JP2008148918A - Mri system and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an MRI system and its control method of securely doing breathing-synchronized imaging concerning a subject organ. <P>SOLUTION: The system is provided with an imaging means that does breathing-synchronized imaging at a predetermined breathing depth concerning the imaging position preset up on a scout image acquired while breathing keeps interrupted, and a control means that controls the process. The control means requests the imaging means to show the breathing depth (X1) when imaging is done with breathing keeps interrupted, and modify the imaging position in accordance with differences between the breathing depth (X2) at the breathing-synchronized imaging time and the breathing depth (X1) when imaging is done with breathing interrupted (105). The breathing depth is obtained from a one-dimensional profile reconstructed by a navigator echo. The imaging position is a place where the coronary artery exists. The breathing-synchronized imaging is done, using cardiogram synchronization together. The breathing-synchronized imaging with cardiogram synchnization used together is done through 3D scanning. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an MRI (Magnetic Resonance Imaging) apparatus and a control method therefor, and in particular, with respect to an imaging position set on a scout image obtained by breath-hold imaging, respiratory synchronization imaging is performed at a predetermined respiration depth. The present invention relates to an MRI apparatus to be performed and a control method thereof.

When imaging the heart, lung field, abdomen, and the like with the MRI apparatus, respiratory synchronization imaging is performed in order to eliminate the influence of body movement. That is, magnetic resonance signals are collected while monitoring the respiration of the subject, and an image is reconstructed using the magnetic resonance signals obtained at a predetermined respiration phase. For the detection of the respiratory phase, a one-dimensional profile reconstructed from a navigator echo is used (for example, see Patent Document 1).
JP 2004-202043 A

  The imaging position is set in advance on the scout image. Although the scout image is captured in the breath holding state, the depth of breathing at the time of breath holding does not necessarily coincide with the depth of breathing at the time of breathing synchronization imaging. For this reason, at the time of respiratory synchronous imaging, the target tissue may deviate from the imaging position set on the scout image, and imaging may not be performed correctly.

  Accordingly, an object of the present invention is to realize an MRI apparatus that reliably performs respiratory synchronization imaging on a target tissue and a control method thereof.

  In one aspect of the invention for solving the above-described problem, an imaging means for performing respiratory synchronization imaging at a predetermined breathing depth for an imaging position set on a scout image obtained by breath-holding imaging, and An MRI apparatus having control means for controlling, wherein the control means causes the imaging means to obtain a breathing depth at the time of breath-hold imaging, and a breathing depth at the time of breath-synchronous imaging. An MRI apparatus characterized in that an imaging position is corrected in accordance with a difference in breathing depth.

  In another aspect of the invention for solving the above-described problem, an MRI apparatus that performs respiration-synchronized imaging at a predetermined respiration depth for an imaging position set on a scout image obtained by breath-holding imaging is controlled. A method for causing an MRI apparatus to obtain a breathing depth at the time of breath-hold imaging and to correct an imaging position according to a difference between a breathing depth at the time of breath-synchronous imaging and a breathing depth at the time of breath-holding imaging. This is a method for controlling an MRI apparatus.

It is preferable that the depth of respiration is obtained based on a one-dimensional profile reconstructed from navigator echoes from the viewpoint of appropriately obtaining the respiration depth.
The imaging position is preferably a position where a coronary artery is present from the viewpoint of obtaining an image for coronary artery diagnosis.

The breath-synchronized imaging is preferably performed using electrocardiographic synchronization in terms of improving image quality.
It is preferable in terms of obtaining a 3D image that the respiratory synchronization imaging combined with the electrocardiographic synchronization is performed by a 3D scan.

  According to the present invention, the MRI apparatus includes: an imaging unit that performs breathing synchronous imaging at a predetermined breathing depth with respect to an imaging position set on a scout image obtained by breath-holding imaging; and a control unit that controls the imaging unit. And the control unit causes the imaging unit to obtain a breathing depth at the time of breath-hold imaging, and performs imaging according to a difference between a breathing depth at the time of breath-synchronous imaging and a breathing depth at the time of breath-holding imaging. Since the position is corrected, it is possible to realize an MRI apparatus that reliably performs respiratory synchronous imaging of a target tissue and a control method thereof.

