Cathryn M. Trott

Improvement in Lesion Detection with Whole-Body Oncologic Time-of-Flight PET

Time-of-flight (TOF) PET has great potential in whole-body oncologic applications, and recent work has demonstrated qualitatively in patient studies the improvement that can be achieved in lesion visibility. The aim of this work was to objectively quantify the improvement in lesion detectability that can be achieved in lung and liver lesions with whole-body 18F-FDG TOF PET in a cohort of 100 patients as a function of body mass index, lesion location and contrast, and scanning time. Methods: One hundred patients with BMIs ranging from 16 to 45 were included in this study. Artificial 1-cm spheric lesions were imaged separately in air at variable locations of each patients lung and liver, appropriately attenuated, and incorporated in the patient list-mode data with 4 different lesion-to-background contrast ranges. The fused studies with artificial lesion present or absent were reconstructed using a list-mode unrelaxed ordered-subsets expectation maximization with chronologically ordered subsets and a gaussian TOF kernel for TOF reconstruction. Conditions were compared on the basis of performance of a 3-channel Hotelling observer signal-to-noise ratio in detecting the presence of a sphere of unknown size on an anatomic background while modeling observer noise. Results: TOF PET yielded an improvement in lesion detection performance (3-channel Hotelling observer signal-to-noise ratio) over non-TOF PET of 8.3% in the liver and 15.1% in the lungs. The improvement in all lesions was 20.3%, 12.0%, 9.2%, and 7.5% for mean contrast values of 2.0:1, 3.2:1, 4.4:1, and 5.7:1, respectively. Furthermore, this improvement was 9.8% in patients with a BMI of less than 30 and 11.1% in patients with a BMI of 30 or more. Performance plateaued faster as a function of number of iterations with TOF than non-TOF. Conclusion: Over all contrasts and body mass indexes, oncologic TOF PET yielded a significant improvement in lesion detection that was greater for lower lesion contrasts. This improvement was achieved without compromising other aspects of PET imaging.

GLEAM: The GaLactic and Extragalactic All-Sky MWA Survey

© Astronomical Society of Australia 2015; published by Cambridge University Press. This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: http://creativecommons.org/licenses/by/4.0/

Epoch of reionization window. I. Mathematical formalism

have neglected a rigorous examination of the error statistics associated with the wedge. Using a quadratic estimator formalism applied to the interferometric measurement equation, we provide a framework for such a rigorous analysis (incorporating a fully covariant treatment of errors). Additionally, we nd that there are strong error correlations at high spatial wavenumbers that have so far been neglected in sensitivity derivations. These error correlations substantially degrade the sensitivity of arrays relying on contributions from long baselines, compared to what one would estimate assuming uncorrelated errors.

Foregrounds in wide-field redshifted 21 cm power spectra

Detection of 21 cm emission of H I from the epoch of reionization, at redshifts > z 6, is limited primarily by foreground emission. We investigate the signatures of wide-field measurements and an all-sky foreground model using the delay spectrum technique that maps the measurements to foreground object locations through signal delays between antenna pairs. We demonstrate interferometric measurements are inherently sensitive to all scales, including the largest angular scales, owing to the nature of wide-field measurements. These wide-field effects are generic to all observations but antenna shapes impact their amplitudes substantially. A dish-shaped antenna yields the most desirable features from a foreground contamination viewpoint, relative to a dipole or a phased array. Comparing data from recent Murchison Widefield Array observations, we demonstrate that the foreground signatures that have the largest impact on the H I signal arise from power received far away from the primary field of view. We identify diffuse emission near the horizon as a significant contributing factor, even on wide antenna spacings that usually represent structures on small scales. For signals entering through the primary field of view, compact emission dominates the foreground contamination. These two mechanisms imprint a characteristic pitchfork signature on the “foreground wedge” in Fourier delay space. Based on these results, we propose that selective down-weighting of data based on antenna spacing and time can mitigate foreground contamination substantially by a factor of ∼100 with negligible loss of sensitivity.

The Low-Frequency Environment of the Murchison Widefield Array: Radio-Frequency Interference Analysis and Mitigation

This is the Accepted Manuscript version of the following article: A. R. Offringa, et al., “The low-frequency environment of the Murchison Widefield Array: radio-frequency interference analysis and mitigation”, Publications of the Astronomical Society of Australia, Vol. 32, March 2015. The final published version is available at: https://doi.org/10.1017/pasa.2015.7

Dissecting a galaxy: mass distribution of 2237+0305

We determine the mass distribution of a spiral galaxy, 2237+0305 using both gravitational lensing and dynamical constraints. We find that lensing can break the disc-halo degeneracy. 2237+0305 has a sub-maximal disc, contributing 57±3 per cent of the rotational support at the disc maximum. The disc mass-to-light ratio is 1.1±0.2 in the I-band and the bulge, 2.9±0.5. The dark matter halo, modelled as a softened isothermal sphere, has a large core radius (13.4±0.4 kpc � 1.4rd) to high accuracy for the best-fit solution. The image positions are reasonably well fitted, but require further rotation information to obtain a unique solution.

