11,961 research outputs found
Objectively measuring signal detectability, contrast, blur and noise in medical images using channelized joint observers
ABSTRACT To improve imaging systems and image processing techniques, objective image quality assessment is essential. Model observers adopting a task-based quality assessment strategy by estimating signal detectability measures, have shown to be quite successful to this end. At the same time, costly and time-consuming human observer experiments can be avoided. However, optimizing images in terms of signal detectability alone, still allows a lot of freedom in terms of the imaging parameters. More specifically, fixing the signal detectability defines a manifold in the imaging parameter space on which different âpossibleâ solutions reside. In this article, we present measures that can be used to distinguish these possible solutions from each other, in terms of image quality factors such as signal blur, noise and signal contrast. Our approach is based on an extended channelized joint observer (CJO) that simultaneously estimates the signal amplitude, scale and detectability. As an application, we use this technique to design k-space trajectories for MRI acquisition. Our technique allows to compare the different spiral trajectories in terms of blur, noise and contrast, even when the signal detectability is estimated to be equal
Detecting a gravitational-wave background with next-generation space interferometers
Future missions of gravitational-wave astronomy will be operated by
space-based interferometers, covering very wide range of frequency. Search for
stochastic gravitational-wave backgrounds (GWBs) is one of the main targets for
such missions, and we here discuss the prospects for direct measurement of
isotropic and anisotropic components of (primordial) GWBs around the frequency
0.1-10 Hz. After extending the theoretical basis for correlation analysis, we
evaluate the sensitivity and the signal-to-noise ratio for the proposed future
space interferometer missions, like Big-Bang Observer (BBO), Deci-Hertz
Interferometer Gravitational-wave Observer (DECIGO) and recently proposed
Fabry-Perot type DECIGO. The astrophysical foregrounds which are expected at
low frequency may be a big obstacle and significantly reduce the
signal-to-noise ratio of GWBs. As a result, minimum detectable amplitude may
reach h^2 \ogw = 10^{-15} \sim 10^{-16}, as long as foreground point sources
are properly subtracted. Based on correlation analysis, we also discuss
measurement of anisotropies of GWBs. As an example, the sensitivity level
required for detecting the dipole moment of GWB induced by the proper motion of
our local system is closely examined.Comment: 19 pages, 6 figures, references added, typos correcte
Observing Strategies for the Detection of Jupiter Analogs
To understand the frequency, and thus the formation and evolution, of planetary systems like our own solar system, it is critical to detect Jupiter-like planets in Jupiter-like orbits. For long-term radial-velocity monitoring, it is useful to estimate the observational effort required to reliably detect such objects, particularly in light of severe competition for limited telescope time. We perform detailed simulations of observational campaigns, maximizing the realism of the sampling of a set of simulated observations. We then compute the detection limits for each campaign to quantify the effect of increasing the number of observational epochs and varying their time coverage. We show that once there is sufficient time baseline to detect a given orbital period, it becomes less effective to add further time coverage-rather, the detectability of a planet scales roughly as the square root of the number of observations, independently of the number of orbital cycles included in the data string. We also show that no noise floor is reached, with a continuing improvement in detectability at the maximum number of observations N = 500 tested here.Peer reviewe
Detecting extreme mass ratio inspirals with LISA using time-frequency methods II: search characterization
The inspirals of stellar-mass compact objects into supermassive black holes
constitute some of the most important sources for LISA. Detection of these
sources using fully coherent matched filtering is computationally intractable,
so alternative approaches are required. In a previous paper (Wen and Gair 2005,
gr-qc/0502100), we outlined a detection method based on looking for excess
power in a time-frequency spectrogram of the LISA data. The performance of the
algorithm was assessed using a single `typical' trial waveform and
approximations to the noise statistics. In this paper we present results of
Monte Carlo simulations of the search noise statistics and examine its
performance in detecting a wider range of trial waveforms. We show that typical
extreme mass ratio inspirals (EMRIs) can be detected at distances of up to 1--3
Gpc, depending on the source parameters. We also discuss some remaining issues
with the technique and possible ways in which the algorithm can be improved.Comment: 15 pages, 9 figures, to appear in proceedings of GWDAW 9, Annecy,
France, December 200
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