65 research outputs found
CONTRAST-ENHANCED ULTRASOUND MONITORING OF PERFUSION CHANGES IN HEPATIC NEUROENDOCRINE METASTASES AFTER SYSTEMIC VERSUS SELECTIVE ARTERIAL 177LU/90Y-DOTATOC AND 213BI-DOTATOC RADIOPEPTIDE THERAPY
Radiopeptide therapy with beta emitter labeled 177Lu/90Y- DOTA(0)-Phe(1)-Tyr(3)-octreotide (DOTATOC) and more recently
also alpha emitting 213Bi-DOTATOC are promising new treatments for neuroendocrine tumors. No early predictors for treatment
response have been recognized and tumor-shrinkage after radiation therapy appears slowly. In some solid tumors a decline in tumor
perfusion was found predictive of final treatment response but the gold standard multiphase computed tomography (CT) has
a high radiation burden. Therefore we evaluated the ability of contrast-enhanced ultrasound (CEUS) to evaluate tumor perfusion
as a response criteria. Materials and Methods: 14 patients with hepatic neuroendocrine tumor (NET) metastases were enrolled
in the retrospective study. Eleven patients were treated with beta-emitting 177Lu/90Y-DOTATOC, either intravenous (i.v.) (n = 5)
or intra-arterial (i.a.) (n = 6) and three patients received alpha-emitting 213Bi-DOTATOC (i.a.). CEUS and contrast-enhanced
CT (CE-CT) were performed before and 3 months after treatment. Results: CE-CT and CEUS presented comparable results in the
baseline study and in the assessment of perfusion changes due to the different treatment regimes. A therapy related decrease in tumor
perfusion is an early predictor of longterm morphologic response. Conclusion: CEUS is a cheap, ubiquitary available and radiation
free technique which showed comparable results for perfusion and diameter of liver metastases compared to CE-CT. Intensity
reduction in an arterial phase CEUS can be seen as a positive sign indicating long term tumor response to treatment. Therefore
CEUS may be considered as an imaging modality for monitoring early treatment after focal alpha and beta targeted therapy.JRC.E.5-Nuclear chemistr
Study of the gluon propagator in the large-N_f limit at finite temperature and chemical potential for weak and strong couplings
At finite temperature and chemical potential, the leading-order
(hard-thermal-loop) contributions to the gauge-boson propagator lead to
momentum-dependent thermal masses for propagating quasiparticles as well as
dynamical screening and Landau damping effects. We compare the
hard-thermal-loop propagator with the complete large-N_f gluon propagator, for
which the usually subleading contributions, such as a finite width of
quasiparticles, can be studied at nonperturbatively large effective coupling.
We also study quantitatively the effect of Friedel oscillations in
low-temperature electrostatic screening.Comment: REVTEX, 23 pages, 20 figure
Lifetime of quasiparticles in hot QED plasmas
The calculation of the lifetime of quasiparticles in a QED plasma at high
temperature remains plagued with infrared divergences, even after one has taken
into account the screening corrections. The physical processes responsible for
these divergences are the collisions involving the exchange of very soft,
unscreened, magnetic photons, whose contribution is enhanced by the thermal
Bose-Einstein occupation factor. The self energy diagrams which diverge in
perturbation theory contain no internal fermion loops, but an arbitrary number
of internal magnetostatic photon lines. By generalizing the Bloch-Nordsieck
model at finite temperature, we can resum all the singular contributions of
such diagrams, and obtain the correct long time behaviour of the retarded
fermion propagator in the hot QED plasma: , where is the plasma frequency and
.Comment: 13 pages, LaTe
On the screening of static electromagnetic fields in hot QED plasmas
We study the screening of static magnetic and electric fields in massless
quantum electrodynamics (QED) and massless scalar electrodynamics (SQED) at
temperature . Various exact relations for the static polarisation tensor are
first reviewed and then verified perturbatively to fifth order (in the
coupling) in QED and fourth order in SQED, using different resummation
techniques. The magnetic and electric screening masses squared, as defined
through the pole of the static propagators, are also calculated to fifth order
in QED and fourth order in SQED, and their gauge-independence and
renormalisation-group invariance is checked. Finally, we provide arguments for
the vanishing of the magnetic mass to all orders in perturbation theory.Comment: 37 pages, 8 figure
Lifetimes of quasiparticles and collective excitations in hot QED plasmas
The perturbative calculation of the lifetime of fermion excitations in a QED
plasma at high temperature is plagued with infrared divergences which are not
eliminated by the screening corrections. The physical processes responsible for
these divergences are the collisions involving the exchange of longwavelength,
quasistatic, magnetic photons, which are not screened by plasma effects. The
leading divergences can be resummed in a non-perturbative treatement based on a
