104. FMRI: APPARENT DIFFUSION COEFFICIENT (ADC)

Question 1

1. What do the different colours in this Apparent Diffusion Coefficient image represent?

Answer 1

DARK REGIONS:
- the water is diffusing slower
- the movement is more restricted
- there are more obstacles present
- the viscosity is increased
- the Apparent Diffusion Coefficient is low
- this is where the stroke will be found

BRIGHT REGIONS:
- the water is diffusing faster
- the movement is less restricted
- there are less obstacles present
- the viscosity is decreased
- the Apparent Diffusion Coefficient is high

NB:
- this is a left Middle Cerebral Artery Stroke

Question 2

2. What is the relation between the intensity of the pixels and the extent of the diffusion?

Answer 2

• they are proportional
• an increase in one leads to an increase in the other

Question 3

3. What do the different colours in this Diffusion Weighted image represent?

Answer 3

BRIGHT REGIONS:
- there is decreased water diffusion
- the Diffusion Weighted Image signal is high
- this is where the stroke will be found

DARK REGIONS:
- there is increased water diffusion
- the Diffusion Weighted Image signal is low

Question 4

4. What do we use the very strong multidirectional gradients for?

Answer 4

• we use them to Map White Tracts

THIS IS BECAUSE:
- they have a lower Apparent Diffusion Coefficient than
the surrounding Grey Matter

THIS TECHNIQUE IS CALLED:
- Diffusion Tensor Imaging
- DTI

Question 5

5. What kind of structures can we image using Diffusion Tensor Imaging (DTI)?

Answer 5

• any structures that include fibres

EXAMPLE:
- muscles
- skeletal muscles
- left ventricle

Question 6

6. What do the different colours in this image represent?

Answer 6

EACH COLOUR:
- represents the different direction that the molecule
(fibre) travels in

BLUE:
- the fibres travel along the Z-Axis
- this is Superior and inferior movement

RED:
- the fibres travel along the X-Axis
- this is transverse movement

GREEN:
- the fibres travel along the y-axis
- they travel in the anterior and posterior direction

Question 7

7. Define: Perfusion.

Answer 7

• this measures the quality of the Vascular Supply to a
  tissue

IT CAN ALSO BE USED:
- to measure tissue activity

Question 8

8. What method does Perfusion make use of?

Answer 8

• it uses a Bolus injection of Gadolinium
• Gadolinium is a contrast agent that is used in MRI
• this is done during ultrafast T2* Acquisition

Question 9

9. What does the Gadolinium Contrast Agent do?

Answer 9

• it causes the temporary decreases in the T2*
• this happens in and around the microvascular regions
• these are made up of many tiny vessels
• these regions have a lot of contrast

Question 10

10. What happens after we have obtained Perfusion data?

Answer 10

WE CAN DETERMINE:
- the blood volume
- the transit time
- the measurement of perfusion

Question 11

11. What can be seen in this image?

Answer 11

• this is the Perfusion Curve
• it is called the Time Intensity Curve

Question 12

12. When do we take different Time Intensity Curves?

Answer 12

• we take them during and after the Gadolinium
  injections
• they are combined together to create a Cerebral Blood
  Volume (CBV) map

Question 13

13. What do we use Perfusion imaging for?

Answer 13

• it is used to evaluate Ischaemic diseases
• this is when an organ does not get enough Blood
  Supply
• it is also used to look at Metabolism

Question 14

14. What do the different colour regions in Cerebral Blood Volume Maps indicate?

Answer 14

DARK REGIONS:
- show that there is low perfusion
- these are the areas where we will find a stroke

BRIGHT REGIONS:
- show the areas of high perfusion
- this is where we will usually find malignant tumours

Question 15

15. Label this image?

Answer 15

STRUCTURE 1:
- Diffusion
- the bright region indicates the area of low diffusion
- this is where we will see a stroke

STRUCTURE 2:
- Perfusion

STRUCTURE 3:
- this is a combination area of perfusion and diffusion
- this is where the stroke is occurring

Question 16

16. Label these images?

Answer 16

STRUCTURE 1:
- this is a T2 Weighted image
- it cannot detect the stroke

STRUCTURE 2:
- cannot detect the stroke

STRUCTURE 3:
- this is a Diffusion Weighted Image
- the areas of decreased diffusion are bright
- this is where the stroke is

STRUCTURE 4:
- this is a Perfusion Image
- the areas of decreased diffusion are dark
- this is where the stroke is taking place