WO2009081787A1 - 磁気共鳴イメージング装置及び磁化率強調画像撮影方法 - Google Patents
磁気共鳴イメージング装置及び磁化率強調画像撮影方法 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
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/563—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution of moving material, e.g. flow contrast angiography
- G01R33/5635—Angiography, e.g. contrast-enhanced angiography [CE-MRA] or time-of-flight angiography [TOF-MRA]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/561—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]
- G01R33/5616—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 gradient refocusing, e.g. EPI
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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 technique for acquiring an image with enhanced magnetic susceptibility at high speed using a magnetic resonance imaging (hereinafter referred to as MRI) apparatus that obtains a tomographic image of an examination region of a subject using a nuclear magnetic resonance phenomenon.
- MRI magnetic resonance imaging
- the MRI apparatus uses a uniform static magnetic field, and the static magnetic field changes locally depending on the magnetic susceptibility of the subject.
- the effect of this local magnetic field change appears as a phase change in the image data.
- An imaging method (hereinafter, referred to as susceptibility-enhanced imaging) that emphasizes this phase change by arithmetic processing is known (Patent Document 1).
- This susceptibility-enhanced imaging is attracting attention as an effective technique for venous MR angiography because it can enhance the susceptibility of reduced hemoglobin in the blood.
- susceptibility-weighted imaging uses a phase change caused by the susceptibility, an echo signal is required when about 70 ms elapses after irradiation with an RF pulse. For this reason, since the repetition time (TR) of the pulse sequence (hereinafter simply abbreviated as “sequence”) cannot be set short, the imaging time becomes long.
- methods for measuring multiple echo signals with a single RF pulse irradiation are known as methods for shortening the imaging time in an MRI apparatus, and typical examples include the echo planar (EPI) method and the first spin echo method. There is (FSE) method.
- An example of magnetic susceptibility enhanced imaging using an echo planar method is disclosed in (Patent Document 2) in order to shorten the imaging time of magnetic susceptibility enhanced imaging.
- an object of the present invention is to obtain a magnetic susceptibility-enhanced image with a good signal-to-noise ratio in magnetic susceptibility enhanced imaging using an echo planar method in an MRI apparatus.
- the present invention applies a phase blip gradient magnetic field, inverts the polarity of a frequency encoding gradient magnetic field, and measures a plurality of echo signals when the plurality of echo signals are measured. Dividing into an echo signal group and a second echo signal group, obtaining image data from the first echo signal group, and obtaining the mask data from the second echo signal group, respectively; To obtain a magnetic susceptibility-enhanced image.
- the MRI apparatus of the present invention includes a measurement control unit that controls measurement of a plurality of echo signals from a subject based on a pulse sequence that applies a phase blip gradient magnetic field and reverses the polarity of a frequency encoding gradient magnetic field, and an echo signal
- An arithmetic processing unit that acquires a magnetic susceptibility-enhanced image using the first processing unit, the arithmetic processing unit divides a plurality of echo signals into a first echo signal group and a second echo signal group, Image data is acquired from the echo signal group, mask data is acquired from the second echo signal group, and a magnetic susceptibility weighted image is acquired from the image data and the mask data.
- the susceptibility-weighted imaging method of the present invention is a measurement that controls measurement of a plurality of echo signals from a subject based on a pulse sequence that applies a phase blip gradient magnetic field and reverses the polarity of a frequency encoding gradient magnetic field. And an arithmetic processing step for obtaining a magnetic susceptibility-enhanced image using an echo signal, and the arithmetic processing step divides a plurality of echo signals into a first echo signal group and a second echo signal group.
- image data is obtained from the first echo signal group
- mask data is obtained from the second echo signal group
- a magnetic susceptibility weighted image is obtained from the image data and the mask data.
- the MRI apparatus of the present invention it is possible to obtain a magnetic susceptibility enhanced image with a good signal-to-noise ratio in magnetic susceptibility enhanced imaging using the echo planar method in the MRI apparatus.
- FIG. 1 is a block diagram showing the overall configuration of an example of the MRI apparatus of the present invention.
- This MRI apparatus uses a nuclear magnetic resonance (NMR) phenomenon to obtain a tomographic image of an object, and as shown in FIG. 1, a static magnetic field generation system 2, a gradient magnetic field generation system 3, and a transmission system 5
- NMR nuclear magnetic resonance
- the static magnetic field generation system 2 generates a uniform static magnetic field in the space around the subject 1 in the direction of the body axis or in the direction perpendicular to the body axis.
- the permanent magnet method or the normal conduction method is provided around the subject 1 Alternatively, a superconducting magnetic field generating means is arranged.
- the gradient magnetic field generation system 3 (gradient magnetic field generation unit) is composed of a gradient magnetic field coil 9 wound in three axial directions of X, Y, and Z, and a gradient magnetic field power source 10 for driving each gradient magnetic field coil 9.
- gradient magnetic fields Gs, Gp, Gf in the three-axis directions of X, Y, Z are applied to the subject 1.
- a slice selection gradient magnetic field pulse (Gs) is applied in one of X, Y, and Z directions to set a slice plane for the subject 1, and a phase encoding gradient magnetic field pulse is applied in the remaining two directions.
- Gp and a frequency encoding (or reading) gradient magnetic field pulse (Gf) are applied to encode position information in each direction into an echo signal.
- the sequencer 4 is a measurement control unit that controls the measurement of echo signals by repeatedly applying a high-frequency magnetic field pulse (hereinafter referred to as “RF pulse”) and a gradient magnetic field pulse in a predetermined sequence.
- RF pulse high-frequency magnetic field pulse
- the sequencer 4 operates under the control of the CPU 8 and sends various commands for measuring echo signals necessary for the reconstruction of the tomographic image of the subject 1 to the transmission system 5, the gradient magnetic field generation system 3, and the reception system 6. By controlling these systems, echo signal measurement is controlled.
