Spin-echo vs gradient-echo pulse sequences
Two pulse-sequence lanes drawn on a shared time axis with excitation aligned at time zero. Top lane, spin echo: a 90 degree excitation, then a 180 degree refocusing pulse at TE over 2, then an echo at TE; the repetition time TR is long and spans the whole width. A note states the 180 degree pulse rephases spins and cancels static B0 inhomogeneity giving true T2. Bottom lane, gradient echo: a smaller flip-angle alpha excitation, an echo formed by reversal of the readout gradient with no 180 degree pulse, marked at a much shorter TE, and a short TR so several excitations repeat across the same width. A note states this is faster with shorter TR but the signal decays with T2 star and is sensitive to susceptibility, not true T2.
Practice the Physics paper
FRCRX is a Part 1 Physics question bank: true/false items with explanations, timed mocks and topic analytics.