Neuroimaging Flashcards
What is structural and functional imaging?
Structural: brain anatomy
Functional: living, dynamic brain
What are lesion studies?
Post mortem studies of functional deficits after brain damage
What did Angelo Mosso discover in the 19th Century?
Functional brain imaging is linked with cerebral blood flow, cognition and brain pulsations in fontanelles of newborns
Mosso measured brain activity by weighing the brain with a balance - tilted balance with increased blood flow
What did Wilhelm Röntgen discover?
German physicist who discovered X-rays of wife’s hand
What is a Crookes tube?
An early X-ray in the late 1800’s
What did Walter Dandy discover in 1919?
Ventriculography and pneumoencephalography
Who addressed problem of lack of contrast in X-rays?
Walter Dandy, US Neurosurgeon, 1919 - removed ventricular cerebrospinal fluid via hole in skull and replaced with air
Who invented EEG?
Hans Berger in 1924 discovered electrical activity of brain can be studied via brainwaves - epileptic seizures combined with fMRI
When were epileptic spikes discovered?
1934
When were stages of sleep discovered?
1953
CT scanning:
Sir Godfrey Hounsfield, 1967, first CT scanner in London
Computed Tomography
X-ray CT/computerised axial tomography/CAT scan
Combines X-rays from many directions to reconstruct volume of interest slices
PET scanning:
Positron Emission Tomography - invasive as injected radioactive tracer, eg Fluorine-18 - fluorodeoxyglucose/FDG = marker of glucose metabolism
Tag active molecule of short lived radioactive tracer - injected into body, decay’s quickly
Tissue tracer concentration/location computed by detecting gamma rays emitted as by-product of decay of injected radioactive tracer
Radioactive tracers - short lives, decay fast, need onsite cyclotron to produce
PET is expensive
High spatial resolution = measures whole brain in millimetres
Lowest temporal resolution = 10-20 second scales
Highest tolerance needed
MRI and DTI scanning:
Magnetic Resonance imaging
Study of brain structure
High resolution
Micro-structural changes using DTI - Diffusion Tensor Imaging to map white matter tracks
Ubiquitous - used everywhere and the ‘workhorse’ of research
MRI scanners: 1.5/3 Tesla strengths
Magnetic field made by super conductive magnet always switched on and needs cooling with liquid helium
MR compatible = do not carry/have metal in body
Magnetic field = like junkyards lifting cars
Cognitive subtraction = which parts of brain respond to different conditions
fMRI = very loud = wear earplugs/headphones!
fMRI scanning:
Functional Magnetic Resonance Imaging
Study brain function since 1990’s
Measures dynamic brain changes every 2 seconds
- task based/resting state - locations of brain functions
Based on BOLD effect - blood oxygenation level dependent
Oxyhaemoglobin - NOT magnetic - diamagnetic
Deoxyhaemoglobin - VERY magnetic - paramagnetic - interacts strongly with scanner
Measures brain activity by regional changes in magnetism
Highest spatial resolution = most detail
Low temporal resolution = every 2 seconds = much slower than EEG/MEG (milliseconds)
Medium tolerance = cannot move/lying down
No radioactivity injected = better than PET
What is temporal and spatial resolution?
Low temporal = takes minutes = more detail = high spatial
High spatial/high temporal = takes seconds = poor detail = low spatial
What is EEG?
Electroencephalography
Functional, non-invasive (conductive gel between scalp and electrodes)
Measures surface of scalp electrical activity
Signal picked up by electrodes in different places and signal source calculated mathematically = inverse problem
Cheap/portable/millisecond speed
Not accurate localisation of function
Lowest spatial resolution = poor detail/fast time
Highest temporal resolution = milliseconds
Lowest tolerance level needed
MEG scanning:
Magnetoencephalography
Measures tiny magnetic fields of scalp brain activity
Complementary with EEG
Position head under helmet-shaped dewar = a vacuum-insulated container/flask (James Dewar)
Contains 100’s of magnetometers
Liquid helium to cool down detectors of scanner
Low spatial resolution - surface of skull - not very accurate localisation of source of signals
Highest temporal resolution = milliseconds
Medium tolerance needed = sit or lie under large helmet
fNIRS
Functional near-infrared spectroscopy
Non-invasive using near-infrared light
Uses BOLD effect: blood oxygenation level dependent
Differences in red absorption spectra of oxy and deoxyhaemoglobin is used to measure changes in blood flow, blood oxygenation levels and blood volume.
Near infrared light does not penetrate deeply through skull or brain = only 5cm = limited spatial resolution = small number of sensors used.
Best for infant brains = really small/transparent skull/really thin
Low spatial resolution BUT more detectors than EEG and still only surface of skull/scalp
Really high temporal resolution
Low tolerance
