Signal amplitude processing

The beam-forming techniques described in the previous chapter are used to acquire echo information from different parts of the imaged cross section by selection of the transducer array elements and manipulation of the relative timings of their transmit and receive signals. These yield echo sequences, which represent the B-mode image lines and define the spatial properties of the image. The brightness of the image at each point along the B-mode line is determined by the amplitude of the echo signals received at the transducer. The echo signals must be processed to produce the final image brightness. The processing methods used are described in this chapter.

Figure 4.1 illustrates, in block-diagram form, the essential elements of the complete B-mode system, and shows that the B-mode amplitude information is processed in various ways before storage in the image memory, from where the image is displayed. Although it is probably easiest to imagine that, as illustrated, amplitude processing is applied to the B-mode image lines only after the beam-former, in practice some must be applied at an earlier stage to allow the beam-forming processes to be carried out. Also, some processing may be carried out after the image memory to improve the displayed image or optimize its characteristics for a particular clinical application.