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

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 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

scholarly journals Instrument concepts for the observation of prominences with future ground-based telescopes

2013 ◽  
Vol 8 (S300) ◽  
pp. 370-375 ◽  
Author(s):  
A. López Ariste
Keyword(s):  
Image Quality ◽  
Magnetic Fields ◽  
Atmospheric Turbulence ◽  
Temporal Resolution ◽  
Field Of View ◽  
Large Field ◽  
Solar Observations ◽  
New Generation

AbstractThe observation of prominences with ground-based telescopes suffers from poor image quality due to atmospheric turbulence when compared with space-borne instruments which, for solar observations, are of similar apertures. To make ground-based instruments competitive, they should rely on spectropolarimetry and the measurement of prominence magnetic fields, a task which no foreseable space instrument will perform. But spectropolarimetry alone does not suffice, and we argue that future instrumentation should combine it with imaging in a large field of view and good temporal resolution. We place numbers on those requirements and give examples of instrumental accomplishments already at work today that forecast a new generation of instruments for the observation of prominences from ground-based telescopes.

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

scholarly journals Co-spatial velocity and magnetic swirls in the simulated solar photosphere

2019 ◽  
Vol 632 ◽  
pp. A97 ◽  
Author(s):  
Jiajia Liu ◽  
Mats Carlsson ◽  
Chris J. Nelson ◽  
Robert Erdélyi
Keyword(s):  
Magnetic Fields ◽  
Total Population ◽  
Spatial Relationship ◽  
Detection Algorithm ◽  
Field Of View ◽  
Solar Photosphere ◽  
Correlation Index ◽  
Physical Conditions ◽  
Spatial Velocity ◽  
The Magnetic Field

Context. Velocity or intensity swirls have now been shown to be widely present throughout the photosphere and chromosphere. It has been suggested that these events could contribute to the heating of the upper solar atmosphere, via exciting Alfvén pulses, which could carry significant amounts of energy. However, the conjectured necessary physical conditions for their excitation, that the magnetic field rotates co-spatially and co-temporally with the velocity field, has not been verified. Aims. We aim to understand whether photospheric velocity swirls exist co-spatially and co-temporally with photospheric magnetic swirls, in order to demonstrate the link between swirls and pulses. Methods. The automated swirl detection algorithm (ASDA) is applied to the photospheric horizontal velocity and vertical magnetic fields obtained from a series of realistic numerical simulations using the radiative magnetohydrodynamics (RMHD) code Bifrost. The spatial relationship between the detected velocity and magnetic swirls is further investigated via a well-defined correlation index (CI) study. Results. On average, there are ∼63 short-lived photospheric velocity swirls (with lifetimes mostly less than 20 s, and average radius of ∼37 km and rotating speeds of ∼2.5 km s−1) detected in a field of view (FOV) of 6 × 6 Mm−2, implying a total population of velocity swirls of ∼1.06 × 107 in the solar photosphere. More than 80% of the detected velocity swirls are found to be accompanied by local magnetic concentrations in intergranular lanes. On average, ∼71% of the detected velocity swirls have been found to co-exist with photospheric magnetic swirls with the same rotating direction. Conclusions. The co-temporal and co-spatial rotation in the photospheric velocity and magnetic fields provide evidence that the conjectured condition for the excitation of Alfvén pulses by photospheric swirls is fulfilled.

Very High Resolution Analysis of the Dynamics of a Coronal Plasmoid

1994 ◽  
Vol 144 ◽  
pp. 593-596
Author(s):  
O. Bouchard ◽  
S. Koutchmy ◽  
L. November ◽  
J.-C. Vial ◽  
J. B. Zirker
Keyword(s):  
High Resolution ◽  
Solar Eclipse ◽  
Total Solar Eclipse ◽  
Field Of View ◽  
Small Field ◽  
High Resolution Analysis ◽  
Ccd Observations ◽  
Resolution Analysis ◽  
Very High ◽  
Small Field Of View

AbstractWe present the results of the analysis of a movie taken over a small field of view in the intermediate corona at a spatial resolution of 0.5“, a temporal resolution of 1 s and a spectral passband of 7 nm. These CCD observations were made at the prime focus of the 3.6 m aperture CFHT telescope during the 1991 total solar eclipse.

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.

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