WO2011034004A1 - 磁気共鳴イメージング装置及び傾斜磁場印加方法 - Google Patents
磁気共鳴イメージング装置及び傾斜磁場印加方法 Download PDFInfo
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- KSBMPPKIKRESMN-UHFFFAOYSA-N C(C1)C1C1C[IH]CC1 Chemical compound C(C1)C1C1C[IH]CC1 KSBMPPKIKRESMN-UHFFFAOYSA-N 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
- G01R33/56509—Correction of image distortions, e.g. due to magnetic field inhomogeneities due to motion, displacement or flow, e.g. gradient moment nulling
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- the present invention relates to a magnetic resonance imaging (hereinafter, referred to as "MRI") relates to a device, more particularly GMN (G radient M oment N ulling ) rephasing method of applying a gradient magnetic field based on the method.
- MRI magnetic resonance imaging
- GMN G radient M oment N ulling
- the MRI device measures NMR signals generated by the spins of the subject, especially the tissues of the human body, and visualizes the form and function of the head, abdomen, limbs, etc. in two or three dimensions Device.
- the NMR signal is given different phase encoding depending on the gradient magnetic field, frequency-encoded, and measured as time series data.
- the measured NMR signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.
- the phase of the spin generated due to movement and movement by a pulse sequence with a rephase gradient magnetic field based on the GMN method is reconverged (rephased) without depending on the speed or acceleration of movement or motion, and the influence on the image quality (that is, artifacts) is eliminated or reduced (hereinafter referred to as rephase effect).
- the rephase gradient magnetic field is applied in at least one of a slice direction, a phase encoding direction, and a frequency encoding direction in a primary or secondary form (for example, Patent Document 1).
- the imaging parameter setting range of the MRI apparatus is often limited by the application timing and application intensity of the gradient magnetic field.
- the number of gradient magnetic field pulses that constitute the rephase gradient magnetic field, the applied intensity, and the gradient magnetic field change rate (dB / dt) per unit time increase as the rephase order increases.
- the gradient magnetic field change rate (dB / dt) per unit time increase as the rephase order increases.
- it is difficult to perform imaging under the setting values of imaging parameters desired by the operator, that is, desired imaging conditions, and the burden on hardware of the MRI apparatus and the subject is increased. It is considered that the same problem occurs in the method for setting the rephase gradient magnetic field in Patent Document 1.
- An object of the present invention is to provide an MRI apparatus and a gradient magnetic field application method capable of obtaining a rephase effect.
- the present invention obtains a rephase gradient magnetic field that is a smaller application amount when it is difficult to apply a rephase gradient magnetic field of a predetermined order according to the value of an imaging parameter that is input and set. At least a portion of the echo signal is measured using a rephase gradient magnetic field that provides a smaller applied amount than the obtained amount.
- the MRI apparatus of the present invention includes a gradient magnetic field generator that generates a gradient magnetic field, an arithmetic processing unit that obtains a rephase gradient magnetic field based on the GMN method, a rephase gradient magnetic field applied to a subject, and the subject.
- a measurement control unit that controls the measurement of echo signals from the sample, and an input / output unit that displays the value of the imaging parameter and receives the input setting, and the arithmetic processing unit converts the input parameter value of the imaging parameter Accordingly, a rephase gradient magnetic field that is smaller in application amount than the rephase gradient magnetic field of the predetermined order is obtained, and the measurement control unit obtains a rephase gradient magnetic field that is applied in an amount less than the rephase gradient magnetic field of the predetermined order. It is characterized by using and measuring.
- the gradient magnetic field application method of the present invention includes an imaging condition setting step that accepts an input of imaging parameter value setting, and a rephasing amount that is less than a predetermined order of the rephasing gradient magnetic field according to the imaging parameter value that has been input and set.
- the rephasing effect based on the GMN method is achieved while reducing the burden on the hardware and subject of the MRI apparatus according to the setting value of the imaging parameter desired by the operator. Further, it is possible to obtain an image in which artifacts due to movement and flow are removed or reduced.
- Timing diagram showing application pattern of secondary rephase gradient magnetic field in frequency encoding direction
- Timing diagram showing parameters used for moment calculation of secondary rephase gradient magnetic field waveform
- Timing diagram showing primary rephase gradient magnetic field application pattern in frequency encoding direction
- Timing diagram showing primary rephase gradient magnetic field application pattern on phase encode axis
- Pulse sequence diagram of 2D gradient echo in which a secondary rephase gradient magnetic field is applied in each of the slice direction, frequency encode direction, and phase encode direction
- (c) 2D gradient echo pulse sequence diagram with no rephase gradient magnetic field applied (a) a flowchart showing the operation flow of the first embodiment, (b)
- FIG. 1 (a) Flow chart showing the operation flow of Example 3, (b) Timing diagram showing a pulse sequence in which a rephase gradient magnetic field is applied only to phase encoding in the low spatial frequency region, and the upper diagram shows the high spatial frequency component. This is a phase encode waveform, and the lower diagram shows a phase encode waveform to which a rephase gradient magnetic field having a low spatial frequency component is added.
- a diagram showing the GUI that the user operates to capture images 10 is a flowchart showing the operation flow of the fourth embodiment. Figure showing a window that presents changes to imaging parameters
- FIG. 1 is a block diagram showing the overall configuration of an embodiment of an MRI apparatus according to the present invention.
- This MRI apparatus uses a NMR phenomenon to obtain a tomographic image of a subject 101.
- a static magnetic field generating magnet 102, a gradient magnetic field coil 103, a gradient magnetic field power supply 109, and a transmission RF coil 104 and RF transmission unit 110, reception RF coil 105 and signal detection unit 106, signal processing unit 107, measurement control unit 111, overall control unit 108, display / operation unit 113, and subject 101 are mounted.
- a bed 112 for taking the subject 101 into and out of the static magnetic field generating magnet 102.
- the static magnetic field generating magnet 102 generates a uniform static magnetic field in the direction perpendicular to the body axis of the subject 101 in the vertical magnetic field method and in the body axis direction in the horizontal magnetic field method.
- a permanent magnet type, normal conducting type or superconducting type static magnetic field generating source is arranged around the.
- the static magnetic field generating magnet 102 is provided with a shim coil or a shim member in order to correct the static magnetic field inhomogeneity.
- the gradient magnetic field coil 103 is a coil wound in the three-axis directions of X, Y, and Z, which are the coordinate system (stationary coordinate system) of the MRI apparatus, and each gradient magnetic field coil is a gradient magnetic field power source 109 that drives it. To be supplied with current.
