What does “Diffusion-weighted imaging (DWI)” mean on a radiology report?
An MRI sequence that shows how freely water moves in tissue. Areas where movement is restricted look bright; it is the most sensitive standard MRI test for a recent stroke.
How "Diffusion-weighted imaging (DWI)" is used in radiology reports
An MRI scan is made of several "sequences", each tuned to show a different property of tissue. Diffusion-weighted imaging measures how freely water molecules can move. In most healthy tissue they move about fairly freely. When they cannot — because cells have swollen, as happens within minutes to hours of an ischaemic stroke, or because fluid is thick, as in an abscess — the area looks bright on DWI and dark on the matching ADC map. Radiologists call that "restricted diffusion".
That is why DWI is part of almost every brain MRI and why reports so often contain the sentence "no restricted diffusion": it is the standard way of checking for a recent stroke. Restricted diffusion is not specific to stroke, though. Some tumours, infections and types of inflammation restrict diffusion too, so the radiologist reads DWI alongside the other sequences.
DWI is also used outside the brain, for example in prostate, liver and some cancer imaging, where it helps show densely packed tissue. In each case it is one piece of evidence that the radiologist combines with the rest of the scan.
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General explanations of common wording, not advice about your own scan. Ask the doctor who ordered it what your results mean for you.
Does this mean something is wrong?
Not on its own. A radiology report describes what the images show, in language written for the doctor who ordered the scan. One term is rarely the whole picture — what it means for you depends on why you were scanned and what else the report says.
If the report worries you, the person who can actually answer that is the doctor who referred you. Understanding the words first usually makes that conversation a better one.
Want your whole report explained?
One term is a start. Radily reads your full report and explains it in plain English — and can talk you through it on video, so you are not reading medical language alone.
Other technical terms
- ArtifactAn abnormal appearance on an image caused by the scanning process, not actual anatomy.
- AttenuationHow much X-rays are absorbed by tissue. Dense tissue (bone) shows high attenuation (bright), while air shows low attenuation (dark).
- AxialCross-sectional images taken in a horizontal plane, like slicing bread.
- ContrastA dye injected or swallowed to make certain tissues show up better on imaging.
- CoronalImages taken from front to back, dividing the body into front and back portions.
- DensityHow solid or compact tissue appears on imaging. High density = bright (bone), low density = dark (air).
This explains a term as it is commonly used in radiology reports. It is not a diagnosis and not medical advice. Discuss your own results with your doctor.