WO2013047275A1 - 磁気共鳴イメージング装置および磁気共鳴イメージング方法 - Google Patents
磁気共鳴イメージング装置および磁気共鳴イメージング方法 Download PDFInfo
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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
- G01R33/5608—Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels
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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
- G01R33/5611—Parallel magnetic resonance imaging, e.g. sensitivity encoding [SENSE], simultaneous acquisition of spatial harmonics [SMASH], unaliasing by Fourier encoding of the overlaps using the temporal dimension [UNFOLD], k-t-broad-use linear acquisition speed-up technique [k-t-BLAST], k-t-SENSE
Definitions
- the present invention measures nuclear magnetic resonance (Nuclear Magnetic Resonance: hereinafter referred to as NMR) signals from hydrogen, phosphorus, etc. in a subject and images nuclear density distribution, relaxation time distribution, etc.
- Resonance Imaging hereinafter referred to as MRI
- MRI Resonance Imaging
- the MRI device measures NMR signals (echo signals) generated by the spins of the subject, especially the tissues of the human body, and forms the shape and function of the head, abdomen, limbs, etc. in two or three dimensions. It is a device that images. In imaging, a phase encoding and a frequency encoding that are different depending on a gradient magnetic field are given to the NMR signal. The measured NMR signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.
- NMR signals echo signals
- Measured NMR signals are placed in k space (data space).
- the k-space scanning trajectory is roughly classified into two types, a Cartesian coordinate system and a non-Cartesian coordinate system, depending on the gradient magnetic field pattern to be applied.
- the orthogonal coordinate system k space is a data space defined by two or three coordinate axes orthogonal to each other.
- the non-orthogonal coordinate system k space is a data space defined by the size and the declination.
- orthogonal system measurement the measurement for obtaining the scanning locus of the non-orthogonal coordinate system
- non-orthogonal measurement the measurement for obtaining the scanning locus of the non-orthogonal coordinate system.
- a k-space (unit k-space) of a predetermined unit is measured while changing the declination, and converted into an orthogonal coordinate system k-space by an interpolation process called gridding.
- gridding an interpolation process
- each unit k space shape is generally a rectangle and is called a blade (see, for example, Non-Patent Document 1).
- An echo signal is obtained by applying a gradient magnetic field with the major axis direction of the blade as the frequency encode direction and the minor axis direction as the phase encode direction.
- non-orthogonal measurement fills k-space by gridding data in multiple unit k-spaces.
- the sampling pitch is different between the frequency encoding direction and the phase encoding direction. For this reason, the data density becomes non-uniform and artifacts occur, preventing improvement in image quality.
- the present invention has been made in view of the above circumstances, and provides a technique for improving image quality while maintaining the advantages of non-orthogonal measurement.
- the present invention reduces artifacts caused by non-uniform data density in k-space in non-orthogonal measurement. For this reason, each unit k space is imaged by inverse Fourier transform, the field of view of the image is expanded in the direction in which the data density is to be increased, and the k-space pitch in the direction in which the field of view is expanded by Fourier transform is expanded. Gridding is performed as a unit k-space with small and increased data volume. This process is repeated for all the blades.
- an echo signal is measured for each unit k space, a measurement unit that acquires unit k space data, the unit k space data is corrected, and the corrected unit k space data is obtained.
- a magnetic resonance imaging apparatus comprising: a field-of-view enlargement unit to be obtained; and a unit signal conversion unit that obtains unit k-space data after correction by Fourier transforming the enlarged image.
- an echo signal is measured for each unit k space by non-orthogonal measurement, and a signal measurement step for acquiring unit k space data, and a unit image that is an image for each unit k space is reconstructed from the unit k space data
- a signal rearrangement step for rearranging the subsequent unit k-space data in the Cartesian coordinate system k-space, and a final imaging step for reconstructing an image by performing inverse Fourier transform on the rearranged data in the rearrangement unit;
- a magnetic resonance imaging method is provided.
- the image quality is further improved while maintaining the advantages of non-orthogonal measurement.
- FIG. 1 is a block diagram showing the overall configuration of the MRI apparatus 100 of the present embodiment.
- the MRI apparatus 100 of the present embodiment obtains a tomographic image of a subject using an NMR phenomenon, a static magnetic field generation system 120, a gradient magnetic field generation system 130, a sequencer 140, a high-frequency magnetic field generation system 150, A high-frequency magnetic field detection system 160 and a calculation system 170 are provided.
- the static magnetic field generation system 120 generates a uniform static magnetic field in the direction perpendicular to the body axis in the space around the subject 101 if the vertical magnetic field method is used, and in the direction of the body axis if the horizontal magnetic field method is used.
- a permanent magnet type, normal conducting type or superconducting type static magnetic field generating source is arranged around the subject 101.
- the gradient magnetic field generation system 130 is a gradient magnetic field coil 131 wound in the three-axis directions of X, Y, and Z, which is the coordinate system (stationary coordinate system) of the MRI apparatus 100, and the gradient magnetic field that drives each gradient magnetic field coil 131.
- the power supply 132 is provided, and the gradient magnetic field power supply 132 of each coil is driven in accordance with a command from a sequencer 140 described later, thereby applying gradient magnetic fields in the three axis directions of X, Y, and Z.
- a slice direction gradient magnetic field pulse is applied in a direction orthogonal to the slice plane (imaging cross section) to set a slice plane for the subject 101, and the remaining planes orthogonal to the slice plane and orthogonal to each other are set.
- a phase encoding direction gradient magnetic field pulse (Gp) and a frequency encoding direction gradient magnetic field pulse (Gf) are applied in two directions, and position information in each direction is encoded into an NMR signal (echo signal).
- the high-frequency magnetic field generation system 150 irradiates the subject 101 with an RF pulse in order to cause nuclear magnetic resonance to occur in the nuclear spins of atoms constituting the biological tissue of the subject 101, and modulates with the high-frequency oscillator (synthesizer) 152. 153, a high frequency amplifier 154, and a high frequency coil (transmission coil) 151 on the transmission side.
- the high-frequency pulse output from the synthesizer 152 is amplitude-modulated by the modulator 153 at a timing according to a command from the sequencer 140, and the amplitude-modulated high-frequency pulse is amplified by the high-frequency amplifier 154 and arranged close to the subject 101.
- the transmission coil 151 the subject 101 is irradiated with the RF pulse.
- the high-frequency magnetic field detection system 160 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the living tissue of the subject 101.
- An amplifier 162, a quadrature detector 163, and an A / D converter 164 are provided.
- the echo signal of the response of the subject 101 induced by the electromagnetic wave irradiated from the transmission coil 151 is detected by the reception coil 161 arranged close to the subject 101, amplified by the signal amplifier 162, and then from the sequencer 140.
- the sequencer 140 controls to repeatedly apply a high-frequency magnetic field pulse (hereinafter referred to as “RF pulse”) and a gradient magnetic field pulse according to a predetermined imaging sequence.
- RF pulse high-frequency magnetic field pulse
- the sequencer 140 operates under the control of the arithmetic system 170 and sends various commands necessary for collecting tomographic image data of the subject 101 to the gradient magnetic field generation system 130, the high-frequency magnetic field generation system 150, and the high-frequency magnetic field detection system 160.
- the arithmetic system 170 performs various data processing, display and storage of processing results, and includes a CPU 171, a storage device 172, an external storage device 173, a display device 174, and an input device 175.
- the tomographic image of the subject 101 is reconstructed using data from the high-frequency magnetic field detection system 160.
- a control signal is transmitted to the sequencer 140 according to the imaging sequence.
- the reconstructed tomographic image is displayed on the display device 174 and recorded in the storage device 172 or the external storage device 173.
- the input device 175 is used by an operator to input various control information of the MRI apparatus 100 and control information of processing performed by the arithmetic system 170, and includes, for example, a trackball or a mouse and a keyboard.
- the input device 175 is disposed in the vicinity of the display device 174, and an operator controls various processes of the MRI apparatus 100 interactively through the input device 175 while looking at the display device 174.
- the transmission coil 151 and the gradient magnetic field coil 131 are opposed to the subject 101 in the static magnetic field space of the static magnetic field generation system 20 into which the subject 101 is inserted, in the case of the vertical magnetic field method, If the horizontal magnetic field method is used, the object 101 is installed so as to surround it. Further, the receiving coil 161 is installed so as to face or surround the subject 101.
- the radionuclide to be imaged by the MRI apparatus is a hydrogen nucleus (proton) which is the main constituent material of the subject, as is widely used in clinical practice.
- proton the main constituent material of the subject
- the form or function of the human head, abdomen, limbs, etc. is imaged two-dimensionally or three-dimensionally.
- the imaging sequence from which the CPU 171 of the arithmetic system 170 gives the control signal to the sequencer 140 includes the pulse sequence in which the application timing of the RF pulse and the gradient magnetic field pulse is determined, the application intensity of the RF pulse and the gradient magnetic field pulse, the application timing, etc. Determined by the parameter to be specified.
- the pulse sequence is preset and held in the storage device 172.
- the parameters are set as imaging conditions by the operator via the input device 175.
- FIG. 2 (a) is a diagram for explaining an imaging sequence 210 based on the hybrid radial method used in the present embodiment.
- FIG. 2B is a diagram for explaining a unit k space (hereinafter referred to as a blade) 220 of the k space measured (scanned) by the imaging sequence 210.
- the RF, Gx, Gy, and Echo axes indicate the RF pulse, the application timing of the gradient magnetic field pulse in the biaxial direction, and the acquisition timing of the echo signal, respectively.
- the imaging sequence 210 of this embodiment is a combination of the FSE method and the hybrid radial method.
- the FSE method a plurality of refocus RF pulses 212 are applied during the time TR from the application of one excitation RF pulse 211 to the application of the next excitation RF pulse 211, and each time the refocus RF pulse 212 is applied.
- Echo signal 215 is acquired.
- different phase encoding is given to each echo signal 215.
- the hybrid radial method is a unit k space (blade) 220 having a measurement trajectory passing through the origin of the k space, and a rotation angle ⁇ that is an angle of the measurement trajectory with respect to the coordinate axis of the k space. Are divided into a plurality of unit k spaces (blades) 220 that are different from each other.
- the measurement is performed in the unit k space (blade) 220, which is a rectangular area including the origin of the k space, as shown in FIG. 2B, during one TR. This is repeated for each TR while changing the angle (rotation angle ⁇ ) that the blade 220 makes with the kx axis of the k space, and the entire k space is measured.
- the waveforms of the gradient magnetic field pulses 213 and 214 are determined so as to realize such k-space scanning (measurement).
- the obtained echo signal 215 is imaged after the gridding process.
- the gridding process is a process of rearranging data acquired by non-orthogonal measurement to the coordinates of grid points in the k space (orthogonal coordinate system k space).
- the k space has regular grid point coordinates.
- data acquired by non-orthogonal measurement does not coincide with the lattice point coordinates in the k space because they pass different trajectories (coordinates) in the k space.
- the data acquired by the non-orthogonal system measurement is rearranged in regular lattice point coordinates (orthogonal coordinate system k-space) by the interpolation process.
- the interpolation processing can be performed using a sinc function or a Kaiser-Bessel function interpolation function.
- the echo signal 215 of one unit k space (blade) 220 is measured (step S1110), and the obtained echo signal 215 is arranged in the k space according to the blade rotation angle ⁇ . Thereafter, gridding processing is performed (step S1120). The processing in steps S1101 and S1102 is performed for all blades (step S1130). Then, two-dimensional inverse Fourier transform is performed on the obtained all k-space data (step S1140), and an image is reconstructed. If the number of channels is 1 or more (multi-channel), finally, multi-channel synthesis is performed to synthesize the images of each channel (step S1150). Here, the number of multi-channels is an integer of 1 or more.
- the sampling pitch in the x direction and y direction are made the same, thereby reducing the density of data arrangement in the k space. Data density non-uniformity and artifacts are reduced. Density reduction is performed on each unit k-space data.
- the arithmetic system 170 of the present embodiment acquires an echo signal according to an imaging sequence 210 that is a pulse sequence of non-orthogonal system measurement, arranges it in k space, and unit k space.
- the measurement unit 310 that obtains data, the unit k-space data acquired by the measurement unit 310 is corrected so as to achieve the above-described purpose, and the correction unit 320 that obtains the corrected unit k-space data, and the correction unit 320
- each part of the arithmetic system 170 are realized by the CPU loading a program stored in advance in the storage device into the memory and executing it.
- the measurement unit 310 measures an echo signal of one unit k space (blade) for each channel by the imaging sequence 210 that is non-orthogonal measurement (step S1210), and the obtained echo signal Is placed in k-space according to the blade rotation angle. Thereby, the measurement unit 310 obtains unit k space data for each channel.
- the correction unit 320 performs a correction process for correcting the unit k space data for each channel (step S1220).
- corrected unit k space data is obtained for each channel. Details of the correction processing will be described later.
- the rearrangement unit 330 performs gridding processing on the corrected unit k-space data for each channel (step S1230).
- the arithmetic system 170 performs the processing from step S1210 to step S1230 for all blades (step S1240), and obtains all k-space data after gridding processing for each channel.
- the imaging unit 340 performs two-dimensional inverse Fourier transform on all the obtained k-space data for each channel (step S1250), and reconstructs an image for each channel (final image).
- the synthesizing unit 350 multi-channel synthesizes the obtained final image for each channel (step S1260).
- multi-channel synthesis may be either absolute value synthesis or complex synthesis.
- phase correction may be included for each channel data.
- the correction unit 320 of the present embodiment performs correction processing for each blade every time the measurement of the blade is finished. Therefore, the correction unit 320 of the present embodiment, as shown in FIG.
- a unit imaging unit 321 that performs inverse Fourier transform on unit k space data that is an echo signal for each blade and reconstructs a unit image
- a unit A field enlargement unit 322 that enlarges the field of view of the image, obtains an enlarged image
- a unit signal conversion unit 323 that obtains corrected unit k space data that is an echo signal after correction for each blade by performing Fourier transform on the enlarged image, Is provided.
- the blade 410 has a width in the minor axis direction of N * ⁇ ky.
- N is an integer of 1 or more that represents the number of phase encodings in the blade 410.
- ⁇ ky is a k-space pitch in the phase encoding direction and is defined by the following equation (1).
- FOVy is a visual field in the phase encoding direction.
- the unit imaging unit 321 performs two-dimensional inverse Fourier transform on the blade 410 (step S1221) to form an image. Thereby, the unit imaging unit 321 obtains a unit image 420 whose field of view in the y direction is FOVy.
- the visual field enlarging unit 322 expands the visual field of the unit image 420 (step S1222), and obtains a unit image (enlarged unit image) 430 after the visual field is expanded.
- the field of view is expanded by adding a predetermined number of pixels having a predetermined pixel value in the direction in which the field of view is to be expanded.
- the direction in which the field of view is to be enlarged is the direction in which the k-space pitch is made dense.
- FIG. 6 illustrates a case where zero is used as a predetermined pixel value, that is, a case where the field of view is expanded by padding with zero in the phase direction.
- the pixel value of the added pixel is not limited to zero.
- the pixel value of the unit image 420 adjacent to the additional region may be used.
- the background noise value of the unit image 420 is known in advance, it may be the value.
- the visual field enlargement ratio is determined so as to increase the density in the ky direction (phase encoding direction).
- FIG. 6 shows an example in which 1/2 of FOVy is added to both sides in the y direction to double the field of view. That is, this is a case where the visual field enlargement ratio is 2. Therefore, in the example of FIG. 6, the visual field in the phase encoding direction is expanded from FOVy to FOVy * 2 by the visual field expansion processing by the visual field expansion unit 322.
- the unit signal converting unit 323 performs a two-dimensional Fourier transform on the enlarged unit image 430 that is a unit image after the visual field is expanded (step S1223), and obtains a corrected blade 440 that is corrected k-space data.
- the number of phase encodes of the corrected blade 440 increases from N to N * 2.
- the k-space pitch in the phase encoding direction is reduced from ⁇ ky to ⁇ ky ′.
- ⁇ ky ′ is defined by the following equation (2).
- the blade 410 increases the number of phase encodes in the blade by performing the correction process of the present embodiment, but the k-space pitch in the phase encode direction is reduced in inverse proportion to the number. For this reason, the width in the minor axis direction (phase encoding direction) on the k space does not change, but the pitch in the same direction increases.
- the field expansion ratio in the phase encoding direction has been described as being doubled for convenience, but the field expansion ratio may be 1 or more, and may be a decimal number.
- the field expansion ratio is n (n is an integer equal to or greater than 1) and the blade 410 is subjected to the correction process of the present embodiment, and the field in the phase encoding direction is expanded n times, the phase encoding in the blade 440 after correction is performed.
- the number increases n times.
- the k-space pitch ⁇ ky ′ in the phase encoding direction of the corrected blade 440 is 1 / n times the k-space pitch ⁇ ky in the phase encoding direction of the blade 410 before correction, as shown in the following equation (3).
- correction processing is added to the imaging processing of the conventional non-orthogonal system measurement shown in FIG.
- a technique called zero padding is used, but it is important that this is performed on an image obtained by imaging k-space data by inverse Fourier transform.
- a so-called zero padding reconstruction technique is known in which a high frequency region of k-space is zero padded and then inverse Fourier transformed.
- this known zero-padded reconstruction is performed on the k-space, and is a technique aimed at improving the apparent spatial resolution of an image obtained by inverse Fourier transform. Therefore, the known zero padding reconstruction technique is different from the technique of the present embodiment, which aims to perform zero padding on an image and make the data density of non-orthogonal measurement uniform.
- FIG. 7 (a) is the final image 511 obtained by the conventional method
- FIG. 7 (b) is the final image 521 obtained by performing the correction processing of this embodiment
- FIG. 7 (c) is FIG. 7 (a).
- FIG. 7 (d) is an image 523 in which the central portion (in the frame) 522 of FIG. 7 (b) is enlarged
- FIG. 7 (d) is the final image 511 obtained by the conventional method
- FIG. 7 (b) is the final image 521 obtained by performing the correction processing of this embodiment
- FIG. 7 (c) is FIG. 7 (a).
- FIG. 7 (d)
- FIG. 7 (f) shows the luminance profile 515 on the line segment connecting C3 and C4 and the luminance profile on the line segment connecting D3 and D4 in FIGS. 7 (c) and 7 (d), respectively. 525.
- the horizontal axis indicates the in-pixel position [pixel]
- the vertical axis indicates the pixel value.
- FIG. 8 (a) shows the data density 516 of data (64 ⁇ 64 pixels) near the center of k-space data immediately before reconstructing the final image obtained by the conventional method
- FIG. 8 (b) Data density 526 of data (64 ⁇ 64 pixels) near the center of k-space data immediately before reconstructing the final image obtained by performing the correction processing of the present embodiment is shown.
- FIG. 8 (c) is a profile 517 on the line segment connecting A1 and A2 and a profile 527 on the line segment connecting B1 and B2 in FIGS. 8 (a) and 8 (b), respectively. is there.
- FIG. 8 (d) is a profile 518 on the line segment connecting A3 and A4 and a profile 528 on the line segment connecting B3 and B4 in FIGS. 8 (a) and 8 (b), respectively. is there.
