Contrast Agents Explained in Simple Language | Radlii

What This Page Covers

This page explains:• What “contrast” means in CT and MRI
• Why contrast is sometimes used
• What radiology report terms like enhancement, washout, or no abnormal enhancement generally refer to
• Common non-diagnostic reasons contrast appears in reports
• How to interpret typical contrast-related wording without drawing medical conclusionsThese explanations are general and educational. They do not replace medical advice or interpretation of any specific finding.

In radiology, contrast is a special substance used during MRI or CT scans to make certain tissues or structures appear clearer.MRI ContrastMRI contrast (often called gadolinium contrast) improves the visibility of:
• Blood vessels
• Areas of inflammation
• Certain types of tissue abnormalitiesFor a full glossary of MRI report terminology, you can visit our MRI Terms Explained page.CT ContrastCT contrast (often iodine-based) helps highlight:
• Blood vessels
• Organs such as the liver, kidneys, and bowel
• Differences between fluid-filled and solid areasIf your report includes technical CT phrases, you may find helpful context in our CT Terms Explained guide.

A radiologist may request contrast when they need to:• Distinguish between different tissues
• See blood flow
• Assess inflammation
• Evaluate an organ in different phases (CT)
• Clarify something that could not be seen well on non-contrast imagesContrast helps radiologists describe what they see more precisely.

“Arterial phase / portal venous phase / delayed phase”These refer to different time points after contrast injection. They allow radiologists to see how organs and blood vessels behave over time.“Enhancement”A structure becomes brighter after contrast.
This simply shows that contrast entered the tissue or area.“No abnormal enhancement”Nothing unusual became brighter after contrast — a reassuring phrase, but still non-diagnostic.“Washout”A finding becomes brighter at first, then less bright on later phases.
This describes contrast behavior, not a diagnosis.“Non-enhancing area”A region did not take up contrast.
This can be due to many benign or non-benign reasons — the description alone is not a diagnosis.Many CT contrast descriptions appear together with general scan terminology. You can explore more of these terms on our CT Terms Explained page.

“Post-contrast images”Images taken after the injection of gadolinium contrast.“Contrast enhancement”An area appears brighter on contrast images.
Radiologists look at the pattern, shape, and location to describe it — not to diagnose from this term alone.“No suspicious enhancement”Nothing looks concerning based on general imaging appearance.“Subtle enhancement”A very mild increase in brightness.
This is simply a descriptive observation.“Ring enhancement”Contrast collects around the outside of an area.
This is a descriptive pattern, not a conclusion.If your report contains wording beyond contrast (such as descriptions of organs, vessels or tissue changes), our Radiology Questions Explained page offers simple explanations of common phrases.

Radiologists often use cautious or neutral wording because:• Many findings are non-specific
• Imaging patterns can overlap
• Descriptions must remain objective
• Diagnosis depends on clinical information, history, and sometimes further imagingThis is why reports list what is seen, not what it means medically.

Contrast does not automaticallyindicate:
• Cancer
• Infection
• Something dangerous
• Something requiring urgent treatmentContrast simply highlights tissue differences.Only the treating doctor can connect imaging findings with symptoms, history, and lab values.For broader educational explanations of terminology that may appear alongside contrast findings, you can explore our Ultrasound Terms, CT Terms, or MRI Terms pages.

**Who decides whether contrast is appropriate for a scan?Decisions about using contrast are made by the treating medical team based on the clinical situation, medical history, and local imaging guidelines.
Radiology reports simply describe how an area appears after contrast is used; they do not comment on an individual patient’s suitability for contrast.Contrast used in MRI and CT has been widely used for many years.
In reports, the mention of contrast simply explains how the images were acquired — not whether the contrast was “safe” or “unsafe” for any individual person.
Medical clearance and safety decisions are made by the treating team, not by the report text.⸻Why do some scans use contrast and others do not?Radiologists select contrast based on the type of information needed.
Sometimes non-contrast images are enough; other times contrast helps show tissues more clearly.
The decision is imaging-based and does not imply anything about the seriousness of a finding.⸻What does “no enhancement” mean in a report?This means the area did not become brighter after contrast was used.
It is simply a visual observation.
It does not indicate whether something is normal or abnormal on its own.⸻Why are contrast patterns described with so much detail?Radiologists describe what they see in precise language so other clinicians understand how an area behaves on imaging.
These descriptions are neutral and non-diagnostic — interpretation always depends on clinical context.⸻Why do reports mention different “phases” in CT scans?Different phases (arterial, portal venous, delayed) show how organs and blood vessels look at different times after contrast enters the body.
This helps radiologists describe appearance that could lead to a diagnosis.⸻Why do some people have tests before receiving contrast?In some hospitals, tests such as kidney function or allergy history are reviewed before contrast is given.
These checks are part of the clinical assessment carried out by the healthcare team and are not determined by the radiology report.⸻What if I have questions about contrast and my own health?Any personal medical concerns — including allergies, kidney function, or previous reactions — should be discussed with the clinician who ordered the scan.
This page is intended only to explain the terminology found in radiology reports.

Upload your report and receive a clear, plain-language explanation — written for patients, free of medical jargon.✔ No diagnosis
✔ No medical advice
✔ Neutral, educational descriptions
✔ Anonymous and privateExplain my report → €59