Brain Imaging: Techniques and Methods, Summaries of Neuroscience

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Behavioral and Integrative Neuroscience

Brain Imaging: Techniques and Methods

PET, fMRI, and Optical Imaging

• Labels of activity, related to blood flow
• Different spatial resolution
• Relatively slow compared with electrophysiology MRI Anatomical view of whole brain Contrast between watery and drier tissues

Comparing different imaging techniques:

spatial resolution, temporal resolution and invasiveness

(From Cohen and Bookheimer 1994)

Magnetic resonance imaging (MRI): makes use of the magnetic

properties of nuclei of atoms (mainly protons in Hydrogen) making up different tissue; the subject is put in a very large (~X10,000 the earth’s) magnetic field; very small amounts of ~radio-frequency electromagnetic pulses are then ‘transmitted’; different tissues react slightly differently, expressed in different decay rates of emitted energy received by the coil surrounding the subject’s head.

functional MRI makes use of the different magnetic properties of hemoglobin

when it is deoxygenated and oxygenated -- as a consequence of blood oxygen level (the BOLD signal).

Positron emission tomography (PET): measures positrons from radioactively-

labeled analogues of metabolic compounds injected into the bloodstream (eg fluorine -18 fluorodeoxyglucose, or FDG, for glucose)--amount of positrons indicates tissue metabolic rate. Or tagged water can be used to monitor blood flow--higher density of positrons when flow increases.

Electro-encephalography (EEG): uses electrodes placed on the scalp to detect

and measure patterns of electrical activity emanating from the brain.

Magneto-encephalography (MEG): uses sensitive magnetometers (SQUIDs) to

measure magnetic fields caused by current flow in brain circuits

Whole-Brain Imaging Techniques

Cellular mechanisms of the linkage between neuronal activity and increased blood flow

• Neuronal signals
• Glial signals

PET and blood flow

Fundamental principles of Magnetic Resonance in protons