WO2012138902A1 - Modulation à base b0 d'excitation b1 dans une irm - Google Patents

Modulation à base b0 d'excitation b1 dans une irm Download PDF

Info

Publication number
WO2012138902A1
WO2012138902A1 PCT/US2012/032387 US2012032387W WO2012138902A1 WO 2012138902 A1 WO2012138902 A1 WO 2012138902A1 US 2012032387 W US2012032387 W US 2012032387W WO 2012138902 A1 WO2012138902 A1 WO 2012138902A1
Authority
WO
WIPO (PCT)
Prior art keywords
radio frequency
magnetic field
static
flip angle
axis
Prior art date
Application number
PCT/US2012/032387
Other languages
English (en)
Inventor
Jozef H. Duyn
Original Assignee
The United States Of America As Represented By The Secretary, Department Of Health & Human Services
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 The United States Of America As Represented By The Secretary, Department Of Health & Human Services filed Critical The United States Of America As Represented By The Secretary, Department Of Health & Human Services
Publication of WO2012138902A1 publication Critical patent/WO2012138902A1/fr

Links

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
    • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/5659—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field
    • 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
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/387—Compensation of inhomogeneities
    • G01R33/3875—Compensation of inhomogeneities using correction coil assemblies, e.g. active shimming
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/56563—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0

