JP2006158762A - Mri apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an MRI apparatus which takes a synchronized photograph of respiration with a good efficiency. <P>SOLUTION: The MRI apparatus comprises a signal collection means (100, 130, 140, 150, 160) for loading a subject with a magnetostatic field, a gradient magnetic field and an RF magnetic field to collect magnetic resonance signals, a respiration detection means (110, 112) for detecting the respiration of the subject, and an image reconstruction means (170) for using the magnetic resonance signal and the respiration detection signal to reconstruct an image at a predetermined respiration phase, wherein the MRI apparatus is furnished with a display means (182) for displaying the subject a respiration situation based on the respiration detection signal in such a way that the subject may visually recognize the respiration situation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an MRI (Magnetic Resonance Imaging) apparatus, and in particular, applies a static magnetic field, a gradient magnetic field, and an RF (radio frequency) magnetic field to a subject, collects magnetic resonance signals, and detects respiration of the subject. The present invention relates to an MRI apparatus for reconstructing an image at a predetermined respiratory phase based on a magnetic resonance signal and a respiratory detection signal.

When photographing an abdomen, a lung field, or the like with an MRI apparatus, respiratory synchronization imaging is performed. That is, the respiration of a subject is detected, and an image is reconstructed using a magnetic resonance signal in a predetermined respiration phase. For detection of respiration, bellows or the like attached to the abdomen is used (for example, see Patent Document 1).
Japanese Patent Laying-Open No. 2004-275380 (page 3-4, FIG. 6)

  In order to correctly perform respiration-synchronized imaging, the respiration depth at the desired respiration phase must always be constant. However, since the depth of respiration changes, a magnetic resonance signal in a desired respiration depth state in a desired respiration phase is not always obtained. For this reason, it takes a considerable time to complete signal acquisition.

  Therefore, an object of the present invention is to realize an MRI apparatus that efficiently performs respiratory synchronous imaging.

  In order to solve the above problems, the present invention provides a signal collecting means for collecting a magnetic resonance signal by applying a static magnetic field, a gradient magnetic field, and an RF magnetic field to a subject, and a respiration detecting means for detecting the respiration of the subject. And an image reconstruction means for reconstructing an image at a predetermined respiratory phase based on the magnetic resonance signal and the respiratory detection signal, wherein the subject is informed of the respiratory state based on the respiratory detection signal An MRI apparatus characterized by comprising display means for displaying on the screen.

It is preferable that the display means displays the breathing state in such a manner that the subject can visually recognize in terms of a large amount of information that can be transmitted.
It is preferable that the display means displays the depth of respiration by a scale in terms of enabling accurate display.

It is preferable that the scale has a mark indicating the target of the depth of respiration in that the target is clear.
It is preferable that the display means displays the depth of respiration according to the light emission position of the light spot because the display is simple.

It is preferable that the light emission position is in five stages from the viewpoint of appropriately quantizing the depth of respiration.
The light emission position is preferably in three stages from the viewpoint of easily quantizing the depth of respiration.
The light emitting positions are preferably different in hue from the viewpoint of good recognizability of the depth of respiration.

  According to the present invention, the MRI apparatus applies a static magnetic field, a gradient magnetic field, and an RF magnetic field to a subject to collect a magnetic resonance signal, a breath detection unit that detects the breathing of the subject, An MRI apparatus having an image reconstruction means for reconstructing an image at a predetermined respiratory phase based on a magnetic resonance signal and a respiratory detection signal, and displaying a respiratory state to a subject based on the respiratory detection signal Since the display means is provided, the subject can adjust his / her breathing state based on the displayed breathing state, thereby efficiently performing the synchronized breathing imaging.

  The best mode for carrying out the invention will be described below in detail with reference to the drawings. 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 present invention relating to the MRI apparatus is shown by the configuration of the 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 coil unit 108. Each of these coil portions has a substantially cylindrical shape and is arranged coaxially with each other.

  A subject 1 to be imaged is mounted on a cradle 500 in a generally cylindrical inner 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.

  In addition, 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 for generating a static magnetic field.

  The gradient coil section 106 generates three gradient magnetic fields for giving gradients 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 (not shown). 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 magnetic resonance signal is a sampling signal for the frequency domain (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 drive unit 130 has three systems of drive circuits (not shown) 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 driving unit 140 gives a driving signal to the RF coil unit 108 to transmit an RF pulse, and excites spins 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. Hereinafter, collection of magnetic resonance signals is also referred to as scanning.

  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. The part consisting of the magnet system 100 or the sequence controller 160 is an example of the signal collecting means in the present invention.

  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 function of this apparatus is 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. The data processing unit 170 is an example of an image reconstruction unit in the present invention.

  The subject 1 is equipped with a respiration sensor 112, through which the respiration detection unit 110 detects respiration of the subject 1, and a respiration detection signal is input to the data processing unit 170. The data processing unit 170 performs respiration-synchronized magnetic resonance imaging based on the respiration detection signal, and reconstructs an image in a predetermined respiration phase.

  The portion composed of the respiration sensor 112 and the respiration detection unit 110 is an example of a respiration detection means in the present invention. The respiration detection may be performed based on the motion of the diaphragm image obtained by magnetic resonance imaging.

  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.

  A display 182 is also connected to the data processing unit 170. The display unit 182 is also composed of, for example, a graphic display. The display 182 is an example of display means in the present invention. The display 182 is provided in the vicinity of the subject 1 and displays a breathing state image output from the data processing unit 170. The breathing state display will be described later.

