Subcomponents of brain T2* relaxation in schizophrenia, bipolar disorder and siblings: A Gradient Echo Plural Contrast Imaging (GEPCI) study

Investigating brain tissue T2* relaxation properties in vivo can potentially guide the uncovering of neuropathology in psychiatric illness, which is traditionally examined post mortem. We use an MRI-based Gradient Echo Plural Contrast Imaging (GEPCI) technique that produces inherently co-registered images allowing quantitative assessment of tissue cellular and hemodynamic properties. Usually described as R2* (=1/T2*) relaxation rate constant, recent developments in GEPCI allow the separation of cellular-specific (R2*_C) and hemodynamic (BOLD) contributions to the MRI signal decay. We characterize BOLD effect in terms of tissue concentration of deoxyhemoglobin, i.e. C_DEOXY, which reflects brain activity. 17 control (CON), 17 bipolar disorder (BPD), 16 schizophrenia (SCZ), and 12 unaffected schizophrenia sibling (SIB) participants were scanned and post-processed using GEPCI protocols. A MANOVA of 38gray matter regions ROIs showed significant group effects for C_DEOXY but not for R2*_C. In the three non-control groups, 71-92% of brain regions had increased C_DEOXY. Group effects were observed in the superior temporal cortex and the thalamus. Increased superior temporal cortex C_DEOXY was found in SCZ (p=0.01), BPD (p=0.01) and SIB (p=0.02), with bilateral effects in SCZ and only left hemisphere effects in BPD and SIB. Thalamic C_DEOXY abnormalities were observed in SCZ (p=0.003), BPD (p=0.03) and SIB (p=0.02). Our results suggest that increased activity in certain brain regions is part of the underlying pathophysiology of specific psychiatric disorders. High C_DEOXY in the superior temporal cortex suggests abnormal activity with auditory, language and/or social cognitive processing. Larger studies are needed to clarify the clinical significance of relaxometric abnormalities.