generalization of the Bloch-Nordsieck model at finite temperature. The
resulting expression of the fermion propagator is free of infrared problems,
and exhibits a {\it non-exponential} damping at large times: , where is the plasma
frequency and .Comment: LaTex file, 57 pages, 11 eps figures include
Increased x-ray attenuation in malignant vs. benign mediastinal nodes in an orthotopic model of lung cancer
PURPOSEStaging of lung cancer is typically performed with fluorodeoxyglucose-positron emission tomography-computed tomography (FDG-PET/CT); however, false positive PET scans can occur due to inflammatory disease. The CT scan is used for anatomic registration and attenuation correction. Herein, we evaluated x-ray attenuation (XRA) within nodes on CT and correlated this with the presence of malignancy in an orthotopic lung cancer model in rats.METHODS1×106 NCI-H460 cells were injected transthoracically in six National Institutes of Health nude rats and six animals served as controls. After two weeks, animals were sacrificed; lymph nodes were extracted and scanned with a micro-CT to determine their XRA prior to histologic analysis.RESULTSMedian CT density in malignant lymph nodes (n=20) was significantly higher than benign lymph nodes (n=12; P = 0.018). Short-axis diameter of metastatic lymph nodes was significantly different than benign nodes (3.4 mm vs. 2.4 mm; P = 0.025). Area under the curve for malignancy was higher for density-based lymph node analysis compared with size measurements (0.87 vs. 0.7).CONCLUSIONXRA of metastatic mediastinal lymph nodes is significantly higher than benign nodes in this lung cancer model. This suggests that information on nodal density may be useful when used in combination with the results of FDG-PET in determining the likelihood of malignant adenopath
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Advanced source apportionment of size-resolved trace elements at multiple sites in London during winter
Trace element measurements in PM10–2.5, PM2.5–1.0 and PM1.0–0.3 aerosol were performed with 2 h time resolution at kerbside, urban background and rural sites during the ClearfLo winter 2012 campaign in London. The environment-dependent variability of emissions was characterized using the Multilinear Engine implementation of the positive matrix factorization model, conducted on data sets comprising all three sites but segregated by size. Combining the sites enabled separation of sources with high temporal covariance but significant spatial variability. Separation of sizes improved source resolution by preventing sources occurring in only a single size fraction from having too small a contribution for the model to resolve. Anchor profiles were retrieved internally by analysing data subsets, and these profiles were used in the analyses of the complete data sets of all sites for enhanced source apportionment.
A total of nine different factors were resolved (notable elements in brackets): in PM10–2.5, brake wear (Cu, Zr, Sb, Ba), other traffic-related (Fe), resuspended dust (Si, Ca), sea/road salt (Cl), aged sea salt (Na, Mg) and industrial (Cr, Ni); in PM2.5–1.0, brake wear, other traffic-related, resuspended dust, sea/road salt, aged sea salt and S-rich (S); and in PM1.0–0.3, traffic-related (Fe, Cu, Zr, Sb, Ba), resuspended dust, sea/road salt, aged sea salt, reacted Cl (Cl), S-rich and solid fuel (K, Pb). Human activities enhance the kerb-to-rural concentration gradients of coarse aged sea salt, typically considered to have a natural source, by 1.7–2.2. These site-dependent concentration differences reflect the effect of local resuspension processes in London. The anthropogenically influenced factors traffic (brake wear and other traffic-related processes), dust and sea/road salt provide further kerb-to-rural concentration enhancements by direct source emissions by a factor of 3.5–12.7. The traffic and dust factors are mainly emitted in PM10–2.5 and show strong diurnal variations with concentrations up to 4 times higher during rush hour than during night-time. Regionally influenced S-rich and solid fuel factors, occurring primarily in PM1.0–0.3, have negligible resuspension influences, and concentrations are similar throughout the day and across the regions
Non-perturbative aspects of screening phenomena in abelian and non abelian gauge theories
When computed to one-loop order in resummed perturbation theory, the
non-abelian Debye mass appears to be logarithmically sensitive to the magnetic
scale . More generally, we show that in higher orders power-like infrared
divergences forbid the use of perturbation theory to calculate the corrections
to Debye screening. A similar infrared problem occurs in the determination of
the mass-shell for the scalar propagator in 2+1-dimensional scalar
electrodynamics. In this context, we provide a non-perturbative approach which
solves the infrared problems and allows for an accurate calculation of the
scalar propagator in the vicinity of the mass-shell.Comment: 29 pages, LaTex, 7 figures (not included, available upon request
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