Definitions

  • Magnetic resonance imaging is an often used research and diagnostic tool.
  • MRI typically involves exposing an object to be imaged to a static magnetic field (B 0 field) that aligns the nuclear spins of hydrogen atoms within the object.
  • B 0 field static magnetic field
  • RF field radio frequency
  • Bi field radio frequency transverse to the Bo field, at a resonance frequency known as the "Larmor frequency” that flips the nuclear spins by a predetermined angle.
  • RF radio frequency
  • MRI systems and apparatuses that operate in the range of 1.5-3.0 T have generally been used in some hospitals and research institutes to acquire images.
  • MRI systems and apparatuses operating with an ultra-high B 0 field of around 7.0T have been used.
  • imperfections in the Bi field can lead to undesired spatial variations in the signal to noise ratio (SNR) and contrast of the acquired image.
  • SNR signal to noise ratio
  • the variations become increasingly apparent at higher Bo field strengths, where the wavelength of the Bi field are shortened, thus leading to increased spatial variations in the amplitude and phase of the Bi field.
  • the Bi field imperfections are significant when imaging most of the human body using a B 0 field of around 3T and when imaging the human head with a Bo field of around 7T. At these levels for the Bo fields, the wavelengths of the RF pulses within the Bi fields approach and/or become smaller than the dimensions of the imaging target.
  • a common response to the Bo field inhomogeneity issue described above includes the use of adiabatic excitation pulses that have reduced sensitivity of the excitation flip angle to Bi inhomogeneity.
  • adiabatic excitation pulses typically require a high level of RF radiation that may expose the subject to unacceptable levels of associated tissue heating.
  • limiting or reducing the power of the B field may still produce images with artifacts and/or reduced tissue contrast and resolution.
  • the inhomogeneity of the B 0 further reduces the ability to generate high-contrast and artifact- free images.
  • An alternative approach to overcome flip angle variations due to Bi field inhomogeneity is to design RF pulses that have a spatial selectivity to compensate for the Bi field imperfections. This can be accomplished only by manipulating the B 0 field with gradient coils or shim coils and applying a spectrally- selective (i.e. Bo-selective) RF pulse. In this approach, the precise shape of the Bo field is dictated by both the Bo field manipulation and the desired flip angle correction.
  • a system for correcting inhomogeneity of a B 0 field.
  • the system includes a first coil to generate a B 0 field along a first axis during an MRI process.
  • a second coil generates a radio frequency field along a second axis that is transverse to the first axis.
  • the system further includes a plurality of shim coils, each configured to generate an auxiliary B 0 field having a particular strength, that are used to correct inhomogeneity of the Bo field.
  • the system further includes a database comprising static magnetization map data, the static magnetization map data corresponding to static magnetization (i.e., Bo field) measurements during the application of a predefined current to each of the individual shim coils.
  • the system further includes a processor to determine a desired B 0 field distribution required to generate a uniform, pre-defined effective flip angle of the at least two radio frequency pulses based on the radio frequency field map data and a duration, a shape, and an amplitude of the at least two radio frequency pulses.
  • the processor determines the combination of static magnetic fields of the individual shim coils that optimally match the desired field distribution for the particular object.
  • the processor calculates the fields that optimize the flip angle uniformity over the object.
  • the processor also calculates a corresponding auxiliary magnetic field strength for each of the plurality of shims to correct the inhomogeneity in the B 0 field and determines a corresponding current level to apply to each of the a plurality of shim coils to achieve the corresponding auxiliary magnetic field strength.
  • the system also includes a control system to supply the corresponding current level to each of the plurality of shim coils.
  • FIG. 1 depicts an exemplary MRI system for correcting inhomogeneity of a static magnetic field.
  • Figs. 2A-B depict Bi field shimming pulse sequences according to an embodiment of the present disclosure.
  • Fig. 3 A depicts the relationship between the effective flip angle and phase distribution according to an embodiment of the present disclosure.
  • Fig. 3B depicts the optimization of the effective flip angle (FA) at different combinations of pulse phases and individual flip angles according to an embodiment of the present disclosure.
  • Fig. 4 is a flowchart depicting an exemplary embodiment of B 0 -based modulation, according to one embodiment of the present disclosure.
  • Fig. 5 depicts the application of shims x, z 2 and x 2 -y 2 during the image acquisition of an oil phantom, according to one embodiment of the present disclosure.
  • RF pulses can be designed to be spatial selective in multiple spatial dimensions such that the pulses have an in- plane spatial selectivity that compensates for the inhomogeneities of the field. While the use of a spatially selective pulse provides flip angle uniformity, it also requires a prohibitively lengthy pulse duration that may result in significant sensitivity to off-resonance effects.
