T13, Neuroengineering and the brain

Question 1

typical size MRI?

Answer 1

2mm

Question 2

What does stokes-einstein relation tells us?

Answer 2

D increases with temperature

D decrease with viscosity

Question 3

what can we say about free diffusion?

Answer 3

mean square displacement will increase linear with time

Question 4

what can we say about restricted diffusion?

Answer 4

• the squere displacment will converge after time
• non-linear
• but we simplify it and suppose that it is linear
• we use ADC apparent diffusion coefficient

Question 5

what do we do to measure diffusion?

Answer 5

1. stejskal-tanner approach?

2. pulsed gradient spin echo?

Question 6

what level of diffusion do I need?

Answer 6

1. level of diffusion weighting??
2. amplitude
3. space

Question 7

what level of diffusion do I need?

Answer 7

1. level of diffusion weighting??
2. amplitude
3. space

Question 8

Does the signal vary with different tissue?

Answer 8

tissues with higher density? will give us stronger signal?

Question 9

why is ADC quantification important?

Answer 9

to be able to see the changes in the different variables, diffusion and ??

Question 10

is there an optimal b-value?

Answer 10

we want to have enough contrast so we can say something about the signal.

• small difference in b-value
• -> poor contrast
• very large b-value
• -> noise–> biased estimate

optimal b-value is somewhere in between

Question 11

eigenvalues?

Answer 11

eigenvector

–> the larger the more diffusion

Question 12

what are the tensor-derived parameters?

Answer 12

1. mean diffusivity
   - -> intra/extra-cellular fraction
   - -> extra-cellular tortuosity
2. fractional anisotrophy
   - ->
3. principal eigenvector
   - -> related to main direction of the axons
   - -> direction of the fibers
   - -> blue: inferior/superior
   - -> green: anterior/posterior
   - -> red: left/right hemisfer

Question 13

limitations with tractography=

Answer 13

1. if we detect a connection we don’t know in what direction the connection is.
2. not all reconstructed fibre tracts are real
3. not all existing fibre tracts are detected
4. different populations are not distinguish

Always look at the images!

Question 14

What is the reason os using this method?

Answer 14

1. discovering stroke
   - -> early detection of strokes still one of the main application
   - -> high signal–> diffusion coeffission is lower?
   - ->
2. brain tumors
   - -> useful to distinguishing tumors from different types of lesions
   - -> higher diffusion coeffision?
   - ->longitudinal studies may be useful to
3. surgical planning
   - -> understanding how white matter fibers are re-organizing
   - ->
4. neurodegenerative diseases
   - -> parkinsons, ALS and so on.

Question 15

current research questions?

Answer 15

1. signal modelling and tractography
2. connectivity
3. biophysical modeling and microstructure
4. functional imaging with DWI
5. acquisation
   - -> faster rates
   - -> better hardware

Question 16

what can we do to resolve crossing fibers?

Answer 16

beyond diffusion tensor….

• -> DTI
• -> Q-ball

problem with these methods?

• -> alot of time
• -> a lot of diffusion direction
• -> more cost

Question 17

what has been made to increase the acquisition rate?

Answer 17

Simultaneous multi-slice acquisitions

• -> new coils have variying sensitivity along z-axis
• -> much shorter acquisition time
• ->

Question 18

what do we mean with structural connectivity?

Answer 18

h

Question 19

trends?

Answer 19

1. investigaring tissue microstructure
   - -> how the signal changes wit increasing diffusion time can tell us about tissue structure
2. alternative diffusion modules
   - -> by varying the frequency we can probe different diffusion regimes. provide information on compartment sizes.
   - -> how big are the axons in different regions
   - ->