Effect Of Different Thresholds Research Articles

Diagnostic performance of contrast enhancement to differentiate benign and malignant renal lesions in CT and MRI: a systematic review and meta-analysis of diagnostic test accuracy (DTA) studies.

To perform a systematic review and meta-analysis of the diagnostic performance of contrast enhancement to differentiate benign and malignant renal lesions using CT and MRI. A systematic literature search of databases was performed between January 1, 1980 and September 26, 2022. We included studies reporting the accuracy of CE thresholds on CT and MRI indeterminate renal lesions, with pathologic examination and follow-up as the reference standard. Studies meeting the inclusion criteria underwent quality assessment with the Cochrane recommendation for diagnostic accuracy study Quality Assessment 2. We excluded studies with high risk of bias. Summary estimates of diagnostic performance were obtained with the bivariate Bayesian model for CT and MRI. Effects of different thresholds and index test modalities were investigated through subgroup analysis. Eleven studies (1372 patients) using CT and six studies (218 patients) using MRI were included. Of the eleven studies, 15 parts from 9 studies were considered for the CT meta-analysis, and 6 parts from 3 studies for the MRI meta-analysis. Diagnostic performance meta-analysis on enhancement found a 96% summary sensitivity (95% CI 92, 98) and a 92% summary specificity (95% CI 85, 96) in 2056 renal lesions for CT; and 82% summary sensitivity (95% CI 65, 89) and an 89% summary specificity (95% CI 77, 95) in 634 lesions for MRI. CT and MRI have high accuracy to determine enhancement and classify renal lesions, and both modalities can be used with confidence for this purpose. There are still some controversies about the optimal thresholds. Future research should evaluate outcomes and decision-making pathways to determine whether basing clinical decisions on a specific threshold on CT and MRI would do more harm than good.

Expressed emotion and early treatment response in family-based treatment for adolescent anorexia nervosa

ABSTRACT This study examined the effect of pre-treatment levels of parental expressed emotion (EE) on early treatment response for adolescent anorexia nervosa (AN). Data were collected from 121 adolescents, ages 12–18, who met DSM-IV criteria for AN excluding the amenorrhea criterion, and their parents. Participants were randomized to family-based treatment (FBT) or adolescent-focused therapy (AFT). To examine the effects of different thresholds of EE, we used two different levels of EE in analyses. Results demonstrated that adolescents who had at least one parent with elevated EE indicated by a lower threshold (i.e. even mild levels) at baseline were less likely to achieve an early treatment response, suggesting that EE might interfere with treatment success from the start of treatment. When high EE was defined by a higher threshold, these effects were no longer significant, regardless of treatment type (FBT or AFT). These findings suggest that adolescents with AN may be more sensitive to EE than other mental illnesses, such that lower thresholds of EE impact the speed with which they are able to reduce symptoms and gain weight in treatment. It may be necessary to target parental EE prior to or early in treatment or pivot to parent-focused treatment to change the trajectory of treatment response. Future research is needed to explore ways parental EE can be reduced.

Asymmetric trichotomous partitioning overcomes dataset limitations in building machine learning models for predicting siRNA efficacy

Chemically modified small interfering RNAs (siRNAs) are promising therapeutics guiding sequence-specific silencing of disease genes. Identifying chemically modified siRNA sequences that effectively silence target genes remains challenging. Such determinations necessitate computational algorithms. Machine learning is a powerful predictive approach for tackling biological problems but typically requires datasets significantly larger than most available siRNA datasets. Here, we describe a framework applying machine learning to a small dataset (356 modified sequences) for siRNA efficacy prediction. To overcome noise and biological limitations in siRNA datasets, we apply a trichotomous, two-threshold, partitioning approach, producing several combinations of classification threshold pairs. We then test the effects of different thresholds on random forest machine learning model performance using a novel evaluation metric accounting for class imbalances. We identify thresholds yielding a model with high predictive power, outperforming a linear model generated from the same data, that was predictive upon experimental evaluation. Using a novel model feature extraction method, we observe target site base importances and base preferences consistent with our current understanding of the siRNA-mediated silencing mechanism, with the random forest providing higher resolution than the linear model. This framework applies to any classification challenge involving small biological datasets, providing an opportunity to develop high-performing design algorithms for oligonucleotide therapies.

