Abstract
The spatial organization of cardiac muscle tissue exhibits a complex structure on multiple length scales, from the sarcomeric unit to the whole organ. Here we demonstrate a multi-scale three-dimensional imaging (3d) approach with three levels of magnification, based on synchrotron X-ray phase contrast tomography. Whole mouse hearts are scanned in an undulator beam, which is first focused and then broadened by divergence. Regions-of-interest of the hearts are scanned in parallel beam as well as a biopsy by magnified cone beam geometry using a X-ray waveguide optic. Data is analyzed in terms of orientation, anisotropy and the sarcomeric periodicity via a local Fourier transformation.
Highlights
The contractile function of the heart relies on an intricate structure spanning multiple length scales: starting with the molecular scales of the myosin motors and the actomyosin assembly, the formation of the sarcomeric units and myofibrils, to the cellular scale of single cardiomyocytes, arrangement of myocyte chains embedded in connective tissue, all the way to the aggregation of cardiomyocyte chains forming a complex cardiac mesh and the scale of the entire organ [1]
While the macroscopic architecture of heart muscle is known for more than hundred years from classical anatomy and histology, the detailed three-dimensional (3d) arrangement of muscle cells and myofibrils cannot be reconstructed from histology alone, due to the invasive nature of sectioning [2]
These results indicate that the heart is a complex 3d mesh of aggregated cardiomyocytes with a supporting fibrous matrix [1,4]
Summary
The contractile function of the heart relies on an intricate structure spanning multiple length scales: starting with the molecular scales of the myosin motors and the actomyosin assembly, the formation of the sarcomeric units and myofibrils, to the cellular scale of single cardiomyocytes, arrangement of myocyte chains embedded in connective tissue, all the way to the aggregation of cardiomyocyte chains forming a complex cardiac mesh and the scale of the entire organ [1]. In order to extract the sarcomeric periodicity from the high-resolution data, a local Fourier-analysis of the electron density was used [13] We implement this approach by an illumination scheme based on three different configurations of the Göttingen Instrument for Nano-Imaging with X-Rays (GINIX). In order to resolve the sarcomeric structure of the heart tissue, the cone beam geometry of a waveguide (WG) illumination was used This configuration, with a scalable geometric magnification M, enables high-resolution scans of a biopsy punch with an FOV of few hundred μm and an effective pixel size of less than 200 nm
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