WO2011018954A1 - 磁気共鳴イメージング装置及び同期計測方法 - Google Patents
磁気共鳴イメージング装置及び同期計測方法 Download PDFInfo
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7203—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal
- A61B5/7207—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal of noise induced by motion artifacts
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7271—Specific aspects of physiological measurement analysis
- A61B5/7285—Specific aspects of physiological measurement analysis for synchronising or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal
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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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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/08—Detecting, measuring or recording devices for evaluating the respiratory organs
- A61B5/0816—Measuring devices for examining respiratory frequency
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/316—Modalities, i.e. specific diagnostic methods
- A61B5/318—Heart-related electrical modalities, e.g. electrocardiography [ECG]
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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
- G01R33/4818—MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space
- G01R33/482—MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space using a Cartesian trajectory
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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
- G01R33/4818—MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space
- G01R33/4824—MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space using a non-Cartesian trajectory
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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
- G01R33/5615—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
- G01R33/5617—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE] using RF refocusing, e.g. RARE
Definitions
- the present invention relates to a magnetic resonance imaging (hereinafter abbreviated as ⁇ MRI '') technique for obtaining a tomographic image of an examination site of a subject using a nuclear magnetic resonance (hereinafter abbreviated as ⁇ NMR '') phenomenon. It is related with synchronous photography technology.
- ⁇ MRI '' magnetic resonance imaging
- ⁇ NMR '' nuclear magnetic resonance
- echo signals at each lattice point on k-space are collected by Cartesian sampling in which sampling parallel to the frequency encoding direction is repeated in the phase encoding direction.
- orthogonal sampling echo signals are sampled repeatedly while changing the phase encoding amount.
- phase encoding direction due to random body motion of the subject or periodic motion such as pulsation. This occurs because when a subject whose position changes during photographing is picked up, a random phase change is added to the echo signal and the echo signal is not placed at the correct position during Fourier transform in the phase encoding direction.
- the main synchronized imaging methods include a respiratory synchronization method that suppresses body motion artifacts caused by respiration and an electrocardiographic synchronization method that suppresses body motion artifacts caused by heart motion or pulsation.
- the repetition time (TR) is limited by the physiological cycle of the living body, and the degree of freedom in setting the imaging parameters is reduced.
- TR repetition time
- TR is set in the range of 900 msec to 1 sec. Therefore, when the electrocardiographic synchronization method is used together when acquiring a T1-weighted image, it is difficult to set an optimal imaging parameter, and it is difficult to obtain a correct contrast.
- Non-cartesian sampling methods have been proposed to reduce body motion artifacts regardless of whether they are periodic or random.
- a radial method for example, see Non-Patent Document 1
- a hybrid radial method for example, see Non-Patent Document 2
- a spiral method for example, see Non-Patent Document 3
- the radial method is a technique for obtaining an echo signal necessary for image reconstruction by performing radial sampling while changing the rotation angle with the rotation point being approximately one point (generally the origin) in the measurement space. Since shooting is completed for each rotation angle, artifacts are unlikely to occur. Further, since sampling is performed in a radial manner, the central portion of the measurement space is measured in an overlapping manner, and artifacts are not noticeable due to the addition effect. Furthermore, even when artifacts occur, since sampling is not performed in a specific direction, the artifacts are scattered in the image, and the artifacts are not conspicuous compared to the orthogonal sampling method.
- the hybrid radial method is a combination of the radial method and phase encoding.
- the measurement space is divided into a plurality of blades with different sampling directions and sampled, and phase encoding is performed within the blade.
- the hybrid radial method has a feature that it can be easily applied to a sequence of a multi-echo method that acquires a plurality of echo signals by applying a single high-frequency magnetic field.
- the multi-echo method applied to the hybrid radial method for example, the FSE method and the echo planar method are known.
- the spiral method is a technique that obtains an echo signal necessary for image reconstruction by sampling in a spiral shape while changing the rotation angle and rotation radius around the rotation point and rotation radius about one point (generally the origin) in the measurement space. .
- the spiral method is applied as a high-speed imaging method because it wastes less time when filling a measurement space and data can be collected efficiently.
- the gradient magnetic field pulse waveform used when reading the echo signal is not a trapezoidal wave, but a combination of a sine wave and a cosine wave. There are few features.
- the non-orthogonal sampling method when imaging a region that is greatly affected by periodic motion, the state of the region to be imaged varies greatly depending on the imaging start timing. Thereby, when the imaging
- the present invention has been made in view of the above circumstances, and provides a technique for obtaining a high-quality and stable image with reduced body motion artifacts with a desired image contrast regardless of the region to be imaged. Objective.
- the imaging sequence using the non-orthogonal sampling method is executed in synchronization with the biological signal only at the start time, and the repetition time (TR) is maintained between each shot in the imaging sequence.
- an imaging sequence that divides a measurement space into a plurality of regions, repeats shots by a non-orthogonal sampling method at predetermined repetition time intervals, and collects echo signals of one or more regions from the subject And a biological signal receiving means for receiving a periodic biological signal of the subject, wherein the biological signal receiving means receives the biological signal.
- the magnetic resonance imaging apparatus is characterized in that the imaging sequence is started after a predetermined delay time and is executed while maintaining the repetition time interval.
- an imaging sequence for collecting one or more echo signals corresponding to a partial area of the measurement space, and repeating the imaging with different partial areas at a predetermined repetition time interval
- a biological signal receiving step for receiving a periodic biological signal of the subject, wherein the imaging step receives the biological signal and then performs the imaging sequence after a predetermined delay time.
- the synchronous measurement method is characterized in that the imaging sequence is repeated while maintaining the repetition time interval.
- a high-quality and stable image with reduced body motion artifacts of a subject can be obtained with a desired image contrast regardless of the part to be imaged.
- the block diagram which shows the whole structure of the MRI apparatus of 1st embodiment Explanatory drawing showing pulse sequence of orthogonal FSE sequence Explanatory drawing showing the state of echo signal group collected in orthogonal FSE sequence in measurement space Explanatory drawing showing pulse sequence of hybrid radial FSE sequence It is a figure which shows the mode of arrangement to the measurement space of the echo signal group collected by the hybrid radial FSE sequence, (a) is 1 blade, (b) is an explanatory view showing the whole measurement space It is a figure for explaining the synchronous imaging method, (a) is a sequence example of ECG synchronization, (b) is an explanatory diagram showing the state of arrangement of the collected echo signal in the measurement space, respectively Explanatory drawing for demonstrating the outline
- FIG. 1 is a block diagram showing an overall configuration of an example of the MRI apparatus 10 of the present embodiment.
- the MRI apparatus 10 of the present embodiment obtains a tomographic image of the subject 1 using the NMR phenomenon, and includes a static magnetic field generation system 2, a gradient magnetic field generation system 3, a sequencer 4, A transmission system 5, a reception system 6, an information processing system 7, and a biological signal detection unit 8.
