ScarGAN: Chained Generative Adversarial Networks to Simulate Pathological Tissue on Cardiovascular MR Scans

Medical images with specific pathologies are scarce, but a large amount of data is usually required for a deep convolutional neural network (DCNN) to achieve good accuracy. We consider the problem of segmenting the left ventricular (LV) myocardium on late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) scans of which only some of the scans have scar tissue. We propose ScarGAN to simulate scar tissue on healthy myocardium using chained generative adversarial networks (GAN). Our novel approach factorizes the simulation process into 3 steps: 1) a mask generator to simulate the shape of the scar tissue; 2) a domain-specific heuristic to produce the initial simulated scar tissue from the simulated shape; 3) a refining generator to add details to the simulated scar tissue. Unlike other approaches that generate samples from scratch, we simulate scar tissue on normal scans resulting in highly realistic samples. We show that experienced radiologists are unable to distinguish between real and simulated scar tissue. Training a U-Net with additional scans with scar tissue simulated by ScarGAN increases the percentage of scar pixels correctly included in LV myocardium prediction from 75.9% to 80.5%.Comment: 12 pages, 5 figures. To appear in MICCAI DLMIA 201

Comorbid conditions explain the association between posttraumatic stress disorder and incident cardiovascular disease

Background Posttraumatic stress disorder ( PTSD ) is associated with risk of cardiovascular disease ( CVD ). Biopsychosocial factors associated with PTSD likely account for some or all of this association. We determined whether 1, or a combination of comorbid conditions explained the association between PTSD and incident CVD . Methods and Results Eligible patients used 1 of 5 Veterans Health Affairs medical centers distributed across the United States. Data were obtained from electronic health records. At index date, 2519 Veterans Health Affairs ( VA ) patients, 30 to 70 years of age, had PTSD diagnoses and 1659 did not. Patients had no CVD diagnoses for 12 months before index date. Patients could enter the cohort between 2008 and 2012 with follow-up until 2015. Age-adjusted Cox proportional hazard models were computed before and after adjusting for comorbidities. Patients were middle aged (mean=50.1 years, SD ±11.0), mostly male (87.0%), and 60% were white. The age-adjusted association between PTSD and incident CVD was significant (hazard ratio=1.41; 95% CI : 1.21-1.63). After adjustment for metabolic conditions, the association between PTSD and incident CVD was attenuated but remained significant (hazard ratio=1.23; 95% CI : 1.06-1.44). After additional adjustment for smoking, sleep disorder, substance use disorder, anxiety disorders, and depression, PTSD was not associated with incident CVD (hazard ratio=0.96; 95% CI : 0.81-1.15). Conclusions PTSD is not an independent risk factor for CVD . Physical and psychiatric conditions and smoking that co-occur with PTSD explain why this patient population has an increased risk of CVD . Careful monitoring may limit exposure to CVD risk factors and subsequent incident CVD

Evolution of the Lyman-alpha Halos around High-Redshift Radio Galaxies

We have obtained the first constraints on extended Ly-alpha emission at z ~ 1 in a sample of five radio galaxies. We detect Ly-alpha emission from four of the five galaxies. The Ly-alpha luminosities range from 0.1 - 4 times 10^43 erg/s and are much smaller than those observed for halos around higher redshift radio galaxies. If the z ~ 1 radio galaxies are the descendents the z >~ 2 radio galaxies, then their Ly-alpha luminosities evolve strongly with redshift as ~(1+z)^5. There do not appear to be strong correlations between other parameters, such as radio power, suggesting that this observed evolution is real and not an observational artifact or secondary correlation. We speculate that this evolution of luminous halos may be due to gas depletion (as gas cools, settles, and forms stars) accompanied by an overall rise in the mean gas temperature and a decrease in specific star-formation rate in and around these massive galaxies.Comment: 5 pages, 4 figures, published in ApJ Letters, 694, L31-35 March 20 200