- 8 (c) and 8 (d) the horizontal axis indicates the in-pixel position [pixel], and the vertical axis indicates the pixel value.
- the data density that shows non-uniform distribution in the conventional method is made uniform by applying the correction processing of this embodiment. This is because the profiles 517, 527, 518, and 528 in FIG. 8 (c) and FIG. 8 (d) are made uniform by suppressing the data density oscillation by performing the correction processing of this embodiment. You can see from
- the case where a multi-channel coil having two or more channels is used as the receiving coil 161 has been described as an example.
- the number of channels may be one.
- the multi-channel combining process in step S1260 in FIG. 5 may not be performed. Further, the synthesis unit 350 may not be provided.
- the magnetic resonance imaging apparatus (MRI apparatus) 100 of the present embodiment measures the echo signal for each unit k space by non-orthogonal measurement, and acquires the unit k space data, and A correction unit 320 that corrects the unit k-space data to obtain corrected unit k-space data, a rearrangement unit 330 that rearranges the corrected unit k-space data in an orthogonal coordinate system k-space, and the rearrangement An imaging unit 340 that reconstructs an image by performing inverse Fourier transform on the data rearranged in the unit 330, and the correction unit 320 is a unit that is an image for each unit k space from the unit k space data.
- the receiving coil 161 used is a multi-channel coil having a plurality of channels
- the measurement unit 310 uses the coil 151 to measure the echo signal for each channel to obtain the unit k space data
- the correction unit 320 corrects the unit k space data for each channel to obtain the corrected unit k space data
- the rearrangement unit 330 reconfigures the corrected unit k space data for each channel.
- the imaging unit 340 obtains the final image for each channel, and the image synthesized by the synthesis unit 350 is the final image for each channel.
- the obtained unit k space data is imaged by inverse Fourier transform, and the field of view of the image is expanded in the direction in which the data density is desired to be increased.
- the field-expanded image is subjected to Fourier transform to obtain corrected unit k-space data in which the k-space pitch in the direction in which the field of view is expanded is small and the data amount is increased. Then, the corrected unit k-space data is gridded to reconstruct the final image.
- body motion artifacts can be reduced by using non-orthogonal measurement.
- the above correction process is performed when an image is reconstructed from the obtained k-space data, the difference in data density for each encoding direction is reduced in each unit k-space, and artifacts due to non-uniform data density Is reduced.
- the unit image 420 is reconstructed from the echo signal in the blade 410 before correction, and in the post-correction blade 440 from the reconstructed image (enlarged unit image) 430 after the field of view expansion.
- Fourier transform is performed twice.
- the number of data to be processed is a power of two
- a fast Fourier transform FFT; Fast Fourier Transform
- the phase encoding number N in the blade 410 before correction is a power of 2
- the number of pixels in the phase encoding direction of the image after field expansion is a power of 2
- FFT cannot be used if it is not a power of 2.
- the number of phase encodings that defines the number of data to be processed in this embodiment is determined from the contrast of the image, the imaging time, and the like, and thus is not necessarily a power of 2.
- a discrete Fourier transform (DFT) is used as a Fourier transform algorithm.
- DFT takes longer processing time than FFT.
- the forward and reverse Fourier transform is repeated for each blade, and therefore, if a DFT having a long processing time is used as the Fourier transform, the time required for the correction process becomes long.
- N is an integer of 1 or more.
- the unit imaging unit 321 sets the number of phase encoding in the phase encoding direction of the blade 410 before correction to a power of 2 before reconstructing the unit image by Fourier transform. Then, a blade 411 whose phase encoding number is a power of 2 is obtained.
- the phase encode direction is padded with zeros in the phase encode direction by a encode, and the number of phase encodes is N + a (a power of 2). Therefore, the blade 411 is referred to as a zero-padded blade 411.
- the number of encodings a to be increased is calculated by the following equation (4).
- ceil () in the expression is an operator that rounds up the value in parentheses to make it an integer.
- C in the equation is a parameter that defines the number of phase encodings after zero padding, and is an integer of 0 or more. In normal cases, C may be 0, but 1 or more may be used. By using a value of 1 or more, the periodicity in the phase encoding direction of each zero-padded blade 411 can be increased and the accuracy of Fourier transform can be increased. Further, when N is a power of 2, C may be 1 or more.
- the pitch in the phase encoding direction of the k space of the zero-padded blade 411 is ⁇ ky like the blade 410.
- the width in the minor axis direction is (N + a) * ⁇ ky.
- the unit imaging unit 321 converts the zero-padded blade 411 into an image by performing a two-dimensional inverse Fourier transform to obtain a unit image 421.
- the field of view of the unit image 421 in the y direction is FOVy.
- the field-of-view enlargement unit 322 enlarges the field of view of the unit image 421 by the method of the present embodiment to obtain an enlarged unit image 431.
- the field of view magnification is 2
- the field of view of the enlarged unit image 431 in the y direction is FOVy * 2.
- the unit signal converting unit 323 performs two-dimensional Fourier transform on the enlarged unit image 431 to obtain a corrected zero-padded blade 441 that is corrected k-space data.
- the number of phase encodes increases from (N + a) to (N + a) * 2.
- the k-space pitch in the phase encoding direction is reduced from ⁇ ky to ⁇ ky ′.
- the unit signal converting unit 323 removes the region corresponding to the encoding number a added by the unit imaging unit 321 from the corrected zero-padded blade 441, and obtains a corrected blade 440 that is a corrected unit k space.
- a region for N * 2 phase encoding at the center of the zero-padded blade 441 after correction is cut out, and the corrected blade 440 is obtained.
- the obtained corrected blade 440 has k-space data with a width in the short axis direction of N * 2 * ⁇ ky ′, that is, N * ⁇ ky, and has the same width in the short axis direction as the blade 410 before correction. .
- the unit imaging unit 321 performs zero padding of the unit k-space data so that the number of data to be processed is a power of 2.
- the unit image is reconstructed from the subsequent unit k-space data, and after the unit signal conversion unit 323 performs Fourier transform on the enlarged image, the unit imaging unit removes the zero-padded portion performed on the unit k-space data.
- the corrected unit k-space data is obtained.
- FFT can be used for inverse Fourier transform by adding a zero padding process for blades that sets the number of data to be processed to a power of two. Accordingly, the reconstruction of the unit image from the unit blade can be speeded up, and the time of the entire imaging process can be shortened.