- the static magnetic field generation system 2 generates a uniform static magnetic field in the body axis direction or in a direction perpendicular to the body axis in the space around the subject 1, and is a permanent magnet system arranged around the subject 1 or It is composed of a normal conduction type or superconducting type magnetic field generating means.
- the gradient magnetic field generation system 3 includes a gradient magnetic field coil 31 wound in three axial directions of X, Y, and Z, and a gradient magnetic field power source 32 that drives each gradient magnetic field coil.
- a gradient magnetic field pulse having components in three axis directions of X, Y, and Z is applied to the subject 1.
- a slice direction gradient magnetic field pulse (Gs) is applied in one of X, Y, and Z to set the slice plane for the subject 1, and the phase encode direction gradient magnetic field pulse (Gp) in the remaining two directions
- Gf frequency encoding direction gradient magnetic field pulse
- the transmission system 5 irradiates a high-frequency magnetic field (RF) pulse to cause nuclear magnetic resonance to occur in the nuclear spins of atoms constituting the biological tissue of the subject 1, and includes a high-frequency oscillator 52, a modulator 53, and a high-frequency amplifier 54. And a high frequency coil (transmission coil) 51 on the transmission side.
- the high-frequency pulse output from the high-frequency oscillator 53 is amplitude-modulated by the modulator 53 at a timing according to a command from the sequencer 4, amplified by the high-frequency amplifier 54, and then transmitted to the transmission coil 51 disposed close to the subject 1. Then, the subject 1 is irradiated as an RF pulse.
- the receiving system 6 detects an NMR signal (echo signal) emitted by nuclear magnetic resonance of nuclear spins constituting the biological tissue of the subject 1, and includes a receiving-side high-frequency coil (receiving coil) 61, an amplifier 62, A quadrature detector 63 and an A / D converter 64 are provided.
- the echo signal of the response of the subject 1 induced by the RF pulse irradiated from the transmission coil 51 is detected by the reception coil 61 arranged close to the subject 1, amplified by the amplifier 62, and then the sequencer 4 Are divided into two orthogonal signals by the quadrature phase detector 63 at the timing according to the command from each of the signals, converted into digital quantities by the A / D converter 64, and sent to the information processing system 7 as received signals.
- the sequencer 4 is a control means that repeatedly performs the irradiation of the RF pulse and the application of the gradient magnetic field pulse in accordance with a predetermined imaging sequence.
- the sequencer 4 operates under the control of the information processing system 7. Is sent to the transmission system 5, the gradient magnetic field generation system 3, and the reception system 6.
- the photographing sequence is created in advance according to the purpose of measurement, and stored as a program and data in a storage device 72 described later in the information processing system 7 or the like.
- the information processing system 7 performs control of the entire operation of the MRI apparatus 10, signal processing, image reconstruction processing, and the like.
- the CPU 71 a storage device 72 such as a ROM and a RAM, and an external storage device 73 such as an optical disk and a magnetic disk ,
- a display device 74 such as a display
- an input device 75 such as a mouse, a trackball, and a keyboard.
- the information processing system 7 performs signal processing, fills the measurement space, and reconstructs an image.
- the reconstructed tomographic image of the subject 1 is displayed on the display device 74 and recorded in the storage device 72 or the external storage device 73.
- the information processing system 7 gives a command to the sequencer 4 in accordance with a photographing sequence stored in advance in the storage device 72 or the like. These processes of the information processing system 7 are realized by the CPU 71 loading a program stored in advance in the storage device 72 or the like into the memory and executing it.
- the imaging sequence is generated by the information management system 7 using imaging parameters input from the operator and a pulse sequence stored in advance, and is stored in the storage device 72 or the like.
- the biological signal detection unit 8 includes devices such as an electrocardiographic sensor, a pulse wave sensor, and a respiration sensor attached to the subject, and a pulse wave generation unit that generates a pulse wave from the biological signal detected by these devices.
- the pulse wave generated by the pulse wave generator is transmitted to the information processing system 7.
- the information processing system 7 outputs an instruction according to the imaging sequence to the sequencer 4 in synchronization with the pulse wave.
- a pulse wave obtained from an electrocardiogram sensor or a pulse wave sensor is called an electrocardiogram waveform
- a pulse wave obtained from a respiration sensor is called a respiration waveform.
- the transmission coil 51, the reception coil 61, and the gradient magnetic field coil 9 are installed in the static magnetic field space of the static magnetic field generation system 2 arranged in the space around the subject 1.
- the transmission coil 51 and the reception coil 61 are provided separately is illustrated, but the present invention is not limited thereto.
- one high frequency coil may be configured to share both functions.
- the MRI apparatus 10 having the above configuration visualizes the form or function of the human head, abdomen, extremities, etc. by imaging the spatial distribution of the density of the spin target to be imaged and the spatial distribution of the relaxation phenomenon of the excited state.
- the imaging target spin species that is currently widely used in clinical practice is proton, which is the main constituent of the subject.
- the signal intensity I of the received signal sent from the receiving system 6 to the information processing system 7 is expressed by the following equation (1).
- k is a constant
- ⁇ is a spin density (proton density)
- T1 and T2 are tissue longitudinal relaxation time and transverse relaxation time
- TR is a pulse sequence repetition time
- TE is an echo time, respectively.
- Both relaxation times T1 and T2 are different for each tissue, and the difference is the image contrast.
- Contrast types include T1 emphasis, T2 emphasis, and proton density emphasis.
- the contrast of the image changes depending on the shooting parameters such as TR and TE set at the time of shooting.
- the TE is set short to reduce the contribution of the TE
- the TR is set short to produce a difference in relaxation time due to the TR.
- TE is set to about 10 msec and TR is set to about 500 to 600 msec.
- TR is set to be long in order to reduce the contribution due to TR
- TE is set to be long in order to obtain a difference in relaxation time due to TE.
- TE is set to about 120 msec and TR is set to about 6000 msec.
- FIG. 2 is a pulse sequence diagram of orthogonal FSE sequence 200.
- RF, Gs, Gp, Gf, AD, and Echo represent axes of RF pulse, slice gradient magnetic field, phase encode gradient magnetic field, frequency encode gradient magnetic field, A / D conversion, and echo signal, respectively. These are the same in each pulse sequence diagram of this specification.
- RF, Gs, Gp, Gf, AD, and Echo represent axes of RF pulse, slice gradient magnetic field, phase encode gradient magnetic field, frequency encode gradient magnetic field, A / D conversion, and echo signal, respectively.
- a slice selection gradient magnetic field pulse 202 is applied together with an excitation RF pulse 201 that applies a high-frequency magnetic field to spins in the imaging plane.
