This paper considers the problem of a tele-echography through a new slave robot carrying an ultrasound probe for remote echographic diagnostic application. This robot is integrated in a master-slave system called 'Robotic Platform for an Interactive Tele-echographic System' (PROSIT ANR French national project). The proposed approach is based on motion capture of an expert gestures during the echography examination. The medical gestures were analyzed in term of position and velocities; the result has been used in the definition of the kinematics specifications of the proposed manipulator. The effective workspace size of a standard echography act, done by medical expert, is determined through an experimental study. The evaluation of the workspace is based on the use of the Vicon Nexus motion capture system. The spherical parallel mechanism (SPM) has been selected because of its characteristics meet the constraints requirements. This architecture offers an excellent stiffness, high precision and a light weight. The design problem of a new parallel probe-holder robot according to the identified experimental workspace for the tele-echography system is presented. In this work, in order to increase the workspace volume of manipulator, a minimal set of geometrical parameters of spherical parallel manipulators are optimized to find the maximum workspace. Seven independent parameters have been identified. The optimal synthesis of spherical parallel manipulators is performed using real-coded genetic algorithms (GA) based method. An optimal study of the orientation workspace is also addressed.