How does diffusion-weighted MRI help differentiate acute ischemia from an abscess?

How does diffusion-weighted MRI help differentiate acute ischemia from an abscess?

• A. Ischemia shows restricted diffusion with high signal on DWI and low ADC; abscess shows restricted diffusion with high DWI signal and very low ADC due to pus, often with ring enhancement.
• B. Ischemia shows high ADC; abscess shows high DWI signal and high ADC.
• C. Both show restricted diffusion with similar ADC.
• D. Ischemia shows diffusion restriction only on ADC but not DWI.

Answer: (A)

Diffusion-weighted MRI measures how freely water molecules move in tissue. When diffusion is restricted, the diffusion-weighted image lights up and the ADC map shows low values. In acute ischemia, cytotoxic edema reduces the extracellular space and severely restricts water movement, so you see high signal on DWI with a low ADC. In a brain abscess, the purulent center is very viscous and densely cellular, causing even more restricted diffusion. That leads to a bright appearance on DWI and an especially low ADC. The abscess often also shows a ring-enhancing capsule after contrast, which is a helpful clue. So the diffusion pattern is restricted in both situations, but the abscess tends to produce a more pronounced (very low) ADC and is typically accompanied by ring enhancement, whereas acute ischemia lacks that ring and has a more typical infarct distribution. The other options misstate the diffusion behavior: diffusion restriction is observed on DWI, not absent there; ischemia does not exhibit high ADC; and the idea that both conditions show similar ADC or that restriction appears only on ADC is inaccurate.

Diffusion-weighted MRI measures how freely water molecules move in tissue. When diffusion is restricted, the diffusion-weighted image lights up and the ADC map shows low values. In acute ischemia, cytotoxic edema reduces the extracellular space and severely restricts water movement, so you see high signal on DWI with a low ADC.

In a brain abscess, the purulent center is very viscous and densely cellular, causing even more restricted diffusion. That leads to a bright appearance on DWI and an especially low ADC. The abscess often also shows a ring-enhancing capsule after contrast, which is a helpful clue. So the diffusion pattern is restricted in both situations, but the abscess tends to produce a more pronounced (very low) ADC and is typically accompanied by ring enhancement, whereas acute ischemia lacks that ring and has a more typical infarct distribution.

The other options misstate the diffusion behavior: diffusion restriction is observed on DWI, not absent there; ischemia does not exhibit high ADC; and the idea that both conditions show similar ADC or that restriction appears only on ADC is inaccurate.