Resolution Correction Research Articles

Atmospheric pollutants in Rosario, Argentina analysed through remote sensing: Wildfires and COVID-19 lockdown effects

Spatial-temporal dynamics of atmospheric pollutants can be analysed by space-based observations, contributing to environmental management and public health interventions. The influence of wildfires and anthropogenic activities on air quality is studied for the city of Rosario and its surroundings, including both urban and non-urban areas. Utilizing advanced satellite-based observations, we assess Aerosol Optical Depth (AOD) and Nitrogen Dioxide (NO2). The study employs Multi-Angle Implementation of Atmospheric Correction (MAIAC) and Moderate Resolution Imaging Spectroradiometer (MODIS) onboard NASA's Terra and Aqua satellites for AOD analysis. NO2 measurements were derived from the Ozone Monitoring Instrument (OMI) on the Aura satellite. Backward trajectory analysis using Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) shows the connection between fire pixels and air masses reaching Rosario. During the COVID-19 lockdown, a period with no significant fire events in the studied region was selected. This provided, for the first time, a baseline on the AOD median value of 0.05 for Rosario city and its surroundings, while NO2 total column median values were close to 3.00 x 1015 molecules/cm2. In a business-as-usual scenario, AOD increased by approximately 52.8% (March 2022) up to 111.3% (March 2019). NO2 median values remain almost the same (March 2019) or reached a median value of 3.38 x 1015 molecules/cm2 (March 2022). During wildfire events, such as March 2023, AOD surged by around 50.9%–108.6% compared to the business-as-usual scenario (March 2019 and March 2022, respectively). NO2 median values ranged from 3.52 x 1015 molecules/cm2 (March 2023) to 3.66 x 1015 molecules/cm (March 01, 2020 to March 19, 2020). NO2 levels correlated with intense fire periods. The analysis provides valuable insights into the complex interplay between natural events, human activities, and air quality dynamics in the region.

Spatially Resolved Observations of Meteor Radio Afterglows With the OVRO‐LWA

AbstractWe conducted an all‐sky imaging transient search with the Owens Valley Radio Observatory Long Wavelength Array (OVRO‐LWA) data collected during the Perseid meteor shower in 2018. The data collection during the meteor shower was motivated to conduct a search for intrinsic radio emission from meteors below 60 MHz known as the meteor radio afterglows (MRAs). The data collected were calibrated and imaged using the core array to obtain lower angular resolution images of the sky. These images were input to a pre‐existing LWA transient search pipeline to search for MRAs as well as cosmic radio transients. This search detected 5 MRAs and did not find any cosmic transients. We further conducted peeling of bright sources, near‐field correction, visibility differencing and higher angular resolution imaging using the full array for these 5 MRAs. These higher angular resolution images were used to study their plasma emission structures and monitor their evolution as a function of frequency and time. With higher angular resolution imaging, we resolved the radio emission size scales to less than 1 km physical size at 100 km heights. The spectral index mapping of one of the long duration event showed signs of diffusion of plasma within the meteor trails. The unpolarized emission from the resolved radio components suggest resonant transition radiation as the possible radiation mechanism of MRAs.

Technical NEMA NU2-2018 Performance Assessment of Time-of-Flight-Integrated Digital PET-CT System.

Aim The objective of this study includes the NEMA (National Electrical Manufacturer Association) NU2-2018 performance evaluation of the uMIvista PET-CT (positron emission tomography-computed tomography) system. Methods The latest NEMA NU2-2018 guidelines have been followed for the evaluation of performance parameters of this PET-CT scanner: axial, tangential, and radial spatial resolution, sensitivity, counting losses, scatter, randomness, random and counting loss correction, image quality, time and energy resolution, image uniformity, and image registration alignment post installation of country first uMIvista PET-CT. Results The measured NEMA sensitivity of the uMIvista PET scanner was 12.053 cps/kBq. The spatial resolutions of the PET were measured as tangential, radial, and transaxial spatial resolutions at 10 mm, with 3.01 mm, 2.95 mm, and 2.93 mm, respectively; at 100 mm, with 3.17 mm, 3.42 mm, and 3.05 mm, respectively; and at 200 mm, with 3.65 mm, 4.54 mm, and 3.17 mm, respectively, at full-width half-maximum (FWHM); while at full-width tenths-maximum (FWTM), the values at 10 mm were 5.79 mm, 5.57 mm, and 5.69 mm, respectively, and at 100 mm were 5.59 mm, 5.96 mm, and 5.91 mm, respectively. The measured time-of-flight (TOF) timing resolution was 302.294 ps and the measured energy resolution was 11.76% with FWHM and FWTM. Conclusion The NEMA NU2-2018 performances of this TOF-integrated digital PET-CT system are extremely good in all parameters.