- an excitation RF pulse 201 that applies a high-frequency magnetic field to spins in the imaging plane.
- a slice rephase pulse 203 for returning the phase of the spin diffused by the slice selective gradient magnetic field pulse 202, and a frequency phase for dispersing the spin phase in advance to generate an echo signal.
- a phase gradient magnetic field pulse 204 is applied.
- an inversion RF pulse 205 for inverting the spin in the slice plane is repeatedly applied.
- a slice selection gradient magnetic field pulse 206 for selecting a slice, a phase encoding gradient magnetic field pulse 207, and a frequency encoding gradient magnetic field pulse 208 are applied, and at the timing of the sampling window 209, the echo signal 210 is applied.
- the echo signal 210 is usually collected as a time-series signal composed of any one of 128, 256, 512, or 1024 sampling data at the timing of each sampling window 209.
- the process from the application of an excitation RF pulse to the collection of a predetermined number (6 in the above example) of echo signals is called unit measurement (shot).
- shots are repeated while changing the area of the phase encoding gradient magnetic field pulses 207 for each time interval (TR) 211, and all echo signals 210 required for the image are obtained for each time interval 212.
- TR time interval
- values such as 64, 128, 256, and 512 are usually selected for one image.
- FIG. 3 shows how the echo signals 210 collected by the orthogonal FSE sequence 200 shown in FIG. 2 are arranged in the measurement space 221.
- an arrow corresponds to one echo signal 210, and the direction of the arrow indicates the direction in which the echo signal 210 is scanned.
- the thickness of the arrow corresponds to the signal intensity of the echo signal 210.
- a case where one shot is repeated 8 times and the echo signals 210 are collected is illustrated. That is, a case where the measurement space 221 is filled with a multi-shot orthogonal system FSE sequence in which a shot for collecting six echo signals 210 with one excitation RF pulse 201 is repeated eight times is illustrated.
- the echo signals 210 are phase-encoded so that they are arranged sequentially from top to bottom (i.e., from -Ky to + Ky), one in each block 222.
- the magnetic field pulses 207 group are controlled.
- the phase encoding gradient magnetic field pulse 207 group is controlled so that echo signals collected at the same echo time are arranged on different lines in the same block 222.
- the subscript of each block 222 in FIG. 3 corresponds to the echo number of the echo signal 210 in each shot arranged in the block 222.
- the echo number is assigned to each echo signal 210 collected in each shot of the orthogonal FSE sequence 200 in the order of collection time. That is, the echo signal has a longer echo time as the echo number increases. Note that the filling order of the measurement space 221 can be changed by changing the method of changing the intensity of the phase encoding gradient magnetic field pulse group 207.
- each block (blade) is filled with an echo signal group obtained by one excitation.
- FIG. 4 is a pulse sequence diagram of the hybrid radial FSE sequence 300.
- FIG. FIG. 5 is a diagram showing a state in which echo signal groups collected by the hybrid radial FSE sequence 300 are arranged in the measurement space 321.
- the hybrid radial FSE sequence 300 is different from the orthogonal FSE sequence 200 in that there is no distinction between the phase encoding gradient magnetic field axis Gp and the frequency encoding gradient magnetic field axis Gf.
- the axes are shown as G1 and G2 axes for convenience.
- the orthogonal FSE sequence 200 a case where six echo signal groups are collected in one shot will be described as an example.
- the measurement space is divided into a plurality of blades (unit areas), and each blade is measured at a rotation angle of a different measurement space.
- One blade has a plurality of parallel trajectories each corresponding to one echo signal.
- the rotation angle of the measurement space is an angle formed by a predetermined axis (in this specification, kx axis) of the measurement space and a trajectory passing through the center of the measurement space in each blade.
- phase encoding is applied to the echo signal measured in the blade.
- each blade 322 is filled with an echo signal group collected by one excitation RF pulse. Therefore, the basic configuration of the pulse sequence for one shot is the same as that of the orthogonal FSE sequence 200.
- a slice selective gradient magnetic field pulse 202 is applied together with an excitation RF pulse 201 that applies a high-frequency magnetic field to spins in the imaging plane.
- an excitation RF pulse 201 that applies a high-frequency magnetic field to spins in the imaging plane.
- a slice rephase pulse 203 for returning the phase of the spin diffused by the slice selective gradient magnetic field pulse 202 and a readout phase for pre-dispersing the phase of the spin to generate an echo signal.
- a phase gradient magnetic field pulse 301 and a read dephase gradient magnetic field pulse 302 are applied.
- an inversion RF pulse 205 for inverting the spin in the slice plane is repeatedly applied.
- a slice selection gradient magnetic field pulse 206 for selecting a slice, a readout gradient magnetic field pulse 307, and a readout gradient magnetic field pulse 308 are applied, and the echo signal 310 is collected at the timing of the sampling window 209. To do.
- the inverted RF pulse 205 is applied six times.
- FIG. 5 (a) is a diagram for explaining the arrangement of echo signals 310 of one blade 322 acquired using one shot of the hybrid radial FSE sequence 300.
- FIG. 5 (a) is a diagram for explaining the arrangement of echo signals 310 of one blade 322 acquired using one shot of the hybrid radial FSE sequence 300.
- an arrow corresponds to one echo signal 310, and the direction of the arrow indicates the direction in which the echo signal 310 is scanned.
- the thickness of the arrow corresponds to the signal intensity of the echo signal 310, and the subscript corresponds to the echo number.
- the echo number is assigned to each echo signal 310 collected in each shot of the hybrid radial FSE sequence 300 in the order of collection time.
- each blade 322 is rotated radially about substantially one point in the measurement space 321.
- FIG. 5 (b) shows a state where the hybrid radial FSE sequence 300 shown in FIG. 4 is repeated and the collected echo signals 310 are arranged in the measurement space 321. Echo signals 310 collected in the same shot are arranged on the same blade 322.
- the subscript 322 is a number (shot number) corresponding to the number of repetitions of the FSE sequence 300 every time interval 311.
- This figure shows an example in which the FSE sequence 300 is controlled so that it rotates counterclockwise by a half turn and scans the measurement space 321 with 8 repetitions.
- an arrow corresponds to one echo signal 310
- the direction of the arrow indicates the direction in which the echo signal 310 is scanned
- the thickness of the arrow corresponds to the signal intensity of the echo signal 310.
- blades having different rotation angles are measured for each shot number.
- 401 is an electrocardiographic waveform acquired by the biological signal detection unit 8
- a time interval 402 is an interval of the electrocardiographic waveform 401 (generally called an RR interval).
- the imaging sequence is started after a time interval 403 (hereinafter, delay time), and the echo signal group 405 is collected within the time interval 404.
- delay time a time interval 403
- echo signal group 405 is collected within the time interval 404.
