What characteristic allows ADC maps to differentiate between old and recent strokes?

The ability of ADC (Apparent Diffusion Coefficient) maps to differentiate between old and recent strokes lies in the change in diffusion properties of water molecules in the affected brain tissue over time. In the acute phase of a stroke, there is cytotoxic edema due to cell swelling, leading to restricted diffusion of water molecules. This appears as a low ADC value on the map.

As time progresses, the nature of the stroke evolves. In older strokes, there is a phase where the initial cytotoxic edema resolves, and the tissue may become more permeable, allowing for more water movement, which results in an increase in the ADC value. This change reflects the different biological processes occurring in the brain tissue from the time of the stroke onset to days or weeks later.

Therefore, by assessing the ADC values and their changes over time, radiologists are able to distinguish between recent and older strokes based on the diffusion properties of water in the affected areas. This characteristic is crucial for accurate diagnosis and management of stroke patients.