Segmentation d'images de transmission pour la correction de l'atténué en tomographie d'émission par positrons

L'atténuation des photons est un phénomène qui affecte directement et de façon profonde la qualité et l'information quantitative obtenue d'une image en Tomographie d'Emission par Positrons (TEP). De sévères artefacts compliquant l'interprétation visuelle ainsi que de profondes erreurs d'exactitudes sont présents lors de l'évaluation quantitative des images TEP, biaisant la vérification de la corrélation entre les concentrations réelles et mesurées.L' atténuation est due aux effets photoélectrique et Compton pour l'image de transmission (30 keV - 140 keV), et majoritairement à l'effet Compton pour l'image d'émission (511 keV). La communauté en médecine nucléaire adhère largement au fait que la correction d'atténuation constitue une étape cruciale pour l'obtention d'images sans artefacts et quantitativement exactes. Pour corriger les images d'émission TEP pour l'atténué, l'approche proposée consiste concrètement à segmenter une image de transmission à l'aide d'algorithmes de segmentation: K-means (KM), Fuzzy C-means (FCM), Espérance-Maximisation (EM), et EM après une transformation en ondelettes (OEM). KM est un algorithme non supervisé qui partitionne les pixels de l'image en agrégats tels que chaque agrégat de la partition soit défini par ses objets et son centroïde. FCM est un algorithme de classification non-supervisée qui introduit la notion d'ensemble flou dans la définition des agrégats, et chaque pixel de l'image appartient à chaque agrégat avec un certain degré, et tous les agrégats sont caractérisés par leur centre de gravité.L'algorithme EM est une méthode d'estimation permettant de déterminer les paramètres du maximum de vraisemblance d'un mélange de distributions avec comme paramètres du modèle à estimer la moyenne, la covariance et le poids du mélange correspondant à chaque agrégat. Les ondelettes forment un outil pour la décomposition du signal en une suite de signaux dits d'approximation de résolution décroissante suivi d'une suite de rectifications appelées détails.L' image à laquelle a été appliquée les ondelettes est segmentée par EM. La correction d'atténuation nécessite la conversion des intensités des images de transmission segmentées en coefficients d'atténuation à 511 keV. Des facteurs de correction d' atténuation (FCA) pour chaque ligne de réponse sont alors obtenus, lesquels représentent le rapport entre les photons émis et transmis. Ensuite il s'agit de multiplier le sinogramme, formé par l'ensemble des lignes de réponses, des FCA par le sinogramme de l'image d'émission pour avoir le sinogramme corrigé pour l'atténuation, qui est par la suite reconstruit pour générer l'image d'émission TEP corrigée. Nous avons démontré l'utilité de nos méthodes proposées dans la segmentation d'images médicales en les appliquant à la segmentation des images du cerveau, du thorax et de l'abdomen humains. Des quatre processus de segmentation, la décomposition par les ondelettes de Haar suivie de l'Espérance-Maximisation (OEM) semble donner un meilleur résultat en termes de contraste et de résolution. Les segmentations nous ont permis une réduction claire de la propagation du bruit des images de transmission dans les images d'émission, permettant une amélioration de la détection des lésions, et améliorant les diagnostics en médecine nucléaire

