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This study examines the current composition of the energy matrix in Colombia, encompassing its legal framework, configuration, impacts, and future projections. This research, based on a systematic literature review, bibliometric analysis, and text mining, reveals that hydroelectric power is the primary source of clean energy. Fossil fuels, although essential for energy availability in the territory, generate the largest carbon footprint, representing a significant environmental challenge. Despite legal efforts and projections towards clean energy, limitations persist in infrastructure, technology, and social acceptance towards energy production projects. The transition to a sustainable energy system requires overcoming these technical, regulatory, and social barriers while integrating legal, environmental, social, and technological aspects into planning to meet the goals of the current matrix's energy transition, which presents a complex landscape that demands comprehensive strategies for a sustainable energy future. [ABSTRACT FROM AUTHOR]

Ceftolozane-tazobactam (CT) is used for the treatment of complicated infections and for multidrug-resistant strains of Pseudomonas aeruginosa and extended-spectrum beta-lactamase-producing enterobacteria. In certain cases, simultaneous administration of CT and parenteral nutrition (PN) may be required, but compatibility of Y-site co-administration is unknown. The aim of this study was to analyse the physicochemical compatibility of CT Y-site administered with PN. We evaluated a protocolized PN approach for critical patients in our center. We studied both bolus infusion (2 g ceftolozane/1 g tazobactam in 1 h) and continuous infusion (CI) (6 g ceftolozane/3 g tazobactam) strategies. Samples were visually observed against light, microscopically inspected, and pH was analysed using a pH meter. The mean lipid droplet diameter (MDD) was determined via dynamic light scattering. CT concentration was quantified using HPLC–HRMS. No alterations were observed through visual or microscopic inspection. Changes in pH were ≤0.2, and changes in osmolarity were less than 5%. MDD remained below 500 nm (284.5 ± 2.1 for bolus CT and 286.8 ± 7.5 for CI CT). CT concentrations at t = 0 h and t = 24 h remained within prespecified parameters in both infusion strategies. CT is physiochemically compatible with PN during simulated Y-site administration at the tested concentration and infusion rates. [ABSTRACT FROM AUTHOR]

The main objective is to analyse gas flow dynamics in a Convergent-Divergent (CD) nozzle and predict its behaviour under various conditions. The model assumes adiabatic, impermeable walls with bidimensional, compressible, steady, subsonic, and turbulent flow. Conservation equations for mass, energy, and momentum form the basis of the mathematical model, which is solved using Reynolds-Averaged Navier-Stokes turbulent models including Standard k-e, Realizable k-e, Standard k-ω, and Shear-Stress Transport k-ω. Evaluation of these models across different Nozzle Pressure Ratios (NPR) shows that Shear-Stress Transport k-ω correlates best with experimental data on static pressure. Three ANSYS products: DesignModeler, Meshing, and Fluent, are used for numerical simulation. The methodology reliably predicts phenomena such as flow separation, Mach disc formation, and nozzle exit regime, crucial for safe and efficient system operation. [ABSTRACT FROM AUTHOR]

Despite the large number of existing varieties of Vitis vinifera L., only few occupy a large niche in today's highly globalized wine market. The increasing consumer demand for diversified products, as well as the changing climatic conditions, make establishing a process of varietal diversification essential to achieve both challenges. It is for this reason that the study of minority varieties, which have a higher level of adaptation to each area of origin, is of particular interest. With the main objective of achieving an in-depth knowledge of minority varieties in Spain, the national research project 'Valorization of Minority Grapevine Varieties for their Potential for Wine Diversification and Resilience to Climate Change' (MINORVIN), has been proposed. Within this extensive project, the present study describes the aroma profiles of 60 single-variety wines, corresponding with 44 different varieties, with 12 of these varieties being studied at the same time in several Spanish regions. Volatile compounds were determined through three consecutive vintages using gas chromatography-mass spectrometry (GC-MS) and gas chromatography–flame ionization detector (GC-FID). Compounds were grouped into major compounds, including alcohols, C6 compounds, esters, acetates, acids, carbonyl compounds, and other type of compounds, and minor compounds, including lactones, terpenes, and C13-norisoprenoids, according to their concentration in the wines being analyzed. Among this last group of compounds, lactones were quantitatively the most abundant, followed by terpenes. This study reflects that minority variety wines show distinctive aromatic profiles, supporting the importance of valuing and promoting the autochthonous minority grapevine varieties for the Spanish winemaking industry. [ABSTRACT FROM AUTHOR]