  • the present disclosure relates to a system and method to shorten the required duration of a multidimensional selective RF pulse by the use of static magnetic field (Bo field) shim coils. In particular, the system uses both linear and non-linear spatial variations in the Bo field to correcting inhomogeneity of a B 0 field .
  • FIG. 1 depicts an exemplary MRI system 100 for correcting inhomogeneity of a Bo field.
  • the MRI system 100 includes, for example, a MRI scanner device ("MRI device") 102 that enables the visualization of organs, organ function, and/or other tissue within a body of a subject, such as a patient.
  • the MRI device 102 includes a primary magnet or coil 104 that generates a uniform magnetic field that is applied across the body of the subject under observation.
  • a body or RF coil 106 of the MRI device 102 emits a RF pulse signal.
  • the RF pulse signal causes the nuclei within the body of the subject to transition their spin orientation, or precess.
  • the frequency of the energy at which this transition occurs is known as the Larmor Frequency.
  • the hydrogen nuclei hydrogen atoms transition back to a lower energy state and reemits the electromagnetic energy at the RF wavelength.
  • the MRI system 100 also includes gradient coils or magnets 107 that allow the magnetic field Bo to be altered very precisely.
  • the gradient magnetic fields generated by the gradient magnets allow image "slices" of the body to be created. By altering the gradient magnetic fields, the magnetic field can be specifically encoded on a selected part of the body.
  • multiple shim coils 108 each apply an auxiliary magnetic field having a particular strength.
  • the MRI system 100 further includes a control system 109 for controlling the auxiliary magnetic field strength of each shim coil 108.
  • the control system 109 includes a database 110 that stores static magnetization map data 112.
  • the static magnetization map data corresponds to static magnetization (i.e., Bo field) measurements that have been previously collected along a first axis during the application of at least one test pulse generated by the RF coil 106.
  • the B 0 field measurements may be obtained by measuring at least two gradient gradient echo signals generated in response to the test pulse.
  • the phase difference between the echo signals may be used to calculate the frequency of the gradient echo signals, which in turn may be used to determine the magnetic strength at various locations of the B 0 field.
  • other methods of determining the B 0 field strength to generate the static magnetization map data 112 may be used.
  • a measurement system 1 12 is used to collect Bi map data for a particular object.
  • the Bi map data corresponds to the amplitude of RF measurements taken along the second axis.
  • one or more test pulses may be generated along the second axis.
  • the test pulse and the acquired signal are used to determine the amplitude of the radio frequency field.
  • a single RF pulses is generated to acquire two or more measurements from which the amplitude of the Bi field may be determined. In other examples, other methods of determining the Bi field strength may be used.
  • the MRI system 100 includes a processor 114 that calculates an effective flip angle of the at least two radio frequency pulses based on the radio frequency field map data and a duration, a shape, and an amplitude of the at least two radio frequency pulses.
  • the processor 114 also calculates a radio frequency phase distribution for the particular object as a function of the determined effective flip angle.
  • the processor 114 further calculates a corresponding auxiliary magnetic field strength for each of the plurality of shims 108 to correct the inhomogeneity in the Bo field based on the radio frequency phase distribution and determines a corresponding current level to apply to each of the a plurality of shim coils to achieve the corresponding auxiliary magnetic field strength.
  • the control system 109 supplies the corresponding current level to each of the plurality of shim coils.
  • the pulse sequence 100 includes a dual pulse slice- selective RF excitation 202 having a slice-selecting gradient of the Bo field indicated generally by 204.
  • the dual RF pulses 202 excite the same slice (not shown) of the subject or object being imaged.
  • the spins of the hydrogen atoms of the selected slice experience a combined effective flip angle that is dependent on the individual flip angles CLi and a 2 , as well as the accumulated phase ( ⁇ ) 206 between the pulses.
  • the time between each pulse in the pulse sequence 202 is represented by ( ⁇ ) 208.
  • Figure IB depicts an alternate Bi field shimming pulse sequence 210 with reduced pulse spacing 202.
  • ⁇ 208 between the pulses is minimized by inverting the polarity of the slice-selection gradient 204 of the Bo field.
  • an in-slice position-dependent phase accumulation is indicated by the trapezoidal shim pulse (S) 212 in the B 0 field.
  • the shim pulse 212 represents a temporary spatially-dependent frequency- shift produced by a combination of the transmitter frequency shift ⁇ , ⁇ -, y-, and z- gradients of x-, y-, and z-, and other higher order shims.
  • the shim pulse 212 is produced during the time ( ⁇ ) 208 between each pulse in the pulse sequences 200 and 210.
  • the effective flip angle (FA) induced by the pulse sequences 200 and 210 can be calculated by:
  • Figure 3A is a graph 300 showing the relationship between the effective flip angle and the phase 106 between pulses 202.
  • the effective flip angle of the excitation becomes 2a, or equal to the sum of the individual flip angles.