- the transmission system 5 irradiates an RF pulse to cause nuclear magnetic resonance to the nuclear spins of atoms constituting the biological tissue of the subject 1, and includes a high frequency oscillator 11, a modulator 12, a high frequency amplifier 13, and a transmission side And a high-frequency coil 14a.
- the high-frequency pulse output from the high-frequency oscillator 11 is amplitude-modulated by the modulator 12 at a timing according to a command from the sequencer 4, and the amplitude-modulated high-frequency pulse is amplified by the high-frequency amplifier 13 and then placed close to the subject 1.
- the subject 1 is irradiated with electromagnetic waves (RF pulses) by being supplied to the high frequency coil 14a.
- the receiving system 6 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the biological tissue of the subject 1, and receives a high-frequency coil 14b on the receiving side, an amplifier 15, and a quadrature detector 16 and an A / D converter 17.
- the response electromagnetic wave (NMR signal) of the subject 1 induced by the electromagnetic wave irradiated from the high-frequency coil 14a on the transmission side is detected by the high-frequency coil 14b arranged close to the subject 1 and amplified by the amplifier 15
- the signals are divided into two orthogonal signals by the quadrature phase detector 16 at a timing according to a command from the sequencer 4, converted into digital quantities by the A / D converter 17, and sent to the signal processing system 7.
- the echo signal converted into the digital quantity is referred to as echo signal data or echo data.
- the signal processing system 7 has an external storage device (storage means) such as an optical disk 19 and a magnetic disk 18 and a display 20 composed of a CRT or the like, and echo data from the reception system 6 is input to the CPU 8 (arithmetic processing unit). Then, the CPU 8 executes arithmetic processing such as signal processing and image reconstruction, and displays the tomographic image of the subject 1 as a result on the display 20 and records it on the magnetic disk 18 of the external storage device.
- the CPU 8 includes a memory corresponding to the K space and stores echo data.
- the description that the echo signal or the echo data is arranged in the K space means that the echo data is written and stored in this memory.
- the operation system 25 is used to input various control information of the MRI apparatus and control information of processing performed by the signal processing system 7, and includes a trackball or mouse 23 and a keyboard 24.
- the operation system 25 is arranged close to the display 20, and the operator interactively controls various processes of the MRI apparatus through the operation system 25 while looking at the display 20.
- the transmission-side and reception-side high-frequency coils 14a and 14b 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 MRI apparatus's imaging target spin species are protons that are the main constituents of the subject as widely used in clinical practice.
- the spatial distribution of proton density and the spatial distribution of the relaxation phenomenon in the excited state By imaging the spatial distribution of proton density and the spatial distribution of the relaxation phenomenon in the excited state, the form or function of the human head, abdomen, limbs, etc. can be photographed two-dimensionally or three-dimensionally.
- FIG. Fig. 2 is a sequence chart showing the sequence shape of the gradient echo type multi-shot echo planar method.
- Gs, Gp, and Gr represent the axes of the slice selection gradient magnetic field, phase encoding gradient magnetic field, and frequency encoding gradient magnetic field, respectively.
- RF, AD, and Echo represent an RF pulse, a sampling window, and an echo signal, respectively.
- 201 is an RF pulse
- 202 is a slice selective gradient magnetic field pulse
- 203 is a slice refocusing gradient magnetic field pulse
- 204 is a phase encoding gradient magnetic field pulse
- 205 is a phase blip gradient magnetic field pulse group
- 206 is a frequency phase gradient magnetic field pulse
- 207 is a frequency encoding gradient magnetic field pulse group
- 208 is a sampling window group
- 209 is an echo signal group.
- the sequencer 4 controls the transmission system 5, the gradient magnetic field generation system 3, and the reception system 6 to measure an echo signal.
- the sequencer 4 measures one echo signal 209 for each readout gradient magnetic field pulse 207 while changing the polarity of the readout gradient magnetic field pulse 207 for each irradiation of the RF pulse 201. This is repeatedly executed at a time interval 210 (repetition time TR), and the number of echo signals necessary for image reconstruction is measured.
- the number of echo signals necessary for image reconstruction is generally about 64, 128, or 256 depending on the matrix of the image to be created.
- the number after-(hyphen) represents a repetition number.
- FIG. 2 (a) shows the first first sequence among a plurality of repetitions, and the second and subsequent repetition sequences are the same as the first one and are omitted. In the sequence diagrams described below, the meanings of the numbers after-(hyphen) are the same.
- a plurality of echo signals are measured by one RF pulse irradiation, so an image can be acquired at a higher speed than a sequence in which one echo signal is measured by one RF pulse irradiation.
- FIG. 2 (a) since six echo signals 209 are measured by one RF pulse 201 irradiation, it can be photographed six times faster. Note that the single shot echo planar method that measures all echo signals necessary for image reconstruction by one RF pulse irradiation can further increase the speed.
- FIG. 2 (b) is a schematic diagram showing an example of the K space 211 in which echo data measured by the echo planar method is arranged.
- the horizontal axis Kx in FIG. 2 (b) corresponds to the sampling time of the echo signal
- the vertical axis Ky corresponds to the total amount of phase encoding gradient magnetic field pulses applied to the phase encoding axis when the echo signal is measured. To do.
- the arrow 212 in FIG. 2 (b) is the order in which echo signals are measured in the K space data acquired using the echo planar method, and the Ky axis direction is from bottom to top (that is, from the negative side to the positive side).
- This is an example in which echo signals are continuously measured (referred to as sequential ordering).
- Lines 212-1 solid line
- 212-2 dotted line
- 212-3 dashed line
- 210-1 first repetition
- 210-2 second repetition
- 210-3 corresponding to the echo signal groups 209-1, 209-2, and 209-3 measured in the third iteration, each line has an echo signal every two Ky-axis directions
- each line 212 includes six echo signals.
