Numerical Investigation of Coil Configurations That Provide Ultrahigh Packing Density of Saccular Aneurysms

The long-term outcome of endovascular coiling of cerebral aneurysms is directly related to the packing density at the time of treatment. In general, the highest packing density achievable is only about 45% due to the quasirandom distribution of currently available coils within aneurysms. We investigated whether packing densities could be maximized via more ordered coil configurations. Three different coil configurations—circular loops, planar spirals, and spherical helices—were investigated. The packing densities achievable in maximally filling the volume of an exemplar human basilar aneurysm with each coil configuration were calculated numerically. Coil packing simulations were also carried out for aneurysms idealized as spheres over diameters ranging from 2 mm to 30 mm. The packing densities with the loop, spiral, and spherical helix configurations were 82%, 60%, and 73%, respectively, for the human aneurysm model; the numbers of coils required were 693, 34, and 13, respectively. Simulations within idealized aneurysms suggest that aneurysms cannot be packed to more than 91% with coils of constant circular cross section. The spherical helix configuration provides a constant packing density (coefficient of variation of 0.4%) over the range of aneurysm diameters studied as compared to the two other configurations (coefficients of variation of 9% and 8%). Coil configurations that allow for ordered filling of cerebral aneurysms can potentially provide packing densities that are twice those currently achieved. The spherical helix configuration seems to be the most technically feasible and stable configuration of the three coil types investigated.