Effect of different thresholds on the accuracy of linear and volumetric analysis of native- and grafted-bone

The study aimed to evaluate the accuracy of Micro-CT in linear and volumetric measurements in native (NB) and grafted bone (GB) areas. A total of 111 biopsies of maxillary sinuses grafted with deproteinized bovine bone (DBB) in humans were evaluated. The linear measurements were performed to measure the length of the NB and GB. Furthermore, the amount of mineralized tissues at the NB and GB was performed. In the histomorphometry analysis the percentage of mineralized tissues at the NB and GB was obtained in two histological sections while the mineralized tissues were measure in the micro-CT varying the thresholds of the grayscale varying from 90-250 to 90-150 with 10 levels of variation between each one was applied. Then these data were correlated in order to check the higher r level between the histomorphometry and micro-CT thresholds intervals. The linear length of the NB was 2.44±0.91mm and 2.48±1.50mm, respectively, for micro-CT and histomorphometry (r =0.57), while the linear length of the GB was 3.63±1.66mm and 3.13±1.45mm, respectively, for micro-CT and histomorphometry (r =0.74) Histomorphometry showed 45.91±11.69% of bone in NB, and 49.57±5.59% of bone and biomaterial in the GB. The total volume of mineralized tissues that were closest to the histometric analysis were 43.75±15.39% in the NB (Threshold:90-240; r = 0.50) and 51.68±8.42% in the GB (Threshold:90-180; r =-0.028). The micro-CT analysis showed good accuracy in the linear analysis in both portions of the biopsies but for volumetric analysis just in NB.

Reproductive tract disease in Irish grazing dairy cows: Retrospective observational study examining its association with reproductive performance and accuracy of 2 diagnostic tests

The detection of reproductive tract disease (RTD) 3 wk postpartum is important because of its effect on subsequent reproductive outcomes. Numerous methods for the diagnosis of RTD are described, some of which are more practical and instantaneous in terms of diagnosis. Two of these methods involve identification of purulent vaginal discharge (PVD) and evidence of ultrasonographic uterine changes indicative of endometritis (UE). The objectives of our retrospective observational study were (1) to assess the association of PVD or UE score at the prebreeding examination (PBE) with the hazard of pregnancy within the subsequent breeding season; (2) to determine the test sensitivity (Se) and specificity (Sp) at the point of sampling of both tests using a Bayesian latent class model; and (3) to determine the effect of varying positivity thresholds on test accuracy. To achieve these objectives, we analyzed an initial data set of 5,049 PBE from 2,460 spring-calved cows in 8 herds between 2014 and 2018. Each PBE was conducted once between 25 and 86 d in milk. At each PBE, vaginal discharge was obtained with a Metricheck device (Simcro) whereas uterine contents were assessed using transrectal ultrasonography. Purulent vaginal discharge was scored on a scale of 0 to 3 depending on discharge character, and UE was scored on a scale of 0 to 4 depending on the presence and consistency of intraluminal fluid. Cows with scores of ≥2 in either test had received treatment. Fertility data were available from 4,756 PBE after data exclusion. The association between PVD or UE score at the PBE and subsequent hazard of pregnancy was analyzed using a Cox proportional hazards model. Cows with a PVD score of 2 or 3 were less likely to conceive than cows with a PVD score 0 [score 2 hazard ratio (HR) = 0.74; 95% confidence interval (CI): 0.59-0.94; score 3 HR = 0.65; 95% CI: 0.51-0.84]. Cows with a UE score of 1, 2, 3, or 4 were less likely to conceive than cows with a UE score of 0 (score 1 HR = 0.82; 95% CI: 0.73-0.93; score 2 HR = 0.79; 95% CI: 0.62-1.00; score 3 HR = 0.43; 95% CI: 0.43-0.90; score 4 HR = 0.39; 95% CI: 0.26-0.58). To determine the Se and Sp of PVD or UE score for diagnosis of RTD at the time of PBE, a Bayesian latent class model was fitted on 2,460 individual cow PBE. Flat priors were used for the Se and Sp of UE, whereas informative priors were used for PVD Se (mode = 65%, 5th percentile = 45%) and Sp (mode = 90%, 5th percentile = 80%) and RTD prevalence (mode = 20%, 5th percentile = 10%). Posterior estimates (median and 95% Bayesian probability intervals; BPI) were obtained using 'rjags' (R Studio). The optimal test thresholds (PVD and UE score ≥1) were selected by assessing the effect of different thresholds on test estimates and using a misclassification cost analysis. Based on these, median (95% BPI) Se for PVD and UE score ≥1 were 44% (29-60%) and 67% (33-100%), respectively. Median Sp for PVD and UE score ≥1 were 90% (86-93%) and 91% (86-93%), respectively. Higher scores in both tests were associated with impaired fertility, and UE scoring with a threshold of ≥1 had the highest test Se and Sp estimates although test Se was conditional on days in milk when the PBE occurred.

