WO2005023107A1 - 磁気共鳴イメージング方法及び装置 - Google Patents
磁気共鳴イメージング方法及び装置 Download PDFInfo
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/563—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution of moving material, e.g. flow contrast angiography
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/5601—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution involving use of a contrast agent for contrast manipulation, e.g. a paramagnetic, super-paramagnetic, ferromagnetic or hyperpolarised contrast agent
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/5602—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by filtering or weighting based on different relaxation times within the sample, e.g. T1 weighting using an inversion pulse
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/563—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution of moving material, e.g. flow contrast angiography
- G01R33/5635—Angiography, e.g. contrast-enhanced angiography [CE-MRA] or time-of-flight angiography [TOF-MRA]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/567—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution gated by physiological signals, i.e. synchronization of acquired MR data with periodical motion of an object of interest, e.g. monitoring or triggering system for cardiac or respiratory gating
- G01R33/5673—Gating or triggering based on a physiological signal other than an MR signal, e.g. ECG gating or motion monitoring using optical systems for monitoring the motion of a fiducial marker
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
- G01R33/5613—Generating steady state signals, e.g. low flip angle sequences [FLASH]
- G01R33/5614—Generating steady state signals, e.g. low flip angle sequences [FLASH] using a fully balanced steady-state free precession [bSSFP] pulse sequence, e.g. trueFISP
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
- G01R33/56509—Correction of image distortions, e.g. due to magnetic field inhomogeneities due to motion, displacement or flow, e.g. gradient moment nulling
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/567—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution gated by physiological signals, i.e. synchronization of acquired MR data with periodical motion of an object of interest, e.g. monitoring or triggering system for cardiac or respiratory gating
- G01R33/5676—Gating or triggering based on an MR signal, e.g. involving one or more navigator echoes for motion monitoring and correction
Definitions
- the present invention relates to a magnetic resonance imaging method and apparatus for imaging and imaging a desired imaging region of an object, and more particularly, to an image of an object using a pulse sequence for applying a presaturation pulse.
- the present invention relates to a technique for reducing variations in echo signal strength when capturing images in synchronization with body movement.
- a magnetic resonance imaging apparatus utilizing the property of a contrast agent such as Gd-DTPA to aggregate in myocardium in a necrotic / infarcted state, the myocardium is extracted as a high signal region by ⁇ -weighted imaging.
- a contrast agent such as Gd-DTPA
- a first Inversion Recovery pulse is first applied to a predetermined slice in synchronization with an ECG R-wave.
- a second Inversion Recovery pulse with a notch is applied to the region excluding the predetermined slice.
- an echo signal is measured using an area included in the predetermined slice as a slice plane.
- Patent Document 1 JP-A-2002-306450
- the present invention reduces the variation in echo signal intensity when capturing an image in synchronization with the body movement of a subject by using a pulse sequence for applying a pre-saturation pulse, thereby reducing an image.
- the purpose is to improve image quality by preventing artifacts that occur above.
- a magnetic resonance imaging method of the present invention is configured as follows. That is
- An adjustment pulse is included, and the second pulse sequence includes an inversion pulse that inverts the longitudinal magnetization of the desired imaging region by 180 degrees.
- the longitudinal magnetization adjustment step is executed at the start of the imaging, and the measurement step is executed after the longitudinal magnetization adjustment step.
- the excitation angle of the adjustment pulse is set to 180 degrees.
- the excitation angle of the adjustment pulse is set to 90 degrees or more and 180 degrees or less.
- the body motion information acquiring step includes detecting an electrocardiographic waveform of the subject and an R wave thereof, and determining the first and second pulse sequences. This is executed for each heartbeat after the elapse of the first waiting time after the detection of the R wave.
- the second pulse sequence executes the measurement sequence after a lapse of a second waiting time from the inversion pulse.
- the method further comprises, before the longitudinal magnetization adjusting step, a contrast agent administering step of administering a contrast agent to the subject, wherein the longitudinal magnetization adjusting step is performed. Is executed after a lapse of a predetermined standby time from the contrast agent administration step.
- the body movement information acquiring step detects a change in the cycle and adjusts the longitudinal magnetization.
