Abstract: The invention concerns a detecting apparatus (12) comprising:—at least two sensors (24, 26, 28), with at least one sensor (24) being an ultrasound transducer adapted to produce ultrasound waves, and—a positioning device (16) defining several compartments (22), each compartment (22) being adapted to hold a sensor (24, 26, 28) and each compartment (22) being located at predetermined location, the positioning device (16) comprising a holder adapted to be fixed on the skull of a subject, the positioning device (16) being adapted to be maintained on the head of the subject using the holder.