Estimation of 1 km downwelling shortwave radiation over the Tibetan Plateau under all-sky conditions

Abstract. Downwelling shortwave radiation (DSR) is the basic driving force for the energy and water cycles of the Earth's climate system. Called the Third Pole of the Earth, the Tibetan Plateau (TP) absorbs a large amount of shortwave radiation and exerts important impacts on global weather and climate change. However, due to coarse spatial resolution and insufficient consideration of factors influencing radiative transfer processes, DSR parameterization schemes still need to be improved when applied to the TP. Based on satellite datasets and meteorological forcing data, all-sky DSR over the TP at a spatial resolution of 1 km was derived using an improved parameterization scheme. The influence of topography and different radiative attenuations were comprehensively taken into account. Specifically, the introduction of cloud multiscattering and topography factors further improves the DSR estimation accuracy. The validation results indicated that the developed parameterization scheme showed reasonable accuracy. By comparing with current, widely used DSR products based on the same in situ observations, the derived DSR performed much better on different spatial and temporal scales. On instantaneous, 10 d and monthly timescales, the root-mean-square errors (RMSEs) of the derived DSR are 132.8–158.2, 70.8–76.5 and 61.3–67.5 W m−2, respectively, which are much smaller than those of current DSR products. The derived DSR not only captured the temporal-variation characteristics that are more consistent with the in situ measurements, but also provided reasonable spatial patterns. Meanwhile, the proposed parameterization scheme demonstrated its superiority in characterizing more details and high dynamics of the spatial pattern of DSR due to its terrain correction and high resolution. Moreover, this parameterization scheme does not need any local correction in advance and has the potential to be extended to other regions in the world.

New method for level-lifetime measurements with thick scintillators

Level lifetimes provide key insight into the structure of atomic nuclei and serve as stringent tests of theoretical descriptions. Though several methods for determining level lifetimes exist for both reaction measurements and decay studies, here the focus is on techniques involving the direct measurement of time differences between population and subsequent depopulation of excited states. The techniques presented herein are broadly applicable across multiple timing ranges, but the approach is specifically described for the βγ timing method. A multi-step, amplitude-dependent time walk correction and timing resolution corrections were employed to address the data analysis complications that arise from using thick scintillators for electron detection. Subsequently, a new Monte Carlo method utilizing measured detector responses obtained from the data, coupled with chi-square minimization, is presented for extracting excited state lifetimes ≳ 100 picoseconds. The framework of this Monte Carlo method is developed for the decay of a state in 68Zn with a known 1.6 ps half life, which is considered prompt given the detection sensitivity of the technique, and then benchmarked using two other excited states in neutron-rich Ni isotopes with 120(34) ps and 1.05(3) ns half lives. Using this new method which takes into account the thick scintillator used, these same half lives were measured to be 135(10) ps and 1.04(24) ns, respectively. The overall good agreement demonstrates the validity of the technique.

Characterisation of a well-type NaI(Tl) detector by means of a Monte Carlo simulation for radionuclide metrology application

A well-type NaI(Tl) detector was modelled and characterised by means of a Monte Carlo simulation, as part of a project to develop a 4πβ (Plastic Scintillator)-4πγ instrument to be used for the primary standardisation of radionuclides at ANSTO. The simulation based on GEANT4 was used to characterise the 4πγ detector in terms of potential dead layer/inactive materials, full energy peak efficiency, coincidence-summing correction, and energy resolution. An excellent agreement was obtained between the simulation results and the experimental measurements.

