WO1997035517A1 - Procede et appareil d'imagerie par resonance magnetique - Google Patents
Procede et appareil d'imagerie par resonance magnetique Download PDFInfo
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- WO1997035517A1 WO1997035517A1 PCT/JP1997/001055 JP9701055W WO9735517A1 WO 1997035517 A1 WO1997035517 A1 WO 1997035517A1 JP 9701055 W JP9701055 W JP 9701055W WO 9735517 A1 WO9735517 A1 WO 9735517A1
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- magnetic field
- resonance imaging
- magnetic resonance
- pulse sequence
- image
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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
-
- 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
Definitions
- the present invention relates to a magnetic resonance imaging (MRI) apparatus, and more particularly to a technique for capturing a high-resolution image with a low readout gradient magnetic field strength.
- MRI magnetic resonance imaging
- a conventional inspection apparatus using magnetic resonance that is, a magnetic resonance imaging apparatus (hereinafter simply referred to as an inspection apparatus) has, for example, a configuration shown in FIG.
- 2601 is a magnet that generates a static magnetic field
- 2602 is a gradient magnetic field generating coil that generates a gradient magnetic field
- 2603 is an object, which is a static magnetic field generating magnet. It is installed in 2601 and the gradient magnetic field generating coil 2602.
- sequencer 2604 sends a command to the gradient magnetic field power supply 2605 and the high frequency pulse generator 2606 to generate a gradient magnetic field and a high frequency magnetic field.
- This high-frequency magnetic field is applied to the subject 2603 through the probe 2607.
- the signal generated from the subject 2603 is received by the probe 2607 and detected by the receiver 2608.
- the detected signal is sent to a computer 2609, where signal processing such as image reconstruction is performed, and the processing result is displayed on a display 26010. Note that the signal and the measurement condition can be stored in the storage medium 2611 as needed.
- the shim coil 2612 includes a plurality of channels, and is supplied with current by a shim power source 2613.
- the current flowing through each coil is controlled by the sequencer 2604.
- the sequencer 2604 sends a command to the shim power supply 2613 to generate an additional magnetic field from the shim coil 2612 to correct the nonuniformity of the static magnetic field.
- sequencer 2604 normally controls each device to operate at a preprogrammed timing and strength.
- this program especially high-frequency magnetic
- the description of the field, the gradient field, and the timing / intensity of signal reception is called a pulse sequence.
- a subject 2603 is placed in a static magnetic field, and a slice gradient magnetic field 201 is applied and a high frequency magnetic field (RF) pulse 202 for magnetizing excitation is applied to apply a magnetic resonance phenomenon to a slice in the target object. Induce.
- RF magnetic field
- phase encoder gradient magnetic field pulse 204 for adding the position information of the phase encoder direction to the magnetization phase is applied, and a 180 degree pulse 205 is applied.
- a magnetic resonance signal (echo) 203 is measured while applying a readout gradient magnetic field pulse 206 to which positional information on the direction is added.
- the number of echo sampling points is usually 6 4 to 5 12 per echo, and the number of echoes to be measured is generally 6 4 to 2 56.
- echoes are arranged in the frequency space (k-space, measurement space) of the image as shown in Fig. 28, and the image is reconstructed by two-dimensional inverse Fourier transform to obtain a tomographic image.
- the number of image matrices is (the number of sampling points of one echo) X (the number of echoes).
- the field of view Wx and the pixel size Wx in the clear direction are Gx, the sampling rate (sampling interval), and the number of sampling points, N, respectively. It is represented by (2).
- Wx AWx N (2) where 7 is the gyromagnetic ratio of the atom to be measured, which is about 4.2.559.59 MHz / T for the target for normal imaging.
- microscopy for obtaining high-resolution images As is evident from equations (1) and (2), microscopy for obtaining high-resolution images, it is conceivable to increase one or both of the sampling rate t and the gradient magnetic field Gx, or to increase the number N of sampling points.
- the resolution is enhanced by increasing the gradient magnetic field, and a gradient magnetic field having a very strong magnetic field strength of usually about 100 to 100 OmT / m is applied.
- the measurement time of the echo does not become long, so that compared to the case where the sampling rate or the number of sampling points is increased, the attenuation of the signal strength due to the relaxation of the magnetization ⁇ the effect of the static magnetic field nonuniformity is reduced, and the image quality is deteriorated. This is because less is needed.
- the present inventor has found the following problems as a result of studying the above-described conventional technology.
- a clinical MR I device which is a conventional magnetic resonance imaging device for measuring the human body
- a device that is large enough to be installed in a limited room such as an examination room is required. It is necessary to generate a gradient magnetic field having a strong magnetic field strength of about 100 to 100 OmTZm while having good linearity over a wide area of about 40 cm in diameter.
- the maximum gradient magnetic field strength that can be generated by current clinical MRI equipment is about 3 OmT / m.
- the principle of the present invention will be described with reference to FIGS. 29A and 29B.
- FIGS. 29A and 29B are projection images obtained by performing an inverse Fourier transform on one of the magnetic resonance signals (echoes) obtained by a predetermined pulse sequence.
- 29A is a projection image obtained by the conventional apparatus
- FIG. 29B is a projection image obtained by the present invention.
- the horizontal axis indicates the readout direction
- the vertical axis indicates the strength of the application.
- the spatial resolution of an image is given by the following equation, where G x is the readout gradient magnetic field strength, m t is the sampling rate, and N is the number of sampling points.
- scale x 1 indicates the spatial resolution determined by the readout gradient magnetic field strength and the sampling period (m t ⁇ N). Previously, this range was displayed as one pixel of the reconstructed image. In addition, the entire area displayed as one pixel was excited to obtain image data, and the results were obtained.
- an area (d x) much smaller than the conventional one-pixel area (X 1) is set as one pixel of the reconstructed image.
- This area d X is a spatial resolution determined by the high-frequency magnetic field and the strength of the gradient magnetic field of the readout.
- the entire image data is obtained by performing a plurality of imagings while changing the excitation location between one pixel in the related art.
- the present invention only a part of the region conventionally displayed as one pixel is excited, and this is used as a new pixel, so that the spatial resolution can be increased.
- the minimum unit of the spatial resolution A determined by the image reconstruction unit by the spatial resolution control unit is the width of one pixel in the image read direction. Specifically, the width of each slice of the slice group excited by irradiation of the high-frequency magnetic field is set as the minimum unit of the spatial resolution A.
