JP5133711B2 - Magnetic resonance imaging apparatus and magnetic resonance image generation method - Google Patents

Description

  The present invention relates to a magnetic resonance imaging (MRI) apparatus and a magnetic resonance image generation method. In particular, a magnetic resonance imaging apparatus that images the imaging region by performing a scan that collects magnetic resonance signals from the imaging region including the artery in the subject, and the magnetism acquired by performing the scan described above. The present invention relates to a magnetic resonance image generation method for generating a magnetic resonance image for an imaging region based on a resonance signal.

  The magnetic resonance imaging apparatus scans the imaging region so as to collect magnetic resonance signals from the imaging region imaged by the subject in the imaging space where the static magnetic field is formed. Here, by irradiating an imaging region with an RF pulse that is an electromagnetic wave, a magnetization vector due to a spin of a proton in the imaging region is excited by a nuclear magnetic resonance (NMR) phenomenon, A magnetic resonance signal generated when the excited magnetization vector returns to the original magnetization vector is collected. Then, the magnetic resonance signals collected by performing this scan are used as raw data, and a magnetic resonance image is reconstructed for the imaging region of the subject.

  Magnetic resonance imaging apparatuses are used in various fields such as the medical field and the industrial field, and an imaging region of a subject is imaged by various imaging methods according to the purpose.

  For example, as an imaging method used in a magnetic resonance imaging apparatus, a balanced SSFP method called FIESTA (Fast Imaging Employing Steady State Precession) is known. This Balanced SSFP method is a gradient echo system, and a phase shift of transverse magnetization caused by a gradient magnetic field applied within a repetition time (TR: Time of repetition) is completely rewound within the TR. A magnetic resonance signal can be collected so as to include a FID (Free Induction Decay) signal and an echo signal, which is a pulse sequence. For this reason, since the signal intensity of the magnetic resonance signal is increased, it is possible to realize high-contrast magnetic resonance image generation at high speed. In particular, in this method, a high-contrast magnetic resonance image can be generated for a blood flow portion flowing in a living body such as a human body (see, for example, Patent Document 1).

  In addition, an imaging method has been proposed that suppresses the occurrence of body motion artifacts in magnetic resonance images due to body motion of a subject that is a living body.

  When the scan is repeated so that the magnetic resonance signals collected from the imaging region including the part where the body motion occurs are continuously filled along the time axis in rows aligned in the phase encoding direction in the k space, Since the signal intensity varies at the position, body motion artifacts may occur in the magnetic resonance image. For example, when the k-space is filled with magnetic resonance signals in the order from the negative maximum position view in the k-space phase encoding direction to the positive maximum position view by the sequential method, A bug may occur.

  For this reason, after detecting the body movement of the subject, body order artifacts are generated by performing view ordering so as to control the order of phase encoding according to the detected detection data. An imaging method for suppressing this has been proposed. For example, when view ordering is performed by the high sort method and magnetic resonance signals are filled in the k-space in the same manner as when body motion is intense for each view, the magnetic resonance is performed. Since the body movement artifact can be moved to the edge of the image, the image quality can be improved. In particular, when a magnetic resonance signal is collected by this high sort method so as to correspond to an FOV having a larger number of views than the target FOV (Field Of View), the body motion is moved outside the target FOV. This is preferable because the artifact is moved (see, for example, Patent Document 2 and Patent Document 3).

  An imaging method that performs the above-described view ordering so as to respond to a respiratory signal generated by the subject's respiratory motion is called a ROPE (Respiratory Ordered Phase Encoding) method. An imaging method in which the view ordering as described above is performed in accordance with a heartbeat signal due to a heartbeat motion of a subject is called a cardiac compensation method.

  In addition to the above, a flow compensation method has been proposed as an imaging method for suppressing the occurrence of artifacts due to blood flow. In the flow compensation method, the occurrence of artifacts due to blood flow is suppressed by correcting the phase of the spin displaced by the blood flow using a gradient pulse called a flow compensation pulse (for example, Patent Documents). 4).

  Angiography called MRA (MR angiography) is performed using a magnetic resonance imaging apparatus. In this MRA, FBI (Fresh Blood Imaging) is known as an imaging method that does not use a contrast agent (see, for example, Patent Document 5 and Patent Document 6).

JP 2003-10148 A Japanese Patent No. 3696677 JP-A-4-82537 Japanese Patent Laid-Open No. 2007-90001 JP 2000-5144 A JP 2004-129724 A

  In the FBI method, an image is generated for an imaging region including an artery in a subject in each of a diastole and a systole. Then, based on the difference value between these images, an MRA image of the imaging region is obtained. This method utilizes the fact that when an imaging region is imaged by the FSE (Fast Spin Echo) method, a phenomenon called a flow void occurs in a portion corresponding to an artery in a magnetic resonance image of the imaging region. ing. For this reason, in the FBI method, the arterial blood flow velocity is high in the systole and the signal strength from the artery is low. In diastole, the arterial blood velocity is slow and the signal strength from the artery is high. Therefore, the MRA image generated based on the difference value between the two images has high contrast in the artery portion.

