Fully refocused gradient recalled echo (FRGRE): factors affecting flow and motion sensitivity in cardiac MRI.

The Fully Refocused Gradient Recalled Echo (FRGRE) magnetic resonance pulse sequence, previously reported as True FISP, was implemented and reported on a GE Signa CV/i 1.5T scanner. The purpose of this research was to optimize the pulse sequence design and scanning parameters to improve image quality for cardiac applications. A 2-D, multi-slice, multi-phase, breathold, segmented k-space, prospectively gated FRGRE sequence was implemented with TE and TR values as short as 0.9 and 3.0 msec, respectively. Pulse sequence design changes were investigated theoretically in terms of moment calculations and by assessing the quality of long- and short-axis cardiac images. The most influential scanning parameter for the improvement of image quality was both a short TR and TE. Placement of the z gradient rephaser immediately before the slice select gradient reduced the accumulated moments and improved image quality. Increasing the slice thickness from 3 to 8-10 mm significantly reduced flow artifact. The number of views per segment was doubled, without decreasing image quality, cutting breathold time in half compared to cardiac scanning with conventional sequences with longer TRs. The optimal flip angle was approximately 60 degrees. The use of a full or fractional echo had no noticeable effect on image quality. Surprisingly, the addition of flow compensation pulses significantly decreased image quality. In summary, optimization of sequence design and scanning parameters significantly reduced flow artifacts seen in FRGRE images.