Concordance de la TEP au 18FDG double phase avec le grade histologique des tumeurs cérébrales

ANGERS-BU Médecine-Pharmacie (490072105) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Développement à partir du concept CACAO (Caméra A Collimation Assistée par Ordinateur) d'un système tomographique adapté à la mesure 3D de plaies contaminées

Le projet de gamma Caméra A Collimation Assitée par Ordinateur (CACAO) est une gamma caméra avec une collimation à grands trous, un mouvement supplémentaire à l'acquisition et un programme de reconstruction spécifique dépendant de l'éloignement de la source. Le concept CACAO a été développé pour réaliser l'image d'un ensemble d'émetteur gamma avec une sensibilité augmentée par rapport à celle des gamma Caméras classiques. Cette thèse étudie la conception d'un algorithme de reconstruction rapide et robuste pour le système CACAO. Nous commençons par une vue d'ensemble des techniques d'imagerie par tomographie en médecine nucléaire. Aprés la modélisation physique du système CACAO, nous présentons le programme de reconstruction qui enchaîne les trois étapes: 1) sommation et décalage 2) déconvolution et filtrage 3) rotation et sommation. La déconvolution est l'étape cruciale qui dégrade le rapport signal sur bruit des images reconstruites. Nous proposons une méthode de reconstruction qui se base sur une optimisation à multi-canaux pour résoudre le problème de la déconvolution...The computer aided collimation gamma camera (CACAO in french) is a gamma camera using a collimator with large holes, a supplementary linear scanning motion during the acquisition and a dedicated reconstruction program taking full account of the source depth. The CACAO system was introduced to improve both the sensitivity and the resolution in nuclear medicine. This thesis focuses on the design of a fast and robust reconstruction algorithm in the CACAO project. We start by an overview of tomographic imaging techniques in nuclear medicine. After modelling the physical CACAO system, we present the complete reconstruction program which involves three steps: 1) shift and sum 2) deconvolution and filtering 3) rotation and sum. The deconvolution is the critical step that decreases the signal to noise ratio of the reconstructed images. We propose a regularised multi-channel algorithm to solve the deconvolution problem. We also present a fast algorithm based on splines functions and preserving the high quality of the reconstructed images for the shift and the rotation steps...ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Amélioration des algorithmes de reconstruction d'image pour la tomographie d'émission par collimation à trous larges et longs

Le projet CACAO - Caméra A Collimation Assistée par Ordinateur - a pour but d'améliorer la qualité des images scintigraphiques. Des collimateurs à trous plus larges et profonds sur les gamma caméras, ainsi qu'un mouvement de balayage supplémentaire dans le protocole d'acquisition permettraient d'améliorer à la fois la résolution spatiale et la sensibilité des caméras; mais cela implique l'utilisation de nouveaux algorithmes de reconstruction. Avant cette thèse, la reconstruction des images CACAO se basait sur un algorithme utilisant pour la déconvolution la transformée de Fourier rapide qui présente un avantage en terme de rapidité et a donné des résultats très intéressants. Cependant un travail basé sur la théorie de l'information nous fait penser qu'il est possible d'obtenir de meilleurs résultats. L'étape limitante du projet étant la déconvolution, le travail de thèse avait pour but d'étudier et d'améliorer cette étape avec de nouveaux algorithmes. Plusieurs algorithmes basés sur une déconvolution appelée minimale avec un traitement ligne par ligne de l'image et l'utilisation de programmation linéaire ont été développés et donnent de bons résultats dans plusieurs cas sur des données exactes. Nous avons ensuite appliqué cette idée au problème dans son ensemble, ce qui donne de bons résultats sur des données exactes et permet également de simplifier la reconstruction. Nous avons aussi effectué la dualisation de nos données qui permet de réduire le temps de calcul et de traiter de plus grandes images. Enfin, nous avons mis au point la déconvolution médiane qui se montre efficace pour des images bruitées.The CACAO project is aimed to improve the quality of scintigraphic images. The use of a collimator with wider and deeper holes should improve both spatial resolution and sensitivity of the system. An added linear scanning motion in the acquisition sequence ensure an overdetermined system but imply new reconstruction algorithms. At the beginning of this work, a fast algorithm based on Fast Fourier Transforms was used to reconstruct the CACAO images. Good results were obtained with it, but not as good as we wanted. An information-theory based work demonstrated that it is possible to get a far better result with CACAO than with the conventional thin hole collimator way. Up to know we failed to show that practically that point. As the limiting step in that algorithm was the deconvolution, we aimed to study and improve this step with new algorithms. Several algorithms based on a deconvolution called minimal, with a line by line proccesing and the use of linear programming were developped and gave mild results with exact data. Then we proposed a new algorithm, still based on a minimal deconvolution, but this time processing the whole image, which give very good results on exact data.We also worked at reducing the processing time. We tried the dualization of our data, which allowed us to solve larger dimensions matrices and speed up the process. Finally we proposed a new reconstruction algorithm based on a median criteria, which appears to be very efficient on on noisy data.ANGERS-BU Lettres et Sciences (490072106) / SudocSudocFranceF