  However, in the FBI method, in order to capture a plurality of images at a plurality of timings as described above, it is necessary to accurately obtain a delay time (Delay Time) from the R wave of the heartbeat signal so as to correspond to each timing. As a result, the throughput of shooting may be reduced.

  In the FBI method, it is necessary to perform imaging by the FSE method in order to generate a flow void in the arterial part during systole, and it is known as an imaging method with high contrast of the blood flow part as described above. The Balanced SSFP method such as FIESTA cannot be used. For this reason, it may be difficult to improve the image quality.

  Therefore, the present invention provides a magnetic resonance imaging apparatus and a magnetic resonance image generation method capable of improving the imaging throughput in MRA and improving the image quality.

  The present invention relates to a magnetic resonance imaging apparatus that performs imaging on a radiographing region by performing a scan that collects magnetic resonance signals from a radiographing region including an artery in a subject. A first image generation unit that generates a first image of the imaging region using the magnetic resonance signals collected in the execution of the scan so as to continuously fill along the time axis; A second image generation unit configured to generate a second image for the imaging region using magnetic resonance signals collected in k-space in the execution of the scan so as to correspond to the high-sort method in the session method; The difference between the first image generated by the first image generation unit and the second image generated by the second image generation unit And a differential image generating section that generates a difference image by performing a process.

  Preferably, the image processing apparatus includes a display unit that displays the difference image generated by the difference image generation unit on a screen.

  Preferably, the imaging region includes a vein.

  Preferably, the RF pulse is repeatedly transmitted at a repetition time such that the spin in the imaging region is in the SSFP state, and gradient pulses are respectively transmitted in the slice selection direction, the phase encoding direction, and the frequency encoding direction in the imaging region. Is transmitted so that the time integration value becomes zero within the repetition time.

  Further, the present invention is a magnetic resonance image generation method for generating a magnetic resonance image for the imaging region based on a magnetic resonance signal collected by a scan performed on the imaging region including an artery in the subject, A first image generation step of generating a first image for the imaging region using magnetic resonance signals collected to continuously fill rows of phase encoding in k-space along a time axis in performing a scan And a second image for generating a second image for the imaging region using the magnetic resonance signals collected in the k space in the execution of the scan so as to correspond to the high sort in the cardiac compensation method. A generating step, a first image generated by the first image generating step, and a second image generating step. And a difference image generation step of generating a difference image by performing differential processing between the second image generated Te.

  Preferably, there is a display step of displaying the difference image generated by the difference image generation step on a screen.

  Preferably, the imaging region includes a vein.

  Preferably, the scan repeatedly transmits an RF pulse at a repetition time such that the spin of the imaging region is in the SSFP state, and each of a slice selection direction, a phase encoding direction, and a frequency encoding direction in the imaging region. First, a gradient pulse is transmitted within the repetition time so that the time integration value becomes zero.

  According to the present invention, it is possible to provide a magnetic resonance imaging apparatus and a magnetic resonance image generation method capable of improving imaging throughput and improving image quality in MRA.

  Hereinafter, an example of an embodiment according to the present invention will be described with reference to the drawings.

(Device configuration)
FIG. 1 is a configuration diagram showing a configuration of a magnetic resonance imaging apparatus 1 in an embodiment according to the present invention.

  As shown in FIG. 1, the magnetic resonance imaging apparatus 1 includes a scan unit 2 and an operation console unit 3, and performs a scan for collecting magnetic resonance signals from an imaging region for imaging the subject SU. Thus, an image is generated for the photographing region.

  Specifically, in the magnetic resonance imaging apparatus 1, an RF pulse is transmitted to the imaging region of the subject in the imaging space B where the static magnetic field is formed, and magnetic resonance generated in the imaging region where the RF pulse is transmitted. The scanning unit 2 scans the imaging region of the subject so as to receive the signal. Thereafter, in the magnetic resonance imaging apparatus 1, the operation console unit 3 generates a magnetic resonance image for the imaging region based on the magnetic resonance signal received by performing the scan.

  In this embodiment, a scan for collecting magnetic resonance signals from an imaging region including an artery and a vein in the subject SU is performed, and an MRA image is generated as a magnetic resonance image for the imaging region.

  The scanning unit 2 will be described.

