2,285 research outputs found
Super-resolution MRI Using Finite Rate of Innovation Curves
We propose a two-stage algorithm for the super-resolution of MR images from
their low-frequency k-space samples. In the first stage we estimate a
resolution-independent mask whose zeros represent the edges of the image. This
builds off recent work extending the theory of sampling signals of finite rate
of innovation (FRI) to two-dimensional curves. We enable its application to MRI
by proposing extensions of the signal models allowed by FRI theory, and by
developing a more robust and efficient means to determine the edge mask. In the
second stage of the scheme, we recover the super-resolved MR image using the
discretized edge mask as an image prior. We evaluate our scheme on simulated
single-coil MR data obtained from analytical phantoms, and compare against
total variation reconstructions. Our experiments show improved performance in
both noiseless and noisy settings.Comment: Conference paper accepted to ISBI 2015. 4 pages, 2 figure
SUPER-RESOLUTION MRI USING FINITE RATE OF INNOVATION CURVES
ABSTRACT We propose a two-stage algorithm for the super-resolution of MR images from their low-frequency k-space samples. In the first stage we estimate a resolution-independent mask whose zeros represent the edges of the image. This builds off recent work extending the theory of sampling signals of finite rate of innovation (FRI) to two-dimensional curves. We enable its application to MRI by proposing extensions of the signal models allowed by FRI theory, and by developing a more robust and efficient means to determine the edge mask. In the second stage of the scheme, we recover the super-resolved MR image using the discretized edge mask as an image prior. We evaluate our scheme on simulated single-coil MR data obtained from analytical phantoms, and compare against total variation reconstructions. Our experiments show improved performance in both noiseless and noisy settings
Magnetic effects on the low-T/|W| instability in differentially rotating neutron stars
Dynamical instabilities in protoneutron stars may produce gravitational waves
whose observation could shed light on the physics of core-collapse supernovae.
When born with sufficient differential rotation, these stars are susceptible to
a shear instability (the "low-T/|W| instability"), but such rotation can also
amplify magnetic fields to strengths where they have a considerable impact on
the dynamics of the stellar matter. Using a new magnetohydrodynamics module for
the Spectral Einstein Code, we have simulated a differentially-rotating neutron
star in full 3D to study the effects of magnetic fields on this instability.
Though strong toroidal fields were predicted to suppress the low-T/|W|
instability, we find that they do so only in a small range of field strengths.
Below 4e13 G, poloidal seed fields do not wind up fast enough to have an effect
before the instability saturates, while above 5e14 G, magnetic instabilities
can actually amplify a global quadrupole mode (this threshold may be even lower
in reality, as small-scale magnetic instabilities remain difficult to resolve
numerically). Thus, the prospects for observing gravitational waves from such
systems are not in fact diminished over most of the magnetic parameter space.
Additionally, we report that the detailed development of the low-T/|W|
instability, including its growth rate, depends strongly on the particular
numerical methods used. The high-order methods we employ suggest that growth
might be considerably slower than found in some previous simulations.Comment: REVTeX 4.1, 21 pages, 18 figures, submitting to Physical Review
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