Retrospective fractional dose reduction in Tc-99m cardiac perfusion SPECT/CT patients: A human and model observer study

BackgroundIn the ongoing efforts to reduce cardiac perfusion dose (injected radioactivity) for conventional SPECT/CT systems, we performed a human observer study to confirm our clinical model observer findings that iterative reconstruction employing OSEM (ordered-subset expectation-maximization) at 25% of the full dose (quarter-dose) has a similar performance for detection of hybrid cardiac perfusion defects as FBP at full dose. MethodsOne hundred and sixty-six patients, who underwent routine rest-stress Tc-99m sestamibi cardiac perfusion SPECT/CT imaging and clinically read as normally perfused, were included in the study. Ground truth was established by the normal read and the insertion of hybrid defects. In addition to the reconstruction of the 25% of full-dose data using OSEM with attenuation (AC), scatter (SC), and spatial resolution correction (RC), FBP and OSEM (with AC, SC, and RC) both at full dose (100%) were done. Both human observer and clinical model observer confidence scores were obtained to generate receiver operating characteristics (ROC) curves in a task-based image quality assessment. ResultsAverage human observer AUC (area under the ROC curve) values of 0.725, 0.876, and 0.890 were obtained for FBP at full dose, OSEM at 25% of full dose, and OSEM at full dose, respectively. Both OSEM strategies were significantly better than FBP with P values of 0.003 and 0.01 respectively, while no significant difference was recorded between OSEM methods (P = 0.48). The clinical model observer results were 0.791, 0.822, and 0.879, respectively, for the same patient cases and processing strategies used in the human observer study. ConclusionsCardiac perfusion SPECT/CT using OSEM reconstruction at 25% of full dose has AUCs larger than FBP and closer to those of full-dose OSEM when read by human observers, potentially replacing the higher dose studies during clinical reading.

Broadband achromatic metasurfaces for sub-diffraction focusing in the visible.

Conventional achromatic optical systems are matured to achieve effective chromatic aberration correction and diffraction-limited resolution by the multiple bulky lenses. The emergence of the super-oscillation phenomenon provides an effective method for non-invasive far-field super-resolution imaging. Nevertheless, most super-oscillatory lenses are significantly restricted by the chromatic aberration due to the reliance on delicate interference; on the other hand, most achromatic lenses cannot break the diffraction limit. In this article, a single-layer broadband achromatic metasurface comprising sub-wavelength anisotropic nanostructures has been proposed to achieve sub-diffraction focusing with a focal length of f=60 µm and a diameter of 20 µm in the visible ranging from 400 nm to 700 nm, which are capable of generating sub-diffraction focal spots under the left-handed circularly polarized incident light with arbitrary wavelength in the working bandwidth at the same focal plane. This method may find promising potentials in various applications such as super-resolution color imaging, light field cameras, and machine vision.

Lattice resolution of vibrational modes in the electron microscope

The combination of aberration correction and ultra high energy resolution with monochromators has made it possible to record images showing lattice resolution in phonon modes, both with a displaced collection aperture and more recently with an on –axis collection aperture. In practice the objective aperture has to include Bragg reflections that correspond to the observed lattice image spacings, and the specimen has to be sufficiently thick for adequate phonon scattered intensity. There has been controversy as to whether the images with the on axis detector are really a consequence of lattice resolution in a phonon mode or just a transfer of information from an image that was formed by elastically scattered electrons. We present results of calculations based on a theory that includes the possibility of dynamical electron diffraction for both incident and scattered electrons and the full phonon dispersion relation. We show that Umklapp scattering from the second Brillouin Zone back to the first Brillouin Zone is necessary for lattice resolution with the on axis detector and that it is therefore reasonable to attribute the lattice resolution to the phonon scattering.

CORR Synthesis: Can Guided Growth for Angular Deformity Correction Be Applied to Management of Pediatric Patellofemoral Instability?

CORR Synthesis: Can Guided Growth for Angular Deformity Correction Be Applied to Management of Pediatric Patellofemoral Instability?