White wine pomace, a by-product from winemaking, was stabilized after the application of thermal blanching (with the aim of deactivating the polyphenoloxidase enzyme), milling, and processing by hydrostatic high-pressure treatment (with the aim of reducing initial microbial loads while preserving phenolic compounds content). The valorized pomace (VP) ingredient was added at different proportions to pork burgers (0.5%, 1%, and 3% w/w) to improve their preservation, and the effect was compared to those produced by sulfites and with a control (without sulfites or VP). Burgers were vacuum-packed and refrigerated for 7 days. Microbiological, color, oxidation, and sensory parameters were analyzed. Neither sulfites nor VP reduced the microbial development of most microorganism groups evaluated (p > 0.05); however, both prevented coliform growth during storage (p < 0.01). The use of sulfites prevented the discoloration of burgers during storage, while VP had no effect (p < 0.001). On the contrary, VP limited lipid and protein oxidation development during storage (p > 0.05), while sulfites had no effect. Therefore, the use of VP from white wine production could have an antioxidant effect but a limited antimicrobial or color-protective effect for the preservation of pork burgers. [ABSTRACT FROM AUTHOR]

Background: Prior implementations of the channelized Hotelling observer (CHO) model have succeeded in assessing the performance of X‐ray angiography systems under a variety of imaging conditions. However, often times these conditions do not resemble those present in routine clinical imaging scenarios, such as having complex anthropomorphic backgrounds in conjunction with moving test objects. Purpose: This work builds up on prior established CHO methods and introduces a new approach to switch from the already established "multiple‐sample" CHO implementation to a "single‐sample" technique. The proposed implementation enables the inclusion of moving test objects upon nonuniform backgrounds by allowing only a single sample to represent the test object present condition that is to be used within the statistical test to estimate the detectability index. Methods: To assess the proposed method, two image data sets were acquired with a clinical X‐ray angiography system. The first set consisted of a uniform background in combination with static test objects while the second consisted of an anthropomorphic chest phantom in conjunction with moving test objects. The first set was used to validate the proposed approach against the multiple‐sample method while the second was used to assess the feasibility of the proposed method under a variety of imaging conditions, including seven object sizes and seven detector target dose (DTD) levels. Results: For the uniform background data set, considering all detectability indices greater or equal than 1, the ratio between the detectability indices of the proposed single‐sample approach versus the multiple‐sample method was 0.997 ± 0.056 (range 0.884–1.159). The average single‐direction width of the 95% confidence intervals (CIs) of the detectability index estimates for the multiple‐sample method was 0.38 ± 0.43 (range 0.03–2.20). For the single‐sample approach, the average width was 2.52 ± 0.63 (range 1.11–5.44). For the anthropomorphic background image set, the results were consistent with classical quantum‐limited signal‐to‐noise ratio (SNR) theory. The magnitude of the detectability indices varied predictably with changes in both object size and DTD, with the highest value associated with the highest dose and the largest object size. Additionally, the proposed method was able to capture differences in the imaging performance for a given test object across the field of view, which was associated with the attenuation levels provided by different features of the anthropomorphic background. Conclusions: A new single‐sample variant of the CHO model to assess the performance of X‐ray angiography imaging systems is proposed. The new approach is consistent with quantum‐limited image quality theory and with a standard implementation of the CHO model. The proposed method enables the assessment of moving test objects in combination with complex, nonuniform image backgrounds, thereby opening the possibility to assess imaging conditions which more closely resemble those used in clinical care. [ABSTRACT FROM AUTHOR]

We analyze the choice of the policy platform that a group of heterogeneous challengers will support to confront the current policy in a subsequent contest between them and the status-quo defenders. The choice of this alternative policy will affect not only the incentives of challengers to get involved in the conflict (intra-group effect), but also the mobilization of status-quo defenders (inter-group effect). We disentangle these two effects and show that the degree of polarization (distance between the alternative and the status-quo policy) depends on how the efforts that groups exert in the contest affect their winning probabilities. Our results illustrate how the conflict resolution rules may affect the degree of polarization in political confrontations. [ABSTRACT FROM AUTHOR]

