245 research outputs found
Spatial orientation of cross-sectional images of coronary arteries: point of view in intracoronary imaging
<p>Abstract</p> <p>Background</p> <p>In studies where cross-sectional images of coronary arteries obtained with different imaging modalities are compared, the importance of correct co-localization and matching of images along the coronary artery longitudinal axis is obvious. However, it appears neglected that correct spatial orientation of the cross-sectional plane may not be obtainable just by rotating the images to ensure co-localization of identifiable landmarks such as sidebranches. A cross-section has two sides, one facing proximally and the other distally, and pairs of images reconstructed corresponding to these opposite points of view are mirror images of each other and not superimposable. This may be difficult if not impossible to recognize and unrecognized it will give rise to flawed results in the development and validation of imaging technologies aimed at plaque characterization (tissue mapping). We determined the imagined point of view for three commercially available intracoronary imaging systems used by invasive cardiologists and illustrate its importance in imaging modality validation.</p> <p>Methods and Results</p> <p>We made an asymmetric phantom and investigated it with two different intravascular ultrasound (IVUS) systems and one optical coherence tomography (OCT) system. The asymmetry of the phantom allowed determination of the spatial orientation of the cross-sectional images. On all tested systems, an observer should imagine herself/himself standing proximal to the cross-section when looking at the intravascular images.</p> <p>Conclusions</p> <p>The tested intracoronary imaging modalities displayed cross-sectional images with a spatial orientation corresponding to a proximal point of view. Knowledge of the spatial orientation is mandatory when comparing and validating different imaging modalities aimed at plaque characterization.</p
Correlated X-ray/Ultraviolet/Optical variability in the very low mass AGN NGC 4395
We report the results of a one year Swift X-ray/UV/optical programme
monitoring the dwarf Seyfert nucleus in NGC 4395 in 2008-2009. The UV/optical
flux from the nucleus was found to vary dramatically over the monitoring
period, with a similar pattern of variation in each of the observed UV/optical
bands (spanning 1900 - 5500 {\AA}). In particular, the luminosity of NGC 4395
in the 1900 {\AA} band changed by more than a factor of eight over the
monitoring period. The fractional variability was smaller in the UV/optical
bands than that seen in the X-rays, with the X-ray/optical ratio increasing
with increasing flux. Pseudo-instantaneous flux measurements in the X-ray and
each UV/optical band were well correlated, with cross correlation coefficients
of >0.7, significant at 99.9 per cent confidence. Archival Swift observations
from 2006 sample the intra-day X-ray/optical variability on NGC 4395. These
archival data show a very strong correlation between the X-ray and b bands,
with a cross-correlation coefficient of 0.84 (significant at >99 per cent
confidence). The peak in the cross correlation function is marginally resolved
and asymmetric, suggesting that X-rays lead the b band, but by 1 hour. In
response to recent (August 2011) very high X-ray flux levels from NGC4395 we
triggered Swift ToO observations, which sample the intra-hour X-ray/UV
variability. These observations indicate, albeit with large uncertainties, a
lag of the 1900 {\AA} band behind the X-ray flux of ~400 s. The tight
correlation between the X-ray and UV/optical lightcurves, together with the
constraints we place on lag time-scale are consistent with the UV/optical
variability of NGC 4395 being primarily due to reprocessing of X-ray photons by
the accretion disc.Comment: 11 pages, 9 figures, 3 tables. Accepted for publication in MNRA
Using H-alpha Morphology and Surface Brightness Fluctuations to Age-Date Star Clusters in M83
We use new WFC3 observations of the nearby grand design spiral galaxy M83 to
develop two independent methods for estimating the ages of young star clusters.
