WO2011059017A1 - 磁気共鳴イメージング装置及び2次元励起調整方法 - Google Patents
磁気共鳴イメージング装置及び2次元励起調整方法 Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/4828—Resolving the MR signals of different chemical species, e.g. water-fat imaging
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7235—Details of waveform analysis
- A61B5/7253—Details of waveform analysis characterised by using transforms
- A61B5/7257—Details of waveform analysis characterised by using transforms using Fourier transforms
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/43—Detecting, measuring or recording for evaluating the reproductive systems
- A61B5/4306—Detecting, measuring or recording for evaluating the reproductive systems for evaluating the female reproductive systems, e.g. gynaecological evaluations
- A61B5/4312—Breast evaluation or disorder diagnosis
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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
- G01R33/483—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy
- G01R33/4833—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy using spatially selective excitation of the volume of interest, e.g. selecting non-orthogonal or inclined slices
- G01R33/4836—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy using spatially selective excitation of the volume of interest, e.g. selecting non-orthogonal or inclined slices using an RF pulse being spatially selective in more than one spatial dimension, e.g. a 2D pencil-beam excitation pulse
Definitions
- the present invention relates to a magnetic resonance imaging (hereinafter referred to as MRI) technique, and more particularly to an imaging technique based on two-dimensional excitation that selectively excites a region restricted in an arbitrary two-dimensional direction.
- MRI magnetic resonance imaging
- 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 and is 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.
- an MRI apparatus uses a high-frequency magnetic field (hereinafter referred to as RF) and a gradient magnetic field to selectively excite an arbitrary planar region having a predetermined thickness by specifying only the one-dimensional direction of the subject.
- RF high-frequency magnetic field
- SS two-dimensional spatial selective excitation
- 2DRF two-dimensional spatial selective excitation
- the SS method can obtain a signal by exciting only the inside of a selected region constrained in the two-dimensional direction, signals from outside the region can be effectively suppressed.
- This SS method is used, for example, in a navigator echo sequence (hereinafter referred to as “navigation echo”) for tracking the movement of the diaphragm (see, for example, Non-Patent Document 2).
- the SS method is used to excite the vicinity of the diaphragm in a cylinder shape in the body axis direction, and from the echo signal generated from this area, the time-dependent change in the diaphragm position in the cylinder axis direction of the area excited in the cylinder shape is detected to perform respiratory motion. Monitor.
- a specific example of applying 2DRF is heart suppression in chest imaging.
- the heart to be suppressed and the thymus and breast to be imaged are close to each other in the chest, fat in the imaged thymus and breast is suppressed, and conversely, the fat component of the heart is not suppressed. .
- an object of the present invention is to provide an MRI apparatus and a two-dimensional excitation adjustment method capable of appropriately two-dimensionally exciting a region where substances having different resonance frequencies are mixed according to imaging conditions.
- the present invention provides a two-dimensional excitation region of a subject comprising a first substance having a first resonance frequency and a second substance having a second resonance frequency.
- two-dimensional excitation is performed for each desired region for the first substance and the second substance based on the imaging conditions related to the two-dimensional excitation and the first resonance frequency and the second resonance frequency.
- the irradiation frequency of the high-frequency magnetic field for two-dimensional excitation is set.
- the MRI apparatus of the present invention uses a pulse sequence with a high-frequency magnetic field and a gradient magnetic field for two-dimensional excitation of a two-dimensional excitation region of a subject placed in a static magnetic field, and uses a two-dimensional excitation region.
- a control unit that controls measurement of echo signals generated from the subject, and the subject includes a first substance having a first resonance frequency and a second substance having a second resonance frequency, and is controlled The two-dimensional excitation of the desired region for the first substance and the second substance based on the imaging conditions related to the two-dimensional excitation and the first resonance frequency and the second resonance frequency.
- an irradiation frequency setting unit for setting an irradiation frequency of a high-frequency magnetic field for two-dimensional excitation.
- the two-dimensional excitation region of the subject including the first substance having the first resonance frequency and the second substance having the second resonance frequency is divided into two.
- an imaging condition input step relating to two-dimensional excitation a step of calculating a first resonance frequency and a second resonance frequency, an imaging condition relating to two-dimensional excitation, a first resonance frequency, and Setting the irradiation frequency of the high-frequency magnetic field for two-dimensional excitation based on the second resonance frequency so that a desired region is two-dimensionally excited for each of the first substance and the second substance; It is characterized by having.
- the MRI apparatus and the two-dimensional excitation adjustment method IV of the present invention it is possible to appropriately two-dimensionally excite a region where substances having different resonance frequencies are mixed according to the imaging conditions.
- Functional block diagram of an example of an MRI apparatus (a) is a pulse sequence diagram by the conventional excitation method, (b) is a pulse sequence diagram of the SS method of the first embodiment.
- Functional block diagram of the control unit of the first embodiment Flowchart of irradiation frequency adjustment processing of the first embodiment Explanatory drawing of UI screen of the first embodiment The figure which shows the spectrum distribution of the resonant frequency in 1st Embodiment Graph showing the relationship between ⁇ F and FA in the first embodiment Graph showing the relationship between ⁇ F and ⁇ in the first embodiment
- Flowchart of irradiation frequency adjustment processing of the third embodiment (a) is a diagram showing a conventional recovery curve of longitudinal magnetization of water and fat, (b) is a diagram showing a recovery curve of longitudinal magnetization of water and fat in the fourth embodiment The figure which shows the relationship between the spectrum distribution of the resonant frequency in 4th Embodiment, and
- FIG. 1 is a functional block diagram of an MRI apparatus 100 according to the present invention.
- An MRI apparatus 100 according to the present invention includes a magnet 102, a gradient magnetic field coil 103, a radio frequency magnetic field (RF) irradiation coil 104, an RF reception coil 105, a gradient magnetic field power source 106, an RF transmission unit 107, and a signal detection unit. 108, a signal processing unit 109, a control unit 110, a display unit 111, an operation unit 112, and a bed 113.
- RF radio frequency magnetic field
- the magnet 102 generates a static magnetic field in an area around the subject 101 (examination space).
- the gradient magnetic field coil 103 is composed of coils in three directions of X, Y, and Z, and each generates a gradient magnetic field in the examination space in accordance with a signal from the gradient magnetic field power supply 106.
- the RF irradiation coil 104 applies (irradiates) RF to the examination space in accordance with a signal from the RF transmission unit 107.
- the RF receiving coil 105 detects an echo signal generated by the subject 101.
- the echo signal received by the RF receiving coil 105 is detected by the signal detection unit 108, subjected to signal processing by the signal processing unit 109, and input to the control unit 110.
- the control unit 110 reconstructs an image from the input echo signal and displays it on the display unit 111. Further, the control unit 110 performs the operations of the gradient magnetic field power source 106, the RF transmission unit 107, and the signal detection unit 108 according to the control time chart held in advance and the imaging parameters input from the operator via the operation unit 112. Control.
- the control time chart is generally called a pulse sequence.
- the bed 113 is for carrying in and out of the examination space with the subject 101 lying down.
- the MRI apparatus 100 may further include a shim coil that corrects the static magnetic field inhomogeneity in the examination space and a shim power source that supplies current to the shim coil.
- MRI imaging targets are water and fat protons, which are the main constituents of the subject 101.
- the spatial distribution of proton density and the relaxation phenomenon of excited protons the shape or function of the human head, abdomen, limbs, etc. is imaged two-dimensionally or three-dimensionally.
- FIG. 2 is a diagram for explaining an example of a pulse sequence by the SS method according to the present invention in comparison with a pulse sequence by a conventional excitation method.
- FIG. 2 (a) shows a pulse sequence by the conventional excitation method
- FIG. 2 (b) shows a pulse sequence by the SS method used in this embodiment.
- the conventional method an example of selectively exciting an arbitrary slice in which only the position in the z-axis direction is specified will be described.
- the SS method shows an example of selectively exciting an arbitrary columnar region in which only the shape on the xy plane is specified.
- the shape specified on the xy plane is a circle.
