2016_Imaging for Physicists

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

• For the phase-encoding (y) and read-out (x) gradients, this means:

y y TG ym ∆ = ∆Φ γ

Tn xG ∆ = ∆Φ

γ

and

m

n

x

x

• 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