- the spatial resolution control unit irradiates the subject in the static magnetic field with a plurality of high-frequency magnetic fields while applying a gradient magnetic field in the readout direction.
- the inside of the subject is excited into slice groups that are perpendicular to and equal to the gradient magnetic field of the readout.
- the gradient magnetic field strength control unit calculates a spatial resolution B determined by the strength of the readout gradient magnetic field and the sampling period.
- a readout gradient magnetic field lower than the resolution A, that is, coarser, is applied to the subject.
- a readout gradient magnetic field is applied such that the spatial function B corresponds to the slice interval.
- the echo with one pixel in the readout direction as the minimum unit of the spatial resolution A is measured.
- the image reconstruction unit constructs an image based on this echo, it is possible to construct an image with a slice thickness of 1 pixel, so that a strong gradient magnetic field is not required and the Microscopy is also applicable.
- a magnetic resonance imaging apparatus comprising: a pulse sequence control unit; and an image reconstructing unit configured to reconstruct an image based on the acquired echo.
- a spatial resolution control unit that sets the spatial resolution in the readout gradient magnetic field direction, and a spatial resolution determined by the intensity of the readout gradient magnetic field is lower (or coarser) than the spatial resolution set by the spatial resolution control unit.
- a gradient magnetic field intensity controller for applying a readout gradient magnetic field.
- the image reconstruction unit sets a minimum unit of the spatial resolution set by the spatial resolution control unit to a width of one pixel in a reset direction of the image. .
- the spatial resolution control unit irradiates the high-frequency magnetic field to selectively excite one part of the subject, thereby obtaining the spatial resolution. Set the resolution.
- the spatial resolution control unit excites the region in the subject into slice groups substantially perpendicular to the readout gradient magnetic field direction and at substantially equal intervals,
- the gradient magnetic field intensity control unit makes the spatial resolution determined by the intensity of the readout gradient magnetic field and the sampling period substantially equal to the interval between the slices.
- the spatial resolution control unit applies an excitation gradient magnetic field in the same direction as the readout gradient magnetic field application direction, and makes the high-frequency magnetic field pulses substantially equally spaced. Irradiate multiple times.
- the pulse sequence control unit includes a first pulse sequence for applying the high-frequency magnetic field and the gradient magnetic field to collect echoes, Executing a second pulse sequence including the spatial resolution control unit and the first pulse sequence, wherein the image reconstructing unit includes: an echo collected by the first pulse sequence; and A difference processing unit is provided for performing a difference process with the echo collected by the pulse sequence.
- the difference processing unit reconstructs each of the echo collected by the first pulse sequence and the echo collected by the second pulse sequence.
- the difference processing is performed on the obtained image.
- the plurality of high-frequency magnetic field pulses have a constant amplitude.
- the plurality of high-frequency magnetic field pulses are amplitude-modulated.
- the plurality of high-frequency magnetic field pulses are frequency-modulated or phase-modulated.
- the pulse sequence control unit controls the pulse sequence while moving a position of the slice group in a direction in which a readout gradient magnetic field is applied. Repeat the sequence a specified number of times.
- the frequency of the high-frequency magnetic field pulse is changed every time the pulse sequence is repeated.
- the magnetic resonance imaging apparatus according to any one of (4) to (11) described above. In the method, the static magnetic field intensity is changed every time the pulse sequence is repeated. (14) In the magnetic resonance imaging apparatus according to any one of (1) to (13), the pulse sequence applies a phase-encoded gradient magnetic field to the subject along with echo collection.
- the intensity of the phase encode gradient magnetic field is substantially equal to the intensity of the readout gradient magnetic field.
- the pulse sequence repeats echo acquisition while changing a readout gradient magnetic field direction.
- the pulse sequence may include an interval between a portion for exciting a slice group in the subject and measurement of an echo. Irradiate 0 degree pulse.
- the image reconstructing unit comprises a plurality of reconstructed images based on echoes acquired in the same pulse sequence. Are integrated.
- FIG. 1 is a block diagram showing a schematic configuration of a magnetic resonance imaging apparatus according to Embodiment 1 of the present invention.
- FIG. 2 is a block diagram showing a schematic configuration of the sequencer according to the first embodiment.
- FIG. 3 is a diagram for explaining the relationship between the spatial resolution set by the spatial resolution control unit and the spatial resolution at the time of readout set by the gradient magnetic field intensity control unit.
- FIG. 4 is a diagram showing an example of echo measurement.
- FIG. 5 is a diagram showing a pulse sequence for explaining the operation of the magnetic resonance imaging apparatus according to the first embodiment.
- FIG. 6 is a diagram showing a pulse sequence of the Daladientko method.
- FIG. 7 is a diagram for explaining a state of excitation generated in a slice group.
- FIG. 8 is a diagram for explaining the principle of generation of the slice group shown in FIG.
- FIG. 9 is a diagram for explaining the movement of the slice shown in FIG.
- FIG. 10 is a diagram showing an example of a pulse sequence for capturing a two-dimensional image.
- FIG. 11 is a diagram showing a state of the measurement space.
- FIG. 12 is a diagram for explaining a method of reconstructing an image from a two-dimensional ecoset.
- FIG. 13 is a diagram for explaining another pulse sequence of the present invention.
- FIG. 14 is a diagram for explaining the relationship between the subject and the visual field in the pulse sequence shown in FIG.
- FIG. 15 is a diagram for explaining another pulse sequence of the present invention.
- FIG. 16 is a diagram for explaining another pulse sequence of the present invention.
- FIG. 17 is a diagram for explaining a method of scanning the measurement space in the pulse sequence shown in FIG.
- FIG. 18 is a flowchart of measurement by the pulse sequence of FIG.
- FIG. 19 shows a photographing method using the spatial resolution control unit according to the first embodiment.
- FIG. 20 is a flowchart of measurement by the pulse sequence of FIG.
- FIG. 21 is a diagram for explaining a method of scanning the measurement space in the pulse sequence according to the second embodiment.
- FIG. 22 shows the field of view and the projection in the pulse sequence according to the second embodiment.
- FIG. 4 is a diagram for explaining a relationship between a visual field and an excitation region.
- FIG. 23 is a diagram showing a pulse sequence according to the third embodiment.
- FIG. 24 is a diagram for explaining a pulse sequence of the magnetic resonance imaging apparatus according to the fourth embodiment of the present invention.
