T2 Relaxation Time Abnormalities in Bipolar Disorder and Schizophrenia

There are substantial abnormalities in the number, density, and size of cortical neurons and glial cells in bipolar disorder and schizophrenia. Because molecule-microenvironment interactions modulate metabolite signals characteristics, these cellular abnormalities may impact transverse (T(2)) relaxation times. We measured T(2) relaxation times for three intracellular metabolites (N-acetylaspartate + N-acetylaspartylglutamate, creatine + phosphocreatine, and choline-containing compounds) in the anterior cingulate cortex and parieto-occipital cortex from 20 healthy subjects, 15 patients with bipolar disorder, and 15 patients with schizophrenia at 4 T. Spectra used in T(2) quantification were collected from 8-cc voxels with varying echo times (30 to 500 ms, in 10-ms steps). Both bipolar disorder and schizophrenia groups had numerically shorter T(2) relaxation times than the healthy subjects group in both regions; these differences reached statistical significance for creatine + phosphocreatine and choline-containing compounds in bipolar disorder and for choline-containing compounds in schizophrenia. Metabolite T(2) relaxation time shortening is consistent with reduced cell volumes and altered macromolecule structures, and with prolonged water T(2) relaxation times reported in bipolar disorder and schizophrenia. These findings suggest that metabolite concentrations reported in magnetic resonance spectroscopy studies of psychiatric conditions may be confounded by T(2) relaxation and highlight the importance of measuring and correcting for this variable. Magn Reson Med 63:1-8, 2010. (C) 2009 Wiley-Liss, Inc.