- echo signals are collected at the same timing, and data necessary for reconstructing an image is obtained in synchronization with the electrocardiogram waveform 401.
- the RR interval is also called a cardiac cycle, and the numbering after the hyphen indicates that the processing is within the cardiac cycle after the nth electrocardiogram waveform 401-n. In the following description, the numbers below the hyphens are omitted unless particularly distinguished.
- electrocardiographic synchronization it is called an electrocardiographic waveform 401, but is generally called a biological signal 401 or a trigger signal 401.
- FIG. 6 (b) shows an example in which the echo signal group 405 collected in this way is arranged in the measurement space 422.
- FIG. Here, an example is shown in which echo signals are collected by the orthogonal sampling method. By changing the phase encoding amount for each echo signal 405, the number of echo signals 405 that can be collected within the time interval 404 for each cardiac cycle is collected and arranged in the measurement space 421. This is repeated until the entire measurement space 421 is filled.
- FIG. 6 (b) shows an example in which the measurement space 421 is sequentially filled from the top in the Ky axis direction from the echo signal 405-1 collected in the first cardiac cycle.
- each shot is executed within the time interval 404 in each cardiac cycle, and the echo signal 310 is collected. Therefore, TR311 needs to be adjusted to the RR interval 402.
- the RR interval is not always constant. Even if it is substantially constant, TR set in an image having a desired contrast generally does not coincide with the RR interval.
- the entire imaging sequence is synchronized instead of every TR. That is, only the start of imaging is synchronized with the electrocardiogram waveform 401, and each subsequent shot is executed at a TR interval as usual.
- the outline of the synchronous imaging method of this embodiment will be described with reference to FIG.
- the ECG synchronization method will be described as an example.
- the total number of shots taken is N (N is a natural number), and 501-n (n is a natural number satisfying 1 ⁇ n ⁇ N) indicates a shot with a shot number n (hereinafter, nth shot).
- 502-n indicates a time difference between the shot start time 503-n of the nth shot and the nearest delay time 403 elapsed time 406 (delay time 406).
- delay time 406 delay time 406
- the information processing system 7 includes a synchronous imaging control unit and realizes the above control. Further, the information processing system 7 includes a biological signal receiving unit that receives a pulse wave from the biological signal detection unit 8 and notifies the synchronous imaging control unit independently of control by the synchronous imaging control unit. These functions of the information processing system 7 are realized by the CPU 71 loading a program stored in the storage device 72 or the like into the memory and executing it.
- FIG. 8 is a processing flow of the photographing process of the present embodiment.
- the synchronous imaging control unit When the synchronous imaging control unit receives an input of imaging parameters from the operator, the synchronous imaging control unit generates an imaging sequence (basic shape of a sequence to be executed) using a pulse sequence held in advance (step S1201). Further, the counter cn for counting the shot number of the shot to be executed is set to 1 (step S1202).
- the synchronous imaging control unit waits for reception of a pulse wave. Upon receiving notification that the pulse wave has been received from the biological signal receiving unit (step S1203), after the delay time input as the imaging parameter has elapsed (step S1204), the cn-th shot is executed according to the imaging sequence (step S1205). . At this time, the shot start time is stored in association with the value of the counter cn.
- the synchronous imaging control unit of the present embodiment performs the imaging process as described above, realizes the synchronous imaging of the present embodiment, and fills the measurement space with an echo signal.
- the synchronous imaging method is not limited to electrocardiographic synchronization.
- the delay time 403 is set as an imaging parameter together with other imaging parameters by the operator.
- the optimum delay time 403 is determined by the part to be imaged and the type of biological signal to be employed. For example, when the biological signal is a heartbeat, generally, the diastolic phase has less movement of the subject 1 and a high-quality image can be obtained. Accordingly, the delay time 403 is determined so as to start shooting in the expansion period. On the other hand, when the biological signal is respiration, the movement of the subject 1 is gentle and the artifacts are less likely to occur when matched with the expiration period. Therefore, the delay time 403 is determined so that shooting is started in the call period.
- the synchronous imaging method is not used, imaging starts at random with respect to the body movement cycle of the living body.
- the state of the blood flow flowing in the blood vessel changes between a systole in which the amount of change in heart motion is the largest and a diastole in which the amount of change is the smallest.
- the depiction of the blood vessel may change for each imaging depending on the start timing with respect to the body motion cycle.
- the repetition time TR of the imaging sequence is close to a multiple of the body movement cycle of the living body (including 1/2 times, 1/3 times, etc.)
- a result close to synchronized shooting is obtained for each shooting, and the obtained image Is close to a predetermined time phase of the body movement cycle, so that the difference in rendering due to the start timing appears significantly. Accordingly, the rendering of the resulting image changes with each shooting.
- the imaging sequence is started after the delay time 403 set by the imaging parameters from the trigger signal (electrocardiogram waveform in FIG. 7) 401 in synchronization with a predetermined biological signal. Therefore, even when the imaging of a part where the influence of the periodic movement is large is repeated, the state of the imaging target part with respect to the periodic movement at the start of each imaging is substantially the same, and the periodic body between the imagings The effects of movement are almost the same. For this reason, it is possible to obtain a stable image without changing the depiction of the subject to be photographed for every photographing. On the other hand, each shot constituting the shooting is executed at a TR interval as usual. Therefore, a desired contrast can be obtained. Further, since the non-orthogonal sampling method is used, the body motion artifact can be reduced.
- a certain state can be depicted for each photographing and a desired contrast can be obtained. Can do. Therefore, it is possible to obtain a stable and high-quality image for each photographing without sacrificing the contrast regardless of the photographing target part including a part that is easily affected by the periodic movement of the living body.
- the number of echoes and the number of blocks in the block of the hybrid radial method are illustrated as 6 and 8 for simplicity of explanation, but the present invention is not limited to this.
- the number of blocks and the number of echoes in the block can be arbitrarily set.
- the MRI apparatus of this embodiment basically has the same configuration as that of the first embodiment.
- the first embodiment once shooting is started, thereafter, all shots are executed once in order at TR intervals.
- whether to accept the result is determined according to the time from the delay time of each shot start time, and when it is not adopted, it is repeatedly executed until it is adopted.
- the imaging process of the present embodiment will be described focusing on a configuration different from that of the first embodiment.
- the time difference 502 is calculated as the absolute value of the time between the start time 503 of the shot 501 and the nearest delay time 406. If the time difference 502 is equal to or greater than a predetermined threshold value, the echo signal collected by the shot 501 is not used for image reconstruction, and the echo signal is collected again under the same conditions.
- the time difference 502 is defined as the time between the delay time 406-1 and the start time 5032.
- the trigger signals 401-1 and 401-2 are received at the end of the main shot. Therefore, the delay times 406-1 and 406-2 can be known.
