With a 1D linear array, where in the out-of-plane dimension is the dimension of the sound beam the narrowest?

With a 1D linear array, where in the out-of-plane dimension is the dimension of the sound beam the narrowest?

• A. Point of mechanical focusing
• B. Point of electronic focusing
• C. The beam is the same width throughout the image
• D. In the far field

Answer: (A)

The out-of-plane (elevation) beam width is determined by focusing in that dimension. With a 1D linear array, elevation focusing is achieved mainly through mechanical focusing of the transducer, not by electronic steering like in the imaging plane. This mechanical focus concentrates the sound waves so the beam becomes the thinnest at the focal depth in the elevation direction. Away from that focal point, diffraction causes the beam to widen, so the slice thickness increases. The far field is where the beam is widest due to continued divergence. So the narrowest elevational beam occurs at the point of mechanical focusing.

The out-of-plane (elevation) beam width is determined by focusing in that dimension. With a 1D linear array, elevation focusing is achieved mainly through mechanical focusing of the transducer, not by electronic steering like in the imaging plane. This mechanical focus concentrates the sound waves so the beam becomes the thinnest at the focal depth in the elevation direction. Away from that focal point, diffraction causes the beam to widen, so the slice thickness increases. The far field is where the beam is widest due to continued divergence. So the narrowest elevational beam occurs at the point of mechanical focusing.