In CT, what does a positive Hounsfield unit value indicate about tissue density?

In CT, what does a positive Hounsfield unit value indicate about tissue density?

• A. It indicates density less than water; e.g., fat
• B. It indicates density equal to water
• C. It indicates density equal to air
• D. It indicates density greater than water; e.g., bone ~1000 HU

Answer: (D)

In CT imaging, Hounsfield units quantify how much a tissue attenuates X-rays, using water as the reference point at 0 HU. Positive values indicate tissues denser than water, meaning they attenuate more X-rays. Air is about -1000 HU, fat is negative HU, and bone is around +1000 HU, with soft tissues typically near 0 to a few dozen HU. So a positive HU value signals density greater than water, such as bone.

In CT imaging, Hounsfield units quantify how much a tissue attenuates X-rays, using water as the reference point at 0 HU. Positive values indicate tissues denser than water, meaning they attenuate more X-rays. Air is about -1000 HU, fat is negative HU, and bone is around +1000 HU, with soft tissues typically near 0 to a few dozen HU. So a positive HU value signals density greater than water, such as bone.