Radiology: Contrast Injection Techniques

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Questions and Answers

What is the typical volume of contrast injected during a CT scan?

50 to 150 mL (correct)

10 to 50 mL

150 to 200 mL

200 to 250 mL

What is a limitation of the hand bolus technique?

Operator expertise is not required

The flow rate is subject to many factors (correct)

It is only used for angiography

It is faster than mechanical injection systems

What is a solution to low contrast enhancement in patients with a low body weight?

Use a different type of contrast agent

Increase the CM volume or flow rate or both (correct)

Increase the flow rate

Decrease the CM volume

What is the purpose of a test bolus in CT imaging?

To determine the optimal scan delay Signup and view all the answers

What is the primary purpose of contrast-enhanced CT (CECT)?

To find pathology by enhancing the contrast between a lesion and surrounding structures Signup and view all the answers

What type of injection system is commonly used in angiography?

Mechanical injection system with a dual injector Signup and view all the answers

What is the primary purpose of the early arterial phase in CT imaging?

To perform angiography imaging Signup and view all the answers

In which phase of CT enhancement is the contrast most likely to be in the veins?

Venous phase Signup and view all the answers

What is the primary advantage of using non-enhanced CT (NECT) over enhanced CT?

NECT is better for detecting calcifications Signup and view all the answers

What is the primary factor that determines the optimal timing of CT enhancement phases?

The pathology being investigated Signup and view all the answers

What is the primary benefit of using the late arterial phase in CT imaging?

It provides optimal enhancement of structures that receive their blood supply from the arteries Signup and view all the answers

What is the minimal visible detectable difference to identify normal versus pathologic tissue in Hounsfield units?

10 Hu Signup and view all the answers

What is the effect of increasing the iodine concentration of the contrast on the selection of injection flow rate?

It increases the flow rate required Signup and view all the answers

What is the purpose of flushing the line with a small amount of saline solution before injecting contrast media?

To ensure the patency of the line Signup and view all the answers

What is the relationship between the iodine concentration and the injection flow rate?

A higher concentration requires a higher flow rate Signup and view all the answers

Why is it necessary to obtain the patient's consent before beginning the procedure?

To ensure the patient understands the risks Signup and view all the answers

What is the benefit of using a 20-gauge catheter compared to an 18-gauge catheter?

It can tolerate lower flow rates Signup and view all the answers

Study Notes

CT Scan Phases and Contrast Enhancement

A lesion can appear hypo- or hyper-vascular compared to surrounding tissue, emphasizing the importance of selecting the correct CT scan phase for the suspected pathology.

CT Scan Phases

Non-enhanced CT (NECT): Detects calcifications, fat in tumors, and fat-stranding (e.g., appendicitis, diverticulitis).
Early Arterial Phase (15-25 seconds after injection): Contrast is still in arteries, optimal for angiography imaging.
Late Arterial Phase (20-30 seconds after injection): Structures receiving blood supply from arteries show optimal enhancement.
Venous Phase (40-50 seconds after injection): Specific phase for studying venous supply, e.g., portal phase.

Contrast Agent

Iodine: Useful contrast agent due to its high atomic number.
Contrast Concentration: 2cm concentration, with varying doses required for different CT scan protocols.

Contrast Injection

Cannula Size: Choose the correct gauge for the IV catheter, as it affects flow rate (e.g., 18-gauge for 5mL/s, 20-gauge for 3mL/s).
Injection Ready: Ensure patency of the line by flushing with saline solution before injecting contrast media.
Volume of Contrast: 50-150mL injected at 1-6mL/s, with a critical scan delay between injection initiation and scanning start.

Bolus Inject Types

Hand Bolus Technique: Manual injection, subject to various factors, requiring operator expertise.
Mechanical Injection Systems: Using an injector, with single or dual injector options, suitable for angiography or dynamic examinations (e.g., liver imaging).

Factors Affecting Contrast Enhancement

Patient Weight: Low enhancement can be addressed by increasing contrast volume or flow rate.
Cardiac Output: Slow rate may cause delayed enhancement, solved by using test bolus or bolus-tracking.

Purpose of Contrast-Enhanced CT

To enhance contrast between lesions and surrounding structures, facilitating pathology detection.

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Description

Test your knowledge of contrast injection techniques in radiology, including the hand bolus technique and scan delay. Learn about the importance of volume and rate of contrast injection.