Transcript 1: Neuropsychology

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
Structural: X-rays
• 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: 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
Contrast
No Contrast
• Plain film
• CT
• Rendered CT
MRI
• Magnetic resonance imaging
• Does not expose individual to X-rays
How does MRI work? A compass analogy
N
Spin of H atoms aligns with
static magnetic field
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
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
& wide sulci
MCA infarct
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.
Functional imaging: Measures brain activity
• 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: 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
• Poor Spatial resolution
Signal V
(when activity starts happening).
+
_
0
neutral
‘rape’
100 200 300
Time (ms)
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)