- RF, Gx, Gy, and Gz are the application of a high-frequency magnetic field (RF) pulse, a gradient magnetic field in the x-axis direction, a gradient magnetic field in the y-axis direction, and a gradient magnetic field in the z direction, respectively. It is a timing chart.
- a constant slice selective gradient magnetic field (Gz) 202 is applied in the z-axis direction when RF 201 is applied.
- a predetermined planar region (slice) in which only the position in the z-axis direction is specified is selectively excited.
- RF (2DRF) 211 is applied together with an oscillating gradient magnetic field (Gx) 212 in the x-axis direction and an oscillating gradient magnetic field (Gy) 213 in the y-axis direction.
- Gx oscillating gradient magnetic field
- Gy oscillating gradient magnetic field
- the echo signal obtained from the excited region is phase-encoded, sampled in time series, and arranged in k-space.
- the Fourier transform is performed on the echo signal (data) arranged in the k space, and an image is acquired.
- values such as 128, 256, and 512 are usually selected for one image.
- values such as 128, 256, 512, and 1024 are selected.
- the present invention provides a high-frequency magnetic field (2DRF) and a gradient magnetic field for performing desired two-dimensional excitation by arranging a subject having a first substance and a second substance having different resonance frequencies in a static magnetic field.
- 2DRF high-frequency magnetic field
- the resonance frequency of the first substance, and the resonance frequency of the second substance are adjusted so that the desired regions of the first material and the second material are two-dimensionally excited, and the adjusted high frequency magnetic field is irradiated to the subject to measure the echo signal.
- the control unit 110 of the MRI apparatus 100 has the functional blocks shown in FIG. 3, and realizes the adjustment process of the high-frequency magnetic field (2DRF) for two-dimensional excitation. That is, as shown in FIG. 3, the control unit 110 includes an excitation region setting unit 320 that sets imaging parameters so as to excite a two-dimensional selection region set by an operator, according to a predetermined pulse sequence, and a pulse sequence.
- an excitation region setting unit 320 that sets imaging parameters so as to excite a two-dimensional selection region set by an operator, according to a predetermined pulse sequence, and a pulse sequence.
- a signal acquisition unit 330 that obtains an echo signal from the two-dimensional selection region, an irradiation frequency setting unit 340 that adjusts and sets the irradiation frequency for 2DRF that excites the two-dimensional selection region, and a two-dimensional selection region UI control unit 350 that controls display on the display unit 111 of the UI screen for setting, and irradiation gain setting that adjusts and sets the irradiation gain of 2DRF (that is, the amplification factor of the RF amplifier) that excites the two-dimensional selection area Unit 360, and a gradient magnetic field setting unit 370 that adjusts and sets a gradient magnetic field applied together with 2DRF that excites the two-dimensional selection region.
- the control unit 110 includes a CPU, a memory, and a storage device, and the above functions are realized by loading a program stored in the storage device into the memory and executing the program.
- the RF irradiation frequency applied when collecting echo signals in the high-frequency magnetic field adjustment processing is determined by a conventional method, that is, an irradiation frequency determined based on an echo signal obtained from the entire imaging region.
- the proton of water hereinafter also simply referred to as water
- the fat proton hereinafter also simply referred to as fat
- the MRI apparatus and the two-dimensional according to the present invention as an example
- the present invention is not limited to water and fat, but can be applied to two or more substances having different resonance frequencies.
- a two-dimensional cylinder region as shown in FIG. 5 is assumed, and a cylinder diameter ⁇ 501 is designated as a parameter representing the shape.
- the length of the cylinder region in the major axis direction is arbitrary and is not particularly limited.
- FA Flip Angle
- the region where the two-dimensional excitation according to the present invention is performed is not limited to the two-dimensional cylinder region, and may be a region having an arbitrary shape.
- two-dimensional excitation is performed using a high-frequency magnetic field having an irradiation frequency that is an average value of the resonance frequency of water protons (first substance) and the resonance frequency of fat protons (second substance).
- the water excitation region and the fat excitation region are both two-dimensional cylinder regions having the same diameter ⁇ at the same position, and the water excitation region flip angle and the fat excitation region flip angle are the same. Both have the same angle FA.
- the configuration and processing procedure of the MRI apparatus 100 of the present embodiment will be described.
- the processing flow of the high-frequency magnetic field adjustment processing for 2DRF of this embodiment will be described based on FIG.
- the entire irradiation frequency F0 is determined from the signal of the entire imaging region by a conventional method.
- the UI control unit 350 displays the UI screen on the display unit 111, and accepts the setting input of the region and / or the position and shape of the two-dimensional excitation region and the flip angle FA that the operator wants to image.
- the operator sets and inputs the area and / or shape of the two-dimensional excitation area and the flip angle FA on the UI screen.
- the UI control unit 350 receives an input of an imaging region and / or a two-dimensional excitation region via the UI screen, the UI control unit 350 notifies the excitation region setting unit 320 of the region.
- the UI control unit 350 displays a UI screen 500 on the display unit 111 for setting the position and shape of the two-dimensional excitation region as shown in FIG.
- the UI screen 500 shown in FIG. 5 displays a positioning image 510 acquired in advance.
- a handle 501 that can set the diameter ⁇ of the cylinder region that is a two-dimensional excitation region
- a handle 502 that can set the two-dimensional excitation region at an arbitrary angle
- a two-dimensional excitation A handle 503 that allows the region to be set at an arbitrary position is displayed. The operator operates these handles to set a desired cylinder area.
- the diameter ⁇ of the cylinder region which is a two-dimensional excitation region, and its flip angle FA may be fixed values previously held by the MRI apparatus.
- the cross-sectional shape of the two-dimensional excitation region in the present embodiment can be arbitrarily set, the cross-sectional shape is not limited to a circle.
- step 402 the two-dimensional excitation region set in step 401 is pre-scanned, and the spectral distribution of the resonance frequency in the two-dimensional excitation region is measured.
- the excitation region setting unit 320 sets imaging parameters so as to excite the two-dimensional excitation region set in step 401 by a predetermined pulse sequence.
- the overall irradiation frequency F0 is used as the RF irradiation frequency.
- the signal acquisition unit 330 executes (pre-scans) the above pulse sequence with the set imaging parameter, and obtains an echo signal from the two-dimensional excitation region.
- an echo signal is obtained without adding phase encoding or slice encoding.
- the irradiation frequency setting unit 340 performs Fourier transform (FT) on the echo signal from the two-dimensional excitation region in the time direction to obtain a resonance frequency (spectrum) distribution in the two-dimensional excitation region.
- FT Fourier transform
- step 403 the irradiation frequency setting unit 340 determines the resonance frequencies F0 W and F0 F of water and fat based on the spectrum distribution created in step 402.
- the protons to be imaged are mainly water and fat protons. Therefore, in the spectrum distribution, the peak 601 present on the high frequency side is changed to the water protons.
- the resonance frequency is F0 W
- 602 existing on the low frequency side is the resonance frequency F0 F of fat protons.
- F0 W and F0 F may be determined from the magnetorotation ratio ⁇ [Hz / T] of the proton of water and the static magnetic field strength B0 [T]. For example, let F0 W be the peak of the spectral distribution closest to the resonance frequency ⁇ B0 [Hz] of water protons.
- F0 F the peak of the spectral distribution closest to F0 W ⁇ B0 [Hz] is defined as F0 F.
- the determination of F0 W and F0 F may be automatically determined by the MRI apparatus as described above, but the irradiation frequency setting unit 340 displays the spectrum distribution as shown in FIG. A user's setting input may be accepted. That is, the operator may determine F0 W and F0 F.
- the irradiation gain setting unit so that the two-dimensional excitation region having the cylinder diameter ⁇ set in step 401 is excited by the flip angle FA. 360 calculates an irradiation gain that achieves the flip angle FA, and the gradient magnetic field setting unit 370 calculates a suitable gradient magnetic field strength.
- the difference between the resonance frequency F0 W of water protons and the irradiation frequency F0 ′ of 2DRF is ⁇ F.
