Spatial Resolution Quantification Research Articles

In Vitro Fossilization for High Spatial Resolution Quantification of Elements in Plant-Tissue Using LA-ICP-TOFMS.

Laser ablation in combination with an inductively coupled plasma time-of-flight mass spectrometer (LA-ICP-TOFMS) is an upcoming method for rapid quantitative element mapping of various samples. While widespread in geological applications, quantification of elements in biotissues remains challenging. In this study, a proof-of-concept sample preparation method is presented in which plant-tissues are fossilized in order to solidify the complex biotissue matrix into a mineral-like matrix. This process enables quantification of elements by using silicone as an internal standard for normalization while also providing consistent ablation processes similar to minerals to reduce image blurring. Furthermore, it allows us to generate a quantitative image of the element composition at high spatial resolution. The feasibility of the approach is demonstrated on leaves of sunflowers (Helianthus annuus), soy beans (Glycine max), and corn (Zea mays) as representatives for common crops, which were grown on both nonspiked and cadmium-spiked agricultural soil. The quantitative results achieved during imaging were validated with digestion of whole leaves followed by ICP-OES analysis. LA-ICP-TOFMS element mapping of conventionally dried samples can provide misleading trends due to the irregular ablation behavior of biotissue because high signals caused by high ablation rates are falsely interpreted as enrichment of elements. Fossilization provides the opportunity to correct such phenomena by standardization with Si as an internal standard. The method demonstrated here allows for quantitative image acquisition without time-consuming sample preparation steps by using comparatively safe chemicals. The diversity of tested samples suggests that this sample preparation method is well-suited to achieve reproducible and quantitative element maps of various plant samples.

Crystal scatter effects in a large-area dual-panel Positron Emission Mammography system.

Positron Emission Mammography (PEM) is a valuable molecular imaging technique for breast studies using pharmaceuticals labeled with positron emitters and dual-panel detectors. PEM scanners normally use large scintillation crystals coupled to sensitive photodetectors. Multiple interactions of the 511 keV annihilation photons in the crystals can result in event mispositioning leading to a negative impact in radiopharmaceutical uptake quantification. In this work, we report the study of crystal scatter effects of a large-area dual-panel PEM system designed with either monolithic or pixelated lutetium yttrium orthosilicate (LYSO) crystals using the Monte Carlo simulation platform GATE. The results show that only a relatively small fraction of coincidences (~20%) arise from events where both coincidence photons undergo single interactions (mostly through photoelectric absorption) in the crystals. Most of the coincidences are events where at least one of the annihilation photons undergoes a chain of Compton scatterings: approximately 79% end up in photoelectric absorption while the rest (<1%) escape the detector. Mean positioning errors, calculated as the distance between first hit and energy weighted (assigned) positions of interaction, were 1.70 mm and 1.92 mm for the monolithic and pixelated crystals, respectively. Reconstructed spatial resolution quantification with a miniDerenzo phantom and a list mode iterative reconstruction algorithm shows that, for both crystal types, 2 mm diameter hot rods were resolved, indicating a relatively small effect in spatial resolution. A drastic reduction in peak-to-valley ratios for the same hot-rod diameters was observed, up to a factor of 14 for the monolithic crystals and 7.5 for the pixelated ones.

Quantifying spatial resolution in a fast neutron radiography system

Neutron imaging is a powerful nondestructive examination modality that has been employed in various applications. Fast neutrons provide advantages over lower energy neutrons, such as examining thicker samples and inducing negligible activation and transmutations. However, fast neutrons interact mostly via elastic scattering with both the neutron detector and the object, causing degradation in spatial resolution. This study explores the quantification of spatial resolution caused by the testing target itself and suggests proper candidate materials for characterizing spatial resolution in terms of modulation transfer function. Knife-edge radiographs of 3 mm, 6 mm, and 5 cm thick Tantalum (Ta) foils, and a 2.54 cm Tungsten (W) cube were acquired using a CCD-based imaging system and a Polyvinyl Toluene (PVT) scintillator at the Ohio State Research Reactor (OSURR)’s fast neutron beam facility. The spatial resolutions calculated were 195 ± 20μm, 224 ± 22μm, 248 ± 25μm, and 435 ± 44μm for 3 mm, 6 mm, and 5 cm Ta foils, and 2.54 cm W cube, respectively. The results showed a worsening spatial resolution with increasing target thickness. Simulations and calculations estimate that elastic scattering kinematics between neutrons and protons in the PVT medium also limits spatial resolution, and it sets a lower limit of ∼44μm on the spatial resolution for 2 MeV neutrons.