- the measuring step being performed immediately after the change in the cycle is detected. And executed.
- the body motion information detecting step detects a position or a displacement of the desired imaging region
- the longitudinal magnetization adjusting step includes the position Is reached at a predetermined position, or when the displacement is within a desired range, the measurement step is entered and executed.
- the body motion information detecting step detects a navigation echo reflecting position or displacement information of the desired imaging region.
- the excitation angle of the adjustment panel is changed for each heartbeat.
- the longitudinal magnetization can be adjusted more quickly and flexibly in accordance with the heartbeat cycle.
- the same pseudo measurement sequence as the measurement sequence is executed after the adjustment panel. Then, the number of repetitions of the first pulse sequence is determined from the echo signal measured in the pseudo measurement sequence.
- the longitudinal magnetization adjusted by the first pulse sequence is smoothly carried over to the second pulse sequence. be able to. Furthermore, the number of repetitions of the first pulse sequence can be determined according to the longitudinal magnetization state.
- the measurement sequence executes the same blank strike measurement sequence as the measurement sequence before executing the measurement sequence.
- the intensity of the echo signal before measurement is stabilized, so that the variation in the intensity of the echo signal is Can be further reduced to further prevent artifacts occurring on the image.
- the number of repetitions of the first pulse sequence executed at the start of imaging and immediately after the change of the cycle is determined. Make it different. Alternatively, the excitation angle of the adjustment pulse is made different.
- a magnetic resonance imaging apparatus of the present invention is configured as follows. That is
- Static magnetic field generating means for applying a static magnetic field to the subject; gradient magnetic field generating means for applying a gradient magnetic field in the slice direction, the phase encoding direction, and the frequency encoding direction to the subject; High-frequency magnetic field transmitting means for irradiating a high-frequency magnetic field pulse for causing resonance, echo signal receiving means for receiving an echo signal emitted by nuclear magnetic resonance, and a signal processing means for performing an image reconstruction operation using the echo signal A stage, an object state detecting means for detecting the state of the object and outputting information reflecting the state, and controlling a pulse sequence for receiving the echo signal corresponding to the object state. And a pulse sequence control unit, wherein the position of the subject is synchronized with information from the subject state detection unit.
- the pulse sequence for photographing the desired photographing region includes a first pulse sequence for adjusting the longitudinal magnetization of a region including the desired photographing region, and a subsequent execution of an echo signal from the desired photographing region.
- the first pulse sequence has an adjustment pulse for exciting longitudinal magnetization of a region including the desired imaging region to a predetermined angle
- the second pulse sequence changes the longitudinal magnetization of the desired imaging region by 180 degrees. It has an inversion pulse that inverts every degree.
- the pulse sequence has a pulse sequence for measuring a navigation echo reflecting position or displacement information of the desired imaging region.
- the subject state detection means detects the position or displacement of the desired imaging region from the navigation echo, and the pulse sequence control means detects when the position comes to a predetermined position, or When the displacement reaches a desired range, the first noise sequence is inserted into the second pulse sequence being executed and executed.
- FIG. 1 is a diagram showing an embodiment in which an empty heartbeat sequence at the start of imaging is composed of (a) only an Inversion Recovery sequence IR, and (b) an Inversion Recovery sequence IR and a signal measurement sequence Acq. .
- FIG. 2 is a diagram showing an embodiment in which an empty heartbeat sequence at the start of imaging is composed of (a) only a Saturation Recovery sequence SR, and (b) a Saturation Recovery sequence SR and a signal measurement sequence Acq.
- FIG. 3 is a diagram showing an embodiment in which an empty heartbeat sequence immediately after an arrhythmia is composed of (a) only a Saturation Recovery sequence SR, and (b) an Inversion Recovery sequence IR and a signal measurement sequence Acq.
- FIG. 4 is a diagram showing an example of a delayed contrast imaging sequence.
- FIG. 5 is a diagram showing an embodiment in which a signal measurement sequence is composed of (a) a measurement sequence only, (b) an idle measurement sequence and a measurement sequence, and (c) is a diagram showing a change in longitudinal magnetization.
- FIG. 6 is a diagram showing an example of a diaphragm navigation.
