Accelerated spin echo imaging with turbo or fast spin echo. The conventional spin echo pulse sequence (left) applies a single 180° pulse following the 90° pulse to generate a single spin echo, filling only one line of k-space each R-R interval. The turbo or fast spin echo pulse sequence (right) applies multiple 180° pulses following the 90° pulse to generate multiple spin echoes. Multiple lines of k-space are filled within each R-R interval by applying a phase encoding gradient with a different amplitude to each echo. In this diagram each phase encoding gradient is colour coded to identify which corresponding line of k-space is filled. The phase encoding applied to each echo is removed by applying an equal and opposite re-winder gradients after each echo is sampled. In this example, four 180° pulses are applied to generate four spin echoes (echo train length or turbofactor = 4). This provides a four-fold acceleration in scan time.