1. Spin echo.
Spin echo. Following a 90° excitatory radiofrequency (RF) pulse with consequent transverse magnetisation, protons begin to de-phase (A–C) and signal amplitude decreases. Application of an 180° RF pulse at time TE/2 causes the protons to precess in the opposite direction. Protons that were initially ‘in front’ now find themselves at the back but begin to ‘catch’ the other protons, which are precessing at a slighter slower frequency (D–F). At time TE the protons regain phase, resulting in a stronger net transversal magnetisation and thus a stronger signal. This signal re-emergence is termed spin echo. This figure is only reproduced in colour in the online version.
Stuart Currie et al. Postgrad Med J 2013;89:
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