- the gradient magnetic field coil 103 and the gradient magnetic field power source 109 constitute a gradient magnetic field generation unit.
- the gradient magnetic field power supply 109 of each gradient coil is driven according to a command from the measurement control unit 111 described later, and supplies a current to each gradient coil.
- gradient magnetic fields Gx, Gy, and Gz are generated in the three axial directions of X, Y, and Z.
- a slice selection gradient magnetic field pulse (Gs) is applied in a direction orthogonal to the slice plane (imaging cross section) to set a slice plane for the subject 101, and the remaining two orthogonal to the slice plane and orthogonal to each other
- Gp phase encoding gradient magnetic field pulse
- Gf frequency encoding gradient magnetic field pulse
- the transmission RF coil 104 is a coil that irradiates the subject 101 with a high frequency magnetic field (hereinafter referred to as RF) pulse, and is connected to the RF transmission unit 110 to be supplied with a high frequency pulse current.
- RF high frequency magnetic field
- the RF transmission unit 110 is driven in accordance with a command from the measurement control unit 111 described later, amplitude-modulates and amplifies the high-frequency pulse, and then transmits to the transmission RF coil 104 disposed close to the subject 101.
- the subject 101 is irradiated with the RF pulse.
- the reception RF coil 105 is a coil that receives an echo signal (NMR signal) emitted by the NMR phenomenon of the nuclear spin constituting the biological tissue of the subject 101, and is connected to the signal detection unit 106 to receive the received echo signal.
- the signal is sent to the signal detector 106.
- the signal detection unit 106 performs detection processing of the echo signal received by the reception RF coil 105. Specifically, the echo signal of the response of the subject 101 induced by the RF pulse irradiated from the RF transmission coil 104 is received by the reception RF coil 105 disposed in the vicinity of the subject 101.
- the signal detection unit 106 amplifies the received echo signal, divides it into two orthogonal signals by quadrature detection, each of which is a predetermined number (for example, 128, 256, 512, etc.) Sampling is performed, and each sampling signal is A / D converted into a digital quantity and sent to a signal processing unit 107 described later. Therefore, the echo signal is obtained as time-series digital data (hereinafter referred to as echo data) composed of a predetermined number of sampling data.
- echo data time-series digital data
- the signal processor 107 performs various processes on the echo data input from the signal detector 106 and sends the processed echo data to the measurement controller 111 described later.
- the measurement control unit 111 mainly transmits various commands for collecting echo data necessary for reconstruction of the tomographic image of the subject 101 to the gradient magnetic field power source 109, the RF transmission unit 110, and the signal detection unit 106. And a control unit for controlling them. Specifically, the measurement control unit 111 operates under the control of the overall control unit 108 described later, and controls the gradient magnetic field power source 109, the RF transmission unit 110, and the signal detection unit 106 based on a predetermined pulse sequence. The application of the RF pulse and the gradient magnetic field pulse to the subject 101 and the detection of the echo signal from the subject 101 are repeatedly executed to collect echo data necessary for reconstructing a tomographic image of the subject 101.
- the overall control unit 108 controls the measurement control unit 111 and controls various data processing and processing result display and storage, and includes an arithmetic processing unit having a CPU and a memory, an optical disk, and a magnetic disk And the like.
- the measurement control unit 111 is controlled to execute echo data collection, and when echo data is input from the signal processing unit 107, the arithmetic processing unit performs signal processing, image reconstruction by Fourier transform, and the like. The processing is executed, and the resulting tomographic image of the subject 101 is displayed on the display / operation unit 108 described later and recorded in the storage unit.
- a display / operation unit (input / output unit) 113 includes a display for displaying a tomographic image of the subject 101, a trackball or a mouse for inputting various control information of the MRI apparatus and control information for processing performed by the overall control unit 108, and And an operation unit such as a keyboard.
- This operation unit is arranged close to the display, and the operator interactively controls various processes of the MRI apparatus through the operation unit while looking at the display.
- the primary rephase means that the phase based on the velocity component is refocused to refocus the phase
- the secondary rephase is to refocus the phase based on the velocity and acceleration. This means that the rephase gradient magnetic field is used.
- the position coordinate x (t) of the spin that is accelerating is expressed by the following equation.
- v represents velocity
- a represents acceleration
- Equation (4) The time integrals appearing in equation (4) are called as follows: As can be seen from the equation (4), at the timing when both of these moments become 0 , the spin phases are all 0 regardless of the initial position x 0 , velocity v, and acceleration a. That is, if a gradient magnetic field waveform in which these moments are all zero is calculated at the timing of the echo time, the phase component due to movement or motion, including the phase due to acceleration motion, can be corrected, and secondary rephase can be realized.
- FIG. 2 shows an example of creating a rephase gradient magnetic field in the frequency encoding direction (Gf) under the condition that the applied intensity of the gradient magnetic field is the same.
- the gradient magnetic field waveform shown in FIG. 2 is determined by the four parameters G, T1, T2, and T3 shown in the drawing.
- each moment of the gradient magnetic field expressed by the equations (5-1), (5-2), and (5-3) is also expressed as a function of these parameters. For this reason, the rephase gradient magnetic field waveform that simultaneously sets the moments of the three gradient magnetic fields to 0 can be determined by solving four simultaneous equations with four variables.
- Equations (6), (7), and equations with (second moment) set to 0 are combined to solve for variables G, T1, T2, and T3.
- the condition (8) in which the sum of the application time of the gradient magnetic field is fixed is added to the simultaneous equations.
- the fixed value is represented as the total application time Ttotal of the three rephase gradient magnetic fields.
- Equation (12) for determining the value of T2 can be obtained.
- T1 and T3 can be determined.
- the rise time is expressed by the equation (13).
- the equation (13) is substituted into the equation that gives T1, T2, and T3.
- Equation (9-4) is expressed by the gradient magnetic field application pattern shown in FIG. 3, it can be written as equation (14), and times t0 to t11 are expressed by equations (15-1) to (15-12).
- t0 0
- t1 r
- t2 T1
- t3 t2 + r
- t4 t3 + r
- t5 t3 + T2
- t6 t5 + r
- t6 t5 + r
- t6 t5 + r
- t6 t5 + r
- t7 t6 + r
- t8 t6 + T3
- t9 t8 + r
- t10 t9 + tm
- t11 t10 + Tm
- Substituting T1, T2, and T3 obtained up to Eq. (13) into Eq. (14), the left side of Eq. (14) representing the second moment is a function of only the gradient magnetic
- G The value of G can be obtained by numerically determining the 0 point of this function using the bisection method.