  • the phase ( ⁇ ) is non-zero, the effective flip angle is reduced.
  • the fractional reduction in the effective flip angle with increasing ⁇ appears to be proportional for various flip angles a, until a approaches 90°.
  • Figure 2A illustrates the dependence of the effective flip angle on ⁇ at selected values of a as determined using the Bloch- Siegert method as represented in Equation (1).
  • the effective flip angle of the 2-pulse excitation reduces with increasing ⁇ ; therefore, the relationship between effective flip angle and ⁇ is dependent on a. As a approaches and equals 90°, the effective flip angle becomes inversely proportional to ⁇ .
  • the flip angle a is proportional to the spatial variation of the Bi field according to:
  • the method of the present disclosure includes generating a spatial distribution cp(r) that counteracts the effects of a(r) on the effective flip angle such that the effective flip angle is constant over space.
  • a target phase at the location r ((p tar get (r) is generated according to: l + cos 2or(r) - 2cos 3 ⁇ 4
  • Figure 3B is a graph 302 illustrating that the optimization of the effective flip angle can be determined at different combinations of pulse phases and individual flip angles when plotted as ⁇ vs. a. As shown, the lowest transmitted radio frequency power required for optimizing the effective flip angle corresponds to a phase of 0 for the individual flip angle. Furthermore, for low ⁇ and effective flip angle values, relatively large changes in the phase ⁇ are needed to compensate for changes in a.
  • the method includes optimizing the currents to the shim coils to correct the inhomogeneity of the Bo field.
  • the shim optimization is represented by c sh i m (r) that approximates (p tar get(r) as provided in Equation (3).
  • c sh i m (r) is determined by applying current pulses (Si) at a time (t) to a number individual shim coils (n) indexed by "i" according to:
  • the current applied to the shim coils can be optimized by minimizing the root mean square difference between cp s him(r) and (ptarget(r) of Equation (2) based on a multi-linear regression using the field associated with each shim coil as independent variables or regressors.
  • knowledge of the field generated by each shim coil is obtained from shim coil calibration scans.
  • knowledge of the field generated by each shim may be obtained during the initial set-up of the MRI system.
  • knowledge of the field generated by each shim may be obtained during calibration scans performed prior to scanning the desired object.
  • Figure 4 illustrates an exemplary method of modulation of the B field using Bo-based shimming according to one aspect of the present disclosure.
  • the method will be described with reference to image acquisitions and scans of one or more phantoms and a human brain using a 7T Siemens ® whole body scanner employing an Agilent Technologies ® shielded-magnet design.
  • the scanner system used five second-order shims having functional shim terms of z 2 , zx, zy, xy, x 2 -y 2 with a maximum strength of 1.6 kHz/cm 2.
  • a continuous current was supplied to the second-order shims.
  • current was provided to the second-order shims intermittently, as necessary.
  • the scanner system also includes zero-order shim term and one or more linear gradient coils for the B 0 field, for example, to effectively achieve at least 9 degrees of shimming for the Bo field. Therefore, the number of individual shim coils (n) used to determine flip angle optimization according to Equation (3) is nine.
  • the zero- order shim term is effectuated through phase adjustments of the RF pulses.
  • the zero-order shim term is effectuated through a frequency shift by a RF synthesizer.
  • other scanners, shims, and/or shim terms may be used.
  • the method 400 includes calibrating each of the individual shim terms at 402, based on applying a known current (S) applied to the individual shims.
  • the calibration of each shim coil includes acquiring a B 0 field map during the application of S, as shown in FIGS 2A-B. Similar to the determination of the static magnetization map data 112, the calibration of the individual shims includes determining the phase difference between two gradient echo signals to determine the frequency and shimmed Bo field strength.
  • the calibration may be performed on a phantom.
  • the phantom has a low dielectric constant.
  • the phantom may include silicon oil.
  • the B 0 field maps may be acquired by applying a gradient echo pulse sequence where the two echo pulses are separated by a time interval ⁇ .
  • the time interval may be 2 ms.
  • the known current pulse (S) is applied during the time interval ⁇ .
  • shim calibration frequency maps are generated for each shim term.
  • the phase for each gradient echo signal generated at 402 are subtracted from each other to determine a frequency, that is then divided by their time interval to generate the calibrated shim Bo field map.
  • the Bo field maps are acquired at two different shim current amplitudes, 406.
  • the shim current amplitudes may be at half of a maximum current and its inverse (max/2 and -max/2) or at half of the maximum current and zero (max/2 and 0).
  • the shim calibration in terms of a generated frequency shift per unit current, is obtained by dividing the difference between the Bo field maps by the difference in the shim currents.
  • the operations at 402, 404, and 406 are performed simultaneously.
  • B field frequency maps are used at 408 to determine the flip angle at a location (a(r)) as described by Equation (2).
