In the assessment of acute stroke, what is the primary purpose of diffusion-weighted MRI?

• A. Detects early ischemic changes with high sensitivity within minutes to hours after stroke onset.
• B. Visualizes cerebral blood flow without contrast.
• C. Determines brain metabolism rates across regions.
• D. Assessing perfusion is the primary role of diffusion-weighted imaging.

Answer: (A)

Diffusion-weighted MRI is most valuable in acute stroke because it detects cytotoxic edema that sharply restricts water diffusion very early after ischemia. This restriction causes a bright signal on diffusion-weighted images and a corresponding low signal on ADC maps, often within minutes to hours of onset. This high sensitivity allows clinicians to identify the acute infarct promptly, guiding urgent treatment decisions. Other imaging approaches—visualizing blood flow without contrast and measuring metabolism—are handled by perfusion imaging and MR spectroscopy, respectively, not diffusion. So the primary purpose is to detect early ischemic changes with high sensitivity soon after stroke onset.