Analytical Ground Truth for Phase-Contrast MRI Experiments and Simulations: Open-Source Precision-Controlled...

We present a fully open-source, air-driven bidirectional, rotational MRI phantom. It enables an accurate and reproducible evaluation of displacement artefacts for any MRI sequence and velocity field and acceleration sensitivity for phase-contrast MRI (PC-MRI) sequences. Its unique feature of analytically defined motion is expected to narrow the gap between simulations and experiments for in-silico and in-vitro experiments using the very same sequence code.

A rotational phantom was bidirectionally driven (clockwise (CW) / counterclockwise (CCW)) by an actively controlled airflow. The rotating cylinder filled with a Polyvinylpyrrolidone-water mixture was monitored via an external laser-based tachometer system. Vendor-supplied and custom open-source PC-MRI sequences were evaluated on a 3T MRI system and used as input for Bloch simulations. Resulting magnitude and velocity images were evaluated against the phantom's ground truth data.

For physiological angular velocities, displacement errors resulted in a 10% radial stretch while apparent acceleration sensitivity is 5% of v_enc. The time difference between velocity and spatial encoding time points of 1.9ms determining the severity of the artefacts could be quantified without prior knowledge of details about the MR sequence. Simulation and experiment yielded excellent agreement.

The phantom enables an easy, precise and repeatable evaluation of motion sensitivity of MR sequences and may offer a future reference measurement. Additional timing parameters of MR sequences may be reported in future literature to improve comparability. The seamless MRI sequence definition for in-silico and in-vitro experiments narrows a significant gap in MR research.

This work establishes a reproducible, standardized validation framework for PC-MRI techniques that can be readily implemented across institutions, facilitating quality assurance procedures and supporting the development of more accurate flow quantification methods in clinical applications.