  • the B frequency maps are determined using the Bloch-Siegert method, based upon an 8 ms irradiation pulse at a frequency of 4 kHz and 2 shifts at +8 kHz and -8 kHz respectively.
  • the B field mapping can then be used to obtain an object-specific frequency map (Bl(r)).
  • the object-specific frequency map (Bl(r)) may then be used to determine a(r) by multiplying the object-specific frequency map by a factor C.
  • C is determined from the duration, shape, and amplitude of the gradient echo pulse sequence applied at 402.
  • the target phase distribution (cptarget (r)) is determined using Equation (3) that is based in part upon the (r), determined at 408.
  • the target phase distribution (cptarget (r)) includes a correction for imperfections in the background field Bo.
  • the correction is derived from the spatially-varied magnetic susceptibility of the object being scanned, which causes additional phase accumulation in the object (cpobject(r)).
  • cpobjectO " is subtracted from ( ta rget (r) provide by Equation (3) prior to calculating the calibrated shim strengths.
  • multi-linear regression is used to determine the desired shim strengths at 412.
  • the shim calibration frequency maps generated at 404 are converted to phase shifts (cpshim) by multiplying the time integral of the modulation pulse (S) amplitude, applied at 402, over the time integral ⁇ .
  • the desired effective flip angle may be used to determine the current that is to be applied to the individual shims.
  • other methods to calculate and determined the desired shim strength may be used.
  • determining the shim strengths requires a particular RF sub-pulse amplitude as this determines the phase accumulation (cp smm ) that is needed to induce the desired effective flip angle.
  • the uniformity of the effective flip angle over a range of RF sub-pulse amplitudes and select the sub-pulse amplitude that induces the greatest uniformity in the effective flip angle.
  • the Bo field is modulated by activation of the optimized and calibrated shims to reduce inhomogeneity of the Bo field.
  • the optimized shims are applied only during the sub-pulse interval ( ⁇ ).
  • the optimized shims may be applied continuously. Continuous application of the shims may be necessary when the switching speed of the shim hardware is limited.
  • Fig. 5 depicts the application of shims x, z 2 and x 2 -y 2 during an image acquisition sequence 500 of an oil phantom.
  • the acquired images 502-512 demonstrate the flexibility of the proposed method in manipulating the effective flip angle within an axial slice selected in a phantom.
  • linear, circular, and ellipsoidal flip angle distributions were generated by applying the x gradient, the z 2 shim, and a combination of the z 2 and x 2 -y 2 shims, respectively.
  • strong spatial variations can be generated with each of these cp s him(r) distributions.
  • the images were acquired using a two-pulse excitation along with continued application of shim terms. The variations in intensity reflect the effective flip angle, as both the RF transmission fields and receiver fields were uniform.
  • inter-pulse spacing D Another consideration for the optimization is the choice of inter-pulse spacing D. Choosing too large of a value for D may result in a range of susceptibility-induced phase accumulation over the object that exceeds 2 ⁇ . Shorter spacing values of D reduces sensitivity to T 2 * decay and off resonance, but increases the required shim strength, gradient switching rates, and may require shorter sub-pulse durations. The latter increases RF peak power and overall power deposition. The 2 ms spacing used above was limited by gradient slew rate. By way of example, and not limitation, the minimal inter-pulse spacing for slice thickness selection during a dual-pulse sequence as shown in FIGS. 2A-B ranges from about 1.0 ms for 5mm slices to about 2.3ms for 1mm slices.
  • Good effective flip angle uniformity may also be achieved without the use of higher order shim terms, either by extending the pulse length through the addition of one or more RF sub-pulses (spokes), or through the addition of independent RF channels.
  • spokes RF sub-pulses
  • independent RF channels By way of example and not limitation, two- spoke designs that make use of independent RF channels have been shown to provide good effective flip angle uniformity in a human brain at 7T. The results suggest that this performance may be achieved without the need for independent radio frequency channels.
  • the level of performance may be increased by combining the two methods. In another aspect, this method may relax the requirements for transmit coil uniformity, and therefore lessen the burden on coil design.
  • the methods described herein are extendable to multi-slice imaging with oblique orientations. Extending the image acquisition to multi-slice two dimensional images will require switching of the higher order shims. In one aspect, this is accomplished by a manipulation of the pulse S, as shown in Figure 1. In another aspect, the pulse S may be extended over the time interval between the radio frequency sub-pulses. In various other aspects, the pulse S may extend across and/or beyond the radio-frequency sub-pulses.
  • shim hardware capable of millisecond- scale switching times may be used for dynamic shimming applications.
  • the methods disclosed herein may also be used in three dimensional scanning.
  • additional second order shims e.g. five additional shims, in addition
  • additional higher order shims are used. Due in part to the spherical symmetry of shim terms generated with many shim designs, the methods disclosed herein may also be used for acquiring oblique slices.

