What is another name for the far zone in an ultrasound beam?

The far zone of an ultrasound beam is commonly referred to as the Fraunhofer zone. This terminology comes from the field of optics, where the Fraunhofer region is characterized by being far enough from the source of a wave that the wavefronts can be considered parallel. In ultrasound, the far zone represents the area beyond the near zone, where the ultrasound beam expands and begins to diverge. This is important for understanding how sound waves behave in tissue and the implications for imaging and resolution. In the far zone, the spatial resolution begins to decrease due to the divergence of the ultrasound beam.

The other terms, such as the near zone (or Fresnel zone), refer to different areas of the ultrasound beam. The near zone is the region close to the transducer where the beam is more focused, and the Fresnel zone is essentially another term for the near zone. The shadow zone is an area behind a large object in the imaging field where fewer ultrasound waves are received. Understanding these terms helps to clarify the physics of ultrasound imaging and ensures that sonographers can effectively interpret ultrasound images based on beam behavior in various zones.