123,094 research outputs found
Faster magnetic resonance imaging in emergency room patients with right lower quadrant pain and suspected acute appendicitis
Purpose: Emergency Departments (ED) are becoming busier, with a resultant increase in the number of imaging referrals. The purpose of this study was to assess the diagnostic accuracy of an abbreviated two sequence magnetic resonance (MR) protocol for evaluating ED patients with right lower quadrant pain and suspected acute appendicitis, with a view to expediting patient turnaround times and imaging costs. Material and methods: Fifty patients (49 females, one male; mean age 25.4 ± 5.2 years) who underwent ED MR imaging from July 2014 to March 2015 for right lower quadrant pain were retrospectively reviewed. MR abdomen/pelvis was performed on 1.5 T MR obtaining axial T1 gradient echo in/out of phase, transverse fast spin echo T2 with fat sat/motion correction, axial/coronal T2 HASTE (half-Fourier acquisition single-shot turbo spin-echo), and axial DWI (diffusion-weighted imaging) sequences. Images were reviewed by two fellowship-trained radiologists on a five-point confidence scale. Mean acquisition/interpretation times for the standard departmental protocol and the proposed abbreviated MR protocol (comprising T2 HASTE and DWI images) were calculated. Sensitivity, specificity, and diagnostic accuracy for the abbreviated protocol against the full protocol were also calculated. Results: Mean scanning time for abbreviated protocol and standard protocol was calculated to be 21.1 minutes and 40.5 minutes, respectively. Mean interpretation time for abbreviated protocol for reader one and two was 4.1 ± 1.5 minutes and 4.5 ± 1.4 minutes, respectively, and for standard protocol was 8.1 ± 1.8 minutes and 7.1 ± 1.4 minutes, respectively. Sensitivity, specificity, and accuracy for the FAST protocol were calculated to be 100% each for reader one and 75%, 100%, and 94%, respectively, for reader two. Conclusions: The proposed abbreviated MR protocol has comparable diagnostic accuracy in diagnosing ED patients with right lower quadrant pain, with significant reduction in imaging/interpretation times. It thus has the potential to be implemented in ED imaging with significant reduction in patient turnaround times and costs
Revival of Silenced Echo and Quantum Memory for Light
We propose an original quantum memory protocol. It belongs to the class of
rephasing processes and is closely related to two-pulse photon echo. It is
known that the strong population inversion produced by the rephasing pulse
prevents the plain two-pulse photon echo from serving as a quantum memory
scheme. Indeed gain and spontaneous emission generate prohibitive noise. A
second -pulse can be used to simultaneously reverse the atomic phase and
bring the atoms back into the ground state. Then a secondary echo is radiated
from a non-inverted medium, avoiding contamination by gain and spontaneous
emission noise. However, one must kill the primary echo, in order to preserve
all the information for the secondary signal. In the present work, spatial
phase mismatching is used to silence the standard two-pulse echo. An
experimental demonstration is presented.Comment: 13 pages, 6 figure
On the impossibility of faithfully storing single-photons with the three-pulse photon echo
The three-pulse photon echo is a well-known technique to store intense light
pulses in an inhomogeneously broadened atomic ensemble. This protocol is
attractive because it is relatively simple and it is well suited for the
storage of multiple temporal modes. Furthermore, it offers very long storage
times, greater than the phase relaxation time. Here, we consider the
three-pulse photon echo in both two- and three-level systems as a potential
technique for the storage of light at the single-photon level. By explicit
calculations, we show that the ratio between the echo signal corresponding to a
single-photon input and the noise is smaller than one. This severely limits the
achievable fidelity of the quantum state storage, making the three-pulse photon
echo unsuitable for single-photon quantum memory.Comment: 6 pages, 4 figure
Ramsey interferometry with generalized one-axis twisting echoes
We consider a large class of Ramsey interferometry protocols which are
enhanced by squeezing and un-squeezing operations before and after a phase
signal is imprinted on the collective spin of particles. We report an
analytical optimization for any given particle number and strengths of
(un-)squeezing. These results can be applied even when experimentally relevant
decoherence processes during the squeezing and un-squeezing interactions are
included. Noise between the two interactions is however not considered in this
work. This provides a generalized characterization of squeezing echo protocols,
recovering a number of known quantum metrological protocols as local
sensitivity maxima, thereby proving their optimality. We discover a single new
protocol. Its sensitivity enhancement relies on a double inversion of
squeezing. In the general class of echo protocols, the newly found
over-un-twisting protocol is singled out due to its Heisenberg scaling even at
strong collective dephasing.Comment: 11+8 pages, 7 figures, comments welcome! ; accepted versio
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