One of the effects of climate change in warm areas is the asynchrony between the dates of the technological and the phenolic maturity of grapes. This is important because the quality and color stability of red wines are directly related to the content and distribution of phenolic compounds. A novel alternative that has been proposed to delay grape ripening and make it coincide with a seasonal period more favorable for the formation of phenolic compounds is crop forcing. This consists of severe green pruning after flowering, when the buds of the following year have already differentiated. In this way, the buds formed during the same season are forced to sprout, initiating a new delayed cycle. The aim of the present work is to study the effect on the phenolic composition and color of wines elaborated from vines fully irrigated (C), grown using conventional non-forcing (NF) and forcing (F) techniques (C-NF and C-F), and wines from vines subjected to regulated irrigation (RI), grown using NF and F techniques (RI-NF and RI-F). The trial was carried out in an experimental vineyard of the Tempranillo variety located in a semi-arid area (Badajoz, Spain) in the 2017-2019 seasons. The wines (four by treatment) were elaborated and stabilized according to the classic methodologies for red wine. All wines had the same alcohol content, and malolactic fermentation was not carried out in any of them. Anthocyanin profiles were analyzed by HPLC, and total polyphenolic content, anthocyanin content, catechin content, the contribution to color due to co-pigmented anthocyanins, and various chromatic parameters were also determined. Although a significant effect of year was found for almost all the parameters analyzed, a general increasing trend in F wines was found for most of them. The anthocyanin profile of F wines was found to differ from that of C wines, especially in delphinidin, cyanidin, petunidin, and peonidin content. These results indicate that by using the forcing technique it was possible to increase the polyphenolic content by ensuring that the synthesis and accumulation of these substances occurred at more suitable temperatures. [ABSTRACT FROM AUTHOR]

Non-anthocyanin compounds (NAN) such as flavonol, flavanol, and phenolic acids should be considered in the characterization of minority red grapevine varieties because these compounds are involved in copigmentation reactions and are potent antioxidants. Sixteen NAN were extracted, identified, and quantified by High Performance Liquid Chromatography (HPLC) from grapes of 28 red genotypes of Vitis vinifera L. grown in Galicia (Northwest of Spain) in 2018 and 2019 vintages. The percentage of total NAN with respect to the total polyphenol content (TPC) values was calculated for each sample and established into three categories: high percentage NAN varieties (NANV), those varieties showing low percentages of NAN (ANV), and finally those varieties showing medium percentages of NAN (NANAV). 'Xafardán' and 'Zamarrica', classified as NANAV, had high values of TPC and showed good percentages of flavonol and flavanol compounds. Principal component analyses (PCA) were performed with flavonol, flavanol, and phenolic acid profiles. The flavonol and flavanol profiles allowed a good discrimination of samples by variety and year, respectively. The flavonol profile should therefore be considered as a potential varietal marker. The results could help in the selection of varieties to be disseminated and in the identification of the most appropriate agronomic and oenological techniques that should be performed on them. [ABSTRACT FROM AUTHOR]

In lobbying competition to influence a policy ranging over a continuum, lottery and share contests can be regarded as two alternative conflict resolution protocols. In the lottery contest, the policy is selected probabilistically whereas in the share contest the policy choice is deterministic. Although these two contest settings are equivalent for risk‐neutral lobbyists, this equivalence fails to hold when they are risk‐averse. We demonstrate that when lobbyists have concave preferences over policies and select their policy proposals, they strategically moderate their claims only under the (probabilistic) lottery setting. This action defuses the conflict and reduces the exerted effort. Consequently, risk‐averse contestants might unanimously prefer the lottery to the share contest. [ABSTRACT FROM AUTHOR]