Home monitoring of vital signs and generation of alerts in a cohort of people living with dementia

AbstractBackgroundPeople with dementia (PwD) are at increased risk of adverse medical events (e.g. infections and falls). These often cause clinical deterioration, and potentially preventable admissions. Remote home monitoring of vital signs using internet‐of‐things technology can identify risk factors for these events – something particular pertinent during the COVID‐19 pandemic. We present data from an on‐going UK Dementia Research Institute and Technology Integrated Health Management (DRI‐TIHM) project. We aim to define algorithms that generate automated alerts, like the hospital‐based NEWS system (Morgan, 1997, Clin Intensive Car), and provide more proactive care for PwD.MethodPwD recorded their systolic/diastolic blood pressure (SBP/DBP), heart rate (HR), temperature (BTM), bodyweight (BW) and oxygen saturation (Sats) daily (figure 1) and data were collected centrally. A ‘monitoring team’ followed algorithms in response to alerts and advised medical attention if required. Events such as infections, were logged and correlated with the data. The dataset was then used to calculate the number of alerts that would have been raised if different thresholds were used.Result52 PwD living at home were included. Patients had a range of dementia diagnoses, most commonly Alzheimer’s disease. In total, 89,894 measurements were collected over 556 days (figure 2). During the pandemic, a sub‐group were given Sats probes and these produced a significant number of false positive results (figure 4f). On sub‐group analysis, PwD with Parkinson’s disease dementia had significantly lower SBP and DBP (p=0.004 and p=0.01 respectively, Mann‐Whitney U) (figure 3a), one of whom suffered from repeated falls (figure 3b).Pilot data were used to set alert thresholds. Average values and number of alerts for each domain are shown (table 1). We then modelled the effect of different thresholds, based on NEWS, to the number of alerts generated (figure 4, table 2). This is informative in optimising sensitivity and specificity of alerts whilst considering the burden on the monitoring service.ConclusionRemote monitoring can be implemented for PwD. These data can be used to generate clinical alerts that may signify adverse medical outcomes. The thresholds need to be adjusted to optimise efficiency in the context of varying reliability of home monitoring devices.

Effect of different thresholds for CT perfusion volumetric analysis on estimated ischemic core and penumbral volumes.