- ⁇ F and flip angle FA, and ⁇ F and cylinder diameter ⁇ are in a relationship as shown in FIGS. 7 and 8, respectively.
- F0 ′ is the average value of F0 W and F0 F , the absolute value of the difference between the irradiation frequency F0 ′ and the resonance frequency F0 W of the proton of water, and the difference between the irradiation frequency F0 ′ and the resonance frequency F0 F of the fat proton
- the absolute value is
- FIG. 7 is a function FA ′ ( ⁇ F) of the flip angle FA ′ with respect to ⁇ F
- FIG. 8 is a function ⁇ ′ ( ⁇ F) of the cylinder diameter ⁇ ′′ with respect to ⁇ F
- the gradient magnetic field setting unit 370 calculates the gradient magnetic field strength G W ′ based on the above equation (2), and the irradiation gain setting unit 360 calculates the irradiation gain T W ′ based on the above equation (3), respectively.
- the signal collection unit 330 is notified of the calculation result.
- step 406 the signal collection unit 330 sets the irradiation frequency of 2DRF calculated in step 404 to F0 ′, and the pulse sequence in which the irradiation gain T W ′ and gradient magnetic field strength G W ′ calculated in step 405 are set.
- the desired area is imaged using.
- the MRI apparatus and the two-dimensional excitation adjustment method of the present embodiment using a high-frequency magnetic field whose irradiation frequency is the average value of the resonance frequency of the first substance and the resonance frequency of the second substance. Perform two-dimensional excitation. At this time, the irradiation gain and the gradient magnetic field strength are set so that the excitation region and the flip angle of each substance are substantially the same, corresponding to the difference ( ⁇ F) between the resonance frequency of each substance and the actual irradiation frequency. Set and two-dimensional excitation is performed.
- the irradiation frequency of the high-frequency magnetic field (2DRF) for two-dimensional excitation is set corresponding to the shape of the spectrum distribution of each substance having a different resonance frequency.
- the spectral distribution of each substance may be distorted, resulting in an asymmetric and broad distribution with respect to its peak position.
- the average value of the resonance frequency of each substance is the irradiation frequency of 2DRF
- the shape of the two-dimensional excitation region of each substance for example, the cylinder diameter ⁇
- the flip angle (FA) deviates from the desired state.
- the irradiation frequency of 2DRF is set corresponding to the shape of the spectral distribution of each substance.
- FIG. 9 shows an example when the spectral distribution of each substance is asymmetric and broad.
- FIG. 9 shows the spectral distribution of water protons and the spectral distribution of fat protons on the same frequency axis.
- the spectral distribution of fat protons is an asymmetric and broad distribution.
- the center-of-gravity frequency and the peak frequency are substantially the same.
- the centroid frequency and the peak frequency do not match.
- the center-of-gravity frequency is obtained from the spectrum distribution of each substance, and the average value of the obtained center-of-gravity frequencies is set as the irradiation frequency of 2DRF.
- the irradiation frequency setting unit 340 calculates the centroid frequency of the spectral distribution of each substance when determining the resonance frequencies F0 W and F0 F of water and fat protons, and this centroid frequency. Are the resonance frequencies F0 W ′ and F0 F ′ of water and fat protons. For example, the irradiation frequency setting unit 340 first performs the peak frequency F0 W in the spectral distribution of water protons and the peak frequency F0 in the spectral distribution of fat protons in the same manner as the processing in step 403 in the first embodiment described above. Find F.
- the irradiation frequency setting unit 340 obtains the center of gravity of the spectrum in the range of about ⁇ 100 [Hz] around F0 W and F0 F , and sets them as F0 W ′ and F0 F ′, respectively.
- F0 W ′ and F0 F ′ satisfy the following equations.
- the spectral distribution of 901 water protons is a substantially symmetric distribution and the spectral distribution of 902 fat protons is asymmetric broad, so F0 W and F0 W ′ are substantially However, F0 F and F0 F ′ have different values.
- the MRI apparatus and the two-dimensional excitation adjustment method of the present embodiment even when the distribution of the resonance frequency of each substance is an asymmetrical and broad distribution with respect to its peak position, Since the irradiation frequency of 2DRF is set corresponding to the shape of the spectral distribution of the substance, the desired region of the subject in which a plurality of substances having different resonance frequencies are mixed is set in the same manner as the effect of the first embodiment described above. Even if the spectral distribution becomes asymmetrical and broad due to inhomogeneous static magnetic field during dimensional excitation, the desired excitation state and flip angle of each substance are substantially the same regardless of the difference in resonance frequency. Excited at.
- a parameter for example, cylinder diameter ⁇
- ⁇ F difference between the resonance frequency of each substance and the irradiation frequency of the high-frequency magnetic field for two-dimensional excitation, and its A limit value for the flip angle of the region
- high-frequency magnetic field adjustment is performed within the range of the obtained limit value to perform desired two-dimensional excitation.
- the present embodiment will be described by taking as an example the case of exciting a two-dimensional cylinder region as in the above-described embodiments.
- the minimum diameter ⁇ min and the maximum flip angle FA MAX of the settable cylinder region can be calculated in advance from the maximum irradiation gain and the maximum gradient magnetic field intensity that can be output from the MRI apparatus.
- the irradiation gain and the gradient magnetic field are determined. Since the intensity is determined, ⁇ min and FA MAX are determined in advance, and high-frequency magnetic field adjustment is performed within the range of the limit values, so that desired two-dimensional excitation cannot be performed.
- step 1001 the operator selects a desired pulse sequence via the pulse sequence selection UI displayed on the display unit 111.
- step 1002 the irradiation frequency setting unit 340 performs the same processing as in steps 401 to 403 in FIG. 4 described above, and determines the resonance frequency F0 W of water protons and the resonance frequency F0 F of fat protons. .
- the designation by the operator of the diameter ( ⁇ ) of the two-dimensional cylinder region and the FA corresponding to step 401 is a provisional setting for obtaining each resonance frequency.
- Step 1003 the irradiation frequency setting unit 340 performs the same processing as Steps 404 and 405 in FIG. 4 described above, and determines the difference ( ⁇ F) between the resonance frequency F0 W of the proton of water and the irradiation frequency F0 ′ of 2DRF. To do.
- step 1004 the excitation region setting unit 320 and the irradiation gain setting unit 360 respectively determine the minimum diameter ⁇ min and the maximum flip angle of the cylinder region that can be excited based on the maximum irradiation gain and the maximum gradient magnetic field intensity that can be output by the MRI apparatus. Find FA MAX .
- step 1005 the excitation region setting unit 320 and the irradiation gain setting unit 360 determine the minimum diameter ⁇ ′ min and the maximum flip angle FA ′ MAX of the cylinder region when the irradiation frequency of 2DRF is shifted by ⁇ F as follows: Find using. Then, the UI control unit 350 is notified of the obtained result.
- FA ' MAX FA MAX * FA' ( ⁇ F) / FA '(0) (7)
- ⁇ ' min ⁇ min * ⁇ ' ( ⁇ F) / ⁇ '(0) (8)
- FA ′ ( ⁇ F) and ⁇ ′ ( ⁇ F) are functions representing the graphs shown in FIGS. 7 and 8, respectively.
- the UI control unit 350 allows the operator to input and set the minimum diameter ⁇ ′ min and the maximum flip angle FA ′ MAX of the cylinder region obtained in step 1005 on the UI screen in step 401 described above. It is displayed as a limit value in showing the range. That is, in step 401 of the processing flow shown in FIG. 4 in the first embodiment described above, the setting input of the flip angle FA is FA ′ MAX so that the setting input of the cylinder diameter ⁇ by the operator is equal to or larger than ⁇ ′ min.
- the UI control unit 350 controls the input settings of the cylinder diameter and the flip angle as follows. In addition, when dB / dt or SAR exceeds the limit value when FA ' MAX or ⁇ ' min is set in the pulse sequence set in step 1001, FA and ⁇ that do not exceed the limit value are shown to the operator. .
