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WO2004099809A1 - Procede d'imagerie par resonance magnetique - Google Patents

Procede d'imagerie par resonance magnetique Download PDF

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Publication number
WO2004099809A1
WO2004099809A1 PCT/EP2004/004989 EP2004004989W WO2004099809A1 WO 2004099809 A1 WO2004099809 A1 WO 2004099809A1 EP 2004004989 W EP2004004989 W EP 2004004989W WO 2004099809 A1 WO2004099809 A1 WO 2004099809A1
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WO
WIPO (PCT)
Prior art keywords
echo signals
phase
echo
space
image
Prior art date
Application number
PCT/EP2004/004989
Other languages
English (en)
Inventor
Ke Cheng Liu
Original Assignee
Siemens Aktiengesellschaft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens Aktiengesellschaft filed Critical Siemens Aktiengesellschaft
Publication of WO2004099809A1 publication Critical patent/WO2004099809A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
    • G01R33/5615—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]

Definitions

  • the present invention relates to a method of magnetic resonance imaging and particularly, to a method of magnetic resonance imaging capable of reducing artifacts and improving the quality of image.
  • US 6,037,771 disclosed a method of magnetic resonance ima- ging, when a three dimensional volume of interest, such as a human tissue, is subjected to a static magnetic field B0 of a magnetic resonance system, the spin magnetic moment will attempt to align with the magnetic field B0. If an external magnetic field Bl is applied to the tissue, the spin moments will precess at the Larmor frequency. When the three dimensional volume is further applied with a radio frequency excitation magnetic field Bl, the magnetic moment Mz originally arranged along B0 may be rotated into the X-Y plane to become a transverse magnetic moment Mt . After the excitation magnetic field Bl is terminated, the excited spin emits a signal which is acquired and processed to form image.
  • magnetic field gradients (Gx, Gy, Gz) are applied on said three dimensional volume, i.e., a read out gra- transducer Gx, a second phase-encoding gradient Gy and a first phase-encoding gradient Gz .
  • a sequence of scanning cycles are preformed in the area to be imaged, in such cycles, said gradients are varied with a particular locating method, to determine the spatial position of the signal .
  • An echo signal is constructed by said result of scanning together with the signal emitted by said excited spins, the echo signals are acquired and digitized, and applied a k-space Fourier transform by a computer, to reconstruct the image.
  • the k-space is also called a frequency space
  • the axes of the original data matrix are called Kx and Ky, respectively, said matrix is divided into four quadrants, and the plane formed by said two axes is call a k-space.
  • TR repetition time
  • the other one is the so-called fast echo acquisition method, as shown in Fig. 1, a number of echo signals are acquired continuously after each of the excitations applied on the three dimensional volume in the static magnetic field B0, ho- wever, only four of those echo signals (1, 2, 3 and 4) are illustrated in the figure 1.
  • the intensities of the signals are gradually attenuating.
  • those echoes are consistent in phase theoretically, however, practically, phase discrepancies exist between those echoes due to the imperfec- tion of the magnetic resonance system, and the phase discrepancies between the echo signals are increasing, as shown in Fig.2.
  • the motion of the substance to be imaged during the signal acquisition procedure may also cause said phase discrepancy.
  • the first echo signal is placed at the centre of the k-space during amplitude modula- tion, and the three subsequent echoes are placed symmetrically on both sides of said first echo, respectively, the amplitudes of the echo signals 1, 2, 3 and 4 are indicated with 11, 21, 31 and 41, respectively.
  • the first echo signal is placed at the centre of the k-space in phase modulation, the three subsequent echoes are placed symmetrically on both sides of said first echo, respectively, the phase differences of the echo signals 1, 2, 3 and 4 are indicated with 12, 22, 32 and 42, respectively.
  • Those signals are then processed using one or several known techniques including the Fourier transform in k-space, to reconstruct the image.
