Which QC test ensures that CT numbers increase proportionally with increasing physical density?

Linearity testing in computed tomography is crucial because it assesses the relationship between the CT numbers, often referred to as Hounsfield units, and the physical densities of materials being imaged. This test ensures that as the physical density of an object increases, the corresponding CT number also increases in a proportional manner.

For example, if an object has a physical density that is twice as much as that of water, the CT number should reflect that dual increase, leading to precise imaging interpretations. Proper linearity indicates that the CT system is accurately representing variations in physical density, which is vital for diagnosing various conditions accurately.

In contrast, other quality control tests serve different purposes. Accuracy testing verifies that the CT numbers correspond correctly to known densities, but it does not directly assess the proportional relationship across a range of densities. Uniformity testing ensures that the CT numbers are consistent throughout the imaging field, while contrast resolution refers to the system’s ability to distinguish between small differences in density, not directly measuring the proportionality of numbers to density changes. Thus, linearity is the essential choice for assessing the integrity of the relationship between CT numbers and physical density.