Which imaging sequence is capable of detecting ischemia within minutes after onset?

Which imaging sequence is capable of detecting ischemia within minutes after onset?

• A. T1
• B. T2
• C. Diffusion-weighted imaging
• D. MR Perfusion

Answer: (C)

The main idea is that acute ischemia causes rapid cytotoxic edema, which restricts water diffusion in affected tissue. Diffusion-weighted imaging is highly sensitive to this restricted diffusion, so ischemic tissue appears bright on DWI within minutes of onset (with low signal on the ADC map). This makes DWI the earliest imaging method to detect stroke-related changes. Conventional T1 and T2 sequences show changes later, as edema evolves over hours to days, so they’re not reliable for detecting ischemia in the first minutes. MR perfusion can reveal blood-flow abnormality quickly and is valuable for identifying tissue at risk, but it reflects perfusion status rather than directly showing the cellular diffusion change that signals early ischemia.

The main idea is that acute ischemia causes rapid cytotoxic edema, which restricts water diffusion in affected tissue. Diffusion-weighted imaging is highly sensitive to this restricted diffusion, so ischemic tissue appears bright on DWI within minutes of onset (with low signal on the ADC map). This makes DWI the earliest imaging method to detect stroke-related changes.

Conventional T1 and T2 sequences show changes later, as edema evolves over hours to days, so they’re not reliable for detecting ischemia in the first minutes. MR perfusion can reveal blood-flow abnormality quickly and is valuable for identifying tissue at risk, but it reflects perfusion status rather than directly showing the cellular diffusion change that signals early ischemia.