WO2001022879A1 - Appareil de diagnostic a imagerie par resonance magnetique (irm) et procede correspondant - Google Patents

Appareil de diagnostic a imagerie par resonance magnetique (irm) et procede correspondant Download PDF

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Publication number
WO2001022879A1
WO2001022879A1 PCT/JP2000/006711 JP0006711W WO0122879A1 WO 2001022879 A1 WO2001022879 A1 WO 2001022879A1 JP 0006711 W JP0006711 W JP 0006711W WO 0122879 A1 WO0122879 A1 WO 0122879A1
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Prior art keywords
magnetic field
image
magnetic resonance
region
resonance imaging
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PCT/JP2000/006711
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English (en)
Japanese (ja)
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Hiromichi Shimizu
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Hitachi Medical Corporation
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Publication of WO2001022879A1 publication Critical patent/WO2001022879A1/fr

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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
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0033—Features or image-related aspects of imaging apparatus classified in A61B5/00, e.g. for MRI, optical tomography or impedance tomography apparatus; arrangements of imaging apparatus in a room
    • A61B5/0037—Performing a preliminary scan, e.g. a prescan for identifying a region of interest
    • 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
    • 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

Definitions

  • the present invention relates to a magnetic resonance imaging diagnostic apparatus (hereinafter, referred to as an MRI apparatus), and more particularly to an MRI apparatus having a spectroscopic imaging measurement function.
  • the spectroscopic imaging method (hereinafter referred to as MRSI method) using a medical magnetic resonance diagnostic apparatus (MRI) is a method of imaging the distribution of a specific chemical species in a living body. Unlike morphological information, chemical information such as glucose metabolism and energy metabolism can be obtained, so it is used for diagnosis at the early stage of disease.
  • MRSr methods such as the 3D-CSP method, which measures chemical shift as chemical information as a time coefficient, have been attempted as MRSI methods.
  • MRSI methods MRSI methods
  • clinical MRI devices that target protons (nuclei) have been attempted.
  • 3D-CSI method spatial information in the x and y directions is phase-encoded, and spectrum information is encoded with the passage of time during signal measurement.
  • MRSI targeting protons interferes with signals of water and fat that exist in the body by two to four orders of magnitude more than metabolites, so it is necessary to use a technique to suppress them.
  • the conventional technique will be described with reference to FIGS.
  • a water spectrum is selectively excited by a CHESS pulse 31, and then a gradient magnetic field 33 is applied to dephase the magnetic field of the water to generate a signal. Avoid it.
  • the gradient magnetic field 34 is applied to dephase the magnetization in this vertical slice (0VS: 0uter Volume Suppression). Repeat this process with different slices until the fat area is fully covered.
  • spectroscopic measurement which is the main measurement, is performed.
  • Fig. 9 illustrates the head transformer surface as an example.
  • the slices 1 to 8 are excited and dephased while changing the direction.
  • eight slices are used to cover the subcutaneous fat, and usually 4 to 8 slices are used.
  • adipose tissue is covered with a plurality of rectangles, it is difficult to accurately cover a fat region, and it has not been possible to sufficiently suppress a signal from fat.
  • it is necessary to increase the number of rectangles which makes setting a rectangular area complicated. Increasing the number of rectangles also increases the length of the pre-process, causing the water to recover due to longitudinal relaxation and insufficient water suppression.
  • At least a double phase encoding loop is used to add spatial coordinate information of two or three axes to a signal, and the measurement takes time. Since the process requires about 20 to 50 ms, there is a problem that the measurement time is further extended.
  • an object of the present invention is to provide an MRI apparatus capable of realizing an MRSI method that can surely suppress unnecessary signals and does not increase the measurement time. Disclosure of the invention
  • a control function a oscillating gradient magnetic field in two or three axial directions is applied to a predetermined high-frequency magnetic field.
  • the fat suppression step in the phase encoding loop becomes unnecessary, and the signal from fat tissue is greatly reduced.
  • the MRI apparatus of the present invention specifically uses such a spatial selection in MRSI measurement. It provides a means to incorporate excitation techniques.
  • the MRI apparatus of the present invention includes a magnetic field generating means for generating each of a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field (RF) in a space where a subject is placed, and a detection device for detecting a magnetic resonance signal generated by the subject.