This single-center study compared three threshold settings for automated analysis of the ischemic core (IC) and penumbral volumes using computed tomographic perfusion, and their accuracy for predicting final infarct volume (FIV) in patients with anterior circulation acute ischemic stroke (AIS). Fifty-two consecutive AIS patients undergoing mechanical thrombectomy (November 2015-March 2018) were included. Perfusion images were retrospectively analyzed using a single CT Neuro perfusion application (syngo.via 4.1, Siemens Healthcare GmbH). Three threshold values (S1-S3) were derived from another commercial package (RAPID; iSchema View) (S1), up-to-date syngo.via default values (S2), and adapted values for syngo.via from a reference study (S3). The results were compared with FIV determined by non-contrast CT. The median IC volume (mL) was 24.6 (interquartile range: 13.7-58.1) with S1 and 30.1 (20.1-53.1) with S2/S3. After removing the contralateral hemisphere from the analysis, the median IC volume decreased by 1.33(0-3.14) with S1 versus 9.13 (6.24-14.82) with S2/S3. The median penumbral volume (mL) was 74.52 (49.64-131.91), 77.86 (46.56-99.23), and 173.23 (125.86-200.64) for S1, S2, and S3, respectively. Limiting analysis to the affected hemisphere, the penumbral volume decreased by 1.6 (0.13-9.02), 19.29 (12.59-26.52), and 58.33 mL (45.53-74.84) for S1, S2, and S3, respectively. The correlation between IC and FIV was highest in patients with successful recanalization (n = 34, r = 0.784 for S1; r = 0.797 for S2/S3). Optimizing thresholds significantly improves the accuracy of estimated IC and penumbral volumes. Current recommended values produce diversified results. International guidelines based on larger multicenter studies should be established to support the standardization of volumetric analysis in clinical decision-making.

Reputation-based discount effect in imitation on the evolution of cooperation in spatial public goods games

Reputation provides important information to society by recording the historical behavior of individuals. The introduction of reputation helps explain the cooperation phenomenon in human society to some extent. However, in previous explanation models, the benefits of a good reputation bring to individuals are generally described from the perspective of future payoffs they can obtain. In reality, the reputation system also affects the process of mutual imitation among individuals. For instance, the willingness of an individual with a high reputation learning from an individual with a low reputation can be greatly discounted. As such, this paper considers the reputation-based discount effect in imitation and extends the research on reputation from the perspective of imitation learning. Specifically, two situations of discount effect are considered. One is based on relative reputation difference, that is, if the reputation of an individual being imitated is too low compared to the strategy updater and the difference between which exceeds a threshold, the probability of imitation will be discounted. The other is based on absolute reputation difference, that is, if the absolute reputation of an individual being imitated falls below a threshold, the probability of imitation will be discounted. The effect of different thresholds and discount parameters on the evolution of cooperation in spatial public goods games is investigated, respectively, in both situations. Simulation results show that the reputation-based discount effect in mutual imitation plays an important role in the emergence and maintenance of cooperative behavior. Especially, low threshold differences for reputation and high discounts can greatly expand the range of parameters in which cooperation emerges. Moreover, compared with the relative reputation situation, the discount effect based on the absolute reputation is more conducive to the evolution of cooperation.

Assessing the Importance of Tree Cover Threshold for Forest Cover Mapping Derived from Global Forest Cover in Myanmar

Comprehensive forest cover mapping is essential for making policy and management decisions. However, creating a forest cover map from raw remote sensing data is a barrier for many users. Here, we investigated the effects of different tree cover thresholds on the accuracy of forest cover maps derived from the Global Forest Change Dataset (GFCD) across different ecological zones in a country-scale evaluation of Myanmar. To understand the effect of different thresholds on map accuracy, nine forest cover maps having thresholds ranging from 10% to 90% were created from the GFCD. The accuracy of the forest cover maps within each ecological zone and at the national scale was assessed. The overall accuracies of ecological zones other than tropical rainforest were highest when the threshold for tree cover was less than 50%. The appropriate threshold for tropical rainforests was 80%. Therefore, different optimal tree cover thresholds were required to achieve the highest overall accuracy depending on ecological zones. However, in the unique case of Myanmar, we were able to determine the threshold across the whole country. We concluded that the threshold for tree cover for creating a forest cover map should be determined according to the areal ratio of ecological zones determined from large-scale monitoring. Our results are applicable to tropical regions having similar ecological zones.

