Flow distortion and signal loss in spiral imaging.
The effect of in-plane motion on the point spread function (velocity PSF) in spiral imaging is studied experimentally and derived mathematically and is shown to consist of a smoothed, trailing edge and fringes around the leading edge. The velocity PSF remains largely in phase with the static PSF, consistent with the absence of signal loss by motion-related phase shifts in central k space. However, single-shot spiral imaging gives no clear improvement in complex and turbulent flow signal uniformity compared with echo-planar imaging with early, central k-space acquisition, which requires explanation given the spiral's earlier coverage of central k space. Alternate leading-edge fringes of the spiral's velocity PSF are in antiphase to the source, and cancellation may occur when these overlap other in-phase signals. Phase variations toward peripheral k space in turbulent flow also cause distortion. It is concluded that spiral imaging may lose complex and turbulent flow signals because of complex PSF distortion.
Gatehouse
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PD
Magnetic Resonance Unit, Royal Brompton Hospital, Chelsea, London, United Kingdom. p.gatehouse@rbh.nthames.nhs.uk
Firmin
D N
DN
D000465:Algorithms; D016477:Artifacts; D003198:Computer Simulation; D017352:Echo-Planar Imaging / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008962:Models, Theoretical; D009068:Movement; D019047:Phantoms, Imaging; D012212:Rheology