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PRISMA flowchart. A search over the Pubmed database yielded 939 studies, after which they were screened in the first round based on their abstracts and in the second round based on the main text of the remaining studies (PET, Positron Emission Tomography; SPECT, Single Photon Emission Computed Tomography; fNIRS, Functional Near Infrared Spectroscopy; MRS, Magnetic Resonance Spectroscopy; CT, Computed Tomography).