  The best mode for carrying out the invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the best mode for carrying out the invention. FIG. 1 shows a block diagram of the MRI apparatus. This apparatus is an example of the best mode for carrying out the invention. An example of the best mode for carrying out the invention related to the MRI apparatus is shown by the configuration of the apparatus. An example of the best mode for carrying out the invention relating to the control method of the MRI apparatus is shown by the operation of this apparatus.

  As shown in the figure, this apparatus has a magnet system 100. The magnet system 100 includes a main magnetic field coil unit 102, a gradient coil unit 106, and an RF (radio frequency) coil unit 108. Each of these coil portions has a substantially cylindrical shape and is arranged coaxially with each other.

  A subject 1 is mounted on a cradle 500 in a lying state in an internal space (bore) of the magnet system 100, and is carried in and out by a conveying means (not shown). The main magnetic field coil unit 102 forms a static magnetic field in the internal space of the magnet system 100. The direction of the static magnetic field is substantially parallel to the direction of the body axis of the subject 1. That is, a so-called horizontal magnetic field is formed. The main magnetic field coil unit 102 is configured using, for example, a superconducting coil. In addition, you may comprise using not only a superconductive coil but a normal conductive coil.

  The magnet system may be a vertical magnetic field type in which the direction of the static magnetic field is perpendicular to the body axis of the subject 1 instead of the horizontal magnetic field type. In the vertical magnetic field method, for example, a permanent magnet is used.

  The gradient coil section 106 generates three gradient magnetic fields for giving a gradient to the static magnetic field strength in the directions of three axes perpendicular to each other, that is, the slice axis, the phase axis, and the frequency axis.

  When the coordinate axes perpendicular to each other in the static magnetic field space are x, y, and z, any of the axes can be a slice axis. In that case, one of the remaining two axes is a phase axis, and the other is a frequency axis. In addition, the slice axis, the phase axis, and the frequency axis can have arbitrary inclinations with respect to the x, y, and z axes while maintaining the perpendicularity therebetween. In this apparatus, the body width direction of the subject 1 is the x direction, the body thickness direction is the y direction, and the body axis direction is the z direction.

  The gradient magnetic field in the slice axis direction is also called a slice gradient magnetic field. The gradient magnetic field in the phase axis direction is also referred to as a phase encode gradient magnetic field. The gradient magnetic field in the frequency axis direction is also referred to as a read out gradient magnetic field. The readout gradient magnetic field is synonymous with the frequency encoding gradient magnetic field. In order to make it possible to generate such a gradient magnetic field, the gradient coil unit 106 has three gradient coils. Hereinafter, the gradient magnetic field is also simply referred to as a gradient.

  The RF coil unit 108 forms an RF magnetic field for exciting spins in the body of the subject 1 in the static magnetic field space. Hereinafter, forming the RF magnetic field is also referred to as transmission of an RF excitation signal. The RF excitation signal is also referred to as an RF pulse.

  An electromagnetic wave generated by the excited spin, that is, a magnetic resonance signal is received by the RF coil unit 108. The RF coil unit 108 may have a separate transmission system and reception system. The magnetic resonance signal is a sampling signal for a frequency domain, that is, a Fourier space.

  If the magnetic resonance signal is encoded in two axes by the gradient in the phase axis direction and the frequency axis direction, the magnetic resonance signal is obtained as a sampling signal for the two-dimensional Fourier space, and the encoding is performed in three axes using the slice gradient. Is obtained as a signal for a three-dimensional Fourier space. Each gradient determines the sampling position of the signal in 2D or 3D Fourier space. Hereinafter, the Fourier space is also referred to as k-space.

  A gradient driving unit 130 is connected to the gradient coil unit 106. The gradient driving unit 130 gives a driving signal to the gradient coil unit 106 to generate a gradient magnetic field. The gradient driving unit 130 includes three systems of driving circuits corresponding to the three systems of gradient coils in the gradient coil unit 106.

  An RF drive unit 140 is connected to the RF coil unit 108. The RF drive unit 140 gives a drive signal to the RF coil unit 108 to transmit an RF pulse, thereby exciting the spin in the body of the subject 1.

