An ultrasonic apparatus for producing three dimensional images using at least one moving curved array transducer for scanning a volume of a region of interest to be imaged, said apparatus comprising: an acoustic front shell having a curved complex shape (23a, 23b, 24a, 24b) wherein a radius of curvature perpendicular to a rotation axle changes progressively from a central area thereof to the edges thereof; an ultrasonic curved linear transducer adapted for swinging movement around the rotation axle underneath said front shell and having a front surface of a shape conforming to the shape of the internal surface (23a, 24a) of said front shell; and drive means (4, 5) for providing said swinging movement of the ultrasonic array transducer around the rotation axle underneath said front shell so as to scan a volume of the region of interest; wherein the ultrasonic curved linear transducer comprises: an external focusing lens made of silicon rubber and including a front face having variable radius of curvature exactly corresponding to that of the front shell in front of said transducer, said variable radius of curvature varying in a manner such as to minimize the distance separating the front face of the focusing lens and the internal surface (23a, 24a) of the shell, and a piezoelectric member for emitting and receiving ultrasonic energy, said piezoelectric member being assembled beneath said focusing lens and having a variable surface curvature compensating for the variable radius of curvature of the focusing lens in a manner such as to enable the transducer to maintain a common elevational focus for all transducer elements of the array transducer, said transducer having an external elevation surface profile parallel to the corresponding internal profile (23a, 24a) of the front shell of the probe. an acoustic front shell having a curved complex shape (23a, 23b, 24a, 24b) wherein a radius of curvature perpendicular to a rotation axle changes progressively from a central area thereof to the edges thereof; an ultrasonic curved linear transducer adapted for swinging movement around the rotation axle underneath said front shell and having a front surface of a shape conforming to the shape of the internal surface (23a, 24a) of said front shell; and drive means (4, 5) for providing said swinging movement of the ultrasonic array transducer around the rotation axle underneath said front shell so as to scan a volume of the region of interest; wherein the ultrasonic curved linear transducer comprises: an external focusing lens made of silicon rubber and including a front face having variable radius of curvature exactly corresponding to that of the front shell in front of said transducer, said variable radius of curvature varying in a manner such as to minimize the distance separating the front face of the focusing lens and the internal surface (23a, 24a) of the shell, and a piezoelectric member for emitting and receiving ultrasonic energy, said piezoelectric member being assembled beneath said focusing lens and having a variable surface curvature compensating for the variable radius of curvature of the focusing lens in a manner such as to enable the transducer to maintain a common elevational focus for all transducer elements of the array transducer, said transducer having an external elevation surface profile parallel to the corresponding internal profile (23a, 24a) of the front shell of the probe. an external focusing lens made of silicon rubber and including a front face having variable radius of curvature exactly corresponding to that of the front shell in front of said transducer, said variable radius of curvature varying in a manner such as to minimize the distance separating the front face of the focusing lens and the internal surface (23a, 24a) of the shell, and a piezoelectric member for emitting and receiving ultrasonic energy, said piezoelectric member being assembled beneath said focusing lens and having a variable surface curvature compensating for the variable radius of curvature of the focusing lens in a manner such as to enable the transducer to maintain a common elevational focus for all transducer elements of the array transducer, said transducer having an external elevation surface profile parallel to the corresponding internal profile (23a, 24a) of the front shell of the probe.