Neuroimaging

Question 1

What is structural and functional imaging?

Answer 1

Structural: brain anatomy

Functional: living, dynamic brain

Question 2

What are lesion studies?

Answer 2

Post mortem studies of functional deficits after brain damage

Question 3

What did Angelo Mosso discover in the 19th Century?

Answer 3

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

Question 4

What did Wilhelm Röntgen discover?

Answer 4

German physicist who discovered X-rays of wife’s hand

Question 5

What is a Crookes tube?

Answer 5

An early X-ray in the late 1800’s

Question 6

What did Walter Dandy discover in 1919?

Answer 6

Ventriculography and pneumoencephalography

Question 7

Who addressed problem of lack of contrast in X-rays?

Answer 7

Walter Dandy, US Neurosurgeon, 1919 - removed ventricular cerebrospinal fluid via hole in skull and replaced with air

Question 8

Who invented EEG?

Answer 8

Hans Berger in 1924 discovered electrical activity of brain can be studied via brainwaves - epileptic seizures combined with fMRI

Question 9

When were epileptic spikes discovered?

Answer 9

1934

Question 10

When were stages of sleep discovered?

Answer 10

1953

Question 11

CT scanning:

Answer 11

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

Question 12

PET scanning:

Answer 12

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

Question 13

MRI and DTI scanning:

Answer 13

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!

Question 14

fMRI scanning:

Answer 14

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

Question 15

What is temporal and spatial resolution?

Answer 15

Low temporal = takes minutes = more detail = high spatial

High spatial/high temporal = takes seconds = poor detail = low spatial

Question 16

What is EEG?

Answer 16

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

Question 17

MEG scanning:

Answer 17

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

Question 18

fNIRS

Answer 18

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