- (a) A diagram showing the positional relationship between each tissue of the subject and the slice cross-section and the diaphragm navigation excitation region.
- the excitation region by the 90-degree pulse and the excitation region by the 180-degree pulse are different.
- FIG. 4 is a diagram showing the generation of a crossed rhombic columnar force navi echo signal.
- FIG. 7 is a diagram showing an embodiment of body motion detection using a diaphragm navigation sequence.
- (a) A diagram showing an example of a diaphragm navigation sequence.
- (b) A diagram showing an example of inserting a diaphragm navigation sequence into the main measurement sequence.
- FIG. 8 is a diagram showing a preferred configuration example of an MRI apparatus to which the present invention is applied.
- FIG. 9 is a diagram showing an example of a gradient echo sequence.
- FIG. 8 shows a preferred configuration example of a magnetic resonance imaging (hereinafter, referred to as MRI) apparatus to which the present invention is applied.
- 801 is a magnet for generating a static magnetic field
- 802 is a subject such as a patient
- 803 is a bed on which the subject 802 is mounted
- 804 irradiates the subject 802 with a high-frequency magnetic field and detects an echo signal from the subject 802.
- 805, 806, and 807 are slice selection, phase encoding, and frequency encoding in X, Y, and Z directions, respectively.
- This is a gradient magnetic field generating coil for generating a gradient magnetic field.
- 808 is a high-frequency magnetic field power supply for supplying power to the high-frequency magnetic field coil 804, and 809, 810, and 811 are gradient magnetic field power supplies for supplying current to the respective gradient magnetic field generating coils 805, 806, and 807, respectively.
- Reference numeral 816 denotes a sequencer, which sends commands to peripheral devices such as gradient magnetic field power supplies 809, 810, 811, high-frequency magnetic field power supply 808, synthesizer 812, modulator 813, amplifier 814, and receiver 815 to control the operation of the MRI apparatus. .
- a storage medium 817 stores data such as photographing conditions.
- Reference numeral 818 denotes a computer which performs image reconstruction by referring to the echo signal input from the receiver 815 and the data in the storage medium 817.
- Reference numeral 819 denotes a display for displaying the result of image reconstruction performed by the computer 818.
- Reference numeral 821 denotes an ECG probe attached to the subject 802 as a subject state detecting means, and 820 denotes an ECG probe.
- An ECG waveform detector that detects the ECG waveform from the ECG probe 821 and sends it to the sequencer 816.
- the sequencer 816 sends a command to the gradient magnetic field power supply 809 811 according to a predetermined sequence, and the gradient magnetic field coils 805-807 generate gradient magnetic fields in each direction.
- the sequencer 816 sends a command to the synthesizer 812 and the modulator 813 to generate a high-frequency magnetic field waveform, and outputs the high-frequency magnetic field (hereinafter, referred to as RF pulse) amplified by the high-frequency magnetic field power supply 808 to the high-frequency magnetic field coil 804. Irradiated to the subject 802.
- the echo signal generated from the subject 802 is received by the high-frequency magnetic field coil 804, amplified by the amplifier 814, and subjected to A / D conversion and detection by the receiver 815.
- the center frequency used as a reference for detection is stored in the storage medium 817 and is read out by the sequencer 816 and set in the receiver 815.
- the detected echo signal is sent to a computer 818 and subjected to image reconstruction processing.
- the result of the image reconstruction or the like is displayed on the display 819.
- the sequencer 816 controls the execution of the sequence in synchronization with the electrocardiogram waveform from the electrocardiogram waveform detector 820.
- a first pulse sequence for adjusting longitudinal magnetization of a region including a desired imaging region of a subject is started at the start of imaging. This is a mode executed before a second pulse sequence for measuring an echo signal from the desired imaging region.
- This sequence is an example of a second pulse sequence, and is hereinafter referred to as a main measurement sequence.
- the present invention is not limited to this main measurement sequence.
- a predetermined time is waited after injecting a T-shortened contrast medium such as Gd-DTPA into a subject.
- This predetermined time is, for example, in the case of delayed contrast imaging, a time interval when the contrast agent accumulates in the infarcted myocardium and the echo signal from the infarcted myocardium becomes a high signal, and is generally called a delay time.
