Comparison of supervised‐learning approaches for designing a channelized observer for image quality assessment in CT

Abstract Background The current paradigm for evaluating computed tomography (CT) system performance relies on a task‐based approach. As the Hotelling observer (HO) provides an upper bound of observer performances in specific signal detection tasks, the literature advocates HO use for optimization purposes. However, computing the HO requires calculating the inverse of the image covariance matrix, which is often intractable in medical applications. As an alternative, dimensionality reduction has been extensively investigated to extract the task‐relevant features from the raw images. This can be achieved by using channels, which yields the channelized‐HO (CHO). The channels are only considered efficient when the channelized observer (CO) can approximate its unconstrained counterpart. Previous work has demonstrated that supervised learning‐based methods can usually benefit CO design, either for generating efficient channels using partial least squares (PLS) or for replacing the Hotelling detector with machine‐learning (ML) methods. Purpose Here we investigated the efficiency of a supervised ML‐algorithm used to design a CO for predicting the performance of unconstrained HO. The ML‐algorithm was applied either (1) in the estimator for dimensionality reduction, or (2) in the detector function. Methods A channelized support vector machine (CSVM) was employed and compared against the CHO in terms of ability to predict HO performances. Both the CSVM and the CHO were estimated with channels derived from the singular value decomposition (SVD) of the system operator, principal component analysis (PCA), and PLS. The huge variety of regularization strategies proposed by CT system vendors for statistical image reconstruction (SIR) make the generalization capability of an observer a key point to consider upfront of implementation in clinical practice. To evaluate the generalization properties of the observers, we adopted a 2‐step testing process: (1) achieved with the same regularization strategy (as in the training phase) and (2) performed using different reconstruction properties. We generated simulated‐ signal‐known‐exactly/background‐known‐exactly (SKE/BKE) tasks in which different noise structures were generated using Markov random field (MRF) regularizations using either a Green or a quadratic, function. Results The CSVM outperformed the CHO for all types of channels and regularization strategies. Furthermore, even though both COs generalized well to images reconstructed with the same regularization strategy as the images considered in the training phase, the CHO failed to generalize to images reconstructed differently whereas the CSVM managed to successfully generalize. Lastly, the proposed CSVM observer used with PCA channels outperformed the CHO with PLS channels while using a smaller training data set. Conclusion These results argue for introducing the supervised‐learning paradigm in the detector function rather than in the operator of the channels when designing a CO to provide an accurate estimate of HO performance. The CSVM with PCA channels proposed here could be used as a surrogate for HO in image quality assessment

Impact of iterative reconstruction algorithms on the applicability of Fourier‐based detectability index for x‐ray CT imaging

International audienc

Agir en situation d’incertitude en agriculture: Regards pluridisciplinaires au Nord et au Sud

Parution suite au colloque " Agir en situation d'incertitude " (22-24 nov 2010, Montpellier )National audienceUn ouvrage collectif qui propose de dépasser les analyses en termes de risques et d’assurances, et offre de nouvelles approches pour rendre compte de l’incertain, du complexe, du long terme, et des capacités des systèmes à apprendre d’un environnement qui change. Agir en situation d’incertitude est une question de survie dans les mondes paysans. Chaque année climatique diffère d’une autre, et la fluctuation des prix sur les marchés mondialisés se répercutent dans la plupart des pays. À plus long terme, l’ampleur et la nature même du changement global demeurent des inconnues, obligeant les acteurs agricoles et ruraux à développer des dynamiques d’adaptation et de sécurisation tenant compte des questionnements techniques, écologiques, économiques, politiques et sociaux à différentes échelles, du local à l’international. Cet ouvrage propose de sortir des analyses en termes de risques et d’assurances et offre de nouvelles approches pour rendre compte de l’incertain, du complexe, du long terme, et des capacités des systèmes à tenir, à se transformer, à apprendre d’un environnement en changement. les auteurs sont des chercheurs qui pratiquent l’échange interdisciplinaire, mais aussi des acteurs du développement. Le pari du regard croisé des disciplines, biotechniques et sciences sociales, se double de la volonté de confronter des réalités du Nord et du Sud. Que ce soit en Europe, en Afrique, ou en Amérique du Sud, le rapport au changement et les protections mises en place face à l’incertitude, sont des constructions socio-techniques

Agir en situation d'incertitude en agriculture: Dynamiques de protection et d'adaptation au Nord et au Sud

Parution suite au colloque "Agir en situation d'incertitude" (22-24 novembre 2010, Montpellier)National audienc

How do pastoral families combine livestock herds with other livelihood security means to survive? The case of the Ferlo area in Senegal