- the scanning direction of the arrow at the echo signal position corresponds to the polarity of the readout gradient magnetic field pulse group 207.
- the interval 213 in the Ky direction of arrows corresponds to the area of each phase blip gradient magnetic field 205, and by changing the starting position of each line 212 with the phase encode gradient magnetic field pulse 204, echo data Can be placed in the K space without overlapping in the Ky direction.
- FIG. 2 (c) is a schematic diagram showing another example of the K space 211 in which echo data measured by the echo planar method is arranged.
- the two-dimensional K-space data arranged in this way is converted into an image by the CPU 8 applying a two-dimensional Fourier transform (for the three-dimensional K-space data, the three-dimensional Fourier transform is applied to the 3D Convert to a dimensional image).
- a two-dimensional Fourier transform for the three-dimensional K-space data, the three-dimensional Fourier transform is applied to the 3D Convert to a dimensional image.
- the contrast of the local area in the image has a different spatial frequency depending on the size of the target part.
- the contrast of an area of 1 pixel size in the image reflects the contrast of echo data in the highest spatial frequency domain in K space (i.e., echo signals measured with a maximum or close phase encoding value).
- the contrast of an area of 10 pixels in the image contributes greatly to the contrast of 10 points of data from the higher spatial frequency in the K space.
- echo time the echo time
- FIG. 3 (a) shows the phase rotation that occurs in the echo signal after application of the RF pulse 201.
- FIG. 3 (a) shows the phase rotation that occurs in the echo signal after application of the RF pulse 201.
- FIG. 3 (a) shows the phase rotation that occurs in the echo signal after application of the RF pulse 201.
- FIG. 3 (a) shows the phase rotation that occurs in the echo signal after application of the RF pulse 201.
- FIG. 3 (a) shows the phase rotation that occurs in the echo signal after application of the RF pulse 201.
- FIG. 3 (a) shows the phase rotation that occurs in the echo signal after application of the RF pulse 201.
- FIG. 3 (a) shows the phase rotation that occurs in the echo signal after application of the RF pulse 201.
- FIG. 3 (a) shows the phase rotation that occurs in the echo signal after application of the RF pulse 201.
- FIG. 3 (a) shows the phase rotation that occurs in the echo signal after application of the RF pulse 201.
- the peak value of the echo signal obtained by the MRI apparatus becomes a curve like 302 in FIG. 3 (b) after the RF pulse 201 is applied.
- T 2 the spin itself excited by the RF pulse 201 is laterally relaxed
- a phase difference occurs in the spin due to the difference in magnetic susceptibility, and this phase difference becomes larger as the echo time becomes longer.
- an echo signal having an echo time of about 70 ms is required. This magnetic susceptibility effect is reflected in the phase of image data reconstructed from echo signals measured with such a long echo time.
- step 401 the sequencer 4 activates a pulse sequence for susceptibility weighted imaging to control echo signal measurement, and the CPU 8 stores the measured echo signal digital data in a memory corresponding to the K space.
- step 403 the CPU 8 applies a filter (Lowpass filter) that passes the low spatial frequency region to the K space data 402.
- a filter Lowpass filter
- step 404 the CPU 8 performs a two-dimensional Fourier transform on the K space data filtered in step 402 to obtain filtered image data 405.
- step 406 the CPU 8 generates image data 407 by performing two-dimensional Fourier transform on the K space data 402 in the same manner as in normal reconstruction.
- the difference between these two image data 405 and 407 is that the image data 407 contains all the phase information, whereas the filtered image data 405 has the phase information corresponding to the high spatial frequency removed by the filter. Therefore, only the wide phase information is included and the local phase information is lost.
- step 408 the CPU 8 obtains a phase image from each of the two image data 405 and 407, respectively, performs phase subtraction (difference) processing, and obtains a phase difference image obtained by extracting only local phase information of the image data 407. . Therefore, only local phase information reflecting the magnetic susceptibility effect is extracted from this phase difference image.
- the CPU 8 creates mask data 410 from the phase data of the phase difference image obtained in step 408 using a weight function corresponding to the phase amount.
- the weight function is a function that converts a phase value in a specific range into a value (mask value) in a specific range using a linear function or an exponential function.
- a linear or non-linear conversion function for converting ⁇ ⁇ ⁇ ⁇ 0 into 0 ⁇ v ⁇ 1 is used ( ⁇ is a phase value, and v is a mask value).
- step 411 the CPU 8 multiplies the created mask data 410 by the image data 407 or its absolute value.
- the image multiplied by the mask is an image in which the contrast by the magnetic susceptibility effect is locally improved.
- step 412 in the case of multi-slice imaging or three-dimensional imaging, the CPU 8 creates image data obtained by multiplying the mask data 410 in step 411 by a plurality of slices, and projects these results to the minimum value (MINIP). As a result, a final magnetic susceptibility-enhanced image 413 is obtained. Note that this step 412 may be omitted, and a two-dimensional susceptibility enhanced image of each slice may be used.
- MINIP minimum value
- susceptibility weighted imaging using the above-mentioned echo planar method can be considered, but simply by combining them, there is no change in measuring an echo signal with a long echo time. Therefore, even if an image is reconstructed from such an echo signal, the signal-to-noise ratio is deteriorated.
- the MRI apparatus and susceptibility-enhanced imaging method of the present invention to solve this problem are described below, and each embodiment of the MRI apparatus and susceptibility-enhanced imaging method of the present invention will be described below.
- the echo signal group measured by the echo planar method is divided into two parts, the first echo signal group measured in the first half and the second echo signal group measured in the second half, and the first echo signal Image data is created from the group, and mask data is created from the second echo signal group.
- the present embodiment will be described in detail based on FIG. 5 and FIG.
- FIG. 5 (a) shows only the phase encoding gradient magnetic field axis (Gp) and the echo signal in the sequence described in FIG. 2 (a), and the others are omitted because they are the same as FIG. 2 (a).
