Axial resolution is also referred to as which of the following?

• A. Longitudinal (Axial) Resolution
• B. Lateral Resolution
• C. Temporal Resolution
• D. Elevation Resolution

Answer: (A)

Axial resolution describes the ability to distinguish two reflectors that lie along the path of the ultrasound beam, in the depth (along-beam) direction. Because this dimension runs along the beam, it is also called longitudinal resolution, or depth resolution. The limit of axial resolution comes from the spatial pulse length, so shorter pulses yield better axial resolution. Spatial pulse length depends on the number of cycles in the pulse and the wavelength; using higher frequency transducers or fewer cycles shortens the pulse and improves depth (axial) separation. Two reflectors must be separated by about half the spatial pulse length to be seen as distinct along the beam. In contrast, lateral resolution depends on beam width across the image, temporal resolution on frame rate, and elevation resolution on the out-of-plane dimension.