- the operator can set the minimum shape and the maximum flip angle of the two-dimensional excitation region that can be set, the shape range of the two-dimensional excitation region, and Since it is possible to know in advance before setting the flip angle, or it becomes impossible to set the shape range and flip angle of the two-dimensional excitation region beyond the range of these limit values, the operator can appropriately and without waste The shape and flip angle of the two-dimensional excitation region can be set.
- the irradiation frequency of the high-frequency magnetic field (2DRF) for two-dimensional excitation so that the shape and flip angle of the excitation region are substantially the same between the first substance and the second substance
- the irradiation gain and gradient magnetic field strength were set.
- at least one of the shape of the excitation region and the flip angle is different between the first substance and the second substance, so that the irradiation frequency of the 2DRF, the irradiation gain, And the gradient magnetic field strength is set.
- the irradiation frequency of 2DRF is set to an intermediate value (not an average value) between the resonance frequencies of the first substance and the second substance.
- the IFIR method which is a type of Arterial Spin Labeling (hereinafter referred to as ASL) method for magnetically labeling blood, is used as an example to explain the case where the flip angle is mainly different between the first substance and the second substance. To do.
- the first inversion pulse is applied slice-selectively to the arterial blood flow inlet, and then the second inversion pulse is applied non-selectively to the slice. Tissue and venous blood are reversed. An image of only arterial blood is obtained by acquiring the echo signal after Null Time, which is the time from the second inversion pulse until the water echo signal becomes substantially zero. Details are described in Non-Patent Document 3.
- FIG. 11 shows the temporal change of longitudinal relaxation immediately after each longitudinal magnetization of water and fat is reversed.
- FIG. 11 (a) shows how the longitudinal magnetization is relaxed when water and fat are excited at the same angle.
- T1 which is a time constant of longitudinal relaxation is smaller than T1 of water
- the relaxation of longitudinal magnetization of fat is faster than relaxation of longitudinal magnetization of water. Therefore, Null Time, in which the magnitude of longitudinal magnetization becomes zero due to longitudinal relaxation and the detected echo signal becomes substantially zero, fat is earlier than water.
- NullNTime of water the longitudinal magnetization of fat greatly recovers and an echo signal from fat is detected.
- the water flip angle FA W and the fat flip angle FA F are made different so that the water Null Time and the fat Null Time become the same 1103.
- Water FA W and fat FA F are set to the optimum flip angles, and a second inversion pulse is used to set water and fat to these flip angles. Note that there is no need to change the flip angle of the first inversion pulse.
- the cylinder diameters ⁇ of water and fat are different, both must be sufficiently large with respect to the field of view (FOV).
- the plateau part of the excitation profile of 2DRF flat part of the excitation profile
- the difference between cylinder diameters ⁇ of water and fat can be ignored and not selected Can be treated as an IR pulse.
- the FA F fat and 180 [deg] because the Null Time fat becomes 160 ⁇ 180 [ms]
- the water Null Time of water is 160 ⁇ 180 [ms]
- the FA The optimal FA W.
- the ratio of the FA W of water to the FA F of the target fat is first determined, and the function FA '( ⁇ F) determined by the high-frequency magnetic field waveform is used to calculate 2DRF
- the irradiation frequency F0 ′ is obtained.
- F0 W and F0 F are determined as the resonance frequencies of water and fat protons as in the first or second embodiment. That is, steps 401 to 403 in the processing flow of the first embodiment shown in FIG. 4 are performed to determine the resonance frequencies of water and fat protons as F0 W and F0 F. At that time, an echo signal obtained by pre-scanning the entire FOV without using a cylinder area is used.
- the irradiation gain setting unit 360 sets the frequency difference as F C according to the following equation.
- F C F0 W -F0 F (9)
- the irradiation gain setting unit 360 sets a flip angle between water and fat.
- the water flip angle is set smaller than the fat flip angle so that both Null Times coincide.
- the target water and fat flip angle may be input by the operator via the UI screen displayed by the UI control unit 350, or may be held inside the MRI apparatus.
- the target fat flip angle is FA F
- the water flip angle is FA W
- the ratio of the water flip angle to fat is ⁇ according to the following equation (10).
- ⁇ FA W / FA F (10)
- the irradiation gain setting unit 360 calculates the irradiation frequency F0 ′ of 2DRF that realizes the expression (10). Specifically, it is as follows. That is, the flip angles FA W and FA F of water and fat can be calculated from the function FA ′ ( ⁇ F) by the following equation.
- FA W FA '( ⁇ F W )
- FA F FA '( ⁇ F F ) Substituting the above equation into equation (10) yields equation (10A).
- the irradiation frequency F0 ′ of 2DRF is calculated from the equation (11-2) with the minimum positive value being ⁇ F F.
- the irradiation frequency F0 ′ is not an average value of the resonance frequencies F0 W and F0 F of water and fat protons, but an intermediate value. In the example of FIG. 12, the intermediate value is closer to fat. Further, since ⁇ F is minimized, the irradiation gain T W can be minimized as a result.
- the irradiation frequency setting unit 340 notifies the UI control unit 350 to that effect, and the UI control unit 350 may indicate a suggestion that the flip angle setting value is impossible to the operator, or ⁇ F
- the ⁇ value or the like from which a solution can be obtained may be set as a limit value that can be set by the operator.
- the above is the description of the processing flow of the calculation method of the irradiation frequency F0 'of 2DRF performed by the irradiation frequency setting unit 340.
- the target imaging is performed using the 2DRF irradiation frequency F0 'thus obtained.
- the MRI apparatus and the two-dimensional excitation adjustment method of the present embodiment depending on the imaging purpose, at least one of the cylinder diameter ⁇ and the flip angle FA, the first substance region and the second substance Since it is set differently depending on the substance region, it is possible to obtain an image suitable for a desired imaging purpose.
- the resonance frequency of the substance to be imaged is dispersed by about 100 to several tens [Hz] in the imaging surface. Therefore, when the spectrum distribution of the resonance frequency in the first to fourth embodiments is acquired from the entire imaging surface, the spectrum distribution includes the dispersion of the resonance frequency. As a result, there is a possibility that the irradiation frequency of 2DRF determined from the spectrum distribution is different from the resonance frequency of the target two-dimensional excitation region.
- the region from which the spectrum distribution is acquired is limited to a local region where the static magnetic field can be regarded as substantially constant so as not to be affected by the static magnetic field inhomogeneity.
- a local region 1402 that is a part of the excited cylinder region 1401 is excited, and the local region 1402 The spectral distribution is acquired using the echo signal.
- the UI screen 500 displays a positioning image 510 acquired in advance.
- the operator sets a two-dimensional excitation region 1401 and a local region 1402 on the positioning image 510.
- the two-dimensional excitation region 1401 is a cylindrical region excited by the SS method
- the local region 1402 is a region of particular interest in the two-dimensional excitation region.
- the cylinder shape is coaxial with the two-dimensional excitation region 1401 and has the same cross-sectional radius.
- the two-dimensional excitation region 1401 and the local region 1402 may be configured to accept any input first.
- the two-dimensional excitation region 1401 when the two-dimensional excitation region 1401 is received first, the two-dimensional excitation region 1401 can be set at an arbitrary position and angle as indicated by an arrow in the figure, and then the local region 1402 is indicated by an arrow in the figure. In the region along the cylinder set as the two-dimensional excitation region 1401, the cylinder can slide in the cylinder axis direction.
- the two-dimensional excitation region 1401 is received as a cylinder coaxial with the set local region 1402.
- both the two-dimensional excitation region 1401 and the local region 1402 are cylinders (cylindrical shapes), and their cross-sectional shapes are circular, but this is not restrictive. These cross-sectional shapes can be arbitrarily set.
- a first method for collecting echo signals from the local region 1402 uses an orthogonal three-section excitation method.
- the orthogonal three-section excitation method will be described in detail based on FIG. FIG. 15 (a) shows a local region to be excited, which is a common portion where three orthogonal cross sections intersect, and FIG. 15 (b) shows a pulse sequence used for the orthogonal three cross-section excitation method.
