FID-acquired-echos (FAcE): a short echo time imaging method for flow artefact suppression.

The FID-Acquired-Echo sequence (FAcE) is a magnetic resonance imaging technique using fractional-echo acquisitions, with sequential separate sampling of the right and left k-space half planes. It reduces the minimal echo times by about a factor of two, compared to conventional full-(gradient)-echo sampling schemes. With this sequence, implemented on a commercial 1.5 Tesla whole body system, high resolution images are acquired with typical echo times between 3 and 4.5 msec. Using short echo times the signal dephasing caused by velocity and higher order spin motion is reduced. Further, due to the modified sampling scheme, the sequence exhibits, for triggered studies, partially a compensation of motion-induced phase shifts in the frequency-encoding direction. Thus, the sequence offers an alternative means for the reduction of motion-induced image artefacts to the use of flow compensating gradients, which usually makes a sequence more sensitive to higher order motion and introduces further eddy currents. Besides potential application for imaging of nuclei and tissues with short T2 relaxation times, and non-ECG-triggered in-flow angiography, the main application seems to be triggered-phase contrast imaging with focus on quantitation of blood flow. Its usefulness is largest in cases with irregular flow patterns, where considerable in-plane flow occurs.