A completely normal brain CT cannot exclude stroke. A completely normal brain CT can exclude cerebral hemorrhage or subarachnoid hemorrhage, but it cannot exclude cerebral infarction. When cerebral infarction first occurs, CT usually cannot show the lesion, especially some small infarcts or lacunar infarcts even after 48 hours, CT cannot show the lesion clearly. In general, larger infarct foci can be clearly shown after 48 hours, and CT can only help to clarify the extent, size, and specific location of the infarct and whether there is obvious brain edema around it. If you want to rule out cerebral infarction in a short time and clarify whether there is a small, microscopic lacunar infarction, you need to do a cranial MRI. Generally, the foci of cerebral infarction can be clearly shown on the cranial MRI one hour after the onset of the disease.