Lateral resolution is primarily determined by which beam property across the scan plane, and can be improved by focusing and higher frequency?

• A. Depth of focus
• B. Wavelength
• C. Lateral resolution is governed by beam width across the scan plane; improved by focusing and higher frequency
• D. Attenuation

Answer: (C)

Lateral resolution is determined by how wide the ultrasound beam is across the scan plane. When the beam is narrow, two reflectors that sit side by side can be distinguished; a wide beam blurs them together. Focusing sharpens the beam, creating a tighter main lobe around the focal point and improving lateral resolution in that region. Using a higher frequency also helps because shorter wavelengths diffract less, leading to a narrower beam for a given aperture and thus better lateral resolution—within the depth where the beam remains well-focused. Keep in mind, higher frequency reduces penetration due to greater attenuation, so the improvement is most evident where the beam stays narrow. Depth of focus describes how long the beam stays narrow along depth, not the immediate lateral resolution, and attenuation relates to signal loss rather than the ability to separate closely spaced objects.