RESUMO
Energy recovery has been achieved in a multipass linear accelerator, demonstrating a technology for more compact particle accelerators operating at higher currents and reduced energy consumption. Energy delivered to the beam during the first four passes through the accelerating structure was recovered during four subsequent decelerating passes. High-energy efficiency was achieved by the use of superconducting accelerating cavities and permanent magnets. The fixed-field alternating-gradient optical system used for the return loop successfully transported electron bunches of 42, 78, 114, and 150 MeV in a common vacuum chamber. This new kind of accelerator, an eight-pass energy recovery linac, has the potential to accelerate much higher current than existing linear accelerators while maintaining small beam dimensions and consuming much less energy per electron.
RESUMO
BACKGROUND: Recurrence of varicose veins after apparently adequate surgery is common. Neovascularisation, the formation of new vascular channels between a venous surgery site and new varicosities, is thought to be an important cause of recurrence. The aim of this study was to provide histological evidence of the 'neovascularisation'process. METHOD: Tissue samples from the region of the previously ligated saphenofemoral junction (SFJ) were taken from 14 limbs with recurrent varicose veins and from nine control limbs. Tissue samples were analysed histologically for overall vascularity, and the presence of intimal circular fibrosis, intimal eccentric fibrosis, medial thickened elastosis, and thrombosis in the microscopic thin walled vessels within the tissue. The same samples were analysed immunohistoligically for S100, a neural marker, and Ki-67 (Mib 1), a marker of endothelial proliferation. Absent S100 and positive Ki-67 were considered as evidence of new vessels. RESULT: No significant difference was found between the venous recurrence and control groups in respect to histological features. S100 positive nerve fibrils were seen associated with dilated venous channels in the majority of both redo and control groups (p=1, Fisher's exact test). Only one section stained positively with Ki-67 (Mib1) in a single vascular channel for a few endothelial cells. The remaining control and redo cases were negative for Mib 1 (p=1, Fisher's exact test). CONCLUSION: We found little evidence of neovascularisation associated with recurrent varicose veins in the saphenofemoral region. The venous channels that develop at the previously ligated SFJ may represent adaptive dilatation of pre-existing venous channels (vascular remodelling), probably in response to abnormal haemodynamic forces.
