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Variability and repeatability of quantitative uptake metrics in [ <sup>18</sup> F]FDG PET/CT imaging of non-small cell lung cancer: impact of segmentation method, uptake interval, and reconstruction protocol
摘要： OBJECTIVES: There is increased interest in various new quantitative uptake metrics beyond standardized uptake value (SUV) in oncology PET/CT studies. The purpose of this study is to investigate the variability and test-retest repeatability (TRT) of metabolically active tumor volume (MATV) measurements and several other new quantitative metrics in non-small cell lung cancer (NSCLC) using [18F]FDG PET/CT with different segmentation methods, user interactions, uptake intervals, and reconstruction protocols. METHODS: Ten advanced NSCLC patients received two whole-body [18F]FDG PET/CT scans at both 60 and 90 min post-injection. PET data were reconstructed with four different protocols. Eight segmentation methods were applied to delineate lesions with and without a tumor mask. MATV, maximum and mean SUV (SUVmax, SUVmean), total lesion glycolysis (TLG), and intralesional heterogeneity features were derived. Variability and repeatability were evaluated using a generalized estimating equations statistical model with Bonferroni correction for multiple comparisons. The statistical model, including interaction between uptake interval and reconstruction protocol, was applied individually to the data obtained from each segmentation method. RESULTS: Without masking, none of the segmentation methods could delineate all lesions correctly. MATV was affected by both uptake interval and reconstruction settings for most segmentation methods. Similar observations were obtained for the uptake metrics SUVmax, SUVmean, TLG, homogeneity, entropy, and zone percentage. No effect of uptake interval was observed on TRT metrics, while the reconstruction protocol affected the TRT of SUVmax. Overall, segmentation methods showing poor quantitative performance in one condition showed better performance in other (combined) conditions. For some metrics, a clear statistical interaction was found between the segmentation method and both uptake interval and reconstruction protocol. CONCLUSIONS: All segmentation results need to be reviewed critically. MATV and other quantitative uptake metrics, as well as their TRT, depend on segmentation method, uptake interval, and reconstruction protocol. To obtain quantitative reliable metrics, with good TRT performance, the optimal segmentation method depends on local imaging procedure, the PET/CT system and/or reconstruction protocol. Rigid harmonization of imaging procedure and PET/CT performance will be helpful in mitigating this variability.
关键词： non-small cell lung cancer,segmentation method,positron emission tomography imaging,repeatability,Variability
更新于2025-09-23 15:21:01
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Effect of substrate coupling on the performance and variability of monolayer MoS2 transistors
摘要： We study the effect of substrate coupling on the variability and the device characteristics of monolayer MoS2 field-effect transistors (FETs). In our experiments, we fabricate and characterize three groups of back-gated FETs on SiO2/Si substrates, where each device set represents a distinct interfacial energy between MoS2 and SiO2. We also study a set of devices constructed on hexagonal boron nitride (h-BN) substrates, representing a fourth group where MoS2 is fully decoupled from SiO2. Our electrical measurement results reveal significant improvements of key FET device metrics (contact resistance, mobility, and subthreshold swing) and marked reduction of device variability with reducing the interfacial energy. We attribute the observed improvements of the device characteristics to the reduction of the interface trap density and the suppression of the charged impurity scattering. This study establishes the critical role of substrate coupling on the performance and variability of monolayer MoS2 FETs.