  As shown in FIG. 1, the scanning unit 2 includes a static magnetic field magnet unit 12, a gradient coil unit 13, an RF coil unit 14, an object moving unit 15, an RF drive unit 22, a gradient drive unit 23, The data collection unit 24 is included, and based on the control signal output from the operation console unit 3, the imaging region of the subject SU is scanned.

  The scanning unit 2 is formed to have a cylindrical shape, for example, and accommodates the subject SU with the columnar space at the center thereof as the imaging space B. The scanning unit 2 is placed on the subject moving unit 15 in the imaging space B where the static magnetic field is formed by the static magnetic field magnet unit 12 when scanning the imaging region of the subject SU. The RF coil unit 14 transmits an RF pulse so as to excite spins in the imaging region of the subject SU, and the gradient coil unit 13 transmits a gradient pulse to the imaging region of the subject SU to which the RF pulse has been transmitted. Then, the RF coil unit 14 receives a magnetic resonance signal generated in the imaging region of the subject SU.

  In the present embodiment, the scanning unit 2 scans an imaging region including an artery and a vein in the subject SU so that rows aligned in the phase encoding direction in the k space are continuously filled along the time axis. To do. In addition to this, the scanning unit 2 performs scanning on this imaging area so as to correspond to the high sort method in the cardiac compensation method.

  Further, here, this scan is performed by a pulse sequence corresponding to the Balanced SSFP method called FIESTA. Specifically, the RF pulse is repeatedly transmitted at a repetition time TR such that the spin of the imaging region of the subject SU is in the SSFP state, and the slice selection direction, the phase encoding direction, and the frequency encoding direction in the imaging region are transmitted. Each of these scans is performed by sending a gradient pulse repeatedly so that the time integration value becomes zero within the time TR.

  Each component of the scanning unit 2 will be described sequentially.

  The static magnetic field magnet unit 12 includes a superconducting magnet (not shown), and is configured to form a static magnetic field in the imaging space B in which the subject SU is accommodated. Here, the static magnetic field magnet unit 12 forms a static magnetic field along the body axis direction (z direction) of the subject SU placed on the subject moving unit 15. That is, the static magnetic field magnet unit 12 is a horizontal magnetic field type. In addition, the static magnetic field magnet unit 12 may be a vertical magnetic field type, and may be configured to form a static magnetic field along a direction in which a pair of permanent magnets face each other.

  The gradient coil unit 13 is configured to form a gradient magnetic field in the imaging space B where the static magnetic field is formed by the static magnetic field magnet unit 12 and to add spatial position information to the magnetic resonance signal received by the RF coil unit 14. Yes. Here, the gradient coil unit 13 includes three systems so as to correspond to the three axial directions orthogonal to each other in the x direction, the y direction, and the z direction. These transmit gradient pulses so as to form gradient magnetic fields in the frequency encoding direction, the phase encoding direction, and the slice selection direction according to the imaging conditions. Specifically, the gradient coil unit 13 applies a gradient magnetic field in the slice selection direction of the subject SU so as to correspond to the imaging region of the subject SU, and the RF coil unit 14 transmits an RF pulse. A slice of the subject SU to be excited is selected. The gradient coil unit 13 applies a gradient magnetic field in the phase encoding direction of the subject SU, and phase encodes the magnetic resonance signal generated in the slice excited by the RF pulse. The gradient coil unit 13 applies a gradient magnetic field in the frequency encoding direction of the subject SU, and frequency encodes the magnetic resonance signal generated in the slice excited by the RF pulse.

  In the imaging space B where a static magnetic field is formed, the RF coil unit 14 transmits an RF pulse that is an electromagnetic wave to form a high-frequency magnetic field, and excites proton spins in the imaging region of the subject SU. The RF coil unit 14 receives an electromagnetic wave generated from protons in the imaging region of the excited subject SU as a magnetic resonance signal.

  Here, as shown in FIG. 1, the RF coil unit 14 includes a transmission coil 14a and a reception coil 14b. Here, the transmission coil 14a is, for example, a birdcage-type body coil, and is disposed so as to surround the imaging region of the subject SU, and transmits an RF pulse. On the other hand, the receiving coil 14b is a detachable surface coil, for example, is disposed so as to correspond to the imaging region of the subject SU, and receives a magnetic resonance signal from the imaging region. For example, the receiving coil 14b is formed with an accommodation space (not shown) that accommodates the imaging region of the subject SU, and is disposed so as to accommodate the imaging region of the subject SU in the accommodation space.

  The subject moving unit 15 includes a cradle 15a and a cradle moving unit 15b, and the cradle 15a is moved between the inside and the outside of the imaging space B based on a control signal output from the control unit 30. The moving unit 15b is configured to move.

