Which value best represents the practical limit of spatial resolution for screen-film mammography?

• A. 15 lp/mm
• B. 9 lp/mm
• C. 25 lp/mm
• D. 6 lp/mm

Answer: (A)

Spatial resolution is limited by the imaging chain’s blur and noise—factors like the finite focal spot size, screen and film blur, motion, and quantum noise set a practical ceiling on how fine detail can be recorded. In conventional screen-film mammography, the usable resolving power sits around 15 line pairs per millimeter, meaning you can reliably discern about that level of detail before image quality degrades from blur and noise. Higher frequencies, such as 25 lp/mm, would require components and conditions that the system typically cannot sustain without losing contrast or increasing dose, while lower frequencies like 9 or 6 lp/mm describe coarser detail that the system can still show but doesn’t represent its maximum capability. So 15 lp/mm reflects the practical limit for this modality.