49 research outputs found
Background discrimination capabilities of a heat and ionization germanium cryogenic detector
The discrimination capabilities of a 70 g heat and ionization Ge bolometer
are studied. This first prototype has been used by the EDELWEISS Dark Matter
experiment, installed in the Laboratoire Souterrain de Modane, for direct
detection of WIMPs. Gamma and neutron calibrations demonstrate that this type
of detector is able to reject more than 99.6% of the background while retaining
95% of the signal, provided that the background events distribution is not
biased towards the surface of the Ge crystal. However, the 1.17 kg.day of data
taken in a relatively important radioactive environment show an extra
population slightly overlapping the signal. This background is likely due to
interactions of low energy photons or electrons near the surface of the
crystal, and is somewhat reduced by applying a higher charge-collecting inverse
bias voltage (-6 V instead of -2 V) to the Ge diode. Despite this
contamination, more than 98% of the background can be rejected while retaining
50% of the signal. This yields a conservative upper limit of 0.7
event.day^{-1}.kg^{-1}.keV^{-1}_{recoil} at 90% confidence level in the 15-45
keV recoil energy interval; the present sensitivity appears to be limited by
the fast ambient neutrons. Upgrades in progress on the installation are
summarized.Comment: Submitted to Astroparticle Physics, 14 page
Argumentation in the 2016 US Presidential Elections:Annotated corpora of television debates and social media reaction
Simultaneous multi slice (SMS) balanced steady state free precession first-pass myocardial perfusion cardiovascular magnetic resonance with iterative reconstruction at 1.5T
Background: Simultaneous-Multi-Slice (SMS) perfusion imaging has the potential to acquire multiple slices, increasing myocardial coverage without sacrificing in-plane spatial resolution. To maximise signal-to-noise ratio (SNR), SMS can be combined with a balanced steady state free precession (bSSFP) readout. Furthermore, application of gradient-controlled local Larmor adjustment (GC-LOLA) can ensure robustness against off-resonance artifacts and SNR loss can be mitigated by applying iterative reconstruction with spatial and temporal regularisation. The objective of this study was to compare cardiovascular magnetic resonance (CMR) myocardial perfusion imaging using SMS bSSFP imaging with GC-LOLA and iterative reconstruction to 3 slice bSSFP.
Methods: Two contrast-enhanced rest perfusion sequences were acquired in random order in 8 patients: 6-slice SMS bSSFP and 3 slice bSSFP. All images were reconstructed with TGRAPPA. SMS images were also reconstructed using a non-linear iterative reconstruction with L1 regularisation in wavelet space (SMS-iter) with 7 different combinations for spatial (λÏ) and temporal (λÏ) regularisation parameters. Qualitative ratings of overall image quality (0â=âpoor image quality, 1â=âmajor artifact, 2â=âminor artifact, 3â=âexcellent), perceived SNR (0â=âpoor SNR, 1â=âmajor noise, 2â=âminor noise, 3â=âhigh SNR), frequency of sequence related artifacts and patient related artifacts were undertaken. Quantitative analysis of contrast ratio (CR) and percentage of dark rim artifact (DRA) was performed.
Results: Among all SMS-iter reconstructions, SMS-iter 6 (Î»Ï 0.001 Î»Ï 0.005) was identified as the optimal reconstruction with the highest overall image quality, least sequence related artifact and higher perceived SNR. SMS-iter 6 had superior overall image quality (2.50â±â0.53 vs 1.50â±â0.53, pâ=â0.005) and perceived SNR (2.25â±â0.46 vs 0.75â±â0.46, pâ=â0.010) compared to 3 slice bSSFP. There were no significant differences in sequence related artifact, CR (3.62â±â0.39 vs 3.66â±â0.65, pâ=â0.88) or percentage of DRA (5.25â±â6.56 vs 4.25â±â4.30, pâ=â0.64) with SMS-iter 6 compared to 3 slice bSSFP.
Conclusions: SMS bSSFP with GC-LOLA and iterative reconstruction improved image quality compared to a 3 slice bSSFP with doubled spatial coverage and preserved in-plane spatial resolution. Future evaluation in patients with coronary artery disease is warranted
Advancements in 3D drillstring mechanics : from the bit to the topdrive
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