PPubMed24 Feb 2016Cited 10×

Phase Error Correction in Time-Averaged 3D Phase Contrast Magnetic Resonance Imaging of the Cerebral Vasculature Correcting Phase Errors in PC-MRI of the Cerebral Vasculature

M. Ethan MacDonald, Nils D. Forkert, G. Bruce Pike, Richard Frayne, Heye Zhang

Abstract

Phase contrast (PC) magnetic resonance (MR) imaging is a powerful method for measuring blood flow velocity in human subjects and can provide key hemodynamic information about the vasculature. However, concern has been raised about measurement accuracy , in particular, the impact of phase error from the application of magnetic gradient fields causing a spatially varying offset in the phase across the image . This bias can limit the accuracy of quantitative PC-MR measurements. For some regions, like the heart, this phase error has been reported to be as large as 10% to 25% . There are two mechan

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Eddy current phase errors have minimal impact on cerebral vessel flow measurements in typical time‑averaged 3D PC‑MRI, and correction schemes do not significantly change VFR.

What’s new

i.Assessed the impact of eddy‑current‑induced phase errors in time‑averaged 3D PC‑MRI of the cerebral vasculature.
ii.Implemented and compared three correction schemes (local bias correction, local polynomial correction, whole‑brain polynomial correction) in a static phantom and 30 healthy subjects.
iii.Demonstrated that while corrections markedly reduce background bias, they do not produce significant changes in vessel volume flow rate measurements.
iv.Provided statistical analysis (ANOVA, Bland‑Altman) showing no significant differences between correction methods.

How they did it

Phase error was first measured in a static head‑sized phantom, then three correction techniques (LBC, LPC, WBPC) were applied to background tissue and vessel VFR measurements in 30 healthy volunteers scanned on a 3 T MR system. VFR per pixel was calculated from cut‑plane velocity integrations, and statistical tests (six‑way and three‑way ANOVA, Kolmogorov‑Smirnov, Bland‑Altman) compared corrected and uncorrected results.

What they found

Phantom phase error measured <2.1 ml/s per pixel; correction reduced bias to <0.6, <0.3, and <0.5 ml/s/pixel for LBC, LPC, and WBPC respectively.
Background bias reduced by 65.6% (LBC), 58.4% (LPC), and 47.7% (WBPC) (p < 0.001).
Vessel VFR differences after correction were -0.04 ± 0.05 ml/s (LBC), 0.09 ± 0.16 ml/s (LPC), and -0.02 ± 0.06 ml/s (WBPC); no significant change (p = 0.997).
No significant differences between the three correction schemes for vessel measurements (p = 0.738).

Caveats

✕Static phantom does not replicate flow dynamics; phase‑error measurements may vary over time.
✕Correction schemes slightly increased variability (coefficient of variation) in vessel VFR measurements.
✕Study focused only on VFR; other hemodynamic metrics such as wall shear stress, pressure, and kinetic energy were not evaluated.
✕Findings apply to a typical brain PC‑MRI protocol and may not generalize to other acquisition settings.

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Phase Error Correction in Time-Averaged 3D Phase Contrast Magnetic Resonance Imaging of the Cerebral Vasculature Correcting Phase Errors in PC-MRI of the Cerebral Vasculature

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