The first method uses the physical extent and morphology of Halpha emission to
estimate the ages of clusters younger than tau ~10 Myr. It is based on the
simple premise that the gas in very young (tau < few Myr) clusters is largely
coincident with the cluster stars, is in a small, ring-like structure
surrounding the stars in slightly older clusters (e.g., tau ~5 Myr), and is in
a larger ring-like bubble for still older clusters (i.e., ~5-10 Myr). The
second method is based on an observed relation between pixel-to-pixel flux
variations within clusters and their ages. This method relies on the fact that
the brightest individual stars in a cluster are most prominent at ages around
10 Myr, and fall below the detection limit (i.e., M_V < -3.5) for ages older
than about 100 Myr. These two methods are the basis for a new morphological
classification system which can be used to estimate the ages of star clusters
based on their appearance. We compare previous age estimates of clusters in M83
determined from fitting UBVI Halpha measurements using predictions from stellar
evolutionary models with our new morphological categories and find good
agreement at the ~95% level. The scatter within categories is ~0.1 dex in log
tau for young clusters (10 Myr) clusters. A
by-product of this study is the identification of 22 "single-star" HII regions
in M83, with central stars having ages ~4 Myr.Comment: 33 pages, 10 figures, 3 tables; published in March Ap
Are CO lines good indicators of the star formation rate in galaxies?
In this paper, we investigate the relevance of using the CO line
emissions as indicators of star formation rates (SFR). For the first time, we
present this study for a relatively large number of CO transitions (12)
as well as over a large interval in redshift (from z0 to z6). For
the nearby sources (D10 Mpc), we have used homogeneous sample of
CO data provided by Bayet et al. (2004, 2006), mixing observational and
modelled line intensities. For higher-z sources (z 1), we have collected
CO observations from various papers and have completed the data set of
line intensities with model predictions which we also present in this paper.
Finally, for increasing the statistics, we have included recent CO(1-0)
and CO(3-2) observations of intermediate-z sources. Linear regressions
have been calculated for identifying the tightest SFR-CO line luminosity
relationships. We show that the \emph{total} CO, the CO(5-4), the
CO(6-5) and the CO(7-6) luminosities are the best indicators of
SFR (as measured by the far-infrared luminosity). Comparisons with theoretical
approaches from Krumholz and Thompson (2007) and Narayanan et al. (2008) are
also performed in this paper. Although in general agreement, the predictions
made by these authors and the observational results we present here show small
and interesting discrepancies. In particular, the slope of the linear
regressions, for J 4 CO lines are not similar between
theoretical studies and observations. On one hand, a larger high-J CO
data set of observations might help to better agree with models, increasing the
statistics. On the other hand, theoretical studies extended to high redshift
sources might also reduce such discrepancies.Comment: 10 pages, 3 figures and 4 tables, Accepted in MNRA
Novel insights into the cardio-protective effects of FGF21 in lean and obese rat hearts
Aims: Fibroblast growth factor 21 (FGF21) is a hepatic metabolic regulator with pleotropic actions. Its plasma concentrations are increased in obesity and diabetes; states associated with an increased incidence of cardiovascular disease. We therefore investigated the direct effect of FGF21 on cardio-protection in obese and lean hearts in response to ischemia.
Methods and Results: FGF21, FGF21-receptor 1 (FGFR1) and beta-Klotho (βKlotho) were expressed in rodent, human hearts and primary rat cardiomyocytes. Cardiac FGF21 was expressed and secreted (real time RT-PCR/western blot and ELISA) in an autocrine-paracrine manner, in response to obesity and hypoxia, involving FGFR1-βKlotho components. Cardiac-FGF21 expression and secretion were increased in response to global ischemia. In contrast βKlotho was reduced in obese hearts. In isolated adult rat cardiomyocytes, FGF21 activated PI3K/Akt (phosphatidylinositol 3-kinase/Akt), ERK1/2(extracellular signal-regulated kinase) and AMPK (AMP-activated protein kinase) pathways. In Langendorff perfused rat [adult male wild-type wistar] hearts, FGF21 administration induced significant cardio-protection and restoration of function following global ischemia. Inhibition of PI3K/Akt, AMPK, ERK1/2 and ROR-α (retinoic-acid receptor alpha) pathway led to significant decrease of FGF21 induced cardio-protection and restoration of cardiac function in response to global ischemia. More importantly, this cardio-protective response induced by FGF21 was reduced in obesity, although the cardiac expression profiles and circulating FGF21 levels were increased.
