Which region of the beam between the transducer and the focal point decreases in size as it approaches the focus?

• A. Near zone
• B. Far field
• C. Focal region
• D. Fresnel zone

Answer: (A)

In ultrasound, the beam is converging as it travels from the transducer toward its focus, so its cross‑section becomes smaller the closer you get to the focal point. This region, where the beam narrows before reaching the smallest diameter at focus, is the near field. The near field is also described as the Fresnel zone in many texts, but the question is specifically pointing to the portion from the transducer to the focus, where the beam width decreases. Beyond the focus, the beam then begins to diverge in the far field. The focal region describes the area around the focus itself, not the entire path leading up to it.