Neuroimaging Methods: Visualising the brain & its injuries Structural (brain structure) –X-rays –CT (Computer Tomography) –MRI (Magnetic Resonance Imaging) Functional (brain function) –Blood flow (PET/SPECT/fMRI). –Neuron’s electrical responses (EEG/EEG) – Special thanks to Chris Rorden, U. South Carolina

X-ray tube projects through head Detector plate measures transmission of X-rays –Bone relatively opaque to X-rays –Soft tissue relatively transparent Use: –broken bones –Angiography Not good for much else Structural: X-rays

Structural: CT scans A series of X-rays are taken at different angles –Computer reconstructs 2D slices Uses: –Stroke –Brain tumors (larger than 2-4 mm) –Enhanced with contrast material –Subdural Hematoma –Evaluation of traumatic Head Injury

CT scan

CTRendered CTPlain film No Contrast Contrast

MRI Magnetic resonance imaging Does not expose individual to X-rays

How does MRI work? A compass analogy Compass needle points North Briefly put magnet on right side: needle points East After magnet is removed, needle points North again (lower energy state) Needles in different fluids will take different time to return to North N N N Spin of H atoms aligns with static magnetic field Briefly apply radiofrequency pulse: spin tipped After RF pulse, H atoms realign (lower energy state) Atoms in different tissues (fat, muscle, etc) require different time to realign (relax).

MRI scans Healthy enlarged ventricles MCA infarct & wide sulci

Types of MRI scan T1 (anatomical): –fast to acquire, –good detail (e.g. white and gray matter). T2 (pathological): –slower to acquire, thus worse resolution. –Excellent for finding lesions.

PET (Positron Emission Tomography SPECT (Single Photon Emission Computerized Tomography) Radioactive oxygen isotope injected into blood Brain regions that use oxygen emit more positrons Functional imaging: Measures brain activity

functional: fMRI fMRI: Functional Magnetic Resonance Imaging -Increase activity in certain brain area -Blood vessels dilate -The % of Oxygen in the blood in that area is changed -The MR machine registers that

Functional: Electroencephalogram (EEG) Measures electrical activity Useful for studying ‘sleep’ When neurons fire, they create electical dipoles. Neurons aligned perpendicular to cortical surface. + -

Event related potentials (ERPs) ERPs are a type of EEG –Continuously collect EEGs –Present many trials of stimuli (words: neutral vs. offensive) –Compute average brain response to stimuli Good temporal resolution (when activity starts happening). Poor Spatial resolution Time (ms) _ Signal  V neutral ‘rape’

In sum, Structural (brain structure) –X-rays –CT (Computer Tomography) –MRI (Magnetic Resonance Imaging) Functional (brain function) –Blood flow (PET/SPECT/fMRI). –Neuron’s electrical responses (EEG/EEG) –Neuron’s magnetic responses (MEG)