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WO2008135878A1 - Dispositif et procédé de résonance magnétique à fréquences multiples - Google Patents

Dispositif et procédé de résonance magnétique à fréquences multiples Download PDF

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Publication number
WO2008135878A1
WO2008135878A1 PCT/IB2008/051571 IB2008051571W WO2008135878A1 WO 2008135878 A1 WO2008135878 A1 WO 2008135878A1 IB 2008051571 W IB2008051571 W IB 2008051571W WO 2008135878 A1 WO2008135878 A1 WO 2008135878A1
Authority
WO
WIPO (PCT)
Prior art keywords
pulses
excitation
resonance
spin system
signals
Prior art date
Legal status (The legal status 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 status listed.)
Ceased
Application number
PCT/IB2008/051571
Other languages
English (en)
Inventor
Muhammed Yildirim
Rudolf M. J. N. Lamerichs
Jochen Keupp
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Philips Intellectual Property and Standards GmbH
Koninklijke Philips NV
Original Assignee
Philips Intellectual Property and Standards GmbH
Koninklijke Philips Electronics NV
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 Philips Intellectual Property and Standards GmbH, Koninklijke Philips Electronics NV filed Critical Philips Intellectual Property and Standards GmbH
Publication of WO2008135878A1 publication Critical patent/WO2008135878A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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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
    • G01R33/483—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy
    • G01R33/485—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy based on chemical shift information [CSI] or spectroscopic imaging, e.g. to acquire the spatial distributions of metabolites
    • 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]
    • G01R33/446—Multifrequency selective RF pulses, e.g. multinuclear acquisition mode
    • 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
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
    • G01R33/3628—Tuning/matching of the transmit/receive coil
    • G01R33/3635—Multi-frequency operation