  A data collection unit 150 is also connected to the RF coil unit 108. The data collection unit 150 collects reception signals received by the RF coil unit 108 as digital data.

  A sequence control unit 160 is connected to the gradient driving unit 130, the RF driving unit 140, and the data collecting unit 150. The sequence controller 160 controls the gradient driver 130 or the data collector 150 to collect magnetic resonance signals.

  The sequence control unit 160 is configured using, for example, a computer. The sequence control unit 160 has a memory. The memory stores a program for the sequence control unit 160 and various data. The function of the sequence control unit 160 is realized by the computer executing a program stored in the memory. Hereinafter, the excitation of the spin and the subsequent acquisition of the magnetic resonance signal are also referred to as a scan.

  The output side of the data collection unit 150 is connected to the data processing unit 170. Data collected by the data collection unit 150 is input to the data processing unit 170. The data processing unit 170 is configured using, for example, a computer. The data processing unit 170 has a memory. The memory stores a program for the data processing unit 170 and various data.

  The data processing unit 170 is connected to the sequence control unit 160. The data processing unit 170 is above the sequence control unit 160 and controls it. The functions of the data processing unit 170 are realized by the data processing unit 170 executing a program stored in the memory.

  The data processing unit 170 stores the data collected by the data collection unit 150 in a memory. A data space is formed in the memory. This data space corresponds to k-space. The data processing unit 170 reconstructs an image by performing inverse Fourier transform on k-space data.

  An electrocardiogram detection electrode 112 is attached to the subject 1, and an electrocardiogram signal detected thereby is input to the data processor 170 through the electrocardiograph 110. The data processing unit 170 performs electrocardiogram-synchronized magnetic resonance imaging based on the electrocardiogram signal.

  A display unit 180 and an operation unit 190 are connected to the data processing unit 170. The display unit 180 is configured by a graphic display or the like. The operation unit 190 includes a keyboard having a pointing device.

  The display unit 180 displays the reconstructed image and various information output from the data processing unit 170. The operation unit 190 is operated by the user and inputs various commands and information to the data processing unit 170. A user can operate the apparatus interactively through the display unit 180 and the operation unit 190.

  FIG. 2 shows an example of a pulse sequence for scanning. This pulse sequence is a pulse sequence by a gradient echo method. In FIG. 2, (1) shows an RF excitation sequence. (2)-(4) show the gradient magnetic field sequence. (5) shows a sequence of magnetic resonance signals. Among the gradient magnetic field sequences, (2) is a slice gradient, (3) is a frequency encoding gradient, and (4) is a phase encoding gradient. The static magnetic field is always applied with a constant magnetic field strength. The same applies hereinafter.

  First, spin excitation by RF pulses is performed. RF excitation is selective excitation under a slice gradient Slice. After RF excitation, a frequency encode gradient Read and a phase encode gradient Phase are applied in a predetermined sequence, and a magnetic resonance signal Signal, that is, an echo is read out. This echo is also called an imaging echo.

  Such a pulse sequence is repeated a predetermined number of times with a repetition time TR, and an echo is read out each time. The echo phase encoding is changed each time it is repeated, and echo signal collection (2D scanning) is performed for the entire two-dimensional k-space by a predetermined number of repetitions. When phase encoding is also performed in the slice direction, echo signal collection (3D scan) is performed for a three-dimensional k-space. A 2D image is reconstructed by performing a two-dimensional inverse Fourier transform on the two-dimensional k-space echo data. A 3D image is reconstructed by performing a three-dimensional inverse Fourier transform on the echo data of the three-dimensional k space.

  FIG. 3 shows an example of a pulse sequence for navigator echo. This pulse sequence is a pulse sequence by a spin echo method. In FIG. 3, (1) shows an RF excitation sequence. (2)-(4) show the gradient magnetic field sequence. (5) shows a magnetic resonance signal (MR), that is, a navigator echo sequence. Among the gradient magnetic field sequences, (2) is a slice gradient (Gs), (3) is a frequency encode gradient (Gr), and (4) is a phase encode gradient (Gp).