Abstract Reducing vulnerability to hazards is a major challenge for pastoral settlements in the dry lands of sub-Saharan Africa. Accumulation of a stock of living animals is a major means of livelihood security that pastoralists use to cope with their constraints, amongst which is high environmental variability. Diversification and long-distance mobility are other means of livelihood security, implying specific family organization. We analysed the combination of these means in ensuring the livelihood security of 508 familial settlements in the rural community of Ferlo, Tessekre (Senegal). At least 40% of the settlements surveyed were small pastoral families, composed of one or two households with small herds (less than 50 cows and 50 sheep). Herds were the major means of livelihood security, but due to lack of a sufficient labour and other assets, the situation of these impoverished families was very precarious. In 28% of the settlements, families combined livestock, crops and non-farming activities as livelihood means. The remaining 32% of the settlements were pastoral settlements supported by large cattle herds and, in many cases, the production of Aïd el Kebir rams (for the major Muslim religious event). Non-farming activities were also present in these settlements with large herds, especially activities in the livestock trade. Diversification can reinforce the function of herds as savings accounts and might also enable the pastoralists to invest in livestock activities. There were three groups of settlements based on the characterization of livelihood security strategies used by pastoral herders. Over time, pastoralists have to utilize several means of security to cope with climatic shocks such as droughts, and familial events such as the death of the familial chief. Family organization (dispersal or grouping), diversification and mobility are important means used to recover after major losses of animals

Le chainon manquant du rempart de Saint-Lizier (Ariège) : étude stratigraphique et architecturale de la courtine effondrée au chemin de Nargach

International audienc

How do pastoral families combine livestock herds with other livelihood security means to survive ? The case of the Ferlo area in Senegal

Le document est disponible en ligne : http://www.pastoralismjournal.com/content/4/1/3International audienceReducing vulnerability to hazards is a major challenge for pastoral settlements in the dry lands of sub-Saharan Africa. Accumulation of a stock of living animals is a major means of livelihood security that pastoralists use to cope with their constraints, amongst which is high environmental variability. Diversification and long-distance mobility are other means of livelihood security, implying specific family organization. We analysed the combination of these means in ensuring the livelihood security of 508 familial settlements in the rural community of Ferlo, Tessekre (Senegal). At least 40% of the settlements surveyed were small pastoral families, composed of one or two households with small herds (less than 50 cows and 50 sheep). Herds were the major means of livelihood security, but due to lack of a sufficient labour and other assets, the situation of these impoverished families was very precarious. In 28% of the settlements, families combined livestock, crops and non-farming activities as livelihood means. The remaining 32% of the settlements were pastoral settlements supported by large cattle herds and, in many cases, the production of Aïd el Kebir rams (for the major Muslim religious event). Non-farming activities were also present in these settlements with large herds, especially activities in the livestock trade. Diversification can reinforce the function of herds as savings accounts and might also enable the pastoralists to invest in livestock activities. There were three groups of settlements based on the characterization of livelihood security strategies used by pastoral herders. Over time, pastoralists have to utilize several means of security to cope with climatic shocks such as droughts, and familial events such as the death of the familial chief. Family organization (dispersal or grouping), diversification and mobility are important means used to recover after major losses of animals. (Résumé d'auteur

Agir en situation d’incertitude. La construction individuelle et collective des régimes de protection et d’adaptation en agriculture

absen

Significant Correlation Between Overall Survival and Mean Lung Dose in Lung Stereotactic Body Radiation Therapy (SBRT)

International audienceBackground: After stereotactic body radiation therapy (SBRT) for medically inoperable stage I non-small-cell lung cancer (NSCLC), more patients die of comorbidities, particularly severe pulmonary insufficiency, than of tumor progression. The aim of this study was to evaluate correlation between lung biologically effective dose (BED) with an α/β ratio of 3 Gy (BED3) and overall survival (OS) for these patients.Methods: From 2012 to 2017, we have developed a prospectively updated institutional database for all first 100 consecutively treated patients with inoperable Stage 1 (T1T2N0M0) NSCLC. All SBRT were conducted on a Novalis Tx® LINAC with two coplanar dynamic conformal arcs (84%) or with coplanar volumetric modulated arc therapy (VMAT) (16%). Mean GTV and PTV were 8.6 cc and 50.8 cc, respectively. The marginal dose prescribed to the PTV was the 80% isodose line (IDL), i.e., 54 Gy in 3 fractions for 76 patients (BED10 = 126 Gy) and 50 Gy in 5 fractions for 24 patients (BED10 = 83.3 Gy). Pulmonary heterogeneity has been taken into account by using Monte Carlo or AAA algorithms. Median follow-up was 25 months.Results: At 1, 2, 3 and 5 years, local control (LC) was respectively 100, 98.2, 98.2, and 77.7%, and OS was respectively 83, 71.2, 58.1, and 33.2% (median OS was 49 months). Significant OS prognostic factors in univariate and multivariate analysis were mean lung BED3 (HR = 1.14, p = 0.01) and PTV volume (HR = 1.01, p = 0.004). A mean lung BED3 ≤ 5 Gy was significantly associated with a doubling of median OS from 29 months to more than 60 months (not achieved, p = 0.0068). For patients with a forced expiratory volume in 1 second (FEV1) ≤ 40%, a mean lung BED3 ≤ 4 Gy was significantly associated with a doubling of median OS from 23 to 46 months (p = 0.019).Conclusion: Mean lung BED3 is strongly and significantly associated with OS in SBRT for inoperable Stage I NSCLC. For all treated patients, a mean lung BED3 ≤ 5 Gy lead to a doubling of median OS. This threshold value should be reduced to 4 Gy for patients with FEV1 ≤ 40%