Definitions

  • the invention relates to a device for magnetic resonance imaging of a body placed in an examination volume.
  • the invention relates to a method for MR imaging and to a computer program for an MR device.
  • MRI magnetic resonance imaging
  • pulse sequences consisting of RF pulses and switched magnetic field gradients are applied to an object (a patient) placed in a homogeneous magnetic field within an examination volume of an MR device.
  • phase and frequency encoded magnetic resonance signals are generated, which are scanned by means of RF receiving antennas in order to obtain information from the object and to reconstruct images thereof. Since its initial development, the number of clinically relevant fields of application of MRI has grown enormously.
  • MRI can be applied to eveiy part of the body, and it can be used to obtain information about a number of important functions of the human body.
  • the pulse sequence which is applied during an MRI scan, plays a significant role in the determination of the characteristics of the reconstiiicted image, such as location and orientation in the object, dimensions, resolution, signal-to-noise ratio, contrast, sensitivity for movements, etcetera.
  • An operator of an MRI device has to choose the appropriate sequence and has to adjust and optimize its parameters for the respective application.
  • MID molecular imaging and diagnostics
  • This definition refers to the in-vivo measurement and characterization of cellular and molecular level processes in human subjects and to the analysis of biomolecules to screen, diagnose and monitor the human health status and to assess potential risks.
  • An important prerequisite for molecular imaging is the ability to image specific molecular targets.
  • 19 F MRI has a high potential in the field of MID and also in pharmaceutical research.
  • 19 F MRI allows the direct quantification of nano particles, which can be used as contrast agents in MID.
  • These nano particles contain 19 F based molecules, such as, e.g., PFOB (perfluoro-octyl bromide).
  • the particles are coated with a functionalized protective and stabilizing lipid layer.
  • the nano particles will bind to protein markers specific to a disease and accumulate at the sites within the body of the patient where the disease is progressing.
  • the accumulated nano particles will show up as bright spots in a corresponding 19 F MR image.
  • a precise determination of the position of the bright spots caused by the accumulated nano particles is required.
  • the excitation properties of a given RF pulse i.e. the excitation profile in terms of flip angle and the spectral bandwidth, is determined by the characteristics of the pulse, i.e. duration, shape, frequency, peak-to-peak power, and phase.
  • the excitation bandwidth of the RF pulse increases as the pulse duration decreases.
  • SAR specific absorption rate
  • an MR device for magnetic resonance imaging of a body placed in an examination volume which comprises means for establishing a substantially homogeneous main magnetic field in the examination volume, means for generating switched magnetic field gradients superimposed upon the main magnetic field, means for radiating RF pulses towards the body, control means for controlling the generation of the magnetic field gradients and the RF pulses, means for receiving and sampling magnetic resonance signals, and reconstruction means for forming MR images from the signal samples.
  • the invention proposes that the MR device is arranged to a) excite nuclear magnetization from a nuclear spin system having two or more resonance lines by subjecting at least a portion of the body to an MR imaging pulse sequence comprising RF pulses, the RF pulses being generated at two or more different carrier frequencies corresponding to the resonance frequencies of said nuclear spin system; b) acquire MR signals from the body; and c) reconstruct an MR image from the acquired MR signals.
  • the MR device of the invention provides a solution to the above-described problems associated with broadband excitation.
  • the technique of the invention can be described as "multi-offset excitation", meaning that RF excitation pulses having different carrier frequencies are irradiated in order to excite the spin system.
  • the different carrier frequencies of the excitation RF pulses correspond to the frequencies of the resonance lines in the chemical shift spectrum of the examined nuclear spin system. In this way, each individual spectral component can be excited on-resonance and narrow-band. Since the RF pulse components can be designed independently, the resulting excitation profile can be tailored to precisely match the spectiiim. This is particularly valuable in the case of imaging probes which show a fixed and a priori known chemical shift spectiiim.
  • the total MR signal obtained is increased in accordance with the invention as compared to conventional techniques that employ only a single earner frequency. This is because the nuclear spins associated with a particular resonance line in the spectiiim will attain precisely the desired flip angle. Hence, an optimized image sensitivity is achieved according to the invention. Furthermore, the required duration of the individual RF excitation pulse components is determined by the widths of the individual resonance lines (or the width of closely lying groups of resonance lines) in accordance with the invention and not - as in the conventional single- frequency excitation techniques - by the width of the whole spectrum. Thus, the invention keeps the necessary RF pulse amplitude Bj and the SAR well within tolerable and allowable limits.
  • the two or more RF excitation pulses having different carrier frequencies are irradiated simultaneously.
  • the RF excitation pulse is a composite pulse resulting from a superposition of the different frequency components.
  • the resulting RF pulse can be generated, e.g., as a combined waveform irradiated over a standard RF transmission channel which is available by default in conventional MR scanners. This can be achieved by employing an appropriate programmable RF waveform generating means in the device of the invention.
  • the different components of the composite RF excitation pulse may have different excitation bandwidths.
  • the different components may have, e.g., envelopes of Gaussian shapes with different pulse durations.
  • the excitation bandwidths of the RF excitation pulses should practicably correspond to the widths of the different resonance lines or the width of closely lying groups of resonance lines of the examined nuclear spin system.
  • the resulting different durations of the RF pulse components determine the waveform of the resulting composite excitation RF pulse.
  • the total RF excitation pulse duration is determined by the pulse component with the narrowest excitation bandwidth.
  • the device of the invention may further be arranged to generate RF excitation pulses at carrier frequencies corresponding to two or more selectable spectral lines of the examined nuclear spin system. In this way, specific resonance lines can be excited selectively or excluded arbitrarily from excitation and thereby from contributing to the final image. It is an advantage of this embodiment of the invention that individual resonance lines of the MR spectrum can be switched on and off in the acquired image at the discretion of the user of the MR device. This enables, e.g., a differentiation between different contrast agents which have characteristic resonance lines in their respective chemical shift spectra.
  • the MR device comprises two or more physically separate RF transmission channels and a corresponding number of independent RF coils for radiating the different RF excitation pulse components towards the examined body.