- the main measurement sequence 105 is started. In this measurement sequence 105, while the patient is holding their breath, in synchronization with the electrocardiogram R-wave (electric signal from the electrocardiogram waveform detector 820), after the waiting time TD from the R-wave 101, the slice as a desired imaging region is obtained.
- an Inversion Recovery (hereinafter, referred to as IR) sequence in which a 180-degree inversion pulse 102 of a slice non-selection is applied as a pre-saturation sequence to the region including.
- IR Inversion Recovery
- Acq signal measurement sequence 103 for measuring an echo signal from a slice which is a desired imaging region is executed for a period of Tacq.
- the idle signal measurement sequence 502 is executed to stabilize the echo signal, and thereafter the echo signal is converted
- the measurement sequence 501 to be measured is executed (refer to FIG. 5 (b).
- the blank shot measurement sequence is a sequence characterized by the following two characteristics.
- Echo signals are not measured, or echo signals are measured but not used for image reconstruction.
- the main measurement sequence 105 is composed of the IR sequence 102 and the Acq sequence 103. Further, the Acq sequence 103 may include only the measurement sequence 501 or may include the blank measurement sequence 502 and the measurement sequence 501.
- a measurement sequence 501 for measuring an echo signal a sequence based on a gradient echo method of the SSFP type (hereinafter referred to as a gradient echo sequence) is frequently used. This is because the repetition time TR shorter than the vertical relaxation time T and the horizontal relaxation time T
- Fig. 9 shows a sequence of gradient records.
- a slice selection gradient magnetic field 911 is applied to, for example, a heart of a subject placed in a static magnetic field, and an RF pulse 912 having a flip angle (eg, 45 °) is generated.
- a flip angle eg, 45 °
- a nuclear magnetic resonance phenomenon is induced in the slice.
- a phase encoding gradient magnetic field 913 is applied to the slice in which the nuclear magnetic resonance phenomenon has been induced.
- a dephase pulse 914 is applied in the frequency encoding direction. Thereby, the phase difference between the nuclear spins in the frequency encoding direction is enlarged.
- an echo signal 917 (for example, a time-series signal including 128, 256, 512, 1024 sampling data, etc.) is received during the A / D sampling interval 916 while the frequency encoding gradient magnetic field 915 is applied.
- a phase encoding gradient magnetic field 918 having a polarity opposite to that of the phase encoding gradient magnetic field 913 and a frequency encoding gradient magnetic field 915 having a polarity opposite to that of the frequency encoding gradient magnetic field 915 and an application amount of 1/2 (gradient magnetic field) are used.
- a rephase gradient magnetic field 919 having an area surrounded by the waveform and the time axis) is applied to the slice. This cancels the phase difference between nuclear spins.
- an RF pulse 910 that is a flip angular force (for example, ⁇ 45 °) is applied.
- the time from when the RF pulse 912 with the flip angle a is applied to when the RF pulse 910 with the flip angular force Sa is applied is repeated as a time TR.
- the RF pulse is continuously applied to the slice, and the amplitude of the phase encoder gradient magnetic field 913 and the polarity of the phase encoder gradient magnetic field 918 having the opposite polarity are changed and applied.
- the required number eg, 128, 256, 512, etc.
- a first pulse for adjusting the longitudinal magnetization of a region including a desired imaging region is provided before the main measurement sequence (second pulse sequence).
- second pulse sequence the application of only the high-frequency magnetic field as the adjustment pulse or the application of the high-frequency magnetic field and the gradient magnetic field is specified. Perform only heart rate.
- the first pulse sequence is defined as a blank heartbeat sequence
- the heart rate at which the blank heartbeat sequence is executed is defined as a blank heartbeat rate, respectively, to be distinguished from the main measurement sequence.
- the non-beating heartbeat sequence will be specifically described.
- FIG. 1 shows an example of an unbeatable heartbeat sequence.
- the blank heart rate is three heartbeats up to heartbeat 1 (101-1) and heartbeat 3 (101-3). However, it is not limited to three heartbeats.
- Fig. 1 (a) shows an example in which the blank heartbeat sequence 104 is composed of only an IR sequence consisting of IR1 (102-1) and IR3 (102-3), which are pre-saturation pulses as longitudinal magnetization adjustment pulses. ing.
