On diffusion-weighted MRI, what finding is most characteristic of acute ischemia?

On diffusion-weighted MRI, what finding is most characteristic of acute ischemia?

• A. Increased diffusion
• B. Restricted diffusion
• C. No diffusion change
• D. Calcifications

Answer: (B)

Diffusion restriction caused by cytotoxic edema is the hallmark of acute ischemia. When energy failure from an occluded vessel disrupts the Na+/K+ pump, water shifts into cells, causing cellular swelling and less extracellular space. This limits water molecule movement, so diffusion is restricted. On diffusion-weighted imaging this appears as bright signal, and it is paired with low signal on the ADC map, confirming true restriction. This pattern can appear within minutes to hours of onset, making it the most characteristic sign of acute ischemia. Increased diffusion would indicate something like vasogenic edema or other processes with more free water movement; no diffusion change wouldn’t reflect the cytotoxic edema, and calcifications are unrelated to diffusion physics.

Diffusion restriction caused by cytotoxic edema is the hallmark of acute ischemia. When energy failure from an occluded vessel disrupts the Na+/K+ pump, water shifts into cells, causing cellular swelling and less extracellular space. This limits water molecule movement, so diffusion is restricted. On diffusion-weighted imaging this appears as bright signal, and it is paired with low signal on the ADC map, confirming true restriction. This pattern can appear within minutes to hours of onset, making it the most characteristic sign of acute ischemia. Increased diffusion would indicate something like vasogenic edema or other processes with more free water movement; no diffusion change wouldn’t reflect the cytotoxic edema, and calcifications are unrelated to diffusion physics.