STRUCTURAL MAGNETIC-RESONANCE IMAGE AVERAGING IN SCHIZOPHRENIA

Objective: Intersubject averaging of structural magnetic resonance (MR ) images has been infrequently used as a means to study group differen ces in cerebral structure throughout the brain. In the present study, the authors used linear intersubject averaging of structural MR images to evaluate the validity and utility of this technique and to extend previous research, conducted using a different approach to image avera ging, in which reduction in thalamic size and abnormalities in peritha lamic white matter tracts in the brains of schizophrenic patients were reported by Andreasen et al. Method: A 1.5-T MR scanner was used to o btain high-resolution, whole brain T1-weighted structural MR images fo r an age-matched sample of 25 schizophrenic patients and 25 normal con trol subjects. A ''bounding box'' procedure was used to create a singl e ''averaged'' brain for the schizophrenic group and for the control g roup. Differences in signal intensity between the two average brains w ere examined on a pixel-wise basis through use of one-tailed effect si ze maps. Results: Effect size maps revealed widespread patchy signal i ntensity differences between the two groups in both cortical and periv entricular areas, including major white matter tracts. The signal inte nsity differences were consistent with cortical thinning/sulcal wideni ng and ventricular enlargement. No differences were found within thala mus or in immediately surrounding white matter. Effect size maps for d ifferences (schizophrenic minus normal subjects) had only small values . Conclusions: These results are consistent with diffuse structural br ain abnormalities of both gray and white matter in schizophrenic popul ations such as the one in this study.