  • this approach has the advantage of fast imaging, however, artifacts exist in the magnetic resonance image which cause the worse quality of the image, because the magnetic resonance imaging system is impossible to be perfect due to the existence of eddy current in the pole plates and the gradient coils.
  • the so called artifact is a criterion for the quality of the image, which indicates the signal intensity of the portion of the magnetic resonance image which do not cor- respond to the spatial distribution of the tissue in the image plane.
  • a method of magnetic resonance imaging which acquires resonance data from a interesting three-dimensioned volume to form image, includes steps of: (1) sending a radio frequency excitation impulse to a selection slice and putting a transverse magnetic field on the slice of the three-dimensioned volume above; (2) generating a first phase-encoding gradient impulse which samples k-space along a first axis traversing the above slice; generating a second phase-encoding gradient impulse which samples k-space along a second axis in the above slice plane; (4) receiving an echo signal and a read out gradient which samples k-space along a third axis vertical to the above second axis in the above slice plane; repeating the steps (2), (3) and (4) to collect the echo signals above- mentioned to form an echo train; the present invention is characterized by: (6) modulating the phases of the respective echo signals in k-space so that the echo signals are arranged essentially in linear fashion according to
  • step (6) arranging the above echo signals in ascending order from small to large according to phase discrepancy, such arrangement also appears in stepped form, approximately in linear arrangement, without the use of the previously mentioned symmetric arrangement. Furthermore, the amplitudes of the above echo signals are modulated in k-space, in which the arrangement order of the echo signals is the same as their order of phase discrepancy.
  • the above echo signals can also be arranged in descending order from large to small according to phase discrepancy. This arrangement also appears in stepped form, approximately in linear arrangement. Similarly, the amplitudes of the above signals are modulated in k-space, in which the arrangement order of the echo signals is the same as their order of phase discrepancy.
  • Fig. 1 shows the case of fast acquiring several echoes after an excitation in the prior art, the intensity of each of the echo signals is substantially successively decreasing;
  • Fig. 2 shows the phase difference value of each of the collected echo signals shown in Fig. 1, the phase differences of the subsequent echo signals being successively increasing;
  • Fig. 3 shows a method of modulating the echo signals in k- space according to the prior art, a typical symmetric arrangement being formed after the modulation;
  • Fig. 4 shows a symmetric arrangement formed after the phase modulation of the echo signals according to the method of Fig. 3;
  • Fig. 5 shows a sequence of echo signals re-arranged in k- space according to an embodiment of the method of the present invention, each of the echo signals being substantially linearly arranged according to the order of their phase differences from small to large;
  • Fig. 6 shows the echo signals of the embodiment in Fig. 5 ha- ving also amplitude modulated correspondingly
  • Fig. 7 shows an image A obtained in the symmetric arrangement mode of the echoes of the prior art , and an image B obtained after linearly arranging the echoes according to their phase differences of the present invention, the artifact in image B is significantly reduced, and the quality of image is enhanced.
  • a three dimensional volume of interest is placed in a static magnetic field B0 of a magnetic resonance imaging system, and a radio frequency excitation magnetic field is further applied to the volume. Af- ter the radio frequency excitation magnetic field is terminated, the excited spin emits magnetic resonance signal to produce phase encoding gradients in three mutually vertical directions, respectively.
  • the magnetic resonance signals are encoded, those echo signal are then acquired and Fourier transform is performed on said echo signal in k-space, to thereby obtain an image.
  • the specific steps are: (1) sending a radio frequency excitation impulse to a selection slice to apply a transverse magnetic field on the slice of said three dimensional volume; (2) generating a first phase-encoding gradient impulse which samples k-space along a first axis transverse to said slice; (3) generating a second phase- encoding gradient impulse which samples k-space along a second in said slice plane; (4) acquiring an echo signal and then acquiring a read out gradient which samples k-space along a third axis perpendicular to said second axis in said slice plane; (5) repeating said steps (2), (3) and (4) to repeatedly acquire sequence of said echo signals to form an echo train.