Conclusion: In an ex vivo Langendorff system, we show that FGF21 induced cardiac protection and restoration of cardiac function involving autocrine-paracrine pathways, with reduced effect in obesity. Collectively, our findings provide novel insights into FGF21-induced cardiac effects in obesity and ischemia
Molecular gas in the galaxy M83. I - The molecular gas distribution
We present CO(1-0) and CO(2-1) Swedish-ESO Submillimetre Telescope (SEST)
observations of the barred spiral galaxy M83 (NGC5236). The maps cover the
entire optical disk. The CO emission is strongly peaked toward the nucleus,
which breaks up into two separate components in the CO(2-1) data due to the
higher spatial resolution. Emission from the bar is strong, in particular on
the leading edges of the bar. The molecular gas arms are clearly resolved and
can be traced for more than 360\degr . Emission in the inter-arm regions is
detected. The average CO CO(2-1)/CO(1-0) line ratio is 0.77. The ratio is lower
than this on the spiral arms and higher in the inter-arm regions. The arms show
regularly spaced concentrations of molecular gas, Giant Molecular Associations
(GMA's), whose masses are of the order 10^7 Msun. The total molecular gas mass
is estimated to be 3.9*10^9 Msun. This mass is comparable to the total HI mass,
but H_2 dominates in the optical disk. In the disk, H_2 and HI show very
similar distributions, including small scale clumping. We compare the molecular
gas distribution with those of other star formation tracers, such as B and
H_alpha images.Comment: 20 pages, 15 figures, A&A accepted. A higher resolution version
available at http://www.astro.su.se/~andreas/publications
Determination of Edema in Porcine Coronary Arteries by T2 Weighted Cardiovascular Magnetic Resonance
Pharmacokinetics and ex vivo whole blood clot formation of a new recombinant FVIII (N8) in haemophilia A dogs
N8, a new recombinant factor VIII (rFVIII) compound developed for the treatment of haemophilia A, is produced in Chinese hamster ovary (CHO) cells and formulated without human- or animal-derived materials. The aim of the present study was to compare the pharmacokinetics (PK) and the procoagulant effect, measured by ex vivo whole blood clot formation, of N8 and a commercial rFVIII in a cross-over study in haemophilia A dogs. N8 and Advate® (100 IU kg−1) were administered intravenously to three haemophilia A dogs. Blood was sampled between 0 and 120 h postdose and FVIII:C analysed. PK parameters maximum plasma concentration, area under the curve, half-life (t½), clearance, mean residence time (MRT) and volume of distribution and incremental recovery were calculated. Whole blood clotting time (WBCT) and thromboelastography (TEG®) were used to determine the haemostatic potential. No adverse reactions were observed with N8 or Advate®. N8 and Advate® exhibited similar PK parameters, with t½ 7.7–11 h and MRT 11–14 h. Both rFVIII compounds corrected the prolonged WBCT (>48 min) to the range of normal dogs (8–12 min), i.e. N8 to 7.5–10.5 min and Advate® to 7.5–11.5 min. N8 and Advate® also normalized the whole blood clot formation according to TEG®. The native whole blood clotting assays (WBCT, TEG®) appeared to be more sensitive to low concentrations of FVIII than assays in citrated plasma samples. In conclusion, comparison of N8 and Advate® in haemophilia A dogs revealed similar safety, similar PK and similar effects in whole blood clot formation assays
Reduced EPO receptor expression may contribute to limited pleiotropic effects of EPO during critical illness
- …