3D time series analysis of cell shape using Laplacian approaches

Background: Fundamental cellular processes such as cell movement, division or food uptake critically depend on cells being able to change shape. Fast acquisition of three-dimensional image time series has now become possible, but we lack efficient tools for analysing shape deformations in order to understand the real three-dimensional nature of shape changes. Results: We present a framework for 3D+time cell shape analysis. The main contribution is three-fold: First, we develop a fast, automatic random walker method for cell segmentation. Second, a novel topology fixing method is proposed to fix segmented binary volumes without spherical topology. Third, we show that algorithms used for each individual step of the analysis pipeline (cell segmentation, topology fixing, spherical parameterization, and shape representation) are closely related to the Laplacian operator. The framework is applied to the shape analysis of neutrophil cells. Conclusions: The method we propose for cell segmentation is faster than the traditional random walker method or the level set method, and performs better on 3D time-series of neutrophil cells, which are comparatively noisy as stacks have to be acquired fast enough to account for cell motion. Our method for topology fixing outperforms the tools provided by SPHARM-MAT and SPHARM-PDM in terms of their successful fixing rates. The different tasks in the presented pipeline for 3D+time shape analysis of cells can be solved using Laplacian approaches, opening the possibility of eventually combining individual steps in order to speed up computations

Mechanical concepts for disc regeneration

Different strategies exist to treat intervertebral disc degeneration. Biological attempts to regenerate the disc are promising. However, degeneration of the disc is always accompanied by alterations of disc height, intradiscal pressure, load distribution, and motion patterns, respectively. Since those preconditions are independent factors for disc degeneration, it is unlikely that regeneration may occur without firstly restoring the physiological status of the affected spinal segment. In vitro and in vivo animal studies demonstrate that disc distraction normalizes intradiscal height and pressure. Furthermore, histological and radiological examinations provided some evidence for regenerative processes in the disc. Only dynamic stabilization systems currently offer the potential of a mechanical approach to intervertebral disc regeneration. Dynamic stabilization systems either using pedicle screws or with an interspinous device, demonstrate restabilization of spinal segments and reduction of intradiscal pressure. Clinical reports of patients with degenerative disc disease who underwent dynamic stabilization are promising. However, there is no evidence that those implants will lead to disc regeneration. Future treatment concepts should combine intradiscal cell based therapy together with dynamic restoration of the affected spinal segment