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/ERP)–

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

Uses:– Stroke – Brain tumors (larger than 2-4 mm)– Enhanced with contrast material– Subdural Hematoma – Evaluation of traumatic Head Injury

CT scan

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

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 • • 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)0 100 200 300

+

_S

ign

al

V neutral

‘rape’

http://brainserver.psych.indiana.edu/

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)