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Questions and Answers
What is the purpose of using contrast agents in CT imaging?
What is the purpose of using contrast agents in CT imaging?
Iodinated contrast agents have a low safety index.
Iodinated contrast agents have a low safety index.
False
What is a common example of an iodine-based IV contrast agent?
What is a common example of an iodine-based IV contrast agent?
Omnipaque 300
A contrast agent with a higher density than the surrounding structure is referred to as a __________ agent.
A contrast agent with a higher density than the surrounding structure is referred to as a __________ agent.
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Match the following contrast agents with their classifications:
Match the following contrast agents with their classifications:
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What characteristic of iodine contributes to the increase in attenuation during imaging?
What characteristic of iodine contributes to the increase in attenuation during imaging?
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Contrast agents can be administered intrathecally or intraarticularly.
Contrast agents can be administered intrathecally or intraarticularly.
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What does osmolality refer to in the context of intravascular contrast media?
What does osmolality refer to in the context of intravascular contrast media?
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What is a characteristic of low-osmolality contrast media?
What is a characteristic of low-osmolality contrast media?
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The viscosity of contrast media can be increased by cooling it.
The viscosity of contrast media can be increased by cooling it.
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What laboratory tests should be performed on patients expected to receive IV contrast media?
What laboratory tests should be performed on patients expected to receive IV contrast media?
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During the bolus phase of contrast enhancement, the arterial structures are filled with __________.
During the bolus phase of contrast enhancement, the arterial structures are filled with __________.
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Which factor is NOT considered a patient factor affecting contrast enhancement?
Which factor is NOT considered a patient factor affecting contrast enhancement?
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In the nonequilibrium phase, contrast media has completely filled the venous structures.
In the nonequilibrium phase, contrast media has completely filled the venous structures.
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The __________ phase is characterized by an attenuation difference of 30 or more Hounsfield units between the aorta and the inferior vena cava.
The __________ phase is characterized by an attenuation difference of 30 or more Hounsfield units between the aorta and the inferior vena cava.
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Match the following phases of tissue enhancement with their description:
Match the following phases of tissue enhancement with their description:
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What characterizes the nonequilibrium phase of CT angiography?
What characterizes the nonequilibrium phase of CT angiography?
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The equilibrium phase can begin as early as 1 minute after the bolus phase.
The equilibrium phase can begin as early as 1 minute after the bolus phase.
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What happens to the contrast agent during the equilibrium phase?
What happens to the contrast agent during the equilibrium phase?
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The phase characterized by an attenuation difference of less than 10 HU is known as the ______.
The phase characterized by an attenuation difference of less than 10 HU is known as the ______.
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Match the CT angiography phases with their characteristics:
Match the CT angiography phases with their characteristics:
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How does the timing of the CT angiography phases get affected?
How does the timing of the CT angiography phases get affected?
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Most routine body images are acquired while the contrast is in the nonequilibrium phase.
Most routine body images are acquired while the contrast is in the nonequilibrium phase.
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What is typically the main limitation of the equilibrium phase for acquiring scans of the liver?
What is typically the main limitation of the equilibrium phase for acquiring scans of the liver?
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What is a disadvantage of the drip infusion method for administering contrast media?
What is a disadvantage of the drip infusion method for administering contrast media?
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The bolus technique uses a slower injection rate for contrast material compared to drip infusion.
The bolus technique uses a slower injection rate for contrast material compared to drip infusion.
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What volume of contrast material is typically injected in the bolus technique?
What volume of contrast material is typically injected in the bolus technique?
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Extravasation refers to the leakage of fluid from a vein into the surrounding ______.
Extravasation refers to the leakage of fluid from a vein into the surrounding ______.
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Which of the following practices helps reduce the risk of contrast extravasation?
Which of the following practices helps reduce the risk of contrast extravasation?
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Match the following techniques with their characteristics:
Match the following techniques with their characteristics:
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Slight swelling at the injection site during IV contrast administration indicates successful injection.
Slight swelling at the injection site during IV contrast administration indicates successful injection.
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What gauge size of indwelling catheter is preferred to reduce the risk of contrast extravasation?
What gauge size of indwelling catheter is preferred to reduce the risk of contrast extravasation?
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Study Notes
Computed Tomography Contrast Agents
- Adjacent tissues have different densities (attenuation) for clear image depiction.
- High inherent contrast in some areas (e.g., chest).
- Pulmonary vessels and ribs have different densities from adjacent lung.
- Contrast agents fill structures with differing densities.
- Positive agents have higher density than the structure.
- Negative agents have lower density than the structure.
Contrast Administration Methods
- Intravascular and gastrointestinal routes are common CT methods.
- Intrathecal and intraarticular administration are less common.
