48,811 research outputs found
Technical Note: Phantom study to evaluate the dose and image quality effects of a computed tomography Organ-based Tube Current Modulation Technique
Purpose
This technical note quantifies the dose and image quality performance of a clinically available organ-dose-based tube current modulation (ODM) technique, using experimental and simulation phantom studies. The investigated ODM implementation reduces the tube current for the anterior source positions, without increasing current for posterior positions, although such an approach was also evaluated for comparison.
Methods
Axial CT scans at 120 kV were performed on head and chest phantoms on an ODM-equipped scanner (Optima CT660, GE Healthcare, Chalfont St. Giles, England). Dosimeters quantified dose to breast, lung, heart, spine, eye lens, and brain regions for ODM and 3D-modulation (SmartmA) settings. Monte Carlo simulations, validated with experimental data, were performed on 28 voxelized head phantoms and 10 chest phantoms to quantify organ dose and noise standard deviation. The dose and noise effects of increasing the posterior tube current were also investigated.
Results
ODM reduced the dose for all experimental dosimeters with respect to SmartmA, with average dose reductions across dosimeters of 31% (breast), 21% (lung), 24% (heart), 6% (spine), 19% (eye lens), and 11% (brain), with similar results for the simulation validation study. In the phantom library study, the average dose reduction across all phantoms was 34% (breast), 20% (lung), 8% (spine), 20% (eye lens), and 8% (brain). ODM increased the noise standard deviation in reconstructed images by 6%–20%, with generally greater noise increases in anterior regions. Increasing the posterior tube current provided similar dose reduction as ODM for breast and eye lens, increased dose to the spine, with noise effects ranging from 2% noise reduction to 16% noise increase. At noise equal to SmartmA, ODM increased the estimated effective dose by 4% and 8% for chest and head scans, respectively. Increasing the posterior tube current further increased the effective dose by 15% (chest) and 18% (head) relative to SmartmA.
Conclusions
ODM reduced dose in all experimental and simulation studies over a range of phantoms, while increasing noise. The results suggest a net dose/noise benefit for breast and eye lens for all studied phantoms, negligible lung dose effects for two phantoms, increased lung dose and/or noise for eight phantoms, and increased dose and/or noise for brain and spine for all studied phantoms compared to the reference protocol
Mapping the invisible hand: a body model of a phantom limb
After amputation, individuals often have vivid experiences of their absent limb (i.e., a phantom limb). Therefore, one’s conscious image of one’s body cannot depend on peripheral input only (Ramachandran & Hirstein, 1998). However, the origin of phantom sensations is hotly debated. Reports of vivid phantoms in the case of congenital absence of the limb show that memory of former body state is not necessary (Brugger et al., 2000). According to one view, phantoms may reflect innate organization of sensorimotor cortices (Melzack, 1990). Alternatively, phantoms could reflect generalization from viewing other people’s bodies (Brugger et al., 2000), a sensorimotor example of the classic theory that understanding oneself follows from understanding the “generalized other” (Mead, 1934, p. 154). Because phantom limbs cannot be stimulated, sensory testing cannot directly compare visual and somatosensory influences on representations of phantom limbs. Consequently, empirical investigation of phantoms is limited
The phantom menace in representation theory
Our principal goal in this overview is to explain and motivate the concept of
a phantom in the representation theory of a finite dimensional algebra
. In particular, we exhibit the key role of phantoms towards
understanding how a full subcategory of the category
of all finitely generated left -modules is
embedded into , in terms of maps leaving or entering .
Contents: 1. Introduction and prerequisites; 2. Contravariant finiteness and
first examples; 3. Homological importance of contravariant finiteness and a
model application of the theory; 4. Phantoms. Definitions, existence, and basic
properties; 5. An application: Phantoms over string algebras
Constraints on Scalar Phantoms
We update the constraints on the minimal model of dark matter, where a stable
real scalar field is added to the standard model Lagrangian with a
renormalizable coupling to the Higgs field. Once we fix the dark matter
abundance, there are only two relevant model parameters, the mass of the scalar
field and that of the Higgs boson. The recent data from the CDMS II experiment
have excluded a parameter region where the scalar field is light such as less
than about 50 GeV. In a large parameter region, the consistency of the model
can be tested by the combination of future direct detection experiments and the
LHC experiments.Comment: 7 pages, 1 figur
MATCHING WITH PHANTOMS
Searching for partners involves informational persistence that reduces future traders' matching probability. In this paper, traders that are no longer available but who left tracks on the market are called phantoms. I examine a discrete-time matching market in which phantom traders are a by-product of search activity, no coordination frictions are assumed, and non-phantom traders may lose time trying to match with phantom traders. The resulting aggregate matching technology features increasing returns to scale in the short run, but has constant returns to scale in the long run. I discuss the labor market evidence and argue that there is observational equivalence between phantom unemployed and on-the-job seekers.Endogenous matching technology; Intertemporal and intratemporal congestion externalities; Information persistence
MPI Phantom Study with A High-Performing Multicore Tracer Made by Coprecipitation
Magnetic particle imaging (MPI) is a new imaging technique that detects the spatial distribution of magnetic nanoparticles (MNP) with the option of high temporal resolution. MPI relies on particular MNP as tracers with tailored characteristics for improvement of sensitivity and image resolution. For this reason, we developed optimized multicore particles (MCP 3) made by coprecipitation via synthesis of green rust and subsequent oxidation to iron oxide cores consisting of a magnetite/maghemite mixed phase. MCP 3 shows high saturation magnetization close to that of bulk maghemite and provides excellent magnetic particle spectroscopy properties which are superior to Resovist® and any other up to now published MPI tracers made by coprecipitation. To evaluate the MPI characteristics of MCP 3 two kinds of tube phantoms were prepared and investigated to assess sensitivity, spatial resolution, artifact severity, and selectivity. Resovist® was used as standard of comparison. For image reconstruction, the regularization factor was optimized, and the resulting images were investigated in terms of quantifying of volumes and iron content. Our results demonstrate the superiority of MCP 3 over Resovist® for all investigated MPI characteristics and suggest that MCP 3 is promising for future experimental in vivo studies
Microwave Radar-Based Breast Cancer Detection:Imaging in Inhomogeneous Breast Phantoms
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