- FIG. 25 is a diagram for explaining the principle of the pulse sequence according to the fourth embodiment shown in FIG.
- FIG. 26 is a block diagram showing a schematic configuration of a conventional magnetic resonance imaging apparatus.
- FIG. 27 is a diagram for explaining a pulse sequence in a conventional magnetic resonance imaging apparatus.
- FIG. 28 is a diagram for explaining the measurement space.
- FIGS. 29A and 29B are diagrams for explaining the principle of the present invention.
- FIG. 1 is a block diagram showing a schematic configuration of a magnetic resonance imaging apparatus according to Embodiment 1 of the present invention, where 101 is a static magnetic field generating magnet, 102 is a gradient magnetic field generating coil, and 103 is a gradient magnetic field generating coil.
- 101 is a static magnetic field generating magnet
- 102 is a gradient magnetic field generating coil
- 103 is a gradient magnetic field generating coil.
- 104 is a sequencer (pulse sequence control unit)
- 105 is a gradient magnetic field power supply
- 106 is a high frequency pulse generator
- 107 is a probe
- 108 is a receiver
- 109 Denotes a computer (image reconstruction unit)
- 110 denotes a display
- 111 denotes a storage medium
- 112 denotes a shim coil
- 113 denotes a shim power supply.
- a static magnetic field generating magnet 101 is a well-known magnet for generating (generating) a static magnetic field.
- a permanent magnet or a superconducting magnet is used.
- the gradient magnetic field generating coil 102 is a well-known coil for generating a gradient magnetic field.
- the body axis direction of the subject 103 is specified in the Z-axis direction, and a position in a plane orthogonal to the Z-axis is specified.
- the gradient magnetic field generating coil 102 is connected to a gradient magnetic field power supply 105, and generates a magnetic field corresponding to a current supplied from the power supply.
- the sequencer 104 is a well-known sequencer in which the operation order and the like can be set in advance.
- the sequencer 104 receives a measurement sequence assembled by the computer 109 as data, and receives the sequence based on the data.
- the device is controlled by outputting operation signals to the high-frequency pulse generator 106, receiver 108, shim power supply 113, storage medium 111, and the like.
- the gradient magnetic field power supply 105 is a well-known power supply, and includes, for example, three power supplies for driving the above-described gradient magnetic field generation coils 102 in the X-axis, Y-axis, and Z-axis directions. o
- the high-frequency pulse generator 106 is a circuit for generating a well-known selective excitation high-frequency pulse for selecting the position of the measurement section.
- a well-known synthesizer that generates a high-frequency wave serving as a reference, It comprises a modulation circuit for modulating the generated high frequency into a predetermined signal, and an amplifier for amplifying the modulated electric signal.
- the probe 107 converts the pulse generated by the high-frequency pulse generator 106 into a magnetic field, guides it to the subject, irradiates it, and receives a signal (echo signal or echo) emitted from the subject, A coil for guiding to the receiver 108.
- the receiver 108 detects (detects) the echo radiated from the subject 103 and guided by the probe 107, converts this result into a digital signal, and outputs it to the computer 109. Yes, it consists of a well-known AZD converter that converts electrical signals into digital information.
- the computer 109 is a well-known information processing device (arithmetic processing unit). For example, the computer 109 outputs the above-described measurement sequence as a set of data, and constructs a tomographic image and the like based on the echo.
- the display 110 is a well-known display device for displaying a video signal output from the computer 109.
- the storage medium 1 1 1 stores the measured echo, tomographic image, measurement conditions, sequence, etc.
- a well-known storage device for storing for example, a magnetic disk device, a semiconductor memory, a magneto-optical storage device, a magnetic tape device, or the like.
- the shim coil 112 is a coil for generating a magnetic field for maintaining the uniformity of the static magnetic field generated by the static magnetic field generating magnet 101, and is supplied with current from the shim power supply 113.
- the shim power supply 113 is a known power supply that supplies a current to the shim coil 112 based on the output of the sequencer 104.
- the magnetic resonance imaging apparatus similarly to the conventional apparatus, among the data of the measurement sequence assembled by the computer 109, in particular, the high-frequency magnetic field, the gradient magnetic field, the timing and intensity of signal reception. Is described as a pulse sequence.
- FIG. 2 is a block diagram illustrating a schematic configuration of the sequencer according to the first embodiment.
- Reference numeral 401 denotes a spatial resolution control unit
- 40 denotes a gradient magnetic field intensity control unit
- 403 denotes a controller.
- the sequencer shown in FIG. 2 controls the high-frequency pulse generator 106, the receiver 108, the shim power supply 113, the gradient magnetic field power supply 105, and the storage medium 111 by the procedure described later.
- the spatial resolution of the image can be higher than the spatial resolution determined by the readout gradient magnetic field intensity and the sampling period.
- the spatial resolution control unit 401 controls the high-frequency pulse generator 106 and the gradient magnetic field power supply 105 to set the spatial resolution of the image to be captured. Is done.
- the gradient magnetic field strength control section 402 controls the gradient magnetic field power supply 105 to set the readout gradient magnetic field strength during echo measurement. However, the gradient magnetic field strength control unit 402 also controls the receiver 108 to measure the echo at the same time. At this time, the spatial resolution determined by the intensity of the readout gradient magnetic field and the sampling period is lower than the spatial resolution set by the spatial resolution control unit 401, that is, the spatial resolution is not coarse.
- FIG. 3 is a diagram for explaining the relationship between the spatial resolution set by the spatial resolution control unit and the spatial resolution at the time of the reset set by the gradient magnetic field intensity control unit. It is.
- FIG. 3 is a simplified two-dimensional display, and shows an example in which the inside of the subject is excited in the spatial resolution control unit 401 into stripes at equal intervals.
- Reference numeral 501 denotes the width of the stripe
- 502 denotes the interval between the stripes
- 503 denotes the projection (projection diagram) obtained by one-dimensional inverse Fourier transform of the echo.
- the horizontal axis indicates the readout direction
- the vertical axis indicates the projection direction
- the scale “B” on the projection 503 is the spatial resolution determined by the readout gradient magnetic field and the sampling period.
- Echo is measured by taking the spatial resolution determined by the read gradient magnetic field strength and the sampling period equal to the fringe interval 502, and a projection 503 obtained by performing inverse Fourier transform on one of the echoes is measured.
