PulseSequenzen

PulseSequenzen, or pulse sequences, are predefined orders of radiofrequency pulses, gradient fields, and data acquisition windows used in magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) spectroscopy. They orchestrate the excitation and timing of spin magnetization to encode spatial or spectral information, control image contrast, and manage scan duration. The choice of sequence influences tissue contrast, signal-to-noise ratio, and sensitivity to motion or susceptibility.

A typical sequence combines RF pulses of specific flip angles, gradient lobes for spatial encoding, and precise timing parameters such as repetition time (TR), echo time (TE), and sometimes inversion time (TI). Readout schemes determine when and how the signal is sampled, while sequence design may include spoiling or refocusing steps to shape residual transverse magnetization. In MRI, sequences translate Bloch-equation dynamics into measurable signals across k-space, enabling reconstruction into images with different contrast mechanisms.

Common MRI sequences include spin-echo, gradient-echo, inversion-recovery, diffusion-weighted imaging, and fast or turbo variants, as well as echo-planar imaging for rapid data acquisition. In MR spectroscopy, specialized sequences such as PRESS, STEAM, and LASER are used to localize signals from specific brain regions and to improve spectral resolution.

Development and application of pulse sequences balance trade-offs among signal-to-noise ratio, spatial resolution, scan time, and artifact suppression. Safety considerations, including specific absorption rate (SAR) and gradient heating, guide sequence design and clinical use.