Which contrast agent is used in CT angiography to visualize the pulmonary arteries when pulmonary embolism is suspected?

• A. Gadolinium-based contrast.
• B. Barium sulfate.
• C. IV iodinated contrast.
• D. Air contrast.

Answer: (C)

To visualize the pulmonary arteries in CT angiography, you need a contrast agent that opacifies arterial blood so the vessels stand out on the CT images. Intravenous iodinated contrast is the agent of choice because iodine has high radiodensity, making the blood inside the arteries appear bright. This contrast allows any filling defects within the bright pulmonary arteries to be seen, which are characteristic of pulmonary embolism.

Gadolinium-based contrast is used mainly for MRI vascular imaging, not CT, because it provides the appropriate signal in MRI but not the same attenuation on CT for detailed arterial visualization. Barium sulfate is designed for outlining the GI tract and isn’t suitable for intravascular use. Air contrast would create dark, nonopacified regions and would degrade, not aid, visualization of the vessels.

So IV iodinated contrast best enables CT angiography to reveal the pulmonary arteries and any clots within them.