425 research outputs found
Are pulmonary embolism and deep-vein thrombosis always one disease?
Pulmonary embolism is traditionally, since autopsy studies by Virchow in the mid 1800s, thought to originate from embolization of a deep-vein thrombosis, resulting in two clinical manifestations of one disease: venous thrombosis. The incidence of deep-vein thrombosis in the population is twice as high as the incidence of pulmonary embolism, i.e. 1 per 1000 and 0.5 per 1000 person-years respectively. The aim of this thesis was to assess whether pulmonary embolism and deep-vein thrombosis are always the same disease or not, and to answer this question with regard to etiology (genetic and acquired risk factors) and anatomical distribution of thrombi in the veins. We studied this question in two populations: the PEDLAR study and the MEGA case-control study. In the PEDLAR study we assessed the origin of pulmonary embolism using a total body Magnetic Resonance Direct Thrombus Imaging technique. We proposed several mecha nisms for the absence of deep-vein thrombi in more than half of the patients with pulmonary embolism. In addition, we investigated the effect of aging on venous valve thickness. This was performed in an ultrasonography study, with participants from 20 to 80 years old (the aging venous valves study). We hypothesized that part of the increasing incidence in venous thrombosis with age can be explained by increasing valve thickness.UBL - phd migration 201
Planar infall of CH3OH gas around Cepheus A HW2
Aims: In order to test the nature of an (accretion) disk in the vicinity of
Cepheus A HW2, we measured the three-dimensional velocity field of the CH3OH
maser spots, which are projected within 1000au of the HW2 object, with an
accuracy of the order of 0.1km/s. Methods: We made use of the European VLBI
Network (EVN) to image the 6.7GHz CH3OH maser emission towards Cepheus A HW2
with 4.5 milli-arcsecond resolution (3au). We observed at three epochs spaced
by one year between 2013 and 2015. During the last epoch, on mid-march 2015, we
benefited from the new deployed Sardinia Radio Telescope. Results: We show that
the CH3OH velocity vectors lie on a preferential plane for the gas motion with
only small deviations of 12+/-9 degrees away from the plane. This plane is
oriented at a position angle of 134 degrees east of north, and inclined by 26
degrees with the line-of-sight, closely matching the orientation of the
disk-like structure previously reported by Patel et al.(2005). Knowing the
orientation of the equatorial plane, we can reconstruct a face-on view of the
CH3OH gas kinematics onto the plane. CH3OH maser emission is detected within a
radius of 900au from HW2, and down to a radius of about 300au, the latter
coincident with the extent of the dust emission at 0.9mm. The velocity field is
dominated by an infall component of about 2km/s down to a radius of 300au,
where a rotational component of 4km/s becomes dominant. We discuss the nature
of this velocity field and the implications for the enclosed mass. Conclusions:
These findings bring direct support to the interpretation that the high-density
gas and dust emission, surrounding Cepheus A HW2, trace an accretion disk.Comment: 9 pages, 4 figures, 2 tables, accepted by Astronomy & Astrophysic
Radiological findings of denosumab treatment for giant cell tumours of bone
Giant cell tumours of bone (GCTB) are benign giant cell-rich tumours typically occurring in the epi-metaphysis of skeletally mature patients. Despite their benign classification, GCTB may be locally aggressive with local recurrence as a challenging issue. Denosumab is a human monoclonal antibody that inhibits osteolysis via the RANK-RANK ligand pathway. There is currently no consensus on optimal treatment duration or imaging modality for monitoring patients on denosumab therapy. This review illustrates the radiological findings of GCTB on denosumab treatment seen on plain radiographs, CT, MRI, PET-CT and DEXA, with reference to the current literature. Recognizing imaging features indicative of a positive response to denosumab is important for therapeutic decision-making. Imaging findings with respect to duration of denosumab treatment, tumour upregulation during treatment, tumour recurrence and malignant transformation are discussed. The development of a sclerotic neocortex and varying degrees of matrix osteosclerosis are seen on plain radiographs. Reconstitution of subarticular bone and articular surface irregularity are optimally evaluated on CT which can also quantify tumour density. MRI demonstrates heterogeneous low signal matrix and is useful to assess decrease in size of cystic and/or soft tissue components of GCTB. A fat-suppressed fluid-sensitive MR sequence is important to detect tumour reactivation. Reduction in F-18-FDG-PET avidity represents an early sensitive sign of response to denosumab treatment. Regardless of imaging modality, close follow-up in a specialist centre and careful evaluation of nonresponders is necessary as local recurrence after cessation of denosumab treatment and malignant transformation of GCTB have been described.Imaging- and therapeutic targets in neoplastic and musculoskeletal inflammatory diseas
The Shroud Around the Twin Radio Jets in NGC 1052
(Abridged) We discuss multiple VLBI continuum and spectral line observations
and WSRT spectroscopy of NGC 1052. Sub-parsec scale features move outward at
approximately 0.26c in bi-symmetric jets, most likely oriented near the plane
of the sky. Absorption and emission signatures reveal ionised, atomic, and
molecular components of the surrounding medium.
