What technology uses magnetic fields to detect activity in the brain by monitoring blood flow?

Functional Magnetic Resonance Imaging (fMRI) is the correct answer because this technology specifically utilizes magnetic fields and radio waves to measure alterations in blood flow that occur in the brain during various activities. As neurons become more active, they require more oxygen, which leads to changes in blood flow to those regions. fMRI detects these changes, allowing researchers and clinicians to infer brain activity patterns.

In contrast, Electroencephalography (EEG) measures electrical activity in the brain, which does not involve the use of magnetic fields related to blood flow. Positron Emission Tomography (PET) involves injecting a radioactive tracer to observe metabolic activity, but also does not focus directly on blood flow in the same way fMRI does. Computed Tomography (CT) primarily provides structural imaging of the brain using X-rays, not focusing on functional changes related to blood flow or brain activity. Thus, fMRI stands out as the only technology among the options provided that combines magnetic fields with the ability to track changes in blood flow linked to brain activity.