Copyright of Estudios Pedagogicos (Valdivia) is the property of Estudios Pedagogicos and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jet.2006.12.001 Byline: Daniel Cardona (a), Clara Ponsati (b) Abstract: We analyze bargaining over the one-dimension characteristic of a public good among n impatient players when decisions require q favorable votes, q[greater than or equal to]2. Stationary subgame perfect equilibrium strategies are characterized for all games with deterministic protocol. We provide a monotonicity condition (satisfied by all single-peak, strictly quasi-concave and concave utilities) that assures uniqueness for every q whenever player's utilities are symmetric around the peak. Without symmetry, the monotonicity condition assures uniqueness for qualified majorities, qn/2, provided that agents are sufficiently patient and utilities satisfy an additional regularity condition. Asymptotic uniqueness is assured for qualified majorities by imposing only the monotonicity condition. Author Affiliation: (a) Dept. Economia Aplicada, Universitat de les Illes Balears,Ctra. Valldemossa km. 7.5, 07071 Palma de Mallorca, Spain (b) Institut d'Analisi EconA[sup.2]mica - C.S.I.C., Barcelona Article History: Received 8 July 2003; Revised 1 December 2006

Purpose: Channelized Hotelling observer (CHO) models have been implemented to assess imaging performance in x‐ray angiography systems. While current methods are appropriate for assessing unprocessed images of moving test objects upon uniform‐exposure backgrounds, they are inadequate for assessing conditions which more appropriately mimic clinical imaging conditions including the combination of moving test objects, complex anthropomorphic backgrounds, and image processing. In support of this broad goal, the purpose of this work was to develop theory and methods to automatically select a subset of task‐specific efficient Gabor channels from a task‐generic Gabor channel base set. Also, previously described theory and methods to manage detectability index (d′) bias due to nonrandom temporal variations in image electronic noise will be revisited herein. Methods: Starting with a base set of 96 Gabor channels, backward elimination of channels was used to automatically identify an "efficient" channel subset which reduced the number of channels retained in the subset while maintaining the magnitude of the d′ estimate. The concept of a pixelwise Hotelling observer (PHO) model was introduced and similarly implemented to assess the performance of the efficient‐channel CHO model. Bias in d′ estimates arising from temporally variable nonstationary noise was modeled as a bivariate probability density function for normal distributions, where one variable corresponds to the signal from the test object and the other variable corresponds to the signal from temporally variable nonstationary noise. Theory and methods were tested on uniform‐exposure unprocessed angiography images with detector target dose (DTD) of 6, 18, and 120 nGy containing static disk‐shaped test objects with diameter in the range of 0.5 to 4 mm. Results: Considering all DTD levels and test object sizes, the proposed method reduced the number of Gabor channels in the final subset by 63–82% compared to the original 96 Gabor channel base set, while maintaining a mean relative performance ((dCHO′/dPHO′)×100%) of 95% ± 4% with respect to the reference PHO model. Experimental results demonstrated that the bivariate approach to account for bias due to temporally variable nonstationary noise resulted in improved correlation between the CHO and PHO models as compared to a previously proposed univariate approach. Conclusions: Computationally efficient backward elimination can be used to select an efficient subset of Gabor channels from an initial channel base set without substantially compromising the magnitude of the d′ estimate. Bias due to temporally variable nonstationary noise can be modeled through a bivariate approach leading to an improved unbiased estimate of d′. [ABSTRACT FROM AUTHOR]

Copyright of Revista Facultad de Ciencias Economicas: Investigacion y Reflexion is the property of Revista Facultad de Ciencias Economicas and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study analyzes the welfare implications of requiring either unanimity or a simple majority in negotiations to distribute a budget among three agents who could previously invest to generate positive consumption externalities for others. This complements Cardona and Rubí-Barceló (2014), who consider only the unanimity case. We show that reducing the majority requirement reduces the profitability of investments, and consequently alleviates overinvestment, which is predominant under unanimous bargaining. Nevertheless, requiring a simple majority reduces the aggregate surplus attained in the bargaining stage. Therefore, the relative performance of the bargaining rules is uncertain. We show how the size of consumption externalities affects this performance. [ABSTRACT FROM AUTHOR]

