A contrast agent, also known as a contrast medium or contrast dye, is a substance that is used to enhance the visibility of internal structures or organs during medical imaging. Contrast agents are used in various imaging techniques, including X-ray, computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound.

The contrast agent works by altering the way that X-rays or electromagnetic waves pass through the body, making certain structures or tissues more visible. This can be especially useful when trying to distinguish between healthy tissue and abnormalities or disease.
In radiology, positive contrast refers to the use of a substance that has a higher density than the surrounding tissue to enhance the visualization of structures or organs in an imaging study.
Positive contrast agents, also known as radiopaque contrast agents, are commonly used in imaging studies such as X-rays, computed tomography (CT), and fluoroscopy. These agents are typically made of materials such as iodine, barium, or gadolinium, which are capable of absorbing X-rays and appearing bright on an imaging study.

When a positive contrast agent is injected or ingested into the body, it fills the space within the structure being imaged, creating a contrast between the structure and the surrounding tissues. This makes the structure more visible on the imaging study, allowing for a more accurate diagnosis or evaluation.

Examples of positive contrast agents used in radiology include iodinated contrast agents for CT and intravenous urography (IVU), barium sulfate for gastrointestinal studies, and gadolinium-based contrast agents for magnetic resonance imaging (MRI).
Positive contrast is also sometimes referred to as "opacification" because the agent makes the structure more opaque or visible on the imaging study.


In radiology, negative contrast refers to the use of a substance that has a lower density than the surrounding tissue to enhance the visualization of structures or organs in an imaging study.
Negative contrast agents, also known as radiolucent contrast agents, are commonly used in imaging studies such as X-rays and fluoroscopy. These agents are typically made of air or gas, such as carbon dioxide, which is less dense than the surrounding tissues and appears dark or black on an imaging study.
Examples of negative contrast agents used in radiology include air, carbon dioxide, and nitrous oxide. Negative contrast agents are commonly used in gastrointestinal studies to visualize the lumen of the intestines or in studies of the respiratory system to visualize the airways.
Negative contrast is sometimes also referred to as "lucency" because the agent makes the structure more translucent or visible on the imaging study.
Ionic contrast
Ionic contrast refers to a type of contrast agent used in medical imaging procedures to enhance the visibility of certain tissues or structures in the body. Specifically, ionic contrast agents are made up of positively and negatively charged ions, which allows them to create a greater difference in electrical charge compared to the surrounding tissues.
When injected into the body, ionic contrast agents can be imaged using techniques such as X-ray or computed tomography (CT) scans, which use the contrast agent to help highlight specific organs or blood vessels. However, ionic contrast agents are generally considered to be less commonly used in modern medical imaging, as they have been largely replaced by newer, safer, and more effective non-ionic contrast agents.
One of the main concerns with ionic contrast agents is that they can cause adverse reactions in some patients, including allergic reactions and kidney damage. Non-ionic contrast agents, which are made up of neutral molecules rather than charged ions, are generally considered to be safer and are now widely used in medical imaging procedures.
Examples of ionic contrast agents include diatrizoate (also known as Hypaque) and iothalamate (also known as Conray). These compounds contain iodine, which is a good contrast agent for X-ray imaging. They are typically injected into a vein in the arm and then circulate through the body, highlighting the blood vessels and other structures.
Non-ionic contrast agents, also known as low osmolar contrast agents, are substances that are used in medical imaging procedures, such as computed tomography (CT) scans or magnetic resonance imaging (MRI), to enhance the visibility of certain tissues or structures. They are similar in function to ionic contrast agents, but have a different chemical structure and lower osmolality, which means they are less likely to cause adverse reactions in patients.Examples of non-ionic contrast agents include iopamidol (also known as Isovue) and gadoteridol (also known as ProHance). These compounds contain iodine or gadolinium, which are good contrast agents for X-ray and MRI imaging, respectively. They are typically injected into a vein in the arm and then circu....

свернуть