Part 1 · Imaging Physics and Radiation Safety

4. Radiographic Densities, Exposure Factors and Image Quality

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Same concept, other depth: Foundation →

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Density	Appearance	Examples	Clinical use
Gas	black	lung, bowel, free air, surgical emphysema	pneumoperitoneum, pneumothorax
Fat	dark grey	subcutaneous fat, fat pads, lipoma, dermoid	displaced elbow fat pads, fat‑fluid level (lipohaemarthrosis)
Soft tissue / fluid	mid grey	heart, liver, muscle, blood, effusion	cannot separate blood, pus, water or tumour on a radiograph
Calcium / bone	white	bone, calcified stones, phleboliths	fractures, calculi
Metal / contrast	brightest	prosthesis, bullets, barium, iodine	devices, contrast studies

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Density

Appearance

Examples

Clinical use

Gas

black

lung, bowel, free air, surgical emphysema

pneumoperitoneum, pneumothorax

Fat

dark grey

subcutaneous fat, fat pads, lipoma, dermoid

displaced elbow fat pads, fat‑fluid level (lipohaemarthrosis)

Soft tissue / fluid

mid grey

heart, liver, muscle, blood, effusion

cannot separate blood, pus, water or tumour on a radiograph

Calcium / bone

white

bone, calcified stones, phleboliths

fractures, calculi

Metal / contrast

brightest

prosthesis, bullets, barium, iodine

devices, contrast studies