- a rectangular parallelepiped area (intersection area) 1524 where three orthogonal sections intersect is excited.
- the intersecting region 1524 is excited so that the cylindrical local region 1402 is inscribed.
- the resonance frequency measured in advance is set as the irradiation frequency F0, and the first gradient magnetic field 1512 is applied in the x-axis direction (Gx) together with the 90-degree pulse 1511 as shown in FIG.15 (b).
- This is applied to excite a predetermined cross section (first cross section) 1521 in the x-axis direction.
- the second gradient magnetic field 1514 is applied in the y axis direction (Gy) together with the first 180 degree pulse 1513 after the echo time (TE) / 4 hours, and the y axis direction specified by this In the region where the cross section (second cross section) 1522 and the first cross section 1521 intersect is excited.
- the third gradient magnetic field 1516 is applied in the z-axis direction (Gz) together with the second 180-degree pulse 1515, and the z-axis direction specified thereby is applied.
- the nuclear magnetization of the region 1524 where the cross section (third cross section) 1523, the first cross section 1521 and the second cross section 1522 intersect is excited.
- the generated echo signals 1517 are collected at a timing of TE / 4 hours after the application of the second 180-degree pulse 1515.
- the order of application axes to which the gradient magnetic field is applied is not limited.
- the second method for collecting echo signals from the local region 1402 uses a two-dimensional excitation method.
- the two-dimensional excitation method will be described in detail based on FIG.
- FIG. 16 shows an excitation region in the case of combining two-dimensional excitation and excitation of one cross section orthogonal to the axis of the cylindrical region excited by this two-dimensional excitation (2D orthogonal 1D method) and It is a figure for demonstrating a pulse sequence.
- FIG. 16 (a) is a diagram for explaining a region excited by the 2D orthogonal 1D method
- FIG. 16 (b) is a pulse sequence diagram of the 2D orthogonal 1D method.
- the cross section and the cylinder region are shown as transparent for explanation.
- a 90-degree pulse (2DRF) 1531 and a first oscillating gradient magnetic field 1532 in the x-axis direction (Gx) and a second oscillating gradient magnetic field 1533 in the y-axis direction (Gy) are applied,
- the cylindrical region 1541 is excited.
- a gradient magnetic field 1535 is applied along with the 180 degree pulse 1534 in the z-axis direction (Gz), and the nuclear magnetization of the crossing region 1543 between the cross-section 1542 and the cylindrical region 1541 Returns the phase of.
- the generated echo signal 1536 is collected at a timing of TE / 2 hours after the application of the 180-degree pulse 1534.
- the processing for the obtained echo signal 1536 and the calculation method of the irradiation frequency F0 'of 2DRF are the same as those in the above-described embodiments.
- the imaging parameters are set so that the intersection area 1543 matches the local area 1402.
- the irradiation frequency used for the 90-degree pulse 1531 in the pulse sequence is the entire irradiation frequency F0 determined in advance by a conventional method.
- a third method for collecting echo signals from the local region 1402 uses a pre-saturation method.
- the presaturation method will be described in detail with reference to FIG.
- the pre-saturation method combines two-dimensional excitation and a pre-saturation pulse, and suppresses an echo signal from a region outside the local region 1402 in the cylindrical region excited by the two-dimensional excitation.
- FIG. 17 (a) is a diagram for explaining a region excited by the 2D pre-saturation method, and is a diagram seen from the x-axis direction.
- FIG. 17 (b) is a pulse sequence diagram of the 2D pre-saturation method.
- the first gradient magnetic field 1552 is applied in the z-axis direction (Gz) together with the first pre-saturation pulse 1551, and the magnetization in the first region 1562 is lost.
- the second gradient magnetic field 1554 is applied in the z-axis direction (Gz) together with the second pre-saturation pulse 1553, and the magnetization in the second region 1563 is lost.
- the magnetization in either the first region 1562 or the second region 1563 may be lost first.
- a first oscillating gradient magnetic field 1556 in the x-axis direction (Gx) and a second oscillating gradient magnetic field 1557 in the y-axis direction (Gy) are applied together with the 90-degree pulse (2DRF) 1555, and in the cylindrical region 1561 A region (non-intersecting region) 1567 outside the first region 1562 and the second region 1563 is excited.
- echo signals generated at the timing after TE time from the application of the 90-degree pulse (2DRF) 1555 are collected.
- the processing for the obtained echo signal and the calculation method of the irradiation frequency F0 'of 2DRF are the same as those in the above-described embodiments.
- the imaging parameters are set so that the non-intersecting region 1567 matches the local region 1402.
- the irradiation frequency used for the 90-degree pulse 1555 in the pulse sequence is the entire irradiation frequency F0 determined in advance by a conventional method.
- the above is the description of the method of collecting echo signals from the local area.
- the signal collection unit 330 executes any one of the above methods and collects echo signals without encoding.
- the collected signal is Fourier transformed in the time direction.
- a spectral distribution in the local region 1402 is obtained.
- the same processing as in each of the above-described embodiments is performed, and the irradiation frequency F0 ′, the irradiation gain T W ′, and the gradient magnetic field strength G W ′ for 2DRF are obtained.
- the spectral distribution from a local region where the static magnetic field can be regarded as substantially constant so as not to be affected by the static magnetic field inhomogeneity. Therefore, even when the resonance frequency shifts due to non-uniformity of the static magnetic field, the irradiation frequency of 2DRF can be set appropriately corresponding to the non-uniformity of the static magnetic field. As a result, it is possible to accurately set the positions and shapes of the excitation regions of the first substance and the second substance and their flip angles.
- FIG. 18 is a functional block diagram of the control unit 110 of the present embodiment.
- the present embodiment further includes a magnetic field adjustment unit 380 that adjusts the magnetic field in the local region.
- the magnetic field adjustment processing by the magnetic field adjustment unit 380 which is different from the above-described fifth embodiment, will be described in the present embodiment.
- Other configurations and other processes are the same as those in the fifth embodiment described above.
- the magnetic field adjustment unit 380 of the present embodiment improves the non-uniformity of the static magnetic field in the region because the resonance frequency of nuclear magnetization in the local region 1402 matches the overall resonance frequency F0.
- the shim current value Is for correcting the static magnetic field inhomogeneity in the local region 1402 is calculated by the conventional method from the volume data or the shim image obtained by the signal collecting unit 330 by the same method as the fifth embodiment. .
- the shim current is calculated only for the axis whose current value can be switched during measurement (scanning).
- the magnetic field adjustment unit 380 controls the shim power supply so that the applied current value to the shim coil in the axial direction is the calculated Is only during the application of 2DRF.
- a shim current value Is is calculated using the static magnetic field strength B1 in the local region 1402 as the static magnetic field strength B0 that realizes the overall frequency F0.
- the shim coil can correct the static magnetic field strength component to the primary component in each axial direction. That is, a current value that matches the overall irradiation frequency F0 and the resonance frequency F calculated from the zeroth-order component of the static magnetic field strength B1 is calculated.
- FIG. 19 shows an imaging result of the local region 1402.
- a plurality of measurement points 1901 are set on the circumferences of the upper surface and the lower surface of the local region 1402 having a cylinder shape with a diameter of ⁇ and a thickness of D. It should be noted that a plurality of measurement points 1901 are desirably arranged on the cylinder axis. Preferably, the measurement points 1901 are isotropically arranged in the axial direction.
- the resonance frequency F calculated from the static magnetic field strength B1 at each measurement point 1901 is projected (Fx, Fy, Fz) in the x-axis, y-axis, and z-axis directions, respectively, and the plotted results are shown in FIG. 20A shows the result of projection in the x-axis direction, FIG. 20B shows the result of projection in the y-axis direction, and FIG. 20C shows the result of projection in the z-axis direction.
- the horizontal axis represents the position in each axial direction, and the vertical axis represents the resonance frequency F calculated from the static magnetic field strength B1.
- Each axial projection result is approximated by a linear expression.
- the shim current value is determined so that these all pass through F0 and have a slope of 0.
