4 - NEUROIMAGING Flashcards
Electromagnetism description
Electromagnetism
- Every electrical dipole generates magnetic field (EMF) around it
- Polarity of field depends on direction of current
- Brain electromagnetic fields very weak but can be measured
- Measurement can be related to activity
EEG & MEG:
- differences
- advantages
- Disadvantages
- positive & negative points
- EEG signal acquisition
Differences
EEG = Noninvasive technique measuring brain electrical activity with electrodes on brain
MEG = same as EEG but measure magnetic field generating by cerebral activity
Advantages
- Non-invasive methods in neuroimaging that have no side-effects or interference in normal
functioning of brain
- Collect data quickly & independently form metabolism (contrary to BOLD & MRI)
- High temporal resolution, one thousand times faster than MRI data
- Do not produce noise
- Subjects can perform tasks during evaluation, even though slightly restrict when considering
MEG
Disadvantages
- Not adequate for source localization, when compared with other neuroimaging methods
- Limited resolution (especially EEG)
- Even though anatomical information can be extrapolated, not provided by equipment
Table
EEG signal acquisition
- Electrodes: Silver or stainless steel, placed on scalp following specific methods of allocation with
conductive gel (wet electrodes) or direct contact to dry scalp (dry electrodes)
- Impedance: Signal-to-noise that can be reduced by movement. Reference electrode usually
placed on midline or ear lobes
- Amplification: One pair of electrodes make up one channel on differential amplifier (bipolar
montage) that is used to amplify difference in voltage between these 2 electrodes, generating
signal
Allocation systems:
- definition
- description
Definition
How resources (neural, cognitive or computational) distributed during brain function or imaging
processes
- Ions going constantly in & out of neurons create, together with ion exchange from neighboring neurons, electrically changed waves leading to formation of cortical dipoles
- EEG reading is sum of non-propagating dendritic & somatic post-synaptic potentials, arising at approximately 10 ms
- Excitatory & inhibitory post-synaptic potentials (EPSP & IPSP) summate spatially & temporally, allowing equipment to identify certain type of neuronal activity
Artifacts:
- definition
- description
Definition
= distortions, errors or unwanted signals in images caused by factors like motion, hardware limitations or
physiological noise, affecting data quality
- Eye lid movement
- Muscle activity (scalp)
- Pacemakers
- Movement (change in impedance)
- Electrode-wire contact
- Poor grounding
- Sweating
Very slow waves of opposite polarity at back of head due to head shaking artifact, likely more prominent posteriorly because patient’s head resting on pillow or chair back, note that looks likeslow roving eye movement, but eye movements more frontally predominant
Brain oscillations:
- description
- frequency ranges
BRAIN OSCILLATIONS
- Rhythmic fluctuations of repeated electrical activity
- Generated by activation of neurons
- Can be spontaneous or as reaction to stimulation
- Modulate both motor output & sensitivity of synapses involved in input acquisition
table
Neuro feed-back training:
- description
- forms
- NFT in rehab
- prerequisites & advantages
NEUROFEEDBACK TRAINING
- Expected or desired aspects of cortical & subcortical activation can be achieved or modified through sensory (visual or auditory) stimulation, controlled by biofeedback system that rely on EEG information
Table
NFT in rehabilitation
- Proven efficient in treatment of great variety of conditions such as epilepsy, ADH & ADHD,
chemical dependency & neurocognitive disorder
- Method can be effectively used to increase cognitive abilities in health individuals & reported by researchers
- In rehab of ABI patients, NFT shown improvement in sensorimotor functions, when applied in combination with facilitation, sensory augmentation & functional training
Prerequisites & advantages
- Improved understanding of meanings & uses of neuronal signals
- Identification of neuroplastic processes relying on cortical & subcortical intervention