- Absolute values 502-3-1 and 502-3-2 of differences between the delay times 406-1 and 406-2 and the start time 503-3 are calculated, and the smaller one is set as the time difference 502.
- Differences 502-4-1 and 502-4-2 between the start time and the delay time are calculated, and the smaller one is set as the time difference 502.
- the optimal delay time 403 is set as an imaging parameter for each imaging target region. Accordingly, the further away from the delay time 406 after the lapse of the delay time 403 from the trigger signal 401, the more easily the influence of the periodic body movement is introduced, and the state fluctuation at the time of measurement is larger.
- a threshold value is provided for the time difference 502 to avoid using echo signals collected in such a state for image reconstruction.
- the synchronous shooting control unit provided in the first embodiment calculates the absolute value of time as a time difference from the start time of the shot to the nearest delay time after the end of each shot.
- the apparatus further includes a time difference calculation unit and a acceptance / rejection determination unit that determines acceptance / rejection of the echo signal obtained in the shot based on the calculation result of the time difference calculation unit.
- the biological signal receiving unit includes a trigger signal storage unit that stores the time when the notification that the pulse wave is received from the biological signal detection unit 8 is received as the trigger reception time.
- FIG. 9 is a processing flow of imaging processing by the synchronous imaging control unit of the present embodiment.
- the trigger signal storage unit stores the trigger reception time independently of the imaging processing every time a pulse wave is received.
- the synchronous imaging control unit When the synchronous imaging control unit receives an input of imaging parameters from the operator, the synchronous imaging control unit generates an imaging sequence using a pulse sequence held in advance (step S1101). Further, the counter cn for counting the shot number of the shot to be executed is set to 1 (step S1102). When receiving the start instruction from the operator, the synchronous imaging control unit waits for reception of a pulse wave. When a pulse wave is received (step S1103), the cn-th shot is executed according to the imaging sequence after the delay time input as the imaging parameter has elapsed (step S1104) (step S1105). At this time, the shot start time is stored in association with the counter value cn.
- the synchronous imaging control unit causes the time difference calculation unit to calculate the time difference scn between the start time 503 of the cn-th shot and the nearest delay time 406 (step S1107). Specifically, if there is a time difference (first time difference) from the latest trigger reception time 401 to the delay time 406 after the delay time 403 has elapsed, and a trigger reception time one time before the latest, the trigger reception time 401 The time difference (second time difference) from the delay time 406 is calculated. The smaller of the first time difference and the second time difference is defined as a time difference scn.
- the synchronous imaging control unit causes the acceptance / rejection determination unit to determine acceptance / rejection of the echo signal obtained in the shot (step S1108). That is, it is determined whether or not the time difference scn is within a predetermined threshold value Smax. As a result of comparing scn and Smax as a result of comparing scn and Smax, the acceptance / rejection determination unit determines that the echo signal obtained in the cn-th shot executed in step S1105 can be adopted. If it is determined that it can be adopted, the synchronous imaging control unit increments cn by 1 (step S1109), waits for the TR time to elapse from the previous shot start time (step S1110), and proceeds to step S1105.
- step S1108 if the time difference scn is larger than the threshold value Smax in step S1108, the acceptance / rejection determination unit determines that the echo signal obtained in the shot cannot be adopted. If it is determined that adoption is not possible, the synchronized shooting control unit executes the cn shot again, and therefore waits for the TR time to elapse without incrementing cn (step S1110), and then proceeds to step S1105. Transition. In step S1105, when the start time associated with the same counter value cn is stored, it is updated to a new start time.
- the synchronous imaging control unit of the present embodiment controls the imaging, realizes the synchronous imaging of the present embodiment, and fills the measurement space with the echo signal determined to be adoptable.
- the TR time is maintained while using the synchronous photographing method in the photographing sequence to which the non-orthogonal sampling method is applied, and thus the same effect as the first embodiment is obtained. Obtainable. Furthermore, according to the present embodiment, when the start time of the shot is far from the delay time 406, the shot with the same shot number is re-executed at a TR interval. Therefore, since the echo signals collected at a timing far away from the delay time 406 and the state of the subject due to the periodic movement are greatly different are not used for image reconstruction, the image quality is further improved.
- the value of Smax used for discrimination is set in advance so that the photographing efficiency does not decrease and the influence of movement is not noticeable. For example, it is set to about 1 second for the respiratory synchronization method, and about several hundred millimeters for the electrocardiogram synchronization method.
- the shot (nth shot) when it is determined that the echo signal acquired in a predetermined shot (for example, the nth shot) is not adopted, the shot (nth shot) is re-executed at the next time interval TR.
- all shots may be sequentially executed in the order of shot numbers in the same manner as in the first embodiment, and a shot (n-th shot) determined not to be adopted after execution of all shots may be performed.
- the MRI apparatus of this embodiment basically has the same configuration as that of the first and second embodiments.
- whether or not to use the collected echo signal is determined based on the time difference between the shots.
- the collected echo signals are weighted according to the time difference for each shot.
- the measurement sequence of the present embodiment will be described focusing on the configuration different from the first embodiment.
- the optimal delay time 403 is selected for each part to be imaged. Therefore, the farther the shot start time is away from the delay time 406, that is, the greater the time difference 502, the lower the quality of the collected echo signal.
- a function that monotonously decreases depending on the time difference 502 is introduced as a weighting coefficient calculation function C (s), and for each shot, an echo value collected as a weighting coefficient is multiplied. By doing in this way, the influence on the reconstructed image of the echo signal collected in the state with the large time difference 502 is suppressed.
- the synchronous shooting control unit provided in the first embodiment calculates the absolute value of the time from the start time of the shot to the nearest delay time as the time difference after the end of each shot.
- a signal intensity correction unit that corrects the signal intensity by multiplying the echo signal obtained by the shot based on the calculation result of the time difference by a weighting coefficient.
- the biological signal receiving unit includes a trigger signal storage unit that stores the time when the notification that the pulse wave is received from the biological signal detection unit 8 is received as the trigger reception time.
- FIG. 10 is a processing flow of photographing processing by the synchronous photographing control unit of the present embodiment.
- the synchronous imaging control unit when receiving an input of imaging parameters from the operator, the synchronous imaging control unit generates an imaging sequence using a pulse sequence held in advance (step S1301). Further, the counter cn for counting the shot number of the shot to be executed is set to 1 (step S1302).
- the synchronous imaging control unit waits for reception of a pulse wave.
- the cn-th shot is executed according to the imaging sequence after the delay time input as the imaging parameter has elapsed (step S1304) (step S1305). At this time, the shot start time is stored in association with the counter value cn.
