CT Scan Contrast Agents

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Questions and Answers

What is osmolality in the context of intravascular contrast media?

A type of intravascular contrast media that does not dissociate into ions in solution

A physical property of intravascular contrast media describing its thickness or friction

The ability of contrast media molecules to separate into charged particles in an aqueous solution

A measure of the number of particles in solution per unit liquid (correct)

Why are conventional radiography barium suspensions not used in CT scans?

They are not available for CT scans

They cause unacceptable streak artifacts (correct)

They are not formulated to resist settling

They are not suitable for oral administration

What is the main reason for using oral contrast material in CT scans of the abdomen and pelvis?

To distinguish loops of bowel from a cyst, abscess, or neoplasm (correct)

To visualize the gastrointestinal tract

To enhance the visibility of bones

To reduce radiation exposure

What is the characteristic of ionic contrast agents?

They are composed of molecules that will separate into charged particles in an aqueous solution Signup and view all the answers

What is a common indication for rectal administration of contrast material?

Some indications for CT scans of the abdomen and pelvis Signup and view all the answers

What is the purpose of using specially formulated barium sulfate solutions in CT scans?

To resist settling and provide uniform opacification of the bowel Signup and view all the answers

Why should barium sulfate not be given if perforation of the gastrointestinal tract is suspected?

Because it may exacerbate the perforation Signup and view all the answers

What is the concentration of barium sulfate in solutions used in CT scans?

1% to 3% Signup and view all the answers

What is the condition referred to when barium leaks into the peritoneal cavity?

Barium peritonitis Signup and view all the answers

Why is a water-soluble iodinated oral contrast agent substituted for barium sulfate solution in cases of suspected perforation?

To prevent barium peritonitis Signup and view all the answers

What is the typical concentration of water-soluble oral contrast agents used in imaging procedures?

2% to 5% Signup and view all the answers

What is a common side effect of using iodinated oral contrast agents?

Diarrhea Signup and view all the answers

In what type of procedures is rectal administration of contrast material necessary?

Rectosigmoid abnormality Signup and view all the answers

What is the primary advantage of using water as a contrast agent?

It does not obscure mucosal surfaces or superimpose abdominal vessels on images Signup and view all the answers

What is the primary role of negative contrast agents in CT colonography?

To ensure adequate colonic distension for polyp detection Signup and view all the answers

What is the purpose of using room air or carbon dioxide as negative contrast agents?

To ensure adequate colonic distension for polyp detection Signup and view all the answers

What is the purpose of administering a contrast agent in a CT scan examination?

To create a temporary, artificial density difference between objects Signup and view all the answers

What is the characteristic of positive contrast agents, such as those containing barium and iodine?

They have a higher density than the surrounding structure Signup and view all the answers

What is the term used to describe contrast agents with a density similar to that of water?

Neutral contrast agents Signup and view all the answers

What is the characteristic of iodinated agents that makes them suitable for intravascular use?

They are water soluble Signup and view all the answers

What is the atomic number (Z) of barium, which is used in barium sulfate solutions?

56 Signup and view all the answers

What is the characteristic of negative contrast agents, such as air or carbon dioxide?

They have a lower density than the surrounding structure Signup and view all the answers

What is the term used to describe the ability of a contrast agent to absorb or scatter radiation?

Attenuation coefficient Signup and view all the answers

Why have other agents, such as those containing elements other than iodine, not become commercially available for widespread clinical use?

They have unacceptable toxic side effects Signup and view all the answers

Study Notes

Contrast Agents

Contrast agents are used to create a temporary, artificial density difference between objects, making them more visible on the image.
There are two types of contrast agents: positive and negative agents.
Positive agents have a higher density than the structure and are typically referred to as "radiopaque" with higher attenuating power and higher Z.
Negative agents have a lower density than the structure and are referred to as "radiolucent" with lower attenuating power and lower Z.
Examples of positive agents include barium and iodine, while negative agents include air and carbon dioxide.

Iodinated Contrast Agents

Iodinated agents are universally used for a variety of radiology examinations because they are water soluble, easy to administer intravascularly, and have a high safety index.
Properties of iodinated agents include:
- Osmolality: the number of particles in solution per unit liquid, compared to blood concentration.
- Viscosity: the physical property of the fluid, affecting its thickness or friction as it flows.
- Ionicity: whether the molecules they contain will separate into charged particles (i.e., ions) when dissolved in an aqueous solution.

Barium Contrast Agents

Barium sulfate solutions are used in the gastrointestinal tract to distinguish loops of bowel from a cyst, abscess, or neoplasm.
Conventional radiography barium suspension cannot be used in CT due to unacceptable streak artifacts.
Barium sulfate solutions specifically designed for CT are available, typically containing a 1% to 3% barium sulfate suspension.
Barium sulfate should not be given if perforation of the gastrointestinal tract is suspected, as it can lead to barium peritonitis.

Iodinated Oral Contrast Agents

Iodinated agents can be diluted and administered orally, typically in a 2% to 5% solution.
These agents stimulate intestinal peristalsis, resulting in diarrhea, and pass through the gastrointestinal tract slightly faster.
Rectal administration of contrast material may be necessary when rectosigmoid abnormality is suspected, using 150 to 200 mL of dilute water-soluble agent (1% to 3%).

Negative Contrast Agents

Water is sometimes used as a negative contrast agent, which will not obscure mucosal surfaces or superimpose abdominal vessels on three-dimensional images.
However, water transits quickly and distends the bowel poorly, requiring adequate distention for effective polyp detection.
Air and carbon dioxide are used as negative contrast agents in CT colonography, particularly useful for polyp detection.
Room air or carbon dioxide is administered via a small flexible rectal catheter, with room air delivered using a standard handheld air bulb insufflator and carbon dioxide delivered using an automated insufflation system.

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Description

Learn about the role of contrast agents in CT scans, including their administration and effects on tissue visibility.