- Gp phase encoding gradient magnetic field axis
- FIG. 2 (a) shows only the phase encoding gradient magnetic field axis (Gp) and the echo signal in the sequence described in FIG. 2 (a), and the others are omitted because they are the same as FIG. 2 (a).
- Gp phase encoding gradient magnetic field axis
- the sequencer 4 executes a combination of sequences suitable for measurement of each echo signal group. That is, in the present embodiment, the measured echo signal group is equally divided into the first half and the second half of the measurement, and is divided into two echo signal groups including an equal number of echo signals.
- a group of three echo signals on the front side is referred to as a first echo signal group
- a group of three echo signals on the rear side is referred to as a second echo signal group.
- the present embodiment is not limited to equal division, and may be non-equal division, but an example of non-equal division will be described later.
- the sequencer 4 makes the phase blip gradient magnetic field pulse 503 applied when measuring the first echo signal group 501 the same as the sequence shown in FIG. Then, after measuring the first echo signal group 501, the phase rephase gradient magnetic field pulse 504 is applied, and the Ky position in the K space is returned to the same position as the first echo signal in the first echo signal group 501. . Thereafter, the phase blip gradient magnetic field pulse 505 is applied again, and the second echo signal group 502 is measured.
- Fig. 5 (b) is an example in which the echo signal group data measured in this way is arranged in the K space.
- the CPU 8 arranges the data of the first echo signal group 501 in the K space and creates the image K space data 506, and arranges the data of the second echo signal group 502 in the K space and masks the K space data. Create 507.
- Each divided region in each K space in FIG. 5 (b) corresponds to each echo time in the echo signal group. That is, the CPU 8 starts from an echo signal with a short echo time in the order of the divided areas 508, 509, and 510 in the image K space data 506 and in the order of the divided areas 511, 512, and 513 in the mask K space data 507.
- the echo signal data is arranged respectively.
- the echo signal data (number after-(hyphen)) is 1) measured in the first sequence on the positive side in the Ky direction, and the echo measured in the second sequence on the negative side in the Ky direction.
- Signal data (the number after-(hyphen) is 2) is arranged (the same applies to the description of K space data in other embodiments described later).
- the image data 407 uses the first echo signal group 501 with a short echo time.
- the mask data 410 can be generated using the second echo signal group 502 having a long echo time.
- the merit of doing this is that the phase of the echo signal shown in FIG. 3 (a) increases in proportion to the echo time, so that a large amount of magnetic susceptibility effect can be captured in the mask data 410. As a result, the contrast due to the magnetic susceptibility effect can be improved.
- the signal strength of the echo signal shown in FIG. 3B decreases as the echo time elapses, the signal strength of the image echo signal group 501 measured on the front side of the sequence increases.
- a magnetic susceptibility-weighted image created using such image K space data 506 and mask K space data 507 is an image having a good contrast due to the signal noise ratio and the magnetic susceptibility effect.
- an echo signal group is measured using the echo planar method sequence shown in FIG.
- the sequencer 4 is a gradient echo type multi-shot echo planar method sequence, as described above, and measures the first echo signal group and the second echo signal group as shown in FIG.
- the echo signal group 602 including the first echo signal group and the second echo signal group is measured using the echo planar method sequence in which the sequence shape is changed as described above.
- step 603 mask K space data 604 and image K space data 605 are generated from the echo signal group 602 measured in step 601.
- the CPU 8 separates the echo signal group 602 measured in step 601 into a first echo signal group 501 measured on the front side of the sequence and a second echo signal group 502 measured on the rear side, and the first The image K space data 605 is generated from the echo signal group 501 and the mask K space data 604 is generated from the second echo signal group 502.
- the filtered mask data 405 is generated from the mask K space data 604.
- the CPU 8 applies a Lowpass filter to the mask K-space data 604, and in step 404-1 performs two-dimensional Fourier transform on the filtered K-space data to obtain post-filter mask data 405. Generate.
- the details of each step are the same as in FIG.
- step 404-2 mask image data 606 is generated from the mask K space data 604.
- the CPU 8 performs two-dimensional Fourier transform on the mask K space data 604 to generate mask image data 606.
- image data 407 is generated from the image K-space data 605.
- the CPU 8 generates image data 407 by performing a two-dimensional Fourier transform on the image K space data 605.
- step 408 a phase subtraction process is performed between the phase of the post-filter mask data 405 and the phase of the mask image data 606 to obtain a phase difference image.
- the CPU 8 obtains the phase from the post-filter mask data 405 and obtains the phase from the mask image data 605. Then, these two phases are subtracted to obtain a phase difference image that is an image representing the phase difference data. Since the mask K-space data 604 has the same spatial frequency data as the image K-space data 605, the mask image data 606 includes all the same phase information as the image data 407. On the other hand, the post-filter mask data 405 has the phase information corresponding to the high spatial frequency removed by the filter.
- phase difference image is an image representing only local phase data in which the magnetic susceptibility effect is reflected.
- Steps 409-413 mask data 410 is generated from the phase difference data of the phase difference image obtained in Step 408, and a susceptibility weighted image 413 is obtained from the mask data 410 and the image data 407.
- the details of each step are the same as in FIG.
- the above is the details of the imaging flow of the magnetic susceptibility enhancement imaging of this embodiment.
- the mask creation processing 409 and subsequent steps are the same as the imaging flow of FIG. 4, but the echo signal for the mask data 410 is completely different, so the magnetic susceptibility-enhanced image 413 by this imaging flow is acquired by the imaging flow of FIG. Compared with the magnetic susceptibility-enhanced image, both the signal noise ratio and the contrast due to the magnetic susceptibility effect are improved.
- the imaging time can be shortened and the echo time is short.
- the first echo signal group is used to create image data with a good signal-to-noise ratio
- the second echo signal group with a long echo time is used to create mask data that incorporates much of the magnetic susceptibility effect. Therefore, it is possible to acquire a magnetic susceptibility-enhanced image with good contrast due to the magnetic susceptibility effect.
