Dr. Rоdriguez is studying hоw the brаin prоcesses feаr аnd reward in patients diagnosed with major depression. To see which specific brain regions are most metabolically active during a task, she injects a small amount of radioactive glucose into her participants. She then asks them to perform a memory recall exercise while a scanner detects the gamma rays emitted as the glucose tracer decays in areas of high neuronal firing (which consume more glucose). The resulting images are color-coded maps showing the relative levels of activity across different parts of the brain. Which neuroimaging technique is Dr. Rodriguez using?