A Prospective Study on Algorithms Adapted to the Spatial Frequency in Tomography

The use of iterative algorithms in tomographic reconstruction always leads to a frequency adapted rate of convergence in that low frequencies are accurately reconstructed after a few iterations, while high frequencies sometimes require many more computations. In this paper, we propose to build frequency adapted (FA) algorithms based on a condition of incomplete backprojection and propose an FA simultaneous algebraic reconstruction technique (FA-SART) algorithm as an example. The results obtained with the FA-SART algorithm demonstrate a very fast convergence on a highly detailed phantom when compared to the original SART algorithm. Though the use of such an FA algorithm may seem difficult, we specify in which case it is relevant and propose several ways to improve the reconstruction process with FA algorithms

Connectivity-Based Parcellation of the Cortical Mantle Using q-Ball Diffusion Imaging

This paper exploits the idea that each individual brain region has a specific connection profile to create parcellations of the cortical mantle using MR diffusion imaging. The parcellation is performed in two steps. First, the cortical mantle is split at a macroscopic level into 36 large gyri using a sulcus recognition system. Then, for each voxel of the cortex, a connection profile is computed using a probabilistic tractography framework. The tractography is performed from q fields using regularized particle trajectories. Fiber ODF are inferred from the q-balls using a sharpening process focusing the weight around the q-ball local maxima. A sophisticated mask of propagation computed from a T1-weighted image perfectly aligned with the diffusion data prevents the particles from crossing the cortical folds. During propagation, the particles father child particles in order to improve the sampling of the long fascicles. For each voxel, intersection of the particle trajectories with the gyri lead to a connectivity profile made up of only 36 connection strengths. These profiles are clustered on a gyrus by gyrus basis using a K-means approach including spatial regularization. The reproducibility of the results is studied for three subjects using spatial normalization

Desmoplastic small round cell tumor: impact of 18F-FDG PET induced treatment strategy in a patient with long-term outcome

The desmoplastic small round cell tumor (DSRCT) is an uncommon and highly aggressive cancer. The role of 18F-FDG PET in management of DSRCT is little reported. We report a case of metastasized abdominal DSRCT detected in a 43-year old patient whose diagnostic and therapeutic approaches were influenced by 18F-FDG PET-CT. The patient is still alive ten years after diagnosis. 18F-FDG PET-CT seems to be a useful method for assessing therapeutic efficiency and detecting early recurrences even in rare malignancies such as DSRCT

Multiple-contrast X-ray micro-CT visualization of colon malformations and tumours in situ in living mice

International audienc

In vivo preclinical low field MRI monitoring of tumor growth following a suicide gene therapy in an orthotopic mice model of human glioblastoma

International audienc

Descripteurs elliptiques de Fourier des contours à trois dimensions (résultats théoriques et applications à l'analyse morphologique en imagerie médicale)

STRASBOURG-Medecine (674822101) / SudocSudocFranceF

Imagerie de diffusion à haute résolution angulaire (étude du modèle q-ball par couplage simulations-fantômes et applications au suivi de fibres et à la parcellisation du cortex)

Par la mesure du déplacement des molécules d'eau au niveau microscopique, l'IRM de diffusion permet d'étudier la microstructure des tissus de la matière blanche de façon non invasive. Dans ce travail de thèse, nous nous intéressons au problème direct soulevé par l'IRM de diffusion : connaissant une géométrie de croisement de fibre précise, quel est le signal fourni par cette technique ? Pour cela nous avons réalisé des fantômes physiques de diffusion, qui, à partir d'acquisitions sur IRM, vont pouvoir nous aider à valider le modèle q-ball. Nous avons également réalisé un simulateur numérique afin de comparer les résultats acquis et simulés. L'une des applications les plus attractives de l'IRM de diffusion est le suivi des faisceaux de fibres de la matière blanche. Pour résoudre ce problème inverse, nous proposons un algorithme de tractographie probabiliste régularisé, utilisant le modèle q-ball. Par delà la simple reconstruction visuelle des trajectoires des faisceaux de fibres de la substance blanche, l'IRM de diffusion et les algorithmes de tractographie permettent d'inférer la connectivité anatomique cérébrale. Nous nous sommes donc également intéressés à la parcellisation du manteau cortical à partir des informations de connectivité. Les enjeux de ce travail sont multiples :L interprétation de la mesure fournie par l'IRM de diffusion n'est pas encore maîtrisée dans son ensemble. Il est donc nécessaire de travailler sur des fantômes physiques ou numériques pour mieux comprendre le phénomène. D'autre part, la structure du cerveau humain est encore mal connue et les outils de tractographie fournis par l'IRM de diffusion permettent de progresser dans ce domaine.In white matter, at microscopic scale, water molecule movement is mainly distributed along axonal fiber bundles. Thanks to the measurement of this water displacement, diffusion MRI allows to study uninvasively white matter tissue microstructure. We interest here first to direct model, raised by diffusion MRI: given a fiber crossing geometry, how is the generated signal? In intend to reply, we developed diffusion physical phantoms and a numerical simulator so that we can compare acquired and simulated results from q-ball model. One of the most powerful application of diffusion MRI is white matter fiber tracking. To resolve this inverse problem, we proposed a new algorithm to infer fiber bundle from q-ball imaging data. This algorithm combines the idea of performing a probabilistic tractography with regularization of the curvature of fiber trajectories. The method is first validated with diffusion phantoms, and then the method is successfully applied to the detection of the auditory tract in three human subjects. Well beyond the simple visualization of fiber bundles, fiber tracking algorithms allow to infer anatomical brain connectivity. We finally addressed the parcellation of cortical mantel using connectivity profiles. The reproducibility of the results is studied for three subjects. Future prospects of this work are numerous: first, diffusion MRI measurement is still not clear and it is necessary to work with numerical or physical phantoms, in order to better understand the phenomenon. Finally, human brain is still far to be well known and tractography algorithms, dint diffusion MRI, constitute an important advance in this field.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Evaluation de la fonction hépatobiliaire de la souris par imagerie scintigraphique

STRASBOURG-Medecine (674822101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Intérêt de l'imagerie par tomographie d'émission de positons au fluorodéoxyglucose dans les infections osseuses

STRASBOURG-Medecine (674822101) / SudocPARIS-BIUM (751062103) / SudocSTRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF