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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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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Using Multiplicative Algebraic Reconstruction Techniques (MART) to Derive Instrument Requirements for Computed Tomography Imaging Spectrographs

Computed Tomography Imaging Spectrographs (CTISs), which are generally slitless or large-aperture spectrographs that observe a wide, dispersed field of view in multiple dispersion angles or diffraction orders, provide a unique opportunity to capture spectral information over an extended source, such as the Sun, but require software reconstruction techniques to be fully utilized. A useful data product that can be recovered from CTIS observations is intensity maps of solar features in single spectral lines. These intensity maps can then be used to determine temperature, density, abundance, and equilibrium properties of the emitting plasma. We apply the multiplicative algebraic reconstruction technique (MART) to example data from a variety of CTIS configurations to determine the capability and limitations of the method to return spectrally-pure maps. By completing this study, we aim to establish a path to derive requirements for CTIS instruments that rely on reconstruction techniques to meet their science objectives.

Amy Winebarger↗
NASA NTRS2023

Investigating the Impact of X-Ray Computed Tomography Imaging on Soluble Organic Matter in the Murchison Meteorite: Implications for Bennu Sample Analyses

X-ray computed tomography (XCT) is a valuable reconnaissance tool for three-dimensional imaging and identification of distinct lithologies in extraterrestrial samples. It will be used as part of the preliminary examination of samples returned from asteroid (101955) Bennu by the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission. However, it must first be established whether x-rays generated during XCT could degrade or alter the organic composition of the returned samples by radiolysis. To test this, we split a crushed sample of the Murchison CM2 meteorite, kept one portion as a control, and irradiated the other portion up to the maximum x-ray dosage (~180 Gy) that a Bennu sample would experience during an XCT imaging experiment. We then extracted organic compounds from both splits and conducted (i) nontargeted soluble organic analyses to compare the chemical distributions of C-, H-, O-, N-, and S-bearing species and (ii) targeted measurements to quantify the abundances of 96 individual soluble organic molecules that included protein amino acids, amines, carboxylic acids, hydroxy acids, carbonyl compounds, polycyclic aromatic hydrocarbons, alcohols, sugars, and N-heterocycles. We found that XCT imaging of the Murchison meteorite had no measurable impact on the relative abundances or enantiomeric compositions of most of the soluble organic compounds targeted in this study. Elevated total abundances of several soluble organic compound classes were observed in the XCT-scanned Murchison sample relative to the control. This is likely related to particle size heterogeneity and specific surface area differences between the sample aliquots used for the extractions, rather than a result of the x-ray exposure. Assuming the samples returned from asteroid Bennu by OSIRIS-REx have a similar composition to carbonaceous chondrites, these data provide confidence that XCT will not significantly alter their soluble organic compositions.

Daniel P Glavin↗
NASA NTRS2024

X-Ray Micro- and Nano-Tomography Analysis of Bennu Samples: A Preliminary Report

X-ray tomography (XCT) is an effective technique for obtaining the 3D structures of returned samples. XCT using synchrotron radiation provides high-resolution CT images with quantitative information. The XCT systems at SPring-8, an SR facility in Japan, have been used to analyze samples returned from the asteroids Itokawa and Ryugu. In this study, we plan to apply SR-XCT to samples returned from the asteroid Bennu.

A Tsuchiyama↗
NASA NTRS2024

Investigating Space Weathering of Ryugu Grains Using Electron Microscopy and X-Ray Computed Tomography

The effects of micrometeorite bombardment and solar wind ion irradiation – collectively known as space weathering – alter the microstructural, chemical, and spectral properties of airless surfaces. Characteristics of space weathering include vesiculated textures, amorphous grain rims (upper ~100 nm), and the production of Fe-bearing nanoparticles (npFe). The resulting modifications in the optical properties of the surface regolith include changes in spectral slope and overall reflectance of the surfaces as well as the attenuation of their characteristic absorption bands across VIS-NIR wavelengths. As the surface is continuously exposed to interplanetary space over time, the accrual of these features complicates the interpretation of remote sensing spectral data and the characterization of returned samples. Laboratory experiments that simulate solar wind irradiation and micrometeoroid impacts using carbonaceous analogs have revealed novel and complex microstructural and chemical changes, including the decrease in organic species concentrations and the reduction of Fe 3+ . In 2020, the Japan Aerospace Exploration Agency (JAXA)’s Hayabusa2 mission returned over 5 g of regolith particles from near- Earth C-type asteroid (162173) Ryugu – a unique opportunity to study space weathering on carbonaceous materials. Initial studies have established that the surface morphology and chemical signatures of space weathering in returned samples share characteristics with laser irradiation experiments simulating micrometeoroid bombardment, indicating that impacts are a significant space weathering mechanism operating on Ryugu. Here, we seek to improve our understanding of space weathering of carbonaceous asteroidal regolith grains by characterizing its effects directly on returned samples to determine the nature of space weathering on Ryugu. To do so, we performed coordinated analyses using electron beam techniques and X-ray computed tomography (XCT) to examine the effects of space weathering on grains returned from the surface of Ryugu by the Hayabusa2 mission.

