FMRI is a device used by doctors or other medical personnel to map brain activity. It stands for functional magnetic resonance imaging. The f at the beginning of fMRI is not capitalized unless it is at the beginning of a sentence.
An fMRI must be interpreted in real time, while an MRI can take still images.
An fMRI machine is a large, bed-sized, expensive medical device that generates intense magnetic fields. For this reason, people with pacemakers are warned not to go near MRI machines. Patients must remove metal objects before entering the machine. To enter the machine, the patient lies down on a horizontal stretcher-like platform that slides into a cylindrical cavity. The patient is magnetically scanned from all sides and an image is generated in real time, which is sent to doctors for further analysis.
An fMRI machine works on the principle of magnetic resonance imaging. The practice was previously known as magnetic resonance tomography (MRT) or nuclear magnetic resonance (NMR).
Functional MRIs allow doctors to trace blood flow in the brain to get a better picture of not only structures but functionality as well.
MRI works in the following way. It’s been known for over 100 years that blood flows to certain areas of the brain when those areas are active. This is because active neurons consume more blood than inactive neurons. Red blood cells carry a substance called hemoglobin throughout the body, including to active neurons. When a neuron is active, it consumes more oxygen, which it receives in the form of hemoglobin.
A patient receiving an fMRI will lie on a platform similar to a horizontal stretcher and slide into a cylindrical cavity.
Hemoglobin is an “oxygen storage molecule” capable of releasing and absorbing oxygen multiple times. Red blood cells contain abundant hemoglobin, which is oxygenated by air from the lungs and then deoxygenated when cells receive oxygen. Oxygenated and deoxygenated hemoglobin have different magnetic properties.
Oxygenated hemoglobin is diamagnetic, meaning it slightly repels a magnetic field. Deoxygenated hemoglobin is paramagnetic, which means that the application of an external magnetic field causes it to become slightly magnetic. Both effects are small but measurable.
When a neuron is active, it consumes more oxygen, which it receives in the form of hemoglobin.
Hemoglobin deoxygenation in neurally active areas is what the fMRI machine captures. This occurs several seconds after the neural activity itself. FMRI machines have been criticized as a scientific tool for a number of reasons, including that some fMRI interpretation theories are unfalsifiable and that different parts of the brain can consume more or less oxygen even if they have roughly the same level of activity. Nevertheless, fMRI has been used successfully for years to diagnose various brain problems. It has also been used in psychology to study which tasks activate which areas of the brain.