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Phase evolution
• The phase shift depends on the strength and duration of the gradient
applied;
( )
t
t
0
0
ω
= Φ
( )
TB T T
∆= ∆= ∆Φ
γ
ω
• In a spin-echo sequence, the spins flip 180° during the 180° pulse.
Thus, a phase difference created before the 180° pulse has the opposite
effect during read-out
y y
m
TG ym
∆ = ∆Φ
γ
• For the phase-encoding (y) and read-out (x) gradients, this means:
x
x
n
Tn xG
∆ = ∆Φ
γ
and