212 research outputs found
Superior metal artifact reduction of tin-filtered low-dose CT in imaging of lumbar spinal instrumentation compared to conventional computed tomography
OBJECTIVE
To compare the image quality of low-dose CT (LD-CT) with tin filtration of the lumbar spine after metal implants to standard clinical CT, and to evaluate the potential for metal artifact and dose reduction.
MATERIALS AND METHODS
CT protocols were optimized in a cadaver torso. Seventy-four prospectively included patients with metallic lumbar implants were scanned with both standard CT (120 kV) and tin-filtered LD-CT (Sn140kV). CT dose parameters and qualitative measures (1 = worst,4 = best) were compared. Quantitative measures included noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and the width and attenuation of the most prominent hypodense metal artifact. Standard CT and LD-CT were assessed for imaging findings.
RESULTS
Tin-filtered LD-CT was performed with 60% dose saving compared to standard CT (median effective dose 3.22 mSv (quartile 1-3: 2.73-3.49 mSv) versus 8.02 mSv (6.42-9.27 mSv; p < .001). Image quality of CT and tin-filtered low-dose CT was good with excellent depiction of anatomy, while image noise was lower for CT and artifacts were weaker for tin-filtered LD-CT. Quantitative measures also revealed increased noise for tin-filtered low-dose CT (41.5HU), lower SNR (2) and CNR (0.6) compared to CT (32HU,3.55,1.03, respectively) (all p < .001). However, tin-filtered LD-CT performed superior regarding the width and attenuation of hypodense metal artifacts (2.9 mm and -767.5HU for LD-CT vs. 4.1 mm and -937HU for CT; all p < .001). No difference between methods was observed in detection of imaging findings.
CONCLUSION
Tin-filtered LD-CT with 60% dose saving performs comparable to standard CT in detection of pathology and surgery related complications after lumbar spinal instrumentation, and shows superior metal artifact reduction
Risk factors for L5 pedicle fractures after single-level posterior spinal fusion
BACKGROUND CONTEXT
Pedicle fractures are a rare but potentially devastating complication of posterior instrumented spinal fusion (PSF). Preoperative awareness of the possible risk factors may help prevent these fractures by modifying the surgical plan. However, the risk factors have not yet been identified.
PURPOSE
To determine the preoperative parameters associated with postoperative L5 pedicle fracture after L4/5 PSF.
STUDY DESIGN
Case control study.
PATIENT SAMPLE
Patients undergoing L4/5 PSF at a single academic institution between 2014 and 2020.
OUTCOME MEASURES
Occurrence of postoperative L5 pedicle fracture.
METHODS
Of 253 patients (female:male, 145:108) undergoing L4/5 PSF from 2014 to 2020, patients with postoperative L5 pedicle fractures were identified retrospectively as "cases" (n = 8, all female, age: 70 ± 10.7 years). As a control group all remaining patients with a follow-up of more than 12 months were allocated (n = 184, 104 females, age: 64.27 ± 13.00 years). In all but 16 cases, anterior support with transforaminal or posterior interbody fusion was performed. Demographic and clinical data (body mass index (BMI)), surgical factors, and comorbidities) were compared. Radiological assessment of spinopelvic parameters was performed using pre- and postoperative standing lateral radiographs.
RESULTS
The overall incidence of L5 pedicle fractures after L4/5 spinal fusion was 3.16%, with a median time from index surgery to diagnosis of 25 days (range, 6-199 days) (75% within the first 32 days postoperatively). Patients with L5 pedicle fractures had higher pelvic incidence (PI) (71° ± 9° vs. 56° ± 11°; p=.001), sacral slope (SS) (45° ± 7° vs. 35° ± 8°; p=.002), L5 slope (30° ± 11° vs. 15° ± 10°, p=.001), L5 incidence (42° ± 14° vs. 26° ± 11°; p= .003), L1-S1 lumbar lordosis (LL) postop (57° ± 10° vs. 45° ± 11°; p=.006), and L4 -S1 LL postop (33° ± 7° vs. 28° ± 7°; p=.049) compared with the control group. Pelvic tilt and PI- LL mismatch were not significantly different. Female gender was a significant risk factor for L5 pedicle fractures (p=.015). BMI (kg/m) was statistically equal in patients with or without pedicle fractures (28.37 ± 5.96 vs. 28.53 ± 16.32; p=.857). There was no significant difference between the groups for approximative bone mineral density assessment (Hounsfield units; 113 ± 60 vs. 120 ± 43; p=.396) using the L3 trabecular region of interest (ROI) measurement. The correlation analysis demonstrated that most of the identified risk factors except for the postoperative L4-S1 lordosis show significant positive associations among each other. All eight patients in the fracture group underwent revision surgery, and the instrumented fusion was extended to the sacrum, with the addition of sacral-alar-iliac or iliac screws, in six cases.
CONCLUSIONS
L5 pedicle fractures occurred in 3% of the patients after single level L4/5 PSF. Risk factors are female gender, higher PI, SS, L5 slope, L5 incidence, and LL postop but not high BMI. These findings can be used for surgical planning and decision of fusion levels
Aharonov-Bohm ring with fluctuating flux
We consider a non-interacting system of electrons on a clean one-channel
Aharonov-Bohm ring which is threaded by a fluctuating magnetic flux. The flux
derives from a Caldeira-Leggett bath of harmonic oscillators. We address the
influence of the bath on the following properties: one- and two-particle
Green's functions, dephasing, persistent current and visibility of the
Aharonov-Bohm effect in cotunneling transport through the ring. For the bath
spectra considered here (including Nyquist noise of an external coil), we find
no dephasing in the linear transport regime at zero temperature.
PACS numbers: 73.23.-b, 73.23.Hk, 73.23.Ra, 03.65.YzComment: 17 pages, 8 figures. To be published in PRB. New version contains
minor corrections and additional discussion suggested by referee. A simple
introduction to the basics of dephasing can be found at
http://iff.physik.unibas.ch/~florian/dephasing/dephasing.htm
Three-dimensional cephalometric evaluation of maxillary growth following in utero repair of cleft lip and alveolar-like defects in the mid-gestational sheep model
Objective: To evaluate maxillary growth following in utero repair of surgically created cleft lip and alveolar (CLA)-like defects by means of three-dimensional (3D) computer tomographic (CT) cephalometric analysis in the mid-gestational sheep model. Methods: In 12 sheep fetuses a unilateral CLA-like defect was created in utero (untreated control group: 4 fetuses). Four different bone grafts were used for the alveolar defect closure. After euthanasia, CT scans of the skulls of the fetuses, 3D re-constructions, and a 3D-CT cephalometric analysis were performed. Results: The comparisons between the operated and nonoperated skull sides as well as of the maxillary asymmetry among the experimental groups revealed no statistically significant differences of the 12 variables used. Conclusions: None of the surgical approaches used for the in utero correction of CLA-like defects seem to affect significantly postsurgical maxillary growth; however, when bone graft healing takes place, a tendency for almost normal maxillary growth can be observed. Copyright (c) 2006 S. Karger AG, Basel
Controlled Dephasing of Electrons by Non-Gaussian Shot Noise
In a 'controlled dephasing' experiment [1-3], an interferometer loses its
coherence due to entanglement with a controlled quantum system ('which path'
detector). In experiments that were conducted thus far in mesoscopic systems
only partial dephasing was achieved. This was due to weak interactions between
many detector electrons and the interfering electron, resulting in a Gaussian
phase randomizing process [4-10]. Here, we report the opposite extreme: a
complete destruction of the interference via strong phase randomization only by
a few electrons in the detector. The realization was based on interfering edge
channels (in the integer quantum Hall effect regime, filling factor 2) in a
Mach-Zehnder electronic interferometer, with an inner edge channel serving as a
detector. Unexpectedly, the visibility quenched in a periodic lobe-type form as
the detector current increased; namely, it periodically decreased as the
detector current, and thus the detector's efficiency, increased. Moreover, the
visibility had a V-shape dependence on the partitioning of the detector
current, and not the expected dependence on the second moment of the shot
noise, T(1-T), with T the partitioning. We ascribe these unexpected features to
the strong detector-interferometer coupling, allowing only 1-3 electrons in the
detector to fully dephase the interfering electron. Consequently, in this work
we explored the non-Gaussian nature of noise [11], namely, the direct effect of
the shot noise full counting statistics [12-15].Comment: 14 pages, 4 figure
Dephasing in sequential tunneling through a double-dot interferometer
We analyze dephasing in a model system where electrons tunnel sequentially
through a symmetric interference setup consisting of two single-level quantum
dots. Depending on the phase difference between the two tunneling paths, this
may result in perfect destructive interference. However, if the dots are
coupled to a bath, it may act as a which-way detector, leading to partial
suppression of the phase-coherence and the reappearance of a finite tunneling
current. In our approach, the tunneling is treated in leading order whereas
coupling to the bath is kept to all orders (using P(E) theory). We discuss the
influence of different bath spectra on the visibility of the interference
pattern, including the distinction between "mere renormalization effects" and
"true dephasing".Comment: 18 pages, 8 figures; For a tutorial introduction to dephasing see
http://iff.physik.unibas.ch/~florian/dephasing/dephasing.htm
Overexpression of Rubisco subunits with RAF1 increases Rubisco content in maize.
