Evolution of the diffusion-weighted signal and the apparent diffusion coefficient in the late phase after minor stroke - A follow-up study

Introduction: Diffusion-weighted imaging (DWI) is mainly used in acute stroke, and signal evolution in the acute phase has been studied extensively. However, patients with a minor stroke frequently present late. Recent studies suggest that DWI may be helpful at this stage, but only very few published data exist on the evolution of the DW-signal in the weeks and months after a stroke. We performed a follow-up study of DWI in the late stages after a minor stroke. Methods: 28 patients who presented 48 hours to 14 days after a minor stroke underwent serial MRI at baseline, 4 weeks, 8 weeks, 12 weeks, 6 months and >= 9 months after their event. Signal intensity within the lesion was determined on T2-weighted images, DW-images and the Apparent Diffusion Coefficient (ADC) map at each time-point, and ratios were calculated with contralateral normal values (T2(r), DWIr, ADC(r)). Results: T2(r) was increased in all patients from the beginning, and showed no clear temporal evolution. ADC(r) normalized within 8 weeks in 83% of patients, but still continued to increase for up to 6 months after the event. The DW-signal decreased over time, but was still elevated in 6 patients after >= 6 months. The evolution of ADC(r) and DWIr showed statistically highly significant inter-individual variation (p < 0.0001), which was not accounted for by age, sex, infarct size or infarct location. Conclusion: The ADC and the DW-signal may continue to evolve for several months after a minor ischaemic stroke. Signal evolution is highly variable between individuals. Further studies are required to determine which factors influence the evolution of the ADC and the DW-signal.