  Here, the cradle 15a of the subject moving unit 15 is a table having a placement surface on which the subject SU is placed. As shown in FIG. 1, the cradle moving unit 15b moves the cradle 15a horizontally and vertically. It is moved in the respective directions with respect to y, and is carried in and out of the imaging space B in which a static magnetic field is formed. As shown in FIG. 1, the cradle 15a is arranged such that a receiving coil 14b for receiving a magnetic resonance signal from the imaging region of the subject SU placed on the placement surface is arranged on the placement surface. It is configured.

  The cradle moving unit 15b of the subject moving unit 15 is configured to move the cradle 15a between the inside and outside of the imaging space B. That is, the cradle moving unit 15b is configured to be accommodated in the imaging space B by moving the cradle 15a from the outside to the inside of the imaging space B. The cradle moving unit 15b includes, for example, a roller drive mechanism, and drives the roller by an actuator to move the cradle 15a in the horizontal direction xz. The cradle moving unit 15b includes, for example, an arm-type drive mechanism, and moves the cradle 15a in the vertical direction y by changing the angle between the two intersecting arms.

  The RF drive unit 22 is configured to drive the RF coil unit 14 to transmit an RF pulse in the imaging space B so as to form a high-frequency magnetic field in the imaging space B. Specifically, the RF drive unit 22 uses a gate modulator (not shown) to output a signal output from an RF oscillator (not shown) based on a control signal output from the operation console unit 3 at a predetermined timing. After the signal is modulated into a predetermined envelope signal, the signal modulated by the gate modulator is amplified by an RF power amplifier (not shown) and output to the RF coil unit 14 to transmit an RF pulse.

  Based on the control signal output from the operation console unit 3, the gradient driving unit 23 applies a gradient pulse to the gradient coil unit 13 to drive the gradient coil unit 13, thereby generating a gradient magnetic field in the imaging space B in which a static magnetic field is formed. It is configured to let you. The gradient drive unit 23 includes three systems of drive circuits (not shown) corresponding to the three systems of gradient coil units 13.

  The data collection unit 24 is configured to collect magnetic resonance signals received by the RF coil unit 14 based on control signals output from the operation console unit 3. Here, in the data collection unit 24, the phase detector (not shown) detects the magnetic resonance signal received by the RF coil unit 14 using the output of the RF oscillator (not shown) of the RF drive unit 22 as a reference signal. Thereafter, using an A / D converter (not shown), the magnetic resonance signal, which is an analog signal, is converted into a digital signal and output.

  The operation console unit 3 will be described.

  As illustrated in FIG. 1, the operation console unit 3 includes a control unit 30, a data processing unit 31, an operation unit 32, a display unit 33, and a storage unit 34. The operation console unit 3 controls the scan unit 2 so as to scan the imaging region of the subject SU. Then, the operation console unit 3 generates a magnetic resonance image for the imaging region of the subject SU based on the magnetic resonance signals collected by the scanning unit 2 performing the scan, and the generated magnetic resonance image is displayed. indicate.

  Each component of the operation console unit 3 will be described sequentially.

  The control unit 30 includes a computer and a memory that stores a program that causes the computer to execute predetermined data processing, and controls each unit. Here, the control unit 30 outputs a control signal to each of the RF drive unit 22, the gradient drive unit 23, and the data collection unit 24 so as to correspond to the set scan condition, thereby executing a scan. At the same time, a control signal is output to the data processing unit 31, the display unit 33, and the storage unit 34 to perform control.

  The data processing unit 31 includes a computer and a memory that stores a program that executes predetermined data processing using the computer, and performs data processing based on a control signal output from the control unit 30. To do. Here, the data processing unit 31 is configured to set scan conditions for performing a scan on the subject SU based on a command input by the operator in the operation unit 32. In addition, the data processing unit 31 uses the magnetic resonance signals collected by the scan unit 2 executing a scan as raw data so as to correspond to the scan conditions set above, and obtains an imaging region of the subject SU. Is configured to generate a magnetic resonance image. Specifically, the magnetic resonance signal collected by the data collection unit 24 by performing the scan is acquired as a digital signal, and image reconstruction processing is performed on the magnetic resonance signal converted into the digital signal, so that the subject A magnetic resonance image is generated for the imaging region of the SU. For example, the magnetic resonance image is reconstructed by performing an inverse Fourier transform on the magnetic resonance signals collected so as to correspond to the k-space. Then, the generated image data of the magnetic resonance image is output to the display unit 33.

  FIG. 2 is a functional block diagram of the data processing unit 31 constituting the operation console unit 3 of the magnetic resonance imaging apparatus 1 in the embodiment according to the present invention.

  As shown in FIG. 2, the data processing unit 31 is configured such that the computer functions as a program as a first image generation unit 311, a second image generation unit 312, and a difference image generation unit 313. Yes.

