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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

TH-C-18A-01: Is Automatic Tube Current Modulation Still Necessary with Statistical Iterative Reconstruction?

Purpose: Automatic tube current modulation (TCM) has been widely used in modern multi-detector CT to reduce noise spatial nonuniformity and streaks to improve dose efficiency. With the advent of statistical iterative reconstruction (SIR), it is expected that the importance of TCM may diminish, since SIR incorporates statistical weighting factors to reduce the negative influence of photon-starved rays. The purpose of this work is to address the following questions: Does SIR offer the same benefits as TCM? If yes, are there still any clinical benefits to using TCM? Methods: An anthropomorphic CIRS chest phantom was scanned using a state-of-the-art clinical CT system equipped with an SIR engine (Veo™, GE Healthcare). The phantom was first scanned with TCM using a routine protocol and a low-dose (LD) protocol. It was then scanned without TCM using the same protocols. For each acquisition, both FBP and Veo reconstructions were performed. All scans were repeated 50 times to generate an image ensemble from which noise spatial nonuniformity (NSN) and streak artifact levels were quantified. Monte-Carlo experiments were performed to estimate skin dose. Results: For FBP, noise streaks were reduced by 4% using TCM for both routine and LD scans. NSN values were actually slightly higher with TCM (0.25) than without TCM (0.24) for both routine and LD scans. In contrast, for Veo, noise streaks became negligible (<1%) with or without TCM for both routine and LD scans, and the NSN was reduced to 0.10 (low dose) or 0.08 (routine). The overall skin dose was 2% lower at the shoulders and more uniformly distributed across the skin without TCM. Conclusion: SIR without TCM offers superior reduction in noise nonuniformity and streaks relative to FBP with TCM. For some clinical applications in which skin dose may be a concern, SIR without TCM may be a better option. K. Li, W. Zhao, D. Gomez-Cardona: Nothing to disclose; G.-H. Chen: Research funded, General Electric Company Research funded, Siemens AG Research funded, Varian Medical Systems, Research funded, Hologic, Inc.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Occupational Radiation Exposure During Endovascular Aortic Repair

PurposeThe aim of the study was to evaluate the radiation exposure to operating room personnel and to assess determinants for high personal doses during endovascular aortic repair.Materials and MethodsOccupational radiation exposure was prospectively evaluated during 22 infra-renal aortic repair procedures (EVAR), 11 thoracic aortic repair procedures (TEVAR), and 11 fenestrated or branched aortic repair procedures (FEVAR). Real-time over-lead dosimeters attached to the left breast pocket measured personal doses for the first operators (FO) and second operators (SO), radiology technicians (RT), scrub nurses (SN), anesthesiologists (AN), and non-sterile nurses (NSN). Besides protective apron and thyroid collar, no additional radiation shielding was used. Procedural dose area product (DAP), iodinated contrast volume, fluoroscopy time, patient’s body weight, and C-arm angulation were documented.ResultsAverage procedural FO dose was significantly higher during FEVAR (0.34 ± 0.28 mSv) compared to EVAR (0.11 ± 0.21 mSv) and TEVAR (0.06 ± 0.05 mSv; p = 0.003). Average personnel doses were 0.17 ± 0.21 mSv (FO), 0.042 ± 0.045 mSv (SO), 0.019 ± 0.042 mSv (RT), 0.017 ± 0.031 mSv (SN), 0.006 ± 0.007 mSv (AN), and 0.004 ± 0.009 mSv (NSN). SO and AN doses were strongly correlated with FO dose (p = 0.003 and p < 0.001). There was a significant correlation between FO dose and procedural DAP (R = 0.69, p < 0.001), iodinated contrast volume (R = 0.67, p < 0.001) and left-anterior C-arm projections >60° (p = 0.02), and a weak correlation with fluoroscopy time (R = 0.40, p = 0.049).ConclusionAverage FO dose was a factor four higher than SO dose. Predictors for high personal doses are procedural DAP, iodinated contrast volume, and left-anterior C-arm projections greater than 60°.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

A novel red emitting phosphor of Eu{sup 3+} doped TTB-type niobate NaSr{sub 2}Nb{sub 5}O{sub 15} for white LEDs

Highlights: ► A novel red phosphor NaSr{sub 2}Nb{sub 5}O{sub 15}:Eu{sup 3+} was synthesized and investigated firstly. ► Crystal structure and characteristic luminescence properties are discussed. ► The charge compensation mechanism is also investigated. ► The intensity of NSN:0.03Eu{sup 3+}, 0.03Li{sup +} is 64.5% of the commercial Y{sub 2}O{sub 3}:Eu{sup 3+}. ► It has good color saturation, the CIE is closed to that of commercial Y{sub 2}O{sub 3}:Eu{sup 3+}. - Abstract: Eu{sup 3+} doped NaSr{sub 2}Nb{sub 5}O{sub 15} series were firstly synthesized by solid-state reaction method. Crystal structure, characteristic luminescence properties as well as charge compensation mechanism are investigated detailedly by X-ray diffraction refinement and photoluminescence spectra measurement. NaSr{sub 2}Nb{sub 5}O{sub 15}:Eu{sup 3+} exhibits strong absorption in near ultraviolet-blue region and intense red emission with CIE chromaticity coordinates (0.638, 0.355) after adding the charge compensation agent upon 398 nm excitation. The integral intensity of NSN:0.03Eu{sup 3+}, 0.03Li{sup +} is 64.5% of the commercial Y{sub 2}O{sub 3}:Eu{sup 3+} and the quantum efficiency is calculated to be 41.5%. The results show that NaSr{sub 2}Nb{sub 5}O{sub 15}:Eu{sup 3+} can be a promising red-emitting phosphor for white LEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2011

{sup 48}Ca HETEROGENEITY IN DIFFERENTIATED METEORITES

Isotopic heterogeneities of {sup 48}Ca have been found in numerous bulk meteorites that are correlated with {sup 50}Ti and {sup 54}Cr anomalies among differentiated planetary bodies, and the results suggest that a rare subset of neutron-rich Type Ia supernova (nSN Ia) was responsible for contributing these neutron-rich iron-group isotopes into the solar system (SS). The heterogeneity of these isotopes found in differentiated meteorites indicates that the isotopic compositions of the bulk SS are not uniform, and there are significant amounts of nSNe Ia dust incompletely mixed with the rest of SS materials during planetary formation. Combined with the data of now-extinct short-lived nuclide {sup 60}Fe, which can be produced more efficiently from an nSN Ia than a Type II supernova ejecta, the observed planetary-scale isotopic heterogeneity probably reflects a late input of stellar dust grains with neutron-rich nuclear statistical equilibrium nuclides into the early SS.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