In acute ischemic stroke, MRI is most helpful in which circumstance?

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In acute stroke, you want both speed and accuracy: CT is done first to quickly rule out hemorrhage and assess obvious large infarcts. MRI adds much more sensitivity for detecting acute ischemia, especially very early or small strokes, and it can evaluate tissue viability with perfusion imaging to distinguish the core infarct from the at-risk penumbra. But MRI isn’t always practical as the initial test because it takes longer, may not be readily available everywhere, and has contraindications. So MRI is best used when you need more information after CT to guide treatment decisions—such as confirming ischemia in cases where CT is nondiagnostic, evaluating posterior circulation strokes, or assessing salvageable tissue to decide on reperfusion therapies. This is why MRI is most helpful in a scenario where further evaluation is needed after CT.