Quantitative ventricular trabeculation assessment in cardiac MRI: optimised blood-pool segmentation, box-counting...

Quantitative assessment of the ventricular trabeculation by fractal dimension (FD) involves complex processing steps which may impact the results. We optimised the automated processing workflow for a reliable assessment of the left and right ventricles at end-diastole and end-systole which is suitable for the automated analysis of large-scale cohorts. Ventricular trabeculae and blood were segmented using a level-set method optimised to exclude pixels outside the heart on short-axis cardiac MRI. FD was derived by box-counting the trabeculae/blood boundary while investigating the impact of box size, sampling and rotation. Alternative non-fractal measures - the convexity related boundary length ratio (BLR) and the trabeculated mass ratio (TMR) - were also investigated.FD values with and without optimisation showed a strong linear correlation (R² = 0.81) and narrow agreement limit (1.96·SD = 0.063) only for the end-diastolic left ventricle. Linear correlation and agreement was good between the optimised FD and BLR values for both ventricles and cardiac phases (R² = 0.70-0.92, 1.96·SD = 0.037-0.064) but not for TMR (R² = 0-0.37, 1.96·SD = 0.16-1.4). FD, BLR and TMR differed significantly (p < 0.001) between end-diastole and end-systole with lower FD (-0.07 ± 0.06) but higher BLR (0.31 ± 0.25) and TMR (0.26 ± 0.13) values at end-systole.The previously used fractal analysis is suboptimal except for assessing the end-diastole left ventricle. The optimised fractal analysis is suitable for the left and right ventricle at end-diastole and end-systole. The easy to compute non-fractal BLR gives equivalent information like FD. The volume-based TMR, on the other hand, captures different features of the trabeculation.