This study analyzes the welfare implications of requiring either unanimity or a simple majority in negotiations to distribute a budget among three agents who could previously invest to generate positive consumption externalities for others. This complements Cardona and Rubí-Barceló (2014), who consider only the unanimity case. We show that reducing the majority requirement reduces the profitability of investments, and consequently alleviates overinvestment, which is predominant under unanimous bargaining. Nevertheless, requiring a simple majority reduces the aggregate surplus attained in the bargaining stage. Therefore, the relative performance of the bargaining rules is uncertain. We show how the size of consumption externalities affects this performance. [ABSTRACT FROM AUTHOR]

Purpose: In previous works, it has been demonstrated that for filtered backprojection (FBP) reconstruction‐based computed tomography (CT) images, the measured CT numbers are biased and the bias level decreases with increasing radiation dose. Low‐dose scans typically include noise reduction schemes to reduce noise level. The purpose of this work was to investigate the potential impact of different noise reduction schemes on the CT number bias. Methods: Three different filtration methods: Gaussian, adaptive trimmed mean (ATM), and anisotropic diffusion (AD) were implemented to reduce noise. All filters were independently applied in three different domains: raw counts, log‐processed sinogram, or reconstructed image domain. A quality assurance phantom was scanned on a benchtop CT cone beam CT system, at dose levels ranging from 0.6 to 4.0 mGy. The conventional FBP reconstructions were performed to reconstruct CT images for the study of CT number biases. The CT number bias of different material inserts in the phantom was then measured. To further study the overall impact of CT number bias together with the potential consequences of noise reduction schemes on both the spatial resolution and noise characteristics, the task‐based detectability of a high‐contrast and high spatial resolution imaging task was used as an example to assess the performance of each noise reduction scheme. To qualitatively assess the impact of these noise reduction schemes on image, an anthropomorphic head phantom was also scanned on the benchtop CT system and processed with the above noise reduction schemes to generate images for demonstration. Results: Our results demonstrated the following major findings: (a) CT number bias can be significantly reduced when the noise reduction schemes are implemented in the raw counts domain; CT number bias cannot be reduced when these noise reduction schemes are implemented either in the reconstructed image domain or in the log‐processed sinogram domain. (b) The extent of CT number bias reduction is dependent on both the material composition and noise reduction parameters. (c) The overall impact of the noise reduction schemes can be studied using the task‐based detectability analysis framework and this framework can be used to select the appropriate parameters in each noise reduction scheme to optimize the performance for a given imaging task. Conclusions: Noise reduction schemes can be used to considerably reduce CT number bias when they are implemented in the raw counts domain; however, their application cannot be arbitrarily extended to either the log‐processed sinogram data domain or image domain. Trade‐offs between bias reduction and overall image quality must be studied for an optimal performance of a given imaging task. [ABSTRACT FROM AUTHOR]

Several techniques have been proposed for the management of perforation of or severe damage to the temporomandibular joint disc, with a wide range of success rates reported. We describe a new method using a pedicled sliding flap of the tragal cartilage. [ABSTRACT FROM AUTHOR]

Background: Y-site administration of total parenteral nutrition (TPN) and drugs is frequently required in the intensive care setting. Amiodarone is commonly administered by continuous intravenous infusion and subject to be co-administered via a Y-site with TPN. The aim of this study is to determine the physicochemical stability of amiodarone Y-site administered with TPN.Methods: Two standard TPN and 2 amiodarone solutions were designed. The 2 TPN differed in the lipid source (Lipofundin MCT/LCT® 20% or SMOFlipid® 20%). The 2 amiodarone solutions were prepared at different concentrations (900 mg and 1200 mg in 250 mL of dextrose 5% in water). Each TPN and amiodarone solutions ran at a rate that simulated a 24-hour Y-site infusion to obtain different admixture samples. Each sample was then visually examined and further tested to determine the mean lipid droplet size distribution by dynamic light scattering and amiodarone concentrations by HPLC.Results: No alterations were detected by visual inspection. Average droplet size remained below 500 nm (252.5 ± 5.9 nm for Lipofundin MCT/LCT® TPN and 327.7 ± 14.4 nm for SMOFlipid® TPN). For the samples obtained after running 900 mg and 1200 mg amiodarone solutions with TPN, the concentrations observed at 24 hours were 0.4491 ± 0.0111 mg/mL and 0.5773 ± 0.0214 mg/mL, respectively. These results represent approximately 100% of the zero-time concentrations and are within ±15% of the predicted values. No degradation products were observed in the chromatograms.Conclusion: Amiodarone is physicochemically compatible with standard TPN via a Y-site administration at the tested amiodarone concentrations. [ABSTRACT FROM AUTHOR]

