Methods and apparatuses for assigning a QoS level to memory requests based on the number of currently outstanding memory requests. In order to allow as large an area as possible to be imaged with high resolution in a short time, the phase centres of the transmitting and receiving antennas are, according to the invention, moved on a circular path parallel to the respective digital focus planes of the imaging system, and are at the same time shifted linearly in a further direction parallel to the respective focus plane. Here, readings are assigned to the facial character strings according to the number of times characteristic symbols appear in facial characters. In an evaluation device of the speed measuring system the speed of the measuring body is formed from an actual output signal of the speed sensor according to an actual output signal of the distance sensor. The stent designs include both a six crown and an eight crown stent which exhibit flexibility and sufficient radial strength to support the vessel.