Cramér-Rao bounds and condition number in SPECT: Comparison between conventional thin holes collimator and emission tomography project with large and long holes collimators

International audienceObjectives:The project of emission tomography with large and long holes collimators (CACAO-TROLL), was proposed some time ago. The use of collimators with larger holes is intended to increase the number of photons detected and therefore the information available to reconstruct the images. This project is however exploratory and most research works in SPECT stick today to the conventional thin hole collimator (CTHC). It may be objected that if the number of photons increases, the information conveyed by each photon is lower. This thought is however inconsistent with our previously published demonstration using information theory. We develop here another approach.Methods:We first derived a formula to express the response function of the CACAO-TROLL acquisition, taking a complete account of the depth dependence and the attenuation of the gamma ray in the collimator. The conventional SPECT response function was modelled by using the formula of Youngho Seo (JNM 2005 vol 46 n 5 pp 868) standing for a VPC-45 LEHR collimator. For both projects, various parameters were tested in a 2D reduction of the problem in the transverse plane.Results:The results show a slight shift between the behaviour of the condition numbers and the Cramér-Rao bounds. For small image size (less than 30x30) the CACAO-TROLL project exhibits a lower condition number than CTHC, and higher Cramér-Rao bounds. For larger sizes, both factors increase steeply for CTHC. Finally, for a proper choice of the holes geometry, the Cramér-Rao bound is more than an order of magnitude better for the CACAO-TROLL project than for CTHC.Conclusions:This calculation confirms, at least in theory, that increasing the number of collected photons and the accuracy of the collimation can lead to better estimates in emission tomography. A good algorithm to fully benefit from this improved acquisition may remain a challenging point. It is to be expected that this calculation may stimulate such research in a near future.</p

Noisy fluctuation of heart rate indicates cardiovascular system instability.

International audienceHeart rate spontaneously fluctuates despite homeostatic regulatory mechanisms to stabilize it. Harmonic and fractal fluctuations have been described. Non-harmonic non-fractal fluctuation has not been studied because it is usually thought that it is caused by apparatus noise. We hypothesized that this fluctuation looking like apparatus noise (that we call “noisy fluctuation”) is linked to challenged blood pressure stabilization and not to apparatus noise. We assessed noisy fluctuation by quantifying the small and fastest beat-to-beat fluctuation of RR-interval by means of spectral analysis (Nyquist power of heart rate variability: nyHRV) after filtering out its fractal component. We observed nyHRV in healthy supine subjects and in patients with vasovagal symptoms. We challenged stabilization of blood pressure by upright posture (by means of a head-up tilt table test). Head-up position on the tilt table dramatically decreased nyHRV (0.128&nbsp;±&nbsp;0.063 vs. 0.004&nbsp;±&nbsp;0.002,p&nbsp;&lt;&nbsp;0.01) in healthy subjects (n&nbsp;=&nbsp;12). Head-up position also decreased nyHRV in patients without vasovagal symptoms (n&nbsp;=&nbsp;24; 0.220&nbsp;±&nbsp;0.058 vs. 0.034&nbsp;±&nbsp;0.015,&nbsp;p&nbsp;&lt;&nbsp;0.05), but not in patients with vasovagal symptoms during a head-up tilt table test (age and sex paired, 0.103&nbsp;±&nbsp;0.041 vs. 0.122&nbsp;±&nbsp;0.069, not significant). Heart rate variability includes a physiological non-harmonic non-fractal noisy fluctuation. This noisy fluctuation indicates low engagement of regulatory mechanisms because it disappears when the cardiovascular system is challenged (upright posture). It also indicates cardiovascular instability because it does not disappear in upright patients before vasovagal syncope, a transient failure of cardiovascular regulation.</p

Computer assisted collimation gamma camera: a new approach to imaging contaminated tissues.

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CACAO a collimation means well suited for pixellated detectors.

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Cancer de la thyroïde et ablation par iode 131 sous Thyrogen: Quand doser la thyroglobuline?

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