Which modality shows 4 lp/mm resolution?

• A. Screen-Film Radiography
• B. Digital radiography
• C. Computed radiography
• D. Fluoroscopy

Answer: (B)

Resolution in line pairs per millimeter reflects how finely a system can distinguish detail. In imaging, screen-film radiography delivers the highest inherent sharpness, often well beyond 4 lp/mm, because fine silver halide crystals and high-quality screens capture very small details. Fluoroscopy is designed for real-time imaging and dose efficiency, so its spatial resolution is typically modest, around 1–2 lp/mm. Computed radiography uses storage phosphor plates, whose practical resolution generally falls in the low single digits, roughly 2–3 lp/mm, depending on the system. Digital radiography, with modern flat-panel detectors and small pixel sizes, is commonly around 3–5 lp/mm, and many units sit near 4 lp/mm. The figure of 4 lp/mm therefore fits digital radiography best, reflecting its detector-based sampling limit rather than the higher resolution of film or the lower resolution of live fluoroscopy.