Background: In cardiovascular imaging, variations within and between observers, and between different acquisitions remain an important issue when interpreting in vivo data. Though there has recently been an increasing interest in ultra-high field MRI to characterize rodent models of cardiovascular diseases, reports concerning its reproducibility are scarce. The purpose of our work was to evaluate the intraobserver, interobserver and interexperiment variability of left ventricular (LV) mass and volumes measurements in mice using an 11.7T MRI scanner and to assess the validity of our results by comparing them with ex vivo measurements.
Methods: 29 C57Bl6/J male mice aged 10-18 weeks were studied, including animals having previously undergone minimally invasive transverse aortic constriction. Imaging was performed on an 11.7 T MRI system (Biospec, Bruker, Germany). The LV systolic function was assessed from a stack of 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. Interobserver (n=24), intraobserver (n=24) and interexperiment (n=12) reproducibility were studied with the Bland and Altman method. LV masses obtained with the MRI were compared with ex vivo morphometric data.
Results: Reproducibility was excellent for the LV mass and end-diastolic volume (EDV) (coefficient of variability - CoV - between 5,38 and 11,77%), good for end-systolic volume (ESV) (CoV between 15,24 and 16.81%) and moderate for data related to the smallest volumes, i.e. the stroke volume (SV) and ejection fraction (EF) (CoV between 14,73 and 20,93%).
Importantly, we demonstrated an excellent correlation between LV mass measurements by weighing or imaging, with a Pearson correlation (r) of 0.92.
Conclusions: In our study, we show that the mouse LV systolic function can be longitudinally assessed on an 11.7T MRI scanner, with excellent reproducibility of LV mass and EDV and a good correlation of LV mass results with ex vivo morphometric measurements. However, we highlight the need to take into account some shortcomings when interpreting MRI data, like moderate reproducibility of very small volumes, focusing on parameters that are the most reproducible or using alternative sequences with better resolution.