Temporally resolved parametric assessment of Z-magnetization recovery (TOPAZ): Dynamic myocardial T₁ mapping using a cine steady-state look-locker approach

Purpose: To develop and evaluate a cardiac phase-resolved myocardial T₁ mapping sequence. Methods: The proposed method for temporally resolved parametric assessment of Z-magnetization recovery (TOPAZ) is based on contiguous fast low-angle shot imaging readout after magnetization inversion from the pulsed steady state. Thereby, segmented k-space data are acquired over multiple heartbeats, before reaching steady state. This results in sampling of the inversion-recovery curve for each heart phase at multiple points separated by an R-R interval. Joint T₁ and B₁⁺ estimation is performed for reconstruction of cardiac phase-resolved T₁ and B₁⁺ maps. Sequence parameters are optimized using numerical simulations. Phantom and in vivo imaging are performed to compare the proposed sequence to a spin-echo reference and saturation pulse prepared heart rate–independent inversion-recovery (SAPPHIRE) T₁ mapping sequence in terms of accuracy and precision. Results: In phantom, TOPAZ T₁ values with integrated B₁⁺ correction are in good agreement with spin-echo T₁ values (normalized root mean square error = 4.2%) and consistent across the cardiac cycle (coefficient of variation = 1.4 ± 0.78%) and different heart rates (coefficient of variation = 1.2 ± 1.9%). In vivo imaging shows no significant difference in TOPAZ T₁ times between the cardiac phases (analysis of variance: P = 0.14, coefficient of variation = 3.2 ± 0.8%), but underestimation compared with SAPPHIRE (T₁ time ± precision: 1431 ± 56 ms versus 1569 ± 65 ms). In vivo precision is comparable to SAPPHIRE T₁ mapping until middiastole (P > 0.07), but deteriorates in the later phases. Conclusions: The proposed sequence allows cardiac phase-resolved T₁ mapping with integrated B₁⁺ assessment at a temporal resolution of 40 ms. Magn Reson Med 79:2087–2100, 2018.