Molecular Positron Emission Tomography and Single-Photon Emission Computed Tomography Imaging for Understanding the Neurobiological Mechanisms of Electroconvulsive Therapy

Electroconvulsive therapy (ECT) effectively treats severe psychiatric disorders such as depression, mania, catatonia, and schizophrenia. Although its exact mechanism remains unclear, ECT is thought to induce neurochemical and neuroendocrine changes. Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) have provided vital insights into ECT's neurobiological effects. This scoping review investigates the role of molecular imaging in understanding these effects. A systematic search across PubMed, EMBASE, Web of Science, Cochrane, and Scopus databases yielded 857 unique records, from which 45 peer-reviewed articles in English with longitudinal PET or SPECT measures in ECT patients were included. The review identifies 2 main research directions: ECT's impact on brain activity and neurotransmitters. Initial research assessed regional cerebral blood flow and regional glucose metabolism during ictal (during ECT), postictal (within 24 hours), short-term (within a week), and long-term (beyond a week) follow-up as markers of brain activity. Initial findings showed an anterior-posterior regional cerebral blood flow gradient during the ictal phase, with subsequent normalization of hypoperfusion in frontal and parietal regions, and persistent long-term effects. Later, research shifted to the monoamine hypothesis of depression, examining ECT's impact on serotonin and dopamine systems via PET imaging. Results on receptor availability post-ECT were mixed, showing both reductions and no significant changes, indicating variable effects. This scoping review further highlights the need to explore new targets, tailor methodologies for patient populations, and foster multicenter studies. Although SPECT has been valuable, advances in PET imaging now make it preferable, offering unparalleled insights into ECT's molecular and neurobiological mechanisms.