- Availability of cost-effective hard- & software that can be used in the recording & analysis EEG signals
- Increased public interest in use & development of neurofeedback systems for monitoring an improvement of cognitive & sensorimotor function in populations of patients & health individuals
Types of frequencies, range, main sources, processes & interest for research / rehab
Table
Event-related potentials:
- ERS/ERD
- EP
ERS/ERD
- Event-related desynchronization (ERD) reflects decrease of oscillatory activity related to
internally or externally modulated events
- ERS balanced by ERD, together demonstrating dynamical state of thalamocortical networks
associated with cortical information-processing changes
EP
- Evoked potentials, also time & phase-locked to presentation of specific physical stimulus but
associated with introduction of information in system, that was not already processed
Dysregulation:
- description
- types
DYSREGULATION
- Hyper & hypoactivation of certain frequencies
- Related to functional loss
- Identifying imbalances can help understand conditions better & assist in treatment
ADD / ADHD
Cognitive deficit
Migraines / headache
Addiction
Depression
PTSD
Anxiety
Stress
Autism
Hypersomnia
Night terrors
Concussion
Insomnia
Tantrums
Frequencies: factors increased & decreased
Table
Desynchronization in cognitive impairment
- α & θ (β to lesser extent): sensitive to cognitive changes in elderly during WM tasks
- MCI: low frontal induced θ response & altered top-down attentional control affecting α & β
synchronization - Synchronization of contralateral γ oscillations in M1 during movement consistent along all ages, while ipsilateral synchronization seems to progressively decrease with age
MCI patients local & distant functional connections in frontotemporal networks disturbed, leading to
deficits in temporal coordination of networks, disturbing neural activity related to stimulus processing
MRI:
- acronym
- advantages / disadvantages
-variety
- modalities
Magnetic reasoning image
Table
Modalities of neuroimaging & aims
Variety
- fMRI (functional MRI)
- MRA (magnetic resonance angiography)
- FLAIR (fluid attenuated inversion recovery)
Modalities
- Anatomical MRI => T1WI, T2WI, FLAIR = study structure of brain
- Functional MRI => fMRI => study cerebral activity by detecting oxygenation variation in blood (BOLD effect)
- Diffusion MRI => DWI (diffusion weighted image) & PDMI (protons density weighted image) => bundle analysis of white matter via water molecule diffusion
T1 weighted:
- description
T1 weighted
→ White matter appears brighter than grey
Hypointense (black) => CSF, edema, tumor, infection, inflammation, hemorrhage & calcification
Hyperintense (white) => Fat, subacute, hemorrhage (hyper chromic), protein rich fluids, blood (slow
flowing) & paramagnetic substances (contrasts
T2 weighted:
- description
- field strength
- low strength: good & negative
2 weighted
→ Grey matter appears brighter than white
Hypointense (black) => CSF, edema, tumor, infection, inflammation, hemorrhage (sub-acute), SDH &
calcification
Hyperintense (white) => Calcification, fibrous tissue, iron (deoxyhemoglobin & methemoglobin) & melanin
Tables
Flair:
- description
FLAIR
- T2WI provide picture with low definition on CSF interfaces, making diagnose of lesions to certain
areas, like cortical sulci, unclear
- FLAIR image suppresses signal from free water in CSF, maintaining hyperintensity of lesion
contrast, since it has very long echo-time
- FLAIR particularly efficient in evaluation of possible vascular injuries, SDH & MS
Purpose:
- T1WI
- T2WI
- FLAIR
- fMRI
Table
Disadvantage of fMRI
Disadvantages of fMRI
- Doesn’t directly measure electric nor metallic activity
- BOLD quantitative, not qualitative
- Requires high T
- Can create more artifacts (high T): air pockets in sinuses
- More sensitive to physiological noise
Diffuse weighted image
Diffuse weighted image
- Detects diffusion of protons
- Detects diffusion of macromolecules
- Obstructing molecules + cell membrane permeability
- B1000 image
- To create functional anisotropy (FA) & apparent diffusion coefficient (ADC) maps
Artifacts:
- description
- possible causes & description of each
ARTIFACTS
- Anything that could lead to mistake in image acquisition