- the synchronous imaging control unit causes the time difference calculation unit to calculate the time difference scn between the start time 503 of the cn-th shot and the nearest delay time 406 (step S1307). Specifically, if there is a time difference (first time difference) from the latest trigger reception time 401 to the delay time 406 after the delay time 403 has elapsed, and a trigger reception time one time before the latest, the trigger reception time 401 The time difference (second time difference) from the delay time 406 is calculated. The smaller of the first time difference and the second time difference is defined as a time difference scn.
- the synchronous imaging control unit causes the signal correction unit to correct the signal intensity of the echo signal obtained by the shot (step S1308).
- the correction is performed by multiplying the echo signal by the weighting coefficient C (scn) obtained from the time difference scn calculated in step S1307.
- the synchronous imaging control unit increments cn by 1 (step S1309), waits for the TR time to elapse from the previous shot start time (step S1310), and proceeds to step S1305.
- the time difference scn is calculated and the signal intensity of the echo signal is corrected at every shot end, but this is not restrictive.
- the time difference scn may be stored in association with the shot number cn of each shot and corrected before image reconstruction.
- FIG. 11 is an example of the weighting factor calculation function C (s) 601 of this embodiment.
- the weighting factor calculation function C (s) 601 shown in this figure is 1 when the time difference s is 0, decreases linearly from 1 as the time difference s increases, and becomes 0 when the time difference s is greater than or equal to Smax.
- the horizontal axis of the figure indicates the time difference 502 between each shot 501 in FIG.
- This weight coefficient calculation function C (s) 601 is expressed by the following equation (2).
- the weight coefficient calculation function C (s) is set in advance and held in the storage device 72 or the like.
- Smax is set in the same manner as in the second embodiment.
- the signal intensity correction unit uses the weighting coefficient calculated by the weighting coefficient calculation function C (s) according to the time difference s of each shot. Correct the intensity. For this reason, in the measurement space, the contribution of the value of the echo signal collected by the shot executed at the timing when the time difference s is large decreases. Therefore, since the image is reconstructed from the echo signals filled in the measurement space in this way, according to this embodiment, it is possible to further suppress the influence of movement, and in addition to the effect obtained in the first embodiment. Further, the image quality is improved.
- echo signals collected within one shot are multiplied by the same weighting factor.
- the low spatial frequency region that is the central portion of the measurement space 321 is measured for each blade 322. For this reason, excessive data exists in the central portion of the measurement space 321.
- the echo signal of each corrected shot may be further multiplied by a weighting factor in accordance with the arrangement position of the measurement space. At this time, the weighting factor is determined such that the greater the distance from the origin, the higher the contribution.
- FIG. 11 (b) shows one blade 322 shown in FIG.
- one blade 322 is a two-dimensional space defined by a phase encoding direction (Ky) and a reading direction (Kx).
- the distance R (kx, ky) 602 from the origin of each point P (kx, ky) 804 in the blade 322 is calculated by the following equation (3).
- the weighting factor is a weighting factor calculation function B (R) that is a monotonically increasing function that increases with an increase in the distance R from the initial value C (scn) in the case of the blade in which the echo signal acquired in the cn-th shot is arranged.
- the weighting coefficient calculation function B (R) 603 has an initial value C (scn) that is different for each shot.From this initial value C (scn), the distance R decreases linearly as the distance R increases, and the distance R becomes a predetermined value Rmax.
- the above is 1.
- the horizontal axis of the figure indicates the distance R from the origin of each sampling point of the echo signal.
- the weight coefficient calculation function B (R) is expressed by the following equation (4).
- the weight coefficient calculation function B (R) is set in advance and held in the storage device 72 or the like. Also, Rmax is set to, for example, half of the number of sampling points in the reading direction is Pnt. Further, the signal strength correction by the weighting factor calculated from the weighting factor calculation function B (R) is performed after the signal strength correction unit performs the signal strength correction by the time difference s.
- each echo signal group weighted with the value of the time difference s is further weighted according to the distance R from the center.
- a large weight here, 1.0
- the influence of the blur can be reduced in the image in which the influence of the movement is suppressed, and the image quality can be further improved.
- the weighting factor when the time difference s exceeds the maximum Smax is set to 0.0 is shown on the basis of the first embodiment.
- the method of this embodiment may be combined with the second embodiment, and the echo signal may be reacquired when the time difference s exceeds Smax.
- the synchronous imaging control unit may include a signal intensity correction unit in addition to the configuration of the second embodiment.
- the linear function is used as the function for calculating the weighting coefficient in FIG. 11 (a).
- the second function is further configured to change the weighting method according to the variable. May be.
- the area may be divided by a threshold value for determining the time difference s, and the weight coefficient may be set. The same applies to the weighting coefficient corresponding to the distance R in FIG. 11 (c).
- the MRI apparatus of this embodiment basically has the same configuration as that of any of the first to third embodiments. However, in the present embodiment, the one that performs three-dimensional measurement is used for the photographing sequence of the main photographing. Hereinafter, the measurement sequence of the present embodiment will be described focusing on the configuration different from the above embodiments.
- the application amount in the slice encode gradient magnetic field pulse application axis (slice axis) direction is also changed.
- the amplitude of the slice encode gradient magnetic field pulse is changed according to the time difference s.
- the optimum delay time 403 is selected for each region to be imaged. Therefore, the farther the shot start time is away from the delay time 406, that is, the greater the time difference 502, the lower the quality of the collected echo signal.
- the amplitude of the slice encode gradient magnetic field pulse is determined so that the echo signal collected in the shot with the smaller time difference 502 collects the echo signal at the center in the slice direction of the measurement space. The amplitude is determined for each shot by introducing a function that monotonously increases in accordance with the time difference s2 as the slice position determination function Kz (s2).
- the synchronization control unit included in the first embodiment calculates the time from the latest delay time 406 to the start time 503 of the next shot as the second time difference after the end of each shot.
- a second time difference calculation unit that performs the determination, and an amplitude determination unit that determines the amplitude of the slice encode gradient magnetic field pulse based on the calculation result of the second time difference calculation unit.
- the biological signal receiving unit includes a trigger signal storage unit that stores the time when the notification that the pulse wave is received from the biological signal detection unit 8 is received as the trigger reception time.
- FIG. 12 is a processing flow of imaging processing by the synchronous imaging control unit of the present embodiment.
- the trigger signal storage unit stores the trigger reception time independently of the imaging processing every time a pulse wave is received.
- the synchronous imaging control unit When the synchronous imaging control unit receives an imaging parameter input from the operator, the synchronous imaging control unit generates an imaging sequence using a pulse sequence held in advance (step S1401). Further, the counter cn for counting the shot number of the shot to be executed is set to 1 (step S1402).
- the synchronous imaging control unit waits for reception of a pulse wave.