- the parallel imaging method is a technique in which echo signals are received in parallel by a plurality of receiving coils and processed using the sensitivity distribution of each receiving coil.
- imaging is accelerated by thinning and collecting echo signals.
- the MRI apparatus of the present embodiment has basically the same configuration as the MRI apparatus 100 of the first embodiment.
- the functions realized by the arithmetic system 170 of the present embodiment are basically the same.
- the reception coil 161 is composed of a plurality of unit coils (channels).
- the calculation system 170 of the present embodiment includes a parallel calculation unit (PI calculation unit) 360 that performs parallel imaging calculation, as shown in FIG.
- the measurement unit 310 of the present embodiment performs measurement for parallel imaging.
- the computation system 170 of this embodiment does not include the synthesis unit 350.
- the measurement unit 310 of this embodiment performs measurement according to the same imaging sequence as that of the first embodiment, but performs measurement by thinning echo signals with each blade.
- the thinning rate is determined in advance.
- the PI calculation unit 360 of this embodiment performs parallel imaging calculation on the image for each blade reconstructed by the unit imaging unit 321. That is, in this embodiment, the aliasing generated in the unit image is developed using the sensitivity distribution.
- each sensitivity distribution is calculated from the measured blade data.
- the measured blade data is gridded once, and the sensitivity distribution is calculated from data obtained by extracting only the k-space center region.
- the measurement unit 310 obtains blade data densely at the center of the k space and sparsely at the other parts. Since the densely acquired k-space center portion represents the sensitivity distribution of each channel, the PI calculation unit 360 extracts the data in this region and calculates the sensitivity distribution used for the parallel imaging calculation. If the parallel imaging to be applied is not a self-calibration type, this process is omitted.
- the outline of the imaging process of this embodiment is basically the same as that of the first embodiment. That is, first, the measurement unit 310 measures an echo signal (step S2110) to obtain unit k space data for each channel. At this time, in this embodiment, the parallel imaging method is used, and echo signals are thinned out and measured. Next, the PI calculation unit 360 calculates a sensitivity distribution from the measurement result (step S2120).
- the correction unit 320 performs a correction process for correcting the unit k space data (step S2130).
- the unit imaging unit 321 performs two-dimensional inverse Fourier transform on the unit k space data (blade) for each channel (step S2131) to obtain a unit image for each channel.
- the PI calculation unit 360 performs parallel imaging calculation on the obtained unit image for each channel (step S2132), and the folding is developed to obtain a developed unit image in which the images of the respective channels are synthesized.
- the visual field enlarging unit 322 expands the visual field with respect to the developed unit image by the same method as in the first embodiment (step S2133), and obtains an enlarged unit image. At this time, a predetermined value is used as the visual field expansion rate.
- the unit signal converting unit 323 performs a two-dimensional Fourier transform on the enlarged unit image by the same method as in the first embodiment (step S2134), and obtains a corrected blade that is corrected unit k space data.
- the rearrangement unit 330 performs the gridding process on the corrected blade (S2140), and the arithmetic system 170 performs the process from step S2110 to step S2140 on all the blades. (Step S2150). Thereafter, the imaging unit 340 performs a two-dimensional inverse Fourier transform on the obtained entire k-space data (step S2160), and reconstructs an image (final image).
- the magnetic resonance imaging apparatus (MRI apparatus) 100 of the present embodiment measures the echo signal for each unit k space by non-orthogonal measurement, and acquires the unit k space data, and A correction unit 320 that corrects the unit k-space data to obtain corrected unit k-space data, a rearrangement unit 330 that rearranges the corrected unit k-space data in an orthogonal coordinate system k-space, and the rearrangement An imaging unit 340 that reconstructs an image by performing inverse Fourier transform on the data rearranged in the unit 330, and the correction unit 320 is a unit that is an image for each unit k space from the unit k space data.
- it further includes a parallel calculation unit 360 that performs parallel imaging calculation for developing folding using a sensitivity distribution, and the measurement unit 310 performs measurement by thinning out the echo signal in the non-orthogonal system measurement. Further, the parallel operation unit 360 expands the unit image to obtain a developed unit image, and the visual field expanding unit 322 uses the developed unit image as the unit image.
- the obtained unit k-space data is interpolated and imaged by inverse Fourier transform to increase the data density. Enlarge the field of view of the image.
- the field-expanded image is Fourier transformed to obtain corrected unit k-space data in which the k-space pitch in the direction in which the field of view is expanded is small and the data amount is increased. Then, the corrected unit k-space data is gridded to reconstruct the final image.
- body motion artifacts can be reduced by using non-orthogonal measurement.
- the correction processing is performed as in the first embodiment, the difference in data density for each encoding direction is reduced in each unit k space, and artifacts due to non-uniform data density are reduced.
- the parallel imaging method in which the measurement is thinned out is used, the measurement time can be shortened while minimizing the deterioration of the image quality.
- multi-channel synthesis is performed in units of blades in the parallel imaging calculation.
- gridding processing of all k-space data of the number of channels is necessary to obtain the final image of the number of channels. Since the gridding process has a large amount of calculation, the time required for the process becomes long if the number of coils of the multi-channel coil is large.
- multi-channel synthesis is performed for each unit k space (blade). That is, since multi-channel combining is performed before the gridding process, the gridding process needs to be performed only for one whole k-space data. Therefore, the calculation amount is small, and the processing time can be shortened accordingly.
- the image quality can be further improved and the total imaging time can be shortened without impairing the characteristics of non-orthogonal measurement.
- the parallel imaging processing is configured to be performed on an image, but the present invention is not limited to this.
- FIG. 12 is a processing flow of imaging processing when k-space parallel imaging is used.
- the case where the self-calibration type is used will be described as an example.
- the measurement unit 310 performs measurement by thinning echo signals with each blade (step S2210), and obtains unit k-space data for each channel.
- the measurement unit 310 performs measurement by thinning out echo signals using the parallel imaging method as in the present embodiment.
- the PI calculation unit 360 calculates a sensitivity distribution from the measurement result (step S2220).
- the PI calculation unit 360 obtains the encoded position data that has been thinned out by the parallel imaging calculation using the calculated sensitivity distribution (step S2230).
- unit k-space data for each channel is also synthesized.
- the PI calculation unit 360 obtains interpolation unit k-space data.
- the correction unit 320 performs correction processing on the interpolation unit k-space data that is the blade data after the parallel imaging processing (step S2240).
- the unit imaging unit 321 converts the interpolation unit k-space data into an image by performing a two-dimensional inverse Fourier transform (step S2241), and obtains a unit image.
