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Is TrueFISP a gradient‐echo or a spin‐echo sequence?
Authors:Klaus Scheffler  Jürgen Hennig
Affiliation:Section of Medical Physics, Department of Diagnostic Radiology, University of Freiburg, Freiburg, Germany. klaus.schleffer@unibas.ch
Abstract:
It is commonly accepted that TrueFISP (balanced FFE, FIESTA) belongs to the class of gradient-echo (GRE) sequences. GRE sequences are sensitive to dephasing effects of the transverse magnetization between the excitation pulse and echo acquisition, and phase coherence is only established directly after and before excitation pulses. However, an analysis of the phase evolution of transverse magnetization in a TrueFISP experiment shows very close similarities to the echo formation of a spin-echo (SE) experiment. If dephasing between excitation pulses is below +/-pi, TrueFISP exhibits a nearly complete refocusing of transverse magnetization at TE = TR/2. Only signals acquired before and after TR/2 show an additional T*2 sensitivity.
Keywords:steady‐state free precession  refocusing  phase coherence  susceptibility
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