80 research outputs found
Suppressing bladder artifacts in bone SPECT of the pelvis.
OBJECTIVE: Bladder-filling reconstruction artifacts have a detrimental effect on the image quality of pelvic bone single photon emission computed tomography (SPECT). Using a simple protocol consisting of forced diuresis coupled with intravenous (IV) hydration, this study was undertaken to obtain an artifact-free pelvic SPECT after discarding the residual urinary activity. METHODS: Thirty patients were enrolled. In group I, pelvic SPECT was performed directly after normal void, whereas in group II, SPECT was preceded by IV injection of 0.5 mg/kg furosemide (maximum 40 mg) coupled with IV infusion of 500 cc of physiologic saline. Bladder-filling reconstruction artifacts were analyzed in group I patients, who had their images reconstructed using both filtered backprojection and iterative algorithms, both qualitatively and quantitatively by means of regions of interest (ROIs) drawn around the artifact-bearing bone areas as well as the corresponding contralateral sites. For group II patients, besides visual analysis, ROIs were placed over the sites corresponding to those of the group I patients. In every patient, total counts of each ROI were normalized to a reference ROI placed over the sacrum, and a ratio was created. RESULTS: Using filtered backprojection, two forms of artifacts were identified in group I patients: first, a streak pattern that extended to the sacro-iliac joint in nine (60%) patients, the hip joint in five (33%), the superior pubic rami in four (27%), the sacrum in three (20%), and the ischium in one (6%); second, a count loss subtype which extended to the hip joints in nine (60%) patients. Corresponding values after iterative reconstruction were two (13%) for the sacro-iliac joint, three (20%) for the hip joint, one (6%) for the superior pubic ramus, and one (6%) for the sacrum. In five (33%) patients, residual count loss artifacts were still identifiable after iterative reconstruction. However in group II, no such effects were observed because the bladder activity reached near background level in 14 (93%) of 15 patients after three successive voids with a 3.5-fold decrease in the mean value of total bladder count in comparison with group I patients. A statistically significant difference was found between artifact- and non-artifact-harboring ROIs in group I whichever the method used for reconstruction, whereas the values of right and left hemi-pelvis ROIs/sacrum in group II were almost identical. CONCLUSIONS: Forced diuresis coupled with parenteral hydration facilitates the acquisition of an artifact-free pelvic SPECT. Especially for clinical questions that focus on femoral heads and pubic bones, applying the aforementioned protocol may improve the diagnostic accuracy of pelvic bone SPECT
NGTS-13b: A hot 4.8 Jupiter-mass planet transiting a subgiant star
We report the discovery of the massive hot Jupiter NGTS-13b by the Next
Generation Transit Survey (NGTS). The V = 12.7 host star is likely in the
subgiant evolutionary phase with log g = 4.04 0.05, T =
5819 73 K, M = 1.30 M, and R =
1.79 0.06 R. NGTS detected a transiting planet with a period of
P = 4.12 days around the star, which was later validated with the Transiting
Exoplanet Survey Satellite (TESS; TIC 454069765). We confirm the planet using
radial velocities from the CORALIE spectrograph. Using NGTS and TESS full-frame
image photometry combined with CORALIE radial velocities we determine NGTS-13b
to have a radius of R = 1.142 0.046 R, mass of M =
4.84 0.44 M and eccentricity e = 0.086 0.034. Some previous
studies suggest that 4 M may be a border between two separate
formation scenarios (e.g., core accretion and disk instability) and that
massive giant planets share similar formation mechanisms as lower-mass brown
dwarfs. NGTS-13b is just above 4 M making it an important addition to
the statistical sample needed to understand the differences between various
classes of substellar companions. The high metallicity, [Fe/H] = 0.25
0.17, of NGTS-13 does not support previous suggestions that massive giants are
found preferentially around lower metallicity host stars, but NGTS-13b does
support findings that more massive and evolved hosts may have a higher
occurrence of close-in massive planets than lower-mass unevolved stars
NGTS-5b: A highly inflated planet offering insights into the sub-Jovian desert
Context: Planetary population analysis gives us insight into formation and
evolution processes. For short-period planets, the subJovian desert has been
discussed in recent years with regard to the planet population in the
mass/period and radius/period parameter space without taking stellar parameters
into account. The Next Generation Transit Survey (NGTS) is optimised for
detecting planets in this regime, which allows for further analysis of the
sub-Jovian desert.