Rayleigh scattering correction for fluorescence spectroscopy analysis

Rayleigh scattering signals, not conforming bilinear and trilinear structure of spectral excitation–emission matrices (EEMs), significantly increases the difficulty of spectral resolution. To eliminate or reduce the interference of Rayleigh scattering, we propose missing data recovery (MDR) coupled with principal component analysis (PCA) or parallel factor analysis (PARAFAC) as a novel strategy for Rayleigh scattering correction and corresponding EEM decomposition. MDR treats the scattering data as missing by weighting them as zeros to remove Rayleigh scattering signals thoroughly. Then, sample signals are dramatically recovery in the scattering missing region during rapid iterative process of PCA or PARAFAC to repair bilinearity and trilinearity of EEMs. For significant Rayleigh scattering leading to severe signal loss, profile constraint on both of excitation and emission spectra following fluorescence spectral laws is further proposed for MDR-PCA and MDR-PARAFAC. It is so as to avoid mathematical reasonable but chemical meaningless solutions. The results reveal MDR-PCA and MDR-PARAFAC enable robust Rayleigh scattering correction and EEM decomposition both for simulated and practical data sets. Without the need of any specific priori knowledge and pretreatment such as wavelength selection, it therefore suggests great potential of the proposed method to be a generalized strategy for robust Rayleigh scattering correction and spectral resolution of EEMs.

Data processing and performance evaluation of a tempo-spatially mixed modulation imaging Fourier transform spectrometer based on stepped micro-mirror.

A novel tempo-spatially mixed modulation imaging Fourier transform spectrometer based on a stepped micro-mirror has the advantages of high throughput, compactness, and stability. In this paper, we present a method of image- and spectrum-processing and performance evaluation, which is utilized to obtain a high-quality reconstructed image without stitching gaps and a reconstructed spectrum with significantly reduced noise and side-lobe oscillation. A theoretical model of instrument line shape and signal-to-noise ratio is established to verify the effectiveness of non-uniformity sampling correction and spectral resolution enhancement. Meanwhile, the performance of the instrument was evaluated combined with experimental results.

Passive optical device for nystagmus correction and ophthalmic resolution enhancement.

In this research, we present a novel device that solves the reduced visual acuity caused by involuntary movements of the retina in nystagmus. The proposed solution comprises a contact lens that moves together with the eyeball and an ophthalmic lens (spectacles). Our work has three parts: numerical simulation of the proposed solution, an experimental optical bench procedure, and a clinical experiment, with nonnystagmus subjects, in which we mimicked the uncontrolled eye movements in nystagmus. In the numerical and experimental bench sections of this study, we show that the proposed optics produces a clear and stable image on a screen. In the clinical study, subjects with the device felt only small movements of the image when they moved their eyes across the field of view. They described a magnification resulting in narrowing the field of view, and therefore had to move their heads to see the space of the room. This follows the theoretical expectation for the proposed concept. Thus, the proposed device may help nystagmus subjects fixate the image on the center of the retina and thus enable improved visual acuity. The device may be used in young children suffering from nystagmus to prevent amblyopia.

Quantification evaluation of 99mTc-MDP concentration in the lumbar spine with SPECT/CT: compare with bone mineral density.

Despite recent technological advances allowing for quantitative single-photon emission computed tomography (SPECT), quantitative SPECT has not been widely used in the clinical practice of osteoporosis. The aim of this study is to evaluate the feasibility of quantitative bone SPECT/CT for measuring lumbar standard uptake value (SUV) in patients with different bone-mineral density (BMD), and investigate the correlation between SUV measured with 99mTc-methylene diphosphonate (MDP) SPECT/CT and BMD assessment by dual-energy X-ray absorptiometry (DXA). A retrospective analysis of 62 cases 99mTc-MDP whole-body bone imaging and local lumbar SPECT/CT tomography were performed. According to the results of dual-energy X-ray bone density examination, they were divided into normal group, osteopenic group, and osteoporosis group. The raw SPECT data were reconstructed using flash3D which includes attenuation correction, scatter compensation, and collimator resolution recovery, SPECT images from this algorithm were calibrated for SUV analysis. Comparing difference of lumbar SUV in different BMD subjects, and investigating the correlation between lumbar SUV and BMD. Data were analyzed by one-way ANOVA and Pearson regression analysis using SPSS 17.0 software. The maximum SUV (SUVmax) and mean SUV (SUVmean) of L1-L4 vertebral in 62 subjects were 7.39 ± 1.84 and 4.90 ± 1.27, respectively. The average BMD was 0.85 ± 0.15 (g/cm2), and the average CT value was 145.88 ± 53.99 (HU). The SUVmax, SUVmean, BMD, and CT values of the lumbar spine were statistically significantly different among the three groups (F = 24.089, 30.501, 94.847, 30.241, all p < 0.001), and the osteopenic group was significantly lower than the normal group (all p < 0.001), the osteoporosis group was significantly lower than the normal group and the osteopenic group (all p < 0.001). Lumbar SUVmax, SUVmean, and BMD were significantly negatively correlated with age (r = -0.328 to -0.442, all p < 0.05), and positively correlated with body weight and CT value (r = 0.299-0.737, all p < 0.05), but no significant correlation with height (r = 0.006-0.175, all p > 0.05). Lumbar SUVmax and SUVmean increased significantly with the increase of BMD (r = 0.638, 0.632, p < 0.001). The SUV of lumbar spine in 99mTc-MDP bone SPECT/CT was significantly different among subjects with different BMD, and the SUV was positively correlated with BMD. These findings justify that quantitative bone SPECT/CT is an applicable tool for clinical quantification of bone metabolism in osteoporosis patients.