关键词： interfacial energy,variability,FET,MoS2
更新于2025-09-23 15:21:01
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Regionalization and Dynamic Parameterization of Quantum Yield of Photosynthesis to Improve the Ocean Primary Production Estimates From Remote Sensing
摘要： Quantum yield of photosynthesis (φ) expresses the efficiency of phytoplankton carbon fixation given certain amount of absorbed light. This photophysiological parameter is key to obtaining reliable estimates of primary production (PPsat) in the ocean based on remote sensing information. Several works have shown that φ changes temporally, vertically, and horizontally in the ocean. One of the primary factors ruling its variability is light intensity and thereby, it can be modeled as a function of Photosynthetically Available Radiation (PAR). We estimated φ utilizing long time-series collected in the North Subtropical Oligotrophic Gyres, at HOT and BATS stations (Pacific and Atlantic oceans, respectively). Subsequently the maximum quantum yield (φm) and Kφ (PAR value at half φm) were calculated. Median φm values were ～0.040 and 0.063 mol C mol photons?1 at HOT and BATS, respectively, with higher values in winter. Kφ values were ～8.0 and 10.8 mol photons m?2 d?1 for HOT and BATS, respectively. Seasonal variability in Kφ showed its peak in summer. Dynamical parameterizations for both regions are indicated by their temporal behaviors, where φm is related to temperature at BATS while Kφ to PAR, in both stations. At HOT, φm was weakly related to temperature and its median annual value was used for the whole data series. Differences in the study areas, even though both belong to Subtropical Gyres, reinforced the demand for regional parameterizations in PPsat models. Such parameterizations were finally included in a PPsat model based on phytoplankton absorption (PPsat?aphy?based), where results showed that the PPsat?aphy?based model coupled with dynamical parameterization improved PPsat estimates. Compared with PPsat estimates from the widely used VGPM, a model based on chlorophyll concentration (PPsat?chl?based), PPsat?aphy?based reduced model-measurement differences from ～62.8 to ～8.3% at HOT, along with well-matched seasonal cycle of PP (R2 = 0.76). There is not significant reduction in model-measurement differences between PPsat?chl?based and PPsat?aphy?based PP at BATS though (37.8 vs. 36.4%), but much better agreement in seasonal cycles with PPsat?aphy?based (R2 increased from 0.34 to 0.71). Our results point to improved estimation of PPsat by parameterized quantum yield along with phytoplankton absorption coefficient at the core.
关键词： quantum yield of photosynthesis,ocean color,phytoplankton primary production,in situ measurements,dynamical parameterization,marine seasonal variability
更新于2025-09-23 15:21:01
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Understanding Tree-to-Tree Variations in Stone Pine (Pinus pinea L.) Cone Production Using Terrestrial Laser Scanner
摘要： Kernels found in stone pinecones are of great economic value, often surpassing timber income for most forest owners. Visually evaluating cone production on standing trees is challenging since the cones are located in the sun-exposed part of the crown, and covered by two vegetative shoots. Very few studies were carried out in evaluating how new remote sensing technologies such as terrestrial laser scanners (TLS) can be used in assessing cone production, or in trying to explain the tree-to-tree variability within a given stand. Using data from 129 trees in 26 plots located in the Spanish Northern Plateau, the gain observed by using TLS data when compared to traditional inventory data in predicting the presence, the number, and the average weight of the cones in an individual tree was evaluated. The models using TLS-derived metrics consistently showed better fit statistics, when compared to models using traditional inventory data pertaining to site and tree levels. Crown dimensions such as projected crown area and crown volume, crown density, and crown asymmetry were the key TLS-derived drivers in understanding the variability in inter-tree cone production. These results underline the importance of crown characteristics in assessing cone production in stone pine. Moreover, as cone production (number of cones and average weight) is higher in crowns with lower density, the use of crown pruning, abandoned over 30 years ago, might be the key to increasing production in combination with stand density management.
关键词： modeling,terrestrial laser scanner,inter-tree variability,stone pinecone production,crown characteristics
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Approach to the evaluation of the functional state of the human body taking into account the variability of medical and biological indicators
摘要： The approach to the evaluation of the functional state of the human body as a system with a set of interrelated functional subsystems of the homeostatic type is proposed. The approach is considered on the basis of an assessment of the state of the respiratory subsystem, which can be described by a complex of statistically stable medical and biological indicators. Indicators obtained during monitoring of the state of polar explorers of the XXI Antarctic expedition at the station "Academician Vernadsky" in difficult conditions that can be attributed to the extreme. It was established that when forming the rules for making decisions on the suitability of winterers for further staying in the conditions of the action of extreme factors it is necessary to consider not only the values of the indicators of the state of the subsystems of the organism, but also their accuracy parameters. The analysis of the uncertainty of the obtained indicators by the proposed information model is carried out. It is shown that in this case it is necessary to take into account the features of a biological object, which has an individual and group variation.
关键词： uncertainty,system of organism,decision making,integral index,variability,biological object,homeostasis,functional state
更新于2025-09-23 15:19:57
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Optimal fiducial points for pulse rate variability analysis from forehead and finger PPG signals
摘要： Objective: The aim of this work is to evaluate and compare five fiducial points for the temporal location of each pulse wave from forehead and finger photoplethysmographic pulse waves signals (PPG) to perform pulse rate variability (PRV) analysis as a surrogate of heart rate variability (HRV) analysis. Approach: Forehead and finger PPG signals were recorded during tilt-table test simultaneously to the ECG. Artifacts were detected and removed and, five fiducial points were computed: apex, middle-amplitude and foot points of the PPG signal, apex point of the first derivative signal and, the intersection point of the tangent to the PPG waveform at the apex of the derivative PPG signal and the tangent to the foot of the PPG pulse defined as intersecting tangents method. Pulse period (PP) time intervals series were obtained from both PPG signals and compared to the RR intervals obtained from the ECG. Heart and pulse rate variability signals (HRV and PRV) were estimated and, classical time and frequency domain indices were computed. Main Results: The middle-amplitude point of the PPG signal (nM ), the apex point of the first derivative (n? A), and the tangents intersection point (nT ) are the most suitable fiducial points for PRV analysis, which result in the lowest relative errors estimated between PRV and HRV indices, higher correlation coefficients and reliability indexes. Statistically significant differences according to the Wilcoxon test between PRV and HRV signals were found for the apex and foot fiducial points of the PPG, as well as the lowest agreement between RR and PP series according to Bland-Altman analysis. Hence, they have been considered less accurate for variability analysis. In addition, the relative errors are significantly lower for nM and n? A features by using Friedman statistics with Bonferroni multiple-comparison test and, we propose nM as the most accurate fiducial point. Based on our results, forehead PPG seems to provide more reliable information for a PRV assessment than finger PPG. Significance: The accuracy of the pulse wave detections depends on the morphology of the PPG. There is therefore a need to widely define the most accurate fiducial point to perform a PRV analysis under non-stationary conditions based on different PPG sensor locations and signal acquisition techniques.
关键词： Fiducial point selection,Transmission and Reflection modes,Pulse rate variability,PPG,ECG,Heart rate variability,Autonomic nervous system,Photoplethysmography
更新于2025-09-19 17:15:36
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Test-retest variability of multifocal electroretinography in normal volunteers and short-term variability in hydroxychloroquine users
摘要： Purpose: To determine measurement variability of N1P1 amplitudes and the R1/R2 ratio in normal subjects and hydroxychloroquine users without retinopathy. Design: Retrospective, observational study. Subjects: Normal subjects (n=21) and 44 patients taking hydroxychloroquine (n=44) without retinopathy. Methods: Multifocal electroretinography (mfERG) was performed twice in one session in the 21 normal subjects and twice within 1 year in the hydroxychloroquine users, during which time no clinical change in macular status occurred. Main outcome measures: N1P1 amplitudes of rings R1–R5, the R1/R2 ratio, and coefficients of repeatability (COR) for these measurements. Results: Values for N1P1 amplitudes in hydroxychloroquine users were reduced compared with normal subjects by the known effect of age, but R1/R2 was not affected by age. The COR for R1–R5 ranged from 43% to 52% for normal subjects and from 43% to 59% for hydroxychloroquine users; for R1/R2 the COR was 29% in normal subjects and 45% in hydroxychloroquine users. Conclusion: mfERG measurements show high test-retest variability, limiting the ability of a single mfERG test to influence a decision to stop hydroxychloroquine; corroborative evidence with a different ancillary test is recommended in a suspicious case.