Abstract

Dans une IRM à champ élevé, une inhomogénéité d'angle de basculement RF due à des effets de longueur d'onde peut conduire à des variations spatiales de contraste et de sensibilité. Les systèmes et les procédés selon l'invention se rapportent à l'utilisation de corrections de champ magnétique B0 non linéaires pour améliorer l'uniformité de l'angle de basculement d'excitation dans une IRM à champ élevé. Le système et les procédés selon l'invention peuvent être utilisés conjointement avec des procédés d'excitation multidimensionnelle existants, y compris ceux qui utilisent une excitation parallèle pour améliorer le contraste et la sensibilité dans une imagerie de résonance magnétique à écho de gradient.
PCT/US2012/032387 2011-04-08 2012-04-05 Modulation à base b0 d'excitation b1 dans une irm WO2012138902A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US201161473610P 2011-04-08 2011-04-08
US61/473,610 2011-04-08

Publications (1)

Publication Number Publication Date
WO2012138902A1 true WO2012138902A1 (fr) 2012-10-11

Family

ID=46046300

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2012/032387 WO2012138902A1 (fr) 2011-04-08 2012-04-05 Modulation à base b0 d'excitation b1 dans une irm

Country Status (1)

Country Link
WO (1) WO2012138902A1 (fr)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102012220462A1 (de) * 2012-11-09 2014-06-12 Siemens Aktiengesellschaft SAR Reduktion mittels B0 spezifischer HF Anregung
CN103983929A (zh) * 2013-02-12 2014-08-13 西门子公司 具有脉冲式均衡磁场梯度的磁共振设备
CN109146852A (zh) * 2018-07-30 2019-01-04 国网江苏省电力有限公司电力科学院研究院 一种基于红外图像的瓷绝缘子串铁帽盘面边缘检测方法
CN109407021A (zh) * 2018-11-23 2019-03-01 上海健康医学院 一种磁共振射频匀场管理系统
CN112716476A (zh) * 2019-10-28 2021-04-30 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
GB2589702A (en) * 2019-09-03 2021-06-09 Robert Oliphant Connell Ian Method and system for reducing magnetic field instabilities in a magnetic resonance system

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110026799A1 (en) * 2008-03-27 2011-02-03 Koninklijke Philips Electronics N.V. Flip angle imaging with improved b1 mapping for multi-rf transmit systems

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110026799A1 (en) * 2008-03-27 2011-02-03 Koninklijke Philips Electronics N.V. Flip angle imaging with improved b1 mapping for multi-rf transmit systems

Non-Patent Citations (9)

