An apparatus for the treatment of a target (C) by pressure waves, comprising a determining device for determining the exact position of the target (C) relative to a reference point (O) for use in the treatment of target (C), comprising:
- an emission device having a radiation source and positioned in a known position relative to the reference point (O) on a side of said target (C), for irradiating a zone containing said target (C);
- a receiver in the form of a bar comprising a linear active part formed from a multiplicity of discrete radiation-sensitive elements defining a line, and whose positions in space are known, said receiver being positioned on a side of said target (C) opposite the side having said emission device, for receiving a resultant image of said target (C) created by irradiation of said target by said emission device;
- means or simultaneously displacing said radiation source and said receiver according to a known displacing speed, and wherein said radiation source is activated at least one time during said displacement for providing at least one image of said target to said receiver;
- calculating means for calculating the position of the receiver at a given instant from the displacing time and from the known displacing speed;
- and
- determining means for determining the position of said target from at least one image of said target.