  In the data processing unit 31, the first image generation unit 311 scans the magnetic resonance signals collected in the k space so that the rows arranged in the phase encoding direction in the k space are continuously filled along the time axis. Is used to generate a first image for the imaging region of the subject SU.

  In the data processing unit 31, the second image generation unit 312 uses the magnetic resonance signals that have been scanned and collected in the k space so as to correspond to the high sort method in the cardiac compensation method. A second image is generated for the imaging region of the sample SU.

  In the data processing unit 31, the difference image generation unit 313 performs difference processing between the first image generated by the first image generation unit 311 and the second image generated by the second image generation unit 312. By doing so, a difference image is generated as an MRA image.

  The operation unit 32 includes operation devices such as a keyboard and a pointing device. The operation unit 32 is input with operation data by an operator and outputs the operation data to the control unit 30.

  The display unit 33 includes a display device such as an LCD (Liquid Crystal Display), and displays an image on the display screen based on a control signal output from the control unit 30. Here, the display unit 33 displays on the display screen an operation image indicating input items for the operator to input operation data. Specifically, a menu image indicating input items to be input for scan parameters when scanning the subject SU is displayed on the display screen. In addition, the display unit 33 receives the image data of the magnetic resonance image generated for the subject SU in the data processing unit 31 and displays it on the display screen.

  In the present embodiment, the display unit 33 displays the difference image generated by the difference image generation unit 313 on the display screen.

  The storage unit 34 includes a memory and stores various data. The storage unit 34 is accessed by the control unit 30 as necessary for the stored data.

(Operation)
Hereinafter, a method for imaging the imaging region of the subject SU, which is a human body, using the magnetic resonance imaging apparatus 1 will be described.

  FIG. 3 is a flowchart showing an operation when imaging the imaging region of the subject SU in the embodiment according to the present invention. FIG. 4 is a diagram showing an image generated when imaging the imaging region of the subject SU in the embodiment according to the present invention.

  When imaging the imaging region of the subject SU, as shown in FIG. 3, a first image C1 is generated for the imaging region of the subject (S11).

  Here, the first image C1 is generated for the imaging region of the subject by performing imaging using an imaging method that does not apply the cardiac compensation method. Specifically, the first image generation unit 311 uses the magnetic resonance signals collected so as to continuously fill the rows aligned in the phase encoding direction along the time axis in the k space, so that the first image generation unit 311 captures the imaging region of the subject SU. A first image C1 is generated for.

  FIG. 5 shows a view number view when a magnetic resonance signal is filled in the k space when generating the first image C1 and a heartbeat signal E by a heartbeat motion of the subject in the embodiment according to the present invention. It is a figure which shows a relationship. In FIG. 5, FIG. 5A shows the heartbeat signal E, where the horizontal axis is the time axis t and the vertical axis is the signal intensity ES of the heartbeat signal E. FIG. 5B shows the order of view numbers view when the heartbeat signal shown in FIG. 5A is measured. FIG. 5C shows a magnetic resonance signal collected when the heartbeat signal shown in FIG. 5A is measured, the horizontal axis is the view number view, and the vertical axis is the signal intensity MS. . For convenience of explanation, in FIG. 5, the heartbeat signal E is shown as a sine wave having a constant period. Further, the view number view is shown in the case where numbers (for example, number 15) are assigned in the order from the view at the negative position (for example, number 1) to the view at the positive position in the phase encoding direction of the k space. Yes.

  As shown in FIG. 5A, magnetic resonance signals are filled in the k space in the order of view numbers view as shown in FIG. 5B along the time axis t of the heartbeat signal measured with a periodic behavior. As described above, by performing the phase encoding at every repetition time TR, the scan unit 2 performs a scan on the imaging region including the artery and the vein in the subject SU. Specifically, as shown in FIG. 5B, for example, the view number is sequentially increased along the time axis t as 1, 2, 3, 4, 5,. Carry out the scan as you do. That is, regardless of the displacement of the heartbeat signal, magnetic resonance signals are repeatedly collected at every time TR so that the phase encoding order and the view number order correspond to each other by the sequential method. In this case, as shown in FIG. 5C, magnetic resonance signals are collected so as to correspond to the displacement of the heartbeat signal.

  In this scan, magnetic resonance signals are collected using a pulse sequence corresponding to the Balanced SSFP method called FIESTA.

  FIG. 6 is a diagram showing a pulse sequence when scanning a subject in the embodiment according to the present invention. In FIG. 6, RF is a time axis for transmitting an RF pulse, Gslice is a time axis for transmitting a gradient pulse in the slice selection direction, and Gread indicates a time axis for transmitting the gradient pulse in the frequency encoding direction. Gwarp indicates a time axis for transmitting a gradient pulse in the phase encoding direction, and in each case, the horizontal axis indicates the time axis t and the vertical axis indicates the pulse intensity.

  In the Balanced SSFP method, RF pulses are repeatedly transmitted at a repetition time TR such that the spin in the imaging region of the subject SU is in the SSFP state. Then, as shown in FIG. 6, by transmitting gradient pulses to be applied to each of the slice selection direction, the phase encoding direction, and the frequency encoding direction so that the time integration value becomes zero within the repetition time TR, The phase shift of transverse magnetization that occurs within the repetition time TR is completely rewound. When this pulse sequence is repeatedly executed, a gradient pulse is applied in the phase encoding direction at every repetition time TR so as to correspond to the view number as described above.

  Then, based on the magnetic resonance signals collected as described above, the first image generation unit 311 generates a first image C1 for the imaging region of the subject SU.

  Specifically, as shown in FIG. 4, the first image C1 is such that the pixel portions corresponding to the arterial portion DM and the vein portion JM have high luminance and the other portions have low luminance. It is formed. That is, the first image C1 is generated as a magnetic resonance image with high contrast for the blood flow portion.

  Next, as shown in FIG. 3, a second image C2 is generated for the imaging region of the subject (S21).

  Here, the second image C2 is generated for the imaging region of the subject by performing imaging using an imaging method to which the cardiac compensation method is applied. That is, the second image generation unit 312 uses the magnetic resonance signals collected in the k space so as to correspond to the high sort method in the cardiac compensation method, and the second image generation unit 312 performs the second image on the imaging region of the subject SU. C2 is generated. In the present embodiment, except that the cardiac compensation method is applied, the scan is performed under the same scan conditions as the scan for generating the first image C1, and then collected by performing the scan. A second image C2 is generated based on the magnetic resonance signal.

  FIG. 7 shows a view number view when a magnetic resonance signal is filled in k-space when generating the second image C2 in the embodiment according to the present invention, and a heartbeat signal E based on a heartbeat motion of the subject. It is a figure which shows a relationship. In FIG. 7, FIG. 7A shows the heartbeat signal E, where the horizontal axis is the time axis t and the vertical axis is the signal intensity ES of the heartbeat signal E. FIG. 7B shows the order of view numbers view when the heartbeat signal shown in FIG. 7A is measured. FIG. 7C shows a magnetic resonance signal collected when the heartbeat signal shown in FIG. 7A is measured, the horizontal axis is the view number view, and the vertical axis is the signal intensity MS. . As in FIG. 5, for convenience of explanation, in FIG. 7, the heartbeat signal E is shown as a sine wave having a fixed period. Further, the view number view is shown in the case where numbers (for example, number 15) are assigned in the order from the view at the negative position (for example, number 1) to the view at the positive position in the phase encoding direction of the k space. Yes.

  As shown in FIG. 7A, magnetic resonance signals are filled in the k space in the order of view numbers view as shown in FIG. 7B along the time axis t of the heartbeat signal measured with a periodic behavior. As described above, by performing the phase encoding at every repetition time TR, the scan unit 2 performs a scan on the imaging region including the artery and the vein in the subject SU. Specifically, when collecting the magnetic resonance signals, the heartbeat signal E detected in advance is used to correspond to the high sort method, as shown in FIG. After the view number view is rearranged according to the scan number, the scan unit 2 performs a scan so as to correspond to the rearranged view number view. For example, phase encoding is performed along the time axis t in the order of the view numbers view of 3, 5, 7, 9, 11, 13, 15, 14, 12, 10, 8, 6, 4, 2, 1. Then, scan. As a result, as shown in FIG. 7C, magnetic resonance signals are collected in the same manner as when the phase of the heartbeat signal fluctuates for each view.

  For this reason, as shown in FIG. 4, in the second image C2 generated based on the magnetic resonance signals collected as described above, the blood flow of the arterial portion DM changes greatly with the heartbeat, so that Since the signal of the pixel corresponding to the artery part DM is moved toward the end of the image, the pixel corresponding to the artery part DM is displayed with low luminance.

  FIG. 8 is a diagram showing a transition of the velocity v of blood flowing in the heartbeat period T on the time axis t in the embodiment according to the present invention. FIG. 8 shows the flow velocity vd of blood flowing through the artery and the flow velocity vj of blood flowing through the vein.

  As shown in FIG. 8, the flow velocity vd of the blood flowing through the artery changes so as to decelerate after accelerating in the systole TS of the cardiac cycle T. After that, in the diastole TK of the heartbeat cycle T, the flow velocity vd of the blood flowing through the artery changes so as to become a substantially constant speed. On the other hand, the flow velocity vj of the blood flowing through the vein changes so as to become a substantially constant speed in both the systole TS and the diastole TK of the heartbeat period T as shown in FIG. That is, blood flows as a pulsating flow in an artery, but blood flows as a steady flow in a vein.