  • a set of indpendent RF coils instead of a single coil is used to transmit the individual frequency components of the RF pulses.
  • Each RF coil is used to transmit a single RF pulse component.
  • the RF pulses having different earner frequencies are superimposed in the same spatial region in the examination volume of the MR apparatus.
  • This embodiment does advantageously not require the application of composite RF excitation pulses according to the invention, which possibly require longer pulse durations and advanced RF waveform generating technology.
  • the invention not only relates to a device but also to a method for magnetic resonance imaging of at least a portion of a body placed in an examination volume of an MR device.
  • the method comprises the following steps: a) exciting nuclear magnetization from a nuclear spin system having two or more resonance lines by subjecting at least a portion of the body to an MR imaging pulse sequence comprising RF pulses, the RF pulses being generated at two or more different carrier frequencies corresponding to the resonance frequencies of said nuclear spin system b) acquiring MR signals from the body; c) reconstructing an MR image from the acquired MR signals.
  • a computer program adapted for carrying out the imaging procedure of the invention can advantageously be implemented on any common computer hardware, which is presently in clinical use for the control of magnetic resonance scanners.
  • the computer program can be provided on suitable data carriers, such as CD-ROM or diskette. Alternatively, it can also be downloaded by a user from an Internet server.
  • Fig. 1 shows an MR scanner according to the invention
  • Fig. 2 illustrates the generation of a composite RF excitation pulse according to the invention
  • Fig. 3 illustrates the waveform of a composite RF excitation pulse in accordance with the invention tailored for the excitation of the 19 F nuclear spins in PFOB.
  • a magnetic resonance imaging device 1 in accordance with the present invention is shown as a block diagram.
  • the apparatus 1 comprises a set of main magnetic coils 2 for generating a stationary and homogeneous main magnetic field, and three sets of gradient coils 3, 4 and 5 for superimposing additional magnetic fields with controllable strength and having a gradient in a selected direction.
  • the direction of the main magnetic field is labelled the z-direction, the two directions perpendicular thereto the x- and y-directions.
  • the gradient coils 3, 4, 5 are energized via a power supply 6.
  • the apparatus 1 further comprises an RF coil arrangement for generating RF fields in an examination volume 7.
  • the RF coil arrangement comprises six independent resonator elements 8, 9, 10, 1 1, 12, 13 which are arranged adjacent to each other on a cylindrical surface around the examination volume 7.
  • the resonator elements 8, 9, 10, 1 1, 12, 13 are used for emitting RF pulses to a body 14.
  • the resonator elements 8, 9, 10, 1 1, 12, 13 are used to generate RF excitation pulses at different carrier frequencies according to the invention.
  • coils 8 and 1 1 are used for a first carrier frequency
  • coils 9 and 12 are used for a second carrier frequency
  • coils 10 and 13 are used for a third earner frequency, wherein each carrier frequency corresponds to a resonance line in the spectiiim of the examined nuclear spin system (for example a molecular species containing several 19 F nuclei).
  • the coils 8, 9, 10, 1 1, 12, 13 are mutually decoupled (e.g. by appropriate decoupling means such as capacitors or inductances coupled between the respective resonator elements, not shown) in order to make sure that an RF signal irradiated via one of the coils is not absorbed by another coil.
  • Each of the six resonator elements 8, 9, 10, 1 1, 12, 13 is connected to an RF switching module 15. Via the switching module 15 the relevant resonator element 8, 9, 10, 1 1, 12, 13 is connected to either a signal transmission channel 16 associated with the respective resonator element or with a signal reception unit 17, that is, in dependence of the mode of operation of the device (either transmit mode or receive mode).
  • the MR device 1 has an individual transmission channel 16 (each including an RF oscillator, a power amplifier and a modulator for determining the duration of the RF irradiation) and a receiver unit 17 including a sensitive pre-amplifier, a demodulator and a digital sampling unit.
  • the transmission channels 16 and the power supply 6 for the gradient coils 3, 4 and 5 are controlled by a control system 18 to generate the MR imaging pulse sequence in accordance with the above-described invention.
  • the control system is usually a microcomputer with a memory and a program control.
  • the control system comprises a programming with a description of an imaging procedure wherein RF pulses are generated simultaneously at the first frequency via the resonator elements 8, 1 1, at the second frequency via the resonator elements 9,12, and at the third frequency via the resonator elements 10, 13.
  • the receiver unit 17 is coupled to a data processing unit 19, for example a computer, for transformation of the received magnetic resonance signals into an image. This image can be made visible, for example, on a visual display unit 20.
  • Fig. 2 illustrates the generation of a composite RF excitation pulse B 1 Ct).
  • RF pulse B 1 Ct) is a superposition of three oscillating components having different carrier frequencies fi, ft, and ft, wherein each of the oscillating signals is modulated by an individual envelope E 1 Ct), E 2 Ct), and E ⁇ Ct).
  • the envelopes E 1 Ct), E 2 Ct), and E ⁇ Ct) are of Gaussian shape and have different durations.
  • the excitation bandwidth of the RF pulse B 1 Ct) is different for each frequency component ft, f 2 , and ft.
  • the composite pulse B 1 Ct) can be generated in the way illustrated in Fig. 1, i.e. by irradiating RF signals oscillating at the frequencies fj, f 2 , and ft over separate transmission channels. It is also possible to generate the RF pulse B 1 Ct) directly and to radiate the signal to the body of the examined patient over a single transmission channel. In this case, an appropriate (programmable) RF waveform generating means would be required.
  • Fig. 3a shows the RF excitation pulse B 1 Ct) (in ⁇ T) more detailed.
  • the diagram shows the x- and y-components of the B 1 field as a function of time (in milliseconds).
  • the chemical shift spectrum of the examined nuclear spin system is shown in Fig. 3b together with excitation profile of the RF excitation pulse B 1 Ct) shown in Fig. 3a.
  • the spectiiim is determined by the resonance frequencies of 19 F nuclei contained in PFOB, which is the imaging probe in the depicted embodiment.
  • the spectrum of PFOB comprises five resonance lines at -25 ppm, -20 ppm, -15 ppm, 20 ppm and 40 ppm.
  • the RF pulse B 1 Ct) includes carrier frequencies ft at -20 ppm, ft at 20 ppm, and ft at 40 ppm.
  • the envelopes E 1 Ct), E 2 (t), and E*(t) are selected such the duration Of E 1 Ct) is 2 milliseconds resulting in a broader excitation bandwidth covering the resonance lines of PFOB at -25 ppm, -20 ppm, and -15 ppm, while the duration of E 1 Ct) and E 2 (t) is 5 milliseconds covering to the resonance lines at 20 ppm and 40 ppm, respectively.
  • the range of the PFOB chemical shift spectrum is 65 ppm.
  • the technique of the invention enables an RF excitation that is adaptive to the MR spectiiim and is thus applicable to any contrast agent with sufficiently resolvable resonance lines.
  • a uniform excitation of the whole spectiiim is achieved.
  • the image sensitivity is maximum because all spectral components contribute to the acquired MR signal.
  • No broadband RF pulses are required such that the SAR can be kept acceptably low.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)