- the second-order rephase gradient magnetic field waveform can be determined by the above solution.
- the condition that the application intensity of the rephase gradient magnetic field is constant is provided.
- the application time and the application intensity may be specified with the application time being constant.
- the rise time can be obtained by using the value of each slew rate in the equation (13), and these values may be used for the calculation. .
- the application pattern of the rephase gradient magnetic field waveform is temporally opposite to the application pattern in the frequency encoding direction. It is possible to ask.
- Equation (21-1) and (21-2) can be expressed as follows:
- the rise time r2 is expressed by the following equation as in the equation (13). Further, when equation (23-1) is substituted into equation (22-1) and G2 is solved, equation (26) is obtained.
- Equation (25) Substituting this into equation (25) and solving for r2, equation (27) is obtained. Substituting this result into equation (24) and solving for G1, equation (28) is obtained. From this result and the following equation, r1 can be obtained.
- the first-order rephase gradient magnetic field waveform can be determined by the above solution.
- the application time of the rephase gradient magnetic field As in the second case, in the above calculation example, conditions are set for the application time of the rephase gradient magnetic field, but the application time and the application intensity may be specified with the application intensity constant.
- the application pattern of the rephase gradient magnetic field waveform is temporally reversed from the application pattern in the frequency encoding direction. It is possible to determine the pulse application time and application intensity.
- the respective rise times can be obtained by using the respective slew rate values in equations (25) and (29). These values can be used for the calculation.
- the gradient magnetic field strength and dB / dt may exceed the limits depending on the imaging conditions. Furthermore, these limits are more easily exceeded by higher-order rephase gradient magnetic fields than by lower orders.
- the applied intensity and dB / dt of the gradient magnetic field superimposed on the gradient magnetic field of the other axis may exceed the limit. This means that a sufficient application time is not secured for the rephase gradient magnetic field. In such a case, a rephase gradient magnetic field waveform of the obtained order cannot be applied.
- the rephasing effect is reduced as much as possible under the set imaging conditions so as to obtain the rephasing effect as much as possible.
- the phase P stay at an arbitrary time T of a spin that is stationary at an arbitrary position x (hereinafter referred to as a stationary spin) is G (T) as an applied gradient magnetic field and T RF as a center time of RF wave application. It is given by
- phase at an arbitrary time T of a spin moving in the phase encoding direction (hereinafter referred to as a moving spin) from an arbitrary position x at an arbitrary speed v constant in the time direction is given by the following equation.
- phase encode amount Ax to be added must be the phase of all the spins at the center time of the echo signal to be measured. Therefore, when the time of the center of the echo signal to be measured and T TE, must hold the following equation.
- Equation (32) can be decomposed into a zero-order moment and a first-order moment, and can be expressed as the following equation.
- Expression (34) is an expression that the gradient magnetic field must satisfy in rephase in the phase encoding direction.
- equations (30) to (34) the following two are defined for stationary spins and moving spins.
- the application time of the gradient magnetic field can be expressed by the following equation.
- equation (35) can be rewritten as
- Equation (37) can be solved for G and ⁇ , and is expressed by the following equation. Since the gradient magnetic field strength and application time are determined from the equation (38), the application pattern of FIG. 5 can be determined by giving Ta, r, and T3.
- the application intensity of the rephase gradient magnetic field in the phase encoding direction obtained by Equation (38), the application intensity superimposed with the gradient magnetic field on the other axis due to oblique, or dB / dt may exceed the limit. is there. This is because sufficient application time is not secured for the rephase gradient magnetic field, and gradient magnetic fields applied in directions other than the phase encoding direction are superimposed by oblique. In such a case, a rephase gradient magnetic field waveform of the obtained order cannot be applied.
- the rephasing order or the like is lowered, or the phase encoding range in which the rephase gradient magnetic field is applied is set, and the rephase gradient magnetic field is not applied outside this range. Try to get the rephasing effect as much as possible.
- a rephase gradient magnetic field including a slice encode gradient magnetic field is also obtained in the slice direction. I can do it. This may be set to T RF to T0 when.
- a rephase gradient magnetic field adapted to the slice encode gradient magnetic field may be applied independently of the slice encode gradient magnetic field, or may be applied in a superimposed manner with the slice encode gradient magnetic field. It should be noted that the moment calculation is different when the rephase gradient magnetic field and slice encode gradient magnetic field are superimposed.
- FIG. 7 shows an example of a pulse sequence to which the rephase gradient magnetic field obtained in the above secondary and primary calculation examples is added.
- FIG. 7 (a) shows the basics of the pulse sequence of the 2D gradient echo method that does not rephase based on the GMN method in all three directions. Based on this basic pulse sequence, Fig. 7 (b) shows a rephasing gradient magnetic field that performs secondary rephasing in the slice direction and frequency encoding direction, and a rephasing gradient magnetic field that performs primary rephasing in the phase encoding direction 2
- a pulse sequence of a dimensional (2D) gradient echo method is shown.
- FIG. 7 (c) shows a pulse sequence of the 2D gradient echo method in which a rephase gradient magnetic field that performs primary rephasing is added in the slice direction and frequency encoding direction, and rephase is not performed in the phase encoding direction.
- the MRI apparatus and gradient magnetic field application method of the present invention obtains a rephase gradient magnetic field that has an application amount smaller than a predetermined number of rephase gradient magnetic fields according to the input imaging parameter value (that is, imaging conditions), and at least partly The echo signal is measured using a rephase gradient magnetic field that has a smaller application amount than the rephase gradient magnetic field of a predetermined order.
- a rephase gradient magnetic field that has a smaller application amount than the rephase gradient magnetic field of a predetermined order.
- the direction in which such rephase gradient magnetic field application control is performed is at least one of a slice direction, a frequency encoding direction, and a phase encoding direction.
- a rephase gradient magnetic field that is applied in an amount smaller than a rephase gradient magnetic field of a predetermined order a rephase gradient magnetic field of an order less than the predetermined order (including the case where the rephase gradient magnetic field is not applied) or for asymmetric measurement is used.
- a rephase gradient magnetic field of an order less than the predetermined order including the case where the rephase gradient magnetic field is not applied
- Each Example which measures at least one part echo signal using a rephase gradient magnetic field is described in detail.
- Example 1 of the MRI apparatus and gradient magnetic field application method of the present invention will be described.
- a rephase gradient magnetic field waveform of a predetermined order based on the GMN method with the setting value of the imaging parameter desired by the operator (i.e., imaging conditions)
- a rephase gradient of an order less than the predetermined order is difficult.