- the shim current value Is calculated by the magnetic field adjustment unit 380 is applied only during the application of 2DRF by the above-described method, and imaging is performed. Other than that, imaging is performed by applying a shim current value Is of 0 or a shim current value that improves static magnetic field inhomogeneity in the entire imaging region.
- a desired excitation profile can be obtained for 2DRF even when the static magnetic field is not uniform in the local region 1402.
- the correction order of the static magnetic field inhomogeneity by the shim coil is not limited to the above.
- the projection results of the static magnetic field strength B1 at each measurement point 1901 in each axial direction can be approximated within a range of orders in which the shim coil in the axial direction can correct the static magnetic field strength.
- the method of calculating the shim current value that achieves the static magnetic field uniformity is not limited to the above method. Various general techniques can be used.
- the static magnetic field inhomogeneity may be corrected using the gradient magnetic field by the gradient magnetic field coil 103. That is, control is performed so that the same amount of current as the shim current value Is calculated by the above method is supplied to each gradient coil 103 as an offset only while 2DRF is applied from the gradient magnetic field power supply 106.
- the static magnetic field inhomogeneity in the local region 1402 can be corrected during 2DRF application even when the MRI apparatus 100 does not include a shim coil.
- the static frequency of the local region is adjusted so that the resonance frequency of the nuclear magnetization of the local selection region matches the previously determined overall irradiation frequency F0. Since the magnetic field inhomogeneity is corrected, the position and shape of the excitation regions of the first substance and the second substance and the flip angle thereof are accurately set without the spectral distribution acquired from the locally selected region becoming broad. It becomes possible.
- MRI device 101 subject, 102 magnet, 103 gradient coil, 104 RF coil, 105 RF probe, 106 gradient magnetic field power supply, 107 RF transmitter, 108 signal detector, 109 signal processor, 110 controller, 111 display Unit, 112 operation unit, 113 bed, 201 RF, 202 gradient magnetic field, 211 RF, 212 vibration gradient magnetic field, 213 vibration gradient magnetic field, 320 excitation region setting unit, 330 signal collection unit, 340 irradiation frequency setting unit, 350 UI control unit , 360 Irradiation gain setting unit, 370 Gradient magnetic field setting unit, 380 Magnetic field adjustment unit
Abstract
Description
次に、本発明に係るMRI装置及び2次元励起調整方法の第1の実施形態を説明する。本実施形態は、水のプロトン(第1の物質)の共振周波数と脂肪のプロトン(第2の物質)の共振周波数の平均値を照射周波数とする高周波磁場を用いて2次元励起を行う。なお、本実施形態では、水の励起領域と脂肪の励起領域は共に同じ位置であって同じ直径φを有する2次元シリンダ領域であり、水の励起領域のフリップアングルと脂肪の励起領域のフリップアングルは共に同じ角度FAとする。以下、本実施形態のMRI装置100の構成と処理手順を説明する。
F0’=(F0W+F0F)/2 (1)
ステップ405で、ステップ404で算出された2DRFの照射周波数F0’に基づいて、ステップ401で設定されたシリンダ直径φを有する2次元励起領域がフリップアングルFAで励起されるように、照射ゲイン設定部360は、そのフリップアングルFAとなるような照射ゲインを計算し、傾斜磁場設定部370は、好適な傾斜磁場強度を算出する。
GW’= GW*φ’/φ (2)
TW’= TW* FA/FA’ (3)
そこで、傾斜磁場設定部370は上記(2)式に基づいて傾斜磁場強度GW’を算出し、照射ゲイン設定部360は上記(3)式に基づいて照射ゲインTW’を算出し、それぞれ信号収集部330に算出結果を通知する。
以上までが、本実施形態の処理フローの説明である。
次に、本発明に係るMRI装置及び2次元励起調整方法の第2の実施形態を説明する。本実施形態は、共振周波数の異なる各物質のスペクトル分布の形状に対応して、2次元励起用の高周波磁場(2DRF)の照射周波数を設定する。
図9の例では、901の水のプロトンのスペクトル分布が実質的に対称な分布であり、902の脂肪のプロトンのスペクトル分布が非対称なブロードであるので、F0WとF0W’とは実質的に同一となるが、F0FとF0F’ は異なる値となる。
F0’’=(F0W’+F0F’)/2 (6)
となる。
次に、本発明に係るMRI装置及び2次元励起調整方法の第3の実施形態を説明する。本実施形態は、各物質の共振周波数と2次元励起用の高周波磁場の照射周波数との差(ΔF)に応じて定まる、2次元励起領域の形状を規定するパラメータ(例えばシリンダ直径φ)やその領域のフリップアングルについての制限値を求めて、求めた制限値の範囲内で高周波磁場調整を行い、所望の2次元励起を行なう。以下、前述の各実施形態と同様に、2次元シリンダ領域を励起する場合を例にして本実施形態を説明する。
FA’MAX = FAMAX * FA’(ΔF) / FA’(0) (7)
φ’min =φmin * φ’(ΔF) /φ’(0) (8)
ここで、FA’(ΔF)とφ’(ΔF)は、それぞれ図7、図8に示すグラフを表す関数である。
ステップ1006で、UI制御部350は、ステップ1005で求められたシリンダ領域の最小直径φ’minと最大フリップアングルFA’MAXとを、前述のステップ401におけるUI画面に、操作者が入力設定可能な範囲を示す上での制限値として表示する。つまり、前述の第1の実施形態における図4に示す処理フローのステップ401において、操作者によるシリンダ直径φの設定入力がφ’min以上となるように、フリップアングルFAの設定入力がFA’MAX以下となるように、UI制御部350はシリンダ直径とフリップアングルの入力設定を制御する。また、ステップ1001で設定されたパルスシーケンスにおいて、FA’MAXやφ’minを設定した場合にdB/dtやSARが限界値を超える場合は、限界値を超えないFAとφを操作者に示す。
以上までが、本実施形態の処理フローの説明である。
次に、本発明に係るMRI装置及び2次元励起調整方法の第4の実施形態を説明する。前述の各実施形態では、励起領域の形状とフリップアングルが第1の物質と第2の物質とで、実質的に同一となるように、2次元励起用の高周波磁場(2DRF)の照射周波数、照射ゲイン、及び傾斜磁場強度を設定した。これに対して、本実施形態は、撮像目的に応じて、励起領域の形状とフリップアングルの少なくとも一方が、第1の物質と第2の物質とで、異なるよう2DRFの照射周波数、照射ゲイン、及び傾斜磁場強度を設定する。例えば、2DRFの照射周波数を第1の物質と第2の物質の共振周波数の中間値(平均値でない)とする。以下、血液を磁気的にラベル化するArterial Spin Labeling(以下、ASL)法の一種であるIFIR法を例にして、1の物質と第2の物質とで主にフリップアングルを異ならせる場合を説明する。
FC = F0W - F0F (9)
ステップ1302で、照射ゲイン設定部360は、水と脂肪のフリップアングルを設定する。例えば、前述のIFIR法の場合の様に、双方のNull Timeが一致するように、水のフリップアングルを脂肪のフリップアングルより少なく設定する。なお、目的とする水と脂肪のフリップアングルは、UI制御部350が表示するUI画面を介して操作者が入力してもよいし、MRI装置が内部で保持してもよい。
