diffusionweighted imaging in the diagnosis of enterovirus 71 encephalitis background in the early phase of viral encephalitis conventional mri may appear normal diffusionweighted imaging dwi is a sensitive tool for detecting early changes in cellular function in the central nervous systempurpose to investigate the usefulness of dwi in the diagnosis of enterovirus 71 ev71 encephalitis and to determine whether dwi is superior to conventional mr sequencesmaterial and methods mri scans in 26 patients were retrospectively evaluated for distribution of lesions on t1weighted images t1wi t2weighted images t2wi fluidattenuated inversion recovery flair and dwi contrasttonoise ratios cnrs were calculated for all regions on each sequence and differences in the four mri sequences were assessed using cnrs apparent diffusion coefficient adc values were measured for all regions to look for true restriction of diffusionresults fifteen out of 26 cases showed positive findings on mr imaging the brain stem was involved in 11 patients cortex and subcortical white matter in four patients dwi was more sensitive in detecting the abnormalities 897 compared to t2wi 487 flair 410 and t1wi 359 and the positive ratio of dwi was significantly higher compared to other sequences furthermore no significant difference was found between t2wi and flair p 0649 the corresponding mean cnrs were 873 257 8359 2928 2422 622 and 13227 7832 on t1wi t2wi flair and dwi respectively the absolute values of cnrs of lesions on dwi were significantly greater than those on other sequencesconclusion dwi appears to be more sensitive in detecting ev71 encephalitis than conventional mri sequences this capability may improve the accuracy in diagnosing ev71 encephalitis especially at the early stage