Improved segmented modified Look-Locker inversion recovery T1 mapping sequence in mice

Object To develop and evaluate a 2D modified Look-Locker (MOLLI) for high-resolution T-1 mapping in mice using a 3T MRI scanner. Materials and methods To allow high-resolution T-1 mapping in mice at high heart rates a multi-shot ECG-triggered 2D MOLLI sequence was developed. In the proposed T-1 mapping sequence the optimal number of sampling points and pause cardiac cycles following an initial adiabatic inversion pulse was investigated in a phantom. Seven native control and eight mice, 3 days post myocardial infarction (MI) after administration of gadolinium were scanned. Two experienced readers graded the visual T-1 map quality. Results In T-1 phantoms, there were no significant differences (<0.4% error) between 12, 15 and 20 pause cardiac cycles (p = 0.1, 0.2 and 0.6 respectively) for 8 acquisition cardiac cycles for 600bpm in comparison to the conventional inversion recovery spin echo T-1 mapping sequence for short T-1's (< 600 ms). Subsequently, all in-vivo scans were performed with 8 data acquisitions and 12 pause cardiac cycles to minimize scan time. The mean native T-1 value of myocardium in control animal was 820.5 +/- 52 ms. The post-contrast T-1 measured 3 days after MI in scar was 264 +/- 59 ms and in healthy myocardium was 512 +/- 62 ms. The Bland-Altman analysis revealed mean difference of only -1.06% of infarct size percentage between T-1 maps and LGE. Conclusions A multi-shot 2D MOLLI sequence has been presented that allows reliable measurement of high spatial resolution T-1 maps in mice for heart rates up to 600bpm.