  • the above mentioned technique pertains to the well known technique of multiple echo acquisition, which is not to be explained here for simplicity.
  • the improvement of the method of the present invention is that a sequence of echo signals are rearranged in k-space.
  • the respective echo signals are modulated in k-space, such that said respective echo signals are arranged essentially in linear fashion ac- cording to phase difference values from small to large.
  • each of the echoes has a certain phase discrepancy, the phase discrepancy 12 of the first echo signal 1 is the smallest one, the phase discrepancy 22 of the second echo signal 2 is slightly larger, the phase discrepancy 32 of the third echo signal 3 is much larger, and the pha- se discrepancy 42 of the fourth echo signal 4 is the largest, it will be a rule that the later the echo signal is acquired the larger the phase discrepancy will be.
  • the sequence of the echo signals in k-space can be altered only by altering the software in accordance with the invention.
  • the echo signals are rearranged according to sequence of their phase discrepancy, from small to large, such that the sequen- ce of the phase discrepancy of the echoes is approximately linearly arranged.
  • the echo signal 1 is arranged in the leftmost for its smallest phase discrepancy 12
  • the second echo signal 2 is arranged in the second position to the left for its slightly larger phase discrepancy 22
  • the third echo signal 3 is arranged in the third position to the left for its much larger phase discrepancy 32
  • the fourth echo signal 4 is positioned in the rightmost end for its largest phase discrepancy 42.
  • the phase shift of each of the echo signals is arranged in a stepped increasing manner, which is approximately in linear relationship as shown by the dotted line in the figure 5.
  • Fig. 6 shows the amplitude modulation of these echo signals, it can be seen that the sequence of arrangement of each of the echoes is the same as that shown in Fig, 5. From left to right, the amplitude 11 of the echo signal 1 is arranged in the leftmost, the amplitude 21 of the second echo signal 2 is arranged in the second to the left, the amplitude 31 of the echo signal 3 is arranged in the third to the left, and the amplitude 41 of the fourth echo signal 4 is arranged at the right end. Then an image is reconstructed from those echo signals using Fourier transform.
  • the excessive phase discrepancy among the echo signals is an important factor that causes the occurrence of artifacts in a magnetic resonance image. It has been known that those phase discrepancies are caused by the imperfection of the system, eddy current or the like, therefore, the prior modifications were made, aiming at those problems.
  • the present invention has been made based on this important discovery.
  • each of the echo signals is rearranged in descending sequence according to the phase difference value thereof, from large to small.
  • the phase shift of each of the echo signals is arranged in a stepped descending order, similarly, the phase of each of the echo signals can be arranged in approximately linear relationship according to phase discrepan- cy.
  • the sequence of arrangement of each of the echo signals is varied correspondingly.
  • Fig. 7 shows an image A obtained in symmetric phase arrangement of the echoes and an image B obtained in linear arrange- ment of the phase discrepancy of the echoes according to the present invention.
  • the significant effects of improvement on the quality of the magnetic resonance image can be seen clearly by comparison.
  • the image A is obtained by the prior art and severe artifacts exist in the image. While the arti- facts in image B are significantly reduced, especially the edges near the boundary of the image are much clearer, the quality of the image is greatly improved.
  • the artifacts can be reduced and the quality of the image can still be improved only by modifying the software of the system, thus the cost of the technical solution of the present invention is relatively low, and an improved magnetic reso- nance system can be marketed in a short time.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)

