Neuroimaging Flashcards
Structural Imaging measures:
- Cortical thickness
- GM-WM blurring
- Abnomal gyral and sulcal folding structure
- Structures often located at the bottom of deep sulci
Surgical resection & MRI
Better memory at follow-up was linked to greater post-surgical residual hippocampal volumes
IMP: of MRI to determine the exact location
Characteristics of MRI based volumetry
- Gold standard
Time consuming
You need a priori hypothesis for a specific area
Manual tracing
Characteristics & Advantages of Voxel-Based Lesion-Symptom mapping
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
Aims of Voxel Based Morphometry
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
How is VBM carried out?
- 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
Compare VLSM & VBM
- 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
VBM study on normal brain development
Groschel et al 2010
> 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
VBM study - Brain volume IQ
Baldeweg et al. 2006
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
Aim of Surface (Vertex) Based Morphometry
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
SBM study: SA & CT IQ
Vuoksimaa et al. (2016)
Surface (Vertex) Based Morphometry
Surface areas correlated IQ
Cortical thickness inversely related to IQ
–>ES are small
VBM & SBM
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
Aim & Uses of DWI
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)
Aim of fMRI
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
fMRI brain activity is measured in:
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.
