In cardiovascular research, there has recently been an interest in ultra-high field MRI to characterize cardiac anatomy and function in rodents. However, reports on the accuracy of the method are scarce. The purpose of our work was to evaluate left ventricular (LV) systolic function in a mouse model of cardiac hypertrophy using an 11.7T MRI machine and to assess the validity of our results by comparing them with ex vivo measurements.

24 C57Bl/6J mice were studied, including 11 animals having undergone a surgical transverse aortic constriction (TAC) and 13 sham animals. Imaging was performed on a 11.7 Tesla Bruker MR scanner. The LV systolic function was assessed from a stack of 1mm thick short-axis views obtained with a FLASH-cine sequence covering the entire ventricles. Using a dedicated software (SegmentTM, Medviso, Sweden), the following volumes (μl) were determined: end-diastolic, end-systolic and stroke volumes. LV ejection fraction (in %) and LV mass (mg) were subsequently deduced. One week after, mice were sacrificed and their LV mass and tibial length (TL) were measured.

As expected, LV mass was significantly higher in the TAC group. When using the previously validated LV mass/tibial length ratio (LV/TL), sham mice showed a ratio of 4.65±0.09mg/mm and 3.83±0.11mg/mm for morphometric and MRI measurements respectively, and TAC mice showed a ratio of 6.50±0.40 and 5.39±0.28 respectively (p<0.05). Systolic dysfunction was highlighted in the TAC group, with a reduced LVEF of 40,64±4,37% (p<0.05). We demonstrated an excellent correlation between LV mass measurements by weighing or imaging, with a Pearson correlation (r) of 0.92 for both LV mass and LV/TL ratio (p<0.05, Fig.).

High-field cardiac MRI is a promising tool to assess and follow LV systolic function and hypertrophy in mouse models of cardiovascular diseases. In this study, compared with ex vivo measurements, MRI showed similar differences between our experimental groups.