Validation of two accelerated 4D flow MRI sequences at 3 T: a phantom study.

Area of Science:

• Cardiovascular Imaging
• Magnetic Resonance Imaging
• Fluid Dynamics

Background:

• Four-dimensional (4D) flow MRI with parallel imaging aims to shorten scan times while maintaining image quality and accuracy compared to 2D flow MRI.
• This study evaluates accelerated 4D flow MRI sequences against standard 2D flow MRI using a flow phantom at 3 Tesla.

Purpose of the Study:

• To compare the accuracy, reproducibility, and scan times of two accelerated 4D flow MRI sequences (GRAPPA2 and k-t-GRAPPA5) against standard 2D flow MRI.
• To assess the impact of velocity encoding (Venc) and measuring plane alignment on flow measurements in both 2D and 4D flow MRI.

Main Methods:

• Two accelerated 4D flow MRI sequences (GRAPPA2, k-t-GRAPPA5) and a standard 2D flow MRI sequence were tested on a flow phantom with constant and pulsatile flow.
• Flow volumes and velocities were analyzed using custom software "Bloodline", with calculated phantom flow used as the reference standard.
• Evaluated parameters included concordance of flow volumes/velocities, reproducibility, and dependency on measuring plane and Venc.

Main Results:

• No significant differences in flow volume or velocity were observed between 2D, 4D flow MRI sequences, and the pump reference for both continuous and pulsatile flow.
• All sequences demonstrated excellent correlation (R=0.99-1.0) with the reference standard and excellent reproducibility (R=0.99).
• Overestimation of Venc had no impact; however, misaligned planes caused underestimation in 2D flow MRI but not in 4D flow MRI. k-t-GRAPPA5 scan time (1:54 min) was significantly shorter than GRAPPA2 (3:56 min).

Conclusions:

• Both accelerated 4D flow MRI sequences provide accurate flow measurements comparable to 2D flow MRI, unaffected by Venc overestimation or plane misalignment.
• The highly accelerated k-t-GRAPPA5 sequence achieves results similar to GRAPPA2 but with a substantial reduction in scan time.
• 4D flow MRI offers a robust and efficient alternative to 2D flow MRI for cardiovascular flow assessment.