Impact of motion correction on reproducibility and spatial variability of quantitative myocardial T₂ mapping

Background: To evaluate and quantify the impact of a novel image-based motion correction technique in myocardial T₂ mapping in terms of measurement reproducibility and spatial variability. Methods: Twelve healthy adult subjects were imaged using breath-hold (BH), free breathing (FB), and free breathing with respiratory navigator gating (FB∈+∈NAV) myocardial T₂ mapping sequences. Fifty patients referred for clinical CMR were imaged using the FB∈+∈NAV sequence. All sequences used a T₂ prepared (T₂prep) steady-state free precession acquisition. In-plane myocardial motion was corrected using an adaptive registration of varying contrast-weighted images for improved tissue characterization (ARCTIC). DICE similarity coefficient (DSC) and myocardial boundary errors (MBE) were measured to quantify the motion estimation accuracy in healthy subjects. T₂ mapping reproducibility and spatial variability were evaluated in healthy subjects using 5 repetitions of the FB∈+∈NAV sequence with either 4 or 20 T₂prep echo times (TE). Subjective T₂ map quality was assessed in patients by an experienced reader using a 4-point scale (1-non diagnostic, 4-excellent). Results: ARCTIC led to increased DSC in BH data (0.85∈±∈0.08 vs. 0.90∈±∈0.02, p∈=∈0.007), FB data (0.78∈±∈0.13 vs. 0.90∈±∈0.21, p∈<∈0.001), and FB∈+∈NAV data (0.86∈±∈0.05 vs. 0.90∈±∈0.02, p∈=∈0.002), and reduced MBE in BH data (0.90∈±∈0.40 vs. 0.64∈±∈0.19 mm, p∈=∈0.005), FB data (1.21∈±∈0.65 vs. 0.63∈±∈0.10 mm, p∈<∈0.001), and FB∈+∈NAV data (0.81∈±∈0.21 vs. 0.63∈±∈0.08 mm, p∈<∈0.001). Improved reproducibility (4TE: 5.3∈±∈2.5 ms vs. 4.0∈±∈1.5 ms, p∈=∈0.016; 20TE: 3.9∈±∈2.3 ms vs. 2.2∈±∈0.5 ms, p∈=∈0.002), reduced spatial variability (4TE: 12.8∈±∈3.5 ms vs. 10.3∈±∈2.5 ms, p∈<∈0.001; 20TE: 9.7∈±∈3.5 ms vs. 7.5∈±∈1.4 ms) and improved subjective score of T₂ map quality (3.43∈±∈0.79 vs. 3.69∈±∈0.55, p∈<∈0.001) were obtained using ARCTIC. Conclusions: The ARCTIC technique substantially reduces spatial mis-alignment among T₂-weighted images and improves the reproducibility and spatial variability of in-vivo T₂ mapping.