- Fig. 1 (b) shows two types of sequences: an IR sequence consisting of IRK102-D-IR3 (102-3) and an Acq sequence consisting of Acql (103_l) -Acq3 (103_3), which is a pseudo measurement sequence.
- the example which comprises the heartbeat sequence 104 is shown. In each case, after the heartbeat 4, the echo signal measured in the main measurement sequence 105 including only the Acq sequence is used for image reconstruction.
- the longitudinal magnetization force S smoothed by the first pulse sequence is added to the second pulse sequence. Can be taken over.
- the blank heart rate may be determined by obtaining the state of longitudinal magnetization from the echo signal intensity. For example, if it is determined that the longitudinal magnetization has not converged to the desired state, the idle heart rate is increased and the idle heartbeat sequence 104 is continued. Conversely, if it is determined that the vertical magnetization has converged to the desired state, the idle beating heartbeat sequence 104 is stopped, and the flow shifts to the main measurement sequence 105.
- the Acq sequence in the blank heartbeat sequence 104 is composed of only the measurement sequence 501 as shown in FIG. It is possible to use either the case where the measurement is performed or the case where the measurement is made up of the idle measurement sequence 502 and the measurement sequence 501 as shown in FIG. 5 (b).
- the blanking measurement sequence 502 is the same sequence as the measurement sequence 501, but does not measure the echo signal or does not use the measured echo signal for image reconstruction. This is the same for other embodiments described later.
- Longitudinal magnetization is continuously tilted at a predetermined angle by an RF pulse and is recovered with a time constant of T
- the purpose of the IR pulse at the time of idling by the IR sequence in the present invention is to equalize the magnitude of longitudinal magnetization when applying the IR pulse in the present measurement sequence (the same applies to the Saturation Recovery pulse described later).
- the purpose of the RF pulse in the idle measurement sequence is to make the longitudinal magnetization uniform when measuring the echo signal. If the magnitude of the longitudinal magnetization is the same, the signal intensity at the time of the echo signal measurement becomes the same, so that no artifact occurs.
- the first embodiment shown in FIG. 1 is an example in which an IR sequence using a 180 ° inversion pulse is applied as an empty heartbeat sequence
- the second embodiment shown in FIG. This is an example of applying a Saturation Recovery (SR) sequence in which the reversal angle of nuclear magnetization is 90 degrees or more and 180 degrees or less.
- SR Saturation Recovery
- FIG. 2 shows an example in which the excitation angle increases with each heartbeat.
- the blank heart rate is three heartbeats up to heartbeat 1 (101-1) and heartbeat 3 (101-3).
- FIG. 2A shows an example in which the non-beating heartbeat sequence 104 is composed of only an SR sequence consisting of SR1 (201_1) -SR3 (201_3) as longitudinal magnetization adjustment pulses.
- Fig. 2 (b) shows two types of sequences, the SR sequence consisting of SR1 (201_1) and SR3 (201-3), and the Acq sequence consisting of Acql (103_l) -Acq3 (103_3).
- the example which comprises is shown.
- the echo signals measured in this measurement sequence 105 consisting only of the Acq sequence after heartbeat 4 are image-reconstructed This is the same as the first embodiment shown in FIG.
- the echo signal intensity can be reduced. Variation can be reduced. As a result, artifacts occurring on the image can be prevented.
- delayed contrast imaging when imaging the infarcted myocardium in synchronization with the R wave of the electrocardiogram, it is possible to reduce the variability of the echo signal intensity from the imaging slice, thus improving diagnostic performance by improving image quality. Can be.
- the first pulse sequence is applied to reduce the variation in echo signal intensity which is a cause of artifacts. Even when the period changes, the echo signal intensity varies. Therefore, in the second embodiment, immediately after the period of the periodic body movement of the subject changes, the first pulse sequence for adjusting the longitudinal magnetization of the region including the desired imaging region of the subject is set to the desired imaging sequence. This is a mode in which an echo signal from a region is inserted into a second pulse sequence for measurement and executed.
- the determination as to whether or not an arrhythmia can be made by, for example, setting thresholds for the upper and lower limits of the cardiac cycle in advance, and comparing the threshold with the length of the cardiac cycle. is there.
- the time interval between the heartbeat 101_n_l and the heartbeat 101_n is shortened due to the arrhythmia (heartbeat 101_n).
- a heartbeat 101-n which is an arrhythmia
- the idle beating heartbeat sequence 104 is inserted and executed immediately after the heartbeat 101_n.
- the blank heart rate is equal to heartbeat 101-n and heartbeat.
- the beat is 101-n + l twice.
- the main measurement sequence 105-2 is executed from the next heartbeat 101-n + 2 as a continuation of the main measurement sequence 105-1.
- the lower limit value of the heartbeat rate for preventing the occurrence of artifacts may be derived in advance for each MRI apparatus, and the number of times equal to or greater than the lower limit value may be applied as the heartbeat rate.
- FIG. 3 (a) shows an example in which the non-beating heartbeat sequence 104 is composed only of the SR sequences having the SR1 (201-1) and SR2 (201_2) forces.
- Fig. 3 (b) shows an IR sequence consisting of IRn (102_n) and IRn + l (102_n + l) and Acq.n_3 (103-n-3) and Acq.n-2 (103-n-2).
- An example is shown in which an empty beating heartbeat sequence 104 is composed of two types of sequences, namely, Acq sequences.
- the non-beating heartbeat sequence 104 is configured only with the IR sequence, or an example in which the non-beating heartbeat sequence 104 is configured with the SR sequence and the Acq sequence. Further, in the Acq sequence in the idle heartbeat sequence 104, the echo signal is not measured, or the echo signal is not used for image reconstruction even if the echo signal is measured, which is different from the first embodiment described with reference to FIGS. This is the same as in each embodiment.
- the configuration of the heartbeat sequence and the heartbeat sequence may be different between the heartbeat sequence at the start of imaging and the heartbeat sequence immediately after the arrhythmia.
- a beating heartbeat sequence at the start of imaging a beating heartbeat sequence composed of an IR sequence and an Acq sequence is executed for a period of three beating heartbeats
- SR a beating heartbeat sequence immediately after an arrhythmia
- SR It is possible to execute a blank beating heartbeat sequence consisting of only a sequence during a period of two blank beating heart rates. In this way, the longitudinal magnetization can be adjusted flexibly in response to the situation where the first noise sequence is executed.
- the empty heartbeat sequence is performed immediately after the arrhythmia, so that the echo signal intensity can be reduced. It is possible to suppress artifacts caused by variations.
- the longitudinal magnetization of the region including the desired imaging region of the subject is changed.
- the region including the desired imaging region is This is a mode in which a first pulse sequence for adjusting longitudinal magnetization is inserted into a second pulse sequence for measuring an echo signal from the desired imaging region and executed.
- FIGS. 6 and 7 An example of the present embodiment assuming respiratory movement will be described with reference to FIGS. 6 and 7, as an example in which the position of a desired imaging region changes due to periodic body movement.
- Diaphragm navigation is one of the techniques for detecting the position or displacement of the heart (Non-Patent Document 1).
- Fig. 6 shows an example of the excitation area in diaphragm navigation.
- FIG. 6 (a) shows the positional relationship between each tissue of the subject, the slice cross section, and the diaphragm navigation excitation area.
- Fig. 6 (b) shows an echo signal (hereinafter referred to as a Navi-Echo signal) from a diamond-shaped column-shaped area 603 where a 90-degree pulse excitation area 601 and a 180-degree pulse excitation area 602 intersect, as viewed from a slice cross section orthogonal to the diaphragm. ).
- Diaphragm navigation directly detects the position or displacement of the diaphragm. As a result, the position or displacement of the heart is indirectly detected.
- Non-patent document 1 US Pat. No. 4,937,526
- FIG. 7 shows an example of a diaphragm navigation sequence for realizing region-selective excitation.
- Two RF pulses a 90-degree pulse 701 and a 180-degree pulse 702, cross the excited regions 601 and 602 at the position of the diaphragm, respectively, and measure the navigation echo signal from the crossed region 603.
