Femke Mathot

5 Novel methods for evaluation of vascularization of nerves 87 Vascular volume measured with micro CT The vascular volume was successfully measured using the micro CT. At 12 weeks, autograft nerves measured 3.53 ± 0.43% and control nerve samples measured 4.83 ± 0.45% vessels. At 16 weeks, this was 4.95 ± 0.44% and 6.19 ± 0.29% vessels for autografts and controls, respectively. These outcomes are depicted in figure 4 . Vascular surface area measured with conventional photography After 12 weeks, the vascular surface area was 25.04 ± 2.77% and 26.87 ± 2.13% vessels for autografts and control nerves, respectively. At 16 weeks, photography measured 28.11 ± 3.47% vessels for autografts and 33.71 ± 2.60% vessels for controls ( figure 5 ). Correlations The vascular volume and vascular surface area were significantly correlated with both time points and groups (r=0.951, p=0.049). DISCUSSION In this study, the authors successfully measured the vasculature of the sciatic nerve in rats to provide more insight in the amount of angiogenesis and the patterns of neoangiogenesis occurring in nerve regeneration. The limited options available to visualize the small vessels of the rat had previously impeded the understanding of the underlying neoangiogenesis patterns after nerve graft reconstruction. The utility of the methods described in the current study is two-fold. First, it provides an objective quantification of the amount of angiogenesis, independently from the size of the vessels, in relation to the size of the nerve. Second, it eminently demonstrates the patterns of angiogenesis in (transplanted) nerves. Nerve revascularization is postulated to be composed of angiogenesis and neoangiogenesis; vessels that sprout into the existing vascular tree and vessels that create new pathways. 27 However, this theory has yet to be objectively described. Angiogenesis is the growth of blood vessels from existing vasculature. Angiogenesis occurs throughout development and forms transvascular tissue pillars that expand with overall growth resulting in the increase in vascularity over time. 28 This process could also be seen in our study, when comparing time points. The vascularization of nerves and in particular, the alignment of vessels in nerves is attributed to a directional role for regenerating axons. 29, 30 Applying the described techniques at several time points after nerve graft implementation may provide insight to the ratio between revascularization components. These techniques may demonstrate the relationship between vessel alignment and the level of nerve regeneration. Thus, allowing us to improve our understanding of the process and the importance of vascular development in nerve grafts. As blood vessels provide little inherent contrast, viscosity is one of the most important properties of the implemented vehicle. 15 With viscosity levels around 20-30, Microfil® is the best available compound that injects both the arterial and venous system and reaches even