  • R0I desired region of interest
  • the signal can be obtained by exciting only the inside of the R0I of the desired shape, the influence of fat and water from the outside of the R0I can be effectively suppressed. This improves the quantitativeness of the spectrum and improves the accuracy of diagnosis.
  • the excitation pulse has a region selectivity, it is not necessary to apply a fat suppression RF pulse in the pre-process performed every time the phase encoding is repeated, thereby shortening the overall length of the pre-process. As a result, the recovery of the water signal can be reduced.
  • the means for setting R0I has a function of displaying a tomographic image taken of a desired slice on a display means as a scout image, and interactively setting R0I on the displayed scout image.
  • the means for calculating the modulation waveform creates an excitation shape function from the shape of R0I, and calculates the modulation waveform of the high-frequency magnetic field almost in real time from the two-dimensional Fourier transform of the excitation shape function.
  • the RF waveform of this selective excitation varies depending on the shape of R0I.Since a scout image is taken and displayed in advance and R0I is set interactively on this scout image, any shape of R0I can be set easily. . In addition, since the RF modulation waveform is generated by the computer from the two-dimensional Fourier transform of the set R0I shape, the RF wave corresponding to R0I is almost real-time.
  • the control means sets a minimum rectangular area including R0I and determines an image matrix size according to the rectangular area.
  • the image matrix size is the size of image data represented by the number of pixels (or poxels) arranged in two dimensions or three dimensions (the number of rows and columns), and the magnitude of the gradient magnetic field that encodes spatial information. Determined by the number of letters. Therefore image matri By determining the matrix size according to the smallest rectangle that covers the R0I shape, it is not necessary to increase the matrix size unnecessarily. As a result, unnecessary phase encoding is not repeated, and MRSI imaging time can be reduced. BRIEF DESCRIPTION OF THE FIGURES
  • FIG. 1 is a flowchart showing a procedure according to an embodiment of the present invention
  • FIG. 2 is a diagram illustrating a method of interactively setting R0I and a matrix setting method
  • FIG. 3 is an example of a sequence to which the present invention is applied.
  • FIG. 4 is a diagram showing the overall configuration of the MRI apparatus of the present invention.
  • FIG. 5 is a diagram showing another example of a sequence to which the present invention is applied.
  • FIG. 6 is a diagram showing a procedure according to another embodiment of the present invention.
  • FIG. 7 is a diagram showing another example of a sequence to which the present invention is applied
  • FIG. 8 is a diagram showing another example of a sequence to which the present invention is applied
  • FIG. 9 is a diagram for explaining conventional fat suppression.
  • FIG. 10 is a diagram showing a sequence in which conventional water suppression and fat suppression are used together.
  • FIG. 4 is a schematic configuration diagram of an MRI apparatus to which the present invention is applied.
  • This MRI apparatus includes a static magnetic field generating magnetic circuit 402 for generating a uniform static magnetic field B0 inside a subject 401, and a gradient magnetic field Gx whose intensity linearly changes in three orthogonal directions x, y and z.
  • the static magnetic field generating magnetic circuit 402 includes an electromagnet or a permanent magnet, and the subject 401 is carried into the static magnetic field space.
  • the gradient magnetic field generation system 403 is composed of a three-axis gradient magnetic field coil 409 and a power supply 410 for supplying a current to the gradient magnetic field, and is a linear type for providing spatial information to a nuclear magnetic resonance signal. And an oscillating gradient magnetic field during R0I selective excitation.
  • the transmission system 404 includes a synthesizer 414 that generates a predetermined high frequency, a modulator 412 that modulates the high frequency generated by the synthesizer 411, a power amplifier 413, and a transmission coil 414a.
  • the modulation waveform modulated by the modulator 412 is calculated and stored by the computer 408 according to a procedure described later, and is provided from the sequencer 407.
  • a high frequency modulated with a predetermined modulation waveform to the transmission coil 414a, a high frequency magnetic field is generated inside the subject 401 to excite nuclear spins.
  • the nuclear spin to be excited is usually 1 H, but may be other nuclei having nuclear spin, such as 31 P and 12 C.
  • the detection system 405 includes a receiving coil 414b for receiving a nuclear magnetic resonance signal emitted from the subject 401, an amplifier 415, a quadrature detector 416, and an A / D converter 417.
  • the nuclear magnetic resonance signal received and amplified by the amplifier 415 is subjected to A / D conversion after quadrature phase detection and input to the computer 408.
  • the transmission coil 414a and the reception coil 414b may be separate as shown, or may be coils for both transmission and reception.