Abstract

L'invention concerne un dispositif pour l'imagerie par résonance magnétique d'un corps (14) placé dans un volume d'examen. Selon l'invention, le dispositif (1) est conçu a) pour exciter une magnétisation nucléaire à partir d'un système de spin nucléaire ayant au moins deux lignes de résonance en soumettant au moins une partie du corps (14) à une séquence d'impulsions d'imagerie par résonance magnétique comportant des impulsions RF, les impulsions RF étant générées à au moins deux fréquences de porteuse différentes (f1, f2, f3) correspondant aux fréquences de résonance dudit système de spin nucléaire; b) pour acquérir des signaux de résonance magnétique provenant du corps (14); c) pour reconstruire une image par résonance magnétique à partir des signaux de résonance magnétique acquis.
PCT/IB2008/051571 2007-05-03 2008-04-24 Dispositif et procédé de résonance magnétique à fréquences multiples Ceased WO2008135878A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP07107442 2007-05-03
EP07107442.1 2007-05-03

Publications (1)

Publication Number Publication Date
WO2008135878A1 true WO2008135878A1 (fr) 2008-11-13

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Country Status (1)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102012205294B3 (de) * 2012-03-30 2013-06-27 Siemens Aktiengesellschaft Verfahren und Steuereinrichtung zur Ansteuerung eines Magnetresonanzsystems
DE102014213722A1 (de) * 2014-07-15 2016-01-21 Siemens Aktiengesellschaft Segmentiertes MR
JP2017200559A (ja) * 2016-05-02 2017-11-09 キル メディカル センター 磁気共鳴映像システム

