- Workshop presentation
- Open Access
In-vivo distortion of through-plane flow by spiral phase-contrast imaging
© Pierce et al; licensee BioMed Central Ltd. 2012
- Published: 1 February 2012
- Phase Curvature
- True Lumen
- Phase Slope
- Radial Phase
- Spiral Imaging
To explain previously unrecognised consequences of two sources of phase curvature over the vessel cross-section in spiral imaging i.e. off-resonance and the velocity-encoded phase-shift.
The effects of off-resonance frequency errors during spiral readouts [Yudilevich and Stark, 1987] are known. Here we explain previously unrecognised intra-voxel dephasing consequences of two sources of phase curvature over the vessel cross-section in through-plane flow imaging using spirals i.e. off-resonance and the velocity-encoded phase-shift, including the consequences for in-vivo measurements.
Laminar through-plane flow phantom (50cm/s) and popliteal artery studies were acquired at Venc=50cm/s with initial off-resonance offsets ± 0 10, 20, 40Hz representing <1ppm at 1.5T. Reference (“Ref”) and velocity-encoded (“Vel”) magnitude and phase images were obtained (as a cine in-vivo). Spiral FOV was 150 mm, 1mm resolution, duration 25.7ms; TE/TR 4.0/32.7 ms, FA 30°, 4 interleaves.
The distortion of the velocity distribution over the in-vivo vessel distorts peak velocity by ~20% at -40Hz off-resonance at these sequence parameters. Separate tests eliminated through-plane gradient fields as a cause, including eddy-current effects after the velocity-encoding pulses.
These effects on magnitude images and velocity distributions at <1ppm off-resonance are potentially difficult for >20ms spiral readouts in small vessel applications at least, perhaps more so near B0-distortions such as lungs. Shorter spirals and avoiding large intra-voxel radial phase shear are some-what incompatible with rapid flow work.
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