  For this reason, the second image C2 is generated by using the magnetic resonance signals collected in the k-space so as to correspond to the high sort method in the cardiac compensation method. As described above, the pixel portion corresponding to the vein portion JM is generated with high luminance, and other portions including the artery portion DM are generated with low luminance.

  When a magnetic resonance signal is collected by this high sorting method so as to correspond to an FOV having a larger number of views than the target FOV, the pixel corresponding to the arterial portion is outside the target FOV. Since the signal is moved, the second image C2 can be generated with more favorable image quality.

  Next, as shown in FIG. 3, a difference image CG between the first image C1 and the second image C2 is generated (S31).

  Here, the difference image generation unit 313 performs difference processing for subtracting the pixel value of the second image C2 from each pixel value of the first image C1 generated as described above, whereby the difference image CG is obtained. Generate. That is, the subtraction value CI obtained by subtracting the pixel values C1 (x, y) and C2 (x, y) of the pixels at the same pixel position (x, y) in the first image C1 and the second image C2. After calculating (x, y), the subtraction value CI (x, y) is used as a pixel value to generate a difference image CG as an MRA image.

  As described above, in the first image C1, the pixels of the arterial portion DM and the vein portion JM have high luminance, and the other portions have low luminance. . On the other hand, in the second image C2, the pixel portion corresponding to the vein portion JM has high luminance, and other portions including the artery portion DM have low luminance.

  Therefore, in the difference image CG generated by performing the difference process between the first image C1 and the second image C2, as shown in FIG. 4, the pixel value of the pixel of the vein portion JM However, the pixel of the arterial portion DM has a large value, whereas only the arterial portion DM is rendered with high luminance. Therefore, the difference image CG is generated as if the arterial portion DM is separated.

  Next, as shown in FIG. 3, the difference image CG is displayed (S41).

  Here, the display unit 33 displays the difference image CG generated as described above on the display screen.

  As described above, in the present embodiment, the first image C1 is generated by performing imaging on the imaging region of the subject SU by an imaging method that does not apply the cardiac compensation method. Then, the second image C2 is generated by performing imaging on the imaging region of the subject SU by an imaging method to which the cardiac compensation method is applied. Since the high sort method is applied to the second image C2 in the cardiac compensation method, the second image C2 is generated as an image in which the signal of the arterial portion is moved to the end or the outside. Thereafter, a difference image CG is generated by performing a difference process between the first image C1 and the second image C2. In the difference image CG, only the arterial portion DM is depicted as described above. In the present embodiment, unlike the FBI method, it is not necessary to accurately obtain the delay time. For this reason, this embodiment can improve imaging throughput. Since data can be collected regardless of the cardiac phase, data collection efficiency can be improved.

  Further, since the present embodiment does not use the flow void phenomenon unlike the FBI method, the imaging method is not limited to the pulse sequence such as the FSE method. For this reason, as shown in the present embodiment, a pulse sequence corresponding to the Balanced SSFP method in which the contrast of the blood flow portion is high can be applied. For this reason, this embodiment can improve image quality.

  Furthermore, as described above, in the present embodiment, the diagnosis efficiency can be improved because the arteries and veins are displayed separately in the MRA image generated for the imaging region including the arteries and veins. .

  Note that the magnetic resonance imaging apparatus 1 of the present embodiment corresponds to the magnetic resonance imaging apparatus of the present invention. Moreover, in said embodiment, the display part 33 is corresponded to the display part of this invention. In the above embodiment, the first image generation unit 311 corresponds to the first image generation unit of the present invention. In the above embodiment, the second image generation unit 312 corresponds to the second image generation unit of the present invention. In the above embodiment, the difference image generation unit 313 corresponds to the difference image generation unit of the present invention. In the above embodiment, the imaging space B corresponds to the static magnetic field space of the present invention.

  Moreover, when implementing this invention, it is not limited to above-described embodiment, A various deformation | transformation form is employable.

  For example, in the above embodiment, the case where the vein is included in the FOV has been described, but the present invention is not limited to this.

  In the above-described embodiment, the case where the scan is performed by the pulse sequence corresponding to the Balanced SSFP method has been described, but the present invention is not limited to this.