  FIG. 2 shows an example of a pulse sequence for scanning. This pulse sequence is a pulse sequence based on a gradient echo method.

  In the figure, (1) shows an RF excitation sequence. (2)-(4) show the gradient magnetic field sequence. (5) shows a sequence of magnetic resonance signals. Of the gradient magnetic field sequence, (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 an α ° pulse is performed. α ° excitation is selective excitation under slice gradient Slice. After the α ° excitation, a frequency encode gradient Read and a phase encode gradient Phase are applied in a predetermined sequence, and a magnetic resonance signal, that is, an echo is read out.

  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 at each repetition, and echo signals are collected for the entire two-dimensional k-space by a predetermined number of repetitions. Note that when phase encoding is performed also in the slice direction, echo signal collection for a three-dimensional k-space is performed. 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 respiratory state image displayed on the display 182. As shown in the figure, the respiratory state image is shown as a waveform of body movement accompanying breathing. In this way, since the breathing state is displayed in a manner that the subject can visually recognize, the amount of information that can be transmitted can be increased.

  The rising process of the waveform is inspiration, and the top is a turning point from inspiration to expiration. The descending process of the waveform is exhalation, and the valley bottom is the turning point from exhalation to inspiration. With respect to the respiratory state image, the target range of the turning point from exhalation to inspiration is set by two parallel lines. This range is the target range for breathing depth.

  Such a breathing state image is displayed on the display 182 and shown to the subject 1, and the subject himself / herself is adjusted to breathe so that the turning point from exhalation to inspiration falls within the target range. This makes it possible to keep the depth of breathing constant at all times. For this reason, it becomes possible to use all the magnetic resonance signals at the time of the maximum expiration in every respiration for image reconstruction. That is, efficient synchronized breathing imaging can be performed.

  The breathing state display is not limited to such an image, and for example, an image as shown in FIGS. 4 to 6 may be used. FIG. 4 is an image simulating an instrument, and shows a breathing state by a pointer 402 that moves along a scale 401. A band-shaped marker 403 is provided at a predetermined position on the scale, which is the target range of the maximum expiration state.

  By showing such a breathing state image to the subject 1 through the display 182 and adjusting the breathing by the subject himself / herself, the depth of breathing can be made constant at all times. An actual instrument may be used instead of an image simulating the instrument. Since the depth of respiration is displayed by the scale of the instrument, precise display is possible. In addition, the scale has a marker indicating the target of the breathing depth, so that the target becomes clear.

  FIG. 5 is an image simulating five light spots 501 to 505 arranged in a vertical line, and shows a breathing state by the position of only one light spot that emits light. Here, the state in which the light spot 505 emits light is set as a target for the depth of respiration. The light spots 501 to 505 can be easily identified by changing the emission color. Since the depth of respiration is displayed according to the light emission position of the light spot, the display becomes simple. Moreover, since the light emission position has five stages, the depth of respiration can be appropriately quantized.

  By showing such a breathing state image to the subject 1 through the display 182 and adjusting the breathing by the subject himself / herself, the depth of breathing can be made constant at all times. Note that an actual light emitter may be used instead of the image simulating the light spot.

  FIG. 6 is an image simulating three light spots 601-603 arranged in a vertical row, and shows a breathing state according to the position of only one light spot. Here, the state where the light spot 603 emits light is set as the target of the depth of respiration. The light spots 601 to 603 can be easily identified by changing the emission color. Since there are three light emission positions, the depth of respiration can be easily quantized.

  By showing such a breathing state image to the subject 1 through the display 182 and adjusting the breathing by the subject himself / herself, the depth of breathing can be made constant at all times. Note that an actual light emitter may be used instead of the image simulating the light spot.

It is a block diagram of an MRI apparatus as an example of the best mode for carrying out the present invention. It is a figure which shows an example of a pulse sequence. It is a figure which shows an example of a respiratory state display. It is a figure which shows an example of a respiratory state display. It is a figure which shows an example of a respiratory state display. It is a figure which shows an example of a respiratory state display.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Subject 100 Magnet system 102 Main magnetic field coil part 106 Gradient coil part 108 RF coil part 110 Respiration detection part 112 Respiration sensor 130 Gradient drive part 160 RF drive part 160 Data collection part 160 Sequence control part 170 Data processing part 180 Display part 182 Display 190 Operation unit 500 Cradle

Claims (8)

A signal collecting means for applying a static magnetic field, a gradient magnetic field and an RF magnetic field to a subject to collect a magnetic resonance signal, a respiration detecting means for detecting the respiration of the subject, a magnetic resonance signal and a respiration detection signal based on An MRI apparatus having image reconstruction means for reconstructing an image in a predetermined respiratory phase,
Display means for displaying the respiratory state to the subject based on the respiratory detection signal;
An MRI apparatus characterized by comprising: The display means displays the breathing state in a manner that the subject can visually recognize,
The MRI apparatus according to claim 1. The display means displays the breathing depth by a scale.
The MRI apparatus according to claim 2, wherein: The scale has an indicator that indicates a breathing depth target,
The MRI apparatus according to claim 3. The display means displays the depth of respiration according to the light emission position of the light spot.
The MRI apparatus according to claim 2, wherein: The light emission position is in five stages.
The MRI apparatus according to claim 5. The light emission position has three stages.
The MRI apparatus according to claim 5. The light emitting positions are different in hue,
The MRI apparatus according to claim 6 or 7, wherein the MRI apparatus is characterized in that:

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