- a magnetic field waveform is obtained, and at least some echo signals are measured using the obtained rephase gradient magnetic field waveform. That is, when it becomes difficult to perform rephasing of a predetermined order based on the GMN method, the rephasing order is lowered.
- the present embodiment is an embodiment suitable for the calculation of the rephase gradient magnetic field waveform in the slice direction and the frequency encode direction, but the rephase gradient magnetic field waveform in the phase encode direction may be obtained in the same way.
- this embodiment will be described in detail with reference to FIG.
- FIG. 8 (a) is a flowchart showing the operation flow of this embodiment.
- This operation flow shows a case where the predetermined order is set to the second order as an example of a case where the rephase of the predetermined order is tried first and the rephase lower than the predetermined order is tried when it cannot be performed.
- this embodiment may be started not only from the second order but also from the third or higher order rephase.
- This operation flow is stored in advance in a storage unit such as a magnetic disk as a program, and is executed by the arithmetic processing unit reading the program into the memory and executing it as necessary.
- a storage unit such as a magnetic disk as a program
- the arithmetic processing unit performs a predetermined-order (here, secondary) rephase gradient magnetic field on one axis under a desired imaging parameter setting value input by the operator via the operation unit 108.
- a desired imaging parameter setting value input by the operator via the operation unit 108.
- the imaging parameter there are a pal sequence repetition time (TR) and an echo time (TE).
- TR pal sequence repetition time
- TE echo time
- the arithmetic processing unit sets a second-order rephase gradient magnetic field in one direction on condition that the set values of imaging parameters such as TR and TE are set. Calculate the waveform.
- the details of the calculation method are as described above.
- step 802 the arithmetic processing unit determines whether or not the predetermined-order (secondary in this case) rephase gradient magnetic field waveform calculated in step 801 can be applied.
- the rephase gradient magnetic field waveform of this predetermined order is applied when the rephase gradient magnetic field waveform cannot be obtained. It is not possible. Specifically, as in the example shown in FIG. 8 (b), the rephasing gradient magnetic field applied in the frequency encoding direction (Gf) overlaps the slice selection gradient magnetic field applied in the slice direction (Gs).
- the arithmetic processing unit compares the rephase gradient magnetic field waveform obtained in step 801 with the upper limit value and the limit value, and determines that the application is not possible if any one of them is exceeded.
- step 803 if it is determined that application is impossible (No), the process proceeds to step 803. On the other hand, if the rephase gradient magnetic field waveform obtained in step 801 does not exceed any upper limit value or limit value, it is determined that application is possible (Yes), and the obtained second-order rephase gradient magnetic field waveform is used.
- the measurement control unit 111 performs imaging using the pulse sequence.
- step 803 the arithmetic processing unit has an order smaller than a predetermined order (here, the first order) in one direction under a set value of a desired imaging parameter input by the operator via the operation unit 108. Calculate the rephase gradient magnetic field waveform. The details of the calculation method are as described above.
- step 804 the arithmetic processing unit determines whether or not a rephase gradient magnetic field waveform having a lower order (here, the first order) than the predetermined order calculated in step 803 can be applied. Since the determination method is the same as that in step 802, detailed description thereof is omitted. If it is determined that application is not possible (No), the process proceeds to step 805, and if it is determined that application is possible (Yes), the pulse sequence using the obtained primary rephase gradient magnetic field waveform is used. Imaging is performed by the measurement control unit 111.
- step 805 the arithmetic processing unit notifies that the rephase gradient magnetic field pulse cannot be applied in the calculated direction under the input set value of the desired imaging parameter (for example, on the display of the display / operation unit 113). Message display) to the operator.
- a window for presenting imaging parameters that can be applied by applying the rephasing gradient magnetic field may be displayed.
- the above is an operation flow for calculating a rephase gradient magnetic field waveform for one direction, but when calculating a rephase gradient magnetic field waveform for each of a plurality of directions, the above processing flow is repeated for each direction, and the conditions specific to the direction are set.
- a suitable rephase gradient magnetic field waveform may be obtained.
- the calculation is performed considering that the application pattern of the rephase gradient magnetic field waveform is opposite in time in the slice direction and the frequency encoding direction.
- the rephase gradient magnetic field may be applied only within a predetermined range of phase encoding.
- a second embodiment of the MRI apparatus and gradient magnetic field application method of the present invention in addition to the rephase gradient magnetic field waveform in which the order of the first embodiment is lowered, a rephase gradient magnetic field waveform for further asymmetric measurement is obtained, and the applicability is determined.
- imaging parameters desired by the operator i.e., imaging conditions
- rephasing with the order of the above-described first embodiment reduced
- a rephase gradient magnetic field for asymmetric measurement is obtained, and an echo signal is measured using the possible rephase gradient magnetic field waveform.
- This embodiment is an embodiment suitable for calculating a rephase gradient magnetic field waveform in the frequency encoding direction.
- the rephase gradient magnetic field waveform for asymmetric measurement and asymmetric measurement will be described.
- an echo signal is sampled symmetrically with respect to the peak position of the echo signal, and symmetrical echo data is acquired.
- the first half is sampled less (shorter) than the second half with respect to the peak position of the echo signal. That is, the peak position of the echo signal is shifted to the first half within the sampling window of the entire echo signal.
- measurement in which the first half of the echo signal is reduced as much as possible and the second half is mainly sampled is also referred to as half echo measurement.
- This asymmetric measurement can reduce the application intensity of the readout gradient magnetic field of the echo signal and narrow the bandwidth, so that the SN of the echo signal and the image can be improved.
- the amount of readout gradient magnetic field applied for measuring the first half of the echo signal (area surrounded by the gradient magnetic field waveform and the time axis) can be reduced, the application intensity of the rephase gradient magnetic field and / or The application time can be reduced as compared with the case of symmetrical measurement.
- the sampling period of the first half of the echo signal can be shortened, more time width in which the rephase gradient magnetic field can be inserted can be secured.
- the rephase gradient magnetic field waveform for asymmetric measurement is obtained to determine whether this application is possible. Perform asymmetric measurement using the obtained rephase gradient magnetic field waveform.
- Tm in Fig. 2 is shortened in the second order
- Tm in Fig. 4 is shortened in the first order
- the rephase gradient magnetic field waveform is applied.
- Tm is shortened, the application amount of the readout gradient magnetic field for sampling the first half of the echo signal is reduced, and as a result, the application intensity and / or application time of the rephase gradient magnetic field is reduced.