A survey for transients and variables with the Murchison Widefield Array 32-tile prototype at 154 MHz

We present a search for transient and variable radio sources at 154 MHz with the Murchison Widefield Array 32-tile prototype. 51 images were obtained that cover a field of view of 1430 deg 2 centred on Hydra A. The observations were obtained over three days in 2010 March and three days in 2011 April and May. The mean cadence of the observations was 26 min and there was additional temporal information on day and year time-scales.

Parametrizing Epoch of Reionization foregrounds: a deep survey of low-frequency point-source spectra with the Murchison Widefield Array

Experiments that pursue detection of signals from the Epoch of Reionization (EoR) are relying on spectral smoothness of source spectra at low frequencies. This article empirically explores the effect of foreground spectra on EoR experiments by measuring high-resolution full-polarization spectra for the 586 brightest unresolved sources in one of the MWA EoR fields using 45 h of observation. A novel peeling scheme is used to subtract 2500 sources from the visibilities with ionospheric and beam corrections, resulting in the deepest, confusion-limited MWA image so far. The resulting spectra are found to be affected by instrumental effects, which limit the constraints that can be set on source-intrinsic spectral structure. The sensitivity and power-spectrum of the spectra are analysed, and it is found that the spectra of residuals are dominated by PSF sidelobes from nearby undeconvolved sources. We release a catalogue describing the spectral parameters for each measured source.

The importance of wide-field foreground removal for 21 cm cosmology: a demonstration with early MWA epoch of reionization observations

In this paper we present observations, simulations, and analysis demonstrating the direct connection between the location of foreground emission on the sky and its location in cosmological power spectra from interferometric redshifted 21 cm experiments. We begin with a heuristic formalism for understanding the mapping of sky coordinates into the cylindrically averaged power spectra measurements used by 21 cm experiments, with a focus on the effects of the instrument beam response and the associated sidelobes. We then demonstrate this mapping by analyzing power spectra with both simulated and observed data from the Murchison Widefield Array. We find that removing a foreground model which includes sources in both the main field-of-view and the first sidelobes reduces the contamination in high k_parallel modes by several percent relative to a model which only includes sources in the main field-of-view, with the completeness of the foreground model setting the principal limitation on the amount of power removed. While small, a percent-level amount of foreground power is in itself more than enough to prevent recovery of any EoR signal from these modes. This result demonstrates that foreground subtraction for redshifted 21 cm experiments is truly a wide-field problem, and algorithms and simulations must extend beyond the main instrument field-of-view to potentially recover the full 21 cm power spectrum.

Stars and dark matter in the spiral gravitational lens 2237+0305

We construct a mass model for the spiral lens galaxy 2237+ 0305, at redshift z(1) = 0.04, based on gravitational-lensing constraints, HI rotation, and new stellar-kinematic information, based on data taken with the Echelle Spectrograph and Imager (ESI) spectrograph on the 10-m Keck-II Telescope. High-resolution rotation curves and velocity dispersion profiles along two perpendicular directions, close to the major and minor axes of the lens galaxy, were obtained by fitting the Mgb-Fe absorption line region. The stellar rotation curve rises slowly and flattens at r similar to 1.5 arcsec (similar to 1.1 kpc). The velocity dispersion profile is approximately flat. A combination of photometric, kinematic and lensing information is used to construct a mass model for the four major mass components of the system -the dark matter halo, disc, bulge and bar. The best-fitting solution has a dark matter halo with a logarithmic inner density slope of gamma = 0.9 +/- 0.3 for rho(DM) alpha r(-gamma), a bulge with M/L(B) = 6.6 +/- 0.3 Gamma(circle dot), and a disc with M/L(B) = 1.2 +/- 0.3 Gamma(circle dot), in agreement with measurements of late-type spirals. The bulge dominates support in the inner regions where the multiple images are located and is therefore tightly constrained by the observations. The disc is submaximal and contributes 45 +/- 11 per cent of the rotational support of the galaxy at 2.2r(d). The halo mass is (2.0 +/- 0.6) x 10(12)M(circle dot), and the stellar to virial mass ratio is 7.0 +/- 2.3 per cent, consistent with typical galaxies of the same mass.