Flow distortion and signal loss in spiral imaging

The effect of in-plane motion on the point spread function (velocity PSF) i n spiral imaging is studied experimentally and derived mathematically and i s shown to consist of a smoothed, trailing edge and fringes around the lead ing edge. The velocity PSF remains largely in phase with the static PSF, co nsistent with the absence of signal loss by motion-related phase shifts in central k space, However, single-shot spiral imaging gives no clear improve ment in complex and turbulent flow signal uniformity compared with echo-pla nar imaging with early, central k-space acquisition, which requires explana tion given the spiral's earlier coverage of central k space. Alternate lead ing-edge fringes of the spiral's velocity PSF are in antiphase to the sourc e, and cancellation may occur when these overlap other in-phase signals. Ph ase variations toward peripheral k space in turbulent flow also cause disto rtion, It is concluded that spiral imaging may lose complex and turbulent f low signals because of complex PSF distortion. Magn Reson Med 41:1023-1031, 1999. (C) 1999 Wiley-Liss, Inc.