Which resolution is directly improved by using shorter pulses at higher frequencies?

• A. Temporal resolution
• B. Axial resolution
• C. Lateral resolution
• D. Contrast resolution

Answer: (B)

Shorter pulses at higher frequencies directly improve axial resolution. Axial resolution is how well we can distinguish two structures that lie along the direction of the ultrasound beam, and it depends on the spatial pulse length—the physical length of the emitted pulse. Higher frequency reduces wavelength, and a shorter pulse length reduces the distance over which a single pulse extends. Since axial resolution is roughly half the spatial pulse length, making the pulse shorter (and at higher frequency) tightens this distance, allowing two closely spaced structures along the beam to be seen as separate. Temporal resolution, lateral resolution, and contrast resolution are governed by other factors such as frame rate, beam width and focusing, and gray-scale processing, respectively, and are not directly improved by shorter pulses at higher frequencies.