Recovery of apparent diffusion coefficient after ischemia-induced spreading depression relates to cerebral perfusion gradient

Transient decreases of the apparent diffusion coefficient (ADC) of water as measured by fast diffusion-weighted imaging (DWI) in the ischemic border zone are thought to reflect cellular swelling associated with spreading depression. DWI and dynamic contrast-enhanced MRI were applied to study the characteristics of spreading depression and the correlation between ADC recovery time and tissue perfusion in focal ischemia. Serial DWI was performed during remote middle cerebral artery occlusion in rats (n = 5) with an echo-planar imaging technique. ADC maps were calculated and ADC values displayed as a function of time in user-defined regions of interest with a time resolution of 12 to 16 seconds. Dynamic contrast-enhanced MRI was performed for qualitative correlation of ADC changes with tissue perfusion. Recovery time of transient ADC decreases correlated with the degree of the perfusion deficit (r = .81, P < .001). Slowly recovering ADC declines were found close to the ischemic core and correlated with severe perfusion deficit, while short-lasting ADC declines were typically found in moderately malperfused or normal tissue. Transient ADC decreases originated in the subcortical and cortical ischemic border zones and propagated along the cortex with a velocity of 2.9 +/- 0.9 mm/min. The variation in the recovery time of transient ADC decreases in the ischemic periphery reflects the gradient of the tissue perfusion. Severely delayed recovery time after spreading depression is thought to represent the ischemic penumbra.