UCLA

Purpose

To develop a single-scan method for B1+ -corrected T₁ mapping and apply it for free-breathing (FB) cardiac MR multitasking without electrocardiogram (ECG) triggering.

Methods

One dual flip-angle (2FA) inversion recovery (IR)-FLASH scan provides two observations of T1∗ (apparent T₁ ) corresponding to two distinct combinations of the nominal FA α and B1+ . Spatiotemporally coregistered T₁ and B1+ spin history maps are obtained by fitting the 2FA signal model. T₁ estimate accuracy and repeatability for single flip-angle (1FA) and 2FA IR-FLASH sequence MR multitasking were evaluated at 3T. A T₁ phantom was first imaged on the scanner table, then on two human subjects' thoraxes in both breath-hold (BH) and FB conditions. IR-turbo spin echo (IR-TSE) static phantom T₁ measurements served as reference. In 10 healthy subjects, myocardial T₁ was evaluated with ECG-free, FB multitasking sequences alongside ECG-triggered BH MOLLI.

Results

For phantom-on-table T₁ estimates, 2FA agreed better with IR-TSE (intraclass correlation coefficient [ICC] = 0.996, mean error ± SD = -1.6% ± 1.9%) than did 1FA (ICC = 0.922; mean error ± SD = -4.3% ± 12%). For phantom-on-thorax, 2FA was more repeatable and robust to respiration than 1FA (coefficient of variation [CoV] = 1.2% 2FA, = 11.3% 1FA). In vivo, in intrasession T₁ repeatability, 2FA (septal CoV = 2.4%, six-segment CoV = 4.4%) outperformed 1FA (septal CoV = 3.1%, six-segment CoV = 5.5%). In six-segment T₁ homogeneity, 2FA (CoV = 7.9%) also outperformed 1FA (CoV = 11.1%).

Conclusion

The 2FA IR-FLASH improves T₁ estimate accuracy and repeatability over 1FA IR-FLASH, and enables single-scan B1+ -corrected T₁ mapping without BHs or ECG when used with MR multitasking.