What is the minimum difference in HU needed for two tissues to be visibly different on a CT scan?

In computed tomography (CT), HU (Hounsfield Units) are key to differentiating between various tissues based on their density. For two tissues to be visibly distinct on a CT scan, a minimum difference of 10 HU is typically required. This threshold is significant because it allows for sufficient contrast between structures, enabling clearer differentiation when interpreting scans.

Tissues that are similar in density may not be distinguishable if the difference in their Hounsfield Units falls below this 10 HU threshold. This is particularly relevant in clinical practice where precise diagnosis can depend on recognizing subtle differences between tissues, such as distinguishing between different types of lesions or assessing the integrity of surrounding tissues.

A difference of less than 10 HU could result in tissues appearing the same or too similar, which can lead to challenges in diagnosis and interpretation. Therefore, the 10 HU distinction is grounded in both the physics of how CT imaging works and practical experience in radiological assessment.