Abstract
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.