- the rephase gradient is calculated by using the Tm for asymmetric measurement in the above-described second-order equation (16) or the first-order equations (26) and (28). Each gradient magnetic field pulse constituting the magnetic field waveform is obtained.
- FIG. 9 is a flowchart showing the operation flow of the present embodiment.
- This operation flow is obtained by further adding processing steps according to the present embodiment to the flowchart of FIG. 8 representing the operation flow of the first embodiment.
- the same processing steps are denoted by reference numerals in the 800s, and the processing steps unique to the present embodiment are denoted by reference numerals in the 900s.
- reference numerals in the 800s the same processing steps
- the processing steps unique to the present embodiment are denoted by reference numerals in the 900s.
- only the added processing steps unique to the present embodiment will be described in detail, and description of the same processing steps as those in FIG. 8 will be omitted.
- step 901 the arithmetic processing unit determines that the secondary rephase gradient magnetic field waveform for symmetrical measurement obtained in step 801 is not applicable (No) in step 802, so the rephase gradient magnetic field for secondary asymmetric measurement is determined. Find the waveform.
- the specific method of obtaining is as described above.
- step 902 the arithmetic processing unit determines whether or not the rephase gradient magnetic field waveform for secondary asymmetric measurement obtained in step 901 can be applied. Since the specific contents of the determination process are the same as those in step 802 described above, description thereof will be omitted. If it is determined that application is impossible (No), the process proceeds to step 803 to obtain a rephase gradient magnetic field waveform of the first-order symmetry measurement. When it is determined that application is possible (Yes), the measurement control unit 111 executes asymmetric measurement by a pulse sequence using the obtained second-order asymmetric measurement rephase gradient magnetic field waveform.
- step 903 the arithmetic processing unit determines that the primary rephase gradient magnetic field waveform for symmetric measurement obtained in step 803 is not applicable (No) in step 804, so the rephase gradient magnetic field for primary asymmetric measurement is determined. Find the waveform.
- the specific method of obtaining is as described above.
- step 904 the arithmetic processing unit determines whether or not the rephase gradient magnetic field waveform for primary asymmetric measurement obtained in step 903 can be applied. Since the specific content of the determination process is the same as that in step 804 described above, description thereof is omitted.
- step 805 the operator is notified that the rephase gradient magnetic field pulse cannot be applied in the calculated direction under the input setting value of the desired imaging parameter. To do.
- a window for presenting imaging parameters that can be applied with the rephasing gradient magnetic field by changing may be displayed.
- the measurement control unit 111 executes asymmetric measurement by a pulse sequence using the obtained rephase gradient magnetic field waveform for the first-order asymmetric measurement.
- step 901 and step 803 may be interchanged.
- the MRI more precisely than the case of the above-described first embodiment, depending on the setting value of the imaging parameter desired by the operator.
- a reorder gradient magnetic field waveform of a possible order can be obtained within the limitations on the hardware of the apparatus and the subject.
- the order of the rephase gradient magnetic field applied in the phase encoding direction is controlled according to the phase encoding. Specifically, the order of the rephase gradient magnetic field is reduced when the maximum value of the rephase gradient magnetic field waveform exceeds the maximum gradient magnetic field strength that can be applied by the gradient magnetic field generation unit. Alternatively, the rephase gradient magnetic field is applied only within a desired phase encoding range.
- phase encoding amount A up representing the upper limit of the application range of the rephase gradient magnetic field in the phase encoding direction and the phase encoding amount A low representing the lower limit are handled, the following can be handled.
- the operator can adjust the phase encoding direction.
- Application control of the rephase gradient magnetic field according to the phase encoding can be performed.
- the arithmetic processing unit can automatically set based on the imaging conditions.
- a normal phase encode gradient magnetic field without the rephase gradient magnetic field is applied.
- step 1001 the arithmetic processing unit obtains a rephase gradient magnetic field waveform of a predetermined order (here, primary) in the phase encoding direction based on the set imaging parameter value, that is, the imaging condition. Since the specific method for obtaining is as described above, the detailed description is omitted.
- step 1002 the arithmetic processing unit determines whether or not the rephase gradient magnetic field waveform in the phase encoding direction obtained in step 1001 can be applied.
- the determination in this step is the application intensity of the rephase gradient magnetic field in the phase encoding direction obtained based on the equation (38) under the imaging conditions, the application intensity superimposed with the gradient magnetic field on the other axis due to oblique or dB / dt Is a determination as to whether or not the upper limit of the gradient magnetic field generator or a predetermined limit is exceeded.
- step 1003 the arithmetic processing unit sets a phase encoding range to which the rephase gradient magnetic field is applied. Specifically, as described above, the application of the rephase gradient magnetic field for each phase encoding is controlled by comparing A max with previously set A up and A low . If the application not (No), if in the case of (a) is A max is greater than the A Stay up-, or if A max A max is greater than the A Stay up-in the case of (b) A When the value is lower than low , in the case of (c), the phase encoding amount exceeds A max . If it is determined that application is impossible (No), the process proceeds to step 1004.
- the range is a range of phase encoding equal to or less than A max , and the imaging control unit 111 performs imaging by applying a rephase gradient magnetic field.
- step 1004 the arithmetic processing unit notifies that the rephase gradient magnetic field waveform cannot be applied in the phase encoding direction under the input setting value of the desired imaging parameter (for example, on the display of the display / operation unit 113). Message display) to the operator. At that time, as in the first embodiment, as shown in FIG. 13, a window for presenting imaging parameters that can be applied with the rephasing gradient magnetic field by changing may be displayed.
- the above description of the operation flow is a description of the rephase gradient magnetic field waveform in the phase encode direction, but the rephase gradient magnetic field waveform in the slice encode direction can be obtained in the same manner.
- the hardware of the MRI apparatus can be used in the phase encoding direction and the slice encoding direction according to the setting value of the imaging parameter desired by the operator.
- the rephase gradient magnetic field waveform of the possible order can be obtained corresponding to the phase encoding and / or the slice encoding.
- the order of the rephase gradient magnetic field and the measurement method are controlled based on the priority set by the operator. Specifically, when the operator gives priority to the rephase effect, the rephase gradient magnetic field waveform is obtained so as to apply a higher-order rephase gradient magnetic field as much as possible.
- the measurement method is controlled so as to improve the image quality by reducing the bandwidth for measuring the echo signal as much as possible. For this reason, this embodiment is particularly suitable for the calculation of the rephase gradient magnetic field waveform in the frequency encoding direction.
