FIESTA (Fast Imaging Employing Steady-state Acquisition) is the GE name for a balanced steady-state gradient echo sequence that Siemens calls TrueFISP and Philips calls balanced-FFE. As described in a prior Q&A, these sequences may be affected by phase shift errors across the image that produce banding artifacts. Such artifacts are particularly prominent at the skull base and other locations where there are susceptibility distortions of the main magnetic field. They are also more problematic in 3D acquisitions where TR values may exceed 10-15 msec.
FIESTA-C is a modification of the basic FIESTA/TrueFISP sequence. The equivalent Siemens product is called CISS (Constructive Interference Steady State). FIESTA-C/CISS is composed of a pair of TrueFISP acquisitions run back-to-back preceded by an automatic shimming procedure. The first uses phase alternation of the RF-pulses (+α, −α, +α, −α, ...) while the second does not (+α, +α, +α, etc). When the paired data sets are combined in maximum intensity projection, the phase errors cancel, resulting in an image largely free of dispersion banding. This combination of paired signals is performed automatically after data collection (which increases reconstruction time slightly).
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Several variations of FIESTA-C/CISS sequences exist. One method is to use four (rather than 2) acquisitions, each phase shifted by 90 degrees. This can improve the reduction of banding artifacts, albeit at the expense of increased imaging time. Another promising method is to use the square root of sum of squares rather than maximum intensity projection to create the final image.
GE offers an interesting variant of FIESTA-C called COSMIC (Coherent Oscillatory State acquisition for the Manipulation of Image Contrast). COSMIC exploits the initial oscillatory state that occurs during transition to FIESTA's steady state. During this period, the MR signal is strongly dependent on the T2/T1, meaning that fluids will produce exceptionally high signals. COSMIC also uses segmented centric (elliptical) k-space sampling to decrease sampling time and a separate variable flip-angle RF-pulse train and recovery period following acquisition to improve signal stability.
Borelli AJ. Non-contrast MR arthrograms generate exquisite images. GE Signa Pulse, Spring, 2008, pp 54-55. (Brief description and examples of GE's COSMIC sequence).
Casselman J, Kuhweide R, Deimling M, et al. Constructive Interference in Steady State‑ 3DFT MR imaging of the inner ear and cerebellopontine angle. AJNR Am J Neuroradiol 1993; 14:47‑57.
What is True FISP, and why is it "truer" than regular FISP?