Effect of Different Thresholds of Drip Irrigation Using Saline Water on Soil Salt Transportation and Maize Yield

Sustainable development of saline water irrigation was restricted in HID (Hetao Irrigation District) by serious yield reduction and severe salt accumulation without an effective irrigation schedule. Field experiments were carried out to study the effects of drip irrigation thresholds on soil salt transportation and maize yield with shallow saline ground water in 2015 and 2016 in HID. The irrigation was triggered by four soil matric potential (SMP) treatments which measured 20 cm beneath the drip emitter. Results indicate that the shape of the wetting body approximated a one-fourth ellipse on the vertical profile perpendicular to the drip line, while the horizontal radius increased with the increase of SMP. Moreover, salt accumulation decreased with the increasing thresholds in the 0–40-cm layer, while the soil salt in the 40–100 cm layer was hardly affected by SMP thresholds under a drip irrigation quota of 22.5 mm. Maize yield showed a quadratic relationship with the SMP threshold, and the irrigation water use efficiency (IWUE) showed a linear increase in response to the decrease in SMP threshold. Taking into account the salt accumulation, yield and IWUE, a SMP threshold higher than −30 kPa is suggested as the appropriate indicator for maize mulched-drip irrigation with shallow saline groundwater in HID.

Snow model sensitivity analysis to understand spatial and temporal snow dynamics in a high‐elevation catchment

AbstractIn this paper, we addressed a sensitivity analysis of the snow module of the GEOtop2.0 model at point and catchment scale in a small high‐elevation catchment in the Eastern Italian Alps (catchment size: 61 km2). Simulated snow depth and snow water equivalent at the point scale were compared with measured data at four locations from 2009 to 2013. At the catchment scale, simulated snow‐covered area (SCA) was compared with binary snow cover maps derived from moderate‐resolution imaging spectroradiometer (MODIS) and Landsat satellite imagery. Sensitivity analyses were used to assess the effect of different model parameterizations on model performance at both scales and the effect of different thresholds of simulated snow depth on the agreement with MODIS data. Our results at point scale indicated that modifying only the “snow correction factor” resulted in substantial improvements of the snow model and effectively compensated inaccurate winter precipitation by enhancing snow accumulation. SCA inaccuracies at catchment scale during accumulation and melt period were affected little by different snow depth thresholds when using calibrated winter precipitation from point scale. However, inaccuracies were strongly controlled by topographic characteristics and model parameterizations driving snow albedo (“snow ageing coefficient” and “extinction of snow albedo”) during accumulation and melt period. Although highest accuracies (overall accuracy = 1 in 86% of the catchment area) were observed during winter, lower accuracies (overall accuracy < 0.7) occurred during the early accumulation and melt period (in 29% and 23%, respectively), mostly present in areas with grassland and forest, slopes of 20–40°, areas exposed NW or areas with a topographic roughness index of −0.25 to 0 m. These findings may give recommendations for defining more effective model parameterization strategies and guide future work, in which simulated and MODIS SCA may be combined to generate improved products for SCA monitoring in Alpine catchments.

Pathotypes of Plasmodiophora brassicae causing damage to oilseed rape in the Czech Republic and Poland

Winter oilseed rape (Brassica napus) is an important crop in the Czech Republic and Poland. Clubroot disease caused by the pathogen Plasmodiophora brassicae is a serious and still-growing problem for oilseed rape growers in both countries. The aim of this study was to evaluate the pathotype composition of P. brassicae populations from the Czech Republic and Poland, according to the three evaluation systems, and to determine soil inoculum loads for representative fields via traditional end-point PCR as well as quantitative PCR analysis. There were considerable differences between the populations of P. brassicae from both countries, and the number of pathotypes varied depending on the evaluation system and the threshold used to distinguish susceptible vs. resistant plant reactions. This is the first study comparing the effect of different thresholds. Using an index of disease (ID) of 25 % to distinguish susceptible vs. resistant reactions, there was a total of seven pathotypes identified based on the differentials of Williams, five with the system of Some et al., and 18 with the European Clubroot Differential (ECD) set. However, based on a threshold of 50 %, there were nine pathotypes according to the evaluation system by Williams, four based on the differentials of Some et al., and 15 with the ECD set. Changing of the thresholds led to the reclassification of some pathotypes. Several pathotypes were common in both countries. High amounts of pathogen DNA were found in many of the field soils analysed by quantitative PCR. There was a weak correlation between soil pH and infestation of P. brassicae for the Polish soils.