关键词： test-retest variability,hydroxychloroquine,multifocal electroretinography
更新于2025-09-19 17:15:36
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Dual-Energy CT Material Density Iodine Quantification for Distinguishing Vascular From Nonvascular Renal Lesions: Normalization Reduces Intermanufacturer Threshold Variability
摘要： OBJECTIVE. The purpose of this study was to determine whether a single, uniform normalized iodine threshold reduces variability and enables reliable differentiation between vascular and nonvascular renal lesions independent of the dual-energy CT (DECT) platform used. MATERIALS AND METHODS. In this retrospective, HIPAA-compliant, institutional review board–approved study, 247 patients (156 men, 91 women; mean age ± SD, 67 ± 12 years old) with 263 renal lesions (193 nonvascular, 70 vascular) underwent unenhanced single-energy and contrast-enhanced DECT scans. One hundred and six nonvascular and 38 vascular lesions were scanned on two dual-source DECT (dsDECT) scanners, and 87 nonvascular and 32 vascular lesions were scanned on two rapid-kilovoltage-switching single-source DECT (rsDECT) scanners. Optimal absolute and normalized (to aorta) lesion iodine thresholds were determined for each platform type and for the entire cohort combined. RESULTS. Mean optimal absolute discriminant thresholds were 1.3 mg I/mL (95% CI, 1.2–1.9 mg I/mL), 1.6 mg I/mL (95% CI, 0.9–1.5 mg I/mL), and 1.5 mg I/mL (95% CI, 1.4–1.7 mg I/mL) for dsDECT, rsDECT, and combined cohorts, respectively. Optimal normalized discriminant thresholds were 0.3 mg I/mL (95% CI, 0.2–0.4 mg I/mL) for both the dsDECT and rsDECT cohorts, and 0.3 mg I/mL (0.3–0.4 mg I/mL) for the combined cohort. The AUC, sensitivity, and specificity for the combined optimal normalized discriminant threshold of 0.3 mg I/mL was 0.96 (95% CI, 0.92–1.00), 0.93 (0.84–0.97), and 0.95 (0.91–0.98), respectively. Normalization resulted in decreased variability and better lesion separation (effect size, 1.77 vs 1.69, p < 0.0001). CONCLUSION. The optimal absolute discriminant threshold for evaluating renal lesions varies depending on the type of DECT platform, though this difference is not statistically significant. Variation can be reduced with a better separation of vascular and nonvascular lesions by normalizing iodine quantification to the aorta.
关键词： renal lesions,dual-energy CT,rapid-kilovoltage switching,iodine,dual source,variability
更新于2025-09-19 17:15:36
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Electron-Conductive, Hole-Blocking Contact for Silicon Solar Cells
摘要： This paper presents a simple mathematical expression to model the effect of statistical dopant fluctuations on threshold voltage (Vth) of junction field-effect transistors (JFETs). The random discrete doping (RDD) in the active device area is used to derive an analytical model to compute the standard deviation, σ Vth,RDD of the Vth-distribution for any arbitrary channel doping profiles. The model shows that the Vth-variability in JFETs depends on the active device area, channel doping concentration, and the depth of the channel depletion region of the gate/channel pn-junction. The model is applied to compute σ Vth,RDD for symmetric and asymmetric source/drain double-gate n-channel JFETs. The simulation results show that the model can be used for predicting Vth-variability in JFETs.
关键词： modeling threshold voltage variability,random discrete doping,process variability in JFETs,statistical dopant fluctuations,JFET threshold voltage variability,Junction field-effect transistor (JFET)
更新于2025-09-19 17:13:59
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High‐frequency standard deviation of the capacity factor of renewable energy facilities – part 1: solar photovoltaic
摘要： It is important to secure for every solar photovoltaic energy installation the highest-possible average (mean) capacity factor, as well as the lowest-possible standard-deviation, this latter computed with high frequency. High-frequency data of solar photovoltaic energy facilities are, however, very hard to be found. There are no estimations in the literature of the standard deviation of the capacity factor of solar photovoltaic energy installations sampled with high frequency. Here we show the data sampled every 5 minutes for the solar photovoltaic energy facilities connected to the Australian National Electricity Market grid during the year 2018. The average capacity factors are about 27-28% flat panel, and 31-32% tracking flat panel. The standard deviations have larger values at about 37-38%, for coefficients of variation 120-130%. As solar photovoltaic energy facilities only produce electricity during the daylight time, that is predictable, the statistic analysis is also applied to the daylight times only. While average daylight-only capacity factors are about twice the previous values, standard deviations are slightly less, for coefficients of variations more than halved at 55-65%. The analysis highlights the extreme variability of solar energy helping the design of the energy storage needed for making possible an efficient, resilient, renewable energy-only grid. The collected and interpreted information and the provided analysis are filing a gap in the area of renewable energy and energy harvesting technology based on wind and solar photovoltaics where variability has been so far underevaluated.
关键词： Solar Energy,Variability Analysis,Australia,Energy Storage,Variability Measures,Renewable Energy
更新于2025-09-19 17:13:59