  Using such a pulse sequence, as shown in FIG. 4, 90 ° excitation is performed on slice A of subject 1, 180 ° excitation is performed on slice B, and navigator echo generated from a straight line portion C where both slices intersect. Is read. The slices A and B are set so that the straight line portion C is substantially parallel to the body axis and is offset from the body axis and extends from the lung field to the abdomen.

  Note that 90 ° excitation may be performed for slice B and 180 ° excitation may be performed for slice A. The slices A and B are basically set at positions where navigator echoes can be appropriately acquired regardless of the slices from which imaging echoes are acquired.

  By performing a one-dimensional inverse Fourier transform on the navigator echo, a signal intensity distribution of a spin on the straight line C, that is, a one-dimensional profile is reconstructed. Since the straight line C is set from the lung field to the abdomen, for example, a profile as shown in FIG. 5 is obtained. This profile is greatly different in signal intensity at the middle part. The portion with low signal intensity corresponds to the lung field, the portion with high signal intensity corresponds to the abdomen, and the intermediate portion corresponds to the diaphragm.

  A portion corresponding to the diaphragm reciprocates in the body axis direction with breathing. Hereinafter, a portion corresponding to the diaphragm is also simply referred to as a diaphragm. FIG. 6 shows the diaphragm displacement associated with respiration. As shown in FIG. 6, the diaphragm moves to the abdomen during inhalation, and moves to the chest during exhalation. The position of the diaphragm represents the depth of breathing.

  FIG. 7 shows a flow diagram of the operation of the apparatus. This operation is performed under the control of the data processing unit 170. Of the various functions of the data processing unit 170, the part relating to control is an example of the control means in the present invention. All parts of the apparatus controlled thereby are an example of the imaging means in the present invention.

  As shown in FIG. 7, in step 101, an imaging position setting and a tracker setting are performed. Imaging position determination and tracker setting are performed by the user. The user performs imaging position setting and tracker setting on the scout image displayed on the display unit 180. A scout image is an image captured in advance in a breath-hold state.

  FIG. 8A shows an example of imaging position setting and tracker setting. As shown in FIG. 8A, for example, an imaging position 802 including a coronary artery is set by a pointing device or the like on a scout image captured from the heart to the upper abdomen. The imaging position 802 is an imaging position for 3D scanning, for example. Note that the imaging position for 2D scanning is not limited thereto.

  A tracker FOV (Field of View) 804 is further set on the scout image, and a tracker 806 is set therein. The tracker FOV 804 is set so that the navigator echo includes a one-dimensional area for generation. A tracker 806 is set on the diaphragm in the tracker FOV 804. Based on such settings, the data processing unit 170 obtains the position X1 of the tracker 806. X1 represents the depth of breathing at the time of breath holding.

  The tracker FOV 804 may have a center scale. In that case, the tracker can be set by matching the central scale with the diaphragm. By setting the central scale as the origin, the depth of respiration can be made a relative depth with respect to the origin.

  In step 103, a gating level is set. The gating level is the depth of breathing for which breathing synchronization imaging is performed. The setting of the gating level is performed by the data processing unit 170 based on the measurement value of the respiration depth of the subject 1.

  The measurement of the depth of respiration is performed using a navigator echo. The measurement is performed over a predetermined time (for example, 30 seconds). Then, the measurement value having the highest frequency is identified from the histogram of the measurement value, and this is set as the gating level X2. The gating level X2 has a predetermined allowable range (for example, about several mm) above and below it.

  FIG. 8B shows an example of the gating level. As shown in FIG. 8B, the gating level 806 'is also in the tracker FOV 804. The position of the gating level 806 'in the tracker FOV 804 is X2. The gating level X2 generally does not coincide with the breathing depth X1 at the time of breath holding, and there is a difference of ΔX, for example, as shown in FIG.

  In step 105, the imaging position is corrected. The data processing unit 170 corrects the imaging position. The data processing unit 170 obtains a difference ΔX = X2−X1 between the gating level X2 and the tracker position X1, and corrects the imaging position according to ΔX.