Anthropomorphic left ventricular mesh phantom: a framework to investigate the accuracy of SQUEEZ using Coherent Point Drift for the detection of regional wall motion abnormalities.

We present an anthropomorphically accurate left ventricular (LV) phantom derived from human computed tomography (CT) data to serve as the ground truth for the optimization and the spatial resolution quantification of a CT-derived regional strain metric (SQUEEZ) for the detection of regional wall motion abnormalities. Displacements were applied to the mesh points of a clinically derived end-diastolic LV mesh to create analytical end-systolic poses with physiologically accurate endocardial strains. Normal function and regional dysfunction of four sizes [1, 2/3, 1/2, and 1/3 American Heart Association (AHA) segments as core diameter], each exhibiting hypokinesia (70% reduction in strain) and subtle hypokinesia (40% reduction in strain), were simulated. Regional shortening ( ) estimates were obtained by registering the end-diastolic mesh to each simulated end-systolic mesh condition using a nonrigid registration algorithm. Ground-truth models of normal function and of hypokinesia were used to identify the optimal parameters in the registration algorithm and to measure the accuracy of detecting regional dysfunction of varying sizes and severities. For normal LV function, values in all 16 AHA segments were accurate to within . For cases with regional dysfunction, the errors in around the dysfunctional region increased with decreasing size of dysfunctional tissue.

On the quantification of spatial resolution for three-dimensional computed tomography of chemiluminescence: erratum.

This erratum clarifies an accidental omission of a citation.

On the quantification of spatial resolution for three-dimensional computed tomography of chemiluminescence.

Three-dimensional computed tomography of chemiluminescence (CTC) for combustion diagnostics is attracting a surged research interest due to recent progress in sensor technologies and reduced costs of high-speed cameras. For example, it has been applied to recover the 3D distributions of intermediate chemical species such as CH* and OH*, heat release rate, and flame topology. Although these applications were demonstrated to be successful, there are still a few drawbacks of this technique that have not be cured. For example, to the best of the authors' knowledge, all the imaging models that have been developed so far ignore the imperfections of cameras such as lens distortion and skewness. However, this will unavoidably introduce errors into the weight matrix. In addition, spatial resolution of a CTC system is a critical performance parameter. However, it has only been studied qualitatively and no quantitative quantification method is reported so far. This work aims to solve these problems by improving the imaging model and developing a method based on edge spread function for the quantification of spatial resolution. Although this work is conducted under the context of CTC for combustion diagnostics, it also provides useful insights for other tomographic modalities such as volumetric laser-induced fluorescence and tomographic laser-induced incandescence.

Respiratory variation in left ventricular cardiac function with 3D double golden-angle whole-heart cine imaging.

To develop a 3-dimensional free-breathing cardiovascular MR technique for quantifying the variation in left ventricular end-diastolic volume (LVEDV) during the respiratory cycle. A 3-dimensional radial trajectory with double golden-angle ordering was used for free-running data acquisition during free breathing in healthy volunteers (N = 8). A respiratory self-gating signal was extracted from the center of k-space, and data were retrospectively binned into eight respiratory phases in end-diastole. Three-dimensional image volumes with 2-mm isotropic spatial resolution were reconstructed with conjugate-gradient sensitivity encoding for acquisition durations of 4.5, 9, and 25 min. The LVEDV was manually segmented for each respiratory phase and acquisition duration. Respiratory-induced variation expressed as minimum LVEDV (during mid-inspiration) relative to maximum LVEDV (during mid-expiration) was 5.9 ± 0.3% for 4.5 min, 5.3 ± 0.4% for 9 min (P = 0.64 versus 4.5 min), and 5.0 ± 0.4% for 25 min (P = 0.25 versus 4.5 min, and P = 1.00 versus 9 min). The proposed technique enables high spatial-resolution quantification of the respiratory variation in LVEDV during free breathing in under 5 min, and was found to be 5 to 6% for healthy volunteers. Magn Reson Med 79:2693-2701, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Optical Access Schemes for High Speed and Spatial Resolution Optical Absorption Tomography in Energy Engineering

