Brain imaging & EEG

Question 1

Static magnetic field

Answer 1

B0 field

Question 2

Spin-Lattice Relaxation:

Answer 2

T1 relaxation: the process where the net magnetization (M) returns to its initial max value (M0) parallel to B0 field

Question 3

T1:

Answer 3

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

Question 4

Spin-Spin Relaxation

Answer 4

T2 relaxation –> the process where the transverse magnetization component (Mxy) decays due to the spins’ dephasing

Question 5

T2:

Answer 5

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

Question 6

Inhomogeneity in the B0 field =

Answer 6

T2 prime (T2') 
Cause the transverse magnetization (mxy) to decay even faster

Question 7

T2*

Answer 7

The time governing the decay of T2’

T2* = the inverse sum of T2 & T2’

Question 8

Applications that use T2*

Answer 8

fMRI

Question 9

Brownian Motion

Answer 9

Water molecules are in continous motion (Brownian motion)

Question 10

Rate of motions determines the T1 & T2 relaxations:

Answer 10

(1) types of spins
2) distance between spins
3) angle between them
4) relative motion

Question 11

TR:

Answer 11

Repetition time (TR) = the time from one RF pulse to the next RF pulse

Question 12

TE:

Answer 12

Echo Time (TE) = from the RF pulse to the time we receive the strongest MRI signal

Question 13

T1 weighted image:

Answer 13

T1 W = short TR & short TE

Question 14

T2 weighted image

Answer 14

T2 W = long TR & long TE

Question 15

Proton Density

Answer 15

Proton density (PD) = Long TR & Short TE

Question 16

Diamagnetic

Answer 16

All electrons are paired - total magnetic moment = 0

Question 17

Paramagnetic

Answer 17

1 / more unpaired electrons: total magnetic moment = small

Question 18

Ferromagnetic (real magnets)

Answer 18

Unpaired electrons all lined up in the same direction: total magnetic moment = large

Question 19

Oxyhaemoglobin is considered what type of magnet

Answer 19

diamagnetic

Question 20

Deoxyhaemoglobin is considered what type of magnet

Answer 20

Paramagnetic

Question 21

Define EEG

Answer 21

EEG (electroencephalography) = the recording of spontaneous electrical activity from the scalp over time (epoch)

Question 22

3 electrodes needed to record EEG:

Answer 22

1. Positive electrode - recording electrode
2. Negative electrode - reference electrode
3. Ground/earth electrode - reduces electrical interference

Question 23

What is the montage in an EEG

Answer 23

Montage - the design of collecting EEG voltage signals from the scalp

Question 24

Referential Montage:

Answer 24

Recording Electrode from reference electrode

Question 25

Bipolar Montage:

Answer 25

recording biopotential between 2 electrodes

Question 26

Define an artifact

Answer 26

Recorded activity that is not of cerebral origin

Question 27

Factors that change the P300 latency & amplitude:

Answer 27

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

Question 28

Stoke Shift:

Answer 28

The energy difference between the peak absorbance & the peak of emission spectrum

Question 29

Components of molecules which absorb light

Answer 29

Fluorophores

Question 30

Why are organic dyes used for fluorescence labelling?

Answer 30

Organic dyes with aromatic rings - this structure has free electrons able to move around freely allowing fluorescent light to be emitted when excited

Question 31

Uses of Fluorescent dyes:

Answer 31

1) analysis of fast, dynamic processes
2) labelling of antibodies
3) organelle labelling
4) Physiological measurements
X - Preparation of specimens w permanent shelf life

Question 32

Fluorescent labelling of cells

Answer 32

• Allows multiple simultaneous labelling
• Can be used for single-molecule labelling
• is subject to bleaching
• CAN be used on living cells

Question 32

Fluorescent labelling of cells

Answer 32

• Allows multiple simultaneous labelling
• Can be used for single-molecule labelling
• is subject to bleaching
• CAN be used on living cells

Question 32

Fluorescent labelling of cells

Answer 32

• Allows multiple simultaneous labelling
• Can be used for single-molecule labelling
• is subject to bleaching
• CAN be used on living cells

Question 33

From which species does green fluorescent protein (GFP) originate:

Answer 33

Jellyfish

Question 34

What is an essential requirement for Fluorescence Resonance Transfer (FRET) to occur:

Answer 34

The emission spectrum of the donor & the absorption spectrum of the acceptor must overlap

Question 35

What immunohistochemical label can be used to identify newly formed hippocampal neurons?

Answer 35

Doublecortin (DCX)

Question 36

Problems with fluorescent techniques:

Answer 36

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

Question 37

Photobleaching definition

Answer 37

Defined as irreversible destruction of an excited fluorophore

Question 38

Methods for countering photobleaching:

Answer 38

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

Question 39

Major application of GFP

Answer 39

Reporter gene assay of promoter activity

Question 40

what does FRET measure

Answer 40

Measurement of molecular interactions