Axial resolution is improved by which change?

Axial resolution is improved by which change?

• A. Decreases spatial pulse length
• B. Decreased pulse amplitude
• C. Decreased imaging depth
• D. Decreased pixel size

Answer: (A)

Axial resolution depends on how long the transmitted pulse is along the beam, i.e., the spatial pulse length. Shorter spatial pulse length lets two structures that are close together in the direction of the beam be distinguished as separate echoes. Spatial pulse length is the product of the number of cycles in the pulse and the wavelength. Therefore, shortening the pulse length—by using fewer cycles in the pulse or by using a higher-frequency transducer that has a shorter wavelength—directly improves axial resolution. The other changes don’t improve axial resolution in the same way: lowering pulse amplitude mainly affects signal strength and penetration, not the ability to separate echoes along the beam; reducing imaging depth doesn’t inherently sharpen axial separation; and decreasing pixel size affects display sampling or lateral detail rather than the intrinsic along-the-beam resolution.

Axial resolution depends on how long the transmitted pulse is along the beam, i.e., the spatial pulse length. Shorter spatial pulse length lets two structures that are close together in the direction of the beam be distinguished as separate echoes. Spatial pulse length is the product of the number of cycles in the pulse and the wavelength. Therefore, shortening the pulse length—by using fewer cycles in the pulse or by using a higher-frequency transducer that has a shorter wavelength—directly improves axial resolution.

The other changes don’t improve axial resolution in the same way: lowering pulse amplitude mainly affects signal strength and penetration, not the ability to separate echoes along the beam; reducing imaging depth doesn’t inherently sharpen axial separation; and decreasing pixel size affects display sampling or lateral detail rather than the intrinsic along-the-beam resolution.