- the visual field enlarging unit 322 expands the visual field of the unit image by the same method as in the first embodiment (step S2242), and obtains an enlarged unit image.
- the unit signal converting unit 323 performs two-dimensional Fourier transform on the enlarged unit image by the same method as in the first embodiment (step S2243), and obtains corrected unit k space data that is a corrected blade.
- the rearrangement unit 330 performs the gridding process on the corrected unit k space data (step S2250).
- the arithmetic system 170 performs the processing from step S2210 to S2250 for all the blades (step S2260).
- the imaging unit 340 performs a two-dimensional inverse Fourier transform on the obtained all k-space data (step S2270), and reconstructs the final image.
- the parallel calculation unit 360 interpolates the unit k space data to obtain the interpolation unit k space data
- the unit imaging unit 321 reconstructs the unit image from the interpolation unit k-space data.
- the arithmetic system 170 includes a combining unit 350, and after the inverse Fourier transform in step S2241, the combining unit 350 combines the images for each channel.
- the MRI apparatus of the present embodiment has basically the same configuration as the MRI apparatus 100 of the first embodiment. Also, each part constituting the arithmetic system 170 of the present embodiment is the same as that of the first embodiment. However, since the timing for performing multi-channel synthesis is different, the flow of imaging processing is different.
- the present embodiment will be described focusing on the configuration different from the first embodiment. Also in the present embodiment, as in the first embodiment, a case where an imaging sequence 210 in which the FSE method is combined with the hybrid radial method is used as a non-orthogonal measurement will be described as an example.
- the receiving coil 161 is a multi-channel coil having two or more channels.
- FIG. 13 is a processing flow of conventional imaging processing.
- the echo signal of one unit k space (blade) of each channel is measured using the imaging sequence 210 (step S3110).
- the unit k space data of each channel is subjected to two-dimensional inverse Fourier transform (step S3120) to obtain a unit image of each channel.
- the unit images of the respective channels are multi-channel synthesized (step S3130).
- the unit image after multi-channel synthesis is Fourier transformed (step S3140) and returned to k-space data.
- a gridding process is performed according to the blade rotation angle (step S3150).
- the processing from step S3110 to step S3150 is performed for all blades (step S3160), and the obtained all k-space data is subjected to two-dimensional inverse Fourier transform (step S3170) to obtain a final image.
- FIG. 14 is a processing flow of the imaging process of the present embodiment.
- the measurement unit 310 measures an echo signal of one unit k space (blade) for each channel by the imaging sequence 210 which is non-orthogonal measurement (step S3210), and uses the obtained echo signal as a blade rotation angle. Put them together in k-space. Thereby, in this embodiment, unit k space data for each channel is obtained.
- the correction unit 320 performs correction processing for correcting the unit k space data for each channel, and the combining unit 350 performs multi-channel combining of the unit images (correction combining processing: step S3220). Thereby, the corrected unit k-space data after multi-channel synthesis is obtained.
- step S3220 first, the unit imaging unit 321 converts the unit k space data for each channel into an image by performing a two-dimensional inverse Fourier transform (step S3221), and obtains a unit image for each channel.
- the synthesizing unit 350 multi-channel synthesizes the unit images for each channel (step S3222) to obtain a synthesized unit image.
- Multi-channel synthesis may be either absolute value synthesis or complex synthesis.
- phase correction may be included for each channel data.
- the visual field enlarging unit 322 expands the field of view of the composite unit image by the same method as in the first embodiment (step S3223), and obtains a composite unit image (enlarged composite unit image) after the visual field expansion.
- the unit signal converting unit 323 performs two-dimensional Fourier transform on the enlarged combined unit image (step S3224), and obtains corrected combined unit k-space data obtained by combining the k-space data of each channel.
- the rearrangement unit 330 performs gridding processing on the corrected composite unit k-space data (S3230).
- the arithmetic system 170 performs the processing from step S3210 to step S3230 for all the blades (step S3240), and obtains all combined k-space data after the gridding processing.
- the imaging unit 340 performs a two-dimensional inverse Fourier transform on the obtained total synthesized k-space data (step S3250) to reconstruct an image (final image).
- the final image obtained here is a composite of the images of all channels.
- the visual field expansion process by the visual field expansion unit 322 is added to the imaging process of the conventional non-orthogonal system measurement shown in FIG.
- FIG. 15 (a) is the final image 611 obtained by the conventional method
- FIG. 15 (b) is the final image 621 obtained by performing the correction processing of the present embodiment
- FIG. 15 (c) is FIG. 15 (a).
- FIG. 15 (d) is an image 623 in which the center part (in the frame) 622 in FIG. 15 (b) is enlarged
- FIG. 15 (f) shows the luminance profile 615 on the line segment connecting C3 and C4 and the luminance profile 625 of the line segment connecting D3 and D4 in FIGS. 15 (c) and 15 (d), respectively. It is.
- artifacts are generated in the final images 611 and 613 obtained by the conventional method, but the artifacts disappeared by performing the correction processing of this embodiment.
- the luminance profiles 614, 624, 615, and 625 of FIGS. 15 (e) and 15 (f) by performing the correction processing of the present embodiment, particularly at the positions indicated by arrows 631, 632, and 633 in the drawing. It can be seen that artifacts are reduced and the luminance profile is smooth.
- the data density that shows non-uniform distribution in the conventional method is made uniform by applying the correction processing of this embodiment.
- the magnetic resonance imaging apparatus (MRI apparatus) 100 of the present embodiment measures the echo signal for each unit k space by non-orthogonal measurement, and acquires the unit k space data, and A correction unit 320 that corrects the unit k-space data to obtain corrected unit k-space data, a rearrangement unit 330 that rearranges the corrected unit k-space data in an orthogonal coordinate system k-space, and the rearrangement An imaging unit 340 that reconstructs an image by performing inverse Fourier transform on the data rearranged in the unit 330, and the correction unit 320 is a unit that is an image for each unit k space from the unit k space data.
- the receiving coil 151 further includes a combining unit 350 that combines the images obtained for each channel, and the measuring unit 310 uses a receiving coil having a plurality of channels, and uses the receiving coil for each channel.
- the echo signal is measured, the unit k space data is acquired, the unit imaging unit 321 reconstructs the unit image for each channel, and the synthesis unit 350 synthesizes the unit image for each channel.
- the combined unit image is obtained, and the visual field expanding unit 322 uses the combined unit image as the unit image.
- the obtained unit k space data is imaged by inverse Fourier transform, and after multi-channel synthesis, the data density is set. Expand the field of view of the image in the direction you want to increase.
