Sequential changes on 23Na MRI after cerebral infarction.

23Na MRI changes from the acute to chronic phase were investigated in seven patients with cerebral infarcts. 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 subacute 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 intracellular 23Na 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 intracellular 23Na 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.