Free-breathing 3 T magnetic resonance T₂-mapping of the heart

Objectives: This study sought to establish an accurate and reproducible T₂-mapping cardiac magnetic resonance (CMR) methodology at 3 T and to evaluate it in healthy volunteers and patients with myocardial infarct. Background: Myocardial edema affects the T₂ relaxation time on CMR. Therefore, T₂-mapping has been established to characterize edema at 1.5 T. A 3 T implementation designed for longitudinal studies and aimed at guiding and monitoring therapy remains to be implemented, thoroughly characterized, and evaluated in vivo. Methods: A free-breathing navigator-gated radial CMR pulse sequence with an adiabatic T₂ preparation module and an empirical fitting equation for T₂ quantification was optimized using numerical simulations and was validated at 3 T in a phantom study. Its reproducibility for myocardial T₂ quantification was then ascertained in healthy volunteers and improved using an external reference phantom with known T₂. In a small cohort of patients with established myocardial infarction, the local T₂ value and extent of the edematous region were determined and compared with conventional T₂-weighted CMR and x-ray coronary angiography, where available. Results: The numerical simulations and phantom study demonstrated that the empirical fitting equation is significantly more accurate for T₂ quantification than that for the more conventional exponential decay. The volunteer study consistently demonstrated a reproducibility error as low as 2 ± 1% using the external reference phantom and an average myocardial T₂ of 38.5 ± 4.5 ms. Intraobserver and interobserver variability in the volunteers were -0.04 ± 0.89 ms (p = 0.86) and -0.23 ± 0.91 ms (p = 0.87), respectively. In the infarction patients, the T₂ in edema was 62.4 ± 9.2 ms and was consistent with the x-ray angiographic findings. Simultaneously, the extent of the edematous region by T₂-mapping correlated well with that from the T₂-weighted images (r = 0.91). Conclusions: The new, well-characterized 3 T methodology enables robust and accurate cardiac T ₂-mapping at 3 T with high spatial resolution, while the addition of a reference phantom improves reproducibility. This technique may be well suited for longitudinal studies in patients with suspected or established heart disease.