How do areas of unrestricted diffusion appear on ADC maps?

Areas of unrestricted diffusion on Apparent Diffusion Coefficient (ADC) maps appear bright. This occurs because unrestricted diffusion indicates that water molecules are moving freely within a particular area of tissue, resulting in higher ADC values. The brightness on the ADC map reflects this increased molecular movement, differentiating it from areas where diffusion is restricted. In contrast, restricted diffusion, which often occurs in pathology such as acute stroke or other cellular crowding scenarios, typically appears dark because the movement of water molecules is limited, leading to lower ADC values. Therefore, understanding the brightness on ADC maps is crucial in various clinical scenarios to identify pathological conditions.