519 research outputs found
A data mining approach to the SAR values over large MR image repositories
Purpose: In magnetic resonance imaging, the radiofrequency energy
absorption arises as one of the main safety concerns, being mainly related with
increased body temperature. Monitoring radiofrequency absorption is achieved
by the estimation of specific absorption rate (SAR), whose implementation lies
on equipment manufacturers, which in turn are not totally enlightening about its
calculus. This work presents an exploratory approach of whole-body SAR
values stored in DICOM metadata aiming to find correlation with body weight,
body mass index (BMI), gender and pulse sequences for abdominal/pelvic
(17.812 series) and head (29.907 series) studies.
Methods and Materials: All studies were acquired in a 3 Tesla scanner with
high-performance gradients. Data were extracted using Dicoogle, a DICOM
metadata mining tool. Several DICOM tags were analysed (e.g. patient weight,
height, gender, sequence name). For each study type, specifically weighted
pulse sequences were related with weight, BMI and gender through boxplot
diagrams, statistical and effect size analysis.
Results: SAR limits were never exceeded. Generally, SAR values tended to
decrease with increasing body weight and BMI values for abdominal/pelvic
studies. On the other hand, head studies showed different trends regarding
distinct pulse sequences. SAR values tend to be higher in male individuals
(p<0,05). As expected, turbo spin echo sequences present the highest SAR
values. The values found for echo gradient spoiled sequence (FLASH) were
also high.
Conclusion: It is confirmed that SAR estimates are related with the analysed
variables. An individual examination of pulse sequences is recommended to
observe trends regarding weight, BMI or gender.publishe
Rotational spectroscopy of the two conformers of 3-methylbutyronitrile (C_4H_9CN) between 2 and 400 GHz
We present high-resolution rotational spectroscopy of the two conformers of 3-methylbutyronitrile (C_4H_9CN). Spectra were taken between 2 and 24 GHz by means of Fourier transform microwave spectroscopy. Spectra between 36 and 403 GHz were recorded by means of frequency modulated (FM) absorption spectroscopy. The analysis yields precise rotational constants and higher order distortion constants, as well as a set of ^(14)N nuclear electric quadrupole coupling parameters for each of the two conformers. In addition, quantum chemical calculations were performed in order to assist the assignments. Frequency calculations yield insight into the vibrational energy structure of the two conformers, from which partition functions and vibrational correction factors are determined. These factors are used to determine experimentally and computationally the energy difference between the two conformers, which is revealed to be negligible. Overall, this study provides precise spectroscopic constants for the search of 3-methylbutyronitrile in the interstellar medium. In particular, this molecule is a perfect test case for our knowledge of branched molecule formation in space
Phase III study of nilotinib versus best supportive care with or without a TKI in patients with gastrointestinal stromal tumors resistant to or intolerant of imatinib and sunitinib
Background This phase III open-label trial investigated the efficacy of nilotinib in patients with advanced gastrointestinal stromal tumors following prior imatinib and sunitinib failure. Patients and methods Patients were randomized 2:1 to nilotinib 400 mg b.i.d. or best supportive care (BSC; BSC without tyrosine kinase inhibitor, BSC+imatinib, or BSC+sunitinib). Primary efficacy end point was progression-free survival (PFS) based on blinded central radiology review (CRR). Patients progressing on BSC could cross over to nilotinib. Results Two hundred and forty-eight patients enrolled. Median PFS was similar between arms (nilotinib 109 days, BSC 111 days; P=0.56). Local investigator-based intent-to-treat (ITT) analysis showed a significantly longer median PFS with nilotinib (119 versus 70 days; P=0.0007). A trend in longer median overall survival (OS) was noted with nilotinib (332 versus 280 days; P=0.29). Post hoc subset analyses in patients with progression and only one prior regimen each of imatinib and sunitinib revealed a significant difference in median OS of >4 months in favor of nilotinib (405 versus 280 days; P=0.02). Nilotinib was well tolerated. Conclusion In the ITT analysis, no significant difference in PFS was observed between treatment arms based on CRR. In the post hoc subset analyses, nilotinib provided significantly longer median O
Rotation-tunneling spectrum and astrochemical modeling of dimethylamine, CHNHCH, and searches for it in space
Methylamine has been the only simple alkylamine detected in the interstellar
medium for a long time. With the recent secure and tentative detections of
vinylamine and ethylamine, respectively, dimethylamine has become a promising
target for searches in space. Its rotational spectrum, however, has been known
only up to 45 GHz until now. Here we investigate the rotation-tunneling
spectrum of dimethylamine in selected regions between 76 and 1091 GHz using
three different spectrometers in order to facilitate its detection in space.