  • the computer 408 reconstructs an image corresponding to the nuclear spin density distribution, relaxation time distribution, spectrum distribution, and the like, and displays the image on the CRT display 428.
  • the operation unit 421 inputs commands necessary for executing a program for processing and various settings by the MRI apparatus incorporated in the computer 408 to the computer 408.
  • the processing executed via the operation unit 421 includes processing for setting an R0I (region of interest) in a predetermined area of the subject, processing for determining an image matrix size according to the R0I, and transmission based on the shape of the R0I.
  • a process for calculating an RF modulation waveform generated by the system 404 is included.
  • the data in the middle of the calculation performed by the computer 408 or final data is stored in the memories 424 and 425.
  • the computer 408 controls the gradient magnetic field generation system 403, the transmission system 404, and the detection system 405 via the sequencer 407 in order to perform imaging according to a predetermined imaging sequence.
  • MRSI measurement using the MRI apparatus having such a configuration will be described. Note that in the embodiments described below, it is assumed that MRSI of protons is performed on the trans-plane (xy plane) of the lower abdomen, but the present method can be similarly applied to other slice planes. Also, fat suppression However, spectra other than fat may be suppressed.
  • FIG. 1 is a diagram showing a flow of MRSI according to the present invention
  • FIG. 2 is a diagram explaining the setting of R0I
  • FIG. 3 is a diagram showing an embodiment of an imaging sequence of the MRSI method according to the present invention.
  • Example 0 In MRSI measurement, a scout image of a desired slice is obtained prior to the main measurement (statroscopic measurement) (FIG. 1, step 11). Scout images can be taken using a general MRI imaging method such as the FSE (Fast Spin Echo) method and the EPI (Echo Planner Imaging) method. The slice selected here is any slice included in the area targeted for the main measurement.
  • FSE Fest Spin Echo
  • EPI Echo Planner Imaging
  • FIG. 2 is a diagram schematically showing a scout image displayed on the display, and 61 shows R0I input with a mouse.
  • any shape can be specified for the R0I shape.
  • the Fourier transform D, (kx, ky) of the shape function D ( X , y) contains more high-frequency components (components at the edges of k-space). In this measurement, it is necessary to expand the k-space. This means a force that increases the amplitude of the oscillating gradient magnetic field, or a longer application time, which entails equipment difficulties and longer imaging times. Therefore, it is practical to avoid unnecessary complexity when inputting the R0I shape.
  • the binary function D (x, y) may be subjected to smoothing as needed.
  • the boundary where the power of ⁇ changes from ⁇ ) to 1 has a certain width, and the function value smoothly decreases from 1 to 0 within this width.
  • the shape function D (x, y) is subjected to a two-dimensional Fourier transform to create a function D ′ ((kx, ky) in k-space. Is calculated (step 14).
  • the gradient magnetic field waveforms Gx (t;) and Gy (t) are predetermined as the imaging sequence of the main measurement.
  • a gradient magnetic field that gives a spiral locus converging at a constant speed from the edge of k-space to the origin Waveforms Gx (t;) and Gy (t) are adopted.
  • Formula (2) shows a specific example of such gradient magnetic field waveforms Gx (t) and Gy (t). These are sin waves and cos waves whose amplitudes attenuate as a linear function of time.
  • T / n represents the rotation period of the spiral in space.
  • ⁇ is a constant that determines the size of the spiral. Normally n is around 10.
  • the gradient magnetic field waveforms Gx (t) and Gy (t) are not limited to the spiral, but may be those that give a zigzag trajectory like the EPI method, as long as the trajectory uniformly covers the k-space. It can also be used.
  • the RF waveform Bl (t) obtained in this way is saved in the memory, and the previous process ends.
  • the MRSI which is the main measurement, is executed (step 15).
  • the amplitude of the RF waveform Bl (t) is experimentally adjusted so that its maximum flip angle is 90 °.
  • FIG. 3 shows an embodiment of the MRSI imaging sequence according to the present invention.
  • spatial selective excitation is applied to the 3D-CSI method.
  • a gradient magnetic field 74, 75 oscillating in the X and y directions is applied together with the excitation pulse 71, so that a two-dimensional region in the xy plane is applied. It excites only the internal magnetization.
  • the slice selection gradient magnetic field Gz is not used.
  • This excitation pulse excites the inside of R0I into a shape of approximately D (x, y). The accuracy of the excitation shape depends on the degree to which the gradient magnetic fields 74 and 75 include high-frequency components in k-space.
  • the x and y spatial information is encoded into the magnetization phase by the phase encoding gradient magnetic fields 76 and 77.
  • a refocus pulse 72 is applied together with a gradient magnetic field Gz73 for selecting a slice, and an echo 78 is generated after a lapse of TE time from the excitation. Eko which occurred in this way One is received as a signal.