- the rephasing gradient magnetic field in the rephasing effect priority will be described.
- the time width is sufficiently long so that the maximum intensity of the rephase gradient magnetic field waveform is below a predetermined upper limit or limit.
- this time width becomes narrow, and there are cases where the rephase gradient magnetic field cannot be inserted.
- the echo signal readout period is shortened so that a rephase gradient magnetic field can be inserted, and a wide time width in which the rephase gradient magnetic field can be inserted is secured.
- the bandwidth is widened, the SN of the image is reduced. For example, when imaging a blood vessel with a high flow velocity, flow artifacts are likely to occur, so it is preferable to give priority to rephase.
- the rephase gradient magnetic field with priority on image quality will be described.
- the sampling period for measuring the echo signal is lengthened to lower the application intensity of the read gradient magnetic field.
- the time width in which the rephase gradient magnetic field can be inserted becomes narrow, and the possibility that the rephase gradient magnetic field cannot be inserted increases.
- the period during which the first half of the echo signal is sampled is reduced as much as possible, and a wide time width in which the rephase gradient magnetic field can be inserted is ensured.
- the bandwidth can be reduced and the applied intensity of the read gradient magnetic field can be reduced.
- the non-target measurement can achieve both the insertion of the rephase gradient magnetic field and the improvement of the image quality. For example, when imaging a blood vessel with a low flow velocity, it is preferable to give priority to image quality because flow artifacts are difficult to occur.
- FIG. 11 shows an example of a user interface for the operator to set the rephase priority or the image quality priority.
- 1101 is an area for displaying subject information
- 1102 is an area for displaying captured images
- 1103 is an area for inputting and setting various imaging conditions
- 1104 is set by 1103, etc.
- the imaging time performed based on the acquired imaging conditions and the spatial resolution of the acquired image are shown.
- the imaging condition setting unit 1103 includes, for example, a rephase gradient magnetic field (GMN pulse) in the slice direction (GMN (Slice)), the phase encoding direction (GMN (Phase)), and the frequency encoding direction (GMN (Freq)).
- a menu for setting an additional condition, a menu for setting a priority (Priority), and a menu for setting a sampling rate of asymmetric measurement (HalfchoEcho) are prepared.
- [Acceleration] (rephase up to the second order), [Velocity] (rephase up to the first order), [Auto] (automatic setting of the rephase order), Off Any of (no rephase gradient magnetic field is applied) can be selected independently in each direction.
- [Acceleration] and [Velocity] a rephase gradient magnetic field waveform of the set order is obtained, and if it cannot be applied, a notification to that effect is given.
- [Auto] obtains a rephase gradient magnetic field waveform of a possible order within the limitations on the hardware of the MRI apparatus and the subject in accordance with the imaging parameter setting value desired by the operator in each of the above-described embodiments. Is done.
- the menu for setting the priority is related to this embodiment, [Repahse] (rephase effect priority), [Acq.Time] (image quality priority), and [Auto] (automatic from subject information). [Rephase] or [Acq Time] can be selected).
- the priority (Priority) is stored and prepared in a storage unit such as a magnetic disk in association with attribute information such as the age and sex of the subject to be imaged and the subject. Based on the correspondence information prepared in advance, the priority (Priority) is determined.
- the flow rate of the internal carotid artery decreases as the subject gets older, so if you are younger than 60 years old, the priority (Rephase) should be 60 years old or older.
- priority is set according to age, and subsequent rephase gradient magnetic field creation processing is performed. Details of the rephase gradient magnetic field waveform creation process will be described later.
- the sampling rate is the ratio ( ⁇ ) of extra sampling to 1/2 of the entire echo signal.
- Means symmetrical measurement in which all echo signals are sampled at ⁇ 100%.
- step 1201 the arithmetic processing unit obtains a secondary rephase gradient magnetic field waveform to be applied in the frequency encoding direction. Since this processing step is the same as step 801 described above, detailed description thereof is omitted.
- step 1202 the arithmetic processing unit determines whether or not the secondary rephase gradient magnetic field waveform calculated in step 1201 can be applied. Since this processing step is the same as step 802 described above, detailed description thereof is omitted. If it is determined that application is impossible (No), the process proceeds to step 1203. If it is determined that application is possible (Yes), the obtained second-order rephase gradient magnetic field waveform is applied in the frequency encoding direction and imaging is performed.
- step 1203 when [Auto] is selected in the priority setting menu shown in FIG. 11, the arithmetic processing unit prioritizes the imaging target and object attribute information stored in the storage unit in advance. Based on the correspondence with the priority (Priority), the priority (Priority) is determined from the imaging target and subject attribute information. If any one of [Rephase] [Acq Time] is selected, the selected one is prioritized and the process proceeds to step 1204.
- step 1204 the arithmetic processing unit determines whether the determination result in step 1203 is rephase priority (Rephase> Acq Time) or image quality priority (Rephase ⁇ Acq Time). If rephase priority (Rephase), the process proceeds to step 1205. If image quality priority (Acq Time), the process proceeds to step 1206.
- step 1205 if rephase priority is given, the arithmetic processing unit changes the rephase order from secondary to primary and obtains the primary rephase gradient magnetic field waveform. Thereby, the maximum application intensity of the rephase gradient magnetic field waveform is reduced so as to meet a predetermined upper limit or limit. In addition, the total number of application times is shortened by reducing the number of rephase gradient magnetic field pulses, and within the insertable time determined by the imaging conditions for which the rephase gradient magnetic field waveform is set (free time between the slice selection gradient magnetic field and the readout gradient magnetic field) To fit in.
- the arithmetic processing unit obtains a secondary rephase gradient magnetic field in asymmetric measurement.
- the secondary rephase gradient magnetic field waveform is obtained in a state where Tm in FIG. 2 is shortened and the time width in which the rephase gradient magnetic field can be applied is extended. Details of how to obtain the second-order rephase gradient magnetic field waveform in asymmetric measurement are as described above, and detailed description thereof is omitted.
- step 1207 the arithmetic processing unit determines whether or not the primary rephase gradient magnetic field waveform obtained in step 1205 or the secondary rephase gradient magnetic field waveform in the asymmetric measurement obtained in step 1206 can be applied. Since this processing step is the same as step 902 or 804 described above, detailed description thereof is omitted. If it is determined that application is impossible (No), the process proceeds to step 1208. When it is determined that application is possible (Yes), imaging is performed by applying the obtained rephase gradient magnetic field waveform in the frequency encoding direction.