- the pulse wave is received (step S1403), after the delay time input as the imaging parameter has elapsed (step S1404), the cn-th shot is executed according to the imaging sequence (step S1405). Since the first shot has a time difference of 0 from the latest delay time, the amplitude of the slice encode gradient magnetic field pulse is 0. At this time, the shot start time ts (cn) is stored in association with the counter value.
- the synchronous imaging control unit calculates the second time difference s2 (cn) of the next shot (here, the cn shot). Specifically, the second time difference calculation unit first calculates the start time ts (cn) of the next shot (step S1408). This is obtained by adding TR to the start time ts (cn-1) of the previous shot (here, the (cn-1) th shot). The calculated start time ts (cn) is stored in association with the counter value cn.
- the delay time 406 after the delay time 403 elapses from the latest trigger reception time 401 is set as the latest delay time
- the latest delay time is subtracted from the start time ts (cn) of the next shot, and the second time difference s2 (cn ) Is calculated (step S1409).
- the synchronous imaging control unit causes the amplitude determination unit to determine the amplitude of the slice encode gradient magnetic field pulse of the next shot (here, the cn-th shot).
- the amplitude determining unit first calculates the slice value of the slice encode gradient magnetic field pulse of the next shot from the slice position function Kz (s2) (step S1410). Then, the amplitude for obtaining the slice value is determined from the function A (Kz) in which the slice value is associated with the amplitude (step S1411).
- the synchronous imaging control unit waits for the elapse of TR time from the previous shot start time (step S1412), moves to step S1405, and executes the cn-th shot. At this time, the amplitude A (Kz) determined by the amplitude determination unit in step S1411 is used.
- FIG. 13 is an example of a slice value determination function Kz (s2) 701 that determines the position in the slice direction in the measurement space according to the second time difference s2.
- the function shown here is a function that increases linearly from 0 in accordance with the time difference s within the effective range (0 ⁇ s ⁇ Smax) of the second time difference s2.
- the horizontal axis of the figure shows the second time difference when collecting echo signals of each shot 501 in FIG.
- the amplitude A (Kz) of the slice encode gradient magnetic field pulse is determined so as to measure the slice having the slice value.
- slice value determination function Kz (s2) shown in FIG. 13 is expressed by the following equation (5).
- Smax is a predetermined threshold as in the above embodiments.
- Kmax is a value of Kz (s2) when the second time difference s2 is Smax.
- Kz (s2) of the present embodiment when the second time difference s2 exceeds Smax, the echo signal obtained in the shot is not used for image reconstruction.
- Kz (s) is set in advance and held in the storage device 72 or the like.
- Kz (s2) calculated by equation (5) is only a positive value, but in the measurement space, it is equivalent, so either Kz (s2) or -Kz (s2) is used. Also good. Alternatively, Kz (s2) may be used first, and then -Kz (s2) may be used when the same second time difference s2 is obtained. Moreover, you may comprise so that a positive / negative value may be assigned alternately for every shot.
- the amplitude of the slice encode gradient magnetic field is determined according to the second time difference from the delay time, a better quality echo signal is sent to the low spatial frequency in the slice direction of the measurement space. Can be placed in the area. Therefore, even in the three-dimensional measurement, a high-quality and stable image can be obtained with a desired contrast as in the first embodiment.
- the same slice value Kz (s2) may be repeatedly obtained.
- the amplitude determination unit may be configured to determine the amplitude in consideration of such a case.
- the amplitude determination process in this case will be described with reference to FIG.
- the amplitude determination process is the process from steps S1408 to S1411 of the above process.
- the slice value Kz (s2) corresponding to each amplitude A (Kz) determined and measured is configured to be held as an executed slice value.
- the second time difference s2 is calculated by the method of steps S1408 and 1409 (step S1501).
- the calculated second time difference s2 is s2cn.
- the slice value Kz (s2cn) is calculated by the slice value determination function Kz (s2) (step S1502). It is determined whether or not a slice having the calculated slice value Kz (s2cn) has been acquired (step S1503). The determination is made based on whether or not Kz (s2cn) calculated as the executed slice value is held, and if it is held, it is determined that it has been executed.
- the calculated amplitude Kz (s2cn) is held as the executed slice value, and the amplitude A (Kz) corresponding to Kz (s2cn) is determined as the amplitude (step S1504). Then, the amplitude determination process ends.
- step S1408 it is determined whether or not the increased second time difference s2cn exceeds a predetermined threshold value Slimit (step S1408). If not, the process returns to step S1402 and continues processing. If it exceeds, A (s) corresponding to the original Kz (s) is set as an amplitude, and is output together with a flag indicating that it has already been executed, and the amplitude determination process is terminated.
- Slimit is set so that the shooting efficiency does not decrease and the influence of movement is not noticeable.
- it may be a function of the second time difference s2.
- the Slimit is increased to increase the possibility of acquiring a slice, and when it is large, the Slimit is decreased and the acquisition slice range is narrowed. .
- the synchronous imaging unit executes the imaging sequence but does not collect the echo signal.
- the echo sequence is collected by executing the imaging sequence, but is not used for image reconstruction.
- the sequence can be executed while maintaining a repetition time, whereby the contrast of the image can be maintained.
- the imaging process other than the slice direction has been described by taking the imaging process of the first embodiment as an example.
- Either may be sufficient.
- a weighting coefficient may be applied to the echo signal in the slice direction as in the third embodiment. By applying a weighting factor also in the slice direction, the image quality is further improved.
- two-dimensional measurement is described as an example, but three-dimensional measurement may be used.
- the hybrid radial sampling method is used as the non-orthogonal sampling method
- the non-orthogonal sampling method is not limited to this.
- a radial sampling method may be used.
- a spiral method in which the measurement space is sampled in a spiral shape may be used.
- the present invention is not limited to the contents disclosed in each of the above embodiments, and can take various forms based on the gist of the present invention.