- Spatial resolution is equal to the fringe interval 502, but since the image information contained is only information of the excited fringe part, the spatial resolution of the projection 503 is the fringe width 501 It can be said that Therefore, when displaying the obtained projection as an image, the minimum unit of the spatial resolution determined by the intensity of the read gradient magnetic field and the sampling period, that is, the interval between stripes 502 in FIG. Instead of pixels, let the stripe width 501 be the width of one pixel of the image. As a result, an image with a spatial resolution higher than the spatial resolution 502 determined by the read gradient magnetic field strength and the sampling period can be obtained.
- one measurement as shown in this figure can measure only a part of the subject.
- Figure 4 shows an example of this repetition, where 504, 505, and 506 are the echoes measured by executing the first, second, and 16th pulse sequences, respectively. A projection obtained by performing an inverse Fourier transform on one of them is shown.
- this shows an image in which the slice group is projected on the X axis.
- the scale “B” is the same as in Figure 2.
- 507 is a complete 7 "logic obtained by synthesizing the respective sections obtained from the first time to the 16th time.
- the pulse sequence is repeated for a total of m times. That is, as shown in Fig. 4, when the ratio between the width of the stripe and the interval between the stripes is 1:16. In this case, first, the pulse sequence is repeated a total of 16 times.
- a projection 504 to 506 is created by performing an inverse Fourier transform on each of the measured echoes, and the projections 504 to 506 are superimposed to synthesize a projection 507 of the entire subject.
- one pixel of the projection is not the minimum unit of the spatial resolution determined by the strength of the readout gradient magnetic field and the sampling period, that is, the fringe interval 501, but the fringe width 501.
- the stripe width 501 is a spatial resolution determined by the high-frequency magnetic field and the readout gradient magnetic field.
- the spatial resolution is determined by the strength of the read gradient magnetic field and the sampling period. Therefore, in order to obtain the same spatial resolution as the projection 507, the gradient of the readout gradient magnetic field is increased according to the equation (3), and the spatial resolution 502 determined by the gradient magnetic field intensity and the sampling period is striped. Width must be equal to 5 0 1
- FIG. 5 shows a pulse sequence for explaining the operation of the magnetic resonance imaging apparatus according to the first embodiment.
- the magnetic resonance imaging apparatus according to the first embodiment will be described.
- a method for setting the spatial resolution of an image in the readout direction of the spatial resolution control unit 401 will be described.
- RF is a high-frequency magnetic field
- 61 is a spatial resolution control part
- 602 is an RF node
- 603 is a gradient pulse for excitation
- 604 is a 180-degree pulse
- 60 is a pulse.
- 5 is a readout gradient magnetic field pulse
- 600 is an echo
- 608 is a gradient magnetic field intensity control part
- G x, G y, and G z indicate gradient magnetic fields in the x, y, and z axis directions, respectively, as described above, and the read-at direction at this time is the X direction.
- the magnetization excited by the plurality of RF pulses 62 is inverted by the 180-degree pulse. Then, it is refreshed (phase inverted) by the readout gradient magnetic field, and an echo 606 is generated.
- the excitation is performed a plurality of times by the excitation pulse 602, a plurality of echoes 606 are generated.
- the number of echoes 606 is equal to the number of RF pulses 602 used for excitation.
- the first echo 606 is an echo 606 generated by the last irradiated RF pulse 602, and the last echo 606 is generated by the first irradiated RF pulse 602. This is echo 6 06.
- the intensity of the readout gradient magnetic field pulse 605 is made equal to that of the excitation gradient magnetic field pulse 603, and the application start time of the read-out gradient magnetic field pulse 605 is adjusted so that the corresponding RF pulse 602 is generated.
- the center of each of the echoes 606 is set to be temporally symmetric with respect to the irradiation center of the 180-degree pulse. By doing so, each echo 606 becomes a spin echo that is not affected by the inhomogeneity of the static magnetic field.
- each echo 600 has a different T2 emphasis degree, and the later echo has a larger T2 emphasis and a lower echo intensity.
- the effects of device characteristics such as eddy currents are slightly different, but the properties of each echo are basically the same.
- the echo may be measured by using an inverted lead-out gradient magnetic field 607 without irradiating the 180-degree pulse 604.
- This echo is called a gradient echo.
- the use of the 180-degree pulse can provide a spin echo that is not affected by the inhomogeneity of the static magnetic field.
- the irradiation of the 180-degree pulse normally requires an extra time of several ms.
- the spatial resolution control section 601 is configured to irradiate a plurality of RF pulses 602 during application of the gradient magnetic field pulse for excitation 603 in the X direction. This configuration itself is a well-known method, and the details are described in Japanese Patent Publication No. 6-34784.
- the excitation region of the subject inside the subject becomes a slice group 702 perpendicular to the X direction, as shown by the bold line in FIG.
- Each slice has the same thickness at regular intervals.
- FIG. 8 shows a diagram for explaining the principle of generation of the slice group shown in FIG. 7.
- the principle of generation of the slice group will be described based on this diagram.
- the waveform in the left column when the waveform in the left column is Fourier-transformed, it becomes as shown in the right column.
- the left column shows the shape of the RF pulse, and the right column shows the corresponding frequency distribution.
- the vertical axis is intensity
- the horizontal axis is time in the left column
- the frequency is in the right column.
- the convolution operation (*) 802 is performed on the waveform 801 of the three peaks of the sinc function with an infinitely spaced pulse train 803 in time, and the product with the square wave 805 is obtained.
- (X) Taking 804, the sinc function is a temporally finite sequence of 3 peaks 8
- 06. 806 corresponds to the pulse 602 in FIG.
- the width of the three sinc function waveforms 80 1 is “a”
- the interval of the pulse train 803 is “b”
- the width of the square wave 805 is b X n (n is a positive integer)
- the sinc function train 806 Is “b”
- the application time of each sinc function is “a”.
- the convolution operation 802 is converted into a product 808, and the product 804 is converted into a convolution operation 810.
- the frequency distribution when irradiating the RF pulse train 806 is a finite sinc function train 8 12 at equal intervals.
- the frequency band of the square wave 807 is 4Za
- the interval between the pulse trains 809 is 1Zb
- the width of the main lobe of the sinc function 811 is 2 / (bxn). 2Z (bxn) corresponds to 501 in FIG. 4 and 1 / b corresponds to 502 in FIG.
