What is the calculation formula for CT number using the linear coefficient?

The calculation formula for the CT number is defined based on the attenuation coefficients of the tissue being measured (u tissue) and that of water (u water). The CT number, also known as Hounsfield units, quantifies the degree to which a material attenuates X-ray beams compared to water.

The correct formula, which is option B, is derived from the difference between the linear attenuation coefficient of the tissue and that of water. By taking the expression (u tissue - u water), we can determine how much more or less the tissue attenuates radiation compared to water. Dividing by the attenuation coefficient of water (u water) standardizes this value and is then multiplied by 1000 to scale it to Hounsfield units.

This approach allows for easy differentiation of various tissues based on their density and atomic composition, ultimately permitting their identification in CT imaging. The CT number is crucial for assessing various conditions and aids in diagnostic imaging by providing a quantitative measure of the radiodensity of tissues.

The formula reflects the fundamental way in which CT imaging works: measuring how different substances absorb X-rays relative to a reference material—water. This relative comparison is essential for creating detailed images that can guide clinical decision-making.