Which statement best describes the relationship between CT numbers and electron density?

The correct statement highlights that CT numbers, also known as Hounsfield Units, are linearly proportional to electron density over a limited range. This relationship is significant in medical imaging and dosimetry because CT numbers offer a standardized way to evaluate the composition of tissues based on their electron density.

In practice, when imaging is performed using a CT scan, the signals generated correspond to varying densities of materials, typically ranging from air (-1000 HU) to dense bone (+1000 HU). The linearity within a limited range indicates that for many soft tissues, there is a consistent and predictable relationship between the measured CT number and the actual electron density of that tissue. This relationship is invaluable for accurately assessing tissue properties when planning treatments in medical dosimetry.

While CT numbers do not provide absolute measurements of density, their relative values across different types of tissues can still inform clinical decisions. Knowledge of this relationship aids in ensuring precise radiation dose calculations, as accurate electron density values are necessary for establishing treatment plans based on the specific tissues being irradiated.