2017 Imaging for Physicists Coursebook

Phase evolution

  t

t   

0

0

• The phase shift depends on the strength and duration of the gradient applied;

 

TB T T    



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

TG ym   



Tn xG   



and

m

y y

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