Native myocardial T1 reference values in a tunisian cohort using MOLLI and SMART1Map : List of Authors.

Native T1 values in cardiac magnetic resonance (CMR) are influenced by acquisition sequence, physiological factors, and site-specific variability, complicating clinical interpretation. The absence of population-specific reference values further limits diagnostic accuracy. This study aimed to establish native T1 reference ranges in a Tunisian population, evaluate sex- and age-related differences using MOLLI 5(3)3 and SMART1Map sequences, and assess inter-site variability of MOLLI measurements across two centers using identical scanners and protocols. Ninety-four healthy volunteers were enrolled: 64 subjects (24 females, 40 males; 5-77 years) were scanned at Site 1 to establish reference values, and 30 subjects (20 females, 10 males; 19-62 years), frequency-matched by age to a subset of Site 1, were scanned at Site 2 to evaluate site-related variability. MOLLI-derived T1 values showed a significant negative association with age (β = -0.84 ms/year, p = 0.012), whereas SMART1Map-derived values were not associated with age (β = 0.30 ms/year, p = 0.556). SMART1Map consistently yielded higher T1 values than MOLLI (global mean ± SD: 1184 ± 70 ms vs. 1049 ± 55 ms; p < 0.001). Sex-related differences were minimal, with only a small apical difference observed for MOLLI (p = 0.023). Multi-center MOLLI measurements showed similar T1 distributions across sites, with minor differences observed at the mid-ventricular level. These findings provide the first Tunisian-specific native myocardial T1 reference values at 1.5 T, highlighting sequence-dependent differences, age-related effects for MOLLI, minimal sex-related influence, and overall inter-site consistency. These findings support the use of locally derived, sequence-specific reference ranges to improve clinical interpretation.