What is a consequence of using a lower-frequency transducer for deep tissue imaging?

• A. It penetrates deeper but with poorer spatial (axial) resolution
• B. It increases axial resolution but reduces penetration
• C. It has no effect on depth or resolution
• D. It worsens lateral resolution only

Answer: (A)

Lower-frequency transducers trade resolution for penetration. In soft tissue, attenuation grows with frequency, so a lower frequency experiences less attenuation and can travel deeper before the signal weakens, letting you image structures that are farther away. However, axial resolution depends on the spatial pulse length, which is tied to wavelength and the number of cycles in the pulse. A longer wavelength at lower frequency means a longer spatial pulse length, so echoes that are close together along the beam path can’t be distinguished as finely. So you get deeper imaging but poorer axial detail. (Lateral resolution can also suffer due to a broader beam at depth, but the main point here is the deeper penetration with reduced axial resolution.)