Validation of HY-2A Remotely Sensed Wave Heights against Buoy Data and Jason-2 Altimeter Measurements

AbstractThe Haiyang-2A (HY-2A; HaiYang means ocean in Chinese) satellite was successfully launched in China on 16 August 2011, carrying the nation’s first operational radar altimeter along with three other microwave sensors. In this study, HY-2A altimeter significant wave height (SWH) data have been validated against National Data Buoy Center (NDBC) buoy and Jason-2 altimeter SWH data over a period of 27 months (from 1 October 2011 to 31 December 2013). During the collocation, the effects of different thresholds of several flags are carefully studied. These flags prove to be useful for the SWH selection and different thresholds are observed to change the results remarkably. The final results show that HY-2A SWHs, with a 0.339-m root-mean-square (RMS) difference and a negative bias of 0.231 m in buoy comparison, have reached the mission target (0.5-m RMS). Nonetheless, the Jason-2 altimeter performs better with a lower RMS difference of 0.292 m and a positive bias of only 0.016 m. In addition, by analyzing the residuals (altimeter minus buoy), the bias for the HY-2A altimeter is found to decline monotonically over the whole range with an overestimation at low sea state (SWH < 1 m), a minor underestimation at middle sea state (1 m < SWH < 5 m), and a severe underestimation at high sea state (SWH > 5 m). However, only an underestimation at high sea state is found for the Jason-2 altimeter. A linear regression is also proposed. The 20 days of the newly processed HY-2A SWHs are investigated and discussed as well, and a slight quality improvement has been observed using these data.

Defining hospital markets - an application to the German hospital sector.

The correct definition of the product market and of the geographic market is a prerequisite for assessing market structures in antitrust cases. For hospital markets, both dimensions are controversially discussed in the literature. Using data for the German hospital market we aim at elaborating the need for differentiating the product market and at investigating the effects of different thresholds for the delineation of the geographic market based on patient flows. Thereby we contribute to the scarce empirical evidence on the structure of the German hospital market. We find that the German hospital sector is highly concentrated, confirming the results of a singular prior study. Furthermore, using a very general product market definition such as “acute in-patient care” averages out severe discrepancies that become visible when concentration is considered on the level of individual diagnoses. In contrast, varying thresholds for the definition of the geographic market has only impact on the level of concentration, while the correlation remains high. Our results underline the need for more empirical research concerning the definition of the product market for hospital services.

Simulating the (Unilateral) Effects of Mergers: Implications of the Oracle/PeopleSoft Case

Unilateral effects analysis has been the single most important innovation in merger control driven by economic theory in recent years. In practice, this requires the use of sophisticated economic tools such as simulation models, which facilitate the quantification of short-term merger effects. In this paper, we study the application of this new device in the landmark merger case between software firms Oracle and PeopleSoft. Despite serious initial concerns the transaction was not blocked, nor even required to be modified in the EU and US. Besides some case-specific issues we highlight the fundamental problems associated with the use of sophisticated economic tools in merger control. The basic questions are: (i) What can merger simulation models actually demonstrate? (ii) What is an adequate standard of proof for their sensible use in merger review? Based on the nature of predictive economic evidence we then develop an adequate standard of proof, i.e. the evidentiary threshold that must be met for a prohibition decision. For a more general treatment we also present a simple analytical model in order to illustrate the effects of different thresholds on legal and economic quality. Finally, our recommendation is to adjust the standard of proof in the direction of a moderate threshold or, more preferably, to switch to a mixed burden of proof. Both suggestions are geared to guaranteeing the fruitful contribution of sophisticated economic evidence to case assessments and, thus, increasing decision quality.

