Semi-automatic detection of myocardial trabeculation using cardiovascular magnetic resonance: correlation with histology and reproducibility in a mouse model of non-compaction

Background: The definition of left ventricular (LV) non-compaction is controversial, and discriminating between normal and excessive LV trabeculation remains challenging. Our goal was to quantify LV trabeculation on cardiovascular magnetic resonance (CMR) images in a genetic mouse model of non-compaction using a dedicated semi-automatic software package and to compare our results to the histology used as a gold standard. Methods: Adult mice with ventricular non-compaction were generated by conditional trabecular deletion of Nkx2-5. Thirteen mice (5 controls, 8 Nkx2-5 mutants) were included in the study. Cine CMR series were acquired in the mid LV short axis plane (resolution 0.086 x 0.086x1mm(3)) (11.75 T). In a sub set of 6 mice, 5 to 7 cine CMR were acquired in LV short axis to cover the whole LV with a lower resolution (0.172 x 0.172x1mm(3)). We used semi-automatic software to quantify the compacted mass (M-c), the trabeculated mass (M-t) and the percentage of trabeculation (M-t/M-c) on all cine acquisitions. After CMR all hearts were sliced along the short axis and stained with eosin, and histological LV contouring was performed manually, blinded from the CMR results, and M-t, M-c and M-t/M-c were quantified. Intra and interobserver reproducibility was evaluated by computing the intra class correlation coefficient (ICC). Results: Whole heart acquisition showed no statistical significant difference between trabeculation measured at the basal, midventricular and apical parts of the LV. On the mid-LV cine CMR slice, the median Mt was 0.92 mg (range 0.07-2.56 mg), M-c was 12.24 mg (9.58-17.51 mg), M-t/M-c was 6.74% (0.66-17.33%). There was a strong correlation between CMR and the histology for Mt, Mc and Mt/Mc with respectively: r(2) = 0.94 (p < 0.001), r(2) = 0.91 (p < 0.001), r(2) = 0.83 (p < 0.001). Intra-and interobserver reproducibility was 0.97 and 0.8 for M-t; 0.98 and 0.97 for M-c; 0.96 and 0.72 for M-t/M-c, respectively and significantly more trabeculation was observed in the Mc Mutant mice than the controls. Conclusion: The proposed semi-automatic quantification software is accurate in comparison to the histology and reproducible in evaluating M-c, M-t and M-t/M-c on cine CMR.