Segmentation of neuroanatomy in magnetic resonance images

Segmentation in neurological Magnetic Resonance Imaging (MRI) is necessary for volume measurement, feature extraction and for the three-dimensional display of neuroanatomy. This thesis proposes several automated and semi-automated methods which offer considerable advantages over manual methods because of their lack of subjectivity, their data reduction capabilities, and the time savings they give. Work has concentrated on the use of dual echo multi-slice spin-echo data sets in order to take advantage of the intrinsically multi-parametric nature of MRI. Such data is widely acquired clinically and segmentation therefore does not require additional scans. The literature has been reviewed. Factors affecting image non-uniformity for a modem 1.5 Tesla imager have been investigated. These investigations demonstrate that a robust, fast, automatic three-dimensional non-uniformity correction may be applied to data as a pre-processing step. The merit of using an anisotropic smoothing method for noisy data has been demonstrated. Several approaches to neurological MRI segmentation have been developed. Edge-based processing is used to identify the skin (the major outer contour) and the eyes. Edge-focusing, two threshold based techniques and a fast radial CSF identification approach are proposed to identify the intracranial region contour in each slice of the data set. Once isolated, the intracranial region is further processed to identify CSF, and, depending upon the MRI pulse sequence used, the brain itself may be sub-divided into grey matter and white matter using semiautomatic contrast enhancement and clustering methods. The segmentation of Multiple Sclerosis (MS) plaques has also been considered. The utility of the stack, a data driven multi-resolution approach to segmentation, has been investigated, and several improvements to the method suggested. The factors affecting the intrinsic accuracy of neurological volume measurement in MRI have been studied and their magnitudes determined for spin-echo imaging. Geometric distortion - both object dependent and object independent - has been considered, as well as slice warp, slice profile, slice position and the partial volume effect. Finally, the accuracy of the approaches to segmentation developed in this thesis have been evaluated. Intracranial volume measurements are within 5% of expert observers' measurements, white matter volumes within 10%, and CSF volumes consistently lower than the expert observers' measurements due to the observers' inability to take the partial volume effect into account

[¹⁸F]fluorination of biorelevant arylboronic acid pinacol ester scaffolds synthesized by convergence techniques

Aim: The development of small molecules through convergent multicomponent reactions (MCR) has been boosted during the last decade due to the ability to synthesize, virtually without any side-products, numerous small drug-like molecules with several degrees of structural diversity.(1) The association of positron emission tomography (PET) labeling techniques in line with the “one-pot” development of biologically active compounds has the potential to become relevant not only for the evaluation and characterization of those MCR products through molecular imaging, but also to increase the library of radiotracers available. Therefore, since the [18F]fluorination of arylboronic acid pinacol ester derivatives tolerates electron-poor and electro-rich arenes and various functional groups,(2) the main goal of this research work was to achieve the 18F-radiolabeling of several different molecules synthesized through MCR. Materials and Methods: [18F]Fluorination of boronic acid pinacol esters was first extensively optimized using a benzaldehyde derivative in relation to the ideal amount of Cu(II) catalyst and precursor to be used, as well as the reaction solvent. Radiochemical conversion (RCC) yields were assessed by TLC-SG. The optimized radiolabeling conditions were subsequently applied to several structurally different MCR scaffolds comprising biologically relevant pharmacophores (e.g. β-lactam, morpholine, tetrazole, oxazole) that were synthesized to specifically contain a boronic acid pinacol ester group. Results: Radiolabeling with fluorine-18 was achieved with volumes (800 μl) and activities (≤ 2 GBq) compatible with most radiochemistry techniques and modules. In summary, an increase in the quantities of precursor or Cu(II) catalyst lead to higher conversion yields. An optimal amount of precursor (0.06 mmol) and Cu(OTf)2(py)4 (0.04 mmol) was defined for further reactions, with DMA being a preferential solvent over DMF. RCC yields from 15% to 76%, depending on the scaffold, were reproducibly achieved. Interestingly, it was noticed that the structure of the scaffolds, beyond the arylboronic acid, exerts some influence in the final RCC, with electron-withdrawing groups in the para position apparently enhancing the radiolabeling yield. Conclusion: The developed method with high RCC and reproducibility has the potential to be applied in line with MCR and also has a possibility to be incorporated in a later stage of this convergent “one-pot” synthesis strategy. Further studies are currently ongoing to apply this radiolabeling concept to fluorine-containing approved drugs whose boronic acid pinacol ester precursors can be synthesized through MCR (e.g. atorvastatin)