The quantum number range is extended to and , yielding an
extensive set of accurate spectroscopic parameters. To search for
dimethylamine, we refer to the spectral line survey ReMoCA carried out with the
Atacama Large Millimeter/submillimeter Array toward the high-mass star-forming
region Sagittarius B2(N) and a spectral line survey of the molecular cloud
G+0.6930.027 employing the IRAM 30 m and Yebes 40 m radio telescopes. We
report nondetections of dimethylamine toward the hot molecular cores Sgr
B2(N1S) and Sgr B2(N2b) as well as G+0.6930.027 which imply that
dimethylamine is at least 14, 4.5 and 39 times less abundant than methylamine
toward these sources, respectively. The observational results are compared to
computational results from a gas-grain astrochemical model. The modeled
methylamine to dimethylamine ratios are compatible with the observational
ratios. However, the model produces too much ethylamine compared with
methylamine which could mean that the already fairly low levels of
dimethylamine in the models may also be too high.Comment: Mon. Not. R. Astron. Soc., accepted. 33 pages including tables,
figures, and appendi
Investigation of the rotational spectrum of CDOD and an astronomical search toward IRAS 162932422
Solar-type prestellar cores and protostars display large amounts of
deuterated organic molecules. Recent findings on CHDOH and CDOH toward
IRAS 16293-2422 suggest that even fully deuterated methanol, CDOD, may be
detectable as well. However, searches for CDOD are hampered in particular
by the lack of intensity information from a spectroscopic model. The objective
of the present investigation is to develop a spectroscopic model of CDOD in
low-lying torsional states that is sufficiently accurate to facilitate searches
for this isotopolog in space. We carried out a new measurement campaign for
CDOD involving two spectroscopic laboratories that covers the 34 GHz-1.1
THz range. A torsion-rotation Hamiltonian model based on the rho-axis method
was employed for our analysis. Our resulting model describes the ground and
first excited torsional states of CDOD well up to quantum numbers and . We derived a line list for radio-astronomical
observations from this model that is accurate up to at least 1.1 THz and should
be sufficient for all types of radio-astronomical searches for this methanol
isotopolog. This line list was used to search for CDOD in data from the
Protostellar Interferometric Line Survey of IRAS 162932422 obtained with the
Atacama Large Millimeter/submillimeter Array. While we found several emission
features that can be attributed largely to CDOD, their number is still not
sufficiently high enough to establish a clear detection. Nevertheless, the
estimate of 2 cm derived for the CDOD column density
may be viewed as an upper limit that can be compared to column densities of
CDOH, CHOD, and CHOH. The comparison indicates that the CDOD
column density toward IRAS 16293-2422 is in line with the enhanced D/H ratios
observed for multiply deuterated complex organic molecules.Comment: 10 pages total, including figures, tables, and references; abstract
slightly shortened; Astron. Astrophys., accepte
Strong absorption by interstellar hydrogen fluoride: Herschel/HIFI observations of the sight-line to G10.6-0.4 (W31C)
We report the detection of strong absorption by interstellar hydrogen
fluoride along the sight-line to the submillimeter continuum source G10.6-0.4
(W31C). We have used Herschel's HIFI instrument, in dual beam switch mode, to
observe the 1232.4763 GHz J=1-0 HF transition in the upper sideband of the Band
5a receiver. The resultant spectrum shows weak HF emission from G10.6-0.4 at
LSR velocities in the range -10 to -3 km/s, accompanied by strong absorption by
foreground material at LSR velocities in the range 15 to 50 km/s. The spectrum
is similar to that of the 1113.3430 GHz 1(11)-0(00) transition of para-water,
although at some frequencies the HF (hydrogen fluoride) optical depth clearly
exceeds that of para-H2O. The optically-thick HF absorption that we have
observed places a conservative lower limit of 1.6E+14 cm-2 on the HF column
density along the sight-line to G10.6-0.4. Our lower limit on the HF abundance,
6E-9 relative to hydrogen nuclei, implies that hydrogen fluoride accounts for
between ~ 30 and 100% of the fluorine nuclei in the gas phase along this
sight-line. This observation corroborates theoretical predictions that -
because the unique thermochemistry of fluorine permits the exothermic reaction
of F atoms with molecular hydrogen - HF will be the dominant reservoir of
interstellar fluorine under a wide range of conditions.Comment: Accepted for publication in Astronomy and Astrophysics (Herschel
special issue). This revised version corrects a typographic error in the HTML
abstract, in which the lower limit on the HF abundance (should be 6E-9) was
previously misstated. The abstract in the PDF version is correct and the
latter has not been modifie
Herschel observations of deuterated water towards Sgr B2(M)
Observations of HDO are an important complement for studies of water, because
they give strong constraints on the formation processes -- grain surfaces
versus energetic process in the gas phase, e.g. in shocks. The HIFI
observations of multiple transitions of HDO in Sgr~B2(M) presented here allow
the determination of the HDO abundance throughout the envelope, which has not
been possible before with ground-based observations only. The abundance
structure has been modeled with the spherical Monte Carlo radiative transfer
code RATRAN, which also takes radiative pumping by continuum emission from dust
into account. The modeling reveals that the abundance of HDO rises steeply with
temperature from a low abundance () in the outer envelope
at temperatures below 100~K through a medium abundance () in
the inner envelope/outer core, at temperatures between 100 and 200~K, and
finally a high abundance () at temperatures above 200~K in
the hot core.Comment: A&A HIFI special issue, accepte
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