What does PDWI high signal mean? PDWI high signal is a term used in cranial MRI that often indicates acute cerebral ridge infarction. After an acute cerebral infarction, there is difficulty in moving water molecules due to intracellular edema, and therefore high signal appears on the MRI PDWI sequence. This usually shows up in patients a few minutes after the infarction, when CT cannot show it. Therefore, PDWI high signal is especially obvious and sensitive for showing acute cerebral infarction, and is widely used in clinical screening of acute cerebral infarction, in addition to being used to show some other inflammatory conditions, such as encephalitis, which can also show high signal.