Searches for double beta decay of Xe134 were performed with EXO-200, a single-phase liquid xenon detector designed to search for neutrinoless double beta decay of Xe136. Using an exposure of 29.6 ...kg·yr, the lower limits of T1/22νββ>8.7×1020 yr and T1/20νββ>1.1×1023 yr at 90% confidence level were derived, with corresponding half-life sensitivities of 1.2×1021 yr and 1.9×1023 yr. These limits exceed those in the literature for Xe134, improving by factors of nearly 105 and 2 for the two antineutrino and neutrinoless modes, respectively.
Searches for double beta decay of 134Xe were performed with EXO-200, a single-phase liquid xenon detector designed to search for neutrinoless double beta decay of 136Xe. Using an exposure of 29.6 kg ...· yr, the lower limits of T2νββ 1=2 > 8.7 × 1020 yr and T0νββ 1=2 > 1.1 × 1023 yr at 90% confidence level were derived, with corresponding half-life sensitivities of 1.2 × 1021 yr and 1.9 × 1023 yr. These limits exceed those in the literature for 134Xe, improving by factors of nearly 105 and 2 for the two antineutrino and neutrinoless modes, respectively.
PET-enabled dual-energy (DE) CT was recently proposed to enable integrated PET and DECT imaging on conventional PET/CT scanners without requiring a second x-ray CT scan. In this method, a 511 keV ...gamma-ray CT is reconstructed from time-of-flight PET emission data. Joint estimation methods such as the maximum-likelihood attenuation and activity (MLAA) or kernel MLAA algorithms can be applied for this purpose. The gamma-ray CT image is then combined with x-ray CT to obtain a DECT image pair. Quantitative reconstruction of gamma-ray CT image requires accurate correction of scatter events in measured emission data. Commonly used scatter correction methods require the determination of a multiplicative scaling factor. Existing methods for scatter scaling are mainly developed for reconstruction of PET activity images. In this work, we develop scatter scaling for improving PET-enabled DECT. We extended the kernel MLAA algorithm to jointly estimate the scatter scaling from the emission data. Simulation results indicate the proposed method can improve image quality of multi-material decomposition in PET-enabled DECT imaging.
This study investigates the potential of cloud-based serverless computing to accelerate Monte Carlo (MC)-based scatter correction (SC) in positron emission tomography (PET) imaging. Especially with ...longer axial field of view, wider acceptance angles and increased number of lines-of-response, SC can pose high computational burden for image reconstruction methods - even when executed on a modern multi-core computing server. In this work we investigate the computational performance of a cloud-based serverless MC simulation using Amazon Web Service (AWS) Lambda and provide a comparison to the computational performance of modern on-premises multi-thread reconstruction server. We find that for our specific application cloud-based SC can outperform local server-based computations by more than an order of magnitude. Adopting cloud-based serverless computing in PET imaging facilities can significantly improve processing times and overall workflow efficiency, with future research exploring additional enhancements through optimized configurations and computational methods.
Laser powder bed fusion (LPBF) – also known as selective laser melting (SLM) – is a technology of additive manufacturing (AM) that offers benefits to the fabrication of implants. This approach can ...create customized and complex parts with low elastic modulus to reduce stress shielding. The use of irregularly shaped powder is not common due to its low flowability and low apparent density. However, its low cost arouses interest in the production of materials by this technology. This work discloses the processing window that allows the fabrication of Ti-53wt.%Nb alloy parts with high density using irregularly shaped powder from hydride–dehydride (HDH) process and analyzes the influence of the process parameters on the microstructure and hardness of the samples manufactured by LPBF. Energy densities (EV) from 16 to 317 J/mm3 were investigated. Experimental density measurements by the Archimedes' principle and pore area fraction were calculated and relating to the density estimated based on X-ray diffraction (XRD) results of the HDH powder. Vickers hardness showed strong correlation to the content of interstitial elements of samples made under different EV. This work proves that is possible to obtain samples with high density using HDH powder in LPBF and that the content of interstitial elements increased with the energy density, as well as the hardness of the alloy.
Contrast recovery coefficient (CRC) is essential for image quality (IQ) assessment in positron emission tomography (PET), typically measured according to the National Electrical Manufacturers ...Association (NEMA) NU 2 standard. This study quantifies systematic uncertainties of the CRC measurement by a numerical investigation of the effects from scanner-independent parameters like voxel size, region-of-interest (ROI) misplacement, and sphere position on the underlying image grid.
CRC measurements with 2D and 3D ROIs were performed on computer-generated images of a NEMA IQ-like phantom, using voxel sizes of 1-4 mm for sphere diameters of 5-40 mm-first in absence of noise and blurring, then with simulated spatial resolution and image noise with varying noise levels. The systematic uncertainties of the CRC measurement were quantified from above variations of scanner-independent parameters. Subsampled experimental images of a NEMA IQ phantom were additionally used to investigate the impact of ROI misplacement at different noise levels.
