**1. Introduction**

128 Neuroimaging – Cognitive and Clinical Neuroscience

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Altered resting-state functional connectivity and anatomical connectivity of

Reliable intrinsic connectivity networks: test-retest evaluation using ICA and dual

Over the last 20 years, SPECT and PET, along with CT and MRI have been the main methodologies used in studies investigating psychiatric disorders. The structural alterations in patients' brains found by CT and MRI are usually quite subtle, while those found by the nuclear imaging modalities (PET and SPECT) are more pronounced. Partly for this reason, the latter methods have led to discoveries in a wide range of psychiatric disorders. In the 90s, region of interest (ROI) method provided only sketchy results due to the low spatial resolution of the nuclear imaging, but rapid progression in analytic and statistical methods in the 2000s had led to more detailed and accurate determinations of the differences in regional cerebral blood flow (rCBF) and glucose metabolic ratios (rGMR) between patients and comparison subjects. On the other hand, whereas an improved understanding of the etiology of psychiatric disorders has led to significant progress in multiple research areas, SPECT and PET studies measuring only the rCBF/rGMR distribution at rest have come to face some limitations for elucidation of the disease pathophysiology. Accordingly, at resting studies using SPECT/PET have tended to focus on certain kinds of clinical information, such as symptomatology and treatment. This review summarizes the history of at rest SPECT and PET studies, and provides a comprehensive survey in psychiatric disorders including schizophrenia, major depressive disorder, bipolar disorder and obsessivecompulsive disorder.
