Brain gray and white matter transverse relaxation time in schizophrenia

Recent in vivo diffusion brain imaging studies of schizophrenic patients ha ve revealed microstructural abnormalities, with low diffusion anisotropy pr esent throughout much of cortical white matter. Brain anisotropy is produce d when proton movement reflects physically restricted water movement, for e xample, by myelin sheaths. Conditions that increase self-diffusion, such as edema, may also alter the longitudinal and transverse relaxation time of p rotons, and it is possible that such changes could explain the observed ani sotropy diminution seen in schizophrenia. To test this possibility, we calc ulated pixel-by-pixel transverse relaxation time (T2) and proton density (P D) maps for gray matter and white matter across eight 5-mm-thick axial slic es of fast spin echo MRI in 10 control men (age 30-57 years) and 10 men wit h schizophrenia (age 32-64 years). Schizophrenics had significantly longer mean white matter T2 (84.0 vs. 81.9 ms, P < 0.03) and gray matter T2 (95.1 vs. 92.2, P = 0.003); their mean white and gray matter PD values were not s ignificantly different from those of controls. Correlations were not signif icant between anisotropy and T2 in either grey or white matter but were sig nificant between anisotropy and PD in white matter. T2 relaxation times are longer in schizophrenics than in controls in both gray and white matter wh ereas anisotropy reduction is restricted to white matter. Taken together, t hese results suggest that the process producing prolonged T2 does not fully account for the abnormally low anisotropy observed selectively in white ma tter in this group of schizophrenic patients. (C) 1999 Elsevier Science Ire land Ltd. All rights reserved.