Which statement about attenuation and density in CT is true?

Which statement about attenuation and density in CT is true?

• A. Air has the highest Hounsfield unit values
• B. Water has the highest Hounsfield unit values
• C. Bone has very high Hounsfield unit values
• D. Fat has higher Hounsfield units than water

Answer: (C)

Attenuation in CT is expressed as Hounsfield units, which translate how much a tissue reduces the X-ray beam. This scale links density and atomic number to a numeric value: higher density and higher effective atomic number give higher HU. Water is the baseline at 0 HU, and air sits far below at about -1000 HU, while fat is just below water around -100 HU. Soft tissues fall in the positive range of tens of HU, depending on composition. Bone stands out because of its mineral content, which causes strong X-ray attenuation, yielding very high HU values—often in the hundreds to thousands. That extreme attenuation makes bone appear bright on CT images. So the statement that bone has very high Hounsfield unit values is the true one.

Attenuation in CT is expressed as Hounsfield units, which translate how much a tissue reduces the X-ray beam. This scale links density and atomic number to a numeric value: higher density and higher effective atomic number give higher HU. Water is the baseline at 0 HU, and air sits far below at about -1000 HU, while fat is just below water around -100 HU. Soft tissues fall in the positive range of tens of HU, depending on composition. Bone stands out because of its mineral content, which causes strong X-ray attenuation, yielding very high HU values—often in the hundreds to thousands. That extreme attenuation makes bone appear bright on CT images. So the statement that bone has very high Hounsfield unit values is the true one.