Purpose: The CT number accuracy, that is, CT number bias, plays an important role in clinical diagnosis. When strategies to reduce radiation dose are discussed, it is important to make sure that the CT number bias is controlled within an acceptable range. The purpose of this paper was to investigate the dependence of CT number bias on radiation dose level and on image contrast (i.e., the difference in CT number between the ROI and the background) in Computed Tomography (CT). Methods: A lesion‐background model was introduced to theoretically study how the CT number bias changes with radiation exposure level and with CT number contrast when a simple linear reconstruction algorithm such as filtered backprojection (FBP) is used. The theoretical results were validated with experimental studies using a benchtop CT system equipped with a photon‐counting detector (XC‐HYDRA FX50, XCounter AB, Sweden) and a clinical diagnostic MDCT scanner (Discovery CT750 HD, GE Healthcare, Waukesha, WI, USA) equipped with an energy‐integrating detector. The Catphan phantom (Catphan 600, the Phantom Laboratory, Salem, NY, USA) was scanned at different mAs levels and 50 scans were performed for each mAs. The bias of CT number was evaluated for each combination of mAs and ROIs with different contrast levels. An anthropomorphic phantom (ATOM 10‐year‐old phantom, Model 706, CIRS Inc. Norfolk, VA, USA) with much more heterogeneous object content was used to test the applicability of the theory to the more general image object cases. Results: Both theoretical and experimental studies showed that the CT number bias is inversely proportional to the radiation exposure level yet linearly dependent on the CT number contrast between the lesion and the background, that is, Bias(μ^1FBP)=αmAs(1+βΔHU). Conclusions: The quantitative accuracy of CT numbers can be problematic and thus needs some extra attention when radiation dose is reduced. In this work, we showed that the bias of the FBP reconstruction increases as mAs is reduced; both positive and negative bias can be observed depending on the contrast difference between a targeted ROI and its surrounding background tissues. [ABSTRACT FROM AUTHOR]

Purpose: Low‐signal correction (LSC) in the raw counts domain has been shown to effectively reduce noise streaks in CT because the data inconsistency associated with photon‐starved regions may be mitigated prior to the log transformation step. However, a systematic study of the performance of these raw data correction methods is still missing in literature. The purpose of this work was to provide such a systematic study for two well‐known low‐signal correction schemes using either the adaptive trimmed mean (ATM) filter or the anisotropic diffusion (AD) filter in the raw counts domain. Methods: Image data were acquired experimentally using an anthropomorphic chest phantom and a benchtop cone‐beam CT (CBCT) imaging system. Phantom scans were repeated 50 times at a reduced dose level of 0.5 mGy and a reference level of 1.9 mGy. The measured raw counts at 0.5 mGy underwent LSC using the ATM and AD filters. Two relevant parameters were identified for each filter and approximately one hundred operating points in each parameter space were analyzed. Following LSC and log transformation, FDK reconstruction was performed for each case. Noise and spatial resolution properties were assessed across the parameter spaces that define each LSC filter; the results were summarized through 2D contour maps to better understand the trade‐offs between these competing image quality features. 2D noise power spectrum (NPS) and modulation transfer function (MTF) were measured locally at two spatial locations in the field‐of‐view (FOV): a posterior region contaminated by noise streaks and an anterior region away from noise streaks. An isotropy score metric was introduced to characterize the directional dependence of the NPS and MTF (viz., ϵNPS and ϵMTF, respectively), with a range from 0 for highly anisotropic to 1 for perfectly isotropic. The noise magnitude and coarseness were also measured. Results: (a) Both the ATM and AD LSC methods were successful in reducing noise streaks, but their noise and spatial resolution properties were found to be highly anisotropic and shift‐variant. (b) NPS isotropy scores in the posterior region were generally improved from ϵNPS = 0.09 for the images without LSC to the range ϵNPS = (0.11, 0.67) for ATM and ϵNPS = (0.06, 0.67) for AD, depending on the filter parameters used. (c) The noise magnitude was reduced across the parameter space of either LSC filter whenever a change along the axis of the controlling parameter led to stronger raw data filtration. Changes in noise magnitude were inversely related to changes in spatial resolution along the direction perpendicular to the streaks. No correlation was found, however, between the contour maps of noise magnitude and the NPS isotropy. (d) Both filters influenced the noise coarseness anisotropically, with coarser noise occurring along directions perpendicular to the noise streaks. The anisotropic noise coarseness was intrinsically and directly related to resolution losses in a given direction: coarseness plots mimic the topography of the 2D MTF, i.e., the coarser the noise, the lower the resolution. Conclusions: Both AD and ATM LSC schemes enable low‐dose CBCT imaging. However, it was found that noise magnitude and overall spatial resolution vary considerably across the parameter space for each filter, and more importantly these image quality features are highly anisotropic and shift‐variant. [ABSTRACT FROM AUTHOR]

