Evolution of apparent diffusion coefficient, diffusion-weighted, and T2-weighted signal intensity of acute stroke

BACKGROUND AND PURPOSE: Serial study of such MR parameters as diffusion-wei ghted imaging (DWI), apparent diffusion coefficient (ADC), ADC with fluid-a ttenuated inversion recovery (ADC(FLAIR)), and T2-weighted imaging may prov ide information on the pathophysiological mechanisms of acute ischemic stro ke. Our goals were to establish the natural evolution of MR signal intensit y characteristics of acute ischemic lesions and to assess the potential of using specific MR parameters to estimate lesion age, METHODS: Five serial echo-planar DWI studies with and without an inversion recovery pulse were performed in 27 patients with acute stroke, The followi ng lesion characteristics were studied: 1) conventional ADC (ADC(CONV)); 2) ADC(FLAIR); 3) DWI Signal intensity (SIDWI); 4) T2-weighted signal intensi ty (SIT2), and 5) FLAIR signal intensity (SIFLAIR), RESULTS: The lesion ADC(CONV) gradually increased from low values during th e first week to pseudonormal during the second week to supranormal thereaft er, The lesion ADCFLAIR showed the same pattern of evolution but with lower absolute values. A low ADC value indicated, with good sensitivity (88%) an d specificity (90%), that a lesion was less than 10 days old, All signal in tensities remained high throughout follow-up, SIDWI showed no significant c hange during the first week but decreased thereafter. SIT2 initially increa sed, decreased slightly during week 2, and again increased after 14 days. S IFLAIR showed the same initial increase as the SIT2 but remained relatively stable thereafter. CONCLUSION: Our findings further clarify the time course of stroke evolutio n on MR parameters and indicate that the ADC map may be useful for estimati ng lesion age, Application of an inversion recovery pulse results in lower, potentially more accurate, absolute ADC values.