Apparent diffusion coefficient decreases and magnetic resonance imaging perfusion parameters are associated in ischemic tissue of acute stroke patients

Perfusion- and diffusion-weighted magnetic resonance imaging scans are thou ght to allow the characterization of tissue at risk of infarction. The auth ors tested the hypothesis that the apparent diffusion coefficient (ADC) dec rease should be associated with the severity of the perfusion deficit in is chemic tissue of acute stroke patients. Perfusion- and diffusion-weighted s cans were performed in 11 patients with sudden onset of neurologic deficits : within the last 6 hours and T2-weighted magnetic resonance imaging scans were obtained after 6 days. Parameter images of the maximum of the contrast agent concentration, time to peak. relative cerebral blood volume, relativ e cerebral blood flow, and relative mean transit time were computed from th e perfusion-weighted data. A threshold function was used to identify tissue volumes with stepwise ADC decreases. An onionlike distribution of successi vely decreasing ADC values was found, with the lowest ADC in the center of the ischemic region. Correspondingly, tissue perfusion decreased progressiv ely from the periphery toward the ischemic core. This effect was most prono unced in the time-to-peak maps, with a linear association between ADC decre ase and time-to-peak increase. Apparent diffusion coefficient values decrea sed from the periphery toward the ischemic core, and this distribution of A DC values was strongly associated with the severity of the perfusion defici t.