- FIG. 7 (a) shows the sequence shape of the first modified example, and only the phase encoding gradient magnetic field axis (Gp) and the echo signal (Echo) are shown as in FIG. 5 (a). Others are the same as in FIG. 5 (a), and the display and description are omitted.
- the difference from the sequence of FIG. 5A is that there is no phase rephase gradient magnetic field pulse 504 before the measurement of the second echo signal group 715, and the polarity of the phase blip gradient magnetic field pulse 714 is different.
- FIG. 7 (b) is a schematic diagram of the K space in which the echo data measured in the sequence of FIG. 7 (a) is arranged, as in FIG. 5 (b).
- the measurement order of the K space data 506 using the data of the first echo signal group 501 and the divided areas 508 to 510 is the same as that in FIG. Since the data is measured with a phase blip gradient magnetic field pulse 714 having a polarity different from that of the sequence of FIG. 5 (a), the measurement order of the K-space divided regions 716 to 718 is the same as the divided regions 511 to 513 of FIG. The reverse is true. Further, since there is no phase rephase gradient magnetic field pulse 504, the echo signals overlap in the first echo signal group 501 and the second echo signal group 715. That is, a part of the measured echo signal group is shared between the first echo signal group 501 and the second echo signal group 715.
- the same echo signal data as the highest region 510 of the image K space data 506 is arranged.
- two echo signals are measured without applying a phase blip gradient magnetic field pulse, and one of the two is measured.
- the overlap may be eliminated.
- the phase rephasing gradient magnetic field pulse 504 is eliminated, the magnitude of the phase blip gradient magnetic field pulse 714 is set to the minimum, and the mask is efficiently used.
- An echo signal group can be measured.
- the intensity of the gradient magnetic field pulse to be applied increases, the effect of eddy current and residual magnetic field generated after application of the gradient magnetic field pulse increases, so that the output of the phase blip gradient magnetic field pulse is minimized as in this modification. It is effective to reduce these effects.
- FIG. 8 shows the sequence shape of the second modified example, showing only the phase encode gradient magnetic field axis (Gp), the frequency encode gradient magnetic field axis (Gr), the sampling window axis (AD), and the echo signal (Echo). .
- the difference from the sequence of FIG. 5 (a) is that when the second echo signal group 804 is measured, the intensity of the frequency encoding gradient magnetic field pulse 802 is large and the application time is shortened, and the phase blip gradient The application time interval of the magnetic field pulse 801 is shortened, and the time of the sampling window 803 is shortened. Furthermore, when the second echo signal group 804 is measured, the reception frequency band of the sampling window 803 is expanded.
- the frequency encoding gradient magnetic field pulse applied when the second echo signal group 804 is measured.
- the intensity of 802 is high and the application time is shortened, and the reception frequency band of the sampling window 803 is expanded more than the reception frequency band of the sampling window 208.
- the sequencer 4 measures the echo signal while performing these controls based on the sequence shown in FIG. According to the sequence shown in FIG. 8, since the measurement time of the second echo signal group 804 can be shortened, the repetition time of the sequence can be shortened.
- the area of the frequency encoding gradient magnetic field pulse 207 for the first echo signal group 501 and the area of the frequency encoding gradient magnetic field pulse 802 for the second echo signal group 804 are If they are the same, by widening the reception frequency band of the sampling window 803, an image having the same spatial information can be created by the two echo signal groups 501 and 804.
- the K-space data acquired in the sequence of FIG. 8 has the same configuration as FIG. 5 (b), but the mask K-space data 707 has a wider sampling bandwidth when it is acquired, so the signal-to-noise ratio Decreases.
- the phase difference data for mask processing calculated in the above-described step 408 can be calculated using the filtered image data 405 and the mask image data 606 obtained from the mask K space data 707.
- the repetition time of the sequence can be shortened, and the photographing time can be shortened compared to the case of the sequence shown in FIG.
- the echo signal group measured by the echo planar method is divided into two groups, and the echo signal measured at the front side of the sequence
- the group is the echo signal group for the image
- the echo signal group measured on the back side is the echo signal group for the mask, which has a high signal-to-noise ratio and improved susceptibility-enhanced contrast. It becomes possible to acquire a rate-weighted image.
- a phase blip gradient magnetic field pulse is applied every two echo signals
- an odd-numbered echo signal group is a first echo signal group
- an even-numbered echo signal group is a second echo signal.
- a group is the sequence shape in which the phase blip gradient magnetic field pulse is applied every two echo signals and the data arrangement in the K space.
- FIG. 9 (a) shows the sequence shape of the gradient echo type multi-shot echo planar method of the present embodiment, and only the phase encoding gradient magnetic field axis (Gp) and the echo signal (Echo), as in FIG. 5 (a). Is shown. Others are the same as in FIG.
- the difference from the sequence in FIG. 5 (a) is that the sequencer 4 applies the phase blip gradient magnetic field pulse 903 every time two echo signals are measured when measuring the echo signal group 904. That is, two echo signals are measured with the same phase encoding.
- FIG. 9 (b) shows an example of the K space in which the data of the echo signal group 904 measured based on the sequence shown in FIG. 9 (a) is arranged.
- the CPU 8 sets the odd-numbered echo signal among the two echo signals measured by the same phase encoding as the first echo signal group, and the even-numbered echo signal as the second echo signal group. To do. Then, the CPU 8 arranges the first echo signal group data in the image K space as the image K space data 911, and arranges the second echo signal group data in the mask K space for masking. This is K-space data 912.
- step 601 the sequencer 4 controls the measurement of the echo signal group 904 based on the sequence shown in FIG.
