Final answer:
The trachea is a low-attenuation structure that allows the imaging beam to pass through more easily, appearing darker on radiological scans compared to denser structures like bones or iodine-filled vessels.
Step-by-step explanation:
The structure in the human body that is considered a low-attenuation structure is the trachea.
When considering radiological imaging, such as CT scans, 'attenuation' refers to how much the tissue reduces the intensity of the imaging beam. A low-attenuation structure allows more of the beam to pass through, appearing darker on the scan. For example, structures filled with air, such as the trachea, typically have low attenuation because air does not absorb or scatter the imaging beam as much as denser structures do.
In contrast, high-attenuation structures, such as an iodine-filled aorta, ribs, and calcified arteries, appear whiter on a CT scan because they absorb more of the imaging beam. Iodine contrasts are especially used to enhance the visibility of blood vessels and help to differentiate between different types of tissue.