- the field-expanded image is subjected to Fourier transform to obtain corrected unit k-space data in which the k-space pitch in the direction in which the field of view is expanded is small and the data amount is increased. Then, the corrected unit k-space data is gridded to reconstruct the final image.
- body motion artifacts can be reduced by using non-orthogonal measurement as in the first embodiment.
- the correction process is performed, the difference in data density for each encoding direction is reduced in each unit k space, and artifacts due to non-uniform data density are reduced.
- multi-channel synthesis is performed for each unit image within the correction process. As described in the second embodiment, since the gridding process with a large amount of calculation is performed only for all the k-space data of 1, the processing time is shortened.
- the image quality can be improved and the processing time can be reduced without impairing the characteristics of non-orthogonal measurement.
- the measurement by the measurement unit 310 may be half measurement.
- Half measurement includes half echo measurement that measures only about half of the frequency encoding direction of the data of each blade and half scan measurement that measures about half of the phase encoding direction. In the present embodiment, either or both of these may be applied.
- step S1210 and step S1220 When half measurement is used, unmeasured data is estimated from approximately half of the acquired measurement data, and the image is reconstructed.
- this estimation process is performed at a timing before the correction process. That is, in the first embodiment, between step S1210 and step S1220, in the second embodiment, between step S2110 and step S2120, or between step S2210 and step S2220, the third implementation. In the embodiment, it is performed between step S3110 and step S3120.
- the non-orthogonal system measurement method to be used is not restricted to this.
- imaging is performed for each blade (unit k space). Therefore, phase encoding is required in the unit k space.
- the density of data is made uniform by canceling the data density in the overlap region of the blade (unit k space). Therefore, the unit k spaces need to overlap each other.
- non-orthogonal measurement methods may be used as long as there is a phase encoding in the unit k space and the condition that the unit k spaces overlap each other.
- Other non-orthogonal measurement methods that satisfy these conditions include, for example, multi-shot spiral scanning and measurement using fan-shaped blades for each blade.
- each unit k-space data corresponding to the blade in the hybrid radial method is created from the acquired echo signal, and the above correction processing is performed on each. That is, a unit image is created by Fourier transform. At this time, gridding is performed if necessary.
- the above embodiments are applied to the unit image, and the field of view is expanded by zero padding or the like in the direction in which the data density is desired to be increased.
- corrected unit k-space data in which the k-space pitch is small and the amount of data is increased is obtained by Fourier transforming the unit image with the field of view enlarged.
- gridding is performed after correction for each blade, but the present invention is not limited to this procedure. You may comprise so that gridding may be performed after correction
- two-dimensional measurement has been described as an example, but three-dimensional measurement may be used.
- each function described as being realized by the arithmetic system 170 in each of the above embodiments may not necessarily be realized by the arithmetic system 170 included in the MRI apparatus 100.
- An information processing apparatus that is independent of the MRI apparatus 100 and that can transmit / receive data to / from the MRI apparatus 100 may be realized.
- 100 MRI apparatus 101 subject, 120 static magnetic field generation system, 130 gradient magnetic field generation system, 131 gradient magnetic field coil, 132 gradient magnetic field power supply, 140 sequencer, 150 high frequency magnetic field generation system, 151 transmission coil, 152 synthesizer, 153 modulator, 154 high frequency amplifier, 160 high frequency magnetic field detection system, 161 receiver coil, 162 signal amplifier, 163 quadrature phase detector, 164 A / D converter, 170 arithmetic system, 171 CPU, 172 storage device, 173 external storage device, 174 display device , 175 input device, 210 imaging sequence, 211 excitation RF pulse, 212 refocusing RF pulse, 213 gradient magnetic field pulse, 215 echo signal, 220 blade, 310 measurement unit, 320 correction unit, 321 unit imaging unit, 322 visual field expansion unit , 323 unit signaling unit, 330 rearrangement unit, 340 imaging unit, 350 synthesis unit, 360 PI operation unit, 410 blade, 411 zero-padded blade, 420 unit image, 421 unit Image,