- Addition of distortions / shadows
- Omission of elements
Table
Omega & Epsilon sign:
- location
- relevance
- variations
Omega & epsilon sign
- Location: central sulcus, posteriorly to M1
- Relevance: hand-motor area (correspond somatosensory area)
- Variations: Omega sign (or sigmoidal hook), epsilon, laterally asymmetric epsilon & null
Bracket sign:
- location
- significance
Bracket sign (marginal sulcus)
- Location: behind central sulcus
- Significance: marks upper limit of postcentral sulcus & appearance of cingulate sulcus on
cortical surface
L or T sign:
- location
- significance
- variations
L or T sign
- Location: superior frontal sulcus + precentral sulcus
- Significance: guide for location of FEF & dlPFC (also partially SMA)
- Variations L & T sign
Insula:
- locations
Insula
Location:
- Anterior: short insula gyri
- Sagittal: long insula gyrus
M sign:
- location
- left hemisphere
- right hemisphere
M sign
- Location: marks inferior frontal gyrus
- Left hemisphere: Broca area covers p. triangularis & p. opercularis
- Right hemisphere: involved in communication, depending on demand
White matter measurements
Measurements:
- Fiber orientation
- Density of bundles / tracts
- Angle of connections
Tactography description
Tractography
- Tracts movement of H+ moving freely, along macro- & microstructures
- Threshold setting of 30+ diffusion, leads to loss of signal (CSF in ventricles)
- Presence of edema will disrupt standard image
2 types of maps created:
- name
- description
Fractional anisotropy maps = shows how much diffusion restricted to different areas. Used for extrapolating fiber density & myelination of bundles
Color coded maps = represents direction, diffusion restricted. Used for determining locations & connections within circuits, as well as aiding surgical planning
Color code
Color code
Cranial caudal => blue
Posterior anterior => green
Right left => red
White matter tracts / bundles
White matter tracts / bundles
- Taxonomic analogues to grey matter ROI
- Shared properties:
o Connectivity
o Volume
o Gross morphology
o Trajectory
o Ontogeny
o Phylogeny
o Function
Commissural fibers
Commissural fibers
Connection between hemispheres
1. Corpus callosum
2. Anterior commissure
3. Fornix
Projection fibers
Projection fibers
Connections to/from neocortex
1. Optic & acoustic fibers
2. Thalamocortical fibers
3. Internal capsule
4. Corticopontine fibers
5. Corticospinal tract
corticospinal tract
Corticospinal tract
- 60% M1 descending axons
- S1 ascending, PMC, SMA
- High variability on exact point of conversion in internal capsule
Association fibers
Association fibers
Connections within hemispheres
1. Short U fibers
2. Inferior longitudinal fasciculus (IFL)
3. Inferior fronto-occipital fasciculus (IFOF)
4. Middle longitudinal fasciculus (MLF)
5. Uncinate
6. Cingulum
Superior longitudinal fascicule:
- 3 types
- connections of each
- functions
- locations
Superior longitudinal fasciculus
SLF 1
→ connecting prefrontal regions with parietal regions
→ involved in higher cognitive functions, acting on planning & analysis interwoven with spatial awareness
SLF 2
→ connecting prefrontal regions with parietal & occipital regions
→ acts on integration between visual information (processed) & cognitive functions, mostly related to
decision making & prospection
SLF 3
→ connecting prefrontal regions with contralateral occipital regions
→ involved visual attention & visual tracking
Image
Loop of optic radiations:
- way
- 3 different types
- description of each
CN2 → LGN
- Meyer’s loop: toward TP, following roof of temporal horn, projecting posterior to inferior lip of calcarine sulcus
- Central projections: runs lateral, superior to roof of temporal horn, projecting posteriorly towards occipital horn, to engage on occipital pole
- Posterior projections: thick bundle forming lateral wall & part of roof of occipital horn, ending at superior lip of calcarine sulcus
Optic radiations lesions & outcomes:
- types (7)
- description
Optic radiations lesions & outcomes
CN2: hemianopia
Chiasma: bitemporal hemianopia
Optic tract (ICA ischemia): nasal hemianopia
Optic tract (posterior): homonymous hemianopia
Meyer’s loop: superior quadrantanopia
Posterior projection: inferior quadrantanopia
V1: hemianopia
