Inherent velocity encoding in EPI-based phase contrast MRI using a modified flyback approach

Motivation: Conventional EPI-based phase contrast (PC) suffers from reduced velocity encoding (Venc) accuracy. The interleaved flyback approach produces two images with inherent Venc in readout direction through alternating readout gradients. Goal(s): To demonstrate, as a proof-of-concept, that the inherent Venc is not only time-efficient but also improves accuracy of EPI-based velocity encoding. Approach: Velocity encoding is given by the phase difference between the positive and negative readout images obtained from the interleaved flyback method. Additional gradient moment smoothing reduces phase encoding artifacts. Results: Preliminary results indicate alignment with the Venc of a GRE-based sequence with a 33% reduction in acquisition time. Impact: Interleaved flyback EPI achieves velocity encoding through the readout gradients rather than Venc gradients and simultaneously addresses key limitations of conventional EPI-based Venc. If shown to match gold-standard accuracy, it could reduce acquisition times by one-third.