REDUCING FLOW ARTIFACTS IN ECHO-PLANAR IMAGING

Echo-planar imaging (EPI) is very susceptible to flow artifacts, Two w ays to improve its flow properties are presented. First, ''partial fly back'' is proposed to reduce artifacts arising from flow in the readou t direction. Near the center of k-space, only the even echoes of the E PI echo-train are used. Partial flyback is shown to improve the readou t-flow properties at the expense of a slight worsening of the phase-en code flow and off-resonance properties. We recommend that the flyback region acquire 95% of the energy in k-space. Second, ''inside-out'' EP I is used to reduce artifacts arising from flow in the phase-encode di rection, Data collection begins at the center of k-space, with separat e interleaves to acquire the top and bottom halves of k-space, Partial flyback is combined with partial-Fourier EPI and inside-out EPI. Part ial-flyback inside-out EPI has worse off-resonance properties than par tial-flyback partial-fourier EPI but demonstrates better flow properti es and does not require partial k-space reconstruction.