Which term refers to the number of scan lines per frame in an ultrasound image?

• A. Line density
• B. Frame rate
• C. Spatial resolution
• D. Pixel density

Answer: (A)

Line density is the term for the number of scan lines that make up one ultrasound frame. Each frame is built from many individual scan lines, so increasing the lines per frame raises line density and enhances lateral sampling across the image. This improves the ability to resolve fine details side-to-side, but it can reduce frame rate if the system must acquire more lines in the same amount of time. The other terms address different ideas: frame rate is how many frames appear per second, not how many lines per frame; spatial resolution is the overall ability to distinguish two closely spaced structures (influenced by line density but not a direct count of lines); and pixel density refers to the digital sampling of the image grid, not the physical scan lines used to form a frame.