is detected as the second candidate. Imaging device. The means for obtaining the position of the predetermined part is
The magnetic resonance imaging apparatus according to claim 4, further comprising an analysis range setting unit that sets a range to be analyzed for detecting the position of the predetermined pixel with respect to the phase profile. The scanning means includes
Before performing the first scan, perform a second scan that repeatedly executes the navigator sequence,
The means for obtaining the position of the predetermined part is
6. The magnetic resonance according to claim 1, wherein a position of the predetermined portion is obtained based on a phase profile of a magnetic resonance signal obtained by executing a navigator sequence in the second scan. Imaging device. The navigator sequence in the second scan is:
The magnetic resonance imaging apparatus according to claim 6, further comprising a gradient magnetic field for providing a phase difference between the magnetization of the predetermined part and the magnetization of blood flowing in the second part.   8. The magnetic resonance imaging apparatus according to claim 6, further comprising a position profile creating unit that creates a position profile representing the position of the predetermined part obtained in the second scan. 9.   The magnetic resonance imaging apparatus according to claim 8, further comprising a range setting unit that sets a range of a position of the predetermined part when body movement due to breathing of the subject is small based on the position profile. When the position of the predetermined part obtained in the first scan is included in the range set by the range setting means, the data obtained by the imaging scan is adopted as data for filling the k space,
When the position of the predetermined part obtained in the first scan is out of the range set by the range setting means, the data obtained by the imaging scan is not adopted as data for filling the k space. The magnetic resonance imaging apparatus according to claim 9.   The magnetic resonance imaging apparatus according to claim 1, wherein the predetermined part is a diaphragm or a liver, and the body fluid is blood. A navigator sequence for collecting magnetic resonance signals from a navigator region including a first part that is displaced in accordance with the body movement of the subject and a second part that is displaced in accordance with the body movement of the subject; Scanning means for performing a scan for performing an imaging sequence for collecting magnetic resonance signals from the imaging region of the specimen;
Means for determining a position of the first part based on a phase profile of a magnetic resonance signal obtained by performing a navigator sequence in the scan;
A magnetic resonance imaging apparatus comprising:
The magnetic resonance imaging apparatus, wherein the navigator sequence in the scan has a gradient magnetic field for providing a phase difference between the magnetization of the first part and the magnetization of the second part.