  As a result, the initially set imaging position 802 is corrected to a new imaging position 802 '. The correction amount is given by a function f (ΔX) of ΔX. The function f (ΔX) is determined empirically. The function f (ΔX) may be approximately a linear function K · ΔX. In that case, the value of K is determined empirically. As a result, the corrected imaging position 802 'coincides with the position of the coronary artery at the gating level X2 (the depth of breathing for which respiratory synchronization imaging is performed).

  In step 107, respiratory synchronization imaging is performed. As shown in FIG. 10, the respiratory synchronization imaging is performed using electrocardiographic synchronization. That is, the R wave of the electrocardiogram signal is used as a trigger, and the navigator echo Nb and the imaging echo Im are collected in accordance with the middle diastole of the heart. Such echo collection is performed for each heartbeat.

  The depth of respiration is obtained from the navigator echo for each heartbeat, and the imaging echo is adopted when it is within the gating level range, and the imaging echo is discarded when it is outside the gating level range. Such echo collection is performed until all the sampling data for the k-space are obtained.

  Such respiration synchronization imaging is performed at the imaging position 802 '. The imaging position 802 'coincides with the position of the coronary artery at the gating level X2. For this reason, respiratory synchronous imaging can be reliably performed for the coronary artery. The imaging target is not limited to the coronary artery, but may be another internal organ that reciprocates with breathing. In that case, the combined use of ECG synchronization is not essential.

1 is a block diagram of an MRI apparatus as an example of the best mode for carrying out the invention. It is a figure which shows an example of the pulse sequence for a scan. It is a figure which shows an example of the pulse sequence for navigator echoes. It is a figure which shows an example of a navigator echo collection site | part. It is a figure which shows an example of a one-dimensional profile. It is a figure which shows an example of the movement of the one-dimensional profile accompanying respiration. It is a flowchart of operation | movement of this apparatus. It is a figure which shows an example of the setting and correction of an imaging position. It is a figure which shows the relationship between the depth of breathing at the time of breath holding, and a gating level. It is a time chart of the respiration synchronous imaging which used electrocardiogram synchronization together.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100: Magnet system 102: Main magnetic field coil part 106: Gradient coil part 108: RF coil part 110: Electrocardiograph 112: Electrode 130: Gradient drive part 140: RF drive part 150: Data collection part 160: Sequence control part 170: Data processing unit 180: Display unit 190: Operation unit 802: Imaging position 804: Tracker FOV
806: Tracker 806 ': Gating level

Claims (10)

An MRI apparatus having an imaging means for performing respiratory synchronization imaging at an imaging position set on a scout image obtained by breath-hold imaging at a predetermined breathing depth and a control means for controlling the imaging means.
The control means causes the imaging means to determine the depth of breathing during breath-hold imaging, and corrects the imaging position according to the difference between the depth of breathing during breath-synchronous imaging and the depth of breathing during breath-hold imaging. An MRI apparatus characterized by being made to perform. The MRI apparatus according to claim 1, wherein the breathing depth is obtained based on a one-dimensional profile reconstructed from a navigator echo. The MRI apparatus according to claim 2, wherein the imaging position is a position where a coronary artery is present. The MRI apparatus according to claim 3, wherein the respiratory synchronization imaging is performed using electrocardiographic synchronization. The MRI apparatus according to claim 4, wherein the respiratory synchronous imaging combined with electrocardiographic synchronization is performed by 3D scanning. A method of controlling an MRI apparatus that performs respiratory synchronization imaging at a predetermined breathing depth for an imaging position set on a scout image obtained by breath-holding imaging,
To MRI equipment,
Let me determine the depth of breathing during breath-hold imaging,
A method of controlling an MRI apparatus, wherein an imaging position is corrected in accordance with a difference between a breathing depth at the time of breathing synchronous imaging and a breathing depth at the time of breathholding imaging. The method of controlling an MRI apparatus according to claim 6, wherein the depth of respiration is obtained based on a one-dimensional profile reconstructed from navigator echoes. The method of controlling an MRI apparatus according to claim 7, wherein the imaging position is a position where a coronary artery is present. The method of controlling an MRI apparatus according to claim 8, wherein the respiratory synchronization imaging is performed using electrocardiographic synchronization. The method for controlling an MRI apparatus according to claim 9, wherein the respiratory synchronous imaging combined with electrocardiographic synchronization is performed by 3D scanning.

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