- step 1208 the arithmetic processing unit obtains a rephase gradient magnetic field waveform for primary asymmetric measurement. Since this processing step is the same as the above-described processing step 903, detailed description thereof is omitted.
- step 1209 the arithmetic processing unit determines whether the rephase gradient magnetic field waveform for primary asymmetric measurement obtained in step 1208 can be applied. Since the specific content of the determination process is the same as that in step 904 described above, description thereof is omitted. If it is determined that application is not possible (No), the process proceeds to step 1210, and the operator is notified that the rephase gradient magnetic field pulse cannot be applied in the frequency encoding direction under the input setting value of the desired imaging parameter. To do. When it is determined that application is possible (Yes), the obtained rephase gradient magnetic field waveform for the first-order asymmetric measurement is applied in the frequency encoding direction to execute asymmetric measurement.
- An image having image quality can be acquired.
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Abstract
Description
2次のリフェーズ傾斜磁場の印加時間と印加強度の求め方を以下に説明する。
(4)式からわかるように、これらのモーメントが共に0となるタイミングでは、初期位置x0、速度v、加速度aの大きさによらず、スピンの位相は全て0となる。つまり、エコー時間のタイミングで、これらのモーメントが全て0となる傾斜磁場波形を算出すれば、加速度運動による位相も含めて、移動又は運動による位相成分を補正でき、2次のリフェーズを実現できる。
(6)式、(7)式そして(2次のモーメント)を0にした式を連立し、変数G,T1,T2,T3について解いていく。ただし、このままでは、解が一意に決まらないので、傾斜磁場の印加時間の総和を固定とした条件(8)を連立方程式に加える。ここでは固定値を3つのリフェーズ傾斜磁場の合計印加時間Ttotalと表す。
この結果を、(9-2)式に代入し、T3について解くと、(11)式が得られる。
ここで、
この場合にはT1,T2,T3を与える式に(13)式を代入する。
t0 = 0 (15-1)
t1 = r (15-2)
t2 = T1 (15-3)
t3 = t2 + r (15-4)
t4 = t3 + r (15-5)
t5 = t3 + T2 (15-6)
t6 = t5 + r (15-7)
t7 = t6 + r (15-8)
t8 = t6 + T3 (15-9)
t9 = t8 + r (15-10)
t10 = t9 + tm (15-11)
t11 = t10 + Tm (15-12)
(13)式までで得られたT1,T2,T3を(14)式に代入すると、2 次のモーメントを表した(14)式の左辺は傾斜磁場の強度Gだけの関数となり、(16)式で表すことができる。
次に、1次のリフェーズ傾斜磁場の印加時間と印加強度の求め方を以下に説明する。 まず、(1)式~(5-2)式までについて、2次の成分を除いた式で書き下す。
速度成分までを考慮したスピンの位置座標x(t)は次式で表される。
T1 = T2 (23-1)
T1+ T2 = Ttotal (23-2)
(22-2)式について、(22-1)式と(23-1)式からG2,T2を消去すると、以下の式が得られる。
ここで、立ち上がり時間r2は(13)式と同様に下式で表される。
さらに、(23-1)式を(22-1)式に代入してG2について解くと(26)式が得られる。
これを(25)式に代入してr2について解くと、(27)式が得られる。
この結果を、(24)式に代入してG1について解くと、(28)式が得られる。
この結果と下式からr1を求めることが出来る。
以上の解法により、1次のリフェーズ傾斜磁場波形を決定できる。
次に、位相エンコード方向に印加するリフェーズ傾斜磁場の印加時間と印加強度の求め方を以下に説明する。
位相エンコード方向では、実施例3で説明するように、位相エンコードの所定範囲内でのみリフェーズ傾斜磁場を印加してもよい。
以上説明したように、本実施例のMRI装置及び傾斜磁場印加方法によれば、操作者が所望する撮像パラメータの設定値に応じて、MRI装置のハードウェアと被検体に対する制限内で、可能な次数のリフェーズ傾斜磁場波形を求めるので、MRI装置のハードウェアと被検体に対する負担を軽減しつつ、GMN法に基づくリフェーズ効果を得ることができる。
と表され、このAmax以上の位相エンコード量を持つ位相エンコードにおいては、撮像パラメータの設定値を変更しない限りリフェーズ傾斜磁場を印加することが出来ない。
また、0又は0に近い位相エンコードにおいては、位相エンコード量も小さいため、移動又は運動に基づくスピンの位相変化も少なくなる。従って、特にリフェーズ傾斜磁場を印加する必要も生じない。
Claims (19)
- 傾斜磁場を発生する傾斜磁場発生部と、
GMN法に基づくリフェーズ傾斜磁場を求める演算処理部と、
前記リフェーズ傾斜磁場を被検体に印加して、該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、
撮像パラメータの値を表示すると共にその入力設定を受け付ける入出力部と、
を備えた磁気共鳴イメージング装置であって、
前記演算処理部は、前記入力設定された撮像パラメータの値に応じて、所定次数のリフェーズ傾斜磁場より少ない印加量となるリフェーズ傾斜磁場を求め、
前記計測制御部は、少なくとも一部のエコー信号を、前記所定次数のリフェーズ傾斜磁場より少ない印加量となるリフェーズ傾斜磁場を用いて計測することを特徴とする磁気共鳴イメージング装置。 - 請求項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、スライス方向、周波数エンコード方向、及び、位相エンコード方向の、少なくとも1方向について、前記所定次数のリフェーズ傾斜磁場より少ない印加量となるリフェーズ傾斜磁場を求めることを特徴とする磁気共鳴イメージング装置。 - 請求項2記載の磁気共鳴イメージング装置において、
前記演算処理部は、前記入力設定された撮像パラメータの値では前記所定次数のリフェーズ傾斜磁場の印加が困難である場合に、前記所定次数より少ない次数のリフェーズ傾斜磁場を求め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、前記リフェーズ傾斜磁場について、その最大強度が、前記傾斜磁場発生部が発生できる最大傾斜磁場強度を超える場合、或いは、その時間変化(dB/dt)が、前記被検体が許容できる上限を超える場合に、前記所定次数より少ない次数のリフェーズ傾斜磁場を求め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、前記所定次数のリフェーズ傾斜磁場の印加が困難である場合に、印加可能となる撮像パラメータの推奨値を前記入出力部に表示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、前記入力設定された撮像パラメータの値では前記所定次数のリフェーズ傾斜磁場の印加が困難である場合に、非対称計測用のリフェーズ傾斜磁場を求め、