Dynamical Delays Between Starburst and AGN Activity in Galaxy Nuclei

Observations of AGN have suggested a possible delay between the peak of star formation (on some scale) and AGN activity. Inefficient fueling (and/or feedback) from fast stellar winds has been invoked to explain this, but we argue this is unlikely in bright systems accreting primarily cold dense gas. We show that such a delay can arise even in bright quasars for purely dynamical reasons. If some large-scale process produces rapid inflow, smaller scales will quickly become gas-dominated. As the gas density peaks, so does the SFR. However, gravitational torques which govern further inflow are relatively inefficient in gas-dominated systems; as more gas is turned into stars, the stars provide an efficient angular momentum sink allowing more rapid inflow. Moreover, the gas provided to the central regions in mergers or strong disk instabilities will typically be ~100 times larger than that needed to fuel the BH; the system is effectively in the 'infinite gas supply' limit. BH growth can therefore continue for some time while the gas supply exhausts, until it has significantly depleted to the point where the BH is finally 'starved.' Both of these effects act together with comparable magnitude, and mean that the peak of BH growth can lag the peak in the SFR measured at a given scale by a timescale corresponding to the gas exhaustion time on that scale (~ 10-100 local dynamical times). This predicts that the inferred delay will vary in a specific manner with the radius over which the star formation rate is measured. We discuss possible implications for the role of AGN feedback in suppressing star formation activity.Comment: 5 pages, 2 figures, accepted to MNRAS Letters (matches accepted version

Quasars and their host galaxies

This review attempts to describe developments in the fields of quasar and quasar host galaxies in the past five. In this time period, the Sloan and 2dF quasar surveys have added several tens of thousands of quasars, with Sloan quasars being found to z>6. Obscured, or partially obscured quasars have begun to be found in significant numbers. Black hole mass estimates for quasars, and our confidence in them, have improved significantly, allowing a start on relating quasar properties such as radio jet power to fundamental parameters of the quasar such as black hole mass and accretion rate. Quasar host galaxy studies have allowed us to find and characterize the host galaxies of quasars to z>2. Despite these developments, many questions remain unresolved, in particular the origin of the close relationship between black hole mass and galaxy bulge mass/velocity dispersion seen in local galaxies.Comment: Review article, to appear in Astrophysics Update

Quasars: the characteristic spectrum and the induced radiative heating

Using information on the cosmic X-ray background and the cumulative light of active galactic nuclei at infrared wavelengths, the estimated local mass density of galactic massive black holes (MBHs) and published AGN composite spectra in the optical, UV and X-ray, we compute the characteristic angular-integrated, broad-band spectral energy distribution of the average quasar in the universe. We demonstrate that the radiation from such sources can photoionize and Compton heat the plasma surrounding them up to an equilibrium Compton temperature (Tc) of 2x10^7 K. It is shown that circumnuclear obscuration cannot significantly affect the net gas Compton heating and cooling rates, so that the above Tc value is approximately characteristic of both obscured and unobscured quasars. This temperature is above typical gas temperatures in elliptical galaxies and just above the virial temperatures of giant ellipticals. The general results of this work can be used for accurate calculations of the feedback effect of MBHs on both their immediate environs and the more distant interstellar medium of their host galaxies.Comment: 15 pages, 5 figures. Revised version accepted for publication in MNRA

Obscured and powerful AGN and starburst activities at z~3.5

We report the discovery of two sources at z=3.867 and z=3.427 that exhibit powerful starburst and AGN activities. They benefit from data from radio to X rays from the CFHTLS-D1/SWIRE/XMDS surveys. Follow-up optical and near-infrared spectroscopy, and millimeter IRAM/MAMBO observations are also available. We performed an analysis of their spectral energy distributions to understand the origin of their emission and constrain their luminosities. A comparison with other composite systems at similar redshifts from the literature is also presented. The AGN and starburst bolometric luminosities are ~10^13 Lsun. The AGN emission dominates at X ray, optical, mid-infrared wavelengths, and probably in the radio. The starburst emission dominates in the far-infrared. The estimated star formation rates range from 500 to 3000Msun/yr. The AGN near-infrared and X ray emissions are heavily obscured in both sources with an estimated dust extinction Av>4, and Compton-thick gas column densities. The two sources are the most obscured and most luminous AGNs detected at millimeter wavelengths currently known. The sources presented in this work are heavily obscured QSOs, but their properties are not fully explained by the standard AGN unification model. In one source, the ultraviolet and optical spectra suggest the presence of outflowing gas and shocks, and both sources show emission from hot dust, most likely in the vicinity of the nucleus. Evidence of moderate AGN-driven radio activity is found in both sources. The two sources lie on the local M_BH-M_bulge relation. To remain on this relation, their star formation rate has to decrease. Our results support evolutionary models that invoke radio feedback as star formation quenching mechanism, and suggest that such a mechanism might play a major role also in powerful AGNs.Comment: Accepted for publication in Astronomy & Astrophysics (12 pages; 6 figures); replaced version includes minor language editing and revised reference

Spectrally resolved fluxes derived from collocated AIRS and CERES measurements and their application in model evaluation: Clear sky over the tropical oceans

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94623/1/jgrd14292.pd