Contrast Media (CM) Uses
- Iodine-based IV contrast (e.g., Omnipaque 300, lohexol).
- Oral/Rectal barium sulfate contrast.
- Patient must sign consent form before CM administration.
Properties of lodinated Agents
- Water-soluble iodinated agents are easy to administer intravascularly.
- High safety index.
- Iodine atoms (atomic number 53) increase attenuation in the bloodstream.
- Increased attenuation is displayed as a change from darker to lighter on the image.
CM Factors
- Concentration of iodine in the solution.
- Osmolality (number of particles in solution per unit liquid).
- High-osmolality media has seven times the osmolality of blood.
- Low-osmolality media has a lower osmolality than blood.
- Iso-osmolar media has the same osmolality as blood.
- Viscosity (resistance of fluid flow).
- Viscosity is affected by temperature and concentration.
- Heating contrast to body temperature decreases viscosity.
Factors Affecting Contrast Enhancement
- Pharmacokinetic factors (concentration, osmolality, viscosity).
- Low concentration requires higher injection rate and volume.
- High injection rate can cause contrast extravasation.
- Low concentration has lower osmolality, fewer adverse effects.
- Pre-warming contrast decreases viscosity for easier flow.
- Patient factors (age, sex, weight, cardiovascular status, renal function, other diseases).
- Equipment factors (e.g., scanner type).
- Larger CM volumes increase time for peak enhancement.
- Injection flow rate affects time to reach and fall off peak enhancement.
- Large patients require higher injection rates.
- Reduced cardiac output increases needed scan delay.
- Slow scanners require larger volume to extend peak plateau.
Methods of CM Delivery
- Drip infusion: contrast is dripped into an IV line.
- Scanning begins after most of the contrast medium is administered (roughly 2-3 minutes).
- Dependent on gravity, flow rates are variable.
- Not ideal for scans of neck, chest, abdomen, or pelvis.
- Cannot produce peak enhancement for CT angiography.
- Bolus technique: rapid injection of contrast media.
- Contrast volume of 50-200 mL, injection rate of 1-6 mL/s.
- Interval between injection and scanning (scan delay) is critical.
- Can be given by hand (syringes) or mechanical injector.
- Hand bolus has variable flow rates.
- Mechanical injectors provide precise flow rates and volumes.
Automatic Injection Triggering
- Two methods: test bolus and bolus triggering.
- Used to individualize scan delay for patient factors.
Performing a Test Bolus
- Steps to perform a test bolus may vary.
- Obtain scout views, and determine target region/obtain slice.
- Injected contrast of 10-20 mL (same rate as diagnostic scans)
- Begin trial scans after injection (typically every 2 seconds for 10-15 scans).
- Analyze graphs of contrast enhancement and time.
- Determine scan delay by adding 3 seconds to time to peak enhancement + twice the image number taken at peak enhancement.
Using Bolus Triggering Software
- Obtain scout views and single slice at area of interest.
- Plan the diagnostic study, set the trigger threshold.
- Start the contrast injection; threshold determines scan start.
- Instruct patient to hold breath during table motion.
Contrast Extravasation
- Leakage of fluid from vein into surrounding tissue during IV administration.
- Most extravasations are not significant (mild swelling/erythema).
- Severe cases can result in tissue necrosis/ulceration.
Contrast Injection Techniques
- Use indwelling catheter sets with flexible plastic cannulas.
- Avoid metal needles.
- Monitor injection site for swelling (indicates extravasation). Stop injection if swelling occurs.
- Warm contrast to body temperature for easier flow through IV catheters.
- Use low osmolality contrast media (LOCM).
Phases of Tissue Enhancement
- Bolus phase: immediately follows injection; arterial structures are enhanced.
- Nonequilibrium phase: follows bolus; venous structures are enhanced; contrast is still brighter in arteries than parenchyma organs .
- Equilibrium phase: contrast is diluted; characterized by an AVID of <10 HU ; intravascular and interstitial concentrations equilibrate.
Scan Timing for Angiography
- Precise scan timing crucial for CT Angiography.
- Too early: misses contrast bolus.
- Too late: insufficient opacification, particularly in small vessels.
Patient Preparation for CT Contrast Media
- Laboratory tests (serum creatinine, blood urea nitrogen) to assess kidney function.
- Fasting required for some examinations (6-8 hours).
Documenting CM Administration
- Needs to include legal documents.
- Name of agent, dose (volume and concentration), flow rate(s), injection site, and adverse effects.
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Description
This quiz covers the principles and administration methods of contrast agents used in computed tomography (CT). It highlights the differences in tissue densities and the properties of iodinated agents. Additionally, it discusses the various routes for contrast media administration and safety considerations.
