CTnummer

CTnummer, also known as the CT number or Hounsfield Unit (HU), is a quantitative measure of radiodensity used in computed tomography (CT) scans. It represents the X-ray attenuation of a specific tissue or material relative to water. The scale is calibrated such that the CT number of pure water is 0 HU, and the CT number of air is -1000 HU.

These numbers are derived from the linear attenuation coefficient of a voxel (a three-dimensional pixel) in the scanned object. Different tissues and materials have distinct CT numbers based on their composition and density. For instance, bone typically has high CT numbers (around 1000 HU or more) due to its high mineral content, while soft tissues like fat have lower CT numbers (ranging from -50 to -100 HU). Blood has a CT number of approximately 40-60 HU, and cerebrospinal fluid is around 10-20 HU.

CT numbers are crucial for image interpretation and analysis in medical imaging. They allow radiologists and clinicians to differentiate between various tissues, identify abnormalities like tumors or calcifications, and monitor the effectiveness of treatments. In medical imaging, the displayed grayscale value of a pixel is directly related to its CT number, enabling visual distinction between structures. Beyond medicine, CT numbers are also utilized in industrial applications for material characterization and quality control. The precise range and interpretation of CT numbers can vary slightly depending on the specific CT scanner and reconstruction algorithms used.