Computed Tomography Chapter 1

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Questions and Answers

What is the primary effect of adding an iodinated agent to the bloodstream during imaging?

Reduces the blood supply to tissues

Decreases the visibility of veins

Temporarily increases beam-attenuating ability (correct)

Eliminates the need for contrast imaging

How does osmolality of contrast media compare to that of blood in low-osmolality contrast solutions?

They have no correlation

It is often significantly lower than blood (correct)

It is higher than blood

It is the same as blood

Which factor is NOT considered a pharmacokinetic factor affecting contrast enhancement?

Concentration

Osmolality

Viscosity

Age of the patient (correct)

What is the purpose of conducting laboratory tests like Serum Creatinine and Blood Urea Nitrogen before administering contrast media?

To evaluate kidney function Signup and view all the answers

Which method can help decrease the viscosity of contrast material prior to injection?

Heating it to body temperature Signup and view all the answers

What is a characteristic of high-osmolality contrast media compared to blood?

It may have up to seven times the osmolality of blood Signup and view all the answers

During patient preparation for CT contrast media, what is an important step related to the intravenous line?

Use a small syringe to flush the line Signup and view all the answers

Which of the following factors does NOT significantly influence the pharmacokinetics of contrast media?

Patient's height Signup and view all the answers

What characterizes the bolus phase of contrast enhancement?

It is marked by an attenuation difference of 30 or more Hounsfield units between the aorta and the inferior vena cava. Signup and view all the answers

During which phase is the contrast medium primarily bright in the arteries but not yet in the veins?

Bolus phase Signup and view all the answers

What is the main differentiating factor between the nonequilibrium phase and the bolus phase?

The presence of opacified venous structures. Signup and view all the answers

What is the usual AVID difference during the nonequilibrium phase?

Between 10 to 30 Hounsfield units Signup and view all the answers

Which phase is primarily associated with CT angiography imaging?

Bolus phase Signup and view all the answers

How long does the nonequilibrium phase typically last?

Slightly over 1 minute Signup and view all the answers

Which of the following statements about the equilibrium phase is accurate?

It is characterized by a delayed distribution of contrast medium. Signup and view all the answers

What occurs to the contrast medium during the equilibrium phase?

It becomes diffusely distributed across all compartments. Signup and view all the answers

What characterizes the equilibrium phase of contrast media?

Contrast in the aorta and inferior vena cava shows an AVID of less than 10 HU. Signup and view all the answers

Why was it difficult to detect liver lesions with older CT scan technology?

Scans were acquired during the equilibrium phase. Signup and view all the answers

How does a patient’s cardiac output affect contrast media phases?

Cardiac output influences the timing of phases due to variations in blood flow. Signup and view all the answers

What is the primary method for administering contrast medium during a drip infusion?

Continuous infusion through an IV line. Signup and view all the answers

When does scanning typically begin during a drip infusion of contrast media?

After roughly 2 to 3 minutes post infusion. Signup and view all the answers

What primary issue arises during the equilibrium phase related to imaging?

Decreased contrast differentiation between vessels and tissues. Signup and view all the answers

What has improved the ability to conduct routine abdomen studies with contrast media?

Faster imaging technology. Signup and view all the answers

What is often the first step in abdominal imaging before contrast-enhanced studies?

Scanning without contrast through the liver. Signup and view all the answers

What is the role of contrast agents in computed tomography?

To enhance the visibility of adjacent tissues with different densities Signup and view all the answers

What characterizes a positive contrast agent in CT imaging?

It contains atoms with a high atomic number that increase attenuation Signup and view all the answers

Which of the following is true regarding iodinated agents used in CT?

Iodinated agents are typically used because of their water solubility and high safety index Signup and view all the answers

Why is the chest region typically noted for high subject contrast in CT imaging?

The pulmonary vessels and ribs have distinct densities compared to aerated lungs Signup and view all the answers

Which of the following methods of contrast administration is the least common in CT imaging?

Intrathecal administration Signup and view all the answers

What distinguishes barium sulfate contrast from iodinated contrast in CT procedures?

Barium sulfate is administered orally or rectally, unlike iodinated contrast Signup and view all the answers

What is a primary reason that iodine atoms in contrast materials increase attenuation in CT imaging?

Iodine atoms have a high atomic number, leading to greater interaction with x-rays Signup and view all the answers

Before a patient undergoes a procedure utilizing contrast media, what is a necessary requirement?