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Publication number Priority date Publication date Assignee Title
US5446384A (en) * 1993-12-27 1995-08-29 General Electric Company Simultaneous imaging of multiple spectroscopic components with magnetic resonance
EP1416291A2 (fr) * 2002-10-30 2004-05-06 Analogic Corporation Système d'examen par résonance quadrupolaire à bande ultra-large utilisant des bobines r.f. découplées
WO2005111645A2 (fr) * 2004-05-07 2005-11-24 Regents Of The University Of Minnesota Elements a courant multiple pour bobines radiofrequences pour resonance magnetique

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5446384A (en) * 1993-12-27 1995-08-29 General Electric Company Simultaneous imaging of multiple spectroscopic components with magnetic resonance
EP1416291A2 (fr) * 2002-10-30 2004-05-06 Analogic Corporation Système d'examen par résonance quadrupolaire à bande ultra-large utilisant des bobines r.f. découplées
WO2005111645A2 (fr) * 2004-05-07 2005-11-24 Regents Of The University Of Minnesota Elements a courant multiple pour bobines radiofrequences pour resonance magnetique

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Title
B.L.TOMLINSON ET AL.: "Fourier synthesized excitation of nuclear magnetic resonance with application to homonuclear decoupling and solvent line suppression", THE JOURNAL OF CHEMICAL PHYSICS, 1973, pages 1775 - 1784, XP009105489 *
BORNERT P ET AL: "CHEMICAL-SHIFT-SENSITIVE NMR IMAGING USING SPECTRUM SIMPLIFICATION BY TAILORED EXCITATION", JOURNAL OF MAGNETIC RESONANCE, ACADEMIC PRESS, ORLANDO, FL, US, vol. 81, no. 1, 1 January 1989 (1989-01-01), pages 167 - 172, XP000006755, ISSN: 1090-7807 *
CARUTHERS SHELTON D ET AL: "In vitro demonstration using F-19 magnetic resonance to augment molecular imaging with paramagnetic perfluorocarbon nanoparticles at 1.5 Tesla", INVESTIGATIVE RADIOLOGY,, vol. 41, no. 3, 1 March 2006 (2006-03-01), pages 305 - 312, XP009104335, ISSN: 0020-9996 *
J.KEUPP ET AL.: "SSFP-based spectral editing for imaging of 19F contrast agents", PROC.INTL.SOC.MAG.RESON.MED. 14, 2006, pages 916, XP002495161 *
KEUPP J ET AL: "Efficient 19F Imaging of Multi-Spectral-Line Contrast Agents: Aliasing serves to minimize time encoding", PROCEEDINGS OF THE ISMRM, 14TH SCIENTIFIC MEETING, SEATTLE, WASHINGTON, USA, 6 May 2006 (2006-05-06), pages 913, XP002491689 *
KUPCE E ET AL: "TEMPLATE EXCITATION IN HIGH-RESOLUTION NMR", JOURNAL OF MAGNETIC RESONANCE. SERIES A, ACADEMIC PRESS, ORLANDO, FL, US, vol. 106, no. 1, 1 January 1994 (1994-01-01), pages 135 - 139, XP000423518, ISSN: 1064-1858 *
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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102012205294B3 (de) * 2012-03-30 2013-06-27 Siemens Aktiengesellschaft Verfahren und Steuereinrichtung zur Ansteuerung eines Magnetresonanzsystems
CN103364744A (zh) * 2012-03-30 2013-10-23 西门子公司 用于控制磁共振系统的方法和控制装置
US9366739B2 (en) 2012-03-30 2016-06-14 Siemens Aktiengesellschaft Activating a magnetic resonance system
CN103364744B (zh) * 2012-03-30 2016-09-28 西门子公司 用于控制磁共振系统的方法和控制装置
DE102014213722A1 (de) * 2014-07-15 2016-01-21 Siemens Aktiengesellschaft Segmentiertes MR
DE102014213722B4 (de) * 2014-07-15 2016-05-25 Siemens Aktiengesellschaft Segmentiertes MR
JP2017200559A (ja) * 2016-05-02 2017-11-09 キル メディカル センター 磁気共鳴映像システム

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