* Cited by examiner, † Cited by third party
Title
BOULANT N ET AL: "Strongly Modulating Pulses for Counteracting RF Inhomogeneity at High Fields", MAGNETIC RESONANCE IN MEDICINE, ACADEMIC PRESS, DULUTH, MN, US, vol. 60, 1 January 2008 (2008-01-01), pages 701 - 708, XP002534872, ISSN: 0740-3194, DOI: 10.1002/MRM.21700 *
CHARLES H CUNNINGHAM ET AL: "Saturated Double-Angle Method for Rapid B1+ Mapping", MAGNETIC RESONANCE IN MEDICINE, vol. 55, no. 6, 8 May 2006 (2006-05-08), pages 1326 - 1333, XP055031547, DOI: 10.1002/mrm.20896 *
LAURA I. SACOLICK ET AL: "B1 mapping by Bloch-Siegert shift", MAGNETIC RESONANCE IN MEDICINE, vol. 63, no. 5, 1 May 2010 (2010-05-01), pages 1315 - 1322, XP055027998, ISSN: 0740-3194, DOI: 10.1002/mrm.22357 *
MICHAEL SCHÄR ET AL: "Simultaneous B0 - and B1+-Map acquisition for fast localized shim, frequency, and RF power determination in the heart at 3 T", MAGNETIC RESONANCE IN MEDICINE, vol. 63, no. 2, 14 January 2010 (2010-01-14), pages 419 - 426, XP055031504, ISSN: 0740-3194, DOI: 10.1002/mrm.22234 *
N. BOULANT ET AL: "B1 and B0 inhomogeneity mitigation in the human brain at 7 T with selective pulses by using average Hamiltonian theory", MAGNETIC RESONANCE IN MEDICINE, vol. 65, no. 3, 14 October 2010 (2010-10-14), pages 680 - 691, XP055031483, ISSN: 0740-3194, DOI: 10.1002/mrm.22658 *
P VAN GELDEREN ET AL: "A Simple B1 Correction Method for High Resolution Neuroimaging", PROCEEDINGS OF THE INTERNATIONAL SOCIETY FOR MAGNETIC RESONANCE IN MEDICINE, 14TH ANNUAL MEETING AND EXHIBITION, SEATTLE, WASHINGTON, USA, 6-12 MAY 2006, vol. 14, 22 April 2006 (2006-04-22), pages 2355, XP055031474 *
SUNG K ET AL: "B1+ Compensation in 3T Cardiac Imaging Using Short 2DRF Pulses", MAGNETIC RESONANCE IN MEDICINE, ACADEMIC PRESS, DULUTH, MN, US, vol. 59, no. 3, 1 January 2008 (2008-01-01), pages 441 - 446, XP002555033, ISSN: 0740-3194, [retrieved on 20080124], DOI: 10.1002/MRM.21443 *
YARNYKH V L: "Actual flip-angle imaging in the pulsed steady state: A method for rapid three-dimensional mapping of the transmitted radiofrequency field", MAGNETIC RESONANCE IN MEDICINE, ACADEMIC PRESS, DULUTH, MN, US, vol. 57, 1 January 2007 (2007-01-01), pages 192 - 200, XP002530750, ISSN: 0740-3194, [retrieved on 20061226], DOI: 10.1002/MRM.21120 *
YU-WEI TANG ET AL: "Real-time feedback optimization of z-shim gradient for automatic compensation of susceptibility-induced signal loss in EPI", NEUROIMAGE, ACADEMIC PRESS, ORLANDO, FL, US, vol. 55, no. 4, 12 January 2011 (2011-01-12), pages 1587 - 1592, XP028120037, ISSN: 1053-8119, [retrieved on 20110120], DOI: 10.1016/J.NEUROIMAGE.2011.01.045 *

