Objectives: It is still hard to detect actual three-dimensional information from experimental small animal organ. Synchrotron radiation-based X-ray phase-contrast imaging (PCXI) at SPring-8 is recently reported to be suitable for several soft tissue evaluations. Here we evaluate the value of three-dimensional visualization and morphometry of cardiac tissue in a hamster DCM model by PCXI.
Methods: PCXI was performed to cardiac tissues in three hamster groups [normal (N), DCM model (D), and DCM model treated with human iPS cell-derived cardiac tissue (T)] before pathological study. Comparing with the structural 2D image from PCXI and the Sirius-Red stained histological images, the densities of several tissue types were determined. Based on the analysis of the density distribution in the three-dimensional reconstruction, the total amount of each tissue type was calculated.
Results: The average volume of image was 1.3х106 pixels/slice and 1308 slices. Estimated density was calculated by the conversion formula [Density(g/cm3) = 8.388х10-4хTIFF (8bit gray scale value) + 0.988]. Comparison with the reconstructed image by PCXI at the same level could determine the three types of densities, high (> 1.067 g/cm3; calcification), normal (1.050-1.067 g/cm3; normal myocardium) and low (<0.050 g/cm3; fibrotic tissue, fat, marginal area). The total amount of high, normal and low density area in each group were calculated and there were significant difference (N vs. D vs. T = 0% vs. 2.1% vs. 1.3%; 74.6% vs. 54.8% vs. 67.3%; 25.4% vs. 43.1% vs. 31.4%, p = 0.076, 0.024, 0.038, respectively). The amount of fibrotic tissue was also estimated by the 3D-images (N: not detected, D: 15.4%, T: 1.9%).
Conclusions: The three-dimensional therapeutic effect was well observed by PCXI at SPring-8 in an experimental DCM hamster model. PCXI would be a promising modality to analyze three dimensional histopathological changes and to evaluate therapeutic effects in experimental small animal hearts.