In ultrasound beam geometry, which zone is defined by the beam diameter increasing with distance from the transducer?

• A. Far Zone
• B. Near Field
• C. Focal Length
• D. Elevation Resolution

Answer: (A)

The main concept is how the ultrasound beam changes size as it travels away from the transducer. After the beam converges to its smallest cross-section at the focal point, it begins to diverge and its diameter increases with distance. This expanding region is the far field (often called the Fraunhofer zone). Beyond the focus, the beam gets wider as you go farther from the transducer. In contrast, the near field is the part before the focus where the beam is still converging toward that smallest diameter. The focal length is simply the distance from the transducer to that focal point, and elevation resolution concerns the beam’s thickness in the elevational direction, not the overall diameter growth with distance.