- the frequency distribution can be considered as a train of pulses with a width of 2 Z (bn).
- the sinc function of three peaks is used as the RF pulse, but an optimized pulse in which the shape of the sinc function with an increased number of peaks is improved may be used.
- the optimized pulse is a pulse whose RF pulse waveform is optimized so that the distortion of the rectangular wave is reduced as much as possible.
- the frequency band of the square wave 807 is (s + 1) / a.
- “S” should be 3 for normal shooting.
- the excitation region in the subject is perpendicular to the direction in which the gradient magnetic field is applied as shown in FIG. To form equally spaced slice groups.
- the state of this excitation is shown in a projection image as shown in FIG. 4.
- the slice thickness 501 is 2 / (bxn), and the interval 502 is 1 / b.
- the thickness W of the excitation region in the readout direction is given by the following equation (4).
- the spatial resolution AWx is equal to the interval 502 of this slice, and is given by the following equation (6).
- the flip angle of each RF pulse should be about 90 Zn degrees, and the flip angle of the entire RF pulse should be about 90 degrees as in the spin echo method. However, if the same slice is to be excited without waiting for a sufficient repetition time, it is better to make the flip angle of the entire RF pulse smaller than 90 degrees, so that the signal attenuation after the second time is smaller. This improves the S / N ratio of the echo.
- the position of the slice group can be shifted by changing the frequency of the carrier used to irradiate the RF pulse train.
- the carrier frequency may be changed by a frequency 2Z (bxn) corresponding to the thickness of the slice.
- the carrier frequency of the RF pulse train 901 is f.
- the carrier frequency of the RF pulse train 903 is f. + 2 / (bxn)
- the excitation profile 904 shifts the excitation profile 902 by 2 Z (bXn).
- Another way to shift the slice position is to change the static magnetic field strength.
- FIG. 10 shows an example of a pulse sequence for capturing a two-dimensional image.
- a two-dimensional image is captured using the above-described spatial resolution control method. The method will be described.
- a pulse sequence using the Fourier transform method for image reconstruction is used.
- the gradient magnetic field pulse 122 for providing position information in the y direction to the magnetization and the phase encode gradient magnetic field pulse 123 for the phase encoding gradient position in the z direction are provided.
- the slice selection gradient magnetic field pulse 1 2 1 to which information is added is added to the pulse sequence shown in Fig. 4.
- the position and thickness at that time can be freely adjusted by the frequency of the carrier of the 180-degree pulse 604 and the intensity of the slice selection gradient magnetic field pulse 121.
- the waveform of the 180-degree pulse is a sinc function of m peaks
- the position z of the cross section and the approximate thickness z are given by the following equations (10) and (11).
- the magnetization is given the position information in the y direction, and the echo shows the k space (measurement space) as shown in Fig. 11. Scan. That is, the first echo is positioned in the negative direction of the ky axis by the gradient magnetic field pulse 122 for diffusion, and moves in the positive direction for each echo by the refresh by the pulse 123 of the phase encoding gradient magnetic field.
- phase-encoding gradient magnetic field pulse 123 since the phase-encoding gradient magnetic field pulse 123 is continuously applied, the echo scans obliquely in the k space. The echo intersects the kx axis at the point where the diffuse gradient pulse 122 is canceled by the phase encode gradient pulse 123. It should be noted that the same phase encoding effect can be obtained by inverting the phase encoding gradient magnetic field pulse 123 and applying it together with the irradiation of the RF pulse 602.
- the field of view Wy in the y-direction is determined by the intensity Gy of the phase-encoding gradient magnetic field pulse 122 and the echo-interval b, and is given by the following equation (1 2).
- Ay WyZ32 (14)
- the pulse sequence is repeatedly executed while changing the position of the slice group as described above. That is, by repeating the measurement nZ twice in total, all information in the readout direction can be obtained. As a result, n / 2 two-dimensional echo sets shown in FIG. 11 are obtained.
- Fig. 12 shows a method for reconstructing an image from a two-dimensional echo set. A method for reconstructing an image will be described below with reference to this figure.
- Image reconstruction is performed by two-dimensional inverse Fourier transform of the two-dimensional echo set obtained in each measurement and then synthesizing.
- 13 1 is the field of view or the reconstructed image
- 13 2 and 13 3 are the first (Fig. 4, 504) and the second (Fig. 4, 505) measurements, respectively.
- the partial images obtained by performing a two-dimensional inverse Fourier transform on the obtained echo set are shown as 13.4 and 13.5, each of which has a width of 1 pixel determined by the intensity of the readout gradient magnetic field and the phase encoder gradient magnetic field.
- 36 indicates the width of one pixel in the readout direction of the reconstructed image.
- the width of one pixel in the phase code direction of the reconstructed image is 135.
- a two-dimensional inverse Fourier transform is performed on the echo set obtained in the first measurement to create a partial image 132.
- Each row of the partial image 132 is arranged in the corresponding row of the reconstructed image.
- echo sets obtained in the second and subsequent measurements are also arranged on the reconstructed image. If this processing is performed up to n Z second echo set, the image reconstruction ends.
- the k-space can be scanned horizontally, and the fast Fourier transform can be applied as it is.
- an image obtained by the above-described procedure is displayed on the display 110, it is usually displayed after all image reconstruction processing is completed.
- a partial image obtained at each repetition of the pulse sequence may be displayed when it is obtained. In the latter case, by using a high-speed signal processing system and a display system, it is possible to gradually increase the display resolution at each repetition.
- the width of the excitation region can be adjusted by the RF pulse. Therefore, by making the width smaller than the field of view, the folding problem can be prevented.
- the field of view can be enlarged by making the sampling rate smaller than the value determined by the method shown above, increasing the number of sampling points by that amount, and measuring the echo while keeping the echo measurement time constant. Normally, the sampling point is doubled and the sampling rate is 1Z2.
- phase encoding direction it is not possible to select an area by an excitation pulse or to expand the field of view by increasing the number of echoes. Therefore, a pulse sequence for area selection is executed prior to imaging.
- Fig. 13 shows an example of this pulse sequence
- Fig. 14 shows the relationship between the subject and the visual field.
- X indicates the readout direction
- y indicates the phase encoding direction.
- the region selection part 247 firstly excites only the outer region 144 of the field of view 144 in the y direction by the RF pulse 241 and the gradient magnetic field pulse 242. By 3, the outer region 1450 is saturated, so that no signal is output.