β= FAW / FAF (10)
ステップ1303で、照射ゲイン設定部360は、(10)式を実現する2DRFの照射周波数F0’を計算する。具体的には、次の通りである。即ち、水と脂肪のフリップアングルFAW、FAFは、関数FA’(ΔF)から、下式で算出できる。
FAW= FA’(ΔFW )
FAF = FA’(ΔFF )
上式を式(10)に代入すると、式(10A)が得られる。
β= FA’(ΔFW ) / FA’(ΔFF ) (10A)
ここで、2DRFの照射周波数F0’と水及び脂肪のプロトンの共振周波数の差をそれぞれΔFW、ΔFFとする。具体的には式(11)で定義する。
ΔFW= F0W - F0’ (11-1)
ΔFF= F0’ - F0F (11-2)
従って、ΔFWとΔFFは、以下の関係にある。
ΔFW + ΔFF = FC (12)
式(12)を(10A)に代入すると、ΔFFの式として(10B)が得られる。
β= FA’(FC-ΔFF ) / FA’(ΔFF ) (10B)
関数(10B)の解が複数ある場合、正の値の最小値をΔFFとして式(11-2)から2DRFの照射周波数F0’を計算する。この場合、照射周波数F0’は、水と脂肪のプロトンの共振周波数F0W、F0Fの平均値でなく中間値となる。図12の例では脂肪寄りの中間値となる。また、ΔFが最小になるので、結果として照射ゲインTWを最小にすることができる。
次に、本発明に係るMRI装置及び2次元励起調整方法の第5の実施形態を説明する。本実施形態では、静磁場不均一がある静磁場空間内に配置された被検体が含む第1の物質と第2の物質の共振周波数が、その静磁場不均一によってシフトする場合において、静磁場不均一に対応して2次元励起用高周波磁場(2DRF)の照射周波数を設定する。
局所領域1402からのエコー信号を収集する第1の方法は、直交3断面励起法を用いる。図15に基づいて直交3断面励起法を詳細に説明する。図15(a)は、直交3断面が交差する共通部分であって励起される局所領域を示し、図15(b)は、直交3断面励起法に用いるパルスシーケンスを示す。直交3断面励起法では、直交する3断面の交差する直方体の領域(交差領域)1524が励起される。ここでは、シリンダ状の局所領域1402が内接するよう交差領域1524を励起する。このような領域を励起するため、事前に計測した共振周波数を照射周波数F0として、図15(b)に示すように、90度パルス1511とともにx軸方向(Gx)に第一の傾斜磁場1512を印加し、x軸方向の所定の断面(第一の断面)1521を励起する。90度パルス1511の印加からエコータイム(TE)/4時間後に、第一の180度パルス1513とともにy軸方向(Gy)に第二の傾斜磁場1514を印加し、これにより特定されるy軸方向の断面(第二の断面)1522と第一の断面1521とが交差する領域の核磁化を励起する。第一の180度パルス1513の印加からTE/2時間後に、第二の180度パルス1515とともにz軸方向(Gz)に第三の傾斜磁場1516を印加し、これにより特定されるz軸方向の断面(第三の断面)1523と第一の断面1521と第二の断面1522とが交差する領域1524の核磁化を励起する。そして、第二の180度パルス1515の印加からTE/4時間後のタイミングで、発生するエコー信号1517を収集する。なお、上記パルスシーケンスにおいて、傾斜磁場を印加する印加軸の順は問わない。
次に、本発明に係るMRI装置及び2次元励起調整方法の第6の実施形態を説明する。前述の第5の実施形態では、静磁場不均一によるスペクトル分布の分散を排除するため、局所領域のスペクトル分布を取得し、その局所領域の静磁場強度に対応して2次元励起用の高周波磁場(2DRF)の照射周波数を求めた。これに対して、本実施形態は、その局所領域の静磁場不均一を補正して、当該領域の核磁化の共振周波数が予め求めた全体照射周波数F0に合致するよう静磁場を調整する。以下、本実施形態における局所領域の静磁場不均一分布の補正方法について詳細に説明する。
Claims (19)
- 静磁場中に配置された被検体の2次元励起領域を2次元励起するための高周波磁場および傾斜磁場を伴うパルスシーケンスを用いて、前記2次元励起領域から発生するエコー信号の計測を制御する制御部を備えた磁気共鳴イメージング装置であって、
前記被検体は、第1の共振周波数を有する第1の物質と第2の共振周波数を有する第2の物質とを有して成り、
前記制御部は、前記2次元励起に係る撮像条件と、前記第1の共振周波数及び前記第2の共振周波数と、に基づいて、前記第1の物質と前記第2の物質についてそれぞれ所望の領域が2次元励起されるように、前記高周波磁場の照射周波数を設定する照射周波数設定部を備えていることを特徴とする磁気共鳴イメージング装置。 - 請求項1の磁気共鳴イメージング装置であって、
前記制御部は、前記2次元励起領域の励起角度と、前記照射周波数と前記第1の共振周波数との周波数差と、に基づいて、前記高周波磁場の照射ゲインを設定する照射ゲイン設定部を備えていることを特徴とする磁気共鳴イメージング装置。 - 請求項2の磁気共鳴イメージング装置であって、
前記照射ゲイン設定部は、前記照射周波数と第1の共振周波数との周波数差と、励起角度との関係を表す、関数又はデータに基づいて、前記高周波磁場の照射ゲイン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の磁気共鳴イメージング装置であって、
前記制御部は、前記2次元励起領域の形状を表すパラメータの値と、前記照射周波数と前記第1の共振周波数との周波数差と、に基づいて、前記傾斜磁場の強度を設定する傾斜磁場設定部を備えていることを特徴とする磁気共鳴イメージング装置。 - 請求項4の磁気共鳴イメージング装置であって、
前記傾斜磁場設定部は、前記照射周波数と第1の共振周波数との周波数差と、前記2次元励起領域の形状を表すパラメータの値との関係を表す、関数又はデータに基づいて、前記傾斜磁場の強度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4の磁気共鳴イメージング装置であって、
前記制御部は、前記2次元励起領域の設定するための入力に応じて、該2次元励起領域の形状を表すパラメータの値を設定する励起領域設定部を備えていることを特徴とする磁気共鳴イメージング装置。 - 請求項1の磁気共鳴イメージング装置であって、
前記制御部は、予め決定された初期照射周波数の高周波磁場を用いて前記2次元励起領域からエコー信号を取得する信号収集部と、を備え、
前記照射周波数設定部は、前記初期照射周波数の高周波磁場を用いて2次元励起領域から取得したエコー信号に基づいて、前記第1の共振周波数と前記第2の共振周波数とを決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7の磁気共鳴イメージング装置であって、
前記照射周波数設定部は、前記初期照射周波数の高周波磁場を用いて2次元励起領域から取得したエコー信号をフーリエ変換して得た、各物質の共振周波数のスペクトル分布に基づいて、前記第1の共振周波数と前記第2の共振周波数とを決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の磁気共鳴イメージング装置であって、
前記照射周波数設定部は、前記第1の共振周波数と前記第2の共振周波数の平均値を前記照射周波数として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8の磁気共鳴イメージング装置であって、
前記照射周波数設定部は、前記各物質の共振周波数のスペクトル分布の形状に応じて、前記第1の共振周波数と前記第2の共振周波数とを決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6の磁気共鳴イメージング装置であって、
前記励起領域設定部は、前記2次元励起領域の形状を表すパラメータの値についての所定の最小値と、前記照射周波数と第1の共振周波数との周波数差と、に基づいて、前記2次元励起領域の形状を表すパラメータの値の設定可能な最小値を求め、
前記最小値を表示する表示部を備えていることを特徴とする磁気共鳴イメージング装置。 - 請求項3の磁気共鳴イメージング装置であって、
前記照射ゲイン設定部は、前記2次元励起領域の励起角度についての所定の最大値と、前記照射周波数と第1の共振周波数との周波数差と、に基づいて、前記2次元励起領域の励起角度についての設定可能な最大値を求め、
前記最大値を表示する表示部を備えていることを特徴とする磁気共鳴イメージング装置。 - 請求項1の磁気共鳴イメージング装置であって、
前記照射周波数設定部は、前記第1の物質の励起角度と前記第2の物質の励起角度とが異なるように、前記第1の共振周波数と前記第2の共振周波数の中間値を前記照射周波数として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7の磁気共鳴イメージング装置であって、
前記照射周波数設定部は、前記2次元励起領域内の局所領域から取得したエコー信号に基づいて、記第1の共振周波数と前記第2の共振周波数とを決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14の磁気共鳴イメージング装置であって、
前記制御部は、前記局所領域の静磁場強度を所定の値に調整する磁場調整部を備え、
前記照射周波数設定部は、前記局所領域の静磁場強度が所定の値に調整された状態で取得されたエコー信号に基づいて、前記照射周波数を決定することを特徴とする磁気共鳴イメージング装置。 - 静磁場中に配置された被検体の2次元励起領域を2次元励起するための高周波磁場および傾斜磁場を伴うパルスシーケンスを用いて、前記2次元励起領域から発生するエコー信号の計測を制御する磁気共鳴イメージング装置における2次元励起調整方法であって、
前記被検体が、第1の共振周波数を有する第1の物質と第2の共振周波数を有する第2の物質とを有して成り、
前記2次元励起に係る撮像条件の入力ステップと、
前記第1の共振周波数及び前記第2の共振周波数を算出するステップと、
前記2次元励起に係る撮像条件と、前記第1の共振周波数及び前記第2の共振周波数と、に基づいて、前記第1の物質と前記第2の物質についてそれぞれ所望の領域が2次元励起されるように、前記高周波磁場の照射周波数を設定するステップと、
を有することを特徴とする2次元励起調整方法。 - 請求項16記載の2次元励起調整方法において、
前記2次元励起領域の励起角度と、前記照射周波数と前記第1の共振周波数との周波数差と、に基づいて、前記高周波磁場の照射ゲインを設定するステップをさらに有することを特徴とする2次元励起調整方法。 - 請求項16記載の2次元励起調整方法において、
前記2次元励起領域の形状を表すパラメータの値と、前記照射周波数と前記第1の共振周波数との周波数差と、に基づいて、前記傾斜磁場の強度を設定するステップをさらに有することを特徴とする2次元励起調整方法。 - 請求項16記載の2次元励起調整方法において、
前記第1の共振周波数及び第2の共振周波数を算出するステップは、