Seven-frequency (1.4 to 43 GHz) VLBA observations show free-free absorption
in the inner parsec, probably together with synchrotron self-absorption. There
is apparently a geometrically thick but patchy structure oriented roughly
orthogonal to the jets. The western jet is receding: it is covered more deeply
and extensively. HI spectral line VLBI reveals atomic gas in front of both
jets. There appear to be three velocity systems. The deepest, at "high
velocities" (receding by 125 to 200 km/s), seems restricted to a shell 1 to 2
pc away from the core, within which this gas might be largely ionised. WSRT
spectroscopy has revealed 1667 and 1665 MHz OH absorption with their line ratio
varying roughly from 1:1 to 2:1 between -35 and 200 km/s. In the high velocity
system the OH profiles are similar to HI, suggesting co-location of that atomic
and molecular gas, and leaving unclear the connection to the H2O masing gas
seen elsewhere. We have also detected both 18cm OH satellite lines in the high
velocity system. They have conjugate profiles: 1612 MHz is in absorption, and
1720 MHz in emission.Comment: 16 pages, 14 figures, LaTeX, includes aa.cls, accepted for
publication in Astronomy and Astrophysic
Resolving the masers in M82
Despite first being detected in the 1970s, surprisingly little is known about
the OH main line maser population in the nearby starburst galaxy M82. Sometimes
referred to as 'kilomasers', they have isotropic luminosities intermediate
between Galactic masers and those found in more distant megamasers. Several
observations have been carried by this group over the last ten years in an
attempt to get a better handle on their nature. High velocity resolution VLA
observations in 2006 showed that almost all of the maser spots, distributed
across the central arcminute of the galaxy, were apparently coincident with
background continuum features, and a handful displayed multiple velocity
components. The majority of those with velocity structure are located on a
blue-shifted arc in the pv-plane, spatially located on an arc northward of the
peculiar source known as B41.95+57.5. Now, new results from high spatial and
spectral resolution observations with the EVN have resolved several of these
masers into multiple spatial components for the first time. The maser emission
is compared with known continuum sources in the galaxy, and we conclude that at
least some of the maser emission is from high-gain maser action.Comment: Six pages, one table, one figure. To appear in proceedings of the
11th EVN Symposium (Bordeaux, 9-12 October 2012
Faint Gigahertz peaked spectrum sources and the evolution of young radio sources
GPS sources are the objects of choice to study the initial evolution of
extragalactic radio sources, since it is most likely that they are the young
counterparts of large scale radio sources. Correlations found between their
peak frequency, peak flux density and angular size provide strong evidence that
synchrotron self absorption is the cause of the spectral turnovers, and
indicate that young radio sources evolve in a self-similar way. The difference
in redshift distribution between young and old radio sources must be due to a
difference in slope of their luminosity functions, and we argue that this slope
is strongly affected by the luminosity evolution of the individual sources. A
luminosity evolution scenario is proposed in which GPS sources increase in
luminosity and large scale radio sources decrease in luminosity with time. It
is shown that such a scenario agrees with the local luminosity function of GPS
galaxies.Comment: Late, 6 pages, 2 figs. To appear in the proceedings of EVN/JIVE
Symposium No 4, New Astronomy Reviews (eds. Garrett et al.). For related
papers, see http://www.ast.cam.ac.uk/~snelle
The proper motion of the Arches cluster with Keck Laser-Guide Star Adaptive Optics
We present the first measurement of the proper motion of the young, compact
Arches cluster near the Galactic center from near-infrared adaptive optics (AO)
data taken with the recently commissioned laser-guide star (LGS) at the Keck
10-m telescope. The excellent astrometric accuracy achieved with LGS-AO
provides the basis for a detailed comparison with VLT/NAOS-CONICA data taken
4.3 years earlier. Over the 4.3 year baseline, a spatial displacement of the
Arches cluster with respect to the field population is measured to be 24.0 +/-
2.2 mas, corresponding to a proper motion of 5.6 +/- 0.5 mas/yr or 212 +/- 29
km/s at a distance of 8 kpc. In combination with the known line-of-sight
