Sequential changes on23Na MRI after cerebral infarction

²³Na MRI changes from the acute to chronic phase were investigated in seven patients with cerebral in-farcts. They showed no signal increase during the first 13 h after the stroke and revealed a definite signal increase thereafter. This reached a maximum 45–82 h after stroke and became slightly less marked in the subactue and chronic phases, probably as a result of disappearance of cerebral oedema. In the early acute phase of stroke,²³Na MRI appears to fail to demonstrate Na⁺ increases in the ischaemic area, due presumably to the invisibility on MRI of intracellular²³Na in the intact brain. The increase more than 13 h after stroke, during which ischaemic cells are likely to die, is presumably because of increased visibility of intracellular²³Na in the dead cells.²³Na MRI is apparently insensitive to early ischaemic changes, but may be useful for assessing the cell viability in the ischaemic brain.