Adaptive optics in the mouse eye: wavefront sensing based vs. image-guided aberration correction.

Adaptive Optics (AO) is required to achieve diffraction limited resolution in many real-life imaging applications in biology and medicine. AO is essential to guarantee high fidelity visualization of cellular structures for retinal imaging by correcting ocular aberrations. Aberration correction for mouse retinal imaging by direct wavefront measurement has been demonstrated with great success. However, for mouse eyes, the performance of the wavefront sensor (WFS) based AO can be limited by several factors including non-common path errors, wavefront reconstruction errors, and an ill-defined reference plane. Image-based AO can avoid these issues at the cost of algorithmic execution time. Furthermore, image-based approaches can provide improvements to compactness, accessibility, and even the performance of AO systems. Here, we demonstrate the ability of image-based AO to provide comparable aberration correction and image resolution to the conventional Shack-Hartmann WFS-based AO approach. The residual wavefront error of the mouse eye was monitored during a wavefront sensorless optimization to allow comparison with classical AO. This also allowed us to improve the performance of our AO system for small animal retinal imaging.

Postprocessing of all-zirconia restorations in digital dental radiographs: a quality assurance predicament

The aim of this study was to describe a quality assurance issue, that is, the production of nondiagnostic high-contrast radiographs when imaging teeth restored with all-zirconia crowns on bitewing radiographs. All-zirconia crowns were imaged with DIGORA Optime photostimulable phosphor (PSP) plates (Soredex/Orion Corp., Helsinki, Finland). To assess the differences in software processing, the PSP plates were scanned into third-party software as well as directly into the twain and native software provided by the manufacturer. Gamma correction, histogram stretch, and scanner resolution settings were adjusted. Vertical bitewings were acquired to increase anatomic coverage. Scanning into third-party software or directly into the twain and native software did not improve contrast. Shifting the lower limit of the histogram stretch to 3 with a gamma correction of 2 resolved the problem. Neither scanner resolution setting nor vertical bitewings improved contrast. The nondiagnostic high-contrast radiographs result from imaging software not effectively displaying the available gray scale. The software processing error appears to be initiated by the high-attenuation characteristics of zirconia. Consequently, radiographs with a high ratio of zirconia crown to normal anatomy are particularly susceptible.

Investigation of dose reduction in cardiac perfusion SPECT via optimization and choice of the image reconstruction strategy

BackgroundWe investigated the extent to which the administered dose (activity) level can be reduced without sacrificing diagnostic accuracy for three reconstruction strategies for SPECT-myocardial perfusion imaging (MPI). MethodsWe optimized the parameters of the three reconstruction strategies for perfusion-defect detection over a range of simulated administered dose levels using a set of hybrid studies (derived from 190 subjects) consisting of clinical SPECT-MPI data modified to contain realistic simulated lesions. The optimized strategies we considered are filtered backprojection (FBP) with no correction for degradations, ordered-subsets expectation-maximization (OS-EM) with attenuation correction (AC), scatter correction (SC), and resolution correction (RC), and OS-EM with scatter and resolution correction only. Each study was evaluated using a total perfusion deficit (TPD) score computed by the Quantitative Perfusion SPECT (QPS) software package. We conducted a receiver operating characteristics (ROC) study based on the TPD scores for each dose level and reconstruction strategy. ResultsFor FBP, the achieved optimum values of the area under the ROC curve (AUC) at 100%, 50%, 25%, and 12.5% of standard dose were 0.75, 0.74, 0.72, and 0.70, respectively, compared to 0.81, 0.79, 0.76, and 0.74 for OS-EM with AC–SC–RC and 0.78, 0.77, 0.74, 0.72 for OS-EM with SC–RC. ConclusionsOur results suggest that studies reconstructed by OS-EM with AC–SC–RC could possibly be reduced, on average, to 25% of the originally administered dose without causing diagnostic accuracy (AUC) to decrease below that of FBP.

