Functional magnetic resonance imaging

Definition, function and process

The Functional Magnetic Resonance Imaging (fMRI) is a functional imaging technique that can visualize the activity level of certain brain areas. Technically, the fMRI is based on magnetic resonance imaging (MRI). The term fMRI (functional magnetic resonance imaging) can also be used. The method is based on the assumption that the activation of a brain region results in an increased blood flow in the latter, which can be measured indirectly via the magnetic properties of hemoglobin.
How does a fMRT work?
Active neurons in the brain consume more energy (glucose) and oxygen. Due to the increased demand, the blood flow in the activated brain regions increases to supply the nerve cells with nutrients.
The fMRI image is dependent on the so-called BOLD contrast (blood oxygenation level dependent). Translated, BOLD means "depending on the oxygen content of the blood". It does not measure oxygen saturation in the brain, but the magnetic strength of hemoglobin. The iron-containing hemoglobin functions as an oxygen transport protein in humans. Depending on whether the hemoglobin has bound oxygen or not, it is different degrees of magnetic.
Here, a distinction is made between oxygenated blood (hemoglobin with bound oxygen) and deoxygenated blood (hemoglobin without bound oxygen). If the activity of neurons increases, the consumption of hemoglobin without bound oxygen also increases. Although oxygen-depleted blood flows down, the nerve cells consume slightly more oxygenated blood than new can flow into the brain area, which increases the proportion of deoxygenated hemoglobin to oxygenated hemoglobin.
Deoxygenated blood and oxygenated blood differ as already mentioned in terms of their magnetic properties. Oxygenated blood is more magnetic (paramagnetic) than oxygenated blood (diamagnetic). This difference can be registered and made visible by the fMRI.
Interpretation of fMRI images
In order to interpret fMRI images, recordings of at least two states must be made. Once in the resting state (without stimulus), and once in the activity state (at the desired stimulus situation). The images can then be compared with each other and show which brain regions were addressed by the stimulus situation. From this, conclusions can be drawn on brain function.
How much does a fMRT cost?
Depending on the time required, an fMRI costs between 400 and 1200Ђ.