In imaging, which technique uses a contrast agent to enhance visibility of blood vessels, organs, and abnormalities?

• A. Ultrasound with Doppler
• B. MRI without contrast
• C. Contrast-enhanced CT
• D. X-ray

Answer: (C)

Using a contrast agent to highlight vessels and organs relies on the principle that injecting a substance into the bloodstream changes how tissues appear on the image, making structures more conspicuous. Contrast-enhanced CT applies an iodinated contrast material intravenously, which increases X-ray attenuation and makes blood vessels, organs, and any abnormalities stand out more clearly on the CT slices. This enhanced visibility is particularly helpful for identifying tumors, inflammation, bleeding, vascular diseases, and other pathologies.

The other options rely more on native tissue contrast or different imaging signals. Ultrasound with Doppler measures blood flow through sound waves and frequency shifts rather than a injected contrast; MRI without contrast doesn’t use a contrast agent to improve visibility, and plain X-ray lacks the contrast enhancement that reveals detailed vascular and organ anatomy.