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102012220462A1 (de) * 2012-11-09 2014-06-12 Siemens Aktiengesellschaft SAR Reduktion mittels B0 spezifischer HF Anregung
DE102012220462B4 (de) 2012-11-09 2023-12-28 Siemens Healthcare Gmbh Verfahren und Vorrichtung zur SAR Reduktion mittels B0 spezifischer HF Anregung
US9709643B2 (en) 2012-11-09 2017-07-18 Siemens Aktiengesellschaft Method and apparatus for SAR reduction using B0 specific RF excitation
DE102013202217A1 (de) * 2013-02-12 2014-08-28 Siemens Aktiengesellschaft MR-Anlage mit gepulsten Ausgleichsmagnetfeldgradienten
DE102013202217B4 (de) * 2013-02-12 2015-05-28 Siemens Aktiengesellschaft MR-Anlage mit gepulsten Ausgleichsmagnetfeldgradienten
US9689952B2 (en) 2013-02-12 2017-06-27 Siemens Aktiengesellschaft Magnetic resonance system with pulsed compensation magnetic field gradients
JP2014151207A (ja) * 2013-02-12 2014-08-25 Siemens Aktiengesellschaft パルス状の補償傾斜磁場を有するｍｒ装置
CN103983929A (zh) * 2013-02-12 2014-08-13 西门子公司 具有脉冲式均衡磁场梯度的磁共振设备
CN109146852A (zh) * 2018-07-30 2019-01-04 国网江苏省电力有限公司电力科学院研究院 一种基于红外图像的瓷绝缘子串铁帽盘面边缘检测方法
CN109407021A (zh) * 2018-11-23 2019-03-01 上海健康医学院 一种磁共振射频匀场管理系统
CN109407021B (zh) * 2018-11-23 2024-02-27 上海健康医学院 一种磁共振射频匀场管理系统
GB2589702A (en) * 2019-09-03 2021-06-09 Robert Oliphant Connell Ian Method and system for reducing magnetic field instabilities in a magnetic resonance system
US11474176B2 (en) 2019-09-03 2022-10-18 Synaptive Medical Inc. Method and system for reducing magnetic field instabilities in a magnetic resonance system
GB2589702B (en) * 2019-09-03 2023-08-23 Robert Oliphant Connell Ian Method and system for reducing magnetic field instabilities in a magnetic resonance system
CN112716476A (zh) * 2019-10-28 2021-04-30 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

Similar Documents

Publication Publication Date Title
US9377517B2 (en) Method of dynamically compensating for magnetic field heterogeneity in magnetic resonance imaging
US8427157B2 (en) Method to determine a predetermined signal amplitude in MR measurements
US8934691B2 (en) System for motion compensated MR parallel imaging
US9097777B2 (en) Method of magnetic resonance imaging for the selection and recording of curved slices
US7863898B2 (en) Method and magnetic resonance system to determine the phase position of a magnetization
JP6071905B2 (ja) 磁気共鳴イメージング装置及び領域撮像方法
US20110026799A1 (en) Flip angle imaging with improved b1 mapping for multi-rf transmit systems
US20140070805A1 (en) Mr imaging with b1 mapping
US10613174B2 (en) Method and magnetic resonance apparatus for maxwell compensation in simultaneous multislice data acquisitions
EP3044604B1 (fr) Irm résistant aux métaux
US9101659B2 (en) Method and apparatus for correction of artifacts in magnetic resonance images
WO2012138902A1 (fr) Modulation à base b0 d'excitation b1 dans une irm
US20140333306A1 (en) Use of gradient coils for correcting higher order bo field inhomogeneities in mr imaging
US9400318B2 (en) Method for determining a control sequence with parallel transmission
US9494662B2 (en) Magnetic resonance method and apparatus for automatic calculation of a maximum pulse-length of an excitation pulse
US20140028314A1 (en) Method and apparatus for acquisition of magnetic resonance data while avoiding signal inhomogeneities
WO2016180983A1 (fr) Irm multi-échos avec correction d'erreurs de phase induite par gradient concomitant
US20120153950A1 (en) Rf shimmed mri slice excitation along a curved spoke k-space trajectory
Finsterbusch B0 inhomogeneity and shimming
Han et al. Pure phase encode magnetic field gradient monitor
US9008400B2 (en) Method and apparatus for correction of artifacts in magnetic resonance images
US11959986B2 (en) MR imaging with spiral acquisition
EP2988145B1 (fr) Procédé et appareil pour acquérir des données de résonance magnétique
Wiggins et al. Universal pulses for MRI at 9.4 Tesla-a feasibility study
US20230251337A1 (en) Method for exciting nuclear spins

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 12719828

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 12719828

Country of ref document: EP

Kind code of ref document: A1