Which technique is used to reveal blood flow and brain activity by comparing images over time?

The technique that reveals blood flow and brain activity by comparing images over time is functional MRI (fMRI). fMRI measures changes in blood flow and, consequently, the associated brain activity. This method operates on the principle that more active brain regions consume more oxygen, which alters the magnetic properties of the blood. By capturing a series of MRI images over time, fMRI can track these changes and help identify which areas of the brain are engaged during specific tasks or stimuli.

In contrast, positron emission tomography (PET) provides insights into metabolic processes and usually requires the administration of a radioactive tracer to measure energy consumption, but does not provide real-time imaging like fMRI. Magnetic resonance imaging (MRI) offers detailed images of the brain's anatomy but does not directly measure brain activity or blood flow. Similarly, computed tomography (CT) focuses on structural imaging and does not provide functional information about brain activity and blood flow. Thus, fMRI stands out for its unique ability to map brain activity by continuously capturing changes in blood flow over time.