  Further, the flow compensation pulse of the flow compensation method may be applied to the pulse sequence shown in the above embodiment. For example, when scanning the imaging area of a subject with an imaging method that does not apply the cardiac compensation method, the flow compensation pulse was applied, while the cardiac compensation method was applied. It is preferable not to apply the flow compensation pulse when scanning the imaging region of the subject by the imaging method. When a flow compensation pulse is applied when scanning an imaging region of a subject by an imaging method that does not apply the cardiac compensation method, artifacts may be generated in the first image C1 due to blood flow of an artery or the like. Since it can prevent generating, it is suitable.

FIG. 1 is a configuration diagram showing a configuration of a magnetic resonance imaging apparatus 1 in an embodiment according to the present invention. FIG. 2 is a functional block diagram of the data processing unit 31 constituting the operation console unit 3 of the magnetic resonance imaging apparatus 1 in the embodiment according to the present invention. FIG. 3 is a flowchart showing an operation when imaging the imaging region of the subject SU in the embodiment according to the present invention. FIG. 4 is a diagram illustrating an image generated when an imaging region of the subject SU is imaged in the embodiment according to the present invention. FIG. 5 shows a view number view when a magnetic resonance signal is filled in the k space when generating the first image C1 and a heartbeat signal E by a heartbeat motion of the subject in the embodiment according to the present invention. It is a figure which shows a relationship. FIG. 6 is a diagram showing a pulse sequence when scanning a subject in the embodiment according to the present invention. FIG. 7 shows a view number view when a magnetic resonance signal is filled in k-space when generating the second image C2 in the embodiment according to the present invention, and a heartbeat signal E based on a heartbeat motion of the subject. It is a figure which shows a relationship. FIG. 8 is a diagram showing a transition of the velocity v of blood flowing in the heartbeat period T on the time axis t in the embodiment according to the present invention.

Explanation of symbols

1: Magnetic resonance imaging apparatus (magnetic resonance imaging apparatus)
2: Scan section,
3: Operation console part,
12: Static magnetic field magnet section,
13: Gradient coil part,
14: RF coil section,
15: Subject moving part,
22: RF drive unit,
23: Gradient drive unit,
24: Data collection unit,
30: control unit,
31: Data processing unit,
32: Operation unit,
33: Display unit (display unit),
34: Storage unit
311: First image generation unit (first image generation unit),
312: second image generation unit (second image generation unit),
313: difference image generation unit (difference image generation unit),
B: Imaging space (static magnetic field space)

Claims (8)

A magnetic resonance imaging apparatus for imaging the imaging region by performing a scan to collect a magnetic resonance signal from an imaging region including an artery in a subject,
A first image is generated for the imaging region using the magnetic resonance signals collected in the execution of the scan so as to continuously fill the rows aligned in the phase encoding direction in the k space along the time axis. A first image generation unit;
A second image for generating a second image for the imaging region using magnetic resonance signals collected in the k-space in the execution of the scan so as to correspond to the high-sort method in the cardiac compensation method. An image generator;
A difference image generation unit that generates a difference image by performing difference processing between the first image generated by the first image generation unit and the second image generated by the second image generation unit And a magnetic resonance imaging apparatus. A display unit for displaying the difference image generated by the difference image generation unit on a screen;
The magnetic resonance imaging apparatus according to claim 1. The imaging region includes a vein,
The magnetic resonance imaging apparatus according to claim 1 or 2. The RF pulse is repeatedly transmitted at a repetition time so that the spin of the imaging region becomes the SSFP state, and the gradient pulse is transmitted in the repetition time in the slice selection direction, the phase encoding direction, and the frequency encoding direction in the imaging region. Performing the scan by transmitting so that the time integral value is zero within
The magnetic resonance imaging apparatus according to claim 1. A magnetic resonance image generation method for generating a magnetic resonance image for an imaging region based on a magnetic resonance signal collected by a scan performed on an imaging region including an artery in a subject,
First image generation for generating a first image for the imaging region using magnetic resonance signals collected to continuously fill rows of phase encoding in k-space along the time axis in performing the scan Steps,
A second image generation step of generating a second image for the imaging region using the magnetic resonance signals collected in the k space in the execution of the scan so as to correspond to the high sort in the cardiac compensation method. When,
Difference image generation step of generating a difference image by performing difference processing between the first image generated by the first image generation step and the second image generated by the second image generation step A magnetic resonance image generation method comprising: A display step of displaying the difference image generated by the difference image generation step on a screen;
The magnetic resonance image generation method according to claim 5. The imaging region includes a vein,
The magnetic resonance image generation method according to claim 5 or 6. The scan repeatedly transmits an RF pulse at a repetition time such that the spin of the imaging region is in the SSFP state, and in the imaging region, a gradient pulse is generated in each of the slice selection direction, the phase encoding direction, and the frequency encoding direction. Is implemented so that the time integration value becomes zero within the repetition time,
The magnetic resonance image generation method according to claim 5.