Which modalities have a spatial resolution of 1.5 lp/mm?

• A. Ultrasonography
• B. Digital radiography
• C. MRI and CT
• D. Screen-Film Radiography

Answer: (C)

Spatial resolution in imaging is about how finely details can be distinguished, and it’s often described in line pairs per millimeter (lp/mm). A value around 1.5 lp/mm indicates a modest ability to separate fine details, which is typical for modalities that image in slices and rely on voxel sampling rather than capturing very fine surface detail.

MRI and CT commonly deliver about this level of detail because their image formation is voxel- or detector-limited rather than film-based. In routine practice, the smallest resolvable features translate to roughly 1 mm voxels in CT and MRI, which corresponds to about 1–2 lp/mm; 1.5 lp/mm sits right in that range. That makes MRI and CT the modalities that match this specific, relatively low spatial-resolution value.

Screen‑film radiography (and even many digital radiography systems) can capture substantially higher spatial frequencies, yielding far more than 1.5 lp/mm, while ultrasound, though capable of high resolution in some directions, is not typically characterized in lp/mm in the same way as CT or MRI.