The tree plays a major ecological role in modern cities. The management of the plants is the subject of requests from urban operators: the diagnosis is essentially visual, even when the extent of internal damage and the associated hazard cannot be precisely evaluated by simple observation. Ultrasonic imaging methods allow answering biological questions related to the adaptation of the tree to exogenous constraints, such as pathogenic attacks, presence, and type of internal damages, the extent of degraded or traumatized areas. The major scientific issues are linked to the image production (reconstruction of the intrinsic parameter from a set of measurements) and to the image interpretation (discrimination for detection of alterations and its positioning). The overall aim of this thesis was to develop an ultrasonic imaging method for the diagnosis of the internal condition of urban trees. The scientific objectives were to develop numerical models to study the factors of influence on the propagation of ultrasonic waves in the cross-section of a tree and to propose an image reconstruction solution, suited for orthotropic materials, allowing the discrimination and positioning of decay. The development of a protocol for the acquisition, processing, analysis and interpretation of ultrasound tomography signals and images is of great importance for wood science. Obtaining reliable and interpretable images is a recurring demand from urban operators. Initially, to set-up the ultrasonic chain of measurement, a comparative experimental study was done to choose the excitation signal parameters, such as shape, temporal duration, and frequency response, and then the choice of a suitable time-of-flight determination technique. Then, we were concerned on evaluating the influence of the orthotropic condition of wood on the propagation of ultrasonic waves, by performing a time-of-flight (TOF) estimation using a raytracing approach, a method used in the field of exploration seismography