Two-Dimensional Adaptive-Surface Elasto-Plastic Asperity Contact Model

When contact problems are solved by numerical approaches, a surface profile is usually described by a series of discrete nodes with the same intervals along a coordinate axis. Contact computation based on roughness datum mesh may be time consuming. An adaptive-surface elasto-plastic asperity contact model is presented in this paper. Such a model is developed in order to reduce the computing time by removing the surface nodes that have little influence on the contact behavior of rough surfaces. The nodes to be removed are determined by a prescribed threshold. The adaptive-surface asperity contact model is solved by means of the element-free Galerkin-finite element coupling method because of its flexibility in domain discretization and versatility in node arrangements. The effects of different thresholds on contact pressure distribution, real contact area, and elasto-plastic stress fields in contacting bodies are investigated and discussed. The results show that this model can help reduce about 48% computational time when the relative errors are about 5%.

Iterative demodulation and decoding of frequency-hopped PSK in partial-band jamming

This paper considers the problem of developing and utilizing side information in a frequency-hopped communication system using phase-shift keying (PSK) and operating in an environment with partial-band jamming. Two aspects of side information are studied. The first deals with estimating the unknown random carrier phase that varies from hop to hop. The second aspect is the detection of jamming signals. We use a serially concatenated convolutional code structure with differential M-ary PSK as the inner code. The iterative receiver uses an expanded trellis in the inner decoder to resolve the phase ambiguity and is augmented by a ratio-threshold test for detecting jammer energy. Performance is compared for different dwell interval lengths and both log-APP and max-log-APP decoding algorithms. This paper also considers the effect of different thresholds on the false alarm and detection probabilities of the ratio-threshold test.

Coronary artery calcium: accuracy and reproducibility of measurements with multi-detector row CT--assessment of effects of different thresholds and quantification methods.

To evaluate the effects of different thresholds and quantification methods on the accuracy and reproducibility of coronary calcium measurements with multi-detector row computed tomography (CT). A cardiac CT phantom containing predetermined calcified cylinders was scanned. Calcium volume and mass were measured at various threshold values ranging from 80 to 230 HU. In 32 patients, two consecutive CT scans were obtained, and the coronary artery calcium score, volume, and mass were measured by one observer at 130- and 90-HU thresholds. Correlation analysis and analysis of variance were performed to evaluate the measurement errors in the phantom study and the interscan variability in the clinical study. In the phantom, mass measurement error varied with threshold and calcium density (P <.01). Mass error was strongly correlated with volume error (r = 0.91, P <.01) but with a much smaller range. In the clinical study, interscan variability of mass measurements was significantly lower than that with other measurement methods for both patients and individual vessels. For the patients, the mean interscan variability of calcium score, volume, and mass at the 130-HU threshold was 20.4%, 13.9%, and 9.3%, respectively. For all methods, interscan variability was not significantly different between the 130- and 90-HU thresholds (P >.05). The mass measurement is more accurate, less variable, and more reproducible in coronary calcium quantification than are measurements with other algorithms. Accurate quantification of calcium in each calcified plaque may require that the threshold be set individually, depending on the calcium density.

The Mixing Ratio of the (p3/2)−1 → (p1/2)−1 Transition in 15O

The mixing ratio of the 3/2− → 1/2−, 6.18 → 0 MeV transition in 15O has been measured using the 14N(p,γγ)15O reaction. The value obtained is −0.141 ± 0.016, confirming previous indications that this mixing ratio is a factor of two larger than is predicted by shell-model calculations which give values consistent with experiment for the corresponding transition in 15N. The discrepancy may be due to uncertainties in the contributions to the E2 strength from the 16O core and to the effect of different thresholds for nucleon emission in the two nuclei. The analysis of the present experiment necessitated a reevaluation of available data regarding M2 strengths in the 1p shell.