予め決定された初期照射周波数の高周波磁場を用いて前記2次元励起領域からエコー信号を取得するステップと、
前記エコー信号を用いて、前記第1の共振周波数と前記第2の共振周波数についてのスペクトル分布を求めるステップと、
前記スペクトル分布に基づいて、前記第1の共振周波数と前記第2の共振周波数とを決定するステップと、
を有することを特徴とする2次元励起調整方法。
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DE102011078868B4 (de) * | 2011-07-08 | 2013-03-28 | Siemens Ag | Frequenzkalibrierung einer Magnetresonanzanlage unter Verwendung der Spektralinformationen mehrerer Echosignale |
WO2014165793A1 (en) * | 2013-04-04 | 2014-10-09 | The Board Of Trustees Of The University Of Illinois | Two-dimensional semi-laser correlation spectroscopy with well-maintained cross peaks |
US20160231396A1 (en) * | 2013-10-16 | 2016-08-11 | Hitachi Medical Corporation | Magnetic resonance imaging apparatus and imaging parameter setting assisting method |
US11089970B2 (en) * | 2015-06-12 | 2021-08-17 | Koninklijke Philips N.V. | Imaging fluid flow into a region of interest |
US11033199B2 (en) * | 2015-06-29 | 2021-06-15 | The Board Of Trustees Of The University Of Illinois | Echo-planar imaging magnetic resonance elastography pulse sequence |
DE102016214608B4 (de) * | 2016-08-05 | 2019-06-27 | Siemens Healthcare Gmbh | Verfahren zu einem Einstellen und/oder Anpassen von Messparametern für eine Messsequenz einer Magnetresonanzuntersuchung |
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Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH11216124A (ja) * | 1998-01-30 | 1999-08-10 | Shimadzu Corp | 核磁気共鳴検査装置 |
JPH11225987A (ja) * | 1998-02-18 | 1999-08-24 | Toshiba Corp | 磁気共鳴イメージング装置 |
JP2001095773A (ja) * | 1999-09-28 | 2001-04-10 | Hitachi Medical Corp | 磁気共鳴画像診断装置 |
JP2003052667A (ja) * | 2001-06-29 | 2003-02-25 | General Electric Co <Ge> | 磁気共鳴イメージング・システム |
JP2003190114A (ja) * | 2001-12-19 | 2003-07-08 | Ge Medical Systems Global Technology Co Llc | Mri装置、mrイメージング方法、およびmrイメージング方法をコンピュータ上で実行するプログラム |
JP2008054738A (ja) * | 2006-08-29 | 2008-03-13 | Hitachi Medical Corp | 磁気共鳴イメージング装置 |
Family Cites Families (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE19543079A1 (de) * | 1995-11-18 | 1997-05-22 | Philips Patentverwaltung | Verfahren zum Bestimmen der räumlichen und/oder spektralen Verteilung der Kernmagnetisierung |
DE19718129A1 (de) * | 1997-04-29 | 1998-11-12 | Siemens Ag | Pulssequenz für ein Kernspintomographiegerät und Kernspintomographiegerät |
AU3754299A (en) * | 1998-04-24 | 1999-11-16 | Case Western Reserve University | Geometric distortion correction in magnetic resonance imaging |
US6373249B1 (en) * | 1999-05-21 | 2002-04-16 | University Of Rochester | System and method for three-dimensional interleaved water and fat image acquisition with chemical-shift correction |
JP4509336B2 (ja) * | 2000-08-31 | 2010-07-21 | 株式会社東芝 | 磁気共鳴装置 |
US6541971B1 (en) * | 2001-06-28 | 2003-04-01 | Koninklijke Philips Electronics, N.V. | Multi-dimensional spatial NMR excitation |
US6980001B2 (en) * | 2002-05-20 | 2005-12-27 | The University Of Sheffield At Western Bank | Methods & apparatus for magnetic resonance imaging |
US6995559B2 (en) * | 2003-10-30 | 2006-02-07 | Ge Medical Systems Global Technology Company, Llc | Method and system for optimized pre-saturation in MR with corrected transmitter frequency of pre-pulses |
EP2899561B1 (en) * | 2006-02-17 | 2021-04-28 | Regents of the University of Minnesota | MRI method for generating a map of the transmit RF field for each coil of a RF coil array |
US8831703B2 (en) * | 2006-10-23 | 2014-09-09 | The General Hospital Corporation | Selective MR imaging of segmented anatomy |
JP5032156B2 (ja) * | 2007-03-05 | 2012-09-26 | 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 | 磁気共鳴イメージング装置および磁気共鳴イメージング方法 |
-
2010
- 2010-11-11 JP JP2011540532A patent/JP5730214B2/ja active Active
- 2010-11-11 US US13/504,590 patent/US9035652B2/en active Active
- 2010-11-11 WO PCT/JP2010/070080 patent/WO2011059017A1/ja active Application Filing
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH11216124A (ja) * | 1998-01-30 | 1999-08-10 | Shimadzu Corp | 核磁気共鳴検査装置 |
JPH11225987A (ja) * | 1998-02-18 | 1999-08-24 | Toshiba Corp | 磁気共鳴イメージング装置 |
JP2001095773A (ja) * | 1999-09-28 | 2001-04-10 | Hitachi Medical Corp | 磁気共鳴画像診断装置 |
JP2003052667A (ja) * | 2001-06-29 | 2003-02-25 | General Electric Co <Ge> | 磁気共鳴イメージング・システム |
JP2003190114A (ja) * | 2001-12-19 | 2003-07-08 | Ge Medical Systems Global Technology Co Llc | Mri装置、mrイメージング方法、およびmrイメージング方法をコンピュータ上で実行するプログラム |
JP2008054738A (ja) * | 2006-08-29 | 2008-03-13 | Hitachi Medical Corp | 磁気共鳴イメージング装置 |
Non-Patent Citations (1)
Title |
---|
TSUTOMU ARAKI, KETTEIBAN MRI KANZEN KAISETSU, 1 August 2008 (2008-08-01), pages 501 * |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2015154911A (ja) * | 2014-01-17 | 2015-08-27 | 株式会社東芝 | 磁気共鳴イメージング装置 |
US10288708B2 (en) | 2014-05-02 | 2019-05-14 | Toshiba Medical Systems Corporation | Magnetic-resonance imaging apparatus |
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