Aims: With high-precision photometric surveys (e.g. with NGTS and TESS),
which aim to detect short period planets especially around M/K-type host stars,
stellar parameters need to be accounted for when empirical data are compared to
model predictions. Presenting a newly discovered planet at the boundary of the
sub-Jovian desert, we analyse its bulk properties and use it to show the
properties of exoplanets that border the sub-Jovian desert.
Methods: Using NGTS light curve and spectroscopic follow-up observations, we
confirm the planetary nature of planet NGTS-5b and determine its mass. Using
exoplanet archives, we set the planet in context with other discoveries.
Results: NGTS-5b is a short-period planet with an orbital period of 3.3569866
+- 0.0000026 days. With a mass of 0.229 +- 0.037 MJup and a radius of 1.136 +-
0.023 RJup, it is highly inflated. Its mass places it at the upper boundary of
the sub-Jovian desert. Because the host is a K2 dwarf, we need to account for
the stellar parameters when NGTS-5b is analysed with regard to planet
populations.
Conclusions: With red-sensitive surveys (e.g. with NGTS and TESS), we expect
many more planets around late-type stars to be detected. An empirical analysis
of the sub-Jovian desert should therefore take stellar parameters into account
NGTS discovery of a highly inflated Saturn-mass planet and a highly irradiated hot Jupiter: NGTS-26 b and NGTS-27 b
We report the discovery of two new transiting giant exoplanets NGTS-26 b and NGTS-27 b by the Next Generation Transit Survey (NGTS). NGTS-26 b orbits around a G6-type main sequence star every 4.52 days. It has a mass of 0.29-0.06+0.07 MJup and a radius of 1.33-0.05+0.06 RJup making it a Saturn-mass planet with a highly inflated radius. NGTS-27 b orbits around a slightly evolved G3-type star every 3.37 days. It has a mass of 0.59-0.07+0.10 MJup and a radius of 1.40±0.04 RJup, making it a relatively standard hot Jupiter. The transits of these two planetary systems were re-observed and confirmed in photometry by the SAAO 1.0-m telescope, 1.2-m Euler Swiss telescope as well as the TESS spacecraft, and their masses were derived spectroscopically by the CORALIE, FEROS and HARPS spectrographs. Both giant exoplanets are highly irradiated by their host stars and present an anomalously inflated radius, especially NGTS-26 b which is one of the largest objects among peers of similar mass
NGTS-11 b (TOI-1847 b): A Transiting Warm Saturn Recovered from a TESS Single-transit Event
We report the discovery of NGTS-11 b (=TOI-1847 b), a transiting Saturn in a
35.46-day orbit around a mid K-type star (Teff=5050 K). We initially identified
the system from a single-transit event in a TESS full-frame image light-curve.
Following seventy-nine nights of photometric monitoring with an NGTS telescope,
we observed a second full transit of NGTS-11 b approximately one year after the
TESS single-transit event. The NGTS transit confirmed the parameters of the
transit signal and restricted the orbital period to a set of 13 discrete
periods. We combined our transit detections with precise radial velocity
measurements to determine the true orbital period and measure the mass of the
planet. We find NGTS-11 b has a radius of 0.817+0.028-0.032 , a mass of
0.344+0.092-0.073 , and an equilibrium temperature of just 435+34-32 K,
making it one of the coolest known transiting gas giants. NGTS-11 b is the
first exoplanet to be discovered after being initially identified as a TESS
single-transit event, and its discovery highlights the power of intense
photometric monitoring in recovering longer-period transiting exoplanets from
single-transit events
The Next Generation Transit Survey (NGTS)
© 2017 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. We describe the Next Generation Transit Survey (NGTS), which is a ground-based project searching for transiting exoplanets orbiting bright stars. NGTS builds on the legacy of previous surveys, most notably WASP, and is designed to achieve higher photometric precision and hence find smaller planets than have previously been detected from the ground. It also operates in red light,maximizing sensitivity to late K and earlyMdwarf stars. The survey specifications call for photometric precision of 0.1 per cent in red light over an instantaneous field of view of 100 deg 2 , enabling the detection of Neptune-sized exoplanets around Sun-like stars and super-Earths around M dwarfs. The survey is carried out with a purpose-built facility at Cerro Paranal, Chile, which is the premier site of the European Southern Observatory (ESO). An array of twelve 20 cm f/2.8 telescopes fitted with back-illuminated deep-depletion CCD cameras is used to survey fields intensively at intermediateGalactic latitudes. The instrument is also ideally suited to ground-based photometric follow-up of exoplanet candidates from space telescopes such as TESS, Gaia and PLATO. We present observations that combine precise autoguiding and the superb observing conditions at Paranal to provide routine photometric precision of 0.1 per cent in 1 h for stars with I-band magnitudes brighter than 13. We describe the instrument and data analysis methods as well as the status of the survey, which achieved first light in 2015 and began full-survey operations in 2016. NGTS data will be made publicly available through the ESO archive
