CT and diffusion-weighted MR imaging in randomized order - Diffusion-weighted imaging results in higher accuracy and lower interrater variability in the diagnosis of hyperacute ischemic stroke

Background and Purpose-Diffusion weighted MRI (DWI) has become a commonly used imaging modality in stroke centers The value of this method as a routine procedure is still being discussed In previous studies CT was always performed before DWI Therefore infarct progression could be a reason for the better result in DWI Methods-All hyperacute (<6 hours) stroke patients admitted to our emergency department with a National Institutes of Health Stroke Scale (NIHSS) score >3 were prospectively randomized for the order in which CT and MRI were performed Five stroke experts and 4 residents blinded to clinical data judged stroke signs and lesion size on the images To determine the interrater variability we calculated kappa values tor both rating groups Results-A total of 50 patients with ischemic stroke and 4 patients with transient symptoms of acute stroke (median NIHSS score 11 range 3 to 27) were analyzed Of the 50 patients 55% were examined with DWI first The mean delay from symptom onset until CT was 180 minutes that from symptom onset until DWI was 189 minutes The mean delay between DWI and CT was 30 minutes The sensitivity of infarct detection by the experts was significantly better when based on DWI (CT/DWI 61/91%) Accuracy was 91% when based on DWI (CT 61%) Interrater variability of lesion detection was also significantly better for DWI (CT/DWI kappa=0 51/0 84) The assessment of lesion extent was less homogeneous on CT (CT/DWI K=0 38/0 62) The differences between the 2 modalities were stronger in the residents ratings (CT/DWI sensitivity 46/81% kappa=0 38/0 76) Conclusions-CT and DWI performed with the same delay after onset of ischemic stroke resulted in significant differences in diagnostic accuracy DWI gives good interrater homogeneity and has a substantially better sensitivity and accuracy than CT even if the raters have limited experience.