Background A working projection in coil embolization of a cerebral aneurysm is usually determined using three-dimensional volume rendering digital subtraction angiography (3D VRDSA), in which the boundary between an aneurysm and its parent artery cannot be identified simultaneously on the front and back surfaces of the vessel. A new method was devised to obtain a more optimal working projection.

Methods 83 patients with aneurysms being treated by embolization were retrospectively evaluated. An aneurysm was accurately distinguished from the parent artery by observation of front, back, proximal and distal sides of the vessel on 3D VRDSA (carving method). An optimal working projection with simultaneous identification of the front and back boundary lines was determined using a translucent vessel complex combined with the carved aneurysm.

Results In 32 aneurysms (38.6%), the optimal working projection was consistent with the working projection that had been used during the procedure. In terminal type aneurysms, the angle difference between the optimal and actual working projections was significantly smaller than in the other types (p<0.05). Aneurysms with a maximal diameter <5 mm showed a significantly larger angle difference between the optimal and actual working projections than aneurysms with a maximal diameter ≥5 mm (p<0.05).

Conclusion In more than half of the patients, the actual working projection was inaccurate. The carving method might be useful to determine working projections, especially for aneurysms other than the terminal type and/or those with a maximal diameter <5 mm.