- step 603 the CPU 8 sets an odd-numbered echo signal measured in the echo signal group 602 as a first echo signal group, and an even-numbered echo signal as a second echo signal group. Then, as shown in FIG. 9 (b), the CPU 8 creates image K space data 911 from the data of the first echo signal group and mask K space data 912 from the data of the second echo signal group, respectively. .
- the measurement order of each divided area in each K space is the same as that in FIG. 5 (b). That is, echo signal data having a short echo time to an echo signal having a long echo time are arranged in the order of divided areas 905, 906, and 907 in the K space 911 and in the order of divided areas 908, 909, and 910 in the K space 912.
- the image K space data 911 in FIG. 9B is used as the image K space data 605 in FIG. 6, and the mask K space data 912 in FIG. 9B is used as the mask K space data 604 in FIG.
- the CPU 8 executes the imaging flow after step 403 shown in FIG. 6, whereby the magnetic susceptibility-enhanced image 413 is acquired. Since the processing content of each step is the same, description is abbreviate
- the echo signal is measured while the frequency encoding gradient magnetic field pulse is inverted, so the spatial information of the odd-numbered echo signal and the even-numbered echo signal is inverted. Will do.
- the peak position of the echo signal measured with the positive frequency encode gradient magnetic field and the peak position of the echo signal measured with the negative frequency encode gradient magnetic field are shifted due to a gradient magnetic field pulse error at the time of echo signal measurement.
- the left-right reversal processing leaves a shift in the echo signal peak position between the odd-numbered echo signal and the even-numbered echo signal, resulting in artifacts in the image (generally, N / 2 artifact).
- the image K space data 911 uses only odd-numbered echo signals
- the mask K space data 912 uses even-numbered echo signals. Therefore, there is an advantage that the N / 2 artifact does not occur.
- the phase blip gradient magnetic field pulse is applied every two echo signals by the echo planar method, and the echo signal group measured at odd number is obtained.
- the first echo signal group and the even-numbered echo signal as the second echo signal group, obtaining a magnetic susceptibility-weighted image with a high signal-to-noise ratio and no N / 2 artifacts Is possible.
- the number of measurement of the echo signal for mask and the number of measurement of the echo signal for image are different from each other, so that the photographing time is shortened.
- the difference from the first embodiment described above is the sequence shape and the data arrangement in the K space due to the difference in the number of mask echo signals and the number of image echo signals.
- FIG. 10 (a) shows a sequence shape of the gradient echo type multi-shot echo planar method of the present embodiment, and shows only an echo signal (Echo) measured in one repetition (shot). Others are the same as the sequence of FIG.
- measurement is performed so that the number of image echo signals and the number of mask echo signals are different.
- measurement is performed such that the number of mask echo signals is smaller than the number of image echo signals.
- FIG. 10 (a) shows a case where four image echo signals 1001 and two mask echo signal groups 1002 are measured, respectively, but this embodiment is not limited to these numbers. .
- the difference from the sequence in FIG. The area of the gradient magnetic field pulse 1013 is different. That is, the application amount of the phase rephase gradient magnetic field pulse 1013 after the measurement of the first echo signal group 1001 and before the measurement of the second echo signal group 1002 is made smaller than 504 in FIG. As a result, the position in the Ky direction at the time of measuring the second echo signal group starts from a higher spatial frequency region than in the sequence of FIG. 5 (a).
- the magnitude of the phase blip gradient magnetic field pulse 1014 applied after the phase rephase gradient magnetic field pulse 1013 is the same as 505 in FIG. 2 (a).
- the sequencer 4 controls the phase encode gradient magnetic field pulse and the phase blip gradient magnetic field pulse to measure each echo signal.
- the filling rate of the echo signal data is different between the image K space and the mask K space.
- the high spatial frequency pass filter is applied to the mask K space data in the creation process of the magnetic susceptibility weighted image, information in the low spatial frequency region of the mask K space data may be small. .
- the mask K-space data has at least data in the high spatial frequency region.
- the echo data is arranged only in the high spatial frequency region of the mask K space, and the echo signal corresponding to the remaining low spatial frequency region is not measured, and the corresponding one of the image K spatial data is measured.
- the same data as the low spatial frequency echo data is used. That is, the CPU 8 fills not only the image K space but also the low spatial frequency region of the mask K space with echo data corresponding to the low spatial frequency region of the image K space.
- FIG. 10 (b) shows the K-space data acquired based on the sequence shown in Fig. 10 (a).
- FIG. 10 (b) is an example in which measured echo data is arranged in the K space based on the sequence of FIG. 10 (a).
- echo data is arranged in the image K space 1011 as in the first embodiment described above. That is, the CPU 8 arranges the data of the echo signal group 1001 measured by the sequencer 4 in the image K space 1011 in the order of the divided areas 1003, 1004, 1005, and 1006.
- data of the echo signal group 1002 is arranged in the mask K space 1012.
- the CPU 8 arranges the data of the echo signal group 1002 measured by the sequencer 4 in the mask K space 1012 in the order of the divided areas 1009 and 1010.
- echo signals corresponding to the divided areas 1007 and 1008 surrounded by the thick frame of the mask K space 1012 are not measured. Therefore, the CPU 8 fills these areas with the same data as the echo data arranged in the same divided areas 1003 and 1004 of the image K space 1011 in the echo signal group 1001 measured for the image.
- all the spatial frequencies in the mask K space are filled with the echo data, so that an image can be created.
- step 601 the sequencer 4 controls the measurement of the echo signal groups 1001 and 1002 based on the sequence shown in FIG. 10 (a), and acquires the echo signal group 602.
- step 603 the CPU 8 creates the K space data 1011 and 1012 for the image and mask shown in FIG. 10B from the echo signal group 602, respectively. At this time, as described above, the CPU 8 shares the data in the low spatial frequency region of the mask K space and the data in the low spatial frequency region of the image K space.
- the image K space data 1011 in FIG. 10B is used as the image K space data 605 in FIG. 6, and the mask K space data 1012 in FIG. 10B is used as the mask K space data 604 in FIG.
- the CPU 8 executes the imaging flow after step 403 shown in FIG. 6, whereby the magnetic susceptibility-enhanced image 413 is acquired. Since the processing content of each step is the same, description is abbreviate
- the low spatial frequency region of the mask K space data 1012 includes image echo data, so the mask K space data 1012 also includes echo data at a point in time when the echo time is short. . Therefore, the phase of the mask image data 606 created in the processing flow of FIG. 6 is the phase of the echo signal measured at a short time of the echo time occupying the low spatial frequency region and the echo time occupying the high spatial frequency region. Both phases of the echo signal measured at a long time point are included.
- the phase of the echo signal occupying the low spatial frequency region becomes dominant.
- the phase data after the phase subtraction processing 408 is dominated by the phase of the echo signal occupying the high spatial frequency region.
- the phase data remaining after the phase subtraction processing 408 is the echo from which the echo signal arranged in the low spatial frequency region is measured from the phase of the echo time when the echo signal arranged in the high spatial frequency region is measured. The difference is left with the phase of time reduced.
- this embodiment can also be applied to the other sequence shapes shown in the first embodiment (that is, FIG. 7 (a), FIG. 8, FIG. 9 (a)).
- the echo signal data is filled with the echo data in the spatial frequency domain in the image echo signal group.
- the example of the sequence of the multi-shot echo planar method has been described as in the first embodiment described above, but all echo signals are transmitted once by the single-shot echo planar method. You may measure by irradiation of RF pulse.
- the measurement of the mask echo signal corresponds to the low spatial frequency region of the K space. While omitting the measurement of the echo signal and dividing it into the image echo signal group and the mask echo signal group, by sharing the echo data of the low spatial frequency region of the K space, while reducing the shooting time, A magnetic susceptibility-enhanced image having a high signal-to-noise ratio and improved contrast of the magnetic susceptibility effect can be acquired.
- FIG. 4 is a diagram for explaining a photographing flow according to the first embodiment.
- FIG. 6 is a diagram for explaining a first preferred modification of the first embodiment.
- FIG. 6 is a diagram for explaining a second preferred modification of the first embodiment.
- FIG. 10 is a diagram for explaining another preferable third modification of the second embodiment.
- FIG. 6 is a diagram for explaining a sequence and K space data according to a third embodiment.
- 1 subject 2 static magnetic field generation system, 3 gradient magnetic field generation system, 4 sequencer, 5 transmission system, 6 reception system, 7 signal processing system, 8 central processing unit (CPU), 9 gradient magnetic field coil, 10 gradient magnetic field power supply, 11 high frequency oscillator, 12 modulator, 13 high frequency amplifier, 14a high frequency coil (transmission side), 14b high frequency coil (reception side), 15 amplifier, 16 quadrature phase detector, 17 A / D converter, 18 magnetic disk, 19 optical disk , 20 display, 201 high frequency pulse, 202 slice selective gradient magnetic field pulse, 203 slice refocus selective gradient magnetic field pulse, 204 phase encode gradient magnetic field pulse, 205 phase blip gradient magnetic field pulse, 206 frequency dephase gradient magnetic field pulse, 207 frequency encode gradient Magnetic field pulse, 208 data sample window, 209 echo signal
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Abstract
Description
本発明のMRI装置は、位相ブリップ傾斜磁場を印加し、周波数エンコード傾斜磁場の極性を反転させるパルスシーケンスに基づいて、被検体からの複数のエコー信号の計測を制御する計測制御部と、エコー信号を用いて磁化率強調画像を取得する演算処理部と、を備え、演算処理部は、複数のエコー信号を第1のエコー信号群と第2のエコー信号群とに分割して、第1のエコー信号群から画像データを、第2のエコー信号群からマスクデータを、それぞれ取得し、画像データとマスクデータとから磁化率強調画像を取得することを特徴とする。
