

Second gradient: Rephasing
Moving protons
Stejskal-Tanner sequence
www.wikipedia.deThree principal axes
The B-value
•
Expresses strength and duration of
gradient field
•
Low B-values:
–
B = 0: T2-weighted image
–
B = 50 - 400
»
Signal loss in fast moving protons
(perfusion)
•
High B-values
–
B > 400
»
Signal loss in slowly moving protons
(diffusion)
The ADC
•
ADC = apparent diffusion coefficient
•
Slope of straight line connecting two
values obtained with different B-values
Signal intensity
0
22,5
45
67,5
90
B-value
50
800
Low b-value
High b-value
Calculation of
signal loss/pixel
ADC image
Calculation of the ADC
(
)
3
3
2
1
λ
λ
λ
+ +
=
ADC