Energetic and spatial constraints of arterial networks

The principle of minimum work (PMW) is a parametric optimization model for the growth and adaptation of arterial trees. A balance between energy dissipation due to frictional resistance of laminar flow (shear stress) and the minimum volume of the blood and vessel wall tissue is achieved when the vessel radii are adjusted to the cube root of the volumetric flow. The PMW is known to apply over several magnitudes of vessel calibers, and in many different organs, including the brain, in humans and in animals. Animal studies suggest that blood flow in arteries is approximately proportional to the cube of the vessel radius, and that arteries alter their caliber in response to sustained changes of blood flow according to PMW. Remodelling of the retinal arteriolar network to long-term changes in blood flow was observed in humans. Remodelling of whole arterial networks occurs in the form of increase or diminishing of vessel calibers. Shear stress induced endothelial mediation seems to be the regulating mechanism for the maintenance of this optimum blood flow/vessel diameter relation. Arterial trees are also expected to be nearly space filing. The vascular system is constructed in such a way that, while blood vessels occupy only a small percentage of the body volume leaving the bulk to tissue, they also crisscross organs so tightly that every point in the tissue lies on the boundary between an artery and a vein. This review describes how the energetic optimum principle for least energy cost for blood flow is also compatible with the spatial constraints of arterial networks according to concepts derived from fractal geometry

Local skin and eye lens equivalent odses in interventional neuroradiology

Purpose  To assess patient skin and eye lens doses in interventional neuroradiology and to assess both stochastic and deterministic radiation risks. Methods  Kerma–area product (P KA) was recorded and skin doses measured using thermoluminescence dosimeters. Estimated dose at interventional reference point (IRP) was compared with measured absorbed doses. Results  The average and maximum fluoroscopy times were 32 and 189 min for coiling and 40 and 144 min for embolisation. The average and maximum P KA for coiling were 121 and 436 Gy cm2, respectively, and 189 and 677 Gy cm2 for embolisation. The average and maximum values of the measured maximum absorbed skin doses were 0.72 and 3.0 Sv, respectively, for coiling and 0.79 and 2.1 Sv for embolisation. Two out of the 52 patients received skin doses in excess of 2 Sv. The average and maximum doses to the eye lens (left eye) were 51 and 515 mSv (coiling) and 71 and 289 mSv (embolisation). Conclusion  The ratio between the measured dose and the dose at the IRP was 0.44 ± 0.18 mSv/mGy indicating that the dose displayed by the x-ray unit overestimates the maximum skin dose but is still a valuable indication of the dose. The risk of inducing skin erythema and lens cataract during our hospital procedures is therefore small.The original publication is available at www.springerlink.com: Michael Sandborg, Sandro Rossitti and Håkan Pettersson, Local skin and eye lens equivalent doses in interventional neuroradiology, 2010, European Radiology, (20), 3, 725-733. http://dx.doi.org/10.1007/s00330-009-1598-9 Copyright: Springer Science Business Media http://www.springerlink.com/</p

Punção cervical lateral para mielografia e coleta do líquido cefalorraqueano: nota técnica

A punção cervical lateral para mielografia ou obtenção de líqüido cefalorraqueano é modificação da técnica de cordotomia ântero-lateral cervical percutânea e pode ser realizada nos níveis atlanto-axial e atlanto-occipital. Técnica simples e segura, oferece em casos específicos vantagens óbvias sobre a punção lombar e cisternal mediana, sem grande desconforto para o paciente