Characteristic quantities of microvascular structures in CLSM volume datasets

Analysis of laser speckle contrast images variability using a novel empirical mode decomposition: comparison of results with laser Doppler flowmetry signals variability

Laser Doppler flowmetry (LDF) and laser speckle contrast imaging (LSCI) have emerged as noninvasive optical modalities to monitor microvascular blood flow. Many studies proposed to extract physiological information from LDF by analyzing signals variability. By opposition, such analyses for LSCI data have not been conducted yet. We propose to analyze LSCI variability using a novel data-driven method: the complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN). CEEMDAN is suitable for nonlinear and nonstationary data and leads to intrinsic mode functions (IMFs). It is based on the ensemble empirical mode decomposition (EEMD) which relies on empirical mode decomposition (EMD). In our work the average frequencies of LSCI IMFs given by CEEMDAN are compared with the ones given by EMD and EEMD. Moreover, LDF signals acquired simultaneously to LSCI data are also processed with CEEMDAN, EMD and EEMD. We show that the average frequencies of IMFs given by CEEMDAN depend on the signal-to-noise ratio (SNR) used in the computation but, for a given SNR, the average frequencies found for LSCI are close to the ones obtained for LDF. By opposition, EEMD leads to IMFs with frequencies that do not vary much when the SNR level is higher than a threshold. The new CEEMDAN algorithm has the advantage of achieving a complete decomposition with no error in the reconstruction but our study suggests that further work is needed to gain knowledge in the adjustment of the added noise level. CEEMDAN, EMD and EEMD are data-driven methods that can provide a better knowledge of LSCI.

Maturation of capillary-like structures in a tube-like construct in perfusion and rotation culture

In an effort to engineer capillary-like networks in vitro, different cultivation methods were compared. Five small-diameter tube-like constructs ('vessel equivalents') were fabricated from porcine gelatin scaffolds and seeded with human adipose tissue stromal cells and umbilical vein endothelial cells. After initial growth, the vessel equivalents were divided. One segment was exposed to pulsatile perfusion and the other was kept in rotating culture. Specimens harvested at the start of the experiments and after 16 days of rotation or perfusion were compared histomorphometrically with respect to capillary-like network formation in the vessel wall. Most capillary-like structures were found in the luminal portion of perfused vessel equivalents. Maturation of these capillary-like structures ascertained by recruitment of alpha-actin-positive cells also reached the highest degree in the luminal portion of perfused specimens. Perfused specimens showed significantly less apoptosis. Pulsatile perfusion promotes the development and maturation of a capillary-like network in this in-vitro approach.