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Module 7 > Neuroimaging > Flashcards

Neuroimaging Flashcards

1
Q

Structural Imaging measures:

A
  • Cortical thickness
  • GM-WM blurring
  • Abnomal gyral and sulcal folding structure
  • Structures often located at the bottom of deep sulci
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2
Q

Surgical resection & MRI

A

Better memory at follow-up was linked to greater post-surgical residual hippocampal volumes

IMP: of MRI to determine the exact location

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3
Q

Characteristics of MRI based volumetry

A
  • Gold standard
    Time consuming
    You need a priori hypothesis for a specific area
    Manual tracing
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4
Q

Characteristics & Advantages of Voxel-Based Lesion-Symptom mapping

A

Voxel wise t-tests to determine strength
–>Lesion present vs. not present

Associate behaviour to lesion site

Advantages over previous methods:

  • All information/behavioural data is statistically analysed on a voxel-by-voxel basis thus ensuring no information is lost (as was the case with other methods)
  • Able to cover large areas
  • Comparable to functional imaging research – similar system
  • Efficient method for mapping behaviour onto lesions in chronic stroke
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5
Q

Aims of Voxel Based Morphometry

A

Aim:
- To identify local different in tissue composition after disregarding gross anatomical differences
- Voxel intensities are measured with a continuous parameter then compared between group/correlated with behaviour or other measurements. Compared using:
> Regression
> T-test

  • To define brain regions for behaviour in question
  • Possible to analyse entire brain OR area of focus. Can assess:
    >Total volumes of tissue types – GM/WM
    >Brain volume
    >Intra-cranial volume

Use:
structural integrity in structural damage
Lesion-symptoms mapping in stroke patients

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6
Q

How is VBM carried out?

A
  • Fully automated segmentation & normalisation
  • Local differences in density/volume are statistically anlaysed

Fit out brain into a small space => normalise it => probability map => smooth it to account for variability

> Doesn’t fit = brain lesion

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7
Q

Compare VLSM & VBM

A
  • BOTH related structure to function
  • Findings of BOTH can be easily compared to health control

VLSM:
Voxel: Binary fashion
- Lesioned & Not lesioned

> Manual tracing of the lesion
Time consuming & subjective
Cannot draw conclusions about areas not analysed

VBM:
Voxel = continuous
i.e. more sensitive when behaviour correlated linearly but not when there is a non-linear relationship

> Defines voxel intensity automatically for each separate voxel

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8
Q

VBM study on normal brain development

Groschel et al 2010

A

> Mapped normal brain development
WM increase – steep increase in first year; Then less rapid growth up to young adulthood
Total GM = peak THEN volume decrease
Total brain volume – increase in first
Brain volume & total WM & GM volume = larger in males

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9
Q

VBM study - Brain volume IQ

Baldeweg et al. 2006

A

Brain volume - Correlation with IQ
>Modest contribution to IQ from global changes

–>Focal WM density reduction = main contribution to IQ
- Sickle cell = white matter intensity difference
Linked to overall IQ

VBM showed widespread bilateral WM abnormalities – extending beyond focal infarction

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10
Q

Aim of Surface (Vertex) Based Morphometry

A

Aim: to understand how the cortex relates to brain development
>Normal & abnormal

Creates surface feature maps using Freesurfer
–>FreeSurfer contains a fully automatic structural imaging stream for processing cross sectional and longitudinal data.

Compared to VBM: Closer correspondence to biological structures

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11
Q

SBM study: SA & CT IQ

Vuoksimaa et al. (2016)

A

Surface (Vertex) Based Morphometry

Surface areas correlated IQ
Cortical thickness inversely related to IQ

–>ES are small

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12
Q

VBM & SBM

A

Idenfying GM differences
Structural changes

SBM:

  • Cortical thickness
  • Provide absolute measure of thickness: Identify inner and outer cortical boundaries
  • Thickness is calculated for every volumetric point

VBM

  • Volumetric measurement
  • Identifies regional or structural volume
  • The Quantity of tissue within a voxel is measured
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13
Q

Aim & Uses of DWI

A

Constructs the most likely path WM will take
See where water is enhanced
Can make specific predictions

Uses:
Map eloquent WM tracts
E.g. Language tracts 
->Arcuate fasciculus
-> Uncinate fasciculus
Evolution of Neonatal stroke in acute phase (25h -7d)
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14
Q

Aim of fMRI

A

Same technology as MRI
Measures brain activity by detecting changes in blood flow
Blood-oxygen-level-dependent (BOLD) contrast

Based on premise: cerebral blood flow & neuronal activation are coupled

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15
Q

fMRI brain activity is measured in:

A

Brain activity is mapped in squares called voxels. Each voxel represents thousands of nerve cells (neurons).
Color is added to the image to create a map of the most active areas in the brain.

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16
Q

fMRI uses

A

Uses:
Post-injury/illness
Brain mapping .e.g mapping eloquent motor cortex
Planning surgery

17
Q

fMRI pros & cons

A

Pros:

  • No risks/radiation
  • Produces high resolution images
  • Objective

Cons
- Person must stay very still
- Expensive
Only blood flow – not individual neurons: Not always easy to tell exactly what kind of brain activity is being represented

18
Q

fMRI & output

A

Voxel-wise t-Test
Output = t-value that is overlaid onto an anatomical layout
Background noise and movement are accounted for

SPM = Statistical Parametric Mapping Software
Construct and assess spatially extended statistically process so as to test hypotheses about functional imaging data

19
Q

Electrophysiology

A

Event related potential (ERP)
- Brain response to direct sensory, cognitive or motor event

  • Location and response time
    E.g, verb generation task
  • Measure voltage change/electric current
    Electical activity of neurons – action potential
  • Excellent temporal
    Weak spatial
20
Q

Transcranical magnetic Stimulation

A

Very popular in experimental neuroscience
Stimulate regions of the brain
->magnetic field (coil) is placed near the head
-> It produces a small electric current = Electromagnetic induction

21
Q

Transcranical magnetic Stimulation Uses:

A

Use:
Measure connection between brain & muscle
Damage from stoke, MS, movement disorder, motor neuron disease
Children: pre-surgery – but contentious

22
Q

WADA test

A

Invasive method
Establishes cerebral language and memory respresentations of each hemisphere

Patient awake
Introduce a barbiturate into the internal carotid artery to inhibit the responses
Look at impact on communication/other functions

Being replaced by:
fMRI
DWI
iERP

23
Q

IMP caution when considering structural imaging

A

May lesions are small, subtle and can be missed by radiologists

IMP: cryptogenic/nonlesional
E.g. epilepsies that are assumed to be non-lesional – but it may be that current radiology cannot pick them up

Module 7 (13 decks)

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