When to use intravenous (IV) contrast in computed tomography (CT) scans?

From the Guidelines

IV contrast should be used in CT scans when enhanced visualization of blood vessels, organs, or tissues is needed, and when not contraindicated, to obtain the most accurate imaging of tumor extent and changes in tumor burden in response to treatment, as recommended by the most recent study 1. When to use IV contrast in CT scans:

• Evaluating vascular structures (e.g., angiography)
• Assessing for tumors or infections
• Examining abdominal or pelvic organs
• Investigating suspected blood clots
• Evaluating kidney function or urinary tract issues The most common IV contrast agents are iodine-based, and the standard dose is typically 1-2 mL per kg of body weight, administered via an IV line just before or during the scan, with a minimum injection rate of 2 to 3 mL/s to obtain adequate enhancement of the pleura and adjacent structures 1. Before administering contrast:
• Check renal function (eGFR >30 mL/min/1.73 m²)
• Screen for allergies to iodine or contrast media
• Ensure proper hydration Contrast enhances image quality by increasing the density difference between tissues, allowing for better differentiation of normal and abnormal structures, and can highlight areas of inflammation, infection, or abnormal blood flow, providing crucial diagnostic information that may not be visible on non-contrast scans 1. It is also important to consider the timing of IV contrast delivery, with a conventional recommended time delay of 50 to 60 seconds for imaging of the chest, and a delayed-phase acquisition at 2 to 4 minutes after IV contrast injection may be helpful in distinguishing tumor from adjacent tissues 1.

From the FDA Drug Label

Because unenhanced scanning may provide adequate diagnostic information in the individual patient, the decision to employ contrast enhancement, which may be associated with risk and increased radiation exposure, should be based upon a careful evaluation of clinical, other radiological, and unenhanced CT findings. Contrast enhancement appears to be greatest immediately after bolus administration (15 seconds to 120 seconds). Utilization of a continuous scanning technique (ie, dynamic CT scanning) may improve enhancement and diagnostic assessment of tumor and other lesions such as abscess, occasionally revealing unsuspected or more extensive disease

The decision to use intravenous (IV) contrast in computed tomography (CT) scans should be based on a careful evaluation of clinical, radiological, and unenhanced CT findings. Key considerations include:

• The potential benefits of contrast enhancement in improving diagnostic assessment
• The risks associated with contrast enhancement, such as increased radiation exposure
• The individual patient's clinical and radiological characteristics IV contrast is most useful when:
• Unenhanced scanning does not provide adequate diagnostic information
• Dynamic CT scanning is used to evaluate tumors or other lesions
• Contrast enhancement is expected to improve diagnostic assessment, such as in the case of abscesses or other conditions 2

From the Research

Indications for IV Contrast in CT Scans

• IV contrast material is used extensively for CT scans in emergency departments to make critical diagnoses 3
• Non-contrast CT scans are performed in patients with limited renal function, allergy to iodinated contrast, or in specific clinical settings such as suspected renal calculus or abdominal aortic aneurysm 4
• IV contrast is administered to define anatomical structures and detect pathologies, with different protocols for vascular, visceral, multiphasic, and split-bolus examinations 5

Safety and Precautions

• Newer research has improved knowledge of IV contrast media tolerance and safety, leading to more liberal guidelines for use 3
• Adverse reactions can occur, and precautions should be taken to avoid them, particularly in patients with kidney disease, shellfish allergies, or thyroid dysfunction 6
• The risk of acute kidney injury (AKI) following IV contrast-enhanced CT scans is a concern, and evidence-based recommendations are needed to guide clinical practice 7

Optimizing IV Contrast Use

• Factors such as patient weight, cardiac output, study delay, and technical characteristics can influence the degree of contrast enhancement obtained 5
• Variables related to contrast medium administration, such as iodine delivery rate and load, can be modified to optimize results 5
• Nanoparticle contrast agents may offer a promising alternative to current clinical contrast agents, with potential benefits including longer circulation half-lives and reduced toxicity 6