Inversion recovery at 7 T in the human myocardium: Measurement of T ₁, inversion efficiency and B₁⁺

At clinical MRI field strengths (1.5 and 3 T), quantitative maps of the longitudinal relaxation time T₁ of the myocardium reveal diseased tissue without requiring contrast agents. Cardiac T₁ maps can be measured by Look-Locker inversion recovery sequences such as ShMOLLI at 1.5 and 3 T. Cardiovascular MRI at a field strength of 7 T has recently become feasible, but doubts have remained as to whether magnetization inversion is possible in the heart due to subject heating and technical limitations. This work extends the repertoire of 7 T cardiovascular MRI by implementing an adiabatic inversion pulse optimized for use in the heart at 7 T. A "ShMOLLI+IE" adaptation of the ShMOLLI pulse sequence has been introduced together with new postprocessing that accounts for the possibility of incomplete magnetization inversion. These methods were validated in phantoms and then used in a study of six healthy volunteers to determine the degree of magnetization inversion and the T₁ of normal myocardium at 7 T within a 22-heartbeat breathhold. Using a scanner with 16 × 1 kW radiofrequency outputs, inversion efficiencies ranging from -0.79 to -0.83 (intrasegment means; perfect 180°would give -1) were attainable across the myocardium. The myocardial T₁ was 1925 ± 48 ms (mean ± standard deviation).