- the RF pulse 244 and the gradient magnetic field pulse 245 is excited by the crusher pulse 246. Saturate the area 1 4 6 so that no signal is output.
- the region to be saturated can be arbitrarily selected by changing the carrier frequency of the RF pulse.
- the polarity of the gradient magnetic field pulses 242 and 245 may be reversed with the carrier frequency kept constant.
- one excitation is performed by using an RF pulse whose excitation is divided into two times and whose excitation profile is only the outer regions 1 45 and 1 46. It is possible to perform saturation outside the visual field by applying a crusher-gradient magnetic field pulse.
- Such an RF pulse waveform can be most easily created by performing an inverse Fourier transform on the excitation profile.
- the excitable region in the phase encoder direction can be narrowed down to the range of the field of view. Can be. Therefore, starting shooting immediately after that will eliminate the problem of aliasing.
- FIG. 15 As another method for selecting the region in the phase encoding direction, instead of using the 180 ° pulse 604 and the gradient magnetic field pulse 121 in FIG. 10 to select the region in the z direction, FIG. There is also a method of using two 180 degree pulses 2 61 and 2 63 as shown in Fig. 15 between the 60 1 and 6 08 pulse sequences. In this method, first, the 180 degree pulse 261, and the gradient magnetic field pulse 262 are used to select the range of the field of view in the phase encoding direction, and then the 180 degree pulse 263 and the gradient in the z direction are selected. The slice direction is selected by the magnetic field pulse 2 64.
- a method of selecting a two-dimensional region by one RF pulse can be used.
- this method see “CJ Hardy and HE Cline,” “Spatial Localization in Two Dimensions Usin Certificate, Designer Pulses, J. of Magn. Reson., Vol. 82, pp. 647-654, 19”. 8 9 ”.
- the spatial resolution in the y direction and the number of pixels are limited by the number of echoes. Therefore, when the number of echoes is insufficient, the k-space division measurement method can be used in which the measurement is divided into multiple times and the number of echoes is increased. In this method, the k space is divided in the ky direction, and measurement is performed in multiple times.
- Figure 16 shows the pulse sequence in this case
- Figure 17 shows the k-space scanning method
- Figure 18 shows the measurement flow chart.
- the pulse sequence in this case uses a gradient magnetic field pulse 28 1 for variable diffusion instead of the gradient magnetic field pulse 122 for diffusion in the pulse sequence of FIG.
- the gradient magnetic field pulse 281 for variable dephase is set so that the scanning position in the k space is at the lowest position as shown in Fig. 17 (710), and the first measurement is performed. Do.
- the measurement here repeats the execution of the sequence while shifting (moving) the position of the slice group.
- the position of the slice group is set to an arbitrary initial position (7 1 1), and measurement is performed (7 1 2). Repeat the measurement while shifting the position of the slice group (7 1 4). Thereafter, allowed The gradient magnetic field gradient pulse 281 is set so that the scanning position is the start position of each measurement (16), and the measurement is repeated as many times as necessary (7 15).
- specific parameters of a pulse sequence for capturing an image with a spatial resolution of 50 um in the readout direction will be described. Will be explained.
- the thickness of the excitation region is the field of view
- Wx 25.6 mm
- the slice interval 1 bZ (r XGx) is 1.6 mm, which is equal to the spatial resolution AWx determined by the intensity of the readout gradient magnetic field pulse and the sampling period, and the number of slices in the field of view is 16.
- the time from the start of excitation to the end of one echo measurement is approximately 3 lms, 18 Since the irradiation time of the 0-degree pulse is 2 ms, it is about 7 Oms even if the rise time of the gradient pulse is included.
- the measurement described above is repeated while shifting the slice position by any of the methods described above in order to obtain information on the entire subject.
- the number of repetitions is 32 because the interval between slices is 1.6 mm and the slice thickness is 50.
- the rate of time change dB / dt of the magnetic field of a pulse having an application time of 120 s or more is 20 T / s. Therefore, when a gradient magnetic field of 48 OmT / m is generated, for example, the magnetic field strength at a position 20 cm from the origin is 96 mT. Generating this magnetic field in accordance with the standard takes 4.8 ms, and the waiting time causes problems such as signal attenuation and longer imaging time.
- the apparatus according to the first embodiment does not require a strong magnetic field as described above, so that microscopy can be performed on the human body.
- Microscopy of the human body is not currently available Depiction of the fine structure of the human body and imaging of the shoulder, elbow and knee joints in the field of orthopedic surgery are mainly performed only at the research level.
- a clinical MRI device can be applied to these application fields.
- the fine structure of the subject can be visualized, it can be used as an alternative to mammography and X-ray diagnosis of osteoporosis currently performed by X-rays.
- the device of the present invention uses magnetic resonance, there is no exposure to X-rays and there is no side effect on the human body, so that there is an advantage that a medical examination is easily performed.
- the spatial resolution in the readout direction is lmm, and the RF pulse uses the sinc function of three peaks.
- the irradiation time for one RF pulse is a 1 22.33 1 m. Become.
- the interval between slices (r XGx) is 32 mm, which is equal to the spatial resolution ⁇ determined by the intensity of the readout gradient magnetic field pulse, and the number of slices in the field of view is eight.
- the time from the start of the excitation to the end of one echo measurement is about 16 ms for the excitation time and about 16 ms for the echo measurement, and the irradiation time for the 180-degree pulse is 2 ms. It is about 40 ms.
- the above measurement is repeated while shifting the slice position in order to obtain information on the entire subject.
- the number of repetitions is 32 because the interval between slices is 32 mm and the thickness of the slice is one turn.
- an image with a field of view of 25 ⁇ 6 ⁇ 25 5, a spatial resolution of lmmx 4 ⁇ , and a number of pixels of 25 ⁇ 6 ⁇ 64 can be obtained with a shooting time of 1.28 s.
- the readout gradient magnetic field intensity may be very small, it is possible to capture a high-resolution image at an extremely high speed with almost all MRI devices.
- FIG. 19 is a diagram showing a pulse sequence of an imaging method using the spatial resolution control unit according to the second embodiment, and this pulse sequence uses the projection method of the MRI apparatus.
- a gradient magnetic field pulse 161, 162 is applied during the irradiation of the RF pulse 602, and a specific 180 degree pulse 604 and a slice selection gradient magnetic field pulse 1221, in the z direction, are applied.
