A round transducer in which the elements are arranged concentrically and creates a cone shaped beam that is symmetric in all dimensions.

A round transducer in which the elements are arranged concentrically and creates a cone shaped beam that is symmetric in all dimensions.

• A. Linear array
• B. Phased array
• C. Annular array
• D. Curved array

Answer: (C)

Understanding how the shape of the active elements shapes the ultrasound beam is key. An annular array uses concentric circular rings as its elements, creating a circular aperture. This circular symmetry means the emitted wavefronts combine to form a beam that is largely the same in all directions around the axis, producing a conical, axisymmetric beam. When the rings are excited with appropriate timing, you get dynamic focusing and a narrow beam that maintains symmetry laterally and elevationally. Other layouts don’t produce that same uniform symmetry. A linear array, with rectangular elements in a line, tends to produce a fan-shaped beam that isn’t symmetric in all directions. A curved array alters the aperture shape but doesn’t inherently guarantee a perfectly circular, axisymmetric cone beam. A phased array refers to the electronic focusing and steering method and can apply to various geometries, but the distinctive round, concentric-ring arrangement yielding a cone-shaped, symmetric beam specifically points to an annular array.

Understanding how the shape of the active elements shapes the ultrasound beam is key. An annular array uses concentric circular rings as its elements, creating a circular aperture. This circular symmetry means the emitted wavefronts combine to form a beam that is largely the same in all directions around the axis, producing a conical, axisymmetric beam. When the rings are excited with appropriate timing, you get dynamic focusing and a narrow beam that maintains symmetry laterally and elevationally.

Other layouts don’t produce that same uniform symmetry. A linear array, with rectangular elements in a line, tends to produce a fan-shaped beam that isn’t symmetric in all directions. A curved array alters the aperture shape but doesn’t inherently guarantee a perfectly circular, axisymmetric cone beam. A phased array refers to the electronic focusing and steering method and can apply to various geometries, but the distinctive round, concentric-ring arrangement yielding a cone-shaped, symmetric beam specifically points to an annular array.