The _____ the pulse duration, the better the axial resolution.

The _____ the pulse duration, the better the axial resolution.

• A. Shorter
• B. longer
• C. Higher
• D. Lower

Answer: (A)

Shorter pulse duration improves axial resolution because axial resolution depends on spatial pulse length—the physical distance the pulse occupies in tissue. A shorter pulse contains fewer cycles and travels a shorter distance before fading. When two reflectors lie close along the beam path, their echoes are separated in time only if the pulse length is short enough; a shorter spatial pulse length makes those echoes more distinct, so two closely spaced interfaces can be resolved along the beam axis. A longer pulse length spreads the echoes out more and blurs nearby interfaces, reducing axial resolution. Higher or lower don’t directly determine this specific effect—the crucial factor is how long the pulse lasts in tissue.

Shorter pulse duration improves axial resolution because axial resolution depends on spatial pulse length—the physical distance the pulse occupies in tissue. A shorter pulse contains fewer cycles and travels a shorter distance before fading. When two reflectors lie close along the beam path, their echoes are separated in time only if the pulse length is short enough; a shorter spatial pulse length makes those echoes more distinct, so two closely spaced interfaces can be resolved along the beam axis. A longer pulse length spreads the echoes out more and blurs nearby interfaces, reducing axial resolution. Higher or lower don’t directly determine this specific effect—the crucial factor is how long the pulse lasts in tissue.