In CT imaging, which of the following tissues has the highest Hounsfield Unit (HU) value?

• A Acute blood clot (~60–80 HU)
• B Calcified tissue/bone cortex (~400–1000 HU) ✓
• C Soft tissue muscle (~40–60 HU)
• D White matter of brain (~25–35 HU)

Explanation

Hounsfield Units are calibrated relative to water (0 HU) and air (-1000 HU). Dense cortical bone and calcifications have the highest HU values, ranging from +400 to +1000 HU, because calcium has much greater X-ray attenuation than soft tissue. Dense compact bone can reach up to +3000 HU. Acute blood clot (60–80 HU) is hyperdense relative to soft tissue due to globin protein. Muscle is 40–60 HU, and brain white matter is 25–35 HU. Fat is -80 to -120 HU. Understanding HU ranges is essential for characterizing lesions on CT (e.g., simple cyst 0–20 HU, lipoma <-80 HU, hemorrhage 60–80 HU).

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.