What is the resolution of fMRI

functional magnetic resonance imaging (fMRI)

 

[engl. functional magnetic resonance imaging (fMRI)], [BIO, DIA], is currently one of the most common imaging methods (magnetic resonance tomography, MRT) to measure changes in physiol. Brain functions that occur during cogn., Emot., Social etc. activities. During an fMRI examination, the person is placed in the strong magnetic field of a scanner, whereby the dipole-like structure of the hydrogen atoms in the body is usually aligned along the direction of the magnetic field. A recurring electromagnetic impulse is used to deflect the hydrogen atoms from their position and to put them in a higher energetic state. When this impulse ends, the atoms swing back again (Relaxation), whereby energy is given off as electromagnetic radiation (resonance). Depending on the blood flow in the brain, this echo will be different. fMRI is based on a non-invasive measurement of oxygen extraction in the blood of active brain tissue. Hemoglobin, which has given up its oxygen, has different magnetic properties than the oxygen-rich oxyhemoglobin. The extraction of oxygen in active brain regions that occurs after approx. 1 to 2 s (so-called Blood Oxygen Level Dependent Response, BOLD) leads to a brief increase in the content of paramagnetic deoxyhemoglobin, the spatial distribution of which allows conclusions to be drawn about the degree of activation of the respective brain region. The spatial resolution of the fMRI is good, but the temporal resolution is limited by the oxygen-dependent reaction times. fMRI examinations can be affected by several interfering effects: properties of the scanner used or the sequence used, instabilities of the system, inconsistencies in data acquisition, distortions and losses of the signal in some cases. Brain regions, physiol. Artifacts, movement artifacts, as well as unintended, overlapping cogn. Activities.

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