Neuroimaging

Neuroimaging

1. Brain Imaging techniques

   • Structural
     • CT
       • Moderately invasive – uses X-rays (ionising radiation)
       • Inexpensive, widely available
       • Low spatial resolution – useful clinically, not for neuroscience research
     • MRI
       • Non-invasive (innocuous) - Uses radio frequency (RF) fields to acquire images
       • Extremely high spatial resolution, e.g. < 1mm3
       • Number one choice for structural brain imaging in neuroscience research
   • Functional
     • PET
       • Moderately invasive: radioactivity is introduced into the body
       • Measures indirect metabolic correlates of neural activity (blood flow, glucose metabolism). Can measure synaptic transmission directly (e.g. by labelling receptors)
       • High spatial resolution
       • Extremely low temporal resolution
       • Extremely expensive!
     • fMRI
       • non-invasive (innocuous)
       • Measures (indirect) metabolic correlates of neural activity (blood flow, oxygen consumption)
       • Has high spatial resolution, e.g. 3mm3
       • Has low temporal precision, because it measures slow processes
       • Moderately expensive
       • Detecting function - history
         • 1881 Angelo Mosso, William James:
           • (human scales and blood to brain)
         • 1897 Paul Broca
           • Frontal temperature inc/s more than temporal temperature. Latter more than occipital temperature”
         • 1928, John Fulton
           • Vascular murmur at occipital cortex, inc/ w/ complexity of visual task
         • 1936, Linus Pauling + Coryell
           • different magnetic properties of oxygenated and deoxygenated blood
         • 1991 John Belliveau + Thomas Brady
           • 1st fMRI images
         • • 1968-73 – Magnetic Resonance Imaging (MRI) developed for structural brain imaging
       • MRI Scanner:
         • Strong magnet: 1.5-7 tesla
         • 1.5 tesla = 15,000 gauss
         • Earth’s magnetic field strength = 0.5 gauss
           • 30,000 X
         • NO METAL!
       • Blood Oxygen Level Dependent (BOLD) signal
         • Neurons active: blood flows to part of the brain to provide oxygen to cells
         • Hemoglobin - differs in response to mag/ fields, depending if has bound to oxygen molecule
           • Deoxygenated = more attracted to mag/fields
         • Ox/d blood distorts mag/field LESS - MR pulse sequences show more MR signal where blood is highly oxy/d or not
         • NET EFFECT = REDUCTION - field inhomogeneity, INC/ - MR signal
         • Properties: