FAST AND ULTRAFAST MR-IMAGING - BASIC PRI NCIPLES AND PULSE SEQUENCES

The aim of this article is the systematic treatment of fast and ultraf ast magnetic resonance imaging (MRI) techniques. Based on the basic pr inciples of signal generation and spatial encoding with magnetic field gradients the differences and important similarities of pulse sequenc es will be explained. We suggest to replace the conventional grouping of pulse sequences in gradient and spin-echo sequences through single and multi-echo sequences, since the latter is more precise and helpful . We illustrate how single-echo sequences such as ''spin-echo'', FLASH , FISP, PSIF CISS and DESS can be derived from a single gradient echo and how multi-echo sequences such as turbo spin-echo, RARE, HASTE and GRASE are based on echo-planar imaging. The different properties, adva ntages and disadvantages of the various sequences will be discussed an d frequently used acronyms will be explained.