What is fMRI?

Functional magnetic resonance imaging is an emerging neuroimaging method. The principle is to use magnetic resonance imaging to measure changes in hemodynamics caused by neuron activity. At present, it is mainly used to study the brain or spinal cord of humans and animals.

Functional magnetic resonance imaging is an emerging neuroimaging method. The principle is to use magnetic resonance imaging to measure changes in hemodynamics caused by neuron activity. At present, it is mainly used to study the brain or spinal cord of humans and animals.

Chinese name

Functional magnetic resonance imaging

Foreign name

functional MRI, fMRI

Belong to

An emerging neuroimaging approach

Used in

Study human or animal brain or spinal cord

Technology

Positron emission tomography

fMRI FMRI fMRI

Functional magnetic resonance imaging (fMRI, f unctional m agnetic r esonance i maging) picture description : Functional magnetic resonance imaging data (yellow to orange) is superimposed on the average brain anatomy image (gray scale) obtained by several people, Shows areas of brain activation when exposed to external stimuli.

Functional magnetic resonance imaging background

Since the 1890s, it has been known that changes in blood flow and blood oxygen (the two are collectively called hemodynamics) are inextricably linked to neuronal activation. Nerve cells consume oxygen when they are activated, and oxygen is transported by red blood cells through the micro blood vessels near the nerve cells. Therefore, when the brain nerve is activated, blood flow in the vicinity increases to supplement the consumed oxygen. There is usually a delay of 1-5 seconds from nerve activation to initiation of hemodynamic changes, and then peaks at 4-5 seconds before returning to baseline (usually accompanied by a slight undershoot). This not only changes the cerebral blood flow in the nerve activation area, but also the concentration of deoxygenated and oxygenated hemoglobin in the local blood, as well as the cerebral blood volume.

Blood oxygen-level dependent (BOLD) was first proposed by Kogawa Seiji et al. In 1990, and then applied by Jiang Jianmin et al. In 1992. Since the neurons themselves do not have the glucose and oxygen needed to store energy, the energy consumed by nerve activation must be replenished quickly. Through the process of hemodynamic response, the blood brings more oxygen than the nerves. Due to the difference in permeability between oxygenated hemoglobin and deoxyheme, changes in the volume of oxygenated blood and hypoxic blood make the magnetic field disturb And can be detected by magnetic resonance imaging. By repeating certain thoughts, actions, or experiences, you can use statistical methods to determine which brain regions have signal changes in the process, so you can find out which brain regions are performing these thoughts, actions, or experiences.

Almost most functional magnetic resonance imaging uses the BOLD method to detect the reaction area in the brain, but because the signal obtained by this method is relative and non-quantitative, people have questioned its reliability. Therefore, other methods that can more directly detect neural activation (such as Oxygen Extraction Fraction (OEF), an estimate of how much oxygenated heme is converted into deoxyheme) have been proposed, but Due to the very weak changes in the electromagnetic field caused by neural activation, too low a signal-to-noise ratio makes it impossible to count and quantify reliably.

The application of functional magnetic resonance imaging is divided into three cases: ^[1]

1. Diffusion imaging. Water molecules in the human body have random diffusion in the form of Brownian motion. This diffusion information is independent of the relaxation times T _{1 and} T ₂ , and it can provide functional information at the molecular level.

2. Perfusion imaging, hemodynamic imaging at the microcapillary level, is traditionally solved by isotope imaging methods. The planar echo imaging method in magnetic resonance imaging not only can provide information about regional cerebral blood flow and cerebral blood flow, but also has a higher spatial resolution than traditional methods.

3. Animated images of tasks. When the human body is doing an activity, there will be corresponding reflections in special areas of the cerebral cortex. Using fMRI to measure the oxygenation level of the brain blood can directly study the brain function.

Functional magnetic resonance imaging

Research using positron emission tomography (PET scans), or PET scanning technology, gave subjects (but very safe) different radioactive substances that were absorbed by active brain cells in the brain. Magnetic resonance imaging (MRI) uses magnetic fields and radio frequency waves to generate pulse energy in the brain, because the pulses can be tuned to different frequency bands, coupling some atoms to the magnetic field. At the moment when the magnetic pulse is turned off, these atoms vibrate (resonance) and return to their original state. A special radio frequency receiver detects these resonances and their channel information to the computer, thereby generating different atoms in the brain area. Position the image.

The new technology of functional magnetic resonance imaging (fMRI) combines the advantages of the above two technologies to realize brain functional imaging by examining the magnetic field changes of blood flow into brain cells. It gives a more accurate structure and Functional relationship.