Assessing physical fitness and physical activity in population-based surveys

Edited by Thomas F. Drury.Includes bibliographical references and index.National Center for Health Statistics. Assessing Physical Fitness and Physical Activity in Population-Based Surveys. Thomas F. Drury, ed. DHHS pub. No, (PHS) 89-1253. Public Health Service. Washington. U.S. Government Printing Office. 1989Part I. Historical Perspectives -- 1. General Population Surveys of the National Center for Health Statistics: An Overview / Nancy D. Pearce -- 2. Cardiovascular Endurance, Strength, and Lung Function Tests in the National Health and Nutrition Examination Surveys / Arthur J. McDowell -- 3. Assessments of Body Composition, Dietary Patterns, and Nutritional Status in the National Health Examination Surveys and National Health and Nutrition Examination Surveys / Dorothy Blair,Jean-Pierre Habicht,andLeeAlekel -- -- Part II. Fundamental Perspectives on Health-Related Physical Fitness and Cardiopulmonary -- Health -- 4. Design Issues and Alternatives in Assessing Physical Fitness Among Apparently Healthy Adults in a Health Examination Survey of the General Population / Jack H. Wilmore -- 5. An Integrative Approach to the Noninvasive Assessment of Cardiovascular and Respiratory Function During Exercise / Karlman Wasserman -- -- Part III. Fundamental Perspectives on Energy Balance, Dietary Patterns, and Physical Activity -- 6. General Considerations Related to Assessing Energy Turnover: Energy Intake or Energy Expenditure / E. R. Buskirk -- 7. Issues Related to Measuring Energy Balance for the National Health and Nutrition Examination Survey / Dorothy Blair -- 8. Measuring Dietary Patterns in Surveys of Physical Fitness and Activity / Catherine E. Woteki -- 9. Design Issues and Alternatives in Assessing Physical Activity in General Population Surveys / Thomas Stephens -- -- Part IV. Special Subpopulation Issues -- 10. Fitness and Activity Assessment of Children and Adolescents / Oded Bar-Or -- 11, Evaluating Fitness and Activity Assessments From the National Children and Youth Fitness Studies I and II / James G. Ross -- 12. Assessing Fitness and Activity Patterns of Women in General Population Studies / Barbara L. Drinkwater -- 13. Exercise Testing and Physical Activity Assessment of Persons with Selected Cardiac Conditions / Nanette Kass Wenger -- 14. Health-Related Fitness of the Older Adult / Everett L. Smith and Catherine Gilligan -- -- Part V. Lessons From Community, National, and International Studies -- 15. Lessons from Tecumseh on the Assessment of Physical Activity and Fitness / Henry J. Montoye -- 16. Fitness and Activity Assessments Among U.S.Army Populations: Implications for NCHS General Population Surveys / James A. Vogel -- 17. Fitness and Activity Measurement in the 1981 Canada Fitness Survey / Thomas Stephens and Cora Lynn Craig -- 18. An International Perspective on Critical Issues in Fitness Testing of U.S. Adults / Roy J. Shephard -- -- Part VI. Contexts of Evaluation -- 19. Genetic Considerations in Physical Fitness / Robert M. Malina and Claude Bouchard -- 20. Biochemical Correlates of Fitness and Exercise / William L. Haskell -- 21. Evaluating the Health Effects of Demanding Work on and off the Job / James S. House and David A. Stiti -- 22. Effects of Physical Activity and Fitness on Health / Arthur S. Leon -- 23. Measurement and Evaluation of Health Behaviors in Relationship to Physical Fitness and Physical Activity Patterns / Steven N. Blair and Harold W. Kohl -- 24. Evaluating Interrelationships Among Physical Fitness and Activity Assessments / Ronald E. LaPorte -- 25. Cardiovascular Epidemiological Research Uses of Fitness Assessments / Erika S. Sivarajan and Victor F. Froelicher -- 26. Epidemiologic Uses of General Population Assessments of Physical Activity Patterns / Robert T. Hyde and Ralph S. Paffenbarger, Jr. -- -- Part VII. Measurement and Analysis Strategies -- 27. Use of Latent VariableModels in Measuring Physical Fitness and Physical Activity / George W. Bohrnstedt and Joseph Lucke -- 28. Applying Regression and Factor Analysis of Categorical Variables to Fitness and Exercise Data / Bengt Muthen and Lynn Short -- 29. Latent Class Analysis / Allan L. McCutcheon -- -- Appendix. Framingham Leisure Time Physical Activity Questionnaire / Andrew L. Dannenberg and Peter W. F. Wilson1989833