[Fast and ultra-fast MRI of the brain]

Fast spin-echo sequences, which are based on the RARE sequence, accelerate MRI significantly. The basic principle of fast- or turbo-spin-echo sequences (FSE, TSE), as well as of the gradient-and-spin-echo sequences (GRASE, TGSE), is the sampling of multiple independently phase-encoded echos after each excitation. The basic principles of these sequences and the potentials and limitations of their clinical application are discussed. Their main advantage is a significant reduction of the time for data acquisition, which allows either a reduction of imaging time or high-resolution images even with T2-weighting. The fast sequences provide all possibilities of contrast variation and of preparation pulses such as fat saturation or water suppression. Despite some restrictions, of which reduced susceptibility is clinically relevant, they can replace conventional spin-echo sequences in brain imaging.