scholarly journals Mitigation of B1+ inhomogeneity using spatially selective excitation with jointly designed quadratic spatial encoding magnetic fields and RF shimming

2016 ◽  
Vol 78 (2) ◽  
pp. 577-587 ◽  
Author(s):  
Yi-Cheng Hsu ◽  
Riccardo Lattanzi ◽  
Ying-Hua Chu ◽  
Martijn A. Cloos ◽  
Daniel K. Sodickson ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Selective Excitation ◽  
Spatial Encoding ◽  
B1 Inhomogeneity ◽  
Rf Shimming

Spatial encoding and image reconstruction

2018 ◽  
pp. 11-13
Author(s):  
Sebastian Kozerke ◽  
Redha Boubertakh ◽  
Marc Miquel
Keyword(s):  
Magnetic Resonance ◽  
Image Reconstruction ◽  
Magnetic Fields ◽  
Spatial Resolution ◽  
Pulse Sequence ◽  
Field Of View ◽  
Space Representation ◽  
Spatial Encoding ◽  
Magnetic Resonance Data ◽  
Resonance Data

In order to form images with the required resolution and anatomical coverage, gradient magnetic fields are used to excite magnetization in a predefined slice or slab, with subsequent spatial encoding to obtain spatial resolution in the slice or slab. It is demonstrated how the spatial encoding principle is implemented and how it can be conceptualized using the so-called k-space representation. The relations between the field of view, spatial resolution, and k-space sampling are illustrated, along with the implementation using a simple pulse sequence. Once magnetic resonance data have been collected in k-space, the process of image reconstruction will yield the final images.

scholarly journals Mitigate B 1 + inhomogeneity using spatially selective radiofrequency excitation with generalized spatial encoding magnetic fields

2013 ◽  
Vol 71 (4) ◽  
pp. 1458-1469 ◽  
Author(s):  
Yi-Cheng Hsu ◽  
I-Liang Chern ◽  
Wei Zhao ◽  
Borjan Gagoski ◽  
Thomas Witzel ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Spatial Encoding

OPTIMIZATION OF THE DANTE PULSE SEQUENCE FOR SELECTIVE NMR EXCITATION IN STRONGLY INHOMOGENEOUS MAGNETIC FIELDS

2004 ◽  
Vol 18 (10n11) ◽  
pp. 1571-1579 ◽  
Author(s):  
M. TODICA ◽  
B. BLÜMICH
Keyword(s):  
Magnetic Fields ◽  
Low Power ◽  
Pulse Sequence ◽  
Response Spectrum ◽  
Selective Excitation ◽  
Unilateral Nmr ◽  
Power Operation ◽  
Echo Pulse ◽  
Frequency Power

The possibility to improve the quality of the selective excitation, at low radio-frequency power, in the strongly inhomogeneous magnetic fields of the NMR-MOUSE is explored. Important safe of RF power is obtained by replacing the standard Hahn echo pulse sequence by DANTE–DANTE echo pulse sequence. The quality of the response spectrum is analyzed in function of the parameters of DANTE pulse sequence. The development of low-power selective excitation in unilateral NMR is an important step towards low-power operation of the NMR-MOUSE to increase its mobility.

Local field of view imaging for alias-free undersampling with nonlinear spatial encoding magnetic fields

2013 ◽  
Vol 71 (3) ◽  
pp. 1002-1014 ◽  
Author(s):  
Hans Weber ◽  
Gerrit Schultz ◽  
Daniel Gallichan ◽  
Jürgen Hennig ◽  
Maxim Zaitsev
Keyword(s):  
Magnetic Fields ◽  
Local Field ◽  
Field Of View ◽  
Spatial Encoding

scholarly journals Robust spatially selective excitation using radiofrequency pulses adapted to the effective spatially encoding magnetic fields

2010 ◽  
Vol 65 (2) ◽  
pp. 409-421 ◽  
Author(s):  
Johannes T. Schneider ◽  
Martin Haas ◽  
Wolfgang Ruhm ◽  
Jürgen Hennig ◽  
Peter Ullmann
Keyword(s):  
Magnetic Fields ◽  
Selective Excitation

Spatial Encoding and the Acquisition of High-Resolution NMR Spectra in Inhomogeneous Magnetic Fields

2004 ◽  
Vol 126 (23) ◽  
pp. 7184-7185 ◽  
Author(s):  
Boaz Shapira ◽  
Lucio Frydman
Keyword(s):  
High Resolution ◽  
Magnetic Fields ◽  
Nmr Spectra ◽  
Spatial Encoding ◽  
High Resolution Nmr

Calculated Coronal Magnetic Fields and Their Comparison with the Coronal Structures as Observed during Five Solar Eclipses

1994 ◽  
Vol 144 ◽  
pp. 559-564
Author(s):  
P. Ambrož ◽  
J. Sýkora
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Coronal Magnetic Field ◽  
Coronal Magnetic Fields ◽  
Solar Eclipses ◽  
Coronal Structures

AbstractWe were successful in observing the solar corona during five solar eclipses (1973-1991). For the eclipse days the coronal magnetic field was calculated by extrapolation from the photosphere. Comparison of the observed and calculated coronal structures is carried out and some peculiarities of this comparison, related to the different phases of the solar cycle, are presented.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

Solar Filaments as Tracers of Subsurface Processes

2000 ◽  
Vol 179 ◽  
pp. 177-183
Author(s):  
D. M. Rust
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Coronal Mass Ejections ◽  
Interplanetary Space ◽  
Intermediate Stage ◽  
Coronal Plasma ◽  
Magnetic Helicity ◽  
The Sun ◽  
New Paradigm ◽  
Solar Filaments

AbstractSolar filaments are discussed in terms of two contrasting paradigms. The standard paradigm is that filaments are formed by condensation of coronal plasma into magnetic fields that are twisted or dimpled as a consequence of motions of the fields’ sources in the photosphere. According to a new paradigm, filaments form in rising, twisted flux ropes and are a necessary intermediate stage in the transfer to interplanetary space of dynamo-generated magnetic flux. It is argued that the accumulation of magnetic helicity in filaments and their coronal surroundings leads to filament eruptions and coronal mass ejections. These ejections relieve the Sun of the flux generated by the dynamo and make way for the flux of the next cycle.

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