What is the average CT number for the lungs in Hounsfield units (HU)?

The average CT number for the lungs in Hounsfield units (HU) is typically around -500. This value reflects the density of lung tissue due to its air content, which is less dense than water and other soft tissues. The Hounsfield scale is used to measure radiodensity in computed tomography (CT) scans, where air has a CT number of approximately -1000, water is defined as 0, and dense tissues or bones provide higher positive values.

In the case of the lungs, the presence of air significantly reduces the density, leading to the average CT number falling around -500. This gives radiologists a standardized way to evaluate lung conditions and differentiate between various types of tissues and fluids that might be present in the thoracic cavity. Understanding this aspect of CT imaging is crucial for diagnosing pulmonary conditions effectively.