In absence of noise and blurring, systematic uncertainties were up to 28.8% and 31.0% with 2D and 3D ROIs, respectively, for the 10 mm sphere, with the highest impact from ROI misplacement. In all cases, smaller spheres showed higher uncertainties with larger voxels. Contrary to prior assumptions, the use of 3D ROIs did not exhibit less susceptibility for parameter changes. Experimental and computer-generated images both demonstrated considerable variations on individual CRC measurements when background coefficient-of-variation exceeded 20%, despite negligible effects on mean CRC.
This study underscores the effect of scanner-independent parameters on reliability, reproducibility, and comparability of CRC measurements. Our findings highlight the trade-off between the benefits of smaller voxel sizes and noise-induced CRC fluctuations, which is not considered in the current version of the NEMA IQ standards. The results furthermore warrant adjustments to the standard to accommodate the advances in sensitivity and spatial resolution of current-generation PET scanners.
This study presents and evaluates a robust Monte Carlo-based scatter correction (SC) method for long axial field of view (FOV) and total-body positron emission tomography (PET) using the uEXPLORER ...total-body PET/CT scanner.
Our algorithm utilizes the Monte Carlo (MC) tool SimSET to compute SC factors in between individual image reconstruction iterations within our in-house list-mode and time-of-flight-based image reconstruction framework. We also introduced a unique scatter scaling technique at the detector block-level for optimal estimation of the scatter contribution in each line of response. First image evaluations were derived from phantom data spanning the entire axial FOV along with image data from a human subject with a large body mass index. Data was evaluated based on qualitative inspections, and contrast recovery, background variability, residual scatter removal from cold regions, biases and axial uniformity were quantified and compared to non-scatter-corrected images.
All reconstructed images demonstrated qualitative and quantitative improvements compared to non-scatter-corrected images: contrast recovery coefficients improved by up to 17.2% and background variability was reduced by up to 34.3%, and the residual lung error was between 1.26% and 2.08%. Low biases throughout the axial FOV indicate high quantitative accuracy and axial uniformity of the corrections. Up to 99% of residual activity in cold areas in the human subject was removed, and the reliability of the method was demonstrated in challenging body regions like in the proximity of a highly attenuating knee prosthesis.
The MC SC method employed was demonstrated to be accurate and robust in TB-PET. The results of this study can serve as a benchmark for optimizing the quantitative performance of future SC techniques.
Ti–13Nb–13Zr (TNZ) parts were produced by selective laser melting under an atmosphere with a relatively high O content using a comprehensive combination of laser powers and laser beam scanning ...velocities. The influence of processing conditions on the density, microstructure, interstitial element contents (N and O), and hardness of as-printed TNZ parts were studied. The N and O contents in the TNZ parts increased on increasing the energy density (ED). Despite the high O content in the chamber during laser processing, it was possible to obtain TNZ parts with high density and relatively low N and O contents, depending on the ED applied. Two different types of microstructure were observed in the TNZ parts: α′ martensite and α/α′ + β phases. Depending on its microstructure, the TNZ parts presented interstitial solid solution hardening and second phase hardening.
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•Densification of parts depends not only on the ED, but mainly on laser parameters.•N and O contents in the parts increased on increasing ED.•Parts with high densification and relatively low N and O contents were obtained.•α′ and α/α′ + β microstructures were observed in the parts.•The hardness increased on increasing N and O contents and the formation of dual-phase.
This work assessed the relationship between image signal-to-noise ratio (SNR) and total-body noise-equivalent count rate (NECR)-for both non-time-of-flight (TOF) NECR and TOF-NECR-in a long uniform ...water cylinder and 14 healthy human subjects using the uEXPLORER total-body PET/CT scanner.
A TOF-NEC expression was modified for list-mode PET data, and both the non-TOF NECR and TOF-NECR were compared using datasets from a long uniform water cylinder and 14 human subjects scanned up to 12 h after radiotracer injection.
The TOF-NECR for the uniform water cylinder was found to be linearly proportional to the TOF-reconstructed image SNR
in the range of radioactivity concentrations studied, but not for non-TOF NECR as indicated by the reduced
value. The results suggest that the use of TOF-NECR to estimate the count rate performance of TOF-enabled PET systems may be more appropriate for predicting the SNR of TOF-reconstructed images.
Image quality in PET is commonly characterized by image SNR and, correspondingly, the NECR. While the use of NECR for predicting image quality in conventional PET systems is well-studied, the relationship between SNR and NECR has not been examined in detail in long axial field-of-view total-body PET systems, especially for human subjects. Furthermore, the current NEMA NU 2-2018 standard does not account for count rate performance gains due to TOF in the NECR evaluation. The relationship between image SNR and total-body NECR in long axial FOV PET was assessed for the first time using the uEXPLORER total-body PET/CT scanner.
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