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Abstract
Description
以下、本発明を適用する第一の実施形態について説明する。以下、本発明の実施形態を説明するための全図において、同一機能を有するものは同一符号を付し、その繰り返しの説明は省略する。
図6(a)に示すように、401は生体信号検出部8が取得した心電波形であり、時間間隔402は心電波形401の間隔である(一般にR-R間隔と呼ばれる)。同期撮影法では、心電波形401を検出後、時間間隔403(以下、ディレイ時間)だけ空けて撮影シーケンスを開始し、時間間隔404内でエコー信号群405を収集する。各心電波形401検出後、同様のタイミングでエコー信号を収集し、心電波形401に同期して、画像を再構成するために必要なデータを得る。なお、R-R間隔は心周期とも呼ばれ、ハイフン以下の付番は、n番目の心電波形401-n後の心周期内での処理であることを示す。なお、以下の説明では、特に区別する必要がない限り、ハイフン以下の付番は省略する。また、心電同期では心電波形401と呼ぶが、一般に、生体信号401またはトリガ信号401と呼ぶ。
次に、本発明を適用する第二の実施形態を説明する。本実施形態のMRI装置は基本的に第一の実施形態と同様の構成を有する。第一の実施形態では、一旦撮影を開始した場合、その後は、全てのショットをTR間隔で順に1回ずつ実行する。一方、本実施形態では、各ショット開始時間のディレイ時刻からの時間によって、結果の採否を決定し、採用されない場合、採用されるまで繰返し実行する。以下、本実施形態の撮影処理について、第一の実施形態と異なる構成に主眼をおいて説明する。
次に、本発明を適用する第三の実施形態を説明する。本実施形態のMRI装置は基本的に第一及び第二の実施形態と同様の構成を有する。第二の実施形態では、各ショットの時間差によって、収集したエコー信号の採否を決定している。本実施形態では、ショット毎の時間差によって、収集したエコー信号に重み付けをする。以下、本実施形態の計測シーケンスについて、第一の実施形態と異なる構成に主眼をおいて説明する。
次に、本発明を適用する第四の実施形態を説明する。本実施形態のMRI装置は基本的に上記第一から第三の実施形態のいずれかと同様の構成を有する。ただし、本実施形態では、本撮影の撮影シーケンスに3次元計測を行うものを用いる。以下、本実施形態の計測シーケンスについて、上記各実施形態と異なる構成に主眼をおいて説明する。
Claims (10)
- 非直交系サンプリング法に基づいて、計測空間の部分領域に対応する1以上のエコー信号の収集を行う撮影シーケンスを用いたショットを、所定の繰り返し時間間隔で、前記部分領域を異ならせて、繰り返す撮影制御部と、
前記被検体の周期的な生体信号を受信する生体信号受信部と、
を備える磁気共鳴イメージング装置であって、
前記撮影制御部は、前記生体信号受信部が生体信号を受信後、所定のディレイ時間後に前記撮影シーケンスを開始し、前記繰り返し時間間隔を維持して前記撮影シーケンスを繰り返すこと
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記生体信号受信部は、前記撮影制御部が撮影シーケンスを実行している間に、生体信号を受信する毎に、当該受信時刻を生体信号受信時刻として記憶する生体信号受信時刻記憶部を備え、
前記撮影制御部は、
前記ショット毎に、当該ショットの開始時刻と、各生体信号受信時刻から前記ディレイ時間経過後のディレイ時刻との間の時間の最小値を時間差として算出する時間差算出部と、
前記時間差が予め定められた閾値を超えている場合、当該ショットで収集したエコー信号を不採用とする採否決定部と、を備え、
前記採否決定部で不採用と決定されたショットを、当該ショット開始から前記繰り返し時間経過後に再度実行すること
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記生体信号受信部は、前記撮影制御部が撮影シーケンスを実行している間に、生体信号を受信する毎に、当該受信時刻を生体信号受信時刻として記憶する生体信号受信時刻記憶部を備え、
前記撮影制御部は、
前記ショット毎に、当該ショットの開始時刻と、各生体信号受信時刻から前記ディレイ時間経過後のディレイ時刻との間の時間の最小値を時間差として算出する時間差算出部と、
前記時間差が大きくなるに従って減少する重み係数を、前記ショットで収集したエコー信号に乗算して補正エコー信号を得る信号強度補正部と、を備えること
を特徴とする磁気共鳴イメージング装置。 - 請求項2記載の磁気共鳴イメージング装置であって、
前記撮影制御部は、
前記時間差が大きくなるに従って減少する重み係数を、前記ショットで収集したエコー信号に乗算して補正エコー信号を得る信号強度補正部をさらに備え、
前記採否決定部で不採用と決定されたショットを、当該ショット開始から前記繰り返し時間経過後に再度実行すること
を特徴とする磁気共鳴イメージング装置。 - 請求項3記載の磁気共鳴イメージング装置であって、
前記撮影制御部は、前記エコー信号の計測空間における原点からの距離が大きくなるに従って増加する第二の重み係数を前記補正エコー信号に乗算する第二の信号強度補正部をさらに備えること
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記撮影シーケンスは、スライスエンコード傾斜磁場を備える3次元の計測空間の計測を行うものであり、
前記生体信号受信部は、前記撮影制御部が撮影シーケンスを実行している間に、生体信号を受信する毎に、当該受信時刻を生体信号受信時刻として記憶する生体信号受信時刻記憶部を備え、
前記撮影制御部は、
ショット毎に、最新の生体信号受信時刻から前記ディレイ時間経過後の時刻と当該ショットの開始時刻との間の時間を第二時間差として算出する第二時間差算出部と、
前記第二時間差が小さいショットで収集したエコー信号ほど、スライス方向の計測空間の中心部に近い位置に配置されるよう前記スライス傾斜磁場パルスの振幅を決定する振幅制御部と、をさらに備えること
を特徴とする磁気共鳴イメージング装置。 - 請求項2記載の磁気共鳴イメージング装置であって、
前記撮影シーケンスは、スライスエンコード傾斜磁場を備える3次元の計測空間の計測を行うものであり、
前記撮影制御部は、
ショット毎に、最新の生体信号受信時刻から前記ディレイ時間経過後の時刻と当該ショットの開始時刻との間の時間を第二時間差として算出する第二時間差算出部と、
前記第二時間差が小さいショットで収集したエコー信号ほど、スライス方向の計測空間の中心部に近い位置に配置されるよう前記スライス傾斜磁場パルスの振幅を決定する振幅制御部と、をさらに備えること
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置において、
前記部分領域は各々が一つのエコー信号に対応する互いに並行な複数の軌跡を有して成るブレードであり、
前記撮影制御部は、1回の撮影シーケンスで1つのブレードに対応する1以上のエコー信号を計測し、前記計測空間の所定の軸に対するブレードの角度を異ならせて、該撮影シーケンスを繰り返すことを特徴とする磁気共鳴イメージング装置。 - 請求項8記載の磁気共鳴イメージング装置において、
前記撮影シーケンスは、FSEシーケンスに基づくものであることを特徴とする磁気共鳴イメージング装置。 - 磁気共鳴イメージング装置おける同期計測方法であって、
非直交系サンプリング法に基づいて、計測空間の部分領域に対応する1以上のエコー信号の収集を行う撮影シーケンスを、所定の繰り返し時間間隔で、前記部分領域を異ならせて、繰り返す撮影ステップと、
前記被検体の周期的な生体信号を受信する生体信号受信ステップと、
を備える磁気共鳴イメージング装置であって、
前記撮影ステップは、前記生体信号を受信後、所定のディレイ時間後に前記撮影シーケンスを開始し、前記繰り返し時間間隔を維持して前記撮影シーケンスを繰り返すこと
を特徴とする同期計測方法。
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