Simultaneous myocardial T1, T2, T1ρ and fat fraction mapping with hybrid dual-echo cartesian acquisition and dictionary matching.

BACKGROUND

T1, T2, T1ρ and fat fraction (FF) are important parameters for diagnosing various pathological changes in the myocardium. However, existing methods either require repeated breath-holds to quantify multiple parameters, or rely on complex image reconstruction to remove artifacts arising from highly undersampled acquisition. To address this technical gap, a free-breathing Dixon-MultiMap technique is proposed to allow for simultaneous myocardial T1, T2, T1ρ and FF mapping in a single scan with conventional single-shot Cartesian acquisition.

METHODS

Dixon-MultiMap employs electrocardiogram-triggered, single-shot dual-echo Cartesian acquisition over 14 consecutive cardiac cycles. A hybrid dual-echo acquisition scheme is designed to acquire four-echo images within a short cardiac acquisition window in the first two cardiac cycles, which are used to obtain FF and B0 field maps with water-fat separation. The derived B0 map is used as prior information for dual-echo water-fat separation of the multi-contrast images acquired in the following cardiac cycles. Subsequently, dictionary matching is performed on the water images for multi-parameter mapping, accounting for spin-history B1+ inhomogeneities. Dixon-MultiMap was optimized through simulations and validated in phantoms, 13 healthy volunteers, and three patients with suspected hypertrophic cardiomyopathy.

RESULTS

In phantoms, Dixon-MultiMap showed strong correlation with reference methods for measuring T1, T2, T1ρ and FF (R² > 0.96). In healthy subjects, Dixon-MultiMap achieved robust water-fat separation, yielding FF comparable to the conventional multi-echo method. Compared with separate breath-hold mapping techniques, Dixon-MultiMap yielded significantly higher T1 values (1348 ± 33 ms vs. 1159 ± 28 ms, p < 0.001), comparable T2 values (46.4 ± 1.7 ms vs. 45.4 ± 1.5 ms, p = 0.96), and a small but statistically significant increase in T1ρ values (55.8 ± 2.6 ms vs. 53.0 ± 1.8 ms, p = 0.01). Pathological changes detected by Dixon-MultiMap were consistent with those identified using conventional mapping techniques in the three patients.

CONCLUSION

The proposed Dixon-MultiMap allows for simultaneous myocardial T1, T2, T1ρ and FF mapping in a free-breathing acquisition of 14 cardiac cycles. Water-fat partial volume was resolved by water-fat separation in Dixon-MultiMap, which improved the accuracy of multi-parameter estimation.