The device that uses a magnetic field to record changes in blood flow and oxygen use in the brain is called an fMRI (functional magnetic resonance imaging) machine.
fMRI is a neuroimaging technique that allows researchers and medical professionals to monitor brain activity by measuring changes in blood flow and oxygenation levels in response to different stimuli or tasks.
It provides valuable insights into the functioning of the brain and is widely used in both research and clinical settings to study various aspects of brain function and disorders.