The Physics and Technology of Diagnostic Ultrasound: A Practitioner's Guide. Robert Gill

and receives along this line of sight. However, the display simply shows echo amplitude as a function of depth, as shown in Figure 3.17.

      This type of display was widely used in the early days of diagnostic ultrasound. It is rarely used now, except occasionally in some eye scans. Its attractions are its simplicity and the ability to measure the depth of the various echoes accurately.

      Figure 3.17 An A-mode display.

      Suggested activities

      1 Get an example of an image from each of the three types of probes described above (i.e. linear, curved and phased arrays). Consider where the lines of sight are in each case (i.e. where the machine directed the beam as it built up the image).

      2 Examine the three images carefully for any visual clues to support your assertion regarding the lines of sight (e.g. the overall shape of the image and the position and direction of artifacts such as shadowing and enhancement, which are discussed in detail in chapter 6).