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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。
本実施形態では、非直交系計測を実現するパルスシーケンスとしてハイブリッドラディアル法を用いる場合を例にあげて説明する。
補間処理は、sinc関数やKaiser-Bessel関数の補間用関数を用いて行うことができる。
好ましくは、kx方向とky方向とのピッチが合致し、データの疎密が解消するよう決定する。図6には、FOVyの1/2ずつ、y方向の両側に追加し、視野を2倍にする場合を例示する。すなわち、視野拡大率を2とする場合である。従って、図6の例では、視野拡大部322による視野拡大処理により、位相エンコード方向の視野は、FOVyからFOVy*2に拡大する。
一方、位相エンコード方向のk空間ピッチは、ΔkyからΔky’に縮小する。なお、Δky’は、以下の式(2)で規定される。
前記チャンネル毎に得られる最終画像を合成する合成部350をさらに備え、前記計測部310は、前記コイル151を用い、前記チャンネル毎に前記エコー信号を計測して前記単位k空間データを得、前記補正部320は、前記チャンネル毎に前記単位k空間データを補正して前記補正後の単位k空間データを得、前記再配置部330は、前記チャンネル毎に前記補正後の単位k空間データを再配置し、前記画像化部340は、前記チャンネル毎に前記最終画像を得、前記合成部350が合成する画像は、前記チャンネル毎の最終画像である。
次に、本発明の第二の実施形態を説明する。本実施形態では、パラレルイメージングを用いる。パラレルイメージング法は、複数の受信コイルでエコー信号をパラレルに受信し、各受信コイルの感度分布を用いて処理する技術である。パラレルイメージング法では、エコー信号を間引いて収集することにより撮像を高速化する。
ここでは、セルフキャリブレーション型のパラレルイメージングを用いる場合を例にあげて説明する。
グリッディング処理は、演算量が多いため、マルチチャンネルコイルのコイル数が多いと、処理に係る時間が長くなる。しかし、本実施形態によれば、単位k空間(ブレード)毎にマルチチャンネル合成が行われる。すなわち、グリッディング処理前にマルチチャンネル合成を行うため、グリッディング処理は、1の全k空間データに対してのみ行えばよい。従って、演算量が少なく、その分、処理時間も短くて済む。
次に、本発明の第三の実施形態を説明する。第一の実施形態では、チャンネル毎に最終画像を得、最後にマルチチャンネル合成を行う。一方、本実施形態では、単位k空間から再構成した単位画像毎にマルチチャンネル合成を行う。
また、本実施形態では、受信コイル161は、2以上のチャンネルを有するマルチチャンネルコイルとする。
マルチチャンネル合成後の単位画像をフーリエ変換し(ステップS3140)、k空間データに戻す。続いて、ブレード回転角に応じてグリッディング処理を行う(ステップS3150)。ステップS3110からステップS3150までの処理を、全ブレードについて行い(ステップS3160)、得られた全k空間データを2次元逆フーリエ変換し(ステップS3170)、最終画像を得る。
Claims (17)
- 非直交系計測により、単位k空間毎にエコー信号を計測し、単位k空間データを取得する計測部と、
前記単位k空間データを補正し、補正後の単位k空間データを得る補正部と、
前記補正後の単位k空間データを直交座標系k空間に再配置する再配置部と、
前記再配置部で再配置後のデータを逆フーリエ変換することにより画像を再構成する画像化部と、を備え、
前記補正部は、
前記単位k空間データから単位k空間毎の画像である単位画像を再構成する単位画像化部と、
前記単位画像の視野を拡大し拡大画像を得る視野拡大部と、
前記拡大画像をフーリエ変換し、補正後の単位k空間データを得る単位信号化部と、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1記載の磁気共鳴イメージング装置であって、
前記視野拡大部は、前記単位画像の位相方向にゼロ詰めして前記拡大画像を得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、
複数のチャンネルを有する受信コイルと、
前記チャンネル毎に得られる最終画像を合成する合成部と、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3記載の磁気共鳴イメージング装置であって、
前記計測部は、前記受信コイルを用い、前記チャンネル毎に、前記エコー信号を計測して前記単位k空間データを得、
前記補正部は、前記チャンネル毎に、前記単位k空間データを補正して前記補正後の単位k空間データを得、
前記再配置部は、前記チャンネル毎に、前記補正後の単位k空間データを再配置し、
前記画像化部は、前記チャンネル毎に、前記最終画像を得、
前記合成部は、前記チャンネル毎の最終画像を合成すること
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、
前記計測部は、前記コイルを用い、前記チャンネル毎に、前記エコー信号を計測して前記単位k空間データを得、
前記単位画像化部は、前記チャンネル毎に、前記単位k空間データから前記単位画像を再構成し、
前記合成部は、前記チャンネル毎の単位画像を合成して合成単位画像を得、
前記視野拡大部は、前記単位画像として、前記合成単位画像を用いること
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、
感度分布を用いて折り返しを展開するパラレルイメージング演算を行うパラレル演算部をさらに備え、
前記計測部は、前記非直交系計測において、前記エコー信号を間引いて計測すること
を特徴とする磁気共鳴イメージング装置。 - 請求項6記載の磁気共鳴イメージング装置であって、
前記パラレル演算部は、前記単位画像の折り返しを展開して展開単位画像を得、
前記視野拡大部は、前記視野を拡大する単位画像として、前記展開単位画像を用いること
を特徴とする磁気共鳴イメージング装置。 - 請求項6記載の磁気共鳴イメージング装置であって、
前記パラレル演算部は、前記単位k空間データを補間し、補間単位k空間データを得、
前記単位画像化部は、前記補間単位k空間データから前記単位画像を再構成すること
を特徴とする磁気共鳴イメージング装置。 - 請求項8記載の磁気共鳴イメージング装置であって、
前記単位画像を合成して合成単位画像を得る合成部をさらに備え、
前記視野拡大部は、前記視野を拡大する単位画像として、前記合成単位画像を用いること
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、
前記単位画像化部は、前記単位k空間データを、処理対象データ数が2のべき乗となるようゼロ詰め後、当該ゼロ詰め後の単位k空間データから前記単位画像を再構成し、
前記単位信号化部は、前記拡大画像をフーリエ変換後、前記単位画像化部が前記単位k空間データに行ったゼロ詰めを取り除く処理を行い、前記補正後の単位k空間データを得ること
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、
前記計測部は、ハーフ計測により前記計測を行うこと
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、
前記非直交系計測は、前記エコー信号が配置されるk空間を、当該k空間の原点を通る計測軌跡を有する単位k空間であって、前記k空間の座標軸に対する前記計測軌跡の角度である回転角が互いに異なる複数の単位k空間に分割して計測するハイブリッドラディアル法を用いた計測であること
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、
前記視野拡大部は、予め定めた拡大率で拡大した視野分の画素をゼロ詰めすること
を特徴とする磁気共鳴イメージング装置。 - 非直交系計測により、単位k空間毎にエコー信号を計測し、単位k空間データを取得する信号計測ステップと、
前記単位k空間データから単位k空間毎の画像である単位画像を再構成する単位画像再構成ステップと、
前記単位画像の視野を拡大し拡大画像を得る視野拡大ステップと、
前記拡大画像をフーリエ変換し、補正後の単位k空間データを得る単位信号化ステップと、
前記補正後の単位k空間データを直交座標系k空間に再配置する信号再配置ステップと、
前記再配置部で再配置後のデータを逆フーリエ変換することにより画像を再構成する最終画像化ステップと、を備えること
を特徴とする磁気共鳴イメージング方法。 - 請求項14記載の磁気共鳴イメージング方法であって、
前記信号計測ステップは、単位k空間毎にエコー信号を間引いて計測して前記単位k空間データを取得し、
前記単位画像の折り返しを展開し、展開単位画像を得るパラレル演算ステップを備え、
前記視野拡大ステップは、前記展開単位画像の視野を拡大して前記拡大画像を得ること
を特徴とする磁気共鳴イメージング方法。 - 請求項14記載の磁気共鳴イメージング方法であって、
前記信号計測ステップは、単位k空間毎にエコー信号を間引いて計測して前記単位k空間データを取得し、
前記単位k空間データを補間し、補間単位k空間データを得るパラレル演算ステップを備え、
前記単位画像再構成ステップは、前記補間単位k空間データから前記単位画像を再構成すること
を特徴とする磁気共鳴イメージング方法。 - 請求項14記載の磁気共鳴イメージング方法であって、
前記信号計測ステップは、チャンネル毎の単位k空間データを取得し、
前記単位画像再構成ステップは、前記チャンネル毎の単位k空間データからチャンネル毎の前記単位画像を再構成し、
前記チャンネル毎の単位画像を合成して合成単位画像を得る画像合成ステップを備え、
前記視野拡大ステップは、前記合成単位画像の視野を拡大して前記拡大画像を得ること
を特徴とする磁気共鳴イメージング方法。
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