Neuroimaging techniques Flashcards
What is Neuroimaging?
Process of producing imaging of brain structure or function of the brain of other parts of the nervous system.
Important for cognitive neuroscience to combine traditional techniques with modern experimental methods to determine how brain function supports mental activity.
EEG?
Is classed as a whole as neuroimaging, however contradictory feelings about it.
Relies on electrode that are sensitive to electrical changes. Very temporally sensitive. Cheap.
Disadvantage - sensitive to nearby electrical pulses.Only measuring really the outer layer of the cortex.
What signals do we detect?
Electric activity: Excitatory, inhibitory, soma action potentials (EEG, MEG, Electrophysiology).
Metabolic response: Glucose consumption and oxygen consumption (Usually PET, Autoradiography)
Haemodynamic response: Blood flow, volume and oxygenation (H215O PET, MIRS, Optical imaging, FMRI, ASL).
MRI
Protons in body when put in a strong magnetic field, they line up with the field. given radio frequency pulse. The rate they realigned depends on local tissue/matter characteristics.
Good for structure
BOLD
Blood Oxygenation Level Dependency. Used in fMRI.
Oxygenated haemoglobin. Rush of blood to activated neurons. Flow changes local magnetic properties.
Early FMRI studies
Kwong et al, 1992. Found increase of signal in occipital area when seeing flickering checkerboard when taken from baseline.
Structural (T1) images
High spatial resolution.
Low temporal reso.
Can distinguish different types of tissue.
Functional (T2) images
Lower spatial resolution.
Higher temporal resolution.
Can relate chabges in signal to an experimental manipulation.
Processing to create final image
Adjust for head movement.
Fit to standard template.
Building a model and fitting them to the data.
End up with a map where there are statisticasl evidecne for given task recruitment.
Then a 2nd level of between-subject analysis.
PET scan
Positron Emission Tomography.
Radioactivity with cyclotron.
Read 2 opposite gamma rays that have been released by a radioactive substance being put into patient. A proton collides with an electron and destroys each other - which releases the gamma into gamma detectors.
Gives a 3D representation of what is going on.
In pharmaceuticals can test where chemicals go.
Tightly controlled - 1/2 a year only.
Why do we use neuroimaging?
How the brain works.
Questions about disorders.
Questions affecting clinical decision making.
Questions about interventions.
Pros and cons of PET
Pro - help know if a drug enters or not.
Early decisions on dose in healthy and patients.
Behavioural/patient studies.
Cons - cannot do multiple times as uses radiation.
Pros and cons of fMRI
Evidence drug gets into the brain.
Gives us something about the function it takes in the brain.
Behavioural/patient studies.
Sentitive but not quantitative.
cASL
Cerebral - Arterial spin labelling.
Change spin of blood.
It is quantitative.
Static image over 5 minute window. Becoming more important.
Can scan every 5 minutes. Spatially quite accurate (wisdom teeth example).
Resting state fMRI
HAVE A LOOK AT THIS
Constraints of imaging
Largely rely on principle of insertion (contrast) - making it qualitative rather than quantitative.
In controls assume that no working memory being used. Depends on how well paradigms are designed - need to control for everything so that you can make accurate inferences.
- Scanner environment gives limitations.
- Depends on sensitivity.
- Limits in temporal and spatial resolution.
EEG analysis
Quantitative EEG - separate frequencies. Less spatially resolved.
Event-Related potentials - Excitatory and inhibitory signals can cause problems.
Magneto Encephalography (MEG)
detects magnetic field changes. Tiny conducting detectors 128-259 (SQUID).
Very fast, very versatile, cortical only. Still sensitive to things happening in the cortex.
Near infra-red spectroscopy imaging
Relies on absobent rate of oxygenated and non oxygenated bloodd though infrared light.
More active neurons - utilise more oxygen.
Exess of oxygenated heamoglobin. Cheapest imaging technique.
Shine infra red light and detectors measure changes in blood.
MRI
REALLY NEED TO LOOK AT THIS.
Impact of structural and functional imaging
In diagnostic radiology.
Particularly in aschemic stroke - clot stops blood circulation.
Nerons will die and necrosis will occur.
Diffusion Weighted Imaging. Identifies part of lesion to know full extent of impact.
Sensitivity to motion.
Magentic resonance Angiography - sensitive to veins or arteries.
What are the diffusion contrasts in MRI?
Isotropy - random movement of water molecules.
Anisotrophy - up and down myelin sheaths.
What are the diffusion contrasts in MRI?
Isotropy - random movement of water molecules in grey matter.
Anisotrophy - up and down myelin sheaths.