これら2つの画像データ405と407の違いは、画像データ407は全ての位相情報を含んでいるのに対し、フィルタ後の画像データ405は、フィルタにより高空間周波数に対応した位相情報が除去されているため、広域的な位相情報のみを含み、局所的な位相情報がなくなっていることである。
本発明のMRI装置及び磁化率強調撮影方法の第1の実施形態を説明する。本実施形態は、エコープレナー法で計測したエコー信号群を、前半で計測された第1のエコー信号群と後半で計測された第2のエコー信号群とで2分割し、第1のエコー信号群から画像データを、第2のエコー信号群からマスクデータを作成する。以下、図5、図6に基づいて本実施形態を詳細に説明する。
なお、本実施形態の説明においては、マルチショットエコープレナー法のシーケンスの例を説明したが、シングルショットエコープレナー法により、全てのエコー信号が1回のRFパルスの照射により計測されてもよい。
次に、本発明のMRI装置及び磁化率強調撮影方法の第2の実施形態を説明する。本実施形態は、位相ブリップ傾斜磁場パルスを2エコー信号毎に印加し、奇数番目に計測されるエコー信号群を第1のエコー信号群、偶数番目に計測されるエコー信号を第2のエコー信号群とする。前述の第1の実施形態と異なる点は、位相ブリップ傾斜磁場パルスを2エコー信号毎に印加するシーケンス形状と、K空間におけるデータ配置である。以下、前述の第1の実施形態と異なる点のみを説明し、同一の点の説明を省略し、図9に基づいて本実施形態を詳細に説明する。
各K空間の各分割領域の計測順序は図5(b)と同様である。すなわち、K空間911では分割領域905,906,907の順で、K空間912では分割領域908,909,910の順で、それぞれエコー時間の短いエコー信号からエコー時間の長いエコー信号のデータが配置される。
次に、本発明のMRI装置及び磁化率強調撮影方法の第3の実施形態を説明する。本実施形態は、マスク用のエコー信号の計測数と画像用のエコー信号の計測数とを異ならせて、撮影時間を短縮する。前述の第1の実施形態と異なる点は、マスク用のエコー信号の計測数と画像用のエコー信号の計測数とが異なることによるシーケンス形状と、K空間におけるデータ配置である。以下、前述の第1の実施形態と異なる点のみを説明し、同一の点の説明は省略する。
Claims (15)
- 所定のパルスシーケンスに基づいて、被検体からのエコー信号の計測を制御する計測制御部と、
K空間に対応する記憶部に前記エコー信号のデータを配置して画像データとマスクデータを取得し、前記画像データと前記マスクデータとから磁化率強調画像を取得する演算処理部と、
を備え、
前記パルスシーケンスは、位相ブリップ傾斜磁場を印加し、周波数エンコード傾斜磁場の極性を反転させて、複数のエコー信号の計測を行う、磁気共鳴イメージング装置であって、
前記演算処理部は、前記複数のエコー信号を第1のエコー信号群と第2のエコー信号群とに分割して、前記第1のエコー信号群から前記画像データを、前記第2のエコー信号群から前記マスクデータを、それぞれ取得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において、
前記演算処理部は、
前記第2のエコー信号群をフーリエ変換してマスク画像データを取得し、
前記第2のエコー信号群にLowpassフィルタを施した後にフーリエ変換してフィルタ後マスクデータを取得し、
前記マスク画像データの位相と前記フィルタ後マスクデータの位相の差分から、前記マスクデータを取得する
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において、
前記演算処理部は、前記複数のエコー信号の内、
前記パルスシーケンスの前側で計測されたエコー信号を第1のエコー信号群とし、
前記パルスシーケンスの後側で計測されたエコー信号を第2のエコー信号群とする
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において、
前記計測制御部は、前記第1のエコー信号群の計測と前記第2のエコー信号群の計測との間に、位相リフェイズ傾斜磁場を印加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において、
前記演算処理部は、前記複数のエコー信号の一部を、前記第1のエコー信号群と前記第2のエコー信号群とで共用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5記載の磁気共鳴イメージング装置において、
前記計測制御部は、前記第1のエコー信号群の計測の際に印加する位相ブリップ傾斜磁場の極性と、前記第2のエコー信号群の計測の際に印加する位相ブリップ傾斜磁場の極性と、を異ならせ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において、
前記計測制御部は、
前記第1のエコー信号群の計測の際に印加する前記周波数エンコード傾斜磁場と比較して、前記第2のエコー信号群の計測の際に印加する前記周波数エンコード傾斜磁場の強度を大きく、かつ、印加時間を短くし、さらに、
前記第2のエコー信号群の計測の際のサンプリングウインドの受信周波数帯域を、前記第1のエコー信号群の計測の際のサンプリングウインドの受信周波数帯域よりも広げ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、
前記演算処理部は、
前記複数のエコー信号の内、奇数番目に計測されたエコー信号を前記第1のエコー信号群とし、
偶数番目に計測されたエコー信号を前記第2のエコー信号群と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において、
前記計測制御部は、2つのエコー信号の計測毎に前記位相ブリップ傾斜磁場を印加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において、
前記計測制御部は、前記第1のエコー信号群のエコー数と前記第2のエコー信号群のエコー数を異ならせることを特徴とする磁気共鳴イメージング装置。 - 請求項10記載の磁気共鳴イメージング装置において、
前記計測制御部は、前記第2のエコー信号群について、前記K空間の高空間周波数領域に対応するエコー信号のみを計測し、
前記演算処理部は、前記第2のエコー信号群についての、前記K空間の低空間周波数領域に対応するエコー信号のデータとして、前記第1のエコー信号群の内の同じ低空間周波数領域に対応するエコー信号のデータを用いることを特徴とする磁気共鳴イメージング装置。 - 所定のパルスシーケンスに基づいて、被検体からのエコー信号を計測する計測工程と、
前記エコー信号を用いて画像データとマスクデータを取得し、前記画像データと前記マスクデータとから磁化率強調画像を取得する演算処理工程と、
を備え、
前記パルスシーケンスは、位相ブリップ傾斜磁場を印加し、周波数エンコード傾斜磁場の極性を反転させて、複数のエコー信号の計測を行う、磁化率強調画像撮影方法であって、
前記演算処理工程は、前記複数のエコー信号を第1のエコー信号群と第2のエコー信号群とに分割して、前記第1のエコー信号群から前記画像データを、前記第2のエコー信号群から前記マスクデータを、それぞれ取得することを特徴とする磁化率強調画像撮影方法。 - 請求項12記載の磁化率強調画像撮影方法において、
前記演算処理工程は、前記複数のエコー信号の内、
前記パルスシーケンスの前側で計測されたエコー信号を第1のエコー信号群とし、
前記パルスシーケンスの後側で計測されたエコー信号を第2のエコー信号群とすることを特徴とする磁化率強調画像撮影方法。 - 請求項12記載の磁化率強調画像撮影方法において、
前記演算処理工程は、
前記複数のエコー信号の内、奇数番目に計測されたエコー信号を前記第1のエコー信号群とし、
偶数番目に計測されたエコー信号を前記第2のエコー信号群とすることを特徴とする磁化率強調画像撮影方法。 - 請求項12記載の磁化率強調画像撮影方法において、
前記計測工程は、前記第1のエコー信号群のエコー数と前記第2のエコー信号群のエコー数を異ならせることを特徴とする磁化率強調画像撮影方法。
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JP2011030625A (ja) * | 2009-07-30 | 2011-02-17 | Hitachi Medical Corp | 磁気共鳴撮像装置 |
WO2012026380A1 (ja) * | 2010-08-25 | 2012-03-01 | 株式会社 日立メディコ | 磁気共鳴イメージング装置及びマルチエコーマルチコントラスト撮像法 |
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US20100277172A1 (en) | 2010-11-04 |
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