前記計測制御部は、前記非対称計測用のリフェーズ傾斜磁場を用いて前記エコー信号の計測を制御することを特徴とする磁気共鳴イメージング装置。 - 請求項6記載の磁気共鳴イメージング装置において、
前記演算処理部は、前記入力設定された撮像パラメータの値では前記所定次数の非対称計測用のリフェーズ傾斜磁場が印加困難である場合に、前記所定次数より少ない次数の非対称計測用のリフェーズ傾斜磁場を求め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、位相エンコード方向に印加するリフェーズ傾斜磁場の次数を、位相エンコードに応じて制御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、
前記演算処理部は、前記リフェーズ傾斜磁場を印加する位相エンコードの範囲を設定し、
前記計測制御部は、前記設定された位相エンコードの範囲でのみリフェー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9記載の磁気共鳴イメージング装置において、
前記入出力部は、前記リフェーズ傾斜磁場を印加する位相エンコードの範囲の上限値と下限値の少なくとも一方の入出力部を備え、
前記演算処理部は、入力設定された前記上限値と前記下限値に基づいて、前記リフェーズ傾斜磁場を印加する位相エンコードの範囲を設定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、
前記入出力部は、リフェーズ優先か画質優先かの選択を受け付ける入出力部を備え、
前記演算処理部は、前記選択に応じて、前記リフェーズ傾斜磁場の次数又は前記エコー信号の計測方法を制御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11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、前記入出力部で前記リフェーズ優先が入力設定された場合に、前記所定次数より少ない次数のリフェーズ傾斜磁場を求めることを特徴とする磁気共鳴イメージング装置。 - 請求項11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、前記入出力部で前記画質優先が入力設定された場合に、前記所定次数以下の次数の非対称計測用リフェーズ傾斜磁場を求めることを特徴とする磁気共鳴イメージング装置。 - 磁気共鳴イメージング装置におけるGMN法に基づくリフェーズ傾斜磁場を印加する方法であって、
撮像パラメータの値の設定入力を受け付ける撮像条件設定ステップと、
入力設定された撮像パラメータの値に応じて、所定次数のリフェーズ傾斜磁場より少ない印加量となるリフェーズ傾斜磁場を求めるリフェーズ傾斜磁場算出ステップと、
少なくとも一部のエコー信号を、前記所定次数のリフェーズ傾斜磁場より少ない印加量となるリフェーズ傾斜磁場を用いて計測する計測ステップと、
を含むことを特徴とする傾斜磁場印加方法。 - 請求項14記載の傾斜磁場印加方法において、
前記リフェーズ傾斜磁場算出ステップは、前記入力設定された撮像パラメータの値では前記所定次数のリフェーズ傾斜磁場の印加が困難である場合に、前記所定次数より少ない次数のリフェーズ傾斜磁場を求めることを特徴とする傾斜磁場印加方法。 - 請求項14記載の傾斜磁場印加方法において、
前記リフェーズ傾斜磁場算出ステップは、前記入力設定された撮像パラメータの値では前記所定次数のリフェーズ傾斜磁場の印加が困難である場合に、非対称計測用のリフェーズ傾斜磁場を求め、
前記計測ステップは、前記非対称計測用のリフェーズ傾斜磁場を用いて前記エコー信号の計測を行うことを特徴とする傾斜磁場印加方法。 - 請求項14記載の傾斜磁場印加方法において、
前記リフェーズ傾斜磁場算出ステップは、前記リフェーズ傾斜磁場を印加する位相エンコードの範囲を設定し、
前記計測ステップは、前記設定された位相エンコードの範囲でのみリフェーズ傾斜磁場を印加することを特徴とする傾斜磁場印加方法。 - 請求項14記載の傾斜磁場印加方法において、
前記撮影条件設定ステップは、リフェーズ優先か画質優先かの選択を受け付け、
前記リフェーズ傾斜磁場算出ステップは、前記入出力部で前記リフェーズ優先が入力設定された場合に、前記所定次数より少ない次数のリフェーズ傾斜磁場を求めることを特徴とする傾斜磁場印加方法。 - 請求項14記載の傾斜磁場印加方法において、
前記撮影条件設定ステップは、リフェーズ優先か画質優先かの選択を受け付け、
前記リフェーズ傾斜磁場算出ステップは、前記画質優先が入力設定された場合に、前記所定次数以下の次数の非対称計測用リフェーズ傾斜磁場を求めることを特徴とする傾斜磁場印加方法。
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JP2014050530A (ja) * | 2012-09-06 | 2014-03-20 | Toshiba Corp | 磁気共鳴イメージング装置及び磁気共鳴イメージング方法 |
JP2015144633A (ja) * | 2014-01-31 | 2015-08-13 | 株式会社東芝 | 磁気共鳴イメージング装置 |
JP2017516586A (ja) * | 2014-06-18 | 2017-06-22 | カチョン ユニバーシティ オブ インダストリー−アカデミック コーオペレイション ファウンデイション | 磁気共鳴画像システムにおけるt2*及び血管画像の同時獲得方法 |
JP2017144351A (ja) * | 2017-06-06 | 2017-08-24 | 東芝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 |
JP2018102352A (ja) * | 2016-12-22 | 2018-07-05 | 株式会社日立製作所 | 磁気共鳴イメージング装置及びパルスシーケンス算出方法 |
JP2021520951A (ja) * | 2018-05-04 | 2021-08-26 | フラウンホーファー−ゲゼルシャフト ツール フエルデルング デア アンゲヴァンテン フォルシュング エー.ファオ. | 磁化の反転状態の評価を伴う動脈スピンラベリング法 |
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CN103202695B (zh) * | 2013-03-20 | 2015-02-18 | 江苏麦格思频仪器有限公司 | 核磁共振成像系统及其方法 |
JPWO2015076082A1 (ja) * | 2013-11-22 | 2017-03-16 | 株式会社日立製作所 | 磁気共鳴イメージング装置 |
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DE102019205914A1 (de) * | 2019-04-25 | 2020-10-29 | Albert-Ludwigs-Universität Freiburg | Magnetresonanzmessung mit prospektiver Bewegungskorrektur |
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JP2021520951A (ja) * | 2018-05-04 | 2021-08-26 | フラウンホーファー−ゲゼルシャフト ツール フエルデルング デア アンゲヴァンテン フォルシュング エー.ファオ. | 磁化の反転状態の評価を伴う動脈スピンラベリング法 |
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US8981775B2 (en) | 2015-03-17 |
US20120169339A1 (en) | 2012-07-05 |
JPWO2011034004A1 (ja) | 2013-02-14 |
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