Which material has the highest possible Hounsfield unit value based on the ranges provided?

Which material has the highest possible Hounsfield unit value based on the ranges provided?

• A. Metal
• B. Bone
• C. Water
• D. Air

Answer: (A)

Hounsfield units measure how strongly a material attenuates X-rays relative to water. The scale runs from about -1000 for air to 0 for water, with higher numbers indicating greater attenuation. The amount of attenuation increases with density and atomic number, so very dense materials attenuate X-rays far more than bone, water, or air. Metals, because of their high density and electron count, push the HU value to the top end of the scale and often reach the scanner’s maximum display value. That’s why metal is the highest HU on typical ranges. Air is the lowest, bone is high but not as high as most metals, and water sits at 0.

Hounsfield units measure how strongly a material attenuates X-rays relative to water. The scale runs from about -1000 for air to 0 for water, with higher numbers indicating greater attenuation. The amount of attenuation increases with density and atomic number, so very dense materials attenuate X-rays far more than bone, water, or air. Metals, because of their high density and electron count, push the HU value to the top end of the scale and often reach the scanner’s maximum display value. That’s why metal is the highest HU on typical ranges. Air is the lowest, bone is high but not as high as most metals, and water sits at 0.