The patient must sign a consent form Signup and view all the answers

What is a significant drawback of the drip infusion method for contrast administration?

It cannot guarantee peak enhancement for CT angiography. Signup and view all the answers

In the bolus technique, what is the critical factor that determines the success of the contrast enhancement?

The scan delay after starting the injection. Signup and view all the answers

Which group of patients is at a higher risk for contrast medium extravasation?

Infants and young children. Signup and view all the answers

What is one of the recommended practices to minimize the risk of extravasation during IV contrast administration?

Monitor the injection site for swelling. Signup and view all the answers

Why is the drip infusion method not recommended for scanning regions like the neck and chest?

All scans taken are done in the non-equilibrium phase. Signup and view all the answers

What volume range is typically injected using the bolus technique for contrast enhancement?

50 to 200 mL Signup and view all the answers

What protocol should be followed when detecting swelling at the injection site during contrast administration?

Stop the injection immediately. Signup and view all the answers

Which of the following should be avoided to reduce the risk of contrast media extravasation?

Employing metal needles for injection. Signup and view all the answers

Study Notes

Contrast Agents in CT

Different tissue densities are required to distinguish adjacent tissues in CT imaging, achieved via distinct attenuation coefficients.
Areas like the chest naturally exhibit high subject contrast due to the significant density differences between pulmonary vessels, ribs, and aerated lung.
Contrast agents alter tissue density; positive agents are denser than tissues, while negative agents are less dense.
Contrast administration methods include intravascular, gastrointestinal, intrathecal, and intraarticular routes.

Common Types of Contrast Media

Iodine-based IV contrast (e.g., Omnipaque 300, Iohexol) is widely used due to water solubility, ease of administration, and high safety index.
Oral/rectal barium sulfate contrast is another common agent.

Properties of Iodinated Agents

Iodine's high atomic number (53) enhances beam attenuation, thus increasing visibility on CT images.
Adding iodinated agents to blood enhances image brightness of well-vascularized structures.

Contrast Media Factors

Concentration: Represents iodine amount in solution.
Osmolality: High-osmolality contrast can be seven times that of blood; low-osmolality is closer to blood levels; iso-osmolar has equal osmolality to blood.
Viscosity: Affected by temperature and concentration; can be reduced by heating prior to injection.

Factors Affecting Contrast Enhancement

Pharmacokinetic factors: Include concentration, osmolality, viscosity.
Patient factors: Age, sex, weight, height, cardiovascular health, renal function, and other diseases.
Equipment factors can also influence outcomes.

Patient Preparation for CT Contrast Media

Pre-procedure lab tests should assess kidney function via serum creatinine (normal: 0.6-1.4 mg/dL) and blood urea nitrogen (normal: 7-25 mg/dL).
Patients may need to fast for 6-8 hours prior to the exam.

Phases of Tissue Enhancement During Contrast Media Injection

Bolus Phase: Immediate post-injection phase; marked by a 30+ HU AVID difference between aorta and IVC. Characterized by bright arterial display.
Nonequilibrium Phase: Follows bolus phase; 10-30 HU AVID difference. Arteries remain brighter than organ parenchyma. Initiates 1 minute post-bolus and lasts about 1 minute.
Equilibrium Phase: Begins 2 minutes post-bolus; dilution of contrast in veins. AVID less than 10 HU. Scans of the liver are least effective in this phase.

Injection Techniques

Drip Infusion: Gravity-fed method over several minutes; scans only captured during the nonequilibrium phase, unsuitable for peak enhancement.
Bolus Technique: Involves rapid injection of 50-200 mL of contrast; scanning occurs shortly after injection. It requires critical timing between injection start and scan initiation.

Extravasation and Its Management

Extravasation refers to unintentional leakage of contrast into surrounding tissue; primarily poses low risk but can cause complications in severe cases.
Guidelines to reduce risk: Utilize flexible plastic cannulas (18-20 gauge), avoid metal needles, and monitor injection sites for swelling during administration. Warm contrast to body temperature before injection.

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Description

This quiz focuses on contrast agents used in computed tomography (CT) as discussed in Chapter 1. Learn how varying tissue densities affect image clarity and contrast, essential for distinguishing adjacent tissues in medical imaging. The quiz also explores inherent contrast in certain body regions.