High resolution acoustical imaging involves hard constraints for the ultrasonic probes which are used: a high resonance center frequency, a very wide bandwidth, a good sensitivity and a strong focusing of the beam. The system which is described uses two kinds of focused transducer: a very broad band 17 MHz center frequency transducer (PZT), and a 45 MHz copolymer transducer. The focal distances are respectively 7 mm and 6 mm in water. The movement of the transducer provides a 6 mm wide and 5 mm

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... deep echographic cross-section with at the rate of 15 images/s. The resolution is respectively at 17 MHz and 45 MHz, 80 ixm and 60 urn in axial and 250 nm and 60 \ira in lateral in the focal zone. The device was tested on fantoms in water and in vivo with applications in Dermatology.