Structures Insonated at 90 Degrees

Structures insonated, i.e. struck by sound waves, at 90 degrees will generate an echo that is directed back to the transducer (image, below left).

In the transverse view of the abdominal aorta (image, below, right), the lateral borders are ill-defined. For this reason the antero-posterior measurement is used, as calliper placement is more precise and the measurement reproducible.