  • Phase encoding (k X, ky) echo signals Oyopi three-dimensional Fourier transform as a function of time t, obtaining scan Bae transfected loss COPIC image (metabolite distribution picture image). It is desirable that the MRSI method be a spin echo type as shown in the figure. Generally, when the frequency of the excitation pulse deviates from the resonance frequency, the shape of the region to be excited and the phase of the transverse magnetization are affected by this offset, but in the spin echo type, this offset is caused by the refocusing 180 ° pulse 72. Can offset the effects of
  • the reconstructed metabolite distribution image may be displayed as it is on the CRT display.
  • the spatial distribution is corrected by multiplying by an inverse function of the excitation shape function! (X, y).
  • the spatial change of the excitation flip angle can be corrected, so that a quantitative metabolite distribution image can be obtained.
  • the MRSI of the present invention does not require the 0VS process for fat suppression, so that the 3D-CSI having a double phase encoding loop can be reduced to the same measurement time as when no suppression process is included. In addition, fat suppression can be effectively performed.
  • FIG. 5 is a diagram showing another embodiment of the 3D-CSI method according to the present invention.
  • This imaging sequence differs from the imaging sequence of FIG. 3 in that water suppression is also used. That is, the water spectrum is excited by the well-known CHESS pulse 81 in each cycle of the phase encoding, and the crash gradient magnetic field 82 is applied to dephase the magnetization of the water.
  • the CHESS pulse 81 has a Sine function, a Gaussian function, and the like, which are appropriately selected and used in consideration of the shape of the excitation spectrum and the application time.
  • the measurement following the application of the crusher gradient magnetic field 82 is the same as the imaging sequence in FIG. That is, the RF modulation waveform is calculated based on R0I set interactively on the scout image in advance, saved in memory, and the RF modulated with this modulation waveform is mixed with the gradient magnetic field oscillating in the x and y directions. Then, a preset R0I is selectively excited, and after phase encoding, a refocus pulse 72 is applied to generate an echo 78.
  • a 3D spectroscopic image can be obtained by changing the slice position and measuring. it can. In this case, if R0I shifts depending on the slice position, R0I can be moved in parallel from the reference position by applying phase modulation to the RF waveform Bl (t).
  • phase modulation as shown in equation (3) may be applied to RF.
  • Equation (3) G (s) is the gradient magnetic field vector, and T is the application time of Bl (t).
  • the phase-modulated RF pulse waveform can be calculated by equation (3).
  • the gradient magnetic field waveform G (s) is determined in advance.
  • R0I61 is interactively specified on the image, and then the smallest rectangular area 62 covering R0I is automatically generated (step 16).
  • This measurement is performed in the phase encode step (kx, ky) corresponding to this image matrix size.
  • the phase encoding step is usually 16 ⁇ 16 or 32 ⁇ 32, and the field of view is square as shown by 63 in FIG.
  • the image matrix is set according to the minimum rectangular area 62 covering R0I, it is not necessary to measure the external pixels where the magnetization is not excited, and the number of times of the phase loop is reduced. it can.
  • the direction of the coordinate axis of the image measurement matrix may be rotated according to the direction of the rectangle at the inclination of R0I61. This Since the region can be set along the ROI shape, the number of repetition steps can be minimized. The rest is the same as the embodiment shown in FIG.
  • FIG. 7 shows an example of the imaging sequence of 3D MRSI.
  • This imaging sequence includes water suppression (application of a CHESS pulse 81 and a crusher gradient magnetic field 82) as in the sequence of FIG. 5, and further includes a phase encoding loop 91 in the slice direction.
  • the gradient magnetic field in the slice direction applied simultaneously with the refocus pulse 72 is a slab selection gradient magnetic field, and can be omitted.
  • the spin echo type MRSI was explained, and the spin echo type was preferred in order to eliminate the influence of the offset from the resonance frequency.
  • the FID type was used for the measurement of short T2 substances. It can also be.
  • Figure 8 shows this example.
  • the phase encodes 76 and 77 are applied in a short time, and the FID is measured immediately.
  • MRSI based on spatially selective excitation has been described using the 3D-CSI method as an example, but spatially selective excitation can be performed using an MRSI sequence using another EPI, FSE, or the like.
  • a signal can be obtained by exciting unnecessary portions, such as fat, exactly along its shape and exciting only necessary portions.
  • a metabolite image from which the fat signal has been accurately removed can be obtained.
  • the preceding process can be shortened, and the recovery of water due to longitudinal relaxation can be reduced.
  • the MRSI can be executed immediately after setting the R0I.

