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f is functional. MRIs are basically huge magnets used for imaging. When you apply a strong magnetic field, different tissue types and densities will react diffe
by jawilson2 10mo ago
f is functional.
MRIs are basically huge magnets used for imaging. When you apply a strong magnetic field, different tissue types and densities will react differently, and the MRI is basically measuring how those tissues react to the magnet. It is very good for imaging soft tissues, but not so much bone. Someone figured out that you can measure blood flow using the MRI, because blood cells react in a magnetic field, then "relax" at a known rate. Since we can measure blood flow, that is correlated with increased brain activity, i.e. since more neurons are firing, they require more energy, and therefore more blood. So, fMRI is using blood flow as a proxy for brain activity.
- parpfish 10mo agoFmri doesn’t measure blood flow, it measures the oxygen level in the blood. Hemoglobin molecules change shape when they carry oxygen and the different shapes react differently to magnets, which is a real stroke of luck
- jawilson2 10mo agoYep, this is why it's also called BOLD imaging, for blood-oxygenation-level-dependent fMRI. I did my PhD is BME and brain-computer interfaces, but it has been a while since I worked in the field.
- physPop 10mo agoit doesn't measure the oxygen level directly either. the bold signal is correlated to dephasing induced by the oxy/deoxy hg ratio that isn't even necessarially localized to the voxel (flow or long range magnetic susceptibility perturbations from nearby accumulated deoxyhg (veins)).