Developing a medical device-grade T 2 phantom optimized for myocardial T 2 mapping by cardiovascular magnetic resonance

Introduction A long T 2 relaxation time can reflect oedema, and myocardial inflammation when combined with increased plasma troponin levels. Cardiovascular magnetic resonance (CMR) T 2 mapping therefore has potential to provide a key diagnostic and prognostic biomarkers. However, T 2 varies by scanner, software, and sequence, highlighting the need for standardization and for a quality assurance system for T 2 mapping in CMR. Aim To fabricate and assess a phantom dedicated to the quality assurance of T 2 mapping in CMR. Method A T 2 mapping phantom was manufactured to contain 9 T 1 and T 2 (T 1 |T 2 ) tubes to mimic clinically relevant native and post-contrast T 2 in myocardium across the health to inflammation spectrum (i.e., 43–74 ms) and across both field strengths (1.5 and 3 T). We evaluated the phantom’s structural integrity, B 0 and B 1 uniformity using field maps, and temperature dependence. Baseline reference T 1 |T 2 were measured using inversion recovery gradient echo and single-echo spin echo (SE) sequences respectively, both with long repetition times (10 s). Long-term reproducibility of T 1 |T 2 was determined by repeated T 1 |T 2 mapping of the phantom at baseline and at 12 months. Results The phantom embodies 9 internal agarose-containing T 1 |T 2 tubes doped with nickel di-chloride (NiCl 2 ) as the paramagnetic relaxation modifier to cover the clinically relevant spectrum of myocardial T 2 . The tubes are surrounded by an agarose-gel matrix which is doped with NiCl 2 and packed with high-density polyethylene (HDPE) beads. All tubes at both field strengths, showed measurement errors up to ≤ 7.2 ms [< 14.7%] for estimated T 2 by balanced steady-state free precession T 2 mapping compared to reference SE T 2 with the exception of the post-contrast tube of ultra-low T 1 where the deviance was up to 16 ms [40.0%]. At 12 months, the phantom remained free of air bubbles, susceptibility, and off-resonance artifacts. The inclusion of HDPE beads effectively flattened the B 0 and B 1 magnetic fields in the imaged slice. Independent temperature dependency experiments over the 13–38 °C range confirmed the greater stability of shorter vs longer T 1 |T 2 tubes. Excellent long-term (12-month) reproducibility of measured T 1 |T 2 was demonstrated across both field strengths (all coefficients of variation < 1.38%). Conclusion The T 2 mapping phantom demonstrates excellent structural integrity, B 0 and B 1 uniformity, and reproducibility of its internal tube T 1 |T 2 out to 1 year. This device may now be mass-produced to support the quality assurance of T 2 mapping in CMR.