Brain imaging & EEG Flashcards
Static magnetic field
B0 field
Spin-Lattice Relaxation:
T1 relaxation: the process where the net magnetization (M) returns to its initial max value (M0) parallel to B0 field
T1:
The time required for the z-component (Mz) to reach about 63% of its max value
Rate of recovery (T1 relaxation) is governed by time T1
Spin-Spin Relaxation
T2 relaxation –> the process where the transverse magnetization component (Mxy) decays due to the spins’ dephasing
T2:
The time required for the signal to fall to approximately 63% of its initial value (when there is only 37% of the signal)
Exponential decay of Mxy is governed by time T2
Inhomogeneity in the B0 field =
T2 prime (T2') Cause the transverse magnetization (mxy) to decay even faster
T2*
The time governing the decay of T2’
T2* = the inverse sum of T2 & T2’
Applications that use T2*
fMRI
Brownian Motion
Water molecules are in continous motion (Brownian motion)
Rate of motions determines the T1 & T2 relaxations:
(1) types of spins
2) distance between spins
3) angle between them
4) relative motion
TR:
Repetition time (TR) = the time from one RF pulse to the next RF pulse
TE:
Echo Time (TE) = from the RF pulse to the time we receive the strongest MRI signal
T1 weighted image:
T1 W = short TR & short TE
T2 weighted image
T2 W = long TR & long TE
Proton Density
Proton density (PD) = Long TR & Short TE
Diamagnetic
All electrons are paired - total magnetic moment = 0
Paramagnetic
1 / more unpaired electrons: total magnetic moment = small
Ferromagnetic (real magnets)
Unpaired electrons all lined up in the same direction: total magnetic moment = large
Oxyhaemoglobin is considered what type of magnet
diamagnetic
Deoxyhaemoglobin is considered what type of magnet
Paramagnetic
Define EEG
EEG (electroencephalography) = the recording of spontaneous electrical activity from the scalp over time (epoch)
3 electrodes needed to record EEG:
- Positive electrode - recording electrode
- Negative electrode - reference electrode
- Ground/earth electrode - reduces electrical interference
What is the montage in an EEG
Montage - the design of collecting EEG voltage signals from the scalp
Referential Montage:
Recording Electrode from reference electrode
Bipolar Montage:
recording biopotential between 2 electrodes
Define an artifact
Recorded activity that is not of cerebral origin
Factors that change the P300 latency & amplitude:
1) habituation to task & repetition of task - decrease in amplitude w repetition of task
2) Task difficulty
3) Mental fatigue - amplitude decreases w time of task
Stoke Shift:
The energy difference between the peak absorbance & the peak of emission spectrum
Components of molecules which absorb light
Fluorophores
Why are organic dyes used for fluorescence labelling?
Organic dyes with aromatic rings - this structure has free electrons able to move around freely allowing fluorescent light to be emitted when excited
Uses of Fluorescent dyes:
1) analysis of fast, dynamic processes
2) labelling of antibodies
3) organelle labelling
4) Physiological measurements
X - Preparation of specimens w permanent shelf life
Fluorescent labelling of cells
- Allows multiple simultaneous labelling
- Can be used for single-molecule labelling
- is subject to bleaching
- CAN be used on living cells
Fluorescent labelling of cells
- Allows multiple simultaneous labelling
- Can be used for single-molecule labelling
- is subject to bleaching
- CAN be used on living cells
Fluorescent labelling of cells
- Allows multiple simultaneous labelling
- Can be used for single-molecule labelling
- is subject to bleaching
- CAN be used on living cells
From which species does green fluorescent protein (GFP) originate:
Jellyfish
What is an essential requirement for Fluorescence Resonance Transfer (FRET) to occur:
The emission spectrum of the donor & the absorption spectrum of the acceptor must overlap
What immunohistochemical label can be used to identify newly formed hippocampal neurons?
Doublecortin (DCX)
Problems with fluorescent techniques:
1) Bleed through: broad peaks cross over into 1 another - get false positive labelling
2) Blur: out of focus light decreases resolution
3) Bleaching: excited fluorophores react to become nonfluorescent
4) phototoxicity: light can harm cells
5) Background/Autofluorescence: Cells have fluorophores too
Photobleaching definition
Defined as irreversible destruction of an excited fluorophore
Methods for countering photobleaching:
1 - scan for shorter times
2 - use high magnification, high NA objective
3 - Use wide emission filters
4 - Reduce excitation intensity
5 - Use antifade reagents (not compatible w viable cells) - protects against fading
Major application of GFP
Reporter gene assay of promoter activity
what does FRET measure
Measurement of molecular interactions
