Echo planar imaging-induced errors in intracardiac 4D flow MRI quantification.

Area of Science:

• Cardiovascular Imaging
• Magnetic Resonance Imaging
• Fluid Dynamics

Background:

• 4D flow MRI (4DFlow) is crucial for assessing intracardiac blood flow.
• EPI acceleration techniques like 4DEPI aim to reduce scan times but may introduce artifacts.
• Comparing 4DEPI with conventional 4DGRE is essential to understand its diagnostic accuracy.

Purpose of the Study:

• To evaluate the accuracy of EPI-accelerated 4D flow MRI (4DEPI) with an EPI factor of 5.
• To compare the performance of 4DEPI against non-EPI gradient echo (4DGRE) for intracardiac flow assessment.

Main Methods:

• Three-dimensional MRI experiments were conducted comparing 4DEPI and 4DGRE.
• Studies included steady flow in tubes, pulsatile flow in a left-ventricle phantom, and intracardiac flow in 10 healthy volunteers.
• 4DEPI was tested with varying gradient orientations relative to flow; flow rates and speeds were quantitatively compared.

Main Results:

• Flow rate errors in steady-flow phantoms reached 12% for 4DEPI when the readout gradient was parallel to high velocities (>2 m/s).
• Phantom and in vivo speed differences between 4DEPI and 4DGRE were generally low (≤5.5% and ≤9% respectively).
• In vivo, the largest mean net forward volume inconsistency for 4DEPI was 6.4 ± 8.5% when the non-blip phase-encoding gradient was parallel to flow.

Conclusions:

• 4DEPI with EPI factor 5 demonstrates potential inaccuracies in velocity and flow rate when flow aligns with readout or blip gradients.
• Despite potential inaccuracies, mean differences in flow rate, voxel-based speed, and median speed were within acceptable ranges (≤10%) for intracardiac flow in healthy volunteers when comparing 4DEPI to 4DGRE.