The focusing technique that uses a curved transducer element to create a focal zone is called

• A. External focusing
• B. Phased array focusing
• C. Lens focusing
• D. Internal focusing

Answer: (D)

Focusing in ultrasound relies on shaping the beam so that energy concentrates at a specific depth. When the transducer element itself is curved, it acts like its own lens, bending the emitted waves toward a focal point. This built-in, or internal, focusing creates a defined focal zone where the beam is narrowest, which enhances lateral resolution at that depth. The focus depth is determined by the curvature and geometry of the crystal, so it is fixed for a given transducer. Other methods achieve focusing without curving the element: an external lens placed in front of the transducer bends the beam, and phased array focusing uses electronic delays across multiple elements to steer and shape the focus at various depths. Because the description specifies a curved transducer element producing a focal zone, the technique is internal focusing.