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Abstract

Une partie de zone d'imagerie subit une excitation bidimensionnelle par application de champ magnétique à gradient d'oscillation dans deux ou trois directions axiales et de radiofréquence, afin de conduire un examen par IRM. En guise de prétraitement, on forme un topogramme (scout-view), puis une zone d'étude est établie de manière interactive sur l'image, une forme d'onde à modulation RF est automatiquement engendrée par transformation de Fourier bidimensionnelle de forme de zone d'étude, et enfin une matrice de mesure pour le plus petit carré couvrant la zone d'étude est automatiquement élaborée. L'examen par IRM se traduit par une modulation RF avec la forme d'onde à modulation RF issue de la phase de prétraitement, moyennant quoi on peut mesurer une matrice d'image issue de cette phase. Etant donné qu'il est possible d'éviter des parties superflues du type tissus graisseux, selon un contour épousant précisément la forme de tels tissus, et d'exciter ainsi uniquement les parties nécessaires, on peut obtenir une image de substance métabolique dont sont entièrement éliminés les signaux superflus. La mise en place interactive de la zone d'étude souhaitée sur la scout-view permet d'établir une zone d'étude dans des conditions simples. Il est possible de réduire le temps de mesure en établissant une matrice carrée de mesure.
PCT/JP2000/006711 1999-09-28 2000-09-28 Appareil de diagnostic a imagerie par resonance magnetique (irm) et procede correspondant WO2001022879A1 (fr)

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JP27528699A JP4416221B2 (ja) 1999-09-28 1999-09-28 磁気共鳴画像診断装置
JP11/275286 1999-09-28

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JP2006175223A (ja) * 2004-12-20 2006-07-06 General Electric Co <Ge> 並列ｒｆ送信による空間−スペクトル励起のための方法及びシステム
WO2008132686A1 (fr) * 2007-04-27 2008-11-06 Philips Intellectual Property & Standards Gmbh Quantification de paramètres caractéristiques de résonance magnétique
GB2460320A (en) * 2008-04-30 2009-12-02 Bruker Biospin Mri Gmbh MRI with magnetic fields for local spatial encoding
CN102342833A (zh) * 2010-08-02 2012-02-08 西门子公司 用于建立磁共振图像的方法和相应的磁共振设备
JP2014511727A (ja) * 2011-03-22 2014-05-19 ザ・ジョンズ・ホプキンス・ユニバーシティー 磁気共鳴スペクトロスコピーイメージングを行うシステムおよび方法
US9921284B2 (en) 2012-09-20 2018-03-20 Hitachi, Ltd. Magnetic resonance imaging apparatus and magnetic resonance imaging method, configured to adjust multi-dimensional selective excitation pulse

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JP4718817B2 (ja) * 2004-09-27 2011-07-06 株式会社東芝 磁気共鳴イメージング装置
JP4995650B2 (ja) * 2007-06-22 2012-08-08 株式会社日立メディコ 磁気共鳴イメージング装置
WO2010044299A1 (fr) * 2008-10-17 2010-04-22 株式会社 日立メディコ Dispositif d'imagerie par résonnance magnétique
US9035652B2 (en) 2009-11-12 2015-05-19 Hitachi Medical Corporation Magnetic resonance imaging apparatus and two-dimensional excitation adjustment method
DE102011004432A1 (de) * 2011-02-20 2012-08-23 Forschungszentrum Jülich GmbH Magnetresonanzverfahren und Kernspintomograph zur Durchführung des Magnetresonanzverfahrens
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Cited By (8)

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Publication number Priority date Publication date Assignee Title
JP2006175223A (ja) * 2004-12-20 2006-07-06 General Electric Co <Ge> 並列ｒｆ送信による空間−スペクトル励起のための方法及びシステム
WO2008132686A1 (fr) * 2007-04-27 2008-11-06 Philips Intellectual Property & Standards Gmbh Quantification de paramètres caractéristiques de résonance magnétique
GB2460320A (en) * 2008-04-30 2009-12-02 Bruker Biospin Mri Gmbh MRI with magnetic fields for local spatial encoding
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