- the range is inverted, and the echoes 606 are measured by applying the gradient magnetic field pulses 163, 164 of the same strength as the gradient magnetic field pulses 161 and 162 during excitation.
- the direction of the gradient magnetic field pulse is a direction determined by G x + G y.
- the spatial resolution control portion 601 of the pulse sequence is basically the same as the method described in Embodiment 1 except that the direction of the gradient magnetic field pulse is changed.
- the projection method requires only one echo in the same direction. Therefore, for example, if the sum is used to improve the S / N ratio, or if the image quality is degraded due to the large amount of tissue diffusion and the whole is integrated, should the S / N ratio be improved using only the first echo? If you want to capture an image of a specific contrast, use only the echo at that echo time.
- Imaging is performed by repeating this pulse sequence twice as shown in FIG.
- the first iteration A (720-724) is performed while shifting the position of the slice group in order to measure the projection in a specific direction (720).
- the carrier frequency of the RF pulse is changed as described above.
- C At this time, G x and G y are fixed.
- the second repetition B (720-726) is performed while changing the intensity of the gradient magnetic field pulses Gx, Gy to change the direction of the projection (726).
- the gradient magnetic field pulses 16 1 and 16 3, 16 2 and 16 4 are kept at the same intensity.
- the changing order of the gradient pulse intensity is such that each echo passes through the origin of k-space and scans the entire k-space.
- each echo scans in k-space as shown in Fig. 21.
- the order of repetition A and repetition B is arbitrary. Normally, repetition in Do A. That is, first, the direction of the projection is determined (720), and A is repeated to measure the complete projection in that direction. I do.
- repetition A different regions are excited, so no waiting time is required.
- repetition B a waiting time is required.
- imaging can be completed in a minimum time.
- Embodiment 1 As a method of creating a projection from each echo repeatedly measured in A, the method described in Embodiment 1 with reference to FIGS. This processing may be performed after the end of the image capturing, but by performing the processing at each time when the repetition A is completed, the processing time after the end of the image capturing can be reduced.
- 18 1 is the object
- 18 2 is the visual field
- 18 3 and 18 4 are the excitation slice groups and excitation regions of the first repetition B
- 18 5 is the The excitation slice group, 186, shows the projection measured in the first repetition B.
- the method of reconstructing an image from the projections in each direction obtained by the above-described procedure may be the same as the method used in a normal X-ray CT apparatus. These include, for example, successive approximation, two-dimensional Fourier transform, and filtered back projection.
- the filter-corrected backprojection method includes a filter correction method using a Fourier transform and a convolution method. These methods are described by Hirokazu Kimura, “Recent Medical Image Diagnosis Equipment”, Asakura Damage Store, 1988.
- FIG. 23 shows a pulse sequence according to the third embodiment, which is another example of the spatial resolution control unit.
- the shape of the pulse 805 in FIG. 8 is changed to a sinc function.
- the spatial resolution control unit 401 as shown in the spatial resolution control unit 601, outputs a plurality of RF signals during application of the gradient magnetic field pulse Irradiate pulse 2 2 2.
- the intensity of each RF pulse is amplitude-modulated so as to be a three-peak sinc function as shown by a dotted line in FIG. 23, for example. This is because the square wave 8 05 shown in Fig.
- each slice 8 1 1 is closer to a rectangle instead of an 8 1 2 force sin c function.
- the number of RF pulses that can be irradiated cannot be increased much because the amplitude of the tail is smaller, and the number of generated echoes is small.
- the number of RF pulses is five. Therefore, when amplitude modulation is used in the pulse sequences of FIGS. 10 and 19, the number of echoes is five. Can only be obtained. In the projection method using the pulse sequence shown in FIG. 19, the number of echoes is sufficient because only one echo is required.
- the Fourier transform method of FIG. 10 requires more echoes. For example, 64 are required. Therefore, as shown in the gradient magnetic field strength control section 608 in FIG. 23, the read-out gradient magnetic field pulse 2 24 and the phase encoder gradient magnetic field pulse are used.
- the number of echoes is increased by inverting and applying 2 25, respectively, and repeating the application. Also, the number of echoes can be reduced by combining this method with the k-space division measurement method described above.
- a high-resolution image can be captured without applying a strong magnetic field to the subject, so that it can be applied to the human body. Microscopy is applicable.
- FIG. 24 is a diagram for explaining the pulse sequence of the magnetic resonance imaging apparatus according to the fourth embodiment of the present invention.
- FIG. 25 shows a diagram for explaining the principle of the pulse sequence shown in FIG. 24.
- the pulse sequence shown in FIG. Will be described.
- the dotted line which is the latter part 3 2 4 of the pulse sequence, is a pulse sequence for normal image capturing such as a well-known spin echo method or echo brainer method.
- the spin echo method has been described as an example.
- the spatial resolution control section 600 comprises a plurality of RF pulses 602, a gradient magnetic field pulse 603, and a force.
- the spoiler-one gradient magnetic field pulses 3 2 1, 3 2 2 and 3 2 3 are applied to G z, G y and G x, respectively.
- the measurement time is wasted, so that the spoiler gradient magnetic field pulses 3 2 1, 3 2 2 and 3 2 3 do not need to be applied.
- the subject is excited by the RF pulse 602 and the gradient magnetic field pulse 603 as shown in FIG. 7 of the first embodiment.
- the situation at this time is schematically shown only in the X direction in FIG.
- the vertical axis represents the magnitude of the transverse magnetization immediately after the end of the spatial resolution control part 601. If a spoiler gradient magnetic field pulse 3 21, 3 2 2, 3 2 3 is applied here, the phase of transverse magnetization is disturbed, and no echo is generated. At this time, the magnitude of the longitudinal magnetization is in a state where the portion where the transverse magnetization is generated is chipped as shown at 342.
- the profile of the transverse magnetization in the lead-out direction is also 342.
- the obtained image D is an image from which information of the slice portion is missing.
- the spatial resolution determined by the readout gradient magnetic field intensity and the sampling period is set to the slice interval 343.
- an image containing information on only the sliced portion can be created.
- the image E can be captured by using only the pulse sequence 324 without using the spatial resolution control part 601. It is enough to take one image of this image E.
- an image including only the slice portion information is created by the pulse sequence of FIG. 24, and the images are combined in the same manner as in FIG. 12 of the first embodiment.
