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What is required to distinguish adjacent tissues in computed tomography images?
What is required to distinguish adjacent tissues in computed tomography images?
Tissues with different densities.
Which substances are examples of positive contrast agents? (Select all that apply)
Which substances are examples of positive contrast agents? (Select all that apply)
Which substances are examples of negative contrast agents? (Select all that apply)
Which substances are examples of negative contrast agents? (Select all that apply)
What makes iodine-based contrast agents suitable for intravenous use?
What makes iodine-based contrast agents suitable for intravenous use?
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What is osmolarity in relation to iodine contrast agents?
What is osmolarity in relation to iodine contrast agents?
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Which type of iodine contrast agent has a higher osmolarity compared to blood?
Which type of iodine contrast agent has a higher osmolarity compared to blood?
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How is the clearance of iodine contrast agents typically achieved?
How is the clearance of iodine contrast agents typically achieved?
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The common formula for iodine contrast dosage for children is ___ ml/kg.
The common formula for iodine contrast dosage for children is ___ ml/kg.
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Iodine contrast agents pose a risk to the fetus during pregnancy.
Iodine contrast agents pose a risk to the fetus during pregnancy.
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What is the effect of iodine contrast agents on breastfeeding?
What is the effect of iodine contrast agents on breastfeeding?
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Study Notes
Contrast Agents
- Contrast agents are used to differentiate adjacent tissues in a computed tomography (CT) scan. This differentiation is done by changing the density of target tissues.
- Contrast agents create artificial differences in density between objects. These differences are temporary and made possible by injecting the contrast agent intravenously or orally.
- There are two types of contrast agents:
- Positive contrast agents are materials that are radiopaque. This means that they block x-rays. These agents have a higher density than the surrounding structures. Examples include barium and iodine.
- Negative contrast agents are materials that are radiolucent. This means that they allow x-rays to pass through. These agents have a lower density than the surrounding structures. Examples include air and carbon dioxide.
Intravascular Contrast Agents
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Iodine-based contrast agents are frequently used because they are:
- Water-soluble
- Easy to administer into blood vessels
- Safe
- Enhance different tissues in various ways
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Iodine-based contrast agents are metabolized differently by normal tissues versus abnormal tissues.
Properties of Iodine Contrast Agents
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Osmolality: The number of particles in a solution per unit of fluid, compared to the blood.
- High Osmolality Contrast Media (HOCM): May have 7 times the concentration of blood.
- Low Osmolality Contrast Media (LOCK): Has about twice the concentration of blood.
- Iso-osmolar Contrast Media (IOCM): Has the same osmolality as blood.
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Viscosity: The thickness of the fluid or its resistance to flow.
- The viscosity of contrast media is influenced by brand, temperature, and concentration.
- Viscosity can affect injectable contrast agents. The smaller needle and catheter size can make injection more difficult.
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Ionicity: Ionized contrast agents contain molecules that form ions in a solution.
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Clearance: Iodine-based contrast agents are not broken down by the body. They are primarily excreted from the body through the kidneys.
- The half-life in patients with normal kidney function is approximately 2 hours.
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Dosage:
- Determined using the concentration of iodine and the volume administered.
- Children's dosages are often based on weight. The most common formula is 2 mL/kg.
- Adult dosages are usually uniform for each protocol. However, weight-based dosage for adults has several advantages.
Pregnancy and Breastfeeding
- CT scans are rarely performed during pregnancy due to concerns about ionizing radiation exposure to the fetus. However, CT scans can be essential in some cases to protect the health of the mother.
- There is no evidence that contrast agents pose a risk to the fetus.
- Small amounts of iodine-based contrast agents administered to the mother are excreted in breast milk.
- For example, if a mother received 150 mL of contrast, her breastfed infant would only ingest 0.015 mL.
- Therefore, it is considered safe for both the mother and the infant to continue breastfeeding after receiving contrast media.
Side Effects
- Iodine-based contrast media is one of the most widely used medications.
- Potential side effects can be categorized based on frequency:
- Common: Nausea, vomiting, flushing, and a metallic taste in the mouth.
- Less Common: Headache, rash, itching, and feeling warm.
- Rare: Seizures, anaphylaxis, and kidney failure.
- While serious side effects are rare, it's important to be aware of them and to seek medical attention if they occur.
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Description
This quiz explores the role of contrast agents in computed tomography (CT) scans. Learn about the differences between positive and negative contrast agents, their properties, and their applications in enhancing image quality. Test your knowledge on intravascular contrast agents and their importance in medical imaging.