Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MED 107- MEDICAL PHYSICS II > 103. FMRI: DIFFUSION > Flashcards

103. FMRI: DIFFUSION Flashcards

1
Q
  1. Define: Diffusion.
A
  • this is the term used to describe moving molecules
  • these molecules are moving due to random thermal
    motion

THIS IS KIND OF MOTION:
- is called Brownian Motion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q
  1. What is Brownian Motion restricted by?
A

IT IS RESTRICTED BY BOUNDARIES SUCH AS:
- ligaments
- membranes
- macromolecules
- pathology

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q
  1. Define: Diffusion Coefficient.
A
  • this is a parameter
  • it describes the rate of diffusion in tissues
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q
  1. What other kinds of motion of molecules can we find in FMRIs?
A
  • microcirculation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q
  1. How is diffusion affected by Gradients?
A

WHEN STRONG GRADIENTS ARE APPLIED:
- diffusion is minimal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q
  1. Define: Apparent Diffusion Coefficient (ADC).
A
  • this is the rate at which molecules diffuse
  • it is measured in mm² per second

TISSUES WILL HAVE A HIGH APPARENT DIFFUSION COEFFICIENT:
- if they experience diffusion that is free

TISSUES WILL HAVE A LOW APPARENT DIFFUSION COEFFICIENT:
- if they experience diffusion that is restricted

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q
  1. What are some characteristics of a High Apparent Diffusion Coefficient?
A
  1. There is free Diffusion
  2. There is a Low Signal Intensity regarding the Diffusion
    Weighted Images that are acquired

EXAMPLE:
- Cerebral Spinal Fluid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q
  1. What are some characteristics of a Low Apparent Diffusion Coefficient?
A
  1. There is restricted Diffusion
  2. There is a High Signal Intensity regarding the Diffusion
    Weighted Images that are acquired

EXAMPLE:
- Grey Matter
- White Matter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q
  1. What is the mathematical relationship between the Apparent Diffusion Coefficient and the Diffusion Weighted Signal?
A
  • they are inversely a proportional
  • an increase in one leads to a decrease in the other
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q
  1. How are Diffusion Weighted Images acquired?
A
  • they are acquired by sensitising the motion of the
    molecules
  • this is done by using strong gradients
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q
  1. How do we make use of strong gradients?
A
  • two equal gradients are applied to either side of the
    180° Radio Frequency Pulse
  • this happens in a Spin Echo Sequence
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q
  1. How are the gradients desgined?
A
  • they are designed to cancel each other out
  • this happens if the spins do not move
  • this is in order to obtain Diffusion Weighted Images
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q
  1. Determine the factors that can be seen in this image?
A
  1. G = gradient
  2. t = time that the gradient is applied
  3. T = period of the pulse
  4. TE = echo time
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q
  1. What does the amount of signal attenuation depend on?
A
  1. Amplitude
  2. The directions of the applied gradients
  3. The Gradient Difference (Gdiff)
  4. The Apparent Diffusion Coefficient (ADC)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q
  1. What equation do we use to measure the degree (attenuation) of the diffusion?
A

b = b-value
= this is the b factor
= it is the degree of diffusion
= it is measured in s / mm²

y = Gyromagnetic Ratio
= MHz / T

G= Gradient Amplitude
= mT / m

δ = Gradient Duration
= m / s

Δ = the time between the two pulses
= this is the time between the 90° and 180° Radio
Frequency Pulses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q
  1. In which axes (planes) are Diffusion Gradients applied in?
A
  • they are applied in the X, Y and Z axes
  • they are combined to produce a Diffusion Weighted
    Image
17
Q
  1. Do the Diffusion gradients need to be strong or weak?
A
  • they need to be strong
  • this is so that they achieve enough Diffusion Weighting
18
Q
  1. How is Diffusion Sensitivity controlled?
A
  • it is controlled by the b factor
  • this is what determines the Diffusion Attenuation
  • this is the degree at which the diffusion happens
19
Q
  1. What is the average b-value?
A
  • it ranges from 550 s/mm²
  • to 1000 s/mm²
20
Q
  1. What happens as the b-value increases?
A
  • the Diffusion Weighting Increases
  • they are inversely proportional
21
Q
  1. Other than the Diffusion Weighting, what else does the b-value control?
A
  • it controls the contrast in the images
22
Q
  1. What effect does a high b-value have on contrast?
A
  • high b-values will exaggerate the differences in a
    tissue’s Apparent Diffusion Coefficient
23
Q
  1. What do we typically use Diffusion Weighted Images to diagnose?
A
  • strokes
  • this is because they are very sensitive
24
Q
  1. How can we tell that a stroke is present using a Diffusion Weighted Image?
A
  • the area where the stroke is happening will be bright
  • this is because there is decreased diffusion
  • this is due to infraction
25
Q
  1. What happens in early strokes?
A
  • the cells will swell
  • they absorb water from the extracellular space
  • the diffusion is restricted
26
Q
  1. What do the changes in the Diffusion Weighted Image help us to identify after someone has had a stroke?
A
  • the locality of the stroke
  • the extent of the impact of the stroke

NB:
- this is seen before we can use other modes of imaging
for more information

27
Q
  1. Can we see the development of a stroke using CT and T2 Weighted Images?
A
  • no
28
Q
  1. Which other body parts do we image using Diffusion Weighted Images?
A
  • the liver
  • the prostate
  • the breast
29
Q
  1. What do we use Diffusion Weighted Images to differentiate between?
A
  • we differentiate between malignant and benign lesions
  • we differentiate between solids and cystic areas

MED 107- MEDICAL PHYSICS II (108 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions