ausblenden:
Schlagwörter:
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Zusammenfassung:
The MR-sequence is an essential tool to measure MR-properties in tissues,
increased contrast between these and quantify relevant data. Besides
furnishing the desired tissue-derived MR signal, the sequence must allow
spatial encoding to take place as efficient as possible to enable patient
compliance, and high-quality MRI at the same time. Starting with a brief
introduction regarding MR-tissue properties and spatial encoding in k-space, I
will describe the fundamental MR toolkit, based on single echo spin-echo (SE) and gradient-echo (GE) and show how these are extended to different multipleecho
regimes. Basic image contrast and how imaging parameters: repetition
time, TR; echo time, TE; flip angle, FA; inversion delay, diffusion gradients,
etc.; influence contrast will be described. The possibility to further enhance
imaging by adequate spin-preparation: inversion or magnetisation transfer
pulses etc.; will also be discussed. Imaging speed can be achieved while
remaining in the single echo regime by faster RF pulsing (shorter TR) giving
valuable information linked with magnetic susceptibility like in the GE-based
FLASH method, based on spoiling of unwanted echoes. Another possibility is
to use multiple (spin) echoes to read out different k-space lines, and hereby
speed up spatial sampling, like in the SE-based method RARE. An alternative
possibility that further extends available image contrast is to retain the full
magnetisation in GE-based sequences and acquire images in the different
steady-state-free-precession regimes. The latter techniques have gained
momentum through the advent of magnetic fingerprinting and are evolving into
another fundamental part of the standard MRI-toolkit.