- a 90-degree pulse 701 is applied as a first RF pulse, and at the same time, a region selection gradient magnetic field 703 is applied. Thereafter, a dephase gradient magnetic field 706 is applied in the frequency encoding direction.
- a 180-degree pulse 702 is applied as a second RF pulse and a region-selecting gradient magnetic field 704 is applied at the same time to excite the 180-degree excitation region 602. .
- a spin echo one signal 705 is generated only in the intersection region 603 including the diaphragm, and this echo signal 705 is used as a navi echo signal with the frequency encoding gradient magnetic field 707 applied. It is measured.
- the measured navigation echo signal is converted into a projected image by Fourier transform, and the projected image is analyzed to detect the position or displacement of the diaphragm.
- the position or displacement of the diaphragm is analyzed to detect the position or displacement of the diaphragm.
- the above-described diaphragm navigation sequence 710 has a waiting time TD between the R wave 101 and the IR pulse 102, or a waiting time TI between the IR pulse 102 and the main measuring sequence 105, or the waiting time TI or the main measuring sequence 105. It can be inserted at any later time.
- FIG. 7 (b) shows an example in which the diaphragm navigation sequence 710 is inserted in the waiting time TD between the R wave 101 and the IR pulse 102.
- the position or displacement of the heart is indirectly detected using the diaphragm navigation sequence 710. Then, when the position of the heart comes to a predetermined position, or when the positional deviation of the heart falls within a predetermined range, it is determined that the slice cross section linked to the position of the heart has come to the predetermined position. Can be.
- the slice cross section is sliced by the main measurement sequence 105.
- a cross section is photographed.
- the execution of the main measurement sequence 105 is interrupted, and only the diaphragm navigation sequence 710 is repeatedly executed, and the position or displacement of the heart is indirectly monitored.
- the above-described empty beating heartbeat sequence 104 is executed by the number of empty beating heartbeats.
- the idle beating heartbeat sequence 104 in this embodiment is the same as that in each of the above-described first and second embodiments, and a detailed description thereof will be omitted. After the end of the idle heartbeat sequence 104, the main measurement is continued by returning to the main measurement sequence 105 shown in FIG. 7 (b).
- the execution of the empty beating heartbeat sequence 104 and the execution of the main measurement sequence 105 are switched, and all echo signals necessary for imaging a slice cross section are measured. Is done.
- the diaphragm navigation sequence 710 may be inserted not only during execution of the main measurement sequence 104 but also during execution of the idle beating heartbeat sequence 104.
- the echo signal from the desired imaging region Variations in intensity can be reduced, and artifacts due to body movements occurring on the image can be prevented to improve image quality.
- the MRI method and apparatus of the present invention are not limited to the above embodiments, and various modifications are possible.
- the present invention can be similarly applied to a force vertical magnetic field type MRI apparatus taking a horizontal magnetic field type MRI apparatus as an example.
- the source of the static magnetic field can be any of a permanent magnet, a superconducting magnet, and a normal conducting magnet.
- the present invention is applied to delayed contrast imaging of a heart as an imaging target.
- a thick blood vessel such as a thoracic aorta or an abdominal aorta
- the present invention can be applied to a simple ECG-gated radiography without using an organ, delayed imaging, or even a simple radiography without synchronization.
- the RF pulse or the SR pulse in the idle heartbeat sequence in which the slice is not selected may be an RF pulse that selectively excites a wide area (slab) including a desired slice.
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Abstract
Description
Claims
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US10/570,397 US7684847B2 (en) | 2003-09-05 | 2004-09-03 | Magnetic resonance imaging method and apparatus |
JP2005513671A JP4634934B2 (ja) | 2003-09-05 | 2004-09-03 | 磁気共鳴イメージング装置 |
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Also Published As
Publication number | Publication date |
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CN1845702A (zh) | 2006-10-11 |
US7684847B2 (en) | 2010-03-23 |
CN100490738C (zh) | 2009-05-27 |
US20070038069A1 (en) | 2007-02-15 |
EP1661513A4 (en) | 2009-07-29 |
EP1661513A1 (en) | 2006-05-31 |
JPWO2005023107A1 (ja) | 2007-11-01 |
JP4634934B2 (ja) | 2011-02-16 |
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