Clinical comparison of four commercial MRI phantoms on a 0.35T MR-linac using a standard clinical TRUFI sequence at a single institution

Purpose

Real‑time magnetic resonance–guided radiation therapy (MRgRT) integrates MRI with a linear accelerator (Linac) for gating and adaptive radiotherapy, which requires robust image‑quality assurance over a large field of view (FOV). Specialized phantoms capable of accommodating this extensive FOV are therefore essential. This study compares the performance of four commercial MRI phantoms on a 0.35 T MR‑Linac.

Methods

Four phantoms: the IBA QUASAR Insight Phantom, the IBA QUASAR MRID^3D Geometric Distortion Phantom, the MagPhan Phantom, and the Sun Nuclear Large Field MRI Distortion Phantom, were evaluated on a 0.35 T MR-Linac using the TRUFI clinical sequence. Mean distortions were measured at gantry angles from 0° to 360° in 30° increments. Clinical imaging parameters (signal-to-noise ratio, uniformity, resolution via modulation transfer function, laser alignment, and twist) were also assessed where applicable.

Results

The QUASAR MRID^3D Phantom enabled separate quantification of B₀ and gradient-induced distortions but showed a notable vertical offset, which did not affect comparisons with other phantoms. Both the MagPhan and QUASAR Insight phantoms provided mean distortion measurements as well as additional imaging parameters (e.g., signal-to-noise ratio, uniformity, resolution). The Sun Nuclear Phantom exhibited higher overall distortion values.

Conclusion

All four phantoms successfully measured distortion at multiple gantry angles on a 0.35 T MR-Linac. The QUASAR MRID^3D Phantom uniquely differentiated B₀ from gradient distortions but required an offset adjustment. The MagPhan and QUASAR Insight phantoms offered comprehensive imaging metrics, while the Sun Nuclear Phantom exhibited relatively higher distortions.