What does air cavity density appear as on a CT image?

On a CT image, air cavity density appears as black. This is due to the fact that air has a significantly lower density compared to soft tissue or bone, resulting in less attenuation of the X-ray beams as they pass through the air-filled cavity. When the X-rays are less attenuated, the corresponding pixel values on the CT image are lower, often represented as darker areas or black.

In CT imaging, different tissues absorb X-rays at different rates, and this is portrayed in shades of gray on the images. For instance, denser tissues such as bone appear white due to higher attenuation, while soft tissues generally appear in varying shades of gray. Therefore, the appearance of air as black is a key aspect in distinguishing it from other tissues on a CT scan. Understanding this density differentiation is crucial for medical dosimetrists in analyzing imaging and planning treatment strategies.