An ultrahot Neptune in the Neptune desert
About one out of 200 Sun-like stars has a planet with an orbital period
shorter than one day: an ultra-short-period planet (Sanchis-ojeda et al. 2014;
Winn et al. 2018). All of the previously known ultra-short-period planets are
either hot Jupiters, with sizes above 10 Earth radii (Re), or apparently rocky
planets smaller than 2 Re. Such lack of planets of intermediate size (the "hot
Neptune desert") has been interpreted as the inability of low-mass planets to
retain any hydrogen/helium (H/He) envelope in the face of strong stellar
irradiation. Here, we report the discovery of an ultra-short-period planet with
a radius of 4.6 Re and a mass of 29 Me, firmly in the hot Neptune desert. Data
from the Transiting Exoplanet Survey Satellite (Ricker et al. 2015) revealed
transits of the bright Sun-like star \starname\, every 0.79 days. The planet's
mean density is similar to that of Neptune, and according to thermal evolution
models, it has a H/He-rich envelope constituting 9.0^(+2.7)_(-2.9)% of the
total mass. With an equilibrium temperature around 2000 K, it is unclear how
this "ultra-hot Neptune" managed to retain such an envelope. Follow-up
observations of the planet's atmosphere to better understand its origin and
physical nature will be facilitated by the star's brightness (Vmag=9.8)
No evidence for a saccadic range effect for visually guided and memory-guided saccades in simple saccade-targeting tasks
International audienceSaccades to single targets in peripheral vision are typically characterized by an undershoot bias. Putting this bias to a test, Kapoula [1] used a paradigm in which observers were presented with two different sets of target eccentricities that partially overlapped each other. Her data were suggestive of a saccadic range effect (SRE): There was a tendency for saccades to overshoot close targets and undershoot far targets in a block, suggesting that there was a response bias towards the center of eccentricities in a given block. Our Experiment 1 was a close replication of the original study by Kapoula [1]. In addition, we tested whether the SRE is sensitive to top-down requirements associated with the task, and we also varied the target presentation duration. In Experiments 1 and 2, we expected to replicate the SRE for a visual discrimination task. The simple visual saccade-targeting task in Experiment 3, entailing minimal top-down influence, was expected to elicit a weaker SRE. Voluntary saccades to remembered target locations in Experiment 3 were expected to elicit the strongest SRE. Contrary to these predictions, we did not observe a SRE in any of the tasks. Our findings complement the results reported by Gillen et al. [2] who failed to find the effect in a saccade-targeting task with a very brief target presentation. Together, these results suggest that unlike arm movements, saccadic eye movements are not biased towards making saccades of a constant, optimal amplitude for the task
Guillain-Barre syndrome associated with preceding hepatitis E virus infection
Objective:The aim of the study was to determine whether Guillain-Barre syndrome (GBS) is associated with preceding hepatitis E virus infection.Methods:The frequency of hepatitis E virus (HEV) infections was determined by anti-HEV serology in a cohort of 201 patients with GBS and 201 healthy controls with a similar distribution in age, sex, and year of sampling. Blood samples from patients with GBS were obtained in the acute phase before treatment. In a subgroup of patients with GBS, blood, stool, and CSF samples were tested for HEV RNA.Results:An increased ratio of anti-HEV immunoglobulin (Ig) M antibodies was found in 10 patients with GBS (5.0%) compared with 1 healthy control (0.5%, odds ratio 10.5, 95% confidence interval 1.3-82.6, p = 0.026). HEV RNA was detected in blood from 3 of these patients and additionally in feces from 1 patient. Seventy percent of anti-HEV IgM-positive patients had mildly increased liver function tests. All CSF samples tested negative for HEV RNA. The presence of anti-HEV IgM in patients with GBS was not related to age, sex, disease severity, or clinical outcome after 6 months.Conclusions:In the Netherlands, 5% of patients with GBS have an associated acute HEV infection. Further research is required to determine whether HEV infections also precede GBS in other geographical areas
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