Rubisco catalyses a rate-limiting step in photosynthesis and has long been a target for improvement due to its slow turnover rate. An alternative to modifying catalytic properties of Rubisco is to increase its abundance within C4 plant chloroplasts, which might increase activity and confer a higher carbon assimilation rate. Here, we overexpress the Rubisco large (LS) and small (SS) subunits with the Rubisco assembly chaperone RUBISCO ASSEMBLY FACTOR 1 (RAF1). While overexpression of LS and/or SS had no discernable impact on Rubisco content, addition of RAF1 overexpression resulted in a >30% increase in Rubisco content. Gas exchange showed a 15% increase in CO2 assimilation (ASAT) in UBI-LSSS-RAF1 transgenic plants, which correlated with increased fresh weight and in vitro Vcmax calculations. The divergence of Rubisco content and assimilation could be accounted for by the Rubisco activation state, which decreased up to 23%, suggesting that Rubisco activase may be limiting Vcmax, and impinging on the realization of photosynthetic potential from increased Rubisco content.This research was supported by the Agriculture and Food Research Initiative from the National Institute of Food and Agriculture, US Department of Agriculture, under award number 2016-67013-24464. Travel to the Australian National University was supported by the Mario Einaudi Center for International Studies, International Research Travel Grant at Cornell University
NNLO corrections to the total cross section for Higgs boson production in hadron-hadron collisions
We present the next-to-next-to-leading order (NNLO) corrections to the total
cross section for (pseudo-) scalar Higgs boson production using an alternative
method than those used in previous calculations. All QCD partonic subprocesses
have been included and the computation is carried out in the effective
Lagrangian approach which emerges from the standard model by taking the limit
where denotes the mass of the top quark. Our results
agree with those published earlier in the literature. We estimate the
theoretical uncertainties by comparing the -factors and the variation with
respect to the mass factorization/renormalization scales with the results
obtained by lower order calculations. We also investigate the dependence of the
cross section on several parton density sets provided by different groups.
Further we study which part of the coefficient functions dominates the cross
section. This is of interest for the resummation of large corrections which
occur near the boundary of phase space. It turns out that depending on the
definition of the total cross section the latter is dominated by the the
soft-plus-virtual gluon corrections represented by and
terms. PACS numbers: 12.38.-t, 12.38.Bx, 13.85.-t,
14.80.Gt.Comment: 61 pages, LaTeX, 15 postscript figures. With respect to the previous
version a more thorough comparison is made between two definitions of the
soft plus virtual gluon approximation. Misprints are corrected and references
are changed. Figs. 8a, 9a are changed into Figs. 8,9 respectively and Figs.
8b, 9b are droppe
Protostellar collapse and fragmentation using an MHD GADGET
Although the influence of magnetic fields is regarded as vital in the star
formation process, only a few magnetohydrodynamics (MHD) simulations have been
performed on this subject within the smoothed particle hydrodynamics (SPH)
method. This is largely due to the unsatisfactory treatment of non-vanishing
divergence of the magnetic field. Recently smoothed particle
magnetohydrodynamics (SPMHD) simulations based on Euler potentials have proven
to be successful in treating MHD collapse and fragmentation problems, however
these methods are known to have some intrinsical difficulties. We have
performed SPMHD simulations based on a traditional approach evolving the
magnetic field itself using the induction equation. To account for the
numerical divergence, we have chosen an approach that subtracts the effects of
numerical divergence from the force equation, and additionally we employ
artificial magnetic dissipation as a regularization scheme. We apply this
realization of SPMHD to a widely known setup, a variation of the 'Boss &
Bodenheimer standard isothermal test case', to study the impact of the magnetic
fields on collapse and fragmentation. In our simulations, we concentrate on
setups, where the initial magnetic field is parallel to the rotation axis. We
examine different field strengths and compare our results to other findings
reported in the literature. We are able to confirm specific results found
elsewhere, namely the delayed onset of star formation for strong fields,
accompanied by the tendency to form only single stars. We also find that the
'magnetic cushioning effect', where the magnetic field is wound up to form a
'cushion' between the binary, aids binary fragmentation in a case, where
previously only formation of a single protostar was expected.Comment: 18 pages, 11 figures. Final version (with revisions). Accepted to
MNRA
Preoperative endoscopic biliary drainage by metal versus plastic stents for resectable perihilar cholangiocarcinoma
Background and Aims: Adequate preoperative biliary drainage (PBD) is recommended in most patients with resectable perihilar cholangiocarcinoma (pCCA). Most expert centers use endoscopic plastic stents rather than self-expandable metal stents (SEMSs). In the palliative setting, however, use of SEMSs has shown longer patency and superior survival. The aim of this retrospective study was to compare stent dysfunction of SEMSs versus plastic stents for PBD in resectable pCCA patients. Methods:In this multicenter international retrospective cohort study, patients with potentially resectable pCCAs who underwent initial endoscopic PBD from 2010 to 2020 were included. Stent failure was a composite end point of cholangitis or reintervention due to adverse events or insufficient PBD. Other adverse events, surgical outcomes, and survival were recorded. Propensity score matching (PSM) was performed on several baseline characteristics. Results: A total of 474 patients had successful stent placement, of whom 61 received SEMSs and 413 plastic stents. PSM (1:1) resulted in 2 groups of 59 patients each. Stent failure occurred significantly less in the SEMSs group (31% vs 64%; P < .001). Besides less cholangitis after SEMSs placement (15% vs 31%; P = .012), other PBD-related adverse events did not differ. The number of patients undergoing surgical resection was not significantly different (46% vs 49%; P = .71). Complete intraoperative SEMSs removal was successful and without adverse events in all patients. Conclusions: Stent failure was lower in patients with SEMSs as PBD compared with plastic stents in patients with resectable pCCA. Removal during surgery was quite feasible. Surgical outcomes were similar.</p
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