In vitro perfusion of engineered heart tissue through endothelialized channels.

In engineered heart tissues (EHT), oxygen and nutrient supply via mere diffusion is a likely factor limiting the thickness of cardiac muscle strands. Here, we report on a novel method to in vitro perfuse EHT through tubular channels. Adapting our previously published protocols, we expanded a miniaturized fibrin-based EHT-format to a larger six-well format with six flexible silicone posts holding each EHT (15×25×3 mm³). Thin dry alginate fibers (17×0.04×0.04 mm) were embedded into the cell-fibrin-thrombin mix and, after fibrin polymerization, dissolved by incubation in alginate lyase or sodium citrate. Oxygen concentrations were measured with a microsensor in 14-day-old EHTs (37°C, 21% oxygen) and ranged between 9% at the edges and 2% in the center of the tissue. Perfusion rapidly increased it to 10%-12% in the immediate vicinity of the microchannel. Continuous perfusion (20 µL/h, for 3 weeks) of the tubular lumina (100-500 µm) via hollow posts of the silicone rack increased mean dystrophin-positive cardiomyocyte density (36%±6% vs. 10%±3% of total cell number) and cross sectional area (73±2 vs. 48±1 µm²) in the central part of the tissue compared to nonperfused EHTs. The channels were populated by endothelial cells present in the reconstitution cell mix. In conclusion, we developed a novel approach to generate small tubular structures suitable for perfusion of spontaneously contracting and force-generating EHTs and showed that prolonged perfusion improved cardiac tissue structure.

Magnetic resonance fiber density mapping of age-related white matter changes.

OBJECTIVES: To introduce fiber density mapping (FDM) for investigation of age-related white matter (WM) changes and to compare its capabilities with conventional diffusion tensor imaging (DTI) post-processing. METHODS: DTI data with 1.9 mm(3) isotropic voxels were acquired from 44 healthy volunteers (18-88 years) at 3T. FDM is a 3-step approach which includes diagonalization of the diffusion tensor, fiber reconstruction for the whole brain, and calculation of fiber density (FD) values. Maps of fractional anisotropy (FA) and mean diffusivity (MD) were additionally calculated. Voxel-based analyses were performed to determine volume clusters of significant correlation with age. Bivariate linear regression models and Hotelling-Williams tests were used to detect significant differences between correlations. RESULTS: FDM detected a larger WM volume affected by age-related changes concomitant with fewer significant clusters compared to FA and MD. This indicates that WM alterations due to normal aging occur rather globally than locally. FD values showed a significant stronger correlation with age in frontal lobes (prefrontal and precentral gyrus), limbic lobes (cingulate and parahippocampal gyrus), the corpus callosum (genu) and temporal lobes. CONCLUSIONS: FDM shows higher sensitivity for detection of age-related WM changes because it includes all surrounding fiber structures into the evaluation of each DTI data voxel.

Differences in metabolism of fiber tract alterations in gliomas: a combined fiber density mapping and magnetic resonance spectroscopic imaging study.

BACKGROUND: Gliomas propagate diffusely throughout and along white matter structures. Glioma-related changes in structural integrity and metabolism are not detectable by standard magnetic resonance (MR) imaging. OBJECTIVE: To investigate differences in the metabolism of fiber tract alterations between gliomas grade II to IV by correlation of fiber density values with metabolite concentrations measured by fiber density mapping and MR spectroscopic imaging. METHODS: Fiber density mapping and MR spectroscopic imaging were performed in 48 patients with gliomas WHO grade II to IV. Fiber density mapping data were used to define fiber tracts in tumoral and peritumoral areas. Structural integrity of fiber tracts was assessed as fiber density ipsilateral-to-contralateral ratio (FD ICR). Metabolite concentrations for choline-containing compounds and N-acetyl-aspartate were computed and correlated to FD ICR values after coregistration with anatomic MR imaging. RESULTS: In tumoral areas, choline-containing compound concentrations of altered fiber tracts were significantly different between low- and high-grade glioma and showed different courses for the correlations of FD ICR and choline-containing czeompounds. In high-grade glioma, increasing fiber destruction was associated with a massive progression in cell membrane proliferation. Peritumoral fiber structures showed significantly decreased N-acetyl-aspartate concentrations for all patients, but only patients with glioblastoma multiforme had significantly decreased fiber density compared with the contralateral side. Glioma grades II and III had significantly higher peritumoral FD ICR than glioblastoma multiforme. CONCLUSION: A multiparametric MR imaging strategy providing information about both structural integrity and metabolism of the tumor is required for detailed assessment of glioma-related fiber tract alterations, which in turn is essential for treatment planning.