L. E. Melendez↗
NASA NTRSDate not supplied

Geochemical Quantification of Olivine Minerals by Atom Probe Tomography

The ability of atom probe tomography (APT) to interrogate small sample volumes with high efficiency makes it uniquely useful in the study of small mineral grains or domains. Although it is frequently employed in the analysis of geological materials, particularly in the characterization of nanoscale chemical heterogeneities, the degree of quantitative accuracy achieved by APT can be difficult to determine.

D W Saxey↗
NASA NTRS1992

Description of a prototype emission-transmission computed tomography imaging system

We have developed a prototype imaging system that can perform simultaneous x-ray transmission CT and SPECT phantom studies. This system employs a 23-element high-purity-germanium detector array. The detector array is coupled to a collimator with septa angled toward the focal spot of an x-ray tube. During image acquisition, the x-ray fan beam and the detector array move synchronously along an arc pivoted at the x-ray source. Multiple projections are obtained by rotating the object, which is mounted at the center of rotation of the system. The detector array and electronics can count up to 10(6) cps/element with sufficient energy-resolution to discriminate between x-rays at 100-120 kVp and gamma rays from 99mTc. We have used this device to acquire x-ray CT and SPECT images of a three-dimensional Hoffman brain phantom. The emission and transmission images may be superimposed in order to localize the emission image on the transmission map.

NASA Discipline Musculoskeletal↗
NASA NTRS1985

Quantitative computed tomography for spinal mineral assessment: current status

Quantitative CT (QCT) is an established method for the noninvasive assessment of bone mineral content in the vertebral spongiosum and other anatomic locations. The potential strengths of QCT relative to dual photon absorptiometry (DPA) are its capability for precise three-dimensional anatomic localization providing a direct density measurement and its capability for spatial separation of highly responsive cancellous bone from less responsive cortical bone. The extraction of this quantitative information from the CT image, however, requires sophisticated calibration and positioning techniques and careful technical monitoring.

Lumbar Vertebrae/radiography↗
NASA NTRS1999

Modeling of polychromatic attenuation using computed tomography reconstructed images

This paper presents a procedure for estimating an accurate model of the CT imaging process including spectral effects. As raw projection data are typically unavailable to the end-user, we adopt a post-processing approach that utilizes the reconstructed images themselves. This approach includes errors from x-ray scatter and the nonidealities of the built-in soft tissue correction into the beam characteristics, which is crucial to beam hardening correction algorithms that are designed to be applied directly to CT reconstructed images. We formulate this approach as a quadratic programming problem and propose two different methods, dimension reduction and regularization, to overcome ill conditioning in the model. For the regularization method we use a statistical procedure, Cross Validation, to select the regularization parameter. We have constructed step-wedge phantoms to estimate the effective beam spectrum of a GE CT-I scanner. Using the derived spectrum, we computed the attenuation ratios for the wedge phantoms and found that the worst case modeling error is less than 3% of the corresponding attenuation ratio. We have also built two test (hybrid) phantoms to evaluate the effective spectrum. Based on these test phantoms, we have shown that the effective beam spectrum provides an accurate model for the CT imaging process. Last, we used a simple beam hardening correction experiment to demonstrate the effectiveness of the estimated beam profile for removing beam hardening artifacts. We hope that this estimation procedure will encourage more independent research on beam hardening corrections and will lead to the development of application-specific beam hardening correction algorithms.

NASA Discipline Musculoskeletal↗
NASA NTRS2002

Imaging the interiors of near-earth objects with radio reflection tomography

Scenarios for mitigation of asteroid comet collisions include the use of explosives to deflect or destroythe projectile. However, as demonstrated by Asphaug et al.( 1998), the outcome of explosive energy transfer to an asteroid or comet (via a bomb or a hypervelocity impact) is extremely sensitive to the pre-existing configuration of fractures and voids.

radio reflection tomography↗
NASA NTRS2014

Observations of MCG-5-23-16 with Suzaku, XMM-Newton and NuSTAR: Disk Tomography and Compton Hump Reverberation

MCG-5-23-16 is one of the first active galactic nuclei (AGNs) where relativistic reverberation in the iron K line originating in the vicinity of the supermassive black hole was found, based on a short XMM-Newton observation. In this work, we present the results from long X-ray observations using Suzaku, XMM-Newton, and NuSTAR designed to map the emission region using X-ray reverberation. A relativistic iron line is detected in the lag spectra on three different timescales, allowing the emission from different regions around the black hole to be separated. Using NuSTAR coverage of energies above 10 keV reveals a lag between these energies and the primary continuum, which is detected for the first time in an AGN. This lag is a result of the Compton reflection hump responding to changes in the primary source in a manner similar to the response of the relativistic iron K line.

NUSTAR↗