Contrast in ultrasound imaging is determined by the machine and is manifested as differences in:

• A. Shades of gray
• B. Frame rate
• C. Depth of field
• D. Phosphor brightness

Answer: (A)

Contrast in ultrasound imaging is about how the machine maps echo strength into brightness differences on the screen. When tissues have different echogenicity, the echoes they return differ in amplitude, and the system translates those amplitudes into varying shades of gray. That grayscale mapping—the dynamic range and compression settings of the machine—defines how distinct those tissue differences appear, so contrast shows up as differences in shades of gray.

Frame rate affects temporal resolution (how smoothly motion is displayed), not the brightness differences between structures. Depth of field concerns focusing and how sharp the image is at various depths, not the relative brightness of tissues. Phosphor brightness relates to display technology and is not the primary factor determining image contrast in modern ultrasound.