Cardiac Cine Imaging in a single Breathhold using Elliptically reordered 3D TrueFISP

Introduction The TrueFISP sequence as proposed by Oppelt et. al. in 1986 (1) offers a high contrast between myocardium and intraventricular cavity, which is desirable for accurate assessment of ventricular function. A significant drawback of TrueFISP is its sensitivity to offresonance effects caused by an imperfect shim, chemical shifts, eddy currents, and Maxwell effects. An extension of the 2D TrueFISP sequence to an ecg-gated 3D TrueFISP sequence is thus not straight forward and requires a very carefully designed acquisition scheme. The current implementation of our gated 3D TrueFISP sequence allows to acquire the complete heart in its diastolic phase within about 20 heartbeats with a resolution of 2 x 2 x 3 mm. In addition, a 3D TrueFISP cine technique with a time resolution of 50 to 90 ms and a spatial resolution of 3 x 4 x 4 mm was implemented. Methods Besides offresonance effects generated by different susceptibilities and chemical shifts, eddy currents are a further source of signal insabilities for the TrueFISP sequence. Linear phase encoding as used for 2D TrueFISP sequences generates a smooth variation of the phase gradient amplitudes, and the nearly balanced amplitudes of the phase encoding gradients before and after the RF pulse act as an intrinsic eddy current compensation. In conventional 3D sampling patterns, however, 3D k-space is scanned line by line for each linearly increasing partition step. As a result, after each completed line scan, the line position is rewinded from the outermost position to the starting position while increasing one step in partition direction. At this point the intrinsic eddy current compensation fails since here the line phase encoding gradients have same amplitudes before (rewinder) and after (prewinder) the RF pulse. An alternating or zigzag sampling trajectory through lines and partitions as shown in Fig. 1 is proposed that eliminates this effect. This sampling pattern provides a smooth and small variation of the kspace encoding position between any successiv step of the encoding procedure.