velocity of the cluster, we derive a 3D space motion of 232 +/- 30 km/s of the
Arches relative to the field. The large proper motion of the Arches cannot be
explained with any of the closed orbital families observed in gas clouds in the
bar potential of the inner Galaxy, but would be consistent with the Arches
being on a transitional trajectory from x1 to x2 orbits. We investigate a
cloud-cloud collision as the possible origin for the Arches cluster. The
integration of the cluster orbit in the potential of the inner Galaxy suggests
that the cluster passes within 10 pc of the supermassive black hole only if its
true GC distance is very close to its projected distance. A contribution of
young stars from the Arches cluster to the young stellar population in the
inner few parsecs of the GC thus appears increasingly unlikely. The measurement
of the 3D velocity and orbital analysis provides the first observational
evidence that Arches-like clusters do not spiral into the GC. This confirms
that no progenitor clusters to the nuclear cluster are observed at the present
epoch.Comment: 22 pdflatex pages including 12 figures, reviewed version accepted by
Ap
Resolving the distance controversy for Sharpless 269: A possible kink in the outer arm
Sharpless 269 (S269) is one of a few HII regions in the outer spiral arm of
the Milky Way with strong water maser emission. Based on data from the Very
Long Baseline Interferometry (VLBI) Exploration of Radio Astrometry (VERA)
array, two parallax measurements have been published, which differ by nearly
. Each distance estimate supports a different structure for the outer
arm. Moreover, given its large Galactocentric radii, S269 has special relevance
as its proper motion and parallax have been used to constrain the Galactic
rotation curve at large radii. Using recent Very Long Baseline Array (VLBA)
observations, we accurately measure the parallax and proper motion of the water
masers in S269. We interpret the position and motion of S269 in the context of
Galactic structure, and possible optical counterparts. S269's 22 GHz water
masers and two close-by quasars were observed at 16 epochs between 2015 and
2016 using the VLBA. We measure an annual parallax for S269 of 0.241
0.012 mas corresponding to a distance from the Sun of
kpc by fitting four maser spots. The mean proper motion for S269 was estimated
as mas and mas for
and respectively, which corresponds
to the motion expected for a flat Galactic rotation curve at large radius. This
distance estimate, Galactic kinematic simulations and observations of other
massive young stars in the outer region support the existence of a kink in the
outer arm at 140 degrees. Additionally, we find more than 2,000
optical sources in the Gaia DR2 catalog within 125 pc radius around the 3D
position of the water maser emission; from those only three sources are likely
members of the same stellar association that contains the young massive star
responsible for the maser emission (S269 IRS 2w).Comment: Accepted for publication in A&
In the Shadow of the Accretion Disk: Higher Resolution Imaging of the Central Parsec in NGC 4261
The physical conditions in the inner parsec of accretion disks believed to
orbit the central black holes in active galactic nuclei can be probed by
imaging the absorption (by ionized gas in the disk) of background emission from
a radio counterjet. We report high angular resolution VLBI observations of the
nearby (about 40 Mpc) radio galaxy NGC 4261 that confirm free-free absorption
of radio emission from a counterjet by a geometrically thin, nearly edge-on
disk at 1.6, 4.8, and 8.4 GHz. The angular width and depth of the absorption
appears to increase with decreasing frequency, as expected. We derive an
average electron density of ~10E4 per cc at a disk radius of about 0.2 pc,
assuming that the inner disk inclination and opening angles are the same as at
larger radii. Pressure balance between the thermal gas and the magnetic field
in the disk implies an average field strength of 0.1 milligauss at a radius of
0.2 pc. These are the closest-in free-free absorption measurements to date of
the conditions in an extragalactic accretion disk orbiting a black hole with a
well-determined mass. If a standard advection-dominated accretion flow exists
in the disk center, then the transition between thin and thick disk regions
must occur at a radius less than 0.2 pc (4000 Schwarzschild radii).Comment: 20 pages including 12 figures. Accepted for publication in Ap
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