Optical diagnostic techniques play an important role in the engineering of modern energy processes. Optical absorption tomography as a diagnostic technique allows imaging of chemical species in flows with spatio-temporal resolution. The optical access scheme employed to acquire the tomographic projections impacts the limiting spatial resolution and imaging speed of the instrument. Our review of conventional optical access schemes indicates that there currently exist no practical schemes that can achieve simultaneous high-speed, high-spatial resolution imaging. Here, we show that advanced solid-state beam deflectors can be used to realize such a system. We evaluated a state-of-the-art electro-optic deflector combining a multi-pass scheme in a space-charged crystal and found that it can achieve a full deflection angle of 216 mrad (12.4°) at 90-kHz scan rate. We present how optical access schemes based on electro-optic deflectors can be arranged, estimating the increased bandwidth requirement for the data acquisition system. Using an existing tomography system and an image reconstruction algorithm, we show by simulation that the spatial resolution under non-optimum conditions can be improved by 38%. We describe in detail our implementation of the spatial resolution quantification algorithm. Our results demonstrate how advances in other disciplines can be exploited to further improve the performance of an optical tomography instrument. We anticipate our assay to motivate further development of optical access schemes as well as optimized image reconstruction algorithms.

High Spatial Resolution Quantification X-ray Microanalysis in a Field Emission Scanning Electron Microscope with an Annular Silicon Drift Detector

High Spatial Resolution Quantification X-ray Microanalysis in a Field Emission Scanning Electron Microscope with an Annular Silicon Drift Detector

Quantification of Cement Hydration through Neutron Radiography with Scatter Rejection

The unique capabilities of neutrons to penetrate materials opaque to X-rays and at the same time to interact with hydrogen make neutron radiography a technique of choice for the nondestructive quantification of hydrogen-containing substances. However, scattering rather than absorption of neutrons by hydrogen atoms can substantially decrease the accuracy of this quantification. Various post-experiment data processing techniques were developed to correct and mitigate the effects of scattering. A complementary “hardware” solution is to simply eliminate the detrimental scattering component from the detected signal through the use of neutron collimators. Compact polycapillary collimators, merely a few millimeters thick, enable accurate, high spatial resolution quantification for a wide range of neutron scattering materials. This paper demonstrates the improved quantification of water absorption with sub- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\hbox{100}}~\mu\hbox{m}$</tex></formula> spatial resolution in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$1 \times 1\times \hbox{2~cm}^{3}$</tex></formula> Portland cement samples. A compact polycapillary neutron collimator (2 mm thick) was used for scatter rejection in our experiments. The results of these measurements indicate that such devices can be attractive for studies where samples must be placed in quite close proximity (e.g., only a few centimeters or closer) from the neutron detector active surface.

Spatially resolved and observer-free experimental quantification of spatial resolution in tomographic images.

We present a novel framework and experimental method for the quantification of spatial resolution of a tomography system. The framework adopts the "black box" view of an imaging system, considering only its input and output. The tomography system is locally stimulated with a step input, viz., a sharp edge. The output, viz., the reconstructed images, is analysed by Fourier decomposition of their spatial frequency components, and the local limiting spatial resolution is determined using a cut-off threshold. At no point is an observer involved in the process. The framework also includes a means of translating the quantification region in the imaging space, thus creating a spatially resolved map of objectively quantified spatial resolution. As a case-study, the framework is experimentally applied using a gaseous propane phantom measured by a well-established chemical species tomography system. A spatial resolution map consisting of 28 regions is produced. In isolated regions, the indicated performance is 4-times better than that suggested in the literature and varies by 57% across the imaging space. A mechanism based on adjacent but non-interacting beams is hypothesised to explain the observed behaviour. The mechanism suggests that, as also independently concluded by other methods, a geometrically regular beam array maintains maximum objectivity in reconstructions. We believe that the proposed framework, methodology, and findings will be of value in the design and performance evaluation of tomographic imaging arrays and systems.

Sub 400 nm spatial resolution extreme ultraviolet holography with a table top laser

We report sub-400 nm spatial resolution with Gabor holography obtained using a highly coherent table top 46.9 nm laser. The hologram was recorded in high resolution photoresist and subsequently digitized with an atomic force microscope. The final image was numerically reconstructed with a Fresnel propagator. Optimal reconstruction parameters and quantification of spatial resolution were obtained with a wavelet analysis and image correlation.