Abstract

La présente invention concerne un procédé d'imagerie par résonance magnétique. Ce procédé implique plusieurs opérations. On envoie sur une tranche de sélection une impulsion d'excitation haute fréquence, et on applique à une tranche formant un volume tridimensionnel situé au-dessus un champ magnétique transversal. On produit une première impulsion à gradient en codage de phase et une seconde impulsion à gradient en codage de phase qui échantillonnent chacune l'espace k. On reçoit un signal d'écho et un gradient de lecture des mesures, recevant de façon répétée les signaux d'écho de façon à former un train d'échos. On module les phases des signaux d'écho dans l'espace k de façon que ces signaux d'écho soient sensiblement agencés de façon linéaire par rapport au déphasage. Il ne reste plus qu'à reconstruire l'image au moyen d'une transformée de Fourier. L'invention permet ainsi de réduire les artéfacts de l'imagerie par résonance magnétique et d'améliorer la qualité de l'image.
PCT/EP2004/004989 2003-05-09 2004-05-10 Procede d'imagerie par resonance magnetique WO2004099809A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CN03123507.7 2003-05-09
CNB031235077A CN100366218C (zh) 2003-05-09 2003-05-09 磁共振成像方法

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WO2004099809A1 true WO2004099809A1 (fr) 2004-11-18

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10048346B2 (en) 2014-02-10 2018-08-14 Siemens Aktiengesellschaft Method and device for controlling a magnetic resonance imaging system
US10368778B2 (en) 2016-04-07 2019-08-06 Shanghai United Imaging Healthcare Co., Ltd. System and method for fast imaging in magnetic resonance imaging

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100145185A1 (en) * 2008-12-04 2010-06-10 Xiaole Hong Extending the resolution of mri data by combining subsets from plural image acquisitions
JP6719902B2 (ja) * 2012-12-18 2020-07-08 コーニンクレッカ フィリップス エヌ ヴェＫｏｎｉｎｋｌｉｊｋｅ Ｐｈｉｌｉｐｓ Ｎ．Ｖ． 分極磁場のファントムベースのｍｒ磁場マッピング
EP2924457B1 (fr) * 2014-03-28 2016-11-02 Albert-Ludwigs-Universität Freiburg IRM "Half Fourier" avec reconstruction iterative
CN112716476B (zh) * 2019-10-28 2024-07-02 通用电气精准医疗有限责任公司 磁共振成像方法及系统、计算机可读存储介质

Citations (2)

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EP0490528A1 (fr) * 1990-12-11 1992-06-17 General Electric Company Correction de résultats de mesure dans le domaine de la résonance magnétique nucléaire acquis par une technique du type echo-planar
EP0572074A1 (fr) * 1992-05-27 1993-12-01 Koninklijke Philips Electronics N.V. Procédé et appareil d'imagerie par résonance magnétique

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CA2187964C (fr) * 1996-10-16 2005-02-01 Kecheng Liu Saisie de multiplicites de couches minces glissantes chevauchees et entrelacees pour l'imagerie a resonance magnetique

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EP0490528A1 (fr) * 1990-12-11 1992-06-17 General Electric Company Correction de résultats de mesure dans le domaine de la résonance magnétique nucléaire acquis par une technique du type echo-planar
EP0572074A1 (fr) * 1992-05-27 1993-12-01 Koninklijke Philips Electronics N.V. Procédé et appareil d'imagerie par résonance magnétique

Non-Patent Citations (3)

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Title
HARVERY P R ET AL: "ECHO-VOLUMAR IMAGING (EVI) AT 0.5 T: FIRST WHOLE-BODY VOLUNTEER STUDIES", MAGNETIC RESONANCE IN MEDICINE, ACADEMIC PRESS, DULUTH, MN, US, vol. 35, no. 1, 1996, pages 80 - 88, XP000580459, ISSN: 0740-3194 *
HENNING J ET AL: "RARE IMAGING: A FAST IMAGING METHOD FOR CLINICAL MR", MAGNETIC RESONANCE IN MEDICINE, ACADEMIC PRESS, DULUTH, MN, US, vol. 3, 1986, pages 823 - 833, XP000885375, ISSN: 0740-3194 *
MULKERN R V ET AL: "Phase-encode order and its effect on contrast and artifact in single-shot RARE sequences", MEDICAL PHYSICS, SEPT.-OCT. 1991, USA, vol. 18, no. 5, pages 1032 - 1037, XP002293011, ISSN: 0094-2405 *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10048346B2 (en) 2014-02-10 2018-08-14 Siemens Aktiengesellschaft Method and device for controlling a magnetic resonance imaging system
US10368778B2 (en) 2016-04-07 2019-08-06 Shanghai United Imaging Healthcare Co., Ltd. System and method for fast imaging in magnetic resonance imaging
US10874326B2 (en) 2016-04-07 2020-12-29 Shanghai United Imaging Healthcare Co., Ltd. System and method for fast imaging in magnetic resonance imaging

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Publication number Publication date
CN100366218C (zh) 2008-02-06
CN1548007A (zh) 2004-11-24

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