- the spatial component determined by the readout gradient magnetic field strength Images with higher spatial resolution than resolution can be obtained.
- the spatial resolution control section 601 can be executed only once at the beginning or once every few repetitions. Good.
- a high-resolution image can be captured without applying a strong magnetic field to the subject.
- microscopy can be applied to the human body.
- the previously excited portion may partially overlap.
Description
Claims
Priority Applications (3)
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US09/155,245 US6222365B1 (en) | 1996-03-28 | 1997-03-27 | Magnetic resonance imaging apparatus and method |
DE69735291T DE69735291T2 (de) | 1996-03-28 | 1997-03-27 | Verfahren und vorrichtung zur bilderzeugung durch magnetresonanz |
EP97908529A EP1016373B1 (en) | 1996-03-28 | 1997-03-27 | Method and apparatus for magnetic resonance imaging |
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JP8/74960 | 1996-03-28 | ||
JP07496096A JP3525007B2 (ja) | 1996-03-28 | 1996-03-28 | 磁気共鳴イメージング装置 |
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PCT/JP1997/001055 WO1997035517A1 (fr) | 1996-03-28 | 1997-03-27 | Procede et appareil d'imagerie par resonance magnetique |
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US (1) | US6222365B1 (ja) |
EP (1) | EP1016373B1 (ja) |
JP (1) | JP3525007B2 (ja) |
CN (2) | CN100366216C (ja) |
DE (1) | DE69735291T2 (ja) |
WO (1) | WO1997035517A1 (ja) |
Cited By (1)
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US20100067865A1 (en) * | 2008-07-11 | 2010-03-18 | Ashutosh Saxena | Systems, Methods and Devices for Augmenting Video Content |
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EP1047951B1 (en) * | 1997-12-12 | 2011-03-30 | Wisconsin Alumni Research Foundation | Rapid acquisition magnetic resonance imaging using radial projections |
JP4318774B2 (ja) * | 1998-12-03 | 2009-08-26 | 株式会社日立メディコ | 磁気共鳴画像診断装置 |
DE19901763B4 (de) * | 1999-01-18 | 2005-12-01 | Siemens Ag | Impulssequenz für ein Kernspintomographiegerät |
JP3699304B2 (ja) * | 1999-08-13 | 2005-09-28 | ジーイー横河メディカルシステム株式会社 | 磁気共鳴撮像装置 |
DE19962846B4 (de) * | 1999-12-24 | 2008-09-25 | Forschungszentrum Jülich GmbH | Bildgebungsverfahren mit keyhole-Technik |
EP1158307A1 (en) * | 2000-04-18 | 2001-11-28 | F.Hoffmann-La Roche Ag | Method for increasing the throughput of NMR spectrometers |
WO2003103491A1 (ja) * | 2002-06-07 | 2003-12-18 | 株式会社日立メディコ | 磁気共鳴イメージング装置 |
CN100392424C (zh) * | 2004-11-15 | 2008-06-04 | 华东师范大学 | 一种用于图形化脉冲序列编译器中实现回波数据重组的方法 |
JP4822850B2 (ja) | 2006-01-16 | 2011-11-24 | 株式会社日立製作所 | 磁気共鳴測定方法 |
WO2011026923A1 (en) * | 2009-09-03 | 2011-03-10 | Medizinische Universität Graz | Super-resolution magnetic resonance imaging |
US20130069650A1 (en) * | 2010-05-28 | 2013-03-21 | Hitachi Medical Corporation | Magnetic resonance imaging apparatus and high-frequency magnetic field pulse modulation method |
JP2013202245A (ja) * | 2012-03-29 | 2013-10-07 | Hitachi Medical Corp | 磁気共鳴イメージング装置及び計測方法 |
DE102012208019B3 (de) * | 2012-05-14 | 2013-10-31 | Universitätsklinikum Freiburg | Kernspintomographieverfahren mit einem Multiband-Hochfrequenzpuls mit mehreren separaten Frequenzbändern |
DE102012209295B4 (de) * | 2012-06-01 | 2014-02-13 | Siemens Aktiengesellschaft | Bestimmung einer objektspezifischen B1-Verteilung eines Untersuchungsobjekts im Messvolumen in der Magnetresonanztechnik |
DE102013206026B3 (de) | 2013-04-05 | 2014-08-28 | Siemens Aktiengesellschaft | Optimierte Gradientenecho-Multiecho-Messsequenz |
JP5752738B2 (ja) | 2013-04-25 | 2015-07-22 | ジーイー・メディカル・システムズ・グローバル・テクノロジー・カンパニー・エルエルシー | スキャン条件決定装置、磁気共鳴イメージング装置、スキャン条件決定方法、およびプログラム |
CN104714198B (zh) * | 2013-12-17 | 2019-05-17 | 北京大学 | 自适应变化选层方向补偿梯度的磁敏感伪影去除方法 |
EP3230758B1 (en) | 2014-12-12 | 2021-01-06 | Koninklijke Philips N.V. | Quiet mr imaging |
JP6887845B2 (ja) * | 2017-03-28 | 2021-06-16 | 日本電子株式会社 | 核磁気共鳴装置 |
BR112020004488A8 (pt) * | 2017-09-07 | 2023-02-14 | Cr Dev Ab | Métodos para formação de imagem de ressonância magnética ponderada por difusão e para projetar um gradiente de campo magnético dependente de tempo assimétrico |
JP7408351B2 (ja) | 2019-11-06 | 2024-01-05 | キヤノンメディカルシステムズ株式会社 | 磁気共鳴イメージング装置 |
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- 1997-03-27 DE DE69735291T patent/DE69735291T2/de not_active Expired - Lifetime
- 1997-03-27 EP EP97908529A patent/EP1016373B1/en not_active Expired - Lifetime
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JPH09262219A (ja) | 1997-10-07 |
CN100366216C (zh) | 2008-02-06 |
EP1016373A4 (en) | 2000-09-06 |
EP1016373B1 (en) | 2006-02-22 |
CN100437140C (zh) | 2008-11-26 |
DE69735291D1 (de) | 2006-04-27 |
JP3525007B2 (ja) | 2004-05-10 |
US6222365B1 (en) | 2001-04-24 |
CN1584624A (zh) | 2005-02-23 |
CN1214622A (zh) | 1999-04-21 |
DE69735291T2 (de) | 2006-08-03 |
EP1016373A1 (en) | 2000-07-05 |
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