Infographics / Ultrasound Physics

Axial vs lateral (azimuthal) resolution

An ultrasound beam narrows from the transducer to a focus and then diverges. In the near field a short pulse (spatial pulse length, SPL) meets two reflectors one behind the other along the beam axis; axial resolution equals about half the SPL. At the focus two reflectors sit side by side separated by one beam width; lateral resolution equals the beam width and is best at the focus. Captions note axial resolution improves with higher frequency, shorter pulse and more damping, while lateral resolution improves with focusing and a narrower beam, and axial resolution is usually better than lateral.

Axial versus lateral resolution of an ultrasound beam An ultrasound beam narrows from the transducer to a focus and then diverges. In the near field a short pulse (spatial pulse length, SPL) meets two reflectors one behind the other along the beam axis; axial resolution equals about half the SPL. At the focus two reflectors sit side by side separated by one beam width; lateral resolution equals the beam width and is best at the focus. Captions note axial resolution improves with higher frequency, shorter pulse and more damping, while lateral resolution improves with focusing and a narrower beam, and axial resolution is usually better than lateral. Axial and lateral resolution of an ultrasound beam transducer SPL axial resolution ≈ ½ SPL focus lateral resolution = beam width Axial (along the beam) ≈ ½ SPL — sharper with higher frequency, shorter pulse, more damping. Lateral (across the beam) = beam width — sharper with focusing or a narrower beam; best at focus. Axial resolution is usually better than lateral resolution.
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