A novel technique for duty cycle correction for reference clocks in frequency synthesizers

Frequency Multipliers to be used with Frequency Synthesizers require duty cycle of nearly 50% and low phase noise contribution to the overall system phase noise for proper operation. In this paper, we first analyze the impact of the imperfect duty cycle clocks on the overall synthesizer system performance, then propose a mixed signal solution based on the fact that the average DC value of a signal is proportional to its duty cycle. The solution uses a feedback loop for coarse and fine duty cycle correction resolution. Proposed duty cycle correction circuit can correct input duty cycle variations from 40% to 60% for a 40MHz input frequency with 50%±0.3% accuracy. Furthermore, in order to estimate the output clock phase noise, a simulation method with supply white noise model is proposed. The circuit is implemented in 65nm UMC CMOS process. Operating from 1.2-V supply, the circuit only dissipates 0.26mA.

Reducing the small-heart effect in pediatric gated myocardial perfusion single-photon emission computed tomography

BackgroundWe compared two reconstruction algorisms and two cardiac functional evaluation software programs in terms of their accuracy for estimating ejection fraction (EF) of small hearts (SH). MethodsThe study group consisted of 66 pediatric patients. Data were reconstructed using a filtered back projection (FBP) method without the resolution correction (RC) and an iterative method based on an ordered subset expectation maximization (OSEM) algorithm with the RC. EF was evaluated using two software programs of quantitative gated single-photon emission computed tomography (SPECT) (QGS) and cardioREPO. We compared the EF of gated myocardial perfusion SPECT to echocardiographic measurement (Echo). ResultsForty-eight of 66 patients had an end-systolic volume < 20 mL which was used as the criterion for being included in the SH group, and the SH effect led to an overestimation of EF. While significant differences were observed between Echo (66.9 ± 5.0%) and QGS-FBP without RC (76.9 ± 8.4%, P < .0001), QGS-OSEM with RC (76.6 ± 8.6%, P < .0001), and cardioREPO-FBP without RC (72.1 ± 10.0%, P = .0011), no significant difference was observed between Echo and cardioREPO-OSEM with RC (67.4 ± 6.1%) in SH group. ConclusionsIn pediatric gated myocardial perfusion SPECT, the SH effect can be significantly reduced when an OSEM algorithm is used with RC in combination with the specific cardioREPO algorithm.

Investigating uncertainty in the simulation of the Antarctic ice sheet during the mid‐Piacenzian

AbstractThe mid‐Piacenzian (~3 Ma) represents the most recent warm period in Earth's history on a geological time scale; it is characterized by a significant rise of global sea level. The simulation of the size and location of the ice sheets and the investigation of the uncertainty in the simulations are potentially helpful for constraining reconstructed sea level changes. In this study, we focus on the behavior of the Antarctic ice sheet (AIS) in the mid‐Piacenzian. We investigate the influence of topography correction, model parameters, climate forcings, and model resolution on the modeled AIS and explore the isolated role of atmospheric and oceanic forcings. Forced by the simulated climate changes with the Norwegian Earth System Model, the Parallel Ice Sheet Model (15 km × 15 km) produces a nearly collapsed West AIS (WAIS) in the mid‐Piacenzian, with no significant retreat of the East AIS (EAIS). The role of increased air temperature plays a key role in the mass loss of the mid‐Piacenzian AIS, while its role is comparable to the role of ocean warming on the melting of the WAIS. In terms of the range of sea level changes, the largest source of uncertainty in the modeled AIS is derived from ice sheet model parameters and climate forcings. Although the employed model parameters, topography correction factors, and model resolution affect the simulated AIS in the mid‐Piacenzian, large‐scale deglaciation of the EAIS in our sensitivity experiments may only be possible with additional warming.