An X-ray computed μ-tomography analysis for the characterization of 3D-heart shape in a model of cardiac plasticity

The understanding of the crucial interplay between heart form and function through the development of new non-invasive methodologies for 3D morphological analysis has always aroused great interest in the cardio-scientists community. The X-ray computed μ- tomography (μ-CT) is a non-destructive 3D imaging technique utilizing X-rays to study the internal structures of materials, objects, or organisms. In this study, μ-CT has been used to investigate the 3D structural organization of the goldfish (Carassius auratus) heart, an emerging natural model for evaluating fundamental aspects of the coordinated physiological mechanisms that maintain cardiac steady-state. Ex-vivo isolated hearts were blocked in diastole, fixed in PFA, and stained in Lugol's solution. After dehydration in graded ethanol, the X-ray projections at different angles (steps 0.1°) were acquired. Mathematical algorithms (Feldkamp-Davis-Kress back-projection algorithm) were used to reconstruct the heart, thus obtaining its cross-sectional images. Using Fiji and Avizo software, 3D images of the sample were obtained and used for the analysis. An essential phase of the data analysis was the identification of various regions obtained with innovative segmentation algorithms. Preliminary investigation provides information about the heart's shape, curvature, symmetry, and chamber structural organization. Atrial and ventricular myocardial arrangement, compact vs trabecular myocardial component, inner atrial and ventricular chamber volumes, and bulbar structure have been studied. The data analyses performed have given a quantitative characterization of the 3D morphological differences between the various heart regions, evaluating the size of the cavities to the tissues that make up the heart. Our work provided the first non-invasive reconstruction of the 3D shape of the goldfish heart. It is of absolute importance to go deep inside the relationship between form and function and the associated physical constraints that shape the hemodynamic response of the goldfish heart, particularly when challenged by various environmental stimuli.