Near infrared light
Absorption of light by blood
Blood
Interpolation
Cerebral Cortex
fMRI
MEG
PET
MEG ( magneto-encephalography ) is a modality that detects the magnetic-flux change in the brain from outside the cranium. This change is caused by the synaptic discharge current from the activities of neurons. The sensor coil is called a SQUID ( superconducting quantum interference device ), which is located and cooled in liquid Helium. The system must be installed in a special room with tight magnetic shielding to shut out electromagnetic noise and terrestrial magnetic effect. This modality is fundamentally superior in measuring neuron activities directly compared to the other indirect measurements of the brain activities, which sometimes gives us the indispensable information. But it suffers from some difficulties of analyzing the data in cases where the brain activities occur over a wide area or multiple areas.