Purpose: Different low‐signal correction (LSC) methods have been shown to efficiently reduce noise streaks and noise level in CT to provide acceptable images at low‐radiation dose levels. These methods usually result in CT images with highly shift‐variant and anisotropic spatial resolution and noise, which makes the parameter optimization process highly nontrivial. The purpose of this work was to develop a local task‐based parameter optimization framework for LSC methods. Methods: Two well‐known LSC methods, the adaptive trimmed mean (ATM) filter and the anisotropic diffusion (AD) filter, were used as examples to demonstrate how to use the task‐based framework to optimize filter parameter selection. Two parameters, denoted by the set P, for each LSC method were included in the optimization problem. For the ATM filter, these parameters are the low‐ and high‐signal threshold levels pl and ph; for the AD filter, the parameters are the exponents δ and γ in the brightness gradient function. The detectability index d′ under the non‐prewhitening (NPW) mathematical observer model was selected as the metric for parameter optimization. The optimization problem was formulated as an unconstrained optimization problem that consisted of maximizing an objective function d ′ ( P ), where i and j correspond to the i‐th imaging task and j‐th spatial location, respectively. Since there is no explicit mathematical function to describe the dependence of d′ on the set of parameters P for each LSC method, the optimization problem was solved via an experimentally measured d′ map over a densely sampled parameter space. In this work, three high‐contrast–high‐frequency discrimination imaging tasks were defined to explore the parameter space of each of the LSC methods: a vertical bar pattern (task I), a horizontal bar pattern (task II), and a multidirectional feature (task III). Two spatial locations were considered for the analysis, a posterior region‐of‐interest (ROI) located within the noise streaks region and an anterior ROI, located further from the noise streaks region. Optimal results derived from the task‐based detectability index metric were compared to other operating points in the parameter space with different noise and spatial resolution trade‐offs. Results: The optimal operating points determined through the d′ metric depended on the interplay between the major spatial frequency components of each imaging task and the highly shift‐variant and anisotropic noise and spatial resolution properties associated with each operating point in the LSC parameter space. This interplay influenced imaging performance the most when the major spatial frequency component of a given imaging task coincided with the direction of spatial resolution loss or with the dominant noise spatial frequency component; this was the case of imaging task II. The performance of imaging tasks I and III was influenced by this interplay in a smaller scale than imaging task II, since the major frequency component of task I was perpendicular to imaging task II, and because imaging task III did not have strong directional dependence. For both LSC methods, there was a strong dependence of the overall d′ magnitude and shape of the contours on the spatial location within the phantom, particularly for imaging tasks II and III. The d′ value obtained at the optimal operating point for each spatial location and imaging task was similar when comparing the LSC methods studied in this work. Conclusions: A local task‐based detectability framework to optimize the selection of parameters for LSC methods was developed. The framework takes into account the potential shift‐variant and anisotropic spatial resolution and noise properties to maximize the imaging performance of the CT system. Optimal parameters for a given LSC method depend strongly on the spatial location within the image object. [ABSTRACT FROM AUTHOR]