Final answer:
Negative contrast agents have a lower specific gravity, which can be used in medical imaging to enhance contrast. Specific gravity is the ratio of a substance's density to that of water. Variations in specific gravity of bodily fluids can indicate certain medical conditions.
Step-by-step explanation:
Negative contrast agents have a lower specific gravity than the surrounding tissues or fluids. Specific gravity is defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material, which is often a liquid such as pure water. Pure water has a specific gravity of 1.0, and when a solute is added to water, it increases the water's specific gravity.
In medical imaging, contrast agents that have a lower specific gravity compared to bodily fluids can be referred to as negative contrast. These could be gases such as air or carbon dioxide that are less dense than body fluids. The variation in density helps to improve the contrast in imaging studies like X-rays or CT scans and can aid in the diagnosis of various conditions. For example, in the case of urine, a high specific gravity could indicate dehydration, whereas a low specific gravity could suggest renal failure.