Abstract. This paper describes a segmentation technique for 2D interventional MR images of liver tumours. Two features of MR data were likely to challenge existing segmentation methods. The first one is the inhomogeneous intratumoral texture, while the second one is the "blurred" appearance and the non-uniform sharpness of the tumour boundary. In order to detect the region of interest, we create the tumour contour map using a multithresholding technique and a measure of similarity between successive contours. Tumours presenting boundaries with non-uniform sharpness are segmented with an algorithm based on pixel aggregation and local textural information.Résumé. Cet article décrit une méthode précise et fiable de segmentation pour des images RM des tumeurs de foie. Les approches traditionnelles de segmentation d'images ne donnent pas de bons résultats dans ce cas-là,à cause de deux caractéristiques particulières des données d'entrée : l'inhomogénéité de la texture intratumorale et l'apparence floue de la paroi des tumeurs. Pour détecter la région d'intérêt, nous créons une carte des contours de la tumeur en utilisant une technique de multi-seuillage et une mesure de similarité entre les contours successifs. Les tumeurs qui présentent des contours flous de contraste variable sont détectées avec un algorithme basé sur l'agrégation des pixels et sur l'information locale de texture.

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Abstract. This work deals with the treatment planning optimization for intravascular brachytherapy (IVB) in peripheral arteries. The objective is both to quantitatively study the validity of different hypotheses required for a reliable application of the treatment with current techniques, and to contribute to the definition and the specification of a new optimized procedure taking into account the actual patient's vessel geometry. The detection of vascular luminal surface was performed by an image analysis process, i.e. virtual active navigation, applied to standard CT data. Dose distribution was calculated according to the formalism proposed and recommended by the AAPM in TG43 and TG60. A method combining simulated annealing and BFGS algorithms was applied to optimize the parameters associated with the dwell points such as their number, positions, and dwell times. Dose-surface histogram (DSH) was used to evaluate the dose distribution results. Four levels of accuracy in target surface description were tested. The application of this optimization method to four different CT data sets including patient data, phantom and animal models showed that the treatment plan can be improved when the actual vessel geometry has been taken into account.

In most planning procedures of intravascular brachytherapy the lesion path is assumed to be a straight line and the dose distribution is essentially specified with respect to the seed. We propose a new approach for the planning of peripheral intravascular brachytherapy based on the characterization of the vessel by virtual exploratory navigation. In order to make the procedure more secure and reliable, the dosimetry planning takes actually account of the geometrical characteristics of the vessel (length, diameter, curvature). Virtual exploratory navigation constitutes the basis of optimal path planning (centering, positioning, trajectory definition) and dosimetry planning for high dose rate brachytherapy. In order to estimate the post-angioplasty vessel centerline and inner surface, a simplified simulation of the transluminal angioplasty procedure is performed using a single pre-angioplasty CT data set. Thanks to the dose rate computation performed in the whole CT volume, the irradiation of the surrounding anatomical structures can be anticipated. A virtual angioscopy like process is used to check the homogeneity of the dose distribution in the vessel wall. Preliminary results obtained from a phantom model and from an animal model of stenosis are reported.