68 research outputs found
PSACNN: Pulse Sequence Adaptive Fast Whole Brain Segmentation
With the advent of convolutional neural networks~(CNN), supervised learning
methods are increasingly being used for whole brain segmentation. However, a
large, manually annotated training dataset of labeled brain images required to
train such supervised methods is frequently difficult to obtain or create. In
addition, existing training datasets are generally acquired with a homogeneous
magnetic resonance imaging~(MRI) acquisition protocol. CNNs trained on such
datasets are unable to generalize on test data with different acquisition
protocols. Modern neuroimaging studies and clinical trials are necessarily
multi-center initiatives with a wide variety of acquisition protocols. Despite
stringent protocol harmonization practices, it is very difficult to standardize
the gamut of MRI imaging parameters across scanners, field strengths, receive
coils etc., that affect image contrast. In this paper we propose a CNN-based
segmentation algorithm that, in addition to being highly accurate and fast, is
also resilient to variation in the input acquisition. Our approach relies on
building approximate forward models of pulse sequences that produce a typical
test image. For a given pulse sequence, we use its forward model to generate
plausible, synthetic training examples that appear as if they were acquired in
a scanner with that pulse sequence. Sampling over a wide variety of pulse
sequences results in a wide variety of augmented training examples that help
build an image contrast invariant model. Our method trains a single CNN that
can segment input MRI images with acquisition parameters as disparate as
-weighted and -weighted contrasts with only -weighted training
data. The segmentations generated are highly accurate with state-of-the-art
results~(overall Dice overlap), with a fast run time~( 45
seconds), and consistent across a wide range of acquisition protocols.Comment: Typo in author name corrected. Greves -> Grev
ALICE: Study of Financial Hardship-Louisiana
Through a series of new, standardized measurements, the United Way ALICE Reports present a broad picture of financial insecurity at the county and town level, and the reasons for why. What we found was startling -- the size of the workforce in each state that is struggling financially is much higher than traditional federal poverty guidelines suggest. The United Way ALICE Project is a grassroots movement stimulating a fresh, nonpartisan national dialogue about how to reverse the trend and improve conditions for this growing population of families living paycheck to paycheck
ALICE: Study of Financial Hardship-Pacific Northwest: Idaho, Oregon and Washington
Through a series of new, standardized measurements, the United Way ALICE Reports present a broad picture of financial insecurity at the county and town level, and the reasons for why. What we found was startling -- the size of the workforce in each state that is struggling financially is much higher than traditional federal poverty guidelines suggest. The United Way ALICE Project is a grassroots movement stimulating a fresh, nonpartisan national dialogue about how to reverse the trend and improve conditions for this growing population of families living paycheck to paycheck
Learning the Effect of Registration Hyperparameters with HyperMorph
We introduce HyperMorph, a framework that facilitates efficient
hyperparameter tuning in learning-based deformable image registration.
Classical registration algorithms perform an iterative pair-wise optimization
to compute a deformation field that aligns two images. Recent learning-based
approaches leverage large image datasets to learn a function that rapidly
estimates a deformation for a given image pair. In both strategies, the
accuracy of the resulting spatial correspondences is strongly influenced by the
choice of certain hyperparameter values. However, an effective hyperparameter
search consumes substantial time and human effort as it often involves training
multiple models for different fixed hyperparameter values and may lead to
suboptimal registration. We propose an amortized hyperparameter learning
strategy to alleviate this burden by learning the impact of hyperparameters on
deformation fields. We design a meta network, or hypernetwork, that predicts
the parameters of a registration network for input hyperparameters, thereby
comprising a single model that generates the optimal deformation field
corresponding to given hyperparameter values. This strategy enables fast,
high-resolution hyperparameter search at test-time, reducing the inefficiency
of traditional approaches while increasing flexibility. We also demonstrate
additional benefits of HyperMorph, including enhanced robustness to model
initialization and the ability to rapidly identify optimal hyperparameter
values specific to a dataset, image contrast, task, or even anatomical region,
all without the need to retrain models. We make our code publicly available at
http://hypermorph.voxelmorph.net.Comment: Accepted for publication at the Journal of Machine Learning for
Biomedical Imaging (MELBA) at https://www.melba-journal.or
Evidence for Black Hole Growth in Local Analogs to Lyman Break Galaxies
We have used XMM-Newton to observe six Lyman Break Analogs (LBAs): members of
the rare population of local galaxies that have properties that are very
similar to distant Lyman Break Galaxies. Our six targets were specifically
selected because they have optical emission-line properties that are
intermediate between starbursts and Type 2 (obscured) AGN. Our new X-ray data
provide an important diagnostic of the presence of an AGN. We find X-ray
luminosities of order 10^{42} erg/s and ratios of X-ray to far-IR luminosities
that are higher than values in pure starburst galaxies by factors ranging from
~ 3 to 30. This strongly suggests the presence of an AGN in at least some of
the galaxies. The ratios of the luminosities of the hard (2-10 keV) X-ray to [O
III]\lambda 5007 emission-line are low by about an order-of-magnitude compared
to Type 1 AGN, but are consistent with the broad range seen in Type 2 AGN.
Either the AGN hard X-rays are significantly obscured or the [O III] emission
is dominated by the starburst. We searched for an iron emission line at ~ 6.4
keV, which is a key feature of obscured AGN, but only detected emission at the
~ 2\sigma level. Finally, we find that the ratios of the mid-infrared (24\mu m)
continuum to [O III]\lambda 5007 luminosities in these LBAs are higher than the
values for Type 2 AGN by an average of 0.8 dex. Combining all these clues, we
conclude that an AGN is likely to be present, but that the bolometric
luminosity is produced primarily by an intense starburst. If these black holes
are radiating at the Eddington limit, their masses would lie in the range of
10^5 to 10^6 M_{sun}. These objects may offer ideal local laboratories to
investigate the processes by which black holes grew in the early universe.Comment: Accepted for publication in Ap
Diaphragm Abnormalities in Patients with End-Stage Heart Failure: NADPH Oxidase Upregulation and Protein Oxidation
Patients with heart failure (HF) have diaphragm abnormalities that contribute to disease morbidity and mortality. Studies in animals suggest that reactive oxygen species (ROS) cause diaphragm abnormalities in HF. However, the effects of HF on ROS sources, antioxidant enzymes, and protein oxidation in the diaphragm of humans is unknown. NAD(P)H oxidase, especially the Nox2 isoform, is an important source of ROS in the diaphragm. Our main hypothesis was that diaphragm from patients with HF have heightened Nox2 expression and p47phox phosphorylation (marker of enzyme activation) that is associated with elevated protein oxidation. We collected diaphragm biopsies from patients with HF and brain-dead organ donors (controls). Diaphragm mRNA levels of Nox2 subunits were increased 2.5–4.6-fold over controls (p \u3c 0.05). Patients also had increased protein levels of Nox2 subunits (p47phox, p22phox, and p67phox) and total p47phox phosphorylation, while phospho-to-total p47phox levels were unchanged. The antioxidant enzyme catalase was increased in patients, whereas glutathione peroxidase and superoxide dismutases were unchanged. Among markers of protein oxidation, carbonyls were increased by ~40% (p \u3c 0.05) and 4-hydroxynonenal and 3-nitrotyrosines were unchanged in patients with HF. Overall, our findings suggest that Nox2 is an important source of ROS in the diaphragm of patients with HF and increases in levels of antioxidant enzymes are not sufficient to maintain normal redox homeostasis. The net outcome is elevated diaphragm protein oxidation that has been shown to cause weakness in animals
CARMA Survey Toward Infrared-bright Nearby Galaxies (STING): Molecular Gas Star Formation Law in NGC4254
This study explores the effects of different assumptions and systematics on
the determination of the local, spatially resolved star formation law. Using
four star formation rate (SFR) tracers (H\alpha with azimuthally averaged
extinction correction, mid-infrared 24 micron, combined H\alpha and
mid-infrared 24 micron, and combined far-ultraviolet and mid-infrared 24
micron), several fitting procedures, and different sampling strategies we probe
the relation between SFR and molecular gas at various spatial resolutions and
surface densities within the central 6.5 kpc in the disk of NGC4254. We find
that in the high surface brightness regions of NGC4254 the form of the
molecular gas star formation law is robustly determined and approximately
linear and independent of the assumed fraction of diffuse emission and the SFR
tracer employed. When the low surface brightness regions are included, the
slope of the star formation law depends primarily on the assumed fraction of
diffuse emission. In such case, results range from linear when the fraction of
diffuse emission in the SFR tracer is ~30% or less (or when diffuse emission is
removed in both the star formation and the molecular gas tracer), to
super-linear when the diffuse fraction is ~50% and above. We find that the
tightness of the correlation between gas and star formation varies with the
choice of star formation tracer. The 24 micron SFR tracer by itself shows the
tightest correlation with the molecular gas surface density, whereas the
H\alpha corrected for extinction using an azimuthally-averaged correction shows
the highest dispersion. We find that for R<0.5R_25 the local star formation
efficiency is constant and similar to that observed in other large spirals,
with a molecular gas depletion time ~2 Gyr.Comment: accepted for publication in ApJ, vol 729, March 10 2011 issue; 30
pages; 14 figures; revised version includes referee's comments; results
unchange
Modeling the Influence of Vitamin D Deficiency on Cigarette Smoke-Induced Emphysema
Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality worldwide. While the primary risk factor for COPD is cigarette smoke exposure, vitamin D deficiency has been epidemiologically implicated as a factor in the progressive development of COPD-associated emphysema. Because of difficulties inherent to studies involving multiple risk factors in the progression of COPD in humans, we developed a murine model in which to study the separate and combined effects of vitamin D deficiency and cigarette smoke exposure. During a 16-week period, mice were exposed to one of four conditions, control diet breathing room air (CD-NS), control diet with cigarette smoke exposure (CD-CSE), vitamin D deficient diet breathing room air (VDD-NS) or vitamin D deficient diet with cigarette smoke exposure (VDD-CSE). At the end of the exposure period, the lungs were examined by a pathologist and separately by morphometric analysis. In parallel experiments, mice were anesthetized for pulmonary function testing followed by sacrifice and analysis. Emphysema (determined by an increase in alveolar mean linear intercept length) was more severe in the VDD-CSE mice compared to control animals and animals exposed to VDD or CSE alone. The VDD-CSE and the CD-CSE mice had increased total lung capacity and increased static lung compliance. There was also a significant increase in the matrix metalloproteinase-9: tissue inhibitor of metalloproteinases-1 (TIMP-1) ratio in VDD-CSE mice compared with all controls. Alpha-1 antitrypsin (A1AT) expression was reduced in VDD-CSE mice as well. In summary, vitamin D deficiency, when combined with cigarette smoke exposure, seemed to accelerate the appearance of emphysemas, perhaps by virtue of an increased protease-antiprotease ratio in the combined VDD-CSE animals. These results support the value of our mouse model in the study of COPD
The Extreme Hosts of Extreme Supernovae
We use GALEX ultraviolet (UV) and optical integrated photometry of the hosts
of seventeen luminous supernovae (LSNe, having peak M_V < -21) and compare them
to a sample of 26,000 galaxies from a cross-match between the SDSS DR4 spectral
catalog and GALEX interim release 1.1. We place the LSNe hosts on the galaxy
NUV-r versus M_r color magnitude diagram (CMD) with the larger sample to
illustrate how extreme they are. The LSN hosts appear to favor low-density
regions of the galaxy CMD falling on the blue edge of the blue cloud toward the
low luminosity end. From the UV-optical photometry, we estimate the star
formation history of the LSN hosts. The hosts have moderately low star
formation rates (SFRs) and low stellar masses (M_*) resulting in high specific
star formation rates (sSFR). Compared with the larger sample, the LSN hosts
occupy low-density regions of a diagram plotting sSFR versus M_* in the area
having higher sSFR and lower M_*. This preference for low M_*, high sSFR hosts
implies the LSNe are produced by an effect having to do with their local
environment. The correlation of mass with metallicity suggests that perhaps
wind-driven mass loss is the factor that prevents LSNe from arising in
higher-mass, higher-metallicity hosts. The massive progenitors of the LSNe
(>100 M_sun), by appearing in low-SFR hosts, are potential tests for theories
of the initial mass function that limit the maximum mass of a star based on the
SFR.Comment: 8 pages, 3 figures, 2 tables, accepted to ApJ, amended references and
updated SN designation
The ACS Nearby Galaxy Survey Treasury II. Young Stars and their Relation to Halpha and UV Emission Timescales in the M81 Outer Disk
We have obtained resolved stellar photometry from Hubble Space Telescope
(HST) Advanced Camera for Surveys (ACS) observations of a field in the outer
disk of M81 as part of the ACS Nearby Galaxy Survey Treasury (ANGST). Motivated
by the recent discovery of extended UV (XUV) disks around many nearby spiral
galaxies, we use the observed stellar population to derive the recent star
formation histories of five ~0.5 kpc-sized regions within this field. These
regions were selected on the basis of their UV luminosity from GALEX and
include two HII regions, two regions which are UV-bright but Halpha-faint, and
one "control" region faint in both UV and Halpha. We estimate our effective SFR
detection limit at ~2 x 10^-4 Msun/yr, which is lower than that of GALEX for
regions of this size. As expected, the HII regions contain massive main
sequence stars (in the mass range 18-27 Msun, based on our best extinction
estimates), while similar massive main sequence stars are lacking in the
UV-bright/Halpha-faint regions. The observations are consistent with stellar
ages 16 Myr in the UV-bright/Halpha-faint
regions. All regions but the control have formed ~10^4 Msun of stars over the
past ~65 Myr. Thus, our results, for at least one small area in the outer disk
of M81, are consistent with an age difference being sufficient to explain the
observed discrepancy between star-forming regions detected in Halpha and those
detected exclusively in UV. However, our data cannot conclusively rule out
other explanations, such as a strongly truncated initial mass function (IMF).Comment: 18 pages, 12 figures, accepted for publication in ApJ, paper with
full resolution figures available:
http://www.nearbygalaxies.org/papers/M81_Halpha_uv.pd
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